Investagation On Electrochemical Performance Of Micro-nano LiFePO₄Positive Material Prepared By Self-assembly

Olivine-structured LiFePO4, a relatievely new positive material for lithium battery, is considered to be one of the best suitable positive materials for its properties of high safety, favorable thermostability, excellent cyclability, environmental friendly as well as low cost.In this paper, a two-step synthesis process to prepare electrochemically active LiFePO4was explored firstly, which demonstrated that the morphology control and tunability of LiFePO4could be approached by structuring FePO4with delicate microsture. FePO4with controllable microstructure, which acted as the precursor of LiFePO4, was synthesized by hydrothermal method synthesized. LiFePO4was prepared based on the structured FePO4by solid state sintering method. Three typical kinds of microstructures were gained then. The synthesis process of LiFePO4with structure-controlled FePO4as the precursor was investigated systematically. The influence of processing parameter on the microstructure of LiFePO4was discussed in detail.Spherical LiFePO4with highly electrochemical performance was prepared successfully.Precipitation-hydrothermal method was employed to prepare FePO4material by using Fe(NO3)3·9H2O, NH4H2PO4and citric acid as raw materials. The influence of reaction time, reaction temperature, the pH value, the ratio of reactants, and the concentration of reactants on the microstructure of the material, was studied systematacially.The results showed that an amazing micro-nano secondary structure of FePO4could be gained by hydrothermal process at120℃for24h by controlling the pH value at1.5, reactant ratio of Fe3+/PO43at1/1.5in0.1mol/L, followed by heat-treatment at550℃for2h.The specific surface area of as-prepared LiFePO4is13.97m2/g.LiFePO4material was prepared by solvent-evaporation methode cooperated with heat treatment with structure-controlled FePO4, lithium oxalate and citric acid as iron, lithium, and carbon sources, respectively. The influence of lithium concentration, carbon type and carbon content on the final microstructure, the morphology and electrochemical performance of the products was researched. The results demonstrated that LiFePO4with high electrochemical performance could be obtained at700℃for1Oh under the condition that the molar ratio of FePO4and Li+was1:1.2, carbon content was7%. The first discharge specific capacity of LiFePO4at0.1C could be up to132.5mAh/g.This paper investigated the inter-relationship between the morphology and elecctrochemiacl performance of LiFePO4/C material. The electrochemical performance of the material with different morphology was studied. The first charge and discharge specific capacity of the micro-nano structured LiFePO4at0.1C was136mAh/g and132.5mAh/g respectively, yielding a coulombic efficiency of97.4%, superior to the samples free of secondary microstructure. It clarified that micro-nano structure could improve the electrochemical performance of LiFcPO4positive material.