Theoretical Design of Solid Electrolytes with Superb Ionic Conductivity: Alloying Effect on Li+ Transportation in Cubic Li6PA5X Chalcogenides

TL;DR

This paper uses first principles modeling to design inorganic solid electrolytes with ultra-low activation energies for Li+ transport, focusing on alloying effects in cubic Li6PA5X chalcogenides to enhance ionic conductivity for safer solid-state batteries.

Contribution

It introduces a systematic approach to reduce Li+ diffusion barriers via alloying and substitution in cubic Li6PA5X electrolytes, advancing solid electrolyte design.

Findings

Inter-octahedral diffusion dominates Li+ transport.

Lower electronegativity and smaller halogen ions reduce diffusion barriers.

Alloying strategies significantly enhance ionic conductivity.

Abstract

It is of great importance to develop inorganic solid electrolytes with high ionic conductivity, thus enabling solid state Li-ion batteries to address the notorious safety issue about the current technology due to use of highly flammable liquid organic electrolytes. On the basis of systematic first principles modelling, we have formulated new inorganic electrolytes with ultra-low activation energies for long-distance diffusion of Li+ ions, through alloying in the cubic Li6PA5X chalcogenides (chalcogen A; halogen X). We find that the long-distance transportation of Li+ is dictated by inter-octahedral diffusion, as the activation energy for Li+ to migrate over a Li6A octahedron is minimal. The inter-octahedral diffusion barrier for Li+ is largely dependent on the interaction with chalcogen anions in the compound. Radical reduction of diffusion barrier for Li+ ions can be realized through isovalent substitution of S using elements of lower electronegativity, together with smaller halogen ions on the X site.