Engineering the pyrolysis and carbonization parameters to regulate the microstructure and its sodium-ion storage performance of hard carbon anodes

Biomass-derived hard carbon has a promising application prospect in the commercial development of sodium-ion batteries due to its advantages of low cost, renewable and abundant sources. Hard carbon anode materials can be obtained by simple pyrolysis and carbonization of biomass. However, the influence of pyrolysis and carbonization on the structure and sodium storage properties of hard carbon anodes is not clear. In this paper, hard carbon materials with different microstructure were obtained by changing the pyrolysis and carbonization parameters, and the relationship between the structure and properties of hard carbon was established, and the best conditions for preparing hard carbon materials with excellent sodium storage performance were obtained. Due to the intact microcrystals of the precursor carbon by slow pyrolysis, large closed pore volume and suitable closed pore size are still developed at the low carbonization temperature of 1100 °C. Therefore, the obtained hard carbon exhibits a specific capacity of 290 mAh g−1 at a current density of 0.05 A g−1. In addition, the hard carbon also shows excellent capacity retention rate at current density of 5 A g−1. The excellent performance of sodium storage indicates that this method has great potential in the preparation of low-cost, high-performance anode materials.