An Atmosphere‐Responsive Protective Strategy Based on Deciphering the Anode Degradation Mechanism in Li–CO ₂ Batteries

Abstract Lithium–carbon dioxide (Li–CO 2 ) batteries, with high energy density and CO 2 utilization, are considered a promising candidate for Mars exploration. However, they continue to face challenges such as limited cycle life and significant polarization caused by anode degradation, which is often overlooked and whose underlying mechanism remains unclear. This work revealed the anode failure mechanism, identifying a water‐triggered degradation process, which depletes active lithium content, and developed an atmosphere‐induced protective strategy. The degradation is triggered by trace water and sustained by the CO 2 component, which results in transforming active lithium into Li 2 CO 3 . Thus, a strategy was provided to respond to the water molecules brought by the semi‐hermetic system and high charging voltage. The protective layer was in situ polymerized and can interact with water molecules, leading to further polymerization, thereby inhibiting side reactions, significantly extending the battery's lifespan. The Li–CO 2 batteries can achieve stable cycling exceeding 1000 h, more than twice the time compared to the unprotected case. This study revealed the fundamental mechanism of anode degradation in Li–CO 2 batteries, providing a theoretical basis for the development of subsequent anode protection strategies. Additionally, it offers a viable method for anode protection in Li–CO 2 batteries.