Surface Modification with F-Doped Carbon Layer Coating on Natural Graphite Anode for Improving Interface Compatibility and Electrochemical Performance of Lithium-Ion Capacitors

F-doped carbon layer coating is an effective surface modification method to enhance the intrinsic conductivity of active materials and facilitate the accommodation of solvated Li+ ions near the carbon surface. Furthermore, it induces the formation of an effective LiF-rich solid electrolyte interface with high electrochemical stability and facile surface diffusion of Li+ ion owing to its low energy barrier. Therefore, by employing a cost-effective coating material poly(vinylidene fluoride) (PVDF), high electrochemical performance in rate capability, cyclability, and energy/power density can be easily achieved without using expensive materials. A uniform and thin coating of an F-doped amorphous carbon layer was fabricated on the natural graphite (NG) surface using 1 wt % of PVDF (NG-F1), followed by a carbonization step. This process resulted in a high energy density of 59.8 Wh kg–1 at a current density of 5.0 A g–1 (100C) in a full cell configuration for lithium-ion capacitors (LICs). In comparison, the pristine NG demonstrated an energy density of 47.3 Wh kg–1. Furthermore, this LIC full cell with NG-F1 showed a lower charge-transfer resistance and a higher capacity retention of 99.4% than pristine NG, even after 500 charge–discharge cycles at 3C.