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-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.