Positive plate, preparation method thereof and lithium ion battery

Abstract

The invention discloses a positive plate and a preparation method thereof and a lithium ion battery, the preparation method of the positive plate comprises the following steps: step 1, adding a waste positive plate and a stripping solvent into a stirring kettle, stirring until a positive coating on a current collector completely falls off, filtering, and demagnetizing filtrate to obtain a positive material liquid; wherein the stripping solvent is prepared from at least two of N-methyl pyrrolidone, dimethylacetamide, N, N-dimethylformamide, triethyl phosphate and dimethyl sulfoxide; 2, adding the positive electrode material liquid and a binder into a stirring kettle, dispersing, demagnetizing and sieving to obtain positive electrode slurry; and 3, coating the positive electrode slurry on a positive electrode current collector, and drying to obtain the positive electrode plate. Compared with the prior art, the method disclosed by the invention has the advantages that the current collector and the positive electrode coating can be efficiently stripped, the impurity content in the recycled positive electrode material is reduced, and the positive electrode slurry can be directly prepared and coated into a positive plate.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a positive electrode sheet and a preparation method thereof, and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in mobile phones, portable computers, camcorders, cameras, electric vehicles, energy storage and other fields due to their high energy density, long cycle life, environmental protection, low self-discharge and other advantages. Due to the widespread use of lithium-ion batteries, the production volume of lithium-ion batteries has also become very large, and some defective products will be produced during the preparation process, especially before the battery is filled with liquid, due to coating, rolling, winding and other processes, resulting in a large number of scrapped pole pieces. The positive electrode materials of these scrapped pole pieces or winding cores are basically not damaged, and the positive electrode materials themselves have a stable structure and a very high recycling rate, so there is an urgent need to find a simple and efficient recycling method to deal with the scrapped pole pieces or winding cores.

[0003] In the prior art, the main method for recycling positive electrode sheets is to obtain positive electrode material powder through crushing, calcining, stripping, primary demagnetization, secondary crushing, and secondary demagnetization, and the recovery rate can reach 83.67%. However, the process is complicated, the recovery rate is low, the carbon content is high, and the BET is large, which seriously affects the regeneration performance of the positive electrode material. Among them, Chinese patent CN115939554A discloses a method for cyclically stripping the current collector and positive electrode material of waste positive electrode sheets with NMP. The method uses 95-99% concentration of NMP and water as a mixed solvent, which can smoothly strip the current collector and positive electrode material, but the positive electrode coating after separation is easy to gel and agglomerate, which is not conducive to subsequent dispersion coating.

[0004] In view of the above-mentioned defects in the current recycling of waste positive electrode sheets, it is indeed necessary to provide a technical solution to the above-mentioned problems. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a positive electrode sheet, which can efficiently strip the current collector and positive electrode coating of the waste positive electrode sheet, reduce the impurity content in the recycled positive electrode material, and directly prepare the positive electrode slurry and coat it into a positive electrode sheet.

[0006] To achieve this object, the present invention provides the following solutions:

[0007] A method for preparing a positive electrode sheet comprises the following steps:

[0008] Step 1: adding the waste positive electrode sheet and the stripping solvent into a stirring kettle, stirring until the positive electrode coating on the current collector is completely detached, filtering, and demagnetizing the filtrate to obtain a positive electrode material solution; wherein the stripping solvent includes at least two of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, triethyl phosphate and dimethyl sulfoxide;

[0009] Step 2: adding the positive electrode material liquid and the binder into a stirring kettle for dispersion, demagnetization, and sieving to obtain a positive electrode slurry;

[0010] Step three: coating the positive electrode slurry on the positive electrode current collector and drying it to obtain a positive electrode sheet.

[0011] Preferably, in step 1, the stripping solvent is a combination of dimethyl sulfoxide and other solvents, and the other solvent is at least one of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide and triethyl phosphate.

[0012] Preferably, in the step 1, the stripping solvent comprises N-methylpyrrolidone and triethyl phosphate, wherein the mass ratio of the N-methylpyrrolidone to the triethyl phosphate is (7-9):(1-3).

[0013] Preferably, in step one, the stripping solvent includes N-methylpyrrolidone, N,N-dimethylformamide and dimethylacetamide, wherein the mass ratio of the N-methylpyrrolidone, the N,N-dimethylformamide and the dimethylacetamide is (4-6):(1-3):(1-2).

[0014] Preferably, in step 1, the stripping solvent comprises N-methylpyrrolidone and N,N-dimethylformamide, wherein the mass ratio of the N-methylpyrrolidone to the N,N-dimethylformamide is (1-2):(1-2).

[0015] Preferably, in step one, the stripping solvent includes N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, triethyl phosphate and dimethyl sulfoxide, wherein the mass ratio of the N-methylpyrrolidone, the dimethylacetamide, the N,N-dimethylformamide, the triethyl phosphate and the dimethyl sulfoxide is (1-3): (0.5-1.5): (2-4): (0.5-1.5): (0.5-1.5).

[0016] Preferably, in step 1, the stripping solvent comprises N-methylpyrrolidone and dimethyl sulfoxide, wherein the mass ratio of the N-methylpyrrolidone to the dimethyl sulfoxide is (2-4):(6-8).

[0017] Preferably, in step one, the waste positive electrode sheet is a waste positive electrode sheet that has not been soaked in electrolyte; the positive electrode coating material of the waste positive electrode sheet includes at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium manganese oxide, ternary material and lithium-rich material.

[0018] Preferably, in the step 1, the mass ratio of the waste positive electrode sheet to the stripping solvent is (35-85): (15-65).

[0019] Preferably, in step 2, the binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber and carboxymethyl cellulose.

[0020] Preferably, in step 1 and step 2, the stirring linear speed of the stirring tank is 3 to 35 m / s.

[0021] Preferably, in step one and step two, the magnetic field strength of the demagnetization is 6000-12000 Gs.

[0022] Preferably, in the step 2, the solid content of the positive electrode slurry is 35-85%.

[0023] Preferably, in step 3, the surface density of the positive electrode sheet is 0.05-0.7 mg / mm 2 .

[0024] The present invention also provides a positive electrode sheet, which is prepared by the above-mentioned positive electrode sheet preparation method; the film resistance of the positive electrode sheet is ≤1Ω / cm 2 ; Peel force ≥15N / m.

[0025] The present invention also provides a lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet and a separator spaced between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet mentioned above.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1) the present invention uses a stripping solvent to impregnate the waste positive electrode sheet, so that the obtained positive electrode material liquid has good dispersibility and no agglomeration, and can be directly prepared into a positive electrode slurry and coated to form a new positive electrode sheet;

[0027] 2) The method for recycling waste positive electrode sheets of the present invention does not require the step of calcination, which effectively avoids the problems of excessive carbon content, excessive specific surface area, poor conductivity, etc. of the positive electrode material caused by calcination in the traditional method;

[0028] 3) In the process of preparing the positive electrode sheet, the stripping solvent used in the present invention can be recycled and reused, thereby maximally reducing the cost of recycling and processing waste positive electrode sheets;

[0029] 4) The method for recycling waste positive electrode sheets of the present invention does not require crushing the positive electrode sheets. Instead, the waste positive electrode sheets are immersed in a stripping solvent and stirred to directly separate the positive electrode material from the current collector, thereby avoiding the problem of excessively high metal impurity content in the positive electrode material caused by the introduction of metal debris into the positive electrode material solution. DETAILED DESCRIPTION

[0030] In order to make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] According to a first aspect of the present invention, a method for preparing a positive electrode sheet is provided, comprising the following steps:

[0032] Step 1: Add the waste positive electrode sheet and the stripping solvent into a stirring kettle, stir until the positive electrode coating on the current collector completely falls off, filter, demagnetize the filtrate, and obtain a positive electrode material liquid; wherein the stripping solvent includes at least two of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, triethyl phosphate and dimethyl sulfoxide; the stripping solvent used in the present invention can be recycled and reused, which maximizes the reduction of the recycling and processing cost of the waste positive electrode sheet; the method of the present invention does not require the calcination step, which effectively avoids the problems of excessive carbon content, excessive specific surface area, poor conductivity, etc. of the positive electrode material caused by calcination in the traditional method. The method of the present invention does not need to crush the positive electrode sheet, but directly separates the positive electrode material from the current collector by impregnating the waste positive electrode sheet with a stripping solvent and stirring, thereby avoiding the problem of excessive metal impurity content in the positive electrode material caused by the introduction of metal debris into the positive electrode material liquid.

[0033] Step 2: Add the positive electrode material liquid and the binder into a stirring kettle for dispersion, demagnetization, and sieving to obtain a positive electrode slurry;

[0034] Step 3: Apply the positive electrode slurry on the positive electrode current collector and dry it to obtain a positive electrode sheet. The positive electrode material liquid recovered from the waste positive electrode sheet of the present invention can be directly used to prepare a positive electrode sheet. By using a stripping solvent to impregnate the waste positive electrode sheet, the obtained positive electrode material liquid has good dispersibility and no agglomeration, and can be directly prepared into a positive electrode slurry and coated to form a new positive electrode sheet.

[0035] In one embodiment of the present invention, in step one, the stripping solvent includes dimethyl sulfoxide, and also includes at least one of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide and triethyl phosphate. The stripping solvent with the best stripping effect and the best dispersibility of the prepared positive electrode slurry is a combination of dimethyl sulfoxide and other solvents, and the other solvent is at least one of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide and triethyl phosphate. Specifically, the stripping solvent is dimethyl sulfoxide, a combination of dimethyl sulfoxide and N-methylpyrrolidone, a combination of dimethyl sulfoxide and dimethylacetamide, a combination of dimethyl sulfoxide and N,N-dimethylformamide, or a combination of dimethyl sulfoxide and triethyl phosphate. Further, the mass ratio of dimethyl sulfoxide to other solvents is (2-3): (1-12), for example, 2:1, 2:1.1, 2:1.2, 2:1.3, 2:1.4, 2:1.5, 2:1.6, 2:1.7, 2:1.8, 2:1.9, 2:2, 3:1, 3:1.1, 3:1.2, 3:1.3, 3:1.4, 3:1.5, 3:1.6, 3:1.7, 3:1.8, 3:1.9. Dimethyl sulfoxide has the largest solubility for the binder in step 2, which is 20% greater than the stripping solvent in the prior art. Using dimethyl sulfoxide as the most preferred stripping solvent can effectively and quickly dissolve the PVDF in the pole piece, thereby achieving the purpose of rapid stripping of the active coating on the pole piece, and is also conducive to forming a uniformly dispersed, non-agglomerated positive electrode slurry.

[0036] According to one embodiment of the present invention, in step 1, the stripping solvent includes N-methylpyrrolidone and triethyl phosphate, wherein the mass ratio of N-methylpyrrolidone to triethyl phosphate is (7-9): (1-3), for example, 7:1, 7:1.1, 7:1.2, 7:1.3, 7:1.4, 7:1.5, 7:1.6, 7:1.7, 7:1.8, 7:1.9, 8:1, 8:1.1, 8:1.5, 8:1.6, 8:1.7, 8:1.8, 8:1.9, 8:1. :1.7, 8:1.8, 8:1.9, 9:1, 9:1.2, 9:1.5, 9:1.7, 9:1.8, 9:1.9, , 7:2, 7:2.2, 7:2.8, 7:2.9, 7:3, 8:2, 8:2.2, 8:2.5, 8:2.6, 8:2.7, 8:2.8, 9:2.2, 9:2.3, 9:2.5, 9:2.9, 9:3, further, the optimal mass ratio is 7:2.

[0037] According to one embodiment of the present invention, in step one, the stripping solvent includes N-methylpyrrolidone, N,N-dimethylformamide and dimethylacetamide, wherein the mass ratio of N-methylpyrrolidone, N,N-dimethylformamide and dimethylacetamide is (4-6):(1-3):(1-2), for example, it can be 4:1:1, 4:2:1, 4:3:1, 4:1:2, 5:1:1, 5:2:1, 5:3:1, 5:1:2, 6:1:1, 6:2:1, 6:3:1, 6:1:2, and further, the optimal mass ratio is 5:2:1.

[0038] According to one embodiment of the present invention, in step one, the stripping solvent includes N-methylpyrrolidone and N,N-dimethylformamide, wherein the mass ratio of N-methylpyrrolidone to N,N-dimethylformamide is (1-2):(1-2), for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 2:1, 2:1.1, 2:1.2, 2:1.3, 2:1.4, 2:1.5, 2:1.6, 2:1.7, 2:1.8, 2:1.9.

[0039] According to one embodiment of the present invention, in step one, the stripping solvent includes N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, triethyl phosphate and dimethyl sulfoxide, wherein the mass ratio of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, triethyl phosphate and dimethyl sulfoxide is (1-3): (0.5-1.5): (2-4): (0.5-1.5): (0.5-1.5).

[0040] In one embodiment of the present invention, in step 1, the stripping solvent includes N-methylpyrrolidone and dimethyl sulfoxide, wherein the mass ratio of N-methylpyrrolidone to dimethyl sulfoxide is (2-4):(6-8).

[0041] In one embodiment of the present invention, in the step 2, the binder includes at least one of polyvinylidene fluoride, styrene butadiene rubber and carboxymethyl cellulose. The mass percentage of the binder to the solid mass in the positive electrode material solution is 0.05-1.5%, for example, it can be 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 1%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, 1.5%.

[0042] In one embodiment of the present invention, in step one, the waste positive electrode sheet is a waste positive electrode sheet that has not been soaked in electrolyte; the positive electrode coating material of the waste positive electrode sheet includes at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium manganese oxide, ternary material and lithium-rich material.

[0043] According to one embodiment of the present invention, in step one, the mass ratio of the waste positive electrode sheet to the stripping solvent is (35-85):(15-65), for example, it can be 35:15, 35:20, 35:30, 35:40, 35:50, 35:65, 50:15, 50:20, 50:30, 50:40, 50:55, 50:65, 70:15, 70:20, 70:30, 70:40, 70:55, 70:65, 85:15, 85:20, 85:30, 85:40, 85:55, 85:65.

[0044] In one embodiment of the present invention, the positive electrode current collector may be any material suitable for use as a positive electrode current collector for lithium-ion batteries in the art, such as aluminum foil or composite aluminum foil.

[0045] In one embodiment of the present invention, in step 1 and step 2, the stirring line speed of the stirring tank is 3 to 35 m / s, for example, 3 m / s, 5 m / s, 8 m / s, 9 m / s, 10 m / s, 15 m / s, 17 m / s, 20 m / s, 25 m / s, 30 m / s, 31 m / s, 32 m / s, 34 m / s, 35 m / s. When the stirring line speed is within this range, sufficient shear force and turbulence intensity can be generated to fully disperse the positive electrode coating and the current collector in the stirring tank to avoid material agglomeration or precipitation.

[0046] According to one embodiment of the present invention, in step 2, the stirring time of the stirring tank is 5 to 7 hours, for example, it can be 5h, 5.1h, 5.2h, 5.3h, 5.4h, 5.5h, 5.6h, 5.7h, 5.8h, 5.9h, 6h, 6.1h, 6.2h, 6.3h, 6.4h, 6.5h, 6.6h, 6.7h, 6.8h, 6.9h, and 7h.

[0047] In one embodiment of the present invention, in step 1 and step 2, the magnetic field strength of demagnetization is 6000-12000Gs, for example, 6000Gs, 7000Gs, 8000Gs, 9000Gs, 10000Gs, 11000Gs, 12000Gs. A higher magnetic field strength can more effectively capture the magnetic particles in the positive electrode slurry, especially those weakly magnetic tiny particles, thereby improving the thoroughness of demagnetization and avoiding the adverse effects of impurities on battery performance, such as reducing battery capacity and increasing internal resistance; at the same time, under the action of a strong magnetic field, the magnetic particles can be adsorbed onto the demagnetization equipment more quickly, thereby shortening the time of the entire demagnetization process and improving production efficiency.

[0048] In one embodiment of the present invention, in step 2, the solid content of the positive electrode slurry is 35-85%, for example, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%. Appropriate solid content helps to optimize the electrode structure and ensure uniform coating of the positive electrode material. This can not only improve the uniformity and consistency of the battery, but also reduce the performance degradation caused by material shedding or structural changes, thereby extending the cycle life of the battery.

[0049] In one embodiment of the present invention, in step 3, the surface density of the positive electrode sheet is 0.05-0.7 mg / mm 2 . Reasonable positive electrode surface density design can also enhance battery safety and optimize battery cycle life. By optimizing the electrode structure and material selection, the risk of excessive heat generated by the battery during charging and discharging can be reduced, thereby avoiding serious safety accidents such as battery thermal runaway or even explosion. In addition, through reasonable process control and material selection, the problem of excessive internal stress or excessive energy consumption of the battery caused by excessive surface density can be avoided, thereby extending the battery cycle life.

[0050] According to a second aspect of the present invention, a positive electrode sheet is provided, which is prepared by the above-mentioned positive electrode sheet preparation method; the film resistance of the positive electrode sheet is ≤1Ω / cm 2 ; Lower membrane resistance means that electrons are conducted more smoothly in the positive electrode sheet, reducing resistance loss, thereby improving the battery's charging and discharging efficiency, which helps the battery complete the charging and discharging process in a shorter time, improving the battery's overall performance, and can also reduce the heat generated by the battery during the charging and discharging process, helping to improve the battery's safety and reliability.

[0051] Peel force ≥ 15N / m. Peel force ≥ 15N / m means that the adhesion between the current collector and the positive electrode coating is stronger, which helps prevent interlayer separation caused by volume expansion or contraction during the charge and discharge process of the battery, thereby improving the stability of the battery structure.

[0052] According to a third aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet described above.

[0053] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer can be one or more of, including but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate or other metals that can form alloys with lithium.

[0054] The graphite may be selected from one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon carbon composites and silicon alloys; the tin-based material may be selected from one or more of elemental tin, tin oxide compounds and tin alloys. The negative electrode current collector is usually a structure or part for collecting current. The negative electrode current collector may be any material suitable for use as a negative electrode current collector for lithium-ion batteries in the art. For example, the negative electrode current collector may include but is not limited to metal foil, and more specifically may include but is not limited to copper foil.

[0055] The separator can be selected from various separators used in lithium-ion batteries known to those skilled in the art, such as polyethylene separators, polypropylene separators, various composite separators, ceramic separators, and the like.

[0056] The secondary battery also includes an electrolyte, which includes an organic solvent, an electrolyte lithium salt and an additive. The electrolyte lithium salt can be LiPF used in high temperature electrolytes. 6 and / or LiBOB; it can also be LiBF used in low temperature electrolytes 4 、LiBOB、LiPF 6 It can also be LiBF used in the overcharge-proof electrolyte 4 、LiBOB、LiPF 6 , LiTFSI; it can also be LiClO 4 、LiAsF 6 、LiCF 3 SO 3 、LiN(CF 3 SO 2 ) 2At least one of the above. The organic solvent may be a cyclic carbonate, including PC and EC; it may also be a chain carbonate, including DFC, DMC, or EMC; it may also be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include but are not limited to at least one of a film-forming additive, a conductive additive, a flame retardant additive, an anti-overcharge additive, an additive for controlling the content of H2O and HF in the electrolyte, an additive for improving low temperature performance, and a multifunctional additive.

[0057] The present invention will be further described below by means of specific examples.

[0058] Example 1

[0059] Preparation of positive electrode:

[0060] Step 1: Add 10 kg of waste positive electrode sheets and 5 kg of stripping solvent into a stirring kettle, stir at a linear speed of 3 m / s until the positive electrode coating on the current collector is completely detached, filter, and demagnetize the filtrate with an 8000 Gs iron remover to obtain a positive electrode material solution; wherein the stripping solvent is dimethyl sulfoxide and triethyl phosphate;

[0061] Step 2: Add the positive electrode material liquid and 0.05 PVDF into a stirring kettle for dispersion, with a stirring line speed of 26 m / s and a stirring time of 6 h, demagnetize with an 8000 Gs iron remover, and sieve to obtain a positive electrode slurry;

[0062] Step 3: Apply the positive electrode slurry on the positive electrode current collector and dry it at 105° C. to obtain a positive electrode sheet.

[0063] Preparation of lithium-ion batteries:

[0064] The negative electrode sheet, the separator and the positive electrode sheet are interlaced and then packaged with an aluminum-plastic film to prepare a battery cell, which is placed in a battery shell, an electrolyte is added, and then sealed to obtain a lithium-ion battery. Among them, the active material of the negative electrode sheet is graphite; the separator is a ceramic separator; the electrolyte salt of the electrolyte is lithium hexafluorophosphate, and the solvent is ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a mass ratio of 1:2:1, and the electrolyte concentration is 1 mol / L.

[0065] Table 1 shows the data of Examples 1 to 11 and Comparative Example 1. The rest is the same as Example 1 and will not be described again.

[0066]

[0067]

[0068] The positive electrode slurries of Examples 1 to 11 and Comparative Example 1 were subjected to fineness tests to characterize the dispersibility of the positive electrode slurries. The test results are shown in Table 2.

[0069] The positive electrode sheets of Examples 1 to 11 and Comparative Example 1 were tested for electrode sheet peeling and membrane resistance using a tensile tester and a membrane resistance meter, respectively. The test results are shown in Table 2.

[0070] Table 2

[0071]

[0072]

[0073] As shown in Table 1, from the comparison of the fineness data of Examples 1 to 11 and Comparative Example 1, it can be seen that the positive electrode slurries of Examples 1 to 11 are very evenly dispersed without agglomeration, while the positive electrode slurry of Comparative Example 1 has agglomeration and caking and cannot be directly prepared into positive electrode sheets; this shows that by using the stripping solvent of the present invention to impregnate waste positive electrode sheets, the obtained positive electrode material liquid has good dispersibility and no agglomeration, can be directly prepared into positive electrode slurry, and coated to form new positive electrode sheets, thereby reducing the cost of recycling waste positive electrode sheets.

[0074] By comparing the fineness data of Example 1 and Comparative Example 1, it can be seen that the dispersion of the positive electrode slurry of Example 1 is better than that of Comparative Example 1, which shows that the use of dimethyl sulfoxide and N-methylpyrrolidone stripping solvents is more conducive to the dissolution and dispersion of the positive electrode coating, because dimethyl sulfoxide has better solubility than PVDF, which can make PVDF better dissolved and dispersed, so a better slurry fineness value is obtained; it also further illustrates that the use of N-methylpyrrolidone alone cannot obtain a uniformly dispersed, non-lump, non-agglomerated positive electrode slurry, and cannot directly prepare a positive electrode sheet.

[0075] Comparing the peeling force data of Example 1 and Comparative Example 1, it can be seen that the peeling force of the positive electrode sheet of Example 1 is better than that of Comparative Example 1. This is because the fineness of the positive electrode slurry of Example 1 is smaller than that of Comparative Example 1, and the slurry dispersion uniformity is also higher, so a positive electrode sheet with higher peeling force can be obtained.

[0076] Comparing the diaphragm resistance data of Example 1 and Comparative Example 1, it can be seen that the diaphragm resistance of the positive electrode sheet of Example 1 is better than that of Comparative Example 1. This is because the fineness of the positive electrode slurry of Example 1 is smaller than that of Comparative Example 1, the slurry dispersion is more uniform, and a positive electrode sheet with a smaller diaphragm resistance can be obtained.

[0077] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can also change and modify the above embodiment. Therefore, the present invention is not limited to the above specific embodiment, and any obvious improvement, replacement or modification made by those skilled in the art on the basis of the present invention belongs to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing a positive electrode sheet, characterized in that: The following steps are involved: Step 1: adding the waste positive electrode sheet and the stripping solvent into a stirring kettle, stirring until the positive electrode coating on the current collector is completely detached, filtering, and demagnetizing the filtrate to obtain a positive electrode material solution; wherein the stripping solvent includes at least two of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, triethyl phosphate and dimethyl sulfoxide; Step 2: adding the positive electrode material liquid and the binder into a stirring kettle for dispersion, demagnetization, and sieving to obtain a positive electrode slurry; Step three: coating the positive electrode slurry on the positive electrode current collector and drying it to obtain a positive electrode sheet.

2. The method for preparing a positive electrode sheet according to claim 1, characterized in that: In the step 1, the stripping solvent is a combination of dimethyl sulfoxide and other solvents, and the other solvent is at least one of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide and triethyl phosphate.

3. The method for preparing a positive electrode sheet according to claim 1, characterized in that: In step one, the waste positive electrode sheet is a waste positive electrode sheet that has not been soaked in electrolyte; the positive electrode coating material of the waste positive electrode sheet includes at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium manganese oxide, ternary material and lithium-rich material.

4. The method for preparing a positive electrode sheet according to claim 1, characterized in that: In the step 1, the mass ratio of the waste positive electrode sheet to the stripping solvent is (35-85): (15-65).

5. The method for preparing a positive electrode sheet according to claim 1, characterized in that: In the step 1 and the step 2, the stirring linear speed of the stirring tank is 3 to 35 m / s.

6. The method for preparing a positive electrode sheet according to claim 1, characterized in that: In the step 1 and the step 2, the magnetic field strength of the demagnetization is 6000-12000 Gs.

7. The method for preparing a positive electrode sheet according to claim 1, characterized in that: In the step 2, the solid content of the positive electrode slurry is 35-85%.

8. The method for preparing a positive electrode sheet according to claim 1, characterized in that: In step 3, the surface density of the positive electrode sheet is 0.05-0.7 mg / mm 2 .

9. A positive electrode sheet, characterized in that: Prepared by the preparation method of the positive electrode sheet according to any one of claims 1 to 8; the film resistance of the positive electrode sheet is ≤1Ω / cm 2 ; Peel force ≥15N / m.

10. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet, characterized in that: The positive electrode sheet is a positive electrode sheet prepared by the method for preparing a positive electrode sheet according to any one of claims 1 to 7 or a positive electrode sheet according to claim 9.

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