Preparation Of Battery Grade Ferric Phosphate By Microwave Crystallization

According to the focus on the cathode materials research recently, we had put forward the research of preparing battery-grade iron phosphate by microwave crystallization. At the same time the effects of reaction conditions on the morphology and the electrochemical properties of iron phosphate were studied. Firstly, battery-grade iron phosphate was synthesized in gas-liquid mixed phase by microwave irritation. Products were characterized by using FT-IR,XRD, SEM and TG-DSC techniques. Temperatures, reaction time, concentration of iron ion, ratio of nitrate and phosphorus iron and acidity were studied in order to find out regular effects on the product yield and particle size. The effects of HNO3 on crystallization were systematically investigated under very low pH from 0.1 to 0.3. Electrochemical performance of lithium batteries were tested through the products prepared under different conditions and homemade iron phosphate was used as precursor. The key factors that affected battery performance were systematically analyzed. Then, during the process of microwave crystallization, dispersants and precipitants were added in order to change product size. Through the using of different dispersants, the change of dispersants concentration, iron ion concentration, ratio of phosphorus and iron and the reaction conditions, such as heating power, the rules for product particle size change were analyzed. The minimum product particle size was determined under the optimum process conditions and its electrochemical performance was systematically tested and analyzed.Experiment results show that HNO3 vaporizes and decomposes into a large number of gas phase, which strengthens and improves crystallization. Besides these it also shortens the crystallization time. And it makes the appearance of crystalline grain become more regular and turn into diamond structures. The purity of orthophosphate iron is improved in low acidity that avoids the hydrolysis of Fe(III). Cyclic voltammograms test shows that synthetic iron phosphate has symmetrical redox peak, which means that lithium ion can be reversible taken off and embedded. But the EIS test shows that the internal resistance of battery is too large, which leads to the low specific capacity of first discharge. The reason is that the product granularity is too large that results in long Li+ diffusion flux and slow rate of Li+ diffusion. Good performance of lithium iron phosphate sample is synthesized by homemade iron phosphate as precursors and the first discharge specific capacity is 125.1 mAh/g at 0.1C.The optimum process conditions of the minimum particle size products are synthesized by reacting for 2 min under 100℃, 600 W and using PEG as the dispersant, urea as the precipitant. The reactant ratio are n(P)/n(Fe)=5,c(PEG)=200g/L, c(Urea)=75g/L, c(Fe)=0.0833 M. On the analysis of electrochemical performance of the products, the results show that comparing with the products without dispersant and precipitant, their electrochemical properties have bigger rise, higher discharge specific capacity, good reversibility and low battery internal resistance.