On the Balance of Intercalation and Conversion Reactions in Battery Cathodes

TL;DR

This paper conducts a thermodynamic analysis of intercalation and conversion reactions in battery cathodes, highlighting how material chemistry and polymorphs influence reaction pathways and voltages.

Contribution

It provides a comprehensive thermodynamic framework to predict reaction preferences in various cathode chemistries, emphasizing the role of polymorphs and transition metal composition.

Findings

High energy polymorphs in oxides promote intercalation.

Sulfides and selenides tend to favor conversion reactions.

Cr-containing cathodes favor intercalation reactions.

Abstract

We present a thermodynamic analysis of the driving forces for intercalation and conversion reactions in battery cathodes across a range of possible working ion, transition metal, and anion chemistries. Using this body of results, we analyze the importance of polymorph selection as well as chemical composition on the ability of a host cathode to support intercalation reactions. We find that the accessibility of high energy charged polymorphs in oxides generally leads to larger intercalation voltages favoring intercalation reactions, whereas sulfides and selenides tend to favor conversion reactions. Furthermore, we observe that Cr-containing cathodes favor intercalation more strongly than those with other transition metals. Finally, we conclude that two-electron reduction of transition metals (as is possible with the intercalation of a $2+$ ion) will favor conversion reactions in the compositions we studied.