Lithium-ion Battery Cathode Material Of Lifepo <sub> 4 </ Sub> Synthesis And Modification Of Research

The development of lithium ion batteries and cathode materials were reviewed in detail. The present study focused on the preparation processes, the modification of materials, the structure characterization, the electrochemical properties, and the kinetics behaviors of LiFePO₄ as cathode for rechargeable lithium batteries.The precursor of LiFePO₄ were characterized by differential thermoanalysis thermogravimetry (DTA-TG). The LiFePO₄ cathode for lithium ion battery was synthesized by high temperature solid-state reaction. The effects of synthesis conditions on physical performance and electrochemical behaviors of LiFePO₄ were studied and the optimum conditions were obtained. The potential capacity diagrams for all samples showed the typical flat potential plateau at 3.4V versus Li/Li⁺. The reaction temperatures and time had important effects on the structure and performance of the products. Large amount of compounds formed as impurities at lower sintering temperatures, which decreased the charge-discharge capacity. The capacity loss at higher sintering temperatures was caused by the utilization of large particles being constrained by their small surface area. The products sintered at 650℃ for 20 hours were uniform small particles and showed excellent electrochemical performance. The first specific discharge capacities were 111.6 mAh·g^-1 at 0.1 C rate for this material.The LiFePO₄ was modified by surface treatment. LiFePO₄/C composite were prepared by solid-state reaction with carbon gel. The structure, morphology of particles, carbon contents were analyzed by x-ray diffraction, scanning electromicroscopy and carbon/sulfur determinator. The resulting carbon contents in these samples were 0%, 5 %, 10%, 22%, respectively. The LiFePO₄/C were pure olivine-type phase. The carbon was dispersed between the grains, reducing the LiFePO₄ grain size and ensuring a good electronic contact. The carbon-doped material exhibited excellent performance. The first specific discharge capacity of the LiFePOVC coated with about 22% carbon sintered at 650℃ was 152.8 mAh·g^-1, and the discharge capacity remainded 151.9 mAh·g^-1 after6 cycles. The capacity fade was about 0.6%. Impedance spectroscopy was used to investigate the kinetics behaviors . It was found that the addition of the carbon lead to the reduction of charge-transfer resistant(Rct) and improved charge-discharge performance. The electrochemical behaviors of LiFePOVC were studied by cyclic voltammetry. This voltammogram indicated that only one electrochemical reaction, corresponding to the peak pair shown around 3.4V vs. Li/Li+, occurred during the charge and discharge of the LiFePC>4. The chemical diffusion coefficient of lithium(DLi+) was measured by using the potential step Chronoamperometry method(PSCA). The magnitude level of the Dy+ in LiFePCVCeathodewas lO^-HT1 W-s"1.LiFei_^gxPO4(x?*=0.Gl? 0.05, 0.1, 015) was synthesized by Mg doping. The Mg-