Studies On Synthesising And Performances Of Vanadium-Based Cathode Materials For Lithium Ion Batteries

Monoclinic Li3V2(PO4)3has attracted much attention due to high reversible capacity, high operate voltage, good thermal tability and low cost. However, the main drawback of pristine Li3V2(PO4)3is its intrinsicly low electronic conductivity(2.4×10-7S·cm-1) which greatly limits its practical applications in lithium ion batteries. Aim to overcome this problem, carbon coating and ion doping have been widely used and many positive effects have been reported.In this work, Li3V2(PO4)3has been synthesized via a sol-gel route using NH4VO3、CH3COOLi·H2O、NH4H2PO4as raw materials. Citric acid was used as reducing agent. TG、XRD、SEM、TEM and EIS were adopted to investigate the effect of reaction temperature and the molar ratio of n(Li)/n(V) on the morphology, structure and electrochemical performance of Li3V2(PO4)3.It showed that the optimum conditions of preparing Li3V2(PO4)3were listed as follows:the molar ratio of n(Li):n(V):n(P)=3.1:2:3, the precursor then was calcined at750℃for6h. The initial discharge capacity of the cathode was127.7mAh·g-1and it nearly didn’t fade after30cycles.In order to improve the electronic conductivity of lithium vanadium phosphate, the effects of doping ion(Ce3+、Na+) on the electrochemical properties of Li3V2(PO4)3were studied in detail. XRD patterns show that doped materials display different crystal lattice parameters and cell volume which may be helpful to electrochemical properties. Among doped materials, Li3V1.95Ce0.05(PO4)3and Li2.98Na0.02V2(PO4)3shows excellent cycle performance and rate performance.Layered LiV3O8has been considered to be one of the most promising cathode materials for lithium-ion bateries because of its high capacity(theoretical capacity is about372mAh·g-1) and inexpensive cost. In this paper, LiV3O8was synthesised with NH4VO3、CH3COOLi·H2O as raw materials via sol-gel method. Besides this, we successfully prepared Cl-doping LiV3O8-xCl2x samples to improve the cycle stability of LiV3O8. Charge-discharge results showed the first discharge capacity of undoped LiV3O8cathode was250.7mAh·g-1which was higher than Cl-doped samples. Proper amount Cl doping (x=0.03) can markedly improve the cycle of LiV3O8at the expense of first discharge capacity.