Influence of Hard Carbon Materials Structure on the Performance of Sodium-Ion Batteries

Sodium-ion batteries are one of the ideal devices for large-scale energy storage systems, and hard carbon is a promising negative electrode material for sodium-ion batteries. In this paper, we carefully study three commercial hard carbon (HC) materials with different structures and find that the interlayer spacing, defects, particle size, and pore size of the materials have significant impacts on the performance. The materials are used to analyze the sodium storage behaviors in the slope and plateau regions through charge/discharge, CV, and GITT tests. To eliminate the adverse impact of overpotential on the metal sodium electrode in the half-cell system, we use a three-electrode system to measure the capacity of different HCs in the slope and plateau regions. It is found that the sodium storage of the slope region is accompanied by both adsorption and intercalation behaviors. The K-HC with the largest interlayer spacing (0.393 nm) and the largest number of defects (AD/AG value is 1.30) has the highest sodium storage specific capacity (288.29 mAh·g–1) and slope area capacity contribution (107.04 mAh·g–1). In addition, the kinetics of different HC materials are studied. The GITT and EIS results indicate that Na+ diffusion is the easiest in A-HC materials, so they exhibit better rate performance. Due to a large number of defects (AD/AG = 1.30) and large layer spacing (0.393 nm), the K-HC material has the highest capacitance contribution (0.2 mV·s–1, 47.6%) and sodium storage specific capacity (288.29 mAh·g–1).