Lithium metal solid state batteries (LMSSB) attract great interest in academia and industry due to their projected high energy density and safety. However, hard short circuits due to the penetration of lithium filaments through the solid electrolyte impede their development for practical application. Here, multi-characterization methods ranging from operando and in situ scanning electron microscopy to ex situ focused ion beam scanning electron microscopy are employed for comprehensive understanding of the cell failure. The rapid failure is attributed to coupled crack propagation and subsequent lithium filament growth during the plating process which is demonstrated in a Li₆PS₅Cl (lithium argyrodite) based LMSSB. Cracking initiates at current constriction spots and voids, where inhomogeneous lithium plating/stripping causes high local stress fields that trigger continuous crack propagation. Lithium filament growth finally leads to a hard short circuit. Considering the low fracture toughness of ceramic electrolytes, strengthening with Al₂O₃ fibers is shown to be effective in significantly improving the critical current density and cycling stability. Our results clearly show that cracks can have a detrimental effect on LMSSB and we suggest focusing on strategies to improve the fracture toughness of thiophosphate electrolytes in order to suppress lithium filament growth.

锂金属固态电池（LMSSB）因其高能量密度和安全性而引起了学术界和工业界的极大兴趣。然而，由于锂丝穿透固体电解质而导致的硬短路阻碍了其实际应用的发展。在这里，采用从操作和原位扫描电子显微镜到异位聚焦离子束扫描电子显微镜的多表征方法来全面了解电池故障。这种快速失效归因于电镀过程中耦合裂纹扩展和随后的锂丝生长，这在基于 Li ₆ PS ₅ Cl（锂银矿）的 LMSSB 中得到了证明。裂纹始于电流收缩点和空隙，其中不均匀的锂电镀/剥离会导致局部高应力场，从而引发连续裂纹扩展。锂丝生长最终导致硬短路。_{考虑到陶瓷电解质的断裂韧性较低，Al 2} O ₃纤维强化可有效显着提高临界电流密度和循环稳定性。我们的结果清楚地表明，裂纹会对 LMSSB 产生不利影响，我们建议重点关注提高硫代磷酸盐电解质断裂韧性的策略，以抑制锂丝生长。