Engineering surface oxygenated functionalities on commercial hard carbon toward superior sodium storage

Hard carbon is the most promising anode material for sodium-ion batteries (SIBs). However, the poor rate capability and low reversible capacity are still big challenges for its wide commerical application in SIBs. However, there are two main barriers before large-scale industrialization, i.e., low reversible capacity and poor rate performance. In this work, we report a novel method enhancing commercial hard carbon anode through a facile chemical treatment. Commercial hard carbon with an expanded carbon interlayer is realized via controllably introducing oxygen functional groups. When employed as anode for SIB, the modified CHC demonstrates a high reversible capacity of 341 mAh g−1 at 20 mA g−1, which is much higher than pristine HC (270 mAh g−1). Excellent rate capability with a capacity of 50 mAh g−1 is maintained at 5000 mA g−1. More importantly, this facile oxidation strategy is also suitable for commercial soft carbon, which also displays significantly enhanced electrochemical performance. The kinetic measurements and theoretical calculation results reveal that the enhanced electrochemical properties should be attributed to the introduced oxygen function groups, which not only facilitate the diffusion of Na ions via enlarging the carbon interlayer distance, but also enhance the absorption capacity to Na ions.