| In the modern world, the energy issue has become an important factor restricting the development of economic and social. The development of renewable and environmentally friendly new energy is an approach to alleviate this problem. Lithium ion batteries have been widely used in the field of electric vehicle and portable electronics for the advantages of high energy density, non-pollution etc. As an important part of LIBs, cathode material is a key to the development of lithium ion batteries. Polyanion-type material, Li3V2(PO4)3, have attracted more attention for its high energy density, capacity, safty, environmental-friendly etc. In this paper, we mainly introduce the synthesis of carbon coated Li3V2(PO4)3 by rheological phase method and hydrothermal method and the study on the structure, morphology and electrochemical property. The details of the paper are as follows:1. The Li3V2(PO4)3 are prepared using a simple and practical rheological phase method. Under the coaction of citric acid and glycine, spherical particles with size of 1-2 u m have been obtained. The XRD and Raman spectrums demonstrate that the residual carbon in the material are amorphous, which have no influence on the material structure. In the range of 3.0-4.3 V, the specific discharge capacity can maintain 89 mA hg-1 at 25 C rate, which is better than that of pure-Li3V2(PO4)3. When operated at 5 C and 10 C rates after 120 cycles, the capacity retention are 98.1% and 94.4%. Good electrochemical properties are maintained at 55 ℃.2. Hydrothermal method is used to synthesize Li3V2(PO4)3/C. The influences of carbon coated process on the property of the materials are discussed. The results show that the morphology of carbon coated after and during hydrothermal process have little difference. The material with carbon coated after hydrothermal process has an initial discharge capacity of 131.0 mAhg-1 at 0.1 C rate in the range of 3.0-4.3 V, which is closed to the theoretical value.94.4 mAhg-1 can be obtained at 25 C rate and after 100 cycles at 5 C and 10 C rates, the capacity retention are 93.1% and 96.0%. All the electrochemical performances are better than that of the material with carbon coated during hydrothermal process, which demonstrate that the material has good rate performance and cycle performance.3. Flake-like Li3V2(PO4)3/C are prepared via hydrothermal method using diethylene glycol as reductant. The morphology of products are changed by adjusting pH. The XRD show that the products at different pH are monocline. The experimental results show that the morphology of products vary from flake-like to spherical-like with the increasing of pH. When pH=0.5,1 and 2, the products are flake-like and when pH=3.5, the products are spherical-like. After high-temperature calcination at 720 ℃, the thickness of the flake-like particles increase.The product obtained at pH=2 has the best electrochemical performances. In the range of 3.0-4.3 V, the discharge capacity at 10 C rate is 117.3 mAhg-1 and after 100 cycles at 1 C rate, the discharge capacity is 123.6 mAhg-1 with a capacity retention of 97.8%. The difference of electrochemical performances at different pH maybe attributed to the changes of morphology. |
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