A General Strategy toward Enhanced Electrochemical and Mechanical Performance of Solid‐State Lithium Batteries through Constructing Covalently Bonded Electrode Materials/Electrolyte Interfaces

Abstract Solid‐state lithium batteries (SSLBs) offer inherent safety and high energy density for next‐generation energy storage, but the large interfacial resistance and poor physical connection between electrode materials and the solid electrolyte (SE) severely impede their practical applications. This work reports a general strategy to introduce covalent bonds between electrode materials and SE, not only reducing interfacial resistance but also enhancing electrochemical stability and mechanical robustness of SSLBs. The covalent bonding is accomplished by functionalizing electrode surfaces with C═C groups, enabling in situ copolymerization with telechelic polymers in the SE. This approach is applicable to various cathode/anode materials and SEs. Particularly, the SSLBs comprising LiFePO₄ cathode, Li_6.75La₃Zr_1.75Ta_0.25O₁₂/(polyethylene oxide (PEO)/lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)/silk composite SE and metallic lithium anode exhibit a specific capacity of 158.4 mAh g⁻¹ and can be cycled at 2 C for 2200 times with >80% retention. Additionally, the SSLBs containing the high nickel‐content LiNi_0.96Co_0.03Mn_0.01O₂ cathode can afford a high specific capacity of 201.8 mAh g⁻¹. Comprehensive experimental examination and theoretical simulations confirm that the lowered interfacial resistance and intimately contacted electrode materials/electrolyte interfaces facilitate Li⁺ transport at different stages of charge. Furthermore, the covalently bonded electrode/electrolyte interfaces also endow SSLBs with outstanding mechanical stability, enabling flexible SSLB pouch cells to operate under various bending states without performance decay.