NaF Modification of Open/Closed Pores Enhancing the Sodium Storage in Hard Carbon

Abstract

Hard carbon (HC) is one of the most promising anode materials in sodium‐ion batteries, and its sodium‐storage performance is closely related to its open/closed pore structures. However, modification of the inner pore structure of HC still remains a challenge. In this work, porous HCs are synthesized using pitch as the precursor, and the open and closed pores in HC are modified by NaF to obtain NaF@HC and polypropylene (PP)@NaF@HC, respectively. In the results, it is proved that NaF modification can construct closed pores in HC and improve Na+ transportation. Furthermore, NaF modification of the open pores effectively inhibits the electrolyte decomposition. Both NaF@HC and PP@NaF@HC exhibit excellent sodium‐storage performance, which delivers the reversible specific capacities of 310 and 323 mAh g−1, corresponding to the initial Coulombic efficiency (ICE) of 72.3% and 82.2%, respectively. Even after 200 cycles, their capacity retentions still maintain 99.5% and 92.8%. Nevertheless, NaF modification of the closed pores increases the sodium deposition barrier, leading to a severe capacity fading of the plateau capacity at a high current rate. In this study, the structural regulation of open and closed pores in HC can be guided, thereby improving its sodium‐storage kinetics.