Charged and Discharged States of Cathode/Sulfide Electrolyte Interfaces in All-Solid-State Lithium Ion Batteries

Abstract

Interfaces between cathodes and sulfide electrolytes exhibit high resistance in all-solid-state lithium ion batteries. In this paper, to elucidate the origin of the high interface resistance we have theoretically investigated the properties of the cathode interfaces with the sulfide electrolyte and oxide electrolyte for comparison. From the density functional molecular dynamics simulations of the LiFePO4/Li3PS4 interface in both discharged and charged states, we have demonstrated the instability of the sulfide interface in the charged state, that is, the lithium depletion and oxidation on the sulfide side near the interface, in contrast to the oxide interfaces. The obtained results imply the formation of a Li-depleted layer around the sulfide interfaces during charging and support the validity of the insertion of oxide buffer layers at the interface to reduce the interface resistance.