The Synthesis And Modification Of Lithium Iron Phosphate As Cathode Material In Lithium Ion Battery

Olivine-type lithium iron phosphate (LiFePO4) has a high theoretical specific capacity of170mAh/g as a cathode material of lithium ion battery. Li+deinsertion/insertion occurs at apotential value of ca.3.45V vs Li+/Li. It has been extensive studied for its cheap, abundantresources, nontoxic, high theoretical capacity and good cycling stability characteristics, butit’s low conductivity and lithium ion diffusion rate make the capacity decay rapidly whencharge and discharge at high rates. Therefore, to improve these drawbacks are the key issuesof lithium ion battery research. In this paper, we synthetized LiFePO4through solvothermalmethod, modified its electrochemical performance in situ adding graphene oxide (GO) inchemical and physical two ways.Olivine-type LiFePO4was synthesized via solvothermal method, regular nanoscaleOlivine-type LiFePO4particles were obtained by adjusting the ratios of DMF to H2O, theconcentration of reactants and addition of sucrose. The results indicated that the regularnanoscale Olivine-type LiFePO4particle could be synthesized when the ratio of DMF toH2O was3:1, the concentration of FeSO47H2O was0.05mol/L(Fe:P:Li=1:1:3), the additionof GO and sucrose have no big effect on the size and morphology of LiFePO4, but when theconcentration of sucrose is too large the particles will occur agglomeration.LiFePO4/Graphene composites were obtained by adding GO with differentconcentrations into precursor. The results showed that the composites have the bestelectrochemical performance with the concentration of GO was2mg/mL, reaction time was15h, annealling time and temperature were3h and500°C separately. The capacity was161.1mAh/g when charged and discharged at0.2C, but the cycling stability was poor. Thenwe introduecd sucrose with different concentation into precursor to investigate the effect on electrochemical performance caused by the addition of sucrose.The results showed that theLiFePO4/Graphene/C composites had better rate performance and cycling stability when themass ratio of sucrose to GO were30:1and50:1.In another way, we blended GO with synthetized LiFePO4physically to improve itselectrochemical properties. The results showed that when the mass ratio of LiFePO4to GOwas100:2, the LiFePO4/G2composite had the best electrochemical performance, whencharged and discharged at0.2C the initial discharge capacity reached164mAh/g, thecapacity reached80mAh/g when at5C.