Repair method of positive active material and preparation method of positive plate

Abstract

The invention provides a repairing method of a positive active material and a preparation method of a positive plate, and belongs to the technical field of secondary battery manufacturing. The repairing method of the positive electrode active material comprises the following steps that a positive plate is put into NMP to be subjected to stripping treatment, so that the positive electrode active material falls off from a positive electrode current collector, and the positive plate is not in contact with electrolyte; carrying out solid-liquid separation treatment on the NMP solution containing the positive electrode active material to obtain filtrate containing the positive electrode active material; carrying out centrifugal treatment on the filtrate to obtain a precipitate containing the positive electrode active material; sequentially carrying out drying treatment, roasting treatment and crushing treatment on the precipitate to obtain a positive electrode active material; wherein the step of roasting treatment is carried out under an anaerobic condition, and the repairing method can realize recycling of positive plate waste materials generated in a positive plate production stage.

Description

Technical Field

[0001] The present application relates to the technical field of secondary battery manufacturing, and in particular to a method for repairing a positive electrode active material and a method for preparing a positive electrode sheet. Background Art

[0002] According to incomplete statistics, the total output of lithium iron phosphate batteries in China will exceed 531.4GWh in 2023 (at this stage, due to the development of new energy vehicles, the demand for power batteries has soared, and the shipments of power battery manufacturers are generally in GWh, 1GWh is about 20,000 lithium batteries). Each 1GWh of lithium-ion batteries requires about 2,500 tons of positive plates. In the process of producing positive plates, there are usually problems such as scrapping of positive plate scraps and scrapping of bad plates, which makes the annual production waste in the production process of positive plates as high as 60,000 to 70,000 tons, which puts great pressure on the production cost and environmental protection of enterprises. At present, the research and development system for the recycling and reuse of positive plates is usually aimed at the positive plates of waste batteries (that is, the positive plates that have been used), and there are few reports on the recycling process of positive plate waste (that is, the positive plates that have not been used) generated in the production stage of positive plates. Therefore, it is urgent to develop a new process that can recycle the positive plate waste generated in the production stage of positive plates. Summary of the invention

[0003] The purpose of this application is to provide a method for repairing positive electrode active materials and a method for preparing positive electrode sheets, which can realize the recycling of positive electrode sheet waste generated in the positive electrode sheet production stage, thereby reducing the production cost of the enterprise and the pressure on environmental protection.

[0004] The embodiment of the present application is implemented as follows:

[0005] In a first aspect, an embodiment of the present application provides a method for repairing a positive electrode active material, comprising the following steps: placing a positive electrode sheet in NMP for stripping treatment to cause the positive electrode active material to fall off the positive electrode current collector, wherein the positive electrode sheet is not in contact with the electrolyte; performing solid-liquid separation treatment on an NMP solution containing the positive electrode active material to obtain a filtrate containing the positive electrode active material; centrifuging the filtrate to obtain a precipitate containing the positive electrode active material; sequentially drying, calcining and crushing the precipitate to obtain the positive electrode active material; wherein the calcining step is performed under anaerobic conditions.

[0006] In the above technical solution, the positive electrode sheet waste generated in the positive electrode sheet production process is processed according to a specific process, and the unused positive electrode active material and positive electrode current collector in the positive electrode sheet waste can be separated and recovered separately. The content of metal impurity ions in the recovered positive electrode active material is low and can be directly used to re-prepare new positive electrode sheets. Through this process, the positive electrode sheet waste generated in the positive electrode sheet production stage can be recycled. Among them, the roasting treatment step is carried out under anaerobic conditions, and the residual binder (organic matter) in the positive electrode active material can be carbonized (that is, the organic matter is converted into conductive carbon) without affecting the inherent conductive agent content in the positive electrode active material, so that the recovered positive electrode active material has better conductivity, and thus the step of adding a conductive agent can be omitted in the process of preparing the slurry using the recovered positive electrode active material.

[0007] In some optional embodiments, the calcining step is performed under an inert atmosphere.

[0008] In the above technical solution, the calcination step is carried out under an inert atmosphere, which has the advantages of conveniently providing oxygen-free conditions and a relatively stable calcination system.

[0009] In some optional embodiments, in the calcination step, the treatment temperature is 350-700° C., and the treatment time is 2-5 hours.

[0010] In the above technical solution, on the basis of oxygen-free calcination, the temperature and duration of the calcination treatment are respectively limited within specific ranges, so that the remaining binder can be carbonized more thoroughly without affecting the inherent conductive agent content in the positive electrode active material.

[0011] In some optional embodiments, the step of placing the positive electrode sheet in NMP for stripping treatment includes: transferring the positive electrode sheet to a rotary drum cleaning tank, in which an ultrasonic device is provided, and starting the rotary drum and the ultrasonic device to strip the positive electrode sheet.

[0012] In the above technical solution, in the step of stripping treatment, the rotary drum and the ultrasonic device are combined to strip the positive electrode active material from the positive electrode current collector more thoroughly and efficiently. The rotary drum can separate the stacked positive electrode sheets by rotating, and the ultrasonic device can impact the junction of the positive electrode active layer and the positive electrode current collector by ultrasonic energy, thereby helping the positive electrode active material to fall off from the positive electrode current collector.

[0013] In some optional embodiments, in the stripping step, the temperature of NMP in the drum cleaning tank is 60-80° C., and the treatment time is 1-4 h; and / or the mass ratio of the positive electrode sheet to NMP is 1:(6-12).

[0014] In the above technical solution, the stripping treatment step is carried out under suitable temperature conditions and duration, and the mass ratio of the positive electrode sheet and NMP is limited to a specific range, which helps the positive electrode active material to fall off from the positive electrode collector, and at the same time, it also helps the positive electrode active material after falling off to be better dispersed in water.

[0015] In some optional embodiments, the step of centrifuging the filtrate to obtain a precipitate containing the positive electrode active material includes: centrifuging the filtrate for a first time to obtain a precipitate intermediate; then, dispersing the precipitate intermediate in NMP and centrifuging it for a second time to obtain a second precipitate containing the positive electrode active material.

[0016] In the above technical solution, two centrifugal treatments are successively adopted, and the binder in the positive electrode active material can be removed more thoroughly by utilizing the property that the positive electrode active material is insoluble in organic solvents but the binder is soluble in organic solvents.

[0017] In some optional embodiments, the step of dispersing the precipitate intermediate in NMP comprises: adding the precipitate intermediate into NMP and stirring, wherein the temperature of NMP is 60-80° C. and the treatment time is 1-4 hours.

[0018] In the above technical solution, during the stirring and dispersing process, the treatment temperature and duration are respectively limited within specific ranges, so that the binder in the positive electrode active material can be fully exposed and dissolved in NMP, so as to be removed by centrifugation.

[0019] In some optional embodiments, the mass ratio of the precipitate intermediate to NMP is 1:(3-6).

[0020] In the above technical solution, during the stirring and dispersing process, the mass ratio of the precipitate intermediate and NMP is limited to a specific range, which helps the binder to be fully dissolved in NMP so as to be removed by centrifugation.

[0021] In some optional embodiments, in the drying step, the drying method is intermittent negative pressure drying, wherein the treatment temperature is 130 to 170° C., the treatment time is 1 to 4 hours; and / or the negative pressure is -0.02 to -0.1 MPa.

[0022] In the above technical solution, the temperature and duration of the drying treatment are limited to specific ranges, respectively, which can achieve a good drying effect without affecting the inherent physical and chemical properties of the positive electrode active material; and being carried out under specific negative pressure conditions helps to maintain the stability of the drying system.

[0023] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode sheet, comprising the following steps:

[0024] The positive electrode active material repaired by the repair method provided in the embodiment of the first aspect is mixed with a binder to obtain a slurry, wherein no additional conductive agent is required to be added to the slurry; the slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet.

[0025] In the above technical solution, the positive electrode active material repaired by the repair method provided in the first embodiment is used to prepare the slurry, which can omit the step of additionally adding a conductive agent, thereby improving the preparation efficiency of the positive electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 A process flow chart of a method for repairing a positive electrode active material provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0029] It should be noted that “and / or” in this application, such as “Feature 1 and / or Feature 2”, refers to the three situations of “Feature 1” alone, “Feature 2” alone, or “Feature 1” plus “Feature 2”.

[0030] In addition, in the description of the present application, unless otherwise specified, the meaning of "multiple" in "one or more" refers to two or more; the range of "value a ~ value b" includes the two end values ​​"a" and "b", and the "unit" in "value a ~ value b + unit of measurement" represents the "unit of measurement" of both "value a" and "value b".

[0031] The following is a detailed description of a method for repairing a positive electrode active material and a method for preparing a positive electrode sheet according to an embodiment of the present application.

[0032] In a first aspect, an embodiment of the present application provides a method for repairing a positive electrode active material, comprising the following steps: placing a positive electrode sheet in NMP for stripping treatment to cause the positive electrode active material to fall off the positive electrode current collector, wherein the positive electrode sheet is not in contact with the electrolyte; performing solid-liquid separation treatment on an NMP solution containing the positive electrode active material to obtain a filtrate containing the positive electrode active material; centrifuging the filtrate to obtain a precipitate containing the positive electrode active material; sequentially drying, calcining and crushing the precipitate to obtain the positive electrode active material; wherein the calcining step is performed under anaerobic conditions.

[0033] It should be noted that "repair of positive electrode active materials" can be understood as the process of processing the positive electrode sheet waste generated during the positive electrode sheet production stage to obtain positive electrode active materials that can be directly reused.

[0034] It should be noted that "the positive electrode sheet is not in contact with the electrolyte" means that the positive electrode sheet is a positive electrode sheet in the production stage, that is, a positive electrode sheet that does not participate in the battery charge and discharge cycle before liquid injection. The specific composition is a current collector, a conductive agent, a binder and a positive electrode active material. The characteristic is that there is no lack of lithium in the positive electrode active material.

[0035] In the present application, the positive electrode sheet waste generated in the production process of the positive electrode sheet is processed according to a specific process, and the unused positive electrode active material and the positive electrode current collector in the positive electrode sheet waste can be separated and recovered separately. The content of metal impurity ions in the recovered positive electrode active material is low and can be directly used to prepare new positive electrode sheets. Through this process, the positive electrode sheet waste generated in the production stage of the positive electrode sheet can be recycled. Among them, the roasting treatment step is carried out under anaerobic conditions, and the residual binder (organic matter) in the positive electrode active material can be carbonized (that is, the organic matter is converted into conductive carbon) without affecting the inherent conductive agent content in the positive electrode active material, so that the recovered positive electrode active material has better conductivity, and thus the step of adding a conductive agent can be omitted in the process of preparing the slurry using the recovered positive electrode active material.

[0036] In order to better understand the technical solution of the present application, some differences between the recycling system of the positive electrode sheets of used batteries and the recycling system of the positive electrode sheet waste generated during the positive electrode sheet production stage are summarized and explained here.

[0037] (1) The positive electrode sheets in waste batteries have undergone long-term charge and discharge cycles, and the positive electrode active materials in the positive electrode sheets lack lithium and have been soaked in electrolyte for a long time, so they are no longer pure materials. However, in the embodiments of the present application, the positive electrode sheets in the production stage have not been soaked in electrolyte and have not participated in charge and discharge cycles. In theory, they are not lacking in lithium and are pure materials.

[0038] (2) During the calcination treatment stage, for conventional recycling systems of positive electrode sheets from waste batteries, in order to remove the organic binder and conductive agent (such as acetylene black) in the positive electrode active material, the calcination is usually carried out under aerobic conditions; however, in the present application, anaerobic calcination is deliberately adopted, which can carbonize the residual organic binder and retain the inherent conductive agent, so that the positive electrode active material after calcination has better conductivity, so that no additional conductive agent needs to be added in the subsequent preparation of the slurry.

[0039] (3) For the conventional recycling system of positive electrode sheets in waste batteries, since the positive electrode active materials after participating in the charge and discharge cycle lack lithium, additional chemical reactions are required in the recycling process to replenish lithium for the positive electrode active materials, so as to obtain positive electrode active materials with physical and chemical properties that meet the requirements and can be used to prepare new positive electrode sheets; while in the embodiments of the present application, the positive electrode sheets in the production stage have not been soaked in electrolyte and have not participated in the charge and discharge cycle. In theory, there is no lack of lithium, so no additional chemical reactions are required to replenish lithium for the positive electrode active materials.

[0040] It should be noted that the method for providing anaerobic conditions is not limited and can be set according to conventional selections in the art.

[0041] As an example, the calcining step is performed under an inert atmosphere, that is, an oxygen-free condition is provided by filling the inert atmosphere.

[0042] In this embodiment, the calcination step is performed under an inert atmosphere, which has the advantages of conveniently providing oxygen-free conditions and a relatively stable calcination system.

[0043] As an example, the inert gas includes at least one of nitrogen and argon.

[0044] In this embodiment, the type of inert gas is not limited, and there are many feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the embodiment of the present application.

[0045] As an example, in the calcination treatment step, the treatment temperature is 350-700°C, for example but not limited to the treatment temperature is any one of 350°C, 400°C, 500°C, 600°C and 700°C or a range between any two of them; the treatment time is 2-5h, for example but not limited to the time is any one of 2h, 3h, 4h and 5h or a range between any two of them.

[0046] In this embodiment, on the basis of oxygen-free calcination, the temperature and duration of the calcination treatment are respectively limited within specific ranges, so that the remaining binder can be carbonized more thoroughly without affecting the inherent conductive agent content in the positive electrode active material.

[0047] As an example, the step of placing the positive electrode sheet in NMP for stripping treatment includes: transferring the positive electrode sheet to a rotary drum cleaning tank, in which an ultrasonic device is provided, and starting the rotary drum and the ultrasonic device to strip the positive electrode sheet.

[0048] In this embodiment, in the step of stripping, a rotary drum and an ultrasonic device are combined, so that the positive electrode active material can be stripped off from the positive electrode current collector more thoroughly and efficiently. The rotary drum (an existing device commonly used in the art, similar to a drum, hollow inside for accommodating positive electrode sheets, with holes on the side wall for easy access of NMP) can separate the stacked positive electrode sheets by rotating, and the ultrasonic device can impact the junction of the positive electrode active layer and the positive electrode current collector through ultrasonic energy, thereby helping the positive electrode active material to fall off from the positive electrode current collector.

[0049] It should be noted that the specifications of the drum are not limited. For example, the mesh specification of the drum (i.e., the size of the holes on the side wall) is 100-400 mesh. The drum of this specific specification can better strip the positive electrode active material from the positive electrode collector and temporarily store the stripped positive electrode collector in the drum.

[0050] It should be noted that the model, power and ultrasonic frequency of the ultrasonic equipment are not limited and can be adjusted according to actual peeling needs.

[0051] As an example, in the stripping treatment step, the temperature of NMP in the drum cleaning tank is 60-80°C, for example but not limited to the treatment temperature of any one of 60°C, 65°C, 70°C, 75°C and 80°C or a range between any two thereof; the treatment time is 1-4h, for example but not limited to any one of 1h, 2h, 3h and 4h or a range between any two thereof; and / or, the mass ratio of the positive electrode sheet to NMP is 1:(6-12), for example but not limited to a mass ratio of any one of 1:6, 1:7, 1:8, 1:9, 1:10, 1:11 and 1:12 or a range between any two thereof.

[0052] In this embodiment, the stripping treatment step is carried out under suitable temperature conditions and duration, and the mass ratio of the positive electrode sheet and NMP is limited to a specific range, which helps the positive electrode active material to fall off from the positive electrode collector, and at the same time, it also helps the positive electrode active material after falling off to be better dispersed in water.

[0053] As an example, after the stripping step and before the solid-liquid separation step, the method further includes taking out the positive electrode current collector in the drum and drying and recovering it under nitrogen.

[0054] In this embodiment, since the peeled positive electrode current collector is also an unused material, recycling and reusing it can also bring relatively ideal economic benefits.

[0055] It should be noted that in the step of solid-liquid separation, the specific separation method is not limited. For example, a vibrating screen with a specification of 100 to 400 meshes can be used for solid-liquid separation.

[0056] As an example, the step of using a vibrating screen to perform solid-liquid separation also includes the step of taking out the material on the screen (i.e., larger-sized fragments of the positive electrode current collector) and drying and recovering them under nitrogen.

[0057] As an example, the step of centrifuging the filtrate to obtain a precipitate containing the positive electrode active material includes: centrifuging the filtrate for the first time to obtain a precipitate intermediate; then, dispersing the precipitate intermediate in NMP and centrifuging it for the second time to obtain a precipitate containing the positive electrode active material.

[0058] In this embodiment, two centrifugal treatments are successively performed, and the binder in the positive electrode active material can be removed more thoroughly by utilizing the property that the positive electrode active material is insoluble in the organic solvent but the binder is soluble in the organic solvent.

[0059] It should be noted that in the two centrifugal treatment steps, the specific rotation speed of the centrifugal device is not limited, for example, it can be any point value between 4000 and 6000 rpm or any range value between the two.

[0060] As an example, the step of dispersing the precipitate intermediate in NMP includes: adding the precipitate intermediate into NMP and stirring, wherein the temperature of NMP is 60-80°C, for example but not limited to the treatment temperature is any one of 60°C, 65°C, 70°C, 75°C and 80°C or a range between any two thereof; the treatment time is 1-4h, for example but not limited to the time is any one of 1h, 2h, 3h and 4h or a range between any two thereof.

[0061] In this embodiment, during the stirring and dispersing process, the treatment temperature and duration are respectively limited within specific ranges, so that the binder in the positive electrode active material can be fully exposed and dissolved in NMP, so as to be easily removed by centrifugation.

[0062] As an example, the mass ratio of the precipitate intermediate to NMP is 1:(3-6), such as but not limited to any one of 1:3, 1:4, 1:5 and 1:6 or a range between any two of the mass ratios.

[0063] In this embodiment, during the stirring and dispersing process, the mass ratio of the precipitate intermediate to NMP is limited to a specific range, which helps the binder to be fully dissolved in NMP so as to be removed by centrifugation.

[0064] As an example, in the drying step, the drying method is intermittent negative pressure drying, wherein the processing temperature is 130-170°C, for example but not limited to the processing temperature being any point value among 130°C, 140°C, 150°C, 160°C and 170°C or a range value between any two thereof; the processing time is 1-4h, for example but not limited to the time being any point value among 1h, 2h, 3h and 4h or a range value between any two thereof.

[0065] In this embodiment, the temperature and duration of the drying process are respectively limited within specific ranges, which can achieve a good drying effect without affecting the inherent physical and chemical properties of the positive electrode active material.

[0066] As an example, the negative pressure is -0.02 to -0.1 MPa.

[0067] In this embodiment, the drying process is carried out under specific negative pressure conditions, which helps to maintain the stability of the drying system.

[0068] It should be noted that, in the method for repairing the positive electrode active material, any process or step not specifically described or limited may be arranged according to conventional selection in the art.

[0069] As an example, after the crushing step, conventional steps such as homogenization, screening, iron removal and packaging by gravity flow are also included.

[0070] As an example, the process flow chart of the method for repairing the positive electrode active material is exemplarily referred to Figure 1 .

[0071] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode sheet, comprising the following steps:

[0072] The positive electrode active material repaired by the repair method provided in the embodiment of the first aspect is mixed with a binder to obtain a slurry, wherein no additional conductive agent is required to be added to the slurry; the slurry is coated on the positive electrode current collector and dried to form a positive electrode sheet.

[0073] In the present application, the positive electrode active material repaired by the repair method provided in the first aspect of the embodiment is used to prepare the slurry, which can omit the step of additionally adding a conductive agent, thereby improving the preparation efficiency of the positive electrode sheet.

[0074] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0075] Example 1

[0076] The present application provides a method for repairing a positive electrode active material, comprising the following steps:

[0077] S0 cuts positive electrode sheets (specifically composed of: positive electrode current collector is aluminum foil, positive electrode active material is 96% LiFePO, binder is 2% polyvinylidene fluoride, conductive agent is 2% acetylene black, by mass percentage) to prepare batteries, and the waste generated in the process of cutting the positive electrode sheets is used as raw materials for repair.

[0078] S1 transfers the positive electrode sheet that has not been in contact with the electrolyte (i.e., the waste cut in step S0) to a rotary drum cleaning tank, in which an ultrasonic device is provided, and starts the rotary drum and the ultrasonic device to perform a stripping treatment on the positive electrode sheet so that the positive electrode active material falls off the positive electrode current collector. The mass ratio of the positive electrode sheet to the NMP in the rotary drum cleaning tank is 1:6, the temperature of the NMP is 70°C, the treatment time is 2h, and the mesh size specification of the rotary drum is 300 meshes.

[0079] S2: The NMP solution containing the positive electrode active material is passed through a 200-mesh vibrating screen for solid-liquid separation to obtain a filtrate containing the positive electrode active material.

[0080] S3 uses a centrifugal pump to pass the filtrate into a centrifuge for the first centrifugal treatment to obtain a precipitate intermediate; then, the precipitate intermediate is added to NMP for stirring and dispersion, and then the dispersed mixed solution is passed into a centrifuge for a second centrifugal treatment to obtain a precipitate containing positive electrode active materials. During the two centrifugal treatments, the speed of the centrifuge is 5000 rpm and the centrifugal time is 30 minutes; during the process of adding the precipitate intermediate to NMP for stirring and dispersion, the mass ratio of the precipitate intermediate to NMP is 1:3, the temperature of NMP is 70°C, and the treatment time is 2 hours.

[0081] S4 uses an intermittent negative pressure dryer to dry the precipitate; the heat source is steam, the processing temperature is 170°C, the processing time is 2h, and the negative pressure is -0.02MPa.

[0082] S5: The dried material is transferred to a pyrolysis furnace and calcined in a nitrogen atmosphere; wherein the treatment temperature is 350°C and the treatment time is 5 hours; then, the calcined material is crushed, homogenized by gravity flow, sieved and iron removed in sequence to obtain the positive electrode active material.

[0083] Example 2

[0084] The present application embodiment provides a method for repairing positive electrode active materials, comprising the following steps: S1 transferring the positive electrode sheet that has not been in contact with the electrolyte (i.e., the waste material cut in step S0 in embodiment 1) to a rotary drum cleaning tank, in which an ultrasonic device is provided, and starting the rotary drum and the ultrasonic device to perform a stripping treatment on the positive electrode sheet so that the positive electrode active material falls off the positive electrode current collector. The mass ratio of the positive electrode sheet to the NMP in the rotary drum cleaning tank is 1:12, the temperature of the NMP is 80°C, the treatment time is 2h, and the mesh specification of the rotary drum is 400 mesh.

[0085] S2: The NMP solution containing the positive electrode active material is passed through a vibrating screen with a specification of 400 meshes for solid-liquid separation to obtain a filtrate containing the positive electrode active material.

[0086] S3 uses a centrifugal pump to pass the filtrate into a centrifuge for the first centrifugal treatment to obtain a precipitate intermediate; then, the precipitate intermediate is added to NMP for stirring and dispersion, and then the dispersed mixed solution is passed into a centrifuge for a second centrifugal treatment to obtain a precipitate containing positive electrode active materials. During the two centrifugal treatments, the speed of the centrifuge is 6000 rpm, and the centrifugal time is 15 minutes; during the process of adding the precipitate intermediate to NMP for stirring and dispersion, the mass ratio of the precipitate intermediate to NMP is 1:6, the temperature of NMP is 80°C, and the treatment time is 2 hours.

[0087] S4 uses an intermittent negative pressure dryer to dry the precipitate; the heat source is steam, the processing temperature is 130°C, the processing time is 4h, and the negative pressure is -0.1MPa.

[0088] S5: The dried material is transferred to a pyrolysis furnace and calcined in a nitrogen atmosphere; wherein the treatment temperature is 700°C and the treatment time is 2 hours; then, the calcined material is crushed, homogenized by gravity flow, sieved and iron removed in sequence to obtain the positive electrode active material.

[0089] Test Example 1

[0090] Physical and chemical properties test of positive electrode active materials

[0091] Test method:

[0092] The positive electrode active materials prepared in Examples 1 to 2 were numbered respectively, and then the appearance, powder compaction density, Al element content, etc. of each sample were tested.

[0093] Table 1 Statistics of physical and chemical properties test results

[0094]

[0095] Referring to Table 1, it can be seen from the test results of Examples 1 to 2 that the positive electrode sheet waste in the positive electrode sheet preparation process is recycled according to the repair method provided in the embodiments of the present application. The physical and chemical properties of the recycled positive electrode active material meet the reference standards for recyclable positive electrode active materials and can be directly used to prepare new positive electrode sheets.

[0096] Test Example 2

[0097] Electrical performance test of positive electrode active materials

[0098] Test method:

[0099] The positive electrode active materials prepared in Examples 1 to 2 were respectively assembled into lithium-ion batteries, and then the 0.1C first efficiency, 0.1C first charge specific capacity and 0.1C first discharge specific capacity of each sample were tested.

[0100] Among them, the steps of battery assembly are as follows:

[0101] S1 is prepared by mixing LiFePO (positive electrode active material) and polyvinylidene fluoride (binder) in a mass ratio of 96:2, and dispersing the mixture in N-methyl-2-pyrrolidone to obtain positive electrode slurry. The positive electrode slurry is then evenly coated on both sides of an aluminum foil. After drying, rolling and vacuum drying, an aluminum lead wire is welded on the foil with an ultrasonic welder to obtain a positive electrode sheet with a thickness of 125 μm.

[0102] S2 is prepared by mixing graphite (negative electrode active material), acetylene black (conductive agent), styrene-butadiene rubber and carboxymethyl cellulose (binder) in a mass ratio of 95:1.5:1.5:2 and dispersing the mixture in deionized water to obtain a negative electrode slurry. The negative electrode slurry is then coated on both sides of a copper foil. The mixture is then dried, rolled and vacuum dried in sequence, and a nickel lead wire is welded on the mixture with an ultrasonic welder to obtain a negative electrode sheet having a thickness of 125 μm.

[0103] S3 winds the prepared positive electrode sheet, negative electrode sheet and ion separator (PP / PE / PP three-layer composite separator) to prepare a bare battery cell, then injects the electrolyte (85% dimethyl carbonate, 12% lithium hexafluorophosphate, 3% PST by mass) into the dried battery, and completes the battery assembly after packaging, standing, formation, shaping and capacity testing.

[0104] Among them, the test method for the 0.1C first charge specific capacity is as follows:

[0105] Place the battery on a battery program-controlled tester for charge and discharge cycles: The test conditions for the first discharge specific capacity are as follows: the test temperature is 25°C, the charge and discharge rate is 0.1C, the voltage range is 0.005~1.5V, and the calculation formula is as follows:

[0106] Q0.1,dis =C 0.1,dis / m;

[0107] m—mass of active substance in grams; Q 0.1,dis —The first discharge specific capacity when charging and discharging at a current rate of 0.1C, in milliampere-hours per gram (mAh / g); C 0.1,dis —The first discharge capacity when charging and discharging at a current rate of 0.1C, in milliampere-hours (mAh).

[0108] Among them, the test method for 0.1C first discharge specific capacity is as follows:

[0109] Place the battery on a battery program-controlled tester for charge and discharge cycles: The test conditions for the first discharge specific capacity are as follows: the test temperature is 25°C, the charge and discharge rate is 0.1C, the voltage range is 0.005~1.5V, and the calculation formula is as follows:

[0110] Q 0.1,cha =C 0.1,cha / m;

[0111] m—mass of active substance in grams; Q 0.1,cha —The first discharge specific capacity when charging and discharging at a current rate of 0.1C, in milliampere-hours per gram (mAh / g); C 0.1,cha —The first discharge capacity when charging and discharging at a current rate of 0.1C, in milliampere-hours (mAh).

[0112] Among them, the calculation formula for the 0.1C first efficiency is as follows:

[0113] CE 0.1 =Q 0.1,dis / Q 0.1,cha x100%; CE0.1—first coulombic efficiency, expressed in (%).

[0114] Table 2 Electrical performance test statistics

[0115]

[0116] Referring to Table 2, it can be seen from the test results of Examples 1 to 2 that the positive electrode active material recovered by the repair method provided in the embodiments of the present application does not require additional conductive agent to be added during the slurry preparation stage, and the performance of the prepared positive electrode sheet also meets the reference indicators and can be directly used to prepare new lithium-ion batteries.

[0117] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

Claims

1. A method for repairing a positive electrode active material, characterized in that: The following steps are involved: placing the positive electrode sheet in NMP for stripping treatment so that the positive electrode active material falls off the positive electrode current collector, wherein the positive electrode sheet is not in contact with the electrolyte; Performing solid-liquid separation on the NMP solution containing the positive electrode active material to obtain a filtrate containing the positive electrode active material; Centrifuging the filtrate to obtain a precipitate containing a positive electrode active material; The precipitate is sequentially dried, calcined and crushed to obtain a positive electrode active material; wherein the calcination step is performed under oxygen-free conditions.

2. The method for repairing the positive electrode active material according to claim 1, characterized in that: The calcination step is performed under an inert atmosphere.

3. The method for repairing the positive electrode active material according to claim 2, characterized in that: In the calcination step, the treatment temperature is 350-700° C. and the treatment time is 2-5 hours.

4. The method for repairing a positive electrode active material according to any one of claims 1 to 3, characterized in that: The step of placing the positive electrode sheet into NMP for stripping treatment comprises: The positive electrode sheet is transferred to a rotary drum cleaning tank, in which an ultrasonic device is provided, and the rotary drum and the ultrasonic device are started to perform a stripping treatment on the positive electrode sheet.

5. The method for repairing the positive electrode active material according to claim 4, characterized in that: In the stripping step, the temperature of the NMP in the drum cleaning tank is 60-80° C., and the treatment time is 1-4 hours; and / or the mass ratio of the positive electrode sheet to the NMP is 1:(6-12).

6. The method for repairing a positive electrode active material according to any one of claims 1 to 3, characterized in that: The step of centrifuging the filtrate to obtain a precipitate containing the positive electrode active material comprises: The filtrate is subjected to a first centrifugal treatment to obtain a precipitate intermediate; then, the precipitate intermediate is dispersed in NMP and subjected to a second centrifugal treatment to obtain a precipitate containing a positive electrode active material.

7. The method for repairing the positive electrode active material according to claim 6, characterized in that: The step of dispersing the precipitate intermediate in NMP comprises: The precipitate intermediate is added into NMP and stirred, wherein the temperature of NMP is 60-80° C. and the treatment time is 1-4 hours.

8. The method for repairing the positive electrode active material according to claim 7, characterized in that: The mass ratio of the precipitate intermediate to NMP is 1:(3-6).

9. The method for repairing a positive electrode sheet according to any one of claims 1 to 3, characterized in that: In the drying step, the drying method is intermittent negative pressure drying, wherein the treatment temperature is 130-170°C and the treatment time is 1-4h; And / or, the negative pressure is -0.02 to -0.1 MPa.

10. A method for preparing a positive electrode sheet, characterized in that: The following steps are involved: The positive electrode active material repaired by the repair method according to any one of claims 1 to 9 is mixed with a binder to obtain a slurry, wherein no additional conductive agent is required to be added to the slurry; the slurry is coated on a positive electrode current collector and dried to form the positive electrode sheet.

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