Optimization of lithium ion conductivity of Li2S-P2S5 glass ceramics by microstructural control of crystallization kinetics

To improve the Li ion conductivity in a glass-ceramic solid electrolyte, the microstructural control for Li2S-P2S5 glass ceramics was investigated based on crystallization kinetics. 75Li2S∙25P2S5 (mol.%) glass was synthesized by a ball-milling method, and glass-ceramics were prepared by crystallization with heat treatment at various temperatures with appropriate holding times. Crystallization kinetics—nucleation rate, I, and crystal growth rate, U, of 75Li2S∙25P2S5 glass—were determined by differential thermal analysis and in situ transmission electron microscopy (TEM). The obtained parameters were referred to optimize the heat treatment conditions. Through the optimization, Li ion conductivity was improved by 80% in comparison with the glass electrolyte, in which a conductivity of 1.33 × 10−3 S cm−1 was achieved at room temperature by controlling the microstructure and the formation of a network structure in the glass matrix. This approach brings out the best performance of 75Li2S∙25P2S5 glass-ceramics. The effective medium theory was adopted to discuss the formation of a fast ion-conducting network for the improvement of Li ion conductivity. The present method can provide an effective preparation route of a glass-ceramic solid electrolyte for all-solid Li-ion batteries. •Crystallization kinetics of 75Li2S∙25P2S5 glass ceramics was investigated.•Nucleation rate and crystal growth rate were determined using DTA and in situ TEM.•Li ion conductivity of the glass ceramics was optimized to 1.33 × 10−3 S cm−1.•The effective medium theory suggests the formation of fast ion-conducting network.