Zinc air battery development for electric vehicles

This report summarizes the results of research conducted during the sixteen month continuation of a program to develop rechargeable zinc-air batteries for electric vehicles. The zinc-air technology under development incorporates a metal foam substrate for the zinc electrode, with flow of electrolyte through the foam during battery operation. In this 'soluble' zinc electrode the zincate discharge product dissolves completely in the electrolyte stream. Cycle testing at Lawrence Berkeley Laboratory, where the electrode was invented, and at MATSI showed that this approach avoids the zinc electrode shape change phenomenon. Further, electrolyte flow has been shown to be necessary to achieve significant cycle life (greater than 25 cycles) in this open system. Without it, water loss through the oxygen electrode results in high resistance failure of the cell. The Phase 1 program, which focused entirely on the zinc electrode, elucidated the conditions necessary to increase electrode capacity from 75 to as much as 300 mAh/sq cm. By the end of the Phase 1 program over 500 cycles had accrued on one of the zinc-zinc half cells undergoing continuous cycle testing. The Phase 2 program continued the half cell cycle testing and separator development, further refined the foam preplate process, and launched into performance and cycle life testing of zinc-air cells.