Interfacial reconstruction unlocks inherent ionic conductivity of Li-La-Zr-Ta-O garnet in organic polymer electrolyte for durable room-temperature all-solid-state batteries

Rigid-flexible coupled composite polymer electrolytes (CPEs, e.g., polyethylene oxide/ Li${}_{6.4}$La${}_3$Zr${}_{1.4}$Ta${}_{0.6}$O${}_{12}$, PEO/LLZTO) hold the promise of integrating the respective merits of organic polymer electrolyte and inorganic ceramic fillers to achieve better all-solid-state batteries (ASSBs), but commonly suffer from poor synergistic effect owing to the ionically/electronically resistive layer on the ceramic surface. Representatively, the Li${}_2$CO${}_3$ passivation layer-isolated LLZTO not only contributes minimally to the Li${}^{+}$ conduction in PEO/LLZTO CPE, but also narrows the available electrochemical window. Herein, an interfacial reconstruction strategy is disclosed based on mild liquid-phase chemical reaction and subsequent self-assembly, allowing the detrimental Li${}_2$CO${}_3$ to fully react with succinic anhydride (SA), and simultaneously constructing a robust ultra-thin lithium succinate (SALi) ionic conductor shell to eradicate its regeneration. Accordingly, the obtained PEO/LLZTO@SALi (PLS) CPE shows a high room-temperature ionic conductivity (1.2 × 10${}^{-4}$ S cm${}^{-1}$), a wide electrochemical window (4.8 V), a notable Li${}^{+}$ transference number (0.37), as well as nonflammability and exceptional compatibility with Li metal in Li/Li symmetric cells (2000 h at 0.2 mA cm${}^{-2}$). More encouragingly, the Li/PLS CPE/LiFePO${}_4$ full ASSB maintains an ultrahigh capacity retention of 84.3% after 1400 cycles at room temperature. This work propels the design of high-performance CPEs through the interfacial modulation of inorganic ceramic fillers. (© 2024 Wiley‐VCH GmbH)