Investigation On Solvothermal Synthesis And Modification Of LiFePO₄ As A Cathode Material For Lithium Ion Batteries

Due to high thermal stability, environmental benignity, long cycling life and the natural abundance of raw materials, lithium iron phosphate has been extensively developed into a possible cathode material replacement for LiCoO2 in lithium ion batteries. However, the key barrier to wide applications was its intrinsically low electrical conductivity and low Li ion diffusion rate. For the obstacles, both the size and orientation control of LiFePO₄ are necessary because lithium-ion diffusion in LiFePO₄ can only occur along [010] direction. Solvothermal method was proved to be an effective way to control the synthesis of LiFePO₄ crystals. In order to solve these problems, some works have been done in this paper as the follows:?1? LiFePO₄ electrode materials were synthesized by using ethylene glycol as the solvent. The morphology and size of the LiFePO₄ particles were strongly dependent on synthetic parameters such as reaction temperature and mole ratio of reactants. When the reaction temperature is at 180?, the size of the particles is very uniform and tiny particles almost not existent. It is difficult to control the particle size and morphology when using deionized water as solvent. With the increase of ethylene glycol, the size of particles changes from micron level to nanoscale gradually and the morphology and size of particles is more and more uniform. So we should use ethylene glycol as solvent. LiFePO₄ particles of 50 um long, head diameter 23 um, middle diameter 19 nm was self-assembed by nanoplates of 30 nm thickness.?2? LiFePO₄ materials were synthesized by using ethylene glycol ?EG? applied solvent. XRD, SEM and TEM showed that the synthesized LiFePO₄ particles are nanoplates with the{010} face prominent and the defect concentrations of the Fe·Li antisite are very low. Cyclic voltammetry measurements showed that the sample can undergone lithium-ion deintercalation and intercalation normally at a large scan rate ?280 mV/s? in 1 M Li2SO₄ aqueous electrolyte and showed excellent rapid charge and discharge performance. The concentration and ratio of reactants differences may lead to different particle size and morphology, then lead to the greatly different electrochemical properties. We must control relevant synthetic parameters strictly to obtain excellent property cathode material for lithium ion batteries.?3? LiFePO₄ materials were synthesized by using polyethylene glycol 400 as surfactant. The morphology and size of the LiFePO₄ particles were strongly dependent on synthetic parameters such as concentration of precursors and volume ratio of Polyethylene glycol 400 and deionized water. When synthetic parameters were shown as follows:the reaction time is 9 h, the reaction temperature is 180?, mole ratio of reactants ?Li+:Fe+:PO₄3-? is 3:1:1, molar concentration of precursors is 0.11 mol/L, volume ratio of polyethylene glycol 400 and water volume ratio is 1:1.25, The obtained LiFePO₄ materials showed the best electrochemical performance.