Study on the hard carbon anode from different precursors for sodium ion batteries

Sodium-ion batteries (SIBs) are commonly utilized in power storage applications. It can be used as alternatives to lithium-ion batteries. Nevertheless, the development of SIBs is restricted by anode materials due to the high redox potential and large irreversible capacity. As a common anode material of SIBs, hard carbon exhibits a substantial interlayer spacing and a excellent reversible specific capacity, while the properties and costs are affected by its precursors. This article mainly describes the sodium storage principle of hard carbon and compares the performances as well as modification methods of hard carbon produced from various precursors. The hard carbon basing on coal has the advantages of low cost due to the abundant reserves of coal precursors and low redox potential. Biomass-based hard carbon has natural pores which can assist the sodium ions transport in carbon materials. We further explain the effects of modification strategies such as heteroatom doping, activation treatment and mechanical ball milling on electrochemical properties of hard carbon. Finally, this paper recognizes the existing problems and corresponding solutions of materials made of hard carbon and looks forward to the future research focus on hard carbon materials.