Method for regenerating lithium iron manganese phosphate positive electrode material and application of lithium iron manganese phosphate positive electrode material

Abstract

The invention provides a method for regenerating a lithium iron manganese phosphate positive electrode material and application of the lithium iron manganese phosphate positive electrode material. The method comprises the following steps: providing lithium manganese iron phosphate powder to be recycled; mixing the lithium manganese iron phosphate powder, tannic acid and lithium acetate, and carrying out hydrothermal reaction to obtain an intermediate for defect repair; mixing the defect-repaired intermediate, a lithium source, a manganese source, a phosphorus source, a carbon source and a doped metal oxide, and then performing post-treatment to obtain precursor microspheres; and sintering the precursor microspheres to obtain the regenerated lithium iron manganese phosphate positive electrode material. According to a synergistic regeneration mechanism of tannic acid and lithium acetate provided by the invention, accurate removal of surface impurities and in-situ repair of bulk phase lithium vacancies are synchronously realized, so that low-cost and low-energy-consumption regeneration of the waste lithium iron manganese phosphate positive electrode material is completed, and efficient repair of a microstructure is completed; finally, the regenerated lithium manganese iron phosphate positive electrode material with a stable structure and excellent electrochemical performance is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a method for regenerating a lithium manganese iron phosphate positive electrode material and application thereof. BACKGROUND

[0002] Lithium manganese iron phosphate (LMFP) is a positive electrode material combining the high safety of lithium iron phosphate and the high voltage of lithium manganese phosphate, and its application scale is expanding. At present, a large number of waste lithium manganese iron phosphate batteries are being produced, and how to efficiently and environmentally recycle them is of great significance for alleviating the shortage of raw materials, reducing environmental load and realizing sustainable development of the industry. The recycling process of waste lithium manganese iron phosphate positive electrode material is mainly divided into wet process and pyrometallurgical process. Although the wet process has a higher recovery rate, it generally has problems such as long process, use of a large amount of acid and alkali reagents, generation of secondary waste liquid, etc., resulting in high cost and lack of environmental friendliness; the pyrometallurgical process has high energy consumption and is usually difficult to directly regenerate high-value-added positive electrode materials.

[0003] In recent years, the regeneration technology based on direct repair is considered as a more promising path due to its short process, low cost and low energy consumption. The above path usually mixes waste positive electrode materials with appropriate amounts of lithium source, iron source, manganese source and other supplementary reagents, and then restores the crystal structure through high-temperature sintering. However, its process faces significant challenges when applied to lithium manganese iron phosphate, the core of which is the difficulty in fully repairing the structural defects of the material, resulting in insufficient structural stability of the regenerated material.

[0004] Therefore, it is urgent to develop a low-cost and low-energy regeneration method that can efficiently repair the microstructure, which is a key problem to be solved in the field. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for regenerating a lithium manganese iron phosphate positive electrode material and application thereof. The present application proposes a synergistic regeneration mechanism of "tannic acid + lithium acetate", which simultaneously realizes the accurate removal of surface impurities and the in-situ repair of bulk lithium vacancies. On this basis, the introduction of doped metal oxides can enter the crystal lattice, widen the lithium ion migration channel, and improve the intrinsic ionic conductivity and structural stability of the material. In summary, the process not only realizes the low-cost and low-energy regeneration of waste lithium manganese iron phosphate positive electrode materials, but also efficiently repairs the microstructure, and finally obtains a regenerated lithium manganese iron phosphate positive electrode material with stable structure and excellent electrochemical performance.

[0006] To achieve this purpose, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a method for regenerating a lithium manganese iron phosphate positive electrode material, which comprises the following steps:

[0008] The lithium manganese iron phosphate powder to be recycled is provided.

[0009] The lithium manganese iron phosphate powder, tannic acid and lithium acetate are mixed to perform a hydrothermal reaction to obtain a defect-repaired intermediate.

[0010] The defect-repaired intermediate, a lithium source, a manganese source, a phosphorus source, a carbon source and a doped metal oxide are mixed, and then post-processing is performed to obtain a precursor microsphere.

[0011] Sintering treatment is performed on the precursor microsphere to obtain a regenerated lithium manganese iron phosphate positive electrode material.

[0012] The present application proposes a synergistic regeneration mechanism of "tannic acid + lithium acetate", wherein the phenolic hydroxyl and carboxyl groups in the tannic acid molecules can selectively chelate Fe 3+ / Mn 3+ oxide impurities, forming soluble metal-tannic acid complexes. The synchronously added lithium acetate not only provides free Li + ions to embed into the lattice lithium vacancies, achieving lithium vacancy repair, but also generates anions through decomposition, which can prevent the over-acidification of tannic acid, maintain the pH stability of the reaction system, prevent the excessive dissolution of Mn / Fe, and preserve the lattice integrity. Therefore, the synergistic regeneration mechanism simultaneously achieves the precise removal of surface impurities and the in-situ repair of bulk lithium vacancies. Secondly, the introduced doped metal oxides can enter the lattice interior, widening the lithium ion migration channels and improving the intrinsic ionic conductivity and structural stability of the material. Finally, the addition of the carbon source not only prevents the oxidation of divalent iron, but also coats the material, improving the electrical conductivity of the material. In summary, the process not only realizes the low-cost and low-energy regeneration of waste lithium manganese iron phosphate positive electrode materials, but also efficiently repairs the microstructure, ultimately obtaining a regenerated lithium manganese iron phosphate positive electrode material with stable structure and excellent electrochemical performance.

[0013] In the present application, when lithium manganese iron phosphate is used as a positive electrode material of a battery, lithium ions are deintercalated and intercalated between the positive and negative electrodes during the charging and discharging process. During this process, part of the lithium ions may be lost due to various reasons such as minor changes in the internal structure of the battery, decomposition of the electrolyte, etc. The electrolyte may also decompose to produce some by-products during the operation of the battery, which may react with lithium ions, leading to the loss of lithium. During the battery cycle, manganese gradually precipitates from the positive electrode material, and a part of the manganese dissolves in the electrolyte to form manganese ions, which further leads to the loss of lithium and manganese elements in lithium manganese iron phosphate. Therefore, by introducing a lithium source, a manganese source and a phosphorus source, the missing elements in the defect-repaired intermediate can be supplemented, so that the molar ratio of each element meets the requirements of the target product.

[0014] It should be noted that the chemical composition of the regenerated lithium manganese iron phosphate positive electrode material conforms to the general formula LiMnx Fe 1-x PO4, wherein 0 < x < 1, for example, can be 0.2, 0.4, 0.6, or 0.8, etc.

[0015] Preferably, the mass ratio of the tannic acid and the lithium manganese iron phosphate powder is (0.3-1):1, for example, can be 0.3:1, 0.5:1, 0.7:1, 0.9:1, or 1:1, etc.

[0016] Preferably, the mass ratio of the lithium acetate and the lithium manganese iron phosphate powder is (0.1-0.4):1, for example, can be 0.1:1, 0.2:1, 0.3:1, or 0.4:1, etc.

[0017] In the present application, the appropriate addition of tannic acid and lithium acetate can not only dissolve impurities, but also supplement lithium, so that impurity removal and lithium vacancy repair are carried out synchronously. On the other hand, lithium acetate buffers the acidity of tannic acid, avoids excessive erosion, removes only surface oxides, and preserves the integrity of the LMFP lattice, Li + is more likely to be embedded in the vacancy than to be occupied by H + under weakly acidic conditions.

[0018] Preferably, during the hydrothermal reaction, the temperature is 180-250℃, for example, can be 180℃, 200℃, 225℃, or 250℃, etc.

[0019] Preferably, the hydrothermal reaction time is 8-12h, for example, can be 8h, 9h, 10h, 11h, or 12h, etc.

[0020] Preferably, according to the content of each element in the defect repair intermediate and the required element molar ratio of the target product, the addition amount of the lithium source, the manganese source, and the phosphorus source is determined.

[0021] Preferably, the lithium source includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, or lithium oxalate.

[0022] Preferably, the manganese source includes any one or a combination of at least two of manganese carbonate, manganese acetate, or manganese oxide.

[0023] Preferably, the phosphorus source includes any one or a combination of at least two of monohydrogen lithium phosphate, dihydrogen lithium phosphate, or phosphoric acid.

[0024] In the present application, if the phosphorus source is phosphoric acid, a slight excess of phosphoric acid not only has the effect of supplementing the phosphorus source, but also the phosphate adsorbed on the surface of the particles forms an electrostatic barrier, which can prevent the nanoparticles from re-aggregating, and the phosphoric acid and the dissolved Fe 2+ / Mn 2 +The reaction generates a compact iron-manganese phosphate surface layer, and inhibits further dissolution of transition metals.

[0025] Preferably, the carbon source comprises any one or a combination of at least two of glucose, sucrose or citric acid.

[0026] Preferably, the mass ratio of the carbon source to the defect-repaired intermediate is (0.05-0.2):1, for example, it can be 0.05:1, 0.1:1, 0.15:1 or 0.2:1, etc.

[0027] Preferably, the doped metal oxide comprises any one or a combination of at least two of zirconium oxide, titanium oxide, aluminum oxide, copper oxide or magnesium oxide.

[0028] Preferably, the mass ratio of the doped metal oxide to the defect-repaired intermediate is (0.01-0.03):1, for example, it can be 0.01:1, 0.02:1 or 0.03:1, etc.

[0029] In the present application, the appropriate amount of doped metal oxide is added, which is beneficial to stabilize the crystal framework, inhibit the Jahn-Teller effect and manganese dissolution in the charging and discharging process; at the same time, it widens the lithium ion migration channel and improves the intrinsic ionic conductivity of the material.

[0030] Preferably, the step of post-treatment comprises sanding and spray drying.

[0031] Preferably, the rotation speed of the sanding is 1000 rpm-1500 rpm, for example, it can be 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm or 1500 rpm, etc.

[0032] Preferably, the particle size D50 of the precursor microspheres is 8 μm-15 μm, for example, it can be 8 μm, 10 μm, 12 μm or 15 μm, etc.

[0033] Preferably, the atmosphere of the sintering treatment is an inert atmosphere. For example, it can be a nitrogen atmosphere, etc.

[0034] Preferably, the sintering treatment is in the form of staged sintering, which comprises a one-stage sintering and a two-stage sintering with increasing temperature.

[0035] Preferably, the temperature of the one-stage sintering is 250℃-350℃, for example, it can be 250℃, 300℃ or 350℃, etc., and the holding time is 2h-5h, for example, it can be 2h, 3h, 4h or 5h, etc.

[0036] Preferably, the temperature of the two-stage sintering is 700-800 DEG C, for example, it can be 700 DEG C, 750 DEG C or 800 DEG C, etc., and the holding time is 10-15 h, for example, it can be 10 h, 11 h, 12 h, 13 h, 14 h or 15 h, etc.

[0037] Preferably, the method comprises the following steps:

[0038] (1) Discharge and disassemble the waste old lithium iron manganese phosphate battery to obtain a positive electrode sheet, then remove the binder in the positive electrode sheet, and filter and separate the current collector and the positive active material, then acid wash the positive active material to remove surface impurities, and crush to obtain a lithium iron manganese phosphate powder to be recovered.

[0039] (2) Mix the lithium iron manganese phosphate powder to be recovered, tannic acid and lithium acetate, add water, then transfer to a high-pressure reaction kettle, and carry out high-pressure high-temperature reaction for 8-12 h at a temperature of 180-250 DEG C to obtain a defect-repaired intermediate; wherein the mass ratio of the tannic acid to the lithium iron manganese phosphate powder to be recovered is (0.3-1):1, and the mass ratio of the lithium acetate to the lithium iron manganese phosphate powder to be recovered is (0.1-0.4):1.

[0040] (3) Analyze the content of Li, Fe and Mn elements in the defect-repaired intermediate to obtain a content analysis result, then determine the addition amount of lithium source, manganese source and phosphorus source according to the content analysis result and the required element molar ratio of the target product.

[0041] Wet sand mill the defect-repaired intermediate, lithium source, manganese source, phosphorus source, carbon source and doped metal oxide in a sand mill to a particle size D50 of 0.25-0.4 μm to obtain a mixed slurry, then spray dry the mixed slurry to obtain a precursor microsphere with a particle size D50 of 8-15 μm; wherein the doped metal oxide includes any one or a combination of at least two of zirconium oxide, titanium oxide, aluminum oxide, copper oxide or magnesium oxide; the mass ratio of the carbon source to the defect-repaired intermediate is (0.05-0.2):1, the mass ratio of the doped metal oxide to the defect-repaired intermediate is (0.01-0.03):1, and the rotation speed of the wet sand mill is 1000-1500 rpm.

[0042] (4) In an inert atmosphere, carry out one-stage sintering and two-stage sintering on the precursor microsphere with increasing temperature, and sieve to obtain a regenerated lithium iron manganese phosphate positive electrode material; wherein the temperature of the one-stage sintering is 250-350 DEG C, and the holding time is 2-5 h; the temperature of the two-stage sintering is 700-800 DEG C, and the holding time is 10-15 h.

[0043] In a second aspect, the present application provides a lithium manganese iron phosphate positive electrode material, which is prepared by the method of the first aspect.

[0044] In a third aspect, the present application provides a lithium ion battery comprising the lithium manganese iron phosphate positive electrode material of the second aspect.

[0045] The numerical ranges of the present application include not only the point values recited above, but also any intervening point values between the recited point values. For the sake of brevity, the numerous details of construction and operation of the present application can not be described in detail herein.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] The present application proposes a synergistic regeneration mechanism of "tannic acid + lithium acetate", in which the phenolic hydroxyl and carboxyl groups in the tannic acid molecules can selectively chelate the dissolved Fe 3+ / Mn 3+ oxide impurities to form soluble metal-tannic acid complexes. The simultaneously added lithium acetate not only provides free Li + ions to repair lithium vacancies in the crystal lattice, but also generates anions from its decomposition to prevent the over-oxidation of tannic acid, maintain the pH stability of the reaction system, prevent the excessive dissolution of Mn / Fe, and preserve the integrity of the crystal lattice. Therefore, the synergistic regeneration mechanism simultaneously achieves the precise removal of surface impurities and the in-situ repair of lithium vacancies in the bulk phase. Secondly, the introduced doped metal oxides can enter the crystal lattice, widening the lithium ion migration channels and improving the intrinsic ionic conductivity and structural stability of the material. Finally, the addition of carbon sources not only prevents the oxidation of divalent iron, but also coats the material, improving its electrical conductivity. In summary, the process not only realizes the low-cost and low-energy regeneration of waste lithium manganese iron phosphate positive electrode materials, but also efficiently repairs the microstructure, ultimately obtaining a regenerated lithium manganese iron phosphate positive electrode material with stable structure and excellent electrochemical performance. DETAILED DESCRIPTION

[0048] The technical solutions of the present application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0049] Example 1

[0050] The present embodiment provides a method for regenerating a lithium manganese iron phosphate positive electrode material, which comprises the following steps:

[0051] (1) Discharge and disassemble the waste lithium iron manganese phosphate battery, obtain the positive electrode sheet, then remove the binder in the positive electrode sheet, and filter and separate the current collector and the positive electrode active material, then acid wash the positive electrode active material to remove surface impurities, and crush to obtain a lithium iron manganese phosphate powder to be recycled.

[0052] (2) Mix the lithium iron manganese phosphate powder to be recycled, tannic acid and lithium acetate, add deionized water, then transfer to a reaction kettle, and carry out a hydrothermal reaction for 10 h at a temperature of 220 DEG C, to obtain a defect-repaired intermediate; wherein the mass ratio of the tannic acid to the lithium iron manganese phosphate powder to be recycled is 0.6:1, and the mass ratio of the lithium acetate to the lithium iron manganese phosphate powder to be recycled is 0.25:1.

[0053] (3) Analyze the content of Li, Fe and Mn elements in the defect-repaired intermediate to obtain a content analysis result, then determine the addition amount of lithium source, manganese source and phosphorus source according to the content analysis result and the required element molar ratio of the target product (chemical formula LiMn 0.6 Fe 0.4 PO4).

[0054] Carry out wet sanding of the defect-repaired intermediate, lithium hydroxide monohydrate, manganese acetate, phosphoric acid, glucose and zirconium oxide in a sand mill to a particle size D50 of 0.28 pm of the particles, to obtain a mixed slurry, then spray dry the mixed slurry to obtain precursor microspheres with a particle size D50 of 12 pm; wherein the mass ratio of the glucose to the defect-repaired intermediate is 0.1:1, the mass ratio of the zirconium oxide to the defect-repaired intermediate is 0.02:1, and the rotation speed of the wet sanding is 1200 rpm.

[0055] (4) Under a nitrogen atmosphere, carry out one-stage sintering and two-stage sintering of the precursor microspheres with increasing temperatures, and sieve to obtain regenerated lithium iron manganese phosphate positive electrode material; wherein the temperature of the one-stage sintering is 300 DEG C, and the holding time is 3.5 h; the temperature of the two-stage sintering is 750 DEG C, and the holding time is 12 h.

[0056] Example 2

[0057] The embodiment provides a method for regenerating lithium iron manganese phosphate positive electrode material, which comprises the following steps:

[0058] (1) Discharge and disassemble the waste lithium iron manganese phosphate battery, obtain the positive electrode sheet, then remove the binder in the positive electrode sheet, and filter and separate the current collector and the positive electrode active material, then acid wash the positive electrode active material to remove surface impurities, and crush to obtain a lithium iron manganese phosphate powder to be recycled.

[0059] (2) The recovered lithium manganese iron phosphate powder, tannic acid and lithium acetate are mixed, deionized water is added, and then transferred to a reaction kettle to carry out a hydrothermal reaction for 8h at a temperature of 250°C to obtain a defect-repaired intermediate; wherein the mass ratio of the tannic acid to the recovered lithium manganese iron phosphate powder is 0.3:1, and the mass ratio of the lithium acetate to the recovered lithium manganese iron phosphate powder is 0.1:1.

[0060] (3) The contents of Li, Fe and Mn elements in the defect-repaired intermediate are analyzed to obtain a content analysis result, and then the addition amounts of a lithium source, a manganese source and a phosphorus source are determined according to the content analysis result and the required element molar ratio of a target product (chemical formula: LiMn 0.6 Fe 0.4 PO4).

[0061] The defect-repaired intermediate, lithium hydroxide monohydrate, manganese acetate, phosphoric acid, glucose and zirconium oxide are wet sand milled in a sand mill to a particle size D50 of 0.28μm to obtain a mixed slurry, and then the mixed slurry is spray dried to obtain precursor microspheres with a particle size D50 of 12μm; wherein the mass ratio of the glucose to the defect-repaired intermediate is 0.05:1, the mass ratio of the zirconium oxide to the defect-repaired intermediate is 0.01:1, and the rotation speed of the wet sand milling is 1200rpm.

[0062] (4) The precursor microspheres are subjected to a one-stage sintering and a two-stage sintering with increasing temperatures in sequence in a nitrogen atmosphere, and after sieving, a regenerated lithium manganese iron phosphate positive electrode material is obtained; wherein the one-stage sintering temperature is 250°C, and the holding time is 5h; the two-stage sintering temperature is 700°C, and the holding time is 15h.

[0063] Example 3

[0064] The embodiment provides a method for regenerating a lithium manganese iron phosphate positive electrode material, and the method comprises the following steps:

[0065] (1) An old lithium manganese iron phosphate battery is discharged and disassembled to obtain a positive electrode sheet, and then the binder in the positive electrode sheet is removed, and the current collector and the positive electrode active material are separated by filtration, and then the positive electrode active material is subjected to acid washing to remove surface impurities, and after crushing, a recovered lithium manganese iron phosphate powder is obtained.

[0066] (2) The recovered lithium manganese iron phosphate powder, tannic acid and lithium acetate are mixed, deionized water is added, and then transferred to a reaction kettle to carry out a hydrothermal reaction for 12h at a temperature of 180°C to obtain a defect-repaired intermediate; wherein the mass ratio of the tannic acid to the recovered lithium manganese iron phosphate powder is 1:1, and the mass ratio of the lithium acetate to the recovered lithium manganese iron phosphate powder is 0.4:1.

[0067] (3) analyzing the content of Li, Fe and Mn elements in the defect-repaired intermediate to obtain a content analysis result, and then determining the adding amount of lithium source, manganese source and phosphorus source according to the content analysis result and the required element molar ratio of the target product (chemical formula LiMn 0.6 Fe 0.4 PO4).

[0068] wet sand milling the defect-repaired intermediate, lithium hydroxide monohydrate, manganese acetate, phosphoric acid, glucose and zirconium oxide in a sand mill to obtain a mixed slurry with a particle size D50 of 0.28 μm, and then spray drying the mixed slurry to obtain precursor microspheres with a particle size D50 of 12 μm; wherein the mass ratio of the glucose to the defect-repaired intermediate is 0.2:1, the mass ratio of the zirconium oxide to the defect-repaired intermediate is 0.03:1, and the rotation speed of the wet sand milling is 1200 rpm.

[0069] (4) performing one-stage sintering and two-stage sintering on the precursor microspheres in a nitrogen atmosphere with increasing temperature, and obtaining regenerated manganese iron lithium phosphate positive electrode material after sieving; wherein the temperature of the one-stage sintering is 350℃, and the holding time is 2h; the temperature of the two-stage sintering is 800℃, and the holding time is 10h.

[0070] Example 4

[0071] The difference between this embodiment and Example 1 is that the mass ratio of the tannic acid to the manganese iron lithium phosphate powder to be recycled is 0.1:1.

[0072] The rest of the methods and parameters remain the same as in Example 1.

[0073] Example 5

[0074] The difference between this embodiment and Example 1 is that the mass ratio of the tannic acid to the manganese iron lithium phosphate powder to be recycled is 1.2:1.

[0075] The rest of the methods and parameters remain the same as in Example 1.

[0076] Example 6

[0077] The difference between this embodiment and Example 1 is that the mass ratio of the lithium acetate to the manganese iron lithium phosphate powder to be recycled is 0.05:1.

[0078] The rest of the methods and parameters remain the same as in Example 1.

[0079] Example 7

[0080] The difference between this example and Example 1 is that the mass ratio of the lithium acetate to the defective intermediate is 0.5:1.

[0081] The rest of the method and parameters remain consistent with Example 1.

[0082] The rest of the method and parameters remain consistent with Example 1.

[0083] Example 8

[0084] The difference between this example and Example 1 is that the mass ratio of the zirconium oxide to the defective intermediate is 0.005:1.

[0085] The rest of the method and parameters remain consistent with Example 1.

[0086] Example 9

[0087] The difference between this example and Example 1 is that the mass ratio of the zirconium oxide to the defective intermediate is 0.05:1.

[0088] The rest of the method and parameters remain consistent with Example 1.

[0089] Example 10

[0090] The difference between this example and Example 1 is that only one step of sintering is performed in step (4), i.e., sintering at 750°C for 15.5h.

[0091] The rest of the method and parameters remain consistent with Example 1.

[0092] Comparative Example 1

[0093] The difference between this comparative example and Example 1 is that the lithium acetate in step (2) is replaced with equal mass of tannic acid.

[0094] The rest of the method and parameters remain consistent with Example 1.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 1 is that the tannic acid in step (2) is replaced with equal mass of lithium acetate.

[0097] The rest of the method and parameters remain consistent with Example 1.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 1 is that no zirconium oxide is added in step (3).

[0100] The rest of the method and parameters remain consistent with Example 1.

[0101] Performance Test

[0102] The regenerated lithium manganese iron phosphate positive electrode material provided in the above examples and comparative examples is assembled into a battery according to the following method:

[0103] The lithium manganese iron phosphate positive electrode material, SP (conductive carbon black), PVDF (polyvinylidene fluoride) and NMP (N-methyl pyrrolidone) are stirred for 2 h by a ball mill stirrer at a mass ratio of 8:1:1:12 to obtain a positive electrode slurry. The prepared positive electrode slurry is evenly coated on an aluminum foil by a doctor blade, and then dried at 130°C and rolled to obtain a positive electrode sheet. A lithium metal sheet is used as a negative electrode, a Celgard 2500 microporous membrane is used as a separator, and a 1 mol / L LiPF6 solution is used as an electrolyte, wherein the solvent of the electrolyte is a mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) at a volume ratio of 1:1:1. A button cell is assembled in a glove box.

[0104] The above button cell is subjected to charge-discharge performance test and cycle performance test.

[0105] The test conditions of the charge-discharge performance include: first circle, constant current charging at 0.1C (1C=170mAh / g) to 4.5V, then constant voltage charging at 4.5V to less than 0.01C, and finally constant current discharging at 0.1C to less than 2.5V. The charge-discharge process of the cycle test is the same as the above, but the constant current charging and discharging process is at 1C, and the cycle number is 300 cycles. The test results are shown in Table 1.

[0106] Table 1

[0107]

[0108] Analysis:

[0109] As shown in Table 1, the present application proposes a synergistic regeneration mechanism of "tannic acid + lithium acetate", wherein the phenolic hydroxyl and carboxyl groups in the tannic acid molecules can selectively chelate the dissolved Fe 3+ / Mn 3+ oxide impurities to form soluble metal-tannic acid complexes. The simultaneously added lithium acetate not only provides free Li +The embedded lithium vacancies in the lattice can repair the lithium vacancies, and the anions generated by the decomposition can prevent the excessive acidification of tannic acid, maintain the pH stability of the reaction system, prevent the excessive dissolution of Mn / Fe, and retain the lattice integrity. Therefore, the synergistic regeneration mechanism simultaneously realizes the precise removal of surface impurities and the in-situ repair of lithium vacancies in the bulk phase. Second, the introduced doped metal oxides can enter the lattice, widening the lithium ion migration channel and improving the intrinsic ionic conductivity and structural stability of the material. Finally, the addition of carbon source not only prevents the oxidation of divalent iron, but also can coat the material to improve the conductivity of the material. In summary, the process not only realizes the low-cost and low-energy regeneration of waste lithium manganese iron phosphate positive electrode materials, but also realizes the efficient repair of the microstructure, and finally obtains a regenerated lithium manganese iron phosphate positive electrode material with stable structure and excellent electrochemical performance.

[0110] As can be seen from the comparison of Example 1 and Examples 4-5, if the mass ratio of tannic acid to the lithium manganese iron phosphate powder to be recovered is too small, there will be too many residual impurities, which will affect the battery capacity; if the mass ratio of tannic acid to the lithium manganese iron phosphate powder to be recovered is too large, it may further damage the material structure.

[0111] As can be seen from the comparison of Example 1 and Examples 6-7, if the mass ratio of lithium acetate to the lithium manganese iron phosphate powder to be recovered is too small, it is not conducive to defect repair; if the mass ratio of lithium acetate to the lithium manganese iron phosphate powder to be recovered is too large, there will be a high lithium residue.

[0112] As can be seen from the comparison of Example 1 and Examples 8-9, if the mass ratio of zirconium oxide to the defect repair intermediate is too small, it is not conducive to the full regulation of the structure; if the mass ratio of zirconium oxide to the defect repair intermediate is too large, the excess zirconium oxide cannot enter the lithium manganese iron phosphate, but instead reduces the reactivity due to its non-reactivity and low conductivity.

[0113] As can be seen from the comparison of Example 1 and Example 10, if only one step of sintering is performed in step (4) instead of using temperature-increasing segmented sintering, the sintering speed is too fast, and the supplemented elements cannot be uniformly distributed to form a complete structure.

[0114] As can be seen from the comparison of Example 1 and Comparative Examples 1-2, if the lithium acetate in step (2) is replaced with an equal amount of tannic acid, the material structure cannot be repaired; if the tannic acid in step (2) is replaced with an equal amount of lithium acetate, the final material contains many impurities, which affects the battery capacity.

[0115] As can be seen from the comparison of Example 1 and Comparative Example 3, if no zirconium oxide is added in step (3), the structural stability of the material cannot be further improved.

[0116] It should be noted that the process of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, that is, it does not mean that the present application must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present application, equivalent replacement of the raw materials selected by the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the scope of protection and disclosure of the present application.

Claims

1. A method of regenerating a lithium iron manganese phosphate cathode material, characterized in that, The method comprises the following steps: providing a lithium iron manganese phosphate powder to be recycled; mixing the lithium iron manganese phosphate powder, tannic acid and lithium acetate, and performing a hydrothermal reaction to obtain a defect-repaired intermediate; mixing the defect-repaired intermediate, a lithium source, a manganese source, a phosphorus source, a carbon source and a doped metal oxide, and then performing post-processing to obtain a precursor microsphere; performing sintering treatment on the precursor microsphere to obtain a regenerated lithium iron manganese phosphate positive electrode material.

2. The method of claim 1, wherein, The mass ratio of the tannic acid to the lithium iron manganese phosphate powder is (0.3-1):1; Preferably, the mass ratio of the lithium acetate to the lithium iron manganese phosphate powder is (0.1-0.4):

1.

3. The method according to claim 1 or 2, characterized in that, During the hydrothermal reaction, the temperature is 180-250°C; Preferably, the hydrothermal reaction time is 8-12h.

4. The method according to any one of claims 1 to 3, characterized in that, According to the content of each element in the defect-repaired intermediate and the required element molar ratio of the target product, the addition amount of the lithium source, the manganese source and the phosphorus source is determined; Preferably, the lithium source comprises lithium hydroxide, lithium carbonate or lithium oxalate, or a combination of any one or at least two thereof; Preferably, the manganese source comprises manganese carbonate, manganese acetate, manganese oxide, or a combination of any one or at least two thereof; Preferably, the phosphorus source comprises monohydrogen lithium phosphate, dihydrogen lithium phosphate or phosphoric acid, or a combination of any one or at least two thereof; Preferably, the carbon source comprises glucose, sucrose or citric acid, or a combination of any one or at least two thereof; Preferably, the mass ratio of the carbon source to the defect-repaired intermediate is (0.05-0.2):

1.

5. The method according to any one of claims 1 to 4, characterized in that, The doped metal oxide comprises zirconium oxide, titanium oxide, aluminum oxide, copper oxide or magnesium oxide, or a combination of any one or at least two thereof; Preferably, the mass ratio of the doped metal oxide to the defect-repaired intermediate is (0.01-0.03):

1.

6. The method according to any one of claims 1 to 5, characterized in that, The post-processing step comprises sand milling and spray drying; Preferably, the sand milling speed is 1000-1500rpm; Preferably, the particle size D50 of the precursor microsphere is 8-15μm.

7. The method according to any one of claims 1 to 6, characterized in that, The sintering treatment atmosphere is an inert atmosphere; Preferably, the sintering treatment is a segmented sintering, which comprises a one-stage sintering and a two-stage sintering with increasing temperature; Preferably, the one-stage sintering temperature is 250-350°C, and the holding time is 2-5h; Preferably, the two-stage sintering temperature is 700-800°C, and the holding time is 10-15h.

8. The method according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: (1) discharging and disassembling a waste lithium iron manganese phosphate battery to obtain a positive electrode sheet, then removing the binder in the positive electrode sheet, and filtering and separating the current collector and the positive electrode active material, and then performing acid washing on the positive electrode active material to remove surface impurities, and crushing to obtain a lithium iron manganese phosphate powder to be recycled; (2) mixing the lithium iron manganese phosphate powder to be recycled, tannic acid and lithium acetate, adding water, and then transferring to a reaction kettle to perform a hydrothermal reaction for 8-12 hours at a temperature of 180-250 DEG C, to obtain a defect-repaired intermediate; wherein the mass ratio of the tannic acid to the lithium iron manganese phosphate powder is (0.3-1):1, and the mass ratio of the lithium acetate to the lithium iron manganese phosphate powder is (0.1-0.4):1; (3) analyzing the content of Li, Fe and Mn elements in the defect-repaired intermediate to obtain a content analysis result, and then determining the addition amount of lithium source, manganese source and phosphorus source according to the content analysis result and the required element molar ratio of the target product; wet sand grinding the defect-repaired intermediate, lithium source, manganese source, phosphorus source, carbon source and doped metal oxide in a sand mill to a particle size D50 of 0.25-0.4 microns to obtain a mixed slurry, and then spray drying the mixed slurry to obtain precursor microspheres with a particle size D50 of 8-15 microns; wherein the doped metal oxide includes any one or a combination of at least two of zirconium oxide, titanium oxide, aluminum oxide, copper oxide or magnesium oxide; the mass ratio of the carbon source to the defect-repaired intermediate is (0.05-0.2):1, the mass ratio of the doped metal oxide to the defect-repaired intermediate is (0.01-0.03):1, and the rotation speed of the wet sand grinding is 1000-1500 rpm; (4) performing one-stage sintering and two-stage sintering on the precursor microspheres in an inert atmosphere with increasing temperature, and obtaining regenerated lithium iron manganese phosphate positive electrode material after sieving; wherein the one-stage sintering temperature is 250-350 DEG C, and the holding time is 2-5 hours; the two-stage sintering temperature is 700-800 DEG C, and the holding time is 10-15 hours.

9. A lithium iron manganese phosphate cathode material, characterized in that, The lithium iron manganese phosphate positive electrode material is prepared by the method of any one of claims 1-8.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises the lithium iron manganese phosphate positive electrode material of claim 9. The lithium ion battery comprises the lithium iron manganese phosphate positive electrode material of claim 9.

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