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 µm) 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.