Inspired by nature: Self-fractal cobalt sulfate composite electrode for sodium ion storage

Abstract

Generally, the metal sulfide itself has poor conductivity, and the volume expansion occurs when it is converted with sodium, which will destroy the integrity of the electrode structure, resulting in poor cycle performance and rate performance. To solve the problems of low initial coulombic efficiency (ICE) and volume expansion of metal compounds used as anodes in sodium-ion batteries (SIBs). Inspired by nature, the CoSO4/hard carbon/graphene (CHG) fractal structure electrode was designed. Self-fractal structures with electron/ion transport channels and high strain tolerance proved to be an effective strategy to overcome these challenges. The fractal dimension (D) is measured by synchronous Small Angle X-ray scattering, and the D remains stable during charging and discharging. The fractal CHG also showed excellent electrochemical performance, especially 97.4% ICE. Theoretical calculation shows that self-fractal CHG can promote the formation of a thin solid electrolyte interface (SEI). Synchrotron radiation absorption spectrum proved the reaction mechanism of CHG. This study not only proves that cobalt sulfate is a feasible strategy for developing high-performance SIBs anodes but also provides an advanced method for measuring the fractal dimension of energy storage electrode materials.