Hydrothermal Synthesis And Modification Of Lithium Ion Second Battery Cathode Material LiFePO₄

Olivine-structured LiFePO4, due to its advantages such as low cost, nontoxicity, environmental friendliness and high safety,is considered as a promising cathode material for lithium-ion batteries. However,the commercialization of LiFePO4as cathode material for lithium-ion batteries is limited by its defects such as low electronic conductivity and slow lithium-ion diffusion.In addition,another problem is Fe2+of divalent iron source is easy to be oxidized during the synthesis process of LiFePO4which will lead to difficulties for the preparation; This article contrasts the different influence between air and inert atmosphere protection hydrothermal method. And then modify LiFePO4with L14P2O7coating.During the air hydrothermal method, FeSO4·7H2O, LiOH·H2O and H3PO4were respectively used as iron source, lithium source and phosphorus source. Optimal synthetic route was studied by adjusting three parameters during the common hydrothermal process:reaction temperature and time, concentrations of precursor.The XRD results indicate that the as prepared LiFePO4was well erystallized with olivine structure,Space lattice pmna,and the synthesized Powders show a regular morphology and relatively large particles wih single size between2and5μm as observed by SEM. Electrochemical performance test results show that electrochemical capacity of the material obtained from common hydrothermal method were generally low, in which material prapared from0.15mol/L precursor heated at180μ for4h was relatively better. The first discharge capacity of it was51.4mAh/g in the0.1C charge-discharge magnification, only30%of its theoretical capacity.During the inert atmosphere protection method,raw materials remain unchanged in this method. At the same time, optimal synthetic route was studied by adjusting three parameters during the common hydrothermal process:reaction temperature and time, concentrations of precursor. XRD show that products was pure phase LiFePO4with good crystallization, as observed by FESEM. it has uniform morphology, single particle size was during50nm and250nm. Electrochemical performance test results showed that material prapared from0.4mol/L precursor heated at240℃for0.5h was relatively better, it discharges125.2mAh/g at0.1C,114.1mAh/g at0.2Cand99.5mAh/g at0.5C for the first cycle.Finally, LiFePO4particles was modified through Li4P2O7coating. AC impedance test results show that the impedance of modified materials is obviously reduced. meanwhile, improved discharge capacity and rate performanceal were obtained. In which LiFePO4coated wtih6wt%Li4P2O7heated at650℃was relatively better, it discharged143.6mAh/g at0.1C,136.4mAh/g a t0.2C and128.9at0.5C for the first cycle. Impressively, the capacity still remains stable without attenuation after cycling for30times.