Dynamic Concentration of Alloying Element on Anode Surface Enabling Cycle‐Stable Li Metal Batteries

Abstract The pursuit of high energy density Li‐based rechargeable batteries has intrigued numerous research interest on Li metal anode. However, several significant challenges, including severe parasitic reactions and growth of Li dendrites, lead to fast electrode failure and impede its practical implantation. Herein, it is revealed that the dynamic concentration of alloying element in Li solid solution can significantly improve the cycling stability. It is demonstrated that the alloying element of Li solid solution continuously evolved in the reaction layer on cycling. Alloying element got enriched on anode surface after Li stripping, and re‐dispersed into the deposited Li during Li plating processes. The alloying element‐rich surface can reduce the Li nucleation barrier and promote the uniform Li plating behavior. Ultrathin Li solid solution foils are fabricated, and the dynamic alloying element concentration mechanism is further verified, and the cycling lifespan of pure Li is doubled. Consequently, a 1.4 Ah laminated pouch cell with ultrathin Li solid solution anode (30 µm) exhibits high energy density of 836 Wh L −1 and stable cycling performance under the harsh conditions with low negative/positive capacity (N/P) ratio of 2 and electrolyte/capacity (E/C) ratio of 2.6 g Ah −1 .