Method for preparing high-purity high-compactness battery-grade ferric phosphate

Abstract

The invention provides a method for preparing high-purity high-compactness battery-grade ferric phosphate. The method comprises the following steps: firstly, enabling a certain amount of iron and 15-35% phosphoric acid to react at 40-100 DEG C so as to generate a phosphoric acid solution with ferrous ions, further heating the material liquid to 60-100 DEG C, adding a complexing agent, introducingozone to carry out oxidation for 3.5-7.5 hours so as to obtain ferric phosphate slurry, filtering the ferric phosphate slurry, repeatedly washing filter cakes, filtering till the filtrate is neutral,drying the collected solid for 2-4 hours, and calcining for 2-4 hours at 400-600 DEG C, thereby obtaining expected ferric phosphate, wherein the complexing agent is one or more of ethidene diamine, triethanolamine, 2-hydroxyl ethylamine, 1,2-propane diamine, 1,3-propane diamine, succinamide and malonamide. The method provided by the invention is simple in process, safe and environmental-friendly,high in atom utilization rate, low in cost and possible in continuous production, and the ferric phosphate prepared by using the method has an iron-phosphorus ratio of 0.96-0.99, a D95 granularity of78-150 nanometers and a compact density of 2.40-2.50g / cm<3>, and is particularly applicable to application as a raw material of lithium battery anode material lithium iron phosphate.

Description

technical field [0001] The invention relates to a preparation method of an inorganic compound, in particular to a preparation method of iron phosphate, and more particularly to a preparation method of high-purity, high-pressure compaction battery-grade iron phosphate. Background technique [0002] Iron phosphate is an important raw material for lithium iron phosphate, the cathode material of lithium batteries. The traditional preparation method of iron phosphate is generally obtained by reacting divalent or trivalent iron salts with phosphoric acid or phosphate. The most commonly used iron salts are ferrous sulfate, chlorine Ferric oxide or ferric nitrate, which will inevitably introduce impurity anions into the product ferric phosphate; in addition, phosphate is used as a precipitant, and ammonia, sodium hydroxide or potassium hydroxide are commonly used in order to adjust the pH value of the reaction solution, This also introduces impurity cations into the product, and the...

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Problems solved by technology

[0003] The Chinese invention patent with the publication number CN102050435 discloses a production method of battery-grade iron phosphate. The method is to dissolve polyferric sulfate into a solution with an iron ion concentration of 0.03-0.3M, and then add a phosphate solution to generate an alkali Formula ferric phosphate slurry, and then the solid-liquid separation of the slurry, the separated basic ferric phosphate is added to the phosphoric acid solution for treatment, the pH value is adjusted, and then filtered, washed, and dried to obtain battery-grade ferric phosphate; the above preparation method is due to the introduction of Sulfate ions need to add additives and remove impurities many times to meet the technical requirements of battery-grade iron phosphate. However, the removal of impurities produces a large amount of waste water, and there is also the problem of high post-treatment costs.

[0004] The Chinese invention application whose publication number is CN105480960 discloses a method for preparing ferric phosphate. The method is to place iron in a phosphoric acid solution, heat and carry out ferric reaction to obtain Fe(H 2 PO 4 ) 2 The reaction solution, then add hydrogen peroxide to the reaction solution to carry out oxidation reaction, add polyethylene glycol and continue to stir simultaneously, make Fe(H 2 PO 4 ) 2 The reaction generates ferric phosphate, then add distilled water to the ferric phosphate liquid, carry out the hydrolysis reaction, carry out solid-liquid separation to the feed liquid after hydrolysis, and wash the solid phase until the pH value reaches near neutrality, dry to obtain solid ferric phosphate, finally The solid ferric phosphate after drying is dried and dehydrated successively to form dehydrated ferric phosphate; the above-mentioned preparation method uses pure iron as raw material and phosphoric acid as the phosphorus source, although the introduction of impurities can be avoided, but the method uses hydrogen peroxide as the oxidant, hydrogen peroxide and containing When the ferrous phosphoric acid solution is mixed, the system formed under stirring is a homogeneous system, but when the hydrogen peroxide is added, it is added in a trickle flow, and the feeding process is easily affected by the fluid flow, forming a certain concentration gradient, resulting in a high concentration of hydrogen peroxide The formation rate of iron phosphate particles in the region is higher than that in the region with low concentration of hydrogen peroxide, and the reaction system is transformed from a homogeneous reaction to a liquid-solid phase reaction. The formation of the solid phase of iron phosphate can cause the solid-liquid phase The uneven mass transfer between the iron phosphate particles causes the difference in particle size due to the difference in the oxidation reaction rate, resulting in uneven particle size distribution of the generated iron phosphate, resulting in low compaction density, which cannot be used for the preparation of high-performance lithium batteries; in addition , the polyethylene glycol dispersant added by this method remains in the product, which will reduce the purity of the product, and adjust the pH value by adding water, and the water consumption is also large

[0005] The Chinese invention patent with the publication number CN103569988 discloses a method for preparing ferric orthophosphate. The method includes the following steps: (a) mixing a complexing agent with a ferrous phosphate compound to obtain a mixed solution; (b) adding to the step (a) adding excess ozone to the obtained mixed solution, heating and reacting to obtain iron orthophosphate seed crystals; (c) mixing the ferric orthophosphate seed crystals obtained in step (b) with ferrous salt solution and phosphorus source solution to obtain a mixed solution; (d) adding excess ozone to the mixed solution obtained in step (c), adjusting the pH of the reaction system to 1-6, and obtaining ferric orthophosphate after the reaction; the above preparation method uses citric acid and citrate as complexing The ferrous ions are complexed by an agent and oxidized by ozone. Although the problem of particle size differences caused by differences in the oxidation reaction rate of ferric phosphate particles can be avoided, the complexing agent added by this method will remain in the ferric phosphate, causing The purity of the product is low, which affects the application of the product, and when adjusting the pH value of the system, a large amount of ammonia, sodium hydroxide and other regulators need to be added, which also brings great trouble for post-processing; in addition, this method uses ferrous sulfate as iron source, the introduced sulfate ion also has the problem of high removal cost