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 || LiNi_0.6Mn_0.2Co_0.2O₂ 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.

可充电锂金属电池作为下一代储能技术引起了广泛关注。然而，在现实电池中同时实现高电池级能量密度和长循环寿命仍然是一个巨大的挑战。在这里，我们研究了锂的降解机制 || LiNi _0.6 Mn _0.2 Co _0.2 O ₂软包电池，并提出了锂厚度、电解质耗尽和固体-电解质界面层结构演变之间的基本联系。当调整兼容电解质中的阳极与阴极容量比时，会发现不同的电池失效过程。出现了 1:1 的最佳阳极与阴极容量比，因为它很好地平衡了锂消耗、电解质耗尽和固体电解质界面结构的速率，从而减缓了电池极化的增加并延长了循环寿命。与传统观点相反，通过在平衡电池中使用超薄锂 (20 µm) 可以观察到较长的循环寿命。原型 350 Wh kg ^-1软包电池 (2.0 Ah) 可实现超过 600 次长时间的稳定循环，容量保持率为 76%，而不会发生电池突然死亡。