Mechano-Electrical Buffer Layer at Grain Boundary Induced Solid State Electrolyte with Ultra-High Mechanical Strength and Electrical Insulation for Stable Lithium Metal Batteries

Abstract

The high sintering temperature, low mechanical properties and instability of lithium metal have consistently hindered the practicality of Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) solid-state electrolytes (SSEs). Herein, a meticulously designed mechano-electrical buffer layer is constructed at grain boundaries (GBs) of LATP by introducing Li₂B₄O₇ (LBO) glass-ceramic. LBO can generate a liquid phase with high Young's modulus and low electronic conductivity at GBs to simultaneously reduce sintering temperature, and enhance the mechanical strength and electrical insulation of LATP. The construction of a mechano-electrical buffer layer at GBs leads to three significant achievements: the reduced sintering temperature from 950 to 750 °C, the enhanced mechanical strength from 9.9 to 117.5 MPa, and the decreased electronic conductivity from 1.2 × 10^-9 to 1.5 × 10^-10 S cm^-1. When coupled with a solid polymer electrolyte, it effectively protects LATP from internal microcrack propagation and electron attack. Remarkably, the critical current density (CCD) of the modified LATP can reach 2 mA cm^-2. Moreover, the lithium metal battery with LiFePO₄ demonstrates outstanding stability of more than 1000 cycles with a capacity retention of 93.3% at 0.2C. This work provides new insights into improving the performance of SSEs by enhancing both mechanical strength and electrical insulation.