Research On The Preparation And Modification Of Battery-grade Iron Phosphate From Ferro-phosphorus By Hydrothermal Method

This paper aims at the focus of the cathode materials of lithium ion battery and the recycling of resources,using Ferro-phosphorus to prepared battery-grade iron phosphate by hydrothermal method was studied.The dissolution of Ferro-phosphorus and the crystallization of iron phosphate were finished in same hydrothermal condition.At the same time the influences of reaction conditions on the purty and the electrochemical properties of iron phosphate were studied.Firstly,Ferro-phosphorus,phosphoric acid,nitric acid were used as raw materials to prepared battery-grade iron phosphate by hydrothermal method.The products were characterized by XRD,TG-DSC,SEM,FT-IR,ICP-Ms and electrochemical testing.The influences of concentration of nitric acid,reaction temperature,reaction time and concentration on the product was studied,and orthogonal experiment was designed,and we also studied the reaction mechanism of preparation of battery-grade iron phosphate by hydrothermal method.Secondly,the influnces of concentration of hydrofluoric acid,immersion time and ultrasonic time on battery-grade iron phosphate were studied,and the rules for morphology and electrochemical properties of battery-grade iron phosphate were analyzed.The experiment results indicated that the product was meet the standard of commercially available battery-grade iron phosphate when the concentration of nitric acid was 3.0mol/L,the reaction temperature was 110?,the concentration was 20g/L and the reaction time was 120 min.At the same time,LiFePO₄/C was synthesized by high temperature solid state method using the product of FePO₄·2H₂O.The charge-discharge test showed that the initial discharge capacity of LiFePO₄/C was 148.9mAh/g at 0.1C and the EIS test showed that the charge transfer resistance of battery was 48?.It is because that the product of iron phosphate contains a variety of trace mental elements,such as Ti,V,Mn,which effectively utilized trace elements in ferro-phosphorus,improving the electrochemical properties of lithium iron phosphate.The modified methods of iron phosphate were used HF and ultrasonic tratement.First,the product of iron phosphate soked 4h in the hydrofluoric acid of 4%,and the morphology,structure and electrochemical properties of battery-grade iron phosphate were analyzed.The results showed that the product of iron phosphate has not changed in structure.But the morphology of product was dispersed to lamellar structure,and there have many micropores in the lamellar structure.At the same time,HF and ultrasonic tratement can shorten the modified time by the analyzasion of the morphology and electrochemical properties of battery-grade iron phosphate.