Synthesis And Modification Study On LiFePO₄ Cathode Material

The cathode materials of LiFePO₄ has been considered as one of the most promising ideal power of hybrid vehicles or electric vehicles,and it became the field of energy storage lithium-ion battery research and production development focus,due to its environment friendly,high theoretical capacity,ideal thermal stability,and good security,etc.However,it has suffered with its low electronic conductivity and lower lithium diffusion kinetics for its construct limitation,which have seriously restricted its application.In this work,Lithium iron phosphate powder was prepared by solvothermal method.Sodium hydroxide worked as lithium source,ferrous sulfate worked as iron source,phosphoric acid worked as the source of phosphate and ethylene glycol worked as solvent and reducing agent.Analysis the structure and electrochemical influence of the order of addition?Li-PO₄-Fe,Fe-PO₄-Li?,adding proportions and Cobalt content to LiFePO₄.Characterized the content and morphology of sample by XRD,SEM,and EDS.The electrochemiacal performance of samples were tested by Cyclic voltammetry.Then,the TiO₂/LiFePO₄ composites were prepared by secondary solvothermal method.Olivine-type lithium iron phosphate prepared by solvothermal method.By changing the order of addition and the ratio of lithium source,an iron source,phosphorus source,LiFePO₄ powder have different morphology including spindle-shaped,sheet,flat balls and particulate.When the order of reactants addition of lithium iron phosphate powder is Li-PO₄-Fe,and the reaction ratio of Li:Fe:PO₄ is 3:1:1,LiFePO₄ powder showed a spindle-shaped monodisperse,the particle size distribution is uniform.After 20 cycles,its discharge capacity was 61.9mAh/g,first charge and discharge efficiency was 90.1%.When the doping amount of Cobalt was 25mol%,Co ions of different doping content were successfully incorporated into the crystal lattice LiFePO₄ and form solid solution.The Cobalt-doped lithium iron phosphate powder appeared spherical and has good dispersion.Compare with LiFePO₄,the cryatal of sample which doped Co ion has a smaller Crystal unit cell volume and shorter the b-axis length and have a better performance.After 20 cycles,its discharge capacity was 65.8mAh/g.the discharge capacity retention ratio was 94.8%.Anatase TiO₂ was added during preparation LiFePO₄ via solvothermal method.We found that nano-TiO₂ can be uniformly dispersed in the lithium iron phosphate particles.when the addition content of TiO₂ was 5mol%,lithium iron phosphate cathode material has better electrochemical properties.After 20 cycles,its discharge capacity was 68.8mAh/g,the discharge capacity retention ratio was 81%.