Ionic Environment Dielectric Modulation Design of Composite Solid‐State Electrolyte for High‐Voltage Lithium‐Metal Batteries

Abstract Composite solid‐state polymer electrolytes (CPEs) have become a key driving force for the industrialization of solid‐state batteries (SSBs) by virtue of their excellent flexibility and processability. Nevertheless, the ionic conduction relaxation of the polymer chain segments leads to localized ion stacking, non‐steady state mass transfer, and concentration polarization issues, limiting the further application of CPEs. Herein, a heterogeneous surface is used to modulate the ionic environment of the dispersed phase in CPEs by incorporating high dielectric material BaTiO 3 and Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) into a flexible crosslinked polyester matrix. The built‐in electric field of the BaTiO 3 /LLZTO heterojunctions guides the dissociation and directional diffusion of Li + , which achieves ionic conductivity of 2.01 × 10 −4 S cm −1 and Li + transference number of 0.62 at 25 °C. Simultaneously, the enhanced interfacial dynamics and optimized Li + percolation at the Li/electrolyte interface mitigate dendritic propagation, enabling ultra‐stable lithium plating/stripping behavior over 2800 h at 0.1 mA cm −2 . Li/LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) full cell demonstrates 81.79% capacity retention after 200 cycles of 4.5 V cut‐off voltage at 0.5C. This work presents a new strategy for material design and interface engineering that aims at achieving high safety and high energy density in SSBs.