Archives for April 2012

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.

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.

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.

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.