A method for preparing battery-grade lithium dihydrogen phosphate

Abstract

The application discloses a preparation method of low-cost battery-grade lithium dihydrogen phosphate, which comprises the following steps: step 1, uniformly mixing lithium iron phosphate black powder with pyrophosphoric acid aqueous solution, introducing air to perform oxidation, and obtaining a mixed solution; step 2, filtering and separating Fe4(P2O7)3 precipitate from the mixed solution obtained in the step 1 to obtain a lithium-containing solution; step 3, adjusting the pH value of the Fe4(P2O7)3 precipitate obtained in the step 2 in water by using phosphoric acid, and filtering to obtain FePO4 precipitate and a phosphoric acid solution; step 4, adjusting the pH value of the lithium-containing solution obtained in the step 2 by using the phosphoric acid solution obtained in the step 3 to convert the lithium-containing solution into a lithium dihydrogen phosphate solution; step 5, evaporating the lithium dihydrogen phosphate solution obtained in the step 4 at low temperature to obtain a supersaturated solution; and step 6, obtaining battery-grade lithium dihydrogen phosphate by cooling crystallization, centrifugation and drying of the supersaturated solution obtained in the step 5. The preparation method has low energy consumption and low cost, and the battery-grade lithium dihydrogen phosphate obtained by the method has a small proportion of fine powder.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a preparation method of low-cost battery-grade lithium dihydrogen phosphate. BACKGROUND

[0002] With the development of the new energy automobile industry, the power battery industry in China has also made great progress. In 2023, the production and sales of new energy vehicles in China reached 9.587 million and 9.495 million, respectively, with a year-on-year increase of 35.8% and 37.9%. With the rapid rise of new energy vehicles and energy storage equipment, the demand for lithium ion batteries has also increased. Lithium iron phosphate batteries are widely used due to their low cost, long life, excellent safety performance and other characteristics.

[0003] At present, the main production methods of lithium iron phosphate (LiFePO4) at home and abroad are focused on high-temperature solid-phase method. In this preparation method, the selection of phosphorus source, lithium source and iron source has always been the focus of people's research. Among them, lithium dihydrogen phosphate can provide both phosphorus source and lithium source. When synthesizing lithium iron phosphate with oxalic acid iron as the main raw material, the compaction density and energy density are higher than those of other processes, becoming the main process scheme and raw material of the third and fourth generations of lithium iron phosphate.

[0004] However, the traditional preparation process of battery-grade lithium dihydrogen phosphate mainly neutralizes phosphoric acid and lithium hydroxide or lithium carbonate, evaporates and crystallizes to form. CN200810044349.X, CN201010118632.X, CN201010602973.7, etc. disclose a method for preparing battery-grade lithium dihydrogen phosphate using phosphoric acid and lithium hydroxide as raw materials, CN200910170206.8 discloses a method for preparing battery-grade lithium dihydrogen phosphate using phosphoric acid and high-purity lithium carbonate as raw materials, CN202211556716.0 discloses a method for preparing battery-grade lithium dihydrogen phosphate using lithium chloride and phosphoric acid as raw materials, and CN202411002661.8 discloses a method for preparing battery-grade lithium dihydrogen phosphate using lithium sulfate and phosphoric acid as raw materials. These process methods need to use high-purity lithium hydroxide or lithium carbonate as raw materials, and the cost of raw materials is high.

[0005] With the rapid development of new energy industry, the market demand for lithium salt has also increased unprecedentedly, and the purification and utilization of waste lithium has become a new development direction. CN202210742435.8 discloses a method for preparing lithium dihydrogen phosphate by lithium precipitation purification of lithium-containing mother liquor, CN202311693817.7 discloses a method for preparing lithium dihydrogen phosphate by using low-cost lithium hydroxide solution as lithium source, CN202311215436.8 discloses a method for preparing battery-grade lithium dihydrogen phosphate by recycling lithium iron phosphate waste, and CN201711457815.2 discloses a method for preparing battery-grade lithium dihydrogen phosphate by using lithium iron phosphate waste. These recycling and purification methods still require high-energy processes such as high-temperature heating evaporation and cooling crystallization, and the process cost is still high. SUMMARY

[0006] The purpose of the present application is to overcome the technical defects of the prior art, such as the complex process and high cost of preparing battery-grade lithium dihydrogen phosphate from waste lithium, and to provide a low-cost method for preparing battery-grade lithium dihydrogen phosphate.

[0007] The technical scheme adopted to achieve the purpose of the present application is as follows:

[0008] A low-cost method for preparing battery-grade lithium dihydrogen phosphate, comprising the following steps:

[0009] Step 1: uniformly mix lithium iron phosphate black powder with pyrophosphoric acid aqueous solution, introduce air for oxidation, and obtain a mixed solution;

[0010] Step 2: filter and separate Fe4(P2O7)3 precipitate from the mixed solution obtained in step 1 to obtain a lithium-containing solution;

[0011] Step 3: adjust the pH value of Fe4(P2O7)3 precipitate obtained in step 2 in water with phosphoric acid, and filter to obtain FePO4 precipitate and a phosphoric acid-containing solution;

[0012] Step 4: adjust the pH value of the lithium-containing solution obtained in step 2 with the phosphoric acid-containing solution obtained in step 3 to convert it into a lithium dihydrogen phosphate solution;

[0013] Step 5: the lithium dihydrogen phosphate solution in step 4 is evaporated at low temperature to become a supersaturated solution;

[0014] Step 6: the supersaturated solution obtained in step 5 is cooled and crystallized, centrifuged and dried to obtain battery-grade lithium dihydrogen phosphate.

[0015] In the above technical scheme, in step 1, the concentration of the pyrophosphoric acid aqueous solution is 30-80%.

[0016] In the above technical solution, in the step 1, the weight ratio of the lithium iron phosphate black powder material to the pyrophosphoric acid aqueous solution is (1.1-1.3):1.

[0017] In the above technical solution, in the step 1, the air is compressed air, and the air flow is 200-500 L / min.

[0018] In the above technical solution, in the step 1, the oxidation time is 10-30 h.

[0019] In the above technical solution, in the step 2, the mixed solution is filtered in a filter press, and the filter press is a plate and frame filter press, a chamber filter press, a vertical filter press, a belt filter press or a closed pressure filter press, and the filter screen is 100-800 meshes.

[0020] In the above technical solution, in the step 3, the mass ratio of Fe4(P2O7)3 to water is (0.5-1.0):1.

[0021] In the above technical solution, in the step 3, the pH value is adjusted to 0.8-3.5.

[0022] In the above technical solution, in the step 4, the pH value is adjusted to 1.5-4.0.

[0023] In the above technical solution, in the step 5, the temperature of low-temperature evaporation is 35-75 DEG C.

[0024] Compared with the prior art, the beneficial effects of the present application are:

[0025] 1. The present application uses battery black powder (lithium iron phosphate black powder) as raw material, which not only effectively reduces the cost of raw materials, but also realizes the recycling of resources, solves the pollution problem of waste batteries to the environment, and improves the industrial value.

[0026] 2. In the preparation process, the pyrophosphoric acid aqueous solution is used as a leaching agent, and no other additives are needed, so that the conventional leaching and separation process is combined into one step to realize the separation of lithium-containing solution and precipitation; the leaching rate of Fe reaches 100%, and the leaching rate of Li reaches more than 98%, realizing the green recycling of resources; the process combines the conventional leaching and separation process into one step, and the process method is simple and reliable, the production cost is low, and it is very beneficial to industrial production.

[0027] 3. The lithium-containing solution is evaporated at low temperature, which reduces the energy consumption by more than 50%, significantly reduces the production cost, and reduces the production cost from multiple dimensions such as raw materials, process and equipment.

[0028] 4. The battery-grade lithium dihydrogen phosphate product prepared by the method is passed through an 80-mesh sieve, and the sieve residue accounts for 70-86%, and the content of the fine powder is small, indicating that the battery-grade lithium dihydrogen phosphate product prepared by the method is not easy to be caked, and does not affect the production and feeding of downstream users. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The process flow chart of the application. DETAILED DESCRIPTION

[0030] The application will be further described in detail below in combination with specific examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0031] Example 1

[0032] A low-cost preparation method of battery-grade lithium dihydrogen phosphate, comprising the following steps:

[0033] Step 1, weigh 100 Kg of aqueous pyrophosphoric acid solution (concentration of 60%) and add it into a stirred tank, then add 110 Kg of lithium iron phosphate black powder into the stirred tank, pass air into the stirred tank at a flow rate of 200 L / min, and stir for 12 h to obtain a mixed solution A;

[0034] Step 2, the mixed solution A is subjected to solid-liquid separation by a plate and frame filter press, and the filter screen mesh number is 500 mesh, and the filter cake after filtration is Fe4(P2O7)3 precipitate, and the filtrate is a lithium-containing solution;

[0035] Step 3, the Fe4(P2O7)3 precipitate obtained in step 2 is added into a stirred tank, pure water is added into the stirred tank, the solid-liquid ratio is controlled to be 2:1, the pH value of the solution is adjusted to be 1.5 by phosphoric acid, and stirring reaction is carried out for 12 h to obtain a mixed solution B, the mixed solution B is subjected to solid-liquid separation by a plate and frame filter press, and the filter screen mesh number is 500 mesh, and the filter cake after filtration is FePO4 precipitate, and the filtrate is a phosphoric acid-containing solution; the FePO4 precipitate after drying can be used as a raw material for preparing lithium iron phosphate positive electrode material, and the phosphoric acid solution can be recycled;

[0036] Step 4, the lithium-containing solution obtained in step 2 is transferred into a reaction kettle, and the pH value is adjusted to 2.0 by using the phosphoric acid-containing solution obtained in step 3 to obtain a lithium dihydrogen phosphate aqueous solution;

[0037] Step 5, the lithium dihydrogen phosphate aqueous solution is evaporated by a low-temperature evaporator at 35℃, and when the specific gravity reaches 1.63, the solution is transferred into a crystallization kettle;

[0038] Step 6, after the solution is cooled to 25℃, battery-grade lithium dihydrogen phosphate is obtained by centrifugation and drying. The product is passed through an 80-mesh sieve, and the sieve residue accounts for 70%.

[0039] Example 2

[0040] A low-cost battery-grade lithium dihydrogen phosphate preparation method comprises the following steps:

[0041] Step 1, take 100 Kg of pyrophosphoric acid aqueous solution (concentration of 70%) and add it into a stirring kettle, then add 120 Kg of lithium iron phosphate black powder into the stirring kettle, pass air into the stirring kettle at a flow rate of 200 L / min, and stir for 15 h to obtain a mixed solution A;

[0042] Step 2, the mixed solution A is subjected to solid-liquid separation through a plate-and-frame filter press, the filter screen mesh number is 500 meshes, the filter cake after filtration is Fe4(P2O7)3 precipitate, and the filtrate is a lithium-containing solution;

[0043] Step 3, the Fe4(P2O7)3 precipitate obtained in Step 2 is added into a stirring kettle, pure water is added into the stirring kettle, the solid-liquid ratio is controlled to be 2:1, the pH value of the solution is adjusted to be 1.0 by using phosphoric acid, and stirring reaction is conducted for 15 h to obtain a mixed solution B; the mixed solution B is subjected to solid-liquid separation through a plate-and-frame filter press, the filter screen mesh number is 500 meshes, the filter cake after filtration is FePO4 precipitate, and the filtrate is a phosphoric acid-containing solution; the FePO4 precipitate after drying can be used as a raw material for preparing lithium iron phosphate positive electrode material, and the phosphoric acid-containing solution can be recycled;

[0044] Step 4, the lithium-containing solution obtained in Step 2 is transferred into a reaction kettle, and the pH value is adjusted to 2.5 by using the phosphoric acid-containing solution obtained in Step 3 to obtain a lithium dihydrogen phosphate aqueous solution;

[0045] Step 5, the lithium dihydrogen phosphate aqueous solution is evaporated by using a low-temperature evaporator at 40℃ until the specific gravity reaches 1.65, and then the solution is transferred into a crystallization kettle;

[0046] Step 6, after the solution is cooled to 25℃, centrifugation and drying are conducted to obtain battery-grade lithium dihydrogen phosphate. The finished product is sieved through an 80-mesh sieve, and the sieve-up material accounts for 78%.

[0047] Example 3

[0048] A low-cost battery-grade lithium dihydrogen phosphate preparation method comprises the following steps:

[0049] Step 1, take 100 Kg of pyrophosphoric acid aqueous solution (concentration of 70%) and add it into a stirring kettle, then add 120 Kg of lithium iron phosphate black powder into the stirring kettle, pass air into the stirring kettle at a flow rate of 200 L / min, and stir for 15 h to obtain a mixed solution A;

[0050] Step 2, the mixed solution A is subjected to solid-liquid separation through a plate-and-frame filter press, the filter screen mesh number is 500 meshes, the filter cake after filtration is Fe4(P2O7)3 precipitate, and the filtrate is a lithium-containing solution;

[0051] Step 3, Fe4(P2O7)3 precipitate is added into a stirred tank, pure water is added, the solid-liquid ratio is controlled to be 2:1, the solution pH value is adjusted to be 2.0 by using phosphoric acid, and stirring is performed for 15 h to obtain a mixed solution B; the mixed solution B is subjected to solid-liquid separation through a plate and frame filter press, the filter screen mesh number is 500 meshes, the filter cake after filtration is FePO4 precipitate, and the filtrate is a phosphoric acid solution; the FePO4 precipitate after drying can be used as a raw material for preparing a lithium iron phosphate positive electrode material, and the phosphoric acid solution can be recycled;

[0052] Step 4, the lithium-containing solution obtained after the mixed solution A is subjected to plate and frame filter pressing is transferred into a reaction kettle, the phosphoric acid-containing solution obtained in step 3 is used to adjust the pH value to 3.0, and a lithium dihydrogen phosphate aqueous solution is obtained;

[0053] Step 5, the lithium dihydrogen phosphate aqueous solution is evaporated by using a low-temperature evaporator at 50 DEG C, and when the specific gravity reaches 1.67, the solution is transferred into a crystallization kettle;

[0054] Step 6, after the solution is cooled to 25 DEG C, centrifugation and drying are performed to obtain a battery-grade lithium dihydrogen phosphate. The finished product is sieved through an 80-mesh sieve, and the sieve-up material accounts for 86%.

[0055] Comparative Example 1

[0056] A battery-grade lithium dihydrogen phosphate preparation method comprises the following steps:

[0057] (1) 835 g of 85% phosphoric acid (analytical pure) is taken, and 2839 g of deionized water is added to prepare a 20% phosphoric acid solution (about 3350 ml).

[0058] (2) At room temperature of 30 DEG C, the phosphoric acid prepared in step (1) is added to a reaction kettle, stirring is started, and 265 g of high-purity lithium carbonate is slowly added until the solution is clear, and then boiled for 30 min.

[0059] (3) The mass concentration of 85% phosphoric acid is added to the reaction kettle, and the pH value is adjusted to 2.50.

[0060] (4) 3 g of activated carbon is added to the lithium dihydrogen phosphate solution with the pH value of 2.50, and stirring is performed for 30 min to remove organic matters in the solution by using activated carbon, and then filtration is performed to obtain a lithium dihydrogen phosphate solution.

[0061] (5) The lithium dihydrogen phosphate solution obtained in step (4) is evaporated and concentrated by using steam heating, when T = 124 DEG C, the solution appears turbid and crystals are precipitated, the solution volume is concentrated from about 3350 ml to about 600 ml, and heating is stopped.

[0062] (6) The lithium dihydrogen phosphate slurry is cooled and crystallized while continuously stirring, and when the temperature drops to 40 DEG C, a large amount of crystals are precipitated, which is a wet lithium dihydrogen phosphate product.

[0063] (7) The wet product is dried at 105℃ for 2h, and then is subjected to air flow crushing to obtain the battery-grade lithium dihydrogen phosphate product A1, which has fine and uniform particle size.

[0064] Comparative Example 2

[0065] A method for preparing battery-grade lithium dihydrogen phosphate, comprising the following steps:

[0066] (1) 5 mol of lithium iron phosphate powder is added into 6 L of oxalic acid solution according to a molar ratio of lithium iron phosphate powder to oxalic acid in the oxalic acid solution of 1:1.2, and the powder is stirred for 15 min to fully dissolve to obtain a slurry;

[0067] (2) Lithium hydroxide is added into the slurry to adjust the pH value to 5, and the stirring is continued for 15 min, and FeC2O4·2H2O and other oxalate precipitates are removed by filtration to obtain a filtrate;

[0068] (3) EDTA is added into the filtrate according to a molar ratio of the total amount of metal in the filtrate to EDTA of 1:1.2 for complexation for 30 min, and then LiOH is added to adjust the pH value to 12, and the stirring is continued for 1 h, and lithium phosphate wet material and mother liquor are obtained by filtration;

[0069] (4) The lithium phosphate wet material is washed with deionized water to remove soluble impurity ions.

[0070] (5) Phosphoric acid (85%) is added into the lithium phosphate wet material to adjust Li / P=0.99 to obtain a lithium dihydrogen phosphate solution;

[0071] (6) The lithium dihydrogen phosphate solution is heated to 120℃ for evaporation until the solid content reaches 60%, and lithium dihydrogen phosphate powder is obtained by cooling crystallization;

[0072] (7) The wet product is subjected to flash drying to obtain battery-grade lithium dihydrogen phosphate powder.

[0073] Comparative Example 3

[0074] A method for preparing battery-grade lithium dihydrogen phosphate, comprising the following steps:

[0075] (1) 1000 g of waste lithium iron phosphate black powder is immersed in 380 g and 160 g of hydrogen peroxide, heated to 90℃, and immersed for 2 h to obtain a leaching solution and a phosphoric acid iron precipitate;

[0076] (2) The leaching solution in step (1) is heated to 90℃, and barium hydroxide is added, and solid-liquid separation is performed to obtain a lithium hydroxide solution;

[0077] (3) Phosphoric acid is added into the lithium hydroxide solution in step (2) to adjust the pH to 2 to obtain a lithium dihydrogen phosphate solution;

[0078] (4) heating the lithium dihydrogen phosphate solution to 120 DEG C to evaporate to solid content of 60%, cooling and crystallizing to obtain lithium dihydrogen phosphate powder, solid-liquid separation to obtain lithium dihydrogen phosphate wet material;

[0079] (5) flash drying the wet product to obtain battery-grade lithium dihydrogen phosphate powder.

[0080] Table 1: comparison of unit production cost of lithium dihydrogen phosphate of each example

[0081]

[0082] From the above example and comparative example analysis results can see the preparation battery-grade lithium dihydrogen phosphate method simple, easy to operate, low production cost, low temperature evaporation crystallization uniform, the product battery-grade lithium dihydrogen phosphate powder small proportion, effectively avoid the particle agglomeration, caking and other problems, conducive to the production process of material conveying, can be used for the preparation of lithium battery cathode material.

[0083] The above only describes the preferred embodiments of the present application, it should be noted that for those skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements should also be considered within the scope of the present application.

Claims

1. A process for the preparation of battery grade lithium dihydrogen phosphate, characterized in that, The method comprises the following steps: Step 1, mixing the lithium iron phosphate black powder with an aqueous pyrophosphoric acid solution, and introducing air to oxidize to obtain a mixed solution; Step 2, filtering the mixed solution obtained in step 1 to separate out Fe4(P2O7)3 precipitate to obtain a lithium-containing solution; Step 3, adjusting the pH value of the Fe4(P2O7)3 precipitate obtained in step 2 in water with phosphoric acid to a pH value of 0.8-3.5, and filtering to obtain FePO4 precipitate and a phosphoric acid-containing solution; Step 4, adjusting the pH value of the lithium-containing solution obtained in step 2 with the phosphoric acid-containing solution obtained in step 3 to a pH value of 1.5-4.0 to convert into a lithium dihydrogen phosphate solution; Step 5, the lithium dihydrogen phosphate solution in step 4 is evaporated at low temperature to become a supersaturated solution, and the temperature of the low-temperature evaporation is 35-50℃; Step 6, the supersaturated solution obtained in step 5 is cooled and crystallized, centrifuged, and dried to obtain battery-grade lithium dihydrogen phosphate.

2. The method of claim 1, wherein the battery grade lithium dihydrogen phosphate is prepared by the steps of: In step 1, the concentration of the aqueous pyrophosphoric acid solution is 30-80%. ​ 3. The method of claim 1, wherein the battery grade lithium dihydrogen phosphate is prepared by the steps of: In step 1, the weight ratio of the lithium iron phosphate black powder to the aqueous pyrophosphoric acid solution is (1.1-1.3):

1. ​ 4. The method of claim 1, wherein the battery grade lithium dihydrogen phosphate is prepared by the steps of: In step 1, the air is compressed air, and the air flow is 200-500 L / min. ​ 5. The method of claim 1, wherein the battery grade lithium dihydrogen phosphate is prepared by the steps of: In step 1, the oxidation time is 10-30 h. ​ 6. The method of claim 1, wherein the battery grade lithium dihydrogen phosphate is prepared by the steps of: In step 2, the mixed solution is filtered in a filter press, and the filter press is a plate-and-frame filter press, a chamber filter press, a vertical filter press, a belt filter press, or a closed and pressurized filter press, and the filter screen is 100-800 mesh. ​ 7. The method for preparing battery-grade lithium dihydrogen phosphate as described in claim 1, characterized in that, In step 3, the mass ratio of Fe4(P2O7)3 to water is (0.5-1.0):1.

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