Preparation And Performance Research Of Low-cost Iron Phosphate Precursor And Lithium Iron Phosphate Cathode Material

Lithium iron phosphate has outstanding advantages such as low cost,high safety,good cycle performance,and stable high temperature performance.It is the preferred cathode material for energy storage batteries and power lithium-ion batteries.Iron phosphate is an important precursor for the preparation of lithium iron phosphate.The new technology of low-cost and high-quality battery-grade iron phosphate has attracted increasing attention.In this paper,a variety of new preparation processes of ferric phosphate are studied,using Fe SO₄·7H₂O and iron powder ferric oxide as iron sources,H₂O₂ and air as oxidants,oxidative precipitation aging and crystallization to synthesize crystalline FePO₄·2H₂O precursors.The FePO₄·2H₂O precursor is prepared into a lithium iron phosphate cathode material to make a battery,and the electrochemical performance of the material is systematically tested and evaluated.This article studies a variety of iron phosphate preparation processes,using ferrous sulfate and iron powder iron red as iron sources,hydrogen peroxide and air as oxidants,oxidative precipitation aging and crystallization to synthesize crystalline iron phosphate precursor.The iron phosphate is roasted to obtain anhydrous FePO₄,which is mixed with battery-grade Li₂CO₃,glucose,and anhydrous ethanol and ball milled for 20 hours to make the slurry fully mixed and uniform.Then the slurry was taken out and dried,the dried material was fully ground with a mortar,and it was fired in a tube furnace under a nitrogen atmosphere at 700°C for 10 hours.LiFePO₄ cathode material was synthesized by carbothermal reduction reaction,and the battery was assembled for characterization.Its electrochemical performance.The main results achieved are as follows:Using Fe SO₄·7H₂O as the iron source,H₃PO₄ as the phosphorus source,and oxidant is Hydrogen peroxide,adjust the p H to 1.5～4.0 with NH₃·H₂O,and the crystalline iron phosphate precursor FePO₄·2H₂O was synthesized through oxidative precipitation aging and crystallization.When the p H is adjusted to 4.5～7.0,the crystalline basic iron phosphate NH₄Fe₂（PO₄）₂（OH）·2H₂O is synthesized by oxidation precipitation aging and crystallization.The process flow is simplified,the acid and alkali are significantly saved,and the cost is significantly reduced.Through aging and crystallization technology,The aging crystallization technology performs secondary crystallization of amorphous FePO₄·2H₂O to obtain crystalline FePO₄·2H₂O.Dissolve iron powder and ferric iron with H₃PO₄,and then use H₂O₂ as oxidant to prepare FePO₄·2H₂O precursor in one step using oxidative precipitation method.The prepared crystalline iron phosphate does not contain sulfur,and the lithium iron phosphate cathode material prepared when the iron powder and ferric iron molar ratio is 1:1 has the best performance.The first charge specific capacity at 0.2 C is 169.7 m Ah/g,and the discharge ratio The capacity is 157.2 m Ah/g,the first coulombic efficiency is 92.8%,the charge and discharge cycle is 100 times at 1 C,and the capacity retention rate is 91.8%.This new technology can use industrial by-products as iron source,which can realize the reaction of mother liquor.Closed recycling,no sulfate by-products,is conducive to further reducing costs.Using iron powder and ferric oxide as the iron source,using cheap air instead of H₂O₂ as the oxidant,oxidative precipitation to prepare a crystalline FePO₄·2H₂O precursor,the lithium iron phosphate cathode material prepared by this has better performance.similar to hydrogen peroxide as the oxidant.The best performance of the lithium iron phosphate cathode material prepared when the iron powder and ferric oxide molar ratio is 1:1,the first charge specific capacity is 167.9 m Ah/g,which is close to the theoretical value.The first discharge specific capacity is 161.9 m Ah/g,and the first coulombic efficiency is 95.9%.The cycle performance is slightly lower at 87.2%.This new method starts with an oxidant,effectively reduces the preparation cost of the iron phosphate precursor,has practical application prospects,and is worthy of further in-depth study.