The Technology Of Microwave Digestion Phosphorus Iron And The Study On Crystallization Mechanism Of Iron Phosphate

With the wide research of lithium ion battery,olivine-structured LiFePO₄ with high theoretical specific capacity,low cost,good thermal stability and abundant sources has become the most development potential cathode materials for lithium ion batteries.As a precursor in the synthesis of LiFePO₄,FePO₄ with the advantage of stable structure,low cost,non-toxic,safety and performance advantages and so on has become an ideal material for the synthesis of LiFePO₄ in phosphate.There are many methods for the synthesis of FePO₄,while the raw materials are not the same.This paper adopts ferro phosphorus,H₃PO₄,HNO₃ as raw material for the synthesis of FePO₄,FePO₄ as raw material for the synthesis of ferro phosphorus chemical includes chemical method,electrolytic method,wet dissolution methods,the paper use a new method-closed microwave digestion ferro phosphorus preparation of FePO4,and a series of performance tests on composite materials.The specific work is as follows:（1）with closed microwave method to digest the ferro phosphorus,nitric acid dosage,microwave power,time,pressure is investigated,considering the digestion rate,time and environmental ultimately determine the nitrate content was 7.5mL,the microwave pressure is0.9MPa,microwave power was 400W,the digestion time is 50min conditions,Ferro phosphorus digestion rate of up to 100%.the digestion solution to crystallization in the external aqueous phase,the proportion of liquid crystalline,and the temperature of the water,placed before crystallization study time,speed and other factors,finally found crystal digestion day according to the ratio of1:5at 85℃of the crystallization of 2h can be made to meet the conditions of the iron phosphate.For SEM,to make the iron phosphate XRD,particle size,TG-DSC spectroscopy,the characterization results show that the iron phosphate prepared in line with the market demand.to make the iron phosphate of SEM,XRD,granularity,TG and DSC were characterized,characterization results showed that the preparation of iron phosphate of uniform particle size distribution,the average particle size of 3.104μm,differential thermal analysis is good,do not contain other impurities,contains about two crystallization water,iron phosphorus ratio 1.009,the yield reached 88.65%,XRD ray analysis,diffraction peak sharp,good crystal shape.At the same time with homemade iron phosphate lithium iron phosphate XRD analysis,crystal sharp,but the iron phosphate for monoclinic crystal,electrochemical performance is not very ideal.（2）phosphorus iron tank in microwave digestion rate can be 100%,so one step inside the microwave digestion and phosphorus iron iron phosphate crystallization of preliminary exploration,adjustment of respectively from three kinds of raw materials and the proportion of water,change and exploration on the nitrate content in the material.Change the amount of phosphorus,iron,adjusted in accordance with the same proportion of other raw materials,final.according to the phosphorus Iron:nitric acid,phosphoric acid=1 g:7.5 mL:4.5 mL,adding deionized water maintain total 32 mL,instrument condition is 0.9 MPa,power is 400 w,time for50 min,when c(Fe³⁺)=7.5g/L,iron phosphate,can be prepared by TG,DSC,XRD and SEM analysis,the preparation of iron phosphate contains no other impurities,contain approximately 2water of crystallization and crystal shape is good,for monoclinic crystal,but the larger particles,preparation of iron phosphate morphology morphology and other methods are greatly different.