The Modification Of Lithium Vanadium Phosphate As Cathode Materials

With the development of economy, the problem of environmental pollution is becoming more and more obvious. The management of the atmospheric environment as well as the continuous development of green energy and environmental protection materials become the promising filed. Lithium ion batteries are considered as the most ideal energy storage material because of their high energy, long cycle life, green environmental protection and other advantages. In recent years, poly anionic phosphate cathode materials has become the hotspot because they have high theoretical capacity, good cycling performance, low price and safety. Li3V2(PO4)3 cathode materials are considered as the promising cathode materials for lithium ion batteries with the advantages of good cycling performance and high theoretical capacity of 197 mAh g-1.As the representative of the traditional carbon sources, glucose and citric acid were used as the source. Li3V2(PO4)3 coated with glucose or citric acid were synthesized via rheological phase reaction method successfully. The structure tests show the fact that all samples are pure phase monoclinic. Carbon coating enhances the growth of the particles,improves cycle performance and rate performance. The discharge capacity of glucose and citric acid are 136 m Ah g-1 and 123 mAh g-1 respectively, higher than that of original one. It is found that the effect of glucose coating on the discharge capacity and cycling performance of the materials is remarkable, while the effect of citric acid on the rate properties of the material is more excellent.In addition, LVP/C has been successfully prepared via rheological phase method withβ-cyclodextrin, a new type of carbon source. And for comparison, uncoated sample was synthesized via the same method. XRD patterns demonstrate the pure monoclinic structure of the coated sample, and sharper diffraction peaks indicate a better crystallinity. The images of SEM show the uniform and optimized particles size, which greatly improves the electrochemical performance. In the 3.0~4.3 V voltage, 0.1 C rate discharge, the first week of the discharge capacity of coated material is 111 mAh g-1at the first week and remains at109.3 mAh g-1 after 50 galvanostatical cycles.Besides, LVP/C samples coated with different amount of alginic acid were successfully prepared via rheological phase method. The best amount of carbon was explored. Microstructure and electrochemical properties show that the best coating amount is 10%. XRD patterns demonstrate the pure monoclinic structure of the coated samples, andsharper diffraction peaks indicate a better crystallinity. The images of SEM show the uniform and optimized particles size. The 10% sample has the smallest particle size of about 0.8 μm. Under 3.0~4.8 V, its initial capacity is 157.6 m Ah g-1 and can maintain at121.1 mAh g-1 after 80 cycles. It shows excellent cycle performance and rate capability.Compared with β-cyclodextrin coating sample, the electrical properties of alginic acid coating material has been enhanced, but the difference between the two sample is not obvious.