Multiscale Collaborative Optimization for Composite Solid Electrolyte to Achieve High‐Performance Lithium Metal Batteries

Abstract Composite solid electrolytes (CSEs) possess significant advantages over individual polymer or inorganic solid electrolytes. However, conventional CSEs suffer from multiple scale issues, including interruptions in ionic transport pathways, incompatibility at heterogeneous interface, and the excessive thickness of electrolytes. Herein, a novel CSE with ultrathin structure (22 µm) based on the strategy of multiscale collaborative optimization (MC‐CSE) is designed. This strategy involves continuous, rapid, and homogeneous Li + transport from macroscale to microscale. i) The bicontinuous structure of MC‐CSE is constructed via in situ polymerization of 1,3‐dioxolane in a continuous yet porous Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (CP‐LLZTO) skeleton, which effectively reduces the barrier for Li⁺ transport at macroscale. ii) The continuous interconnected CP‐LLZTO and poly 1,3‐dioxolane (PDOL) phases within MC‐CSE ensures continuous Li + transport at mesoscale. iii) CP‐LLZTO and PDOL synergistic interaction at heterogeneous interface, which facilitates the rapid and homogeneous Li + transport at microscale. Consequently, the MC‐CSE shows both high ionic conductivity and Li⁺ transference number (1.04 mS cm −1 and 0.87). The cells assembled with MC‐CSE exhibit outstanding low‐temperature (−20 °C) and high‐voltage (4.5 V) performance. The strategy of multiscale collaborative optimization provides a promising perspective for the viability of lithium metal batteries at various conditions.