A Generic Si-Doped Strategy for Hard Carbon Derived from Wuliangye Distillers’ Grains to Achieve High-Performance Sodium Ion Batteries

Hard carbon is considered an exemplary anode material for sodium ion batteries (SIBs) due to its lower voltage platform and higher layer spacing. However, the sodium storage performance of hard carbon is suboptimal, and its initial Coulombic efficiency (ICE) is low, thus posing significant challenges to its practical application. Here, silicon-doped porous hard carbon is successfully synthesized as an anode material for SIBs through recycling low-cost Wuliangye distillers' grains as the precursor. The substitution of silicon atoms for carbon atoms in the carbon framework leads to an increased interlayer spacing, thereby enhancing the reversible specific capacity and ICE. Additionally, the linear control of the roasting temperature results in the production of hard carbon with a high specific surface area (525.23 m2 g–1). Concomitantly, the presence of micropores enhances the infiltration of the electrolyte and facilitates the transportation of sodium ions. As a result, the prepared silicon-doped hard carbon achieves a reversible specific capacity of 280.6 mAh g–1 at 20 mA g–1, while maintaining a capacity retention of 102.6% after 100 cycles. Moreover, full sodium ion batteries are assembled to examine the application prospects using Mg-doped Na0.67MnO2 as the cathode and silicon-doped hard carbon as the anode, delivering a high reversible capacity of 281.5 mAh g–1 and a capacity retention rate of 91.9%. The low-cost doping strategy proposed in this work provides a promising approach toward the commercialization of hard carbon anodes for SIBs.