Sodium storage performance of a high entropy sulfide anode with reduced volume expansion†

Metal sulfides are prominent candidates for sodium-ion battery (SIB) anodes owing to their high theoretical capacities and superior conductivities, but their performance is hindered by volume expansion during cycling. This study introduces an approach for mitigating these issues by incorporating high-entropy structures into sulfides. We synthesized a high-entropy sulfide (HES) (FeCoNiCuZn)In₂S₄ (MS5) and medium- and low-entropy sulfides for comparison. Physical and chemical characterization confirmed the successful formation of the HES, the uniform distribution of elements and the presence of sulfur vacancies. We show that high-entropy doping alleviates volume expansion during cycling and enhances sodium storage capacity, thereby improving electrochemical performance. After 800 cycles at a current density of 1 A g⁻¹, MS5 exhibits a reversible capacity of 412.7 mA h g⁻¹. When the current density is increased to 5 A g⁻¹, it can still stably cycle for 800 cycles with a capacity retention rate of up to 88%. Density functional theory calculations supported the experimental findings, indicating that the introduction of high-entropy structures enhances the structural stability and Na⁺ migration, and increases the number of reactive sites. This study highlights the potential of HES materials for use in the anodes of next-generation SIBs, offering insights into their design and application in improved energy-storage solutions.