Method for recycling waste lithium batteries to synthesize nanoscale lithium phosphate

Abstract

The invention discloses a method for recycling waste lithium batteries to synthesize nanoscale lithium phosphate, which comprises the following steps: calcining and slurrying positive electrode black powder of the waste lithium batteries to obtain slurry, and carrying out acid leaching and impurity removal to obtain pure lithium liquid; and adding a phosphorus salt solution into the pure lithium solution or the concentrated lithium solution obtained by concentrating the pure lithium solution, reacting and concentrating to obtain the nano-scale lithium phosphate. According to the synthesis method disclosed by the invention, the phosphorus salt is prepared into a solution form, and the solid-to-liquid ratio of the phosphorus salt is limited by adopting a specific calculation method, so that not only can lithium phosphate with the purity of 99% or above be synthesized, but also high-activity nanoscale lithium phosphate can be obtained, and the size range of the nanoscale lithium phosphate is less than or equal to 700nm; meanwhile, according to different positive electrode black powder components of the waste lithium batteries, uniform particle size morphology regulation and control can be realized, product stability among different batches is formed, and the method is suitable for large-scale industrial application.

Description

A method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate Technical Field

[0001] This invention belongs to the field of waste lithium battery recycling technology, and particularly relates to a method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate. Background Technology

[0002] Currently, the mainstream production route for LFP uses iron phosphate and lithium carbonate as raw materials and prepares them through solid-state sintering. Although this route is mature, it still has the following inherent disadvantages: (1) High energy consumption: Poor uniformity of solid-state mixing often requires higher sintering temperatures and longer reaction times, resulting in high energy consumption; (2) Product performance bottleneck: Traditional processes have high requirements for the consistency of precursors, making it difficult to avoid defects such as iron dislocations and lithium vacancies, which restricts further improvement in product capacity and rate performance.

[0003] Currently, lithium iron phosphate, which integrates both phosphorus and lithium sources, is not directly used as a raw material for LFP because morphology control is the core technology when using lithium phosphate as an LFP raw material. The morphology and particle size of lithium phosphate are directly inherited by the final synthesized LFP. In order to manufacture high-performance lithium iron phosphate with higher tap density, there are very stringent requirements for the crystal morphology and tap density of the precursor lithium phosphate.

[0004] Existing lithium phosphate products are prepared from raw materials such as ores and salt lakes, and also from recycled lithium batteries. The conventional steps in the recycled lithium battery lithium phosphate preparation process are: calcination of battery black powder, slurry formation, acid leaching, impurity removal, concentration, and then addition of solid phosphate salts to react and obtain lithium phosphate. The amount of phosphate salt added is considered to determine the theoretical lithium phosphate production. Currently, the resulting lithium phosphate is all micron-sized, with low activity, and cannot be directly used as a raw material for the preparation of lithium iron phosphate products.

[0005] Based on this, a novel synthesis process for preparing lithium phosphate by recycling waste lithium batteries is designed to obtain highly active lithium phosphate, which can be used as a raw material or a nucleating agent for iron phosphate and directly applied to the preparation of lithium iron phosphate products. This allows for the control of upstream raw materials to obtain LFP materials with more complete crystal structures and fewer defects. Summary of the Invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a novel method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate, so as to obtain highly active lithium phosphate.

[0007] Technical solution: The present invention provides a method for synthesizing nano-sized lithium phosphate from recycled waste lithium batteries, comprising the following steps:

[0008] (1) The positive electrode black powder of waste lithium battery is calcined and pulped to obtain slurry, and then purified lithium liquid is obtained after acid leaching and impurity removal;

[0009] (2) A phosphate salt solution is added to a pure lithium solution for reaction and concentration to obtain nano-sized lithium phosphate; wherein the liquid-to-solid ratio of the added phosphate salt solution is determined by the following formula:

[0010] ;

[0011] In the formula: C is the concentration of lithium in the pure lithium liquid (g / L); L / S is the liquid-to-solid ratio of the slurry; W is the percentage of lithium in the cathode black powder.

[0012] Alternatively, the method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate according to the present invention includes the following steps:

[0013] (1) The positive electrode black powder of waste lithium battery is calcined and pulped to obtain slurry, and then purified lithium liquid is obtained after acid leaching and impurity removal;

[0014] (2) The obtained pure lithium liquid is concentrated to obtain concentrated lithium liquid;

[0015] (3) Add a phosphate salt solution to the concentrated lithium solution to react and concentrate it to obtain nano-sized lithium phosphate; wherein the liquid-to-solid ratio of the added phosphate salt solution is determined by the following formula:

[0016] ;

[0017] In the formula: C is the concentration of lithium in the concentrated lithium solution (g / L); L / S is the liquid-to-solid ratio of the slurry; W is the percentage of lithium in the cathode black powder.

[0018] This invention is based on existing purified lithium liquid obtained through calcination, leaching, and impurity removal. By adding phosphate salts according to the theoretical amount of lithium phosphate to form a solution and limiting the solid-liquid ratio, nanoscale highly active lithium phosphate can be obtained. Simultaneously, it can achieve morphological stability between different batches of recycled cathode black powder with different compositions, enabling large-scale industrial utilization.

[0019] Furthermore, the solids ratio L / S of the black powder slurry formed in the synthesis process of this invention can be (3-10):1

[0020] Furthermore, the phosphate salt used in the synthesis process of this invention can be selected from at least one of trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, monoammonium phosphate, or ammonium phosphate. The amount of phosphate salt added is 1.01-1.3 times the theoretical amount of lithium phosphate.

[0021] Furthermore, the calcination temperature of the cathode black powder used in the synthesis process of this invention is 500-600℃, and the calcination time is 2-4 hours.

[0022] Furthermore, the acid leaching process used in the synthesis process of this invention involves leaching the lithium iron phosphate black powder slurry with acid and an oxidizing agent for 3-8 hours. The acid used can be selected from oxalic acid, formic acid, citric acid, or benzenesulfonic acid, and its addition amount is 1-1.1 times the theoretical amount of dissolved lithium. The oxidizing agent used can be selected from oxygen, hydrogen peroxide, chlorine, concentrated sulfuric acid, or concentrated nitric acid, and its addition amount is 1-1.1 times the theoretical amount of dissolved lithium.

[0023] Furthermore, the impurity removal process used in the synthesis process of this invention includes a one-step impurity removal using an alkaline solution and a two-step impurity removal using a chelating resin. The alkaline solution is selected from one of sodium hydroxide solution, lithium hydroxide solution, or ammonia water, and its addition amount is used to adjust the pH of the acid leaching solution to 6-9.

[0024] Beneficial effects: Compared with the prior art, the significant advantages of this invention are: by preparing phosphate salts into solution and using a specific calculation method to limit the solid-liquid ratio, this synthesis method can not only synthesize lithium phosphate with a purity of over 99%, but also obtain highly active nanoscale lithium phosphate with a size range of ≤700nm; at the same time, the particle size morphology can be uniformly controlled according to the cathode black powder of waste lithium batteries with different lithium contents, achieving stable product performance between different batches, and is suitable for large-scale industrial applications. Attached Figure Description

[0025] Figure 1 is a diagram of the lithium phosphate powder sample prepared in Example 1 of the present invention;

[0026] Figure 2 is a scanning electron microscope image of the lithium phosphate prepared in Example 1;

[0027] Figure 3 is a scanning electron microscope image of the lithium phosphate prepared in Comparative Example 1;

[0028] Figure 4 is a scanning electron microscope image of the lithium phosphate prepared in Example 2;

[0029] Figure 5 shows the scanning electron microscope image of the lithium phosphate prepared in Comparative Example 2;

[0030] Figure 6 is a scanning electron microscope image of the lithium phosphate prepared in Example 3;

[0031] Figure 7 shows the scanning electron microscope image of the lithium phosphate prepared in Comparative Example 3;

[0032] Figure 8 is a scanning electron microscope image of the lithium phosphate prepared in Example 4;

[0033] Figure 9 shows the scanning electron microscope image of the lithium phosphate prepared in Comparative Example 4;

[0034] Figure 10 is a scanning electron microscope image of the lithium phosphate prepared in Example 5;

[0035] Figure 11 is an electron micrograph of the lithium phosphate prepared in Comparative Example 5. Detailed Implementation

[0036] The technical solution of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0037] In the following embodiments and comparative examples of the present invention, the positive electrode black powder is obtained by puncturing and discharging the recycled waste lithium iron phosphate batteries, disassembling and separating the casing, separator and foil, and then collecting them.

[0038] In this embodiment of the invention, the liquid-to-solid ratio of the phosphate salt solution is determined by the following formula:

[0039] ;

[0040] In the formula: C is the lithium concentration in pure lithium liquid (g / L) or concentrated lithium liquid (g / L); L / S is the liquid-to-solid ratio of the black powder slurry; W is the percentage value of lithium in the cathode black powder.

[0041] Example 1

[0042] The main components of the positive electrode black powder in Example 1 are shown in Table 1 below.

[0043] Table 1. Main components of the positive electrode black powder in Example 1

[0044]

[0045] The method for synthesizing nano-sized lithium phosphate from recycled waste lithium batteries in this embodiment includes the following steps:

[0046] (1) After calcining the positive electrode black powder at a high temperature of 550℃ for 2 hours, water is added to the calcined positive electrode black powder according to the liquid-solid ratio L / S of 4:1, and the mixture is slurried for 0.5 hours to obtain black powder slurry.

[0047] (2) Add 1.05 times the theoretical amount of dissolved lithium in oxalic acid and 1.1 times the theoretical amount of dissolved lithium in hydrogen peroxide to the black powder slurry for acid leaching for 4 hours. After filtration, lithium-containing leachate and leachate residue are obtained respectively.

[0048] (3) Add 25% ammonia water to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to 6 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0049] (4) The lithium concentration C of the pure lithium liquid was measured to be 5 g / L. Trisodium phosphate was used as the phosphate salt, and its addition amount was 1.05 times the theoretical amount of lithium phosphate. Trisodium phosphate solution was prepared according to the water-to-solid ratio of 3.35:1 and added to the pure lithium liquid. Lithium phosphate was obtained by MVR reaction concentration.

[0050] The lithium phosphate powder synthesized in Example 1 is shown in Figure 1, and its purity is shown in Table 2. Its scanning electron microscope image is shown in Figure 2, revealing that the finished lithium phosphate particle size is 300 nm.

[0051] Table 2. Lithium phosphate composition synthesized in Example 1

[0052]

[0053] Comparative Example 1

[0054] This comparative example is basically the same as Example 1, except that the phosphate salt is added directly in solid form. The specific steps are as follows:

[0055] (2) After calcining the positive electrode black powder at a high temperature of 550℃ for 2 hours, water is added to the calcined positive electrode black powder according to a liquid-solid ratio of 4:1 (L / S), and the mixture is slurried for 0.5 hours to obtain black powder slurry.

[0056] (2) Add 1.05 times the theoretical amount of dissolved lithium in oxalic acid and 1.1 times the theoretical amount of dissolved lithium in hydrogen peroxide to the black powder slurry for acid leaching for 4 hours. After filtration, lithium-containing leachate and leachate residue are obtained respectively.

[0057] (3) Add 25% ammonia water to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to 6 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0058] (4) The lithium concentration C of the pure lithium liquid was measured to be 5 g / L. Trisodium phosphate was used as the phosphate salt and the amount added was 1.05 times the theoretical amount of lithium phosphate. It was added to the pure lithium liquid and concentrated by MVR reaction to obtain lithium phosphate.

[0059] The electron microscope scanning image of Comparative Example 1 is shown in Figure 3. The particle size of the finished lithium phosphate is 3.4 μm; and its purity is shown in Table 3.

[0060] Table 3. Lithium phosphate composition synthesized in Comparative Example 1

[0061] Example 2

[0062] The main components of the positive electrode black powder in this Example 2 are shown in Table 4 below.

[0063] Table 4 Main components of the positive electrode black powder in Example 2

[0064]

[0065] The method for synthesizing nano-sized lithium phosphate from recycled waste lithium batteries in this embodiment includes the following steps:

[0066] (1) After calcining the positive electrode black powder at a high temperature of 550℃ for 2 hours, water is added to the calcined positive electrode black powder according to a liquid-solid ratio of 4:1 (L / S), and the mixture is slurried for 0.5 hours to obtain black powder slurry.

[0067] (2) Add 1.05 times the theoretical amount of dissolved lithium in oxalic acid and 1.1 times the theoretical amount of dissolved lithium in hydrogen peroxide to the black powder slurry for acid leaching for 4 hours. After filtration, lithium-containing leachate and leachate residue are obtained respectively.

[0068] (3) Add 25% ammonia water to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to about 6 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0069] (4) After the pure lithium liquid is concentrated by MVR, its lithium concentration C is measured to be 20 g / L. Trisodium phosphate is used as the phosphate salt, and its addition amount is 1.05 times the theoretical amount of lithium phosphate. Trisodium phosphate solution is prepared according to the water-to-solid ratio of 12.4:1 and added to the pure lithium liquid. Lithium phosphate is obtained by MVR reaction concentration.

[0070] The purity of the lithium phosphate synthesized in Example 2 is shown in Table 5. Its scanning electron microscope image is shown in Figure 4, revealing that the finished lithium phosphate particle size is 500 nm.

[0071] Table 5. Lithium phosphate composition synthesized in Example 2

[0072]

[0073] Comparative Example 2

[0074] This comparative example is basically the same as Example 2, except that the phosphate salt is added directly in solid form. The specific steps are as follows:

[0075] (1) After calcining the positive electrode black powder at a high temperature of 550℃ for 2 hours, water is added to the calcined positive electrode black powder according to a liquid-solid ratio of 4:1 (L / S), and the mixture is slurried for 0.5 hours to obtain black powder slurry.

[0076] (2) Add 1.05 times the theoretical amount of dissolved lithium in oxalic acid and 1.1 times the theoretical amount of dissolved lithium in hydrogen peroxide to the black powder slurry for acid leaching for 4 hours. After filtration, lithium-containing leachate and leachate residue are obtained respectively.

[0077] (3) Add 25% ammonia water to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to about 6 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0078] (4) After the pure lithium liquid is concentrated by MVR, its lithium concentration C is measured to be 20 g / L. Trisodium phosphate is used as the phosphate salt, and its addition amount is 1.05 times the theoretical amount of lithium phosphate. It is added to the pure lithium liquid and concentrated by MVR reaction to obtain lithium phosphate.

[0079] The purity of the lithium phosphate synthesized in Comparative Example 2 is shown in Table 6. Its scanning electron microscope (SEM) image is shown in Figure 5, revealing that the finished lithium phosphate particle size is 1.9 μm.

[0080] Table 6. Lithium phosphate composition synthesized in Comparative Example 2

[0081] Example 3

[0082] The main components of the positive electrode black powder in Example 3 are shown in Table 7 below.

[0083] Table 7 Main components of the positive electrode black powder in Example 3

[0084]

[0085] The method for synthesizing nano-sized lithium phosphate from recycled waste lithium batteries in this embodiment includes the following steps:

[0086] (1) After calcining the positive electrode black powder at a high temperature of 500℃ for 4 hours, water is added to the calcined positive electrode black powder according to a liquid-solid ratio of 5:1 (L / S), and the mixture is slurried for 1 hour to obtain black powder slurry.

[0087] (2) Add benzenesulfonic acid (1.01 times the theoretical amount of dissolved lithium) and oxygen (1.05 times the theoretical amount of dissolved lithium) to the black powder slurry and leach for 5 hours. After filtration, lithium-containing leachate and leach residue are obtained respectively.

[0088] (3) Add a 32% sodium hydroxide solution to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to about 8 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0089] (4) After the pure lithium liquid is concentrated by MVR, its lithium concentration C is measured to be 15 g / L. Monoammonium phosphate is used as the phosphate salt, and its addition amount is 1.1 times the theoretical amount of lithium phosphate. The monoammonium phosphate solution is prepared according to the water-solid ratio of 8.52:1 and added to the pure lithium liquid. Lithium phosphate is obtained by MVR reaction concentration.

[0090] The purity of the lithium phosphate synthesized in Example 3 is shown in Table 8. Its scanning electron microscope image is shown in Figure 6, revealing that the finished lithium phosphate particle size is 200 nm.

[0091] Table 8. Lithium phosphate composition synthesized in Example 3

[0092]

[0093] Comparative Example 3

[0094] This comparative example is basically the same as Example 3, except that the phosphate salt is added directly in solid form. The specific steps are as follows:

[0095] (1) After calcining the positive electrode black powder at a high temperature of 500℃ for 4 hours, water is added to the calcined positive electrode black powder according to a liquid-solid ratio of 5:1 (L / S), and the mixture is slurried for 1 hour to obtain black powder slurry.

[0096] (2) Add benzenesulfonic acid (1.01 times the theoretical amount of dissolved lithium) and oxygen (1.05 times the theoretical amount of dissolved lithium) to the black powder slurry and leach for 5 hours. After filtration, lithium-containing leachate and leach residue are obtained respectively.

[0097] (3) Add a 32% sodium hydroxide solution to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to about 8 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0098] (4) After the pure lithium liquid is concentrated by MVR, its lithium concentration C is measured to be 15 g / L. Monoammonium phosphate is used as the phosphate salt, and its addition amount is 1.1 times the theoretical amount of lithium phosphate. It is added to the pure lithium liquid and concentrated by MVR reaction to obtain lithium phosphate.

[0099] The purity of the lithium phosphate synthesized in Comparative Example 3 is shown in Table 9. Its scanning electron microscope (SEM) image is shown in Figure 7, and the particle size of the finished lithium phosphate is 1.8 μm.

[0100] Table 9. Lithium phosphate composition synthesized in Comparative Example 3

[0101] Example 4

[0102] The main components of the positive electrode black powder in Example 4 are shown in Table 10 below.

[0103] Table 10 Main components of the positive electrode black powder in Example 4

[0104]

[0105] The method for synthesizing nano-sized lithium phosphate from recycled waste lithium batteries in this embodiment includes the following steps:

[0106] (1) After calcining the positive electrode black powder at a high temperature of 600℃ for 4 hours, water is added to the calcined positive electrode black powder according to a liquid-solid ratio of 4:1 (L / S), and the mixture is slurried for 0.5 hours to obtain black powder slurry.

[0107] (2) Add 1.02 times the theoretical amount of dissolved lithium in citric acid and 1.02 times the theoretical amount of dissolved lithium in hydrogen peroxide to the black powder slurry and leach for 4 hours. After filtration, lithium-containing leachate and leach residue are obtained respectively.

[0108] (3) Add 25% ammonia water to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to about 7 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0109] (4) After the pure lithium liquid is concentrated by MVR, its lithium concentration C is measured to be 10 g / L. Monoammonium phosphate is used as the phosphate salt, and its addition amount is 1.08 times the theoretical amount of lithium phosphate. The monoammonium phosphate solution is prepared according to the water-to-solid ratio of 6.8:1 and added to the pure lithium liquid. The lithium phosphate is obtained by MVR reaction concentration.

[0110] The purity of the lithium phosphate synthesized in Example 4 is shown in Table 11. Its scanning electron microscope image is shown in Figure 8, revealing that the finished lithium phosphate particle size is 200 nm.

[0111] Table 11 Lithium phosphate composition synthesized in Example 4

[0112]

[0113] Comparative Example 4

[0114] This comparative example is basically the same as Example 4, except that the phosphate salt is added directly in solid form. The specific steps are as follows:

[0115] (1) After calcining the positive electrode black powder at a high temperature of 600℃ for 4 hours, water is added to the calcined positive electrode black powder according to a liquid-solid ratio of 4:1 (L / S), and the mixture is slurried for 0.5 hours to obtain black powder slurry.

[0116] (2) Add oxalic acid and hydrogen peroxide, which are 1.02 times the theoretical amount of dissolved lithium, to the black powder slurry and leach for 4 hours. After filtration, lithium-containing leachate and leach residue are obtained respectively.

[0117] (3) Add 25% ammonia water to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to about 7 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0118] (4) After the pure lithium liquid is concentrated by MVR, its lithium concentration C is measured to be 20 g / L. Monoammonium phosphate is used as the phosphate salt, and its addition amount is 1.08 times the theoretical amount of lithium phosphate. It is added to the pure lithium liquid and concentrated by MVR reaction to obtain lithium phosphate.

[0119] The purity of the lithium phosphate synthesized in Comparative Example 4 is shown in Table 12. Its scanning electron microscope (SEM) image is shown in Figure 9, and the particle size of the finished lithium phosphate is 1.4 μm.

[0120] Table 12 Lithium phosphate composition synthesized in Comparative Example 4

[0121]

[0122] Example 5

[0123] The main components of the positive electrode black powder in Example 5 are shown in Table 13 below.

[0124] Table 13 Main components of the positive electrode black powder in Example 5

[0125]

[0126] The method for synthesizing nano-sized lithium phosphate from recycled waste lithium batteries in this embodiment includes the following steps:

[0127] (1) After calcining the positive electrode black powder at a high temperature of 600℃ for 4 hours, water is added to the calcined positive electrode black powder according to a liquid-solid ratio of L / S of 10:1, and the mixture is slurried for 0.5 hours to obtain black powder slurry.

[0128] (2) Add 1.02 times the theoretical amount of dissolved lithium in citric acid and 1.02 times the theoretical amount of dissolved lithium in hydrogen peroxide to the black powder slurry and leach for 4 hours. After filtration, lithium-containing leachate and leach residue are obtained respectively.

[0129] (3) Add 25% ammonia water to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to about 7 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0130] (4) After the pure lithium liquid is concentrated by MVR, its lithium concentration C is measured to be 30 g / L. Monoammonium phosphate is used as the phosphate salt, and its addition amount is 1.08 times the theoretical amount of lithium phosphate. The monoammonium phosphate solution is prepared according to the water-to-solid ratio of 8.79:1 and added to the pure lithium liquid. The lithium phosphate is obtained by MVR reaction concentration.

[0131] The purity of the lithium phosphate synthesized in Example 4 is shown in Table 14. Its scanning electron microscope image is shown in Figure 10, revealing that the finished lithium phosphate particle size is 500 nm.

[0132] Table 14 Lithium phosphate composition synthesized in Example 5

[0133]

[0134] Comparative Example 5

[0135] This comparative example is basically the same as Example 5, except that the phosphate salt is added directly in solid form. The specific steps are as follows:

[0136] (1) After calcining the positive electrode black powder at a high temperature of 600℃ for 4 hours, water is added to the calcined positive electrode black powder according to a liquid-solid ratio of L / S of 10:1, and the mixture is slurried for 0.5 hours to obtain black powder slurry.

[0137] (2) Add oxalic acid and hydrogen peroxide, which are 1.02 times the theoretical amount of dissolved lithium, to the black powder slurry and leach for 4 hours. After filtration, lithium-containing leachate and leach residue are obtained respectively.

[0138] (3) Add 25% ammonia water to the lithium-containing leachate to adjust the pH of the lithium-containing leachate to about 7 for one-step impurity removal, and then remove impurities by LSC-500 aminophosphonic acid resin to obtain pure lithium liquid.

[0139] (4) After the pure lithium liquid is concentrated by MVR, its lithium concentration C is measured to be 30 g / L. Monoammonium phosphate is used as the phosphate salt, and its addition amount is 1.08 times the theoretical amount of lithium phosphate. It is added to the pure lithium liquid and concentrated by MVR reaction to obtain lithium phosphate.

[0140] The purity of the lithium phosphate synthesized in Comparative Example 5 is shown in Table 15. Its scanning electron microscope image is shown in Figure 11, and the particle size of the finished lithium phosphate is 1.1 μm.

[0141] Table 15. Lithium phosphate composition synthesized in Comparative Example 5

[0142]

[0143] As can be seen from the lithium phosphate composition tables of the embodiments and comparative examples, both the synthesis process of the present invention and existing synthesis processes can yield lithium phosphate products with high purity, meeting the requirements for battery-grade lithium phosphate.

[0144] However, further examination of the accompanying drawings of the embodiments of the present invention reveals that nanoscale lithium phosphate can be obtained by using a phosphate salt solution and limiting a specific liquid-solid ratio. In particular, in Examples 1 and 4, where the lithium concentration C ≤ 10 g / L, nanoscale lithium phosphate can still be formed even at low lithium concentrations. The nanoscale lithium phosphate particle size range obtained using this method is ≤ 700 nm. As shown in the accompanying drawings, the maximum particle sizes in Examples 1 to 5 are 300 nm, 500 nm, 200 nm, 200 nm, and 500 nm, respectively. Furthermore, uniform particle size morphology control can be achieved based on the cathode black powder from waste lithium batteries with different lithium contents, ensuring stable product performance across different batches. In contrast, existing synthesis methods that directly add solid phosphate salts yield micron-sized lithium phosphate with a size of 1.1-3.4 μm.

[0145] In addition to the above embodiments, it should be noted that the technical effects claimed by the present invention can be achieved by using the preparation process and the limited parameter range of the present invention, and therefore no further examples will be provided to support these claims.

Claims

1. A method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate, characterized in that, Includes the following steps: (1) The positive electrode black powder of waste lithium batteries is calcined and slurried to obtain a slurry, and then purified by acid leaching and impurity removal to obtain pure lithium liquid; (2) Phosphate salt solution is added to the pure lithium liquid for reaction and concentration to obtain nano-sized lithium phosphate; wherein, the liquid-solid ratio of the added phosphate salt solution is determined by the following formula: In the formula: C is the concentration of lithium in the pure lithium liquid (g / L); L / S is the liquid-to-solid ratio of the slurry; W is the percentage of lithium in the cathode black powder.

2. A method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate, characterized in that, Includes the following steps: (1) The positive electrode black powder of waste lithium battery is calcined and pulped to obtain slurry, and then purified lithium liquid is obtained after acid leaching and impurity removal; (2) The obtained pure lithium liquid is concentrated to obtain concentrated lithium liquid; (3) Add a phosphate salt solution to the concentrated lithium solution to react and concentrate it to obtain nano-sized lithium phosphate; wherein the liquid-to-solid ratio of the added phosphate salt solution is determined by the following formula: In the formula: C is the concentration of lithium in the concentrated lithium solution (g / L); L / S is the liquid-to-solid ratio of the slurry; W is the percentage of lithium in the cathode black powder.

3. The method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate according to claim 1 or 2, characterized in that, The solid ratio L / S of the slurry is (3-10):

1.

4. The method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate according to claim 1 or 2, characterized in that, The phosphate salt is selected from at least one of trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, monoammonium phosphate, or ammonium phosphate.

5. The method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate according to claim 1 or 2, characterized in that, The amount of phosphate salt added is 1.01-1.3 times the theoretical amount of lithium phosphate.

6. The method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate according to claim 1 or 2, characterized in that, The calcination temperature of the positive electrode black powder is 500-600℃, and the calcination time is 2-4h.

7. The method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate according to claim 1 or 2, characterized in that, The acid leaching process involves leaching the lithium iron phosphate black powder slurry with acid and oxidant for 3-8 hours. The acid used is selected from one of oxalic acid, formic acid, citric acid, or benzenesulfonic acid, and its addition amount is 1-1.1 times the theoretical amount of dissolved lithium.

8. The method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate according to claim 7, characterized in that, The oxidant is selected from one of oxygen, hydrogen peroxide, chlorine, concentrated sulfuric acid, or concentrated nitric acid, and the amount added is 1-1.1 times the theoretical amount of dissolved lithium.

9. The method for recycling waste lithium batteries to synthesize nano-sized lithium phosphate according to claim 1 or 2, characterized in that, The impurity removal includes a one-step impurity removal using an alkaline solution and a two-step impurity removal using a chelating resin. The alkaline solution is selected from sodium hydroxide solution, lithium hydroxide solution, or ammonia water, and the amount added is to adjust the pH of the acid leaching solution to 6-9.

Images