High-Crystallinity Urchin-like VS Anode for High-Performance Lithium-Ion Storage.

VS 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 VS 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 VS > octopus-like VS > seagrass-like VS > flower-like VS. Among them, urchin-like VS 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 VS and kinetics behavior of Li ion diffusion. A better fundamental understanding on Li storage behavior in VS 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.