An Atmosphere-Responsive Protective Strategy Based on Deciphering the Anode Degradation Mechanism in Li-CO2 Batteries.

Lithium-carbon dioxide (Li-CO2) batteries, with high energy density and CO2 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 CO2 component, which results in transforming active lithium into Li2CO3. 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-CO2 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-CO2 batteries, providing a theoretical basis for the development of subsequent anode protection strategies. Additionally, it offers a viable method for anode protection in Li-CO2 batteries.