Preparation And Modification Study Of Cathode Material Li₃V₂（PO₄）₃for Lithium-ion Batteries

More and more attention are focused on Li₃V₂（PO₄）₃which has NASICONstructure as the cathode material of lithium ion battery for its high safety and highspecific capacity recent years.In this paper,pure monoclinic Li₃V₂（PO₄）₃was produced by sol-gel method.The effects of LiOH concentration, the temperature and time of calcination on thestructure and electrochemical properties of Li₃V₂（PO₄）₃were investigated. Theresults showed that the optimal reaction conditions were determined as theconcentration of LiOH equaled0.3mol/L at a calcination temperature of750℃for10hours. Under the optimal conditions, the product showed uniform particle sizedistribution and the best electrochemical performance.To improve the electronic and ion conductivity of Li₃V₂（PO₄）₃,themodification of Li₃V₂（PO₄）₃was studied by doping Ni²⁺and Co²⁺in this paper. Thedifferent samples such as Ni²⁺、Co²⁺and their mixture were synthesized by sol-gelmethod. A lot of techniques such as x ray diffraction （XRD）, transmission electronmicroscopy （TEM）, accompanied with charge/discharge curves and electrochemicalimpedance spectroscopy were employed to reveal the effect of different ions dopingon the structures and electrochemical properties of Li₃V₂（PO₄）₃. Results showed,the monoclinic structure of Li₃V₂（PO₄）₃was not changed by doping Ni²⁺and Co²⁺,the electrochemical performance was best when the amount of Ni²⁺doping was5%while the amount of Co²⁺doping was3%, and the cell volume was reduced, thestructure is more stable, the conductivity increased and the polarization of batterywas restrained during charge-discharge process due to doping Ni²⁺and Co²⁺, theirelectrochemical performance especially charged and discharged under heavycurrent rate enhanced significantly., The results of the sample ofLi₃(Ni_0.05Co_0.03V_0.92)₂（PO₄）₃obtained by Ni²⁺、Co²⁺mixture doping showed,synergistic effect was found due to the mixture doping, at the same time，thedischarge capacity was increased and the electrochemical performance and cyclelife especially charge and discharged under heavy current rate enhancedsignificantly，the electronic conductivity was improved greatly.The effect of glucose coated on the surface of Li₃V₂（PO₄）₃on electrochemicalproperties was investigated. Results showed that when the amount of glucose was 10%, the conductivity and electrochemical reversibility of Li₃V₂（PO₄）₃wereimproved significantly and the polarization of battery decreased. Theelectrochemical performance and discharge special capacity were improved whenthe battery charge and discharged under low current...