The Effect of Electrolytes and Cathodes on the Electrochemical Performance of Lithium/sulfur Batteries

Hyo-Jun Ahn
School of Materials Science and Engineering,
Gyeongsang National University, Jinju, KOREA

The lithium/sulfur battery has a high theoretical specific energy of 2600Wh/kg, which has been a strong incentive for next generation battery. However, it is difficult to obtain high utilization and long cycle life because of insulating nature of sulfur and solubility of lithium polysulfides in organic electrolytes. These problems could be overcome by optimization of sulfur electrode structure and electrolytes. In this presentation, I will review the previous approaches and report my recent results such as rate capability and cycling property using sulfur-carbon nanocomposite cathode and modified electrolytes.

Overview of the Gas Handling Requirements for a Li/O2 Battery

Paul Albertus
Robert Bosch, LLC

For a Li/O2 battery system to achieve a high energy per mass and volume and thereby enable long-range electric vehicles, a technology is needed to handle the gases entering and exiting the cell. Such a technology should be light weight and compact and both supply contaminant-free O2 during discharge and prevent the loss of any volatile cell components during charge. While the highest energy per mass and volume may ultimately be obtained with a technology that allows the use of ambient air, another option is the use of an oxygen tank, which would create a completely closed system. In this talk I will give an overview of the requirements for gas handling in a Li/O2 battery system, including acceptable mass and volume as well as energy use. Calculations for an oxygen tank will be presented.

Carbon Cycle 2.0

A. Paul Alivisatos
Department of Chemistry
University of California, Berkeley

Scientists across LBNL have come together to participate in a broad new program of research to help provide the basis for a sustainable energy future called, Carbon Cycle 2.0. This includes efforts in climate modeling, energy analysis, building efficiency, combustion, batteries and energy storage, biofuels, carbon capture and sequestration, solar PV and artificial photosynthesis.

The program seeks to provide a common energy analysis component for all of these efforts, as well as links to scenario based climate models to help understand what the prospective impacts of each program could be.

Beyond Lithium-ion Batteries

K. Amine, A. Abouimrane , J. Liu, Z. Zhang, P. Du, K.C. Lau, H-H Wang, L. Curtiss
Argonne National laboratory

Lithium-sulfur and lithium-air batteries are attractive because they have the potential of providing 2 to 5 times the energy density of the lithium-ion batteries currently on the market. However, lithium-air batteries suffer from large polarization between charge and discharge and poor cycleability due to electrolyte decomposition and the high potential needed to remove lithium from Li2O. In the case of lithium-sulfur batteries, although progress has recently been made by fabrication of a carbon-sulfur composite [1,2], substantial improvements are still needed. The main challenge is the poor cycle life resulting from the dissolution of polysulfide in the organic electrolyte and its migration to the anode. Moreover, to overcome the insulator characteristic of sulfur (5 × 10−30 S/cm at 25 °C) and Li2S (final product of Li-S cell), special carbon (e.g., carbon mesopores [1]) or high amounts of carbon [2] are needed for high current density applications. Another drawback of lithium-sulfur batteries is that the voltage output is close to 1.8 V, and the cell cannot be cycled over 3.6 V.

In this paper, we report on a new battery system based on selenium and selenium-sulfur composite. Selenium has a melting point of 217 ºC and an electronic conductivity of 10-5 S cm-1, which is 20 orders of magnitude higher than that of sulfur because the gap between the valence band and the conduction band is reduced with decreasing atomic number. In earlier preliminary work, we investigated the electrochemical properties of selenium as a host for lithium ions. We found that this new class of electrodes can compete with the lithium-sulfur system in terms of energy density, even though the theoretical capacity of the Li /Se system based on the formation of Li2Se is only 675 mAh g-1, much lower than that of the Li/S system (1675 mA g-1). However, the high density of selenium (4.82 g/cm3) versus sulfur (2.07 g/cm3) makes the volumetric capacity of these materials very close (~3253 Ah/l for selenium and ~3467 Ah/l for sulfur). Furthermore, we found that the Li/Se system delivers an output voltage at least 0.5 V higher than that of Li/S and could surpass the Li/S system in terms of volumetric energy density. Furthermore, S-Se mixtures are miscible in all proportions and many selenium-sulfur composites including Se5S, Se5S2, Se5S4, SeS, Se3S5, SeS2 are already reported. Those known Se-S materials can offer higher theoretical capacities than the selenium alone ranging from 675-1550 mAh.g-1 with improved conductivity compared to pure sulfur. The potential Se-S systems will allow for tunable electrodes, combining the high capacities of S-rich systems with the high conductivity associated with the d-electron containing Se. Unlike Li/Sulfur system, both Se and SexSy can be cycled to 4.6V without failure. We will also report on new improvement in cycle life of lithium air using two ether-based electrolytes; tetraglyme (tetra (ethylene glycol) dimethyl ether. TEGDME) and a siloxane (tri(ethylene glycol) methyltrimethyl silane, 1NM3).

References

1. J. Xiulei, T.L. Kyu, & L. F. Nazar, Nature Mater., 8, 500-506 (2009).
2. B. Zhang, X. Qin, G.R. Li & X.P. Gao, Energy Environ. Sci., 3, 1531–1537 (2010).

Protective Layers for the Lithium Electrode based on Ceramic Phases

Jordi Cabana
Environmental Energy Technologies Division
Lawrence Berkeley National Laboratory

Battery systems based on lithium metal as the negative electrode could lead to gains in specific energy over Li-ion technologies. This is particularly the case in lithium sulfur (Li/S) and lithium/air (Li/air) batteries, which are increasingly gaining the attention of the scientific community. However, there are major technical obstacles which have thwarted this advancement for two decades. These include shape change and dendrite formation, which lead to short cycle lifes and, potentially, to short-circuits that severely compromise the safety of the device. This is in addition to side reactions with liquid electrolytes, which consume charge and generally lead to poorer performance with time.

A solution that has been long explored is that of using solid state electrolytes.1 More recently, battery systems with dual liquid-solid electrolytes have been proposed.2 In this case, a thin solid layer acts as a barrier layer between lithium and the liquid electrolyte. It must be ionically conductive and mechanically stable in order to prevent dendritic growth. A number of inorganic crystalline and amorphous phases are known to have suitable electrical properties.3 However, they pose the challenge of processing into a thin pinhole-free membrane. Further, most of them contain a transition metal, making them highly susceptible to reduction. During this presentation, strategies toward membranes based on ceramic conductors that can be used as protective layers for the lithium electrode will be discussed. Emphasis will be placed on sintering and composite architectures, as well as on the interfacial redox stability against metallic Li of the resulting structures. Electrochemical testing in Li symmetric cells will be used to evaluate the desired figures of merit.

Acknowledgements
This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

References:
J.W. Fergus, J. Power Sources 195 (2010) 4554.
M-Y Chu, S. Visco, L.C. De Jonghe, U.S. Patent No. 6402795, 2004.
P. Knauth, Solid State Ionics 180 (2010) 911.

Beyond Lithium Ion: The Lithium/Sulfur Cell

Elton Cairns
Environmental Energy Technologies Division
Lawrence Berkeley National Lab

Current lithium ion cells are reaching their maximum energy storage capability (~200 Wh/kg) and are still not able to provide a safe, low-cost battery of sufficient energy storage capability for electric vehicles of more than 100-mile range. A new generation of battery with a specific energy of at least 400 Wh/kg, low cost (<$200/kWh), good safety, and low environmental impact is urgently needed. The next generation of rechargeable cells must have a theoretical specific energy well above 1000 Wh/kg (as compared to ~550 Wh/kg for Li-ion cells). The Li/S cell is probably the most attractive candidate for the next cell beyond the Lithium Ion cell. It has a theoretical specific energy of 2600 Wh/kg, and an estimated practical specific energy of about 600 Wh/kg.

The commercial development of the Li/S cell has been prevented by the short cycle life of the sulfur electrode caused by the rapid capacity loss. This capacity loss is attributed to: 1) the solubility of lithium polysulfides in the (organic solvent) electrolyte, 2) possible loss of contact between the (non-conductive) sulfur and the current collector, 3) the large volume change of the sulfur as it is charged and discharged (76%). Various approaches have been taken to solve these problems, with some success. A selection of attempts to improve the performance and cycle life of the Li/S cell will be reviewed and discussed, along with recent results from our laboratory.

Requirements for Li-protection in Li/air Cells

Jake Christensen
Robert Bosch, LLC

Li-metal based cells, including Li/air, are attractive due to their high gravimetric energy density, but safely recharging Li metal over hundreds of cycles remains a significant challenge. This is due in part to the fact that Li metal electrodes are chemically and morphologically unstable in most, if not all, liquid electrolytes and must be protected with a solid electrolyte, for which there are few working prototypes. Here we examine the principle requirements of such a protection layer from a systems perspective. In addition to possessing high ionic conductivity, mechanical strength, and chemical stability against both lithium and the positive electrode constituents, these materials must be thin (< 50 µm,) cheap (< $100/m2), and defect free. We conclude that further fundamental materials and processing research and development are needed to attain these objectives.

Nanoscale Design for High Energy Batteries

Yi Cui
Department of Materials Science and Engineering
Stanford University

Si and S have an ultrahigh capacity of lithium storage and suitable voltage as anodes and cathodes, respectively, for future high energy batteries. The combination of Si-S can generate four times specific energy of the existing C-LiCoO2 system. However, Si and S has many materials challenges to be overcome. The development of nanotechnology in the past two decades has generated great capability of controlling materials at the nanometer scale and has enabled exciting opportunities to design materials to overcome these challenges. In this talk, I will show how to develop fundamental principles through single nanostructure measurement and how to design rationally nanostructured materials to address all those materials challenges. I will show the excitingly high performance on both Si and S electrodes.

Gas cleaning – Perspectives from Catalytic Processes

Søren Dahl
Haldor Topsøe A/S

Gas cleaning where specific substances are removed down to a very low level is required in many catalytic processes either to avoid deactivation of catalysts or for environmental reasons. One example is ammonia synthesis where all oxygen-containing molecules have to be removed from the synthesis gas since the ammonia synthesis catalyst otherwise will be severely poisoned. Another example is production of chemicals like e.g. methanol from synthesis gas obtained from gasification of coal or biomass; here thorough cleaning of the gas from a lot of substances like heavy metals, S, Cl, and NH3 is required.

The technologies usually used for gas cleaning are scrubbing with liquids or absorption by solids. The presentation will review the possibility to use similar technologies for full or partly removal of water and CO2 from air to be used in Li-air batteries. By simple assumptions it is evaluated how different methods and process designs will influence the energy densities of the Li-air battery on the system level.

Transport and Mechanical Properties of Pure and Composite Solid Lithium Electrolytes

Nancy J. Dudney(1), Wyatt E. Tenhaeff(1), Sergiy Kalnaus(1), Adrian S. Sabau(1), Erik G. Herbert(2), Kunlun Hong(3)
(1)Material Science and Technology Division, Oak Ridge National Laboratory
(2)Department of Material Science, University of Tennessee
(3)Center for Nanophase Materials, Oak Ridge National Laboratory

Solid electrolyte materials are investigated for lithium and Li-ion batteries with both planar and 3D architectures. For lithium metal batteries, it may be desirable to use multiple electrolytes fabricated as a thin-film laminate or dispersed composite electrolyte in order to provide adequate ion transport, electrochemical compatibility, and robust mechanical properties to stabilize the lithium interface and prevent dendrites. Results of studies of both bulk and interfacial properties for composite electrolytes will be reported for ceramic and polymeric electrolytes. Simulation methods have been developed to provide a means to extrapolate to optimized architectures and compositions.

Acknowledgement: Research has been supported by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, and by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy.

Li-Air and Li-Sulfur Technology in an Automotive System Context

Thomas A. Greszler
Manager, Electrochemical Cell Design
Electrochemical Energy Research Laboratory
General Motors Research and Development

Li-ion batteries are now penetrating the automotive market, and this will increase at a rate largely dependent on liquid fuel prices and the cost of automotive Li-ion battery systems. As a first step in determining what is “beyond Li-ion”, we will project cell weight, volume, and cost reductions achievable through successful implementation of advanced Li-ion materials. We will then consider the potential for Li-air and Li-S chemistries to enable automotive systems that surpass advanced Li-ion-based systems.

A New Class of Aqueous Insertion Reaction Electrodes With Rapid Kinetics And Long Cycle Life

Robert A. Huggins
Department of Materials Science and Engineering
Stanford University

One of the major problems related to the integration of renewable energy sources with the large scale electric distribution grid has to do with the high frequency of short-term transients. The amelioration of this problem requires energy storage systems that can operate at very high rates, and with a high efficiency over a very large number of cycles.

The structural features that lead to the exceptional performance of a new group of insertion reaction electrode materials in aqueous electrolyte electrochemical systems for this purpose will be described.

Experiments have already demonstrated the outstanding properties of some members of this family. In one case, over 40,000 full cycles have already been achieved at a very high (17C) rate, with a coulomb efficiency of 99.8%. In another, over 5,000 full cycles at an 8.3 C rate have shown no measurable decrease in capacity.

Air Electrodes for Lithium-Air batteries with Weak Alkaline Aqueous Electrolyte

Nobuyuki Imanishi
Mie University, Japan

Lithium-air secondary batteries with a lithium metal anode and an air cathode are an attractive energy storage system because they have high theoretical energy density. Two types of lithium-air batteries have been developed, namely, non-aqueous and aqueous types. We have studied aqueous type of lithium-air batteries, which consist of a lithium electrode, an aqueous electrolyte with LiCl, and an air electrode. A protected lithium electrode, Li/PEO18LiTFSI/Li1+xTi2-xAlx(PO4)3 was stable in a saturated LiOH with 10 M LiCl aqueous electrolyte, which showed a pH value of ca. 9.

In this study, applicability of air electrodes in this moderately alkaline aqueous solution were examined. Carbon electrodes with perovskite-type oxide catalysts were used as air electrodes. The catalytic activity for oxygen reduction and evolution, and chemical, electrochemical stabilities were evaluated for these perovskites. Various carbon materials are studied for the long term polarization in the LiOH-LiCl electrolyte. The effect of ion exchange membranes is also investigated which are applied to avoid direct deposition of solid LiOH on the air electrode.

Expand EV’s Value – Mobility and Beyond

Haruyoshi Kumura
Nissan Motor Company

Nissan LEAF, launched in 2010 to the market, has some EV unique features, such as acceleration performance, handling and stability, quietness and IT support system. I’d like to share the voices of our valued customers of Nissan LEAF and the signs of new era. On the way to the practical use, many questions and issues have been solved. The key question was the safety of the large capacity battery onboard.

Not only will I touch on our stories behind the research and development of Nissan LEAF, but I will also touch on the story of Nissan LEAF’s activity at the recovery of Tohoku earthquake and discuss about the future EV society with renewable energy promotion by its battery. The broader perspective expands EV value.

A Nonaqueous Li-Air Battery with Protected Anode: Perspectives on Improving the Cycle Life

Dong Joon Lee
Energy Lab, Samsung Advanced Institute of Technology

While Li-air battery has recently become one of the most actively studied power sources for future electric vehicles, its short cycle life still remain a hurdle in the development of practical batteries. Li dendrite formation and electrolyte decomposition are frequently discussed as main causes of cell failure. We constructed a nonaqueous Li-air cell with protected Li anode employing two different nonaqueous electrolytes on cathode and anode sides respectively. With carefully designed cycling conditions, the discharge and charge of the cell could be repeated more than 100 times without significant degradation of performance. A post-mortem analysis of the eventually failed cell was performed and the tasks for further improvement of the cycle life will be discussed in the presentation.

New Nanostructured Electrodes for Li-ion and Li-S Batteries with Long Cycle Life

Jun Liu
Pacific Northwest National Laboratory

Li metal is studied as the anode materials for Li-ion and Li-S batteries, but protection of the reactive Li surface is a significant challenge. In this presentation, we will discuss new strategies to avoid undesirable reactions on the electrode surfaces. Our new electrode design can significantly reduce the formation of the surface reaction products, and thus greatly improve the cycling stability. Excellent high rate capability and long cycle stability are obtained as compared with traditional electrodes. Specific examples will be provided for Li-S batteries, and the fundamental reaction mechanisms will be discussed.

High Energy, High Power Rechargeable Lithium-Sulfur Batteries for Scalable Electrochemical Energy Storage Systems

Arumugam Manthiram
Materials Science and Engineering Program
The University of Texas at Austin

Energy, power, cycle life, safety, and cost are important criteria in employing rechargeable battery technologies for transportation and stationary storage of electricity produced by renewable sources like solar and wind. The energy density of current lithium-ion batteries is limited by the cathode capacity of < 200 mAh/g at ~ 4 V. Interestingly, sulfur cathodes offer an order of magnitude higher capacity (theoretical capacity: 1,675 mAh/g) at an operating voltage of ~ 2.1 V. While the high capacity can significantly enhance the energy density of the batteries, the lower operating voltage can also offer better safety. However, the commercialization of rechargeable lithium-sulfur batteries is impeded by two major challenges: (i) poor cycle life due to the dissolution of the polysulfide intermediates (Li2S8, Li2S6, and Li2S4) formed during the charge-discharge process and (ii) low electrochemical utilization of sulfur cathodes due to the high insulating nature of sulfur and the discharge product Li2S. To overcome these difficulties, this presentation will focus first on a series of composite cathodes with unique nanostructures that improve the electrical conductivity and utilization of active materials. For example, sulfur-carbon nanocomposites synthesized by a scalable in situ sulfur deposition route exhibit much better electrochemical performance than pristine sulfur. Similarly, sulfur-polypyrrole composites in which the sulfur particles are coated by a nanolayer of polypyrrole show improved capacity and cyclability. The presentation will then focus on the fabrication of a scalable, binder/current collector-free, nanostructured sulfur-carbon nanotube (S-CNT) composite cathode without employing toxic solvents during electrode processing, which exhibits excellent capacity retention at high rates, e.g., >1,000 mAh/g capacity after 50 cycles at 1C rate. Finally, a novel lithium-sulfur battery structure with an interlayer between the separator and the cathode to capture the polysulfide ions exhibits significantly improved energy and power. These materials and strategies are scalable and can enable packaged cells with an anticipated energy density of > 600 Wh/kg and power density of > 1000 W/kg, which are three times higher than those of current lithium-ion batteries.

Understanding the Complexity (simplicity) of Li-O2 Interfaces

Nenad Markovic, Ram Subbaraman, Jakub Jirkovsky, Gustav Wiberg
Materials Science Division, Argonne National Laboratory

The Li-O2 battery is generating a great deal of interest because theoretically it possesses a specific energy 5-10 times that of a conventional Li-ion battery. Very little is known about the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in lithium-air battery cathodes based on aprotic organic electrolytes. A systematic study using both traditional RDE measurements as well as cell level measurements in conjunction with various characterization techniques will be presented. We begin by drawing analogies between the oxygen electrode reactions in the aqueous electrolyte, in particular alkaline electrolyte, and the aprotic (Li+ free) non-aqueous electrolytes. Employing extended surfaces of Au we will demonstrate that the ORR in these electrolytes is governed by the same principles that dictate the reaction mechanisms in protic solvents. We will also employ R(R)DE techniques to both quantitatively and qualitatively determine the reaction products namely the superoxide and peroxide. This will be used to determine the stability of the various ethers and carbonate solvents toward the superoxide species. Extending this study to Li+ based solvents will be used to further determine the products formed, their stability, their strength of adsorption to the electrode surface, and the measure of reversibilities achieved using RDE measurements. Furthermore, using an electrochemical voltammetric finger printing technique, we will aim to understand the nature of products formed in the presence of Li+ cations and the ease of their re-chargeability. Extending this approach to study carbonaceous materials will help us better delineate the role of morphology, nature of carbon and the relative geometry effects on observed reversibility of Li-O¬2 cathode interfaces. A careful study on the role of surface active groups and their impact on both the reduction and oxidation reactions will be studied both in a traditional three-electrode setup as well as our in-house design battery cell design (KF cell). The presence of side reactions that can occur at the cathode interfaces, particularly related to electrolyte oxidation will be discussed briefly. This will help us to understand the reaction that determines the observed charging plateaus. The KF cell then allows us to both determine the potentials at which gasses are generated/consumed using a pressure-change measurement, which can then in conjunction with DEMS be used to identify the nature of products formed during the charging process. Also, using the “expected products” in the battery directly we determine the expected voltages at which they can be oxidized and correlate them with the real battery charging potentials. This helps us to draw a conclusion regarding the nature of products formed during discharge and the potential charging reactions.

Atmospheric Contamination in Non-aqueous Li-air Batteries: Implications from a Membrane Separation Perspective.

Bryan D. McCloskey
Research Staff Member
IBM Almaden Research Center

Among many challenges being addressed to develop practical Li air batteries, relatively little attention has been devoted to the effects of atmospheric contamination on the active cathode chemistry in Li air cells, as most researchers discharge cells under either pure oxygen or zero air. Reaction of Li2O2, the dominant discharge product in nonaqueous Li-O2 cells, with certain atmospheric gasses could lead to formation of products which require high overpotentials to oxidize, leading to losses in both energy efficiency and cyclability. Even in aqueous Li-O2 cells, CO2 contamination is a critical issue, as it reacts with the dominant discharge product, lithium hydroxide, to form sparingly soluble lithium carbonate, which dramatically reduces the capacity of the cell. Furthermore, the deleterious effects of O2, N2, H2O and CO2 on a cyclable lithium metal anode have been extensively explored. Clearly, if rechargeable Li-air batteries are to ever achieve a specific and volumetric energy density significantly higher than Li-ion batteries, novel, compact, energy efficient air purification technologies will need to be developed. One such possible system could be membrane-based.

This presentation will outline the effects of three atmospheric gasses- nitrogen, carbon dioxide, and water- on the Li-O2 electrochemistry. Afterwards, the viability of using a compact membrane system to separate N2, CO2, and H2O from O2, with the end goal of providing the highest purity O2 for a Li-O2 cell, will be discussed.

Renewable Fuels

John Newman
University of California, Berkeley

Renewable fuels are a long-term solution to the world’s energy needs. It is a significant challenge to find efficient ways to harness solar and wind energy that are cost-competitive with fossil fuels. Because renewable sources are intermittent, energy storage is essential to renewable fuel production. In this work, we discuss modular approaches to making solar fuels. We use back-of-the-envelope calculations to evaluate production schemes, including energy storage with batteries. A relationship that predicts the required sales price of energy storage is also discussed.

First-principles Study of the Oxygen Evolution Reaction and Polaronic Hole Transport in the Lithium-air Battery

Shuye Ping Ong
MIT

The lithium-air battery is a promising alternative to existing rechargeable batteries. However, there are substantial challenges, such as poor reversibility, cyclability, rate capability, and energy efficiency, which limit commercialization. Currently, the charge and discharge mechanisms and their relationship to the battery parameters are not clearly understood.

In this talk, we present our study of the mechanisms of the oxygen evolution reaction (OER) and electronic conduction in lithium peroxide (Li2O2) using first-principles calculations. Li2O2, the primary product during discharging, is an insulator and is suspected to increase the charging overpotential, thereby deteriorating the Li-air battery performance. We show that i) the OER process on low-index surfaces of Li2O2 is kinetically limited by the oxygen evolution, not by the extraction of Li+ ions and/or electrons, and that ii) the formation and migration of hole polaron VLi+ pairs is a possible electronic conduction mechanism in Li2O2.

Ionic Liquid-based Electrolytes for Next Generation Batteries

Stefano Passerini
Institute of Physical Chemistry and MEET
University of Muenster, Germany

The rise of global environmental concerns is pushing science and industry toward the development and realization of improved electrochemical storage systems for a more efficient and effective use of energy. This is especially true in the mobility field where the present use of energy is, in fact, based on the immediate but rather inefficient and polluting conversion of fossil fuels because of the lack of effective energy storage systems.

Present high-energy battery technologies, namely Li-ion batteries, do not allow the realization of electric vehicles capable of a 500 km driving range with one battery charge. In fact, even considering the most optimistic estimation on the development of Li-Ion batteries (250 Wh/kg), which would correspond to more than 33% of the theoretical specific energy calculated on the active material weight only, it is clear that the 500 km range cannot be achieved with Li-ion (the battery weight would be more than 400 kg).

Much higher specific capacities can be achieved using lithium metal/element chemistries (Li/S, Li/O2 etc.). However, the long-term cycling stability of lithium metal anodes has been, so far, preventing the development of lithium metal-based battery chemistries.

In this work the improvements obtained by using battery electrolytes containing ionic liquids (ILs) will be presented

Progress in Research on Lithium Oxygen Batteries

Rouven Scheffler & Angela Speidel
Volkswagen Research

Lithium oxygen batteries show a very high theoretical gravimetric energy density which makes them an attractive candidate for high energy batteries to enable long-distance electric driving and mass market penetration of electric vehicles. Before commercialization many challenges need to be solved. In our talk we discuss lithium (alkyl) carbonate formation as possible reason for the increasing overpotential during charge. Besides, we show that gas analytics during cycling is crucial for electrolyte research which is of fundamental importance to improve cycleability of lithium oxygen batteries.

First-Principles Study of Low Electron Conductivity in Li peroxide for Li-air Batteries

Su-Huai Wei, Joongoo Kang, Yufeng Zhao, Chunmei Ban, and Anne C. Dillon
National Renewable Energy Laboratory

Rechargeable lithium batteries represent one of the most important developments in electrical energy storage and application. However, the energy density of state-of-the-art Li-ion batteries is still too small for some practical applications. Recently, Li-air batteries (LABs) have received new attention as a promising energy storage system beyond Li-ion batteries because their specific energy densities could be 5-10 times greater than those of the Li-ion batteries. However, although LABs offer the promise of very high energy density, its utilizations are hindered by both poor rate capability and significant polarization in cell voltage, primarily due to the formation of Li2O2 in the air cathode and poor electron conductivity in Li2O2. Here, using hybrid density functional theory, we demonstrate that the self-trapping of electrons in small polarons could be the origin of the low electron mobility in Li2O2. The low electron mobility is an intrinsic property of Li2O2 that originates from the molecular nature of the conduction band states of Li2O2 and the strong spin polarization of the O 2p state. We will discuss in detail how the low electron mobility affects the performance of LABs. Furthermore, based on our understanding of the mechanism, we will propose approaches to improve the performance of LABs at high current densities, such as selecting optimal growth direction of Li2O2 via substrate control, designing alternative carrier conduction paths for the cathode reaction, and/or introducing electron-deficient nano boron-carbon sheets to enhance the conductivity.

Aqueous Electrolyte Polyionic Electrochemical Cells for Scaled Stationary Energy Storage

Jay Whitacre
Carnegie Mellon University

This presentation will cover the scaling implementation of large-scale energy storage electrochemical batteries. The core devices use an asymmetric/hybrid configuration wherein the anode consists of carbon and the cathode is an MnO2 – based alkali intercalation compound (either Na4Mn9O18 or cubic spinel -MnO). Data will be presented showing that large scale industrially packaged individual batteries with over 30 Wh in capacity have be produced and qualified. Further data will show that packs of these batteries in the kWh range have been effectively implemented in field-testing. This will include support for both smaller off-grid applications with bus voltages in the in the 20 to 100 V range, as well as, grid compatible systems with bus voltages in excess of 1000 V.

Key topics to be addressed include: (1) a description of our path to scaled production of these devices, (2) lifetime performance of this system in temperatures ranging from minus 10˚C through 60˚C, (3) data from third party field tests in relevant applications showing the performance of our batteries under application specific load profiles, and (3) our vision for future implementation of this technology on a massive scale.

Beyond Lithium Ion: A Reality Check

Stanley Whittingham
SUNY, Binghamton

Although current Lithium-ion batteries dominate the portable electrochemical storage market, there is limited room for improvement. They have a theoretical energy density approaching 1 kWh/kg, but in practice deliver no more than 200 Wh/kg. Similarly within a year they will be delivering close to 1 kWh/liter, over 30% of theoretical.

Metal (lithium) oxygen and Lithium sulfur have the capability to exceed these values on a weight basis, and indeed Li/S already does. However, their volumetric capacities are likely to be significantly lower than Li-ion even if all the technical challenges are overcome. I will discuss the opportunities and challenges.
This work is being supported by NYSERDA.

Lithium Metal for Rechargeable Polymer and Metal-Air Batteries: Challenges and Opportunities

Karim Zaghib
Institut de Recherche d’Hydro-Québec

Hydro-Québec (HQ) inititated research on lithium metal/solid polymer electrolyte (SPE) rechargeable batteries in 1980. Since then, research on lithium-based batteries has expanded worldwide. Several new polymer and solid electrolytes with improved conductivity were developed from the improved understanding of the major parameters controlling ion migration, such as favorable polymer structure, phase diagram between solvating polymer and lithium salt and the identification of new lithium counter-anions. Despite the significant progress so far, the quest for a highly conductive dry polymer at room temperature still continues. Currently, the developers of the all-lithium polymer battery (LPB) use the option of heating the polymer electrolyte to enable high-power performance, as required for the electric vehicle and energy storage. The many LPB developers are considering the two approaches as worthy alternatives to be explored. HQ has expanded their efforts to investigate Li-air batteries based on the experience gained from R&D of Li polymer batteries.

This presentation provides an overview and summary of the progress in developing lithium-metal-based batteries made from dry polymer, ionic liquid-polymer and polymer–ceramic electrolytes for rechargeable Li polymer batteries and Li-air batteries. Some in-situ techniques will be described that allow us to control surface passivation (SEI) of lithium, which is the key challenge to obtain acceptable cycle life with these batteries.