Intra-atomic Hund's exchange interaction determines spin states and energetics of Li-rich layered sulfides for battery applications

TL;DR

This study uses advanced first-principles calculations to explore how intra-atomic Hund's exchange influences the spin states and energetics of Li-rich layered sulfides, impacting battery performance.

Contribution

We developed an efficient DFT+DMFT approach to accurately describe spin states and energetics in Li-rich sulfides, addressing a key challenge in theoretical modeling.

Findings

High-spin to low-spin transition causes non-monotonic intercalation voltage behavior

Spin and charge fluctuations explain electronic structure changes

Correlated electron insights are crucial for battery material design

Abstract

Motivated by experimental suggestions of anionic redox processes helping to design higher energy lithium ion-battery cathode materials, we investigate this effect using first-principles electronic structure calculations for Li-rich layered sulfides. We identify the determination of the energetic contribution of intra-atomic Hund's exchange coupling as a major obstacle to a reliable theoretical description. We overcome this challenge by developing a particularly efficient flavor of charge-self-consistent combined density functional + dynamical mean-field theory (DFT+DMFT) calculations. Our scheme allows us to describe the spin ground states of the transition metal d shell, the electronic structure of the materials, and its energetics. As a result of the high-spin to low-spin transition the average intercalation voltage shows intriguing non-monotonic behavior. We rationalize these findings by an analysis of the fluctuations of spin and charge degrees of freedom. Our work demonstrates the relevance of most recent insights into correlated electron materials for the physics of functional materials such as Li-ion battery compounds.