Method for preparing iron phosphate from ferric oxide

Abstract

The invention discloses a method for preparing iron phosphate from ferric oxide, wherein the method comprises the following steps: S1, adding elemental iron into a mixed acid solution to obtain a rawmaterial solution; S2, adding ferric oxide into the raw material solution under a heating condition to obtain a crude iron phosphate solution; S3, adding an oxidizing agent into the crude iron phosphate solution, and carrying out heat preservation to obtain iron phosphate slurry; and S4, carrying out solid-liquid separation on the iron phosphate slurry, collecting a solid phase, washing, and calcining to obtain anhydrous iron phosphate. The iron phosphate prepared by the method has two crystal forms, the ratio of the two crystal forms is controlled through the combination of elemental iron andferric oxide, and the iron-phosphorus ratio of the finally prepared iron phosphate is controlled; according to the method, the thickness of the iron phosphate crystal is controlled by regulating andcontrolling the concentration of phosphate radicals; according to the method, iron phosphate is obtained through reaction in a sulfur-free environment, so that the sulfur content in an iron phosphatefinished product is greatly reduced.

Description

technical field [0001] The invention relates to the technical field of lithium ion battery materials, in particular to a method for preparing iron phosphate by using ferric oxide. Background technique [0002] Lithium iron phosphate is a kind of cathode material for lithium-ion batteries. It is characterized by large discharge capacity, good safety, long life, low price, non-toxic, non-polluting, and wide source of raw materials. Lithium iron phosphate batteries are widely used in electric tools, UPS, emergency lights, warning lights and miner's lamps; lithium iron phosphate batteries are also an important development direction of power batteries for new energy vehicles, and are used in electric buses; in addition, they are also used in the field of energy storage . The P-O bond in the lithium iron phosphate crystal is stable and difficult to decompose. Even at high temperature or overcharge, it will not collapse and generate heat or form strong oxidizing substances like li...

AI Technical Summary

Problems solved by technology

[0004] The technical status of iron phosphate raw material enterprises is: the iron-phosphorus ratio of most enterprises' products is 0.96-0.97, and a few enterprises can reach more than 0.97, but the S content exceeds the standard, reaching more than 0.01%. In order to prepare iron phosphate with low impurity content, related technologies adopt Refined ferrous sulfate, ferric chloride, ferric nitrate, ferric chloride or high-purity iron powder and sulfuric acid are used as raw materials. Although the obtained ferric phosphate has low impurity content, the cost of raw materials is high

There are also attempts to use cheap titanium dioxide by-product ferrous sulfate to synthesize, the production cost is low, but because of the high impurity content such as Mn, Mg, Ti and Ca in the ferrous sulfate raw material, the impurity content of the final ferric phosphate product is also high

There are also scholars who study the impurity removal of ferrous sulfate. Whether it is using iron powder to purify and remove impurities, or using phosphate and sulfide precipitation to remove impurities, it is difficult to remove impurities, especially the complete removal of Mn and Mg.

There is also an attempt to use resin adsorption to remove impurities, because the solution contains a large amount of Fe 2+ Will be preferentially adsorbed by the resin, thus hindering the removal of impurity metal ions

[0005] At the same time, the control of key indicators such as iron-phosphorus ratio, impurity elements, specific surface area and moisture is rarely mentioned in related technologies

The composition of the obtained ferric phosphate is unstable, and acid salts are easily formed if the conditions are not properly controlled, resulting in a low iron-to-phosphorus ratio, only about 0.96; although there are also iron-to-phosphorus ratios that reach 0.97-1.00, such ferric phosphate usually contains a small amount of hydroxide Iron, adsorbs a large amount of impurity ions, resulting in high S, Mn, and Mg impurity ions, which is difficult to meet the requirements of battery-grade iron phosphate

[0006] In addition, the crystal form of iron phosphate has a great influence on the properties (such as compacted density, specific capacity, etc.) of the obtained lithium iron phosphate

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