TBD

We have recently shown thin-film systems combining energy-harvesting devices possible in large-area electronics with embedded power electronics based on thin-film transistors (TFTs), creating complete powering systems. Power inverters are built to perform DC to AC conversion from large thin-film solar cells, enabling substantial wireless power delivery to mobile load devices or to other physical “planes” (layers) in a large-scale thin-film system. To realize non-rigid planes, we use low-temperature amorphous-silicon (a-Si) processing for TFTs in the power circuits [1]. We previously illustrated how TFT characteristics (e.g. ft) impact performance of these systems; in this paper we show how provision of output power is affected by stability of TFTs in the thin-film circuits and how degradation can be mitigated. Results are presented for a TFT LC-oscillator-based inverter [1,2], drawing DC power from an a-Si solar module (Vopasymp;35V) and transmitting this through near-field inductive coupling to load devices. The oscillator is two cross-coupled, SiNx-passivated, back-channel-etched TFTs (W/L=3600/6mu;m) with planar Cu inductors (10cm^2, L=150mu;H, R=35Omega;) forming tanks at TFT drains; the inductors resonate with the TFT capacitances (Ctasymp;30pF) enabling wireless power transfer (>20mW). We fabricate our inverters on free-standing 50mu;m polyimide at process temperatures <180C. We show that output power decrease over time results from TFT instability, caused by threshold-voltage shift. For Vop<35V and a SiNx TFT dielectric, this is from moderate gate field (on average <10^6 V/cm) Vt shift [3] of oscillator TFTs of the form t^β with β=0.40 (previously associated with defect creation at the a-Si-dielectric interface). The oscillator stress conditions are complex, as large AC swings at TFT drain/gate nodes result in devices moving between linear/saturation regimes, with biasing voltages oscillating about a non-zero average, Vop. DC stressing in 3 regimes (Vds>Vgs, Vds1 [2]. We show that large L/R ratio inductors, achievable by large-area patterning, make the power-inverter less sensitive to long-term TFT drift. Raising gate nitride deposition temperature can improve the dielectric-channel interface, reduce Vt shift [3] and maintain gm. At higher temperatures, however, larger misalignments result between device layers, requiring larger source/drain overlaps to maintain successful operation (hence larger Ct). We show experimental data for this tradeoff, noting that larger Ct affects the positive feedback condition, output power and power-transfer efficiency. 1.Rieutort-Louis et al. IEDM 2012 2.Hu et al. CICC 2012 3.Kattamis et al. EDL 2007

High performance metallic interconnects, contacts and electrodes are key elements in the realization of flexible, stretchable, and wearable electronic devices. Current fabrication methods are based on vacuum based technologies that are slow and expensive. This talk will discuss on our recently developed methods for the solution-based fabrication of metallic conductors that are high performance, and compatible with flexible, stretchable, and wearable circuits. In this method, a thin polymer layer is synthesized from compliant substrates such as plastics, elastomers, and textiles. Electroless metal deposition is subsequently carried out on the polymer-modified substrate to form conductive metallic coating. Importantly, this method is compatible with printing technology for fabricating structures spanning from nanometer to many centimeter scales.

The integration of graphene films that exhibit outstanding electrical, optical and mechanical properties with reliable inorganic materials makes them attractive for applications in high performance, flexible electronics. Although several recent studies report the fabrication of flexible organic material-based devices using graphene, significant challenges still remain in the integration of graphene films with inorganic materials for high performance, flexible energy devices. In this talk, we present a route to fabricate flexible energy harvesting devices and photovoltaic cells by combined use of inorganic materials, such as PbZrxTi-1xO3 ribbons and Si membranes, and graphene films which provide an intrinsic stretchability and optical transmittance. The resulting devices presented stable operation without a serious change in electronic properties under high strain.

Physically integrated Ag films as wrap-around contacts to the emitter layer of core-shell radial pn-junction Si microwire array photovoltaics hold potential for cost-effective, large-area devices. State-of-the-art Si microwire photovoltaics use a transparent conducting oxide top contact, which involves intensive processing. Furthermore, indium tin oxide contacts cannot be used in a flexible polymer embedded device due to mechanical fracturing when the device is peeled from the substrate. It has been demonstrated that a thin metal film can be integrated into the base of the Si microwire array without electrical shorting. Employing evaporated films of Al₂O₃ as electrical insulation layers, Ag films were deposited to provide wrap-around contacts to only the emitter shells of silicon microwires. These Ag films also served as a back reflectors to enhance the absorption of the solar cell. Wrap-around contact devices exhibited open circuit voltage of 220 mV and short circuit current density of 0.6 mA cm^-2 under 400 mW cm^-2 of ELH simulated solar illumination. The lower than expected energy conversion efficiency can be attributed to Ag film blocking light absorption. Enhanced light absorption in wrap-around contact devices are expected increase the short circuit current density compared to conventional pn junction Si microwire devices, leading to higher device efficiencies.

Innovation in mobile industry is strongly related to the availability of new technology enablers - such as new functional materials - which may allow the large scale production of innovative devices with increased performance and new form factors. In particular, the recent 2D materials research area has the potential to introduce radical advancements beyond the state-of-the-art technology.
Graphene has already demonstrated a great potential for radical technological innovations in a plenty of R&D fields. Thanks to its outstanding physical properties, it offers new solutions for electronics and optoelectronics, sensing, energy storage and harvesting.
These features are combined with the peculiar two dimensional nature of the material, which provides completely new opportunities in terms of form factors and materials assembly and engineering. Last but not least, scalability to mass production has been demonstrated for various graphene materials, together with compatibility with low cost manufacturing processes, such as printing and roll-to-roll techniques. Therefore, graphene may represent an important technological platform for the next generation of mobile devices.
Power consumption is a major challenge in the development of innovative mobile devices.
Graphene is an ideal material for the development of portable energy storage components, thanks to the high specific surface area, the superior electrical conductivity, a high chemical tolerance and a broad electrochemical window. In addition, graphene is a “solution-processable” material, thus allowing the preparation of colloidal suspensions suitable for printing applications. Graphene and functionalized graphene inks can be used to fabricate batteries and supercapacitors, demonstrating the potential of graphene technology in the field of energy storage.
New power management solutions can be combined with new sensing capabilities and form factors in portable devices, enabling advantageous solutions for distributed sensors networks. High sensitivity of graphene-based sensors has been demonstrated in various fields, spanning from chemical sensors to photodetectors, and 2D materials are ideal candidates for the actual achievement of flexibility and stretchability.
Graphene technology may enable a combination of flexible components with low cost autonomous sensors, thus opening new opportunities in the field of portable electronic devices.

Organics and metal oxides are two emerging families of semiconducting materials that promise to revolutionize the area of thin-film transistors. A key and highly attractive characteristic associated with these two classes of electronic materials is the processing versatility they have to offer. For instance, they can be processed by vacuum and/or solution-based methods onto large-area substrates at relatively low temperatures, hence enabling the use of inexpensive temperature-sensitive substrate materials such as plastic. However, making semiconductor processing compatible with the substrate alone is not enough for developing state-of-the-art transistors and is often the case that the other important device components, such as the conductive electrodes and the gate dielectric, need also to be processed under similar low-temperature conditions. Although, solution processing of conductive electrodes is relatively straightforward, processing of high quality gate dielectrics over large areas has proven to be challenging. In this talk, I will present some of our latest work on solution-processable gate dielectrics for use in low-power thin-film transistors and circuits based on organics and metal oxides semiconductors. The dielectric materials investigated include a range of solution processed self-assembling monolayer nanodielectrics, high-k relaxor ferroelectric polymers as well as high-k inorganic metal oxide dielectrics grown at room temperature in ambient atmosphere.

Copper zinc tin sulfo-selenide Cu2ZnSn(SSe)4 (CZTS) is a low-cost alternative semiconductor material used as absorber in solar cells. CZTS monograins approach was considered to be a potential candidate for futuristic low-cost production technology of solar panels. For CZTS (and also CIGS) solar cell, CdS deposited by chemical bath deposition (CBD) is still the most efficient buffer layer. However, development of Cd-free buffer layer is hugely demanded in perspective scaling-up production of CZTS and CIGS solar cells due to the harmfullness of Cd.
In this work, we report on synthesis and use of a zinc-based buffer layer for CZTS monograin solar cell. Zn-based buffer layer was deposited onto CZTS absorber layer by employing a simple, non-vacuum and scalable CBD method. Morphology and chemical composition of the ZnS(O,OH) film was characterized by SEM, XPS and Raman spectroscopies. Effect of thickness, morphology as well as chemical composition of the deposited ZnS(O,OH) buffer layer onto efficiency of the CZTS solar cell was intensively investigated. For instant, our best CZTS monograin solar cell with a ZnS(O,OH) buffer layer showed an efficiency of 3.8%, open-circuit voltage of 616 mV, short-circuit current density of 13.2 mA/cm2, and fill factor of 46.3%.

The combination of low electrical performance and the incompatibility with high throughput manufacturing are the two important technological bottlenecks that limit the use of amorphous silicon (a-Si) thin-film transistor (TFT) technology in a range of fast emerging optoelectronic applications. As a result, recent effort towards research and development of novel TFT materials has been intensifying. One family of electronic materials that promises to overcome the technological bottlenecks faced by a-Si is the metal-oxide semiconductors. To date, and only few years since their functionality-proof has been accomplished, oxide based TFTs have managed to outperform incumbent technologies (i.e. a-Si TFTs) and are fast approaching that of polycrystalline Si [1]. Additionally, metal oxide semiconductors offer the tremendous advantage of processing versatility making them compatible with low-cost solution-based processing methodologies. Despite their desirable potential, however, state-of-the-art oxide based TFTs still require somewhat high processing temperatures (250-300 °C) that render the technology incompatible with flexible, low cost plastic substrates [2].
Here we report the development of zinc oxide (ZnO) based TFTs processed from solution using an aqueous metal-complex precursor at temperatures below 180 °C. Optimised devices exhibit electron mobility in excess of 10 cm²/Vs and an on/off channel current ratio of over 10⁷. The method is so robust that fully functional transistors with electron mobilities over 1 cm²/Vs can be obtained at processing temperatures as low as 100 °C. Such drastic improvements in processing conditions are attributed to the formation of a unique and somewhat unusual metal complex formed between the precursor molecule and the solvent, and the formation of a highly crystalline and ultra-thin (le; 5 nm) ZnO film. Using this low-temperature processed ZnO TFTs combined with a novel hybrid metal-oxide dielectric, we were able to demonstrate high-performing low-voltage flexible electronic circuits. Moreover, apart from the conventional calcination process, we also examined a UV-assisted oxide conversion process in an effort to reduce the processing temperature down to the range of merely 85-90 °C without comprising device performance. In summary, this work defines a new approach towards high performance, solution processed oxide electronics for a host of applications and can be viewed as a significant step towards next generation metal oxide TFTs.
[1] Street, R. A., Thin-Film Transistors. Advanced Materials, 21, 2007 (2009).
[2] Kim, M. G., et al., Low-temperature fabrication of high-performance metal oxide thin-film electronics via combustion processing. Nature Materials 10, 382 (2011).

The development of next-generation electrical energy storage is challenged by strong variations in power - the dynamics of energy supply and demand - as well as by the need for substantially higher gravimetric and volumetric energy density. Both renewables and conventional energy sources are profoundly time-varying sources. This reality underscores the need for hybrid energy storage systems that integrate storage devices having different power-energy profiles, where higher power devices manage power transients and thus complement high energy density storage devices with lower power capability. Such notions are known for electrochemical storage applications, e.g., battery-supercapacitor combinations.
A variety of nanostructured storage devices have been featured in recent years, with increased attention to electrostatic devices for their high power capability cf. electrochemical devices. Combining electrostatic and electrochemical capacitors (ESC&’s and ECC&’s) in a hybrid circuit presents a new challenge in that the fundamental mechanisms are distinctly different, producing different nonlinear performance profiles that depend on voltage, scan rate, cycling history, and materials and device structure. Electrochemical devices involve structure and reaction dependent charge transport as well as electrolyte
limitations, while electrostatic devices are limited by tunneling and dielectric breakdown.
We have begun to analyze how best to integrate ESC and ECC devices into hybrid systems, based on dynamic simulation of their time-varying behavior as well as their dependence on material and nanodevice design. using MatLab&’s Simulink to identify synergistic arrangements which transfer power between them to capture, store, and delivery energy efficiently. Results indicate that the maximum energy density is reached 15× faster and is more efficient for the hybrid configuration than for either device operating independently. Proper capacity balance between ESC and ECC&’s enables the ESC to capture and
transfer higher power components to the ECC while avoiding energy loss associated with leakage currents in ESC devices. The results suggest design guidelines for hybrid configurations and suggest material and nanostructure parameters critical to the storage efficiency of the system. Following these guidelines, the ultimate storage performance (gravimetric, volumetric, and cost) may be best if the hybrid functionality can be achieved by integrating device types (e.g., ESC and ECC) at the nanoscale.

To meet the increasing energy demands for next-generation portable and flexible devices, the energy density of supercapacitors should be substantially increased without sacrificing the power density and cycle life. In this work, we focused on the development of high-performance and flexible solid-state asymmetric supercapacitor (ASC) devices based on one-dimensional core-shell nanowire (NW) electrodes. Core-shell NWs were grown directly on flexible conductive substrates, which not only provide good strain accommodation, but also enable the fabrication of flexible SC devices without the need of binder. Hydrogenated TiO₂ (denoted as H-TiO₂) NWs grown on carbon cloth have demonstrated to have a good conductivity than pristine TiO₂ NWs. By using these H-TiO₂ NWs as core (conducting scaffold) to support electrochemically active MnO₂ and carbon shells, these core-shell NW electrodes exhibited improved electrochemical performance. We assembled a flexible solid-state ASC device with H-TiO₂@MnO₂ core-shell NWs as positive electrode and H-TiO₂@C core-shell NWs as negative electrode. This device operated at a 1.8 V voltage window was able to delivered a high specific capacitance of 139.6 Fg^-1, maximum volumetric energy density of 0.30 mWhcm^-3 (59 Whkg^-1) and volumetric power density of 0.23 W cm^-3 (45 kWkg^-1). Additionally, the device exhibits excellent cycling performance (8.8% capacitance loss after 5000 cycles) and good flexibility. The capability of developing complex nanostuctrued electrodes could advance the design and fabrication of high-performance and flexible ASCs.

Kesterite Cu2ZnSnS4 (CZTS) thin film had been successfully deposited on molybdenum coated glass with non-vacuum solution-based chemical spray pyrolysis method. High temperature annealing up to 530 °C under selenium vapor gives highly crystalline Cu2ZnSn(S,Se)4 (CZTSSe) film with grain size up to 800 nm. No secondary phase is observed in the final CZTSSe film as detected by X-ray diffraction (XRD) and Raman spectroscopy. PV solar cell efficiency of 2.8% had been achieved without detail optimization. The device suffers from very low short circuit current (Jsc) and low fill factor (FF) which may attribute to the high series resistance caused by both bulk and interface recombination. To our knowledge, this is the first time so far reported fabrication of CZTSSe solar cell device with chemical spray pyrolysis method.

Develop supercapacitors easily integrables in micro-electronic circuit is one of the key challenge to improve micro-electronic devices performances [1]. Elaborate silicon based micro-supercapacitors should facilitate it. Non-doped porous silicon nanowires based electrodes show promising results to reach this goal [2].
This work concerns the elaboration and the electrochemical characterization of silicon nanowires (SiNWs) based electrodes for micro-supercapacitors.
SiNWs based electrodes are elaborated by Chemical Vapor Deposition (CVD) on highly doped silicon substrate via localized gold catalysis. Their parameters (length, diameter, density and doping level) can be monitored by the Vapor Liquid Solid (VLS) method and checked after the growth by SEM [3]. Electrochemical performances of theses electrodes are characterized evaluated in an organic electrolyte (NEt4BF4, PC, 1M) and an ionic liquid (EMI-TFSI) by Electrochemical Impedance Spectroscopy and dynamic electrochemistry (cyclic voltametry and galvanostatic charge/discharge).
This work focuses mainly on the influence of SiNWs parameters and electrolyte on the nanostructured electrodes electrochemical performances and charge/discharge stability. SiNWs length, density and doping level have been identified as key parameters to improve electrode capacity. An increase of the SiNWs doping level enables to obtain electrodes with a quasi-ideal supercapacitor behavior. Pure capacitive storage of these highly doped electrodes has also been underlined [4].
A 440 µF.cm-2 capacity, i.e. about 75 fold bulk silicon capacity, has been reached by using dense, highly doped, 50 µm long silicon nanowires. All devices built with two nanostructured silicon electrode show highly stable cycle efficiency (99 %) and capacity over at least 100 000 cycles for current density ranging from 5 µA.cm-2 to 1 mA.cm-2. The use of ionic liquid as electrolyte enables to enlarge the potential window and thus improve devices performances.

[1] J.W. Choi, J. McDonough, S. Jeong, J.S. Yoo, C.K. Chan, Y. Cui, Nano Lett., 2010, 10, 1409
[2] J.R. Miller, P. Simon, Science, 2008, 321, 651
[3] P. Gentile, A. Solanki, N. Pauc, F. Oehler, B. Salem, G. Rosaz, T. Baron, M. Den Hertog ,V. Calvo, Nanotechnol. , 2012, 23, 215702
[4] F. Thissandier, A. Le Comte, O. Crosnier, P. Gentile, G. Bidan, E. Hadji, T. Brousse, S. Sadki, Electrochem. Comm., 25 (2012) 109-111

Lithium-ion (Li+) batteries are a very promising energy storage technology that is used in a wide range of applications. There is a need to develop cost efficient rechargeable Li+ batteries with high capacities. Currently, graphite is used as state-of-the-art anode material. The lithiation capacity of graphite is ~372 mA h g-1. However, recent research has shown that the lithiation capacity for silicon is ~3579 mA h g-1. Hence Si is a very promising candidate to replace graphite as anode material for future Li+ batteries. Unfortunately, the volume of the Si anode increases by 270% resulting in its destruction and loss of capacity.
In this paper we report the development of amorphous (Si, Ge) and (a-SiGe) thin films for anode applications grown by pulsed laser deposition (PLD) and rf sputtering. In PLD, a KrF laser operating at 248 nm and having 325 mJ energy per shot was used to ablate a Si/Ge under vacuum. The distance between target and substrate is ~ 4 cm. Typically, the number of shots was used during ranged from 10000 to 20000. In rf sputtering, the rf power was varied from 50 W to 200 W. The films were deposited in Ar atmosphere having a pressure of 10-1 torr during deposition.
The capacity of the deposited films was tested using a half-cell reaction. The characterization and the capacities of the deposited films will be discussed in detail.

Magnesium ion batteries are emerging as a viable high energy density alternative to Li batteries that also circumvents potential Li supply risks [1]. Most research has focused on the design of cathode materials for Mg batteries [2, 3]. Mg metal, while being safer than metallic Li, results in poor reversibility and dendrite formation, while less severe than with Li, can still occur. The rechargeability can be improved by using an insertion anode, but studies of high-capacity anodes are scarce [4].
We present results of ab initio studies of the behaviour of Mg atoms in bulk Ge, Si, and Sn matrices as potential anode materials. We show that inserted Mg atoms act as interstitial defects occupying tetragonal (T) sites of the matrices. In all cases, Mg-Si/Sn/Ge interactions have covalent-polar nature. To understand charge/discharge performance of potential anode materials, we further investigate diffusion of Mg atoms in the three anode materials. A single Mg atom has the lowest migration barrier in Sn (0.49 eV) what is about 0.5 eV smaller compared to that for Si. In all considered systems, an increase of Mg concentration leads to a reduction of Mg migration barriers (by up to 0.5 eV for Si), but Mg atoms still have the lowest migration barriers in Sn. We conclude that Sn is the most attractive anode material in terms of charge/discharge rate. We also investigate the effect of host lattice deformation induced by Mg insertion on diffusion. We find that Mg diffusivity is extremely sensitive to changes in the lattice: the variation of Si lattice constant within 1% of its ideal value can induce changes in migration barriers of about 10%.
[1] S.W. Kim et al., Adv Energy Mater 2, 710 (2012).
[2] http://www.pelliontech.com/
[3] S. Yang et al., J Phys Chem C 116, 1307 (2012)
[4] M. Morita et al., Electrochem Solid State Lett 4, A177 (2001)

A lithium-sulfur (Li-S) battery has a high theoretical capacity of 1675 mAh g-1 of element sulphur (S) and a high nominal theoretical energy density of 2600 Wh kg-1 of cell weight, which offers a significant energy density improvement compared to the mainstream lithium-ion batteries (150 Wh kg-1). Furthermore, elemental S is readily available and poses less risk to the environment than the phosphates that are currently used in the lithium-ion (Li-ion) batteries. Therefore, sulfur has been considered as a very promising cathode material for the next generation high energy density rechargeable batteries. In this work, unique carbon materials with various hierarchical pores were synthesized from zinc containing metal-organic frameworks (MOFs). This presents a novel method and rationale for utilizing carbonized MOFs for sulphur loading to fabricate cathode structures for lithium-sulphur batteries. High temperature pyrolysis of MOFs is shown to produce carbon with tunable hierarchical porous morphology. We have selected different MOFs - all based on zinc metal centres, because zinc can be readily eliminated as metallic vapour during high temperature pyrolysis, thus avoiding the additional step of dissolving the liberated metal oxide to free the carbon. Starting with different MOFs, it is possible to produce variations in the pore volume, surface area and size distribution in the resulting carbon structures which can then serve as hosts for sulphur loading to make Li-S batteries. It is found that cathode materials made from MOFs derived carbon with a higher mesopore volume (2-50 nm) exhibit increased initial discharge capacity, whereas carbon with a higher micropore (< 2nm) proportion leads to cathode materials with better cycle stability.

Flexible lithium battery is gaining much attention because of the appearance of new soft electronic device such as rollup display and wearable computers. Flexible current collector, inevitable component for bendable battery, is fabricated using porous membrane as a substrate material. New flexible current collector not only provide low resistance but also provide template for nanostructured anode. Silicon, anodic material known to have highest theoretical charge capacity, in the form of nano-fibril structure was simply obtained by RF-magnetron sputtering on flexible current collector. Bendable lithium batteries using new flexible current collector and resulting Si nano-fibril anode showed improved coulombic efficiency and higher discharge capacity which excced performance of conventional copper foil based current collector. It is expected that excellent electrochemical performance combined by facile fabrication of flexible current collector and resulting anode will provide new approach for bendable lithium battery with high energy capacity.

The electrical wire explosion method is a simple, low-cost and environment-friendly method to produce various kinds of scalable nano-sized powders. The properties of nanopowders produced by the electrical wire explosion process rely on many conditions such as materials, wire diameter, feeding distance, capacitor voltage, and ambient media. Herein, we demonstrate the formation of Ni/NiO nanocomposite electrode by the partial oxidation of initially prepared Ni or Ni/Ni(OH)2 nanopowders at 300 oC in air. These precursor powders were prepared by the electrical explosion using Ni wires with a diameter of 0.2 mm and length of 40 mm under oleic acid or deionized water media. Especially, underwater electric explosion resulted in the formation of Ni(OH)2 nanosheets containing tiny Ni nanoparticles. After the calcination of as-prepared Ni/Ni(OH)2 nanocomposites, the conversion to Ni/NiO was observed, maintaining the morphology of as-prepared powders. Additionally, large surface area (120 m2/g) was estimated due to the dehydration reaction of Ni(OH)2 during calcinations. Li-electroactivities in these Ni/Ni(OH)2 nanocomposites were further investigated using cyclic voltammetry and galvanostatic cycling in the low-voltage range.
* Address all correspondence to this author.
TEL: +82-31-219-2468; E-mail: dwkim@ajou.co.kr

We demonstrate the formation of multiphasic Ge-based nanocomposites comprising Ge, Cu3Ge, and CuGeO3 by thermal reduction process of initially prepared one-dimensional (1-D) CuGeO3 nanorods. CuGeO3 nanorods were prepared using hydrothermal process without any template and surfactant at 180 oC. The as-synthesized CuGeO3 nanorods exhibit single crystalline 1-D morphology with a diameter of ~40 nm and length of ~700 nm. By the thermochemical reduction of CuGeO3 nanorods under H2 flow at 200-300 oC, the rod-shaped morphology was retained but their phase partially transformed into a mixture of Ge and Cu3Ge. Especially the formation of Cu3Ge led to the improved electronic conductivity of these nanocomposites, compared with as-prepared CuGeO3 nanorods. We also evaluated the series of electrochemical properties such as cyclic voltammetry, galvanostatic cycling, and rate capability related to the phase evolution during thermochemical reduction process. The enhanced electrochemical performance in these multiphasic nanocomposite rods can be further discussed based on the efficient charge-transfer mechanism.

It has been known for some time that silicon can incorporate large amounts of Li with a specific capacity of 4200 mAh/g, about a factor of 11 larger than for state of the art graphite anodes. However, silicon and silicon-based negative electrodes exhibit huge volume expansion (ca. 270%) during lithiation/delithiation, resulting in mechanical disintegration of electrode and rapid capacity fading. Therefore, relaxation of the stress caused by the expansion and contraction of Li-Si alloy materials is important to obtain a good cyclability. In this study, we prepared oriented silicon nanowire arrays (SiNWs) on n-type silicon substrate by metal-assisted chemical etching in aqueous HF solution containing AgNO₃. The electrochemical properties of the SiNWs electrode were systematically investigated. The material characteristics have been analyzed by Cyclic voltammetry (CV), XRD, SEM and TEM. The performance of SiNWs electrode have been examined by galvanostatic charge/discharge cycling. In order to understand the fundamental mechanism of the lithium reaction to silicon and phase transformation in lithiated silicon (Li_xSi) phase during first cycle, we have investigated the lithium insertion and removal process in SiNWs by means of electron energy-loss spectroscopy (EELS) as well.

The spinel-structured LiMn2O4 and LiNi0.5Mn1.5O4 cathodes are of great interest because of the 3-D paths of Li+, high operating voltages, moderate theoretical capacities, and acceptable environmental friendliness. The LiMn2O4 cathodes suffer from poor cycling efficiency for long time operation, especially at high temperature, which is caused by the dissolution of manganese ion and the structural instability. Structural instability can be improved by incorporating cations, such as nickel ion, into the lattices, which, in turn, improves the cycle performance of the battery. Recently, the nanoparticles with the silica core have attracted great interest. SiO2-Li(Ni,Mn)2O4 nanospheres with the core-shell structure are valuable in enhancing the structural strength, since SiO2 particles ensures its high thermal stability.
In this work, SiO2-Li(Ni,Mn)2O4 core-shell nanoparticles are prepared and assembled as the cathode in a Li coin cell, and characterized its electrochemical properties. As the first step, monodispersed spherical silica nanoparticles are prepared from an alkaline solution of tetraethyl orthosilicate (TEOS). The nanoparticles are separated from the solution with a centrifugal machine. With the silica nanospheres in hand, the surface of SiO2 nanoparticles is modified and the MnCO3 layers are formed by the precipitation from the solution containing a manganese salt, a surfactant, urea, and the dispersed silica nanoparticles. The nanospheres of the SiO2 core covered with MnO2 layers are formed by heating the SiO2-MnCO3 in a furnace. Then, SiO2-LiMn2O4 or SiO2-Li(Ni,Mn)2O4 core-shell nanospheres are prepared by a solid-state reaction method from the SiO2-MnO2, NiCl2, and Li salt. The morphology and crystalline structures were analyzed by both a scanning electron microscope (JEOL JSM-6380) and X-ray diffraction (RigakuD/max 2700V/VP). The lithium batteries were assembled in a coin-type (CR2032) cell and galvanostatically cycled, using a multichannel battery cycler (Maccor S4000). The electrochemical characteristics of SiO2-Li(Ni,Mn)2O4 core-shell nanoparticle cathodes will be presented and discussed in detail.

Homogeneous LiF/Fe/Graphene hybrid material as cathode for lithium ion batteries have been synthesized firstly by a facile two-step strategy, which not only avoids the use of highly corrosive reagents and expensive precursors but also fully takes advantage of the excellent electronic conductivity of graphene. The capacity remains above 150 mA h g-1 after 180 cylces, indicating high reversible capacity and stable cyclability. Both the variation tendency of the capacity and the TEM image of the active materail after cycling reveal that the nano-LiF with a size of 100 nm underwent a pulverization process. Ex situ XRD and HRTEM studies on the cycled active material clearly confirmed the formation of FeFx and coexistence of LiF and FeFx at the charged state. By modification and optimization, the electrochemical performance will be further improved and the combination of nano-LiF with ultrafine Fe anchored on graphene sheets could open up a novel avenue for the application of fluorides as cathode materials.

Si nanocrystals embedded in SiOx nanoparticles as an anode material for Lithium-ion batteries were prepared using chemical reaction of Si precursor. High resolution transmission electron microscopy with x-ray diffraction analysis revealed that Si nanocrystals with the size of 5 nm were well dispersed in amorphous SiOx matrix. The electrochemical performances of these materials as anode materials for lithium ion batteries showed a reversible capacity of about 900 mAh/g with stable cycle performance over 50 cycles.

Self-catalyzed polyaniline (PANI) nanocoating on the surface of 0.4Li2MnO3 0.6LiMn0.33Ni0.33Co0.33O2 powders were prepared by chemical oxidative polymerization in the presence of hydrochloric acid (HCl) with aid of Mn+4 ions of the pristine as oxidants. The composition ratio of transition metals and the refined lattice parameters of PANI-coated 0.4Li2MnO3 0.6LiMn0.33Ni0.33Co0.33O2 were quite similar to those of the parent sample, indicating that polyaniline coating process had little effect on the crystallographic structure. Galvanostatic battery testing showed enhanced rate performance in the PANI-coated electrode comparing to uncoated pristine electrode: the discharge capacity of PANI-coated electrode was 98 mAhg-1 at a high current density of 480 mAg-1 (2.4 C rate), while the uncoated sample showed 68 mAhg-1 at the same rate. Furthermore, the discharge capacity was retained at 94%, while that of the pristine electrode was retained at 85%. This result suggests that self-catalyzed polyaniline nanocoating on the surface of cathode electrode act as a highly efficient protective layer at a high potential (4.8 V vs. Li0), thus allowing the electrode to operate at high rates.

This study investigates the effect of alumina (Al2O3) coating on lithium titanate (Li4Ti5O12) particles synthesized using a microwave-assisted method. Microwave heating is capable of rapidly coating Al2O3 layers on the surface of spinel Li4Ti5O12 within 6 min. The thickness of Al2O3 layer (i.e., 1-4 nm) is an increasing function of aluminum nitrate concentration under the microwave irradiation. The Al2O3-Li4Ti5O12 anode shows higher reversible capacity and better rate-capability compared to pristine Li4Ti5O12. The presence of Al2O3 coating significantly improved the high-rate capability of the composite anode with high Coulombic efficiency, indicating good reversibility of Li+ insertion/de-insertion. This can be ascribed to the fact that the Al2O3 layers perk up the conduction pathway among Li4Ti5O12 powders, thus improving electronic conduction and reducing cell polarization. Accordingly, the Al2O3 coating plays a crucial role in determining its electrochemical performance.

Silicon is a promising candidate for electrodes in lithium ion batteries due to its large theoretical energy density (4200 mAh/g). However, its poor capacity retention, caused by pulverization of Si structure during cycling, restrict its practical application. Recently, silicon nanotube structure has been proved being capable of accommodating large volume changes associated with lithiation in battery applications. We developed a new method to prepare nanotubed form of silicon which could be extended to large area without silane. The prepared electrodes exhibit high initial coulombic efficiencies (i.e., >85%) and stable capacity retention (>75% after 200 cycles), due to an unusual, underlying mechanics that is dominated by free surfaces. For further improving its performance, we insert graphite into the silicon nanotube by plasma-enhanced chemical vapor deposition (PECVD) method to enhance its conduction with the substrate. The capacity retention could be increased to over 90% after 200 cycles. Herein, we report on the preparation of silicon-graphite nanotubes and their highly reversible lithium storage and excellent high-rate capability. This result suggests that the as-prepared silicon-graphite nanotubes are promising candidates as the anode materials of rechargeable Li-ion batteries.

Next generation rechargeable batteries are required to have higher energy density compared to the state-of-art battery. The energy density of the commercial lithium ion battery cannot meet the stringent requirements, whereas the lithium-air battery has high theoretical specific energy coming up to 11700 Wh/kg because lithium-air battery is based on discharge reaction between Li and oxygen to yield Li2O2.[1-2] However, very little is known about the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the cathode of lithium-air battery. Moreover, lithium oxides like Li2O and Li2O2 is formed in cathode, which are impossible to be thermodynamically decomposed leading to an enormous irreversible reaction. Therefore, many efforts to overcome this problem have focused on finding proper catalysts to improve the ORR and OER. As reported previously, because one-dimensional materials in the form of nanowires, nanorods or nanotube have much higher surface area and better electronic conductivity than the bulk material, they have shown significant enhancement for the electrochemical reaction of various energy devices like fuel cell, lithium ion battery and solar cells.[3] So, we judged that the morphological effect of 1D nanomaterials could contribute to the enhanced ORR and OER property of lithium-air battery.
In this study, manganese oxides catalyst were synthesized, which have bulk, nanowires, and nanotubes, and their catalytic effects have been compared in the morphological or structural viewpoint.

A highly compressed hybrid glass doped with Cro/CrOx was prepared for energy storage and generation materials. The resulting glass shows a low thermal conductivity and high compressibility. When the laser beam goes through a solid medium, the density wave is usually linear; because, in solid media, heat doesn&’t decay through the solid medium effectively. Interestingly, the highly compressed doped glass shows a strong ‘acoustic response&’ as strong as liquid. In laser experiment, we also calculated ‘the coefficient of phonon diffraction (D)&’, which is proportional to the coefficient of thermal conductivity. The number (D) was FIVE times smaller than that of normal glasses; the thermal conductivity of the doped glass is FIVE times less than that of normal glasses. In addition, the diffraction efficiency, absorption light efficiency, (45%) of the doped glass is higher than that of methanol (25%), which means the COMPRESSIBILITY of the doped glass is as effective as liquid. Thus, Cr doped glass serves as a ‘effective heat storage and generator material.&’ The energy and heat captured in the doped glass gets transferred into expansion or compression effectively and thus creates acoustic wave more effectively.

The LiMn2O4-based spinels are presently one of the most promising cathode materials for high power lithium-ion batteries for hybrid electric vehicle (HEV), plug-in HEV, EV and energy storage systems because of its low cost, safety and excellent rate capability. Major drawback of spinel cathode has been noticed to be the interfacial reaction with electrolyte followed by Mn2+-dissolution and structural degradation, in particular, at elevated temperature. Crystal structure, interfacial structure and rate performance of spinel cathode can be stabilized by cation-doping for Mn atom and consequent control of Mn valence. We report here the evaluation of rate performance of cation-doped 4V spinel cathodes at elevated temperature and high rate- and high temperature-induced changes in structure and surface chemistry.
Acknowledgments
This work was supported by a grant from the Fundamental Materials & Components Technology Developing Program of Knowledge & Economy.

We synthesized free-standing tin chalcogenide nanocrystals(NCs) by means of novel gas-phase photolysis using an Nd:YAG pulsed laser. Gas phase precursors of Sn, S, and Se were tetramethyl tin, hydrogen sulfide, and dimethyl selenium, respectively. The composition and phase were controlled by their partial pressure in a closed reactor, yielding a series of orthorhombic phase SnSxSe1-x, and hexagonal Sn(SxSe1-x)2, (0le;xle;1). The SnSxSe1-x NC have a uniform diameter with an average value of 10nm, while the Sn(SxSe1-x)2 NC exhibits a sheet morphology (with a thickness of 10nm). The quantum-confined NC anchored on reduced graphene oxide exhibit a sensitive photo-detection behavior upon the UV-visible-NIR light irradiation. Moreover, the NC showed cycling performance and capacity when used as an anode material for the lithium ion batteries. This novel synthesis method of tin chacogenide NC is expected to contribute to expand the applications in high-performance energy conversion systems.

Nanoclay minerals play a promising role as additives in the liquid electrolyte to form a gel electrolyte for quasi-solid-state dye-sensitized solar cells (DSCs) because of their high chemical stability, unique swelling ability, ion exchange capacity and rheological properties. Here we report the improved performance of a quasi-solid-state gel electrolyte comprising a liquid electrolyte and synthetic hydrotalcite nanoclay. The calculated apparent diffusion coefficient (Dapp) of I3- for liquid (5.4 x 10-7 cm2/s) and nanoclay gel electrolyte (4.6 x 10-7 cm2/s) illustrates that the diffusion of redox ions is not much affected by the viscosity of nanoclay gel electrolyte. The power conversion efficiency can be achieved as high as 10.1% under 0.25 sun and 9.6% under full sun for nanoclay gel electrolyte and 8.8 % to that of liquid electrolyte. Almost 10 % improvement in efficiency is achieved with nanoclay gel electrolyte, the major contribution being the increased VOC, which are combined contributions from upraised conduction band energy of TiO2 and retardation of interfacial (TiO2/electrolyte) recombination. Higher Voc with undiminished photocurrent is achieved with nitrate-hydrotalcite nanoclay gel electrolyte for organic as well as for inorganic dye (D35 and N719) systems. Other factors such as weight percentage of nanoclay in electrolyte, photoanode thickness, illumination intensity and the solvent type of the electrolyte have also been investigated. This study demonstrates that nanoclay in electrolyte facilitates the improvement in efficiency of DSCs while alleviating the critical practical technological problems like solvent leakage and evaporation.
Keywords: Quasi-solid state, Anionic nanoclay, Hydrotalcite; Gel electrolyte, Dye-sensitized solar cells (DSCs)

The various designs and power needs of soft portable electronic equipments, such as roll-up display, electric paper and wearable systems for personal multimedia require the development of flexible energy devices. Supercapacitors have played an increasingly important role in power source applications, since they combine the advantages of high power of conventional capacitors and the high specific energy of batteries. In this talk, I will present the capacitive performance of nitrogen-containing carbon nanotubes (CNxNTs) with polyaniline (PANI) or poly(3,4-ethylenedioxythiophene) (PEDOT) nanocomposite electrodes. CNxNTs directly grown on carbon cloth were coated with protonated polyaniline (PANI) in situ during the polymerization of aniline, whereas PEDOT on CNxNTs-CC was synthesized by electrochemical method. The resultant structures of the PANI/CNxNTs-CC and PEDOT/CNxNTs-CC nanocomposites exhibit a coaxial and uniform coating of CNxNTs with PANI or PEDOT, respectively, with shell thickness ~30-50 nm, well within the diffusion length of protons in the polymers. The electrochemical properties and capacitive behavior of the supercapacitor electrodes were carried out by cyclic voltammetry and galvanostatic charge-discharge measurements. All these nanocomposite electrodes showed improved mechanical integrity, higher electronic conductivity, and exhibited larger specific capacitance and power density than the polymer alone. In a separate study, the electrochemical performance of PANI-nanowires on CC was tested when the cell is bent under high curvature. No deterioration was observed. For applications of flexible supercapacitors, these nano-architectural templates can have advantages in terms of light-weight, cost-effective manufacturability, form factor, and packaging flexibility, which is essential for sustainable flexible supercapacitors development and commercialization.

As a high surface area and electrically conductive material, graphene including chemically modified graphene, and negative curvature carbons, are promising as electrode materials for ultracapacitors and batteries, and as component materials in fuel cells, topics that we have done research on[1-6]. Graphene/graphite foam provides an excellent framework for attaching various nanostructures for use as a composite electrode in ultracapacitors and/or batteries [7]. Pristine graphene grown by CVD methods in large area[8] may eventually be stacked with dielectric layers like h-BN to make very high power density ultracapacitors. I will cover in this talk a variety of research projects underway in our group related to electrical energy storage and also describe what I think are some important new directions in carbon and first row element research for the next 10-20 years, and will suggest that once such materials are made, they will play an important important applications in energy storage. (As a historical footnote: our micromechanical exfoliation approaches [9,10] conceived of in 1998 yielded multilayer graphene and one paper described in detail how monolayer graphene could be obtained [10].) [Current or prior support of our work by the W. M. Keck Foundation, NSF, DARPA ‘iMINT&’, DARPA ‘CERA&’, ONR, SWAN NRI, ARO, AEC, DOE, Graphene Energy Inc.,and the SRC, is appreciated.]
1. Meryl D. Stoller et al., Nano Letters (2008), 8 (10), 3498-3502.
2. Zhu, Yanwu et al., Science 332, 1537-1541 (2011).
3. Stoller, Meryl D, et al.,Physical Chemistry Chemical Physics (2012), 14, 3388-3391.
4. Zhang, Li Li et al.,Nano Letters (2012), 12, 1806-1812.
5. Zhu, Xianjun; et al.,ACS Nano (2011), 5(4), 333-3338.
6. Lai, Linfei et al.,Energy & Environmental Science (2012), 5, 7936-7942.
7. Ji, Hengxing et al.,Nano Letters (2012), 12, 2446-2451.
8. Li, X. S et al.,Science 324, 1312-1314 (2009).
9. Lu XK, Yu MF, Huang H, and Ruoff RS, Tailoring graphite with the goal of achieving single sheets, Nanotechnology, 10, 269-272 (1999).
10. Lu XK et al.,Applied Physics Letters, 75, 193-195 (1999).

Carbon nanotube-interweaved-nanocrystal spherical composites composed of electrochemically active nanocrystals and CNTs with three-dimensional (3D) open porous nanostructures have been successfully synthesized by a facile spray technology, followed by thermal annealing. The produced composites have a hierarchically conductive pathway and interconnected pore networks, which achieves rapid electron and ion transport for electrochemical energy storage. As-fabricated energy-storage electrodes show battery-like capacity and supercapacitor-like power performance.

The superior properties of graphene, like high mechanical and chemical stabilities, specific area and excellent conductivity, lead to many potential applications in electronics, sensors, electrodes and nano-composites [1,2]. As a very promising substitute of batteries, supercapacitors with graphene electrode are found to exhibit longer circle life, high charge rate and energy density. The two main energy storage mechanisms of supercapacitors are electrical double layer (EDL) capacitance (surface ion absorption) and pseudocapacitance (redox reaction)[3,4]. Significantly, the intrinsic capacitance of graphene is as high as the upper limit of EDL capacitance for all carbon materials. Here we report supercapacitors with reduced graphene oxide as the electrode materials. The graphene was prepared from graphite oxide (GO) in two steps: exfoliating graphite with Hummer&’s method; reducing dispersed GO sheets with reducing agent. The interlayer distance was determined with XRD measurement. The interlayer distance for GO plates is 6.66Å (2theta;=13.2°) due to function groups such as carboxyl and hydrocyl during oxidation. However, it decrease to 3.61Å (2theta;=24.6°) after reduction, which indicates most of the oxygen function groups have been successfully removed. Raman spectrum shows a very clear broaden D band at 1352.3 cm-1 and G band at 1590.1 cm-1. And the intensity ration of D/G ratio is close to 1, further indicating the deoxygenation in the reducing process. The pore sizes of graphene sheets are around 4 nm, obtained by Barret-Joyner-Halenda (BJH) method.. The electrodes of supercapacitors were made by coating graphene on Ni mesh, mixed with katzen black as conductive additives and TAB-teflonionized acetylene black as binder. The coin cells were assembled by isolation of ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4)) using Celguard 3501 porous membrane as a separator. The cyclic voltammetry curves of the symmetric supercapacitors in ionic liquid maintain a near rectangular shape at scan rates of 20mV/s, 50mV/s, and 100mV/s, and respond quickly to voltage changes at each end, which proves a good capacitance behavior and rapid diffusion of electrolyte ions. Nyquist plots show a semicircle in high frequency region and straight spike in low frequency region. The equivalent series resistance of electrodes extracted from the real impedance intercept is 12 ohm, indicating a good charge-discharge rate and power density.
Acknowledgement: This work was supported by the World Class University (WCU) program through a grant provided by the Ministry of Education, Science and Technology (MEST) of Korea (Project No. R31-10026).
References
[1] Geim, A. K.; Novoselov, K. S. The rise of graphene. Nat. Mater. 2007, 6, 183 191.
[2] Li, X.; Wang, X.; Zhang, L.; Lee, S.; Dai, H. Chemically derived, ultrasmooth graphene nanoribbon semiconductors. Science 2008, 319 , 1229 1232.
[3] Conway, B. E. Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications; Plenum Publishers: New York, 1999.
[4] Simon, P.; Gogotsi, Y. Nat. Mater.2008 , 7, 845 -854.

Electrochemical supercapacitors using nano-carbon materials and electrolyte have very high capacitances but the maximum operating voltage is considerably low because of the breakdown of electrolyte. In many of supercapacitors, extremely dense and long carbon nanotube (CNT) forests were used to utilize much larger surface area resulting higher capacitances. Atomic layer deposition (ALD) is known as an advanced deposition system in which high aspect ratio (<100) structures can be conformally coated. Therefore, ALD can deliver conformal coatings on CNT forest as long as it meets the process window. However, the electric energy in a capacitor is proportional to the capacitance and squares with the maximum voltage. Having a higher voltage across the capacitors would be a great advantage to achieve a higher electric energy. Here, we report the hybrid supercapacitors using CNT forests and ALD dielectrics. Curly CNT forests are grown on Cu foil by supergrowth CVD process and then CNT forests are coated with high-k dielectric layers, hafnium oxide (HfO₂), using ALD technique. Two identical electrodes are brought together sandwiching an electrolyte (tetraethylammonium tetraflouroborate (TEABF₄) salts in propelyne carbonate) with a separator. In this hybrid structure, when a voltage is applied between the electrodes there is a certain fraction of the voltage dropping across the dielectrics and the remaining fraction falls within the electrolyte. The hybrid supercapacitor using HfO₂ (~35 nm) and supergrowth CNT forest showed a good cyclability (175 cycles) at the operation voltage of 3.5 V.

Wearable energy storage has proven to be an underdeveloped cornerstone to the advancement of smart and electronic textile applications. Our work on textile supercapacitors aims to provide a solution to the wearable energy challenges. Over the course of the last few years, our research has focused on developing devices made entirely of non-toxic materials and fabricated with well-established textile construction and printing techniques (knitting and screen printing) while providing performances comparable to the conventional packaged supercapacitors. Applications include powering wearable antennas, sensors, or harvesting energy from piezoelectric, thermoelectric and solar textile devices.
This work will provide a brief overview of the research conducted on wearable energy storage in the last few years, and define key metrics to consider when designing wearable energy storage, such as capacitance per area (F/cm²).
Our previous work focused on screen printing custom activated carbon inks into cotton and polyester textiles, achieving high mass per area (5 mg/cm²) in both fabrics. Our devices showed excellent gravimetric capacitance of 85 F/g with ESR as low as 4 Omega;-cm², (Jost et al., Energy and Environmental Science, 2011 (4) 5060-5067). Our most recent work has focused on fabricating our own carbon fiber current collectors knitted as a part of a full sheet of fabric. Knitting allows for the simultaneous fabrication of the different e-textile components to be integrated alongside our energy storage devices. These knitted current collectors are then screen printed with the same activated carbon paint, and employs a solid “no leak” electrolyte. The devices show capacitances per area of 510 mF/cm² per device, the highest reported capacitance for an all carbon textile system. We will show such results from cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy.

For the practical realization of portable, low-cost microdevices, integrated microscale energy storage is an important area that requires further development. Supercapacitors fill an important role in this energy storage landscape, with good power density and cycle lifetime relative to battery technologies. However, current commercial supercapacitors are primarily constructed with activated carbon electrodes, which are difficult to fabricate in a planar, on-chip configuration. Photoresist, by its very nature, is readily patternable, and can be pyrolyzed to form a conductive, porous carbon material, ideal for supercapacitor electrodes. The low cost and scalability of this technique make it attractive for integration into the fabrication of mobile or autonomous microelectronic and MEMS devices. We report on the optimization, characterization, and electrochemical activation of pyrolyzed photoresist for supercapacitor applications.
The physical and electrical properties of the pyrolyzed carbon film depend highly on pyrolysis conditions as well as post-pyrolysis treatments. In particular, the capacitance of the resulting carbon film can be optimized through changing the gaseous environment present during pyrolysis, which modifies the surface wettability of the material. Improving the wettability is a key consideration in increasing the accessibility of pore space to electrolyte and will be discussed. Additional treatments, including electrochemical activation, will be presented to show increased pseudocapacitance. We will present a thorough characterization of the electrode material as well as electrochemical data from techniques including cyclic voltammetry, galvanostatic charge/discharge, and AC impedance. Lifetime cycling in a variety of electrolytes, including ionogels, will also be shown to demonstrate the robust performance of the material over 10000 charge/discharge cycles and progress made toward a solid-state, flexible microsupercapacitor.

The field of graphene has stimulated a great deal of research since its isolation in 2004. The Kaner group has spent the last decade exploring new routes to graphene including chemical exfoliation, graphite oxide reduction, chemical vapor deposition and laser scribing. These methods have led to proof-of-concept devices from practical chemical sensors to memory storage to high performance supercapacitors. This talk will detail our many years of graphene-related research and highlight our most recent venture into 3-D graphene architectures. By creating electrically connected graphene layers with high surface area, light-weight electronics and high energy density storage devices look promising.

Micro-scale supercapacitors could provide an important complement to micro-batteries in a variety of applications, including portable electronic equipments, wireless sensors networks and other multifunctional micro-systems thanks to their fast charge and discharge rates (compared with rechargeable batteries) and long cycle life (hundreds of thousands of cycles). Most of them are nevertheless based on liquid electrolytes (aqueous or organic), which can be a major issue when it comes to the realization of functional components using silicon micro-fabrication technology.
This study reports the preparation of all-solid-state planar interdigitated micro-supercapacitors, using common micro-fabrication techniques, and based on ruthenium oxide pseudo capacitive materials prepared by electrodeposition from an aqueous solution of ruthenium chloride. A thin film of Au/Ti on the silicon substrate serves as the current collector. A photoresist wall between the fingers ensures a perfect separation of the two gold electrodes. Then, the gold surface is roughened by performing cyclic voltammetry in 0.5 M sulfuric acid solution [1] to increase the adherence of the ruthenium oxide deposit on the current collector. The electrochemical performance of the non-encapsulated cells were examined by electrochemical impedance spectroscopy and cyclic voltammetry in a solution of 0.5 M sulfuric acid and using a gel polymer PVA-H3PO4-H2O [2]. A specific capacitance of 11.4 mF/cm2 (per active area) was obtained at a scan rate of 500 mV/s in a solution of 0.5 M sulfuric acid. A comparison of performance for micro-supercapacitors with different electrolytes (liquid, gel, solid) will be presented in the final paper.

[1] L.D. Burke, P.F. Nugent, J. Electroanal. Chem., 444 (1988), 19.
[2] W. Yong-gang, Z. Xiao-gang, Electrochim. Acta, 49 (2004), 1957.

Although there have been reports on flexible batteries and supercapacitors, these are mainly thinned-down versions of conventional devices. Truly printable storage devices that can be easily fabricated using large-scale, solution-based, roll-to-roll processing, while still exhibiting good electrochemical performance, are still demanded. Although there have been plenty of reports on synthesis of new and advanced nanostructured materials for improvement of energy storage capacity and efficiency in batteries and supercapacitors, many of the proposed processing routes are not capable to be scaled up for large production of the device. In some cases, the process is too sophisticated to be efficiently used in a manufacturing line. In some other cases, the material cannot survive the manufacturing process and its property will deteriorate over process or over time. Having said that, many industries on manufacturing of batteries and supercapacitors are still sticking to conventional material and do not tend to approach novel high performance nanostructured materials developed by many researchers around the world.
In this context, we&’re willing to address this gap between nanostructured materials and actual workable devices. Through a scalable processing route a nanostructured manganese dioxide and Polyaniline are synthesized and transformed into form of a printable ink.The ink is used for screen printing of electrodes on ultra thin graphite paper for a supercapacitor device. No significant change in nanostructure of the active material was observed due to ink preparation and printing process. Through a roll-to-roll applicable route, the device is assembled using a fully solid polymer electrolyte based on PMMA and LiClO4 and the performance of the device is evaluated. Rectangular shape of the CV curves shows good cycling and low internal resistance. A reasonably good capacity of 89 and 121 F/g at a scan rate of 2 mV/s was obtained for MnO2 and PANI based electrodes respectively.
The columbic efficiency was calculated to be 92.8% and 90.1% for MnO2 and PANI respectively. The IR drop for MnO2 based electrodes are higher than that of PANI at a current density of 1 mA/cm2. The cyclability and capacity retention of the device based on MnO2 is better than PANI.

The current trend with portable electronics lies in continuous miniaturization, while enhancing the functionality and reliability of existing components. This has raised the demand for sufficiently compact on-chip energy storage. Microscale supercapacitors have great potential to complement or replace batteries and electrolytic capacitors in a variety of applications. However, conventional micro-fabrication techniques have proven to be cumbersome in building cost-effective micro-devices, thus limiting their widespread application. Here, we recently demonstrated high-performance ultrathin (<100 µm) supercapacitors by the direct laser scribing of graphene electrodes using a consumer grade LightScribe DVD burner [1]. Most recently, we successfully implemented this technique for the scalable fabrication of planar graphene micro-supercapacitors over large areas [2]. The process is simple, inexpensive and does not require masks, additional processing or sophisticated operation. More than 100 micro-supercapacitors can be produced on a single disc in 30 minutes or less. These devices are built on flexible substrates for flexible electronics and on-chip uses that can be integrated with MEMS or CMOS in a single chip. Remarkably, this technique allows for the fabrication of micro-devices without the use of organic binders, conductive additives or polymer separators that are often needed in commercial supercapacitors, thus leading to improved performance because of the ease with which ions can access the active material. A power density of ~200 W/cm3 was achieved which is among the highest values reported so far. These micro-supercapacitors exhibit exceptional electrochemical stability under different bending and twisting conditions; making them promising for the next generation of flexible portable electronics.
References:
[1] Maher F. El-Kady, Veronica Strong, Sergey Dubin, Richard B. Kaner, Science 335, 1326-1330 (2012)
[2] Maher F. El-Kady, Richard B. Kaner, Submitted (2012)

We have prepared flexible, transparent, dielectric capacitors by spraycasting very thin networks of single walled nanotubes (SWNTs) or silver nanowires (AgNWs) onto either side of free standing polymer films. Impedance spectroscopy showed these structures to behave as a capacitor in combination with a series resistance. Those capacitors with SWNT electrodes displayed optical transmittance between 57% and 74%, capacitances ranging from 0.4 to 1.1 mu;F/cm2 and series resistances ranging 400 Omega;/sq-10 kOmega;/sq. However, using AgNW electrodes gave similar transmittance and capacitance but series resistance as low as 60 Omega;/sq. Finally, he properties of these capacitors were invariant under flexing.

Conventional Li-ion batteries are manufactured by slot die or reverse roll coating electrode materials on metal foils and rolling the cathode-separator-anode sandwich into ‘jellyroll&’ cells, which are then packaged inside metal canisters to form cylindrical or prismatic cells. This limitation in form factor of batteries places several constraints in utilization of space in portable electronics. Moreover, the low mass loading achievable using these techniques and the weight of the inactive metal foils limits the energy density. If the components of a battery, including electrodes, separator, electrolyte and the current collectors can be designed as paints and applied sequentially to build a complete battery, on any arbitrary surface, it would have significant impact on the design, implementation and integration of energy storage devices. Here, we establish a paradigm change in battery assembly by fabricating rechargeable Li-ion batteries solely by multi-step spray painting of its components on a variety of materials such as metals, glass, glazed ceramics and flexible polymer substrates. A typical spray painted Li-ion battery was based on lithium cobalt oxide (LCO) cathode, lithium titanium oxide (LTO) anode where a lithium ion conducting microporous gel electrolyte (MGE) was used as a separator. A cell spray painted on 25 cm² area was able to hold 30 mAh of capacity at 2.4 V and was cycled for more than 60 cycles with ~98% coulombic efficiency. The total device thickness was <500 mu;m. Spray painted batteries can be made with any arbitrarily shaped footprint and could lead to higher energy density and better utilization of spaces in portable electronics, with added mechanical stability and safety.

An important trend in electronics involves the development of materials and fabrication techniques that enable the use of unconventional substrates, such as polymer films, metal foils, paper sheets or rubber slabs. The last possibility is particularly challenging because the systems must accommodate not only bending but also stretching, sometimes to high levels of strain (>100%). Although several approaches are available for the electronics, a persistent difficulty is in energy storage devices and power supplies that have similar mechanical properties, to allow their co-integration with the electronics. In this talk we describe a set of materials and design concepts for a rechargeable lithium ion battery technology that exploits thin, low modulus, silicone elastomers as substrates, with a segmented design of the active materials, and unusual ‘self-similar&’ interconnect structures. The result enables reversible levels of stretchability up to 300%, while maintaining energy densities of ~1.1 mAh/cm2. Stretchable wireless power transmission systems provide means to charge these types of batteries, without direct physical contact.

There has been a global trend to develop a safe lithium-ion battery with high energy density that meets the emerging applications in the mobile electronics. The research effort on the cathode has been centered on high-Ni-content and lithium-rich transition metal oxides, which can deliver a reversible capacity of more than 200 mAh/g. However, naturally unstable Ni3+ ions are apt to reduce to Ni2+ on the cathode surface in the form of NiO, and this reaction accelerates with increasing temperatures. Further structural instability from the higher oxidation state of Ni4+ with increasing cut-off voltages leads to substantial oxygen generation from the lattice at elevated temperatures. Recently, larger amounts of Ni were substituted by electrochemical inactive Mn ions to render such inherent problems, but increasing the Mn content increased the charge transfer resistance, resulting in decreased electrochemical performance (rate capability). On the contrary, increasing Mn content preserves initial structural integrity during the high-temperature heating as well as electrochemical cycling. In this regard, coating or core-shell methods on the cathode material may lead to solve both rate capability and thermal instability upon delithiated states. In the case of anode materials, nano-structured Si-based composite materials showed promise of significantly higher specific capacity than that of the conventional graphite anode, but larger amounts of heat generation from the nano-sized Si in spite of carbon coating is still great concern.
In this talk, I am going to present recent activities on high capacity cathode and anode materials with thermal stability of lithium-ion batteries for mobile electronics.

Metallic Tin as anode has been considered in Li- ion batteries due to its high specific capacity and appropriate Li storage potential. However, the Sn anode experience large volume expansion during lithiation process, which inhibits from practical application. In order to overcome these limitations, one solution is to use Sn in carbon matrices such as one dimensional carbon nanotubes (CNT) or two dimensional graphene sheets.
In our study, Tin nanoparticles have been grown over Graphene Nanosheets (GNSs) through thermal evaporation. The vertically oriented GNS thin film has been synthesized by microwave plasma enhanced chemical vapor deposition at relatively low temperature (673K).
The thicknesses of the nanoparticle films and their surface chemistry have been investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The electron microscopy images show that Tin nanoparticles are less than 50nm in size and are attached to the walls of graphene sheets. Electrochemical properties of Sn nanoparticles attached to the graphene sheets are studied by cyclic voltammetry (CV) and galvanostatic cycling at a constant current density. Thin film anode assembled in Swagelok cells exhibited an initial discharge capacity of 655 mA/g and reduced to 606 mA/g at the second cycle at current of 50µA. The cell gave constant discharge capacity even after 30 cycles. Similar performance has been exhibited even when the discharge current was increased upto 250µA.

Nanoporous Si networks fabricated by a simple and scalable solution process using hydrofluoric acid were found to have good capacity and cycling performance during cycling with Li. These nanoporous Si networks can be released from Si wafers and transferred to many flexible and conductive substrates. An initial discharge capacity of 2000mAh/g was found to be stable over 20 cycles. The capacity is maintained above 1000mAh/g after 2000 cycles (2C rate). Structure characterization revealed that the nanoporous Si networks remain intact and connected to the current collector after cycling. Thus, nanoporous Si networks anodes are promising candidates for the development of high performance lithium batteries especially in mobile applications.

Sulfur is an exciting cathode material with high specific capacity of 1,673 mAh/g for high-energy batteries although its development has been impeded by rapid capacity fading due to three major materials problems: large volume expansion during lithiation, dissolution of intermediate polysulfides, and low ionic/electronic conductivity. Herein, we report a novel concept of monodisperse polymer-encapsulated hollow sulfur nanospheres as cathode materials for lithium-sulfur batteries, presenting a rational design to address all the aforementioned materials challenges. Compared with currently available methods for sulfur cathode modification, our simple, room-temperature, one-step aqueous solution synthesis is highly scalable for low-cost and high-energy batteries. We demonstrate high specific discharge capacities at different current rates (1179, 1018, and 990 mAh/g at 0.1C, 0.2C and 0.5C, respectively), and we show exceptional long cycling stability with a capacity decay as low as 0.046% per cycle at 0.5C and Coulombic efficiency of 98.5% over 1000 cycles.

Silicon is an attractive anode material for lithium ion batteries because of its highest theoretical capacity. However, intrinsic properties of silicon, e.g. pulverization due to repeating volume change in cycling, and low lithium ion diffusivity in silicon, set hindrances for silicon to be used in high power-density battery. Here we find porous structured silicon can give great performance as the anode material for lithium ion battery. Theoretical study shows the pores can help to stabilize the structure by means of providing additional spaces to accommodate large volume change during cycling, and therefore release the stress and strain inside silicon. In addition, pores introduce large surface area accessible to electrolyte, which helps to shorten the diffusion length for lithium ions. Experimentally, porous silicon nanowires were synthesized by electroless etching on silicon wafer. By combining with an alginate binder, the porous silicon nanowire shows capacity larger than 1000 mAh/g after 2000 cycles at current rate of 4 A/g. Control studies illustrate the good cycling performance mainly comes from the porous structure, while alginate binder also helped to certain degree as compared to commonly used polyvinylidene fluoride (PVDF). Beyond that, we have developed a scalable method to get porous silicon nanoparticles, which can be synthesized in a large quantity and cost-efficient way. While anodes using porous silicon nanoparticles exhibited specific capacity above 1000 mAh/g at current rate of 0.4 A/g, we have found that when wrapped with reduced graphene oxide, porous silicon nanoparticles showed much improved performance, with specific capacity above 1400 mAh/g and 1000 mAh/g at current rates of 1 A/g and 2 A/g, respectively, and stable operation up to 200 cycles tested. We attribute the overall good performance to the unique combination of porous silicon that can accommodate large volume change during cycling and provide large surface area accessible to electrolyte, and reduced graphene oxide that can sever as elastic and electrically conductive matrix for the porous silicon nanoparticles.

Solar cells fabricated from CuInSe2 (CISe) and Cu(In,Ga)Se2 (CIGSe) thin films via the 3-stage co-evaporation under high vacuum conditions have achieved 20% efficiencies . The more economical solution based deposition of CISe or CIGSe with the use of hydrazine had yielded high efficiency of 15.2%. Other non-vacuum approaches such as nanoparticle approach or nano-ink approach have also produced decent efficiencies. An easy and direct aqueous spray pyrolysis approach to deposit CuInS2 (CIS) thin film followed by selenization to form CuIn(S,Se)2 (CISSe) was demonstrated to achieve power conversion efficiency of 4% under standard AM1.5 illumination. Aqueous spray pyrolysis is an environmentally friendly and safe approach as compared to hydrazine and it does not involve any ligands or carbon compound that will affect device performance. This deposition technique also has the ability to scale up easily.
The tuning of spray deposition rate coupled with an excess of sulfur in precursor spray solution had successfully prevent the oxidation of Mo substrate at high temperatures. The avoidance of organic solvent result in carbon free CIS thin film formed which was subsequently verified by Energy Dispersive X-Ray analysis (EDX). The presence of carbon layer in the device might possibly affect the electrical properties of the device. In addition, EDX analysis did not detect any impurities (O, Cl etc) in the film.
Selenization of as deposited CIS to form CISSe was important as it assist in grain growth. Selenization temperature of 460°C is deployed for duration 30 min. The bandgap of CISSe was reduced as Se replace S during the process. High performance CIGS devices had a bandgap of around 1.17eV. Structural characterization of CIS and CISSe thin films were performed by Scanning Electron Microscopy, X-Ray Diffraction and Raman Spectroscopy.

Currently, communication system using radio frequency (RF) is the mainstream of functional devices. In the case of wireless communication devices such as cell phone, tablet PC, and medical device, it can transmit electrical signal from one device to another device without the use of any wire. Even, to remove wire for power charging, many efforts are made to transmit electrical power using RF technology. However, this technology is not suitable for transmitting power due to limitations such as, low power efficiency, path loss, and noise caused by interference of outside objects. These problems are critical challenges when RF technology is applied to power transfer between implanted human sensory system and external interfaces because the path loss of RF electromagnetic wave in water is much more severe than that of air as 80% of human body is composed of water molecules that vary the electrical conductivities at every tissue level. To overcome the limits, this paper focuses on magnetic induction communication (MIC), which uses magnetic coupling of a pair of coils to transmit a signal and a power between devices. For magnetic field, the path loss due to water or other liquid medium is quite smaller than that of RF wave. So far, most of the research results have shown power transfer using macro-size coil structure. However, medical implant communication poses serious challenges on physical dimensions of the implant device and thus the size of the transmitter. Moreover, the micro-size antenna can have poor transmittance efficiency due to its small size effect. Therefore, micro-size antennas with advanced structures are investigated to overcome these challenges. This paper describes the coil designs and characteristics of power transfer between transmitter (Tx) and receiver (Rx) with a high transmittance efficiency. Various designing micro-size coils of Rx antenna were fabricated by photolithography process, with different widths, turns, and diameters. To enhance the receiving efficiency, we added nano-structures such as carbon nanotube (CNT) or nanowire to the micro-antenna structure. Nanotube/wire provides a better effect to concentrate magnetic field as well as the increases of surface density. Additionally, we have observed that the despite of the smaller physical dimensions, these induction based coil systems are capable of relatively significant power transfer at resonant frequencies. It can be an ideal characteristic to protect other human organs or implanted devices.

Lithium-ion batteries are integral to today&’s information-rich society. Continual efforts have been devoted to the development of lithium-ion batteries with higher capacity and improved electrochemical performance for future advanced portable devices. With the highest theoretical charge capacity (4200mAh/g) and relative low Li-uptake potential (<0.5V vs. Li/Li+), silicon has attracted intensive researches to replace graphite (capacity of 372mAh/g) as new type lithium-ion battery anode. Yet silicon suffers from pulverization and subsequently disconnects from current collector due to severe volume variation upon lithiation and delithiation. Here we reported a three-dimensional porous Cu supported Si architecture as lithium-ion battery anode with improved cycleability and rate capability. The capacity is as high as 2400mAh/g at current density of 1.4A/g, with 90.5% capacity retention after 200 cycles. For higher charge/discharge rate, our battery delivered a reversible capacity of about 1500mAh/g under current density of 12.6A/g, with 83% capacity retention after 1000 cycles. The improved electrochemical performance is ascribed to the three-dimensional porous Cu structure, which provides structural support to the Si active material and allows facile strain relaxation of Si during charge and discharge processes.

Transition-metal oxides (TMOs) have recently attracted great attention as the promising high-performance materials for next-generation lithium-ion batteries because of their much higher lithium storage capacities than that of commercial used graphite (372 mAh/g).[1] TiO2-based materials are one of good candidates due to its high capacity, chemical stability, environmental benignancy and low cost. However, similar to other TMOs materials, one major challenge for the TiO2-based materials used as the anodes is large changes in structure and volume during the lithium ion insertion/extraction process resulting in poor cycling stability. One possible approach to improve the electrochemical performance of TiO2 materials is to use well-configured nanostructures ranging from zero-dimensional nanoparticles to multidimensional assembles.[2,3] In this work, the TiO2 nanotubes were prepared by a simple hydrothermal process without the use of an autoclave. These TiO2 nanotubes have high special surface area of up to 260 m2/g with hollow cores and open tips. To further enhance the conductivity of TiO2 nanotubes, glucose was added to form carbon-coated TiO2 nanotube composites. The TiO2 nanotube/carbon composites show high reversible capacities of 180-695 mAh/g at 0.1-5C and almost full capacity retention over 50 cycles after the second cycle. The enhanced electrochemical performance could be attributed to the ultrathin structure of nanotubes allowing good and rapid lithium ion diffusion.
Reference:
[1] J. H. Ku, Y.S. Jung, K.T. Lee, C.H. Kim and S.M. Oh, Journal of the Electrochemical Society, 2009, 156, A688;
[2] Z. Yang, G. Du, Z. Guo, X. Yu, Z. Chen, T. Guo and H. Liu, Journal of Materials Chemistry, 2011, 21, 8591;
[3] Z.Y. Wang, L. Zhou, X. W. Lou, Advanced Materials, 2012, 24 (14), 1903.

We report the use of water-triethylene glycol(TEG) as a solvent to synthesizeLiFePO4 (LFP) nanorodswith uniform size. TEG, a reducing agent in the reaction, promotes the formation of LiFePO4. Crystal phase and growth behavior were monitored by powder X-ray diffraction (XRD), synchrotron X-ray Diffraction, as well as transmission electron microscopy(TEM), while particles morphologies were investigatedwithscanning electron microscope (SEM).Three crystal growth mechanisms during the synthesis were interpreted based on the time study of the samples.Initially, the nucleation of LFP (20nm thick sheets) occurred accompanying with the formation of Fe3(PO4)2 8H2O(vivianite). This metastable phase evolved into spindle-like olivine LiFePO4 through oriented attachment (OA) of LFP primary nanosheets. With the increasing reaction time, the pH decreased with the concurrent formation of LiFePO4. The dissolution-recrystallization process, i.e. Ostwald ripening (OR), results in evenly distributed LiFePO4 nanorodsdue to the increased solubility of LiFePO4.The mechanism (from nanosheet to spindleto rod) revealed by this study will help develop guidelines to control the size and morphological features of LFP more precisely.

All solid state batteries (SSBs) are believed to have higher system level volumetric energy density and greater safety compared to the commercially available Li-ion batteries based on flammable liquid electrolytes. Safe and high energy density batteries are highly desired for the future generation electric vehicles and batteries in portable consumer electronics. Electrolyte has a significant role in limiting the energy density (Wh/L and Wh/kg) of a cell. For an ideal solid state electrolyte high electrochemical stability window (>5.5 V vs Li/Li⁺), high ionic conductivity at room temperature (RT) with negligible grain boundary resistance is necessary. It should also have stability against chemical reaction with both anode and cathode materials under processing and operating conditions. Li₇La₃Zr₂O₁₂ (LLZO) with garnet structure is one such electrolyte with high Li-ion conductivity at RT (~10^-4-10^-3 S/cm for cubic phase and ~10^-6 S/cm for tetragonal phase). In literature all the ionic conductivity measurements were done for 2-3 mm thick and 60-98% dense LLZO pellets. So far there have been no serious efforts to develop thin and flexible films based on LLZO. Thick pellets of ceramic based electrolytes are prone to fail when a battery is exposed to mechanical or thermal shock. This also limits the fabrication of large area cells with different form factors. In this work we have studied the chemical interaction of tetragonal phase of LLZO powder with N-methyl pyrrolidone (NMP) and polyvinyl di-fluoride (PVDF). Both NMP and PVDF are commonly used for battery material processing. Chemical interaction of tetragonal-LLZO was studied with PVDF and NMP separately and also in a mixture of PVDF and NMP. X-ray diffraction, thermal gravimetric analysis and Raman spectra all confirmed the partial phase transformation of tetragonal-LLZO to cubic-LLZO at RT in the presence of PVDF or NMP or both PVDF and NMP. Electron diffraction was used to further study the phase transformation of tetragonal LLZO.

Cathode materials of Li-ion batteries have been developing to achieve high energy density for the burgeoing technogies such as electric vehicles and eneegy storage systems. Recent studies have been focused on fluoro-polyanion compounds because of their high potential and good stability. Among known fluoro-polyanions compounds, LiVPO4F is a promising cathode material because of its high potential (4.2V) and large theoretical capacity (156mAh/g). Moreover, LiVPO4F shows good reversible capacity (more than 120 mAh/g at a C/2 rate after 200 cycles) and high thermal stability even at the charged state[1,2]. However, a complicated synthetic process is a main drawback of LiVPO4F to be widely utilized. Typically, LiVPO4F is synthesized via an intermediate compound, VPO4 which is obtained by CTR (Carbon Thermal Reduction) reaction. This two-step process via an intermediate compound, VPO4, can be problematic and difficult to obtain high purity LiVPO4F.
In this study, high-purity LiVPO4F is easily synthesized by simple single-step solid-state reaction without using an intermediate compound, VPO4. We will discuss about the developed synthetic process, mechanism And electrochemical performance of LiVPO4F. Also, we will show that the developed process can extend to other fluoride compounds.
[1] J. Barker Journal of Power Sources 146 (2005) 516-520
2] H.Haung, Journal of Power Sources 189 (2009) 748-751

SOFC (Solid Oxide Fuel Cell) is considered as a promising eco-friendly energy source of the future because of its high energy conversion efficiency with its high operating temperature. This leads to challenges in commercialization due to the difficulties in ensuring stability and reliability of sealant and connecting materials at high temperatures. Thus, various attempts have been made to lower the operating temperature in order to solve these issues. A proposition was made to manufacture a layered planner SOFC module structure by layering and co-sintering YSZ (Yttria Stabilized Zirconia) sheets together to develop a structure with low volume and high degree of cell integration. In this study, the solid electrolyte layers and the supporting layers were formed on the YSZ green sheet through the tape casting method in order to prepare one-bodied multi-layer SOFC structure. And LSM powders were made into paste for cathode electrode and NiO powders for anode. These pastes were screen-printed on the YSZ green sheets with porosity control. Various phenomena occurred during co-firing such as warpage, interfacial reaction between electrode and ceramic body, and delamination were analyzed to suppress them and the optical condition for one-bodied SOFC was investigated.

Layered metal sulfides were initially investigated as cathode materials for Li-ion batteries back in 1980s. Recently there are renewed interests to use metal sulfides as alternative anode materials. Layered Cu2WS4 with a tetragonal structure was synthesized for the first time by Pruss et al [Pruss et al, Angew. Chimie. Int. Ed., 1993, 32, 256-257]. We were successful in preparing Cu2MoS4, an isostructure of Cu2WS4 and have evaluated these materials Cu2MS4 (M = Mo, W) for Li batteries application. The theoretical capacities of Cu2MoS4 and Cu2WS4 are 152 and 122mAh/g, respectively assuming 2 electrons transfer. The capacities can be as high as 610 and 488mAh/g, respectively for a full conversion reaction of 8 electrons transfer. From experiment, Cu2MoS4 gives an initial capacities of about 180 mAh/g and 450mAh/g when discharged to 1.6V and 1V vs. Li/Li+, respectively, corresponding to 2 and 6 electrons transfer. About 120mAh/g of it is reversible between a 1.6 and 3V range with relatively good cycleability. But capacity fading is significant when tested between 1 and 3V. We attributed this to Cu dissolution from the material. Cycle performance can be improved by making graphene-composite with Cu2MoS4. Physical characterization by scanning electron microscopy and surface area analysis, as well as studies on charge-discharge mechanism by X-ray diffraction and cyclic voltammetry were conducted and the results will be presented at the meeting.

In this contribution we present the use poly(3,4-ethylenedioxythiophene) (PEDOT) as a model compound for the optimization of electroactive polymer-based supercapacitors. As there are many variables that affect the morphology and charge storage properties of electrochemically deposited films, the deposition conditions were systematically investigated to obtain films with the highest possible capacitance. The different variables included: type and concentration of electrolyte, film thickness, and deposition method (potentiostatic, galvanostatic, and potentiodynamic). This evaluation was done for both aqueous and non-aqueous electrolytes; the latter encompassing conventional propylene carbonate-based electrolytes as well as ionic liquids. We also tested a variety of different electrode materials ranging from flexible metallic substrates to 3D metallic structures to 3D carbon foams. By using the 3D electrodes we are able to increase the surface area of the electrode allowing us to deposit larger amounts of electroactive polymer. The electrode and device performance, as well as the electrochemical stability, was evaluated using cyclic voltammetry and galvanic cycling whereas the morphological characterization was done using profilometry, SEM, and optical microscopy.

An efficient microwave-assisted polyol (MP) approach is report to prepare SnO2/graphene hybrid as an anode material for lithium ion batteries. The key factor to this MP method is to start with uniform graphene oxide (GO) suspension, in which a large amount of surface oxygenate groups ensures homogeneous distribution of the SnO2 nanoparticles onto the GO sheets under the microwave irradiation. The period for the microwave heating only takes 10 min. The obtained SnO2/graphene hybrid anode possesses a reversible capacity of 967 mAh g-1 at 0.1 C and a high Coulombic efficiency of 80.5% at the first cycle. The cycling performance and the rate capability of the hybrid anode are enhanced in comparison with that of the bare graphene anode. This improvement of electrochemical performance can be attributed to the formation of a 3-dimensional framework. Accordingly, this study provides an economical MP route for the fabrication of SnO2/graphene hybrid as an anode material for high-performance Li-ion batteries.

Research on improving performance of supercapacitor for next generation energy storage medium has become an important issue. In particular, recent efforts to integrate pseudo capacitance materials and carbon nanotubes have been focused to realize high power and energy densities of electrode. We developed a carbon nanotube (CNT)/MnOx core-shell structured electrode in order to achieve high-rate performance and reasonably high capacitance. Amorphous manganese oxide, one of promising pseudo capacitive material, was electrochemically deposited onto surface of bare yarn electrode which was prepared by twisting multiwalled carbon nanotube sheets. The shell part of nano-structured MnOx film is advantageous for pseudo-capacitive reaction by compensating its poor electrical conductivity. Due to single composite electrode in micro-scale (about 20 mu;m in diameter) and its flexibility, it can be used for specific application such as micro-scale, miniaturized devices where the use of two-dimensional typical film type supercapacitor is limited.

Continuous down-scaling of electronic devices and circuits, increased speed and integration densities has led to severe problems with thermal management of computer chips [1]. Further progress in information technologies requires more efficient heat removal methods. Thermal interface materials (TIMs) - applied between the heat sources and heat sinks - are essential ingredients of efficient thermal management. The function of TIMs is to fill the micro-scale gaps between two contacting materials to enhance the heat conduction through the interfaces. It has been suggested that increasing the thermal conductivity of commercial TIMs from ~5 W/mK to about ~25 W/mK at room temperature (RT) would allow for an additional increase in the clock frequency. It was recently demonstrated that the use of graphene as a filler in TIMs allows one to substantially increase their effective thermal conductivity [2-3]. However, the efficiency of TIMs is not determined by the thermal conductivity alone. One needs to minimize the overall thermal resistance between the heat source and the heat sink. The latter requires a low thermal contact resistance of TIMs with the given surfaces and a small bond line thickness (BLT). In this presentation, we report the results of testing of various types of TIMs under realistic conditions. In this work TIM&’s performance was evaluated from the temperature rise in the computer CPU. The tested TIMs included the highly rated commercial products such as Ice-Fusion, GC Extreme, Arctic Alumina, Zalman, EC 360 and Arctic Silver Céramique 2. We used the same cleaning procedure and mounting pressure in experiments with five different computers and a laptop. The control experiments were performed with computer chips without any TIMs applied. In the overclocking trials we compared the respective temperature maximums to that of the control setup using a program that logs temperature fluctuations. It was found that TIMs with the highest value of the thermal conductivity are not necessarily those that minimize the CPU temperature rise. The viscosity of TIMs was a major factor determining the performance of TIMs. The latter suggests that TIMs with graphene fillers that require low loading fractions for achieving the high thermal conductivity have a substantial advantage over the conventional TIMs.
The work in Balandin group was supported, in part, by SRC - DARPA through FCRP Functional Engineered Nano Architectonics (FENA) center and the Winston Chung Global Energy center at UCR.
[1] A. A. Balandin, “Chill out: New materials and designs can keep chips cool, IEEE Spectrum, 29, 35 (2009).
[2] K.M.F. Shahil and A.A. Balandin, "Graphene - multilayer graphene nanocomposites as highly efficient thermal interface materials," Nano Letters, 12, 861 (2012).
[3] V. Goyal and A.A. Balandin, "Thermal properties of the hybrid graphene-metal nano-micro-composites: Applications in thermal interface materials," Applied Physics Letters, 100, 073113 (2012).

Porous tubular carbon nanorods with large surface area and improved electrochemical properties have been successfully prepared. The synthesis involves the preparation of rod-like nickel-hydrazine complexes in reverse micelles, coating the rod-like templates with a phenolic resin and silica, thermal treatment to carbonize phenolic resin and decompose nickel complex, and finally etching of the silica and nickel to obtain tubular carbon nanorods. With the help of silica coating, aggregation is prevented during carbonization. The etching of SiO2 also results in a good water dispersity of the products. We have been able to identify the optimal calcination temperature to produce tubular carbon nanorods that possess both large surface area and high electrical conductivity, and therefore show excellent electrochemical performances. The specific capacitance of the designed carbon nanomaterials is 132 F/g which is very close to the calculated specific capacitance (141 F/g) and is much higher than that of pure CNTs possessing the similar structure (50-100 F/g). Notably the energy density is 7.8 Wh/kg at power density of 22.5 kW/kg, which far exceeds the power requirement of PNGV (Partnership for a New Generation of Vehicles, 15 kW/kg). The strategy of preparing tubular carbon nanorods using hard templates in reverse micelles promises a robust and useful method for designing nanomaterials with improved electrochemical performance.

In this study, we report the effect of the crystallographic orientation of silicon nanowires (SiNWs) on electrochemical performance as an anode material. We synthesize vertically aligned SiNWs from differently oriented Si substrates with axial orientations of Si <100>, <110> and <111> by the metal-assisted chemical etching method. To investigate the influence of a carbon matrix on SiNWs, different ratios of carbon/SiNWs are incorporated into the anode materials. The electrochemical performance of the <110>-SiNWs is greatly improved with an increasing carbon/SiNWs ratio from 0.5 to 2 compared to the <100> and <111>-SiNWs. The electrochemical results reveal that the reversible capacity of more than 3,200 mAh g-1 at a current rate of 0.1 C was obtained by using <110>-SiNWs with a carbon/SiNWs ratio of 2. The enhanced electrochemical performance is attributed to the relatively large interspacing between atoms along the <110> direction and this is much larger than those along the <100> and <111> directions. We also suggest that a large amount of carbon accommodate the volume expansion that occurred during the Li insertion/extraction processes and increased the electronic conductivity.

Titania-nanoparticle-based solar paint is developed using simple and facile method which gives a conversion efficiency of 3.6% on FTO/glass substrates under fully room temperature processing. This paint can be applied easily either by doctor blading or by simple hand-held brush painting. It cures quite quickly making the cell fabrication process time saving as well. On a flexible ITO/PET substrate also an efficiency of 1.4% is achieved using the same paint by a fully room temperature fabrication protocol. The efficiency can be enhanced to 2.4% with the addition of a light harvesting layer. The paint was made by varying and optimizing the tBA: TiO2 weight ratio to achieve high quality adherent films with good transport properties, dye loading, IPCE and hence conversion efficiency. The weight ratio between tBA and TiO2 nanoparticles is the key to the success of the binder-free room temperature paste protocol. In addition to the ratio of solvent precursors, another important parameter required to be optimized for the best performance of the titania electrode for DSSC is the film thickness. The effective optical absorption length, internal light scattering, series resistance all depend on the thickness and morphology in a fairly complex way. This is all the more important for the case of room temperature processing because the electronic grain connectivity, which is a critical parameter governing the optoelectronic performance, has no thermal assistance. A detailed study was performed to show the effect of film thickness (varied from 3 µm to 17 µm) on the transport properties and eventually on the DSSC performance using impedance measurements. The effect of annealing on the solar cell I-V characteristic was also explored for the case of FTO glass substrate. Annealing at 450oC leads to a significant enhancement of efficeincy to 5%, as expected, due to better sintering of grains and hence improvements in the solar cell quality factors. The details of all the corresponding optimizations will be presented and discussed.

Because of the superior characteristics of silicon, such as stability and efficiency, many research groups have continued to study silicon solar cells actively. The sub-micrometer thickness of single-crystal silicon by advanced manufacturing techniques can realize thin, light-weight and flexible silicon solar cell deviated from the wafer based rigid device. In this paper, we deal with thin film Schottky-junction solar cells made from n-type single-crystal silicon membrane and p-doped graphene on plastic substrate by transfer printing. We have obtained interesting results that show the improved efficiency of thin silicon solar cell due to the work function modulation of graphene by doping process. In addition, this process decreases the cell series resistance and increases the open circuit voltage. Moreover, graphene/n-Si solar cell on the plastic substrate also exhibits the stable energy conversion characteristic under the bending state. Although, the thin film Schottky-junction solar cells still have lower efficiency, additional study will lead to much more available in near future.

All-solid-state thin film lithium batteries have been roundly received attention as energy storage source in various filed such as MEMS, CMOS, and smart cards devices, and some innovated properties are recently required such as stretchable and flexibility. In order to fulfill a requirement, using the conventional polymer substrate is needed. However, the cathode thin film, which is a critical component of thin film battery, certainly calls for annealing process to achieve great crystallizability. Eventually, the polymer substrate goes through sudden changes because of its poor resistance to high temperature, so a new direction of crystallization should be considered.
Here, we fabricated flexible Sn-LiMn2O4 cathode thin film on polyimide (PI) substrate. The deposited cathode thin films were crystallized by the intense pulsed light treatment (IPL) which consisted of a xenon flash lamp which has a broad spectrum, so that it could cover the plasmon excitation wavelength of cathode thin film. Structural properties of the thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The electrochemical properties were evaluated as a half cell by WBC3000 battery cycler. The results of this study shows the applicability of well-crystallized cathode film at low temperature, and it will be an important method in flexible devices.

This study focused on the synthesis of Pt/MWCNT electrocatalyst prepared by polyol method. As a support material was used MWCNT treated by sonochemical method using sulphuric acid -nitric acid mixture and sulphuric acid -hydrogen peroxide mixture. Structural and electrochemical characterization of synthesized Pt/MWCNT was carried out by XRD method and cyclic voltammetry, respectively. According to the XRD analysis the particle size of Pt was determined 2 nm. The electrochemical activity of catalyst that is indicated by the electrochemical active surface area is studied by cyclic voltammetry using screen printed carbon electrode.

Fuel cell is next generation energy device that converts chemical energy to electrical energy directly without any mechanical conversion processes. Polymer Electrolyte Membrane Fuel Cell (PEMFC) has advantages of low operating temperature, highly efficient energy conversion compared with other energy conversion devices and its safe operation. So it has been developed for electric vehicles. But it has problems that a large amount of noble metal catalysts are needed to overcome slow catalytic process and mass transfer loss is occurred due to water flooding phenomenon.
In this study, Poly(N-isopropylacrylamide) (PNIPAM) is added to the cathode of PEMFC to improve the performance. PNIPAM is known for its temperature induced change from hydrophilic to hydrophobic material and volumetric change with shrinkage of polymer chain. It could enhance the cathode structure that has larger secondary pores and less dead platinum in primary pore of supporting carbon for fast mass transfer and efficient platinum utilization. This improvement is analyzed by the electrochemical single-cell measurements and half-cell measurements including cyclic voltammetry (CV), CO stripping, rotating disk electrode (RDE) method and electrochemical impedance spectroscopy (EIS). For structural and compositional analysis, X-ray diffraction (XRD), Hg porosimetry and X-ray photoelectron spectroscopy (XPS) are carried out. Therefore, we suggest the possibility of enhancement of PEMFC performance by simple addition of the polymer.

Polymer electrolyte membrane fuel cell (PEMFC) is focused because of increasing demand on new green alternative power source because this type of fuel cell has high efficiency and make no pollution like CO2 emission. However, there are many challenges to commercialize the PEMFC because of its manufacturing price. Because of sluggish reaction in PEMFC, a large amount of Pt should be used for PEMFC operation. To lower manufacturing price of PEMFC, the improvement of cathode performance and less use of Pt metal at cathode of PEMFC are the most important issues. In addition, the long term durability of cathode materials for commercialization of PEMFC is also concerned.
Recently, to resolve these issues, many researches about the morphology controls of Pt nanoparticles have been carried out. Among these, the researches about Pt nanocluster are received attention because it can induce another catalytic effect due to its special shape.
In this study, we fabricate the carbon supported Pt nanocluster for oxygen reduction reaction (ORR) and the physical and electrochemical measurements are committed such as HR-TEM images, cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and so on. In addition, the durability of this is committed by potential cycling method. From these, it is expected that Pt nanocluster can be used as ORR electrocatalysts for PEMFC.

In this work, we reported the one-step preparation of TiO2/reduced graphene oxide nanoheterostructures with a facile hydrothermal method. The samples were prepared by reacting graphene oxide (GO), which was obtained from Hummers&’ method, with P-25 TiO2 nanoparticles in the alkaline hydrothermal reaction [1]. During the hydrothermal process, reduction of GO was accompanied with the deposition of TiO2 nanotubes, resulting in the formation of TiO2/RGO nanoheterostructures. Because of the considerably high electrical conductivity of RGO [2], the photoexcited electrons of TiO2 nanotubes would preferentially transfer to RGO, leaving positively charged holes in TiO2 to achieve charge carrier separation. Time-resolved photoluminescence spectra were collected to quantitatively analyze the electron transfer event between TiO2 and RGO and its dependence on RGO content [3]. To evaluate the photoconversion efficiency, the samples were used as photoanode in the photoelectrochemical cell for methanol oxidation. As compared to the pristine TiO2 nanotubes, TiO2/RGO samples displayed 2.7-fold enhancement in photocurrent generation under white light illumination. The significantly imporved photocatalytic performance of the present TiO2/RGO nanoheterostructures shall foster further interests to investigate their practical applications in technologically important areas such as photo-assisted methanol fuel cell.
[1] A. Nakahira, T. Kubo, C. Numako, Inorg. Chem. 2010, 49, 5845-5852.
[2] D. Chen, H. Feng, J. Li, Chem. Rev. 2012, DOI: cr300115g.
[3] Y.-C. Chen, Y.-C. Pu, Y.-J. Hsu, J. Phys. Chem. C 2012, 116, 2967minus;2975.

Graphene is considered as a promising ultracapacitor material toward high power and energy density because of its high conductivity and high surface area without pore tortuosity. However, the two-dimensional (2D) sheets tend to aggregate during electrode fabrication process and align perpendicular to the flow direction of electrons and ions, which can reduce the available surface area, and limit the electron and ion transport. This makes it hard to achieve scalable device performance as the loading level of the active material increases. Here, we report a strategy to solve these problems by transforming the 2D graphene sheet to crumpled paper ball structure. Compared to flat or wrinkled sheets, the crumpled graphene balls can deliver much higher specific capacitance and better rate performance. More importantly, devices made with crumpled graphene balls are significantly less dependent on the electrode mass loading. Performance of graphene-based ultracapacitors can be further enhanced by using flat graphene sheets as binder for the crumpled graphene balls, thus eliminating the need for less active binder materials.

The dominating material for lithium ion anodes is graphite. Despite being safe and easy to process, its capacity is significantly lower than that of other materials. Silicon is a very promising alternative as anode material. It exhibits a high theoretical capacity of 4200 mAh/g, while carbonaceous material has a charge storage capacity of only 372mAh/g. However, it is well known that during charging and discharging in a lithium ion battery, silicon materials experience large volume change (up to 300%), resulting in internal cracks of active materials, leading to poor cyclability. Research shows that reducing the silicon particle size can solve this problem. Thus, silicon nanostructures have attracted interest for use in lithium ion batteries. Carbon nanotubes have high electrical conductivity and surface area, which allows them to function well as electrode material in electrolytic cells. In this work, we use a combination of silicon quantum dots (SiQDs) and carbon nanotubes as anode materials. Silicon quantum dots are generated using a plasma-enhanced chemical vapor deposition technique, and their surface is modified with a 12-carbon long aliphatic chain to impart solubility in non-polar solvents. They are applied onto a nanotube-based layer using a wet-phase deposition technique. SEM and TEM analysis conform that they form a conformal coating onto the nanotube surface. Annealing is applied to form a solid carbide bond. The composite material is tested in half-cells to study its capacity and cyclability.

There is growing interest in the development of a new generation of electrical devices, whereby all the device components are optically transparent. Some common examples include transparent displays within personal mobile devices, smart glasses and vehicle windscreens. These kinds of applications will enable a more seamless interaction between our physical environment and the rapidly expanding digital environment.
All-transparent devices will require embedded transparent energy storage capabilities. Presently, electrochemical systems are the preferred means to provide energy storage within portable electronic devices. However, to date, relatively little work has been carried out exploring the capabilites of batteries and supercapacitor devices also possessing high optical transmittance.
It&’s well know that the electrical properties of transparent conductors based on thin film nanomaterial networks deviate from bulk-like values as the film thickness is decreased. This deviation may be described using percolation theory, and is useful for guiding the design of thi film electrodes with a combination of transmittance and sheet resistance acceptable for a given application.
Recently, we have applied this understanding towards the design of transparent supercapacitors (T > 80%) based on thin film networks of carbon nanotubes. Here it was demonstrated that network equivalent series resistance and capacitance are also controlled by percolation effects as film thickness is decreased (i.e. with increasing transmittance). These two properties determine the achievable power and energy capabilities, respectively, of the overall transparent energy storage device.
Although the effects of percolation in such systems are difficult to avoid, there are a number of avenues for improvement. Transition metal oxides are being heavily explored for use within supercapacitor electrodes to increases energy density through reversible pseudocapacitive redox processes. This strategy is also applicable to transparent SC electrodes. Therefore, following on from our initial work, we are investigating the properties of composite supercapacitor electrodes prepared by the inclusion of a variety of layered transition metal oxides such as RuO2, MnO2, WO3, and MoO3. These layered materials, exfoliated using liquid phase processing methods, have high ratio of surface area to volume ratio and therefore addition of small quantities can significantly enhance the achievable energy stored within thin film SC electrodes, while maintaining high through electrode optical transmittance.
Furthermore, nanomaterial network electrodes prepared in this work may be deposited onto flexible substrates, a capability of growing interest for future portable electronic devices.

In recent times, advances in microelectronics and portable devices has attracted battery research towards development of high performance micro battery. Various three dimensional (3D) electrode morphologies, usually prepared by templating of active material, has been suggested and applied to overcome the shortfalls of conventional Thin film (2D) micro batteries . These 3D micro or nano structures not only reduces ionic diffusion path length to increase power density, but also increases areal energy density. But when it comes to integrate complete 3D batteries , methods generally used are relatively complex, time consuming and costly.

Here we report on low cost Soft Lithography Techniques to pattern 3D micro electrodes for lithium ion battery application. The method is demonstrated by patterning nanosized TiO2 (anatase) and LiFePO4 in various 3D morphologies, and provides flexibility to tailor electrode microstructure for optimum ionic-electronic wiring, required for high power density .
Electrodes were charged at various c-rate and shows excellent capacity retention. LiFePO4 shows 100mAh/g at 20C charge, and TiO2 anatase retain 95mAh/g at 10C rate charge.
However, the aspect ra