| 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 LiVPO4F and Li3V2(PO4)3 as cathode materials for rechargeable lithium batteries.The cathode material LiVPO4F was prepared by carbothermal reduction reaction. The effect of synthesis conditions on the physical performance and electrochemical behavior of LiVPO4F was studied and the synthesis conditions were optimized. The results showed that with the increase of sintering temperature, the growth of crystal is quickened and the crystal becomes more perfect. The grains are breaked easily and new phase of Li3V2(PO4)3 forms if the temperature is too high. It was also found that the specific capacity and cycling performance of LiVPO4F vary with synthesis conditions, while the charge-discharge curves are similar. The initial discharge capacity of LiVPO4F synthesized on the optimized condition is 119 mAh·g-1, and the capacity retains 89 mAh·g-1 after 30 cycles.The modification of LiVPO4F by doping was studied. The effect of the content of Al-doped on the structure, morphology and electrochemical properties was investigated. The results indicate that doped-Al does not affect the structure of the material but can considerably decrease the cell volume. Appropriate amount of doped-A1 can make the particle size of LiV1-xAlxPO4F smaller. The initial charge and discharge capacity of LiV1-xAlxPO4F samples are decreased but the corresponding coulombic efficiency and cycling performance are enhanced. LiV0.97Al0.03PO4F exhibits good cycling performance. The capacity fading of LiV0.97Al0.03PO4F is only 13.7%, but the capacity fading of LiVPO4F is 25.2%. The LiV1-xAlxPO4F samples were studied by AC impedance and it was found that LiV0.97Al0.03PO4F shows the lowest Rct value and the biggest exchange current density. The difference between the oxidation potential and the reduction potential of LiV0.97Al0.03PO4F is samller by 0.05V than that of LiVPO4F, indicating the enhancement of the reversibility of electrode reaction due to doping. Though modification by doping can enhance the cycling performance of the materials, their capacity fading is still notable.Synthesizing technologies of LiVPO4F with much lower temperature and shorter time was first exploited by sol-gel method in aqueous solution. It was found that the proportion of starting materials, pH of complex solution, sintering temperature and time are very important for the characteristics of LiVPO4F. Electrochemical test showed that the initial charge and discharge capacities of LiVPO4F powder synthesized on the optimized condition are 150,136mAh·g-1 respectively, the capacity fading is only 14.7% after 100 cycles, especially, cycling performance at 1C is improved.Li3V2(PO4)3 was prepared by carbothermal reduction reaction. The effect of synthesis conditions on the physical performance and electrochemical behavior of Li3V2(PO4)3 was studied and the synthesis conditions were optimized. The results show that the sintering temperature and time play an important role in the crystal structure and morphology of Li3V2(PO4)3. The Li3V2(PO4)3 material synthesized at 800C for 20h has perfect crystal structure and narrow particle size distribution. The specific capacity and cycling performance of Li3V2(PO4)3 vary with the synthesis conditions, but the charge-discharge curves are similar. The Li3V2(PO4)3 samples synthesized on different conditions were studied by AC impedance. It was found that the Li3V2(PO4)3 material synthesized at 800℃for 20h shows the lowest Rct value and the biggest exchange current density. Cyclic voltammetry was performed and three couples of oxidation and reduction peaks were identified, which is in well agreement with the first charge-discharge curve.Li3V2(PO4)3 was prepared by low temperature solid-state reaction with V2O5·nH2O hydro-gel, LiOH·H2O, NH4H2PO4 and C as starting materials.Compared with the carbothermal reduction reaction, lower sintering temperature and shorter sintering time are involved in the low temperature solid-state reaction. The results show that the sintering temperature and time are important for the crystal structure and morphology of Li3V2(PO4)3. The optimized sintering temperature and time were 550℃and 12h. Electrochemical test showed that the initial discharge capacity of Li3V2(PO4)3 powder synthesized at the optimized conditions is 130mAh g-1, the capacity fading is only 11.5% after 100 cycles, especially, and the cycling performance at 1C is improved. The Li3V2(PO4)3 samples synthesized on different conditions were studied by AC impedance. It was found that Li3V2(PO4)3 synthesized at 550℃for 12h shows the lowest Rct value and the biggest exchange current density. The Li3V2(PO4)3 sample was investigated by cyclic voltammetry and three couples of oxidation and reduction peaks were found, which is in well agreement with the first charge-discharge curve.The kinetics behaviors of LiVPO4F and Li3V2(PO4)3 were studied by means of linear sweep voltammetry and the potentiostatic intermittent titration technique (PITT). It was found that the exchange current density is increased with Li interacted into LiVPO4F and Li3V2(PO4)3. And the magnitude level of diffusion coefficient (Dli+) in LiVPO4F and Li3V2(PO4)3 material is 10-13,10-14 cm2.s-1 respectively. Doping and synthesized method can affect the exchange current density and diffusion coefficient (Dli+).
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