CN-117430106-B - Method for preparing lithium iron phosphate from iron hydroxy phosphate and ferrous oxalate and application

CN117430106BCN 117430106 BCN117430106 BCN 117430106BCN-117430106-B

Abstract

The invention provides a method for preparing lithium iron phosphate from ferric phosphate and ferrous oxalate, which comprises the steps of purifying ferrous sulfate to form ferrous sulfate solution, sequentially adding hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution and ammonia water into the solution to react to form mixed slurry, heating and preserving heat to the mixed slurry, washing and press-filtering to form ferric phosphate precursors with different iron-phosphorus ratios, carrying out flash evaporation drying and high-temperature sintering and crushing to obtain ferric phosphate precursors with different specific surface areas, crushing and mixing the ferric phosphate precursors to obtain a ferric phosphate finished product, mixing ferric phosphate with high-iron-phosphorus ratio and ferric phosphate with low-iron-phosphorus ratio according to a certain proportion, adding a carbon source and an additive to form the mixed slurry, and carrying out the procedures of ball milling, sand milling, spray drying, sintering, crushing, screening, batch mixing, packaging and the like to obtain the lithium iron phosphate finished product.

Inventors

SUN JIE
XU CHENG
Lin Pingjun
YU MENGHUA
WANG BIN
WANG XIAOTING
LIU CHAO
YAO YUAN
YANG JI
WEI YIHUA
HE ZHONGLIN
HE JIANHAO
XU ZHONGZHU
MEI JING
CHENG GUANGCHUN
LIN SHUO

Assignees

湖北融通高科先进材料集团股份有限公司

Dates

Publication Date: 20260512
Application Date: 20230908

Claims (10)

1. A method for preparing lithium iron phosphate from iron hydroxy phosphate and ferrous oxalate, the method comprising: step S1, adding a phosphorus source and a precipitator into a titanium dioxide byproduct ferrous sulfate for purification, and obtaining a ferrous sulfate solution after filter pressing and purification; s2, adding a proper amount of phosphoric acid into the ferrous sulfate solution to reduce the pH value of the ferrous sulfate solution; Step S3, sequentially adding hydrogen peroxide, phosphoric acid, monoammonium phosphate solution and ammonia water into ferrous sulfate solution, reacting for a period of time to form mixed slurry, heating the mixed slurry for a period of time, washing and filtering for a plurality of times to form a high iron-phosphorus ratio hydroxyl ferric phosphate precursor and a low iron-phosphorus ratio hydroxyl ferric phosphate precursor, wherein when the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio of Fe/P=1.475-1.490, the high iron-phosphorus ratio hydroxyl ferric phosphate precursor is formed, and when the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio of Fe/P=1.460-1.465, the low iron-phosphorus ratio hydroxyl ferric phosphate precursor is generated; s4, carrying out flash evaporation drying on the high-iron-phosphorus-ratio hydroxyl ferric phosphate precursor and the low-iron-phosphorus-ratio hydroxyl ferric phosphate precursor in a flash evaporator, and sintering at a high temperature for a certain time to obtain finished products of the hydroxyl ferric phosphate precursors with different iron-phosphorus ratios and different specific surface areas; S5, crushing the sintered material by using a mechanical mill, and mixing by using a spiral mixer to obtain a finished product of the hydroxyl ferric phosphate with high iron-phosphorus ratio and high specific surface area and a finished product of the hydroxyl ferric phosphate with low iron-phosphorus ratio and low specific surface area; S6, mixing a finished product of the hydroxyl ferric phosphate with high iron-phosphorus ratio and low specific surface area according to a certain proportion, and then proportioning with ferrous oxalate, lithium phosphate, lithium carbonate and ammonium dihydrogen phosphate according to a certain proportion, and adding a certain amount of carbon source and additive to form a mixture; step S7, sanding the mixture to obtain nano sanding slurry, and spray drying the nano sanding slurry to obtain spray material; S8, placing the spray material into a box furnace for sintering to obtain a sintered material, and crushing the sintered material by using a jet mill to obtain a crushed material; And S9, further sieving, mixing and packaging the crushed materials to obtain a lithium iron phosphate finished product.
2. The method for preparing lithium iron phosphate from ferric hydroxy phosphate and ferrous oxalate according to claim 1, wherein in the step S1, the phosphorus source is one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate and sodium phosphate, the precipitant is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide and ammonia water, and the phosphorus source is [0.001-0.005]: 0.007], the purification reaction temperature is 40 ℃, the reaction pH value is 2.2-2.5, and the reaction time is 1 h.
3. The method for preparing lithium iron phosphate from iron hydroxyphosphate and ferrous oxalate according to claim 1, wherein in the step S2, the phosphoric acid is added in a molar ratio of n (Fe): n (phosphoric acid) =1:0.15.
4. The method for preparing lithium iron phosphate from ferric hydroxy phosphate and ferrous oxalate according to claim 1, wherein in the step S3, the number of times of water washing is multiple, the impurities of magnesium, manganese and sulfur are mainly washed out in the first time of water washing, the pH value is adjusted to 6.5-7.0 by adding 1:1 diluted ammonia water in the last time of water washing to wash out SO 4 2- ions, the concentration of hydrogen peroxide is 30-60%, and the heat preservation time is 3 hours after the mixed slurry is heated to 60-80 ℃.
5. The method for preparing lithium iron phosphate from iron hydroxyphosphate and ferrous oxalate according to claim 1, wherein the step S3 comprises: Step S31, adding excessive hydrogen peroxide into the ferrous sulfate solution, and continuing to oxidize for a certain time; step S32, adding a phosphoric acid solution into the oxidized ferrous sulfate solution, adding water into ammonium dihydrogen phosphate powder to dissolve and prepare a 30% ammonium dihydrogen phosphate solution, and adding the ammonium dihydrogen phosphate solution into the oxidized ferrous sulfate solution, wherein the dissolution temperature is 30-40 ℃; And S33, adding ammonia water into the ferrous sulfate solution, regulating the pH value of the solution to be 3.00+/-0.02, reacting for a period of time to form mixed slurry, heating and preserving the mixed slurry for a period of time, and then washing and press-filtering for a plurality of times to form the iron phosphate precursors with different iron-phosphorus ratios.
6. The method for preparing lithium iron phosphate from iron hydroxy phosphate and ferrous oxalate according to claim 1, wherein in the step S4, the inlet air temperature of the flash evaporator is controlled to be 220+/-20 ℃, the outlet air temperature is controlled to be 110+/-5 ℃, the sintering atmosphere is air, the sintering temperature is 535-560 ℃ and the sintering time is 4-5 hours, in the step S5, the particle size D10 is more than or equal to 1.0 μm, the D50 is 6-15 μm, the D90 is less than or equal to 60 μm, the mixing frequency of the mixer is controlled to be 35+/-2 Hz, and the mixing time is 1-2 hours.
7. The method for preparing lithium iron phosphate from iron hydroxyphosphate and ferrous oxalate according to claim 1, wherein in the step S5, the high iron-phosphorus ratio is higher than that of the iron hydroxyphosphate finished product with specific surface area, the specific surface area satisfies bet=15-20 m 2 /g, and the low iron-phosphorus ratio is lower than that of the iron hydroxyphosphate finished product with specific surface area satisfies bet=5-10 m 2 /g.
8. The method for preparing lithium iron phosphate from ferric hydroxy phosphate and ferrous oxalate according to claim 1, wherein in the step S6, according to the molar ratio, li: fe, P= [1.03-1.04]:1: [1.03-1.04], the carbon source is added in an amount of 300-3000ppm based on the carbon content in the final product, the carbon source is one or more of sucrose, glucose, citric acid, starch and polyethylene glycol, and the additive is one or more of titanium dioxide, ammonium metavanadate and niobium pentoxide; in the step S7, the sand grain size in the sand grain slurry is controlled to be 0.45-0.75 mu m, in spray drying, the air inlet temperature is 200-220 ℃, the air outlet temperature is 80-110 ℃, the air blowing frequency is 80Hz, the spray grain size in the spray grain is controlled to be D50=20-40 mu m, in the step S8, the sintering atmosphere is nitrogen, the sintering temperature is 750-780 ℃, the heating rate is 3 ℃ per minute, the sintering time is 8-12h, and the sintering material is obtained after natural cooling and cooling, in the crushing process, the air pressure is controlled to be 0.2-0.4Mpa, the grading frequency is 80-200Hz, and the particle size of the crushed material satisfies D10>0.35 mu m, D50=0.7-2.0 mu m, D90<10 mu m and D100<30 mu m.
9. A lithium ion battery positive electrode material, wherein the lithium ion battery positive electrode material is lithium iron phosphate prepared by the method for preparing lithium iron phosphate by using the hydroxyl ferric phosphate and ferrous oxalate according to any one of claims 1-8.
10. A lithium ion battery comprising the lithium ion battery positive electrode material of claim 9.

Description

Method for preparing lithium iron phosphate from iron hydroxy phosphate and ferrous oxalate and application Technical Field The invention relates to the technical field of preparation methods of lithium ion battery anode materials, in particular to a method for preparing lithium iron phosphate from iron hydroxy phosphate and ferrous oxalate and application thereof. Background The lithium iron phosphate anode material is the lithium battery anode material which is most rapidly developed in China at present, has wide raw material sources and low price, and is widely applied to the fields of automobiles, electric tools, energy storage equipment, emergency power supply equipment, mobile power supplies and the like in the domestic battery industry. Wherein the new energy electric vehicle is a main application field, and the share of the lithium iron phosphate is more than 45% of the total amount of the lithium iron phosphate. Compared with other anode materials, the lithium iron phosphate has the advantages of safety, environmental protection, low cost, long cycle life, good high-temperature performance and the like, and is one of the anode materials of the lithium ion battery with the highest potential. The existing methods for preparing lithium iron phosphate mainly comprise a solid phase method, a carbothermic reduction method, a sol-gel template method and the like. For example, CN105024073A discloses a lithium ion battery anode material ferric hydroxy phosphate and a preparation method thereof, wherein the molecular formula of the lithium ion battery anode material is Fe 2.95(PO4)2(OH)2, and the preparation method comprises the steps of adding water into H 3PO4 solution and FeCl 3 solid powder, uniformly mixing, adding methyl triethyl ammonium chloride to adjust pH to 2.0-3.5, controlling the temperature to 150-200 ℃ for hydrothermal synthesis reaction for 30 hours to obtain a reaction solution, and carrying out centrifugal separation, cleaning and drying on the reaction solution to obtain Fe 2.95(PO4)2(OH)2. Lithium iron phosphate prepared from hydroxyl ferric phosphate is synthesized from phosphorus ferric waste residue, phosphoric acid and hydrogen peroxide serving as by-products of phosphorus chemical industry in journal of performance research of lithium ion battery anode materials, so that lithium iron phosphate is prepared. However, the method has the advantages of high reaction temperature, long reaction time, harsh reaction conditions, high production requirement on equipment, low production efficiency and no compliance with the current market lithium iron phosphate cost reduction requirement. In addition, the method has high cost and price of raw materials, more impurities in the finished product are difficult to remove, the product performance of the hydroxy ferric phosphate is affected, and the product performance of the lithium iron phosphate is also affected. Disclosure of Invention In view of the above, the present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, the invention provides a method for preparing lithium iron phosphate from iron hydroxy phosphate and ferrous oxalate and application thereof. The method takes ferrous sulfate as a material, hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate and ammonia water are added to synthesize hydroxyl ferric phosphate, and ferrous oxalate, lithium phosphate, lithium carbonate and ammonium dihydrogen phosphate are taken as raw materials to prepare the lithium iron phosphate with high compaction density and high capacity. The method has high production efficiency and low production cost, and is suitable for large-scale industrial production. The method comprises the steps of adding a phosphorus source and a precipitant into titanium dioxide byproduct ferrous sulfate for purification, performing filter pressing purification to obtain a ferrous sulfate solution, adding a proper amount of phosphoric acid into the ferrous sulfate solution to reduce the pH value of the ferrous sulfate solution, sequentially adding hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution and ammonia water into the ferrous sulfate solution for reaction for a period of time to form a mixed slurry, heating and preserving the mixed slurry for a period of time, washing and press-filtering for a plurality of times to form a ferric phosphate precursor with different iron-phosphorus ratios, performing flash evaporation drying on the ferric phosphate precursor in a flash evaporator, sintering for a certain time at a high temperature to obtain ferric phosphate precursor finished products with different iron-phosphorus ratios, crushing the sintered materials by a mechanical mill, mixing the ferric phosphate finished products with different specific surfaces by a spiral belt mixer, mixing the ferric phosphate with high specific surface area and the ferric phosphate with low specific surface area a