Design of hard carbon anode with low specific surface area and low porosity in sodium ion battery

Abstract Among various anode materials, such as hard carbon, which as the most promising material, has shown great advantages in terms of reserves, initial coulombic efficiency and cycle stability. By studying the mechanism of storing sodium ions in hard carbon, it is found that the specific surface area and porosity of hard carbon are the key factors that affect hard carbon as a battery anode material. Hard carbon is obtained by setting different precursors and different pyrolysis temperatures. These carbons have different surface areas and porosities. The electrochemical performance was tested separately, and the results show that hard carbon materials with low specific surface area and low porosity usually showed higher initial coulombic efficiency (ICE), superior rate performance, larger reversible capacity and stronger cycle stability. This is because the hard carbon with low specific surface area reduces the contact area between the electrode and the electrolyte, thereby reducing the loss of sodium ions. In addition, the micropores on the surface shorten the diffusion distance of sodium ions. Also, the resulting low-defect structure has a high degree of graphitization and a good degree of order, which enhances electrical conductivity, increases reversible capacity, and makes the structure more stable. This article introduces several types of methods for constructing hard carbon anode with low specific surface area and low porosity, and by influencing the internal structure of the electrode, thereby enhancing ICE and other properties. This provides a new idea for constructing anodes with superior performance.