Synthesis Of LiV₃O₈ Cathode Material For Lithium-ion Battery

Rapid development of economic greatly promotes the development of energy storage devices. Currently, the most widely used storage devices are the lithium-ion batteries （LIBs）. Traditional commercial LiCoC₂ material can not meet the needs of society because of the low capacity, high cost. Monoclinic layered LiV₃O₈, due to high capacity, low cost, easy to prepare, are considered to be the most promising cathode material. However, it exist incompletely reversible phase change during the charge-discharge cycles, resulting in the capacity recession. At present, various methods are proposed to improve the performance of UV₃O₈ material. In this paper, we focus on improving the preparation method, doping and morphology control to prepare a high-performance LiV₃O₈ cathode material.LiV₃O₈ is prepared by a facile alcohol-assisted rheological phase method. X-ray diffraction （XRD）、scanning electron microscopy （SEM） are used to characterize material phase, constant current test, cyclic voltammetry（CV）, electrochemical impedance spectroscopy （EIS） are used to test the electrochemical properties. The results show that materials fabricated at 500℃ for 2h exhibit the best electrochemical performance. At a current density of 0.5C (1C=300 mA g^-1), the maximum discharge capacity of the material is 236.2 mAh g^-1, after 70 cycles, the capacity remains at 213.6 mAh g^-1, capacity retention rate is 90.3%.Fe³⁺ doped LiV_3-xFe)xO₈ （x=0.0,0.1,0.3,0.5）are successfully prepared by rheological phase method calcinated at 360℃ for 10h. XRD results confirm that a small amount of Fe³⁺ doping does not change the material structure and dopant materials reduce the crystallinity of the material. SEM results show that the doped materials are made up of layered nanoparticles, which are facilitates electrolyte penetration and diffusion of lithium ions. The electrochemical test results indicate x=0.1 is the optimal doping level. At a current density of 0.5C, the discharge capacity of LiV2.9Fe_o.1O₈ still reaches to 240.8 mAh g^-1 after 50 cycles. When the current density is increased to 10C (3000 mA g^-1), it delivers a discharge capacity of 147.2 mAhg^-1 at the 100th cycle, showing excellent electrochemical properties. EIS tests show that impedance does not significantly increase during cycles.Different morphologies precursor materials are prepared through the hydrothermal method. The addition of OP emulsifier and the holding time have important effect on the morphology of the precursor. When the holding time changes from 48h-60h-72h, the morphologies of the precursor change from agglomeration nanosheets-nanoribbons-uniform nanoribbons. Sintering the precursor with LiOH, electrochemical tests show that the LiV₃O₈ nanosheet materials display the best electrochemical performance. At a current density of 0.5C, the discharge capacity is 221.1 mAh g^-1 after 60 cycles; at a high current densities （2.0C、5.0C）, after 180 cycles the capacity retention rate remains a high level. Furthermore, the article also given an explanation to the evolution of the material morphology.