Tailoring asymmetric discharge-charge rates and capacity limits to extend Li-O2 battery cycle life

Abstract

Widespread issues with the fundamental operation and stability of Li-O2 cells impact cycle life and efficiency. While the community continues to research ways of mitigating side reactions and improving stability to realize Li-O2 battery prospects, we show that limiting the depth-of-discharge while unbalancing discharge/charge rate symmetry can extend Li-O2 battery cycle life by ensuring efficient reversible Li2O2 formation, markedly improving cycle life. Systematic variation of the discharge/charge currents shows that clogging from discharging the Li-O2 cell at high current (250 μA) can be somewhat negated by recharging with a lower applied current (50 μA), with a marked improvement in cycle life achievable. Our measurements determined that specific reduction of the depth of discharge in decrements from equivalent capacities of 1000 mAhg-1 to 50 mAhg-1 under symmetric discharge/charge currents of 50 μA strongly affected the cumulative discharge capacity of each cell. A maximum cumulative discharge capacity was found to occur at ~10 % depth of discharge (500 mAhg-1) and the cumulative discharge capacity of 39,500 mAhg-1 was significantly greater than cells operated at higher and lower depths of discharge. The results emphasize the importance of appropriate discharge/charge rate and depth of discharge selection for other cathode/electrolyte combinations for directly improving cycle life performances of Li-O2 batteries.