Ball Milling Assisted Sol-Gel Method Synthesize Li₃V₂（PO₄）₃/C Cathode Material And Study On Its Modification

Ball milling assisted sol-gel method was used to synthesize Li3V2(PO4)3/C, and Li3(VyLix)2(PO4)3/C, particles coated by ZnO, modification of morphology and polyanion substitution were used to improve its electrochemical performance, respectively. In the end, effects of different carbon content on lithium diffusion coefficient of the samples were inverstigated. XRD, SEM, TEM, TEM-EDS, CV, EIS and charge-discharge experiments were used to inverstigate the effects of synthetical route and modified methods on structures, morphologies, electrochemical performance and diffusion coefficient of lithium of the final products.The synthetical technology of Li3V2(PO4)3/C indicated that calcined temperature and time, carbon contents and amounts of oxalic acid all effected its morphology and electrochemical performance. When charge and discharge at1C, initial discharge capacity was121.2mAh·g-1,50th discharge capacity was120.9mAh·g-1, capacity retention rate was99.75%.Modifying studies on Li3V2(PO4)3/C indicated that Li3(VyLix)2(PO4)3/C, Li3V2(PO4)3/C coated by ZnO, and modification of morphology were all able to improve its electrochemical performance.①whenx=0.06,Li3(VyLi)2(PO4)3/C possessed the best electrochemical performance. Initial discharge capacity and capacity retention rate was5.0mAhg-1and2.3%higher than those of x=0, respectively.②When the ZnO content was5%, capacity retention rate was12.6%higher than that of0%at1C in the potential of3.0-4.8V.③optimizing sol-gel and ball milling route to obtained ultrafine particles with narrow size distribution, and about10nm carbon layer well covered on the suface. Discharge capacities of the sample were as high as122.6and113.8mAh·g-1at5C and10C, respectively.50capacity rentention rate was100%at1C.Diffusion dynamics study on Li3V2(PO4)3/C indicated that carbon content had signficant effection on lithium diffusion coefficient. Among them, sample with7.5%carbon content possesses the highest lithium diffusion coefficient. In solid phase, lithium diffusion coefficients are1.025×-10,3.046×10-10and0.701×10-10cm2·S-1, which corresponds to the three oxidation peaks in CV curves, and those of the first and third reductive peaks are1.436×10-10and2.056×10-10cm·S-1, respectively. In liquid phase, lithium diffusion coefficients are0.504×10-7,1.075x10-7and0.163×10-7cm2·S-1and0.507×10-10,0.133×10-10cm2·S-1, respectively. The lithium diffusion coefficients correspond to residual reductive peak are increasing by the carbon content.