(201ad) Morphological Control of Li3VO4 via Solvothermal Synthesis and Electrochemical Performance for Lithium-Ion Batteries

Lithium-ion batteries are considered as promising power sources for portable electronics and electric vehicles because of the high energy density and power density. However, the current commercial graphitic anode materials could not satisfy the safety and energy density requirements of electric vehicles. Another well-known anode material Li₄Ti₅O₁₂ also could not meet the energy density requirement due to its relatively high operating potential and low theoretical capacity. Much effort has been paid to searching for new alternatives for the commercial graphite anode materials. Recently, Li₃VO₄ anode with β polymorph has been reported as a promising insertion type material. It can accommodate up to two mole of Li, corresponding to a theoretical capacity of 395 mAh g–1, which is higher than that of Li₄Ti₅O₁₂. Besides its high capacity, Li₃VO₄ also has an appropriate voltage window (0.5-0.8 V vs. Li+/Li), which avoids the safety issue associated with the formation of Li dendrites and guarantees high voltage of the full cell. Thus, these advantages make Li₃VO₄ a promising anode material among the current studied materials. In the present work, we report a facile solvothermal approach to yield Li₃VO₄ using mixed solvents of deionized water (DIW) and absolute ethanol (EtOH). The morphology of Li₃VO₄ greatly changes while tuning the volume ratio of EtOH/DIW. Coral-shaped particles, self-assembled hierarchical microsphere, cube-like particle, sheet-like structure are obtained when the volume ratios of EtOH to DIW range from 30:0, 20:10, 15:15, 10:20 to 0:30. The Li-storage properties are studied in half-cell assembly and the sample with self-assembled hierarchical microsphere (volume ratio of EtOH to DIW water at 15-15) demonstrates the best performance. Furthermore, the subsequent carbon coating process on the microsphere sample has significantly improved the capacities at both low (350 to 430 mAh g^–1 at 100 mA g^–1) and high current (180 to 350 mAh g^–1 at 2 A g^–1) conditions with excellent cycling stability as well. The structural characteristics and morphology of the carbon coated and carbon free 15-15 samples are characterized using XRD, field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM). The electrochemical performance between the carbon free 15-15 and carbon coated 15-15 in the potential range of 0.1-3.0 V was also systematically investigated.