Synthesis And Electrochemical Performance Of LiMnPO₄for Cathode Material Of Lithium-ion Batteries

As the materials of lithium ion battery, olivine-type LiMnPO4has been concerned as a new generation of positive material for its good thermal stability, high theoretical capacity, excellent cycle performance, cheap raw materials and friendly environment. However, LiMnPO4has poor electronic conductivity and low ionic conductivity, which restrict its development. To improve the electrochemical performance of LiMnPO4material, we synthesized LiMnPO4by high temperature solid phase method in this paper. Glucose coating and metal doping were studied to improve the performance of LiMnPO4. The crystal structure, surface morphology, electrochemical properties and microstructure of dynamics of LiMnPO4/C has studied through X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Charge/Discharge performance and Cyclic Voltammetry.The cathode material LiMnPO4/C was synthesized by solid state reaction method using LiH2PO4、MnCO3and glucose as raw materials. The preparation conditions were discussed firstly. The reaction mechanism of synthesizing LiMnPO4was studied by DSC-TG analysis, so we decided the preliminary calcinations temperature is750℃and soaking time is5hour. The condition that synthesized LiMnPO4was determined by carbon modification and different metal doping and iron doping amount. Glucose coating had obviously improved the electrochemical performance and specific capacity was35mA·h·g-1Doping metal ion could also improve the electrochemical performance and moderate iron doping improved the discharge specific capacity from35mA·h·g-1to110.1mA·h·g-1.The influence of different carbon modification and different metal doping and iron doping amount on the structure, morphology, and the discharge specific capacity and cycle performance of LiMnPO4was also studied. We found carbon modification could reduce the partical size of LiMnPO4and improve the internal conductivity and the speed of lithium ion diffusion. Different metal doping could influence the electrochemical performance in which iron doping improve the electrochemical performance signally. By contrast, we found the sample of LiMn0.9Fe0.1PO4/C under750℃-10h had the best electrochemical performance, and the first discharge specific capacity was110.1mA·h·g-1at0.05C, and remained in80mA·h·g-1after cycling50times. And the first discharge specific capacity was40mA·h·g-1at0.2C, and no attenuation after cycling50times.