Regeneration and restoration method of waste lithium iron phosphate

Abstract

The invention relates to a waste lithium iron phosphate regeneration repair method, which comprises: crushing a waste lithium iron phosphate positive plate, and carrying out anaerobic pyrolysis on the obtained crushed material to obtain waste lithium iron phosphate positive powder; supplementing a lithium source, supplementing a phosphorus source, mixing with the waste lithium iron phosphate positive electrode powder, and carrying out reduction roasting to obtain a lithium iron phosphate repairing material; and screening and demagnetizing the obtained lithium iron phosphate repairing material to obtain the regenerative lithium iron phosphate. According to the regeneration repair method provided by the invention, a reducing agent does not need to be additionally added, and the carbon generated by anaerobic pyrolysis is used as a reducing agent for reducing roasting, so that the conductivity of the regeneration type lithium iron phosphate is improved, and the specific capacity, the cycle performance and the rate capability of the regeneration type lithium iron phosphate are also improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource recovery, relates to a method for recovering lithium iron phosphate, and in particular to a method for regenerating and repairing waste lithium iron phosphate. Background Art

[0002] At present, the recycling technologies for waste lithium iron phosphate mainly include wet recycling, pyrolysis recycling, and wet-pyrolysis combined recycling. However, existing recycling technologies often face many problems when processing waste lithium iron phosphate. For example, the recovered lithium iron phosphate material has a significant decline in key performance indicators such as specific capacity, rate performance, and cycle stability, making it difficult to meet the requirements for reuse. The possible reason is that during the recycling process, the crystal structure of lithium iron phosphate is destroyed and the lattice is distorted, which hinders the insertion and extraction of lithium ions and deteriorates the electrochemical properties of the material.

[0003] Furthermore, heat treatment is a key process in the recycling of waste lithium iron phosphate (LIFP), with the goal of removing residual organic matter from the material. However, in practice, there's a significant conflict between the removal of organic matter and the structural integrity of LFP. Completely removing organic matter typically requires higher heat treatment temperatures or longer treatment times. However, higher temperatures or extended treatment times can cause the LFP's crystal structure to collapse, destroying its structural integrity and further exacerbating the decline in material performance. Lowering the heat treatment temperature or shortening the treatment time can maintain the material's structure to a certain extent, but it fails to completely remove the organic matter. Residual organic matter can adversely affect the electrochemical properties of the recycled material.

[0004] To improve the performance of regenerated lithium iron phosphate, existing technologies typically use additional reducing agents for reduction roasting. However, the addition of additional reducing agents not only increases recycling costs but can also introduce impurities, affecting the purity and performance stability of the regenerated lithium iron phosphate, while also increasing process complexity.

[0005] Therefore, how to completely remove organic matter in the process of regenerating and repairing waste lithium iron phosphate while maintaining the integrity of the structure and without adding additional reducing agents is a technical problem that technicians in this field urgently need to overcome. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a regeneration and repair method for waste lithium iron phosphate. This regeneration and repair method does not require the addition of additional reducing agents, and relies on carbon generated by anaerobic pyrolysis as a reducing agent for reduction roasting. It not only improves the conductivity of the regenerated lithium iron phosphate, but also improves the specific capacity, cycle performance and rate performance of the regenerated lithium iron phosphate.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a regeneration and repair method for waste lithium iron phosphate, which comprises:

[0009] (1) crushing the waste lithium iron phosphate positive electrode sheets, and performing anaerobic pyrolysis on the crushed materials to obtain waste lithium iron phosphate positive electrode powder;

[0010] (2) supplementing the lithium source and the phosphorus source and mixing them with the waste lithium iron phosphate positive electrode powder described in step (1), and performing reduction roasting to obtain a lithium iron phosphate repair material;

[0011] (3) The lithium iron phosphate repair material obtained in step (2) is screened and demagnetized to obtain regenerated lithium iron phosphate.

[0012] The regeneration and repair method provided by the present invention does not require the additional use of a reducing agent, and the purpose of reduction can be achieved by relying solely on the charcoal produced by anaerobic pyrolysis. Moreover, the control of the anaerobic pyrolysis conditions can reduce the adverse effects of anaerobic pyrolysis on the crystal structure of lithium iron phosphate, thereby improving not only the conductivity of the regenerated lithium iron phosphate, but also the specific capacity, cycle performance and rate performance of the regenerated lithium iron phosphate.

[0013] In one embodiment of the present invention, the particle size D50 of the crushed material in step (1) is 10 μm to 50 μm.

[0014] In one embodiment of the present invention, the crushed material in step (1) is dried before anaerobic pyrolysis.

[0015] In one embodiment of the present invention, the drying temperature is 80° C. to 120° C., and the drying time is more than 2 hours.

[0016] In one embodiment of the present invention, the anaerobic pyrolysis in step (1) includes a first anaerobic pyrolysis and a second anaerobic pyrolysis performed sequentially.

[0017] In one embodiment of the present invention, the temperature of the first anaerobic pyrolysis is 450° C. to 550° C., and the time is 1 hour to 2 hours.

[0018] In one embodiment of the present invention, the temperature of the second anaerobic pyrolysis is 700° C. to 800° C., and the time is 1 hour to 2 hours.

[0019] In one embodiment of the present invention, the gauge pressure of the anaerobic pyrolysis in step (1) is 0.1 MPa to 0.2 MPa.

[0020] In one embodiment of the present invention, the heating rate of the anaerobic pyrolysis in step (1) is 5°C / min to 10°C / min.

[0021] In one embodiment of the present invention, the reduction roasting in step (2) is carried out in a protective atmosphere; the protective atmosphere includes nitrogen and / or an inert gas.

[0022] In one embodiment of the present invention, the temperature of the reduction roasting in step (2) is 650°C to 750°C.

[0023] As a preferred technical solution of the regeneration and repair method provided by the present invention, the regeneration and repair method comprises the following steps:

[0024] (1) crushing the waste lithium iron phosphate positive electrode sheets to obtain crushed materials with a particle size D50 of 10 μm to 50 μm; drying the obtained crushed materials at 80° C. to 120° C. for more than 2 hours; and then performing anaerobic pyrolysis to obtain waste lithium iron phosphate positive electrode powder;

[0025] The gauge pressure of the anaerobic pyrolysis is 0.1 MPa to 0.2 MPa; the anaerobic pyrolysis includes a first anaerobic pyrolysis and a second anaerobic pyrolysis performed sequentially, with a heating rate of 5°C / min to 10°C / min; the temperature of the first anaerobic pyrolysis is 450°C to 550°C, and the time is 1 hour to 2 hours; the temperature of the second anaerobic pyrolysis is 700°C to 800°C, and the time is 1 hour to 2 hours;

[0026] (2) supplementing the lithium source and the phosphorus source and mixing them with the waste lithium iron phosphate positive electrode powder in step (1), and performing reduction roasting in a protective atmosphere to obtain a lithium iron phosphate repair material;

[0027] The reduction roasting temperature is 650°C to 750°C;

[0028] (3) The lithium iron phosphate repair material obtained in step (2) is screened and demagnetized to obtain regenerated lithium iron phosphate.

[0029] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The regeneration and repair method provided by the present invention does not require the additional use of a reducing agent, and the purpose of reduction can be achieved only by relying on the charcoal produced by anaerobic pyrolysis. Moreover, the control of the anaerobic pyrolysis conditions can reduce the adverse effects of anaerobic pyrolysis on the crystal structure of lithium iron phosphate, which not only improves the conductivity of the regenerated lithium iron phosphate, but also improves the specific capacity, cycle performance and rate performance of the regenerated lithium iron phosphate. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0033] A certain embodiment of the present invention provides a method for regenerating and repairing waste lithium iron phosphate, the method comprising:

[0034] (1) crushing the waste lithium iron phosphate positive electrode sheets, and performing anaerobic pyrolysis on the crushed materials to obtain waste lithium iron phosphate positive electrode powder;

[0035] (2) supplementing the lithium source and the phosphorus source and mixing them with the waste lithium iron phosphate positive electrode powder in step (1), and performing reduction roasting to obtain a lithium iron phosphate repair material;

[0036] (3) The lithium iron phosphate repair material obtained in step (2) is screened and demagnetized to obtain regenerated lithium iron phosphate.

[0037] The regeneration and repair method provided by the present invention does not require the additional use of a reducing agent, and the purpose of reduction can be achieved only by relying on the charcoal produced by anaerobic pyrolysis. Moreover, the control of the anaerobic pyrolysis conditions can reduce the adverse effects of anaerobic pyrolysis on the crystal structure of lithium iron phosphate, which not only improves the conductivity of the regenerated lithium iron phosphate, but also improves the specific capacity, cycle performance and rate performance of the regenerated lithium iron phosphate.

[0038] Waste lithium iron phosphate cathode sheets typically have a multi-layer composite structure, with core components including lithium iron phosphate, a binder, a conductive agent, a current collector, and residual electrolyte. Crushing produces a crushed material, primarily composed of the cathode active material, the conductive agent, and the binder, and possibly also containing electrolyte. The present invention reduces the median particle size of the target cathode active material through crushing, increases the contact area between the conductive agent and binder in the crushed material and the heat source, and enhances the effectiveness of subsequent anaerobic pyrolysis.

[0039] During anaerobic pyrolysis, organic materials such as conductive agents and binders are pyrolyzed into substances such as amorphous carbon. This amorphous carbon can be evenly deposited on the surface of the lithium iron phosphate particles, replacing the additional reducing agent required in traditional processes. Conductive agents such as carbon black remaining in the waste lithium iron phosphate do not decompose under anaerobic pyrolysis conditions, but can form a conductive network with the amorphous carbon generated by pyrolysis, laying the foundation for subsequent reduction roasting and the conductivity of the regenerated lithium iron phosphate. After reduction roasting, olivine-phase LiFePO4 is obtained, its surface evenly coated with a conductive carbon layer, significantly improving specific capacity, rate performance, and cycle stability, meeting the requirements for reuse as a positive electrode material.

[0040] In one embodiment of the present invention, the reduction roasting can use the carbon produced by oxygen-free pyrolysis as a reducing agent to reduce the Fe 3+ Reduction to Fe 2+, while inhibiting Li + The volatilization of lithium and phosphorus sources allows the supplementary lithium and phosphorus sources to diffuse into the LiFePO4 lattice, filling the Li and P vacancies caused by the cycle, repairing the lattice distortion, and making the lattice structure complete.

[0041] Optionally, the lithium source includes any one of lithium carbonate, lithium hydroxide or lithium phosphate, or a combination of at least two of them. Typical but non-limiting combinations include a combination of lithium carbonate and lithium hydroxide, a combination of lithium hydroxide and lithium phosphate, a combination of lithium carbonate and lithium phosphate, and a combination of lithium carbonate, lithium hydroxide and lithium carbonate.

[0042] Optionally, the phosphorus source includes any one of diammonium phosphate, lithium phosphate or ammonium phosphate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of diammonium phosphate and lithium phosphate, a combination of diammonium phosphate and ammonium phosphate, a combination of lithium phosphate and ammonium phosphate, or a combination of diammonium phosphate, lithium phosphate and ammonium phosphate.

[0043] In one embodiment of the present invention, the lithium source and the phosphorus source are used in such an amount that the molar ratio of Li, Fe, and P in the mixed material is 1 to 1.04:1:1, preferably 1:1:1.

[0044] In one embodiment of the present invention, the particle size D50 of the crushed material in step (1) is 10 μm to 50 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm or 50 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] In one embodiment of the present invention, the crushed material in step (1) is dried before anaerobic pyrolysis.

[0046] Drying before pyrolysis can prevent possible moisture from vaporizing during subsequent anaerobic pyrolysis, thereby avoiding particle agglomeration and structural damage caused by vaporization.

[0047] In one embodiment of the present invention, the drying temperature is 80° C. to 120° C., and the drying time is more than 2 hours.

[0048] The drying temperature is 80°C to 120°C, for example, 80°C, 90°C, 100°C, 110°C or 120°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] The drying time is more than 2 hours, for example, it can be 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. It can be understood that the longer the drying time, the more it can reduce the impact of possible moisture, but too long a time cannot further reduce the moisture. In one embodiment of the present invention, the drying time is controlled to be 2 hours.

[0050] In one embodiment of the present invention, step (1) anaerobic pyrolysis includes a first anaerobic pyrolysis and a second anaerobic pyrolysis performed sequentially.

[0051] The use of a first and second anaerobic pyrolysis process at successively higher temperatures can reduce the damage to the lithium iron phosphate lattice caused by pyrolysis. Typically, the binder in waste lithium iron phosphate positive electrode sheets is polyvinylidene fluoride (PVDF). Under the first anaerobic pyrolysis conditions, the binder and any residual electrolyte are effectively removed. Simultaneously, the oxygen-free environment effectively inhibits the oxidative combustion of organic matter, causing it to be directionally converted into amorphous carbon. This amorphous carbon is uniformly deposited in a nanoscale, amorphous form on the surface and in the pores of the LiFePO4, forming a preliminary carbon coating.

[0052] Then, in the second anaerobic pyrolysis at elevated temperature, part of the amorphous carbon undergoes graphitization, which improves the electrochemical performance of the regenerated lithium iron phosphate to a certain extent. + PO4 3- and Fe 2+ It can migrate within the lattice to fill lithium vacancies and lattice distortion defects.

[0053] In one embodiment of the present invention, the temperature of the first anaerobic pyrolysis is 450° C. to 550° C., and the time is 1 hour to 2 hours.

[0054] The temperature of the first anaerobic pyrolysis is 450°C to 550°C, for example, 450°C, 480°C, 500°C, 520°C or 550°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0055] The time of the first anaerobic pyrolysis is 1 h to 2 h, for example, 1 h, 1.5 h or 2 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] In one embodiment of the present invention, the temperature of the second anaerobic pyrolysis is 700° C. to 800° C., and the time is 1 hour to 2 hours.

[0057] The temperature of the second anaerobic pyrolysis is 700° C. to 800° C., for example, 700° C., 720° C., 750° C., 780° C. or 800° C., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0058] The time of the second anaerobic pyrolysis is 1 h to 2 h, for example, 1 h, 1.5 h or 2 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0059] During the anaerobic pyrolysis process, appropriately increasing the system pressure can inhibit the volatilization of low-boiling-point organic matter and promote its deep decomposition into carbon, thereby improving the electrochemical performance of the final regenerated lithium iron phosphate.

[0060] In one embodiment of the present invention, the gauge pressure of the anaerobic pyrolysis in step (1) is 0.1 MPa to 0.2 MPa, for example, it can be 0.1 MPa, 0.12 MPa, 0.15 MPa, 0.16 MPa, 0.18 MPa or 0.2 MPa, but is not limited to the listed values, and the remaining values ​​within the numerical range not listed are also applicable.

[0061] The heating rate of anaerobic pyrolysis affects the rate of gas production by pyrolysis of organic matter, and also affects the uniformity of carbon deposition on the surface of lithium iron phosphate. If the heating rate of anaerobic pyrolysis is too high, it will cause lattice distortion of lithium iron phosphate and hinder the diffusion of lithium ions.

[0062] In one embodiment of the present invention, the heating rate of the anaerobic pyrolysis in step (1) is 5°C / min to 10°C / min, for example, 5°C / min, 6°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0063] In one embodiment of the present invention, the reduction roasting in step (2) is carried out in a protective atmosphere; the protective atmosphere includes nitrogen and / or an inert gas.

[0064] Optionally, the inert gas includes helium and / or argon.

[0065] In one embodiment of the present invention, the temperature of the reduction roasting in step (2) is 650°C to 750°C, for example, 650°C, 700°C or 750°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0066] Optionally, the reduction roasting time in step (2) can be more than 4 hours.

[0067] As a preferred technical solution of the regeneration and repair method provided by the present invention, the regeneration and repair method comprises the following steps:

[0068] (1) crushing the waste lithium iron phosphate positive electrode sheets to obtain crushed materials with a particle size D50 of 10 μm to 50 μm; drying the obtained crushed materials at 80° C. to 120° C. for more than 2 hours; and then performing anaerobic pyrolysis to obtain waste lithium iron phosphate positive electrode powder;

[0069] The gauge pressure of the anaerobic pyrolysis is 0.1 MPa to 0.2 MPa; the anaerobic pyrolysis includes a first anaerobic pyrolysis and a second anaerobic pyrolysis performed sequentially, with a heating rate of 5°C / min to 10°C / min; the temperature of the first anaerobic pyrolysis is 450°C to 550°C, and the time is 1 hour to 2 hours; the temperature of the second anaerobic pyrolysis is 700°C to 800°C, and the time is 1 hour to 2 hours;

[0070] (2) supplementing the lithium source and the phosphorus source and mixing them with the waste lithium iron phosphate positive electrode powder in step (1), and performing reduction roasting in a protective atmosphere to obtain a lithium iron phosphate repair material;

[0071] The temperature of reduction roasting is 650℃~750℃;

[0072] (3) The lithium iron phosphate repair material obtained in step (2) is screened and demagnetized to obtain regenerated lithium iron phosphate.

[0073] Example 1

[0074] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, comprising the following steps:

[0075] (1) The waste lithium iron phosphate positive electrode sheets are crushed to obtain crushed materials with a particle size D50 of 30 μm; the obtained crushed materials are dried at 100° C. for 2 h; and then subjected to anaerobic pyrolysis to obtain waste lithium iron phosphate positive electrode powder;

[0076] The gauge pressure of the anaerobic pyrolysis was 0.15 MPa. The anaerobic pyrolysis included a first anaerobic pyrolysis and a second anaerobic pyrolysis performed sequentially, with a heating rate of 8°C / min. The temperature of the first anaerobic pyrolysis was 500°C and the time was 1.5 hours. The temperature of the second anaerobic pyrolysis was 750°C and the time was 1.5 hours.

[0077] (2) supplementing the lithium source (lithium carbonate) and the phosphorus source (ammonium phosphate) and mixing the waste lithium iron phosphate positive electrode powder from step (1), and performing reduction roasting in a nitrogen atmosphere to obtain a lithium iron phosphate repair material;

[0078] The reduction roasting temperature is 700℃ and the time is 4h;

[0079] The amount of lithium source and phosphorus source used is such that the molar ratio of Li, Fe, and P in the mixed material is 1:1:1;

[0080] (3) The lithium iron phosphate repair material obtained in step (2) is screened and demagnetized to obtain regenerated lithium iron phosphate.

[0081] Example 2

[0082] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, comprising the following steps:

[0083] (1) crushing the waste lithium iron phosphate positive electrode sheets to obtain crushed materials with a particle size D50 of 10 μm; drying the obtained crushed materials at 80° C. for 2 h; and then performing anaerobic pyrolysis to obtain waste lithium iron phosphate positive electrode powder;

[0084] The gauge pressure of the anaerobic pyrolysis is 0.1 MPa; the anaerobic pyrolysis includes a first anaerobic pyrolysis and a second anaerobic pyrolysis performed sequentially, with a heating rate of 5°C / min; the temperature of the first anaerobic pyrolysis is 450°C and the time is 2 hours; the temperature of the second anaerobic pyrolysis is 700°C and the time is 2 hours;

[0085] (2) supplementing the lithium source (lithium carbonate) and the phosphorus source (ammonium phosphate) and mixing the waste lithium iron phosphate positive electrode powder from step (1), and performing reduction roasting in a nitrogen atmosphere to obtain a lithium iron phosphate repair material;

[0086] The reduction roasting temperature is 650℃ and the time is 4h;

[0087] The amount of lithium source and phosphorus source used is such that the molar ratio of Li, Fe, and P in the mixed material is 1:1:1;

[0088] (3) The lithium iron phosphate repair material obtained in step (2) is screened and demagnetized to obtain regenerated lithium iron phosphate.

[0089] Example 3

[0090] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, comprising the following steps:

[0091] (1) crushing the waste lithium iron phosphate positive electrode sheets to obtain crushed materials with a particle size D50 of 50 μm; drying the obtained crushed materials at 120° C. for 2 h; and then performing anaerobic pyrolysis to obtain waste lithium iron phosphate positive electrode powder;

[0092] The gauge pressure of the anaerobic pyrolysis is 0.2 MPa; the anaerobic pyrolysis includes a first anaerobic pyrolysis and a second anaerobic pyrolysis performed sequentially, with a heating rate of 10°C / min; the temperature of the first anaerobic pyrolysis is 550°C and the time is 1 hour; the temperature of the second anaerobic pyrolysis is 800°C and the time is 1 hour;

[0093] (2) supplementing the lithium source (lithium carbonate) and the phosphorus source (ammonium phosphate) and mixing the waste lithium iron phosphate positive electrode powder from step (1), and performing reduction roasting in a nitrogen atmosphere to obtain a lithium iron phosphate repair material;

[0094] The reduction roasting temperature is 750℃ and the time is 4h;

[0095] The amount of lithium source and phosphorus source used is such that the molar ratio of Li, Fe, and P in the mixed material is 1:1:1;

[0096] (3) The lithium iron phosphate repair material obtained in step (2) is screened and demagnetized to obtain regenerated lithium iron phosphate.

[0097] Example 4

[0098] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, which is the same as that of Example 1 except that drying is not performed before anaerobic pyrolysis.

[0099] Example 5

[0100] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, which is the same as that of Example 1 except that the temperature of the first anaerobic pyrolysis is 400°C.

[0101] Example 6

[0102] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, which is the same as that of Example 1 except that the temperature of the first anaerobic pyrolysis is 600°C.

[0103] Example 7

[0104] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, which is the same as that of Example 1 except that the temperature of the second anaerobic pyrolysis is 650°C.

[0105] Example 8

[0106] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, which is the same as that of Example 1 except that the temperature of the second anaerobic pyrolysis is 850°C.

[0107] Example 9

[0108] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, which is the same as Example 1 except that the gauge pressure of anaerobic pyrolysis is 0 MPa.

[0109] Example 10

[0110] This embodiment provides a method for regenerating and repairing waste lithium iron phosphate, which is the same as that of Example 1 except that the heating rate of anaerobic pyrolysis is 20°C / min.

[0111] Performance Characterization

[0112] The regenerated lithium iron phosphate obtained in Examples 1 to 10 was used to prepare a lithium iron phosphate battery. The preparation process mainly included: uniformly mixing the regenerated lithium iron phosphate, a conductive agent (acetylene black), and a binder (PVDF) in a mass ratio of 8:1:1, coating the mixture on an aluminum foil current collector, drying and rolling the mixture, and then cutting out the positive electrode sheet. The lithium sheet was used as the counter electrode to form a CR2032 button battery.

[0113] The electrochemical performance of the button cell was assembled, and the 0.1C first discharge capacity, the capacity retention rate after 50 cycles at 0.1C at room temperature, and the 0.5C rate discharge capacity retention rate were tested in the voltage range of 2.0V to 3.75V. The results are shown in Table 1.

[0114] Table 1

[0115]

[0116]

[0117] In summary, the regeneration and repair method provided by the present invention does not require the additional use of a reducing agent, and the purpose of reduction can be achieved only by relying on the carbon generated by anaerobic pyrolysis. Moreover, the control of the anaerobic pyrolysis conditions can reduce the adverse effects of anaerobic pyrolysis on the crystal structure of lithium iron phosphate, which not only improves the conductivity of the regenerated lithium iron phosphate, but also improves the specific capacity, cycle performance and rate performance of the regenerated lithium iron phosphate. Specifically, during anaerobic pyrolysis, organic matter such as conductive agents and binders are pyrolyzed into substances such as amorphous carbon, and amorphous carbon can be evenly deposited on the surface of lithium iron phosphate particles, replacing the additional reducing agent required in the traditional process. The conductive agent such as carbon black remaining in the waste lithium iron phosphate does not decompose under anaerobic pyrolysis conditions, and can form a conductive network with the amorphous carbon generated by pyrolysis, laying the foundation for subsequent reduction roasting and the conductivity of the regenerated lithium iron phosphate. After reduction roasting, olivine phase LiFePO4 can be obtained, and its surface is evenly coated with a conductive carbon layer, and the specific capacity, rate performance and cycle stability are significantly improved, which can meet the application requirements of being used as a positive electrode material again.

[0118] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for regenerating and repairing waste lithium iron phosphate, characterized in that: The regeneration and repair method comprises: (1) crushing the waste lithium iron phosphate positive electrode sheets, and performing anaerobic pyrolysis on the crushed materials to obtain waste lithium iron phosphate positive electrode powder; (2) supplementing the lithium source and the phosphorus source and mixing them with the waste lithium iron phosphate positive electrode powder described in step (1), and performing reduction roasting to obtain a lithium iron phosphate repair material; (3) The lithium iron phosphate repair material obtained in step (2) is screened and demagnetized to obtain regenerated lithium iron phosphate.

2. The regeneration and repair method according to claim 1, characterized in that: The particle size D50 of the crushed material in step (1) is 10 μm to 50 μm.

3. The regeneration and repair method according to claim 1 or 2, characterized in that: The crushed material in step (1) is dried before anaerobic pyrolysis; Preferably, the drying temperature is 80° C. to 120° C., and the drying time is more than 2 hours.

4. The regeneration and repair method according to any one of claims 1 to 3, characterized in that: The anaerobic pyrolysis in step (1) includes a first anaerobic pyrolysis and a second anaerobic pyrolysis performed sequentially.

5. The regeneration and repair method according to claim 4, characterized in that: The temperature of the first anaerobic pyrolysis is 450°C to 550°C, and the time is 1h to 2h; Preferably, the temperature of the second anaerobic pyrolysis is 700° C. to 800° C., and the time is 1 hour to 2 hours.

6. The regeneration and repair method according to claim 4 or 5, characterized in that: The gauge pressure of the anaerobic pyrolysis in step (1) is 0.1 MPa to 0.2 MPa.

7. The regeneration and repair method according to any one of claims 4 to 6, characterized in that: The heating rate of the anaerobic pyrolysis in step (1) is 5°C / min to 10°C / min.

8. The regeneration and repair method according to any one of claims 1 to 7, characterized in that: The reduction roasting in step (2) is carried out in a protective atmosphere; The protective atmosphere includes nitrogen and / or an inert gas.

9. The regeneration and repair method according to any one of claims 1 to 8, characterized in that: The temperature of the reduction roasting in step (2) is 650°C to 750°C.

10. The regeneration and repair method according to claim 1, characterized in that: The regeneration and repair method comprises the following steps: (1) crushing the waste lithium iron phosphate positive electrode sheets to obtain crushed materials with a particle size D50 of 10 μm to 50 μm; drying the obtained crushed materials at 80° C. to 120° C. for more than 2 hours; and then performing anaerobic pyrolysis to obtain waste lithium iron phosphate positive electrode powder; The gauge pressure of the anaerobic pyrolysis is 0.1 MPa to 0.2 MPa; the anaerobic pyrolysis includes a first anaerobic pyrolysis and a second anaerobic pyrolysis performed sequentially, with a heating rate of 5°C / min to 10°C / min; the temperature of the first anaerobic pyrolysis is 450°C to 550°C, and the time is 1 hour to 2 hours; the temperature of the second anaerobic pyrolysis is 700°C to 800°C, and the time is 1 hour to 2 hours; (2) supplementing the lithium source and the phosphorus source and mixing them with the waste lithium iron phosphate positive electrode powder in step (1), and performing reduction roasting in a protective atmosphere to obtain a lithium iron phosphate repair material; The reduction roasting temperature is 650°C to 750°C; (3) The lithium iron phosphate repair material obtained in step (2) is screened and demagnetized to obtain regenerated lithium iron phosphate.

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