Study Of Preparation Of Iron Phosphate By Coprecipitation And The Synthesis Of LiFePO₄/C Composites As Cathode Materials

With the rapid development of society,people's awareness of environmental protection and energy development has gradually increased,and they have started to pursue efficient,convenient,green,safe and reliable energy.LiFePO₄ material has attracted extensive attention due to its advantages of widely available,low cost,high theoretical capacity,stable cycling performance and good thermal stability,etc,has become the most promising new generation lithium ion battery cathode material.However,its low electron conductivity and poor performance have hindered the commercialization process.This paper aims to improve the electrochemical performance of LiFePO₄ materials,by changing the different synthesis process conditions to prepare the precursor of iron phosphate with fine primary particle size and uniform particle size distribution,achieving the purpose of optimizing the size and performance of target product of lithium iron phosphate secondary particles.In this paper,with ferrous sulfate and ammonium phosphate as raw materials,hydrogen peroxide as oxidant,surfactant as dispersant and particle size regulator,by changing the drop rate of ammonium phosphate,raw material molar feeding ratio,stirring speed,type and dosage of surfactant,respectively,by coprecipitation synthetic iron phosphate powder.Using the impinging stream rapid precipitation method to strengthen the feed and change the different inlet velocity to prepare iron phosphate powder.LiFePO₄/C composites was prepared by carbothermal reduction with the synthesis of iron phosphate as precursor.The structural characterization of the iron phosphate materials was synthesized by the particle size distribution,XRD,Fe and P content were measured.The electrochemical performance of lithium iron phosphate materials were tested by constant current charge-discharge method.The results showed that the average particle size(D₅₀)of iron phosphate decreased with the increase of the drop rate of ammonium phosphate,increased with the increase of iron and phosphorus mole feeding ratio,decreased with the increase of stirring speed,the first decrease and then increase with the increase of CTAB dosage,the first increase and then decrease with the increase of SDS dosage.When the drop rate of ammonium phosphate is 80rpm,the iron and phosphate molar feeding ratio is 1:1.1,the stirring speed is 750rpm,the amount of CTAB is 1.5g or SDS is 2.5g,the particle size of the synthetic iron phosphate is small.The optimum addition of glucose was 20%of the total mass.The charge-discharge performance of lithium iron phosphate are good and the cycling performance is stable under different current density.This shows that the iron phosphate particles prepared by this method are fine,and the particle size distribution is uniform,which is beneficial of a crystal to the synthesis of lithium iron phosphate.The iron phosphate synthesized by the rapid precipitation method of impingement flow as a crystal to synthesize lithium iron phosphate,the charge-discharge cycles were tested by 0.1C,0.2C,0.5C and 1C in turn.When the gas velocity was 1.5L/min,1.0L/min and 0.5L/min,the initial discharge capacity was 140mAh/g,137mAh/g and128mAh/g,the discharge capacity and cycling stability were excellent under different current density.Return 0.1C to test 10 cycles,the 1.5L/min gas velocity of lithium iron phosphate discharge capacity increased,while the discharge capacity of lithium iron phosphate under the gas velocity of 1.0L/min and 0.5L/min remained unchanged.This indicates that the electrode material under the gas velocity of 1.0L/min and 0.5L/min has fallen off during the test,and the material structure under the gas velocity of1.5L/min has not been damaged.