Lithium manganese iron phosphate material as well as preparation method and application thereof

Abstract

The invention provides a lithium manganese iron phosphate material and a preparation method and application thereof, the preparation method comprises the following steps: (1) mixing an iron source, a manganese source, a phosphorus source, a complexing agent and a solvent to obtain a mixed material, mixing the mixed material with a first lithium source, and carrying out a one-step reaction to obtain a first slurry; (2) mixing the first slurry, a second lithium source and an antioxidant, and performing two-step reaction to obtain second slurry; and (3) carrying out solid-liquid separation treatment on the second slurry to obtain a solid material, and calcining the obtained solid material to obtain the lithium manganese iron phosphate material. The lithium manganese iron phosphate material prepared by the method disclosed by the invention is uniform in particle size distribution, relatively good in uniformity and relatively high in purity, and the electrochemical performance of the lithium ion battery can be greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of battery materials and relates to a lithium manganese iron phosphate material and a preparation method and application thereof. Background Art

[0002] At present, lithium-ion batteries are the mainstream power batteries, and their cathode materials mainly use lithium iron phosphate, ternary materials, lithium cobalt oxide, lithium manganese oxide, etc. Among them, lithium manganese iron phosphate (LMFP) is widely used in lithium-ion battery cathodes due to its advantages of low cost, high safety, long cycle life, high voltage and wide source of raw materials. It has the advantages of both the excellent rate performance of lithium iron phosphate and the high voltage platform of lithium manganese phosphate, and has gradually become an advanced choice to replace lithium iron phosphate, and will become an important choice in the future new energy vehicle and energy storage market.

[0003] Lithium manganese iron phosphate has the characteristics of high voltage platform and energy density. It is one of the most popular and promising positive electrode active materials for preparing power lithium-ion batteries. The current preparation methods of lithium manganese iron phosphate mainly include high-temperature solid-phase method and co-precipitation method.

[0004] CN118666263A discloses a ferromanganese phosphate precursor, lithium ferromanganese phosphate, and a preparation method and application thereof. The divalent ferromanganese phosphate precursor ammonium ferromanganese phosphate is first prepared by a coprecipitation method, which is then calcined, dehydrated and deaminated to generate hydrogen manganese ferrophosphate, and then the hydrogen manganese ferrophosphate and lithium salt are mixed and sintered to form lithium ferromanganese phosphate.

[0005] CN118373399A discloses a method for preparing a lithium iron phosphate positive electrode material and a lithium battery, the method comprising: adding a lithium source, an iron source, a phosphorus source, a first carbon source, a dopant and a dispersant into a solvent in a preset proportion for mixing and grinding to obtain a first mixture; drying the first mixture and performing a first sintering in an inert gas atmosphere to obtain a lithium iron phosphate precursor; adding borohydride, deionized water, a second carbon source and a dispersant to the lithium iron phosphate precursor for pretreatment to obtain a lithium iron phosphate precursor mixture; mixing, grinding and drying the lithium iron phosphate precursor mixture, and then performing a second sintering in an inert gas atmosphere to obtain a coated doped lithium iron phosphate positive electrode material.

[0006] The method described in the above scheme is not easy to control the particle size and distribution of the product, the uniformity of the obtained material is poor, and the performance is significantly affected by the precursor. Summary of the invention

[0007] The object of the present invention is to provide a lithium iron manganese phosphate material and a preparation method and application thereof. The lithium iron manganese phosphate material prepared by the method of the present invention has a uniform particle size distribution and good uniformity, and the lithium iron manganese phosphate material has a high purity, which can greatly improve the electrochemical performance of lithium-ion batteries.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a lithium iron manganese phosphate material, the preparation method comprising the following steps:

[0010] (1) mixing an iron source, a manganese source, a phosphorus source, a complexing agent and a solvent to obtain a mixed material, and mixing the mixed material with a first lithium source to obtain a first slurry through a one-step reaction;

[0011] (2) mixing the first slurry, the second lithium source and the antioxidant to obtain a second slurry through a two-step reaction;

[0012] (3) performing solid-liquid separation on the second slurry to obtain a solid material, and performing calcination on the obtained solid material to obtain the lithium manganese iron phosphate material.

[0013] The present invention pre-mixes an iron source, a manganese source, a phosphorus source and a complexing agent, and then adds a part of a lithium source to carry out a one-step reaction. The lithium source in the one-step reaction is used as a lithium supplement and also for adjusting pH. This part of lithium will form a uniform phase with the iron, manganese and lithium co-precipitation reaction. The remaining lithium source and an antioxidant are then added to carry out a two-step reaction. The lithium source in the two-step reaction can also be used as a lithium supplement and for adjusting pH. This part of lithium will be embedded in the unfilled vacant lithium obtained by the previous reaction to obtain lithium iron manganese phosphate, which is beneficial to the flow of lithium during the charge and discharge process. The obtained solid material is calcined to obtain a lithium iron manganese phosphate material. The lithium iron manganese phosphate material has a uniform particle size distribution, good uniformity and high purity.

[0014] Preferably, the iron source in step (1) comprises any one of ferrous sulfate, ferrous carbonate, ferrous chloride, ferrous nitrate or ferrous acetate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of ferrous sulfate and ferrous acetate, a combination of ferrous chloride and ferrous nitrate, or a combination of ferrous chloride and ferrous acetate.

[0015] Preferably, the manganese source in step (1) comprises any one of manganese sulfate, manganese carbonate, manganese chloride, manganese nitrate or manganese acetate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of manganese sulfate and manganese acetate, a combination of manganese chloride and manganese nitrate, or a combination of manganese sulfate and manganese nitrate.

[0016] Preferably, the phosphorus source in step (1) comprises any one of phosphoric acid, trisodium phosphate or diammonium phosphate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of phosphoric acid and diammonium phosphate, a combination of phosphoric acid and trisodium phosphate, or a combination of trisodium phosphate and diammonium phosphate, etc.

[0017] Preferably, the complexing agent in step (1) comprises any one of citric acid, oxalic acid, EDTA or triammonium citrate, or a combination of at least two of them. Typical but non-limiting combinations include a combination of citric acid and triammonium citrate, a combination of citric acid and oxalic acid, or a combination of oxalic acid and EDTA.

[0018] Preferably, the solvent in step (1) comprises water.

[0019] Preferably, in step (1), the first lithium source comprises lithium hydroxide and / or lithium carbonate.

[0020] Preferably, the molar ratio of the iron element in the iron source, the manganese element in the manganese source and the phosphorus element in the phosphorus source in step (1) is 1:(0.8-1.2):(1.8-2.2), for example: 1:0.8:1.8, 1:1:2, 1:1.2:2, 1:0.8:2.2 or 1:1:1.2, etc., not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the molar ratio of the complexing agent to the iron element in the iron source is (0.1-1):1, for example: 0.1:1, 0.2:1, 0.5:1, 0.8:1 or 1:1, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, taking the total molar amount of the first lithium source in step (1) and the second lithium source in step (2) as 100%, the molar amount of the first lithium source is 60-90%, for example: 60%, 65%, 70%, 80% or 90%, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the pH of the one-step reaction in step (1) is 2 to 8, for example, 2, 3, 5, 6 or 8, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] Preferably, the atmosphere of the one-step reaction in step (1) comprises a nitrogen atmosphere.

[0025] Preferably, the temperature of the one-step reaction in step (1) is 20°C to 70°C, for example, 20°C, 30°C, 40°C, 60°C or 70°C, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the reaction time of step (1) is 1 h to 3 h, for example, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] Preferably, the antioxidant in step (2) comprises ascorbic acid.

[0028] Preferably, the molar ratio of the antioxidant to the iron in the first slurry is (0.5-1):1, for example: 0.5:1, 0.6:1, 0.7:1, 0.8:1 or 1:1, etc., and is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, in step (2), the second lithium source comprises lithium hydroxide and / or lithium carbonate.

[0030] Preferably, the pH of the two-step reaction in step (2) is 8 to 12, for example, 8, 9, 10, 11 or 12, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the temperature of the second-step reaction in step (2) is 70°C to 95°C, for example, 70°C, 75°C, 80°C, 90°C or 95°C, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, the time of the two-step reaction in step (2) is 1 h to 3 h, for example, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] Preferably, the solid-liquid separation in step (3) is followed by drying.

[0034] Preferably, the drying temperature is 100°C to 120°C, for example, 100°C, 105°C, 110°C, 115°C or 120°C, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the drying time is 2 h to 5 h, for example, 2 h, 2.5 h, 3 h, 4 h or 5 h, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] Preferably, the temperature of the calcination treatment in step (3) is 600°C to 700°C, for example, 600°C, 620°C, 650°C, 680°C or 700°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, the calcination time in step (3) is 2 h to 4 h, for example, 2 h, 2.5 h, 3 h, 3.5 h or 4 h, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0039] In a third aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the lithium iron manganese phosphate material as described in the second aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The lithium manganese iron phosphate material prepared by the method of the present invention has a uniform particle size distribution and good uniformity, and the purity of the lithium manganese iron phosphate material is high, which can greatly improve the electrochemical performance of lithium ion batteries.

[0042] (2) The compacted density of the lithium manganese iron phosphate material prepared by the method of the present invention can reach 2.292 g / cm 3 The powder resistance can reach below 164Ω·cm, the manganese dissolution can reach below 263ppm, the iron dissolution can reach below 130ppm, the 0.1C first efficiency of the prepared battery can reach above 98.2%, the 0.1C charge specific capacity can reach above 149.2mAh / g, and the 0.1C discharge specific capacity can reach above 146.8mAh / g. By adjusting the preparation conditions and the addition amount of each material, the compaction density of the lithium manganese iron phosphate material can reach 2.318g / cm 3 Above, the powder resistance can reach below 123Ω·cm, the manganese dissolution can reach below 219ppm, the iron dissolution can reach below 90ppm, the 0.1C first efficiency of the prepared battery can reach above 98.5%, the 0.1C charge specific capacity can reach above 152.2mAh / g, and the 0.1C discharge specific capacity can reach above 16.850.0mAh / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the preparation process of the lithium iron manganese phosphate material of the present invention.

[0044] Figure 2 This is the XRD diagram of the lithium iron manganese phosphate material obtained in Example 1 of the present invention.

[0045] Figure 3 This is a SEM image of the lithium iron manganese phosphate material obtained in Example 1 of the present invention.

[0046] Figure 4 This is an SEM magnified image of the lithium manganese iron phosphate material obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0048] Example 1

[0049] This embodiment provides a lithium iron manganese phosphate material. The schematic diagram of the preparation process of the lithium iron manganese phosphate material is as follows: Figure 1 As shown, the lithium manganese iron phosphate material is prepared by the following method:

[0050] (1) ferrous sulfate, manganese sulfate and phosphoric acid were mixed with water in a molar ratio of 1:1:2, and citric acid was added in an amount of 0.5 times the molar amount of iron. After mixing evenly, lithium hydroxide was added in an amount of 0.8 times the total molar amount of iron and manganese. The pH was adjusted to 5, and the mixture was reacted at 50° C. in a nitrogen atmosphere for 2 h to obtain a first slurry.

[0051] (2) mixing the first slurry, lithium hydroxide having a molar amount of 0.2 times the total molar amount of iron and manganese, and an antioxidant having a molar amount of 1 times the iron, adjusting the pH to 10, and reacting at 80° C. for 2 hours to obtain a second slurry;

[0052] (3) After filtering and washing the second slurry, the solid-liquid mixture was dried at 110° C. for 3 h, and the solid material obtained after drying was calcined at 650° C. for 3 h to obtain the lithium manganese iron phosphate material.

[0053] The XRD pattern of the lithium manganese iron phosphate material is as follows Figure 2 As shown, the physical phase of the lithium manganese iron phosphate material prepared by the method of the present invention is mainly 55 type lithium manganese iron phosphate.

[0054] The SEM image of the lithium manganese iron phosphate material is as follows Figure 3-Figure 4 As shown, the particle size distribution of the lithium manganese iron phosphate material prepared by the method of the present invention is uniform and has high uniformity.

[0055] Example 2

[0056] This embodiment provides a lithium iron manganese phosphate material. The schematic diagram of the preparation process of the lithium iron manganese phosphate material is as follows: Figure 1 As shown, the lithium manganese iron phosphate material is prepared by the following method:

[0057] (1) mixing ferrous sulfate, manganese sulfate and phosphoric acid with water in a molar ratio of 1:1:2 and adding oxalic acid in an amount of 0.5 times the molar amount of iron, and after mixing evenly, adding lithium hydroxide in an amount of 0.6 times the total molar amount of iron and manganese, adjusting the pH to 2, and reacting at 20° C. in a nitrogen atmosphere for 3 hours to obtain a first slurry;

[0058] (2) mixing the first slurry, lithium hydroxide having a molar amount of 0.4 times the total molar amount of iron and manganese, and an antioxidant having a molar amount of 1 times the iron, adjusting the pH to 8, and reacting at 70° C. for 3 hours to obtain a second slurry;

[0059] (3) After filtering and washing the second slurry, the solid-liquid mixture was dried at 100° C. for 5 h, and the solid material obtained after drying was calcined at 600° C. for 4 h to obtain the lithium manganese iron phosphate material.

[0060] Example 3

[0061] This embodiment provides a lithium iron manganese phosphate material. The schematic diagram of the preparation process of the lithium iron manganese phosphate material is as follows: Figure 1 As shown, the lithium manganese iron phosphate material is prepared by the following method:

[0062] (1) ferrous sulfate, manganese sulfate and phosphoric acid were mixed with water in a molar ratio of 1:1:2, and citric acid was added in an amount of 0.5 times the molar amount of iron. After mixing evenly, lithium hydroxide was added in an amount of 0.9 times the total molar amount of iron and manganese. The pH was adjusted to 8, and the mixture was reacted at 70° C. in a nitrogen atmosphere for 1 h to obtain a first slurry.

[0063] (2) mixing the first slurry, lithium hydroxide having a molar amount of 0.1 times the total molar amount of iron and manganese, and an antioxidant having a molar amount of 1 times the iron, adjusting the pH to 12, and reacting at 95° C. for 1 hour to obtain a second slurry;

[0064] (3) After filtering and washing the second slurry, the solid-liquid mixture was dried at 120° C. for 2 h, and the solid material obtained after drying was calcined at 700° C. for 2 h to obtain the lithium manganese iron phosphate material.

[0065] Example 4

[0066] The only difference between this embodiment and embodiment 1 is that the molar ratio of the lithium hydroxide in step (1) to the lithium hydroxide in step (2) is 9.5:0.5, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0067] Example 5

[0068] The only difference between this embodiment and embodiment 1 is that the molar ratio of the lithium hydroxide in step (1) to the lithium hydroxide in step (2) is 5:5, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0069] Example 6

[0070] The only difference between this embodiment and embodiment 1 is that the pH of the reaction in step (1) is 1, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0071] Example 7

[0072] The only difference between this embodiment and embodiment 1 is that the pH of the reaction in step (1) is 9, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0073] Example 8

[0074] The only difference between this embodiment and embodiment 1 is that the reaction temperature in step (1) is 80° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0075] Example 9

[0076] The only difference between this embodiment and embodiment 1 is that the pH of the reaction in step (2) is 7, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0077] Example 10

[0078] The only difference between this embodiment and embodiment 1 is that the pH of the reaction in step (2) is 13, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0079] Embodiment 11

[0080] The only difference between this embodiment and embodiment 1 is that the reaction temperature in step (2) is 60° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0081] Example 12

[0082] The only difference between this embodiment and embodiment 1 is that the reaction temperature in step (2) is 100° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0083] Comparative Example 1

[0084] The only difference between this comparative example and Example 1 is that the lithium source is added in step (1), and the other conditions and parameters are exactly the same as those in Example 1.

[0085] Comparative Example 2

[0086] The only difference between this comparative example and Example 1 is that the lithium source is added in step (2), and the other conditions and parameters are exactly the same as those in Example 1.

[0087] Performance Test:

[0088] (1) The lithium iron manganese phosphate materials obtained in the embodiment and the comparative example were tested. The test results are shown in Table 1:

[0089] Table 1

[0090]

[0091]

[0092] (2) The lithium manganese iron phosphate material prepared in the embodiment and the comparative example was mixed with acetylene black and a binder (polyvinylidene fluoride PVDF) in a mass ratio of 90:5:5, and a solvent N-methylpyrrolidone was added for slurry adjustment (the binder content was adjusted to 5 wt % by adding a solvent). After the slurry was mixed evenly, it was coated on a current collector aluminum foil (aluminum foil thickness 15 μm, slurry coating thickness 45 μm), and a positive electrode sheet (compacted density 2-2.5 g / cm ) was obtained after drying, rolling and punching. 3 ). With metallic lithium as the negative electrode, the assembly process of the 2032 button battery was completed in a vacuum glove box. Finally, the battery was packaged with a battery sealer and tested. The test results are shown in Table 2:

[0093] Table 2

[0094]

[0095]

[0096] As can be seen from Table 1-2, from Examples 1-12, the compacted density of the lithium manganese iron phosphate material prepared by the method of the present invention can reach 2.292 g / cm 3 Above, the powder resistance can reach below 164Ω·cm, the manganese dissolution can reach below 263ppm, the iron dissolution can reach below 130ppm, and the specific surface area can reach 19.12m 2 / g (under the conditions of meeting the above requirements, a smaller specific surface area is more conducive to processing), the 0.1C initial efficiency of the obtained battery can reach more than 98.2%, the 0.1C charging specific capacity can reach more than 149.2mAh / g, and the 0.1C discharge specific capacity can reach more than 146.8mAh / g. By adjusting the preparation conditions and the addition amount of each material, the compaction density of the lithium manganese iron phosphate material can reach 2.318g / cm 3 Above, the powder resistance can reach below 123Ω·cm, the manganese dissolution can reach below 219ppm, the iron dissolution can reach below 90ppm, the 0.1C first efficiency of the prepared battery can reach above 98.5%, the 0.1C charge specific capacity can reach above 152.2mAh / g, and the 0.1C discharge specific capacity can reach above 16.850.0mAh / g.

[0097] By comparing Example 1 with Examples 4-5, it can be seen that in the preparation process of the lithium iron manganese phosphate material of the present invention, the proportion of the lithium source added in step (1) and step (2) will affect its performance. By controlling the proportion of the lithium source added in step (1) to 60% to 90% of the total lithium source, a lithium iron manganese phosphate material with excellent performance can be obtained. If the proportion of the lithium source added in step (1) is too high, the activity of lithium will decrease and the charge and discharge capacity will decrease. If the proportion of the lithium source added in step (1) is too low, the uniformity of the lithium iron manganese phosphate will decrease and the lithiation effect will be reduced.

[0098] By comparing Example 1 with Examples 6-7, it can be seen that in the preparation process of the lithium manganese iron phosphate material of the present invention, the pH of the reaction in step (1) will affect its performance. By controlling the pH of the reaction in step (1) to 2-8, a lithium manganese iron phosphate material with excellent performance can be obtained. If the pH of the reaction in step (1) is too high, other impurities such as lithium manganese pyrophosphate will be produced, which will increase the powder resistance of the positive electrode material and thus affect the electrical properties of the product. If the pH of the reaction in step (1) is too low, the stability of the lithium manganese iron phosphate material obtained will be reduced, and the dissolution of manganese and iron will increase.

[0099] By comparing Example 1 with Example 8, it can be seen that in the preparation process of the lithium iron manganese phosphate material of the present invention, the temperature of the reaction in step (1) will affect its performance. By controlling the temperature of the reaction in step (1) to 20-70° C., a lithium iron manganese phosphate material with excellent performance can be obtained. If the temperature of the reaction in step (1) is too high, the iron and manganese dissolution of the positive electrode material is significantly increased, thereby affecting the physical and chemical properties of the product.

[0100] By comparing Example 1 with Examples 9-10, it can be seen that in the preparation process of the lithium manganese iron phosphate material of the present invention, the pH of the reaction in step (2) will affect its performance. By controlling the pH of the reaction in step (2) to 8-12, a lithium manganese iron phosphate material with excellent performance can be obtained. If the pH of the reaction in step (2) is too high, the powder resistance becomes larger, thereby affecting the electrical performance. If the pH of the reaction in step (2) is too low, the properties of the obtained lithium manganese iron phosphate will also be slightly reduced.

[0101] By comparing Example 1 with Examples 11-12, it can be seen that in the preparation process of the lithium iron manganese phosphate material of the present invention, the temperature of the reaction in step (2) will affect its performance. By controlling the temperature of the reaction in step (2) to 70-95° C., a lithium iron manganese phosphate material with excellent performance can be obtained. If the temperature of the reaction in step (2) is too high, the iron and manganese dissolution of the positive electrode material will increase, thereby affecting the performance of the product. If the temperature of the reaction in step (2) is too low, the compaction density of the obtained lithium iron manganese phosphate is significantly reduced.

[0102] From the comparison between Example 1 and Comparative Examples 1-2, it can be seen that the stepwise addition of lithium source in the present invention is conducive to forming a single homogeneous material with good physical and chemical properties.

[0103] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing lithium manganese iron phosphate material, characterized in that: The preparation method comprises the following steps: (1) mixing an iron source, a manganese source, a phosphorus source, a complexing agent and a solvent to obtain a mixed material, and mixing the mixed material with a first lithium source to obtain a first slurry through a one-step reaction; (2) mixing the first slurry, the second lithium source and the antioxidant to obtain a second slurry through a two-step reaction; (3) performing solid-liquid separation on the second slurry to obtain a solid material, and performing calcination on the obtained solid material to obtain the lithium manganese iron phosphate material.

2. The preparation method according to claim 1, characterized in that The iron source in step (1) comprises any one of ferrous sulfate, ferrous carbonate, ferrous chloride, ferrous nitrate or ferrous acetate, or a combination of at least two thereof; Preferably, the manganese source in step (1) comprises any one of manganese sulfate, manganese carbonate, manganese chloride, manganese nitrate or manganese acetate, or a combination of at least two thereof; Preferably, the phosphorus source in step (1) comprises any one of phosphoric acid, trisodium phosphate or diammonium phosphate, or a combination of at least two thereof; Preferably, the complexing agent in step (1) comprises any one of citric acid, oxalic acid, EDTA or triammonium citrate, or a combination of at least two thereof; Preferably, the solvent in step (1) comprises water; Preferably, in step (1), the first lithium source comprises lithium hydroxide or lithium carbonate.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the molar ratio of the iron element in the iron source, the manganese element in the manganese source, and the phosphorus element in the phosphorus source is 1:(0.8-1.2):(1.8-2.2); Preferably, the molar ratio of the complexing agent to the iron element in the iron source is (0.1-1):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that: Taking the total molar amount of the first lithium source in step (1) and the second lithium source in step (2) as 100%, the molar amount of the first lithium source is 60 to 90%.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The pH of the one-step reaction in step (1) is 2 to 8; Preferably, the atmosphere of the one-step reaction in step (1) comprises a nitrogen atmosphere; Preferably, the temperature of the one-step reaction in step (1) is 20°C to 70°C; Preferably, the one-step reaction time in step (1) is 1 h to 3 h.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The antioxidant in step (2) comprises ascorbic acid; Preferably, the molar ratio of the antioxidant to the iron in the first slurry is (0.5-1):1; Preferably, in step (2), the second lithium source comprises lithium hydroxide or lithium carbonate.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The pH of the two-step reaction in step (2) is 8 to 12; Preferably, the temperature of the second step reaction in step (2) is 70°C to 95°C; Preferably, the time for the two-step reaction in step (2) is 1 h to 3 h.

8. The preparation method according to any one of claims 1 to 7, characterized in that: Step (3) drying after solid-liquid separation; Preferably, the drying temperature is 100°C to 120°C; Preferably, the drying time is 2h to 5h; Preferably, the calcination temperature in step (3) is 600° C. to 700° C.; Preferably, the calcination treatment time in step (3) is 2h to 4h.

9. A lithium iron manganese phosphate material, characterized in that: The lithium manganese iron phosphate material is prepared by the preparation method according to any one of claims 1-8.

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

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