Study On Synthesis, Doping And Property Of Vandium Oxide As Cathode Materials

Compared with the traditional cathode materials like LiCoO2, the layer V6O13and VO2(B)have advantages such as high specific capacity, high energy density, synthesised easily, andthe materials cheaply, etc. Because of high value of application, more and more researchersregard V6O13and VO2(B) as a new generation Li-ion cathode material which have potential ofdevelopment and application. The synthetic methods of vanadium oxide are solid phasemethod and hydrothermal method, but these are difficult to prepare the pure phase forvanadium oxide because the condition of the synthesis and influencing factor are difficult tocontrol. The solvothermal produce the compound that has special valance, can control themorphology of the product, can dope uniformity, and so on.In this paper, we prepared V6O13by solid phase method and hydrothermal method, andprepared V6O13and VO2(B) by solvothermal. After comparing with electrochemicalperformance of vanadium oxide by different method, we found that the vanadium oxideprepared by solvothermal had good electrochemical performance. In this paper, the syntheticprocess of solvothermal was researching primarily, discussing the solvothermal syntheticprocess of V6O13and VO2(B) respectively. We also discussed the influence of product phaseand electrochemical performance by the proportion of ethanol and water, the holdingtemperature and the holding time of solvothermal, calcination temperature and otherconditions, finally got the optimal process of prepared electrochemical performance.To improve structure stability of V6O13and VO2(B) during the insertion and extraction ofLi ion, we doped Mn2+, Ni2+into V6O13respectively, and doped Cu2+, Ti4+into VO2(B). Wesynthetized the bulk and tubular MnV2O6by solvothermal at the same time, and preliminarydiscussed the charge and discharge performance of the MnV2O6. After doping Mn2+, Ni2+intothe V6O13, would find that Mn2+or Ni2+can be doped into the crystal lattice of the V6O13cathode materials. The V6O13morphology had changed after doping, the structure stability ofV6O13and VO2(B) during the insertion and extraction of Li ion had improved afterdoping,the electric conductivity had also improved. The CV and EIS text indicated that Mn2+or Ni2+replaced the vanadium position, the degree of destruction of materials had reducedduring the insertion and extraction of Li ion, the capacity attenuation had restrained, the cycleperformance also improved. After doping Cu2+into the VO2(B), with Mn2+doping, the Fermilevel of Li in VO2(B) and the conductivity had improved, that improved ability of the Liions insertion and extraction and the charge and discharge stability. When the amount of doping Cu2+is1.03at.%, the charge and discharge performance of VO2(B) had improved atlow and high rate, the discharge specific capacity for the first time is317.1mAh/g at0.132C,after51cycles, the specific capacity still kept234.3mAh/g. After doping Ti4+into VO2(B),it made the cathode materials have the high electrical conductivity and improved the ability ofLi insertion and extraction and the structure stability, especially improved the cathodematerials charge and discharge performance at high rate. When the amount of doping Ti4+is0.68at.%, the specific discharge capacity of VO2(B) was171mAh/g at6.563C, and keep83.6%after50cycles.The discharge specific capacity of bulk MnV2O6was409mAh/g at the electric currentdensity was40mA/g, but the capacity attenuated fast.The tubular MnV2O6can reduce thedistance of Li ion diffusion at the interface, thus lead to the MnV2O6form amorphous stateduring the charge and discharge process, the discharge specific capacity was216mAh/g at theelectric current density is40mA/g, the structure would destroy during the cycles process, theperformance also reduced.