Preparation And Modification Of The High Voltage LiMnPO₄ Cathode And Study On The Performance Of Full Battery

During recent years, lithium ion battery has achieved great progress in the energy density and rate capability which is considered the most promising power system for electric vehicle of choce. LiMnP04 has the advantages of low cost, safety, environmental protection, high theoretical capacity and high stable working voltage platform showing great potential in lithium-ion battery. However, as a result of very poor conductivity electrochemical performance is not ideal which limits its application.In this paper, hydrothermal synthesis process optimization of LiMnPO4 material, in-situ carbon coating and synthesis of Li4Ti5O12 anode material have been studied. We also research the microstructure and electrochemical properties of fast ion conductor composite and solid solution materials of metal ion dopied.Li3PO4 micronparticles with narrow diameter distribution and uniform particles were prepared by chemical precipitation method. As the same time, a high voltage cathode material LiMnP04 was synthesized in ethanol water system by hydrothermal method using PEG-400 as organic carbon source, MnSO4·H2O for manganese source. There are a series of optimization of process parameters among the reaction time, reaction temperature, volume proportion of alcohol aand water and the concentration of reactants. Then we use the dual carbon composite of VC and its reduction to improve the electrochemical performance. At last we get the LiMnPO4/C composite cathode with the best performance after heat treatment.We calculate the energy gap of Fe, Mg doped LiMnPO4 by the first principle. At the same time, the corresponding LiMn1-xFexPO4/C and LiMn1-xMgxPO4/C cathode materials were synthesized for experiment verification. The results show that Fe, Mg cation doping does not change the main phase. But the crystal structure parameters changed significantly. The regulation of the energy gap has the direct impact of electronic conductivity of LiMnPO4 material and has a positive relationship with the electrochemical properties. The LiMn3/4Fe1/4PO4C and LiMn23/24Mg1/24PO4/C have the best discharge capacity. The theoretical calculation results are consistent with the experimental results.In this paper, the aluminum based AAO was used for porous hierarchical micro nano structure templatre. Multilevel micro nano structure of LiAlO2 lithium fast ion conductor was prepared by situ hydrothermal method. After heat treatment, the LiMnPO4/C-LiAlO2 nano composite cathode material was obtained. We make use of the conductivity of LiAlO2 fast ion conductor and the excellent electronic conductivity of nano carbon to improve the comprehensive properties. The amount of LiAlO2 has an optimum value and the material discharge capacity increased bu 10%.The PVP and urea were introduced as activator for the lithium salts-TiO2 reaction system to improve the solid phase method in order to synthetize Li4Ti5O12 anode materal. The prepared materials have good discharge capacity, cycleperformance and rate characteristics. It can achieve the theoretical capacity of 95% at 0.5 C.The discharge capacity of the whole cellsystem LiMn23/24 Mg1/24PO4/Li4Ti5O12 assembly reached the theoretical capacity of 80%. The capacity retention rate is more than 90% after 100 cycles. It's a promising battery system.