Facile Synthesis Of Cobalt Vanadate Anode Materials And Their Electrochemical Properties

With flexible structure, multi-metal synergy effects, interface lithium storage,cobalt salts of vanadium exhibits good electrochemical activity, which can be used as potential lithium-ion battery anode materials. This paper selects vanadium cobalt salt as the research object. Different synthetic methods were used for preparing the different morphologies of vanadium cobalt anode materials. A variety of materials characterization techniques were adopted to test the as-prepared materials chemical components and structures. Besides, the electrochemical properties and reaction mechanism of these materials were analyzed to explore the instinct relationship between crystal structure and performance.Firstly, pencil-shaped Co₇V₄O₁₆（OH）₂（H₂O） was prepared by the hydrothermal method. Its crystal structure, chemical composition and surface elements were investigated. The results shows that the as-prepared products are Co₇V₄O₁₆（OH）₂（H₂O）. Furthermore, pH, temperature and hydrothermal time which have great impact on the sample size and morphology have been studied. By changing the addition amounts of reactants, products with different morphologies have been prepared. Co₇V₄O₁₆（OH）₂（H₂O） with unique columnar hexagonal pyramid structure has good electrochemical performance. The capacity can stay at around 252 mA h g^-1 after 300 cycles at a current density of 1000 mA g^-1. On the basis of the study, precursors with different sizes have been obtained by controlling the hydrothermal temperature. 3D hierarchical structure Co₃V₂O₈ can be prepared after heat treatment of the precursors. The structure and morphology of the materials were characterized to study the relationship between hierarchical structure morphology and electrochemical properties. The Co₃V₂O₈ with hierarchical structure derived from the 1 um precursor not only keep the original shape of a pencil morphology, the hierarchical structure composed of the nanoparticles are also more loosely, producing more interval holes, thus improving the electrochemical activity. Co₃V₂O₈ hierarchical structure with the size of 1 um exhibits the highest electrochemical reaction activity. And The specific capacity can be as high as 680 mA h g^-1 after 300 cycles under the current density of 500 mA g^-1.Hexagonal Co₂V₂O₇·3.3H₂ O nanosheets precursor was prepared using precipitation methods. The porous hexagonal Co₃V₂O₈ nanosheets could be obtained after sintering. Studies on the influence of different sintering temperature on the sample morphology and performance have been adopted. The results show that the samples obtained at 450 o C exhibit excellent electrochemical performance.BET surface analysis found that the specific surface area of the materials was 14.17m2 g^-1, Charging and discharging test showed that the capacity under the current density of 1000 mA g^-1 decline in the early stage but rise gradually, and remains steady at 1900 mA h g^-1 after 750 cycles. Interfacial storage mechanism have been put forward to explain this special capacity change phenomenon. Porous Co₃V₂O₈ single chip gradually stratificate in the process of charging and discharging, thus increasing areas and hole volume can induce more active sites. Its increasing layer space and hole numbers provide more lithium storage space. With the evolution of morphology, the interface between Co O and amorphous Lix V2O5 array increased,which could provides more lithium ion storage interface.