Lithium manganese iron phosphate recovery method, lithium manganese iron phosphate material, secondary battery and electric device

Abstract

The invention provides a lithium manganese iron phosphate recovery method, a lithium manganese iron phosphate material, a secondary battery and an electric device. The lithium manganese iron phosphate recovery method comprises the following steps: heating a positive pole piece containing lithium manganese iron phosphate at 400-800 DEG C to obtain an initial recovery solid material; sieving the initially recycled solid material to obtain lithium manganese iron phosphate recycled powder; raw materials including at least one of a lithium source, an iron source and a manganese source are supplemented into the lithium manganese iron phosphate recycled powder, and a lithium manganese iron phosphate precursor is obtained; and sintering the lithium manganese iron phosphate precursor at 600-800 DEG C to obtain the lithium manganese iron phosphate regenerated material. The method for recovering the lithium manganese iron phosphate provided by the invention is simple in process operation and low in energy consumption, at least one element such as lithium, manganese and iron is supplemented into a crystal structure, so that the crystal structure is recovered to the original crystal structure, and the repair and regeneration of all elements of the lithium manganese iron phosphate are realized.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and in particular, to a method for recycling lithium iron manganese phosphate, a lithium iron manganese phosphate material, a secondary battery, and an electrical device. Background Art

[0002] In recent years, with the increasingly wide application range of lithium-ion batteries, lithium-ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Among them, lithium iron manganese phosphate batteries, as a new type of power battery, have broad application prospects. With the development of various industries, a large number of retired lithium iron manganese phosphate batteries will be generated in the future. Under the pressure of rising material costs and environmental protection, the effective recycling of these materials is an irresistible trend.

[0003] Therefore, there is an urgent need to develop a method for recycling lithium iron manganese phosphate. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a method for recycling lithium iron manganese phosphate, a lithium iron manganese phosphate material, a secondary battery, and an electrical device, which can achieve the full-element repair and regeneration of lithium iron manganese phosphate, and has simple process operation and low energy consumption.

[0005] The first aspect of the present application provides a method for recycling lithium iron manganese phosphate, specifically including the following steps:

[0006] Heat the positive electrode sheet including lithium iron manganese phosphate at 400°C - 800°C to obtain an initial recycled solid material;

[0007] Screen the initial recycled solid material to obtain a lithium iron manganese phosphate recycled powder;

[0008] Supplement raw materials in the lithium iron manganese phosphate recycled powder, and the raw materials include at least one of a lithium source, an iron source, and a manganese source, to obtain a lithium iron manganese phosphate precursor;

[0009] Sinter the lithium iron manganese phosphate precursor at 600°C - 800°C to obtain a lithium iron manganese phosphate recycled material.

[0010] Accordingly, in this application, the spent cathode electrode sheet containing lithium iron phosphate manganese is sintered after supplementing corresponding elements to obtain lithium iron phosphate manganese recycled material. The advantage of this direct recycling process is that it requires less raw materials for repairing metal salts, does not involve a large amount of organic solvents and acidic substances, slows down environmental pollution, and has simple process operation and low energy consumption. For lithium iron phosphate manganese batteries, the direct cause of capacity attenuation is the loss of elements such as lithium and manganese during long-term charge and discharge processes. In this application, at least one element such as lithium, manganese, and iron is supplemented into the crystal structure to restore its original crystal structure, realizing the repair and recycling of all elements of lithium iron phosphate manganese.

[0011] In some embodiments, the cathode electrode sheet includes a binder, and the binder includes fluorine element.

[0012] Due to the Jahn-Teller effect of Mn in lithium iron phosphate manganese 3+ it will cause lattice distortion, resulting in a decrease in the lithium ion diffusion coefficient of the lithium iron phosphate manganese material. The direct recycling process retains the fluorine element-containing binder remaining in the cathode electrode sheet during the recycling process. When the cathode electrode sheet is heated to 400°C - 800°C, the binder can decompose to generate fluorine element. During the sintering process, the fluorine element diffuses into the cathode material to achieve fluorine doping. The fluorine-doped lithium iron phosphate manganese cathode material has a higher specific capacity compared to the undoped lithium iron phosphate manganese cathode material. Introducing fluorine element can enhance the electronic conductivity, intercalation potential, and cycling performance, and at the same time alleviate the manganese dissolution phenomenon of the lithium iron phosphate manganese material, making the cycling performance of the lithium iron phosphate manganese recycled material more excellent than that of the lithium iron phosphate manganese raw material.

[0013] In some embodiments, the raw material supplement step includes: adding at least one of a lithium source, an iron source, and a manganese source, such that the molar ratio of lithium element, manganese element, the sum of iron element and phosphorus element is Li:(Mn + Fe):P = 1 - 1.05:0.94 - 1:1, to obtain a lithium iron phosphate manganese precursor.

[0014] By controlling the ratio of each element, it is beneficial to balance the tap density, specific capacity, and conductivity of the lithium iron phosphate manganese material, making the tap density, specific capacity, and conductivity of the lithium iron phosphate manganese material relatively high, and enabling the lithium ion battery to have good cycling performance.

[0015] In some embodiments, the manganese source includes one or a combination of manganese chloride, manganese oxalate, manganese acetate, manganese carbonate, iron manganese oxalate, iron manganese carbonate, etc.

[0016] In this application, by selecting a suitable manganese source, the above manganese source can undergo pyrolysis at the above sintering temperature and be supplemented into the crystal structure to realize the repair and recycling of manganese element in lithium iron phosphate manganese.

[0017] In some embodiments, before the sintering step, the carbon content of the lithium iron manganese phosphate precursor is tested, and a carbon source is supplemented according to the carbon content so that the carbon content of the lithium iron manganese phosphate precursor is 1%-2%.

[0018] In the embodiments of the present application, by supplementing the carbon source, a carbon coating layer can be formed on the surface of the lithium iron manganese phosphate particles during sintering or the original carbon coating layer can be repaired. The carbon coating layer can improve the conductivity of the lithium iron manganese phosphate material.

[0019] In some embodiments, the sintering temperature of the sintering step is 650°C - 750°C.

[0020] In the technical solution of the present application, by reasonably controlling the sintering temperature, the particles can be bonded in different temperature ranges to make them densified.

[0021] In some embodiments, before the sintering step, the lithium iron manganese phosphate precursor is mixed, sanded, and spray-dried. Among them, the particles of the lithium iron manganese phosphate precursor are sanded to Dv50 ≤ 0.7 μm.

[0022] By sanding, the particles can be fully refined. Nanoscale lithium iron manganese phosphate has higher reaction activity and better electrochemical performance. By spray-drying, the materials in the lithium iron manganese phosphate precursor are mixed evenly, forming a granular system with relatively uniform dispersion and refined particle size, reducing the generation of caking phenomena and improving the powder properties.

[0023] In some embodiments, the sieving step includes primary sieving and secondary sieving. The mesh number of the primary sieving is less than that of the secondary sieving, and the mesh number of the primary sieving ≥ 200 meshes.

[0024] By sieving, large particle substances such as metal foils and other impurities can be sieved out to obtain lithium iron manganese phosphate recycled powder. By the way of two-stage sieving, large particle substances such as metal foils and other impurities can be sieved out more finely to obtain lithium iron manganese phosphate recycled powder.

[0025] In the second aspect, the present application provides a lithium iron manganese phosphate material, in which the lithium iron manganese phosphate material is doped with fluorine element, and the mass content of the fluorine element in the lithium iron manganese phosphate material is 500 ppm - 5000 ppm.

[0026] Since the lithium iron manganese phosphate material provided by the present application is doped with 500 ppm - 5000 ppm of fluorine element, it has good electrical conductivity and high specific capacity.

[0027] In the third aspect, the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate, and an electrolyte. The positive electrode plate includes a current collector and the above-mentioned lithium iron manganese phosphate material.

[0028] The secondary battery provided by the present application contains the lithium iron manganese phosphate material provided by the second aspect above, so the secondary battery provided by the present application has good cycle performance.

[0029] Fourthly, the present application provides an electrical device including at least one selected from the above lithium iron manganese phosphate material or the above secondary battery. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0031] Figure 2 is Figure 1 The exploded view of the secondary battery according to an embodiment of the present application shown.

[0032] Figure 3 It is a schematic diagram of a battery module according to an embodiment of the present application.

[0033] Figure 4 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0034] Figure 5 is Figure 4 The exploded view of the battery pack according to an embodiment of the present application shown.

[0035] Figure 6 It is a schematic diagram of an electrical device using the secondary battery according to an embodiment of the present application as a power source.

[0036] Figure 7 It is a scanning electron microscope image of the lithium iron manganese phosphate material obtained in Example 1 of the present application.

[0037] Description of the Reference Numerals:

[0038] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Embodiments

[0039] Hereinafter, embodiments of the recovery method of lithium iron manganese phosphate, the lithium iron manganese phosphate material, the secondary battery, and the electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0040] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0042] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0043] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0044] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0045] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0046] In recent years, with the increasingly wide application range of lithium-ion batteries, lithium-ion batteries are widely used in energy storage power systems such as hydro, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Among them, lithium iron manganese phosphate batteries, as a new type of power battery, have broad application prospects. With the development of various industries, a large number of retired lithium iron manganese phosphate batteries will be generated in the future. Under the pressure of rising material costs and environmental protection, it is an irresistible trend to effectively recycle these materials.

[0047] The main reasons for the failure of lithium-ion cathode materials are as follows: Lithium-ion batteries that have undergone long cycles will be accompanied by the loss of elements such as Ni, Co, Mn, and Li. The irreversible phase transformation caused by lithium loss, such as the formation of spinel phase and rock salt phase in layered cathode; the thickening of the solid electrolyte interface (SEI) layer accelerates the loss of lithium; the Jahn-Teller effect of manganese ions leads to manganese dissolution during long-term charge and discharge processes. The Jahn-Teller effect was first proposed by H.A. Jahn and E.T. Teller in 1937 and is sometimes also called the Jahn-Teller distortion, which refers to a special case of the splitting of ion energy levels in a crystal field. The asymmetric occupation of electrons in degenerate orbitals will cause the geometric configuration of the molecule to distort, thereby reducing the symmetry of the molecule and the degeneracy of the orbitals, and further lowering the energy of the system.

[0048] The current mainstream battery recycling process is wet recycling, that is, processes such as alkali dissolution, inorganic / organic acid leaching, and biological leaching are used. First, elements such as lithium, iron, and phosphorus are leached into the solution, and then precipitants and complexing agents are added for precipitation respectively to obtain the corresponding lithium, iron, and phosphorus salts as precursors to re-synthesize new cathode materials. However, such methods have relatively long process flows, are complex to operate, and may cause secondary pollution in wet processes such as leaching and impurity removal and precipitation. Therefore, the recycling and regeneration cost is relatively high.

[0049] At present, there is little research on the recycling of lithium iron manganese phosphate batteries. Today, in the face of energy shortage and environmental pollution, lithium-ion batteries, as clean energy, play an irreplaceable role. And lithium iron manganese phosphate batteries, as a new type of battery, have broad application prospects. Therefore, it is urgent to develop a recycling method for lithium iron manganese phosphate.

[0050] Based on this, the present application proposes a method for recycling lithium iron manganese phosphate, which includes the following steps:

[0051] Heat the positive electrode sheet including lithium iron manganese phosphate at 400°C - 800°C to obtain an initial recycled solid material;

[0052] Sieve the initial recycled solid material to obtain lithium iron manganese phosphate recycled powder;

[0053] Supplement raw materials in the lithium iron manganese phosphate recycled powder, and the raw materials include at least one of a lithium source, an iron source, and a manganese source, to obtain a lithium iron manganese phosphate precursor;

[0054] Sinter the lithium iron manganese phosphate precursor at 600°C - 800°C to obtain a lithium iron manganese phosphate recycled material.

[0055] Specifically, after the waste lithium iron manganese phosphate battery is disassembled step by step, the positive electrode, negative electrode, and separator are separated, and the positive electrode sheet including lithium iron manganese phosphate is heated in an inert atmosphere. Optionally, the inert atmosphere includes, but is not limited to, a combination of one or more of N2, Ar, He, Ne, Kr, and Xe. The heating temperature is 400°C - 800°C, and optionally, the heating time is 1h - 6h. Exemplarily, the heating temperature is any value among 400°C, 500°C, 600°C, 700°C, 800°C or between any two values. Exemplarily, the heating time is any value among 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, 3.5h, 4.0h, 4.5h, 5.0h, 5.5h, 6.0h or between any two values. Preferably, the heating temperature is 400 - 600°C, and the heating time is 2h - 4h. Optionally, the reaction vessel can be selected from a box furnace, a roller hearth kiln, a rotary kiln, etc. After heating, an initial recycled solid material containing the positive electrode current collector is obtained.

[0056] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material. In the present application, the positive electrode active material can include, but is not limited to, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, etc. The positive electrode current collector can be a metal foil or a composite current collector. For example, the metal foil can be an aluminum foil, and the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.

[0057] Regarding sieving the initial recycled solid material, the present application has no special limitation on the sieving tool. By sieving, large particle substances such as metal foils are sieved out to obtain lithium iron manganese phosphate recycled powder.

[0058] The elements of the lithium iron manganese phosphate powder are tested by inductively coupled plasma (ICP) spectrometry to obtain the molar ratio of Li:(Mn+Fe):P. The testing method can refer to standards such as YS / T 1006.2-2014, GB / T 23367.2-2009 or YS / T 1028.5-2015. According to the ratio of Li:(Mn+Fe):P, at least one raw material of lithium source, iron source and manganese source is added to obtain the lithium iron manganese phosphate precursor. Usually, during the use of the battery, the phosphorus element will not be lost or the loss is small. Therefore, the phosphorus element is used as the reference 1 to quantitatively supplement other missing elements.

[0059] Among them, the lithium source, iron source and manganese source are lithium-containing compounds, iron-containing compounds and manganese-containing compounds respectively. Optionally, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium oxide, lithium nitride, lithium fluoride, lithium sulfide, lithium carboxymethyl cellulose. Optionally, the iron source includes one or several of ferrous oxalate, ferrous sulfate, ferrous acetate, ferrous chloride, iron carbonate, iron manganese oxalate, iron manganese carbonate.

[0060] The lithium iron manganese phosphate precursor is sintered in an inert atmosphere. Optionally, the inert atmosphere includes, but is not limited to, a combination of one or more of N2, Ar, He, Ne, Kr, Xe. The sintering temperature is 600°C - 800°C. Optionally, the sintering time is 8h - 16h. Exemplarily, the sintering temperature is any value among 600°C, 700°C, 800°C or between any two values. Exemplarily, the sintering time is any value among 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h or between any two values. The choice of sintering temperature will affect the performance of lithium iron manganese phosphate, so a suitable sintering temperature needs to be selected. Optionally, the reaction vessel can be a box furnace, a roller hearth kiln or a rotary kiln, etc. After sintering, the lithium iron manganese phosphate recycled material is obtained.

[0061] In the technical solution of the present application, the present application obtains the lithium iron manganese phosphate recycled material by supplementing corresponding elements to the waste positive electrode plate containing lithium iron manganese phosphate and then sintering. The advantage of this direct regeneration process is that it requires less raw materials for repairing metal salts, does not involve a large amount of organic solvents and acidic substances, slows down environmental pollution, and has simple process operation and low energy consumption; for lithium iron manganese phosphate batteries, the direct cause of capacity attenuation is the loss of elements such as lithium and manganese during long-term charge and discharge processes. The present application restores the original crystal structure by supplementing at least one element such as lithium, manganese, and iron into the crystal structure, realizing the repair and regeneration of all elements of lithium iron manganese phosphate.

[0062] In some embodiments, the positive electrode plate contains a binder, and the binder contains fluorine elements.

[0063] The binder contains fluorine elements. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0064] Mn in lithium iron manganese phosphate 3+ The Jahn-Teller effect of [Mn] will cause lattice distortion, resulting in a decrease in the lithium ion diffusion coefficient of the lithium iron manganese phosphate material. When the positive electrode sheet is heated to 400°C - 800°C, the binder can decompose to produce fluorine elements. The direct regeneration process retains the fluorine element-containing binder remaining in the positive electrode sheet during the recovery process, and fluorine doping is achieved by the diffusion of fluorine elements into the positive electrode material during the sintering process. The fluorine-doped lithium iron manganese phosphate positive electrode has a higher specific capacity per gram compared to the undoped lithium iron manganese phosphate positive electrode. Introducing fluorine elements can enhance the electronic conductivity and cycling performance while alleviating the manganese dissolution phenomenon of the lithium iron manganese phosphate material, making the cycling performance of the recycled lithium iron manganese phosphate better than that of the raw lithium iron manganese phosphate material. It may be because, during the sintering process, F-M bonds (M represents transition metal elements) are formed. Fluorine elements have a stronger ionic bond form compared to oxygen elements, and the binding ability of F-M bonds is stronger than that of O-M bonds. Fluorine substituting the oxygen position in the lattice can induce lattice distortion and enhance the specific capacity in the positive electrode material; after doping with fluorine, the unit cell volume increases. The increase in the unit cell volume can broaden the lithium ion diffusion path, shorten the lithium ion diffusion path, enhance lithium ion diffusion, improve the conductivity of the lithium iron manganese phosphate material, and exhibit better electrochemical performance.

[0065] In some embodiments, the recovery method of the present application effectively utilizes the fluorine elements in the binder of the positive electrode sheet, so that the recycled lithium iron manganese phosphate obtained can be doped with 500 ppm - 5000 ppm of fluorine elements.

[0066] In some embodiments, the raw material supplement step includes: adding at least one of a lithium source, an iron source, and a manganese source, so that the molar ratio of lithium element, manganese element, the sum of iron element, and phosphorus element is Li:(Mn + Fe):P = 1 - 1.05:0.94 - 1:1, to obtain a lithium iron manganese phosphate precursor.

[0067] By controlling the ratio of each element, it is beneficial to take into account the tap density, specific capacity, and conductivity of the lithium iron manganese phosphate material, so that the lithium iron manganese phosphate material has a higher tap density, a higher specific capacity, and a higher conductivity, and the secondary battery containing the aforementioned lithium iron manganese phosphate material has better cycling performance.

[0068] In some embodiments, the manganese source includes one or a combination of manganese chloride, manganese oxalate, manganese acetate, manganese carbonate, iron manganese oxalate, and iron manganese carbonate.

[0069] After long-term use of lithium iron manganese phosphate batteries, manganese is easily dissolved in the electrolyte and even deposited on the negative electrode. Therefore, manganese supplementation is the core of the recycling of lithium iron manganese phosphate cathode materials. In this application, by selecting a suitable manganese source, the above-mentioned manganese source can pyrolyze at the above-mentioned sintering temperature and be supplemented into the crystal structure to achieve the repair and regeneration of manganese elements in lithium iron manganese phosphate.

[0070] In some embodiments, before the sintering step, the carbon content of the lithium iron manganese phosphate precursor is tested, and a carbon source is supplemented according to the carbon content so that the carbon content of the lithium iron manganese phosphate precursor is 1%-2%.

[0071] The carbon content can be measured by instruments and methods well-known in the art. For example, a carbon-sulfur analyzer can be used to test the carbon content. Optionally, the carbon source includes one or more of glucose, sucrose, citric acid, polypropylene, polyvinyl alcohol, and polyethylene glycol.

[0072] In the embodiments of this application, by supplementing the carbon source, a carbon coating layer can be formed on the surface of the lithium iron manganese phosphate particles during sintering or the original carbon coating layer can be repaired. The carbon coating layer can improve the conductivity of the lithium iron manganese phosphate material. The carbon coating layer can at least partially cover the surface of the lithium iron manganese phosphate particles. For example, the surface of the lithium iron manganese phosphate particles can be completely covered by the carbon coating layer, or only a partial area of the surface of the lithium iron manganese phosphate particles can be covered by the carbon coating layer.

[0073] In some embodiments, the sintering temperature of the sintering step is 650°C - 750°C.

[0074] Exemplarily, the sintering temperature is any value among 650°C, 700°C, 750°C or between any two values. Optionally, the sintering time is 10h - 16h. Exemplarily, the sintering time is any value among 10h, 11h, 12h, 13h, 14h, 15h, 16h or between any two values. After sintering, a lithium iron manganese phosphate recycled material is obtained.

[0075] In the technical solution of this application, by reasonably controlling the sintering temperature, the particles can be bonded in different temperature ranges to make them densified.

[0076] In some embodiments, before the sintering step, the lithium iron manganese phosphate precursor is mixed, sanded, and spray-dried, wherein the particles of the lithium iron manganese phosphate precursor are sanded to Dv50 ≤ 0.7μm.

[0077] Mix a lithium source, an iron source, a manganese source, a carbon source, and lithium iron manganese phosphate recovery powder, etc., for example, it can be put into a stirring tank for mixing. Feed the mixed lithium iron manganese phosphate precursor into a sand mill through a diaphragm pump for sanding, so that the Dv50 of the particles ≤ 0.7 μm. Optionally, the sanding speed is 600 - 1000 r / min. During the process of maintaining stirring, feed it into a spray dryer through a peristaltic pump for spray drying. Optionally, the outlet air temperature of the spray drying is 100°C - 120°C to obtain a dried lithium iron manganese phosphate precursor.

[0078] In the technical solution of this application, sanding can make the particles fully refined. Nano-scale lithium iron manganese phosphate has higher reaction activity and better electrochemical performance. Spray drying makes the materials in the lithium iron manganese phosphate precursor mix evenly, forming a granular system with relatively uniform dispersion and refined particle size, reducing the generation of caking and improving the powder performance.

[0079] In some embodiments, the sieving step includes primary sieving and secondary sieving. The mesh number of the primary sieving is less than that of the secondary sieving, and the mesh number of the primary sieving ≥ 200 meshes.

[0080] Exemplarily, sieves with mesh numbers of 200 meshes, 250 meshes, 300 meshes, 350 meshes, 400 meshes, 450 meshes, etc. can be selected. Exemplarily, a 200-mesh sieve can be selected for primary sieving, and a 300-mesh sieve can be selected for secondary sieving; or a 200-mesh sieve can be selected for primary sieving, and a 400-mesh sieve can be selected for secondary sieving; or a 250-mesh sieve can be selected for primary sieving, and a 400-mesh sieve can be selected for secondary sieving, etc.

[0081] Sieving can screen out large-particle substances, such as metal foil and other impurities, etc., to obtain lithium iron manganese phosphate recovery powder. By means of two-stage sieving, large-particle substances, such as metal foil and other impurities, etc., can be screened out more finely to obtain lithium iron manganese phosphate recovery powder.

[0082] In some embodiments, a lithium iron manganese phosphate material is provided. The lithium iron manganese phosphate material is doped with fluorine element, and the mass content of fluorine element in the lithium iron manganese phosphate material is 500 ppm - 5000 ppm.

[0083] By doping 500 ppm - 5000 ppm of fluorine element in the lithium iron manganese phosphate material, the lithium iron manganese phosphate material can have good electrical conductivity and high specific capacity.

[0084] In some embodiments, a secondary battery is provided, including a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a current collector and the above-mentioned lithium iron manganese phosphate material.

[0085] In some embodiments, an electrical device is provided, including at least one selected from the above-mentioned lithium iron manganese phosphate material or the above-mentioned secondary battery.

[0086] In addition, the secondary battery and the electrical device of the present application will be described below with reference to the drawings as appropriate.

[0087] In one embodiment of the present application, a secondary battery is provided.

[0088] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0089] [Positive Electrode Plate]

[0090] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0091] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0092] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material on a polymer material substrate. Among them, the metal material can be aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc., and the polymer material substrate can be a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. In a preferred embodiment, the current collector is aluminum foil.

[0093] In some embodiments, the positive electrode active material includes a lithium iron manganese phosphate material obtained by the method of the first aspect of the present application.

[0094] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0095] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] In some embodiments, the positive electrode sheet can be prepared by the following method: dispersing the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry, and the solvent can be, for example, N-methylpyrrolidone; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0097] [Negative electrode sheet]

[0098] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0099] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0100] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material on the polymer material substrate, where the metal material can be copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc., and the polymer material substrate can be a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0101] In some embodiments, the negative electrode active material can be a negative electrode active material for batteries well-known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0102] In some embodiments, the negative electrode film layer may also optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0103] In some embodiments, the negative electrode film layer may also optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, the negative electrode film layer may also optionally include other additives, such as a thickener, which may be sodium carboxymethyl cellulose (CMC-Na) or the like.

[0105] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the above components for preparing the negative electrode plate, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent to form a negative electrode slurry. The solvent may be deionized water, for example; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0106] [Electrolyte]

[0107] The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid state.

[0108] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0109] In some embodiments, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluoro bis(oxalate) phosphate, and lithium tetrafluorooxalate phosphate.

[0110] In some embodiments, the solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0111] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0112] [Separator]

[0113] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0114] In some embodiments, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0115] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0116] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0117] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and as plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0118] The present application does not particularly limit the shape of the secondary battery, and it can be cylindrical, square, or any other shape. For example, Figure 1 is a secondary battery 5 with a square structure as an example.

[0119] In some embodiments, referring to Figure 2 , the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte infiltrates in the electrode assembly 52. The number of the electrode assemblies 52 included in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0120] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries included in the battery module can be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery module.

[0121] Figure 3 Shown as an example is battery module 4. Refer to Figure 3 , in battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0122] Optionally, battery module 4 can further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0123] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0124] Figure 4 and Figure 5 Shown as an example is battery pack 1. Refer to Figure 4 and Figure 5 , in battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0125] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but not limited thereto.

[0126] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0127] Figure 6It is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be adopted.

[0128] The device as another example can be a mobile phone, a tablet computer, a laptop computer, etc. The device usually requires being thin and light, and a secondary battery can be adopted as the power source.

[0129] Embodiment

[0130] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified for the manufacturers, they are all conventional products that can be obtained through commercial purchase.

[0131] Recovery of lithium iron phosphate

[0132] Embodiment 1

[0133] After the waste lithium-ion battery is disassembled step by step, the positive electrode, negative electrode, and separator are separated. The taken-out positive electrode plate is put into a box furnace and heated at 500 °C for 2 h in a nitrogen atmosphere to obtain an initial recovered solid material. Among them, during the heating process, the binder polyvinylidene fluoride (PVDF) fails and decomposes fluorine elements.

[0134] Take out the positive electrode plate from the box furnace, coarsely crush it, and sequentially screen it through 200-mesh and 400-mesh sieves to separate the lithium iron phosphate positive electrode powder from the aluminum foil, and lithium iron phosphate recovered powder can be obtained.

[0135] The element ratio of the lithium iron phosphate powder is tested by inductively coupled plasma (ICP) spectrometry, and the molar ratio of lithium element, manganese element, iron element, and phosphorus element is Li:Mn:Fe:P = 0.98:0.447:0.479:1. Take 1 kg of lithium iron phosphate recovered powder, and according to the test results of ICP, add lithium carbonate, iron oxalate, and manganese oxalate to make the molar ratio of lithium element, manganese element, iron element, and phosphorus element Li:Mn:Fe:P = 1:0.48:0.48:1.

[0136] The carbon content of the lithium iron phosphate recovered powder is tested by a carbon-sulfur analyzer, and the test result of the carbon content is 1.3%. Supplement 20 g of glucose to achieve a target carbon content of about 1.5%.

[0137] Lithium carbonate, iron oxalate, manganese oxalate, lithium iron manganese phosphate recycled powder and glucose were successively added to a stirring tank, stirred evenly, and then sent to a sand mill through a diaphragm pump. Sand milling was carried out at a speed of 1000 r / min until the Dv50 of the particles was 0.3 μm. The lithium iron manganese phosphate precursor after sand milling was transferred back to the stirring tank from the sand mill and kept stirring, and then sent to a spray dryer through a peristaltic pump for spray drying to obtain a dried lithium iron manganese phosphate precursor. Under a nitrogen atmosphere, the lithium iron manganese phosphate precursor was sintered at 700 °C for 12 h to obtain a recycled lithium iron manganese phosphate material.

[0138] Example 2

[0139] The difference from Example 1 is only that the heating temperature of the positive electrode plate is 400 °C and the heating time of the positive electrode plate is 1 h.

[0140] Example 3

[0141] The difference from Example 1 is only that after the rough crushing of the positive electrode plate, only a 200-mesh sieve is used for sieving.

[0142] Example 4

[0143] The difference from Example 1 is only that the lithium source, manganese source and iron source are supplemented in the ratio of Li:Mn:Fe:P = 1.05:0.49:0.49:1.

[0144] Example 5

[0145] The difference from Example 1 is only that the sintering temperature of the lithium iron manganese phosphate precursor is 750 °C and the sintering time is 16 h.

[0146] Example 6

[0147] The difference from Example 1 is only that the sintering temperature of the lithium iron manganese phosphate precursor is 650 °C and the sintering time is 10 h.

[0148] Example 7

[0149] The difference from Example 1 is only that the sintering temperature of the lithium iron manganese phosphate precursor is 780 °C and the sintering time is 12 h.

[0150] Example 8

[0151] The difference from Example 1 is only that the supplemented manganese source is replaced with manganese carbonate.

[0152] Example 9

[0153] The difference from Example 1 is only that the supplemented lithium source and iron source are lithium hydroxide and iron carbonate, and the carbon source is polyvinyl alcohol. 70 g of polyvinyl alcohol is added to achieve a target carbon content of about 2.0%.

[0154] Example 10

[0155] The difference from Example 1 is only that the sanding is stopped when Dv50 = 1 μm, and then it is transferred to spray drying.

[0156] Comparative Example 1

[0157] The difference from Example 1 is only that the positive electrode sheet is not sieved after being broken.

[0158] Comparative Example 2

[0159] The difference from Example 1 is only that the heating temperature of the positive electrode sheet is 300 °C.

[0160] Comparative Example 3

[0161] The difference from Example 1 is only that the sintering temperature of the lithium iron manganese phosphate precursor is 850 °C.

[0162] Comparative Example 4

[0163] Fresh lithium iron manganese phosphate material is used, and this fresh lithium iron manganese phosphate material can be directly purchased on the market or prepared by methods well-known to those skilled in the art.

[0164] In addition, the lithium iron manganese phosphates obtained in the above Examples 1 to 10 and Comparative Examples 1 to 4 are respectively prepared into coin cells and secondary batteries as follows for performance testing.

[0165] (1) Preparation of positive electrode sheet:

[0166] The recycled lithium iron manganese phosphate, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) with a mass ratio of 92:2.5:5.5 are mixed, and the solvent N-methylpyrrolidone (NMP) is added and stirred until the system becomes homogeneous. After grinding for 10 min, a positive electrode slurry with a solid content of 50 wt% is prepared.

[0167] The positive electrode slurry is evenly coated on both sides of the positive electrode current collector aluminum foil (with a thickness of 6 μm), dried at 85 °C for 4 h, then cold-pressed, and then trimmed and sliced, and dried in a vacuum at 85 °C for 4 h to obtain a positive electrode sheet, where the thickness of the single-sided positive electrode active material layer is 200 μm.

[0168] (2) Preparation of negative electrode sheet:

[0169] Graphite, conductive agent Super P, and binder polytetrafluoroethylene (PTFE) with a mass ratio of 95:2:3 are mixed in the solvent N-methylpyrrolidone (NMP) to form a negative electrode active slurry with a solid content of 50 wt%.

[0170] The negative electrode active paste is coated on a current collector copper foil (with a thickness of 9 μm), dried at 85 °C for 4 h, then cold-pressed, followed by edge trimming and blanking, and further dried under vacuum at 85 °C for 4 h to obtain the negative electrode sheet substrate; wherein, the thickness of the single-sided negative electrode active material layer is 150 μm.

[0171] (3) Preparation of coin cells:

[0172] A lithium sheet (with a thickness of 500 μm) is used as the negative electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) with a volume ratio of 1:1:1 is used as the electrolyte. Together with the positive electrode sheet prepared above, a coin cell is assembled in a coin cell assembly box.

[0173] (4) Preparation of secondary batteries:

[0174] The negative electrode sheet is used as the negative electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) with a volume ratio of 1:1:1 is used as the electrolyte. Together with the positive electrode sheet prepared above, a full cell is assembled in a low-humidity room.

[0175] The test process of the relevant parameters of the positive electrode active material in the examples and comparative examples of this application is as follows:

[0176] 1. ICP

[0177] In this application, the composition of the positive electrode active material is determined by inductively coupled plasma (ICP) spectrometry. For example, reference can be made to the standards YS / T 1006.2-2014, GB / T 23367.2-2009, or YS / T 1028.5-2015. Specifically, according to the examples of this application, an inductively coupled plasma emission spectrometer can be used to measure according to the manufacturer's instructions.

[0178] 2. Carbon content

[0179] In this application, the carbon content is determined using a carbon-sulfur analyzer. Specifically, according to the examples of this application, the carbon content is determined by the following method: Oxygen is introduced into the combustion furnace, and the sample is oxidized by oxygen at high temperature in the combustion furnace, so that the carbon and sulfur in the sample are oxidized to CO2, CO, and SO2. The generated oxides are loaded into the sulfur detection cell by oxygen after passing through the dust removal and water purification devices to measure sulfur. Thereafter, the mixed gas containing CO2, CO, SO2, and O2 enters the heated catalyst furnace together. In the catalyst furnace, CO is catalytically converted to CO2 and SO2 is catalytically converted to SO3. After this mixed gas enters the sulfur removal reagent tube, it is introduced into the carbon detection cell to measure carbon. The residual gas is discharged to the outside by the analyzer. At the same time, the analysis results of carbon and sulfur are displayed in the form of %C and %S.

[0180] 3. Compaction Density

[0181] In this application, the compaction density of the powder can be determined with reference to Standard GB / T 24533-2009. Specifically, a powder compaction density meter can be used for determination.

[0182] 4. Powder Resistivity

[0183] In this application, the resistivity of the powder is determined by the four-probe method. Specifically, according to the embodiments of this application, the resistivity is determined by the following method: Fill the positive electrode material into the equipment cavity. Fix four copper plates with a length of 1.5 cm * width of 1 cm * thickness of 2 mm equidistantly on a line. The distance between the middle two copper plates is L (1 cm to 2 cm). The base material for fixing the copper plates is an insulating material. During the test, press the lower end faces of the four copper plates on the measured electrode plate. Connect the two end copper plates to a direct current I, measure the voltage V between the middle two copper plates, read the values of I and V three times, and take the average values of I and V. V / I is the resistance of the electrode plate at the test location.

[0184] 5. Specific Capacity

[0185] According to the embodiments of this application, the capacitance test per unit area of the positive electrode film can be carried out according to the following steps: Step 1): Fully discharge the button cell containing the positive electrode plate, and after standing for 5 minutes, charge it to the cut-off voltage. Specifically, during the charging process, first charge it at a constant current of 1 / 3C to the cut-off voltage, and then charge it at a constant voltage of the cut-off voltage until 0.03C. The charging capacity C0 obtained at this time is the discharge capacity of the positive electrode film. Step 2): Measure and calculate the total area of the positive electrode film (here, the total area refers to the coating area; if it is double-sided coating, the coating areas on both sides need to be added). Step 3): According to the capacitance per unit area of the positive electrode film = discharge capacity (mAh) of the positive electrode film / total area (cm 2 ), calculate the capacitance per unit area of the positive electrode film.

[0186] 6. Cycle Capacity Retention Rate

[0187] 1. The secondary battery is left standing at 25°C for 30 min and discharged at 0.33C to 2.5V. It is left standing at 25°C for 30 min and charged at a constant current and constant voltage of 1C to 3.65V with a cut-off current of 0.05C. It is left standing at 25°C for 30 min and discharged at 0.33C to 2.5V (one cycle). After repeating the cycle 100 times, measure its capacity. The ratio to the initial capacity is the 25°C / 1C 100-cycle capacity retention rate.

[0188] Table 1: Performance Test Results of Examples 1 to 10 and Comparative Examples 1 to 4

[0189]

[0190] According to the above results, compared with Comparative Examples 1 to 3, Examples 1 to 10 have lower resistivity, higher gram capacity, and higher cycle capacity retention rate. Figure 7 This is a scanning electron microscope image of the lithium manganese iron phosphate material obtained in Example 1 of the present application. It can be seen from the image that the material particles are uniform and the morphology is regular.

[0191] In comparative example 1, since no screening treatment was performed, the lithium iron manganese phosphate precursor contained a large amount of aluminum impurities with a low melting point. After sintering, it preferentially formed aluminum carbide with carbon, which reduced the compaction density. At the same time, since the carbon was consumed by aluminum, the carbon coating layer of the lithium iron manganese phosphate was uneven, resulting in reduced conductivity. In comparative example 2, since the heating temperature of the positive electrode plate was too low, the polyvinylidene fluoride (PVDF) in the positive electrode plate had not yet decomposed and failed, and the positive electrode material could not be desorbed and recovered, resulting in the inability to recover the lithium iron manganese phosphate material. In comparative example 3, since the sintering temperature was too high, the lithium iron manganese phosphate material obtained had poor conductivity.

[0192] Compared with Comparative Example 4, Examples 1 to 10 have higher fluorine content and higher gram capacity, indicating that fluorine-doped lithium manganese iron phosphate materials, such as lithium manganese iron phosphate with a fluorine content of 500ppm-5000ppm by mass, have higher gram capacity.

[0193] In summary, the method for recovering lithium manganese iron phosphate provided in the present application restores the original crystal structure by adding at least one element such as lithium, manganese, and iron to the crystal structure, thereby realizing the repair and regeneration of all elements of lithium manganese iron phosphate, and realizing simple, environmentally friendly, safe, and high-yield recovery of lithium iron phosphate materials, so that the secondary battery containing the obtained lithium manganese iron phosphate material exhibits better conductivity, higher capacity, and better cycle performance.

[0194] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for recycling lithium iron manganese phosphate, characterized in that, Specifically, it includes the following steps: Heat the positive electrode sheet including the lithium iron manganese phosphate at 400°C - 800°C to obtain an initial recycled solid material; Sieve the initial recycled solid material to obtain lithium iron manganese phosphate recycled powder; Supplement raw materials in the lithium iron manganese phosphate recycled powder, and the raw materials include at least one of a lithium source, an iron source, and a manganese source to obtain a lithium iron manganese phosphate precursor; Sinter the lithium iron manganese phosphate precursor at 600°C - 800°C to obtain a regenerated lithium iron manganese phosphate material.

2. The recycling method of a lithium iron manganese phosphate according to claim 1, characterized in that The positive electrode sheet includes a binder, and the binder includes fluorine element.

3. The recycling method of a lithium iron manganese phosphate according to claim 2, characterized in that The step of supplementing the raw materials includes: adding at least one of a lithium source, an iron source, and a manganese source, so that the molar ratio of lithium element, manganese element, the sum of iron element and phosphorus element is Li:(Mn + Fe):P = 1 - 1.05:0.94 - 1:1 to obtain the lithium iron manganese phosphate precursor.

4. The recycling method of a lithium iron manganese phosphate according to any one of claims 1 - 3, characterized in that The manganese source includes one or a combination of more of manganese chloride, manganese oxalate, manganese acetate, manganese carbonate, iron manganese oxalate, and iron manganese carbonate.

5. The recycling method of a lithium iron manganese phosphate according to any one of claims 1 - 3, characterized in that Before the sintering step, test the carbon content of the lithium iron manganese phosphate precursor, and supplement a carbon source according to the carbon content so that the carbon content of the lithium iron manganese phosphate precursor is 1% - 2%.

6. The recycling method of a lithium iron manganese phosphate according to any one of claims 1 - 3, characterized in that The sintering temperature of the sintering step is 650°C - 750°C.

7. The recycling method of a lithium iron manganese phosphate according to any one of claims 1 - 3, characterized in that Before the sintering step, mix, sand mill, and spray dry the lithium iron manganese phosphate precursor, wherein the particles of the lithium iron manganese phosphate precursor are sand milled to Dv50 ≤ 0.7 μm.

8. The recycling method of a lithium iron manganese phosphate according to any one of claims 1 - 3, characterized in that The sieving step includes primary sieving and secondary sieving. The mesh number of the primary sieving is less than the mesh number of the secondary sieving, and the mesh number of the primary sieving ≥ 200 meshes.

9. A lithium iron manganese phosphate material, characterized in that, The lithium iron manganese phosphate material is doped with fluorine element, and the mass content of the fluorine element in the lithium iron manganese phosphate material is 500 ppm - 5000 ppm.

10. A secondary battery, characterized in that, It includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a current collector and the lithium iron manganese phosphate material according to claim 9.

11. An electrical device, characterized in that, It includes at least one selected from the lithium iron manganese phosphate material according to claim 9 or the secondary battery according to claim 10.

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