Bimodal particle size lithium phosphate prepared from waste lithium iron phosphate battery powder

Abstract

The invention discloses double-peak particle size lithium phosphate prepared from waste lithium iron phosphate battery powder, which is prepared by the following steps: leaching the lithium iron phosphate battery powder in nitric acid, adding an oxidizing agent to obtain a liquid containing hetero-lithium nitrate, adjusting the pH value of the liquid containing hetero-lithium nitrate, filtering and concentrating to obtain a concentrated lithium liquid; a surfactant and phosphate are added into the concentrated lithium solution, the phosphate is added in two steps, the adding rate of the first step is lower than that of the second step, and lithium phosphate is obtained after full reaction; and finally, washing and drying to obtain high-purity lithium phosphate with a double-peak particle size structure. A nitric acid system is adopted for leaching reaction and impurity removal, and high-purity lithium phosphate can be obtained by utilizing the high-temperature decomposition characteristic of ammonium nitrate; and on the basis, the addition rate of the phosphate is set step by step, so that the lithium phosphate with the large and small particle sizes and the double-peak particle size structure is prepared.

Description

Technical Field

[0001] The invention belongs to the field of battery recycling and processing, and in particular relates to bimodal particle size lithium phosphate prepared from waste lithium iron phosphate battery powder. Background Art

[0002] Currently, there are two main methods for recovering lithium iron phosphate and producing lithium phosphate: one is phosphoric acid leaching, followed by purification of the lithium solution and reaction with phosphate to produce lithium phosphate; the other is sulfuric acid leaching, followed by purification of the lithium solution and reaction with phosphate to produce lithium phosphate. However, the former method has a slower leaching reaction rate and a longer leaching cycle, and the latter method cannot produce lithium phosphate with a purity exceeding 99.9%.

[0003] Current research on lithium phosphate development technology is mainly focused on improving the purity of lithium phosphate. For example, Chinese patent CN 116969430 B discloses a method for recovering and preparing battery-grade lithium phosphate from waste lithium iron phosphate battery positive electrode sheet powder, which can reduce the amount of impurities leached and improve the purity of lithium phosphate.

[0004] With the development of the application of iron phosphate in batteries, lithium phosphate with ordinary particle size can no longer meet the needs of batteries. Studies have found that the use of lithium phosphate with bimodal particle size to prepare batteries can achieve the following: 1. Large particle size particles increase the compaction density. High compaction density helps to store more energy in a limited space, which is especially important for electric vehicles and energy storage systems; 2. Improve conductivity. The presence of small particles can increase the conductivity of the material, help increase the diffusion rate of lithium ions, and thus improve the charge and discharge performance of the battery; 3. Improve rate performance. Materials with bimodal particle size distribution can provide more lithium ion transmission channels, thereby improving the rate performance of the battery, which means that the battery can be quickly charged and discharged in a short time without losing too much capacity; 4. Enhance cycle stability. Lithium phosphate materials with bimodal structure can better maintain structural stability during the cycle. This stability helps to extend the service life of the battery and reduce capacity attenuation during the cycle.

[0005] However, there is currently no research on the purification of lithium phosphate from waste lithium iron phosphate and its specific particle size distribution, micromorphology, etc.

[0006] Based on this, a method for preparing high-purity and bimodal particle size lithium phosphate based on waste lithium iron phosphate battery powder is studied. Summary of the Invention

[0007] Purpose of the invention: The technical problem to be solved by the present invention is how to prepare high-purity lithium phosphate with a bimodal particle size structure based on waste lithium iron phosphate battery powder.

[0008] Technical solution: The bimodal particle size lithium phosphate prepared from waste lithium iron phosphate battery powder is prepared by the following steps:

[0009] (1) leaching lithium iron phosphate battery powder in a nitric acid system and adding an oxidant to obtain a lithium nitrate solution;

[0010] (2) adjusting the pH of the impure lithium nitrate solution to 6-8, filtering, removing fluorine, and concentrating to obtain a concentrated lithium solution;

[0011] (3) calculating the total amount of phosphate added based on the lithium ion content in the lithium iron phosphate battery powder, adding a surfactant and phosphate to the concentrated lithium solution, wherein the phosphate is added in two steps, and the addition rate of the first step is lower than the addition rate of the second step, to obtain lithium phosphate;

[0012] (4) The lithium phosphate is washed and dried to obtain lithium phosphate with a bimodal particle size.

[0013] The present invention combines nitric acid leaching and lithium solution purification with phosphate reaction, utilizing the property of ammonium nitrate that it is easy to decompose at high temperatures to prepare high-purity lithium phosphate. Furthermore, during the synthesis of lithium phosphate, the size of the lithium phosphate particles is regulated by controlling the rate of phosphate addition to form lithium phosphate with a "bimodal" structure. Specifically, the phosphate is added to the lithium solution in two steps: in the first step, the phosphate is slowly introduced into the lithium solution, i.e., the phosphate supersaturation in the system is maintained at a low level, the rate of crystal nucleation is slow, and the solute has more time to deposit on the surface of existing crystal nuclei, promoting grain growth, and ultimately obtaining larger grains; in the second step, the rate of phosphate introduction into the lithium solution is controlled to be high. At this time, the supersaturation of ammonium phosphate in the system is rapidly increased compared to the supersaturation caused by the phosphate addition rate in the first step, resulting in a local supersaturation that is much higher than the supersaturation caused by the phosphate addition rate in the first step, resulting in a nucleation rate that is much higher than the growth rate, forming a large number of fine crystal nuclei, and ultimately obtaining smaller grains; at high supersaturation, the system tends to reduce energy by generating new crystal nuclei (rather than growing existing grains), producing small-sized particles, and ultimately obtaining lithium phosphate with a bimodal particle size.

[0014] Furthermore, in step (3) of preparing lithium phosphate of the present invention, when the phosphate is added in two steps, in the first step, the total time of phosphate addition is controlled to be 2-4 hours, and when the amount of phosphate added accounts for 40-50% of the total amount of phosphate added, the addition is stopped and the reaction is carried out for 2-3 hours; in the second step, the remaining phosphate is added, the total addition time is controlled to be 1-2 hours, and the reaction is carried out for 0.5-1 hour.

[0015] Furthermore, in step (1) of preparing lithium phosphate of the present invention, the amount of nitric acid added is such that the pH value of the system reaches 2-3, the temperature of the leaching reaction is 60-80° C., and the leaching reaction time is 2-3 hours.

[0016] Furthermore, in the step (1) of preparing lithium phosphate of the present invention, the oxidant is hydrogen peroxide, and the amount of hydrogen peroxide added is the theoretical amount of Fe 2+ All oxidized to Fe3+ 1.1-2.3 times the required computational effort.

[0017] Furthermore, in step (2) of preparing lithium phosphate of the present invention, the defluorination is carried out by passing the filtered impurity-removed liquid through a defluorination resin column at a flow rate of 0.5-1BV / h; the concentration of the concentrated lithium liquid is 20-30g / L.

[0018] Furthermore, in step (3) of preparing lithium phosphate of the present invention, the amount of surfactant added is 0.015-0.05% of the mass of the concentrated lithium solution, and the surfactant is one or more of ammonium citrate, polyethylene glycol, and methyl cellulose.

[0019] Furthermore, in step (3) of preparing lithium phosphate of the present invention, the phosphate includes at least one of monoammonium phosphate, diammonium phosphate or ammonium phosphate.

[0020] Furthermore, in step (3) of preparing lithium phosphate of the present invention, the phosphate is added in two steps in the form of a solution with a concentration of 150-250 g / L.

[0021] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: the bimodal particle size lithium phosphate is prepared by using a nitric acid system and removing impurities, and then utilizing the high-temperature decomposition characteristics of ammonium nitrate to obtain lithium phosphate with a purity of more than 99.9%; and by adding phosphate in steps and controlling the addition rate of the first step to be lower than the addition rate of the second step, a bimodal particle size structure of lithium phosphate with large and small particle sizes is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a graph showing the particle size test data of the lithium phosphate prepared in Example 1;

[0023] Figure 2 This is a graph showing the particle size test data of the lithium phosphate prepared in Example 2;

[0024] Figure 3 This is a graph showing the particle size test data of the lithium phosphate prepared in Comparative Example 1;

[0025] Figure 4 This is a graph showing the particle size test data of the lithium phosphate prepared in Comparative Example 2;

[0026] Figure 5 This is a graph showing the particle size test data of the lithium phosphate prepared in Example 3. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described in detail below with reference to the embodiments and drawings.

[0028] It should be noted that the total amount of phosphate added in the present invention is obtained based on the theoretical calculation of the lithium ion content in the lithium iron phosphate battery powder. In order to fully react, the amount added is 1.63 times the calculated amount. The theoretical calculated amount of oxidant is the amount of Fe in the leachate of lithium iron phosphate battery powder. 2+ All oxidized to Fe 3+ Required amount.

[0029] The main components of the lithium iron phosphate battery powder used in the following embodiments of the present invention are shown in Table 1 below:

[0030] Table 1 Main components of lithium iron phosphate battery powder

[0031]

[0032]

[0033] Example 1

[0034] In this embodiment, bimodal lithium phosphate is prepared from waste lithium iron phosphate battery powder, and its purity is 99.96%. It is prepared by the following steps:

[0035] (1) Take 500g of lithium iron phosphate battery powder, add 1000mL of pure water and stir to slurry for 0.5h, add nitric acid at 60℃ to adjust the pH of the slurry to 3, and react for 2h, then add 200g of hydrogen peroxide with a mass fraction of 30% (the amount added is the theoretical Fe 2+ All oxidized to Fe 3+ 2.3 times the required calculated amount), react for 0.5 h and filter to obtain a lithium nitrate solution containing impurities;

[0036] (2) adding ammonia water to the impurity-containing lithium nitrate solution at 60° C. for 1 h to adjust the pH to 7.5, and then filtering to obtain a decontaminated solution; passing the decontaminated solution through a fluorine removal resin column at a rate of 1 BV / h to obtain a lithium-containing solution; and then concentrating the lithium solution to 30 g / L at 80° C. to obtain a concentrated lithium solution;

[0037] (3) Weighing 167 g of ammonium phosphate and preparing it into an ammonium phosphate solution with a concentration of 150 g / L; adding 0.02% by weight of methyl cellulose to the concentrated lithium solution at 70° C.; then adding the ammonium phosphate solution in two steps, i.e., in the first stage, adding 50% of the amount, adding for 4 hours, and reacting for 2 hours, then adding the remaining ammonium phosphate solution, adding for 1 hour, and reacting for 0.5 hours, and finally filtering, washing, and drying at 220° C. to obtain the lithium phosphate product.

[0038] Test the particle size data of its lithium phosphate, such as Figure 1 As shown, two peaks are clearly formed in the figure.

[0039] Example 2

[0040] In this embodiment, the bimodal particle size lithium phosphate prepared from waste lithium iron phosphate battery powder has a product purity of 99.92%, and is specifically prepared by the following steps:

[0041] (1) 1000 g of lithium iron phosphate battery powder was added to 2000 mL of pure water and stirred for 1 h. Nitric acid was added at 70° C. to adjust the pH of the slurry to 3 and reacted for 2 h. 400 g of 30% hydrogen peroxide was added and reacted for 0.5 h. After that, the mixture was filtered to obtain a lithium nitrate solution containing impurities.

[0042] (2) adding ammonia water to the impurity-containing lithium nitrate solution at 70° C. for 1.5 h to adjust the pH to 8, and then filtering to obtain a decontaminated solution; passing the decontaminated solution through a fluorine removal resin column at a rate of 1 BV / h to obtain a lithium-containing solution; and then concentrating the lithium solution to 30 g / L at 80° C. to obtain a concentrated lithium solution;

[0043] (3) Weighing 334 g of ammonium phosphate and preparing it into an ammonium phosphate solution with a concentration of 150 g / L; adding 0.02% methyl cellulose to the concentrated lithium solution at 80° C.; then adding the ammonium phosphate solution in two steps, i.e., in the first stage, adding 40% of the amount, adding for 3 hours, and reacting for 2 hours, then adding the remaining ammonium phosphate solution, adding for 2 hours, and reacting for 0.5 hours, and finally filtering, washing, and drying at 200° C. to obtain the lithium phosphate product.

[0044] Test the particle size data of its lithium phosphate, such as Figure 2 As shown, two peaks are clearly formed in the figure.

[0045] Comparative Example 1: Ammonium phosphate is not added step by step

[0046] The preparation steps of Comparative Example 1 are basically the same as those of Example 1, except that ammonium phosphate is not added stepwise. The preparation steps of Comparative Example 1 specifically include the following steps:

[0047] (1) 500 g of lithium iron phosphate battery powder was added to 1000 mL of pure water and stirred for 0.5 h. Nitric acid was added at 60° C. to adjust the pH of the slurry to 2. After reacting for 2 h, 300 g of 30% hydrogen peroxide was added. After reacting for 0.5 h, the mixture was filtered to obtain a lithium nitrate solution containing impurities.

[0048] (2) adding aqueous ammonia to the impurity-containing lithium nitrate solution at 60° C. for 1 hour to adjust the pH to 7.5, and then filtering to obtain a decontaminated solution; passing the decontaminated solution through a fluorine removal resin column at a rate of 1 BV / h to obtain a lithium-containing solution; and then concentrating the lithium solution to 30 g / L at 80° C. to obtain a concentrated lithium solution;

[0049] (3) Weighing 167 g of ammonium phosphate and preparing it into an ammonium phosphate solution with a concentration of 150 g / L; adding 0.02% methyl cellulose to the concentrated lithium solution at 70° C.; then adding the ammonium phosphate solution, controlling the addition time to 5 h, and then reacting for 2.5 h. The final product was obtained after filtering, washing, and drying at 220° C.

[0050] Test the particle size data of its lithium phosphate, such as Figure 3 As shown, there is only one peak in the graph.

[0051] Comparative Example 2

[0052] The preparation steps in Comparative Example 2 are basically the same as those in Example 2, except that ammonium phosphate is not added stepwise. The purity of the product is 99.91%, and the product is prepared by the following steps:

[0053] (1) 1000 g of lithium iron phosphate battery powder was added to 2000 mL of pure water and stirred for 1 h. Nitric acid was added at 70° C. to adjust the pH of the slurry to 3 and reacted for 2 h. 400 g of 30% hydrogen peroxide was added and reacted for 0.5 h. After that, the mixture was filtered to obtain a lithium nitrate solution containing impurities.

[0054] (2) adding ammonia water to the impurity-containing lithium nitrate solution at 70° C. for 1.5 h to adjust the pH to 8, and then filtering to obtain a decontaminated solution; passing the decontaminated solution through a fluorine removal resin column at a rate of 1 BV / h to obtain a lithium-containing solution; and then concentrating the lithium solution to 30 g / L at 80° C. to obtain a concentrated lithium solution;

[0055] (3) Weighing 334 g of ammonium phosphate and preparing it into an ammonium phosphate solution with a concentration of 150 g / L; adding 0.02% methyl cellulose to the concentrated lithium solution at 80° C.; then adding the ammonium phosphate solution, controlling the addition time to 5 h, and then reacting for 3.5 h. The final product was obtained after filtering, washing, and drying at 220° C.

[0056] Test the particle size data of its lithium phosphate, such as Figure 4 As shown, there is only one peak in the graph.

[0057] Comparative Example 3 - Sulfuric Acid System Leaching

[0058] The preparation steps of Comparative Example 3 are basically the same as those of Example 1, except that a sulfuric acid system is used for leaching, and specifically include the following steps:

[0059] (1) 500 g of lithium iron phosphate battery powder was added to 1000 mL of pure water and stirred for 0.5 h. Sulfuric acid was added at 60 ° C to adjust the pH of the slurry to 3 and reacted for 2 h. Then, 200 g of 30% hydrogen peroxide was added and reacted for 0.5 h. After that, the mixture was filtered to obtain a lithium sulfate solution.

[0060] (2) adding ammonia water to the impurity-containing lithium sulfate solution at 60° C. for 1 h to adjust the pH to 7.5, and then filtering to obtain a decontaminated solution; passing the decontaminated solution through a fluorine removal resin column at a rate of 1 BV / h to obtain a lithium-containing solution; and then concentrating the lithium solution to 30 g / L at 80° C. to obtain a concentrated lithium solution;

[0061] (3) Weighing 167 g of ammonium phosphate and preparing it into an ammonium phosphate solution with a concentration of 150 g / L; adding 0.02% methyl cellulose to the concentrated lithium solution at 70° C.; then adding the ammonium phosphate solution in two steps, i.e., in the first stage, the addition amount is 50%, the addition time is 4 hours, and the reaction time is 2 hours, and then the remaining ammonium phosphate solution is added, the addition time is 1 hour, and the reaction time is 0.5 hours. Finally, the lithium phosphate product is obtained after filtering, washing, and drying at 220° C.

[0062] Example 3

[0063] In this embodiment, the bimodal particle size lithium phosphate prepared from waste lithium iron phosphate battery powder has a product purity of 99.95%, and is specifically prepared by the following steps:

[0064] (1) 500 g of lithium iron phosphate battery powder was added to 1000 mL of pure water and stirred for 0.5 h. Nitric acid was added at 80° C. to adjust the pH of the slurry to 3 and reacted for 2 h. Then, 200 g of 30% hydrogen peroxide was added and reacted for 0.5 h. After that, the mixture was filtered to obtain a lithium nitrate solution containing impurities.

[0065] (2) adding ammonia water to the impurity-containing lithium nitrate solution at 60° C. for 1 h, and then filtering to obtain a decontaminated solution; passing the decontaminated solution through a fluorine removal resin column at a rate of 1 BV / h to obtain a lithium-containing solution; and then concentrating the lithium solution to 30 g / L at 80° C. to obtain a concentrated lithium solution;

[0066] (3) Weighing 167 g of ammonium phosphate and preparing it into an ammonium phosphate solution with a concentration of 150 g / L; adding 0.03% of ammonium citrate to the concentrated lithium solution at 70° C.; then adding the ammonium phosphate solution in two steps, i.e., in the first stage, the addition amount is 45%, the addition time is 2 h, and the reaction time is 2 h, then the remaining ammonium phosphate solution is added, the addition time is 1 h, and the reaction time is 0.5 h. Finally, the lithium phosphate product is obtained after filtering, washing, and drying at 220° C.

[0067] Test the particle size data of its lithium phosphate, such as Figure 5 As shown, two peaks are clearly formed in the figure.

[0068] Ingredient testing

[0069] The lithium phosphate products obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were tested for the content of main components, and the results obtained are shown in Table 2 below.

[0070] Table 2 Main components of lithium phosphate prepared in Examples 1-3 and Comparative Examples 1-3

[0071]

[0072]

[0073] As shown in Table 2, the purity of the bimodal lithium phosphate prepared by the method of the present invention for preparing bimodal lithium phosphate with waste lithium iron phosphate battery powder can reach above 99.9%, which is much higher than 96.8% of Comparative Example 3.

[0074] In addition to the above embodiments, it should be noted that in the present invention, the ammonium phosphate salt in each stage is added to the concentrated lithium solution at a uniform rate, and the uniform addition makes the particle size of the final lithium phosphate more uniform; and the ammonium phosphate salt is prepared into an ammonium phosphate solution with a concentration of 150-250 g / L and added to the concentrated lithium solution.

[0075] The term "full reaction" as used herein refers to the formation of lithium phosphate of the desired particle size. Therefore, the full reaction time after adding the phosphate at each stage is determined based on the time required to form the desired lithium phosphate particle size. In Examples 1-3, to form lithium phosphate with dual particle sizes of approximately 2-3 μm and 60-70 μm, the full reaction time after adding ammonium phosphate in the first step was 2 hours, and after adding ammonium phosphate in the second step, the full reaction time was 0.5 hours.

[0076] In the present invention, the amount of surfactant added is preferably 0.015-0.05% of the mass of the concentrated lithium solution. If too much surfactant is added, it will be adsorbed on the surface of the product, affecting the purity and performance of the product. For example, when preparing a lithium salt product, excess surfactant may remain in the product, adversely affecting the electrochemical properties and stability of the product. If too little or no surfactant is added, the surface tension cannot be fully reduced, resulting in uneven dispersion of substances such as ammonium phosphate in the concentrated lithium solution, prone to agglomeration, resulting in insufficient reaction, affecting the quality and yield of the product.

[0077] The preparation process of the present invention and the parameter ranges defined therein can achieve the technical effects claimed by the present invention, and therefore no further examples are given to illustrate the technical effects. Furthermore, the phosphate is added in two steps at a uniform rate.

Claims

1. A bimodal particle size lithium phosphate prepared from waste lithium iron phosphate battery powder, characterized in that: Prepared by the following steps: (1) leaching lithium iron phosphate battery powder in a nitric acid system and adding an oxidant to obtain a lithium nitrate solution; (2) adjusting the pH of the impure lithium nitrate solution to 6-8, filtering, removing fluorine, and concentrating to obtain a concentrated lithium solution; (3) calculating the total amount of phosphate added based on the lithium ion content in the lithium iron phosphate battery powder, adding a surfactant and phosphate to the concentrated lithium solution, wherein the phosphate is added in two steps, and the addition rate of the first step is lower than the addition rate of the second step, to obtain lithium phosphate; (4) The lithium phosphate is washed and dried to obtain lithium phosphate with a bimodal particle size.

2. The bimodal particle size lithium phosphate according to claim 1, characterized in that In step (3), when the phosphate is added in two steps, the total phosphate addition time in the first step is controlled to be 2-4 hours, and the addition is stopped when the amount of phosphate added accounts for 40-50% of the total phosphate added, and the reaction is carried out for 2-3 hours; the remaining phosphate is added in the second step, the total addition time is controlled to be 1-2 hours, and the reaction is carried out for 0.5-1 hour.

3. The bimodal particle size lithium phosphate according to claim 1, characterized in that In step (1), the amount of nitric acid added is such that the pH value of the system reaches 2-3, the temperature of the leaching reaction is 60-80° C., and the leaching reaction time is 2-3 hours.

4. The bimodal particle size lithium phosphate according to claim 1, characterized in that In step (1), the oxidant is hydrogen peroxide, and the amount of hydrogen peroxide added is the theoretical amount of Fe 2+ All oxidized to Fe 3+ 1.1-2.3 times the required computational effort.

5. The bimodal particle size lithium phosphate according to claim 1, characterized in that In step (2), the defluorination is carried out by passing the filtered impurity-removed liquid through a defluorination resin column at a flow rate of 0.5-1BV / h; the concentration of the concentrated lithium solution is 20-30g / L.

6. The bimodal particle size lithium phosphate according to claim 1, characterized in that In step (3), the amount of surfactant added is 0.015-0.05% of the mass of the concentrated lithium solution, and the surfactant is one or more of ammonium citrate, polyethylene glycol, and methyl cellulose.

7. The bimodal particle size lithium phosphate according to claim 1, characterized in that In step (3), the phosphate includes at least one of monoammonium phosphate, diammonium phosphate or ammonium phosphate.

8. The bimodal particle size lithium phosphate according to claim 1, characterized in that In step (3), the phosphate is added in two steps in the form of a solution with a concentration of 150-250 g / L.

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