Ferric manganese phosphate precursor and preparation method thereof, lithium ferric manganese phosphate positive electrode material and preparation method thereof, positive plate and lithium ion battery

Abstract

The invention provides an iron manganese phosphate precursor and a preparation method thereof, a lithium iron manganese phosphate positive electrode material and a preparation method thereof, a positive plate and a lithium ion battery. The chemical formula of the ferromanganese phosphate precursor is MnaFebPO4, (a / b) is more than or equal to 0.67 and less than or equal to 9, and (a + b) is more than or equal to 1.15 and less than or equal to 1.43; the ferromanganese phosphate precursor has a secondary particle structure formed by primary particles, the Dmax of the ferromanganese phosphate precursor is 30-40 [mu] m, and the average particle size of the primary particles is 50-500 nm. The molar ratio of Mn to Fe in the manganese iron phosphate precursor is controlled within the range, and the high-voltage characteristic of manganese is combined with the stability characteristic of iron, so that the structural stability of the lithium manganese iron phosphate positive electrode material in the charge-discharge process is improved, the dissolution of transition metal ions and the decomposition of the electrode material are reduced, and the service life of the lithium manganese iron phosphate positive electrode material is prolonged. Therefore, the discharge capacity and the cycling stability of the lithium manganese iron phosphate positive electrode material can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular, to a manganese iron phosphate precursor, a preparation method thereof, a lithium manganese iron phosphate cathode material, a preparation method thereof, a cathode sheet, and a lithium-ion battery. Background Art

[0002] Currently, commonly used new energy power generation such as hydropower, geothermal energy, wind energy, tidal energy, and solar energy is restricted by the spatio-temporal environment and usage conditions, and large-scale energy storage devices are required to store the electricity generated by new energy sources, so as to truly solve the sustainability problem of energy production and consumption. Lithium-ion batteries have received extensive attention from researchers and the market due to their advantages such as high working voltage, low self-discharge, large energy density, long cycle life, no memory effect, and environmental friendliness. Due to the safety and cost advantages of lithium iron phosphate batteries, they have received unprecedented attention from the market and researchers. However, the current lithium iron phosphate cathode material has reached a development bottleneck, and it is difficult to improve the energy density to meet the higher market demand. Since iron has a relatively low voltage platform, after introducing manganese element with a high voltage platform on the basis of lithium iron phosphate, a lithium manganese iron phosphate (LMFP) cathode material with a higher average voltage can be obtained. Its energy density is 10-15% higher than that of lithium iron phosphate, and at the same time, it still has the high safety of phosphate-based cathode materials and the low-cost advantage compared with ternary cathode materials. Therefore, LMFP has attracted extensive attention from the industrial community and relevant researchers.

[0003] The solid-phase method and the co-precipitation precursor method are commonly used methods for synthesizing LMFP. Among them, the solid-phase method has a simple synthesis process and stable and controllable raw materials. However, it is difficult to disperse the raw materials evenly during the physical mixing process, and the synthesized LMFP has slightly poor crystallinity and consistency, low powder compaction, and obvious disadvantages in discharge capacity and long-term cycle performance. The co-precipitation precursor method uses a manganese iron precursor to prepare LMFP. Since the metal elements in the manganese iron precursor are highly homogeneously distributed, the synthesized LMFP has excellent performance and good consistency. However, at present, the improvement of the compaction density, discharge capacity, and cycle stability of LMFP by the co-precipitation precursor method is relatively limited. Summary of the Invention

[0004] The main object of the present invention is to provide a manganese iron phosphate precursor, a preparation method thereof, a lithium manganese iron phosphate cathode material, a preparation method thereof, a cathode sheet, and a lithium-ion battery, so as to solve the problems of low compaction density, low discharge capacity, and poor cycle stability of the lithium manganese iron phosphate cathode material in the prior art.

[0005] To achieve the above object, according to one aspect of the present invention, a manganese iron phosphate precursor is provided. The chemical formula of the manganese iron phosphate precursor is Mn a Fe bPO4, where 0.67 ≤ (a / b) ≤ 9 and 1.15 ≤ (a + b) ≤ 1.43; the manganese iron phosphate precursor has a secondary particle structure formed by primary particles, the Dmax of the manganese iron phosphate precursor is 30 - 40 μm, and the average particle size of the primary particles is 50 - 500 nm.

[0006] Further, the D10 of the above-mentioned manganese iron phosphate precursor is 1 - 3 μm, the D50 is 5 - 10 μm, and the D90 is 18 - 30 μm; and / or, the specific surface area of the manganese iron phosphate precursor is 5.0 - 11.0 m 2 / g; and / or, the tap density of the manganese iron phosphate precursor is 0.5 - 2.0 g / cm 3 .

[0007] According to another aspect of the present invention, there is provided a method for preparing the aforementioned manganese iron phosphate precursor, the preparation method comprising the following steps: Step S1, mixing a divalent manganese source, a trivalent iron source, an antioxidant and water to obtain a manganese iron mixed solution; Step S2, under a protective gas, dropping the manganese iron mixed solution, a phosphoric acid solution and an ammonia water solution into water under stirring in parallel to successively carry out a coprecipitation reaction and aging to obtain a manganese iron phosphate precursor.

[0008] Further, the temperature of the coprecipitation reaction is 20 - 45°C; and / or, the time for parallel dropping is the time of the coprecipitation reaction, and the time of the coprecipitation reaction is 10 - 20 h; and / or, the stirring speed of the coprecipitation reaction is 250 - 650 rpm; and / or, the pH value of the solution in the coprecipitation reaction is 2 - 5; preferably, the coprecipitation reaction includes a first coprecipitation reaction and a second coprecipitation reaction carried out successively, the time of the first coprecipitation reaction is 5 - 10 h; and / or, the stirring speed of the first coprecipitation reaction is 350 - 650 rpm; and / or, the pH value of the solution in the first coprecipitation reaction is 3 - 5; and / or, the time of the second coprecipitation reaction is 5 - 10 h; and / or, the stirring speed of the second coprecipitation reaction is 250 - 350 rpm; and / or, the pH value of the solution in the second coprecipitation reaction is 2 - 3; and / or, the temperature of aging is 20 - 45°C; and / or, the time of aging is 1 - 5 h.

[0009] Further, the total concentration of manganese and iron elements in the above-mentioned manganese-iron mixed solution is 0.25 to 2.5 mol / L; and / or, the concentration of the antioxidant in the manganese-iron mixed solution is 0.001 to 0.05 mol / L; and / or, the concentration of the phosphoric acid solution is 0.25 to 2.5 mol / L; and / or, the concentration of the ammonia water solution is 0.25 to 5 mol / L; and / or, the ratio of the total moles of manganese in the divalent manganese source and iron in the trivalent iron source to the moles of phosphate radicals in the phosphoric acid solution is (1.15 to 1.43):1; and / or, the divalent manganese source is selected from any one or more of manganese sulfate, manganese carbonate, manganese nitrate, manganese oxalate, manganese acetate, and manganese chloride; and / or, the trivalent iron source is selected from any one or more of iron sulfate, iron nitrate, iron oxalate, iron acetate, and iron chloride; and / or, the antioxidant is selected from any one or more of ascorbic acid, hydrazine hydrate, and sodium borohydride.

[0010] According to another aspect of the present invention, a method for preparing a lithium iron phosphate manganese cathode material is provided. The preparation method includes: sequentially performing a mixing treatment, a drying treatment, and a sintering treatment on raw materials including the aforementioned manganese iron phosphate precursor, a carbon source, a phosphorus source, and a lithium source with water to obtain the lithium iron phosphate manganese cathode material.

[0011] Further, the above-mentioned mixing treatment is a sanding treatment, and the particle size D50 in the slurry after the sanding treatment does not exceed 0.6 μm; and / or, the drying treatment is a spray drying treatment, and the inlet air temperature of the spray drying treatment is 200 to 400 °C; and / or, the outlet air temperature of the spray drying treatment is 90 to 120 °C; and / or, the heating rate of the sintering treatment is 2 to 5 °C / min; and / or, the temperature of the sintering treatment is 650 to 800 °C; and / or, the heat preservation time of the sintering treatment is 5 to 15 h; and / or, the ratio of the moles of lithium in the lithium source, the total moles of manganese and iron in the manganese iron phosphate precursor, and the moles of phosphorus in the phosphorus source is (1.1 to 1.4):(1.1 to 1.3):(1.11 to 1.37); preferably, the raw materials further include a doped metal source, and the ratio of the moles of lithium in the lithium source to the moles of the doped metal in the doped metal source is (1.1 to 1.4):0.003; and / or, the mass ratio of the carbon source in the raw materials is 1% to 30%; and / or, the mass ratio of water to the raw materials is (65 to 200):100; preferably, the lithium source is selected from any one or more of lithium hydroxide, lithium carbonate, lithium oxalate, and lithium nitrate; and / or, the phosphorus source is selected from any one or more of lithium phosphate, lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; and / or, the doped metal source is selected from any one or more of a magnesium source, a titanium source, an aluminum source, a tungsten source, a vanadium source, a niobium source, a nickel source, a cobalt source, and a yttrium source; and / or, the carbon source is selected from any one or more of glucose, citric acid, sucrose, chitosan, polyethylene glycol, polyvinyl alcohol, conductive carbon black, carbon nanotubes, and graphene.

[0012] According to another aspect of the present invention, there is provided a lithium iron manganese phosphate cathode material, which is prepared by the aforementioned preparation method; preferably, the tap density of the lithium iron manganese phosphate cathode material is 2.41-2.55 g / cm 3 .

[0013] According to another aspect of the present invention, there is provided a positive electrode sheet, including a current collector and a positive electrode active layer, and the positive electrode active layer contains the aforementioned lithium iron manganese phosphate cathode material.

[0014] According to another aspect of the present invention, there is provided a lithium ion battery, including a positive electrode sheet, an electrolyte and a negative electrode sheet, and the positive electrode sheet is the aforementioned positive electrode sheet.

[0015] Applying the technical solution of the present invention to control the molar ratio of Mn and Fe in the lithium iron manganese phosphate precursor within the above range, the combination of the high-voltage characteristics of manganese and the stable characteristics of iron helps to improve the structural stability of the lithium iron manganese phosphate cathode material during charge and discharge, reduce the dissolution of transition metal ions and the decomposition of the electrode material, and thus helps to improve the discharge capacity and cycle stability of the lithium iron manganese phosphate cathode material. The lithium iron manganese phosphate precursor has a secondary particle structure formed by primary particles, and this structure is beneficial to improving the tap density and electrical properties of the lithium iron manganese phosphate cathode material. Controlling the Dmax of the lithium iron manganese phosphate precursor within the above range helps to form a denser structure during the subsequent sintering process, which thus helps to further improve the tap density of the lithium iron manganese phosphate cathode material, and further helps to increase the energy density of the battery. Controlling the average particle size of the primary particles within the above range helps to reduce the diffusion path of lithium ions and increase the diffusion rate of lithium ions, and thus helps to improve the rate performance of the lithium iron manganese phosphate cathode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0017] Figure 1 shows the SEM image of the lithium iron manganese phosphate precursor in Example 2 of this application;

[0018] Figure 2 shows the SEM image of the lithium iron manganese phosphate cathode material in Example 2 of this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0020] Term Explanation: In this application, Dmax represents the maximum particle size in the particle size distribution.

[0021] As analyzed in the background art of this application, there are problems in the prior art of lithium iron manganese phosphate cathode materials, such as low tap density and discharge capacity, and poor cycle stability. To solve the above problems, this application provides a manganese iron phosphate precursor and its preparation method, a lithium iron manganese phosphate cathode material and its preparation method, a cathode sheet, and a lithium ion battery.

[0022] In a typical embodiment of this application, a manganese iron phosphate precursor is provided. The chemical formula of the manganese iron phosphate precursor is Mn a Fe b PO4, where 0.67 ≤ (a / b) ≤ 9 and 1.15 ≤ (a + b) ≤ 1.43; the manganese iron phosphate precursor has a secondary particle structure formed by primary particles. The Dmax of the manganese iron phosphate precursor is 30 - 40 μm, and the average particle size of the primary particles is 50 - 500 nm.

[0023] Controlling the molar ratio of Mn and Fe in the manganese iron phosphate precursor within the above range, combining the high-voltage characteristics of manganese with the stable characteristics of iron, helps to improve the structural stability of the lithium iron manganese phosphate cathode material during charge and discharge, reduce the dissolution of transition metal ions and the decomposition of the electrode material, and thus helps to improve the discharge capacity and cycle stability of the lithium iron manganese phosphate cathode material. The manganese iron phosphate precursor has a secondary particle structure formed by primary particles, and this structure is beneficial to improving the tap density and electrical properties of the lithium iron manganese phosphate cathode material. Controlling the Dmax of the manganese iron phosphate precursor within the above range helps to form a denser structure during the subsequent sintering process, which in turn helps to further improve the tap density of the lithium iron manganese phosphate cathode material and thus helps to increase the energy density of the battery. Controlling the average particle size of the primary particles within the above range helps to reduce the diffusion path of lithium ions and increase the diffusion rate of lithium ions, thus helping to improve the rate performance of the lithium iron manganese phosphate cathode material.

[0024] In an embodiment of this application, the chemical formula of the above manganese iron phosphate precursor is Mn a Fe b PO4, where 1 ≤ a / b ≤ 2.3 and 1.2 ≤ a + b ≤ 1.3, which helps to further improve the mutual synergistic effect between Mn and Fe, and thus helps to further improve the structural stability of the lithium iron manganese phosphate cathode material during the cycling process.

[0025] In an embodiment of this application, the average particle size of the above primary particles is 100 - 150 nm, which helps to improve the structural stability of the lithium iron manganese phosphate cathode material while reducing the diffusion path of lithium ions, and thus helps to improve the rate performance and cycle stability of the lithium iron manganese phosphate cathode material.

[0026] In one embodiment of the present application, the D10 of the above-mentioned iron manganese phosphate precursor is 1-3 μm, the D50 is 5-10 μm, and the D90 is 18-30 μm; and / or, the specific surface area of the iron manganese phosphate precursor is 5.0-11.0 m 2 / g; and / or, the tap density of the iron manganese phosphate precursor is 0.5-2.0 g / cm 3 .

[0027] Controlling the particle size distribution, specific surface area, and tap density of the iron manganese phosphate precursor within the above ranges helps the lithium iron manganese phosphate cathode material to form a tight and uniform structure during the compaction process, reducing the risk of a decrease in the compaction density or uneven distribution of the porosity inside the electrode caused by an overly large or small particle distribution, thereby helping to improve the compaction density and electrochemical performance consistency of the lithium iron manganese phosphate cathode material.

[0028] In another typical embodiment of the present application, a preparation method of the aforementioned iron manganese phosphate precursor is provided. The preparation method includes the following steps: Step S1, mixing a divalent manganese source, a trivalent iron source, an antioxidant, and water to obtain a manganese iron mixed solution; Step S2, under a protective gas, co-currently dropping the manganese iron mixed solution, phosphoric acid solution, and ammonia water into water under stirring to perform a co-precipitation reaction and aging in sequence to obtain the iron manganese phosphate precursor.

[0029] In Step S1, by mixing the divalent manganese source and the trivalent iron source with the antioxidant and water to form a manganese iron mixed solution, this process helps the uniform distribution of metal ions in the solution. The uniformly distributed metal ions help to form a consistent iron manganese phosphate precipitate in the subsequent co-precipitation reaction, reducing the risk of material inhomogeneity and performance degradation caused by local metal concentration differences. The presence of the antioxidant in the manganese iron mixed solution helps to control the oxidation state of metal ions, thereby helping to reduce the generation of side reactions. In Step S2, performing the co-precipitation reaction under a protective gas can effectively isolate oxygen and reduce the oxidation of metal ions. By co-currently dropping the manganese iron mixed solution, phosphoric acid solution, and ammonia water into water under stirring, it helps to more precisely control the pH value and reaction rate of the reaction, thereby helping to control the morphology and size of the primary particles and secondary particles of the iron manganese phosphate precursor. The aging step helps to further optimize the crystallinity and morphology of the precursor, helps to form a more uniform secondary particle structure, and thereby helps to improve the compaction density and electrochemical activity of the lithium iron manganese phosphate cathode material.

[0030] The above-mentioned protective gas is selected from any one or more of nitrogen, helium, and argon.

[0031] In an embodiment of the present application, the aged product is sequentially subjected to solid-liquid separation, washing, drying and classification to obtain a manganese iron phosphate precursor; preferably, the drying temperature is 50-180 °C.

[0032] In an embodiment of the present application, the temperature of the coprecipitation reaction is 20-45 °C; and / or, the time of co-flow dropping is the time of the coprecipitation reaction, and the time of the coprecipitation reaction is 10-20 h; and / or, the stirring speed of the coprecipitation reaction is 250-650 rpm; and / or, the pH value of the solution in the coprecipitation reaction is 2-5; preferably, the coprecipitation reaction includes a first coprecipitation reaction and a second coprecipitation reaction carried out in sequence, and the time of the first coprecipitation reaction is 5-10 h; and / or, the stirring speed of the first coprecipitation reaction is 350-650 rpm; and / or, the pH value of the solution in the first coprecipitation reaction is 3-5; and / or, the time of the second coprecipitation reaction is 5-10 h; and / or, the stirring speed of the second coprecipitation reaction is 250-350 rpm; and / or, the pH value of the solution in the second coprecipitation reaction is 2-3; and / or, the aging temperature is 20-45 °C; and / or, the aging time is 1-5 h.

[0033] Too high a temperature may cause the particles to grow too fast, forming larger or irregular particles; while too low a temperature may affect the reaction rate and crystallization quality. Controlling the temperature of the coprecipitation reaction within the above range helps to balance the reaction rate and the crystallization process, thus helping to obtain a precursor with moderate particle size and uniform morphology. Controlling the time of the coprecipitation reaction, especially controlling the time of the first coprecipitation reaction and the second coprecipitation reaction within the above range, helps to control the growth of primary particles and the formation of secondary particles, thus helping to improve the tap density of the manganese iron phosphate precursor. Too fast stirring may cause the primary particles to break, affecting the formation of secondary particles; while too low a stirring speed may cause particle agglomeration. Controlling the stirring speed of the coprecipitation reaction, especially the stirring speed of the first coprecipitation reaction and the second coprecipitation reaction within the above range, helps to control the degree of particle aggregation and optimize the structure and size of secondary particles. Too low or too high a pH value may affect the particle size and morphology. Controlling the pH value of the solution in the coprecipitation reaction, especially the pH value of the solution in the first coprecipitation reaction and the second coprecipitation reaction within the above range, can control the precipitation rate of metal ions, optimize the particle growth conditions, and control the morphology and size of the manganese iron phosphate precursor. The aging process helps to further optimize the crystallinity and morphology of the precursor. Controlling the aging temperature and time within the above range helps to form a more uniform and consistent secondary structure. At the same time, this also helps to reduce impurities and improve the purity of the material, thus helping to improve the discharge capacity and cycle stability of the lithium manganese iron phosphate cathode material.

[0034] In an embodiment of the present application, the total concentration of manganese and iron elements in the above-mentioned manganese-iron mixed solution is 0.25 to 2.5 mol / L; and / or, the concentration of the antioxidant in the manganese-iron mixed solution is 0.001 to 0.05 mol / L; and / or, the concentration of the phosphoric acid solution is 0.25 to 2.5 mol / L; and / or, the concentration of the ammonia water solution is 0.25 to 5 mol / L; and / or, the molar ratio of the total moles of manganese in the divalent manganese source and iron in the trivalent iron source to the moles of phosphate radicals in the phosphoric acid solution is (1.15 to 1.43):1; and / or, the divalent manganese source is selected from any one or more of manganese sulfate, manganese carbonate, manganese nitrate, manganese oxalate, manganese acetate, and manganese chloride; and / or, the trivalent iron source is selected from any one or more of iron sulfate, iron nitrate, iron oxalate, iron acetate, and iron chloride; and / or, the antioxidant is selected from any one or more of ascorbic acid, hydrazine hydrate, and sodium borohydride.

[0035] High-concentration metal ion solutions can accelerate the coprecipitation reaction rate and shorten the reaction time. However, excessively high concentrations may cause the particles to grow too fast and have non-uniform sizes, affecting the tap density of the iron manganese phosphate precursor. Controlling the total concentration of manganese and iron elements in the manganese-iron mixed solution within the above range helps improve the uniformity of the metal ion distribution and control the growth rate and size of primary and secondary particles. Controlling the concentration of the antioxidant in the manganese-iron mixed solution within the above range helps reduce the oxidation of metal ions without excessively affecting the chemical composition of the material, which helps improve the purity of the iron manganese phosphate precursor. Controlling the concentrations of the phosphoric acid solution and the ammonia water solution within the above range helps better control the pH value in the coprecipitation reaction solution, thereby helping to more precisely control the morphology and size of the iron manganese phosphate precursor.

[0036] In another typical embodiment of the present application, a method for preparing a lithium iron manganese phosphate cathode material is provided. The preparation method includes: sequentially performing mixing treatment, drying treatment, and sintering treatment on raw materials including the aforementioned iron manganese phosphate precursor, carbon source, phosphorus source, and lithium source with water to obtain the lithium iron manganese phosphate cathode material.

[0037] Using the iron manganese phosphate precursor as the manganese source and iron source for forming the lithium iron manganese phosphate cathode material, which is sequentially mixed, dried, and sintered with the carbon source, phosphorus source, lithium source, and water to obtain the lithium iron manganese phosphate cathode material. The preparation method is simple, and the prepared lithium iron manganese phosphate cathode material has high tap density, discharge capacity, and cycle stability.

[0038] In an embodiment of the present application, the above-mentioned mixing treatment is sanding treatment, and the particle size D50 in the slurry after sanding treatment does not exceed 0.6 μm; and / or, the drying treatment is spray drying treatment, and the inlet air temperature of the spray drying treatment is 200-400 °C; and / or, the outlet air temperature of the spray drying treatment is 90-120 °C; and / or, the heating rate of the sintering treatment is 2-5 °C / min; and / or, the temperature of the sintering treatment is 650-800 °C; and / or, the heat preservation time of the sintering treatment is 5-15 h; and / or, the molar ratio of lithium element in the lithium source, the total molar of manganese element and iron element in the lithium iron phosphate precursor, and the molar of phosphorus element in the phosphorus source is (1.1-1.4):(1.1-1.3):(1.11-1.37); preferably, the raw material further includes a doping metal source, and the molar ratio of lithium element in the lithium source to the doping metal in the doping metal source is (1.1-1.4):0.003; and / or, the mass ratio of the carbon source in the raw material is 1%-30%, preferably 5%-10%; and / or, the mass ratio of water to the raw material is (65-200):100; preferably, the lithium source is selected from any one or more of lithium hydroxide, lithium carbonate, lithium oxalate and lithium nitrate; and / or, the phosphorus source is selected from any one or more of lithium phosphate, lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate; and / or, the doping metal source is selected from any one or more of magnesium source, titanium source, aluminum source, tungsten source, vanadium source, niobium source, nickel source, cobalt source and yttrium source; and / or, the carbon source is selected from any one or more of glucose, citric acid, sucrose, chitosan, polyethylene glycol, polyvinyl alcohol, conductive carbon black, carbon nanotubes and graphene.

[0039] Controlling the particle size D50 of the slurry after sanding treatment within the above range helps to improve the uniformity of the distribution of each component and increase the contact area between each component, thereby helping to form a lithium iron phosphate cathode material with better structural consistency. Controlling the inlet air temperature and outlet air temperature of the spray drying treatment within the above range helps to improve the drying efficiency and increase the particle size uniformity and structural stability of the powder. Controlling the heating rate, temperature and heat preservation time of the sintering treatment within the above range helps to promote the crystallization of the material, improve its conductivity and structural stability, and a reasonable heating rate helps to reduce the stress generated inside the material, reduce the formation of cracks, and improve the integrity and consistency of the material.

[0040] Including but not limited to, the above-mentioned magnesium source is magnesium oxide, the titanium source is titanium oxide, the aluminum source is aluminum oxide, the tungsten source is tungsten oxide, the vanadium source is vanadium oxide, the niobium source is niobium oxide, the nickel source is nickel oxide, the cobalt source is cobalt oxide, and the yttrium source is yttrium oxide.

[0041] In an embodiment of the present application, the above-mentioned sintering treatment is carried out in a protective gas, and the protective gas is selected from any one or more of nitrogen, helium and argon.

[0042] In an embodiment of the present application, the above spray drying is centrifugal spray drying or pressure spray drying. The frequency of the centrifugal atomization disk for centrifugal spray drying is 40 - 100 Hz, and the frequency of the pressure atomization disk for pressure spray drying is 100 - 400 Hz.

[0043] In an embodiment of the present application, the product after the above sintering treatment is sequentially subjected to air flow pulverization and demagnetization to obtain a lithium iron phosphate manganese cathode material; preferably, the temperature of the air flow pulverization is 100 - 200 °C.

[0044] In an embodiment of the present application, the above carbon source is a combination of glucose and polyethylene glycol, and the mass ratio of glucose to polyethylene glycol is 5:(2 - 5), specifically, it can be 5:2, 5:3, 5:4, 5:5, and the range values between any two ratios.

[0045] Glucose decomposes during sintering to form carbon, providing good electrical conductivity for the lithium iron phosphate manganese material. And polyethylene glycol decomposes more slowly under high temperature conditions, which helps to form a more stable carbon skeleton and construct a more uniform and dense conductive network. Controlling the mass ratio of glucose to polyethylene glycol within the above range helps to further improve the tap density, discharge capacity, and cycle stability of the lithium iron phosphate manganese cathode material.

[0046] In an embodiment of the present application, the above doping metal source is a combination of a magnesium source and a titanium source, and the molar ratio of magnesium element in the magnesium source to titanium element in the titanium source is 2:(1 - 2), specifically, it can be 2:1, 2:1.1, 2:1.2, 2:1.3, 2:1.4, 2:1.5, 2:1.6, 2:1.7, 2:1.8, 2:1.9, 2:2, and the range values between any two ratios.

[0047] Magnesium can enter the lattice, helping to enhance the lithium ion transmission path and at the same time reducing the dissolution of manganese ions, maintaining the structural integrity of the material during cycling. The doping of titanium can further strengthen the lattice of the material, preventing volume changes during the insertion and extraction of lithium ions, thereby improving the cycle stability and lifespan of the material. Controlling the mass ratio of the magnesium source to the titanium source within the above range helps to improve the synergistic cooperation between the two, thereby helping to enhance the structural stability of the lithium iron phosphate manganese cathode material, and thus helping to improve the cycle stability of the lithium iron phosphate manganese cathode material.

[0048] In another typical embodiment of the present application, a lithium iron phosphate manganese cathode material is provided. The lithium iron phosphate manganese cathode material is prepared by the aforementioned preparation method; preferably, the tap density of the lithium iron phosphate manganese cathode material is 2.41 - 2.55 g / cm 3 .

[0049] The lithium iron manganese phosphate cathode material prepared by the method of the present application has a high tap density, discharge capacity and cycle stability. Controlling the tap density of the lithium iron manganese phosphate cathode material within the above range helps to further improve the cycle stability of the lithium iron manganese phosphate cathode material.

[0050] In another typical embodiment of the present application, a positive electrode sheet is provided, which includes a current collector and a positive electrode active layer, and the positive electrode active layer contains the aforementioned lithium iron manganese phosphate cathode material.

[0051] Since the above positive electrode sheet contains the lithium iron manganese phosphate cathode material of the present application, the positive electrode sheet has a high discharge capacity and cycle stability.

[0052] In another typical embodiment of the present application, a lithium ion battery is provided, which includes a positive electrode sheet, an electrolyte and a negative electrode sheet, and the positive electrode sheet is the aforementioned positive electrode sheet.

[0053] Since the above positive electrode sheet contains the lithium iron manganese phosphate cathode material of the present application, the battery has a high discharge capacity, cycle stability and safety.

[0054] The beneficial effects of the present application will be further described below in conjunction with embodiments.

[0055] Example 1

[0056] Dissolve manganese sulfate and iron sulfate in water according to the element molar ratio (Mn:Fe = 50:50), and add ascorbic acid to prepare a manganese-iron mixed solution with a total concentration of manganese and iron metal ions of 1.2 mol / L and a concentration of ascorbic acid of 0.002 mol / L. Prepare 1 mol / L phosphoric acid solution and 2 mol / L ammonia water solution. Introduce nitrogen into the reaction kettle, control the reaction temperature at 25 °C, and the stirring speed of the first coprecipitation at 500 rpm. Then drop the manganese-iron mixed solution, phosphoric acid solution and ammonia water solution into the reaction kettle in parallel. The time of parallel dropping is the time of the first coprecipitation reaction and the second coprecipitation reaction. Control the rate of the peristaltic pump to keep the pH of the solution at 4 during the reaction. After reacting for 5 h, enter the second coprecipitation reaction, adjust the stirring speed to 300 rpm, control the rate of the peristaltic pump to keep the pH of the solution at 2 during the reaction, and continue to react for 5 h. Then age at 25 °C for 3 h, filter to obtain lithium iron manganese phosphate precipitate, wash and filter press repeatedly 3 times, then dry at 120 °C, and then classify to obtain the lithium iron manganese phosphate precursor powder Mn 0.6 Fe 0.6 PO4, the classification particle size is D10 = 2.60 μm, D50 = 6.25 μm, D90 = 22.37 μm, Dmax = 35.83 μm, the average particle size of the primary particles in the lithium iron manganese phosphate precursor is 150 nm, and the specific surface area of the lithium iron manganese phosphate precursor is 7.36 m 2 / g, the tap density of the manganese iron phosphate precursor is 1.1 g / cm 3 .

[0057] Lithium carbonate, the above-mentioned manganese iron phosphate precursor, lithium dihydrogen phosphate, magnesium oxide, and titanium dioxide were mixed according to the elemental molar ratio (Li:(Mn + Fe):P:Mg:Ti = 1.125:1.1:1.12:0.002:0.001), and then glucose and polyethylene glycol were added for mixing to obtain a mixture. The mass ratio of glucose in the mixture was 5%, and the mass ratio of polyethylene glycol in the mixture was 2%. The mixture was mixed and stirred with water for 2 h, and the mass ratio of the mixture to water was 100:150. After sand grinding, a slurry with a D50 particle size of 0.55 μm was obtained. The inlet air temperature of the centrifugal atomizer was set to 290 °C, the outlet air temperature was 100 °C, the frequency of the centrifugal atomization disk was 50 Hz. After spray drying, a dried material was obtained, and it was heated to 750 °C at a rate of 2 °C / min in a nitrogen atmosphere and then sintered for 12 h. Finally, after pulverization and demagnetization, a lithium manganese iron phosphate cathode material was obtained.

[0058] Example 2

[0059] The difference from Example 1 is that manganese sulfate and ferric sulfate were dissolved in water according to the elemental molar ratio (Mn:Fe = 60:40), and ascorbic acid was added to prepare a manganese iron mixed solution with a total concentration of manganese and iron metal ions of 1.25 mol / L and a concentration of ascorbic acid of 0.0025 mol / L. A 1 mol / L phosphoric acid solution and a 2 mol / L ammonia water solution were prepared. Nitrogen was introduced into the reaction kettle, the reaction temperature was controlled at 25 °C, and the stirring speed of the first coprecipitation was 500 rpm. Then, the manganese iron mixed solution, phosphoric acid solution, and ammonia water solution were added dropwise into the reaction kettle in parallel. The time of parallel dropwise addition was the time of the first coprecipitation reaction and the second coprecipitation reaction. The rate of the peristaltic pump was controlled to keep the pH of the solution at 4 during the reaction. After reacting for 5 h, it entered the second coprecipitation reaction. The stirring speed was adjusted to 300 rpm, and the rate of the peristaltic pump was controlled to keep the pH of the solution at 2 during the reaction. The reaction continued for 5 h, and then it was aged at 25 °C for 3 h. The manganese iron phosphate precipitate was obtained by filtration, washed and pressure filtered 3 times repeatedly, dried at 120 °C, and then classified to obtain the manganese iron phosphate precursor powder Mn 0.75 Fe 0.5 PO4, the classification particle sizes were D10 of 1.85 μm, D50 of 5.68 μm, D90 of 20.48 μm, Dmax of 34.75 μm. The average particle size of the primary particles in the manganese iron phosphate precursor was 120 nm, and the specific surface area of the manganese iron phosphate precursor was 8.71 m 2 / g, the tap density of the manganese iron phosphate precursor is 0.93 g / cm 3 .

[0060] Lithium carbonate, the above-mentioned lithium iron manganese phosphate precursor, lithium dihydrogen phosphate, magnesium oxide, and titanium dioxide are mixed according to the elemental molar ratio (Li:(Mn + Fe):P:Mg:Ti = 1.125:1.1:1.12:0.002:0.001), and then glucose and polyethylene glycol are added for mixing to obtain a mixture. The mass ratio of glucose in the mixture is 5%, and the mass ratio of polyethylene glycol in the mixture is 2%. The mixture is mixed and stirred with water for 2 h, and the mass ratio of the mixture to water is 100:150. After sand grinding, a slurry with a D50 particle size of 0.55 μm is obtained. The inlet air temperature of the centrifugal atomizer is set to 290 °C, the outlet air temperature is 100 °C, the frequency of the centrifugal atomization disk is 50 Hz. After spray drying, a dried material is obtained, and it is heated to 750 °C at a rate of 2 °C / min in a nitrogen atmosphere and sintered for 12 h. Finally, after pulverization and demagnetization, a lithium iron manganese phosphate cathode material is obtained.

[0061] Example 3

[0062] The difference from Example 1 is that manganese sulfate and iron sulfate are dissolved in water according to the elemental molar ratio (Mn:Fe = 70:30), and ascorbic acid is added to prepare a manganese-iron mixed solution with a total concentration of manganese and iron metal ions of 1.3 mol / L and a concentration of ascorbic acid of 0.0035 mol / L. A 1 mol / L phosphoric acid solution and a 2 mol / L ammonia water solution are prepared. The reaction kettle is purged with nitrogen, the reaction temperature is controlled at 25 °C, and the stirring speed of the first coprecipitation is 500 rpm. Then, the manganese-iron mixed solution, the phosphoric acid solution, and the ammonia water solution are added dropwise into the reaction kettle in parallel. The time for the parallel dropwise addition is the time for the first coprecipitation reaction and the second coprecipitation reaction. The rate of the peristaltic pump is controlled to keep the pH of the solution at 4 during the reaction. After reacting for 5 h, it enters the second coprecipitation reaction. The stirring speed is adjusted to 300 rpm, and the rate of the peristaltic pump is controlled to keep the pH of the solution at 2 during the reaction. The reaction continues for 5 h, and then it is aged at 25 °C for 3 h. The lithium iron manganese phosphate precipitate is obtained by filtration, washed and pressure-filtered 3 times repeatedly, dried at 120 °C, and then classified to obtain the lithium iron manganese phosphate precursor powder Mn 0.91 Fe 0.39 PO4, the classification particle sizes are D10 is 1.89 μm, D50 is 5.86 μm, D90 is 18.37 μm, Dmax is 32.63 μm, the average particle size of the primary particles in the lithium iron manganese phosphate precursor is 100 nm, the specific surface area of the lithium iron manganese phosphate precursor is 10.36 m 2 / g, and the tapped density of the lithium iron manganese phosphate precursor is 0.81 g / cm 3 .

[0063] Lithium carbonate, the above-mentioned iron manganese phosphate precursor, lithium dihydrogen phosphate, magnesium oxide, and titanium dioxide were mixed according to the elemental molar ratio (Li:(Mn+Fe):P:Mg:Ti = 1.125:1.1:1.12:0.002:0.001). Then, glucose and polyethylene glycol were added and mixed to obtain a mixture. The mass ratio of glucose in the mixture was 5%, and the mass ratio of polyethylene glycol in the mixture was 2%. The mixture was mixed and stirred with water for 2 h, and the mass ratio of the mixture to water was 100:150. After sand grinding, a slurry with a D50 particle size of 0.55 μm was obtained. The inlet air temperature of the centrifugal atomizer was set at 290 °C, the outlet air temperature was 100 °C, and the frequency of the centrifugal atomization disk was 50 Hz. After spray drying, a dried material was obtained, and it was sintered at 750 °C for 12 h with a heating rate of 2 °C / min under a nitrogen atmosphere. Finally, after pulverization and demagnetization, a lithium iron manganese phosphate cathode material was obtained.

[0064] Example 4

[0065] The difference from Example 1 was that the molar ratio of manganese element in manganese sulfate to iron element in iron sulfate was 73:28, and finally a lithium iron manganese phosphate cathode material was obtained.

[0066] Example 5

[0067] The difference from Example 1 was that the pH value of the solution in the first coprecipitation reaction was controlled to be 3, and the pH value of the solution in the second coprecipitation reaction was controlled to be 2, to obtain an iron manganese phosphate precursor powder Mn 0.6 Fe 0.6 PO4, the classification particle sizes were D10 of 2.40 μm, D50 of 5.95 μm, D90 of 24.45 μm, Dmax of 38.72 μm, the average particle size of the primary particles in the iron manganese phosphate precursor was 145 nm, the specific surface area of the iron manganese phosphate precursor was 8.16 m 2 / g, and the tapped density of the iron manganese phosphate precursor was 1.03 g / cm 3 , and finally a lithium iron manganese phosphate cathode material was obtained.

[0068] Example 6

[0069] The difference from Example 1 was that the pH value of the solution in the first coprecipitation reaction was controlled to be 5, and the pH value of the solution in the second coprecipitation reaction was controlled to be 3, to obtain an iron manganese phosphate precursor powder Mn 0.6 Fe 0.6 PO4, the classification particle sizes were D10 of 2.51 μm, D50 of 5.87 μm, D90 of 24.39 μm, Dmax of 38.93 μm, the average particle size of the primary particles in the iron manganese phosphate precursor was 140 nm, the specific surface area of the iron manganese phosphate precursor was 9.34 m 2 / g, the tap density of the manganese iron phosphate precursor is 0.98 g / cm 3 , and finally the lithium manganese iron phosphate cathode material is obtained.

[0070] Example 7

[0071] The difference from Example 1 is that the pH value of the solution in the first coprecipitation reaction is controlled to be 4, and the pH value of the solution in the second coprecipitation reaction is controlled to be 4, obtaining the manganese iron phosphate precursor powder Mn 0.6 Fe 0.6 PO4, the classification particle sizes are D10 is 2.30 μm, D50 is 5.57 μm, D90 is 23.45 μm, Dmax is 37.23 μm, the average particle size of the primary particles in the manganese iron phosphate precursor is 122 nm, and the specific surface area of the manganese iron phosphate precursor is 10.56 m 2 / g, the tap density of the manganese iron phosphate precursor is 0.97 g / cm 3 , and finally the lithium manganese iron phosphate cathode material is obtained.

[0072] Example 8

[0073] The difference from Example 1 is that the pH value of the solution in the first coprecipitation reaction is controlled to be 6, and the pH value of the solution in the second coprecipitation reaction is controlled to be 1, obtaining the manganese iron phosphate precursor powder Mn 0.6 Fe 0.6 PO4, the classification particle sizes are D10 is 2.10 μm, D50 is 6.39 μm, D90 is 22.55 μm, Dmax is 36.72 μm, the average particle size of the primary particles in the manganese iron phosphate precursor is 110 nm, and the specific surface area of the manganese iron phosphate precursor is 12.17 m 2 / g, the tap density of the manganese iron phosphate precursor is 0.95 g / cm 3 , and finally the lithium manganese iron phosphate cathode material is obtained.

[0074] Example 9

[0075] The difference from Example 1 is that the stirring speed of the first coprecipitation reaction is controlled to be 350 rpm, and the stirring speed of the second coprecipitation reaction is controlled to be 250 rpm, obtaining the manganese iron phosphate precursor powder Mn 0.6 Fe 0.6 PO4, the classification particle sizes are D10 is 1.95 μm, D50 is 5.96 μm, D90 is 20.58 μm, Dmax is 34.67 μm, the average particle size of the primary particles in the manganese iron phosphate precursor is 143 nm, and the specific surface area of the manganese iron phosphate precursor is 8.17 m 2 / g, the tap density of the manganese iron phosphate precursor is 1.03 g / cm 3 , and finally the lithium manganese iron phosphate cathode material is obtained.

[0076] Example 10

[0077] The difference from Example 1 is that the stirring speed of the first coprecipitation reaction is controlled at 650 rpm, and the stirring speed of the second coprecipitation reaction is controlled at 350 rpm to obtain the manganese iron phosphate precursor powder Mn 0.6 Fe 0.6 PO4, the classification particle sizes are D10 = 2.34 μm, D50 = 5.69 μm, D90 = 21.45 μm, Dmax = 32.86 μm, the average particle size of the primary particles in the manganese iron phosphate precursor is 146 nm, and the specific surface area of the manganese iron phosphate precursor is 8.21 m 2 / g, and the tap density of the manganese iron phosphate precursor is 1.01 g / cm 3 , and finally the lithium manganese iron phosphate cathode material is obtained.

[0078] Example 11

[0079] The difference from Example 1 is that the stirring speed of the first coprecipitation reaction is controlled at 650 rpm, and the stirring speed of the second coprecipitation reaction is controlled at 450 rpm to obtain the manganese iron phosphate precursor powder Mn 0.6 Fe 0.6 PO4, the classification particle sizes are D10 = 1.93 μm, D50 = 7.12 μm, D90 = 19.48 μm, Dmax = 33.89 μm, the particle size of the primary particles in the manganese iron phosphate precursor is 130 nm, and the specific surface area of the manganese iron phosphate precursor is 10.71 m 2 / g, and the tap density of the manganese iron phosphate precursor is 0.98 g / cm 3 , and finally the lithium manganese iron phosphate cathode material is obtained.

[0080] Example 12

[0081] The difference from Example 1 is that the stirring speed of the first coprecipitation reaction is controlled at 200 rpm, and the stirring speed of the second coprecipitation reaction is controlled at 200 rpm to obtain the manganese iron phosphate precursor powder Mn 0.6 Fe 0.6 PO4, the classification particle sizes are D10 = 2.95 μm, D50 = 7.96 μm, D90 = 24.58 μm, Dmax = 37.73 μm, the average particle size of the primary particles in the manganese iron phosphate precursor is 113 nm, and the specific surface area of the manganese iron phosphate precursor is 11.23 m 2 / g, and the tap density of the manganese iron phosphate precursor is 0.91 g / cm 3 , and finally the lithium manganese iron phosphate cathode material is obtained.

[0082] Example 13

[0083] The difference from Example 1 is that the addition of titanium dioxide is cancelled, and lithium carbonate, manganese iron phosphate precursor, lithium dihydrogen phosphate, and magnesium oxide are mixed according to the elemental molar ratio (Li:(Mn+Fe):P:Mg = 1.125:1.1:1.12:0.003), and finally the lithium manganese iron phosphate cathode material is obtained.

[0084] Example 14

[0085] The difference from Example 1 is that the addition of polyethylene glycol is cancelled, and the mass proportion of glucose in the mixture is 7%, and finally the lithium manganese iron phosphate cathode material is obtained.

[0086] Comparative Example 1

[0087] The difference from Example 1 is that the molar ratio of manganese element in manganese sulfate to iron element in iron sulfate is 30:70, and finally the lithium manganese iron phosphate cathode material is obtained.

[0088] Comparative Example 2

[0089] The difference from Example 1 is that the co-current dropping is cancelled, and the manganese iron mixed solution, phosphoric acid solution, and ammonia water solution are added to water for coprecipitation reaction, and finally the lithium manganese iron phosphate cathode material is obtained.

[0090] Comparative Example 3

[0091] The difference from Example 1 is that ferrous sulfate is used to replace iron sulfate, and ammonium dihydrogen phosphate is used to replace the phosphoric acid solution and ammonia water solution, and the pH value of the coprecipitation solution is controlled at 4, and finally the lithium manganese iron phosphate cathode material is obtained.

[0092] The lithium manganese iron phosphate cathode materials prepared in the examples and comparative examples were subjected to tap density tests; the lithium manganese iron phosphate cathode materials prepared in the examples and comparative examples were used to prepare cathode plates, and then assembled with anode plates, electrolytes, and diaphragms into batteries for electrical performance tests. The test conditions were: the initial cycle 0.2C charge specific capacity, initial cycle 0.2C charge ratio capacity, initial cycle 0.2C Coulomb efficiency, and capacity retention rate of 1C cycle for 1000 cycles were tested within the voltage range of 2.0 - 4.5V. The tap density and electrical performance test results are shown in Table 1.

[0093] Table 1

[0094]

[0095]

[0096] Figure 1 This is the SEM image of the manganese iron phosphate precursor in Example 2 of the present application. From Figure 1 it can be measured that the average particle size of the primary particles of the manganese iron phosphate precursor is 120 nm.

[0097] Figure 2 This is the SEM image of the lithium iron manganese phosphate cathode material in Embodiment 2 of this application. From Figure 2 it can be seen that the morphology of the lithium iron manganese phosphate cathode material of this application is relatively regular.

[0098] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0099] Controlling the molar ratio of Mn and Fe in the lithium iron manganese phosphate precursor within the above range, combining the high-voltage characteristics of manganese with the stable characteristics of iron, helps to improve the structural stability of the lithium iron manganese phosphate cathode material during charge and discharge, reduce the dissolution of transition metal ions and the decomposition of the electrode material, and thus helps to improve the discharge capacity and cycle stability of the lithium iron manganese phosphate cathode material. The lithium iron manganese phosphate precursor has a secondary particle structure formed by primary particles, and this structure is beneficial to improving the tap density and electrical properties of the lithium iron manganese phosphate cathode material. Controlling the Dmax of the lithium iron manganese phosphate precursor within the above range helps to form a denser structure during the subsequent sintering process, which thus helps to further improve the tap density of the lithium iron manganese phosphate cathode material, and further helps to increase the energy density of the battery. Controlling the average particle size of the primary particles within the above range helps to reduce the diffusion path of lithium ions and increase the diffusion rate of lithium ions, and thus helps to improve the rate performance of the lithium iron manganese phosphate cathode material.

[0100] The above are only the embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A manganese iron phosphate precursor, characterized in that, The chemical formula of the manganese iron phosphate precursor is Mn a Fe b PO4, where 0.67 ≤ (a / b) ≤ 9 and 1.15 ≤ (a + b) ≤ 1.43; the manganese iron phosphate precursor has a secondary particle structure formed by primary particles, the Dmax of the manganese iron phosphate precursor is 30 - 40 μm, and the average particle size of the primary particles is 50 - 500 nm.

2. The lithium iron manganese phosphate precursor according to claim 1, wherein The D10 of the manganese iron phosphate precursor is 1 to 3 μm, the D50 is 5 to 10 μm, and the D90 is 18 to 30 μm; and / or, the specific surface area of the manganese iron phosphate precursor is 5.0 to 11.0 m 2 / g; and / or, the tapped density of the manganese iron phosphate precursor is 0.5 to 2.0 g / cm 3 .

3. A method for preparing the manganese iron phosphate precursor according to claim 1 or 2, characterized in that, The preparation method includes the following steps: Step S1: Mix a divalent manganese source, a trivalent iron source, an antioxidant, and water to obtain a manganese-iron mixed solution; Step S2: Under a protective gas, drop the manganese-iron mixed solution, a phosphoric acid solution, and an ammonia water solution into water under stirring in a co-current manner to successively carry out a coprecipitation reaction and aging to obtain a manganese iron phosphate precursor.

4. The preparation method according to claim 3, characterized in that, The temperature of the coprecipitation reaction is 20 - 45 °C; and / or, the time of the co-current dropping is the time of the coprecipitation reaction, and the time of the coprecipitation reaction is 10 - 20 h; and / or, the stirring speed of the coprecipitation reaction is 250 - 650 rpm; and / or, the pH value of the solution in the coprecipitation reaction is 2 - 5; Preferably, the coprecipitation reaction includes a first coprecipitation reaction and a second coprecipitation reaction carried out successively. The time of the first coprecipitation reaction is 5 - 10 h; and / or, the stirring speed of the first coprecipitation reaction is 350 - 650 rpm; and / or, the pH value of the solution in the first coprecipitation reaction is 3 - 5; and / or, the time of the second coprecipitation reaction is 5 - 10 h; and / or, the stirring speed of the second coprecipitation reaction is 250 - 350 rpm; and / or, the pH value of the solution in the second coprecipitation reaction is 2 - 3; and / or, the temperature of the aging is 20 - 45 °C; and / or, the time of the aging is 1 - 5 h.

5. The preparation method according to claim 3 or 4, characterized in that, The total concentration of manganese element and iron element in the manganese-iron mixed solution is 0.25 - 2.5 mol / L; and / or, the concentration of the antioxidant in the manganese-iron mixed solution is 0.001 - 0.05 mol / L; and / or, the concentration of the phosphoric acid solution is 0.25 - 2.5 mol / L; and / or, the concentration of the ammonia water solution is 0.25 - 5 mol / L; and / or, the molar ratio of the total moles of manganese element in the divalent manganese source and iron element in the trivalent iron source to the moles of phosphate radical in the phosphoric acid solution is (1.15 - 1.43):1; and / or, the divalent manganese source is selected from any one or more of manganese sulfate, manganese carbonate, manganese nitrate, manganese oxalate, manganese acetate, and manganese chloride; and / or, the trivalent iron source is selected from any one or more of iron sulfate, iron nitrate, iron oxalate, iron acetate, and iron chloride; and / or, the antioxidant is selected from any one or more of ascorbic acid, hydrazine hydrate, and sodium borohydride.

6. A preparation method of a lithium iron manganese phosphate cathode material, characterized in that, The preparation method includes: Mixing, drying, and sintering in sequence the raw materials including the manganese iron phosphate precursor as claimed in claim 1 or 2, a carbon source, a phosphorus source, and a lithium source with water to obtain the lithium manganese iron phosphate cathode material.

7. The preparation method according to claim 6, characterized in that, The mixing treatment is sand milling treatment, and the particle size D50 in the slurry after the sand milling treatment does not exceed 0.6 μm; and / or, the drying treatment is spray drying treatment, the inlet air temperature of the spray drying treatment is 200 - 400 °C; and / or, the outlet air temperature of the spray drying treatment is 90 - 120 °C; And / or, the heating rate of the sintering treatment is 2 to 5 °C / min; and / or, the temperature of the sintering treatment is 650 to 800 °C; and / or, the holding time of the sintering treatment is 5 to 15 h; And / or, the molar ratio of lithium element in the lithium source, the total molar of manganese element and iron element in the lithium iron phosphate precursor, and phosphorus element in the phosphorus source is (1.1 to 1.4):(1.1 to 1.3):(1.11 to 1.37); Preferably, the raw material further includes a doping metal source, and the molar ratio of lithium element in the lithium source to the doping metal in the doping metal source is (1.1 to 1.4):0.003; And / or, the mass ratio of the carbon source in the raw material is 1% to 30%; and / or, the mass ratio of water to the raw material is (65 to 200):100; Preferably, the lithium source is selected from any one or more of lithium hydroxide, lithium carbonate, lithium oxalate, and lithium nitrate; And / or, the phosphorus source is selected from any one or more of lithium phosphate, lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; And / or, the doping metal source is selected from any one or more of magnesium source, titanium source, aluminum source, tungsten source, vanadium source, niobium source, nickel source, cobalt source, and yttrium source; And / or, the carbon source is selected from any one or more of glucose, citric acid, sucrose, chitosan, polyethylene glycol, polyvinyl alcohol, conductive carbon black, carbon nanotubes, and graphene.

8. A lithium iron manganese phosphate cathode material, characterized in that, The lithium iron manganese phosphate cathode material is prepared by the preparation method described in claim 6 or 7; preferably, the tap density of the lithium iron manganese phosphate cathode material is 2.41 to 2.55 g / cm 3 .

9. A positive electrode sheet, comprising a current collector and a positive electrode active layer, characterized in that, The positive electrode active layer contains the lithium iron phosphate positive electrode material described in claim 8.

10. A lithium-ion battery, comprising a positive electrode sheet, an electrolyte, and a negative electrode sheet, characterized in that, The positive electrode sheet is the positive electrode sheet described in claim 9.

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