Closed-Pore Controlling in Hard Carbon Anode via NaOH Activation for High-Efficiency Sodium Storage

Hard carbon (HC) is a highly promising negative electrode for sodium-ion batteries (SIBs). To promote their practical application in sodium-ion batteries, just like graphite materials in the negative electrode of lithium batteries, it is essential to develop HC materials with high reversible capacity and high initial Coulombic efficiency (ICE). Herein, we propose a facile NaOH activation process to create abundant closed pores within bamboo-derived hard carbon. The results show that specific structure optimization can significantly enhance the low-voltage plateau capacity of the modified hard carbon negative electrode and simultaneously deliver a high reversible capacity and high initial Coulombic efficiency (ICE). The optimized BHC-1400–0.2 electrode exhibits a reversible discharge capacity of 334.4 mAh g–1, which is largely attributed to the substantial contribution of the low-voltage plateau region, predominantly (73%) from the low-voltage plateau region, and a high ICE of 88.7%. In addition, the anode presents a reversible capacity of 268.9 mAh g–1 after 500 cycles at 300 mA g–1, corresponding to a capacity retention of 93.4%. Therefore, this work provides a viable technical route for manufacturing high-performance, low-cost, hard carbon anodes for SIBs.