A method for preparing a high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material

Abstract

The present invention belongs to the technical field of electrode materials, and specifically relates to a method for preparing a high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material. The magnesium and titanium in the present invention respectively replace part of the lithium and iron, that is, through substitution at different positions, defects and impurity energy levels are formed in the lithium manganese iron phosphate material. The magnesium and titanium act synergistically to improve the conductivity of the lithium manganese iron phosphate and increase the battery capacity of the material. The modified glucose containing lauryl ester in the present invention can promote the proliferation of electrode materials and the interlacing between the positive electrode material layers due to the alkyl chain, thereby increasing the specific surface area of the battery, improving the coating performance, specific surface area, cycle life and safety performance of the battery. The primary coating layer (i.e., the hexafluorobutyl ester hydrophobic coating layer) reduces the water absorption rate, overcoming the disadvantage that the high specific surface area causes significant water absorption in the battery during and after the battery production process.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and in particular relates to a method for preparing a high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material. Background Art

[0002] Lithium iron phosphate (LFP) has a similar theoretical capacity of 170 mAh / g, similar to LFP. However, due to its operating voltage of 4.1V, its theoretical energy density approaches 700 Wh / kg, a 15-20% increase over LFP. This higher energy density makes LFP cathode material potentially capable of exceeding the current upper limit of battery range. Furthermore, LFP material costs approximately 28% less than LFP. Considering LFP's low-temperature performance, safety, and cycling performance, its use as a positive electrode material for power batteries has become a growing trend.

[0003] The patent application with publication number CN105470510A discloses a modified lithium iron manganese phosphate cathode material and a preparation method thereof. The modified lithium iron manganese phosphate cathode material has a chemical composition of Li 1-y Ti y Fe 1-x Mn x PO4, where x ranges from 0.2≤x≤0.6, and y ranges from 0.01≤y≤0.1. First, a titanium-doped lithium iron manganese phosphate precursor is prepared by a high-speed shear emulsifier, and then the precursor is mixed with a carbon source and sintered to finally prepare a modified lithium iron manganese phosphate material. This method has a short reaction time, simple operation, reacts under normal pressure, the precursor particle size is controllable, and the yield is as high as over 99%. The electrochemical performance is excellent, with a first discharge capacity of 155.8mAh / g at a rate of 0.1C, a capacity retention rate of 97.4% after 100 cycles at a rate of 1C, and a discharge capacity of 115.4mAh / g at 8C. However, its first discharge capacity cannot be better.

[0004] Patent application publication number CN115332516A discloses a magnesium-nickel co-doped lithium iron manganese phosphate positive electrode material and its preparation method. The material comprises a positive electrode active material and a coating material composited on the surface of the positive electrode active material. The positive electrode active material comprises a lithium iron manganese phosphate matrix and magnesium and nickel co-doped within the lithium iron manganese phosphate matrix, with the magnesium doping percentage being 0.5-3% by weight and the nickel doping percentage being 0.5-3% by weight. The preparation method comprises the following steps: S1, dissolving a lithium source, a phosphorus source, an iron source, a manganese source, a magnesium source, and a nickel source in a solvent and continuously stirring, then dropwise adding a carbon source until the mixture forms a gel; S2, drying the gel mixture to obtain a xerogel; S3, calcining the xerogel in a protective atmosphere to obtain a carbon-coated magnesium-nickel co-doped lithium iron manganese phosphate positive electrode material. However, this invention fails to achieve improved electrical conductivity and discharge specific capacity.

[0005] The lithium manganese phosphate prepared in the existing public technology has low electronic conductivity and ion diffusion coefficient, making it difficult to obtain a lithium manganese iron phosphate positive electrode material with high battery capacity and high energy density. Summary of the Invention

[0006] In response to at least one technical problem or defect in the above-mentioned background technology, the present invention proposes a method for preparing a high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material, and obtains a lithium manganese iron phosphate positive electrode material with high battery capacity and high energy density by co-doping with titanium and magnesium and coating with a modified carbon source.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] The present invention provides a method for preparing a high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material, wherein the general formula of the high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material is Li 1-y Fe 1-x-z Mn z Ti x Mg y PO4, where 0 <x≤0.01,0<y≤0.01,0.6<x+z≤0.61,

[0009] The preparation method comprises the following steps:

[0010] (1) Lithium manganese iron phosphate cathode material Li coated with high specific surface area 1-y Fe 1-x-z Mn z Ti x Mg y PO4: add the iron source, manganese source, lithium source, phosphorus source, titanium source, magnesium source and the first organic carbon source into the reaction container according to a certain molar stoichiometric coefficient ratio, fully grind and mix evenly, add water, and mix evenly again to obtain a lithium manganese iron phosphate precursor slurry;

[0011] Wherein, the first organic carbon source is modified glucose containing lauryl ester;

[0012] (2) drying the lithium iron manganese phosphate precursor slurry obtained in step (1), and sintering it in a protective atmosphere to obtain a primary-coated titanium-magnesium co-doped lithium iron manganese phosphate positive electrode material;

[0013] (3) mixing the once-coated titanium-magnesium co-doped lithium manganese iron phosphate positive electrode material obtained in step (2) with a second organic carbon source, and sintering the mixture in a protective atmosphere to obtain the high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material.

[0014] The preparation method of the modified glucose containing lauryl ester comprises the following steps:

[0015] Glucosamine, hexafluorobutyl acrylate and lauryl acrylate are reacted to obtain the lauryl acrylate-containing modified glucose.

[0016] Preferably, the mass ratio of glucosamine, hexafluorobutyl acrylate and lauryl acrylate is 500-2000:1:60-540. The reaction temperature is 70-80° C. and the reaction time is 60-120 minutes.

[0017] Specifically, the preparation method of the modified glucose containing lauryl ester comprises the following steps:

[0018] 10 to 20 parts of glucosamine, 0.01 to 0.02 parts of hexafluorobutyl acrylate, 1.2 to 5.4 parts of lauryl acrylate, 100 to 200 parts of white oil, and 3 to 6 parts of n-butylamine are weighed by weight, heated and stirred for reaction, and then the white oil is distilled off to obtain the modified glucose containing lauryl acrylate.

[0019] Modified glucose containing lauryl ester is obtained by addition reaction of glucosamine, hexafluorobutyl acrylate and lauryl acrylate, which is used to increase the escape of carbon dioxide and the specific surface area of the coating layer.

[0020] The iron source is at least one of ferric oxide, ferrous sulfate, ferric sulfate, ferric phosphate, and ferrous oxalate;

[0021] The manganese source is at least one of manganous acetate, manganese dioxide, manganese oxalate, and manganese carbonate;

[0022] The lithium source is at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate;

[0023] The phosphorus source is at least one of ferric phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate;

[0024] The titanium source is at least one of titania, titanium trioxide, titanium tetraoxide, and titanium oxalate;

[0025] The magnesium source is at least one of magnesium oxide, magnesium carbonate, magnesium sulfate, and magnesium hydroxide;

[0026] The second organic carbon source is at least one of polyvinyl alcohol, glucose, polyethylene glycol, and polydopamine.

[0027] Furthermore, the first organic carbon source accounts for 5.4% of the total mass of the iron source, manganese source, lithium source, phosphorus source, titanium source and the first organic carbon source reaction raw materials, and the second organic carbon source accounts for 3.6% of the total mass of the once-coated titanium-magnesium co-doped lithium manganese iron phosphate positive electrode material and the second organic carbon source reaction raw materials.

[0028] The second organic carbon source is polyvinyl alcohol.

[0029] The sintering temperature in step (2) is 500-800° C. and the sintering time is 6-10 hours;

[0030] The sintering temperature in step (3) is 300-800° C., and the sintering time is 3-5 hours.

[0031] The present invention also provides a high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material prepared by the preparation method.

[0032] The present invention also provides the use of the high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material in the preparation of lithium ion batteries.

[0033] Beneficial effects of the present invention:

[0034] (1) The magnesium and titanium in the present invention respectively replace part of the lithium and iron, that is, form defects and impurity energy levels in the lithium iron manganese phosphate material through substitution at different positions. Magnesium and titanium work synergistically to improve the conductivity of the lithium iron manganese phosphate and increase the battery capacity of the material.

[0035] (2) The modified glucose containing lauryl ester in the present invention can promote the proliferation of electrode materials and the interlacing between positive electrode material layers due to the alkyl chain, thereby increasing the specific surface area of the battery, improving the coating performance, specific surface area, cycle life and safety performance of the battery. The primary coating layer (i.e., the hexafluorobutyl ester hydrophobic coating layer) reduces the water absorption rate, overcoming the disadvantage that the high specific surface area causes significant water absorption in the battery during and after the battery production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a graph showing the first discharge at 0.2C of a battery assembled with the lithium iron phosphate cathode material prepared in Example 1. DETAILED DESCRIPTION

[0037] Example 1

[0038] The general formula of the high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material is Li 1-y Fe 1-x-z Mn z Ti x Mg y PO4, where x = 0.01, y = 0.01, z = 0.6.

[0039] (1) Mixing and grinding: FePO4, MnC2O4, Li2CO3, NH4H2PO4, TiO, and MgO were mixed in a molar ratio of 0.39:0.6:0.5:1:0.01:0.01 to obtain a mixed powder. Glucose was added as a primary carbon source in an amount of 5.4% of the total weight of the above raw materials. The mixed powder was added to deionized water and mixed and ground by ball milling or other means for 2 hours to obtain a lithium manganese iron phosphate precursor slurry.

[0040] (2) Drying: The lithium manganese iron phosphate precursor slurry obtained in step (1) was dried and granulated by spray drying (inlet temperature: 260° C., outlet temperature: 110° C.) to obtain a precursor powder.

[0041] (3) Sintering: Sintering the precursor powder described in step (2) under a protective atmosphere (650° C., 8 h) to obtain a sintered material; naturally cooling to room temperature to obtain a carbon-coated titanium-magnesium co-doped lithium manganese iron phosphate material.

[0042] (4) Secondary coating: The carbon-coated titanium-magnesium co-doped lithium manganese iron phosphate material described in step (3) and PVA as a secondary carbon source (3.6% of the total mass of the raw materials (carbon-coated titanium-magnesium co-doped lithium manganese iron phosphate material and PVA)) were added to deionized water, ultrasonically vibrated for 1 hour, filtered, and dried in a vacuum drying oven at 120°C for 4 hours. The dried mixture was sintered in a protective atmosphere at 10°C min -1 The temperature was raised to 350℃ and sintered for 1h, then sintered at 15℃min -1 The temperature was raised to 650° C. and sintered for 4 h, and then cooled to room temperature to obtain a secondary coated lithium manganese iron phosphate positive electrode material.

[0043] Example 2

[0044] The general formula of the high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material is Li 1-y Fe 1-x-z Mn z Ti x Mg y PO4, where x = 0.01, y = 0.01, z = 0.6.

[0045] (1) Weigh 10 g of glucosamine, 0.01 g of hexafluorobutyl acrylate, 1.2 g of lauryl acrylate, 100 g of white oil, and 3 g of n-butylamine, stir at 70°C for 120 minutes, and then distill off the white oil to obtain modified glucose containing lauryl acrylate.

[0046] (2) Mixing and grinding: FePO4, MnC2O4, Li2CO3, NH4H2PO4, TiO, and MgO were mixed in a molar ratio of 0.38:0.6:0.5:1:0.01:0.01 to obtain a mixed powder. Modified glucose containing lauryl ester was added as a primary carbon source in an amount of 5.4% of the total mass of the above raw materials. The mixed powder was added to deionized water and mixed and ground by ball milling or other means for 3 hours to obtain a lithium manganese iron phosphate precursor slurry.

[0047] (3) Drying: The lithium manganese iron phosphate precursor slurry obtained in step (2) was dried and granulated by spray drying (inlet temperature: 280° C., outlet temperature: 130° C.) to obtain a precursor powder.

[0048] (4) Sintering: Sintering the precursor powder obtained in step (3) under a protective atmosphere (650° C., 8 h) to obtain a sintered material; naturally cooling to room temperature to obtain a carbon-coated titanium-magnesium co-doped lithium manganese iron phosphate material.

[0049] (5) Secondary coating: The carbon-coated titanium-magnesium co-doped lithium manganese iron phosphate material obtained in step (4) and PVA (3.6% of the total mass of the raw materials (titanium-magnesium co-doped lithium manganese iron phosphate material and PVA)) were added to deionized water, ultrasonically vibrated for 1 hour, filtered, and dried in a vacuum drying oven at 120°C for 4 hours. The dried mixture was sintered in a protective atmosphere at 10°C min -1 The temperature was raised to 350℃ and sintered for 1h, then sintered at 15℃min -1 The temperature was raised to 650° C. and sintered for 4 h, and then cooled to room temperature to obtain a secondary coated lithium manganese iron phosphate positive electrode material.

[0050] Example 3

[0051] The general formula of the high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material is Li 1-y Fe 1-x-z Mn z Ti x Mg y PO4, where x = 0.01, y = 0.01, z = 0.6.

[0052] (1) Weigh 20 g of glucosamine, 0.02 g of hexafluorobutyl acrylate, 5.4 g of lauryl acrylate, 200 g of white oil, and 6 g of n-butylamine, stir at 80°C for 60 minutes, and then distill off the white oil to obtain modified glucose containing lauryl acrylate.

[0053] (2) Mixing and grinding: FePO4, MnC2O4, Li2CO3, NH4H2PO4, TiO, and MgO were mixed in a molar ratio of 0.39:0.6:0.5:1:0.01:0.01 to obtain a mixed powder. Modified glucose containing lauryl ester was added as a primary carbon source in an amount of 5.4% of the total mass of the raw materials. The mixed powder was added to deionized water and mixed and ground by ball milling or other means for 5 hours to obtain a lithium manganese iron phosphate precursor slurry.

[0054] (3) Drying: The slurry obtained in step (2) was dried and granulated by spray drying (inlet temperature 300°C, outlet temperature 160°C) to obtain a precursor powder.

[0055] (4) Sintering: Sinter the precursor powder described in (3) under a protective atmosphere (650° C., 8 h) to obtain a sintered material; and naturally cool to room temperature to obtain a carbon-coated lithium manganese iron phosphate material.

[0056] (5) Secondary coating: The carbon-coated lithium manganese iron phosphate material described in (4) and PVA (3.6% of the total mass of the raw materials) as a secondary carbon source were added to deionized water, ultrasonically shaken for 1 hour, filtered, and dried in a vacuum drying oven at 120°C for 4 hours. The dried mixture was sintered in a protective atmosphere at 10°C min -1 The temperature was raised to 350℃ and sintered for 1h, then sintered at 15℃ min -1 The temperature was raised to 650° C. and sintered for 4 h, and then cooled to room temperature to obtain a secondary coated lithium manganese iron phosphate positive electrode material.

[0057] Comparative Example 1

[0058] (1) Mixing and grinding: FePO4, MnC2O4, Li2CO3, NH4H2PO4, and TiO were mixed in a molar ratio of 0.39:0.6:0.5:1:0.01. Glucose was added as a primary carbon source in an amount of 5.4% of the total weight of the raw materials. The mixed powder was added to deionized water and mixed and ground by ball milling or other means for 3 hours to obtain a lithium manganese iron phosphate precursor slurry.

[0059] (2) Drying: The slurry obtained in step (1) was dried and granulated by spray drying (inlet temperature 280°C, outlet temperature 145°C) to obtain a precursor powder.

[0060] (3) Sintering: Sinter the precursor powder described in (2) under a protective atmosphere (650° C., 8 h) to obtain a sintered material; and naturally cool to room temperature to obtain a carbon-coated titanium-doped lithium manganese iron phosphate material.

[0061] (4) Secondary coating: The carbon-coated titanium-doped lithium manganese iron phosphate material described in (3) and PVA (3.6% of the total mass of the raw materials) as a secondary carbon source were added to deionized water, ultrasonically shaken for 1 hour, filtered, and dried in a vacuum drying oven at 120°C for 4 hours. The dried mixture was sintered in a protective atmosphere at 10°C min -1 The temperature was raised to 350℃ and sintered for 1h, then sintered at 15℃min -1 The temperature was raised to 650° C. and sintered for 4 h, and then cooled to room temperature to obtain a secondary coated lithium manganese iron phosphate positive electrode material.

[0062] Comparative Example 2

[0063] (1) Mixing and grinding: FePO4, MnC2O4, Li2CO3, NH4H2PO4, and MgO were mixed in a molar ratio of 0.39:0.6:0.5:1:0.01. Glucose was added as a primary carbon source in an amount of 5.4% of the total weight of the raw materials. The mixed powder was added to deionized water and mixed and ground by ball milling or other means for 4 hours to obtain a lithium manganese iron phosphate precursor slurry.

[0064] (2) Drying: The slurry obtained in step (1) was dried and granulated by spray drying (inlet temperature 280°C, outlet temperature 145°C) to obtain a precursor powder.

[0065] (3) Sintering: Sinter the precursor powder described in (2) under a protective atmosphere (650° C., 8 h) to obtain a sintered material; and naturally cool to room temperature to obtain a carbon-coated magnesium-doped lithium manganese iron phosphate material.

[0066] (4) Secondary coating: The carbon-coated magnesium-doped lithium manganese iron phosphate material described in (3) and PVA (3.6% of the total mass of the raw materials) as a secondary carbon source were added to deionized water, ultrasonically shaken for 1 hour, filtered, and dried in a vacuum drying oven at 120°C for 4 hours. The dried mixture was sintered in a protective atmosphere at 10°C min -1 The temperature was raised to 350℃ and sintered for 1h, then sintered at 15℃min -1 The temperature was raised to 650° C. and sintered for 4 h, and then cooled to room temperature to obtain a secondary coated lithium manganese iron phosphate positive electrode material.

[0067] Comparative Example 3

[0068] (1) Mixing and grinding: FePO4, MnC2O4, NH4H2PO4, and Li2CO3 are mixed in a molar ratio of 0.4:0.6:0.5:1. Glucose is added as a primary carbon source in an amount of 5.4% of the total weight of the raw materials. The mixed powder is added to deionized water and mixed and ground by ball milling or other means for 3 hours to obtain a lithium manganese iron phosphate precursor slurry.

[0069] (2) Drying: The slurry obtained in step (1) was dried and granulated by spray drying (inlet temperature 280°C, outlet temperature 145°C) to obtain a precursor powder.

[0070] (3) Sintering: Sinter the precursor powder described in (2) under a protective atmosphere (650° C., 8 h) to obtain a sintered material; and naturally cool to room temperature to obtain a carbon-coated lithium manganese iron phosphate material.

[0071] (4) Secondary coating: The carbon-coated lithium manganese iron phosphate material described in (3) and PVA (3.6% of the total mass of the raw materials) as a secondary carbon source were added to deionized water, ultrasonically shaken for 1 hour, filtered, and dried in a vacuum drying oven at 120°C for 4 hours. The dried mixture was sintered in a protective atmosphere at 10°C min -1 The temperature was raised to 350℃ and sintered for 1h, then sintered at 15℃min -1 The temperature was raised to 640°C and sintered for 4 hours, and then cooled to room temperature to obtain a secondary coated lithium manganese iron phosphate positive electrode material.

[0072] Test Example 1

[0073] 1. Electrochemical performance test

[0074] (1) Using an analytical balance (accuracy 0.0001 g), weigh polyvinylidene fluoride binder (PVDF) in N-methylpyrrolidone (NMP), stir and completely dissolve; then add the positive electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 and carbon black conductive agent (SP), stir evenly to obtain a positive electrode slurry; wherein the mass ratio of the composite material, PVDF, and SP is 8:1:1.

[0075] (2) The positive electrode slurry was evenly coated on aluminum foil using a coater and dried in a vacuum drying oven. After removing the solvent NMP, it was rolled and punched to obtain a disc with a diameter of 16.0 mm as the positive electrode sheet.

[0076] (3) The above-mentioned positive electrode sheet is used as the positive electrode, the metal lithium sheet is used as the negative electrode, the PEPP composite film is used as the battery separator, and 1.0 molL -1 LiPF6 / (DMC+DMC) was used as the electrolyte, in which the volume ratio of EC to DMC was 1:1, and CR2032 button batteries were assembled.

[0077] (4) The button cell was subjected to a cyclic charge and discharge test at a charge and discharge rate of 0.2C, a test temperature of 25.0°C, and a charge and discharge voltage of 2.5V to 4.5V.

[0078] The first discharge curve of the battery assembled with the lithium iron phosphate cathode material prepared in Example 1 at 0.2C is shown in the figure below: Figure 1 shown.

[0079] The test results of the positive electrode materials prepared in the above examples and comparative examples are shown in Table 1 below:

[0080] Table 1

[0081]

[0082] As can be seen from Table 1, Example 3, i.e., the lithium manganese iron phosphate coated with modified glucose reacted at 80°C, exhibits the best initial discharge capacity and capacity retention. A comparison of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 demonstrates that the co-doping of magnesium and titanium significantly improves the battery and cycling performance of the lithium manganese iron phosphate cathode material. A comparison of Examples 1, 2, and 3 demonstrates the superior effect of modified glucose coating, enhancing the electrochemical performance of the cathode material while increasing the specific surface area.

[0083] 2. Water content test

[0084] The moisture content of the material is determined according to the Karl Fischer method in GB / T 6283. The initial moisture content is M0, and the moisture content measured after standing in air at 25°C for 5 hours is M1. The difference M1-M0 can be compared to analyze the material's resistance to water absorption.

[0085] The test results of the positive electrode materials prepared in the above examples and comparative examples are shown in Table 2 below:

[0086] Table 2

[0087] serial number M0(ppm) M1(ppm) Moisture difference (ppm) Example 1 343.5 549.6 206.1 Example 2 326.7 557.8 231.1 Example 3 353.2 612.3 259.1 Comparative Example 1 311.6 704.2 392.6 Comparative Example 2 356.7 764.3 407.6 Comparative Example 3 324.8 748.1 423.3

[0088] According to the comparison of the moisture difference values of each case in Table 2, both titanium-magnesium co-doping and modified glucose coating can improve the water absorption performance of the positive electrode material, thereby reducing the absorption of unavoidable moisture in the air by the positive electrode material during processing and extending its service life in practical applications.

Claims

1. A method for preparing a high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material, characterized in that: The general formula of the high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material is Li 1-y Fe 1-x-z Mn z Ti x Mg y PO4, where 0 <x≤0.01,0<y≤0.01,0.6<x+z≤0.61, The preparation method comprises the following steps: (1) High specific surface area carbon-coated lithium manganese iron phosphate cathode material Li 1-y Fe 1-x-z Mn z Ti x Mg y PO4: add the iron source, manganese source, lithium source, phosphorus source, titanium source, magnesium source and the first organic carbon source into the reaction container according to a certain molar stoichiometric coefficient ratio, fully grind and mix evenly, add water, and mix evenly again to obtain a lithium manganese iron phosphate precursor slurry; Wherein, the first organic carbon source is modified glucose containing lauryl ester; (2) drying the lithium iron manganese phosphate precursor slurry obtained in step (1), and sintering it in a protective atmosphere to obtain a primary-coated titanium-magnesium co-doped lithium iron manganese phosphate positive electrode material; The sintering temperature is 650°C and the sintering time is 8 hours; (3) mixing the primary coated titanium-magnesium co-doped lithium manganese iron phosphate positive electrode material obtained in step (2) with a second organic carbon source, and sintering the mixture in a protective atmosphere to obtain the high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material; The second organic carbon source is polyvinyl alcohol; The sintering process is: 10℃ min -1 The temperature was raised to 350℃ and sintered for 1h, then sintered at 15℃ min -1 The temperature was raised to 650℃ and sintered for 4h.

2. The preparation method according to claim 1, wherein The preparation method of the modified glucose containing lauryl ester comprises the following steps: The modified glucose containing lauryl acrylate is obtained by the addition reaction of glucosamine, hexafluorobutyl acrylate and lauryl acrylate.

3. The preparation method according to claim 2, wherein The mass ratio of the glucosamine, hexafluorobutyl acrylate and lauryl acrylate is 500-2000:1:60-540.

4. The preparation method according to claim 2, wherein The temperature of the addition reaction is 70-80° C., and the time of the addition reaction is 60-120 minutes.

5. The preparation method according to claim 1, wherein The iron source is at least one of ferric oxide, ferrous sulfate, ferric sulfate, ferric phosphate, and ferrous oxalate; The manganese source is at least one of manganous acetate, manganese dioxide, manganese oxalate, and manganese carbonate; The lithium source is at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; The phosphorus source is at least one of ferric phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; The titanium source is at least one of titania, titanium trioxide, titanium tetraoxide, and titanium oxalate; The magnesium source is at least one of magnesium oxide, magnesium carbonate, magnesium sulfate and magnesium hydroxide.

6. The preparation method according to claim 1, wherein The first organic carbon source accounts for 5.4% of the total mass of the iron source, manganese source, lithium source, phosphorus source, titanium source and the first organic carbon source reaction raw materials, and the second organic carbon source accounts for 3.6% of the total mass of the once-coated titanium-magnesium co-doped lithium manganese iron phosphate positive electrode material and the second organic carbon source reaction raw materials.

7. A high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the high specific surface area carbon-coated lithium manganese iron phosphate positive electrode material as claimed in claim 7 in the preparation of lithium ion batteries.

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