Tailoring Asymmetric Discharge-Charge Rates and Capacity Limits to Extend Li-O2 Battery Cycle Life

Widespread issues with the fundamental operation and stability of Li-O-2 cells impact cycle life and efficiency. While the community continues to research ways of mitigating side reactions and improving stability to realize Li-O-2 battery prospects, we show that limiting the depth-of-discharge while unbalancing discharge/charge rate symmetry can extend Li-O-2 battery cycle life by ensuring efficient reversible Li2O2 formation, markedly improving cell efficiency. Systematic variation of the discharge/charge currents shows that clogging from discharging the Li-O-2 cell at high current (250A) can be somewhat negated by recharging with a lower applied current (50A), 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 1000mAhg(-1) to 50mAhg(-1) under symmetric discharge/charge currents of 50A strongly affect the cumulative discharge capacity of each cell. A maximum cumulative discharge capacity occurs at approximate to 10% depth of discharge (500mAhg(-1)) and the cumulative discharge capacity of 39,500mAhg(-1) is significantly greater than that of 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 the cycle life performance of Li-O-2 batteries.