Reversible energy storage based on LiF-I- reaction using spent CFx cathode

Graphite fluorides (CF_x) have been widely applied as the cathode material for primary lithium batteries with the advantages of high electrochemical capacity and outstanding reliability under extreme conditions, but the electrode reaction between CF_x and lithium cation (Li⁺) is basically irreversible because of the ultra-stable lithium fluoride (LiF) product. This work certifies a LiF-based energy storage process through the formation of interhalogens with iodine anions (I⁻) using spent CF_x cathode. By experimental and computational methods, the electrode mechanism is clarified as: 2LiF + I⁻ + C - e⁻ → Li⁺ + CF + LiFI (3.2–3.6 V vs. Li/Li⁺), during which the solvation state of Li⁺-I^- pair is pivotal. However, for the same reason, this kind of electrode mechanism is vulnerable to different counter electrode paired, because of the influence of the internal electric field on the ion distribution in the solution. This work reveals the potential of LiF as the electrode active material, and provides a new idea for the design of CF_x-based rechargeable batteries.