Beyond Transition Metal Oxide Cathodes for Electric Aviation: The Case of Rechargeable CF_x

Current and next-generation transition metal oxide-based rechargeable battery chemistries are likely to fall short of the specific energy needed to electrify aircraft. One approach to enabling electric aviation is making high specific energy primary battery chemistries such as the Li-CFx chemistry rechargeable. Though Li-CFx possesses nearly triple the specific energy of current Li-ion cells, numerous fundamental issues related to the overall reaction mechanism exist. In this work, we use density functional theory calculations to build a fundamental understanding of possible reaction mechanisms. The direct formation of LiF and graphite seems unlikely because of the sluggish kinetics of F diffusion in CFx. The discharge occurs likely via lithium ion diffusion into the CFx host to form an LiCF ternary compound. Reasonable agreement between the open-circuit voltage (OCV) determined experimentally (∼4.05 V) and from DFT (4.27 ± 0.14 V) for the formation of ternary LiCF is obtained. Suppressing LiF formation by stabilizing the intermediate ternary LiCF could thus enable rechargeability of the Li-CFx chemistry.