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 cell efficiency. 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 affect the cumulative discharge capacity of each cell. A maximum cumulative discharge capacity occurs at ∼10 % depth of discharge (500 mAhg−1) and the cumulative discharge capacity of 39,500 mAhg−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-O2 batteries.