A near-single-ion conducting polymer-in-ceramic electrolyte for solid-state lithium metal batteries with superior cycle stability and rate capability

Composite solid-state electrolytes (CSE) represent a promising alternative to conventional porous separators and organic liquid electrolyte systems in commercialized lithium metal battery (LMBs), offering effective dendrite suppression, high interfacial compatibility and enhanced cycle life. This study introduces a polymer-in-ceramic electrolyte, which is synthesized by blending perovskite-type inorganic electrolyte Li_1.5La_1.5TeO₆ (LLTeO) with polymethyl methacrylate (PMMA) and polyvinylidene fluoride (PVDF), denoted as PMMA/PVDF-LLTeO. The resulting CSE features a dense, non-porous structure, high mechanical strength, excellent thermal stability, and a broad electrochemical window. Notably, with the incorporation of a high ceramic filler content (up to 70 %), the CSE promotes a hybrid ion transport mechanism, yielding a near-single-ion conducting behavior with an ion transference number of 0.833, and a high elastic modulus of approximately 1 GPa. These attributes collectively contribute to the suppression of dendrite growth, as analyzed through multiphysics-based simulations. Li//Li symmetric cells using PMMA/PVDF-LLTeO-70 exhibit robust lithium stripping-plating stability, with a critical current density of 0.45 mA cm⁻². Furthermore, the corresponding Li//LiFePO₄ cells exhibit superior rate performance and cyclic stability, achieving over 150 cycles with a capacity retention rate of 92.2 % at high temperatures (60 °C). This research highlights the potential of the proposed CSE with high-temperature applications, significantly improving the safety and performance of LMBs.