Synthesis And Electrochemical Performance Of LiV₃O₈Cathode Materials For Lithium Ion Batteries

Currently, the development of mobile phones, laptops and pure electric vehicles greatly promote the development of lithium ion batteries. However, the cathode material has been a bottleneck in the development of lithium ion batteries. Monoclinic LiV3O8has excellent intercalated-Li performance with advantages of high specific capacity, easy preparation and low cost when used as lithium-ion battery cathode material, but its electrochemical performance is significantly affected by preparation methods, and the capacity drops rapidly with cycling. To improve LiV3O8electrochemical properties, we take the modification research by meas of controlling morphology and surface coating. The main research contents and results are as follows:1. Cookies-shaped LiV3O8materials were successfully synthesized by a facile ethylene glycol-assisted sol-gel method. The LiV3O8compound fabricated at550℃delivers an initial specific discharge capacity of255.2mAh g-1between2.0and4.0V at a current density of50mA g-1, and possesses the capacity retention of90.2%after50cycles. Furthermore, the compound also shows good rate capability. By analysis of inductively coupled plasma emission spectrometer (ICP), the cookies-like LiV3O8has very little dissolution of vanadium in the electrolyte after100cycles, indicating good electrochemical reversibility and structural stability.2. Hierarchical plate-arrayed LiV3O8is synthesized by freeze drying method with polyacrylamide (PAM) as surfactant followed by calcination at500℃. As a cathode material for lithium-ion batteries, the plate arrayed LiV3O8delivers high discharge capacities of133.7and111.8mAh g-1at the200th cycle at current densities of1500and3000mA g-1respectively, with capacity retentions of99and90%from the15th to200th cycles. Electrochemical impedance spectroscopy (EIS) test indicates that the LiV3O8electrode always has very low impedance during the3rd to180th cycles. The improved electrochemical performance is attributed to the high crystallinity and the uniform arrayed structure of LiV3O8, which can facilitate the fast electron transport and Li ion diffusion in the electrode, and make the electrolyte penetrate quickly, thus leading to greatly-improved cycling performance at high current densities.3. Surface coated-LiV3O8cathode materials with Al2O3are successfully synthesized via the facile thermolysis process of Al(NO3)3. The0.5wt.%Al2O3-coated LiV3O8exhibits an enhanced cyclic stability at various charge-discharge current densities. At a current density of100mA g-1, it delivers an initial specific discharge capacity of283.1mAh g-1between2.0and4.0V, and still obtains205.7mAh g-1after100cycles. Under higher current densities, Al2O3-coated LiV3O8also shows better cycling stability than the pristine one. Cyclic voltammerry (CV) tests show that Al2O3coating can hinder the irreversible phase transition of the LiV3O8material, meanwhile the Al2O3coating layer acts as a protective shield to prevent the active material from direct contact with electrolyte and depresses the dissolution of V ion in the electrolyte, hence reducing the capacity fading of the electrodes.