Stress–Strain Engineering with Lithium Solid Solution/Lithium Alloy Composite Anodes for Stable Lithium‐Metal Batteries

Abstract High‐performance thin lithium (Li) metal anodes are indispensable for high‐energy‐density Li metal batteries, yet their electrochemical‐mechanical instability precipitates rapid failure. Uncontrolled lithium plating, accompanied by severe side reactions and the formation of a porous, non‐compact deposit, swells the electrode and generates destructive stress. An in situ investigation of stress, strain, and their spatial distributions during charge/discharge cycling identifies the coupled volume variation and stress–strain evolution as an operando descriptor of degradation and underpins the rational design of a dual‐phase Li−Ag solid‐solution/Li 22 Sn 5 alloy composite anode. Ag in Li−Ag solid solution enhances the affinity with Li + for uniform Li plating, whereas a rigid, ion‐permeable Li 22 Sn 5 scaffold confines volume expansion. LiNi 0.6 Co 0.2 MnO 0.2 (NCM622)||Li−Ag/Li 22 Sn 5 pouch cell exhibits a markedly lower internal‐pressure rise during cycling than NCM622||Li counterpart under identical conditions. Specifically, the latter shows a 58% higher pressure increase than the NCM622||Li−Ag/Li 22 Sn 5 pouch cell after charging from 0% to 100% SOC in the 5th cycle. The 1.3 Ah laminated NCM622||Li−Ag/Li 22 Sn 5 (40 µm‐thick anode) pouch cell retains 87% capacity over 100 cycles when operating at an industry‐relevant N/P ratio of 1.5 and electrolyte budget of 2.6 g Ah −1 . Mechanical‐electrochemical coupling of Li metal anode design, therefore, offers a practical route to long‐lifespan Li metal batteries.