Regenerative and repaired lithium iron phosphate battery positive electrode material and preparation method thereof

Abstract

The invention discloses a regenerated and repaired lithium iron phosphate battery positive electrode material, which is prepared from the following raw materials: retired lithium iron phosphate powder, an organic solvent, an ammonium-containing cosolvent, a transition metal compound additive and lithium salt, the solid mass ratio of the retired lithium iron phosphate powder in the organic solvent is 10-40%. The organic solvent, the cosolvent containing ammonium radicals and PVDF are mixed, the dissolution and removal rate of PVDF can be increased at high temperature and high pressure, and the electrochemical performance of the repaired battery material is improved. The transition metal compound and the preparation raw materials are mixed and modified, so that the rate capability of the regenerated and repaired lithium material battery can be improved.

Description

Technical Field

[0001] The present invention relates to the field of recycling of waste lithium batteries, and particularly to a regenerated and repaired cathode material for lithium iron phosphate batteries and a preparation method thereof. Background Art

[0002] With the extensive development of new energy technologies, the consumption of new energy power battery resources has increased sharply. Recycling retired batteries can alleviate the problem of the sharp decline in power battery resources. Existing methods for recycling power batteries mainly rely on hydrometallurgical recycling processes, which have the defects of long process, high pollution, and high cost. After retirement, the lithium iron phosphate cathode material has poor cycle performance and rate performance. After multiple cycles of retirement, it still retains a complete olivine structure. How to remove impurities such as PVDF without damaging the original structure of the material and then perform high-temperature lithium supplementation and repair is an important issue for the regeneration and repair of retired lithium iron phosphate battery cathode materials.

[0003] Chinese Patent Application CN114835098A discloses a method for wet repair and regeneration of waste lithium iron phosphate cathode materials, which directly repairs damaged lithium iron phosphate cathode materials by wet repair, maximally recovers the chemical composition in the lithium iron phosphate cathode materials, and avoids damage to the crystal structure of the materials. However, the wet repair process is long, polluting, and costly. Chinese Patent CN118324112A discloses an in-situ regeneration and repair process for waste lithium iron phosphate battery cathode materials, including lithium iron phosphate with crystal water; by adding a lithium source and a modified coating material and calcining at high temperature, regenerated lithium iron phosphate is prepared, which has the advantages of high purity and excellent electrical conductivity. However, the compatibility between the excessively added modified coating material and the recycled lithium iron phosphate is poor, and the electrochemical rate is not high. Summary of the Invention

[0004] In order to remove impurities such as PVDF and then perform lithium supplementation and repair without damaging the original structure of lithium iron phosphate, the first aspect of the present invention provides a regenerated and repaired cathode material for lithium iron phosphate batteries, and the preparation raw materials include retired lithium iron phosphate powder, organic solvent, ammonium-containing cosolvent, transition metal compound additive, and lithium salt; the retired lithium iron phosphate powder accounts for 10-40% of the total mass of the retired lithium iron phosphate powder, organic solvent, and ammonium-containing cosolvent during the impurity removal process.

[0005] As an implementation manner, the retired lithium iron phosphate powder accounts for 20-40% of the total mass of the retired lithium iron phosphate powder, organic solvent, and ammonium-containing cosolvent during the impurity removal process.

[0006] As an implementation manner, the retired lithium iron phosphate powder accounts for 30% of the total mass of the retired lithium iron phosphate powder, organic solvent, and ammonium-containing cosolvent during the impurity removal process.

[0007] During the experiment, the inventor found that by mixing an organic solvent, an ammonium group-containing co-solvent with PVDF, the dissolution and removal rate of PVDF can be increased, and the electrochemical performance of the battery material after subsequent repair can be improved. It is speculated that the possible reason is that the organic solvent, the ammonium group-containing co-solvent and the molecular chain of PVDF undergo a nucleophilic substitution reaction, and the controlled scission of the long-chain polymer is achieved under high temperature and high pressure conditions. NH4 + The ammonium ion attacks the PVDF long chain into short chains, reducing its adhesiveness, promoting the solvent to dissolve PVDF, promoting the swelling and dissolution of PVDF under high temperature and high pressure conditions, and increasing the shedding rate of PVDF.

[0008] As an implementation method, the organic solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, dimethylacetamide, and N,N-dimethylformamide.

[0009] As an implementation method, the retired lithium iron phosphate powder contains polyvinylidene fluoride, the co-solvent contains ammonium ions, and the molar ratio of fluoride ions to ammonium ions in the polyvinylidene fluoride is 1:(1-3).

[0010] As an implementation method, the molar ratio of fluoride ions to ammonium ions in the polyvinylidene fluoride is 1:1.

[0011] The molar number of fluoride ions in the polyvinylidene fluoride is obtained by testing with ion chromatography.

[0012] As an implementation method, the transition metal compound additive is selected from at least one of lithium aluminum titanium phosphate, V 2 O 5 、WO 3 。

[0013] As an implementation method, the addition amount of the transition metal compound additive is 1000-5000 ppm of the total amount of the preparation raw materials.

[0014] As an implementation method, the addition amount of the transition metal compound additive is 1500-3000 ppm of the total amount of the preparation raw materials.

[0015] As an implementation method, the addition amount of the transition metal compound additive is 2000 ppm of the total amount of the preparation raw materials.

[0016] The inventors further found that modifying by mixing a transition metal compound with the preparation raw materials can improve the rate performance of the lithium material battery after regeneration and repair. The reason may be that the metal elements in the transition metal compound can provide a faster channel for electron transfer, improving the rate performance of the lithium battery after regeneration and repair. Especially when the addition amount of the transition metal compound is 2000 ppm of the total amount of the preparation raw materials, the rate performance is the best. However, when the addition amount of the transition metal compound exceeds the preferred range, a large amount of the transition metal compound will react with Li in the material to form lithium compounds during the synthesis process, resulting in a decrease in the lithium content in lithium iron phosphate and affecting the specific capacity of the battery. And it will also cause the pH of the material to rise, affecting the viscosity of the subsequent cell slurry. When the addition amount is lower than the preferred range, it is not evenly dispersed in the material, and the improvement of the ion mobility is not obvious.

[0017] As an implementation manner, the lithium salt includes but is not limited to at least one of lithium hydroxide, lithium nitrate, lithium chloride, lithium sulfate, lithium acetate, lithium carbonate, lithium borohydride, and lithium bicarbonate.

[0018] As an implementation manner, the mass fraction of lithium in the regenerated and repaired cathode material of the lithium iron phosphate battery is 4.2 - 4.5 wt%.

[0019] The second aspect of the present invention provides a preparation method for a regenerated and repaired cathode material of a lithium iron phosphate battery, comprising the following steps:

[0020] S1 Mix and stir the retired lithium iron phosphate powder with an organic solvent and an ammonium - containing co - solvent, control the reaction temperature and pressure, and after the reaction, centrifuge and dry to obtain the retired lithium iron phosphate powder after impurity removal;

[0021] S2 Mix the retired lithium iron phosphate powder after impurity removal with the ground transition metal compound additive, water, and a lithium salt, then spray granulate in an inert gas environment, load into a crucible, and perform a roasting process in an inert atmosphere;

[0022] S3 Crush, screen, and demagnetize to obtain the regenerated and repaired cathode material of the lithium iron phosphate battery.

[0023] As an implementation manner, in the step S1, the stirring is performed using a paddle + upright cutter head.

[0024] As an implementation manner, in the step S1, the reaction temperature is 25 - 160 °C, and the reaction pressure is 0 - 10 MPa.

[0025] As an implementation manner, in the step S1, the reaction temperature is 130 - 160 °C, and the reaction pressure is 5 - 10 MPa.

[0026] As an implementation manner, in the step S1, the reaction temperature is 150 °C, and the reaction pressure is 8 MPa.

[0027] As an implementation manner, during the sanding process in step S2, the total mass of the transition metal compound additive and the lithium salt accounts for 30%-40% of the total mass of the transition metal compound additive, water and lithium salt.

[0028] As an implementation manner, the D50 particle size after sanding in step S2 is 80-400 nm.

[0029] As an implementation manner, the D50 particle size after sanding in step S2 is 200 nm.

[0030] As an implementation manner, the inert gas environment in step S2 is a nitrogen atmosphere.

[0031] As an implementation manner, the temperature of spray granulation in step S2 is 180-240 °C.

[0032] As an implementation manner, the roasting process in step S2 includes low-temperature roasting and high-temperature roasting. The temperature of the low-temperature roasting is 300-500 °C, and the temperature of the high-temperature roasting is 600-900 °C.

[0033] As an implementation manner, the total time of the roasting process is 3-20 h. The roasting process includes roasting at 300-500 °C for 1-10 h and roasting at 600-900 °C for 3-10 h.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) For the regenerated and repaired cathode material of lithium iron phosphate battery of the present invention, the use of an organic solvent, an ammonium group-containing co-solvent and PVDF mixed can improve the dissolution and removal rate of PVDF and improve the electrochemical performance of the repaired battery material.

[0036] (2) For the regenerated and repaired cathode material of lithium iron phosphate battery of the present invention, the modification by mixing the transition metal compound with the preparation raw materials can improve the rate performance of the lithium material battery after regeneration and repair.

[0037] (3) For the regenerated and repaired cathode material of lithium iron phosphate battery of the present invention, the use of lithium titanium aluminum phosphate as the transition metal compound additive can also play a role in lithium supplementation and improve the cycle performance of lithium iron phosphate.

[0038] (4) For the regenerated and repaired cathode material of lithium iron phosphate battery of the present invention, two-stage temperature roasting is adopted in the roasting process. The low-temperature roasting completely removes PVDF, and the high-temperature roasting realizes lithium supplementation and surface modification of the retired lithium iron phosphate.

[0039] (5) In the preparation method of the regenerated and repaired cathode material for lithium iron phosphate batteries of the present invention, a paddle + vertical cutter head stirring is adopted in the reaction of step S1, which can prevent the slurry from turning into a jelly state. After lithium supplementation and sintering, the specific capacity is excellent, and the rate performance and cycling performance are good. Description of the Drawings

[0040] Figure 1 Pictures of the first specific capacity test of Examples 1, 2, Comparative Example 1, and 2 at 3.75 - 2.0 V and 0.1 C;

[0041] Figure 2 Pictures of the first specific capacity test of Examples 3 - 6 at 3.75 - 2.0 V and 0.1 C;

[0042] Figure 3 Pictures of the first specific capacity test of Examples 7 - 10 at 3.75 - 2.0 V and 0.1 C;

[0043] Figure 4 Pictures of the first specific capacity test of Examples 11 - 14 at 3.75 - 2.0 V and 0.1 C;

[0044] Figure 5 Pictures of the rate performance test of Examples 1, 2, and Comparative Example 1 at 3.75 - 2.0 V and 1.0 CC / 1.0 CD;

[0045] Figures 1-5 In the figure: 1: Comparative Example 1; 2: Comparative Example 2; 3: Example 1; 4: Example 2; 5: Example 3; 6: Example 4; 7: Example 5; 8: Example 6; 9: Example 7; 10: Example 8; 11: Example 9; 12: Example 10; 13: Example 11; 14: Example 12; 15: Example 13; 16: Example 14.

[0046] Figure 6 SEM photograph of the repaired cathode material for lithium iron phosphate batteries of Comparative Example 1;

[0047] Figure 7 SEM photograph of the repaired cathode material for lithium iron phosphate batteries of Example 1. Detailed Description of the Invention

[0048] Example 1

[0049] A regenerated and repaired cathode material for lithium iron phosphate batteries, the preparation raw materials include retired lithium iron phosphate powder, organic solvent, ammonium - containing co - solvent, transition metal compound additive, and lithium salt; the retired lithium iron phosphate powder accounts for 30% of the total mass of the retired lithium iron phosphate powder, organic solvent, and ammonium - containing co - solvent during the impurity removal process.

[0050] The mass of the retired lithium iron phosphate powder is 30 g, and the retired lithium iron phosphate powder contains 0.6 g of polyvinylidene fluoride. The retired lithium iron phosphate powder is the core of the lithium iron phosphate power lithium battery after normal use and scrapping by BYD.

[0051] The organic solvent is dimethylacetamide, and the total mass of the retired lithium iron phosphate powder + organic solvent + ammonium-containing co-solvent is 100 g.

[0052] The ammonium-containing co-solvent is ammonium sulfate, and the molar ratio of fluoride ions to ammonium ions is 1:1. The purity of the ammonium sulfate is 50 wt%, and the addition amount is 1.234 g.

[0053] The transition metal compound additive is lithium aluminum titanium phosphate, and the addition amount is 2000 ppm of the total amount of the preparation raw materials.

[0054] The lithium salt is lithium hydroxide.

[0055] The mass fraction of lithium in the regenerated and repaired cathode material of the lithium iron phosphate battery is 4.3 wt%.

[0056] A preparation method of a regenerated and repaired cathode material of a lithium iron phosphate battery includes the following steps:

[0057] S1 Mix and stir the retired lithium iron phosphate powder with an organic solvent and an ammonium-containing co-solvent, control the reaction temperature and pressure, and after the reaction, centrifuge and dry to obtain the retired lithium iron phosphate powder after impurity removal;

[0058] S2 Mix the retired lithium iron phosphate powder after impurity removal with the ground transition metal compound additive, lithium salt and water, then spray granulate in an inert gas environment, load into a crucible, and carry out a roasting process in an inert gas environment;

[0059] S3 Crush, screen, and demagnetize to obtain the regenerated and repaired cathode material of the lithium iron phosphate battery.

[0060] In step S1, the stirring is carried out using a paddle + vertical cutter head.

[0061] In step S1, the reaction temperature is 150 °C and the reaction pressure is 8 MPa.

[0062] In the grinding process of step S2, the total mass of the transition metal compound additive and the lithium salt accounts for 35% of the total mass of the transition metal compound additive, water and lithium salt.

[0063] In step S2, the D50 particle size after grinding is 200 nm.

[0064] In step S2, the inert gas environment is a nitrogen gas environment

[0065] In step S2, the temperature of the spray granulation is 200 °C.

[0066] In the roasting process of step S2, it includes roasting at 400°C for 3 hours and roasting at 700°C for 5 hours.

[0067] The SEM photograph of the cathode material of the repaired lithium iron phosphate battery is shown in Figure 7 . There are no impurities in the electron microscope photograph of the repaired lithium iron phosphate, and the photograph imaging is clean.

[0068] Example 2

[0069] A regenerated and repaired cathode material for lithium iron phosphate batteries, the specific implementation method is the same as that of Example 1, the difference is that the organic solvent is dimethyl sulfoxide.

[0070] Example 3

[0071] A regenerated and repaired cathode material for lithium iron phosphate batteries, the specific implementation method is the same as that of Example 1, the difference is that the organic solvent is N,N-dimethylformamide.

[0072] Example 4

[0073] A regenerated and repaired cathode material for lithium iron phosphate batteries, the specific implementation method is the same as that of Example 1, the difference is that the organic solvent is N-methylpyrrolidone.

[0074] Example 5

[0075] A regenerated and repaired cathode material for lithium iron phosphate batteries, the specific implementation method is the same as that of Example 1, the difference is that the ammonium-containing co-solvent is ammonia water, and the molar ratio of fluoride ions to ammonium ions is 1:1. The mass fraction of the ammonia water is 25wt%, and the addition amount is 0.66g.

[0076] Example 6

[0077] A regenerated and repaired cathode material for lithium iron phosphate batteries, the specific implementation method is the same as that of Example 1, the difference is that the retired lithium iron phosphate powder accounts for 40% of the total mass of the retired lithium iron phosphate powder, organic solvent and ammonium-containing co-solvent during the impurity removal process.

[0078] Example 7

[0079] A regenerated and repaired cathode material for lithium iron phosphate batteries, the specific implementation method is the same as that of Example 1, the difference is that the lithium salt is lithium carbonate.

[0080] Example 8

[0081] A regenerated and repaired cathode material for lithium iron phosphate batteries, the specific implementation method is the same as that of Example 1, the difference is that the lithium salt is lithium acetate.

[0082] Example 9

[0083] A cathode material for a regenerated lithium iron phosphate battery, the specific implementation method is the same as that of Example 1, the difference is that the transition metal compound additive is V 2 O 5 .

[0084] Example 10

[0085] A cathode material for a regenerated lithium iron phosphate battery, the specific implementation method is the same as that of Example 1, the difference is that the transition metal compound additive is WO 3 .

[0086] Example 11

[0087] A cathode material for a regenerated lithium iron phosphate battery, the specific implementation method is the same as that of Example 1, the difference is that the roasting process in step S2 includes roasting at 500 °C for 3 h and roasting at 800 °C for 5 h.

[0088] Example 12

[0089] A cathode material for a regenerated lithium iron phosphate battery, the specific implementation method is the same as that of Example 1, the difference is that the roasting process in step S2 includes roasting at 350 °C for 3 h and roasting at 700 °C for 5 h.

[0090] Example 13

[0091] A cathode material for a regenerated lithium iron phosphate battery, the specific implementation method is the same as that of Example 1, the difference is that the ammonium-containing co-solvent is ammonia water, and the molar ratio of fluoride ions to ammonium ions is 1:1.5.

[0092] Example 14

[0093] A cathode material for a regenerated lithium iron phosphate battery, the specific implementation method is the same as that of Example 1, the difference is that the ammonium-containing co-solvent is ammonia water, and the molar ratio of fluoride ions to ammonium ions is 1:2.5.

[0094] Comparative Example 1

[0095] A cathode material for a regenerated lithium iron phosphate battery, the specific implementation method is the same as that of Example 1, the difference is that the retired lithium iron phosphate powder accounts for 20% of the total mass of the retired lithium iron phosphate powder, organic solvent and ammonium-containing co-solvent during the impurity removal process.

[0096] The preparation raw materials do not contain ammonium-containing co-solvents.

[0097] The SEM photos of the repaired cathode material of the lithium iron phosphate battery are shown in Figure 6 . There is a layer of colloidal substance and cluster-type conductive agent on the surface of lithium iron phosphate in the electron microscope photos.

[0098] Comparative Example 2

[0099] A regenerated and repaired lithium iron phosphate battery positive electrode material, the specific implementation method is the same as Example 1, the difference is that the preparation raw material does not contain a transition metal compound additive.

[0100] Performance Testing

[0101] The carbon content of the positive electrode materials of the lithium iron phosphate batteries after repair in the embodiment and the comparative example was tested using a carbon-sulfur meter. The retired lithium iron phosphate powder contained more carbon compound impurities. The carbon content in the retired lithium iron phosphate powder was about 4.1%. The carbon content test can evaluate the impurity removal effect in the regenerated and repaired lithium iron phosphate batteries.

[0102] The mass ratio of active material: conductive agent: PVDF is 90:5:5, and the compacted density of the pole piece is 2.3g / cm 3 , assembled into a 2032-type button battery. The active material is the repaired material of the embodiment and the comparative example, and the conductive agent is conductive carbon black.

[0103] After assembly, the battery capacity performance was tested at 25°C, 3.75-2.0V voltage, and 0.1C charge and discharge rate. The test results are shown in Table 1 and the test diagram is shown in Figures 1-4 .

[0104] After assembly, the cycle performance of the batteries of Examples 1-2 and Comparative Example 1 was tested at 25°C, 3.75-2.0V, 1.0CC / 1.0CD. See the test graph. Figure 5 0.5CC / 0.5CD, 1.0CD, 2.0CD, 3.0CD test comparative examples 1-2, the rate performance of embodiment 1, the test results are shown in Table 2.

[0105] Table 1

[0106] Carbon content 0.1C gram capacity Comparative Example 1 2.53 150.5 Comparative Example 2 1.96 154.8 Example 1 1.99 154.9 Example 2 1.92 155 Example 3 1.85 154.9 Example 4 1.94 155.1 Example 5 1.88 154.9 Example 6 1.92 154.9 Example 7 186 154.2 Example 8 1.84 153.9 Example 9 1.96 154.1 Example 10 1.92 154.5 Example 11 1.90 154.2 Example 12 1.94 154.6 Example 13 1.88 154.5 Example 14 1.89 154

[0107] Table 2

[0108]

[0109]

Claims

1. A regenerated and repaired lithium iron phosphate battery positive electrode material, characterized in that: The preparation raw materials include retired lithium iron phosphate powder, organic solvent, transition metal compound additive, ammonium radical-containing cosolvent, and lithium salt; the retired lithium iron phosphate powder accounts for 10-40% of the total mass of the retired lithium iron phosphate powder, organic solvent and ammonium radical-containing cosolvent during the impurity removal process.

2. The regenerated and repaired lithium iron phosphate battery positive electrode material according to claim 1, characterized in that: The organic solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, dimethylacetamide, and N,N-dimethylformamide.

3. The regenerated and repaired lithium iron phosphate battery positive electrode material according to claim 1, characterized in that: The retired lithium iron phosphate powder contains polyvinylidene fluoride, and the molar ratio of fluoride ions in the polyvinylidene fluoride to ammonium ions in the ammonium-containing auxiliary solvent is 1:(1-3).

4. The regenerated and repaired lithium iron phosphate battery positive electrode material according to claim 1, characterized in that: The transition metal compound additive is selected from at least one of lithium aluminum titanium phosphate, V2O5, and WO3.

5. The regenerated and repaired lithium iron phosphate battery positive electrode material according to claim 1, characterized in that: The addition amount of the transition metal compound additive is 1000-5000ppm of the total amount of the preparation raw materials.

6. A method for preparing the regenerated and repaired lithium iron phosphate battery positive electrode material according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: mixing and stirring the retired lithium iron phosphate powder with an organic solvent and a co-solvent containing ammonium radicals, controlling the reaction temperature and pressure, and centrifugally drying after the reaction to obtain the retired lithium iron phosphate powder after impurities are removed; S2: mixing the decommissioned lithium iron phosphate powder after impurities removal with the transition metal compound additive after sand grinding, water, and lithium salt, and then spraying granulating in an inert atmosphere environment, filling in a bowl, and performing a roasting process in an inert gas environment; S3 is crushed, sieved, and demagnetized to obtain a regenerated and repaired lithium iron phosphate battery positive electrode material.

7. The method for preparing the regenerated and repaired lithium iron phosphate battery positive electrode material according to claim 6, characterized in that: In step S1, the reaction temperature is 25-160° C., and the reaction pressure is 0-10 MPa.

8. The method for preparing the regenerated and repaired lithium iron phosphate battery positive electrode material according to claim 6, characterized in that: The D50 particle size after sand grinding in step S2 is 80-400 nm.

9. The method for preparing the regenerated and repaired lithium iron phosphate battery positive electrode material according to claim 6, characterized in that: The calcination process in step S2 includes low-temperature calcination and high-temperature calcination. The temperature of the low-temperature calcination is 300-500°C, and the temperature of the high-temperature calcination is 600-900°C.

10. The method for preparing the regenerated and repaired lithium iron phosphate battery positive electrode material according to claim 9, characterized in that: The total time of the roasting process is 3-20 hours, and the roasting process includes roasting at 300-500° C. for 1-10 hours and roasting at 600-900° C. for 2-10 hours.

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