Conversion-type fluoride cathodes: Current state of the art

Conversion-type transition metal fluoride cathodes offer a 200%–300% higher theoretical energy density limit than state-of-the-art intercalation cathodes. Recent publications have reshaped our understanding of the reaction mechanism in these materials. Herein, we review recent reports highlighting how active material dissolution, particle fusing, electrolyte consumption, and the resultant capacity fade can be mitigated by rational electrolyte design. Recent work has established the possibility of high discharge rate in transition metal fluorides at significant active material mass fraction; we examine the relationship between rate capability and active material fraction. Tuning transition metal fluoride chemistry via cation and anion substitution has demonstrated the potential to improve its electrochemical properties. A brief technoeconomic analysis is presented to highlight the practical advantages of different transition metal chemistries.