Boosting the High Capacitance-Controlled Capacity of Hard Carbon by Using Surface Oxygen Functional Groups for Fast and Stable Sodium Storage

Heteroatom doping is identified as an effective strategy to enhance the electrochemical performance of hard carbon. However, the effect of oxygen on biomass-based hard carbon is usually ignored. Herein, oxygen-doped carbon microspheres are fabricated with a lignin-based oxygen source, endowing the carbon microspheres with a high capacitance-controlled capacity and stable cycling performance. In addition, the quality of oxygen doping and microsphere morphology is regulated by using different ratios of lignin. As an anode for sodium-ion batteries, the optimal oxygen-doped carbon microspheres can deliver a high reversible capacity (310.4 mAh g–1 at 25 mA g–1) and long life span. Moreover, when paired with NaNi1/3Fe1/3Mn1/3O2, the full cells can display a capacity of 313.3 mAh g–1 at 25 mA g–1 and an excellent rate performance (218.7 mAh g–1 at 500 mA g–1). Based on first principles, the oxygen functional groups provided by lignin exhibit a strong Na+ adsorption capability, demonstrating that oxygen functional groups, especially C═O, play a pivotal role in the capacitance-controlled process. This work presents an idea for the material design and heteroatom doping of high-performance sodium-ion battery anode materials.