Method for repairing and regenerating waste lithium iron phosphate

Abstract

The invention provides a method for repairing and regenerating waste lithium iron phosphate, and belongs to the technical field of recycling of lithium ion battery materials. The preparation method of the regenerated lithium iron phosphate active material comprises the following steps: obtaining waste lithium iron phosphate powder from a positive plate of a waste lithium iron phosphate battery, mixing the waste lithium iron phosphate powder with a lithium source, a ferrous reducing agent and a carbon source according to a specific ratio, and carrying out two-stage calcination in an atmosphere containing a hydrogen-nitrogen mixed gas to obtain the regenerated lithium iron phosphate active material. The regenerated lithium iron phosphate active material can be directly obtained. The method has the characteristics of short process, simplicity in operation and easiness in industrial popularization, waste materials in the process are free of acid and alkali waste liquid, high-pollution gas and the like, and the method is environment-friendly; meanwhile, the regenerated lithium iron phosphate material is high in compaction density and good in machinability, and the electrochemical performance of the formed battery is still excellent.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery material recycling and regeneration, and in particular to a method for directly repairing and regenerating waste lithium iron phosphate. Background Art

[0002] With the popularization of lithium iron phosphate materials in new energy vehicles, the demand for lithium-ion batteries has increased year by year, and the scrap volume of waste lithium iron phosphate batteries has also increased. It is expected that automotive lithium-ion batteries will begin to be scrapped on a large scale in 2025. At present, the recycling technology of waste lithium iron phosphate battery materials mainly focuses on two process routes: wet leaching and dry roasting.

[0003] Wet leaching is mainly to obtain lithium, iron and phosphorus solutions containing impurities by adding acid or alkali to dissolve, and then to form iron phosphate by adding weak alkali to adjust the pH value, filter, and then add sodium carbonate to the filtrate, filter and purify, and finally obtain lithium carbonate and iron phosphate. The recovery process is complicated, there are many impurities in the leaching solution, the corresponding impurity removal process is also complicated, and many equipments are invested. In addition, by-products are easily generated in the whole process, and a large amount of waste acid, waste alkali and waste water are generated, which is not conducive to environmental protection.

[0004] Dry roasting is to achieve element recombination through high temperature, that is, the residual carbon in the lithium iron phosphate waste is removed by roasting to obtain oxidized lithium iron phosphate, and then a small amount of lithium source and carbon source are added to remix, and then mixed and roasted to obtain regenerated lithium iron phosphate. However, this process requires long-term high-temperature roasting and high equipment requirements. The prepared lithium iron phosphate has low compaction density, poor electrochemical capacity and high impurity content. The entire roasting cycle lasts more than 15 hours and does not include material cooling time. The reagents are added too many times, the process is complicated, and the cost is high, which is not conducive to actual industrial application.

[0005] In addition, patent document CN114824546A discloses a method for recycling waste lithium iron phosphate, which includes: firstly roasting waste high-carbon lithium iron phosphate powder or lithium iron phosphate pole piece to obtain oxidized lithium iron phosphate; then coating and sintering the oxidized lithium iron phosphate with carbon source material twice to obtain regenerated lithium iron phosphate / carbon composite material. This method adopts three-stage roasting, with the highest temperature reaching 700-780℃, and the feeding process is complicated and the flow is long.

[0006] Therefore, how to achieve low-cost, short-process rapid repair and regeneration of active materials in waste lithium iron phosphate batteries is a difficult problem that needs to be solved urgently during industrial application. Summary of the invention

[0007] Based on this, it is necessary to provide a method for repairing and regenerating waste lithium iron phosphate, which adopts a one-step molten salt calcination method, significantly reduces the number of feeding times, significantly reduces the calcination temperature and time, has the advantages of short process and low cost, and facilitates the industrial recycling of waste lithium iron phosphate.

[0008] The present invention adopts the following technical solution:

[0009] The invention discloses a method for repairing and regenerating waste lithium iron phosphate, comprising the following steps: obtaining waste lithium iron phosphate powder from a positive electrode sheet of a waste lithium iron phosphate battery; mixing the waste lithium iron phosphate powder with a lithium source, a ferrous reducing agent and a carbon source, and calcining the mixture in an atmosphere containing a hydrogen-nitrogen mixed gas to obtain a regenerated lithium iron phosphate active material; wherein the calcination comprises a first-stage calcination and a second-stage calcination, the first-stage calcination temperature is 200-300° C.; the second-stage calcination temperature is 600-650° C.

[0010] Preferably, the first stage calcination time is 1 to 3 hours, and the second stage calcination time is 1 to 5 hours, so as to ensure that the components of the system can react and recombine effectively during different calcination periods.

[0011] In some of the embodiments, the mass ratio of waste lithium iron phosphate powder to lithium source, ferrous reducing agent and carbon source is 100:(5-10):(2.5-5):(1-3).

[0012] In some of the embodiments, the lithium source is selected from at least one of lithium nitrate, lithium tetrafluoroborate, and lithium acetate, which can cooperate with the reaction system to ensure that the structure of waste lithium iron phosphate that is missing lithium due to failure is repaired. At the same time, these lithium sources produce reducing substances after thermal decomposition that can reduce and repair the failed oxidized atomic structure.

[0013] In some of the embodiments, the ferrous reducing agent is selected from at least one of ferrous sulfate, ferrous oxalate, ferrous chloride, and ferrous lactate, and can cooperate with the reaction system to ensure that the failed oxidized atomic structure is reduced and repaired, while supplementing the number of missing iron atoms, and does not introduce metal atoms other than the lithium iron phosphate structure to affect its purity.

[0014] In some of the embodiments, the carbon source includes at least one of sucrose, glucose, crystal sugar, fructose, cyclodextrin, starch, and ascorbic acid, which can cooperate with the reaction system to ensure that the carbon coating structure lost during the failure process is fully repaired and its related electrochemical properties are restored.

[0015] In some of the embodiments, the atmosphere contains 3-7% hydrogen-nitrogen mixed gas, which can cooperate with the reaction system to ensure that the failed oxidized atomic structure is reduced and repaired.

[0016] In some of the embodiments, the process steps for obtaining waste lithium iron phosphate powder are: disassembling waste lithium iron phosphate batteries to obtain positive electrode sheets; immersing the positive electrode sheets in an immersion solution, separating the solid and the liquid, drying, and grinding to obtain waste lithium iron phosphate powder.

[0017] The soaking liquid can be any one of water, N-methylpyrrolidone, ferrous sulfate aqueous solution, ferrous nitrate aqueous solution, ferric chloride aqueous solution, or a combination of at least two of them, which can ensure that the waste lithium iron phosphate positive electrode powder falls off from the current collector aluminum foil to obtain high-purity waste lithium iron phosphate powder. The soaking process condition parameters are: solid-liquid ratio 1-100g / mL, soaking time 10-60min, which can ensure that the waste lithium iron phosphate positive electrode powder falls off from the current collector aluminum foil, and no microscopic chemical reaction will occur due to excessive soaking time.

[0018] In some of the embodiments, the step of grinding is further included after mixing the waste lithium iron phosphate powder with the lithium source, the ferrous reducing agent and the carbon source, so as to ensure that the materials are fully mixed.

[0019] The molar ratio of lithium, iron and phosphorus in the regenerated lithium iron phosphate active material obtained by the present invention is (1-1.1):(0.9-1.05):(1-1.08), which is consistent with the ratio of lithium, iron and phosphorus in commercial lithium iron phosphate active materials on the market.

[0020] The present invention can also provide a lithium iron phosphate battery, and the regenerated lithium iron phosphate active material prepared by the above-mentioned method for repairing and regenerating waste lithium iron phosphate can ensure the comprehensive electrochemical performance advantages.

[0021] Compared with the prior art, the core advantages of the present invention are:

[0022] The present invention obtains waste lithium iron phosphate powder from the positive electrode of waste lithium iron phosphate batteries, mixes the waste lithium iron phosphate powder with a lithium source, a ferrous reducing agent, and a carbon source in a specific ratio, and places the waste lithium iron phosphate powder in an atmosphere containing a hydrogen-nitrogen mixed gas for two-stage calcination, thereby directly obtaining a pure phase of regenerated lithium iron phosphate active material. The method has the characteristics of short process, simple operation, and easy industrial promotion. The waste in the process does not contain acid and alkali waste liquid, highly polluting gas, etc., and is environmentally friendly; at the same time, the regenerated lithium iron phosphate material has a high compaction density and good processability, and the electrochemical performance of the formed battery is still excellent.

[0023] In the technical solution of the present invention, waste lithium iron phosphate powder is compounded with lithium source, ferrous reducing agent, carbon source and hydrogen-nitrogen mixed gas of specific types and proportions, which can comprehensively ensure the reduction and repair of the structure of lithium deficiency, failed oxidized atomic structure and carbon-coated structure in waste lithium iron phosphate due to failure. In particular, calcination with a specific lithium source can generate reducing substances after pyrolysis to reduce and repair the failed oxidized atomic structure of waste lithium iron phosphate, which can not only reduce the amount of reducing agent used, but also make the structure of the regenerated lithium iron phosphate more stable.

[0024] The present invention adopts a one-step molten salt calcination, which significantly reduces the calcination temperature and time, and significantly reduces the number of times of adding materials, that is, calcination is directly carried out after one-time addition, without adding materials and calcining in steps, and the calcination temperature is lower than that of the prior art, the calcination time is greatly shortened, the repair and regeneration effect reaches the commercial lithium iron phosphate standard, the equipment investment cost is low, and there is no need for a multi-step impurity removal process, which has the possibility of industrial application.

[0025] The present invention provides a method for recycling, repairing and regenerating the positive electrode material of waste lithium iron phosphate batteries, which is applicable to waste lithium iron phosphate batteries of various series, that is, waste lithium iron phosphate batteries can use the recycling, repairing and regenerating method provided by the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the process flow of the method for repairing and regenerating waste lithium iron phosphate of the present invention;

[0027] Figure 2 These are XRD test diagrams of the repaired and regenerated lithium iron phosphate active material (Repaired LFP), standard lithium iron phosphate (Standard LFP), and spent lithium iron phosphate positive electrode material (Spent LFP) in Example 1. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand the present invention more clearly. The following embodiments are only used to illustrate the present invention, but are not only used to limit the scope of the present invention. Based on the specific embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work belong to the protection scope of the present invention. In the embodiments of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; in the embodiments of the present invention, if not specifically specified, the technical means used are conventional means well known to those skilled in the art.

[0029] Example 1

[0030] refer to Figure 1 As shown, this embodiment provides a method for repairing and regenerating waste lithium iron phosphate, comprising the following steps:

[0031] S1, manually disassemble the waste lithium iron phosphate battery to obtain the positive electrode sheet, add water according to the solid-liquid ratio of 30g / mL to soak the solution for 10min, separate the solid and liquid, dry the waste lithium iron phosphate positive electrode material, grind it, and obtain the waste lithium iron phosphate powder.

[0032] The liquid (water) separated in this process is returned to the soaking process for recycling.

[0033] S2, the waste lithium iron phosphate powder obtained in step S1 is mixed evenly with lithium nitrate, ferrous sulfate and sucrose in a mass ratio of 100:5:3.5:2, and ground for 10 minutes, and then placed in a tubular furnace under a 5% hydrogen-nitrogen mixed gas atmosphere for calcination. The temperature of the first stage calcination is 300°C, the heating rate is 5°C / min, and the insulation time is 3h; then it is raised to the temperature of the second stage calcination at 650°C, the heating rate is 5°C / min, and the insulation time is 3h. When the temperature of the tubular furnace drops to room temperature, take it out to obtain the repaired and regenerated lithium iron phosphate active material.

[0034] S3, washing the repaired and regenerated lithium iron phosphate active material obtained in step S2 with water and ethanol respectively, and then drying it, and then matching it with commercial negative electrode graphite material to make a soft-pack battery, to obtain a lithium iron phosphate lithium-ion battery and conduct an electrochemical performance test.

[0035] The XRD comparison diagram of the repaired LFP in this example, the standard LFP and the spent LFP is shown in Figure 2 .

[0036] Depend on Figure 2 It can be seen that:

[0037] The structure of the waste lithium iron phosphate active material has changed, and the XRD spectrum shows that it contains substances such as ferric oxide and iron phosphate, which makes the active material invalid or partially invalid; while in the lithium iron phosphate after repair and regeneration in Example 1, the invalid ferric oxide, iron phosphate and other substances have disappeared, and pure phase lithium iron phosphate has been obtained after repair.

[0038] Example 2

[0039] This embodiment provides a method for repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Example 1, specifically including:

[0040] S1, manually disassemble the waste lithium iron phosphate battery to obtain the positive electrode sheet, add water according to the solid-liquid ratio of 50g / mL for solution immersion treatment for 15min, separate the solid and liquid, take out the waste lithium iron phosphate positive electrode material, dry it, grind it, and obtain the waste lithium iron phosphate powder. The liquid (water) separated in this process is returned to the immersion treatment process for recycling.

[0041] S2, the waste lithium iron phosphate powder obtained in step S1 is mixed evenly with lithium nitrate, ferrous oxalate and fructose in a mass ratio of 100:7:5:3, and ground for 15 minutes, and then placed in a tubular furnace under a 5% hydrogen and nitrogen mixed gas atmosphere for calcination. The temperature of the first stage calcination is 250°C, and the insulation time is 2h; then it is raised to the temperature of the second stage calcination 650°C, and the insulation time is 2h. When the temperature of the tubular furnace drops to room temperature, it is taken out to obtain the repaired and regenerated lithium iron phosphate active material.

[0042] S3, washing the repaired and regenerated lithium iron phosphate active material obtained in step S2 with water and ethanol respectively, and then drying it, and then matching it with commercial negative electrode graphite material to make a soft-pack battery, to obtain a lithium iron phosphate lithium-ion battery and conduct an electrochemical performance test.

[0043] Example 3

[0044] This embodiment provides a method for repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Example 1, specifically including:

[0045] S1, manually disassemble the waste lithium iron phosphate battery to obtain the positive electrode sheet, add saturated ferrous sulfate solution according to the solid-liquid ratio of 30g / mL for solution immersion treatment for 20min, separate the solid and liquid, take out the waste lithium iron phosphate positive electrode material, dry it, grind it, and obtain the waste lithium iron phosphate powder. The liquid (water) separated in this process is returned to the immersion treatment process for recycling.

[0046] S2, the waste lithium iron phosphate powder obtained in step S1 is mixed with lithium nitrate, ferrous oxalate and starch in a mass ratio of 100:6:4:1, and ground for 20 minutes, and then placed in a tubular furnace under a 3% hydrogen and nitrogen mixed gas atmosphere for calcination. The temperature of the first stage calcination is 300°C, the insulation time is 2 hours, and then it is raised to the temperature of the second stage calcination 600°C, and the insulation time is 4 hours. When the temperature of the tubular furnace drops to room temperature, it is taken out to obtain the repaired and regenerated lithium iron phosphate active material.

[0047] S3, washing the repaired and regenerated lithium iron phosphate active material obtained in step S2 with water and ethanol respectively, and then drying it, and then matching it with commercial negative electrode graphite material to make a soft-pack battery, to obtain a lithium iron phosphate lithium-ion battery and conduct an electrochemical performance test.

[0048] Example 4

[0049] This embodiment provides a method for repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Embodiment 1, except that:

[0050] S1, manually disassemble the waste lithium iron phosphate battery to remove the positive electrode sheet, and add saturated ferrous nitrate solution according to the solid-liquid ratio of 50g / mL for solution immersion treatment.

[0051] S2, the waste lithium iron phosphate powder obtained in step S1 is mixed with lithium tetrafluoroborate, ferrous oxalate and glucose in a mass ratio of 100:8:3.5:3, and ground for 30 minutes, and then placed in a tubular furnace under a 7% hydrogen-nitrogen mixed gas atmosphere for calcination. The temperature of the first stage calcination is 300°C, the insulation time is 2h, and then it is raised to the temperature of the second stage calcination 600°C, and the insulation time is 2h. When the temperature of the tubular furnace drops to room temperature, it is taken out to obtain the repaired and regenerated lithium iron phosphate active material.

[0052] Example 5

[0053] This embodiment provides a method for repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Embodiment 1, except that:

[0054] Step S2: The waste lithium iron phosphate powder obtained in step S1 is mixed evenly with lithium acetate, ferrous lactate, and cyclodextrin in a mass ratio of 100:6:4.5:3, and ground for 15 minutes, and then placed in a tubular furnace under a 7% hydrogen-nitrogen mixed gas atmosphere for calcination. The temperature of the first stage calcination is 300°C, and the insulation time is 1 hour, and then it is raised to the temperature of the second stage calcination 650°C, and the insulation time is 2 hours. When the temperature of the tubular furnace drops to room temperature, it is taken out to obtain the repaired and regenerated lithium iron phosphate active material.

[0055] Example 6

[0056] This embodiment provides a method for repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Embodiment 1, except that:

[0057] In step S1: after manually disassembling the waste lithium iron phosphate battery to obtain the positive electrode sheet, water is added according to a solid-liquid ratio of 40g / mL to perform solution immersion treatment for 16 minutes.

[0058] Step S2: The waste lithium iron phosphate powder obtained in step S1 is mixed evenly with lithium nitrate, ferrous sulfate, and crystal sugar in a mass ratio of 100:10:5:2, and ground for 15 minutes, and then placed in a tubular furnace under a 5% hydrogen-nitrogen mixed gas atmosphere for calcination. The temperature of the first stage calcination is 300°C, and the insulation time is 2 hours, and then it is raised to the temperature of the second stage calcination 650°C, and the insulation time is 1 hour. When the temperature of the tubular furnace drops to room temperature, it is taken out to obtain the repaired and regenerated lithium iron phosphate active material.

[0059] Comparative Example 1

[0060] This comparative example provides a method for repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Example 1, with the only difference being that the reducing agent ferrous sulfate is omitted in step S2.

[0061] Comparative Example 2

[0062] This comparative example provides a method for directly repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Example 1, with the only difference being that the lithium source lithium nitrate is omitted in step S2.

[0063] Comparative Example 3

[0064] This comparative example provides a method for repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Example 1, with the only difference being that in step S2, the first stage calcination is omitted, and the temperature is directly raised to 650° C. for calcination, and the insulation time is 3 hours.

[0065] Comparative Example 4

[0066] This comparative example provides a method for repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Example 1, with the only difference being that the second stage calcination is omitted in step S2, and the temperature is only raised to 300° C. for calcination, and the insulation time is 6 hours.

[0067] Comparative Example 5

[0068] This comparative example provides a method for repairing and regenerating waste lithium iron phosphate, and its process steps are basically the same as those in Example 1, except that in step S1, the lithium source is replaced by common lithium carbonate instead of lithium nitrate.

[0069] Comparative Example 6

[0070] This comparative example refers to a method for recycling waste lithium iron phosphate disclosed in patent document CN114864930A, specifically referring to Example 1, and the steps include: (1) mixing waste lithium iron phosphate, lithium source, iron source, phosphorus source and additives, grinding and drying, and sintering the obtained dry powder in an oxygen atmosphere to obtain oxidized lithium iron phosphate powder; (2) mixing the oxidized lithium iron phosphate powder, additives and carbon source, grinding and drying them again, and sintering the obtained dry powder in an inert atmosphere. After the sintering is completed, the powder is graded and crushed to finally obtain a regenerated lithium iron phosphate / carbon composite material.

[0071] The physical and chemical properties of the repaired and regenerated lithium iron phosphate active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 6 were tested respectively.

[0072] The test results are shown in the table below:

[0073]

[0074] It can be seen from the above table:

[0075] The molar ratio of lithium, iron and phosphorus in the repaired and regenerated lithium iron phosphate active material obtained in Examples 1 to 6 is (1 to 1.1): (0.9 to 1.05): (1 to 1.08), which is consistent with the ratio of lithium, iron and phosphorus in commercial lithium iron phosphate active materials on the market, and has high compaction density and good processing performance. Compared with Comparative Examples 1 to 6, the comprehensive properties of the repaired and regenerated lithium iron phosphate active material are better.

[0076] The repaired and regenerated lithium iron phosphate active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 6 were subjected to electrochemical testing, and the specific steps included:

[0077] The positive electrode material (5wt% lithium iron phosphate active material, 2.5wt% acetylene black, 0.5wt% conductive agent, 2wt% polyvinylidene fluoride) was stirred and slurried in N-methylpyrrolidone solvent, and the positive electrode slurry was coated on aluminum foil to obtain a positive electrode sheet; graphite was used as the negative electrode. A polypropylene microporous film was used as a separator, and a 1mol / L LiPF6 electrolyte was prepared with EC and DEC in a mass ratio of 1:1 as solvents, and assembled into a soft-pack battery for electrochemical performance testing.

[0078] The first charge and discharge specific capacity test: the voltage range is 2.5-3.5V, the current density is 0.1C, and the test results are shown in Table 1. Among them, 1C is the current required for the battery to discharge the rated capacity of 170mAh / g within 1h.

[0079] Cycle performance test: Under the conditions of voltage range of 2.5~3.5V and current density of 1C, after a certain number of charge and discharge cycles (different positive electrode materials correspond to different number of cycles), the charge specific capacity and discharge specific capacity are tested respectively, and the capacity retention rate is calculated.

[0080] The electrochemical performance test results of the soft-pack battery prepared by using the repaired and regenerated lithium iron phosphate active material are shown in the following table:

[0081]

[0082]

[0083] It can be seen from the above table:

[0084] Compared with Comparative Examples 1 to 6, the soft-pack batteries assembled from the regenerated lithium iron phosphate obtained in Examples 1 to 6 have excellent electrochemical properties, all reaching the performance standards of commercial lithium iron phosphate materials. The repair and regeneration process is simple and has the potential for industrial application.

[0085] In addition, it is worth noting that the present invention has found through a large number of experimental investigations that:

[0086] (1) In the present invention, the lithium source is preferably at least one of lithium nitrate, lithium tetrafluoroborate, and lithium acetate; the ferrous reducing agent is preferably at least one of ferrous sulfate, ferrous oxalate, ferrous chloride, and ferrous lactate; the carbon source can be selected from at least one of sucrose, glucose, crystal sugar, fructose, cyclodextrin, starch, and ascorbic acid; the mass ratio of the lithium source, the ferrous reducing agent, and the carbon source is preferably (5-10): (2.5-5): (1-3); the combination system of the above components can comprehensively ensure the structural reorganization and regeneration structural stability of the waste lithium iron phosphate powder under specific calcination conditions.

[0087] (2) Waste lithium iron phosphate powder is charged once with a lithium source, a ferrous reducing agent, and a carbon source of a specific type and ratio, and calcined in two stages under a hydrogen-nitrogen mixed gas condition. The temperature of the first stage calcination is preferably controlled at 200-300°C, and the temperature of the second stage calcination is preferably controlled at 600-650°C. The total calcination time does not exceed 8 hours, so as to ensure that a pure phase lithium iron phosphate repair and regeneration material is obtained.

[0088] Among them, the first stage calcination process mainly realizes the reduction of trivalent iron and the reorganization of the structure of waste lithium iron phosphate through the low eutectic point (in the molten state) of a specific type of lithium salt and reducing agent; the second stage calcination process mainly re-synthesizes the reduced divalent iron, lithium salt and waste lithium iron phosphate into a regenerated lithium iron phosphate with stable structure (the molar ratio of lithium, iron and phosphorus elements is 1-1.1:0.9-1.05:1-1.08). The two-stage temperature calcination makes the Li / Fe / P elements sinter and fuse evenly, and is also beneficial to the growth of lithium iron phosphate particles, surface smoothness and the attachment of secondary carbon sources, ensuring or even improving the electrochemical performance of regenerated lithium iron phosphate used in power batteries.

[0089] (3) During the soaking process of the positive electrode sheets disassembled from the waste lithium iron phosphate batteries, the solid-liquid ratio can be maintained at 1 to 100 g / mL, preferably 10 to 60 g / mL; the solution soaking treatment is controlled to be 5 to 60 minutes, preferably 10 to 30 minutes. The soaking solution is preferably any one of N-methylpyrrolidone, ferrous sulfate solution, ferrous nitrate solution, ferric chloride solution, and pure water, or a combination of at least two. This soaking process step can reduce impurities in the waste lithium iron phosphate active material, and the solution soaking can be recycled to reduce pollution.

[0090] The waste lithium iron phosphate batteries in the waste lithium iron phosphate repair and regeneration method of the present invention may include lithium iron phosphate batteries for application scenarios such as new energy power vehicles, energy storage systems, and consumer electronic products, and the models include soft-pack aluminum-plastic film, square aluminum shell batteries, cylindrical lithium iron phosphate batteries, etc.

[0091] It is necessary to point out that the above embodiments are limited to further elaboration and explanation of the technical solution of the present invention, and are not further limitations of the technical solution of the present invention. The method of the present invention is only a preferred implementation scheme, and is not used to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for repairing and regenerating waste lithium iron phosphate, characterized in that: The steps include: Obtaining waste lithium iron phosphate powder from the positive electrode sheet of waste lithium iron phosphate batteries; The waste lithium iron phosphate powder is mixed with a lithium source, a ferrous reducing agent, and a carbon source, and calcined in an atmosphere containing a hydrogen-nitrogen mixed gas to obtain a regenerated lithium iron phosphate active material; The calcination includes a first stage calcination and a second stage calcination, the first stage calcination temperature is 200-300°C; the second stage calcination temperature is 600-650°C.

2. The method for repairing and regenerating waste lithium iron phosphate according to claim 1, characterized in that: The mass ratio of waste lithium iron phosphate powder to lithium source, ferrous reducing agent and carbon source is 100:(5-10):(2.5-5):(1-3).

3. The method for repairing and regenerating waste lithium iron phosphate according to claim 1 or 2, characterized in that: The lithium source is selected from at least one of lithium nitrate, lithium tetrafluoroborate and lithium acetate; and / or The ferrous reducing agent is selected from at least one of ferrous sulfate, ferrous oxalate, ferrous chloride and ferrous lactate; and / or The carbon source is selected from at least one of sucrose, glucose, crystal sugar, fructose, cyclodextrin, starch and ascorbic acid.

4. The method for repairing and regenerating waste lithium iron phosphate according to claim 1 or 2, characterized in that: The atmosphere contains 3-7% hydrogen-nitrogen mixed gas.

5. The method for repairing and regenerating waste lithium iron phosphate according to claim 1 or 2, characterized in that: The process steps for obtaining waste lithium iron phosphate powder are: Disassemble the waste lithium iron phosphate battery to obtain the positive electrode; The positive electrode sheet is immersed in an immersion solution, solid-liquid separation is performed, drying is performed, and grinding is performed to obtain waste lithium iron phosphate powder.

6. The method for direct repair and regeneration of waste lithium iron phosphate according to claim 5, characterized in that: The soaking liquid is any one of water, N-methylpyrrolidone, ferrous sulfate aqueous solution, ferrous nitrate aqueous solution, and ferric chloride aqueous solution, or a combination of at least two of them.

7. The method for repairing and regenerating waste lithium iron phosphate according to claim 6, characterized in that: The soaking process parameters are as follows: solid-liquid ratio of 1 to 100 g / mL and soaking time of 10 to 60 min.

8. The method for direct repair and regeneration of waste lithium iron phosphate according to claim 1 or 2, characterized in that: The method further includes a grinding step after mixing the waste lithium iron phosphate powder with a lithium source, a ferrous reducing agent and a carbon source.

9. The method for repairing and regenerating waste lithium iron phosphate according to claim 1 or 2, characterized in that: The molar ratio of lithium, iron and phosphorus in the regenerated lithium iron phosphate active material is (1-1.1): (0.9-1.05): (1-1.08).

10. A lithium iron phosphate battery, characterized in that: A regenerated lithium iron phosphate active material prepared by the method for repairing and regenerating waste lithium iron phosphate as described in any one of claims 1 to 9.

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