B, N Co‐Doped Hard Carbon Nano‐Sponge Enhancing Half and Full Cell Performance in Na‐Ion Batteries

Abstract Hard carbon is a promising anode material for next‐generation sodium‐ion batteries (NIBs) due to its high specific capacity, low working potential, and excellent structural stability. This research focuses on synthesizing boron‐ and nitrogen‐co‐doped hard carbon (BNHC), which shows enhanced sodium storage properties in half and full‐cell configurations. The BNHC is prepared using a simple, scalable sol‐gel method followed by pyrolysis for carbonization. Its 3D nano‐sponge structure provides abundant active sites for sodium storage, while the low surface area and optimal interlayer distance minimize volume expansion during high‐rate charge/discharge cycles, ensuring exceptional cycling stability. Compared to undoped hard carbon, BNHC demonstrates significantly improved sodium storage performance. The BNHC electrode achieves a reversible capacity of ≈310 mAh g⁻¹ with ultra‐long cycling stability at high current rates and robust rate capability. It delivers ≈115 mAh g⁻¹ at an exceptionally high current density of 10 A g⁻¹. Further, BNHC//NaFePO 4 full cell demonstrates excellent cycling stability with ≈206 mAh g⁻¹ at a 150 mA g⁻¹ current rate. This study paves the way to commercializing hard carbon as an anode material for sodium‐ion batteries.