Synthesis And Electrochemical Properties Of Doped Lithium Vanadium Phosphate Electrode Material

As one of most promising candidate materials for lithium-ion batteries, lithiumvanadium phosphate as cathode materials have attracted substantial attention relying onits high safety, easier to judge of charged state, and good cycled stability, etc. In thispaper, we mainly discussed the properties of lithium vanadium phosphate, using thehigh-temperature solid-phase and sol-gel method to prepare monoclinic lithiumvanadium phosphate material with multiple charge and discharge platforms. In order tofind out the optical process parameters, we explored different synthesis methods,different sintered temperatures, and different sintered time. Afterwards, by dopingmodification, we look forward to the develop high-performance cathode material oflithium vanadium phosphate. Main works were followed:（1）Li₃V₂（PO₄）₃/C cathode material. Studying the electrochemical performancedifferences of Li₃V₂（PO₄）₃,prepared by solid-phase method and sol–gel method.Experiments showed that the materials of cycle performance synthesised from sol-gelmenthod was better than solid-phase method, the material properties to sinter10h wasbetter than20h, and better cycle performance with14%sucrose. Moreover in sol-gel,when the ratio of citric acid and LiOH.H₂O reached1/2, the cycle performance ofmaterial was superior to others.（2）Li₃V_2-xCr_x（PO₄）₃/C cathode material. We have studied confirmed that the Crcontent of Cr existed an optimum value（x=0.1）, namely Li₃V_1.9Cr_0.1（PO₄）₃/C material,prepared by sol–gel. Li₃V_2-xCr_x（PO₄）₃/C（x=0,0.1,0.25,0.5） materials, The initialdischarge specific capacity of Li₃V_1.9Cr_0.1（PO₄）₃/C material was higher than othermaterials, and the capacity retention rate was slightly lower than thatLi₃V_1.75Cr_0.25（PO₄）₃/C, but capacity retention rate of Li₃V_1.75Cr_0.25（PO₄）₃/C was the best. In a word, Li₃V_1.9Cr_0.1（PO₄）₃/C had a better comprehensive electrochemical performance.（3）Li₃V_2-xAl_x（PO₄）₃/C cathode material. Similarly, experiments showed that thecontent of Al had an optimal ratio （x=0.1）, prepared by sol-gel to synthesis Li₃V_2-xAl_x（PO₄）₃/C （x=0,0.1,0.2,0.5）, namely Li₃V_1.9Al_0.1（PO₄）₃/C material. The initial dischargespecific capacity of undoped sample was reached to the highest, then decreased with theAl3+content increased. The capacity retention rate initial increased and then decreasedafter100cycles of the initial discharge capacity. It reached to95.8%with an optimum Alcontent of0.1.（4）Li₃V_1.9Cr_0.1-xAl_x（PO₄）₃/Ccathodematerial.The material of Li₃V_1.9Cr_0.1-xAl_x（PO₄）₃/C （x=0,0.02,0.04,0.06,0.08,0.10）obtained from sol-gel method. Below1C rate, thecapacity first increased then decreased with increasing Al content after100cycles. Whenthe content of Al was0.04, the capacity retention rate of Li₃V_1.9Cr_0.06Al_0.04（PO₄）₃/C wasthe best, and almost100%. The discharge capacities were higher than other materialswith a low magnification and a high magnification. The comprehensive properties ofLi₃V_1.9Cr_0.06Al_0.04（PO₄）₃/C were the best. In55℃and the magnification of0.5C, Li₃V_1.9Cr_0.06Al_0.04（PO₄）₃/C、Li3V1.9Cr0.04Al0.06（PO₄）₃/C、Li₃V_1.9Cr_0.02Al_0.08（PO₄）₃/C were chargedand discharged, the capacity increased with increasing the content Al3+after100cycles.However, the capacity retention rate first increased then decreased with increasing theAl3+content.（5）Li₃V_2-xCo_x（PO₄）₃/C cathode material. We used the same method （sol–gel） tosynthesisLi₃V_2-xCo_x（PO₄）₃/C（x=0,0.04,0.1,0.2）.After100cycles below0.5C magnification, the specific capacity first increased then decreased with increasing Co content. Whenthe content of Co reached to0.1, the specific capacity of Li₃V_1.9Co_0.1（PO₄）₃/C was thehighest, and the capacity retention rate was reached to98.4%.