Synergistic Regulation of Multi‐Interface Chemistry by Functional Carbon Dots for High‐Performance Composite Solid Electrolytes

Low ionic conductivity, poor mechanical strength, and unstable interface structure are still the main factors hindering the practical application of polymer solid-state lithium metal batteries (SSLMBs). In this work, we have developed a unique composite filler (LLZTOCDs) for solid polymer electrolytes to address these challenges through synergistic regulation of multi-interface chemistry. The LLZTOCDs is prepared via thermal treatment of N,S,F-codoped carbon dots (NSFCDs) and Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) inorganic electrolyte. Here, the detrimental Li₂CO₃ on the LLZTO surface is converted into a fast ion-conducting and an electron-insulating interlayer of LiF and Li₃N, and the carbon dots self-assemble into a functional organophilic coating on the outermost layer, which acts as a bridge between the LLZTO and the polymer. This unique structure enhances the compatibility and ion-exchange kinetics between the LLZTOCDs and the polymer, significantly improving the mechanical strength and Li⁺ transport. Additionally, the oxygen vacancies formed in situ at the LLZTOCDs interface provide an anion confinement effect, increasing lithium salt dissociation, and enhancing the Li⁺ transference number to 0.85. Therefore, the solid battery constructed with LLZTOCDs exhibits excellent electrochemical stability, long-cycle life, and high ionic conductivity (1.96 × 10^- ⁴ S cm^-1 at 25 °C), providing a feasible strategy for practical applications.