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

Abstract 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.