Fluorinated Carbons as Rechargeable Li-Ion Battery Cathodes in the Voltage Window of 0.5-4.8 V.

Fluorinated carbon (CF) cathodes have the highest theoretical energy density among lithium primary batteries. However, it is still a huge challenge to be reversible. Here, CF is proposed as a high-performance cathode material for rechargeable lithium-ion batteries in the extended voltage window of 0.5-4.8 V. Specifically, the fluorinated graphite CF exhibits an initial specific discharge capacity of 1382 mAh g (2362 Wh kg) and a specific discharge capacity of 782 mAh g at the 2nd cycle and maintains a specific discharge capacity of 543 mAh g (508 Wh kg) after the 20th cycle. This rechargeable behavior is associated with the conversion of CF to LiF + C (>1.5 V) and then to LiFC (0.5-1.5 V) during the initial discharge process; LiFC is reversible to LiF + C in the following charge-discharge process (0.5-4.8 V). By extending the voltage window, CF cathodes can show new electrochemical behaviors. Our research has provided new Li-free cathode materials for rechargeable batteries and insights for improving the performance of a Li/CF secondary battery.