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

Biomass-derived hard carbon anode has a promising use in the commercial development of sodium-ion batteries because of its advantages of low cost and renewable and abundant sources. Hard carbon anode materials can be obtained by sequential pyrolysis and carbonization of biomass. However, the influence of the pyrolysis and carbonization conditions on their structure and sodium-ion storage properties is not clear. We have produced hard carbon materials with different microstructures by changing the pyrolysis and carbonization parameters, and the relationship to the structure and properties of the hard carbon was established, and the best conditions for preparing a material with excellent sodium-ion storage performance were obtained. Due to the microcrystals of the precursor carbon remaining intact under slow pyrolysis, a large closed pore volume and suitable closed pore size were developed at a low carbonization temperature of 1100 °C. Therefore, the obtained hard carbon has a specific capacity of 290 mAh g−1 at a current density of 0.05 A g−1 and has an excellent capacity retention rate at a current density of 5 A g−1. Its excellent sodium-ion storage performance indicates that this production method has great potential for the preparation of low-cost, high-performance anode materials.