Basic Research On Preparation Of Ferric Phosphate From Reduced Iron Powder As Iron Source

One of the major problem facing the world today is energy and environmental protection.As the world's research on environmentally friendly new energy sources continues to deepen,the development of energy storage batteries has progressed rapidly.Among them,lithium-ion batteries have received extensive attention due to their high energy ratio,long service life,high power tolerance,good safety and environmental friendliness.Therefore,it is of great scientific significance and great commercial value to vigorously develop lithium-ion batteries that are inexpensive,meet market demands,and have a wide range of applications.LiFePO₄ is one of the best cathode materials for lithium batteries.The lithium-ion battery made of it has stable structure,long service life,good thermal stability,low hygroscopicity and excellent charge-discharge cycle performance.It has always been a research hotspot for power lithium batteries.At present,the main synthetic method of LiFePO₄ is to use ferric phosphate as iron source,with lithium source compounds and additives to prepare LiFePO₄.The low conductivity and low diffusion coefficient of lithium ions limit the large-magnification output current of lithium iron phosphate.It is necessary to precisely control the ratio of phosphorus to iron and the content of phosphorus and iron.The particle size of the product also has a great influence on its electrochemical performance.Both the lithium iron phosphate battery industry and other iron phosphate-related industries have put forward higher requirements for high-quality iron phosphate,so high-quality iron phosphate has also been the focus of industrial synthesis and scientific basic research,It is also a practical production difficulty in the industry.In this thesis,iron phosphate was prepared from reduced iron powder dissolved by mixed acid via mixture of sulphuric acid and phosphoric acid and mixture of nitric acid and phosphoric acid.The effects of the molar ratio of iron to phosphorus,the reaction temperature and the concentration of the reaction solution on the dissolving iron powder process were discussed and the sedimentation conditions were discussed.Iron phosphate samples were characterized by XRD,SEM,FTIR,TG,particle size analysis and other analytical techniques.The conclusion as follows:1)In the preparation of iron phosphate by sulfuric acid and phosphoric acid,when the molar ratio of iron to phosphorus is 1.1:1,the temperature is 80?,and the iron concentration is 2mol/L in dissolving iron powder process,the result of dissolving iron powder process is the best.In the aging process,the H₂O₂solution was added at a ratio of Feand H₂O₂is 1:1 and the p H was continuously adjusted with ammonia water at 80?.After aging for 2 hours,via filtering,washing and drying,iron phosphate can be prepared.2)In the preparation of iron phosphate by nitric acid and phosphoric acid,when the molar ratio of iron to phosphorus is 1.1:1,the temperature is 80?,and the iron concentration is 2mol/L in dissolving iron powder process,the result of dissolving iron powder process is the best.In the aging process,the formic acid solution was added at a ratio of Feand formic acid is 1:1.5 at 90?.After aging for 1 hour,via filtering,washing and drying,iron phosphate can be prepared.3)During the aging process,as FePO₄ is formed,the concentration increases continuously,and a supersaturated solution is formed.FePO₄ begins to crystallize,forming a sheet-like primary crystal of 30 nm to 50 nm.As the crystals continue to increase,they are agglomerated into a spherical crystal of 3?m to 5?m finally.