Decoding Chemo‐Mechanical Failure Mechanisms of Solid‐State Lithium Metal Battery Under Low Stack Pressure via Optical Fiber Sensors

All solid-state lithium (Li) metal batteries (ASSLBs) using ceramic-polymer hybrid solid electrolytes hold the promise for high-performance energy storage application, but they still suffer from the interfacial deterioration and dendritic Li penetration issues, particularly under low stack pressures. Therefore, understanding and mastering the underlying chemo-mechanical failure mechanisms become essential. Herein, the chemo-mechanical evolutions by operando monitoring the amplitude and heterogeneity of interfacial stress through an embedded optical fiber sensor are revealed. It is found that the uneven stripping/deposition of Li metal induces rapid and non-uniform stress growth at the interface, deteriorating interfacial contact with the Li-filament growth. Based on these insights, Li metal is replaced with an architectural lithium-tin anode, which demonstrates uniform stress and improved performance even under low stack pressure. This work not only offers a quantitative way to operando track the uniformity of interfacial stress but also provides critical insights into mastering the chemo-mechanics of ASSLBs.