Lithium manganese iron phosphate positive electrode material and preparation method thereof

Abstract

The invention provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof, and belongs to the technical field of lithium ion batteries. The lithium manganese iron phosphate positive electrode material is lithium manganese iron phosphate / lithium titanium phosphate / carbon, the chemical formula of the lithium manganese iron phosphate / lithium titanium phosphate / carbon is LiMnxFe1-xPO4 / LiTi2 (PO4-y) 3 / C, x is more than 0.5 and less than 1, y is more than 0 and less than 4, and the crystal structure of the lithium titanium phosphate is an NASCON structure and has the characteristic of oxygen deficiency. According to the present invention, with the lithium titanium phosphate coating, the particle growth of the lithium iron manganese phosphate can be effectively regulated so as to achieve the high compaction density, and the lithium titanium phosphate with the oxygen defect characteristic has the high ionic conductivity so as to effectively improve the gram volume and the rate capability of the lithium iron manganese phosphate positive electrode material; the oxygen-deficient lithium titanium phosphate composite lithium manganese iron phosphate material has the advantages of high compaction density and excellent gram volume and rate capability, and has important application value and popularization prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium manganese iron phosphate positive electrode material and a preparation method thereof. Background Art

[0002] Lithium iron manganese phosphate has the advantages of high operating voltage and high energy density due to the introduction of manganese, which has attracted widespread attention and industrial interest. In order to further improve the energy density of lithium iron manganese phosphate materials, it is necessary to develop lithium iron manganese phosphate material technologies and products with high compaction density and high specific capacity. In order to achieve high energy density lithium iron manganese phosphate, various methods have been developed to regulate the growth of lithium iron manganese phosphate particles to achieve high compaction density and electrochemical performance.

[0003] The conventional way to control the growth of lithium iron manganese phosphate particles is carbon coating, which is used to inhibit the growth of particles during high-temperature sintering. However, excessive carbon content sacrifices the capacity of the material and reduces the compaction density of the material. In order to effectively and better achieve high compaction density and electrochemical performance, the industry has developed an optimization method. Tianjin Scholland Technology Co., Ltd. disclosed a method for preparing high compaction density lithium iron manganese phosphate materials in patent CN113072049 A, which adds a manganese source, an iron source, a dispersant and deionized water to a sealable container, passes a protective gas, adds diluted phosphoric acid to a sealed container, uniformly nucleates, washes, dries, and sinters for the first time at high temperature to form spherical particles, and then adds lithium hydroxide and glucose, and performs high-temperature second sintering and high-temperature third sintering respectively to obtain nano-spherical lithium iron manganese phosphate / carbon materials, which greatly improves the electrochemical performance and compaction density of the material. Nantong Jintong Energy Storage Power New Materials Co., Ltd. proposed in patent CN115744861A to use ammonium manganese iron phosphate precursor to prepare high compaction density lithium manganese iron phosphate positive electrode material, in which the precursor index parameters are strictly required: particle size D50 is 5-20 um, Span>1.2; 0.5 g / cm 3 <TD<2.0 g / cm 3 , 0.5m 2 / g<SSA<3.0 m 2 / g; crystallinity is I(121) / I (010)>0.3, FWHM(010)<0.25, FWHM(121)<0.25.

[0004] However, the preparation method of Tianjin Scholland Technology Co., Ltd.'s patented technology is rather complicated, while Nantong Jintong Energy Storage Power New Materials Co., Ltd.'s patented technology requires the preparation of special precursors, neither of which is conducive to the large-scale production and application of lithium manganese iron phosphate. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a lithium iron manganese phosphate positive electrode material and a preparation method thereof. The present invention introduces oxygen-deficient lithium titanium phosphate to develop a lithium iron manganese phosphate / lithium titanium phosphate / carbon positive electrode material with high compaction density and high electrochemical performance.

[0006] In the first aspect, the present invention provides a lithium iron manganese phosphate positive electrode material, wherein the lithium iron manganese phosphate positive electrode material is lithium iron manganese phosphate / lithium titanium phosphate / carbon, and its chemical formula is LiMn x Fe 1-x PO4 / LiTi2(PO 4-y )3 / C, 0.5<x<1, 0<y<4, lithium titanium phosphate is composited on the surface of lithium manganese iron phosphate to improve the balance between compaction density and electrochemical performance.

[0007] Preferably, the chemical formula of the lithium iron manganese phosphate positive electrode material of the present invention is LiMn x Fe 1-x PO4 / LiTi2(PO 4-y )3 / C, 0.6≤x≤0.8, 0<y<4.

[0008] Preferably, the powder compaction density of the lithium manganese iron phosphate positive electrode material of the present invention is ≥2.35g / cm 3 .

[0009] Preferably, the crystal structure of lithium titanium phosphate in the lithium iron manganese phosphate positive electrode material of the present invention is a NASCON structure, having oxygen defect characteristics, and the content of lithium titanium phosphate in the lithium iron manganese phosphate positive electrode material is ≤3wt%.

[0010] Preferably, the lithium titanium phosphate of the present invention is prepared by the following steps: mixing a lithium source, a titanium source, a phosphorus source, an auxiliary agent and a solvent, dispersing and grinding to form a mixed solution, then drying, and finally sintering at a high temperature under an inert atmosphere to obtain an oxygen-deficient lithium titanium phosphate material, wherein the chemical formula of the oxygen-deficient lithium titanium phosphate material is LiTi2(PO 4-y )3,0<y<4.

[0011] Preferably, the lithium source, titanium source and phosphorus source are used in an amount according to a Li:Ti:P molar ratio of 1:2:3.

[0012] Among them, the lithium source is selected from one of lithium carbonate, lithium dihydrogen phosphate or lithium hydroxide; the titanium source is selected from one of titanium dioxide or tetrabutyl titanate; the phosphorus source is selected from one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate or lithium phosphate; the auxiliary agent is selected from one of oxalic acid, citric acid or polyvinyl alcohol, and the solvent is deionized water.

[0013] In a second aspect, the present invention provides a method for preparing a lithium manganese iron phosphate positive electrode material, which comprises the following preparation steps: 1) A first lithium source, a titanium source, a first phosphorus source, an auxiliary agent, and a solvent are mixed to form a mixed solution, which is then dried and finally sintered at a high temperature of 600-900° C. in an inert atmosphere for 5-10 hours to prepare an oxygen-deficient lithium titanium phosphate material; 2) The lithium iron manganese phosphate precursor or its raw materials, iron source, manganese source, second phosphorus source, carbon source, second lithium source, solvent and oxygen-deficient lithium titanium phosphate are mixed uniformly, ground and dried to obtain a precursor P1; 3) The precursor P1 is sintered at a high temperature of 670-780°C for 5-20 hours to prepare a high compaction density lithium manganese iron phosphate / lithium titanium phosphate / carbon positive electrode material.

[0014] Preferably, the first lithium source and the second lithium source of the present invention are selected from one of lithium carbonate, lithium dihydrogen phosphate or lithium hydroxide; the titanium source is one of titanium dioxide or tetrabutyl titanate; the first phosphorus source is selected from one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate or lithium phosphate; the auxiliary agent is selected from one of oxalic acid, citric acid or polyethylene propylene alcohol; the lithium iron manganese phosphate precursor is selected from one of ferromanganese phosphate, lithium iron manganese phosphate, ferromanganese oxalate or manganese iron oxide; the iron source is selected from one of ferric phosphate, ferrous oxalate or ferric oxide; the manganese source is selected from one of manganese phosphate, ammonium manganese phosphate, manganese oxalate, manganese carbonate, manganese dioxide or manganese tetroxide; the second phosphorus source is selected from one of ammonium dihydrogen phosphate, phosphoric acid, lithium phosphate or lithium dihydrogen phosphate; the carbon source is selected from one or more of glucose, sucrose, cyclodextrin, starch, polyethylene glycol; the inert atmosphere is one of nitrogen or argon, preferably nitrogen; the solvent is preferably deionized water.

[0015] The lithium manganese iron phosphate precursor or its raw materials, iron source, manganese source, second phosphorus source, and second lithium source are added according to the molar ratio of Li:Mn:Fe:P of 1:(0.6-0.8):(0.2-0.4):1. Compared with the prior art, the present invention has the following technical effects:

[0016] The lithium iron manganese phosphate / lithium titanium phosphate / carbon positive electrode material prepared by the present invention is composed of oxygen-deficient lithium titanium phosphate composite lithium iron manganese phosphate. The oxygen-deficient lithium titanium phosphate is nano-particle size, which can be combined with the surface of lithium iron manganese phosphate particles through phosphate groups. During the high-temperature sintering process, the growth of the lithium iron manganese phosphate positive electrode material can be effectively inhibited to prevent the particles from growing too large. At the same time, the oxygen-deficient lithium titanium phosphate has a NASCON structure, and the presence of lattice oxygen defects can increase the carrier density and further increase the diffusion and migration speed of lithium ions. The oxygen-deficient lithium titanium phosphate composite lithium iron manganese phosphate material has the advantages of high compaction density, gram capacity, and excellent rate performance.

[0017] The oxygen-deficient lithium titanium phosphate introduced in the present invention has the advantage of higher ionic conductivity compared to stoichiometric lithium titanium phosphate, can effectively improve the discharge performance and rate performance of lithium manganese iron phosphate materials, and can significantly expand the application range of lithium manganese iron phosphate materials. DETAILED DESCRIPTION

[0018] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. 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. Example 1

[0019] This embodiment provides a lithium iron manganese phosphate positive electrode material, wherein the lithium iron manganese phosphate positive electrode material is lithium iron manganese phosphate / lithium titanium phosphate / carbon, and the chemical formula is LiMn 0.6 Fe 0.4 PO4 / LiTi2(PO 4-y )3 / C, 0<y<4, which is prepared by the following specific preparation steps: Lithium carbonate, ammonium dihydrogen phosphate, titanium dioxide, polyvinyl alcohol, and deionized water were mixed, dispersed and ground to form a mixed solution, which was then dried and finally sintered at 900 °C in a nitrogen inert atmosphere for 10 h to obtain an oxygen-deficient lithium titanium phosphate material LiTi2(PO 4-y )3, 0<y<4, wherein lithium carbonate, ammonium dihydrogen phosphate and titanium dioxide are added according to the Li:Ti:P molar ratio of 1:2:3, the mass of polyvinyl alcohol is 5 times the mass of the prepared oxygen-deficient lithium titanium phosphate, the prepared lithium titanium phosphate particle size is 60 nm, and it is sintered in an inert nitrogen atmosphere and has oxygen defect characteristics.

[0020] Add ferromanganese oxalate, lithium dihydrogen phosphate, glucose, and the oxygen-deficient lithium titanium phosphate material prepared in step 1) into deionized water according to the designed proportion for dispersion, wet grinding to 200 nm, drying, and high-temperature sintering at 730°C in a nitrogen atmosphere for 10 hours, wherein Mn / Fe in ferromanganese oxalate is 6:4, the molar ratio of ferromanganese oxalate to lithium dihydrogen phosphate is 1:1, the amount of glucose added is 15% of the mass of lithium ferromanganese phosphate, and the mass of the oxygen-deficient lithium titanium phosphate material is 1% of the mass of lithium ferromanganese phosphate. . Example 2

[0021] This embodiment provides a lithium iron manganese phosphate positive electrode material. Compared with Embodiment 1, the difference is that the mass of the lithium titanium phosphate material with oxygen defects in step 2) is 0.5% of the mass of the lithium iron manganese phosphate. Example 3

[0022] This embodiment provides a lithium iron manganese phosphate positive electrode material. Compared with Embodiment 1, the difference is that the mass of the lithium titanium phosphate material with oxygen defects in step 2) is 2.0% of the mass of the lithium iron manganese phosphate. Example 4

[0023] This embodiment provides a lithium iron manganese phosphate positive electrode material. Compared with Example 1, the difference is that the mass of the lithium titanium phosphate material with oxygen defects in step 2) is 3.0% of the mass of the lithium iron manganese phosphate, the sintering temperature is 780°C, the sintering time is 5 hours, and the remaining operations and parameters are exactly the same as those in Example 1. Example 5

[0024] This embodiment provides a lithium manganese iron phosphate positive electrode material. Compared with embodiment 1, the difference is that in step 1), lithium hydroxide, ammonium dihydrogen phosphate, tetrabutyl titanate, oxalic acid, and citric acid are dispersed in deionized water, dispersed and ground to form a rheological phase, and then dried and sintered at 600 ° C in a nitrogen inert atmosphere for 10 hours to prepare oxygen-deficient lithium titanium phosphate LiTi2 (PO 4-y )3, 0<y<4, wherein lithium hydroxide, ammonium dihydrogen phosphate, and tetrabutyl titanate are added according to the molar ratio of Li:Ti:P of 1:2:3, the mass of oxalic acid and citric acid is 20% of the mass of the prepared oxygen-deficient lithium titanium phosphate, and the remaining operations and parameters are exactly the same as those in Example 1. The prepared lithium titanium phosphate particles are sintered in an inert nitrogen atmosphere and have oxygen-deficient characteristics. Example 6

[0025] This embodiment provides a lithium manganese iron phosphate positive electrode material. Compared with embodiment 1, the difference is that in step 1), lithium dihydrogen phosphate, titanium dioxide, oxalic acid, and citric acid are dispersed in deionized water, dispersed and ground to form a rheological phase, and then dried and sintered at 700 ° C in a nitrogen inert atmosphere for 5 hours to prepare oxygen-deficient lithium titanium phosphate LiTi2 (PO 4-y )3, 0<y<4, wherein lithium dihydrogen phosphate and titanium dioxide are added according to the molar ratio of Li:Ti:P of 1:2:3, the mass of oxalic acid and citric acid is 20% of the mass of the prepared oxygen-deficient lithium titanium phosphate, and the other operations and parameters are exactly the same as those in Example 1. The prepared product is sintered in an inert nitrogen atmosphere and has oxygen-deficient characteristics. Example 7

[0026] This embodiment provides a lithium iron manganese phosphate positive electrode material. Compared with Example 1, the difference is that in the step 2), manganese iron oxide, lithium dihydrogen phosphate, starch and the oxygen-deficient lithium titanium phosphate prepared in step 1) are used as raw materials, wherein manganese iron oxide and lithium dihydrogen phosphate are added according to the molar ratio of Li:Mn:Fe:P of 1:0.6:0.4:1, the amount of starch added is 12% of the mass of the lithium iron manganese phosphate, the mass of the oxygen-deficient lithium titanium phosphate material is 1% of the mass of the lithium iron manganese phosphate, and the remaining operations and parameters are exactly the same as those in Example 1. Example 8

[0027] This embodiment provides a lithium iron manganese phosphate positive electrode material, which is different from that in the step 2), iron phosphate, lithium carbonate, manganese tetraoxide, phosphoric acid, cyclodextrin and oxygen-deficient lithium titanium phosphate are used as raw materials, wherein iron phosphate, lithium carbonate, manganese tetraoxide and phosphoric acid are added according to a Li:Mn:Fe:P molar ratio of 1:0.6:0.4:1, the amount of cyclodextrin added is 12% of the mass of the lithium iron manganese phosphate, the mass of the oxygen-deficient lithium titanium phosphate material is 1% of the mass of the lithium iron manganese phosphate, and the remaining operations and parameters are exactly the same as those in the embodiment 1. Example 9

[0028] This embodiment provides a lithium iron manganese phosphate positive electrode material. Compared with embodiment 1, the difference is that the lithium iron manganese phosphate precursor (LiMn prepared by hydrothermal method) is used in step 2). 0.6 Fe 0.4 PO4 precursor, washed and dried before use), sucrose, polyethylene glycol and oxygen-deficient lithium titanium phosphate as raw materials, wherein the molar ratio of Li:Mn:Fe:P is 1:0.6:0.4:1, the amount of sucrose and polyethylene glycol added is 4% and 7% of the mass of lithium manganese iron phosphate, and the oxygen-deficient LiTi2(PO 4-y )3 The material mass is 1% of the mass of lithium manganese iron phosphate, and the remaining operations and parameters are exactly the same as those in Example 1. Example 10

[0029] This embodiment provides a lithium manganese iron phosphate positive electrode material, the chemical formula of which is LiMn 0.7 Fe 0.3 PO4 / LiTi2(PO 4-y )3 / C, compared with Example 1, the difference is that in the step 2), the Mn / Fe molar ratio is 7:3, the sintering temperature is 710°C, the sintering time is 10h, and the other operations and parameters are exactly the same as those in Example 1. Embodiment 11

[0030] This embodiment provides a lithium manganese iron phosphate positive electrode material, the chemical formula of which is LiMn 0.8 Fe 0.2 PO4 / LiTi2(PO4-y )3 / C, compared with Example 1, the difference is that in the step 2), the Mn / Fe molar ratio is 8:2, the sintering temperature is 670°C, the sintering time is 20h, and the other operations and parameters are exactly the same as those in Example 1. Comparative Example 1

[0031] This comparative example provides a lithium iron manganese phosphate positive electrode material. Compared with Example 1, the difference is that step 1 is omitted and step 2) lithium titanium phosphate raw materials with oxygen defects are not added to the raw materials. The remaining operations and parameters are exactly the same as those in Example 1. Comparative Example 2

[0032] This embodiment provides a lithium manganese iron phosphate positive electrode material. Compared with Example 1, the difference is that step 1 is omitted. In step 2), no oxygen-deficient lithium titanium phosphate raw material is added to the raw materials. The sintering temperature is 710°C and the sintering time is 10 hours. The remaining operations and parameters are exactly the same as those in Example 1. Comparative Example 3

[0033] This embodiment provides a lithium manganese iron phosphate positive electrode material. Compared with Example 1, the difference is that in step 1), the sintering atmosphere is air atmosphere, and stoichiometric lithium titanium phosphate is prepared. In step 2), the oxygen-deficient lithium titanium phosphate raw material is replaced with stoichiometric lithium titanium phosphate, and the remaining operations and parameters are exactly the same as in Example 1.

[0034] The lithium manganese iron phosphate materials prepared in the above embodiments and comparative examples were subjected to button cell capacity test and powder compaction density test. The test results are shown in Table 1, where: (1) Button battery test The button cell battery test is carried out in accordance with the national standard "Nano lithium iron phosphate GB / T 33822-2017", as follows: Preparation of positive electrode sheets: The prepared lithium manganese iron phosphate positive electrode material, carbon black (SP), polyvinylidene fluoride (PVDF) and nitrogen methyl pyrrolidone (NMP) are mixed in a mass ratio of 90:5:5:40, and the positive electrode slurry is obtained after high-speed mixing for 30 minutes. The slurry is evenly coated on the aluminum foil with a scraper, placed in a forced air drying oven, and dried at 120°C for 20 minutes. The dried electrode sheet is then rolled and cut to prepare the positive electrode sheet.

[0035] Button cell assembly: The above-mentioned positive electrode sheet, separator, lithium sheet negative electrode, and 1 mol / L LiPF6 electrolyte (the solvent is dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) in a mass ratio of 1:1:1) are used to assemble a 2032 button cell.

[0036] Button battery test: voltage 2.0-4.2 V, charging mode is cross-current-constant voltage mode, cross-current charging current is 0.1C, constant voltage cut-off current is 0.05C, discharge current is 0.1C, 1C.

[0037] (2) Powder compaction density The lithium manganese iron phosphate material samples prepared in Examples 1 to 11 and Comparative Examples 1 to 3 were placed in a mold. During the compression process of external force, as the powder moved and deformed, larger gaps were filled, the contact area between particles increased, and an embryo with a reduced volume was formed. The size of the embryo was measured and the compaction density was calculated. The test results are shown in Table 1.

[0038] Table 1

[0039] According to Table 1, we can see that: The lithium iron manganese phosphate materials in Examples 1 to 9 and Comparative Examples 1 to 3 have the same chemical composition: LiMn 0.6 Fe0 .4 PO4 / C, Examples 1 to 9 are prepared by the method of the present invention. Compared with the lithium manganese iron phosphate material prepared from lithium titanium phosphate without adding oxygen defects in Comparative Examples 1 to 2, it has the advantages of high compaction density, high gram capacity, and high capacity retention rate under rate, and can achieve higher compaction density and gram capacity.

[0040] Further comparison of Example 1 with Comparative Examples 1 and 2 revealed that after adding oxygen-deficient lithium titanium phosphate to prepare lithium manganese iron phosphate, the gram capacity of 0.1C and 1C was significantly improved; at a sintering temperature of 730°C for Comparative Example 1, due to the lack of effective inhibition, the lithium manganese iron phosphate particles grew up, and the compaction density was as high as 2.50 g / cm 3 , but the gram capacity is low, and the 0.1C discharge capacity is only 145.7 mAh / g, which cannot achieve a balance between compaction density and gram capacity. In order to compare at the same compaction density level, Comparative Example 2 reduces the sintering temperature to 710 ° C, and the compaction density is at the same level as Example 1, but the gram capacity is still poor, and the 0.1C discharge capacity is only 148.7 mAh / g, which is much lower than 154.1 mAh / g in Example 1, indicating that oxygen-deficient lithium titanium phosphate has better effects in inhibiting particle growth, balancing compaction density and electrochemical performance.

[0041] Further comparison of Example 1 and Comparative Example 3 revealed that the 0.1C gram capacity of the lithium iron manganese phosphate positive electrode material prepared by adding a stoichiometric ratio of lithium titanium phosphate in Comparative Example 3 was slightly lower than that of Example 1, and the 1C gram capacity was significantly lower than that of Example 1 (141.1 mAh / g vs 146.7 mAh / g). The lower capacity retention rate indicates that the oxygen-deficient lithium titanium phosphate can better improve the rate performance of the lithium iron manganese phosphate material due to its higher lithium ion conductivity.

[0042] Further comparison of Examples 2-4 with Example 1 revealed that the lithium manganese iron phosphate prepared by adding different amounts of oxygen-deficient lithium titanium phosphate can achieve the effects of high compaction density, high gram capacity, and high rate performance.

[0043] Further comparison of Examples 5-9 with Example 1 revealed that the use of different raw materials to prepare oxygen-deficient lithium titanium phosphate, and on this basis to prepare oxygen-deficient lithium titanium phosphate-lithium iron manganese phosphate material, had comparable effects, demonstrating that the lithium iron manganese phosphate positive electrode material method implemented in the present application has good universality in terms of raw materials.

[0044] Further analysis of Examples 10-11 revealed that with the increase of manganese content, when the molar content of manganese element was greater than 0.6, the oxygen-deficient lithium titanium phosphate-lithium iron manganese phosphate positive electrode material prepared by the method of the present invention had a higher compaction density and better gram capacity utilization, and achieved better results, further proving the universality of the method of the present invention for lithium iron manganese phosphate positive electrode materials.

[0045] The applicant declares that the present invention is explained by the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A lithium manganese iron phosphate positive electrode material, characterized in that: The lithium iron manganese phosphate positive electrode material is lithium iron manganese phosphate / lithium titanium phosphate / carbon, and its chemical formula is LiMn x Fe 1-x PO4 / LiTi2(PO 4-y )3 / C, 0.5<x<1, 0<y<4.

2. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The chemical formula of the lithium iron manganese phosphate positive electrode material is LiMn x Fe 1-x PO4 / LiTi2(PO 4-y )3 / C, 0.6≤x≤0.8, 0<y<4.

3. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The powder compaction density of the lithium manganese iron phosphate positive electrode material is ≥2.35g / cm 3 .

4. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The crystal structure of lithium titanium phosphate in the lithium iron manganese phosphate positive electrode material is a NASCON structure with oxygen defect characteristics, and the content of lithium titanium phosphate in the lithium iron manganese phosphate positive electrode material is ≤3wt%.

5. The lithium iron manganese phosphate positive electrode material according to claim 4, characterized in that: The lithium titanium phosphate is prepared by the following steps: mixing a lithium source, a titanium source, a phosphorus source, an auxiliary agent and a solvent, dispersing and grinding to form a mixed solution, then drying, and finally sintering at a high temperature under an inert atmosphere to obtain an oxygen-deficient lithium titanium phosphate material. The chemical formula of the oxygen-deficient lithium titanium phosphate material is LiTi2(PO 4-y )3,0<y<4.

6. The lithium iron manganese phosphate positive electrode material according to claim 5, characterized in that: The amounts of the lithium source, titanium source and phosphorus source are in accordance with the molar ratio of Li:Ti:P of 1:2:

3.

7. The lithium iron manganese phosphate positive electrode material according to claim 6, characterized in that: The lithium source is selected from one of lithium carbonate, lithium dihydrogen phosphate or lithium hydroxide; the titanium source is selected from one of titanium dioxide or tetrabutyl titanate; the phosphorus source is selected from one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate or lithium phosphate; the auxiliary agent is selected from one of oxalic acid, citric acid or polyvinyl alcohol, and the solvent is deionized water.

8. A method for preparing the lithium iron manganese phosphate positive electrode material according to any one of claims 1 to 6, characterized in that: The specific preparation steps are as follows: 1) Mixing a first lithium source, a titanium source, a first phosphorus source, an auxiliary agent and a solvent, dispersing and grinding to form a mixed solution, then drying, and finally sintering at a high temperature of 600-900° C. in an inert atmosphere for 5-10 hours to prepare an oxygen-deficient lithium titanium phosphate material; 2) The lithium iron manganese phosphate precursor or its raw materials, iron source, manganese source, second phosphorus source, carbon source, second lithium source, solvent and oxygen-deficient lithium titanium phosphate, are mixed uniformly, ground and dried to obtain a precursor P1; 3) The precursor P1 is sintered at a high temperature of 670-780°C in an inert atmosphere for 5-20 hours to prepare lithium manganese iron phosphate / lithium titanium phosphate / carbon positive electrode material.

9. The method for preparing the lithium iron manganese phosphate positive electrode material according to claim 8, characterized in that: The first lithium source and the second lithium source are selected from one of lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide; the titanium source is selected from one of titanium dioxide or tetrabutyl titanate; the first phosphorus source is selected from one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate or lithium phosphate; the auxiliary agent is selected from one of oxalic acid, citric acid or polyvinyl alcohol; the lithium iron manganese phosphate precursor is selected from one of ferromanganese phosphate, lithium iron manganese phosphate, ferromanganese oxalate or manganese iron oxide; the iron source is selected from one of ferric phosphate, ferrous oxalate or ferric oxide; the manganese source is selected from one of manganese phosphate, ammonium manganese phosphate, manganese oxalate, manganese carbonate, manganese dioxide or manganese tetroxide; the second phosphorus source is selected from one of ammonium dihydrogen phosphate, phosphoric acid, lithium phosphate or lithium dihydrogen phosphate; the carbon source is selected from one or more of glucose, sucrose, cyclodextrin, starch or polyethylene glycol; the inert atmosphere is selected from one of nitrogen or argon, and the solvent is deionized water.

10. The method for preparing the lithium iron manganese phosphate positive electrode material according to claim 8, characterized in that: The lithium manganese iron phosphate precursor or its raw materials, iron source, manganese source, second phosphorus source, and second lithium source are added according to the molar ratio of Li:Mn:Fe:P of 1:(0.6-0.8):(0.2-0.4):1.

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