Optimizing nitrogen-doped bamboo-derived hard carbon as anodes of sodium-ion batteries

Hard carbon made from bamboo has been considered as a promising anode material for sodium-ion batteries because of its renewability and high-performance. Nitrogen-doping can significantly improve the electrochemical performance of carbon materials through enhancing the conductivity and maintaining the stability. In this work, two series of N-doped hard carbon materials derived from bamboo were prepared by heating the mixture of hard carbon and melamine at different temperatures from 700 to 900 degrees C with various mass ratios of melamine to hard carbon 1:1, 2:1 and 3:1. The non-porous structure of the carbon particles made it difficult to achieve a high nitrogen content, and nitrogen would not be successfully doped into carbon at too high temperatures. Nitrogen doping into hard carbon would affect the structure and electrochemical properties. Among as-prepared samples, the one prepared with a mass ratio of 1:1 at 800 degrees C exhibited optimum performance with a high reversible specific capacity of 329.1 mAh center dot g- 1 and high initial Coulombic efficiency of 85.5 % at 30 mA center dot g- 1. Moreover, it had excellent rate capability of 206.2 mAh center dot g- 1 at 1.5 A center dot g- 1. After 100 cycles at 0.3 A center dot g- 1, the capacity retention rate was 92.9 %. The results showed that the electrochemical performance of samples was strongly related to the doped nitrogen content, the disordered degree and the conductivity of N-doped hard carbon.