New insights into aliovalent substituted halide solid electrolytes for cobalt-free all-solid state batteries

Halide solid electrolytes (SEs) have garnered significant attention due to their decent ionic conductivity and exceptional high-voltage stability. However, their structure-property relationship remains enigmatic. In this work, we synthesize a range of Li3-xLu1-xZrxCl6 (LLZC, 0 < x < 1) solid solutions to investigate the influence of lithium ion and vacant site contents on ionic conductivity. Contrary to our previous understanding, it is found that achieving a balance in lithium ion and vacant site content, rather than aliovalent substitution-induced structural changes that introduce stacking faults, plays a crucial role in optimizing ion transport in a hexagonal close packing (hcp) anion framework. This balance culminates in the highest ionic conductivity (1.5 mS cm(-1)) and lowest activation energy (0.285 eV) of LLZC. In addition, aliovalent substitution strengthens the oxidative stability of halide SSEs but reduces their reduction stability. Using LLZC as SEs and LiMn2O4 as cathodes, cobalt-free all-solid-state batteries undergo 1000 cycles of stable cycling at 0.3 C with negligible capacity decay.

Automated summary

This study investigates the influence of lithium ion and vacant site contents on ionic conductivity by synthesizing a range of solid solutions. It is found that achieving a balance in lithium ion and vacant site content is crucial for optimizing ion transport in a hexagonal close packing anion framework. The highest ionic conductivity and lowest activation energy are achieved in LLZC.