Method for preparing lithium iron manganese phosphate positive electrode material from lithium iron phosphate waste material

Abstract

The invention relates to a method for preparing a lithium iron manganese phosphate positive electrode material by using a lithium iron phosphate waste material, which comprises the following steps: (1) weighing the lithium iron phosphate waste material, a manganese source, a lithium source and a phosphorus source according to the stoichiometric ratio of each element in LixMnyFezPO4, and uniformly mixing with a first carbon source in a solvent to obtain a first slurry, carrying out primary sanding, primary spray drying and primary sintering treatment to obtain a first sintered material; and (2) uniformly mixing the first sintered material and a second carbon source in a solvent to obtain second slurry, and carrying out secondary sanding, secondary spray drying and secondary sintering treatment to obtain the lithium manganese iron phosphate positive electrode material. By adopting the preparation method and regulating and controlling the addition amount of the first carbon source and the second carbon source, the lithium manganese iron phosphate positive electrode material with uniform grain size can be prepared, the specific surface area is low, the surface carbon coating layer is compact and uniform, the material compaction can be effectively improved, and the material Mn dissolution can be reduced; and the lithium ion battery constructed by the material has high specific capacity and better rate capability.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and specifically to a method for preparing lithium manganese iron phosphate cathode material using lithium iron phosphate waste. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, the demand for lithium-ion batteries has surged, leading to an explosive growth in the number of waste batteries. Lithium iron phosphate (LFP) batteries, due to their high safety and long cycle life, occupy a significant market share in the power battery and energy storage fields. However, improper disposal of large quantities of retired LFP batteries will result in resource waste and environmental pollution.

[0003] Currently, the main methods for recycling lithium iron phosphate (LFP) waste include hydrometallurgy, pyrometallurgy, and remediation / regeneration technologies. Hydrometallurgy requires strong acids or alkalis, resulting in complex processes, long preparation cycles, high energy consumption, and the potential introduction of impurities. While pyrometallurgy is simple to operate, LFP's unique olivine crystal structure necessitates roasting at temperatures far exceeding those of lithium cobalt oxide and lithium manganese oxide, requiring extremely high temperatures to reduce the metal. This leads to additional resource depletion and the generation of harmful gases. Remediation / regeneration technologies do not damage the material; they directly repair the crystal structure of the cathode material without metal leaching, thereby restoring its electrochemical performance. Although LFP can be repaired through high-temperature roasting with added lithium, the repaired LFP often suffers from excessively high carbon content and poor cycle life, failing to meet the demands of extended battery life. Therefore, simply repairing and utilizing LFP has limited value.

[0004] Lithium manganese iron phosphate (LMFP), as an upgraded material of lithium iron phosphate, not only has a higher operating voltage than lithium iron phosphate, but also has advantages in cost and safety performance compared to ternary materials. Therefore, it is widely recognized as a feasible alternative to lithium iron phosphate. If lithium iron phosphate waste can be converted into high-value-added LMFP materials, it can not only reduce raw material costs, but also achieve closed-loop recycling of waste batteries, which is in line with the concept of green circular economy.

[0005] Therefore, developing a low-cost and efficient method for preparing high-performance manganese iron phosphate using lithium iron phosphate waste as raw material has significant industrial value and environmental implications. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for preparing lithium manganese iron phosphate cathode materials using lithium iron phosphate waste. After determining the elemental proportions of the lithium iron phosphate waste, it is mixed with a manganese source, phosphorus source, lithium source, and a first carbon source, then milled, sprayed, and sintered under an inert atmosphere to obtain a first sintered material. The first sintered material is then mixed with a second carbon source and subjected to a second milling, carbon coating, spraying, inert atmosphere sintering, crushing, sieving, and impurity removal to obtain the lithium manganese iron phosphate cathode material. By controlling the amount of the first and second carbon sources added, the particle size after the first crystallization and the density and uniformity of the carbon coating layer are adjusted, thereby obtaining a lithium manganese iron phosphate cathode material with low specific surface area and high specific capacity.

[0007] This invention provides the following technical solutions:

[0008] The first aspect of this invention provides a method for preparing lithium manganese iron phosphate cathode material using recycled lithium iron phosphate waste, comprising the following steps:

[0009] (1) According to Li x Mn y Fe z The stoichiometric ratio of each element in PO4 is determined by weighing lithium iron phosphate waste, manganese source, lithium source and phosphorus source, and mixing them evenly with the first carbon source in a solvent to obtain a first slurry. After one sand milling, the slurry is spray-dried to obtain a first spray material. The first spray material is then sintered under an inert atmosphere to obtain a first sintered material.

[0010] (2) The first sintering material and the second carbon source are mixed evenly in a solvent to obtain a second slurry. After secondary sand milling, the slurry is subjected to secondary spray drying to obtain a second spray material. The second spray material is subjected to secondary sintering under an inert atmosphere. After crushing, sieving, and impurity removal, the lithium manganese iron phosphate cathode material is obtained.

[0011] The Li x Mn y Fe z In the molecular formula of PO4, 1.0≤x≤1.05, 0.2≤y≤0.8, 0.2≤z≤0.8, and y+z=1;

[0012] The amount of the first carbon source added satisfies that the carbon content accounts for 0.1wt%-0.5wt% of the target mass of the prepared lithium manganese iron phosphate cathode material; the amount of the second carbon source added satisfies that the carbon content accounts for 1.3wt%-2wt% of the target mass of the prepared lithium manganese iron phosphate cathode material; wherein, the target mass of the prepared lithium manganese iron phosphate cathode material is the mass of the theoretically obtainable lithium manganese iron phosphate cathode material.

[0013] Based on the amounts of lithium iron phosphate waste, manganese source, lithium source, and phosphorus source added, calculate the mass m of the lithium manganese iron phosphate cathode material prepared without introducing the first carbon source and the second carbon source. The theoretically obtainable mass of lithium manganese iron phosphate cathode material with the addition of the first carbon source and the second carbon source is M = m / (1-ab), where a and b are set values. a is the percentage of carbon content introduced by the first carbon source into the target lithium manganese iron phosphate cathode material, 0.1wt%≤a≤0.5wt%, and b is the percentage of carbon content introduced by the second carbon source into the target lithium manganese iron phosphate cathode material, 1.3wt%≤b≤2wt%.

[0014] Based on the carbon content M×a introduced into the target preparation of lithium manganese iron phosphate cathode material by adding the first carbon source, the theoretical amount of the first carbon source required is calculated as m1=(M×a) / k, where k is the mass percentage of carbon atoms in the first carbon source.

[0015] Based on the carbon content M×b introduced into the target preparation of lithium manganese iron phosphate cathode material by adding the second carbon source, the theoretical amount of the first carbon source required is calculated as m1=(M×b) / l, where l is the mass percentage of carbon atoms in the second carbon source.

[0016] Furthermore, the chemical formula of the lithium manganese iron phosphate cathode material is Li x Mn y Fe z PO4@C.

[0017] Furthermore, in step (1), the lithium iron phosphate waste mainly comes from lithium iron phosphate separated from waste batteries, electrode sheets and scrap materials, as well as scrap materials from the lithium iron phosphate production process.

[0018] Furthermore, in step (1), the content of each element in the lithium iron phosphate waste is tested before use. For example, the content of elements such as Li, Fe, and P in the lithium iron phosphate waste can be obtained by inductively coupled plasma spectrometry (ICP), the content of Fe can be detected by potassium dichromate titration, the content of P can be determined by quinoline-molybdenum-copper gravimetric method, and the carbon content can be detected by carbon-sulfur analyzer.

[0019] Further, in step (1), the manganese source includes, but is not limited to, one or more of manganese tetroxide, manganese acetate, manganese oxalate, manganese trioxide, and manganese ferrous phosphate; the lithium source includes, but is not limited to, one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; the phosphorus source includes, but is not limited to, one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, and lithium dihydrogen phosphate; and the first carbon source includes, but is not limited to, one or more of glucose, polyethylene glycol, sucrose, starch, and citric acid.

[0020] Further, in step (1), the solid content of the first slurry is preferably 30%-50%.

[0021] Furthermore, in step (1), the first sand milling step involves using a horizontal sand mill to wet mix the first slurry.

[0022] Furthermore, in step (1), the medium for the first grinding is preferably 0.2 mm-1 mm zirconia balls.

[0023] Further, in step (1), the particle size D50 of the first slurry after one sand milling is preferably 0.4μm-0.6μm.

[0024] Further, in step (1), the primary spray drying is a two-fluid spray, pressure spray, or centrifugal spray; preferably, in the primary spray drying step: the inlet air temperature is 200-280℃, and the outlet air temperature is 80-120℃; more preferably, the moisture content of the first spray material is 0.5%-3%, and the particle size D50 of the first spray material is 15μm-30μm.

[0025] Further, in step (1), the inert atmosphere includes one or more of nitrogen, argon, and carbon dioxide.

[0026] Furthermore, in step (1), the primary sintering process is carried out in a tubular furnace or an atmosphere box sintering furnace.

[0027] Furthermore, in step (1), the temperature of the first sintering treatment is preferably 500-700℃, and the time is preferably 4-10h.

[0028] Further, in step (2), the second carbon source includes one or more of glucose, polyethylene glycol, sucrose, starch, and citric acid.

[0029] Furthermore, in step (2), the solid content of the second slurry is preferably 30%-50%.

[0030] Furthermore, in step (2), the second sand milling step involves using a horizontal sand mill to wet mix the second slurry.

[0031] Furthermore, in step (2), the medium for the secondary sand milling is preferably 0.2 mm-1 mm zirconium oxide.

[0032] Furthermore, in step (2), the particle size D50 of the second slurry after secondary sand milling is preferably 0.25μm-0.45μm.

[0033] Further, in step (2), the secondary spray drying is a two-fluid spray, pressure spray, or centrifugal spray; preferably, in the secondary spray drying step: the inlet air temperature is 200-280℃, and the outlet air temperature is 80-120℃; more preferably, the moisture content of the second spray material is 0.5%-3%, and the particle size D50 of the second spray material is 15μm-30μm.

[0034] Further, in step (2), the inert atmosphere includes one or more of nitrogen, argon, and carbon dioxide.

[0035] Furthermore, in step (2), the secondary sintering process is carried out in a tube furnace or an atmosphere box sintering furnace.

[0036] Furthermore, in step (2), the temperature of the secondary sintering treatment is preferably 700-780℃, and the time is preferably 6-12h.

[0037] Furthermore, in step (2), the pulverization step involves: airflow pulverization, and the material particle size D is adjusted by controlling the pulverization and grading frequency. min ≥0.2μm, 0.3μm≤D50≤1.1μm, D max ≤12μm.

[0038] The second aspect of the present invention provides a lithium manganese iron phosphate cathode material, which is prepared by the method described in the first aspect.

[0039] A third aspect of the present invention provides a lithium-ion battery comprising the lithium manganese iron phosphate cathode material described in the second aspect.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] 1. This invention provides a method for preparing lithium manganese iron phosphate cathode material using lithium iron phosphate waste. Using lithium iron phosphate waste as the main raw material, a first sintered material is obtained through a process of micro-carbon supplementation followed by primary milling, spraying, and sintering crystallization. This first sintered material is then subjected to a second milling, spraying, and sintering process with a second carbon source to obtain a lithium manganese iron phosphate cathode material with a dense and uniform carbon layer coated on its surface. This preparation method is simple, requires minimal equipment, and fully utilizes all elements in the lithium iron phosphate waste, avoiding resource waste while reducing the raw material cost for preparing lithium manganese iron phosphate. It is suitable for large-scale production applications.

[0042] 2. The lithium manganese iron phosphate cathode material prepared by the above method has low cost, uniform grain size and good roundness, low specific surface area, no floating carbon generation, good dispersibility and dense and uniform surface carbon coating layer, which can effectively improve material compaction and reduce Mn dissolution. The lithium-ion battery constructed with it exhibits high discharge specific capacity and better rate performance. Attached Figure Description

[0043] Figure 1 This is a scanning electron microscope (SEM) image of the lithium manganese iron phosphate cathode material prepared in Example 1 of the present invention;

[0044] Figure 2 This is a SEM image of the lithium manganese iron phosphate cathode material prepared in Comparative Example 1 of this invention;

[0045] Figure 3 Charge-discharge curves of a coin cell constructed using the lithium manganese iron phosphate cathode material prepared in Example 3 of this invention under 0.1C conditions. Detailed Implementation

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. "Comprising" or "containing" as used herein means that it may include or contain other components in addition to the stated components. "Comprising" or "containing" as used herein may also be replaced with the closed form "is" or "consisting of".

[0047] As described in the background section, lithium iron phosphate (LFP) waste presents challenges such as high recycling difficulty, high energy consumption, and complex recycling processes. In contrast, lithium manganese iron phosphate (LMFP) not only has a higher operating voltage than LFP but also offers cost and safety advantages compared to ternary lithium batteries, making it a viable alternative to LFP. Converting LFP waste into high-value-added LMFP materials would not only reduce raw material costs but also enable closed-loop recycling of used batteries, aligning with the principles of a green circular economy.

[0048] Based on this, the present invention provides a method for preparing lithium manganese iron phosphate cathode material using recycled lithium iron phosphate waste. This method can make full use of lithium iron phosphate waste and prepare high-energy-density lithium manganese iron phosphate cathode material at low cost. The specific steps include:

[0049] (1) According to Li x Mn y Fe z The lithium iron phosphate waste, manganese source, lithium source and phosphorus source are weighed according to the stoichiometric ratio of each element in PO4, and mixed evenly with the first carbon source in a solvent to obtain the first slurry. After one sand milling, it is spray dried once to obtain the first spray material. The first spray material is placed in an inert atmosphere for one sintering treatment to obtain the first sintered material.

[0050] (2) The first sintering material and the second carbon source are mixed evenly in a solvent to obtain a second slurry. After secondary sand milling, the slurry is subjected to secondary spray drying to obtain a second spray material. The second spray material is subjected to secondary sintering under an inert atmosphere. After crushing, sieving, and impurity removal, the lithium manganese iron phosphate cathode material is obtained.

[0051] The Li x Mn y Fe z In the molecular formula of PO4, 1.0≤x≤1.05, 0.2≤y≤0.8, 0.2≤z≤0.8, and y+z=1;

[0052] The amount of the first carbon source added satisfies that the carbon content accounts for 0.1wt%-0.5wt% of the target mass of the prepared lithium manganese iron phosphate cathode material; the amount of the second carbon source added satisfies that the carbon content accounts for 1.3wt%-2wt% of the target mass of the prepared lithium manganese iron phosphate cathode material; wherein, the target mass of the prepared lithium manganese iron phosphate cathode material is the mass of the theoretically obtainable lithium manganese iron phosphate cathode material.

[0053] The mass of the lithium iron phosphate cathode material prepared according to the above target was calculated by the following method: based on Li x Mn y Fe z The stoichiometric ratio of each element in PO4 is used to determine the amount of lithium iron phosphate waste, manganese source, lithium source, and phosphorus source to be added. The mass m of lithium manganese iron phosphate cathode material prepared without the introduction of the first carbon source and the second carbon source is calculated. The mass of lithium manganese iron phosphate cathode material that can be theoretically prepared by adding the first carbon source and the second carbon source is M = m / (1-ab), where a and b are set values. a is the percentage of carbon content introduced by the first carbon source in the target lithium manganese iron phosphate cathode material, 0.1wt%≤a≤0.5wt%, and b is the percentage of carbon content introduced by the second carbon source in the target lithium manganese iron phosphate cathode material, 1.3wt%≤b≤2wt%.

[0054] Based on the carbon content M×a introduced into the target preparation of lithium manganese iron phosphate cathode material by adding the first carbon source, the theoretical amount of the first carbon source required is calculated as m1=(M×a) / k, where k is the mass percentage of carbon atoms in the first carbon source.

[0055] Based on the carbon content M×b introduced into the target preparation of lithium manganese iron phosphate cathode material by adding the second carbon source, the theoretical amount of the first carbon source required is calculated as m1=(M×b) / l, where l is the mass percentage of carbon atoms in the second carbon source.

[0056] To address the problem of recycling and reusing lithium iron phosphate (LFP) waste, this invention provides a method for converting LFP waste into high-value-added lithium manganese iron phosphate (LMP) cathode material. On one hand, it fully utilizes the lithium, iron, manganese, and phosphorus elements in the LFP waste, along with other lithium, manganese, and phosphorus sources, to prepare LMP. Simultaneously, it utilizes the carbon coating layer of the LFP waste itself, along with a trace amount of carbon supplementation (a first carbon source), to form a first sintered material with uniform elemental distribution and suitable particle size through a single milling, spray drying, and sintering process. Then, it is combined with a suitable amount of a second carbon source through a second milling, spray drying, and sintering process to form a LMP cathode material with a dense and uniform carbon layer on its surface. The above preparation method has a simple process flow, low equipment requirements, can fully utilize the various elements in the LFP waste, effectively reduces the preparation cost of LMP, and is suitable for industrial applications.

[0057] In the above preparation method, the amount of the first carbon source and the second carbon source added will affect the electrochemical performance of the prepared lithium manganese iron phosphate cathode material. The amount of the first carbon source added mainly affects the particle size of the first sintered material and the amount of floating carbon generated during the secondary milling process. If the amount of the first carbon source added is too low, the particles of the first sintered material will be too large, making it difficult to mill during the secondary milling process. This will easily lead to uneven composition in the final cathode material. However, the amount of the first carbon source added should not be too high either. Too much first carbon source added will generate more floating carbon during the secondary milling process, which will easily clog the equipment and make the components of the material easily dispersed unevenly. This is not conducive to the compaction of the material and the integrity of the carbon coating, thus affecting the material performance. Therefore, in this invention, the amount of the first carbon source added needs to be controlled within a suitable range, that is, the amount of the first carbon source added should meet the requirement that the carbon content accounts for 0.1wt%-0.5wt% of the mass of the target prepared lithium manganese iron phosphate cathode material, such as 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, etc., including but not limited to the listed mass percentages. Within this range, problems such as excessively large particles in the first sintering material and excessive floating carbon during the secondary sand milling process can be effectively avoided. In addition, unlike the first carbon source mentioned above, the second carbon source is mainly added to carbon-coat lithium manganese iron phosphate, in order to reduce the conductivity of lithium manganese iron phosphate and improve the stability of the material. Therefore, the amount of the second carbon source added should not be too low. If the amount added is too low, some lithium manganese iron phosphate will have missing coating layers on the surface, resulting in partial exposure of lithium manganese iron phosphate particles. This will not only affect its conductivity, but also lead to manganese dissolution, reducing the material's cycle and capacity performance. However, the amount of the second carbon source added should not be too high either. If the content of the second carbon source is too high, it will increase intergranular carbon and floating carbon, affecting the compaction performance of the cathode material. To ensure the density and uniformity of the carbon coating layer on the surface of lithium manganese iron phosphate, and to prevent excessive carbon source content from affecting battery energy density, the amount of the second carbon source added must meet the requirement that the carbon content accounts for 1.3wt%-2wt% of the target mass of the prepared lithium manganese iron phosphate cathode material, such as 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, etc., including but not limited to the mass percentages listed above.

[0058] The lithium manganese iron phosphate cathode material prepared by the preparation method provided by the present invention has low cost, uniform grain size and good roundness, low specific surface area, no floating carbon generation, good dispersibility and dense and uniform surface carbon coating layer, which can effectively improve material compaction and reduce Mn dissolution, thereby improving the discharge specific capacity and rate performance of lithium-ion batteries constructed from it.

[0059] In this invention, the aforementioned lithium manganese iron phosphate cathode material comprises a lithium manganese iron phosphate core and a carbon coating layer on its surface, the chemical formula of which is Li. x Mn y Fe zPO4@C, where 1.0≤x≤1.05, 0.2≤y≤0.8, 0.2≤z≤0.8, and y+z=1.

[0060] In step (1) of this invention, the lithium iron phosphate waste can be derived from lithium iron phosphate separated from waste batteries, electrode sheets and scrap materials, as well as waste materials from the lithium iron phosphate production process. Before use, the content of each element in the lithium iron phosphate waste is tested. For example, the content of elements such as Li, Fe and P in the lithium iron phosphate waste can be obtained by inductively coupled plasma spectrometry (ICP). Alternatively, the content of Fe can be detected by potassium dichromate titration, the content of P can be determined by quinoline molybdenum copper gravimetric method, and the carbon content can be detected by carbon-sulfur analyzer.

[0061] In step (1) of this invention, the manganese source includes, but is not limited to, one or more of manganese tetroxide, manganese acetate, manganese oxalate, manganese trioxide, and ferrous manganese phosphate; the lithium source includes, but is not limited to, one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; the phosphorus source includes, but is not limited to, one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, and lithium dihydrogen phosphate; the first carbon source includes, but is not limited to, one or more of glucose, polyethylene glycol, sucrose, starch, and citric acid; the types of lithium source, manganese source, iron source, phosphorus source, and carbon source are not limited in this invention, and other materials conventionally used in the art may also be used.

[0062] In step (1) of the present invention, the solid content of the first slurry is preferably 30%-50%, such as 30%, 35%, 40%, 45%, 50%, etc., including but not limited to the solid content listed above.

[0063] In step (1) of the present invention, in the above-mentioned first sand milling step: a horizontal sand mill is used to wet mix the first slurry; wherein, 0.2mm-1mm zirconia balls are used as the sand milling medium, and the particle size D50 of the first slurry after the first sand milling is controlled in the range of 0.4μm-0.6μm, for example 0.4μm, 0.45μm, 0.5μm, 0.55μm, 0.6μm, etc.

[0064] In step (1) of the present invention, the above-mentioned primary spray drying can be two-fluid spray, pressure spray or centrifugal spray; preferably, in the primary spray drying step: the inlet air temperature is 200-280℃ and the outlet air temperature is 80-120℃; more preferably, the moisture content of the first spray material formed after primary spray drying is 0.5%-3%, for example 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc., and the particle size D50 of the first spray material is 15μm-30μm, for example 15μm, 20μm, 25μm, 30μm, etc.

[0065] In step (1) of the present invention, the inert atmosphere includes one or more of nitrogen, argon, and carbon dioxide.

[0066] In step (1) of the present invention, the first sintering process is carried out in a tube furnace or an atmosphere box sintering furnace. Preferably, the temperature is raised to 500-700°C at a heating rate of 1-5°C / min and held for 4-10 hours for the first sintering process.

[0067] In step (2) of the present invention, the second carbon source includes one or more of glucose, polyethylene glycol, sucrose, starch, and citric acid. The present invention does not limit the type of the second carbon source, and other carbon source materials commonly used in the art can also be used.

[0068] In step (2) of the present invention, the solid content of the second slurry is preferably 30%-50%, such as 30%, 35%, 40%, 45%, 50%, etc., including but not limited to the solid content listed above.

[0069] The solid content of both the first and second slurries affects the material dispersion uniformity and the crystallization process. Too low a solid content (<30%) leads to decreased drying efficiency during spraying, resulting in insufficient drying and continued evaporation of excess moisture during subsequent sintering, thus impacting the crystallization process. Conversely, too high a solid content (>50%) increases slurry viscosity, causing uneven raw material dispersion and particle adhesion or nozzle clogging during spraying. Therefore, it is preferable to control the solid content of the first and second slurries within the range of 30%-50% to optimize the crystallization process, material uniformity, and processability.

[0070] In step (2) of the present invention, in the above-mentioned secondary sand milling step: a horizontal sand mill is used to wet mix the second slurry; preferably, 0.2mm-1mm zirconia balls are used as the sand milling medium, and the particle size D50 of the first slurry after the first sand milling is controlled within the range of 0.25μm-0.45μm, for example, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, etc.

[0071] In step (2) of the present invention, the above-mentioned secondary spray drying can be two-fluid spray, pressure spray or centrifugal spray; preferably, in the secondary spray drying step: the inlet air temperature is 200-280℃ and the outlet air temperature is 80-120℃; more preferably, the moisture content of the first spray material formed after secondary spray drying is 0.5%-3%, for example 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc., and the particle size D50 of the second spray material is 15μm-30μm, for example 15μm, 20μm, 25μm, 30μm, etc.

[0072] In this invention, the water content in the first and second spray materials affects the crystallization process and the dispersibility of the particles. If the water content is too high, the specific surface area of ​​the prepared lithium manganese iron phosphate cathode material is large and the compaction density is low, which affects the discharge capacity of the lithium battery constructed from it.

[0073] In step (2) of the present invention, the inert atmosphere includes one or more of nitrogen, argon, and carbon dioxide.

[0074] In step (2) of this invention, the secondary sintering process is carried out in a tube furnace or an atmosphere box sintering furnace. Preferably, the temperature is raised to 700-780°C at a heating rate of 1-5°C / min and held for 6-12 hours for secondary sintering.

[0075] In step (2) of this invention, air jet milling is used to perform the above-mentioned milling operation, and the particle size of the material is adjusted by controlling the milling and grading frequency to meet the D requirement. min ≥0.2μm, 0.3μm≤D50≤1.1μm, D max ≤12μm.

[0076] The present invention also provides a lithium manganese iron phosphate cathode material, which is prepared by the above preparation method.

[0077] In addition, the present invention provides a lithium-ion battery comprising the above-mentioned lithium manganese iron phosphate cathode material, which exhibits high specific capacity and excellent rate performance.

[0078] The present invention will be further described below with reference to specific embodiments and accompanying drawings, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0079] The lithium iron phosphate waste used in the following examples and comparative examples comes from the same source, as detailed below:

[0080] Waste materials from lithium iron phosphate production were collected, crushed, and analyzed using inductively coupled plasma atomic emission spectrometry (ICP). The molar percentage of each element in the waste material was calculated based on the waste material's mass and the relative atomic masses of each element. The molar percentages of the elements were: Li:Fe:P = 1.04:0.97:1, and carbon accounted for 1.3% of the total mass.

[0081] Example 1

[0082] This embodiment relates to the preparation of a lithium iron phosphate cathode material, and the specific steps are as follows:

[0083] (1) According to Li 1.02 Mn 0.6 Fe 0.4The stoichiometric ratio of elements in PO4 is Li:Mn:Fe:PO4. 3- =1.02:0.6:0.4:1, weigh out lithium iron phosphate waste, lithium carbonate, ammonium dihydrogen phosphate and manganese acetate dihydrate and mix them together, add an appropriate amount of glucose, the amount of glucose added is sufficient to meet the requirement that the carbon content accounts for 0.1 wt% of the target mass of lithium manganese iron phosphate cathode material; then add deionized water, stir and disperse for 0.5 h to obtain the first slurry with a solid content of 30%.

[0084] The first slurry was milled using a sand mill with zirconia balls of 0.3-0.4 mm diameter as the milling media, until the slurry particle size D was reached. 50 The particle size was approximately 0.4 μm. The milled slurry was then spray-dried using a two-fluid spray drying process, with the inlet air temperature controlled at 200℃ and the outlet air temperature at 80℃, resulting in a moisture content of 2.9% and a particle size D... 50 The first spray material has a diameter of 26.3 μm.

[0085] The first spray material was loaded into a tube furnace for sintering. The sintering atmosphere was carbon dioxide. Before heating, the gas flow rate was increased to blow carbon dioxide to reduce the oxygen content in the furnace to below 50 ppm. The heating rate was controlled at 1℃ / min, the sintering temperature was 500℃, and the sintering time was 10h. After sintering, the furnace was cooled to room temperature to obtain the first sintered material.

[0086] (2) The first sintering material is mixed with polyethylene glycol and citric acid (the mass ratio of polyethylene glycol to citric acid is 2:1). The total amount of polyethylene glycol and citric acid added meets the requirement that the carbon content accounts for 1.9 wt% of the target mass of lithium manganese iron phosphate cathode material. Then deionized water is added and stirred and dispersed for 0.5 h to obtain a second slurry with a solid content of 30%.

[0087] The second slurry was milled using a sand mill with zirconia balls of 0.3-0.4 mm diameter as the milling media, until the slurry particle size D was reached. 50 The particle size was approximately 0.25 μm. The milled slurry was then spray-dried using a two-fluid spray dryer, with the inlet air temperature controlled at 260℃ and the outlet air temperature at 110℃, resulting in a moisture content of 1.21% and a particle size D... 50 The second spray material has a diameter of 28.3 μm.

[0088] The second spray material is loaded into a sagger and placed in an atmosphere box sintering furnace for sintering. The sintering atmosphere is nitrogen, and the oxygen content in the furnace is controlled to be reduced to below 50 ppm. The heating rate is controlled at 5℃ / min, the sintering temperature is 780℃, and the sintering time is 6h. After sintering, the furnace is cooled to room temperature to obtain the secondary sintered material.

[0089] The secondary sintering material was pulverized using an air jet mill. Parameters such as the grading frequency and pulverizing pressure were adjusted to control the finished particle size within D. min≥0.2μm, 0.3μm≤D 50 ≤0.6μm, D max Within the ≤8μm range, after sieving to remove impurities, lithium manganese iron phosphate cathode material is obtained.

[0090] The SEM image of the lithium manganese iron phosphate cathode material prepared in this embodiment is shown below. Figure 1 As shown, the prepared lithium manganese iron phosphate cathode material has uniform grain size and good roundness, and no floating carbon is observed. This also indicates that the carbon coating layer on the surface of the cathode material prepared by the above method is dense, which is beneficial to reduce the specific surface area and improve the material compaction.

[0091] Example 2

[0092] This embodiment relates to the preparation of a lithium manganese iron phosphate cathode material, which differs from Embodiment 1 only in the preparation of the first sintering material. The specific steps are as follows:

[0093] (1) According to Li 1.02 Mn 0.2 Fe 0.8 The stoichiometric ratio of elements in PO4 is Li:Mn:Fe:PO4. 3- =1.02:0.2:0.8:1, weigh out lithium iron phosphate waste, lithium hydroxide, diammonium hydrogen phosphate and manganese tetroxide and mix them together, add polyethylene glycol and starch (the mass ratio of polyethylene glycol and starch is 3:1), the total amount of polyethylene glycol and starch added meets the requirement that the carbon content accounts for 0.5 wt% of the target mass of lithium manganese iron phosphate cathode material; then add deionized water, stir and disperse for 0.5 h to obtain the first slurry with a solid content of 50%.

[0094] The first slurry was milled using a sand mill with zirconia balls of 0.6-0.8 mm diameter as the milling media, until the slurry particle size D was reached. 50 The particle size was approximately 0.6 μm. The milled slurry was then spray-dried using a centrifugal spray dryer, with the inlet air temperature controlled at 280℃ and the outlet air temperature at 120℃, to obtain a moisture content of 0.73% and a particle size D... 50 The first spray material has a diameter of 25.4 μm.

[0095] The first spray material was loaded into a tube furnace for sintering. The sintering atmosphere was argon. Before heating, the gas flow rate was increased to blow argon to reduce the oxygen content in the furnace to below 50 ppm. The heating rate was controlled at 2℃ / min, the sintering temperature was 700℃, and the sintering time was 4h. After sintering, the furnace was cooled to room temperature to obtain the first sintered material.

[0096] (2) The corresponding lithium manganese iron phosphate cathode material was prepared by operating in the same manner as in Example 1.

[0097] Example 3

[0098] This embodiment relates to the preparation of a lithium iron phosphate cathode material, and the specific steps are as follows:

[0099] (1) According to Li 1.02 Mn 0.6 Fe 0.4 The stoichiometric ratio of elements in PO4 is Li:Mn:Fe:PO4. 3- =1.02:0.6:0.4:1, weigh out lithium iron phosphate waste, lithium hydrogen phosphate, phosphoric acid, manganese oxalate and manganese trioxide and mix them together, add citric acid and sucrose (the mass ratio of citric acid and sucrose is 1:2), the total amount of citric acid and sucrose added meets the requirement that the carbon content accounts for 0.3 wt% of the target mass of lithium manganese iron phosphate cathode material; then add deionized water, stir and disperse for 0.5 h to obtain the first slurry with a solid content of 40%.

[0100] The first slurry was milled using a sand mill with zirconia balls of 0.6-0.8 mm diameter as the milling media, until the slurry particle size D was reached. 50 The particle size was approximately 0.45 μm. The milled slurry was then spray-dried using a centrifugal spray dryer, with the inlet air temperature controlled at 240℃ and the outlet air temperature at 110℃, resulting in a moisture content of 1.52% and a particle size D... 50 The first spray material has a diameter of 21.7 μm.

[0101] The first spray material was loaded into a sagger and placed in an atmosphere box sintering furnace for sintering. The sintering atmosphere was argon. Before heating, the gas flow rate was increased to blow argon gas and reduce the oxygen content in the furnace to below 50 ppm. The heating rate was controlled at 5℃ / min, the sintering temperature was 600℃, and the sintering time was 4h. After sintering, the furnace was cooled to room temperature to obtain the first sintered material.

[0102] (2) The first sintering material is mixed with glucose and polyethylene glycol (the mass ratio of glucose to polyethylene glycol is 1:2). The total amount of glucose and polyethylene glycol added meets the requirement that the carbon content accounts for 1.7 wt% of the target mass of lithium manganese iron phosphate cathode material. Then deionized water is added and stirred and dispersed for 0.5 h to obtain a second slurry with a solid content of 35%.

[0103] The second slurry was milled using a sand mill with zirconia balls of 0.3-0.4 mm diameter as the milling media, until the slurry particle size D was reached. 50 The particle size was approximately 0.38 μm. The milled slurry was then spray-dried using a centrifugal spray dryer, with the inlet air temperature controlled at 250°C and the outlet air temperature at 110°C, to obtain a particle size of 1.3% moisture and a particle size D... 50 The second spray material has a diameter of 25.9 μm.

[0104] The second spray material is loaded into a sagger and placed in an atmosphere box sintering furnace for sintering. The sintering atmosphere is nitrogen, and the oxygen content in the furnace is controlled to be reduced to below 50 ppm. The heating rate is controlled at 1.5℃ / min, the sintering temperature is 750℃, and the sintering time is 12h. After sintering, the furnace is cooled to room temperature to obtain the secondary sintered material.

[0105] The secondary sintering material was pulverized using an air jet mill. Parameters such as the grading frequency and pulverizing pressure were adjusted to control the finished particle size within D. min ≥0.2μm, 0.3μm≤D 50 ≤0.7μm, D max Within the ≤10μm range, after sieving to remove impurities, lithium manganese iron phosphate cathode material is obtained.

[0106] Example 4

[0107] This embodiment relates to the preparation of a lithium iron phosphate cathode material, and the specific steps are as follows:

[0108] (1) According to Li 1.02 Mn 0.58 Fe 0.42 The stoichiometric ratio of elements in PO4 is Li:Mn:Fe:PO4. 3- =1.02:0.58:0.42:1, weigh out lithium iron phosphate waste and mix it with lithium carbonate, phosphoric acid, anhydrous ferrous manganese phosphate and manganese tetroxide, add starch and sucrose (mass ratio of starch to sucrose is 1:2), the total amount of starch and sucrose added meets the requirement that the carbon content accounts for 0.4 wt% of the target mass of lithium manganese iron phosphate cathode material; then add deionized water, stir and disperse for 0.5 h to obtain the first slurry with a solid content of 38%.

[0109] The first slurry was milled using a sand mill with zirconia balls of 0.6-0.8 mm diameter as the milling media, until the slurry particle size D was reached. 50 The particle size was approximately 0.5 μm. The milled slurry was then spray-dried using pressure spray drying, with the inlet air temperature controlled at 230℃ and the outlet air temperature at 105℃, resulting in a moisture content of 1.83% and a particle size D... 50 The first spray material has a diameter of 25.4 μm.

[0110] The first spray material was loaded into a sagger and placed in an atmosphere box sintering furnace for sintering. The sintering atmosphere was nitrogen. Before heating, the gas flow rate was increased to purge nitrogen and reduce the oxygen content in the furnace to below 50 ppm. The heating rate was controlled at 3℃ / min, the sintering temperature was 700℃, and the sintering time was 6h. After sintering, the furnace was cooled to room temperature to obtain the first sintered material.

[0111] (2) The first sintering material is mixed with glucose and polyethylene glycol (the mass ratio of glucose to polyethylene glycol is 1:2). The total amount of glucose and polyethylene glycol added meets the requirement that the carbon content accounts for 1.65 wt% of the target mass of lithium manganese iron phosphate cathode material. Then deionized water is added and stirred and dispersed for 0.5 h to obtain a second slurry with a solid content of 42%.

[0112] The second slurry was milled using a sand mill with zirconia balls of 0.3-0.4 mm diameter as the milling media, until the slurry particle size D was reached. 50 The particle size was approximately 0.38 μm. The milled slurry was then spray-dried using a centrifugal spray dryer, with the inlet air temperature controlled at 250°C and the outlet air temperature at 110°C, to obtain a particle size of 1.3% moisture and a particle size D... 50 The second spray material has a diameter of 25.9 μm.

[0113] The second spray material is loaded into a sagger and placed in an atmosphere box sintering furnace for sintering. The sintering atmosphere is nitrogen, and the oxygen content in the furnace is controlled to be reduced to below 50 ppm. The heating rate is controlled at 1.5℃ / min, the sintering temperature is 750℃, and the sintering time is 12h. After sintering, the furnace is cooled to room temperature to obtain the secondary sintered material.

[0114] The secondary sintering material was pulverized using an air jet mill. Parameters such as the grading frequency and pulverizing pressure were adjusted to control the finished particle size within D. min ≥0.2μm, 0.3μm≤D 50 ≤0.7μm, D max Within the ≤10μm range, after sieving to remove impurities, lithium manganese iron phosphate cathode material is obtained.

[0115] Example 5

[0116] This embodiment relates to the preparation of a lithium manganese iron phosphate cathode material. The only difference from Embodiment 3 is that the solid content of the first slurry is 52% and the solid content of the second slurry is 20%. All other operations are the same, and the corresponding lithium manganese iron phosphate cathode material is prepared.

[0117] Example 6

[0118] This embodiment relates to the preparation of a lithium manganese iron phosphate cathode material, and the only difference from Embodiment 3 is:

[0119] In step (1), the milled slurry is spray-dried using pressure spraying, with the inlet air temperature controlled at 190℃ and the outlet air temperature at 75℃, to obtain a moisture content of 3.36% and a particle size D. 50 The first spray was 25.6 μm, and all other operations were the same.

[0120] In step (2), the milled slurry is spray-dried using centrifugal spray drying, with the inlet air temperature controlled at 180℃ and the outlet air temperature at 75℃, to obtain a moisture content of 4.79% and a particle size D. 50 The second spray was 27μm, and all other operations were the same.

[0121] The corresponding lithium iron manganese phosphate cathode material was prepared.

[0122] Comparative Example 1

[0123] This comparative example relates to the preparation of a lithium manganese iron phosphate cathode material. The difference from Example 1 is that the lithium manganese iron phosphate cathode material is prepared by a single sintering process. The specific steps are as follows:

[0124] According to Li 1.02 Mn 0.6 Fe 0.4 The stoichiometric ratio of elements in PO4 is Li:Mn:Fe:PO4. -3 =1.02:0.6:0.4:1, weigh out lithium iron phosphate waste, lithium carbonate, ammonium dihydrogen phosphate and manganese acetate and mix them together. Add an appropriate amount of glucose, the amount of glucose added is sufficient to meet the requirement that the carbon content accounts for 2.0 wt% of the target mass of lithium manganese iron phosphate cathode material. Then add deionized water and stir to disperse for 0.5 h to obtain a slurry with a solid content of 30%.

[0125] The slurry was milled using a sand mill with zirconia balls of 0.3-0.4 mm diameter as the milling media, until the slurry particle size D was reached. 50 The particle size was approximately 0.4 μm. The milled slurry was then spray-dried using a two-fluid spray drying process, with the inlet air temperature controlled at 200℃ and the outlet air temperature at 80℃, resulting in a moisture content of 4.21% and a particle size D... 50 It is a spray material with a diameter of 22.8 μm.

[0126] The sprayed material was loaded into a tube furnace for sintering. The sintering atmosphere was carbon dioxide. Before heating, the gas flow rate was increased to blow carbon dioxide to reduce the oxygen content in the furnace to below 50 ppm. The heating rate was controlled at 1℃ / min, the sintering temperature was 700℃, and the sintering time was 10h. After sintering, the furnace was cooled to room temperature to obtain lithium manganese iron phosphate cathode material.

[0127] The SEM image of the lithium manganese iron phosphate cathode material prepared in this comparative example is shown below. Figure 2 As shown, the prepared lithium manganese iron phosphate cathode material exhibits significant differences in grain size and generates numerous intergranular carbon layers, which affects material compaction, increases the material's specific surface area, and makes material processing difficult.

[0128] Comparative Example 2

[0129] This comparative example relates to the preparation of a lithium manganese iron phosphate cathode material. The only difference from Example 3 is that in step (1), the total amount of citric acid and sucrose added meets the requirement that the carbon content accounts for 0.9 wt% of the target mass of the prepared lithium manganese iron phosphate cathode material, and in step (2), the total amount of glucose and polyethylene glycol added meets the requirement that the carbon content accounts for 1.1 wt% of the target mass of the prepared lithium manganese iron phosphate cathode material. All other operations are the same, and the corresponding lithium manganese iron phosphate cathode material is prepared.

[0130] Application and performance testing

[0131] The lithium manganese iron phosphate cathode materials prepared in the above examples and comparative examples were used to construct coin cells and their electrochemical performance was tested, as follows:

[0132] (1) Assembly of button cells

[0133] Preparation of positive electrode sheet: The above-mentioned lithium manganese iron phosphate positive electrode material, binder (PVDF) and conductive agent (SP) are mixed in a mass ratio of 90:5:5, and NMP solvent is added to homogenize the slurry. After the slurry is suitable, it is coated on an infrared flat plate coating machine. Aluminum foil is used as the current collector. After coating, the electrode sheet is vacuum dried, rolled, die-cut, selected and weighed to obtain the positive electrode sheet.

[0134] The weighed electrode sheets were transferred to a Micron glove box, and the water and oxygen content in the glove box was controlled to be <0.1ppm for button cell assembly. The button cell casing was selected as CR2032 model, the negative electrode was lithium sheet, the separator was a polypropylene microporous membrane Celgard 2300, and the electrolyte was a 1mol / L LiPF6 solution of ethylene carbonate / dimethyl carbonate / diethyl carbonate (volume ratio of 1:1:1).

[0135] (2) Performance Testing

[0136] Electrochemical performance testing: The assembled coin cells were tested using a Blue Electric testing system. The constant temperature chamber was set to 25°C (room temperature). The coin cell test voltage range was 2.0-4.5V. 0.1C and 1C charge-discharge tests were performed: The cells were charged to 4.5V using a 0.1C constant current / constant voltage charging method and discharged to 2.0V using a 0.1C constant current / constant voltage discharging method. The discharge capacity was recorded, and the specific capacity under 0.1C rate conditions was calculated based on the mass of the active material in the electrode. Similarly, the cells were charged to 4.5V using a 1C constant current / constant voltage charging method and discharged to 2.0V using a 1C constant current / constant voltage discharging method. The discharge capacity was recorded, and the specific capacity under 1C rate conditions was calculated based on the mass of the active material in the electrode.

[0137] Carbon content test: The carbon content in each lithium manganese iron phosphate cathode material was tested using a carbon-sulfur analyzer in accordance with GB / T 20123-2006.

[0138] Specific surface area (BET) test: The BET method was performed using a specific surface area analyzer in accordance with GB / T 19587-2017.

[0139] Powder compaction density test: The compaction density was tested using a Sansi powder compactor, referring to the national standard GB / T 24533-2009. Test conditions: 4T. After zeroing the instrument, 1g ± 0.0050g of sample was weighed, and the constant pressure time was 30s. The results were recorded.

[0140] The test results are shown in Table 1 below:

[0141] Table 1

[0142]

[0143] As shown in Table 1, compared to the coin cell constructed with lithium manganese iron phosphate cathode material prepared by a single sintering process in Comparative Example 1, the coin cell constructed with lithium manganese iron phosphate cathode material prepared by a combination of micro-carbon supplementation, single crystallization, and secondary carbon coating in Example 1 exhibits superior discharge capacity under high-rate conditions. Furthermore, as shown in Examples 3, 5, and 6, the solid content of the first and second slurries, as well as the water content of the first and second sprayed materials, all affect the specific capacity of the battery during cathode material preparation.

[0144] Furthermore, as shown in Example 3 and Comparative Example 2, although the total amount of carbon source added during the preparation of lithium manganese iron phosphate cathode materials is the same in both examples, the control of the amount of the first and second carbon sources added has a significant impact on the carbon content and specific surface area of ​​the prepared cathode materials. In Comparative Example 2, the amount of the first carbon source added is relatively large, while the amount of the second carbon source added is relatively small. The prepared cathode material has a low carbon content and a small specific surface area. This is because excessive first carbon source produces more floating carbon, leading to a decrease in the carbon content contained in the material. Additionally, insufficient second carbon source results in an insufficiently dense carbon layer formed on the material surface, affecting the conductivity and stability of the material. Therefore, compared to the lithium manganese iron phosphate cathode material prepared in Example 3, the discharge capacity of the coin cell constructed from the lithium manganese iron phosphate cathode material prepared in Comparative Example 2 is significantly reduced under different rate conditions.

[0145] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing lithium manganese iron phosphate cathode material using recycled lithium iron phosphate waste, characterized in that, Includes the following steps: (1) According to Li x Mn y Fe z The stoichiometric ratio of each element in PO4 is determined by weighing lithium iron phosphate waste, manganese source, lithium source and phosphorus source, and mixing them evenly with the first carbon source in a solvent to obtain a first slurry. After one sand milling, the slurry is spray-dried to obtain a first spray material. The first spray material is then sintered under an inert atmosphere to obtain a first sintered material. (2) The first sintering material and the second carbon source are mixed evenly in a solvent to obtain a second slurry. After secondary sand milling, the slurry is subjected to secondary spray drying to obtain a second spray material. The second spray material is subjected to secondary sintering under an inert atmosphere. After crushing, sieving, and impurity removal, the lithium manganese iron phosphate cathode material is obtained. The Li x Mn y Fe z In the molecular formula of PO4, 1.0≤x≤1.05, 0.2≤y≤0.8, 0.2≤z≤0.8, and y+z=1; The amount of the first carbon source added satisfies that the carbon content accounts for 0.1wt%-0.5wt% of the target mass of the prepared lithium manganese iron phosphate cathode material; the amount of the second carbon source added satisfies that the carbon content accounts for 1.3wt%-2wt% of the target mass of the prepared lithium manganese iron phosphate cathode material; wherein, the target mass of the prepared lithium manganese iron phosphate cathode material is the mass of the theoretically obtainable lithium manganese iron phosphate cathode material.

2. The method according to claim 1, characterized in that, In step (1), the manganese source includes one or more of manganese tetroxide, manganese acetate, manganese oxalate, manganese trioxide, and manganese ferrous phosphate; The lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate. The phosphorus source includes one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, and lithium dihydrogen phosphate. The first carbon source includes one or more of glucose, polyethylene glycol, sucrose, starch, and citric acid.

3. The method according to claim 1, characterized in that, Step (1) must include at least one of the following features: (1) The solid content of the first slurry is 30%-50%; (2) In the first sand milling step: the first slurry is wet-mixed using a horizontal sand mill; (3) The medium used in the first grinding is 0.2mm-1mm zirconia balls; (4) The particle size D50 of the first slurry after one sand milling is 0.4μm-0.6μm.

4. The method according to claim 1, characterized in that, In step (1), the primary spray drying is a two-fluid spray, pressure spray, or centrifugal spray; In the single spray drying step: the inlet air temperature is 200-280℃, and the outlet air temperature is 80-120℃; The moisture content of the first spray material is 0.5%-3%; The particle size D50 of the first spray material is 15μm-30μm.

5. The method according to claim 1, characterized in that, In step (1), the inert atmosphere includes one or more of nitrogen, argon, and carbon dioxide; The primary sintering process is carried out in a tubular furnace or an atmosphere box sintering furnace. The temperature of the first sintering process is 500-700℃, and the time is 4-10h.

6. The method according to claim 1, characterized in that, Step (2) must include at least one of the following features: (1) The second carbon source includes one or more of glucose, polyethylene glycol, sucrose, starch, and citric acid; (2) The solid content of the second slurry is 30%-50%; (3) In the secondary sand milling step: the second slurry is wet-mixed using a horizontal sand mill; (4) The medium used in the secondary sand milling is 0.2mm-1mm zirconium oxide; (5) The particle size D50 of the second slurry after secondary sand milling is 0.25μm-0.45μm.

7. The method according to claim 1, characterized in that, In step (2), the secondary spray drying is a two-fluid spray, pressure spray, or centrifugal spray; In the secondary spray drying step: the inlet air temperature is 200-280℃, and the outlet air temperature is 80-120℃; The second spray material has a moisture content of 0.5%-3%; The particle size D50 of the second spray material is 15μm-30μm.

8. The method according to claim 1, characterized in that, Step (2) must include at least one of the following features: (1) The inert atmosphere includes one or more of nitrogen, argon, and carbon dioxide; (2) The secondary sintering process is carried out in a tube furnace or an atmosphere box sintering furnace; (3) The temperature of the secondary sintering treatment is 700-780℃ and the time is 6-12h; (4) In the pulverization step: airflow pulverization is used, and the particle size D of the material is adjusted by controlling the pulverization and grading frequency. min ≥0.2μm, 0.3μm≤D50≤1.1μm, D max ≤12μm.

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

10. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the lithium manganese iron phosphate cathode material as described in claim 9.

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