Nanocatalysis for Primary and Secondary High Energy Lithium Oxygen Cells

Abstract : The objective of the technical program was to develop practical Lithium-Air battery technology towards achieving high specific energy and power densities. It involved a unique cathode material based on elastic hollow carbon spheres (200 and ~500 nm) with a Co3O4 nanocluster catalyst encapsulated in it, designated as Co@C. We evaluated the Co@C/O2 cathodes based on the silica templates of 500nm and 200 nm in an electrolyte consisting of a carbonate-based mixed solvent and a blend of lithium salts. Cold pressed carbon composites with the PTFE binder were found to provide the highest capacities involved in O2 reduction. The dual shell architecture of these materials was well preserved in these electrodes despite the high pressure used in electrode fabrication. The Co@C cathodes exhibited capacities of 2500 to 3000 mAh/g range in Li/O2 cells at a low current density, 0.1mA/cm2, whereas cathodes based on a commercial carbon blend provided capacities in the 800 mAh/g range. Higher discharge currents resulted in a sharp decrease in the capacity, but without losing the capacity advantage of the Co@C material. Despite the very high capacities observed for Co@C materials, there was no evidence to support that lithium oxide was preferentially deposited inside the nanoshells. Uniform coverage of lithium oxide over the entire exposed carbon surfaces was observed instead. Despite the very high discharge capacities observed with the Co@C/O2 cathode, it was poorly rechargeable. Only one charging cycle with nearly equal specific capacities was possible.