Synthesis Vanadium Cobalt Oxide Electrodematerials Of Lithium Ion Battery And Their Electrochemical Properties

Lithium ion batteries which could achieve reversible energy conversion have been draw much interests. As the core component of the LIB, active materials of cathode were faced with some problems, such as, lower theoretical capacity and weaker cycling stability at high rate. While the active materials of anode were still fronted with lower cycling stability even if their theoretical capacity was much higher than the materials of cathode.Both of the inherents limited the application of LIB to some extent. One-step method of calcination and poly-assisted two-step methods due to its simple and easy operating to synthesize LIB materials with special structure have made the modification of materials come ture. Concrete contents were as followed:1. Vanadium pentoxide nanorods with regular morphology were obtained through a one-step Calcining as-synthesized materials of VO(acac)2 method at high temperature in air. The electrochemical results showed that V2O5 nanorods maintained a discharge specific capacity of 226.4 mAh g-1 at 1C after 200 cycles. As the current density was increased to 1500 mA g-1, the nanorods still gained a discharge specific capacity of 142.1 mAh g-1.2. The hierarchical nanosheet-assembled V2O5 ultra micro-spheres with a diameter of about 20 um were obtained using two-step methods:one is the poly-assisted template-free solvothermal reaction; the other is solid sintering of the gained precursors at high temperature in air. The vanadium source, VO(acac)2, and the solvothermal reaction time were firstly investigated the influence on the properties of obtained products. And the optimum experiment conditions were that 0.75 g VO(acac)2 was dissolved into 40 ml the solvent of ethylene glycol and reacted for 17 h. The micro-spheres as active materials of cathode revealed an initial discharge specific capacity of 275.7 mAh g-1 as the current density was 300 mA g-1 and still received a discharge specific capacity of 243.8 mAh g"1 after 200 cycles with the capacity retention rate of 88.43%. Although the current density was added up to 1500 mAh g-1, the micro-spheres still obtained the discharge specific capacity of about 200 mAh g-1 and the capacity retention ratio was as high as 78.41%. The excellent electrochemical properties were attributed to its stable hierarchical nanosheet-assembled spherical structure. Hierarchical structure was beneficial to the charge transport and thus reduced the possible occurring volume expansion.3. Different structure Co3O4 materials as anode of LIB were gained through a same two-step method with Ethylene glycol as solvent. The cobalt source, Co(NO3)2·9H2O, Co(CH3COO)2·4H2O, CoSO4·7H2O, CoCl2·6H2O, and different solvothermal duration(8,12,24 h) were discussed. Accordingly to the top properties, the suitable material was Co (NO3)2·9H2O and the the perfect solvent time was 12 h. The properties of double-shell yolk-shell sub-microsphere through 12 h thermal treatment were superior to the other two samples (8 h-Co single yolk-shell,12 h-Co sub-microspheres,24-Co triple-shell micro-spheres).12-Co samples still obtained the discharge specific capacity 1091 mAh g-1 at a current density of 178 mAh g-1 after 70 cycles. The excellent electrochemical performance was mainly ascribed to its special yolk-shell structure, which not only could shorten the transport distance of electron and ion but also could effectively reduce the volume effect generated during the charge and discharge process.4. Compared to different V/Co molar ratio (5:1,3:1,2.5:1,2:1), the phase, structure and electrochemical properties of the obtained vanadium cobalt precursors through the same two-step method and the corresponding calcination samples was changed. When the V/Co molar ratio was 2.5:1, the synthesized two phase hollow CoV2O6 microspheres through the sintering process as LIB anode materials at 400? showed a discharge specific capacity of 315.6 mAh g-1 at a current density of 500 mA g-1 after 100 cycles. The hollow structure and the synergy effect of complex oxides had an important effect on the electrochemical properties.