Enabling high ionic conductivity in yttrium-based lithium halide electrolytes by composition modulation for all-solid-state batteries

Chloride electrolytes have again become a focus of research in recent years due to the oxidative stability at high potential. Y-based chlorides such as Li3YCl6 have a considerable ionic conductivity of similar to 10(-4) S/cm. The ionic conductivity of a solid-state electrolyte (SSE) is closely related to its crystal structure. Low lithium concentration composition is beneficial for lithium-ion conduction structure. Due to the presence of more free octahedral sites, the crystal structure with Pnma space group has a better ion diffusion compared to the crystal structure with P-3m1 space group with hexagonal close-packed structure (hcp). In addition to this, the doping of cations with higher valence states results in more lithium vacancy compensation in the crystal structure, which is a significant modification to improve the ionic conductivity of the chloride. Herein, ab initio molecular dynamics (AIMD) simulations were performed to investigate the effects of the lithium-deficient state configuration and the cation Nb5+ doping modification on the ion conduction of LiaYClb solid-state electrolytes. The lithium-deficient state composition structure has shifted the material space group structure from P-3m1 to Pnma, which facilitates the diffusion of lithium ions. The Nb5+ doping has increased the chance of lithium ion co-diffusion and disordered the lithium ion sites near the Y(Nb) cation site, resulting in a lower ab-plane diffusion barrier and a significant improvement of lithium ion migration. A series of lithium-deficient state compositions and Nb-doped chlorides were synthesized. Li2.31Y0.98Nb0.02Cl5.31 is obtained by solid sintering preparation with an ionic conductivity close to 1.0 x 10(-3) S/cm and high electrochemical stability. The full cell of Li(2.31)Y(0.9)8Nb(0.02)Cl(5.31) matched with bare LiCoO2 maintains stability for 100 cycles. (c) 2023 Elsevier Ltd. All rights reserved.

Automated summary

Chloride electrolytes have regained attention in recent years due to their stability at high potential. Y-based chlorides, such as Li3YCl6, have a significant ionic conductivity of around 10(-4) S/cm. The crystal structure of solid-state electrolytes (SSE) plays a crucial role in their ionic conductivity. A low lithium concentration composition and cation doping can improve the ion diffusion in the crystal structure. By performing ab initio molecular dynamics (AIMD) simulations, it was found that lithium-deficient state composition and Nb5+ doping can enhance the ion conduction of LiaYClb electrolytes. Experimental synthesis of lithium-deficient state compositions and Nb-doped chlorides resulted in Li2.31Y0.98Nb0.02Cl5.31, which exhibited high ionic conductivity and electrochemical stability in solid sintering preparation. The full cell of Li(2.31)Y(0.9)8Nb(0.02)Cl(5.31) matched with bare LiCoO2 showed stability over 100 cycles.