A solid phase repair and regeneration method for waste lithium iron phosphate positive electrode material and regenerated positive electrode material

Abstract

The present invention discloses a solid-phase repair and regeneration method for waste lithium iron phosphate positive electrode materials and a regenerated positive electrode material, belonging to the technical field of waste lithium-ion battery resource utilization. The solid-phase repair and regeneration method of the present invention comprises: mixing the waste lithium iron phosphate material with NH4H2PO4 powder in solid phase, carrying out a first reaction under an air atmosphere, adding lithium salt according to a stoichiometric ratio after the reaction is completed, carrying out a second reaction to obtain an intermediate material; washing with alcohol and water, drying to obtain a dry material; after heat treatment, adding an iron source, a carbon source and water to mix, granulating, drying, sintering, obtaining a sintered product, crushing, grading and sorting to obtain a regenerated lithium iron phosphate material. The solid-phase repair and regeneration method of the present invention can controllably remove impurities in the recycled material, and can balance the differences between different incoming materials. It is suitable for quantitative production and solves the fundamental problem of lithium iron phosphate repair and regeneration.

Description

Technical Field

[0001] The present invention relates to the technical field of resource recovery of waste lithium-ion batteries, and in particular to a solid-phase repair and regeneration method for waste lithium iron phosphate positive electrode materials and a regenerated positive electrode material. Background Art

[0002] Although there are many technologies for repairing and regenerating lithium iron phosphate, they are basically centered around impurity removal, element addition, and solid-phase sintering, and have not solved the practical application problems of solid-phase repair and regeneration. The core problems of the current batch repair and regeneration of lithium iron phosphate include: (1) Al, Fe, and C impurities in the recycled materials exceed the standard. Among them, Al impurities are introduced by the current collector and are mostly removed by alkali washing + water washing. However, lithium iron phosphate materials have side reactions in alkaline systems, which can easily cause changes in the material structure and introduce new impurities; Fe impurities are introduced inside the material contact equipment and there is currently no suitable method to remove them. The introduced iron impurities can easily cause self-discharge of the battery, greatly reducing the battery life and safety; C impurities come from the binder, conductive agent, and the coating layer of the material. The existing technology is to remove them in a trace oxygen atmosphere, but it can easily lead to oxidation of the lithium iron phosphate material, the reaction conditions are difficult to control, and the batch consistency of the material is poor. (2) The lithium iron phosphate produced by various manufacturers is quite different, and the product iterations of the same manufacturer are also very frequent, resulting in great differences in the physical and chemical properties of the recycled lithium iron phosphate materials, including obvious differences in basic properties such as morphology, particle size, specific surface area, tap compaction, and capacity. Since the solid-phase repair method cannot balance the differences between different incoming materials, it cannot be mass-produced and is currently only in the small-batch trial stage.

[0003] Therefore, it is urgent to study new solid-phase repair and regeneration methods for waste lithium iron phosphate positive electrode materials to solve the above problems. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention provides a solid-phase repair and regeneration method for waste lithium iron phosphate cathode materials and a regenerated cathode material. This solid-phase repair and regeneration method can controllably remove impurities from the recycled material and balance the differences between different incoming materials, making it suitable for mass production and resolving fundamental issues in the repair and regeneration of lithium iron phosphate.

[0005] The technical solutions of the present invention are as follows:

[0006] A first aspect of the present invention provides a solid-phase repair and regeneration method for waste lithium iron phosphate positive electrode materials, the solid-phase repair and regeneration method comprising the following steps:

[0007] S1: After mixing the waste lithium iron phosphate material with NH4H2PO4 powder in solid phase, the first reaction is carried out under air atmosphere. After the reaction is completed, lithium salt is added according to the stoichiometric ratio and a second reaction is carried out to obtain an intermediate material.

[0008] S2: The intermediate material is washed with alcohol and water, and then dried to obtain a dry material.

[0009] S3: The dried material is subjected to heat treatment to obtain a heat-treated material.

[0010] S4: Then, an iron source, a carbon source and water are added to the heat-treated material to obtain a mixed material, which is granulated, dried and sintered to obtain a sintered product.

[0011] S5: Crushing, grading and sorting the sintered product to obtain regenerated lithium iron phosphate material.

[0012] Preferably, in step S1, the waste lithium iron phosphate material and the NH4H2PO4 powder are mixed in a stoichiometric ratio.

[0013] Preferably, in step S1, the temperature of the first reaction is 180-195° C., and the time is 6-10 h.

[0014] Preferably, in step S1, the lithium salt is Li2CO3.

[0015] Preferably, in step S1, the temperature of the second reaction is 180-195° C., and the time is 4-6 hours.

[0016] Preferably, in step S2, the raw material for the alcohol wash includes at least one of ethanol, methanol, and isopropanol; and / or the solid content of the alcohol wash is controlled to be 10-20%; and / or the number of alcohol washes is 3-4 times; and / or the solid content of the water wash is 30-50%; and / or the number of water washes is 1-2 times; and / or the drying temperature is 80-120°C.

[0017] Preferably, in step S3, the temperature of the heat treatment is 450-550° C., and / or the time of the heat treatment is 2-4 hours, and / or the atmosphere of the heat treatment is air or oxygen.

[0018] Preferably, in step S4, the iron source includes ferric phosphate and other iron sources; the other iron sources include at least one of ferrous oxalate, ferrous citrate, and ferric oxide; the carbon source includes at least one of starch and glucose; the molar ratio of the Li3PO4 precursor in the heat-treated material to the ferric phosphate in the mixed material is 1:2, and the molar ratio of the Li3PO4 precursor in the heat-treated material to the iron element in the other iron sources is 1:1; the amount of carbon source added is such that the carbon content of the sintered product accounts for 1.2-1.5wt% of the sintered product.

[0019] Preferably, in step S4, the granulation is performed by ball milling or sand milling; and / or the sintering temperature is 700-820° C., and the sintering time is 8-15 h.

[0020] The second aspect of the present invention provides a repaired and regenerated lithium iron phosphate positive electrode material prepared by the solid-phase repair and regeneration method described in the first aspect.

[0021] The beneficial technical effects of the present invention are:

[0022] The lithium iron phosphate solid-phase regeneration technology of the present invention sequentially heats waste lithium iron phosphate material with ammonium dihydrogen phosphate and lithium carbonate to convert the iron and lithium elements in the lithium iron phosphate into iron phosphate and lithium phosphate in the solid phase, while also removing the aluminum and iron impurities. Subsequently, the material is heated again at high temperature to remove the binder and conductive agent impurities, resulting in pure iron phosphate and lithium phosphate precursors. This precursor is then mixed with an iron source and a carbon source and sintered again to obtain the regenerated lithium iron phosphate material.

[0023] The regeneration method of the present invention does not require a complex leaching and precipitation process, has a short process flow, does not require acid or alkali solution, has low energy consumption, and has little pollution. At the same time, the present invention converts waste lithium iron phosphate into iron phosphate and lithium phosphate precursors. The converted precursors can be more flexibly granulated, coated and sintered again. The particle size, morphology and content of the regenerated product are controllable. The regeneration method has high compatibility and practicality, can control the quality of the product, and is suitable for scaled-up application. DETAILED DESCRIPTION

[0024] The present invention will be described in detail below with reference to the embodiments.

[0025] The first aspect of the present invention provides a solid phase repair and regeneration method for waste lithium iron phosphate positive electrode materials, comprising the following steps:

[0026] S1: Mix the waste lithium iron phosphate material with NH4H2PO4 powder in the solid phase, press the powder after mixing evenly, and carry out the first reaction under air atmosphere. After the reaction is completed, add lithium salt according to the stoichiometric ratio (i.e., the amount of lithium salt added is determined according to reaction equations (4)-(7)) and carry out the second reaction to obtain the intermediate material.

[0027] S2: The intermediate material is washed with alcohol and water, and then dried to obtain a dry material.

[0028] S3: The dried material is subjected to heat treatment to obtain a heat-treated material.

[0029] S4: Then, an iron source, a carbon source and water are added to the heat-treated material, mixed, granulated, dried and sintered to obtain a sintered product.

[0030] S5: Crushing and classifying the sintered products to obtain regenerated lithium iron phosphate materials.

[0031] It is understandable that the present invention converts the iron and lithium elements in the lithium iron phosphate into iron phosphate and lithium phosphate in the solid phase by heating the waste lithium iron phosphate material with ammonium dihydrogen phosphate and lithium carbonate in sequence, and can also remove the impurities of aluminum and iron. Then, the binder and conductive agent impurities are removed by high-temperature heating again to obtain pure iron phosphate and lithium phosphate precursors. The precursors are further mixed with iron source and carbon source and sintered again to obtain regenerated lithium iron phosphate material. The regeneration method does not require a complicated leaching and precipitation process, has a short process flow, does not require acid and alkali solution, has low energy consumption, and has little pollution. At the same time, the present invention converts waste lithium iron phosphate into iron phosphate and lithium phosphate precursors. The converted precursors can be granulated, coated and sintered more flexibly again. The particle size, morphology and content of the regenerated product are controllable. The regeneration method has high compatibility and practicality, can control the quality of the product, and is suitable for scaled-up application.

[0032] In some embodiments, step S1 is: solid-phase mixing of waste lithium iron phosphate material and NH4H2PO4 powder, compacting the powder after mixing evenly, and performing a first high-temperature reaction under air atmosphere. The specific reaction formula is as follows:

[0033] 2LiFePO4+2NH4H2PO4+1 / 2O2→2LiH2PO4+2FePO4+2NH3+H2O (1);

[0034] 2Al+6NH4H2PO4→2Al(H2PO4)3+6NH3+3H2 (2);

[0035] Fe+2NH4H2PO4→Fe(H2PO4)2+2NH3+H2 (3);

[0036] After the reaction is completed, lithium salt is added according to the stoichiometric ratio to carry out a second reaction to obtain an intermediate material; in the second reaction,

[0037] The reaction formula of the second high temperature reaction includes:

[0038] LiH2PO4+Li2CO3→Li3PO4+CO2+H2O (4);

[0039] Al(H2PO4)3+3Li2CO3→2Li3PO4+AlPO4+3CO2+3H2O (5);

[0040] 3Fe(H2PO4)2+6Li2CO3→4Li3PO4+Fe3(PO4)2+6CO2+6H2O (6);

[0041] Fe3(PO4)2+3 / 2H2O+3 / 4O2→Fe(OH)3+2FePO4 (7).

[0042] It is understandable that after the first reaction, the impurity iron and aluminum in the waste lithium iron phosphate material can be converted into Fe(H2PO4)2 and Al(H2PO4)3. The lithium iron phosphate material will also generate LiH2PO4 and FePO4 under the action of NH4H2PO4 and oxygen. Among them, LiH2PO4 can react with the added lithium salt to generate Li3PO4 in the second reaction. The converted Li3PO4 and FePO4 can be used as precursors for synthesizing lithium iron phosphate again. After the impurity iron and aluminum are converted into Fe(H2PO4)2 and Al(H2PO4)3, they can react with the added lithium salt to obtain AlPO4, FePO4 and Fe(OH)3. Among them, AlPO4 can be dissolved and removed in step S2, and FePO4 and Fe(OH)3 can continue to be used to synthesize regenerated lithium iron phosphate.

[0043] In some embodiments, in step S1, the amounts of the waste lithium iron phosphate material and the NH4H2PO4 powder are determined according to a stoichiometric ratio, specifically a molar ratio determined according to reaction formulas (1)-(3), and the specific ratio needs to be determined according to the composition.

[0044] In some embodiments, in step S1, the temperature of the first reaction is 180-195° C., and the time is 6-10 h.

[0045] In some embodiments, in step S1, the lithium salt is Li2CO3.

[0046] In some embodiments, in step S1, the temperature of the second reaction is 180-195° C., and the time is 4-6 hours.

[0047] In some embodiments, in step S2, the raw material for alcohol washing includes at least one of ethanol, methanol, and isopropanol.

[0048] In some embodiments, the solid content of the alcohol wash is controlled to be 10-20%.

[0049] In some embodiments, the alcohol washing is performed 3-4 times.

[0050] In some embodiments, the water wash has a solid content of 30-50%.

[0051] In some embodiments, the water washing is performed 1-2 times.

[0052] In some embodiments, the drying temperature is 80-120°C.

[0053] It is understandable that the material after the second high-temperature reaction is washed with alcohol and water and then dried to remove AlPO4 and some soluble impurities.

[0054] In some embodiments, in step S3, the heat treatment temperature is 450-550° C., and / or the heat treatment time is 2-4 hours.

[0055] In some embodiments, the heat treatment atmosphere is air or oxygen.

[0056] It is understood that during the third heat treatment, the iron phosphate recrystallizes, and at the same time, the binder, conductive agent, and carbon impurities are oxidized and removed. After the reaction is completed, the waste lithium iron phosphate is converted into Li3PO4 and FePO4 (containing a small amount of Fe2O3). The chemical changes during the heat treatment process include:

[0057] PVDF+O2→HF+H2O+CO+CO2 (8);

[0058] C+O2→CO2 (9);

[0059] 2Fe(OH)3→Fe2O3+3H2O (10).

[0060] In some embodiments, in step S4, the iron source includes but is not limited to iron phosphate; the iron source includes iron phosphate and other iron sources; the other iron sources include at least one of ferrous oxalate, ferrous citrate, and ferric oxide; the carbon source includes at least one of starch and glucose; in the heat-treated material, the molar ratio of the Li3PO4 precursor in the heat-treated material to the iron phosphate in the mixed material is 1:2, and the molar ratio of the Li3PO4 precursor in the heat-treated material to the iron element in the other iron sources is 1:1; and the carbon source is added in an amount such that the final carbon content accounts for 1.2-1.5wt% of the sintered product. The present invention does not limit the amount of water added, as long as it can achieve granulation. For example, the amount of water added can be such that the overall solid content is 30-50% after the water is added.

[0061] In some embodiments, in step S4, the granulation is performed by ball milling or sand milling; and / or the sintering temperature is 700-820° C., and the sintering time is 8-15 h.

[0062] In some embodiments, step S4 comprises: adding an iron source, a carbon source, and water to the heat-treated material and mixing them uniformly, then performing ball milling / sand milling to granulate the material according to the particle size requirements, controlling the appropriate particle size range, then drying to evaporate the water, and finally sintering the material under a nitrogen atmosphere to obtain a sintered product. The reaction process is as follows:

[0063] Li3PO4+Fe 2+ / 3+ +2FePO4+carbon source→3LiFePO4+CO2+H2O (11).

[0064] The second aspect of the present invention provides a repaired and regenerated lithium iron phosphate positive electrode material prepared by the solid-phase repair and regeneration method described in the first aspect.

[0065] The following are specific examples.

[0066] Example 1

[0067] A solid phase repair and regeneration method for waste lithium iron phosphate positive electrode materials comprises the following steps:

[0068] (1) According to the stoichiometric ratio, 500.00 g of waste lithium iron phosphate material (0.21 wt% aluminum impurities and 0.02 wt% iron impurities) was solid-phase mixed with 364.60 g of NH4H2PO4 powder. After mixing evenly, the mixture was reacted at 180 ° C in an air atmosphere for 10 h (first high-temperature reaction). Subsequently, 234.20 g of lithium carbonate powder was added according to the stoichiometric ratio and reacted at 195 ° C for 4 h (second high-temperature reaction).

[0069] (2) After the reaction, the mixture was washed three times with ethanol solvent to control the solid content to 10%, and then washed twice with water to control the solid content to 50%. The mixture was then dried at 80°C.

[0070] (3) The dried material was heat treated at 550°C in air for 4 h.

[0071] (4) Battery-grade ferrous oxalate powder (450.21 g), ferric phosphate powder (483.91 g), and glucose (260.43 g) were added in a stoichiometric ratio and mixed with water (3.0 L). After mixing evenly, the mixture was ball-milled / sand-milled to control D50 < 1 μm and Dmax < 12 μm, followed by spray drying and finally heat treatment at 700 °C for 15 h under a nitrogen atmosphere.

[0072] (5) After sintering, the regenerated lithium iron phosphate material is obtained by crushing, grading and sorting.

[0073] Example 2:

[0074] A solid phase repair and regeneration method for waste lithium iron phosphate positive electrode materials comprises the following steps:

[0075] (1) According to the stoichiometric ratio, 1250.00 g of waste lithium iron phosphate material (0.18 wt% aluminum impurities and 0.03 wt% iron impurities) was solid-phase mixed with 906.57 g of NH4H2PO4 powder. After mixing evenly, the mixture was reacted at 195°C in an air atmosphere for 6 h. Subsequently, 582.34 g of lithium carbonate powder was mixed and reacted at 180°C for 6 h.

[0076] (2) After the reaction, methanol was used to control the solid content to 10%, and the mixture was washed three times. Water was used to control the solid content to 40%, and the mixture was washed twice. The mixture was dried at 120°C after washing.

[0077] (3) The dried material was heat treated at 450°C in an oxygen atmosphere for 6 h.

[0078] (4) The method is the same as that in Example 1, except that stoichiometric battery-grade Fe2O3 powder, iron phosphate powder (the mass ratio of iron phosphate powder to Fe2O3 powder is 1.93:1), and starch are added, and 5.5 L of water is added and mixed. After mixing evenly, ball milling / sand milling is performed to granulate the product, and D50 is controlled to be less than 1 μm and Dmax is controlled to be less than 12 μm. After spray drying, the product is heat treated at 820°C for 11 h in a nitrogen atmosphere.

[0079] (5) After sintering, the regenerated lithium iron phosphate material is obtained by crushing, grading and sorting.

[0080] Example 3:

[0081] A solid phase repair and regeneration method for waste lithium iron phosphate positive electrode materials comprises the following steps:

[0082] (1) According to the stoichiometric ratio, 200 g of waste lithium iron phosphate material (0.17 wt% aluminum impurities and 0.02 wt% iron impurities) was solid-phase mixed with 144.79 g of NH4H2PO4 powder. After mixing evenly, the mixture was reacted at 190°C in an air atmosphere for 8 h. Subsequently, 93.00 g of lithium carbonate powder was added and reacted at 185°C for 4.5 h.

[0083] (2) After the reaction, the solid content was controlled to 20% by isopropyl alcohol and washed 4 times, and the solid content was controlled to 50% by water and washed once, and then dried at 100°C.

[0084] (3) The dried material was heat treated at 500°C for 5 h in an oxygen atmosphere.

[0085] (4) The method is the same as that in Example 1, except that battery-grade ferrous citrate powder, ferric phosphate powder (the mass ratio of ferric phosphate powder to ferrous citrate powder is 0.62:1), and glucose are added in a stoichiometric ratio, and 1.5 L of water is added and mixed. After mixing evenly, ball milling / sand milling is performed to granulate the mixture, and D50 is controlled to be less than 1 μm and Dmax is controlled to be less than 12 μm. After spray drying, the mixture is heat treated at 750°C under a nitrogen atmosphere for 8 h.

[0086] (5) After sintering, the regenerated lithium iron phosphate material is obtained by crushing, grading and sorting.

[0087] Comparative Example 1:

[0088] A solid phase repair and regeneration method for waste lithium iron phosphate positive electrode materials comprises the following steps:

[0089] The waste lithium iron phosphate material was placed in a 1.5 mol / L sodium hydroxide solution with a solid content of 20%. After reacting for 1 hour, it was washed to a neutral pH, dried at 100°C, sintered at 600°C in a nitrogen atmosphere for 3 hours, and separated by airflow to obtain the regenerated lithium iron phosphate material.

[0090] Comparative Example 2:

[0091] A solid-phase repair and regeneration method for waste lithium iron phosphate positive electrode materials is basically the same as Example 1, except that the temperature and time of the first high-temperature reaction in step (1) are different. In this example, the temperature of the first high-temperature reaction is 210°C and the time is 8 hours.

[0092] Comparative Example 3:

[0093] A solid-phase repair and regeneration method for waste lithium iron phosphate positive electrode materials is basically the same as Example 1, except that the temperature and time of the second high-temperature reaction in step (1) are different. In this example, the temperature of the second high-temperature reaction is 240°C and the time is 5 hours.

[0094] Comparative Example 4:

[0095] A solid-phase repair and regeneration method for waste lithium iron phosphate positive electrode materials is basically the same as Example 1, except that the temperature and time of the first and second high-temperature reactions in step (1) are as follows: in this example, the temperature of the first high-temperature heating is 210°C and the time is 6 hours; the temperature of the second high-temperature heating is 240°C and the time is 4 hours.

[0096] Comparative Example 5:

[0097] A solid phase repair and regeneration method for waste lithium iron phosphate positive electrode material is basically the same as Example 1, except that the temperature of the heat treatment in step (3) is 600°C and the time is 4 hours.

[0098] Comparative Example 6:

[0099] A solid phase repair and regeneration method for waste lithium iron phosphate positive electrode material is basically the same as Example 1, except for the solid content and washing times of the ethanol solvent washing in step (2); in this embodiment, the solid content of the alcohol washing is adjusted to 30% and the washing is performed once.

[0100] Test example:

[0101] The lithium iron phosphate cathode materials regenerated in the test examples and comparative examples were tested using the following test methods:

[0102] (1) Aluminum content test: After the regenerated lithium iron phosphate material was dissolved in aqua regia and fixed to volume, the aluminum content in the sample was determined by inductively coupled plasma emission spectrometry.

[0103] (2) Carbon content test: The sample is heated in a high-temperature furnace and combusted with oxygen, so that the carbon in the sample is quantitatively oxidized to CO2. The mixed gas is collected in a gas burette after passing through a desulfurizer, and the volume is measured. The mixed gas is then passed through an absorber filled with potassium hydroxide solution to absorb the CO2, and the remaining oxygen is returned to the gas burette. The difference in volume before and after absorption is the volume of CO2 generated, which is converted into carbon content based on the volume of CO2.

[0104] (3) Gram capacity test: The regenerated sample was mixed with PVDF binder and super P conductive agent in a ratio of 97.5:1.5:1.0, coated, and roll-pressed to form a positive electrode sheet. The positive electrode was then assembled into a button cell with a lithium sheet as the counter electrode. The electrolyte used was 1 mol / L lithium hexafluorophosphate (EC:DEC=1:1). The charge and discharge test was carried out at a rate of 0.05C.

[0105] The test results are shown in the following table.

[0106] Table 1 Tests of the positive electrode materials after repair in the examples and comparative examples

[0107] Aluminum impurities Carbon content 0.1C gram capacity Example 1 41ppm 1.35％ 156.4mAh / g Example 2 62ppm 1.32％ 155.1mAh / g Example 3 54ppm 1.38％ 156.6mAh / g Comparative Example 1 146ppm 2.21％ 154.1mAh / g Comparative Example 2 56ppm 1.38％ 142.4mAh / g Comparative Example 3 45ppm 1.44％ 146.7mAh / g Comparative Example 4 61ppm 1.50％ 139.2mAh / g Comparative Example 5 51ppm 1.37％ 155.0mAh / g Comparative Example 6 358ppm 1.41％ 156.1mAh / g

[0108] As can be seen from Table 1, the aluminum impurity and carbon content of the repaired positive electrode material obtained in the embodiment of the present invention are both within the standard range. Compared with the traditional solid-phase regeneration method in Comparative Example 1, the lithium iron phosphate regenerated by the present invention has high purity and high capacity.

[0109] Furthermore, preliminary experiments and a comparison of Example 1 and Comparative Examples 2-5 in Table 1 indicate that, in the repair method of the present invention, the temperatures for the first and second high-temperature reactions must be between 180°C and 195°C. Temperatures that are too low result in a slow reaction rate or even no reaction at all, while temperatures that are too high can easily produce impurities, affecting the purity of the material during subsequent synthesis. The third heat treatment temperature must be between 450°C and 550°C. Temperatures that are too low result in incomplete removal of carbon impurities, while temperatures that are too high can easily lead to increased energy consumption and increased costs.

[0110] Comparison of Example 1 and Comparative Example 6 shows that limiting the solid content and number of alcohol washings can improve the purity of the regenerated lithium iron phosphate.

[0111] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiment. It is understood that other improvements and variations directly derived or imagined by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the scope of protection of the present invention.

Claims

1. A solid phase repair and regeneration method for waste lithium iron phosphate positive electrode materials, characterized in that: The solid phase repair and regeneration method comprises the following steps: S1: After mixing the waste lithium iron phosphate material with NH4H2PO4 powder in solid phase, the mixture is subjected to a first reaction in an air atmosphere. After the reaction is completed, lithium salt is added according to a stoichiometric ratio and a second reaction is carried out to obtain an intermediate material; S2: washing the intermediate material with alcohol and water, and drying it to obtain a dry material; S3: The dried material is subjected to heat treatment to obtain a heat-treated material; S4: then adding an iron source, a carbon source and water to the heat-treated material to obtain a mixed material, granulating, drying and sintering to obtain a sintered product; S5: crushing and classifying the sintered product to obtain regenerated lithium iron phosphate material; In step S1, the temperature of the first reaction is 180-195° C. and the time is 6-10 hours; In step S1, the temperature of the second reaction is 180-195° C. and the time is 4-6 hours; In step S2, the solid content of the alcohol washing is controlled to be 10-20%; the number of alcohol washings is 3-4 times; In step S3, the heat treatment temperature is 450-550° C., and / or the heat treatment time is 2-4 hours.

2. The solid phase repair and regeneration method according to claim 1, characterized in that: In step S1, the waste lithium iron phosphate material and the NH4H2PO4 powder are mixed according to a stoichiometric ratio.

3. The solid phase repair and regeneration method according to claim 1, characterized in that: In step S1, the lithium salt is Li2CO3.

4. The solid phase repair and regeneration method according to claim 1, characterized in that: In step S2, the raw material for alcohol washing includes at least one of ethanol, methanol, and isopropanol; and / or, The solid content of the water washing is 30-50%; and / or, The number of times of washing is 1-2 times; and / or, The drying temperature is 80-120°C.

5. The solid phase repair and regeneration method according to claim 1, characterized in that: In step S3, the atmosphere of the heat treatment is air or oxygen.

6. The solid phase repair and regeneration method according to claim 1, characterized in that: In step S4, the iron source includes ferric phosphate and other iron sources; the other iron sources include at least one of ferrous oxalate, ferrous citrate, and ferric oxide; the carbon source includes at least one of starch and glucose; The molar ratio of the Li3PO4 precursor in the heat-treated material to the iron phosphate in the mixed material is 1:2, and the molar ratio of the Li3PO4 precursor in the heat-treated material to the iron element in the other iron sources is 1:1; the amount of the carbon source added is such that the carbon content of the sintered product accounts for 1.2-1.5wt% of the sintered product.

7. The solid phase repair and regeneration method according to claim 1, characterized in that: In step S4, the granulation is performed by ball milling or sand milling; and / or the sintering temperature is 700-820° C., and the sintering time is 8-15 hours.

8. A repaired and regenerated lithium iron phosphate positive electrode material prepared by the solid-phase repair and regeneration method according to any one of claims 1 to 7.