Semi-Ionic C-F bond enabling fluorinated carbons rechargeable as Li-ion batteries cathodes

Fluorinated carbon (CF_x) cathodes possess the highest theoretical energy density among lithium primary batteries. However, achieving reversibility in CF_x remains a significant challenge. This work employs a high-voltage sulfolane electrolyte and achieves a highly reversible CF_x cathodes in lithium-ion batteries (LIBs) via fine modification of the C-F bond character. The improved reversibility of CF_x originates from the semi-ionic CF_x phase, with a superior bond length and weaker bond energy than a covalent bond. This characteristic significantly mitigates the challenges encountered during the charging process. We screen and identify the fluorinated graphene CF_1.12 as a suitable cathode, providing an appropriate fluorine content and sufficient semi-ionic C-F bonds for rechargeable LIBs. This fluorinated graphene CF_1.12 exhibits an initial discharge specific capacity of 814 mAh g^-1 and a reversible discharge specific capacity of 350 mAh g^-1. This work provides a new clue for chemical bond regulation studies and provides insights into stimulating reversibility of primary-cell cathodes.