Rational Design of High-Performance Li_1.5La_1.5TeO₆-Based Composite Solid Electrolyte for Lithium Metal Batteries with Fast-Charging and Long-Life Stability

Solid-state electrolytes (SSEs) are increasingly recognized for their potential to enhance the performance of lithium-metal batteries (LMBs). In this study, to tackle the inherent trade-offs in SSEs between mechanical stability and ionic conductivity, we propose a composite solid electrolyte (CSE) by integrating perovskite Li_1.5La_1.5TeO₆ (LLTeO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and a polymer blend of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). This rational design features an ion-conducting double-network, enhanced mechanical flexibility, and robustness, which facilitate improved ion migration, excellent compatibility with lithium electrodes, and effective dendrite suppression. The CSE demonstrates a mechanical strength of 27 MPa, an impressive ionic conductivity of 0.826 mS cm^-1, and a broad electrochemical window of 4.88 V. The Li//Li symmetric cells display stable cycling for over 600 h at 1 mA cm^-2. Additionally, the corresponding Li//LiFePO₄ (LFP) and Li//LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cells exhibit remarkable rate performance and cyclic stability. Specifically, the Li/CSE/LFP cell sustains a high capacity of 131.7 mAh g^-1 after 300 cycles at 3C, achieving a capacity retention rate of 98.1% and an average Coulombic efficiency of 100%. This research presents a viable strategy for the development of solid-state LMBs, offering high energy density, extended cycle life, and enhanced safety.