Lithium iron phosphate repairing material, repairing and recycling method thereof, positive plate and lithium ion battery

Abstract

The invention provides a lithium iron phosphate repair material and a repair and recovery method thereof, a positive plate and a lithium ion battery, and the repair and recovery method comprises the following steps: washing the positive plate disassembled from the lithium ion battery with an organic solvent to remove lithium salt in the positive plate; carrying out first calcination treatment on a to-be-treated object containing the positive pole piece after the lithium salt is removed so as to destroy a carbon coating layer and separate a positive active material layer from a positive current collector; and coarsely crushing the separated positive electrode active material layer, mixing the crushed positive electrode active material layer with a lithium supplementing material, and carrying out secondary calcination treatment on the mixed material to obtain the lithium iron phosphate repairing material. According to the repair and recovery method provided by the invention, large-scale environment-friendly repair and recovery of lithium iron phosphate in the waste lithium ion battery can be realized, and the lithium iron phosphate repair material with excellent cycle performance can be obtained.

Description

Technical Field

[0001] The present application relates to the technical field of battery recycling, and in particular to a lithium iron phosphate repair material and a repair and recycling method thereof, a positive electrode sheet and a lithium ion battery. Background Art

[0002] In recent years, with the production and use of lithium-ion batteries, the amount of waste lithium-ion batteries has gradually increased, leading to the accumulation of waste lithium-ion batteries. At present, for retired lithium iron phosphate positive electrode material cells, the traditional recycling method is mainly to recover lithium salts and other metal salts through wet leaching. However, the wet leaching recovery process is long and the operation process is complicated. It requires the use of a large amount of inorganic strong acids and alkalis, which is easy to cause secondary pollution and difficult to achieve zero emissions in the production process. There is a great pressure on the environmental protection. In addition, there are also methods that try to repair and recycle retired battery materials through direct repair and regeneration, but the cycle performance of the repaired lithium iron phosphate positive electrode material is usually poor. Summary of the invention

[0003] Based on this, the present application provides a lithium iron phosphate repair material and its repair and recovery method, a positive electrode sheet and a lithium ion battery, which can realize large-scale environmentally friendly repair and recovery of lithium iron phosphate in waste lithium ion batteries, and obtain lithium iron phosphate repair materials with excellent cycle performance.

[0004] The first aspect of the present application provides a method for repairing and recovering lithium iron phosphate in a lithium-ion battery, comprising:

[0005] The positive electrode sheet disassembled from the lithium-ion battery is washed with an organic solvent to remove the lithium salt in the positive electrode sheet; wherein the positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer and a carbon coating layer, the carbon coating layer is arranged between the positive electrode current collector and the positive electrode active material layer, the positive electrode active material layer comprises lithium iron phosphate, and the carbon coating layer comprises conductive carbon and an aqueous binder;

[0006] The object to be treated, which contains the positive electrode sheet after the lithium salt is removed, is subjected to a first calcination treatment to destroy the carbon coating layer and separate the positive electrode active material layer from the positive electrode current collector;

[0007] The separated positive electrode active material layer is roughly broken and then mixed with a lithium supplement material, and the mixed material is subjected to a second calcination treatment to obtain a lithium iron phosphate repair material.

[0008] In some embodiments of the present application, one or more of the following conditions are met:

[0009] (1) The temperature of the first calcination treatment is 350°C to 450°C;

[0010] (2) The first calcination time is less than or equal to 1 hour, and can be selected from 15 minutes to 60 minutes.

[0011] In some embodiments of the present application, the object to be processed further comprises a lithium-containing protective material;

[0012] Optionally, the lithium-containing protective material includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium sulfate;

[0013] Optionally, the mass proportion of the lithium-containing protective material in the positive electrode plate after removing the lithium salt is 0.05%~1%.

[0014] In some embodiments of the present application, one or more of the following conditions are met:

[0015] (1) The washing time is less than or equal to 30 minutes, and can be selected from 5 seconds to 30 minutes;

[0016] (2) The organic solvent includes one or more of methanol, ethanol, acetone and carbonate organic solvents;

[0017] Optionally, the carbonate organic solvent includes one or more of dimethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and butylene carbonate;

[0018] (3) The aqueous binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, styrene-butadiene rubber, and polyvinyl alcohol.

[0019] In some embodiments of the present application, one or more of the following conditions are met:

[0020] (1) The temperature of the second calcination treatment is 500°C to 800°C, and can be 600°C to 750°C;

[0021] (2) The second calcination treatment time is 2h~10h;

[0022] (3) Optionally, the lithium supplement material is mixed with the coarsely broken positive electrode active material layer in a mass ratio of (1-20):100.

[0023] In some embodiments of the present application, the separating the positive electrode active material layer is roughly broken and then mixed with the lithium supplement material, comprising:

[0024] The coarsely broken positive electrode active material layer is mixed with the lithium supplement material and then subjected to ball milling treatment;

[0025] Optionally, the ball milling process is performed at a rotation speed of 300 rpm to 500 rpm;

[0026] Optionally, the ball milling treatment time is 30 min to 60 min.

[0027] The second aspect of the present application provides a lithium iron phosphate repair material, which is prepared by the repair and recovery method described in the first aspect of the present application.

[0028] In some embodiments of the present application, the lithium iron phosphate repair material includes a base particle containing lithium iron phosphate, and a protective layer covering at least a portion of the surface of the base particle, wherein the protective layer contains lithium fluoride.

[0029] The third aspect of the present application provides a positive electrode sheet comprising the lithium iron phosphate repair material described in the second aspect of the present application.

[0030] The fourth aspect of the present application provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect of the present application.

[0031] The repair and recycling method provided in the present application can achieve large-scale repair and recycling of lithium iron phosphate in waste lithium-ion batteries through the sequential coordination of various steps, and has a short process and high yield. It does not involve solvents such as strong acids and strong alkalis, is environmentally friendly, can maximize the use of discarded and retired battery cell electrodes, and can obtain lithium iron phosphate repair materials with excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a morphological diagram of a lithium iron phosphate repair material according to an embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to facilitate understanding of the present application, the present application will be described more comprehensively below. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0034] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unclearly recorded range; and any lower limit can be combined with other lower limits to form an unclearly recorded range, and any upper limit can be combined with any other upper limit to form an unclearly recorded range. In addition, although not clearly recorded, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unclearly recorded range.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be noted that, unless otherwise specified, the term "and / or" used herein includes any and all combinations of one or more related listed items, and "above" and "below" are inclusive of the number, and the meaning of "multiple" in "one or more" is more than two.

[0036] Herein, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​within the numerical interval is considered to be continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval only refers to integers within the numerical interval, including the two endpoint integers of the numerical range, and each integer between the two endpoints, is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows broadly including numerical interval types such as percentage intervals, ratio intervals, and ratio intervals.

[0037] In this article, if there are multiple steps involved in the method flow, unless there is a clear different description in this article, there is no strict order restriction for the execution of these steps, and they can be executed in other orders than described. Moreover, any step can include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn, alternating or simultaneously with other steps or parts of sub-steps or stages of other steps.

[0038] The above application content of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0039] In a first aspect, the present application provides a method for repairing and recovering lithium iron phosphate in a lithium-ion battery, which may include the following steps S1 to S3:

[0040] S1: washing the positive electrode sheet disassembled from the lithium-ion battery with an organic solvent to remove the lithium salt in the positive electrode sheet; wherein the positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer and a carbon coating layer, the carbon coating layer is arranged between the positive electrode current collector and the positive electrode active material layer, the positive electrode active material layer comprises lithium iron phosphate, and the carbon coating layer comprises conductive carbon and an aqueous binder;

[0041] S2: subjecting the object to be treated, including the positive electrode sheet after the lithium salt is removed, to a first calcination treatment to destroy the carbon coating layer and separate the positive electrode active material layer from the positive electrode current collector;

[0042] S3: The separated positive electrode active material layer is roughly broken and then mixed with a lithium supplement material, and the mixed material is subjected to a second calcination treatment to obtain a lithium iron phosphate repair material.

[0043] It is understood that the "aqueous binder" mentioned in the present application refers to a water-soluble or water-dispersible polymer, including but not limited to one or more of sodium carboxymethyl cellulose, polyacrylic acid, styrene-butadiene rubber and polyvinyl alcohol.

[0044] The present application specifically provides the above-mentioned repair and recycling method for positive electrode plates and lithium-ion batteries provided with a carbon coating layer and containing an aqueous binder. In step S1, the positive electrode plates are washed with an organic solvent so that the lithium salt remaining on the positive electrode plates in the electrolyte after disassembly can be dissolved in the organic solvent. In this way, the lithium salt in the positive electrode plates can be removed, which is beneficial to reduce the impedance of the lithium iron phosphate repair material and improve the cycle performance.

[0045] In step S2, after the first calcination treatment, the aqueous binder in the carbon coating layer can be melted and decomposed, thereby destroying the carbon coating layer, and realizing the separation of the positive electrode active material layer and the positive electrode current collector, and achieving a higher separation rate; at the same time, the positive electrode binder (such as polyvinylidene fluoride) contained in the positive electrode active material layer will not decompose or only decompose in a trace amount, reducing the adverse effects of HF and other substances generated after the decomposition of the positive electrode binder on the lithium iron phosphate positive electrode material (such as corroding the interior of the positive electrode material and destroying the material structure), and improving the cycle performance of the lithium iron phosphate repair material.

[0046] In step S3, the mixed material is subjected to a second calcination treatment, which can realize the lithium replenishment of the lithium replenishing material to the lithium iron phosphate, and can also make the positive electrode binder contained in the positive electrode active material layer melt and decompose into carbon and wrap it on the surface of the lithium iron phosphate. At the same time, the HF generated by the melt decomposition will also be reacted by the lithium replenishing material to generate a protective layer containing LiF and cover the surface of the lithium iron phosphate. In this way, not only can the adverse effects of HF and other substances on the lithium iron phosphate positive electrode material be reduced (such as corroding the interior of the positive electrode material and destroying the material structure), but the generated LiF-containing protective layer can also protect the lithium iron phosphate, thereby improving the ionic conductivity, chemical stability and cycle performance of the lithium iron phosphate repair material.

[0047] In this way, the repair and recycling method provided in the present application can realize large-scale repair and recycling of lithium iron phosphate in waste lithium-ion batteries through the cooperation of the above steps S1 to S3. The whole process is short, the yield is high, the process is simple, the operability is strong, and it does not involve solvents such as strong acids and strong alkalis. It is environmentally friendly, can maximize the utilization of discarded retired battery cell electrodes, and can obtain lithium iron phosphate repair materials with excellent cycle performance.

[0048] In some embodiments, the conductive carbon includes one or more of superconducting carbon, carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0049] In some embodiments, the method used to disassemble the positive electrode plate from the lithium-ion battery in step S1 can be refined disassembly.

[0050] In some embodiments, after washing the positive electrode plates disassembled from the lithium-ion battery with an organic solvent, step S1 may further include: condensing and recovering the organic solvent and then reusing it until the organic solvent is saturated with lithium salt and then discarded.

[0051] In some embodiments, the temperature of the first calcination treatment is 350° C. to 450° C. For example, the temperature of the first calcination treatment can be 350° C., 360° C., 370° C., 380° C., 390° C., 400° C., 410° C., 420° C., 430° C., 440° C., 450° C. or within a range consisting of any of the above values.

[0052] The temperature of the first calcination treatment is controlled within the above range, that is, the low-temperature calcination is performed first, which can melt and decompose the aqueous binder in the carbon coating layer, thereby destroying the carbon coating layer and realizing the separation of the positive electrode active material layer and the positive electrode current collector; at the same time, it can also prevent the positive electrode binder (such as polyvinylidene fluoride) contained in the positive electrode active material layer from decomposing or only decompose in a trace amount, thereby reducing the adverse effects of HF and other substances generated after the decomposition of the positive electrode binder on the lithium iron phosphate positive electrode material (such as corroding the interior of the positive electrode material and destroying the material structure), and improving the cycle performance of the lithium iron phosphate repair material.

[0053] In addition, controlling the temperature of the first calcination treatment within the above range can also reduce the metal in the current collector (such as aluminum in aluminum foil) from entering the lithium iron phosphate, and reduce the adverse effects of the metal entering the lithium iron phosphate on the lithium iron phosphate repair material (such as reduced cycle performance and rate performance), so that the lithium iron phosphate repair material has higher cycle performance and rate performance.

[0054] In some embodiments, the positive electrode active material layer includes a positive electrode binder, and the positive electrode binder includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and fluorine-containing acrylate resin.

[0055] In some embodiments, the first calcination time is less than or equal to 1 hour. For example, the first calcination time can be 1 minute, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes or within the range of any of the above values; it can be optionally 15 minutes to 60 minutes.

[0056] Controlling the time of the first calcination treatment within the above range can reduce the metal in the current collector (such as aluminum in aluminum foil) entering the lithium iron phosphate, reduce the content of the metal in the lithium iron phosphate, and reduce the adverse effects of the metal entering the lithium iron phosphate on the lithium iron phosphate repair material (such as the reduction of cycle performance and rate performance), so that the lithium iron phosphate repair material has higher cycle performance and rate performance.

[0057] In some embodiments, the object to be processed further comprises a lithium-containing protective material, which can prevent a small amount of positive electrode binder in the positive electrode sheet from decomposing and generating HF, thereby reducing its negative impact on the material.

[0058] In some embodiments, the lithium-containing protective material includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, and lithium sulfate.

[0059] In some embodiments, the mass proportion of the lithium-containing protective material in the positive electrode sheet after the lithium salt is removed is 0.05% to 1%.

[0060] In some embodiments, the washing time is less than or equal to 30 minutes. For example, the washing time can be 1 second, 5 seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes or within the range of any of the above values; it can be selected from 5 seconds to 30 minutes.

[0061] By controlling the washing time within the above range, on the one hand, the lithium salt on the positive electrode plate can be removed as fully as possible; on the other hand, it can also reduce the damage to the material structure caused by the dissolution of active ions in the lithium iron phosphate due to too long a time, so that the lithium iron phosphate repair material has a higher cycle performance.

[0062] In some embodiments, the organic solvent includes one or more of methanol, ethanol, acetone and carbonate organic solvents; optionally, the carbonate organic solvent includes one or more of dimethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and butylene carbonate.

[0063] In some embodiments, after washing the positive electrode plate with an organic solvent, the process further includes drying the washed positive electrode plate; optionally, the drying temperature is less than or equal to 100° C., and the drying time is 15 min to 60 min.

[0064] In some embodiments, the temperature of the second calcination treatment is 500° C. to 800° C., and may be 600° C. to 750° C. For example, the temperature of the second calcination treatment may be 500° C., 510° C., 530° C., 550° C., 570° C., 590° C., 600° C., 610° C., 630° C., 650° C., 670° C., 690° C., 700° C., 710° C., 730° C., 750° C., 770° C., 790° C., 800° C. or within a range consisting of any of the above values.

[0065] The temperature of the second calcination treatment is controlled within the above range, which can not only achieve sufficient lithium replenishment of lithium iron phosphate by the lithium replenishing material, but also enable the positive electrode binder contained in the positive electrode active material layer to fully melt and decompose into carbon and wrap it on the surface of the lithium iron phosphate. At the same time, HF generated by the melting and decomposition will react with the lithium replenishing material to generate a protective layer containing LiF and cover the surface of the lithium iron phosphate, thereby protecting the lithium iron phosphate, thereby improving the ionic conductivity, chemical stability and cycle performance of the lithium iron phosphate repair material.

[0066] In some embodiments, the second calcination treatment lasts for 2 hours to 10 hours.

[0067] In some embodiments, the lithium supplement material is mixed with the coarsely broken positive electrode active material layer in a mass ratio of (1-20):100.

[0068] In some embodiments, the lithium supplement material includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, and lithium sulfate.

[0069] Thus, the present application performs calcination treatment twice, including a first calcination treatment (i.e., a low-temperature calcination treatment) and a second calcination treatment (i.e., a high-temperature calcination treatment), which is compared with a single high-temperature calcination treatment in which the positive electrode plate after removal of lithium salt and rough breaking is mixed with the lithium supplement material and then directly subjected to a high-temperature calcination treatment (i.e., step S2 is omitted). Although the single high-temperature calcination treatment can also achieve the destruction of the carbon coating layer and the separation of the positive electrode active material layer and the positive electrode current collector, the higher calcination temperature can easily cause the metal in the current collector (such as aluminum in aluminum foil) to enter the lithium iron phosphate, resulting in a higher content of the metal in the lithium iron phosphate, leading to a decrease in its cycle performance and rate performance. The present application uses two calcination treatments. Since the calcination temperature during the first calcination treatment is relatively low, the amount of metal in the current collector that enters the lithium iron phosphate will be relatively much less. At the same time, since the positive electrode active material layer has been separated from the current collector during the second calcination treatment, the total amount of the aforementioned metal that enters the lithium iron phosphate will be relatively small after two calcination treatments. This allows the lithium iron phosphate repair material to have relatively high cycle performance and rate performance.

[0070] In some embodiments, the step S3 of roughly crushing the separated positive electrode active material layer and then mixing it with the lithium supplement material may include: mixing the roughly crushed positive electrode active material layer and the lithium supplement material and then subjecting them to ball milling treatment.

[0071] In some embodiments, the ball milling process is performed at a rotation speed of 300 rpm to 500 rpm.

[0072] In some embodiments, the ball milling treatment time is 30 min to 60 min.

[0073] In a second aspect, the present application provides a lithium iron phosphate repair material, which is prepared by the repair and recovery method described in the first aspect of the present application.

[0074] In some embodiments, the lithium iron phosphate repair material includes a base particle containing lithium iron phosphate, and a protective layer covering at least a portion of the surface of the base particle, wherein the protective layer contains lithium fluoride. The protective layer containing lithium fluoride (LiF) can protect the lithium iron phosphate base particles, thereby improving the ionic conductivity, chemical stability and cycle performance of the lithium iron phosphate repair material.

[0075] As an example, whether lithium iron phosphate repair materials contain lithium fluoride can be tested by the following method: the lithium iron phosphate repair material is subjected to X-ray photoelectron spectroscopy (XPS) testing to detect whether the material contains elements such as Li, F, C, Fe, P, O and the content of each element, and to comprehensively determine whether it contains lithium fluoride.

[0076] In some embodiments, in the lithium iron phosphate repair material, the molar ratio of lithium element to metal element is 1.01-1.10, and can be optionally 1.03-1.08.

[0077] As an example, the molar ratio of lithium to metal elements in lithium iron phosphate repair materials can be tested by the following method: the lithium iron phosphate repair material is subjected to inductively coupled plasma (ICP) testing to detect the contents of elements such as Li, Fe, and P in the material, based on which the molar ratio can be calculated.

[0078] In a third aspect, the present application provides a positive electrode sheet comprising the lithium iron phosphate repair material described in the second aspect of the present application.

[0079] In some embodiments, the lithium iron phosphate repair material can be used as a positive electrode material and applied to a positive electrode sheet.

[0080] In a third aspect, the present application provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect of the present application.

[0081] In some embodiments, the lithium-ion battery further includes a negative electrode sheet, a separator and an electrolyte. During the battery charging and discharging process, lithium ions are inserted and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0082] In a fifth aspect, the present application provides an electronic device comprising the lithium-ion battery described in the fourth aspect of the present application.

[0083] In some embodiments, the type of electronic device is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device can include, but is not limited to, power tools, electric cars, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, etc.

[0084] Example

[0085] The following are specific examples, which more specifically describe the contents disclosed in this application, and these examples are only for illustrative purposes, because it is obvious to those skilled in the art that various modifications and variations are made within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0086] Example 1

[0087] (1) The discarded lithium iron phosphate battery cells are separated into positive electrode plates through fine disassembly equipment, and then the plates are washed with dimethyl carbonate (DMC) for 5 seconds and then placed in an oven for drying. The organic solvent is condensed and recovered and reused until the lithium salt is saturated and then discarded.

[0088] (2) The dried positive electrode sheet is calcined at 400°C for 15 min to destroy the carbon coating layer (the carbon coating layer contains carboxymethyl cellulose and carbon black) therein, thereby separating the current collector Al foil and the positive electrode active material layer (the positive electrode active material layer contains lithium iron phosphate, polyvinylidene fluoride and carbon black).

[0089] (3) The positive electrode active material layer was coarsely crushed and mixed with lithium carbonate (the mass ratio of lithium carbonate to the positive electrode active material layer was 5:100), and then ball milled at 300 rpm for 30 min to obtain a mixture; thereafter, the mixture was placed in a tubular furnace and calcined at 650° C. in an inert atmosphere for 6 h to obtain a lithium iron phosphate repair material.

[0090] Example 2

[0091] The preparation method is similar to that of Example 1, with the main difference being that in step (2), the calcination temperature is 350°C.

[0092] Example 3

[0093] The preparation method is similar to that of Example 1, with the main difference being that in step (2), the calcination temperature is 450°C.

[0094] Example 4

[0095] The preparation method is similar to that of Example 1, with the main difference being that in step (2), the calcination temperature is 500°C.

[0096] Example 5

[0097] The preparation method is similar to that of Example 1, with the main difference being that in step (2), the calcination time is 30 min.

[0098] Example 6

[0099] The preparation method is similar to that of Example 1, with the main difference being that in step (2), the calcination time is 1 h.

[0100] Example 7

[0101] The preparation method is similar to that of Example 1, with the main difference being that in step (2), the calcination time is 2 h.

[0102] Example 8

[0103] The preparation method is similar to that of Example 1, with the main difference being that in step (1), the washing time is 5 min.

[0104] Example 9

[0105] The preparation method is similar to that of Example 1, with the main difference being that in step (1), the washing time is 30 min.

[0106] Example 10

[0107] The preparation method is similar to that of Example 1, with the main difference being that in step (1), the washing time is 60 min.

[0108] Embodiment 11

[0109] The preparation method is similar to that of Example 1, with the main difference being that in step (2), lithium carbonate is added to the positive electrode sheet before calcination, and the mass proportion of lithium carbonate in the positive electrode sheet is 0.5%.

[0110] Comparative Example 1

[0111] The preparation method is similar to that of Example 1, with the main difference being that the calcination treatment in step (2) is omitted, and in step (3), the positive electrode sheet is directly broken into pieces and mixed with lithium carbonate, while other conditions remain unchanged.

[0112] Comparative Example 2

[0113] The preparation method is similar to that of Example 1, with the main difference being that the washing treatment in step (1) is omitted.

[0114] The lithium iron phosphate repair materials or lithium ion batteries prepared in Examples 1 to 11 and Comparative Examples 1 to 2 were subjected to relevant performance tests. The test results are shown in Table 1 below. In Table 1, "first calcination temperature" refers to the calcination temperature in step (2), and "first calcination time" refers to the calcination time in step (2).

[0115] Among them, the test conditions or test standards for each performance test item are as follows:

[0116] (1) Element content test in materials

[0117] Inductively coupled plasma (ICP) was used to test the content of each element in the lithium iron phosphate repair material.

[0118] (2) Cyclic performance test

[0119] The lithium iron phosphate repair materials of each embodiment and comparative example were assembled into button cells according to the following method, and the electrochemical performance was tested according to the following method:

[0120] The lithium iron phosphate repair materials of each embodiment and comparative example were mixed with binder PVDF and conductive carbon black at a mass ratio of 90:5:5 to make a slurry, coated and dried to make a positive electrode sheet, and then a metal lithium sheet was used as a negative electrode, celgard2400 was used as a separator, and 1 mol / L LiPF6+EC / DMC was used as an electrolyte to assemble a CR2025 button battery. Finally, a charge and discharge test was carried out on a button battery test cabinet, and a 1C cycle performance test was carried out after 2 cycles of charge and discharge at a rate of 0.1C; wherein, 100 th The cycle maintenance rate refers to the capacity retention rate after 100 cycles under the 1C cycle performance test.

[0121] Table 1

[0122]

[0123] In Table 1, by comparing Examples 1 to 11 with Comparative Example 2, it can be seen that washing the positive electrode sheet disassembled from the lithium-ion battery with an organic solvent to remove the lithium salt can effectively improve the cycle performance of the lithium iron phosphate repair material. By comparing Examples 1 to 4, it can be seen that controlling the calcination temperature within a suitable range can enable the lithium iron phosphate repair material to obtain higher cycle performance.

[0124] By comparing Examples 1 to 11 with Comparative Example 1, it can be seen that after the calcination treatment of step (2) is omitted in Comparative Example 1, under such conditions, since the active material layer is not separated from the current collector, it is difficult to fully mix with the lithium supplement material. At the same time, during the calcination at 650° C. in step (3), the current collector Al will melt and wrap the powder. Under such conditions, the cycle performance of the material obtained is poor. This shows that the present application performs the first calcination treatment on the positive electrode plate after removing the lithium salt, which is beneficial to the improvement of the cycle performance of the lithium iron phosphate repair material.

[0125] By comparing Examples 1, 5 to 7, it can be seen that controlling the sintering time within a suitable range can enable the lithium iron phosphate repair material to obtain higher cycle performance. By comparing Examples 1, 8 to 10, it can be seen that controlling the washing time within a suitable range can enable the lithium iron phosphate repair material to obtain higher cycle performance. By comparing Example 1 with Example 11, it can be seen that adding a lithium-containing protective material before calcining the positive electrode sheet in step (2) is beneficial to improving the cycle performance of the lithium iron phosphate repair material.

[0126] In addition, it can be seen from Figure 1 that the lithium iron phosphate repair material obtained by the repair in this application has a relatively regular morphology.

[0127] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0128] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for repairing and recovering lithium iron phosphate in a lithium-ion battery, characterized in that: include: The positive electrode sheet disassembled from the lithium-ion battery is washed with an organic solvent to remove the lithium salt in the positive electrode sheet; wherein the positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer and a carbon coating layer, the carbon coating layer is arranged between the positive electrode current collector and the positive electrode active material layer, the positive electrode active material layer comprises lithium iron phosphate, and the carbon coating layer comprises conductive carbon and an aqueous binder; The object to be treated, which contains the positive electrode sheet after the lithium salt is removed, is subjected to a first calcination treatment to destroy the carbon coating layer and separate the positive electrode active material layer from the positive electrode current collector; The separated positive electrode active material layer is roughly broken and then mixed with a lithium supplement material, and the mixed material is subjected to a second calcination treatment to obtain a lithium iron phosphate repair material.

2. The repair and recycling method according to claim 1, characterized in that: Meet one or more of the following conditions: (1) The temperature of the first calcination treatment is 350°C to 450°C; (2) The first calcination time is less than or equal to 1 hour, and can be selected from 15 minutes to 60 minutes.

3. The repair and recovery method according to claim 1 or 2, characterized in that: The object to be processed further comprises a lithium-containing protective material; Optionally, the lithium-containing protective material includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium sulfate; Optionally, the mass proportion of the lithium-containing protective material in the positive electrode plate after removing the lithium salt is 0.05%~1%.

4. The repair and recovery method according to claim 1 or 2, characterized in that: Meet one or more of the following conditions: (1) The washing time is less than or equal to 30 minutes, and can be selected from 5 seconds to 30 minutes; (2) The organic solvent includes one or more of methanol, ethanol, acetone and carbonate organic solvents; Optionally, the carbonate organic solvent includes one or more of dimethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and butylene carbonate; (3) The water-based binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, and styrene-butadiene rubber.

5. The repair and recovery method according to claim 1 or 2, characterized in that: Meet one or more of the following conditions: (1) The temperature of the second calcination treatment is 500°C to 800°C, and can be 600°C to 750°C; (2) The second calcination treatment time is 2h~10h; (3) Optionally, the lithium supplement material and the coarsely crushed positive electrode active material are mixed in a mass ratio of (1-20):

100.

6. The repair and recovery method according to claim 1 or 2, characterized in that: The method of roughly breaking the separated positive electrode active material layer and mixing it with the lithium supplement material comprises: The coarsely broken positive electrode active material layer is mixed with the lithium supplement material and then subjected to ball milling treatment; Optionally, the ball milling process is performed at a rotation speed of 300 rpm to 500 rpm; Optionally, the ball milling treatment time is 30 min to 60 min.

7. A lithium iron phosphate repair material, characterized in that: It is prepared by the repair and recovery method described in any one of claims 1 to 7.

8. The lithium iron phosphate repair material according to claim 7, characterized in that: The lithium iron phosphate repair material comprises a base particle containing lithium iron phosphate, and a protective layer covering at least a portion of the surface of the base particle, wherein the protective layer contains lithium fluoride; Optionally, in the lithium iron phosphate repair material, the molar ratio of lithium element to metal element is 1.01-1.

10.

9. A positive electrode sheet, characterized in that: Contains the lithium iron phosphate repair material as described in claim 7 or 8.

10. A lithium ion battery, characterized in that: Including the positive electrode sheet as described in claim 9.

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