One-dimensional van der Waals V₂Se₉ as a conversion-type anode material for advanced Li rechargeable batteries

Volume expansion of active materials during lithium storage is one of the main issues in Li-ion batteries (LIBs) that should be addressed. In particular, large volume changes and particle cracking are problematic for electrode materials based on conversion reaction, which are considered attractive anode materials with high energy densities. In this study, a one-dimensional van der Waals (1D vdW) material, V₂Se₉, is proposed as a conversion-type anode material for LIBs. The V₂Se₉ electrode material has a 1D chain molecular structure with vdW interactions between chains to form a bulk crystal structure. The spaces between the 1D chains act as structural buffers and provide short Li⁺ diffusion paths that can improve the electrochemical performance of the electrode materials. The V₂Se₉ electrode exhibits a high reversible capacity of 563.3 mAh g⁻¹ at 100 mA g⁻¹ and a high rate capability of 109.1 mAh g⁻¹ at 3200 mA g⁻¹. The capacity retention of V₂Se₉ electrodes is 83.72% after 100 cycles. Synchrotron X-ray diffraction and X-ray absorption spectroscopy reveal the formation of Li₂Se and V metal, indicating that Li ion storage occurs via the conversion reaction. The structural stability of V₂Se₉ is demonstrated using SEM measurements of the discharged and charged V₂Se₉ electrodes during cycling. These results demonstrate the reaction mechanism of V₂Se₉ and highlight the potential of 1D vdW materials as high-performance anode materials in LIBs.