High-Crystallinity Urchin-like VS₄ Anode for High-Performance Lithium-Ion Storage

VS₄ anode materials with controllable morphologies from hierarchical microflower, octopus-like structure, seagrass-like structure to urchin-like structure have been successfully synthesized by a facile solvothermal synthesis approach using different alcohols as solvents. Their structures and electrochemical properties with various morphologies are systematically investigated, and the structure-property relationship is established. Experimental results reveal that Li⁺ ion storage behavior in VS₄ significantly depends on physical features such as the morphology, crystallite size, and specific surface area. According to this study, electrochemical performance degrades on the order of urchin-like VS₄ > octopus-like VS₄ > seagrass-like VS₄ > flower-like VS₄. Among them, urchin-like VS₄ demonstrates the best electrochemical performance benefiting from its peculiar structure which possesses large surface area that accommodates the volume change to a certain extent, and single-crystal thorns that provide fast electron transportation. Kinetic parameters derived from EIS spectra and sweep-rate-dependent CV curves, such as charge-transfer resistances, Li⁺ ion apparent diffusion coefficients and stored charge ratio of capacitive and intercalation contributions, both support this claim well. In addition, the EIS measurement was conducted during the first discharge/charge process to study the solid electrolyte interface (SEI) formation on urchin-like VS₄ and kinetics behavior of Li⁺ ion diffusion. A better fundamental understanding on Li⁺ storage behavior in VS₄ is promoted, which is applicable to other vanadium-based materials as well. This study also provides invaluable guidance for morphology-controlled synthesis tailored for optimal electrochemical performance.