Separating cationic and anionic redox activity in antiperovskite Li$_2$Fe)SO

TL;DR

This study investigates how separating cationic and anionic redox activities in lithium-rich antiperovskite cathodes affects their electrochemical performance, revealing that focusing on cationic processes enhances stability and capacity.

Contribution

It demonstrates that isolating cationic redox activity improves cycling stability and capacity in lithium-rich antiperovskites, highlighting synthesis conditions as a key performance factor.

Findings

High initial capacity of ~400 mAh/g with anionic process

Improved cycling stability by restricting to cationic processes

Synthesis conditions critically influence electrochemical performance

Abstract

Lithium-rich antiperovskite promise to be a compelling high-capacity cathode material due to existence of both cationic and anionic redox activity. Little is however known about the effect of separating the electrochemical cationic from the anionic process and the associated implications on the electrochemical performance. In this context, we report the electrochemical properties of the illustrative example of three different Li$_2$Fe)SO materials with a focus on separating cationic from anionic effects. With the high voltage anionic process, an astonishing electrochemical capacity of around 400~mAh/g can initially be reached. Our results however identify the anionic process as the cause of poor cycling stability and demonstrate that fading reported in previous literature is avoided by restricting to only the cationic processes. Following this path, our Li$_2$Fe)SO-BM500 shows strongly improved performance indicated by constant electrochemical cycling over 100 cycles at a capacity of around 175~mAh/g at 1~C. Our approach also allows us to investigate the electrochemical performance of the bare antiperovskite phase excluding extrinsic activity from initial or cycling-induced impurity phases. Our results underscore that synthesis conditions are a critical determinant of electrochemical performance in lithium-rich antiperovskites, especially with regard to the amount of electrochemical secondary phases, while the particle size has not been found a crucial parameter. Overall, separating and understanding the effects of cationic from anionic redox activity in lithium-rich antiperovskites provides the route to further improve their performance in electrochemical energy storage.