Firming up renewables is becoming increasingly important, especially in areas where expansion of transmission and distribution infrastructure has not kept pace with the growth of renewables. While there are no immediate solutions for transmission and distribution bottlenecks, significant deployment of energy storage can provide infrastructure deferrals and better manage variability caused by renewables. Based on our experience in building large solar power plants around the world, we believe an approach based on distributed energy storage with modest capacities can benefit a wide range of applications including firming of commercial and industrial size solar plants, backup power for off-grid solar and wind, island grids, and various behind the meter applications. These applications require storage technologies that are readily scalable from kWh systems at the consumer side to large MWh class utility scale systems. Recent advances in electrochemical energy storage have improved the reliability and lifetime of batteries along with reduced cost. Pilot scale deployment of storage systems employing lithium ion, lead acid, and sodium sulfur batteries have validated the usefulness these systems in regulation, distributed storage, and SmartGrid applications. In addition to these established technologies, there is a growing realization that redox flow batteries may provide low cost, modular, and scalable solutions for grid scale storage applications. In this paper, we will review technical and economic challenges for deployment of energy storage at grid tied solar plants and present scenarios where energy storage could be deployed cost effectively.

At present, the World&’s electricity grids are powered primarily by heat derived from combustion of fossil hydrocarbons or fission of the rare isotope 235U. These sources are not sustainable and must eventually be replaced by renewables, of which the most prominent are wind and sun. But both wind and sun are intermittent and unsuited to maintaining a reliable supply of electric power unless supplemented by unprecedented quantities of massive electricity storage. At present there is no demonstrably satisfactory strategy for providing such storage, and this shortcoming is frequently referred to as the Achilles&’ Heel of Renewable Energy.
A bruited cost goal for such massive storage is a modest 100 $/kWh , whereas present pricing can be as much as thirty-fold this. Hence, storage sufficient to back up a typical day of American electricity consumption [~12×10^9 kWh] could cost upwards of 10 T$ . Electricity storage on this level is unprecedented, its likely candidate technologies have never yet been scaled up and proven in practice, and the economic effects of such preemptive expenditures are unknown.
Fortunately, there is general agreement that fossil fuel should remain in adequate supply until at least 2030, giving both governments and utilities a little breathing room to discern how such an energy transition might be organized. Unfortunately, many current predictions call for severe fossil fuel shortages by 2070, while there is nearly universal agreement that a transition to intermittent renewable energy is ultimately inevitable. Therefore, construction of massive electricity storage can not be delayed indefinitely! In consequence, this presentation will argue that:
1. Prudent precautionary behavior dictates that we begin sooner rather than later to make our energy transition. We can not know the future, and a costly “too soon” is far preferable to a catastrophic “too late”.
2. Future technological development can not be foretold. Hence we should abandon our worship of thrift by generously funding Research Development & Demonstration programs for a huge range of envisioned massive storage modalities, including but not necessarily limited to (a) flow batteries, (b) metal-air batteries, (c) liquid metal batteries, (d) CO2 capture and recycling into synthetic liquid fuels, (e) advanced adiabatic compressed air energy storage, (f) isothermal compressed air energy storage, (g) ocean renewable energy storage, (h) underground pumped hydro, and (i) others. Immediate RD&D at the level of a hundred billion dollars a year would go a long way to removing our uncertainties about these modalities, while being small change compared to the total cost of providing mankind with the necessary energy storage.
3. If the RD&D is jump-started now, mankind should be sufficiently knowledgeable by 2030 to embark upon the massive building program that prudence dictates be nearing completion in 2070. To procrastinate is unwise.

Recent work on Vanadium Redox Flow Batteries (VRFB) in our team has focused serially on improving performance, current density at high efficiency, performance at extremes of state of charge and cyclability. Many of these features are dominated by membrane processes. Thus, we have extensively characterized membranes ex situ and in situ to determine their underlying physical chemistry and their behavior in the cell. We will report on this work and findings for a series of different membrane types. We then will relate our basic data on membrane uptake and transport properties to behavior such as cross-over and capacity fade in operating cells.

Redox flow batteries (RFBs) have attracted considerable research interests primarily due to their ability to store large amount of power and energy, up to multi-MW and -MWh, respectively.1 Traditional aqueous RFBs however are generally low energy density systems limited by water electrolysis potential window and active materials&’ concentrations. In this regard, a nonaqueous RFB system is attractive because it offers the expansion of the operating potential window, which has a direct impact on the system energy and power densities.
Here we report the development of nonaqueous Li-organic redox flow battery (LORFB) based on a modified redox active organic molecule as the positive electrolyte and lithium metal as the negative electrode.2 Molecular modification of quinone-based and ferrocene-based organic materials have demonstrated significantly improved solubility in common organic solvent, enabling the organic molecules to function as energy bearing active materials in the positive electrolyte. The synthesis and the electrochemical study of the two organic materials and the performance of the noanaqeuous flow cell using the modified organic redox couple as positive electrolyte will be reported.

Renewable energy sources including wind and solar can supply a significant amount of electrical energy in the United States and around the world. However, because of their intermittent nature the potential of these two energy sources can be fully exploited only if a suitable energy storage system is provided. Considering the requirements of high energy capacity, high round-trip conversion efficiency, and cost of this application, the Hydrogen-Bromine (H2-Br2) fuel cell has been identified as a highly attractive electrical energy storage system. The H2-Br2 fuel cell has many advantages such as extremely fast reaction kinetics, high energy storage capacity, and low cost. This presentation will discuss the unique features and the advantages and disadvantages of this hydrogen-bromine system and the materials and system challenges in the development of this system for large scale electrical energy storage.

Low-cost and scalable energy storage is vitally important for an electric grid with increasing integration of renewable energy sources such as wind and solar. Flow batteries, which store active electrochemical “fuel” in external reservoirs and pump them into an ion-exchange/electron-extraction power stack to deliver electricity, are considered promising candidates. To meet long-term performance and cost requirements for grid storage, a system-level cost of about $100/kWh is desired. Amongst flow battery systems, one of the most well-developed is the vanadium redox battery (VRB), which has 40 Wh/L-reactants and 20-35 Wh/L at the system level. Projected system costs currently range between $300-$800/kWh for VRBs.
Accordingly, alternative strategies are sought to increase the energy density of flow batteries and decrease system-level cost. Duduta et al. demonstrated a novel approach, the semi-solid flow cell (SSFC), in which the nominal molar concentration of the flow electrodes (also known as catholyte and anolyte) is markedly increased by integrating solid-state intercalation compounds into a flowing, mixed-conducting suspension.The SSFC approach has been explored to date only for non-aqueous Li-ion chemistry, where the combination of higher effective molarity and higher cell voltage in principle allows energy density to exceed that of aqueous flow batteries by over ten-fold.
An SSFC based on aqueous chemistry is of interest for scalable low-cost storage, despite the lower cell voltage compared to their non-aqueous counterparts. In this paper, the LiTi2(PO4)3/LiFePO4 (LTP/LFP) couple is used to demonstrate for the first time an aqueous semi-solid flow cell (A-SSFC). In order to interpret the coupled electrochemical and advective response inherent to SSFCs, rheological and transport properties of the suspensions are measured, and used to guide computational modeling of charge/discharge behavior with concurrent non-Newtonian flow. Sources of inefficiency resulting from flow-induced equilibration and chemical side reactions are separated. High coulombic efficiency is demonstrated, and operating conditions (including the amount and rate of pumping) for optimal round-trip coulombic efficiency are determined. A main remaining challenge for practical application is shown to be the side reactions prevalent in aqueous Li-ion chemistry, including cathode stability and anode-mediated hydrolysis.

The demand for large-scale electrical energy storage (EES) devices has been growing for both improved efficiency and flexibility of the current grid infrastructure and to enable a higher penetration of stochastic renewable sources such like solar and wind onto the grid. Among the most promising technologies for the grid-scale EES are redox flow batteries (RFBs), which are capable of storing a large quantity of electricity (multi-MWs/MWhs) in a relatively simple and straightforward design. There are several RFB technologies, however, the all-vanadium redox flow battery (VRFB) has received significant attention because of its excellent electrochemical reversibility, high round-trip efficiency, and negligible cross-contamination between positive and negative electrolytes. Systems up to multi-MWs have been demonstrated for grid applications and renewable integration. With support from the Department of Energy-Office of Electricity&’s Energy Storage Program, PNNL developed a mixed-acid electrolyte (hydrochloric and sulfuric acid) for the VRFB with significant improvements in thermal stability and solubility over the conventional, sulfate only system. Recently, PNNL scientists demonstrated a 1 kW /1 kWh VRFB prototype system based on the mixed acid electrolyte. The system successfully operated at more than 1.1 kW over the entire operational range (15 % - 85 % SOC) at 80 mA cm-2 with an energy efficiency of 82 % and energy capacity of 1.4 kWh. Without any active heat management, the system operated stably at electrolyte temperatures exceeding 45°C free of any precipitation for extended period of time. By operating stably at elevated temperatures (> 40°C), the mixed acid system enables significant advantages over the conventional sulfate system, namely; 1) high stack energy efficiency due to better kinetics and lower electrolyte resistance, 2) lower viscosity resulting in reduced pumping losses, 3) lower capital cost by minimizing thermal management system, and 4) higher system efficiency.
Even though the demonstrated VRFB technology has shown significant promise, cost and durability issues associated with this battery system must still be addressed for widespread deployment to be achieved. Current efforts at PNNL are focused on addressing several of these issues, namely: low cost separator development, improved current density operation, capacity degradation, and new low temperature electrolyte.
This work supported by the US-DOE Office of Electricity Energy Storage Program - Dr. Imre Gyuk.

A Redox Flow Battery (RFB) possesses several key advantages that make this technology potentially well suited for large scale energy-storage applications. This is especially true of applications that require high energy-to-power requirements (i.e., multiple-hour discharge times at rated power), since the power and energy of a RFB system are independent variables. However, the initial capital cost of flow batteries has been the major barrier to commercialization of RFB technology. One attractive path to cost reduction is the development of RFB cells with substantially higher power densities than conventional RFB cells. The cost of the cell components comprises a significant portion of the total RFB system cost, especially at low production volumes, since cell parts are custom-built components made of relatively expensive materials. United Technologies Research Center (UTRC) has developed vanadium-redox battery (VRB) cells with order-of-magnitude higher power densities than conventional RFB cells, utilizing the same material set as is used in conventional RFB cells. This advanced cell-design technology can theoretically be applied to other RFB chemistries as well. UTRC&’s high power density RFB cells take full advantage of the inherent power and energy independence of the RFB architecture in a manner that had not been previously exploited; namely, flow-battery cells can be designed for high power, independent of the quantity of reactants stored in the tanks of a RFB system, and this power density is much higher than can be achieved with conventional batteries due to the forced-convective flow of the RFB reactants. Some of the key concepts utilized to enable these high performance RFB cells will be described, as well as the multiple key benefits of high power density RFB cells. UTRC has demonstrated this technology in complete RFB systems and the current maturity level of the technology will be highlighted. Additionally, some potential research opportunities to further improve RFB technology will be presented, including advanced cell materials (e.g., electrodes, membranes) that are optimized for high performance RFB cells.
Acknowledgements
The author would like to thank multiple colleagues at UTRC who have been an essential part of UTRC&’s advanced flow-battery team. The work to be presented herein was funded, in part, by the Advanced Research Projects Agency - Energy (ARPA-E), U.S. Department of Energy (DOE) under Award Number DE-AR0000149.

Energy policies enacted throughout the United States and the European Union have directed utility companies to provide upwards of 60% of all energy produced to come from renewable sources by 2050. Solar and wind energy sources can already provide a significant percentage of this target, but they must be paired with viable grid-scale energy storage to counteract the dependency on season, weather, and day-night cycles.
Few grid-scale storage options are mature enough for widespread adoption, but redox flow batteries (RFB) have been positioned as strong candidates due to their steady development over the past several decades. Features such as the separation of power and energy capacity along with scalability have driven interest in this technology. Transition metal-based aqueous systems have received the most attention, but limitations related to solubility, membrane permeability, and cell voltage have not resulted in rampant commercial success. Further advancements will have to come from the development of new redox chemistries, larger cell potentials, and fast redox kinetics.
Recently, Sandia National Laboratories' research efforts have focused on flow battery electrolyte development through redox “non-innocent” ligands for metal-based compounds. This strategy makes use of ligand-based electrochemistry separate from the metal center to take advantage of the entire mass of the complex. This also results in increased stability of the complex&’ structure by reducing changes in bonding caused by oxidation chemistry at the metal center. The abundance of well-characterized, reversible charge transfer events exhibited by these compounds has the potential to greatly improve their energy density and make them the next state-of-the-art. This talk will detail our current efforts on the synthesis, electrochemistry, and flow cell performance of these redox-active compounds.

Large-scale energy storage is required to meet a multitude of current energy challenges. These challenges include modernizing the grid, incorporating intermittent renewable energy sources (so as to dispatch continuous electrical energy), improving the efficiency of electricity transmission and distribution, and providing flexibility of storage independent of geographical and geological location. In addition, such storage would be scalable for centralized or distributed use.
The technology approach considered here is based on using very low cost iron electrolytes in a flow battery that will be economically feasible and competitive. Capital cost for this system is estimated to be $200/kW (without power conditioning) and, based on 10 hours of energy storage, $20/kWh (for a decoupled system). Additional advantages of this approach are that abundant, non-toxic, and non-corrosive materials are used to provide an energy storage solution that has inherently safe operation and is environmentally friendly. This approach will further reduce downstream lifecycle costs (including maintenance and disposal) that are often underestimated. Relevant scientific literature illustrates that the chemistry has been demonstrated in laboratory cells, which involved a ferrous/ferric ion redox couple for the positive half-cell and a ferrous/iron metal couple for the negative half-cell.
In this presentation we will describe our recent work involving many aspects of the all iron battery system. The chemistry of the system is being studied to reduce hydrogen evolution, increase iron ion solubility, and still favor practical reaction potentials. Novel electrode designs are being investigated to enhance the power density and the plating capacity for a hybrid flow battery system where iron is plated within the stack for a DOE Office of Electricity funded program. Under a separate ARPA-E program, we are investigating a slurry approach to decouple the negative electrode. This decoupled design will allow the energy and power to be independently scaled.

Flow batteries promise economy of scale because of their modular architecture in which tank and stack size dictate energy and power capability, respectively. Conventional flow batteries incorporate redox-active solutions that employ a flow-through current collector confined to the power stack. Recently, an alternative flow-battery framework, the semi-solid flow cell, was introduced in which a flow-with current collector is employed via integration of active materials in an electron-conducting carbon suspension. The cycling performance of a given electrode couple in either of these frameworks results from the interplay among kinetic effects (e.g., pore size and reactive surface area), bulk electron- and ion-transfer, porosity, and viscous dissipation. The high electronic conductivity in solution-based frameworks lends their use toward materials with facile reaction kinetics and ion transfer. In contrast, suspension-based frameworks incorporate nanoporous electron-conductor capable of enhancing sluggish kinetics of redox-active molecules. In this work, we consider these tradeoffs in the context of sparingly soluble active-material systems wherein reaction kinetics, ion transfer, diffusion, phase transformation, and viscous dissipation compete during cycling. Through multi-scale simulation and experiment the performance of such active-material systems will be explored in both solution- and suspension-based frameworks. We acknowledge support for this work from the Joint Center for Energy Storage Research (JCESR).

The ability to store large amounts of electrical energy is of increasing importance with the growing fraction of electric generation from intermittent renewable sources such as wind and solar. Flow batteries can independently scale the power (electrode area) and energy (arbitrarily large storage volume) components of the system by maintaining all electro-active species in fluids. Wide-scale utilization of flow batteries is limited by the abundance and cost of these materials, particularly those utilizing redox-active metals and precious metal electrocatalysts. Here we describe the development of a flow battery based on the aqueous redox chemistry of small organic molecules called quinones. The redox active materials contain no metals and can be very inexpensive. We will report electrochemical studies of molecules undergoing fast and reversible two-electron two-proton reduction to hydroquinones on carbon without the addition of electrocatalyst. We will report the performance of an aqueous flow battery involving the quinone/hydroquinone couple, which has achieved a peak power density exceeding 100 mW/cm2 at the time this abstract is being written. The absence of active metal components in both redox chemistry and catalysis represents a significant shift away from modern batteries. This new approach may enable massive electrical energy storage at greatly reduced cost.

Low-cost, modular energy storage systems are sought to improve the grid efficiency and to enable widespread use of intermittent renewable energy sources [Z. Yang et al., Chem. Rev., 111 (2011)]. Redox flow batteries may offer the best combination of cost, efficiency, and scalability to enable grid storage applications. Current aqueous flow battery technologies, such as the state-of-the-art all-vanadium system, offer high stability and efficiency but are limited to low energy densities (< 40 Wh/L) , which, in turn, lead to high system-level costs($750-830/kWh, $3000-$3310/kW) [Dunn et al., Science, 334 (2011)]. Employing non-aqueous solvents offers a wider window of electrochemical stability that enables cell operation dramatically higher potentials than their aqueous counterparts (> 3 V as compared to 1.5 V). Higher cell voltages lead to higher energy density and typically higher roundtrip efficiency, which together reduce energy cost.
Taking advantage of these wider electrochemical windows requires the development of appropriate electrochemically-active materials and the application of these materials in a high capacity flowable format. Redox-active organic molecules are of particular interest as key electrochemical and physical properties can be modulated via tailoring of the redox-active moiety or the surrounding molecular structure. Moreover, earlier work on organic electrodes for lithium (Li)-ion batteries has led to the identification of a number of promising materials and to the establishment of some key design principles [Brushett et al., Adv. Energy Mat. 2 (2012)]. Here, we will discuss our research efforts on the development of suitable materials and electrolytes for non-aqueous Li-ion redox flow batteries with a focus on alkoxybenzene and quinoxaline derivatives as electroactive materials. Specifically, we will employ a suite of electroanalytical techniques, in combination with quantum calculations, to gain insight into the charge transfer and storage mechanisms, the solution-phase interactions with the electrolyte, and the charged state stability of these two families of redox-active materials.

The integration of renewable energy sources into the electric grid is an integral part of a secure energy future. Due to the intermittent nature of these resources, large-scale energy storage devices must be developed in order for these technologies to be fully utilized. Redox flow batteries (RFBs) are among the most promising systems poised to address these issues. Despite many compelling attributes, new chemistries must be discovered for RFBs to realize their full potential. Presented here is the use of metal oxide clusters commonly known as polyoxometalates (POMs) in RFBs. The battery exploits the ability of these compounds to undergo highly reversible multi-electron redox processes, as well as the fact that they are stable over a wide range of pH values and temperatures. In addition, the POMs contain both vanadium and tungsten with redox processes that are separated by about 1 V. This approach allows the same compound to serve as both the cathode and the anode. The battery has coulombic efficiencies greater than 95% with relativity low capacity fading over 100 cycles. Iterations on the materials have also been performed in order to determine the influence of elemental composition, geometry, and structure on the performance of the battery. Current efforts are also focused on increasing the solubility of the compounds by the systematic modification of the counter cations. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Novel carbon materials have been synthesized for their applications in electrochemical capacitors. Using KOH activation of microwave exfoliated graphite oxide (MEGO), a porous carbon (activated MEGO, or a-MEGO) with a BET surface area of up to 3100 m2/g, a high electrical conductivity, and a low oxygen and hydrogen content was obtained. This sp2-bonded carbon apparently has a continuous 3D network of highly curved, atom-thick walls that form primarily 0.6- to 5-nm-width pores. Two-electrode supercapacitor cells constructed with a-MEGO yielded gravimetric capacitance of up to 200 F/g (normalized to carbon) and energy density of above 20 Wh/Kg (normalized to a typical supercapacitor device) with ionic liquid electrolytes. The energy density can be further improved to more than 50 Wh/Kg by constructing a hybrid supercapacitor using Li-ion electrolyte. A parametric study of the loading of KOH to activate MEGO (to generate a-MEGO) and the temperature of activation was performed to study their effects on the BET surface area and supercapacitor performance. In addition, mechanical pressure was applied to consolidate the carbon, leading to a higher mass density. After compression, the gravimetric capacitance remained about the same, but the volumetric capacitance was significantly improved, yielding a high volumetric energy density in the capacitor. A-MEGO can act as an efficient scaffold for hosting other active materials used for electrochemical capacitors due to its unique pore distribution. For example, MnO2/a-MEGO composites have been synthesized by in situ deposition of nanometer-thick MnO2 through the 3D porous structure of a-MEGO. Furthermore, when a-MEGO was made as paper-like morphology, it has demonstrated very high power density of up to 500KW/Kg, indicating a-MEGO potentially has multiple functions in future energy storage devices.
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References:
[1] Yanwu Zhu, Shanthi Murali, Meryl D. Stoller, K. J. Ganesh, Weiwei Cai, Paulo J. Ferreira, Adam Pirkle, Robert M. Wallace, Katie A. Cychosz, Matthias Thommes, Dong Su, Eric A. Stach, Rodney S. Ruoff, Science 332, 1537, 2011
[2] Shanthi Murali, Jeff Potts, Scott Stoller, Joono Park, Meryl Stoller, Lili Zhang, Yanwu Zhu and Rodney S. Ruoff, Carbon, 2012, 50, 3482-3485
[3] Shanthi Murali, Neil Quarles, Li Li Zhang, Jeffrey R. Potts, Ziqi Tan, Yalin Lu, Yanwu Zhu, Rodney S. Ruoff, Nano Energy 2013, in press
[4] Meryl D. Stoller, Shanthi Murali, Neil Quarles, Yanwu Zhu, Jeffrey R. Potts, Xianjun Zhu, Hyung-Wook Ha and Rodney S. Ruoff, Phys. Chem. Chem. Phys., 2012, 14, 3388-3391
[5] Xin Zhao, Lili Zhang, Shanthi Murali, Meryl D. Stoller, Qinghua Zhang, Yanwu Zhu, and Rodney S. Ruoff, ACS Nano, 2012, 6, 5404-5412

The environmental concerns over the use of fossil fuels and their resource constraints, have spurred great interest in generating electric energy from renewable sources. Wind and solar energy are among the most abundant and potentially readily available. However, wind and solar are not constant and reliable sources of power. To smooth out the intermittency of renewable energy production, electrical energy storage will become necessary. Supercapacitors (also called electrochemical capacitors), as one of energy storage systems, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. The performance of supercapacitors is mainly determined by the electrochemical activity and kinetic feature of the electrode materials. In this talk, we will focus on the recent advances in fabrication of nano-electrode materials for high performance supercapacitors. The most widely used active electrode materials for supercapacitors are carbon, conducting polymers, and both noble and transition-metal oxides. Recently, graphene, a single atomic plane of graphite, is expected to be an excellent electrode material for supercapacitors due to its superior electrical conductivity, high specific surface area, and chemical stability. In the last, this talk will also present the integration of supercapcitors energy storage and their applications.

Binder free single walled carbon nanotubes were self-assembled to form a highly dense 20µm thick carbon nanotube electrode to be used in electrochemical capacitors. Fabrication of symmetric nanotube capacitors using these electrodes and highly ionically conducting polyvinyl alcohol based hydrogel membranes soaked in aqueous sulfuric acid resulted in a capacitor with power density as high as 1040 KW/kg based on mass of both electrodes. The time constant of the assembled capacitor was ~ 15 ms and was dependent on the concentration of sulfuric acid. Equivalent circuit modeling of the impedance spectra showed that the small time constant was associated with decrease in the Warburg diffusion resistance. The capacitors also showed good cycling stability even at 10,000 cycles. The electrodes showed no observable degradation even after the 10,000 cycles.

High energy and power densities energy storage devices are urgently demanded to meet challenges of the fast development of large-scale electric energy storage such as wireless electric tools, hybrid electric vehicles and industrial energy management. The development of supercapacitors has focused on the use of graphene, due to its excellent electric and mechanical properties, chemical stability, high specific surface area up to 2675 m2/g, and feasibility for large-scale production (especially the chemically modified graphene CMG). Most of works on graphene-based nanocomposites have been achieved by incorporating guest nanoparticles onto 2D graphene sheets. However, those structures suffer from graphene aggregation, which causes inferior ionic accessibility and thus modest improvement in the cell performance. The randomly and loosely stacked graphene sheets have large interface resistance, which would make it difficult for ions to gain access to the electrode surfaces. In our report, we fabricate a novel type of N-doped hierarchically 3D macroporous CMG films electrode (NCMG) through a facile ultrafiltration method using graphene oxide (GO) and polystyrene (PS) as precursors. After calcinations in N2 atmosphere at 1000°C, the as-prepared GO/PS composites become interconnected macroporous NCMG film. The NCMG film holds novel hierarchically porous architectures, which could intrinsically optimize ion transport and also provide sufficient contact area between the electrode and electrolyte. The resultant 3D macroporous NCMG film shows high specific capacitance (150 F g-1), excellent rate capability, and long cycle life (98% of the initial capacitance), NCMG is an attractive scaffold candidate for conducting polymers and metal oxides. Finally, the electrode structure and fabrication method described in this study is simple and should thus be readily applicable to other graphene-based energy storage and conversion applications.

Designing batteries for long cycle life requires understanding of the many inter-related mechanisms that affect battery life. A123 Systems LLC has commercialized batteries which have demonstrated several thousand cycles even at elevated discharge rates and elevated temperatures. One factor which affects life in lithium-ion batteries is adhesion of the active material to the current collector, both in the dry as-made electrode and in the internal environment of the battery in which the electrode is wetted by electrolyte. We term the latter “wet adhesion”.
It is known that volume change in the anode active material (10% for graphite based anode, ~300% for Si based anode) can lead to disconnection of particles of active material from the current collector over the course of cycling. It is also known that high water content is detrimental to cell cycle life, because of reactions of water with the electrodes and electrolyte. In this study, we examined the interaction between moisture content and adhesion. To understand the factors that affect wet adhesion, anode electrodes were tested by immersing them in electrolyte which was exposed to ambient air at about 30% relative humidity from 0 up to 3 hours. Electrodes were made by combining graphite or silicon with a binder and conductive additive and coating onto copper foil. For the electrolyte with zero exposure to moisture, no wet adhesion failure was observed; on the other hand, when electrolyte exposure time was greater than 5 minutes, complete delamination of anode coating layer occurred. Fundamentally, this moisture induced wet adhesion failure can be attributed to the formation of HF as a result of the well-known LiPF₆/H₂O reaction. The HF then attacks the bond between the binder and the copper foil.

The increase in installed and planed renewable power plants with a geographic, seasonal and weather dependent generation of electricity pushes the need of adequate energy storage systems, especially high energy density materials. Furthermore the efficient reduction of carbon dioxide (CO2) is of high interest, because fossil fuel remains an important energy source for the next decades.
In this work, electropositive metals and in particular lithium, are used as high energy density, large scale energy storage material. According to its position in the standard reduction potential table (-3 V), lithium can reduce even very low reactive gases as CO2 and nitrogen (N2) and form valuable products. The strongly exothermic reaction of lithium with CO2 and N2 yields thermal energy of 39 kJ and 10 kJ per gram lithium, respectively. These values are comparable to the combustion of coal in an oxygen atmosphere with 33 kJ/g carbon. Lithium thereby reduces CO2 to valuable carbon monoxide (CO), which can be further converted with hydrogen from renewable sources to methanol or gasoline. The solid product of the reaction of lithium with CO2 is lithium carbonate (Li2CO3), the starting material for all other lithium compounds. Thus, no volatile environmentally critical waste products are emitted into the atmosphere.
In addition to the conversion of the stored chemical energy into thermal energy, the combustion of lithium in N2 enables an efficient access to ammonia. Today, the production of this energy carrier and fertilizer, accounts for more than 3% of the world primary energy demand.
In both cases, the solid combustion products can be electrochemically recycled using stranded renewable energy resources.
In this work we report on the combustion of molten lithium in an atmosphere consisting of carbon dioxide and air. For the first time, we show the atomization of molten lithium with a single-fluid swirl nozzle. The spray is characterized in an argon atmosphere in order to prevent reaction of the lithium with the atmosphere. The temperature and the appearance of the lithium spray as a function of the process pressure were characterized. The diameter of the lithium particles were measured optically. The lithium spray was ignited in hot atmospheres of carbon dioxide and air. Ignition conditions and temperatures are presented. The solid combustion products are characterized by XRD measurements and chemical analysis.
The results are put in correlation with the combustion of individual lithium particles. Solid lithium particles of in a size of 60 - 150 µm, dispersed in our lab, are examined in a laminar flat flame burner. We found power plant usable particle temperatures up to 4000 K. Beneath the temperature measurement, the chemical composition of particle samples at the reactor outlet was checked.

Ion transport and adsorption in microporous solids are critical phenomena governing the performance of many essential instruments, including energy storage devices (1-7). These processes also play a critical role in functioning of various biological systems on a cellular level. The limited understanding of such processes is largely hindered by the lack of experimental techniques capable of identifying the sites of ion adsorption and the concentration of ions at the nanoscale. In our work for the first time we harness the high penetrating power and sensitivity of neutron scattering to isotope substitution to directly observe changes in the ion concentration as a function of the applied potential and the pore size (2). In contrast to prior studies (5-7), the distribution of ion density within the pores of different sizes can be measured within the same material. Since materials with different pore size distributions inevitably exhibit different microstructures and different concentrations of defects and surface functional groups, the proposed method offers a unique and very important ability to study the effects of the pore size and surface chemistry independently.
We demonstrate that depending on the solvent properties and the solvent-pore wall interactions, either enhanced or reduced ion electro-adsorption may take place in sub-nanometer pores (2). We further demonstrate the pore size dependence of the ion adsorption from various solutions under no applied potential (2). More importantly, we demonstrate the route to identify the critical pore size below which either enhanced or reduced sorption of ions takes place (2). The proposed methodology opens new avenues for systematic in-situ studies of complex structure-property relationships governing adsorption of ions under applied potential.
Acknowledgement: This work was partially supported by the US Army Research Office (contract number W911NF-12-1-0259). The research at ORNL&’s High Flux Isotope Reactor was sponsored by the Laboratory Directed Research and Development Program and the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
References:
1. Kajdos A, Kvit A, Jones F, Jagiello J, & Yushin G (2010) J. Am. Chem. Soc. 132, 3252.
2. Boukhalfa S, He L, Melnichenko YB, & Yushin G (2013) Angewandte Chemie International Edition 125, 4716-4720.
3. Kondrat S, Georgi N, Fedorov MV, & Kornyshev AA (2011) PCCP 13, 11359-11366.
4. Choi NS, Chen ZH, Freunberger SA, Ji XL, Sun YK, Amine K, Yushin G, Nazar LF, Cho J, & Bruce PG (2012) Angewandte Chemie-International Edition 51, 9994-10024.
5. Raymundo-Pinero E, Kierzek K, Machnikowski J, & Beguin F (2006) Carbon 44, 2498-2507.
6. Chmiola J, Yushin G, Gogotsi Y, Portet C, & Simon P (2006) Science 313, 1760-1763.
7. Salitra G, Soffer A, Eliad L, Cohen Y, & Aurbach D (2000) Journal of the Electrochemical Society 147, 2486-2493.

Cost of current lithium ion battery manufacturing technology (from raw materials to the battery testing) is nearly three times higher than the target set by US Department of Energy (US-DOE). Cost reduction for manufacturing requires advanced techniques on electrode processing part that increase production while reducing the scrap rate. Developing novel materials and material-processing techniques are very critical to reduce the battery cost. However, implementing advanced non-destructive (ND) quality control (QC) techniques to reduce the scrap rate provides another option for substantial cost reduction. Currently, electrode thickness variation and certain flaws such as pinholes, agglomerates, and blisters in the electrodes are not detected during electrode coating. Costs can be added until the battery devices are tested, and the associated scrap rates increase the costs of lithium secondary cells to an unacceptable level. If electrode flaws and contaminants could be detected “in-line” near the particular processing steps generating them and before electrochemical testing, the electrode area consisting of the flaws could be identified, and conditions could be adjusted to eliminate those defects in a timely manner hence, reducing the scrap rate. In this work, in-line laser caliper and thermography were implemented novel non-destructive evaluation methods to detect the flaws associated during electrode coating process in a slot-die coater. The laser caliper sensors were mounted and subsequently aligned on a slot-die coater. Various effects such as substrate vibration, temperature, surface reflectivity and laser positions, on the thickness measurement during slot-die coating were examined. The laser caliper setup was used to monitor the wet thickness of the cathode and anode during coating, and the precision of the in-line laser thickness measurement was about ± 2%. Thickness deviation obtained for cathodes was typically ± 2.3% to 2.0%, and for anodes, typically ± 2.2% to 2.6%, The homogeneity of dry electrodes was examined by IR thermography. Temperature profiles in the IR thermography images of dry electrodes were evaluated to detect any flaws and inhomogeneity present across the electrodes. The increase or decrease in the temperature profiles indicated defects/flaws in the electrodes which could not be observed in digital images. An increase in the temperature profile suggests the presence of agglomerates, and a decrease in the temperature profile indicates pinholes and blisters present in the electrode. This QC demonstration presents the proof of concept for the ND evaluation of LIB electrodes during coating by a slot-die coater.
Acknowledgement:
This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy for the Vehicle Technologies Office's Applied Battery Research Program.

The pursuit of next generation rechargeable batteries has been hindered by safety and efficiency issues associated with the use of lithium metal anode, which is essential for the success of high energy density battery system such as lithium sulfur and lithium oxygen batteries. Many methods have been proposed and tested in order to overcome these challenges, but a satisfactory solution has not yet been attained. Pulse plating (PP) has been widely used in metal electrodeposition process, but interestingly, it is rarely studied in lithium battery system. In this study, we demonstrate that lithium plating morphology and cycling efficiency is greatly improved with optimal set of PP parameters. Also, the deposition of smooth lithium layer resulting from the beneficial PP regime leads to improvement of the average lithium cycling efficiency from around 75% using direct current (DC) deposition, to above 90% under PP waveform. The effects of various PP waveforms on lithium deposition have been compared and discussed in detail in the present report.

We present preliminary results on a processing protocol that transforms organic waste products such as cocoa pod and coconut shell into high surface area activated carbon for application as electrode in electrochemical energy storage and conversions systems. The scanning electron microscope and the transmission electron microscope are used to acquire structural and morphological information of the activated carbon, and the surface area and porosity analysis is performed on Micromeritics ASAP 2020 analyzer. Initial results indicate surface area greater than 2000m2/g.

Development of inexpensive, flexible, lightweight, and sustainable energy-storage materials is essential to meet the predicted increase in demand for energy storage in today&’s society. The devices based on conducting polymer are highly interesting in this respect. Polypyrrole (Ppy) as one of popular conducting polymers has been attracted for the subject of great interest due to its easy polymerization and wide practical application. The various characteristics of Ppy have been investigated with regard to their morphologies using electrochemical conditions.
We investigated the growth of nano and microstructure Ppy-modified doughnut on an electrode to make a high efficient device for good energy storage. Ppy&’s doughnut size enabled to be controlled by electrochemical technique. Ppy film was also polymerized by direct current (DC) amperometry and alternative current (AC) of impedance spectroscopy. In DC amperometry, the curves with current density-time were measured in the monomer pyrrole solution. The magnitude and phase were measured by AC impedance. In addition, electrochemical parameter was changed for each method to find an optimized condition. It was identified that Ppy doughnut size was approximately 150 nm width and 250 nm height that polymerized by DC waveform, and 3.6 um width and 2.4 um height that polymerized by AC waveform. The good energy-storage property of Ppy coated electrode was proved through cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS) with three-electrode configuration. In CV analysis, redox current in micro-sized Ppy coated electrode is significantly increased up to 1.8 times, compared with nano-sized Ppy coated electrode.
We present a micro and nano structure of Ppy doughnut for the high capacity of energy storage with low-cost and easy scale-up.

Flow batteries have well-recognized attributes of modular scalability and independently variable power and energy, but can be mechanically complex due to the need for simultaneous control of flow and electrochemistry, necessitating of pumps, sensors, valves, and seals. Towards the development of simpler, robust, passively driven, lower-cost flow battery architectures, we demonstrate a proof-of-concept prototype of a novel gravity fed flow battery using electronically-conductive semi-solid flow electrodes. The demonstrated design (i) uses gravity as the fluid driving force, (ii) can be readily manufactured using stackable low-cost injection molded pieces, and (iii) is controlled by a single actuator. The design, electrochemical performance, and theoretical analysis of the prototype device will be discussed.
This work was initially supported by the Advanced Research Projects Agency-Energy (ARPA-E), US Department of Energy, and subsequently by the Joint Center for Energy Storage Research (JCESR).

Simple and cost effective electrospinning process is employed here for the preparation of TiO2 nanofibers. Polyvinylpyrrolidone (PVP) and Titanium tetra isopropoxide (TTIP) in ethanol and acetic acid solution is used as precursor (sol) for electrospinning. As-spun fibrous network is subjected to heat in air at 600 oC/min resulting in nanofibers having high aspect ratio. The XRD pattern confirms the presence of crystalline TiO2 in the sample after heat treatment. The granular fibrous morphology of the TiO2 fibers is verified through Scanning Electron Microscope (SEM) and Tunneling Electron Microscope (TEM). Electrochemical properties of the fibers as working electrodes of supercapacitor is studied using cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) in Na2SO4 electrolyte.

Redox-capacitors are electrochemical energy storage devices using the electric double layer capacity at the electrode-electrolyte interface and pseudocapacity by redox reactions with faraday process. Since redox-capacitors are able to be higher energy density than conventional electric double layer capacitors and higher power density than batteries with long cycle life, they attract attention as maintenance-free power supplies. In this study, we use quinonic and hydroquinonic compounds as redox active materials in negative and positive electrodes, respectively. Quinonic and hydroquinonic compounds can charge/discharge by proton insertion/extraction. We demonstrated the inexpensive metal-free energy storage devices driven by proton-rocking-chair mechanism in non-flammable aqueous solution. Since the hydroquinonic compounds are easily dissolved into water, it is difficult to use directly as active materials. Then, we supported them on the surface of carbon materials. As a result, we found that supporting in nanometer-pores of activated carbon (MSC-30, Kansai-Netsu-Kagaku) is most favorable for the utilization of redox reaction of organic compounds with long cycle lifetime. We demonstrated aqueous redox-capacitors using hydroquinonic supported by nanometer-pored activated carbon as cathode and quinonic supported by nanometer-pored activated carbon as anode. This capacitor shows the high energy density (20 Wh/kg) in the applied potential range between 0-1 V and high power density with long cycle lifetime (more than 1000 cycles). This value is about three times larger than that of the electric double layer capacitor using only activated carbon electrodes.

A primary impediment for wide-spread adoption of grid-scale renewable energy sources is their inherent intermittency. This problem is acute for solar energy, prompting interest in energy storage technologies that are feasible at very large scale. As an alternative to batteries, synthesis of fuels from sunlight is one promising option, and requires optimized photoelectrochemical devices and materials; however, significant improvements will be needed in efficiency and stability of these materials for this to be a viable alternative. In prior work, atomic layer deposited TiO2-protected photoanodes coated with an ultra-thin layer of known oxidation catalyst (Ir) were demonstrated to achieve highly efficient water oxidation without the Fermi level pinning often seen in common silicon/metal and silicon/electrolyte systems. With an optimized tunnel oxide, single-junction silicon devices were shown to achieve a photovoltage of 550 mV under one sun while increasing the device lifetime from minutes without the ALD-TiOnot;2 to over 8 hours [1]. More recently, it was shown that ALD-TiO2 protection is viable for a number of metal catalysts and that the protection layer can be tailored to different thicknesses with a relatively modest penalty in water oxidation overpotential [2]. In this presentation, we will report on the relationship between the thickness of the ALD-TiO2 protection layer and the device photovoltage and stability. In particular, the photovoltage of MIS photoanodes is seen to decrease as the ALD-TiO2 layer thickness is increased. The flat band voltage as measured by solid-state capacitance-voltage measurements, however, is constant with changing TiO2 thickness, indicating that fixed charge in the oxide is not the source of this voltage drop. The effects of the asymmetric TiO2/SiO2 oxide bilayer in the MIS anode on electronic carrier transport and the chemical stability of the structure will be discussed.

In recent years, considerable attention was focused on the research of energy grids and on the establishment of renewable energy sources such as solar and wind. Since these sources produce energy only intermittently, adequate energy storage facilities are necessary. Therefore, the development of closed energy cycles based on solid, high energy density storage materials is required.
Electropositive metals, and in particular lithium, can be electrochemically produced using stranded energy and in an energy cycle discharged and full recycled. The discharging is done by combustion of the lithium metal in a carbon dioxide (CO2) or nitrogen (N2) stream. The reaction of lithium with N2 offers an efficient access to ammonia, whereas with CO2 valuable carbon monoxide (CO) is produced, which can be further converted to methanol or gasoline. The solid reaction products of both reactions - lithium compounds such as lithium carbonate (Li2CO3) and lithium oxide (Li2O) - can be recycled using stranded renewable energy resources.
In this work, combustion of lithium in different environments is studied by spectroscopic methods. The combustion of both, bulk lithium pellets and atomized lithium spray is characterized and compared. Lithium pellets up to 1 g weight were molten on a stainless steel heater in a pressure-controlled vessel and ignited by an electrical HV spark. Ignition was successful only well above the melting temperature, indicating that a considerable amount of gaseous lithium is necessary to start the reaction. In air, the reaction was vigorous with a bright flame. Solid combustion products grew in a coral shape from the reaction center, and substantial amounts of aerosol were generated. Reaction with other gases (CO2 and N2) was less intense.
For practical burners, spray combustion of liquid lithium is more attractive for various reasons. The lithium spray was generated with a stainless steel injector with an up to 0.6 mm diameter nozzle. With an inlet pressure up to 5 bar, a flow as high as 400 mg/s was achieved. The resulting spray has a lithium particle size of around 140 µm and was ignited in a pressure-controlled reactor.
For both burners, the combustion process was characterized by several spectroscopic techniques including temporally- and spatially-resolved analysis of chemiluminescence spectra. Products (both solid and aerosol) are analyzed using elementary analysis, X-ray diffraction, and wet-chemical and microscopic techniques. The composition of the products depends critically on the position within the reaction zone. In air, Li2O is produced in the outer flame layers, whereas lithium nitride (Li3N) was found in the center. Exposed to ambient air, the products are converted to the thermodynamically stable carbonate in the course of days.
The results show the potential of a lithium based closed energy cycle.

In order to make flow batteries cost-competitive for large-scale stationary storage, significant reductions must be made in the cost of the redox-active materials. Organic molecules such as quinones offer potentially dramatic cost reductions to the storage medium. Quinones also provide the ability to tune the redox and solubility properties of the molecules through the incorporation of various substituent groups onto the aromatic ring.
We will report the electrochemical properties of several substituted quinone molecules. These results indicate that quinones can be synthetically modified to span a range of reduction potentials, while showing rapid and reversible reduction kinetics. Functional group tuning on the quinone yields molecules with high and low reduction potentials, which has allowed construction of a metal-free aqueous flow battery. These organic electrolytes are strong candidates for large-scale energy storage in a flow battery.

Large-scale energy storage represents a key challenge for renewable energy and new systems with low cost, high energy density and long cycle life are desired. In this article, we develop a new lithium/polysulfide (Li/PS) semi-liquid battery for large-scale energy storage, with lithium polysulfide (Li2S8) in ether solvent as a catholyte and metallic lithium as an anode. Unlike previous work on Li/S batteries with discharge products such as solid state Li2S2 and Li2S, the catholyte is designed to cycle only in the range between sulfur and Li2S4. Consequently all detrimental effects due to the formation and volume expansion of solid Li2S2/Li2S are avoided. This novel strategy results in excellent cycle life and compatibility with flow battery design. The proof-of-concept Li/PS battery could reach a high energy density of 170 W h kg-1 and 190 W h L-1 for large scale storage at the solubility limit, while keeping the advantages of hybrid flow batteries. We demonstrated that, with a 5 M Li2S8 catholyte, energy densities of 97 W h kg-1 and 108 W h L-1 can be achieved. As the lithium surface is well passivated by LiNO3 additive in ether solvent, internal shuttle effect is largely eliminated and thus excellent performance over 2000 cycles is achieved with a constant capacity of 200 mA h g-1. This new system can operate without the expensive ion-selective membrane, and it is attractive for large-scale energy storage.

The corrosion behavior of chromia and alumina forming austenitic stainless steels has been evaluated in the presence of molten nitrate salt mixture consisting of NaNO3 (60 wt%) and KNO3 (40 wt%). The corrosion tests were conducted at 550C & 650C in flowing air environment for up to 500 hrs. The test coupons were exposed to thin salt film (1-2 mg/cm2)as well as immersed in the molten salt pool. Physical characteristics associated with melt evaporation was examined by TGASEM/EDS and X-ray diffraction techniques were used to examine the composition and structure of the corrosion products. Mechanism for the observed enhanced corrosion of alloys (when compared with oxidation in air) is proposed and presented.

Niobium oxide (Nb2O5) has been recently introduced as high performance electrode material for supercapacitors. It has been shown that orthorhombic Nb2O5 (T-Nb2O5) exhibits very fast lithium intercalation/de-intercalation, resulting in a charge storage mechanism referred to as intercalation capacitance. So far, the excellent performance of T-Nb2O5 has only been demonstrated for thin film electrodes. We have successfully prepared a layered Nb2O5/carbon composite with highly crystallized orthorhombic Nb2O5 through controlled oxidation of layered Nb2C (also called Nb2C-MXene).The as-prepared Nb2O5/C retains the two dimensional structure of the precursor with Nb2O5 nanocrystals or nanorods formed between the MXene layers. A detailed study of oxidation temperature and duration was conducted to produce nanocrystalline T-Nb2O5. XRD, SEM and Raman spectroscopy studies show a uniform formation of T-phase of Nb2O5 after oxidation of Nb2C at 800C for 1 hour. The preliminary electrochemical characterization of 100-mu;m thick shows very promising performance, with a specific capacitance of about 150 F/g at 0.5 mV/s in 1M LiClO4 EC:DMC (1:1 volume ratio) with a coulombic efficiency close to 100%, which represents a highly reversible Li+ intercalation/de-intercalation process. The performance of developed electrodes is believed to be highly dependent on the layered two-dimensional structure of the Nb2O5/carbon composite.

Sodium (Na)-ion battery offers as an attractive option for low-cost grid-scale energy storage due to the abundance of Na. Tin (Sn) has a high theoretical capacity of 847 mAh/g as an anode material for Na-ion battery, but faces tremendous challenges: large volume expansion, sluggish kinetics and unstable solid electrolyte interface (SEI) formation. A successful demonstration of Sn based anode with high cycling life has not yet been achieved. In this article, we demonstrate that an anode consisting of a Sn thin film deposited on a mesoporous cellulose fiber substrate simultaneously addresses all of these challenges associated with Sn anodes. Low-cost, earth-abundance wood cellulose fiber with natural softness can effectively release the mechanical stress in Sn anode accumulated during the sodiation process, which was confirmed experimentally and computationally. Fibers with a nature-designed hierarchical and multi-channels structure also function as an electrolyte reservoir that allows the ion transport from both outer and inner surface of the fiber, which effectively addressed the sluggish Na ion transport. A stable cycling performance up to 400 cycles with a capacity around 200 mAh/g is demonstrated; a significant improvement from any Sn nanostructures in literature and our control experiments. The mesoporous, conductive, soft cellulose fiber substrate can be utilized as a new platform for low-cost Na-ion batteries.
Publication: Tin Anode for Sodium-Ion Batteries Using Natural Softwood Fiber as Mechanical Buffer and Electrolyte Reservoir, Nano Letters (2013) DOI: 10.1021/nl400998t

A research into Na-ion battery has been under focus lately due to its advantages in specific applications such as large scale power grid system. Among the candidates of cathode materials, layered oxides materials of general formula NaMO₂ (M = Cr, Mn, Fe, Co, Ni, etc.) exhibit one of the largest theoretical capacity along with simple crystal structure. A typical layered oxide electrode like NaNiO₂ was first studied by Braconnier et. al. in 1982. It was shown that approximately 0.2 Na could be cycled within the voltage range of 2.0 - 3.5 V. Recently, Vassilaras et. al. reported the same system with an initial charge capacity of 199 mAh/g (0.85 Na) followed by 147 mAh/g (0.63 Na) subsequent discharge capacity within the voltage range of 2.0 - 4.5 V. However, low capacity retention and coulombic efficiency still remain big challenges.
Here we report the electrochemistry of monoclinic NaNiO₂ together with mechanistic study of the charge/discharge cycles using ex-situ and in-situ XRD techniques within the voltage range of 2.0 - 4.2 V. The monoclinic NaNiO₂ is known to form an O prime;3-phase, where Na occupies octahedral interlayer. During the first charge, electrode undergoes a series of phase changes corresponding to a series of NaNiO₂ phases. During subsequent charge, however, the electrode could go back to only Na_0.91NiO₂ phase, and an approximate average of 0.5 Na could be reversibly cycled. Interesting aspects regarding the phase change and electrochemistry in terms of its stability will be discussed in details.

Na-ion batteries have attracted great attention recently as the high energy electrochemical storage devices for the grid scale applications because they potentially have lower cost and less safety and environmental concerns than lithium-ion batteries. However, Na ions have the large radius (~70% larger than Li ions), which makes it difficult to find suitable cathode materials to accommodate the Na ions and allow reversible and rapid ion insertion and extraction. Recently, Na0.44MnO2 and Na3V2(PO4)3 have been demonstrated to be good cathode materials. However, the application of these materials is still very limited because the overall performance of full-cell batteries and the synthesis/process cost have not satisfied the industry&’s requirement. In this work, we synthesized Na0.44MnO2 and Na3V2(PO4)3 using a low-cost and scalable ball milling method and demonstrated stable full cells with high capacity. A capacity of ~107 mAh/g was obtained at ~0.5C current density and the capacity retention was ~95% after 100 cycles. In another effort, the rate performance of Na3V2(PO4)3 was greatly improved by carbon coating. A capacity of ~100 mAh/g was obtained at ~0.4C.

Magnesium (Mg) battery is considered as a relatively safe (vs lithium), cost-effective, and high energy density energy storage technology due to its use of dendrite-free, abundant, and divalent magnesium metal as anode. However, the development of magnesium battery has been hindered by electrolytes; in fact there are only a limited number of electrolytes for reversible Mg electrochemical plating/stripping, and handling these electrolytes is a relatively hazardous process, which prohibits further applications. Furthermore, there is limited understanding on the structure-property relationship for Mg battery electrolytes, which is critical for developing reliable electrolytes. In this presentation, we will report a rechargeable Mg battery with a new Mg ion conducting electrolyte, which can facilitate the electrochemical reversibility of magnesium with 100% coulombic efficiency. The detailed results of spectroscopic characterization for this electrolyte will be presented to have better mechanistic understandings for Mg electrochemical behaviors on Mg metal anode. Cell testing results of coin cells, which consist of Mg metal anode, new electrolyte, and Chevrel phase cathode material (Mo6S8), present a stable cycling performance for 82% of theoretical capacity (122mAh/g). This result opens a potential opportunity of applying low cost Mg battery for the grid energy storage application.

Our research at PNNL has focused on the development of low-cost sodium-metal halide batteries as an energy storage device for renewable energy applications since the major barrier in commercializing sodium-metal halide battery is relatively high cost compared to NaS battery. We took two approaches including: (i) intermediate-temperature Na-NiCl2 (IT-ZEBRA) battery operating at 200°C or less and (ii) Zn-based battery. IT-ZEBRA battery can utilize compressive polymer seals enabling a low-cost high throughput manufacturing process and can also achieve prolonged cycle life due to the suppressed degradation at a lower operating temperature. Since one of the major costs for ZEBRA battery is the cost of nickel, the use of zinc, of which the price is less than 1/8 compared to nickel, can significantly decrease material cost. In this presentation, the results of our low-cost Na metal-halide batteries including long-term cyclability and power capability will be discussed in detail.

Thermal energy storage has a vital role to play in effective and efficient use of renewable energy resources and industrial waste heat. Keys to such a technology include materials developments and heat exchange during charge and discharge processes. This report concerns the materials development particularly Phase Change Materials (PCMs). PCMs are the most promising materials for thermal energy storage due to their high energy density and nearly isothermal charge / discharge processes. However, the use of PCMs particularly molten salts suffers from (i) low thermal conductivities (leading to a slow charging/discharging rate and hence low power density), and (b) chemical incompatibility with containers (causing corrosion and hence a short life span). We introduce a micro-structured composite material consisting of a molten salt based PCM, a ceramic supporting material and a carbon based thermal conductivity enhancement material (TCEM). We will show that (i) the properties of supporting material determine the dispersion of the TCEM in the PCM and hence the thermal conductivity enhancement, and (ii) a right combination of the PCM, the TCEM and the supporting material can give a microstructure that is able to encapsulate the molten salt and give a substantial enhancement in the thermal conductivity.

Our EFRC for Electrocatalysis, Transport Phenomena, and Materials for Innovative Energy Storage is focused on fundamental research toward understanding processes in a novel, rechargeable organic fuel based high-density energy storage system. This concept assumes the reversible, electrochemical, oxidative dehydrogenation of organic fuels in a PEM fuel cell to generate protons and electrons (‘virtual hydrogen storage&’). In combination with an air cathode, the fuel cell produces dehydrogenated compounds, water and power (Reaction 1). To recharge the proposed regenerative fuel cell, the reactions can be reversed and the hydrogen depleted organic liquid is rehydrogenated electrochemically. The use of energy dense liquid instead of H2 alleviates the hydrogen economy problems associated with hydrogen gas.
LHn + n/2 O2 --> L + n/2 H2O (1)
The key components of the system are: (i) organic liquid carriers (LHn) amenable to electro(de)hydrogenation, (ii) electrocatalysts, and (iii) compatible PEM. The fundamental challenge is reversible electrocatalysis for dehydrogenation of organic carriers. We will discuss a strategy and progress toward the development of single-site catalysts for selective and efficient electrodehydrogenation of LHn to L, and preliminary results for electrohydrogenation of L back to LHn. The advantage of a molecular electrocatalyst is that it allows for a tunable active site and fundamental investigation of reaction mechanisms. We have studied a diaminodialkene iridium complex, Ir(I)-trop2DACH, known to catalytically dehydrogenate primary alcohols in a chemical reaction using stoichiometric benzoquinone (BQ) which plays role of both oxidant and base.1 We have demonstrated the successful separation of electron and proton transfer events using a chemical oxidant and a base. We also have shown microscopic reversibility of this system using a reductant and the conjugate acid of the base. Moreover, BQ as the 2e-/2H+ acceptor was replaced with an electrode and a base, thereby transitioning this system to an electrochemical setting. We will report evidence for electrocatalysis and bulk electrolysis data for dehydrogenation of alcohols and hydrogenation of carbonyl compounds with high selectivity and Faradaic efficiency.
Acknowledgment: This work was supported as part of the Center for Electrocatalysis, Transport Phenomena, and Materials (CETM) for Innovative Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001055.
(1) Königsmann, M.; Donati, N.; Stein, D.; Schönberg, H.; Harmer, J.; Sreekanth, A.; Grützmacher, H. Angew. Chem. Int. Ed. Eng. 2007, 46, 3567.

Hydrogen has been widely recognized as one of the most efficient and clean energy carriers with water as the only by-product when used in energy converting devices, such as fuel cells and internal combustion engines. Hydrogen storage is one of the key technologies for the hydrogen economy. Storage of hydrogen at near ambient temperature for on-board automotive application is a major challenge in contemporary materials science. Significant hydrogen storage capacity can be achieved in materials such as metal hydrides and chemical hydrides using temperature control to operate for hydrogen uptake and release. However, most of these materials suffer from high temperature requirement for hydrogen desorption, side reactions, the difficulty of off-board regeneration and poor kinetics. In this presentation, we report preparation of novel materials with highly exposed cationic sites that give rise to a strong interaction with hydrogen to enable significant hydrogen storage via physisorption at near ambient temperature. Hydrogen storage in these materials is realized using pressure swing adsorption technology (PSA). The adsorption reversibility and material stability will be demonstrated through a series of experimental measurements.
KEY WORDS: hydrogen storage, physisorption, pressure swing adsorption technology (PSA)
[1] Cheng, H., et al., “An Enhanced Hydrogen Adsorption Enthalpy for Fluoride Intercalated Graphite Compounds”, Journal of the American Chemical Society, 2009. 131(49): p. 17732-17733
[2] Cheng, H., et al., “Hydrogen spillover in the context of hydrogen storage using solid-state materials”, Energy & Environmental Science, 2008. 1(3): p. 338-354

One of the major barriers to the adoption of solid oxide fuel cells (SOFCs) is the short lifetime of the cell stacks. SOFCs must have a lifetime of at least 40,000-80,000 hours in order to be economically viable, but current SOFC stacks fail before that limit. One of the main modes of failure is the degradation of the interconnects. Stainless steel interconnects are more cost effective than ceramic interconnects but the high temperatures and the oxidizing environment of the cathode lead to the formation of a chromium oxide scale that increases the stack resistance. Stainless steel interconnects can also cause chromium poisoning of the cathode in which chromium from the interconnect enters the vapor phase and blocks the active sites. One method to avoid these obstacles is to coat the interconnect in a ceramic such as La(x)Sr(1-x)MnO3 (LSM). The coating would act as a diffusion barrier both against chromium diffusing into the cathode and oxygen diffusing into the interconnect while maintaining a low series resistance. LSM has been deposited using both thermal spray and electrophoretic deposition and compared in a dual atmosphere setup using impedance spectroscopy to analyze the performance of the coatings. The oxide growth kinetics and chemical composition of the scale was examined in order to optimize the LSM coating.

Saudi Arabia is one of the major oil producing countries. Yet, its geographical position makes the country also in a privileged location concerning sun exposure. Therefore, the development of alternative and renewable solar and photovoltaic power supply devices is attracting increasing attention for a sustainable future. However, solar power is intermittent and site-specific. Leverage of continuous energy supply needs to be achieved with the integration of energy storage systems in the grid. One possibility is the use of solid oxide electrolysis cells (SOECs), solid oxide fuel cells (SOFCs) operating in reverse, which are high temperature energy storage devices that convert heat and electrical power into chemical energy by producing hydrogen from steam. Hydrogen is attractive as energy carrier and as a clean fuel for a number of applications. Conventional SOECs use oxygen-ion conducting electrolytes, which possess several problems for practical applications, including the need of separating produced H2 from unreacted H2O, cell performance degradation due to the oxidation of hydrogen electrode, low current efficiency during the electrolysis process, etc. This talk will discuss the use of proton-conducting oxide electrolytes as an alternative that may solve some of the current issues; since water is formed at the air electrode, proton-conducting SOECs can produce dry H2 and oxidation of Ni, commonly used for the hydrogen electrode, is prevented. Furthermore, the current efficiency of the cell is kept high by the water-rich environment, which facilitates proton formation depressing the formation of other charge carriers. The main problem of conventional proton-conducting electrolytes is their chemical stability in the presence of steam. The new and necessary direction for the research on proton-conducting SOECs will be discussed, which is the development of film electrolytes made of chemically stable proton-conducting oxides.