Preparation method of manganese hydrogen phosphate precursor and preparation method of carbon-coated lithium iron manganese phosphate material

Abstract

The invention relates to the technical field of battery materials, in particular to a preparation method of a manganese hydrogen phosphate precursor and a preparation method of a carbon-coated lithium iron manganese phosphate material. The preparation method of the manganese hydrogen phosphate precursor comprises the following steps: reacting oxalic acid, manganese carbonate, ammonium dihydrogen phosphate and water, and sequentially carrying out solid-liquid separation and drying to obtain the manganese hydrogen phosphate precursor. The preparation method of the carbon-coated lithium manganese iron phosphate material comprises the following steps: sequentially grinding, spray-drying and calcining a mixture of a manganese hydrogen phosphate precursor, an iron source, a phosphorus source, a lithium source and a carbon source to obtain the carbon-coated lithium manganese iron phosphate material. According to the preparation method of the manganese hydrogen phosphate precursor, oxalic acid is added, a high-stability complex can be formed under the condition that the pH value of a reaction system is not controlled, divalent manganese is prevented from being oxidized into trivalent manganese, and the utilization rate of the divalent manganese is increased; the carbon-coated lithium iron manganese phosphate material prepared by taking the manganese hydrogen phosphate precursor prepared by the method as a raw material has excellent performance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a method for preparing a manganese hydrogen phosphate precursor and a method for preparing a carbon-coated lithium manganese iron phosphate material. Background Art

[0002] As the energy crisis worsens, lithium-ion secondary batteries are considered to be energy conversion and energy storage devices with good development prospects. Lithium-ion secondary batteries are widely used in mobile phones, computers, automobiles, energy storage and other fields due to their advantages such as high voltage platform, high energy density, environmental friendliness and long service life. With the continuous expansion of application scenarios, the requirements for the energy density of lithium-ion secondary batteries are also getting higher and higher. The phosphate material of olivine-structured LiMPO4 (M=at least one of Fe, Mn, Co, Ni and V) is considered to be a lithium-ion secondary battery positive electrode material with good application prospects.

[0003] Compared with lithium iron phosphate, lithium iron manganese phosphate (LiMn x Fe 1-x PO4, 0<x<1) battery material has the same specific capacity as lithium iron phosphate (theoretical capacity is 170mAh / g), but has a higher voltage platform (4.1V), which can increase the energy density by about 20% on the basis of LiFePO4. Therefore, in the future development of power batteries, the use of Mn-doped lithium iron phosphate, that is, lithium iron manganese phosphate, has become a trend.

[0004] Among the many methods for synthesizing lithium iron manganese phosphate precursors, the coprecipitation method has a simple synthesis process, uniform material mixing, low heat treatment temperature, easy preparation of nano-scale particles, and controllable morphology. However, when preparing lithium iron manganese phosphate precursors, it is difficult for Fe and Mn to be evenly distributed in the main structure of the material, which will lead to Mn 3+ The Jahn-Teller effect is serious, which affects the cycle and rate performance of the battery.

[0005] In view of this, this invention is proposed. Summary of the invention

[0006] The first object of the present invention is to provide a method for preparing a manganese hydrogen phosphate precursor. By adding oxalic acid, the transition metal Mn can form a highly stable complex without controlling the pH of the reaction system, thereby preventing divalent manganese from being oxidized to trivalent manganese, thereby improving the utilization rate of divalent manganese.

[0007] The second object of the present invention is to provide a method for preparing a carbon-coated lithium manganese iron phosphate material. The steps are simple and the manganese hydrogen phosphate precursor prepared by the above method is used as a raw material, so that the prepared carbon-coated lithium manganese iron phosphate material has excellent electrochemical properties.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] In a first aspect, the present invention provides a method for preparing a manganese hydrogen phosphate precursor, comprising the following steps:

[0010] After oxalic acid, a manganese source, a phosphorus source and water are reacted, solid-liquid separation and drying are performed in sequence to obtain the manganese hydrogen phosphate precursor.

[0011] Further, it includes at least one of the following features (1) to (3);

[0012] (1) The molar ratio of the oxalic acid, the manganese source and the phosphorus source is (1.0-1.2):1:(1.0-1.2);

[0013] (2) the manganese source comprises at least one of manganese carbonate, manganese sulfate or manganese chloride;

[0014] (3) The phosphorus source includes at least one of diammonium phosphate or diammonium hydrogen phosphate.

[0015] Further, the reaction temperature is 60-80°C;

[0016] And / or, the reaction time is 0.5 to 2 hours.

[0017] Furthermore, the drying temperature is 100-110° C., and the drying time is 10-15 hours.

[0018] In a second aspect, the present invention further provides a method for preparing a carbon-coated lithium manganese iron phosphate material, comprising the following steps:

[0019] The manganese hydrogen phosphate precursor, the iron source, the phosphorus source, the lithium source and the carbon source are sequentially ground, spray dried and calcined to obtain the carbon-coated manganese iron lithium phosphate material;

[0020] Wherein, the manganese hydrogen phosphate precursor is prepared by the preparation method of the manganese hydrogen phosphate precursor as described above.

[0021] Furthermore, the invention comprises at least one of the following features (1) to (4):

[0022] (1) The iron source includes at least one of ferrous oxalate, ferrous acetate or ferrous sulfate;

[0023] (2) the phosphorus source comprises at least one of diammonium phosphate or diammonium hydrogen phosphate;

[0024] (3) The lithium source includes at least one of lithium carbonate, lithium oxalate or lithium acetate;

[0025] (4) The carbon source includes at least one of sucrose or glucose.

[0026] Furthermore, in the mixture, the ratio of the molar number of Li, the total molar number of Mn and Fe, and the molar number of P is (1.0-1.1):1:(1.0-1.1).

[0027] Furthermore, in the mixture, the molar ratio of C to P is (0.05-0.08):1.

[0028] Further, the grinding speed is 300-500 rpm / min;

[0029] And / or, the grinding time is 3 to 5 hours.

[0030] Furthermore, the calcination includes: heat preservation treatment at 750-850° C. for 8-12 hours.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The preparation method of the manganese hydrogen phosphate precursor provided by the present invention can form a highly stable complex of the transition metal Mn by adding oxalic acid without controlling the pH of the reaction system, thereby preventing divalent manganese from being oxidized to trivalent manganese, thereby improving the utilization rate of divalent manganese.

[0033] 2. The preparation method of the carbon-coated lithium manganese iron phosphate material provided by the present invention has simple steps. The manganese hydrogen phosphate precursor prepared from the manganese hydrogen phosphate precursor of the present invention is used as a raw material. The prepared carbon-coated lithium manganese iron phosphate material has excellent electrochemical properties. As a positive electrode material of a battery, it is beneficial to improve the cycle and rate performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 This is the XRD spectrum of the manganese hydrogen phosphate precursor prepared in Example 1 of the present invention.

[0036] Figure 2 This is the XRD spectrum of the carbon-coated lithium manganese iron phosphate material prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0037] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0038] The following is a detailed description of the preparation method of the manganese hydrogen phosphate precursor and the preparation method of the carbon-coated lithium manganese iron phosphate material of the present invention.

[0039] In some embodiments of the present invention, a method for preparing a manganese hydrogen phosphate precursor is provided, comprising the following steps:

[0040] After oxalic acid, a manganese source, a phosphorus source and water are reacted, solid-liquid separation and drying are performed in sequence to obtain a manganese hydrogen phosphate precursor.

[0041] The chemical formula of the manganese hydrogen phosphate precursor is MnHPO4·3H2O.

[0042] In the preparation method of the manganese hydrogen phosphate precursor of the present invention, oxalic acid is added, so that the transition metal Mn can form a highly stable complex without controlling the pH of the reaction system, thereby preventing divalent manganese from being oxidized to trivalent manganese, thereby improving the utilization rate of divalent manganese. In the synthesis of the manganese hydrogen phosphate precursor, the addition of oxalic acid plays the role of a chelating agent and a reducing agent. The principle is that the carboxyl group generated after oxalic acid ionization can easily react with Mn 2+ Form a highly stable coordination compound to maintain stable divalent manganese (Mn 2+ ) form, while preventing it from being oxidized to trivalent manganese (Mn 3+ ).

[0043] The method for preparing the manganese hydrogen phosphate precursor of the present invention has short reaction cycle, low synthesis cost and simple process.

[0044] In some embodiments of the present invention, the molar ratio of oxalic acid, manganese source and phosphorus source is (1.0-1.2):1:(1.0-1.2); typically but not limiting, for example, the molar ratio of oxalic acid, manganese source and phosphorus source can be 1:1:1, 1.05:1:1.05, 1.1:1:1.1, 1.15:1:1.15, 1.2:1:1.2 or a range of any two thereof; preferably, the molar ratio of oxalic acid, manganese carbonate and diammonium phosphate is 1:1:1. Too much oxalic acid addition will result in too low acidity of the reaction solution and too high cost of wastewater treatment and discharge; too little oxalic acid addition will result in insufficient carboxyl groups to react with Mn after oxalic acid ionization. 2+ The formation of highly stable coordination compounds may cause Mn 2+ Oxidized to Mn 3+ Produce Jahn-Teller effect.

[0045] In some embodiments of the present invention, the manganese source includes at least one of manganese carbonate, manganese sulfate, or manganese chloride.

[0046] In some embodiments of the present invention, the phosphorus source includes at least one of monoammonium phosphate or diammonium hydrogen phosphate.

[0047] In some embodiments of the present invention, the reaction temperature is 60-80°C; typically but not limiting, for example, the reaction temperature can be 60°C, 70°C, 80°C or a range of any two thereof.

[0048] In some embodiments of the present invention, the reaction time is 0.5 to 2 h; typically but not limiting, for example, the reaction time can be 0.5 h, 1 h, 1.5 h, 2 h or a range consisting of any two thereof.

[0049] In some embodiments of the invention, solid-liquid separation comprises filtration.

[0050] In some embodiments of the present invention, the drying temperature is 100-110°C, and the drying time is 10-15 h; typically but not limitatively, for example, the drying temperature can be 100°C, 105°C, 110°C or a range consisting of any two thereof; the drying time can be 10 h, 11 h, 12 h, 13 h, 14 h, 15 h or a range consisting of any two thereof.

[0051] In some specific embodiments of the present invention, the method for preparing a manganese hydrogen phosphate precursor comprises the following steps:

[0052] S1. Dissolve oxalic acid in deionized water and stir at 55-65° C. to obtain solution A;

[0053] S2. According to the molar ratio of oxalic acid, manganese carbonate and ammonium dihydrogen phosphate being 1:1:1, manganese carbonate and ammonium dihydrogen phosphate are added to solution A, and the mixture is reacted at 60-80° C. for 0.5-2 h to obtain solution B;

[0054] S3. Filter solution B and dry it at 100-110° C. for 10-15 h to obtain a manganese hydrogen phosphate precursor (MnHPO4·3H2O).

[0055] In some embodiments of the present invention, a method for preparing a carbon-coated lithium manganese iron phosphate material is also provided, comprising the following steps:

[0056] A manganese hydrogen phosphate precursor (MnHPO4·3H2O), an iron source, a phosphorus source, a lithium source and a carbon source are mixed to obtain a mixture; the mixture is successively ground, spray-dried and calcined to obtain a carbon-coated lithium manganese iron phosphate material (LiFe 1-x Mn x PO4 / C, 0<x<1);

[0057] Wherein, the manganese hydrogen phosphate precursor is prepared by using the above-mentioned preparation method of the manganese hydrogen phosphate precursor.

[0058] The preparation method of the carbon-coated lithium manganese iron phosphate material of the present invention has simple steps; the manganese hydrogen phosphate precursor prepared by the preparation method of the manganese hydrogen phosphate precursor of the present invention is used as a raw material, so that the prepared carbon-coated lithium manganese iron phosphate material has excellent electrochemical properties and is used as a positive electrode material of a battery, which is beneficial to improving the cycle and rate performance of the battery.

[0059] In some embodiments of the invention, the iron source includes at least one of ferric oxalate, ferric acetate, or ferrous sulfate.

[0060] In some embodiments of the present invention, the phosphorus source includes at least one of monoammonium phosphate or diammonium hydrogen phosphate.

[0061] In some embodiments of the present invention, the lithium source includes but is not limited to at least one of lithium carbonate, lithium oxalate or lithium acetate.

[0062] In some embodiments of the present invention, the carbon source includes, but is not limited to, at least one of sucrose or glucose.

[0063] In some embodiments of the present invention, in the mixture, the ratio of the molar number of Li, the total molar number of Mn and Fe, and the molar number of P is (1-1.1):1:(1-1.1).

[0064] In some embodiments of the present invention, in the mixture, the molar ratio of C and P is (0.05-0.08):1; typically but not limitatively, for example, in the mixture, the molar ratio of C and P can be 0.05:1, 0.06:1, 0.07:1, 0.08:1 or a range of any two thereof.

[0065] In some embodiments of the present invention, the grinding speed is 300-500 rpm / min; typically but not limiting, for example, the grinding speed can be 300 rpm / min, 350 rpm / min, 400 rpm / min, 450 rpm / min, 500 rpm / min or a range of any two thereof.

[0066] In some embodiments of the present invention, the grinding time is 3 to 5 hours; typically but not limiting, for example, the grinding time can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours or a range consisting of any two thereof.

[0067] In some embodiments of the invention, the milling comprises ball milling.

[0068] In some embodiments of the present invention, calcination includes: heat treatment at 750-850°C for 8-12 hours; typically but not limitatively, for example, the calcination temperature can be 750°C, 770°C, 790°C, 810°C, 830°C, 850°C or a range consisting of any two thereof; the calcination time can be 8h, 9h, 10h, 11h, 12h or a range consisting of any two thereof.

[0069] In some embodiments of the present invention, calcination is performed under a protective atmosphere; preferably, the protective atmosphere comprises a nitrogen atmosphere.

[0070] In some specific embodiments of the present invention, the method for preparing the carbon-coated lithium manganese iron phosphate material comprises the following steps:

[0071] S1. Mix a manganese hydrogen phosphate precursor (MnHPO4·3H2O), an iron source, a phosphorus source, a lithium source and a carbon source with a solvent, and then ball mill the mixture at a speed of 300-500 rpm / min for 3-5 hours to obtain a slurry C. Preferably, the solvent includes but is not limited to water. In the slurry C, the ratio of the molar number of Li, the total molar number of Mn and Fe and the molar number of P is (1-1.1):1:(1-1.1), and the molar ratio of C to P is (0.05-0.08):1.

[0072] S2. After spray drying the slurry C, heat treatment is performed at 750-850° C. for 8-12 hours under a protective atmosphere to obtain a carbon-coated lithium manganese iron phosphate material.

[0073] Example 1

[0074] The method for preparing the manganese hydrogen phosphate precursor provided in this embodiment comprises the following steps:

[0075] S1. Dissolve oxalic acid in deionized water and stir at 60° C. to obtain solution A;

[0076] S2. According to the molar ratio of oxalic acid, manganese carbonate and ammonium dihydrogen phosphate being 1:1:1, manganese carbonate and ammonium dihydrogen phosphate were added to solution A, and the mixture was reacted at 60° C. for 1 h to obtain solution B;

[0077] S3, filtering solution B, and drying at 105°C for 12 hours to obtain manganese hydrogen phosphate precursor MnHPO4·3H2O;

[0078] The XRD pattern of the manganese hydrogen phosphate precursor prepared in this example is as follows: Figure 1 shown.

[0079] Example 2

[0080] The method for preparing the manganese hydrogen phosphate precursor provided in this embodiment comprises the following steps:

[0081] S1. Dissolve oxalic acid in deionized water and stir at 70° C. to obtain solution A;

[0082] S2. According to the molar ratio of oxalic acid, manganese carbonate and diammonium phosphate of 1.1:1:1.1, manganese carbonate and diammonium phosphate were added to solution A, and the mixture was reacted at 70° C. for 0.5 h to obtain solution B;

[0083] S3. Filter solution B and dry it at 110° C. for 10 h to obtain a manganese hydrogen phosphate precursor MnHPO4·3H2O.

[0084] Example 3

[0085] The method for preparing the manganese hydrogen phosphate precursor provided in this embodiment comprises the following steps:

[0086] S1. dissolving oxalic acid in deionized water, stirring at 80° C. to obtain solution A;

[0087] S2, adding manganese carbonate and diammonium phosphate to solution A in a molar ratio of oxalic acid, manganese carbonate and diammonium phosphate of 1.2:1:1.2, reacting at 80°C for 1h to obtain solution B;

[0088] S3. Filter solution B and dry it at 115° C. for 12 h to obtain a manganese hydrogen phosphate precursor MnHPO4·3H2O.

[0089] Example 4

[0090] The method for preparing the carbon-coated lithium manganese iron phosphate material provided in this embodiment comprises the following steps:

[0091] S1. According to the molar ratio of Li, Fe, Mn and P being 1:0.8:0.2:1 and the molar ratio of C and P being 0.07:1, the manganese hydrogen phosphate precursor MnHPO4·3H2O, ferric oxalate, ammonium dihydrogen phosphate, lithium carbonate and sucrose of Example 1 were mixed with deionized water and ball-milled at a speed of 300 rpm / min for 5 h to obtain slurry C;

[0092] S2, spray-drying the slurry C, and then heat-treating it at 750° C. for 9 h in a N2 atmosphere, and then naturally cooling it to room temperature to obtain a carbon-coated lithium manganese iron phosphate material;

[0093] The XRD spectrum of the carbon-coated lithium manganese iron phosphate material prepared in this embodiment is as follows: Figure 2 shown.

[0094] Example 5

[0095] The method for preparing the carbon-coated lithium manganese iron phosphate material provided in this embodiment comprises the following steps:

[0096] S1. According to the molar ratio of Li, Fe, Mn and P being 1.05:0.8:0.2:1 and the molar ratio of C and P being 0.05:1, the manganese hydrogen phosphate precursor MnHPO4·3H2O, ferric acetate, ammonium dihydrogen phosphate, lithium carbonate, sucrose and deionized water of Example 2 were mixed and ball-milled at a speed of 400 rpm / min for 4 hours to obtain slurry C;

[0097] S2. After spray drying the slurry C, heat-treat it at 800° C. for 9 h in a N2 atmosphere, and then naturally cool it to room temperature to obtain a carbon-coated lithium manganese iron phosphate material.

[0098] Example 6

[0099] The method for preparing the carbon-coated lithium manganese iron phosphate material provided in this embodiment comprises the following steps:

[0100] S1. According to the molar ratio of Li, Fe, Mn and P being 1.1:0.8:0.2:1 and the molar ratio of C and P being 0.06:1, the manganese hydrogen phosphate precursor MnHPO4·3H2O, ferrous sulfate, ammonium dihydrogen phosphate, lithium carbonate, sucrose and deionized water of Example 3 were mixed and ball-milled at a speed of 500 rpm / min for 4 hours to obtain slurry C;

[0101] S2. After spray drying the slurry C, heat-treat it at 850° C. for 9 h in a N2 atmosphere, and then naturally cool it to room temperature to obtain a carbon-coated lithium manganese iron phosphate material.

[0102] Comparative Example 1

[0103] The preparation method of the manganese hydrogen phosphate precursor provided in this comparative example is referred to Example 1, except that oxalic acid is not added in step S1, and step S2 is directly performed. The preparation method of the carbon-coated lithium manganese iron phosphate material provided in this comparative example is referred to Example 3.

[0104] Comparative Example 2

[0105] The preparation method of the manganese hydrogen phosphate precursor provided in this comparative example refers to Example 1, the only difference being that in step S2, the reaction temperature is room temperature.

[0106] The preparation method of the carbon-coated lithium manganese iron phosphate material provided in this comparative example refers to Example 3.

[0107] Test example

[0108] The carbon-coated lithium iron manganese phosphate positive electrode materials prepared in Examples 4 to 6 and Comparative Examples 1 to 2 were respectively made into lithium-ion batteries. The specific method is: the carbon-coated lithium iron manganese phosphate positive electrode material, polyvinylidene fluoride (PVDF), Super-p (conductive carbon black) and N-methylpyrrolidone are homogenized, wherein the mass ratio of the carbon-coated lithium iron manganese phosphate positive electrode material, PVDF and Super-p is 90:5:5, and the solid content of the slurry is 30%. Then, the circular pole piece is obtained by coating, drying and punching, and finally, the circular pole piece, diaphragm and lithium sheet are assembled into a button battery in a glove box for testing. The button battery is charged and discharged in the voltage range of 2.0 to 4.5V, the charge and discharge current is 1C, and the charge and discharge cycle is 800 cycles. The test results are shown in Table 1.

[0109] Table 1

[0110]

[0111]

[0112] It can be seen from the data in Table 1 that the carbon-coated lithium manganese iron phosphate material prepared by the method described in the present invention has a higher first discharge capacity and first efficiency than Comparative Example 1 and Comparative Example 2, and has excellent electrochemical performance; after 800 cycles at 1C, it still has a high capacity retention rate and excellent cycle performance.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a manganese hydrogen phosphate precursor, characterized in that: The steps include: After oxalic acid, a manganese source, a phosphorus source and water are reacted, solid-liquid separation and drying are performed in sequence to obtain the manganese hydrogen phosphate precursor.

2. The method for preparing a manganese hydrogen phosphate precursor according to claim 1, characterized in that: The method comprises at least one of the following features (1) to (3); (1) The molar ratio of the oxalic acid, the manganese source and the phosphorus source is (1.0-1.2):1:(1.0-1.2); (2) the manganese source comprises at least one of manganese carbonate, manganese sulfate or manganese chloride; (3) The phosphorus source includes at least one of diammonium phosphate or diammonium hydrogen phosphate.

3. The method for preparing a manganese hydrogen phosphate precursor according to claim 1, characterized in that: The reaction temperature is 60-80°C; And / or, the reaction time is 0.5 to 2 hours.

4. The method for preparing a manganese hydrogen phosphate precursor according to claim 1, characterized in that: The drying temperature is 100-110° C., and the drying time is 10-15 hours.

5. A method for preparing a carbon-coated lithium manganese iron phosphate material, characterized in that: The steps include: A manganese hydrogen phosphate precursor, an iron source, a phosphorus source, a lithium source and a carbon source are mixed to obtain a mixture; the mixture is sequentially ground, spray-dried and calcined to obtain the carbon-coated lithium manganese iron phosphate material; Wherein, the manganese hydrogen phosphate precursor is prepared by the method for preparing a manganese hydrogen phosphate precursor according to any one of claims 1 to 4.

6. The method for preparing the carbon-coated lithium manganese iron phosphate material according to claim 5, characterized in that: The method comprises at least one of the following features (1) to (4): (1) The iron source includes at least one of ferrous oxalate, ferrous acetate or ferrous sulfate; (2) the phosphorus source comprises at least one of diammonium phosphate or diammonium hydrogen phosphate; (3) The lithium source includes at least one of lithium carbonate, lithium oxalate or lithium acetate; (4) The carbon source includes at least one of sucrose or glucose.

7. The method for preparing the carbon-coated lithium manganese iron phosphate material according to claim 5, characterized in that: In the mixed material, the ratio of the molar number of Li, the total molar number of Mn and Fe, and the molar number of P is (1.0-1.1):1:(1.0-1.1).

8. The method for preparing the carbon-coated lithium manganese iron phosphate material according to claim 5, characterized in that: In the mixture, the molar ratio of C to P is (0.05-0.08):

1.

9. The method for preparing the carbon-coated lithium manganese iron phosphate material according to claim 5, characterized in that: The grinding speed is 300-500 rpm / min; And / or, the grinding time is 3 to 5 hours.

10. The method for preparing the carbon-coated lithium manganese iron phosphate material according to claim 5, characterized in that: The calcination comprises: heat preservation treatment at 750-850° C. for 8-12 hours.

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