An in-situ generated composite solid-state electrolyte towards high-voltage lithium metal batteries

The solid-state electrolyte (SSE) has promising applications in next-generation lithium (Li) metal batteries (LMBs) because of its significantly enhanced safety and more compatible interface characteristics than flammable traditional liquid electrolytes. However, only a few attempts have achieved high-performance high-voltage LMBs, which is attributed to the fact that both high ionic conductivity and good compatibility with electrodes can hardly be achieved simultaneously. Herein, a composite solid-state electrolyte (CSE) based on star-shaped siloxane-based polymer electrolyte coupled with Li6.75La3Zr1.75Ta0.25O12 (LLZTO) ceramic fillers is designed and prepared through a facile in-situ polymerization method. The obtained CSE exhibits high ionic conductivity (i.e., 1.68 × 10−4 S cm−1 at a temperature of 60 °C), superior anodic stability, and high Li-ion transference number (i.e., 0.53) because of the multifunctional synergistic effect of the polymer electrolyte with LLZTO ceramic fillers. Moreover, the as-developed CSE shows excellent compatibility with Li anodes. As a result, the as-developed CSE enables the development of long-life 4.4-V-class solid-state LMBs with a LiCoO2 cathode, with 79.7% capacity retention and 99.74% average Coulombic efficiency after 500 cycles at a 0.5 C rate. Postmortem analysis of cycled batteries confirms that such superior battery performance can be mainly ascribed to the formation of a compatible electrode/electrolyte interface. Furthermore, excellent safety features can be observed in LiCoO2/Li pouch batteries. This work provides an important guide for the rational design of SSEs for high-voltage LMBs.