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

Fluorinated carbon (CFx) cathodes have the highest theoretical energy density among lithium primary batteries. However, it is still a huge challenge to be reversible. Here, CFx 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 CF0.88 exhibits an initial specific discharge capacity of 1382 mAh g⁻¹ (2362 Wh kg⁻¹) and a specific discharge capacity of 782 mAh g⁻¹ at the 2nd cycle and maintains a specific discharge capacity of 543 mAh g⁻¹ (508 Wh kg⁻¹) after the 20th cycle. This rechargeable behavior is associated with the conversion of CFx to LiF + C (>1.5 V) and then to Li1+xFC (0.5-1.5 V) during the initial discharge process; Li1+xFC is reversible to LiF + C in the following charge-discharge process (0.5-4.8 V). By extending the voltage window, CFx 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/CFx secondary battery.