Symposium Organizers
Sangtae Kim University of California-Davis
Shu Yamaguchi University of Tokyo
Manfred Martin RWTH Aachen University
K2: Transport and Kinetics I
Session Chairs
Juergen Janek
Manfred Martin
Tuesday PM, April 26, 2011
Room 2010 (Moscone West)
2:30 PM - **K2.1
Ion Transport in Metal Hydrides and Its Application to Energy Conversion.
Hitoshi Takamura 1
1 Department of Materials Science, Tohoku University, Sendai Japan
Show AbstractAs a new class of ionic conductors, metal hydrides have been attracting much attention. As well as oxides, hydrides comprising of alkaline- and rare-earth elements tend to show ionic bonding nature. Depending on crystal structure and defect concentration, ionic species can be highly mobile. This paper comprises of two parts; the first part is devoted to cation transport such as Li+ in complex metal hydrides. Our group has reported that lithium borohydride (LiBH4) shows Li+ conductivity of 10-3 S/cm accompanied by phase transition from orthorhombic to hexagonal structure at 115 oC. Recent development in ion transport in the complex metal hydrides is presented including the stabilization of the high ion-conductive phase, spectroscopic analysis, and high-pressure study to clarify the ion transport in polymorphs and activation volumes for ion conduction. The second part is devoted to hydride-ion, i.e. negatively charged hydrogen, transport in metal hydrides. To date, hydride-ion transport in metal hydrides have been reported for simple alkaline-earth hydrides such as CaH2. In this paper, hydride-ion transport in MgY2H8 and Ca4ZrH10 having CaF2- or BiF3-type structure is discussed. These hydrides can be prepared at 800 oC under 5 GPa by using a cubic-anvil-type apparatus. Local structure and transport property of the metal hydrides have been investigated by means of NMR, Raman, and impedance spectroscopy. Trend in chemical shift of 1H shows an agreement with negativity of hydrogen in the hydrides estimated by first-principles calculation. In addition, the diffusion coefficient of hydrogen is estimated to be on the order of 10-7 cm2/s at around 300 oC. In the presentation, application of ion-transport phenomena in metal hydrides to energy conversion will be also reviewed.
3:00 PM - K2.2
Defect Chemistry and Electrical Properties of Pr-ceria Solid Solution from the Nano- to Micro-scale.
Sean Bishop 1 , Jae-Jin Kim 1 , Todd Stefanik 2 , Di Chen 1 , Yener Kuru 1 , Harry Tuller 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Nanocerox, Ann Arbor, Michigan, United States
Show AbstractIn nano-crystalline ceramics, the grain boundary volume fraction is large relative to micro-crystalline materials and can therefore be a dominant factor in determining electrical, chemical, and mechanical properties. For example, the typically positive nature of grain boundaries in oxides decreases oxygen vacancy concentration in small grains as space charge regions overlap, reducing ionic conductivity. Also, the boundaries have different defect formation energies from the bulk, resulting in different oxygen partial pressure (pO2) dependencies and changes in defect induced dilation (chemical expansion). Pr-cerium oxide (PCO) solid solutions are particularly interesting oxygen ion conductors to study because both Pr and Ce can change valence, meaning that as pO2 is decreased from high to low values, PCO transitions through a mixed ionic electronic conducting (MIEC) region to an ionic region and then back into an MIEC region while undergoing chemical expansion due to defect formation. In this presentation, results of thermo-gravimetric, high temperature x-ray diffraction, and electrical conductivity measurements performed on micro-crystalline and nano-crystalline bulk samples of PCO will be shown. In addition, measurements on PCO thin films will be discussed.
3:15 PM - K2.3
Ionic and Electronic Transport in Ag2S-GeS2 Nanocomposites with Size-controlled Ag2S Nanoparticles.
Robert Wang 1 , Ravisubhash Tangirala 1 , Guillermo Garcia 2 1 , Simone Raoux 3 , Delia Milliron 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 , University of California, Berkeley, Berkeley, California, United States, 3 , IBM, Yorktown Heights, New York, United States
Show AbstractElectrochemical metallization memory cells using Ag-Ge-S for the active material are among the best performing and are currently under intense development toward commercialization. There is some evidence that the Ag-Ge-S material used in these cells consists of Ag-rich nanoparticles dispersed in an amorphous, Ge-rich matrix; however the structure-property relationships of Ag-Ge-S are poorly understood. To systematically investigate these structure-property relationships, we use a modular nanocomposite formation technique to create Ag2S nanocrystal – GeS2 matrix composites with well-defined and size-controlled Ag2S nanocrystals and highly regular, sub-nm particle-to-particle spacing. Using impedance spectroscopy, dc measurements, and in situ x-ray diffraction we evaluate the Ag2S nanocrystal size-effects on charge transport and crystal phase between 130°C and 230°C. For example, at 130°C the electronic transference number increases from 0.1 to 0.6 as the Ag2S nanocrystal size increases from 4 nm to 12 nm. The temperature range explored encompasses the Ag2S superionic phase transition temperature, which also allows us to assess the potential impact of size-dependent phase transitions on the electronic and ionic properties of the composites.
3:30 PM - **K2.4
Defect Structure and Complete Representation of All Mass and Charge Transport Properties of Mixed Conducting La2NiO4+δ.
Han-Ill Yoo 1 , Hong-Seok Kim 1
1 WCU Hybrid Materials Programme, Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractLa2NiO4+δ is a mixed ionic electronic conductor with its ionic conductivity even larger than that of YSZ, thus, attracting worldwide attentions for electrochemical applications based on its superb mixed conductivity. This oxide is quite unusual in that it has oxygen interstitials and electron holes as majority-type disorders across its entire stability range, and furthermore they deviate positively from the ideal dilute solution behavior. We will quantitatively elucidate the positively-deviating defect structure of the oxide by taking account of the hole degeneracy. It is further proposed that all the isothermal mass and charge transport properties of a mixed conductor be completely represented by a simple 2×2 Onsager transport coefficient matrix L such that Jk=-LkmXm, where Jk and Xm being the flux and driving force of the ionic carriers (k,m=i) and electronic carriers (k,m=e), respectively. We will demonstrate experimentally the Onsager reciprocity relations Lie=Lei with unprecedented precision and introduce a very simple experiment to determine, once and for all, the three independent coefficients in association with the thermodynamic equation of state for the nonstoichiometry (δ). By using this experiment, we will establish for the system of La2NiO4+δ the matrix and discuss its salient features including the ion-electron interference upon their transfer. Finally we will calculate the transport properties of La2NiO4+δ of present interest to compare with the literature values available.
4:30 PM - **K2.5
Strain-induced Conductivity Effects - Ionic Conduction and Diffusion in Nano-scaled Solid Electrolyte Multilayers.
Juergen Janek 1 , Halit Aydin 1 , Carsten Korte 1
1 Institute of Physical Chemistry, Justus-Liebig-University, Giessen Germany
Show AbstractRecently the influence of strain on the ionic conductivity in solid electrolytes has attracted increasing interest, and strain as a concept to design improved electrolytes is under discussion [1,2]. As a contribution to this discussion we carried out systematic experiments on the ionic transport in nanoscaled multilayers composed of two different oxide phases with varying lattice misfit. In particular, we investigated the effect of coherency strain on the ionic transport properties along hetero-interfaces of zirconia-based solid electrolytes [2,3]. The results show that elastic effects can lead to significant conductivity effects, however, these are smaller than effects of interfacial disorder in incoherent systems. In addition to conductivity measurements we performed 18O tracer experiments in these multilayers systems, in order to investigate the diffusion in different regions of strained or disordered multilayers. References:[1] J. A. Kilner, Ionic Conductors - Feel the Strain, Nature Mater. 7 (2008) 838-839.[2] A. Kushima, B. Yildiz, Oxygen ion diffusivity in strained yttria stabilized zirconia: where is the fastest strain? J. Mater. Chem. 20 (2010) 4809-4819. [3] C. Korte, N. Schichtel, D. Hesse, and J. Janek, Influence of Interface Structure on Mass Transport in Phase Boundaries between different Ionic Materials – Experimentals Studies and Formal Considerations, Chem. Monthly (Monatshefte für Chemie) 140 (2009) 1068-1080.[4] N. Schichtel, C. Korte, D. Hesse, and J. Janek, Elastic Strain at Interfaces and its Influence on Ionic Conductivity – Theoretical Considerations and Experimental Studies, Phys. Chem. Chem. Phys. 11 (2009) 3043-3048.
5:00 PM - K2.6
Effect of Reactive Surface Modifications on Oxygen Transport in Perovskite-type Mixed Conducting Oxides.
Michael Schroeder 1 , Jianxin Yi 1
1 Institute of Physical Chemistry, RWTH Aachen, Aachen Germany
Show AbstractGeometric or compositional surface modifications often play an important role with respect to the transport properties of ion conducting high temperature materials. Often, these modifications are implemented on purpose, in order to enhance transport of particular species, as is the case with porous electrodes in SOFC or porous surfaces in oxygen separation membranes. In contrast, surface modifications that occur during long-term operation at high temperatures may have a detrimental effect on the transport properties. A recent example is the reactive surface modification of perovskite-structured oxygen separation membranes in the presence of corrosive gases such as carbon dioxide or sulfur dioxide. Membrane materials that consist of substantial amounts of earth alkaline metals - as is the case with Ba0.5Sr0.5Co0.8Fe0.2O3-δ, a compound that delivers one of the highest oxygen separation fluxes known to date - undergo a reactive surface modification in contact with CO2, which includes the formation of earth alkali carbonates. The modified surface very efficiently blocks the oxygen transport across the membrane and may render the membrane unusable within minutes of operation. The details of the surface modification process were recently studied in our lab for the case of Ba0.5Sr0.5Co0.8Fe0.2O3-δ and related compositions [1]. Formation of earth-alkali carbonates was found to occur all over the surface, however, the effect was more pronounced at grain boundaries, indicating that these constitute pathways for fast transport of earth-alkali ions. It was found that the formation of surface carbonates does not lead to complete decomposition of the perovskite phase. Instead, precipitation of cobalt oxide from the parent material compensates for the loss of earth alkali, and a cobalt-depleted perovskite is formed subjacent to the carbonate layer. Obviously, the cobalt-depleted perovskite exhibits a better resistance towards carbon dioxide than the initial composition. We observed similar surface modification with materials of the composition BaCo1-x-yFexNbyO3-δ. By increasing the fraction of niobium, the resistance towards carbon dioxide could be improved. A similar trend was found for SrCo0.8Fe0.2O3-δ doped with titanium [2]. This appears to constitute a general concept: Introducing high-valent d-block elements increases the acidity of the perovskite material. This leads to a reduced reactivity towards carbon dioxide, which itself is an acidic gas. However, the enhanced stability comes at the cost of a reduced oxygen separation flux.
[1] Yi, J., Schroeder M., Weirich, T.E., Mayer, J., Chem. Mater, in press. DOI: 10.1021/cm101665r.
[2]Zeng, Q., Zu, Y. B., Fan, C. G., Chen, C. S., J. Membr. Sci. 335 (2009) 140.
5:15 PM - K2.7
Transport Properties of Epitaxial SrTi1-xFexO3 Thin Films.
Miri Markovich 1 , Jaume Roqueta 2 , Jose Santiso 1 , Avner Rothschild 2
1 Material Engineering, Technion, Haifa Israel, 2 Nanoscience and Nanotechnology, CIN2 (CSIC-ICN). Campus UAB , Barcelona, Bellaterra, Spain
Show AbstractSrTi1-xFexO3 (STF) is a model system for complex oxide solid solutions. The complete solubility of Fe in Ti sites (or vice versa) enables to tune optical, transport, and electrochemical properties. This remarkable tunability opens up exciting opportunities for applications in different electronic, optoelectronic, and electrochemical devices. Epitaxial thin films provide a rich platform for exploring the physicochemical properties of the STF system. In this work we investigate the transport properties of STF epitaxial films deposited by Pulsed Laser Deposition (PLD). STF thin films (20 -200 nm thick) of different Fe content from 25% up to 100% were deposited on single crystal LaAlO3 (LAO) substrates. Cube-on-cube epitaxial relationship between film and substrate was obtained, as confirmed by high-resolution XRD. The in-plane conductivity of STF films with different compositions (Fe/Ti ratio) and thicknesses was measured as a function of temperature and oxygen partial pressure by means of impedance spectroscopy. Both reversible porous Pt electrodes and irreversible dense Au electrodes were used, and the frequency and pO2 dependencies of the different contributions to the impedance spectra enabled to distinguish between ionic and electronic conductivities. The results will be discussed at the meeting.
5:30 PM - K2.8
Mesoporous Thin Films of the Solid Solution CeO2-ZrO2: Charge Transport in Nanostructured Mixed Conductors.
Pascal Hartmann 1 , Torsten Brezesinski 1 , Andriy Lotnyk 2 , Lorenz Kienle 2 , Juergen Janek 1
1 Physikalisch-Chemisches Insitut, Justus-Liebig-Universitaet Giessen, Giessen Germany, 2 Technische Fakultaet, Christian-Arbrechts-Universitaet zu Kiel, Kiel Germany
Show AbstractWe prepared nanocrystalline mesoporous thin films of the solid solution CexZr1-xO2(CZO) by a sol-gel route starting from CeCl3 and ZrCl4. Thin films were deposited by a dip-coating technique on various substrates. A well defined microstructure of spherical mesopores was introduced via an evaporation induced self assembly (EISA) process of block-copolymers.[1] Using scanning electron microscopy the film thickness was evaluated to about 140 nm and the pore diameter to about 15 nm. The average crystallite size ranges from 4 to 20 nm, depending on the composition, and was determined using x-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). In additional experiments the chemical composition and structure of the material was investigated with grazing incidence small angle x-ray scattering (GISAXS), x-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). The electrical conductivity of the films was studied as function of composition (x), temperature (T) and oxygen partial pressure (pO2) using interdigitated platinum microelectrodes and impedance spectroscopy. This first systematic study of the electrical charge transport properties of a high surface area functional oxide ceramics led to the following major results: CZO films show a 5 to 10 times higher total conductivity compared to microcrystalline bulk samples.[2] For pure ceria the conductivity was about three orders of magnitude higher, which is in good agreement with the space charge model introduced by Tschoepe and Maier.[3],[4] Even more remarkable is the pO2-dependence of the conductivity that is yet not explained with a point defect models. For bulk CZO samples with high ceria contents the conductivity varies proportional to (pO2)^-1/6 for reducing atmospheres (pO2: 10^-1 to 10^-5 bar) as expected for a mixed ionic electronic conductor with the composition MeO2. However, the mesoporous CZO samples showed a two times higher dependence proportional to (pO2)^-1/3. This dependence has yet not been reported for bulk nanocrystalline material and appears to be a result of the high surface area of the material (< 100 m^2/g). Samples with low ceria content showed no change of the conductivity with changing pO2, like the bulk material.[5] [1] Smarsly, B. M., and Antonietti, M., J. Inorg. Chem. 2006, 1111-1119[2] Chiodelli, G., Flor, G., Scagliotti, M., Solid State Ionics 1996, 91, 109-121.[3] Tschoepe, A., Birringer, R., J. Electroceram. 2001, 7, 169-177.[4] Kim. S., Maier, J., J. Electrochem., Soc. 2002, 149, J73-J83[5] Lee, J.-H., Yoon, S. M., Kim, B.-K., Kim, J., Lee, H.-W., Soong, H.-S., Solid State Ionics 2001, 144, 175-184.
5:45 PM - K2.9
Electric-field-enhanced Ionic Diffusivity in Electrolytes: A Model Study.
Doo Seok Jeong 1 , Suyoun Lee 1 , Byung-ki Cheong 1
1 Thin Film Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractNanoionics-related phenomena have attracted great attention for their possible applications to nonvolatile memory devices including resistive and electrochemical random access memories. Basically, these applications are based on ionic transport in solid ionic conductor or electrolyte so that the understanding of the ionic transport is important. The drift and diffusion of ions is most probable mechanisms for ionic transport. The drift and the diffusion of ions are attributed to the electrostatic and the chemical potential gradients of the ions, respectively. The mathematical form of the drift and diffusion of ions is expressed in terms of first-order approximation so that the form is valid in a limited range of both electrostatic and chemical potential gradients. In ionic systems at the nano scale, electrostatic potential gradient as well as chemical potential gradient will be considerably high so that one should make sure the validity of the first-order approximation.In this study, the time-dependent distribution of cation A^z+ and anion X^z- in AX solid electrolyte was calculated by means of the drift-diffusion of the ions. From the calculation we could judge whether the Nernst-Einstein equation is valid in the system under investigation first. In this calculation, no first-order approximation was employed because the breakdown of the first-order approximation probably takes place if the gradient of chemical or electrostatic potential is high. The distribution of the ions was calculated for both blocking and non-blocking contact cases. And the calculated result was compared with that with the first-order approximation.
Symposium Organizers
Sangtae Kim University of California-Davis
Shu Yamaguchi University of Tokyo
Manfred Martin RWTH Aachen University
K6: Li-Conductors
Session Chairs
Gerbrand Ceder
Janko Jamnik
Thursday AM, April 28, 2011
Room 2010 (Moscone West)
9:15 AM - **K6.1
Particle Size Effects on Li-ion Diffusion in Materials for Rechargeable Li Batteries.
Gerbrand Ceder 1 , Rahul Malik 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractRechargeable lithium batteries use cathode materials which can reversibly intercalate Li-ions and electrons. The ionic diffusivity of lithium therefore plays an important role in Li batteries as it can limit the power rate at which a battery can be charged or discharged. Reducing particle size down to the nano regime is sometimes used to use materials with poor Li transport, even though the higher surface area can lead to higher reactivity with the electrolytes. I will demonstrate that in LiFePO4, an important material for rechargeable batteries, the excellent performance of the material in nanoscale particles is not due to a reduction of the transport distance, but rather due to a change in the Li diffusion constant with particle size. (1) Diffusion in LiFePO4 is through one-dimensional tunnels. In nanoparticles only a few or no defects tend to be present in these tunnels, leading to unimpeded Li transport through them. But in larger crystals defects block Li sites that are deeper into the crystal. Getting past these defects requires slow cross-tunnel transport. This cross-over leads to a much lower diffusion constant in larger crystals. This size effect on the diffusion constant is likely to be common to all materials with one-dimensional diffusion channels. We will also show how the very high Li diffusion constant in nanosized materials can lead to rechargeable batteries with very high power capability. (2) (1) R. Malik, D. Burch, M. Bazant, et al., Particle Size Dependence of the Ionic Diffusivity, Nano Letters, 10 (10), 4123-4127 (2010). (2) B. Kang, G. Ceder, Battery Materials for Ultrafast Charging and Discharging, Nature, Vol. 458, Issue 7235, Pages 190-193 (2009).
9:45 AM - K6.2
The Effect of Al-substitution on the Electrode Properties of LiCoO2 in a Sulfide Solid Electrolyte.
Xiaoxiong Xu 1 , Kazunori Takada 1 , Ken Watanabe 1 , Isao Sakaguchi 1 , Kosho Akatsuka 1 , Bui Hang 1 , Tsuyoshi Ohnishi 1 , Takayoshi Sasaki 1
1 , National Institute for Materials Science, Tsukuba, Ibaraki, Japan
Show AbstractAlthough lithium-ion batteries have been on market for almost twenty years, the safety issue arising from combustible organic electrolytes remains unsolved. The most effective solution is the use of nonflammable solid electrolytes. However, a drawback of the solid-state system is poor power density. In this study, the effect of Al-substitution in LiCoO2 on the electrode properties was investigated in a sulfide solid electrolyte, and it was found that the introduction of Al is effective in reducing the electrode resistance and thus improving the rate capability of solid-state lithium batteries. When the Al was substituted for Co, the electrode resistance began to decrease. Increasing amount of the Al led it to a minimum and then increased it again. This tendency is very similar to that observed in our previous studies [1], in which formation of coating layer on the surface of the LiCoO2 particles reduced the electrode resistance, and further application thickening the coating layer increased it again. Moreover, the minimum resistance and the highest rate capability were coincident between the studies. These results suggest that the introduction of the Al forms surface layers on the LiCoO2 particles acting as the coating layer in our previous studies. In order to verify the speculation, the influence of post-annealing on the rate capability was investigated. Although the post-annealing did not change the morphology and the crystal structure of the LiCoO2 particles, the electrode resistance was sensitive to the post-annealing condition, which strongly supports our speculation that the improvement of the rate capability by the Al-substitution does not come from enhanced ionic conduction in the bulk but from the surface modification. That is, part of the introduced Al is segregated to form a surface layer acting as a buffer layer and suppresses the highly-resistive interfacial layer induced by nanoionics.
10:00 AM - K6.3
Computational Modeling of Lithium Ion Conduction in Li-Fe-O Structures.
Kah Chun Lau 1 , Maria Chan 2 , Jeff Greeley 2 , Larry Curtiss 1 2
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe concept of using lithium-transition-metal oxides (e.g. Li-Fe-O) with a high Li2O content, as electrocatalysts for lithium-oxygen cells, has been explored (1,2), with a particular emphasis on Fe. Experimentally, lithium can be extracted both electrochemically and chemically from the defect antifluorite-type structure, Li5FeO4 (or 5Li2O-Fe2O3). For chemically delithiated Li5FeO4, the lithium extraction is accompanied predominantly by the release of oxygen. From experiments, X-ray absorption spectroscopy (XAS) data show no evidence of Fe3+ to Fe4+ oxidation, but rather a change in coordination of the Fe3+ ions. To understand the basic mechanism behind these delithiated Li-Fe-O compounds, a theoretical study based on density functional theory (DFT) and classical molecular dynamics (MD) modeling is carried out. Besides the computed X-ray diffraction patterns (XRD) and the energetics of delithiated products, the mobility and ionic conduction of the ions within the materials will be presented. The implications of using Li-Fe-O electrodes for lithium-oxygen cells will be discussed. References:1. C.S. Johnson, et. al. Chem. Mater. 2010, 22, 1263-1270.2. L. Trahey, et. al. J. Mater. Chem. (in review).
10:15 AM - K6.4
Synthesis and Li+ ion Migration Studies of Li6PY5X (Y=S, Se) (X = Cl, Br, I).
Rayavarapu Prasada Rao 1 , Stefan Adams 1
1 Materials Science and Engineering, National University of Singapore, Singapore Singapore
Show AbstractRechargeable all-solid-state lithium (Li)- or Li-ion batteries (AS-LIBs) are attractive power sources for applications, like ‘smart’ credit cards and medical implants. They require a Li-fast ion (super-ionic) conductor (FIC) as the solid electrolyte. The purpose is to improve safety and stability over conventional batteries with liquid electrolyte. Finding a solid electrolyte with high ionic conductivity is thus the key to building practical solid-state batteries. There have been numerous developments on materials such as lithium rich sulfide glasses as solid electrolyte. However, low current density remains a major obstacle in these electrolyte systems.Argyrodites form a class of chalcogenide structures related to the mineral Ag8GeS6, which includes various Ag+ or Cu+ ion conductors such as A7PS5X (A= Ag+, Cu+). Recently, Deiseroth et al. (Angew. Chem.,2008, 120, 767) could synthesize the analogue cubic Li+ argyrodytes with formula Li6PS5X (X = Cl, Br, I) and Li7PS6. 7Li-NMR relaxation and impedance experiments report an intrinsic local lithium mobility of the Li-argyrodite crystals as high as 10-2 - 10-3 S/cm at room temperature close to the mobility in liquid electrolytes comprising of LiPF6 salt in various carbonates. With such high lithium mobilities, these materials should be ideal for use as solid electrolytes in lithium ion batteries. We could prepared the argyrodite-type phases Li6PY5X (Y=S,Se) (X = Cl, Br, I) through a faster glass-ceramic process. Appropriate mixtures of P2S5, Li2S,P, Se, Li2Se and LiX (X=Cl,Br,I) are converted into glassy Li6PY5X (Y=S,Se) (X = Cl, Br, I) by mechanical milling and subsequently annealed at 550°C for 3 hours in steel tubes sealed under Ar atmosphere. In-situ XRD characterization of the resulting samples confirmed the crystalline nature with space group F-43m throughout the temperature range between 300 and 520 K. In the case of Li6PS5Br an ionic conductivity of the order of 10-4 S/cm is reached at room temperature. While ion transport studies for the silver and copper thiophosphates can be based on the detailed available anharmonic structure refinements, no comparably detailed studies are so far available for the Lithium compounds due to the low scattering power of Li and phase transitions preventing low-temperature single crystal studies. Therefore we designed an optimized force-file that reproduces lattice constants and thermal expansion and applied it to study ion transport pathways in the Li6PS5X phases by Molecular Dynamics simulations in combination with the bond valence analysis of energy landscapes for the mobile Li+. The three-dimensional pathways consist of low-energy local pathway cages. The degree of interconnection of these cages determines the actual long range Li+ migration pathways and hence the dc ionic conductivity.
11:00 AM - **K6.5
Designing Nanoparticulate Based Semi-Solid Electrochemical Fuels for Novel Flow Cells.
Yet-Ming Chiang 1 , W. Craig Carter 1 , Bryan Ho 1 , Victor Brunini 1 , Yajie Dong 1 , Nir Baram 1 , Vanessa Wood 2 , Mihai Duduta 1 , Pimpa Limthongkul 1 , David Young 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich Switzerland
Show AbstractWe recently demonstrated a new electrical storage concept, the semi-solid flow cell (SSFC), that utilizes flowable suspensions of energy-dense cathode and anode particles in liquid electrolytes as rechargeable “fuels” delivered to a power stack analogous to those in fuel cells and flow batteries. This chemistry and architecture aims to combine the best attributes of rechargeable batteries and fuel cells. Extraction of electrochemical energy requires that the semi-solids be mixed electronic-ionic conductors. Electronic conductivity is accomplished by using nanoscale conductors to produce flowable yet electronically conductive suspensions to facilitate charge transfer from storage material particles. In this talk, characterization and analysis of the electrochemical systems using in-situ conductivity and rhelogical probes, electrochemical testing, and synchrotron X-ray tomography, will be presented.
11:30 AM - K6.6
Bond-valence Based Computational Design of High Performance Lithium Ion Battery Cathode Materials.
Stefan Adams 1
1 Materials Science & Eng., National University of Singapore, Singapore Singapore
Show AbstractA major challenge in lithium ion battery research is still to design cathodes that combine high energy density with high power density. Building on our earlier systematic adjustment of bond valence (BV) parameters to bond softness, it is demonstrated how the BV mismatch is linked to the energy scale and provides a general Morse-type force-field for analyzing low-energy pathways in ion conducting solid or mixed conductors by either an energy landscape approach or molecular dynamics (MD) simulations. For a wide range of Lithium oxides we could thus model ion transport pathways and compare the outcome with earlier geometric approaches.Using atomistic Molecular Dynamics simulations based on this approach as well as ab initio models, various strategies to enhance the power performance of safe low cost Lithium ion battery cathode materials are explored here. Strategies include homogeneous aliovalent doping, tailoring the concentration of disorder (antisite defects), and interface engineering (heterogeneous doping in cathode:electrolyte nanocomposites). NaFe′ doped LiFePO4 and amblygonite-type “high voltage” cathode materials tavorite LiVPO4F and LiFeSO4F are used as examples for investigating the effects of aliovalent dopants and antisite disorder on the Lithium pathways and hence on the power performance, as the amblygonite-type structure exhibits channels for one-dimensional low-energy migration in combination with moderate energy thresholds for "back-up" pathways in the perpendicular directions mitigating the effects of channel blocking in other mixed conductors with strictly one-dimensional Li+ motion. The interplay of FeLi blocking Li+ pathways and LiFe′ or NaFe′ connecting parallel pathways has a complex influence on the value and anisotropy of ion mobility. Li+ ion conductivity in the LixFePO4 phase of LixFePO4:Li4P2O7 nanocomposites is discussed as a model for power performance enhancement by interface engineering.
11:45 AM - K6.7
Directed Synthesis of Complex Phosphates for Lithium-ion Batteries Electrolytes.
Anna Potapova 1 , Andrey Novoselov 1 , Sergey Stefanovich 2 , Galina Zimina 1
1 Department of Chemistry and Chemical Engineering for Rare and Dispersed Elements, Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow Russian Federation, 2 Department of Chemistry, Lomonosov Moscow State University, Moscow Russian Federation
Show AbstractTo date, solid-state electrolytes have ceased to be completely new objects of research because of discovery and synthesis of hundreds to thousands of new compounds with high ionic conductivity. Nevertheless, the problem of finding new superionic materials has not lost its relevance because they are indispensable for a fully solid-state fuel cells, gas and liquid sensors and miniature lithium-ion batteries. As a result of systematic study on the ternary Li3PO4-Na3PO4-In(Sc,Yb)PO4 system, a number of complex NASICON-like phosphates MI3MIII2(PO4)3 (MI=Li, Na; MIII=Sc, In and Yb) were discovered. Discrete nanosized phases, their polymorphic modifications as well as numerous solid solutions samples were synthesized and characterized with X-ray powder diffraction analysis and infra-red spectroscopy. The resulting compounds have complex polymorphism, which contributes to their high ionic conductivity. Ionic conductivity of the complex phosphates Li3In2(PO4)3, Na3In2(PO4)3 and Na3Sc2(PO4)3 was investigated with impedance spectroscopy. Ionic conductivity of Li3In2(PO4)3 was measured to be ~10-3 S/cm, and about 10-2 S/cm for Na3In2(PO4)3 and Na3Sc2(PO4)3 samples at 300°C. Iso- (Li, Na) and heterovalent (Ti, Zr) substitution in the cation sublattice, which increases the mobility of the conducting Li+ cation and allows tracing the evolution of structural changes was performed. Thus, the ionic conductivity of Li3In2(PO4)3, Na3In2(PO4)3 and Na3Sc2(PO4)3–based compounds was enhanced up to about 10-1 S/cm at 300°C. These phases can be recommended as solid-state electrolytes in various power sources and application of the complex phosphate Li3In2(PO4)3 as a promising cathode material for lithium-ion batteries is under consideration now.
12:00 PM - **K6.8
Li Ion Migration Along/Across the Interfaces.
Janko Jamnik 1 2 , Miran Gaberscek 1 2
1 , National Institute of Chemistry, Ljubljana Slovenia, 2 , Center of Excellence: Low-Carbon Technologies, Ljubljana Slovenia
Show AbstractWithin the last two decades the energy density and in particular the power density of commercial Li-batteries and laboratory cells have been greatly improved. Surprisingly, enormous amount of how-to-prepare knowledge has a little pedant in mechanistic understanding of equilibrium and even less of nonequilibrium properties. In particular, the impact of interfaces within the electrode composite on the charge and mass transport has hardly been systematically addressed. In this paper the transport of Lithium ions and electrons across and along the boundaries within the electrode material is discussed in terms of well-established concepts used in solid state ionics for many decades. We show that many phenomena well-known from the studies of chemical diffusion and ion migration in polycrystalline materials are met also in battery composites. On the other hand the microstructural complexity, variety of different interfaces and very broad compositional range of interest exceed significantly the relative simplicity of the »model« polycrystalline materials. We discuse the effects of Li ion incorporation, electronic interphase contacting, heterogeneous doping and electrode porosity on the electrochemical properties in terms of tailored experiments and phenomenological modelling.