Rationally Regulating Closed Pore Structures by Pitch Coating to Boost Sodium Storage Performance of Hard Carbon in Low‐voltage Platforms

Abstract Hard carbon (HC) materials with rich closed pore structures and nano‐scaled soft carbon coating layer have emerged as promising anode in sodium‐ion batteries (SIBs). However, it still remains a tremendous challenge to precisely regulate closed pore structures and soft carbon coating thicknesses for achieving excellent electrochemical performance in SIBs at low‐voltage platforms. Herein, PCHC‐10 with abundant and suitable‐sized closed pore size (0.45 nm) and nano‐scaled soft carbon coating layer has been accurately designed by chemical crosslink reaction between the pre‐oxidized phenolic resin and a small addition of pitch to form ester‐based bond. As anode, PCHC‐10 delivered large reversible capacity of 359.8 mAh g −1 within 0.001–2.5 V, and high capacity of 242.8 mAh g −1 in low voltage platforms (≤0.15 V). Besides, PCHC‐10 anode exhibits 91.4% capacity retention for 100 cycles, and Na 3 V 2 (PO 4 ) 3 //PCHC‐10 full cell has superior rate performance and high energy density of 231.2 Wh kg −1 . Furthermore, the detailed electrochemical storage behaviors and theoretical calculations revealed that the HC owning closed pore‐size of 0.45 nm has the strongest Na + storage abilities in low‐voltage platforms. This work presents a novel insight for constructing HC with suitable‐sized closed pore structures and soft coating layer to boost Na + storage capability in low‐voltage platforms.