Preparation and Electrochemical Properties of Cubic ZnSe/SnSe@C Composites for Sodium Ion Battery Cathode

Nano-cube ZnSn(OH)₆ precursor was prepared by hydrothermal reaction at room temperature with zinc chloride, tin tetrachloride and sodium hydroxide as raw materials and polyethylene glycol-4000 as additive. Cubic ZnSe/SnSe@C composites were prepared by carbon coating the precursor with dopamine hydrochloride and high temperature selenization. The microstructure and phase composition of the composites prepared under different molar ratios of zinc chloride to tin tetrachloride (1∶1, 1∶2, 2∶1), as well as their electrochemical properties as anode materials for sodium ion batteries were studied. The results show that when the molar ratio of zinc chloride to tin tetrachloride was 1∶2 and 2∶1, there were aggregated nanoparticles in the composites, and no carbon uniformly coated cube particles were found. When the molar ratio of zinc chloride to tin tetrachloride was 1∶1, the cube had a regular shape and evenly dispersed, whose surface was uniformly coated with a layer of carbon. The phase of all composites consisted of ZnSe and SnSe, and had a good crystallization. After cycling for 40 cycles at the current density of 100 mA · g⁻¹, the mass specific capacity of the composite under zinc chloride to tin tetrachloride molar ratio of 1∶1 still maintained 410 mA · h · g⁻¹, and the Coulomb efficiency was about 94.6%, which was significantly higher than those of the composites prepared under zinc chloride to tin tetrachloride molar ratio of 1∶2 or 2∶1. After cycling for 200 cycles at a high current density of 1 A · g⁻¹, the mass specific capacity of the composite prepared under the zinc chloride to tin tetrachloride of 1∶1 could still reach 330 mA · h · g⁻¹, and the Coulomb efficiency was close to 100%,indicating excellent cyclic stability. Compared with those of zinc chloride to tin tetrachloride molar ratio of 1∶2 or 2∶1, the composite prepared under zinc chloride to tin tetrachloride molar ratio of 1∶1 had lower charge transfer impedance and faster ion diffusion rate, and showed excellent electrochemical performance.