Tungsten Sulfide with Expanded Interlayer for Long-Life and Wide-Temperature Mg-Ion Batteries

Abstract

Magnesium ion batteries (MIBs) receive concentrated attention owing to their high intrinsic advantages such as theoretical volumetric energy densities. However, poor cycling performances and low-temperature electrochemical properties remain major technical issues in MIBs. Electrode materials impose a great influence on the electrochemical characteristics of MIBs. 2D transition metal dichalcogenides (TMDs) are potentially excellent electrode materials for MIBs on account of their open framework and outstanding electrochemical characteristics. In this work, the pre-intercalation modification strategy is adopted to design the K⁺ pre-intercalated WS₂ material as the electrode material of MIBs. Structural characterizations and density functional theory (DFT) calculations demonstrate that the Mg²⁺ diffusion barrier in the K⁺ pre-intercalated WS₂ is effectively lowered accompanied by the interlayer expansion in the layered structure, aiding quick ion diffusion and reliable Mg²⁺ ion storage. Consequently, the K-WS₂ electrode demonstrates excellent electrochemical performances, a reversible capacity of 217 mA h g⁻¹ at 0.2 A g⁻¹ with outstanding cycling stability. In addition, the K-WS₂ electrode is capable of running smoothly at low temperatures, showing superior capacity preservation of 97% upon completion of 1000 cycles at −30 °C. This work supplies an uplifting means to the modification and optimization of cutting-edge electrode materials for MIBs.