Engineering of Closed Pores and Transport Channels in Polymer-Derived Hard Carbon via Chemical Vapor Deposition for Sodium-Ion Batteries

The morphology and pore structure of hard carbon (HC) anodes play a key role in contributing to the reversible capacity and Na + transport dynamics. However, the underlying storage mechanism as well as the effective modulation strategy for simultaneously enhancing both capacity and fast-charging performance remain underexplored. Herein, we propose an effective strategy, chemical vapor deposition (CVD) on temperature-controlled polyetheretherketone (PEEK)-derived HCs, to elucidate Na + storage behavior under the evolution of morphology and pore structure. It is demonstrated that the in situ surface deposition of graphite domains induced by CVD not only seals open pores to form additional closed pores but also constructs the optimized carbon network that serves as transport channels, thereby enhancing Na + transport kinetics. Furthermore, the carbon layer with short-range order facilitates the formation of closed pores and primarily functions as a transport channel for sodium ions. The optimized HC sample exhibits a high reversible capacity of 342.6 mAh g –1, impressive rate performance (258.6 mAh g –1 at 5 C) and stable cycling performance (81.7% after 2000 cycles at 5 C). This work reveals the Na + storage mechanism of polymer-derived HCs with abundant closed pores and offers an effective strategy for regulating polymer-derived HCs to achieve fast-charging sodium-ion batteries.