Fluorinated soft carbon as an ultra-high energy density potassium-ion battery cathode enabled by a ternary phase K FC

Fluorinated carbons (CFx) have been widely applied as lithium primary batteries due to their ultra-high energy density. It will be a great promise if CFx can be rechargeable. In this study, we rationally tune the C-F bond strength for the alkaline intercalated CFx via importing an electronegative weaker element K instead of Li. It forms a ternary phase KxFC instead of two phases (LiF + C) in lithium-ion batteries. Meanwhile, we choose a large layer distance and more defects CFx, namely fluorinated soft carbon, to accommodate K. Thus, we enable CFx rechargeable as a potassium-ion battery cathode. In detail, fluorinated soft carbon CF1.01 presents a reversible specific capacity of 339 mA h g−1 (797 Wh kg−1) in the 2nd cycle and maintains 330 mA h g−1 (726 Wh kg−1) in the 15th cycle. This study reveals the importance of tuning chemical bond stability using different alkaline ions to endow batteries with rechargeability. This work provides good references for focusing on developing reversible electrode materials from popular primary cell configurations.