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

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 BaTiO₃ and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) into a flexible crosslinked polyester matrix. The built-in electric field of the BaTiO₃/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_0.8Co_0.1Mn_0.1O₂ (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.