Preparation Of Iron Phosphate And Lithium Iron Phosphate Materials With Spray Drying Method

Lithium iron phosphate is an very important lithium-ion battery cathode material and has a broad prospect of application.As an important precursor of lithium iron phosphate material,the performance of FePO₄ directly affects the electrochemical performance of Li FePO₄.At present,the preparation process of FePO₄ and Li FePO₄ is tedious and water consumption.It's of great significance to develop novel methodof preparation of FePO₄ and Li FePO₄.In this paper,on account of the existing problems of preparation of FePO₄ and LiFePO₄,prepare FePO₄ by spray drying method and used as precursor to prepare LiFePO₄ is studied.FePO₄ of spherical morphology was prepared with NH3·H₂O as pH regulator.Li FePO₄/C was prepared by using it as precursor.The effect of molar ratio of Fe:Li,calcination temperature,calcination time and the amount of carbon source on the electrochemical performance of Li FePO₄/C was investigated.In addition,Formic acid was used as homogeneous precipitant to prepare FePO₄ of high electrochemical activity.Based on the previous synthetic process of Li FePO₄/C,high electrochemical performance of FA-LFP/C was prepared with FePO₄ as precursor.The effect of the amount of formic acid and reaction time on the performance of FePO₄ was investigated.The function and mechanism of formic acid was analyzed.Finally,Fe₂NH₄OH?PO₄?2·2H₂O was prepared with formic acid as addictives through hydrothermal method.The electrochemical activity of Fe₂NH₄OH?PO₄?2·2H₂O was researched.The main research results are as follows:Firstly,Fe?NO₃?₃·9H₂O and NH₄H₂PO₄ were used as raw materials,NH3·H₂O was used as pH regulator,FePO₄ was successfully prepared by spray drying method.The specific surface area of FePO₄ is 2.9m2·g,the particle size of FePO₄ is 1-5?m in diameter.LiFePO₄/C was prepared by using it as precursor,the effect of calcination temperature,calcination time,molar ratio of Fe:Li and the amount of carbon source on the electrochemical performance was investigated.When the temperature is 600?,the calcination time is 18 hours,the molar ratio is Fe:Li=1:1.02,the amount of carbon source is 30g·mol-1,the as prepared LiFePO₄/C exhibits the best electrochemical performance.The discharge capacity of LiFePO₄/C at 0.1C is 153.8 mAh·g-1,at 5C is 91.6mAh·g-1;without obviously capacity fading after cycling 200 circles at 1C.Secondly,high performance FePO₄ was prepared withformic acid as homogeneous precipitant through spray drying method.High electrochemical performance FA-LFP/C was prepared by using it as precursor.The performance of FePO₄ was evaluated based on electrochemical performance of Li FePO₄/C.The effect of reaction time and the amount of formic acid on the performance of FePO₄ was investigated.When reaction time is 30 hours,the molar ratio of Fe3+/FA is 1:20,the FePO₄ shows the best electrochemical activity,the FA-LFP/C shows the best electrochemical performance.Electrochemical test shows that the discharge capacity of FA-LFP/C at 0.2C is 158.4mAh·g-1,at 10 C is 107.3mAh·g-1,with capacity retention of 96% after cycling 300 circles at 1C,which exhibits excellent rate performance and cycling performance.Products at different synthesis stages were characterized by XRD,FTIR,TG,XPS to explore the function and mechanism of formic acid.The result shows that formic acid reacted with NO3-increased the p H value of solution and achieved the goal of homogenous precipitation of iron phosphate.In the meantime,formic acid regulated the morphology of particles and reduced particle size.This method is simple and saving-water,suitable for the industrial preparation of FePO₄ materials.Finally,the precursor of Fe₂NH₄OH?PO₄?2·2H₂O was prepared by hydrothermal method.The effect of reaction temperature,reaction time,amount of formic acid,the volume ratio of EG/H₂ O and the amount of CTAB was investigated.The result shows that 130?,14 h,50ml formic acid,volume ratio of 7:3 and 2‰ of CTAB is the optimum synthesis condition.The morphology of Fe₂NH₄OH?PO₄?2·2H₂O is ellipsoid,the particle size of which is 0.5²?m in diameter.In addition,LiFePO₄/C was prepared by using it as precursor.The electrochemical test shows that the discharge capacity of it at 0.1C is 161.6 mAh·g-1,the capacity retention is 85% after cycling 200 circles at 1C.SEM result shows that the morphology of Li FePO₄/C isn't kept well after chemical lithiation process compared with precursor.