Preparation method of low-cost battery-grade lithium dihydrogen phosphate

Abstract

The invention discloses a low-cost battery-grade lithium dihydrogen phosphate preparation method, which comprises: 1, uniformly mixing a lithium iron phosphate black powder material and a pyrophosphoric acid aqueous solution, introducing air, and oxidizing to obtain a mixed solution; step 2, filtering and separating out Fe4 (P2O7) 3 precipitate from the mixed solution obtained in the step 1 to obtain a lithium-containing solution; step 3, precipitating the Fe4 (P2O7) 3 obtained in the step 2 in water, adjusting the pH value with 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 with the phosphoric acid solution obtained in the step 3, and converting the lithium-containing solution into a lithium dihydrogen phosphate solution; step 5, evaporating the lithium dihydrogen phosphate solution in the step 4 at low temperature to obtain a supersaturated solution; and step 6, carrying out cooling crystallization, centrifugation and drying on the supersaturated solution obtained in the step 5 to obtain the battery-grade lithium dihydrogen phosphate. The preparation method disclosed by the invention is low in energy consumption and low in cost, and the micro powder in the obtained battery-grade lithium dihydrogen phosphate is relatively small in proportion.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery positive electrode materials, and in particular relates to a method for preparing low-cost battery-grade lithium dihydrogen phosphate. Background Art

[0002] Along with the development of the new energy vehicle industry, my country's power battery industry has also made great progress. In 2023, China's new energy vehicle production and sales will reach 9.587 million and 9.495 million respectively, 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, and excellent safety performance.

[0003] At present, the main production methods of lithium iron phosphate (LiFePO4) at home and abroad are focused on the 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 phosphorus source and lithium source at the same time. When it is synthesized with iron oxalate as the main raw material, compared with other process paths, the compaction density and energy density are higher than other processes, becoming the main process solution and raw material for the third and fourth generation lithium iron phosphate.

[0004] However, the traditional preparation process of battery-grade lithium dihydrogen phosphate is mainly prepared by neutralization of phosphoric acid and lithium hydroxide or lithium carbonate, evaporation and crystallization. CN200810044349.X, CN201010118632.X, CN201010602973.7, etc. disclose methods 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 require the use of high-purity lithium hydroxide or lithium carbonate as raw materials, and the raw material cost is relatively high.

[0005] With the rapid development of the new energy industry, the market demand for lithium salts 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 purifying lithium-containing mother liquor, CN202311693817.7 discloses a method for preparing lithium dihydrogen phosphate using low-cost lithium hydroxide return solution intermediate process products as lithium sources, 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 ferrous phosphate waste. Such recycling and purification methods also ultimately have to go through high-energy consumption processes such as high-temperature heating evaporation and cooling crystallization, and the process cost is still relatively high. Summary of the invention

[0006] The purpose of the present invention is to provide a low-cost method for preparing battery-grade lithium dihydrogen phosphate in order to address the technical defects in the prior art of using waste lithium to prepare battery-grade lithium dihydrogen phosphate, which is complex and costly.

[0007] The technical solution adopted to achieve the purpose of the present invention is:

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

[0009] Step 1, mixing lithium iron phosphate black powder and pyrophosphoric acid aqueous solution evenly, introducing air to oxidize, and obtaining a mixed solution;

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

[0011] Step 3, precipitating the Fe4(P2O7)3 obtained in step 2 in water, adjusting the pH value with phosphoric acid, and filtering to obtain FePO4 precipitate and phosphoric acid solution;

[0012] 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, and converting 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, crystallized, centrifuged, and dried to obtain battery-grade lithium dihydrogen phosphate.

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

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

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

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

[0019] In the above technical scheme, in step 2, the mixed solution is passed into a filter press for filtration, 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 mesh.

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

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

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

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

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention 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 problem of environmental pollution caused by waste batteries, and enhances industrial value;

[0026] 2. In the preparation process, the present invention uses pyrophosphoric acid aqueous solution as the leaching agent, without other additives, and combines the conventional leaching and separation processes into one step to achieve the separation of the lithium-containing solution and the precipitate; the final 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 processes into one step, the process method is simple and reliable, the production cost is low, and it is very conducive to industrial production.

[0027] 3. The lithium-containing solution adopts low-temperature evaporation, which reduces energy consumption by more than 50%, significantly reduces production costs, and reduces production costs from multiple dimensions such as raw materials, processes, and equipment.

[0028] 4. The battery-grade lithium dihydrogen phosphate product prepared by the present invention passes through an 80-mesh sieve, and the material on the sieve accounts for 70-86%, and the fine powder accounts for a smaller proportion, indicating that the battery-grade lithium dihydrogen phosphate product prepared by the present invention is not easy to agglomerate and does not affect the production and feeding of downstream users. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Example 1

[0032] A method for preparing low-cost battery-grade lithium dihydrogen phosphate comprises the following steps:

[0033] Step 1, weighing 100 kg of pyrophosphoric acid aqueous solution (concentration of 60%) and adding it into a stirred tank, adding 110 kg of lithium iron phosphate black powder thereto, introducing air at a flow rate of 200 L / min, and stirring for 12 h to obtain a mixed solution A;

[0034] Step 2, the mixed solution A is passed through a plate and frame filter press for solid-liquid separation, the filter mesh number is 500 mesh, 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 to a stirred tank, pure water is added thereto, the solid-liquid ratio is controlled to be 2:1, the pH value of the solution is adjusted to 1.5 with phosphoric acid, and the reaction is stirred for 12 hours to obtain a mixed solution B, and the mixed solution B is passed through a plate and frame filter press for solid-liquid separation, the filter mesh number is 500 mesh, and the filter cake after filtration is the FePO4 precipitate, and the filtrate is a phosphoric acid solution; the FePO4 precipitate can be used as a raw material for making lithium iron phosphate positive electrode materials after drying, 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 with 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 at 35° C. using a low-temperature evaporator until the specific gravity reaches 1.63, and the solution is transferred to a crystallization kettle;

[0038] Step 6: After the solution is cooled to 25°C, it is centrifuged and dried to obtain battery-grade lithium dihydrogen phosphate. The finished product is sieved through an 80-mesh sieve, and the sieve-surface material accounts for 70%.

[0039] Example 2

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

[0041] Step 1, weighing 100 kg of pyrophosphoric acid aqueous solution (concentration of 70%) and adding it into a stirred tank, adding 120 kg of lithium iron phosphate black powder thereto, introducing air at a flow rate of 200 L / min, and stirring for 15 h to obtain a mixed solution A;

[0042] Step 2, the mixed solution A is passed through a plate and frame filter press for solid-liquid separation, the filter mesh number is 500 mesh, 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 to a stirred tank, pure water is added thereto, the solid-liquid ratio is controlled to be 2:1, the pH value of the solution is adjusted to 1.0 with phosphoric acid, and the mixture is stirred for 15 hours to obtain a mixed solution B; the mixed solution B is passed through a plate and frame filter press for solid-liquid separation, the filter mesh number is 500 mesh, and the filter cake after filtration is the FePO4 precipitate, and the filtrate is a phosphoric acid solution; the FePO4 precipitate can be used as a raw material for making lithium iron phosphate positive electrode materials after drying, and the phosphoric acid 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 with 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 at 40° C. using a low-temperature evaporator until the specific gravity reaches 1.65, and the solution is transferred to a crystallization kettle;

[0046] Step 6: After the solution is cooled to 25°C, it is centrifuged and dried to obtain battery-grade lithium dihydrogen phosphate. The finished product is sieved through an 80-mesh sieve, and the sieve-surface material accounts for 78%.

[0047] Example 3

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

[0049] Step 1, weighing 100 kg of pyrophosphoric acid aqueous solution (concentration of 80%) and adding it into a stirred tank, adding 130 kg of lithium iron phosphate black powder thereto, introducing air at a flow rate of 200 L / min, and stirring for 20 hours to obtain a mixed solution A;

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

[0051] Step 3, adding Fe4(P2O7)3 precipitate to a stirred tank, adding pure water thereto, controlling the solid-liquid ratio to be 2:1, adjusting the pH value of the solution to 2.0 with phosphoric acid, stirring and reacting for 15 hours to obtain a mixed solution B; passing the mixed solution B through a plate and frame filter press for solid-liquid separation, the filter mesh number is 500 mesh, and the filter cake after filtration is FePO4 precipitate, and the filtrate is a phosphoric acid solution; the FePO4 precipitate can be used as a raw material for making lithium iron phosphate positive electrode materials after drying, and the phosphoric acid solution can be recycled;

[0052] Step 4, the lithium-containing solution obtained after the mixed solution A passes through a plate-frame filter press is transferred into a reaction kettle, and the pH value is adjusted to 3.0 with the phosphoric acid-containing solution obtained in step 3 to obtain a lithium dihydrogen phosphate aqueous solution;

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

[0054] Step 6: After the solution is cooled to 25°C, it is centrifuged and dried to obtain battery-grade lithium dihydrogen phosphate. The finished product is sieved through an 80-mesh sieve, and the sieve-surface material accounts for 86%.

[0055] Comparative Example 1

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

[0057] (1) Take 835 g of 85% phosphoric acid (analytical grade) and add 2839 g of deionized water to prepare a 20% phosphoric acid solution (about 3350 ml).

[0058] (2) At room temperature of 30° C., add the phosphoric acid prepared in step (1) into a reaction kettle, start stirring, and slowly add 265 g of high-purity lithium carbonate until the solution becomes clear and boil for 30 minutes.

[0059] (3) Add 85% mass concentration of phosphoric acid into the reactor and adjust the pH value to 2.50.

[0060] (4) Add 3 g of activated carbon to the above-mentioned lithium dihydrogen phosphate solution with a pH of 2.50 and stir for 30 min. Use the activated carbon to attach organic matter in the solution and filter out impurities to obtain a lithium dihydrogen phosphate solution.

[0061] (5) Evaporation concentration: The lithium dihydrogen phosphate solution obtained in step (4) is heated by steam. When T=124°C, turbidity appears in the solution, i.e., crystals are precipitated. The volume of the solution is concentrated from the original about 3350 ml to about 600 ml, and the heating is stopped.

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

[0063] (7) The wet product was dried at 105° C. for 2 h, and then subjected to air flow pulverization to obtain a battery-grade lithium dihydrogen phosphate product A1, which had fine particles with uniform particle size.

[0064] Comparative Example 2

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

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

[0067] (2) adding lithium hydroxide to the slurry to adjust the pH value to 5, continuing stirring for 15 minutes, filtering to remove FeC2O4·2H2O and other oxalate precipitates to obtain a filtrate;

[0068] (3) adding EDTA to the filtrate at a molar ratio of the metal content to EDTA of 1:1.2 for complexation for 30 min, then adding LiOH to adjust the pH value to 12, stirring for 1 h, and filtering to obtain lithium phosphate wet material and mother liquor;

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

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

[0071] (6) heating the lithium dihydrogen phosphate solution to 120° C. to evaporate until the solid content reaches 60%, and cooling and crystallizing to obtain lithium dihydrogen phosphate powder;

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

[0073] Comparative Example 3

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

[0075] (1) Take 1000g of waste lithium iron phosphate black powder, add 380g and 160g of hydrogen peroxide for leaching, heat to 90°C, and leach for 2h to obtain a leachate and iron phosphate precipitate;

[0076] (2) heating the leachate in step (1) to 90° C., adding barium hydroxide, and performing solid-liquid separation to obtain a lithium hydroxide solution;

[0077] (3) adding phosphoric acid to 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° C. to evaporate until the solid content reaches 60%, cooling and crystallizing to obtain lithium dihydrogen phosphate powder, and separating the solid from the liquid to obtain lithium dihydrogen phosphate wet material;

[0079] (5) The wet product is flash dried to obtain battery-grade lithium dihydrogen phosphate powder.

[0080] Table 1 Comparison of unit production costs of lithium dihydrogen phosphate in various embodiments

[0081]

[0082]

[0083] From the above-mentioned embodiments and comparative example analysis results, it can be seen that the method for preparing battery-grade lithium dihydrogen phosphate of the present invention is simple, easy to operate, and has low production cost. The low-temperature evaporation crystallization is uniform, and the proportion of fine powder in the obtained battery-grade lithium dihydrogen phosphate product is small, which effectively avoids problems such as particle agglomeration and agglomeration, is beneficial to the transportation of materials in the production process, and can be used to prepare lithium battery positive electrode materials.

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing low-cost battery-grade lithium dihydrogen phosphate, characterized in that: The steps include: Step 1, mixing lithium iron phosphate black powder and pyrophosphoric acid aqueous solution evenly, introducing air to oxidize, and obtaining a mixed solution; Step 2, filtering the mixed solution obtained in step 1 to separate Fe4(P2O7)3 precipitate to obtain a lithium-containing solution; Step 3, precipitating the Fe4(P2O7)3 obtained in step 2 in water, adjusting the pH value with phosphoric acid, and filtering to obtain FePO4 precipitate and phosphoric acid 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, and converting it 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; Step 6: The supersaturated solution obtained in step 5 is cooled, crystallized, centrifuged, and dried to obtain battery-grade lithium dihydrogen phosphate.

2. The method for preparing low-cost battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that: In the step 1, the concentration of the pyrophosphoric acid aqueous solution is 30-80%.

3. The method for preparing low-cost battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that: In the step 1, the weight ratio of the lithium iron phosphate black powder to the pyrophosphoric acid aqueous solution is (1.1-1.3):

1.

4. The method for preparing low-cost battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that: In the step 1, the air is compressed air, and the air flow rate is 200-500L / min.

5. The method for preparing low-cost battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that: In the step 1, the oxidation time is 10-30h.

6. The method for preparing low-cost battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that: In step 1 and step 2, the mixed solution is passed through a filter press for filtration, 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 mesh.

7. The method for preparing low-cost battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that: In step 1 and step 3, the mass ratio of Fe4(P2O7)3 to water is (0.5-1.0):

1.

8. The method for preparing low-cost battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that: In step 1 and step 3, the pH value is adjusted to 0.8-3.

5.

9. The method for preparing low-cost battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that: In step 1 and step 4, the pH value is adjusted to 1.5-4.

0.

10. The method for preparing low-cost battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that: In the step 1 and the step 5, the temperature of the low temperature evaporation is 35 to 75°C.

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