The Fabrication Of Nano-sized Vanadium Compounds And Their Electrochemistry Performances

Compared with conventional cathode materials for lithium-ion batteries,vanadium compounds are considered very promising cathode materials for rich resources,no pollution to the environment and high electrochemical specific capacity.Controlling synthesis of vanadium compounds micro/nano structures and improving its electrochemical performance have been received great attention in recent years.In this paper,nano-sized vanadium compounds such as mesoporous NH₄V₄O₁₀ nanoflowers,ultra-long?NH₄?₂V₆O₁₆·1.5H₂O nanowires,Na_0.33V₂O₅ nanobelts were synthesized by an eco-friendly surfactant assisted a simple and green approach and can be used as cathode materials for lithium-ion batteries.The phase structure and morphology of the products were characterized by X-ray diffraction?XRD?,Fourier transform infrared spectrometer?FTIR?,Brunauer-Emmett-Teller?BET?,Scanning electron microscopy?SEM?,Field emission scanning electron microscopy?FESEM?and Transmission electron microscopy?TEM?.At the same time,the products were assembled into button-type batteries.The electrochemical performances of the products were tested by electrochemical workstations and land battery systems.Besides,the factors which effect morphologies,structures and electrochemical performance were discussed.And the formation mechanisms of the different vanadium compounds micro/nano structures were studied.The main results are as follows:?1?Mesoporous NH₄V₄O₁₀ nanoflowers with clear outline and highly uniform morphologies were prepared by hydrothermal approach?140?,16 h?with NH₄VO₃and H₂C₂O₄.2H₂O as initial materials,?-CD as surfactant.The nanoflowers are composed of nanoflakes with 200-300 nm in width and the length up to micron levels.The nanoflakes also exist mesopores with an average size of 2-4 nm.And,the reaction conditions such as reaction time and the amount of?-CD were investigated.And the Ostwald theory could be used to explain the growth mechanism.The possible growth process and mechanism of the NH₄V₄O₁₀ were also proposed and were expected to prepare other nano-sized vanadium compounds.Finally,the electrochemical properties of the nanoflowers were tested.Compared with different morphology of the NH₄V₄O₁₀material,it was concluded that the nanoflowers electrode has a high rate of lithium transition during the lithiation/delithiation process.The nanoflowers,whether under a small current density or high current density,maintained higher specific discharge capacities and good electrochemical stability.For the nanoflowers,the initial discharge specific capacities of 242.8 mAh g^-1 and 149.4 mAh g^-1 are observed at 200 mA g^-1 and1000 mA g^-1,respectively.Even at 1000 mA g^-1,it still retains 103.5 mAh g^-1?about69.2%retention capacity?after 200 cycles.?2?The ultra-long?NH₄?₂V₆O₁₆·1.5H₂O nanowires with a width of 200-300 nm and a length of more than 150?m were fabricated by chitosan surfactant assisted hydrothermal reaction?180?,24 h?with NH₄VO₃,H₂O₂ and HNO₃ as raw materials.The optimum reaction conditions and mechanism were determined by changing reaction parameters?time,temperature and the amount of H₂O₂?.Besides,the electrochemical properties of the ultra-long?NH₄?₂V₆O₁₆·1.5H₂O nanowires were tested.The results show that the ultra-long nanowires present high electrochemical storage capacity and good cyclic stability.The nanowires deliver initial discharge specific capacity of 183.6 mAh g^-1 at 50 mA g^-1.After 150 cycles,they still retained discharge specific capacity of 161.6 mAh g^-1.?3?The Na_0.33V₂O₅ nanobelts with a width of 150 nm and the length up to micron levels were synthesized by hydrothermal method?140°C,14 h?and then calcination method?400°C,4 h?with NH₄VO₃,H₂C₂O₄.2H₂O,C₂H₄O₂ and NaCl as raw materials.The electrochemical properties of the nanobelts were tested.The Na_0.33V₂O₅ nanobelts can maintain good structural stability and capacitance reversibility during the multi-step intercalation and deintercalation of lithium ion in Na_0.33V₂O₅.It also maintained higher specific discharge capacities and good electrochemical stability under a small or high current density test.It exhibits high specific capacity of 288.5 mAh g^-1 at current density of 200 mA g^-1.Even at 1500 mA g^-1,the nanobelts deliver discharge specific capacity of 205.3 mAh g^-1.After 120 cycles,they still retained discharge specific capacity of 175.3 mAh g^-1?about 85.4%retention capacity?.