Preparation And Electrochemical Performance Of Low Dimensional Lithium Vanadium Oxides As Cathode Materials For Lithium-ion Batteries

Lithium vanadium oxides as cathode materials have the properties of high capacity and low cost, which make them become one kind of the most evaluative potential cathode materials for lithium ion batteries. Low-dimensional materials with high specific surface area and small size can efficiently improve the electrochemical properties of electrode materials.The macroscopic performance of electrod material in lithium ion battery was measured by half cell method usually. Minor research was facus on the micromechanism of lithium ion batteries three-electrode system in electrochemical field. The electrochemical properties of electrode materials are measured by electrochemical workstation with three-electrode system. For three-electrode system, the insitu performance tests can be done. The operation of three-electrode system is easy and the results are stable with high accuracy.In this work, V₂O₅ and LiV₃O₈ materials with micro-nano-structure were studied. The V₂O₅ and LiV₃O₈ fibers were synthesized by electrospinning, and the LiV₃O₈ films were synthesized by spin-coating method. The structure and morphology of V₂O₅ and LiV₃O₈ were characterized by X-ray diffraction（XRD） and scanning electron microscope（SEM） techniques. The electrochemical properties of V₂O₅ and LiV₃O₈ were tested by electrochemical workstation through three-electrode system. The micromechanism of charge-discharge of LiV₃O₈ films were also analyzed by electrochemical strain microscopy（ESM）. The results are as follows:1. The different concentration of V₂O₅ fibers were synthesized by electrospinning with V₂O₅ powder and 30% H₂O₂ solution as raw material, the precursor fibers were dried then thermal annealing at 500 oC in air for 1 h. The optimum electrochemical properties was obtained in V₂O₅ fiber with 0.21 mol/L concentration, and the diameter distribution of V₂O₅ fiber was in the range of 200 to 400 nm. It was shown in Chronopotentionmetry（CP） curves that there was the highest specific capacity of the optimum samples, which indicated the good reversibility of V₂O₅ fiber in the electrochemical processes.2. For improving the solubility and stability of V₂O₅ solution, LiV₃O₈ solution were prepared by using V₂O₅ powder, LiOH·H2O powder and 30% H₂O₂ solution as raw materials. LiV₃O₈ films were synthesized by sol-gel spin-coating method. The effect of different annealing temperature and time on morphology, structure and electrochemical properties of LiV₃O₈ films cathode materials were studied. The optimum electrochemical properties was obtained in the LiV₃O₈ film, which was sintered at 400 oC in air for 10 h, and the corresponding grain size of the thin film was from 50 to 200 nm. Obvious anodic oxidation and cathodic reduction peaks after fifth cycle were shown in CV curves of the optimum samples. It was observed in the ESM results of the optimum samples that the amplitude response was weaker after discharge and stronger after charge, confirming that the electrochemical strain responses correlated with Li-ion concentration.3. LiV₃O₈ fibers were synthesized by electrospinning. After annealing at 400 oC in air for 1 h, the optimum electrochemical properties was obtained in LiV₃O₈ ceramic fibers with diameter in the range of 130 to 200 nm. CV curves of the optimum samples confirmed that there were three anodic oxidation peaks which corresponded to Li+ de-intercalation, and cathodic reduction peaks which attributed to Li+ intercalation, respectively.