A regenerated lithium iron phosphate positive electrode material, preparation method and application

Abstract

The present invention discloses a regenerated lithium iron phosphate cathode material, a preparation method, and an application thereof. The preparation method comprises: crushing the lithium iron phosphate cathode sheets to be regenerated, wherein the particle size of the crushed lithium iron phosphate cathode sheets is no greater than 50 mm; drying the crushed lithium iron phosphate cathode sheets, adding a cracking auxiliary material to the dried lithium iron phosphate cathode sheets, placing the dried lithium iron phosphate cathode sheets in a cracking furnace for anaerobic cracking, separating the aluminum sheets and lithium iron phosphate powder in the mixture, collecting the lithium iron phosphate powder and removing impurities from the mixture to obtain a lithium iron phosphate composite material, i.e., the regenerated lithium iron phosphate cathode material. The present invention adopts anaerobic cracking technology, retains the carbon coating layer, and has a simple and efficient process, low energy consumption, low operating cost, and better environmental performance. The performance indicators of the regenerated lithium iron phosphate cathode material are comparable to those of commercial lithium iron phosphate cathode materials, with a first discharge specific capacity of up to 154 mAh / g and a first discharge efficiency of up to 93%.

Description

Technical Field

[0001] The present invention relates to the field of lithium iron phosphate positive electrode materials, and in particular to a regenerated lithium iron phosphate positive electrode material, a preparation method and applications thereof. Background Art

[0002] With rising lithium battery raw material costs and continuous advancements in battery structure optimization technology, lithium iron phosphate batteries are gaining favor in the automotive and energy storage markets due to their lower cost, superior thermal stability, and superior structural stability compared to the high-cost, low-safety ternary lithium batteries. In the future, both production and consumer markets will see an increasing amount of waste lithium iron phosphate batteries and defective products from the production process. For resource utilization purposes, efficient recycling of lithium iron phosphate battery materials is a key trend.

[0003] There have been a lot of reports on the recycling and reuse of lithium iron phosphate batteries. The processes can be roughly divided into wet processes and dry processes.

[0004] The wet process mainly recycles or purifies high-value elements or raw materials of lithium iron phosphate batteries, such as lithium and iron phosphate. However, the process inevitably involves the generation of waste liquid and the use of expensive reagents, which causes environmental problems and increases the material costs of enterprises. At the same time, due to the low content of high-priced metal elements in lithium iron phosphate, the high processing cost brings greater survival pressure to enterprises. The dry process route is mainly divided into: battery discharge, fine disassembly, crushing, sintering and impurity removal, composition regulation and particle size control, inert atmosphere sintering and repair, etc. For example, the patent with publication number CN112658000A provides a method for recycling and regenerating scraps of lithium iron phosphate battery positive electrode sheets. The patent uses a process of coarse crushing of the positive electrode sheets, followed by inert atmosphere calcination, fine crushing, primary impurity removal, secondary sintering, air flow milling, secondary impurity removal, etc. to finally obtain lithium iron phosphate products. However, the process is complicated, and multiple high-temperature sinterings result in huge energy consumption and increased costs. In addition, multiple crushings lead to increased impurities and higher impurity removal costs, which reduces the commercial value of lithium iron phosphate repair and reuse. Patent publication number CN113036253A provides a method for selective oxidation-reduction regeneration of lithium iron phosphate. This method uses a mixture of water vapor and carbon dioxide to control the oxidizing atmosphere to sinter the lithium iron phosphate electrode once, then separate it, and finally control its composition under a high-temperature inert atmosphere to obtain a lithium iron phosphate product. This patent simplifies the process, but during the single oxidizing atmosphere sintering process, not only does it destroy the carbon coating on the surface of the lithium iron phosphate, but it also partially oxidizes the divalent iron in the lithium iron phosphate into trivalent iron, which is difficult to reduce during the subsequent sintering process, increasing the difficulty of composition control.

[0005] Based on the above problems, it is necessary to design a solution that simplifies the process, retains the carbon coating of lithium iron phosphate to the greatest extent, and realizes the regeneration of lithium iron phosphate. Summary of the Invention

[0006] The purpose of the present invention is to provide a regenerated lithium iron phosphate cathode material, preparation method, and application scheme that simplifies the process, can maximize the preservation of the lithium iron phosphate carbon coating, and achieve lithium iron phosphate regeneration. The specific scheme is as follows:

[0007] In one aspect, the present invention provides a method for preparing a regenerated lithium iron phosphate positive electrode material, comprising the following steps:

[0008] S1: crushing the lithium iron phosphate positive electrode sheets to be regenerated, wherein the particle size of the crushed lithium iron phosphate positive electrode sheets is not greater than 50 mm, and the lithium iron phosphate positive electrode sheets to be regenerated are lithium iron phosphate positive electrode sheet scraps and / or defective lithium iron phosphate battery positive electrode sheets from a battery factory;

[0009] S2: drying the crushed lithium iron phosphate positive electrode sheet, wherein the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 1%;

[0010] S3: adding a cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet, and then placing the dried lithium iron phosphate positive electrode sheet with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the anaerobic cracking atmosphere is ≤0.2%, and the cracking is carried out at a cracking temperature of 400-600°C for 0.5-2 hours, and the residence time of the cracking gas in the cracking furnace is controlled to be less than 10 seconds, to obtain a mixture including aluminum sheet, cracking auxiliary material and lithium iron phosphate powder;

[0011] S4: separating the aluminum flakes, cracking auxiliary materials, and lithium iron phosphate powder in the mixture, collecting the lithium iron phosphate powder, and removing impurities from the lithium iron phosphate powder to obtain a lithium iron phosphate composite material;

[0012] S5: Break up the lithium iron phosphate composite material to D99≤15um to obtain the final regenerated lithium iron phosphate positive electrode material.

[0013] As a preferred embodiment of the method for preparing the regenerated lithium iron phosphate positive electrode material described in this patent, in step S3, the cracking auxiliary material includes one or more of calcium oxide, potassium oxide and sodium oxide;

[0014] In step S1, the particle size of the crushed lithium iron phosphate positive electrode sheet is no more than 30 mm.

[0015] As a preferred solution of the method for preparing the regenerated lithium iron phosphate positive electrode material described in this patent, the particle size of the cracking auxiliary material is greater than 100 mesh and the Mohs hardness is greater than 6.0.

[0016] As a preferred embodiment of the method for preparing the regenerated lithium iron phosphate positive electrode material described in this patent, in step S2, the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1:(25-50).

[0017] As a preferred embodiment of the method for preparing the regenerated lithium iron phosphate positive electrode material described in this patent, in step S3, the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 0.5%;

[0018] The residence time of the gas produced by cracking in the cracking furnace is controlled to be less than 3s.

[0019] As a preferred embodiment of the method for preparing the regenerated lithium iron phosphate positive electrode material described in this patent, in step S3, the cracking furnace includes a roller kiln, a rotary kiln and a tubular furnace.

[0020] As a preferred embodiment of the method for preparing the regenerated lithium iron phosphate positive electrode material described in this patent, in step S4, the lithium iron phosphate powder is removed mainly to remove aluminum, copper and iron.

[0021] As a preferred embodiment of the method for preparing the regenerated lithium iron phosphate positive electrode material described in this patent, the impurity removal methods for the lithium iron phosphate powder include color separation, magnetic separation, gravity separation and flotation.

[0022] On the other hand, the present invention also provides a regenerated lithium iron phosphate positive electrode material, which is a regenerated lithium iron phosphate positive electrode material prepared according to the above-mentioned preparation method of the regenerated lithium iron phosphate positive electrode material. The regenerated lithium iron phosphate positive electrode material includes carbon-coated lithium iron phosphate and conductive agent carbon. The carbon-coated lithium iron phosphate is a lithium iron phosphate with a carbon coating layer coated on the surface.

[0023] In another aspect, the present invention further provides an application of a regenerated lithium iron phosphate cathode material in the preparation of a lithium iron phosphate battery, wherein the regenerated lithium iron phosphate cathode material prepared above is used alone for the preparation of a lithium iron phosphate battery; or

[0024] The regenerated lithium iron phosphate positive electrode material prepared above is composited with commercial lithium iron phosphate positive electrode material or repaired and regenerated lithium iron phosphate positive electrode material for the preparation of lithium iron phosphate batteries. The repaired and regenerated lithium iron phosphate positive electrode material is a lithium iron phosphate positive electrode material that can be reused in the preparation of lithium iron phosphate batteries after the lithium iron phosphate positive electrode sheet scraps and / or waste lithium iron phosphate positive electrode material are repaired and regenerated by any chemical or physical method. Commercial lithium iron phosphate positive electrode material refers to lithium iron phosphate positive electrode material purchased from the market.

[0025] Compared with the prior art, the present invention has at least one or more of the following beneficial effects:

[0026] 1. This method prevents water, oxygen, and cracking gas (such as fluorine-containing substances) from reacting with lithium iron phosphate and / or carbon in the lithium iron phosphate positive electrode sheet by simultaneously controlling the moisture content, oxygen content, and the residence time of the cracking gas in the cracking furnace. The three control conditions of moisture content, oxygen content, and the residence time of the cracking gas in the cracking furnace cooperate with each other, work synergistically, and are indispensable. The adopted anaerobic cracking technology can well retain the carbon coating on the surface of the lithium iron phosphate particles. In addition, although traditional sintering or roasting can remove PVDF (polyvinylidene fluoride), it will also cause the iron in the lithium iron phosphate positive electrode sheet to oxidize; traditional sintering or roasting will remove the conductive agent carbon and PVDF residual carbon while also removing the carbon coating on the surface of the lithium iron phosphate, increasing the difficulty of subsequent process repair; the present invention effectively retains the conductive agent carbon and the carbon coating through one-step anaerobic cracking, reducing the subsequent addition of carbon sources, and the resulting regenerated lithium iron phosphate positive electrode material does not need to be carbon-coated or supplemented with a conductive agent again, and can be directly used for battery manufacturing, which saves costs and simplifies the process flow;

[0027] 2. Introduce cracking auxiliary materials to completely crack PVDF into carbon rather than fluorinated biphenyls. After PVDF is thermally decomposed, hydrogen fluoride, vinylidene fluoride monomer, and fluorinated substituted benzenes (biphenyls) will be produced; among these substances, hydrogen fluoride, vinylidene fluoride monomer, and fluorinated substituted benzenes will be removed in the form of gas, but the fluorinated substances in the cracking residue are not easy to remove completely and will adhere to the lithium iron phosphate powder, thereby affecting the initial charge and discharge capacity, causing particle adhesion and affecting the purity of the electrolyte; in general, the cracking process needs to ensure that PVDF is completely decomposed, and the remaining carbon is used as a supplementary carbon coating layer for the lithium iron phosphate material to achieve direct regeneration of the lithium iron phosphate material. To achieve this goal, it is necessary to introduce cracking auxiliary materials to ensure that under the process conditions, PVDF is completely cracked into carbon rather than fluorinated biphenyls.

[0028] 3. One-step pyrolysis achieves the regeneration effect of the lithium iron phosphate positive electrode sheet, which can not only remove the residual electrolyte on the surface of the lithium iron phosphate positive electrode sheet, but also remove PVDF to make its adhesion ineffective. The lithium iron phosphate powder is separated from the surface of the aluminum sheet, saving more than double the energy compared to the traditional two-step sintering;

[0029] 4. The present invention expands the size of the lithium iron phosphate positive electrode sheet entering the cracking furnace to 50mm through pre-treatment crushing, which can effectively reduce the introduction of aluminum impurities during the pre-treatment process and reduce the aluminum impurity content to below 500ppm after cracking;

[0030] 5. The regenerated lithium iron phosphate cathode material obtained by the present invention effectively reduces the addition of conductive agents at the battery manufacturing end. At the same time, the performance indicators of the regenerated lithium iron phosphate cathode material are comparable to those of commercial lithium iron phosphate cathode materials. The first discharge specific capacity can reach up to 154mAh / g, and the first discharge efficiency can reach up to 93%;

[0031] 6. This application not only has a simple and efficient process, but also has low energy consumption. The operating cost is lower than the traditional lithium iron phosphate regeneration method and it is more environmentally friendly.

[0032] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is a process flow chart of the method for preparing regenerated lithium iron phosphate positive electrode material described in this patent;

[0035] Figure 2 This is a TEM test image of the regenerated lithium iron phosphate positive electrode material of Example 1 of this patent;

[0036] Figure 3 This is the first charge and discharge curve of the regenerated lithium iron phosphate positive electrode material of Example 1 of this patent.

[0037] Among them, 1-carbon coating layer. DETAILED DESCRIPTION

[0038] The following describes the embodiments of the present invention in detail, clearly and completely describing the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0039] The term "anaerobic" in this application means that the oxygen content is infinitely close to 0 (<0.5%).

[0040] To address the shortcomings and deficiencies of the prior art, the present invention provides a regenerated lithium iron phosphate cathode material, preparation method, and application. The regenerated lithium iron phosphate cathode material produced using this method does not require further carbon coating or conductive agent supplementation and can be directly used in battery manufacturing.

[0041] To achieve the above object, the present invention adopts the following technical solutions:

[0042] First, the regenerated lithium iron phosphate cathode sheets are pyrolyzed in an oxygen-free atmosphere after adding pyrolysis auxiliary materials to remove residual electrolyte and impurities such as PVDF on the surface, making the lithium iron phosphate cathode sheets loose and easier to separate. Then, through sorting and other processes, impurities such as aluminum, copper, and iron in the lithium iron phosphate are removed, and the introduction of other impurities is controlled to maximize the purity of the lithium iron phosphate in the lithium iron phosphate powder. This process is characterized by high efficiency, low cost, and good environmental performance, and can effectively recycle the regenerated lithium iron phosphate cathode sheets.

[0043] This solution is mainly aimed at recycling the leftover lithium iron phosphate cathode sheets and defective lithium iron phosphate battery cathode sheets from battery factories and obtaining recycled lithium iron phosphate cathode materials, such as Figure 1 The preparation method flow chart shown in FIG. 1 , wherein the technical solution comprises the following steps:

[0044] S1: crushing the lithium iron phosphate positive electrode sheets to be regenerated, wherein the particle size of the crushed lithium iron phosphate positive electrode sheets is not greater than 50 mm, and the lithium iron phosphate positive electrode sheets to be regenerated are lithium iron phosphate positive electrode sheet scraps and / or defective lithium iron phosphate battery positive electrode sheets from a battery factory;

[0045] S2: drying the crushed lithium iron phosphate positive electrode sheet, wherein the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 1%; preferably, the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 0.5%, wherein the moisture content of the dried lithium iron phosphate positive electrode sheet is measured by an online testing instrument;

[0046] S3: adding a cracking auxiliary material having a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to the dried lithium iron phosphate positive electrode sheet, and then placing the dried lithium iron phosphate positive electrode sheet with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the anaerobic cracking atmosphere is ≤0.2%, and the cracking is carried out at a cracking temperature of 400-600°C for 0.5-2h, and the residence time of the gas generated by the cracking (i.e., the cracking gas) in the cracking furnace is controlled to be less than 10s, to obtain a mixture including aluminum sheets, cracking auxiliary materials and lithium iron phosphate powder; the residence time of the cracking gas is controlled by controlling the gas flow rate of the cracking furnace; preferably, the residence time of the gas generated by the cracking in the cracking furnace is controlled to be less than 3s, and the cracking furnace includes but is not limited to a roller kiln, a rotary kiln and a tubular furnace; the cracking auxiliary material includes one or more of calcium oxide, potassium oxide and sodium oxide, and preferably the cracking auxiliary material has a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to facilitate separation after thermal decomposition; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1:(25-50). The addition of a cracking auxiliary material completely cracks the PVDF in the regenerated lithium iron phosphate cathode into solid carbon and gaseous fluoride, preventing the residual fluoride from affecting the subsequent application of the lithium iron phosphate cathode. At the same time, the solid carbon formed by the cracking carbon serves as a supplement to the carbon coating of the lithium iron phosphate cathode. After adding the cracking auxiliary material, the residual fluorine content in the lithium iron phosphate powder after anaerobic cracking was detected to be less than 100ppm. If the cracking auxiliary material is not added, the residual fluorine content in the lithium iron phosphate powder will usually reach 1000ppm.

[0047] S4: separating the aluminum flakes, cracking auxiliary materials, and lithium iron phosphate powder in the mixture, collecting the lithium iron phosphate powder, and removing impurities from the lithium iron phosphate powder to obtain a lithium iron phosphate composite material; the lithium iron phosphate powder is removed mainly to remove impurities such as aluminum, copper, and iron, and the impurity removal methods include but are not limited to color separation, magnetic separation, gravity separation, and flotation; the lithium iron phosphate composite material includes carbon-coated lithium iron phosphate and conductive agent carbon, wherein the carbon-coated lithium iron phosphate is lithium iron phosphate with a carbon coating layer coated on the surface;

[0048] S5: The lithium iron phosphate composite obtained in step S4 is ground to a particle size of ≤15 μm to obtain a regenerated lithium iron phosphate positive electrode material. D99 ≤15 μm indicates that at least 99% by weight of the lithium iron phosphate composite has a particle size of ≤15 μm. In this example, the lithium iron phosphate composite is ground to an industry standard particle size of ≤15 μm.

[0049] The obtained regenerated lithium iron phosphate cathode material is mainly used in the preparation of lithium iron phosphate batteries, and the regenerated lithium iron phosphate cathode material is used alone in the preparation of lithium iron phosphate batteries: or

[0050] The regenerated lithium iron phosphate positive electrode material is composited with commercial lithium iron phosphate positive electrode material or repaired and regenerated lithium iron phosphate positive electrode material for the preparation of lithium iron phosphate batteries. The repaired and regenerated lithium iron phosphate positive electrode material is a lithium iron phosphate positive electrode material that can be reused in the preparation of lithium iron phosphate batteries after the lithium iron phosphate positive electrode sheet scraps and / or waste lithium iron phosphate positive electrode material are repaired and regenerated by any chemical or physical method. Commercial lithium iron phosphate positive electrode material refers to lithium iron phosphate positive electrode material purchased from the market.

[0051] On the other hand, the present invention also provides a regenerated lithium iron phosphate positive electrode material, which is prepared according to the above-mentioned preparation method of the regenerated lithium iron phosphate positive electrode material, and the regenerated lithium iron phosphate positive electrode material includes carbon-coated lithium iron phosphate and conductive agent carbon.

[0052] Example 1

[0053] This embodiment provides a method for preparing a regenerated lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0054] 1. Using the leftover lithium iron phosphate cathode sheet as raw material, crush the leftover lithium iron phosphate cathode sheet into particles no larger than 50 mm. The larger the size of the leftover lithium iron phosphate cathode sheet, the less likely it is to be introduced into the crushing process, such as aluminum powder.

[0055] 2. Drying the crushed lithium iron phosphate positive electrode sheet to ensure that the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 0.5%; wherein the moisture content of the dried lithium iron phosphate positive electrode sheet is obtained by detecting it using an online testing instrument;

[0056] 3. Adding a cracking auxiliary material having a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to the dried lithium iron phosphate positive electrode sheet, then placing the dried lithium iron phosphate positive electrode sheet with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, and the cracking is carried out at a cracking temperature of 500° C. for 1 hour, and the residence time of the gas generated by the cracking (i.e., the cracking gas) in the cracking furnace is controlled to be less than 3 seconds, to obtain a mixture, wherein the mixture includes lithium iron phosphate powder, the cracking auxiliary material and aluminum sheet; the residence time of the cracking gas is controlled by controlling the gas flow rate of the cracking furnace, and the furnace body type of the cracking furnace includes but is not limited to a roller kiln, a rotary kiln and a tubular furnace; the cracking auxiliary material includes one or more of calcium oxide, potassium oxide and sodium oxide, and preferably the cracking auxiliary material has a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to facilitate separation after thermal decomposition; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1:(25-50). The addition of a cracking auxiliary material completely cracks the PVDF in the regenerated lithium iron phosphate cathode into solid carbon and gaseous fluoride, preventing the residual fluoride from affecting the subsequent application of the lithium iron phosphate cathode. At the same time, the solid carbon formed by the cracking carbon can be used as a supplement to the carbon coating of the lithium iron phosphate cathode. After adding the cracking auxiliary material, the residual fluorine content in the lithium iron phosphate powder after anaerobic cracking was detected to be less than 100ppm.

[0057] 4. Vibration screening is performed on the mixture to separate lithium iron phosphate powder, aluminum flakes and cracking auxiliary materials. Vibration screening balls are added to the vibration screening device. The material of the vibration screening balls is rubber. The vibration screening time is 10 minutes and the mesh size of the screen is 20-325 mesh.

[0058] 5. After the separation is completed, the collected lithium iron phosphate powder is subjected to impurity removal to obtain a lithium iron phosphate composite. The lithium iron phosphate powder is mainly removed from impurities such as aluminum, copper and iron. The impurity removal methods include but are not limited to color sorting, magnetic separation, gravity separation and flotation. The lithium iron phosphate composite includes carbon-coated lithium iron phosphate and conductive carbon. The carbon-coated lithium iron phosphate is lithium iron phosphate with a carbon coating layer 1 coated on the surface;

[0059] 6. Break up the lithium iron phosphate composite obtained in step 5 to a particle size of D99≤15um to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99≤15um means that at least 99% by weight of the lithium iron phosphate composite has a particle size of less than or equal to 15 microns. In this example, the lithium iron phosphate composite is broken up to the industry standard by grinding, i.e., a particle size of less than or equal to 15 microns. Figure 2 As shown, the advantage of the regenerated lithium iron phosphate positive electrode material is that there is no need to re-carbon-coat the regenerated lithium iron phosphate positive electrode material, while retaining the conductive agent carbon, the regenerated lithium iron phosphate positive electrode material can be directly prepared into slurry for lithium iron phosphate battery manufacturing.

[0060] The performance of the obtained regenerated lithium iron phosphate cathode material is tested. First, the regenerated lithium iron phosphate cathode material needs to be prepared into a button battery. The steps are as follows:

[0061] 1. Prepare the regenerated lithium iron phosphate cathode material and polyvinylidene fluoride (PVDF) obtained by the above method in a mass ratio of 90:10. First, dissolve PVDF in an appropriate amount of N-methylpyrrolidone (NMP) and stir magnetically for 1 hour until the solution becomes transparent. Then add the regenerated lithium iron phosphate cathode material to the above solution and stir for 8 hours for use. During the mixing process, remove the material adhering to the wall and mix it into the slurry;

[0062] 2. Then apply the mixed slurry on a smooth aluminum sheet, and then bake the coated aluminum sheet in a vacuum drying oven at 80°C for 12 hours. Cut the baked aluminum sheet into discs with a diameter of 14 mm and press them under a pressure of 2 MPa to serve as the positive electrode of the button battery.

[0063] 3. Button cells were assembled in a glove box filled with dry argon, using a metallic lithium sheet as the negative electrode, Celgard 2400 as the separator, and a 1.0 mol / L electrolyte consisting of LiPF6 / EC+DMC+EMC. The volume ratio of LiPF6 / EC, DMC, and EMC was 1:1:1. The cells were assembled into a button cell and allowed to stand for 12 hours before testing. LiPF6 represents lithium hexafluorophosphate, EC represents ethylene carbonate, DMC represents dimethyl carbonate, and EMC represents ethyl methyl carbonate.

[0064] The prepared button battery was subjected to relevant charge and discharge tests:

[0065] The button battery is charged to 3.75V at a constant current of 0.2C, and then discharged to 2.7V at a constant current of 0.2C. After cyclic charge and discharge, calculate the gram capacity of the active material in the positive electrode of the button battery.

[0066] The regenerated lithium iron phosphate cathode material obtained in this embodiment was tested by transmission electron microscopy (TEM), and the results were as follows: Figure 2 As shown, from Figure 2 It can be seen that the regenerated lithium iron phosphate positive electrode material particles obtained in this embodiment have a carbon coating layer on the surface, indicating that the method provided in this embodiment can retain the carbon coating layer on the surface of the lithium iron phosphate to the greatest extent.

[0067] Figure 3 The first charge and discharge curve of the regenerated lithium iron phosphate positive electrode material of this embodiment is shown in FIG. Figure 3 It can be obtained that the first discharge specific capacity of the regenerated lithium iron phosphate positive electrode material can reach 154 mAh / g, and the first discharge efficiency can reach 93%.

[0068] Example 2

[0069] This embodiment provides a method for preparing a regenerated lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0070] 1. Using the leftover lithium iron phosphate cathode sheet as raw material, crush the leftover lithium iron phosphate cathode sheet into particles no larger than 50 mm. The larger the size of the leftover lithium iron phosphate cathode sheet, the less likely it is to be introduced into the crushing process, such as aluminum powder.

[0071] 2. Drying the crushed lithium iron phosphate positive electrode sheet to ensure that the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 0.5%; wherein the moisture content of the dried lithium iron phosphate positive electrode sheet is obtained by detecting it using an online testing instrument;

[0072] 3. Adding a cracking auxiliary material having a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to the dried lithium iron phosphate positive electrode sheet, and then placing the dried lithium iron phosphate positive electrode sheet with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, and the cracking is carried out at a cracking temperature of 400°C for 2 hours, and the residence time of the gas generated by the cracking (i.e., the cracking gas) in the cracking furnace is controlled to be less than 3 seconds, to obtain a mixture, wherein the mixture includes lithium iron phosphate powder, the cracking auxiliary material and aluminum sheet; the residence time of the cracking gas is controlled by controlling the gas flow rate of the cracking furnace, and the furnace type of the cracking furnace includes but is not limited to a roller kiln, a rotary kiln and a tubular furnace; the cracking auxiliary material includes one or more of calcium oxide, potassium oxide and sodium oxide, and preferably the cracking auxiliary material has a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to facilitate separation after thermal decomposition; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1:(25-50). The addition of a cracking auxiliary material completely cracks the PVDF in the regenerated lithium iron phosphate cathode into solid carbon and gaseous fluoride, preventing the residual fluoride from affecting the subsequent application of the lithium iron phosphate cathode. At the same time, the solid carbon formed by the cracking carbon can be used as a supplement to the carbon coating of the lithium iron phosphate cathode. After adding the cracking auxiliary material, the residual fluorine content in the lithium iron phosphate powder after anaerobic cracking was detected to be less than 100ppm.

[0073] 4. Vibration screening is performed on the mixture to separate lithium iron phosphate powder, aluminum flakes and cracking auxiliary materials. Vibration screening balls are added to the vibration screening device. The material of the vibration screening balls is rubber. The vibration screening time is 10 minutes and the mesh size of the screen is 20-325 mesh.

[0074] 5. After the separation is completed, the collected lithium iron phosphate powder is subjected to impurity removal to obtain a lithium iron phosphate composite material. The lithium iron phosphate powder is removed mainly to remove impurities such as aluminum, copper and iron. The impurity removal methods include but are not limited to color separation, magnetic separation, gravity separation and flotation. The lithium iron phosphate composite material includes carbon-coated lithium iron phosphate and conductive carbon;

[0075] 6. The lithium iron phosphate composite obtained in step 5 is broken down to a particle size of D99 ≤ 15 μm to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99 ≤ 15 μm means that at least 99% by weight of the lithium iron phosphate composite has a particle size of 15 μm or less. In this example, the lithium iron phosphate composite is broken down by grinding to an industry standard particle size of 15 μm or less.

[0076] The obtained regenerated lithium iron phosphate positive electrode material was prepared into a button battery according to the method for preparing a button battery in Example 1, and the prepared button battery was subjected to relevant charge and discharge tests:

[0077] The button battery was charged to 3.75V at a constant current of 0.2C, and then discharged to 2.7V at a constant current of 0.2C. The charge and discharge cycle was repeated to calculate the gram capacity of the active material in the positive electrode of the button battery. The test showed that the first discharge specific capacity of the regenerated lithium iron phosphate positive electrode material can reach 142mAh / g, and the first discharge efficiency can reach 88%.

[0078] Example 3

[0079] This embodiment provides a method for preparing a regenerated lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0080] 1. Using the leftover lithium iron phosphate cathode sheet as raw material, crush the leftover lithium iron phosphate cathode sheet into pieces no larger than 50 mm. The larger the size of the leftover lithium iron phosphate cathode sheet, the better to reduce the introduction of impurities such as aluminum powder during the crushing process.

[0081] 2. Drying the crushed lithium iron phosphate positive electrode sheet to ensure that the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 0.5%; wherein the moisture content of the dried lithium iron phosphate positive electrode sheet is obtained by detecting it using an online testing instrument;

[0082] 3. Adding a cracking auxiliary material having a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to the dried lithium iron phosphate positive electrode sheet, and then placing the dried lithium iron phosphate positive electrode sheet with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, and the cracking is carried out at a cracking temperature of 600°C for 0.5 hour, and the residence time of the gas generated by the cracking (i.e., the cracking gas) in the cracking furnace is controlled to be less than 10 seconds to obtain a mixture, wherein the mixture includes lithium iron phosphate powder, the cracking auxiliary material and aluminum sheet; the residence time of the cracking gas is controlled by controlling the gas flow rate of the cracking furnace, and the furnace type of the cracking furnace includes but is not limited to a roller kiln, a rotary kiln and a tubular furnace; the cracking auxiliary material includes one or more of calcium oxide, potassium oxide and sodium oxide, and preferably the cracking auxiliary material has a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to facilitate separation after thermal decomposition; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1:(25-50). The addition of a cracking auxiliary material completely cracks the PVDF in the regenerated lithium iron phosphate cathode into solid carbon and gaseous fluoride, preventing the residual fluoride from affecting the subsequent application of the lithium iron phosphate cathode. At the same time, the solid carbon formed by the cracking carbon can be used as a supplement to the carbon coating of the lithium iron phosphate cathode. After adding the cracking auxiliary material, the residual fluorine content in the lithium iron phosphate powder after anaerobic cracking was detected to be less than 100ppm.

[0083] 4. Vibration screening is performed on the mixture to separate lithium iron phosphate powder, aluminum flakes and cracking auxiliary materials. Vibration screening balls are added to the vibration screening device. The material of the vibration screening balls is rubber. The vibration screening time is 10 minutes and the mesh size of the screen is 20-325 mesh.

[0084] 5. After the separation is completed, the collected lithium iron phosphate powder is subjected to impurity removal to obtain a lithium iron phosphate composite material. The lithium iron phosphate powder is removed mainly to remove impurities such as aluminum, copper and iron. The impurity removal methods include but are not limited to color separation, magnetic separation, gravity separation and flotation. The lithium iron phosphate composite material includes carbon-coated lithium iron phosphate and conductive carbon;

[0085] 6. The lithium iron phosphate composite obtained in step 5 is broken down to a particle size of D99 ≤ 15 μm to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99 ≤ 15 μm means that at least 99% by weight of the lithium iron phosphate composite has a particle size of 15 μm or less. In this example, the lithium iron phosphate composite is broken down by grinding to an industry standard particle size of 15 μm or less.

[0086] The obtained regenerated lithium iron phosphate positive electrode material was prepared into a button battery according to the method for preparing a button battery in Example 1, and the prepared button battery was subjected to relevant charge and discharge tests:

[0087] The button battery was charged to 3.75V at a constant current of 0.2C, and then discharged to 2.7V at a constant current of 0.2C. The charge and discharge cycle was repeated to calculate the gram capacity of the active material in the positive electrode of the button battery. The test showed that the first discharge specific capacity of the regenerated lithium iron phosphate positive electrode material can reach 147mAh / g, and the first discharge efficiency can reach 91%.

[0088] Example 4

[0089] This embodiment provides a method for preparing a regenerated lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0090] 1. Using the leftover lithium iron phosphate cathode sheet as raw material, crush the leftover lithium iron phosphate cathode sheet into particles no larger than 30 mm;

[0091] 2. Drying the crushed lithium iron phosphate positive electrode sheet to ensure that the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 1%; wherein the moisture content of the dried lithium iron phosphate positive electrode sheet is obtained by detecting it using an online testing instrument;

[0092] 3. Adding a cracking auxiliary material having a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to the dried lithium iron phosphate positive electrode sheet, and then placing the dried lithium iron phosphate positive electrode sheet with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, and the cracking is carried out at a cracking temperature of 600°C for 1 hour, and the residence time of the gas generated by the cracking (i.e., the cracking gas) in the cracking furnace is controlled to be less than 3 seconds, to obtain a mixture, wherein the mixture includes lithium iron phosphate powder, the cracking auxiliary material and aluminum sheet; the residence time of the cracking gas is controlled by controlling the gas flow rate of the cracking furnace, and the furnace body type of the cracking furnace includes but is not limited to a roller kiln, a rotary kiln and a tubular furnace; the cracking auxiliary material includes one or more of calcium oxide, potassium oxide and sodium oxide, and preferably the cracking auxiliary material has a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to facilitate separation after thermal decomposition; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1:(25-50). The addition of a cracking auxiliary material completely cracks the PVDF in the regenerated lithium iron phosphate cathode into solid carbon and gaseous fluoride, preventing the residual fluoride from affecting the subsequent application of the lithium iron phosphate cathode. At the same time, the solid carbon formed by the cracking carbon can be used as a supplement to the carbon coating of the lithium iron phosphate cathode. After adding the cracking auxiliary material, the residual fluorine content in the lithium iron phosphate powder after anaerobic cracking was detected to be less than 100ppm.

[0093] 4. Vibration screening is performed on the mixture to separate lithium iron phosphate powder, aluminum flakes and cracking auxiliary materials. Vibration screening balls are added to the vibration screening device. The material of the vibration screening balls is rubber. The vibration screening time is 10 minutes and the mesh size of the screen is 20-325 mesh.

[0094] 5. After the separation is completed, the collected lithium iron phosphate powder is subjected to impurity removal to obtain a lithium iron phosphate composite material. The lithium iron phosphate powder is removed mainly to remove impurities such as aluminum, copper and iron. The impurity removal methods include but are not limited to color separation, magnetic separation, gravity separation and flotation. The lithium iron phosphate composite material includes carbon-coated lithium iron phosphate and conductive carbon;

[0095] 6. The lithium iron phosphate composite obtained in step 5 is broken down to a particle size of D99 ≤ 15 μm to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99 ≤ 15 μm means that at least 99% by weight of the lithium iron phosphate composite has a particle size of 15 μm or less. In this example, the lithium iron phosphate composite is broken down by grinding to an industry standard particle size of 15 μm or less.

[0096] The obtained regenerated lithium iron phosphate positive electrode material was prepared into a button battery according to the method for preparing a button battery in Example 1, and the prepared button battery was subjected to relevant charge and discharge tests:

[0097] The button battery was charged to 3.75V at a constant current of 0.2C, and then discharged to 2.7V at a constant current of 0.2C. The charge and discharge cycle was repeated to calculate the gram capacity of the active material in the positive electrode of the button battery. The test showed that the first discharge specific capacity of the regenerated lithium iron phosphate positive electrode material can reach 146mAh / g, and the first discharge efficiency can reach 92%.

[0098] Example 5

[0099] This embodiment provides a method for preparing a regenerated lithium iron phosphate positive electrode material, which specifically includes the following steps:

[0100] 1. Using the leftover lithium iron phosphate cathode sheet as raw material, crush the leftover lithium iron phosphate cathode sheet into particles no larger than 30 mm;

[0101] 2. Drying the crushed lithium iron phosphate positive electrode sheet to ensure that the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 1%; wherein the moisture content of the dried lithium iron phosphate positive electrode sheet is obtained by detecting it using an online testing instrument;

[0102] 3. Adding a cracking auxiliary material having a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to the dried lithium iron phosphate positive electrode sheet, and then placing the dried lithium iron phosphate positive electrode sheet with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, and the cracking is carried out at a cracking temperature of 400°C for 1 hour, and the residence time of the gas generated by the cracking (i.e., the cracking gas) in the cracking furnace is controlled to be less than 10 seconds to obtain a mixture, wherein the mixture includes lithium iron phosphate powder, the cracking auxiliary material and aluminum sheet; the residence time of the cracking gas is controlled by controlling the gas flow rate of the cracking furnace, and the furnace body type of the cracking furnace includes but is not limited to a roller kiln, a rotary kiln and a tubular furnace; the cracking auxiliary material includes one or more of calcium oxide, potassium oxide and sodium oxide, and preferably the cracking auxiliary material has a particle size greater than 100 mesh and a Mohs hardness greater than 6.0 to facilitate separation after thermal decomposition; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1:(25-50). The addition of a cracking auxiliary material completely cracks the PVDF in the regenerated lithium iron phosphate cathode into solid carbon and gaseous fluoride, preventing the residual fluoride from affecting the subsequent application of the lithium iron phosphate cathode. At the same time, the solid carbon formed by the cracking carbon can be used as a supplement to the carbon coating of the lithium iron phosphate cathode. After adding the cracking auxiliary material, the residual fluorine content in the lithium iron phosphate powder after anaerobic cracking was detected to be less than 100ppm.

[0103] 4. Vibration screening is performed on the mixture to separate lithium iron phosphate powder, aluminum flakes and cracking auxiliary materials. Vibration screening balls are added to the vibration screening device. The material of the vibration screening balls is rubber. The vibration screening time is 10 minutes and the mesh size of the screen is 20-325 mesh.

[0104] 5. After the separation is completed, the collected lithium iron phosphate powder is subjected to impurity removal to obtain a lithium iron phosphate composite material. The lithium iron phosphate powder is removed mainly to remove impurities such as aluminum, copper and iron. The impurity removal methods include but are not limited to color separation, magnetic separation, gravity separation and flotation. The lithium iron phosphate composite material includes carbon-coated lithium iron phosphate and conductive carbon;

[0105] 6. The lithium iron phosphate composite obtained in step 5 is broken down to a particle size of D99 ≤ 15 μm to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99 ≤ 15 μm means that at least 99% by weight of the lithium iron phosphate composite has a particle size of 15 μm or less. In this example, the lithium iron phosphate composite is broken down by grinding to an industry standard particle size of 15 μm or less.

[0106] The obtained regenerated lithium iron phosphate positive electrode material was prepared into a button battery according to the method for preparing a button battery in Example 1, and the prepared button battery was subjected to relevant charge and discharge tests:

[0107] The button battery was charged to 3.75V at a constant current of 0.2C, and then discharged to 2.7V at a constant current of 0.2C. The charge and discharge cycle was repeated to calculate the gram capacity of the active material in the positive electrode of the button battery. The test showed that the first discharge specific capacity of the regenerated lithium iron phosphate positive electrode material can reach 138mAh / g, and the first discharge efficiency can reach 85%.

[0108] The beneficial effects of the present invention are:

[0109] 1. This method prevents water, oxygen, and cracking gas (such as fluorine-containing substances) from reacting with lithium iron phosphate and / or carbon in the lithium iron phosphate positive electrode sheet by simultaneously controlling the moisture content, oxygen content, and the residence time of the cracking gas in the cracking furnace. The three control conditions of moisture content, oxygen content, and the residence time of the cracking gas in the cracking furnace cooperate with each other, work synergistically, and are indispensable. The adopted anaerobic cracking technology can well retain the carbon coating on the surface of the lithium iron phosphate particles. In addition, although traditional sintering or roasting can remove PVDF (polyvinylidene fluoride), it will also cause the iron in the lithium iron phosphate positive electrode sheet to oxidize; traditional sintering or roasting will remove the conductive agent carbon and PVDF residual carbon while also removing the carbon coating on the surface of the lithium iron phosphate, increasing the difficulty of subsequent process repair; the present invention effectively retains the conductive agent carbon and the carbon coating through one-step anaerobic cracking, reducing the subsequent addition of carbon sources, and the resulting regenerated lithium iron phosphate positive electrode material does not need to be carbon-coated or supplemented with a conductive agent again, and can be directly used for battery manufacturing, which saves costs and simplifies the process flow;

[0110] 2. Introduce cracking auxiliary materials to completely crack PVDF into carbon rather than fluorinated biphenyls. After PVDF is thermally decomposed, hydrogen fluoride, vinylidene fluoride monomer, and fluorinated substituted benzenes (biphenyls) will be produced; among these substances, hydrogen fluoride, vinylidene fluoride monomer, and fluorinated substituted benzenes will be removed in the form of gas, but the fluorinated substances in the cracking residue are not easy to remove completely and will adhere to the lithium iron phosphate powder, thereby affecting the initial charge and discharge capacity, causing particle adhesion and affecting the purity of the electrolyte; in general, the cracking process needs to ensure that PVDF is completely decomposed, and the remaining carbon is used as a supplementary carbon coating layer for the lithium iron phosphate material to achieve direct regeneration of the lithium iron phosphate material. To achieve this goal, it is necessary to introduce cracking auxiliary materials to ensure that under the process conditions, PVDF is completely cracked into carbon rather than fluorinated biphenyls.

[0111] 3. One-step pyrolysis achieves the regeneration effect of the lithium iron phosphate positive electrode sheet, which can not only remove the residual electrolyte on the surface of the lithium iron phosphate positive electrode sheet, but also remove PVDF to make its adhesion ineffective. The lithium iron phosphate powder is separated from the surface of the aluminum sheet, saving more than double the energy compared to the traditional two-step sintering;

[0112] 4. The present invention expands the size of the lithium iron phosphate positive electrode sheet entering the cracking furnace to 50mm through pre-treatment crushing, which can effectively reduce the introduction of aluminum impurities during the pre-treatment process and reduce the aluminum impurity content to below 500ppm after cracking;

[0113] 5. The regenerated lithium iron phosphate cathode material obtained by the present invention effectively reduces the addition of conductive agents at the battery manufacturing end. At the same time, the performance indicators of the regenerated lithium iron phosphate cathode material are comparable to those of commercial lithium iron phosphate cathode materials. The first discharge specific capacity can reach up to 154mAh / g, and the first discharge efficiency can reach up to 93%;

[0114] 6. This application not only has a simple and efficient process, but also has low energy consumption. The operating cost is lower than the traditional lithium iron phosphate regeneration method and it is more environmentally friendly.

[0115] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a regenerated lithium iron phosphate positive electrode material, characterized in that: The steps include: S1: crushing the lithium iron phosphate positive electrode sheets to be regenerated, wherein the particle size of the crushed lithium iron phosphate positive electrode sheets is not greater than 50 mm, and the lithium iron phosphate positive electrode sheets to be regenerated are lithium iron phosphate positive electrode sheet scraps and / or defective lithium iron phosphate battery positive electrode sheets from a battery factory; S2: drying the crushed lithium iron phosphate positive electrode sheet, wherein the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 1%; S3: adding a cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet, and then placing the dried lithium iron phosphate positive electrode sheet with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the anaerobic cracking atmosphere is ≤0.2%, and the cracking is carried out at a cracking temperature of 400-600°C for 0.5-2 hours, and the residence time of the cracking gas in the cracking furnace is controlled to be less than 10 seconds, to obtain a mixture including aluminum sheet, cracking auxiliary material and lithium iron phosphate powder; the residual fluorine content in the lithium iron phosphate powder is less than 100 ppm; wherein the cracking auxiliary material includes one or more of calcium oxide, potassium oxide and sodium oxide; S4: separating the aluminum flakes, cracking auxiliary materials, and lithium iron phosphate powder in the mixture, collecting the lithium iron phosphate powder, and removing impurities from the lithium iron phosphate powder to obtain a lithium iron phosphate composite; the lithium iron phosphate composite comprises carbon-coated lithium iron phosphate and conductive carbon, wherein the carbon-coated lithium iron phosphate is a lithium iron phosphate having a carbon coating layer coated on its surface; S5: breaking up the lithium iron phosphate composite material to D99≤15um to obtain a regenerated lithium iron phosphate positive electrode material.

2. The method for preparing a regenerated lithium iron phosphate cathode material according to claim 1, characterized in that: The particle size of the cracking auxiliary material is greater than 100 meshes and the Mohs hardness is greater than 6.

0.

3. The method for preparing a regenerated lithium iron phosphate cathode material according to claim 1, wherein: In step S3, the residence time of the gas generated by cracking in the cracking furnace is controlled to be less than 3 seconds; In step S2, the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 0.5%.

4. The method for preparing a regenerated lithium iron phosphate cathode material according to any one of claims 1 or 2, characterized in that: The mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1:(25-50).

5. The method for preparing a regenerated lithium iron phosphate cathode material according to claim 1, wherein: In step S3, the cracking furnace includes a roller kiln, a rotary kiln and a tubular furnace; In step S4, the lithium iron phosphate powder is impurity-removed mainly to remove aluminum, copper and iron.

6. The method for preparing a regenerated lithium iron phosphate cathode material according to claim 1 or 5, characterized in that: The methods for removing impurities from lithium iron phosphate powder include color separation, magnetic separation, gravity separation and flotation.

7. The method for preparing a regenerated lithium iron phosphate cathode material according to claim 1, characterized in that: In step S1, the particle size of the crushed lithium iron phosphate positive electrode sheet is no more than 30 mm.

8. A regenerated lithium iron phosphate positive electrode material, characterized in that: The regenerated lithium iron phosphate positive electrode material prepared by the method for preparing a regenerated lithium iron phosphate positive electrode material according to any one of claims 1 to 7, wherein the regenerated lithium iron phosphate positive electrode material comprises carbon-coated lithium iron phosphate and conductive carbon.

9. Application of a regenerated lithium iron phosphate cathode material in the preparation of a lithium iron phosphate battery, characterized in that: The regenerated lithium iron phosphate positive electrode material according to claim 8 is used alone for the preparation of a lithium iron phosphate battery; or The regenerated lithium iron phosphate positive electrode material according to claim 8 is composited with a commercial lithium iron phosphate positive electrode material or a repaired and regenerated lithium iron phosphate positive electrode material for use in the preparation of a lithium iron phosphate battery.

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