Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries

The rechargeable lithium metal battery has attracted wide attention as a next-generation energy storage technology. However, simultaneously achieving high cell-level energy density and long cycle life in realistic batteries is still a great challenge. Here we investigate the degradation mechanisms of Li || LiNi0.6Mn0.2Co0.2O2 pouch cells and present fundamental linkages among Li thickness, electrolyte depletion and the structure evolution of solid-electrolyte interphase layers. Different cell failure processes are discovered when tuning the anode to cathode capacity ratio in compatible electrolytes. An optimal anode to cathode capacity ratio of 1:1 emerges because it balances well the rates of Li consumption, electrolyte depletion and solid-electrolyte interphase construction, thus decelerating the increase of cell polarization and extending cycle life. Contrary to conventional wisdom, long cycle life is observed by using ultra-thin Li (20 mu m) in balanced cells. A prototype 350 Wh kg(-1) pouch cell (2.0 Ah) achieves over 600 long stable cycles with 76% capacity retention without a sudden cell death. The development of Li metal batteries requires understanding of cell-level electrochemical processes. Here the authors investigate the interplay between electrode thickness, electrolyte depletion and solid-electrolyte interphase in practical pouch cells and demonstrate the construction of high-energy long-cycle Li metal batteries.

Automated summary

The study investigates the degradation mechanisms of Li || LiNi0.6Mn0.2Co0.2O2 pouch cells and shows that an optimal anode to cathode capacity ratio of 1:1 can balance well the rates of Li consumption, electrolyte depletion, and solid-electrolyte interphase construction to extend the cycle life of the cell. Contrary to conventional wisdom, long cycle life is observed with ultra-thin Li in balanced cells. A prototype 350 Wh kg(-1) pouch cell achieves over 600 stable cycles with 76% capacity retention.