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

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//NaFePO₄ 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.