Preparation And Electrochemical Characterization Of The Vanadium Oxides Based Compounds As Cathode Material For Lithium-Ion Batteries

In the paper, the development of rechargeable lithium batteries and cathode materials were reviewed in detail. The aims of the present study were to focus on the preparation processes, the modification of materials, the structural characterization, the electrochemical properties, and the kinetics behaviors of the layered vanadium oxides-based compounds as cathode materials for rechargeable lithium batteries.The structural characterization of the precursor and the samples of vanadium oxides-based compounds were measured by means of differential thermoanalysis thermogravimetry (DTA-TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma (ICP). Their Electrochemical behaviors as cathode materials for rechargeable lithium batteries were studied by galvanostatic charge-discharge, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) techniques. The effects of synthesized conditions, structure, particle size, morphology on the electrochemical properties were studied and the prepared conditions were optimized.A new sol-gel the process of preparation V2O5 was proposed. The V2O5 nH2O gel was prepared by dissolving V2O5 in the 10% H2O2 at ambient temperature, and after aging for 4 days. The V2O5T1H2O gel was dried at 100C under vacuum, and gave the precursor V2O5. Heat treatment of the precursor at 320 C for 4h produced V2O5 samples. The charge-discharge and the cyclic voltammogram characteristics were compared with those of the samples of molten V2O5-sol-gel method. The measurements showed that prepared V2O5 by H2O2 - sol-gel method had the first discharge specific capacity of 305mAhg-1 and more than 20% irreversible capacity fading after the first cycle. It could maintain a discharge specific capacity of 190mAhg-1 at 0.1C rate after 30 cycles. The irreversible loss was related to an irreversible phase transformation of V2O5 when the first was discharged to below 2.3V.In order to solving the problems of low conductivity and a relatively low Li+ ion diffusion coefficient in the V2O5 matrix, a series of inorganic-organic hybrid materials (PANI)xV2O5 were prepared from V2O5-nH2O hydro-gels and aniline monomer by in situ oxidative polymerization of aniline in the solution. XRD showed that intercalation ofpolymers expanded the distance of the V2O5 interlayer. The hybrid material (PANI)o.3V2O5 showed the best electrochemical performance among several (PANI)XV2O5. In order to optimize electrochemical performance of the (PANI)0.3V2O5, oxygen post-treatment was carried out by heating the as-prepared samples at 80 C for 10h. The results showed that a reversible specific discharge of 235 mAh g-1 was maintained after 35 cycles at a current rate of 0.1 C, which increased over 10% compared with that of without oxygen post-treated material, and increased over 20% compared with that of the pristine V2O5. Under higher current rate of 0.4C, the corresponding to the value of reversible specific discharge was 160 mAhg-1. The improving of the electrochemical performance by oxygen treatment was probably due to the fact that the reduced V2O5 was re-oxidized and the PANI in the V2O5 interlayer couple oxidative formed longer chains.The LiV3O8 precursor was obtained from V2O5 nH2O hydro-gels and Li2CO3 and dried at 80C for 10h under vacuum. The LT-LiV3O8 (LT: low temperature) sample was obtained after calcination at 350C for 10h. The presence of a small amount of strongly bound water could lead to a larger interlayer distance, and enhanced the mobility of lithium ion in the LiV3O8. Compared with the conventional high temperature (HT) solid phase reaction methods obtained HT-LiV3O8, this method had the advantages of lower synthesis temperature and smaller particle size of the sample. The electrochemical experiments showed that the active material LT-LiV3O8 had the first discharge capacity of 232 mA h g-1 at a current rate of 0.1C, and a reversible specific discharge of 158 mA h g-1 was maintained after 100 cycles. Its the capacity fading w...