A lithium iron manganese phosphate positive electrode material and its preparation method and application

Abstract

The present invention discloses a lithium iron manganese phosphate positive electrode material and a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) mixing manganese acetylacetonate, iron acetylacetonate, a phosphorus source and an organic solvent to obtain an organic solution, wherein the manganese in the manganese acetylacetonate is trivalent manganese and the iron in the iron acetylacetonate is trivalent iron; (2) heating the organic solution obtained in step (1) and then evaporating to obtain a solid gel; (3) mixing a lithium source, a carbon source and water with the solid gel obtained in step (2), drying, calcining under an inert gas, and cooling to obtain the lithium iron manganese phosphate positive electrode material. The method can prepare a lithium iron manganese phosphate positive electrode material in which iron and manganese are uniformly mixed, and the positive electrode material has a high specific capacity and cycle performance.

Description

Technical Field

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

[0002] Compared with ternary batteries, lithium iron phosphate batteries have higher safety and lower cost advantages. They have the advantages of good thermal stability, long cycle life, environmental friendliness, and abundant raw material sources. They are currently the most promising positive electrode material for power lithium-ion batteries. They are gaining favor from more automobile manufacturers and their market share is constantly increasing. Especially in the energy storage market, lithium iron phosphate has broad application prospects.

[0003] However, the LiFePO4 material has a low lithium deintercalation potential platform (about 3.4V), which reduces the overall energy density of the battery and limits its development in electric vehicles. The working voltage of LiMnPO4 to Li is 4.1V. If LiMnPO4 can obtain a specific capacity equivalent to that of LiFePO4, it means that the energy density will be 35% higher than that of LiFePO4. At the same time, low raw material cost and environmental friendliness are also the advantages of LiMnPO4. However, the conductivity of LiMnPO4 is very low, almost an insulator, only one thousandth of LiFePO4; at the same time, there will be a Jahn-Teller effect during the redox reaction, resulting in poor material rate performance and low discharge specific capacity.

[0004] From the current research status, it can be seen that LiMn x Fe (1-x) PO4 positive electrode material has high energy density, which can compensate for the shortcomings of LiFePO4 positive electrode material in this regard, while improving the problem of low rate and discharge specific capacity of LiMnPO4 positive electrode material, and increasing the possibility of phosphoric acid positive electrode material becoming power lithium-ion battery material.

[0005] There are many methods for synthesizing lithium manganese iron phosphate. Currently, a single high-temperature solid-phase method is used to prepare LiMn x Fe (1-x) PO4 material, it is difficult to accurately control the ratio of iron and manganese when preparing the precursor, and the transition metal is difficult 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. The co-precipitation reaction of phosphate with ferrous salt, manganese salt and oxidant has the following problems: since the pH of ferric phosphate precipitation is low, while the pH of manganese phosphate precipitation is high, at a higher pH, ferrous salt reacts with oxidant to obtain ferric hydroxide, resulting in high content of ferric hydroxide, low purity and low phosphorus content.

[0006] At the same time, since manganese exists in a stable divalent form, the phosphorus-manganese ratio in the formed divalent manganese phosphate is less than 1, and an additional phosphorus source needs to be supplemented.

[0007] Therefore, it is necessary to find a method that can achieve uniform mixing of iron and manganese at the atomic level and make the ratio of phosphorus to iron and manganese reach the theoretical value, so as to prepare a lithium manganese iron phosphate positive electrode material with high capacity and high cycle performance. Summary of the invention

[0008] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a lithium iron manganese phosphate positive electrode material and a preparation method and application thereof, which can prepare a lithium iron manganese phosphate positive electrode material with a uniform mixture of iron and manganese, and the positive electrode material has a high specific capacity and cycle performance.

[0009] The above technical objectives of the present invention are achieved through the following technical solutions:

[0010] A method for preparing a lithium iron manganese phosphate positive electrode material comprises the following steps: (1) mixing manganese acetylacetonate, iron acetylacetonate, a phosphorus source and an organic solvent to obtain an organic solution, wherein the manganese in the manganese acetylacetonate is trivalent manganese and the iron in the iron acetylacetonate is trivalent iron; (2) heating the organic solution obtained in step (1) and then evaporating it to obtain a solid gel; (3) mixing a lithium source, a carbon source and water with the solid gel obtained in step (2), drying, calcining under an inert gas, and cooling to obtain the lithium iron manganese phosphate positive electrode material.

[0011] Preferably, in step (1), the CAS number of the manganese acetylacetonate is 14284-89-0.

[0012] Preferably, in step (1), the CAS number of the ferric acetylacetonate is 14024-18-1.

[0013] Preferably, in step (1), the phosphorus source is phosphoric acid.

[0014] Preferably, in step (1), the mass concentration of the phosphoric acid is 80%-95%.

[0015] Further preferably, in step (1), the mass concentration of the phosphoric acid is 85%-95%.

[0016] Preferably, in step (1), the organic solvent is at least one of toluene, methanol, n-butanol, glacial acetic acid and ethylene glycol.

[0017] Preferably, in step (1), the manganese acetylacetonate, the iron acetylacetonate and the phosphorus source are mixed in a molar ratio of (Fe+Mn) to P of 1:(1-1.1).

[0018] Further preferably, in step (1), the manganese acetylacetonate, the iron acetylacetonate and the phosphorus source are mixed in a molar ratio of (Fe+Mn) to P of 1:1.

[0019] Preferably, in step (1), the mixing method is to first mix manganese acetylacetonate and iron acetylacetonate to obtain a mixture, then dissolve the mixture in the organic solvent, and then add phosphoric acid dropwise to mix.

[0020] Preferably, in step (1), manganese acetylacetonate and iron acetylacetonate are mixed in a molar ratio of iron to manganese of (0.1-5):1 to obtain a mixture.

[0021] Further preferably, in step (1), manganese acetylacetonate and iron acetylacetonate are mixed in a molar ratio of iron to manganese of (0.25-4):1 to obtain a mixture.

[0022] Preferably, in step (1), the mixture is dissolved in the organic solvent at a ratio of (3-15) g / 100 g.

[0023] Further preferably, in step (1), the mixture is dissolved in the organic solvent at a ratio of (5-10) g / 100 g.

[0024] Preferably, in step (2), the temperature after heating is 100-150°C.

[0025] Further preferably, in step (2), the temperature after heating is 110-140°C.

[0026] Preferably, in step (3), the solid gel is mixed with a lithium source and a carbon source according to a molar ratio of (Fe+Mn):Li:carbon source=1:(1.0-1.5):(0.1-0.5).

[0027] Further preferably, in step (3), the solid gel is mixed with a lithium source and a carbon source according to a molar ratio of (Fe+Mn):Li:carbon source=1:(1.0-1.2):(0.3-0.5).

[0028] Preferably, in step (3), the mass of water added accounts for 10%-45% of the total mass.

[0029] Further preferably, in step (3), the mass of the added water accounts for 20%-35% of the total mass.

[0030] Preferably, in step (3), the lithium source is at least one of lithium acetate, lithium hydroxide, lithium carbonate and lithium oxalate.

[0031] Preferably, in step (3), the carbon source is at least one of glucose, sucrose and fructose.

[0032] Preferably, in step (3), the drying method is spray drying.

[0033] Preferably, in step (3), the calcination temperature is 500-1000° C. and the calcination time is 5-25 h.

[0034] Further preferably, in step (3), the calcination temperature is 600-850° C., and the calcination time is 6-20 h.

[0035] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above.

[0036] The application of the lithium iron manganese phosphate positive electrode material as described above in the preparation of lithium ion batteries.

[0037] The beneficial effects of the present invention are:

[0038] (1) In the preparation method of the lithium iron manganese phosphate positive electrode material of the present invention, an acetylacetone complex of trivalent manganese and trivalent iron is used in an organic phase to be co-heated with phosphoric acid, and the organic solvent is evaporated to prepare a solid gel. On the one hand, phosphorus, iron and manganese are uniformly mixed, which is beneficial to the subsequent preparation of lithium iron manganese phosphate and improves the specific capacity and cycle performance of the material. In the aqueous phase, manganese is stably present in a divalent state, resulting in a phosphorus-manganese ratio in the prepared manganese phosphate of less than 1, and the precipitation conditions of iron and manganese in the aqueous phase are different, making it difficult to achieve uniform mixing of iron and manganese. On the other hand, as the organic solvent evaporates, a eutectic of iron phosphate and manganese phosphate is formed, and trivalent manganese is still stably present, achieving (Fe+Mn):P=1:1, thereby ensuring sufficient phosphorus content for the next step of synthesizing lithium iron manganese phosphate and avoiding the problem of adding a phosphorus source.

[0039] (2) In the preparation method of the lithium iron manganese phosphate positive electrode material of the present invention, the iron and manganese in the generated solid gel are both in a trivalent state combined with phosphate. When the lithium iron manganese phosphate is subsequently sintered with a lithium source and a carbon source to prepare the lithium iron manganese phosphate, the generation of metal oxides or metal elements is avoided, thereby further improving the specific capacity and cycle performance of the material.

[0040] (3) In the preparation method of the lithium manganese iron phosphate positive electrode material of the present invention, in the stage of evaporating the organic solution, a high boiling point organic solvent that is easily soluble in manganese acetylacetonate and iron acetylacetonate is selected, and under co-heating conditions, as the organic solvent evaporates, acetylacetone is taken out together, or the temperature is directly raised to the boiling point of acetylacetone to make acetylacetone directly volatilize. The reaction equation is as follows:

[0041] Fe(C5H7O2)3+H3PO4→FePO4+3C5H8O2↑

[0042] Mn(C5H7O2)3+H3PO4→MnPO4+3C5H8O2↑ BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a SEM image of the lithium manganese iron phosphate positive electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with specific embodiments.

[0045] Embodiment 1:

[0046] A method for preparing a lithium manganese iron phosphate positive electrode material comprises the following steps:

[0047] (1) According to the molar ratio of iron to manganese of 1:1 and (Fe+Mn):P=1:1, manganese acetylacetonate (CAS No.: 14284-89-0), iron acetylacetonate (CAS No.: 14024-18-1), and phosphoric acid with a mass concentration of 90% were selected;

[0048] (2) after mixing manganese acetylacetonate and iron acetylacetonate, dissolving the mixture in ethylene glycol at a ratio of 8 g / 100 g, and adding phosphoric acid dropwise to mix, to obtain an organic solution of phosphorus iron manganese;

[0049] (3) heating the organic solution at 140° C. and evaporating to dryness to obtain a solid gel, and recovering the organic solvent;

[0050] (4) mixing the solid gel with lithium carbonate and glucose at a molar ratio of (Fe+Mn):Li:carbon source=1:1.1:0.4, adding 25% of the total mass of deionized water, mixing well, and spray drying;

[0051] (5) The product obtained in step (4) is calcined at 800° C. for 15 h under the protection of an inert gas, and naturally cooled to room temperature to obtain a finished product of lithium manganese iron phosphate positive electrode material.

[0052] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above, and its SEM image is as follows Figure 1 shown.

[0053] Embodiment 2:

[0054] A method for preparing a lithium manganese iron phosphate positive electrode material comprises the following steps:

[0055] (1) According to the molar ratio of iron to manganese of 4:1 and (Fe+Mn):P=1:1, manganese acetylacetonate (CAS No.: 14284-89-0), iron acetylacetonate (CAS No.: 14024-18-1), and phosphoric acid with a mass concentration of 95% were selected;

[0056] (2) after mixing manganese acetylacetonate and iron acetylacetonate, dissolving the mixture in methanol at a ratio of 10 g / 100 g, and adding phosphoric acid dropwise to mix, to obtain an organic solution of phosphorus iron manganese;

[0057] (3) heating the organic solution at 135° C. and evaporating to dryness to obtain a solid gel, and recovering the organic solvent;

[0058] (4) mixing the solid gel with lithium hydroxide and sucrose at a molar ratio of (Fe+Mn):Li:carbon source=1:1.2:0.5, adding 20% ​​of the total mass of deionized water, mixing well, and spray drying;

[0059] (5) The product obtained in step (4) is calcined at 850° C. for 10 h under the protection of an inert gas, and naturally cooled to room temperature to obtain a finished product of lithium manganese iron phosphate positive electrode material.

[0060] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above.

[0061] Embodiment 3:

[0062] A method for preparing a lithium manganese iron phosphate positive electrode material comprises the following steps:

[0063] (1) According to the molar ratio of iron to manganese of 0.25:1 and (Fe+Mn):P=1:1, manganese acetylacetonate (CAS No.: 14284-89-0), iron acetylacetonate (CAS No.: 14024-18-1), and phosphoric acid with a mass concentration of 85% were selected;

[0064] (2) after mixing manganese acetylacetonate and iron acetylacetonate, dissolving the mixture in n-butanol at a ratio of 5 g / 100 g, and adding phosphoric acid dropwise to mix, to obtain an organic solution of phosphorus iron manganese;

[0065] (3) heating the organic solution at 110° C. and evaporating to dryness to obtain a solid gel, and recovering the organic solvent;

[0066] (4) mixing the solid gel with lithium acetate and fructose in a molar ratio of (Fe+Mn):Li:carbon source=1:1.0:0.3, adding 35% of the total mass of deionized water, mixing well, and spray drying;

[0067] (5) The product obtained in step (4) is calcined at 600° C. for 20 h under the protection of an inert gas, and naturally cooled to room temperature to obtain a finished product of lithium manganese iron phosphate positive electrode material.

[0068] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above.

[0069] Comparative Example 1: (The difference from Example 1 is that it is prepared by aqueous phase coprecipitation)

[0070] A method for preparing a lithium manganese iron phosphate positive electrode material comprises the following steps:

[0071] (1) preparing a mixed solution of iron nitrate and manganese nitrate with a total metal ion concentration of 1.0 mol / L in a molar ratio of iron to manganese of 1:1;

[0072] (2) adding phosphoric acid with a mass concentration of 90% to the mixed solution;

[0073] (3) adding a 1.0 mol / L sodium hydroxide solution dropwise until the pH of the mixed solution reaches 6.0;

[0074] (4) solid-liquid separation, washing the solid material with deionized water;

[0075] (5) calcining the washed product at 400° C. for 3 h to obtain a calcined material;

[0076] (6) mixing the calcined material with lithium carbonate and glucose in a molar ratio of (Fe+Mn):Li:carbon source=1:1.1:0.4, adding 25% of the total mass of deionized water, mixing well, and spray drying;

[0077] (7) Under the protection of inert gas, calcined at 800° C. for 15 h, and naturally cooled to room temperature to obtain a finished product of lithium manganese iron phosphate positive electrode material.

[0078] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above.

[0079] Comparative Example 2: (The difference from Example 2 is that it is prepared by aqueous phase coprecipitation)

[0080] A method for preparing a lithium manganese iron phosphate positive electrode material comprises the following steps:

[0081] (1) preparing a mixed solution of iron nitrate and manganese nitrate with a total metal ion concentration of 1.0 mol / L in a molar ratio of iron to manganese of 4:1;

[0082] (2) adding phosphoric acid with a mass concentration of 95% to the mixed solution;

[0083] (3) adding a 1.0 mol / L sodium hydroxide solution dropwise until the pH of the mixed solution reaches 6.0;

[0084] (4) solid-liquid separation, washing the solid material with deionized water;

[0085] (5) calcining the washed product at 400° C. for 3 h to obtain a calcined material;

[0086] (6) mixing the calcined material with lithium hydroxide and sucrose according to a molar ratio of (Fe+Mn):Li:carbon source=1:1.2:0.5, adding 20% ​​of the total mass of deionized water, mixing well, and spray drying;

[0087] (7) Under the protection of inert gas, calcined at 850° C. for 10 h, and naturally cooled to room temperature to obtain a finished product of lithium manganese iron phosphate positive electrode material.

[0088] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above.

[0089] Comparative Example 3: (The difference from Example 3 is that it is prepared by aqueous phase coprecipitation)

[0090] A method for preparing a lithium manganese iron phosphate positive electrode material comprises the following steps:

[0091] (1) preparing a mixed solution of iron nitrate and manganese nitrate with a total metal ion concentration of 1.0 mol / L at a molar ratio of iron to manganese of 0.25:1;

[0092] (2) adding phosphoric acid with a mass concentration of 85% to the mixed solution;

[0093] (3) adding a 1.0 mol / L sodium hydroxide solution dropwise until the pH of the mixed solution reaches 6.0;

[0094] (4) solid-liquid separation, washing the solid material with deionized water;

[0095] (5) calcining the washed product at 400° C. for 3 h to obtain a calcined material;

[0096] (6) mixing the calcined material with lithium acetate and fructose according to a molar ratio of (Fe+Mn):Li:carbon source=1:1.0:0.3, adding 35% of the total mass of deionized water, mixing well, and spray drying;

[0097] (7) Under the protection of inert gas, calcined at 600° C. for 20 h, and naturally cooled to room temperature to obtain a finished product of lithium manganese iron phosphate positive electrode material.

[0098] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above.

[0099] Comparative Example 4: (The only difference from Example 1 is that the manganese in manganese acetylacetonate is divalent manganese)

[0100] A method for preparing a lithium manganese iron phosphate positive electrode material comprises the following steps:

[0101] (1) According to the molar ratio of iron to manganese of 1:1 and (Fe+Mn):P=1:1, manganese acetylacetonate (CAS No.: 14024-58-9), iron acetylacetonate (CAS No.: 14024-18-1), and phosphoric acid with a mass concentration of 90% were selected;

[0102] (2) after mixing manganese acetylacetonate and iron acetylacetonate, dissolving the mixture in ethylene glycol at a ratio of 8 g / 100 g, and adding phosphoric acid dropwise to mix, to obtain an organic solution of phosphorus iron manganese;

[0103] (3) heating the organic solution at 140° C. and evaporating to dryness to obtain a solid gel, and recovering the organic solvent;

[0104] (4) mixing the solid gel with lithium carbonate and glucose at a molar ratio of (Fe+Mn):Li:carbon source=1:1.1:0.4, adding 25% of the total mass of deionized water, mixing well, and spray drying;

[0105] (5) The product obtained in step (4) is calcined at 800° C. for 15 h under the protection of an inert gas, and naturally cooled to room temperature to obtain a finished product of lithium manganese iron phosphate positive electrode material.

[0106] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above.

[0107] Comparative Example 5: (The only difference from Example 2 is that the manganese in manganese acetylacetonate is divalent manganese)

[0108] A method for preparing a lithium manganese iron phosphate positive electrode material comprises the following steps:

[0109] (1) According to the molar ratio of iron to manganese of 4:1 and (Fe+Mn):P=1:1, manganese acetylacetonate (CAS No.: 14024-58-9), iron acetylacetonate (CAS No.: 14024-18-1), and phosphoric acid with a mass concentration of 95% were selected;

[0110] (2) after mixing manganese acetylacetonate and iron acetylacetonate, dissolving the mixture in methanol at a ratio of 10 g / 100 g, and adding phosphoric acid dropwise to mix, to obtain an organic solution of phosphorus iron manganese;

[0111] (3) heating the organic solution at 135° C. and evaporating to dryness to obtain a solid gel, and recovering the organic solvent;

[0112] (4) mixing the solid gel with lithium hydroxide and sucrose at a molar ratio of (Fe+Mn):Li:carbon source=1:1.2:0.5, adding 20% ​​of the total mass of deionized water, mixing well, and spray drying;

[0113] (5) The product obtained in step (4) is calcined at 850° C. for 10 h under the protection of an inert gas, and naturally cooled to room temperature to obtain a finished product of lithium manganese iron phosphate positive electrode material.

[0114] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above.

[0115] Comparative Example 6: (The only difference from Example 3 is that the manganese in manganese acetylacetonate is divalent manganese)

[0116] A method for preparing a lithium manganese iron phosphate positive electrode material comprises the following steps:

[0117] (1) According to the molar ratio of iron to manganese of 0.25:1 and (Fe+Mn):P=1:1, manganese acetylacetonate (CAS No.: 14024-58-9), iron acetylacetonate (CAS No.: 14024-18-1), and phosphoric acid with a mass concentration of 85% were selected;

[0118] (2) after mixing manganese acetylacetonate and iron acetylacetonate, dissolving the mixture in n-butanol at a ratio of 5 g / 100 g, and adding phosphoric acid dropwise to mix, to obtain an organic solution of phosphorus iron manganese;

[0119] (3) heating the organic solution at 110° C. and evaporating to dryness to obtain a solid gel, and recovering the organic solvent;

[0120] (4) mixing the solid gel with lithium acetate and fructose in a molar ratio of (Fe+Mn):Li:carbon source=1:1.0:0.3, adding 35% of the total mass of deionized water, mixing well, and spray drying;

[0121] (5) The product obtained in step (4) is calcined at 600° C. for 20 h under the protection of an inert gas, and naturally cooled to room temperature to obtain a finished product of lithium manganese iron phosphate positive electrode material.

[0122] A lithium manganese iron phosphate positive electrode material is prepared by the preparation method as described above.

[0123] Among them, the manganese acetylacetonate (CAS No.: 14284-89-0) used in Examples 1-3 is trivalent manganese, and the manganese acetylacetonate (CAS No.: 14024-58-9) used in Comparative Examples 4-6 is divalent manganese; Comparative Examples 1-3 adopt aqueous phase co-precipitation. During the precipitation process, as the pH of the mixed solution increases, the amount of precipitate first increases-remains unchanged-and then increases-remains unchanged, that is, due to the different pH values ​​of iron and manganese precipitation, iron phosphate is precipitated first, and then manganese phosphate.

[0124] The products obtained in the examples and comparative examples were subjected to ICP (inductively coupled plasma spectrometer) to detect the molar ratio of iron, manganese and phosphorus. The results are shown in Table 1:

[0125] Table 1: Molar ratio of iron, manganese and phosphorus in the product

[0126] Fe:Mn:P Example 1 1:1:2 Example 2 4:1:5 Example 3 1:4:5 Comparative Example 1 1:1:1.66 Comparative Example 2 4:1:4.66 Comparative Example 3 1:4:3.66 Comparative Example 4 1:1:1.67 Comparative Example 5 4:1:4.67 Comparative Example 6 1:4:3.67

[0127] Test example:

[0128] The lithium manganese iron phosphate positive electrode material obtained in the embodiment and the comparative example, acetylene black as a conductive agent, PVDF as a binder, are mixed at a mass ratio of 8:1:1, and a certain amount of organic solvent NMP is added, and then coated on aluminum foil after stirring to make a positive electrode sheet, and a metal lithium sheet is used for the negative electrode; the diaphragm is a Celgard2400 polypropylene porous membrane; the solvent in the electrolyte is a solution composed of EC, DMC and EMC in a mass ratio of 1:1:1, the solute is LiPF6, and the concentration of LiPF6 is 1.0 mol / L; 2023 button batteries are assembled in a glove box. The battery is tested for charge and discharge cycle performance, and the 0.2C and 1C discharge specific capacities are tested within the cut-off voltage range of 2.0-4.3V; the electrochemical performance test results are shown in Table 2:

[0129] Table 2: Electrochemical performance test results

[0130]

[0131] It can be seen from Table 2 that the 0.2C discharge capacity of the lithium manganese iron phosphate positive electrode material prepared by the preparation method of the present application can reach more than 149.3 mAh / g, the 1C discharge capacity can reach more than 142.4 mAh / g, and the capacity retention rate after 500 cycles at 1C can reach more than 94.06%.

[0132] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a lithium manganese iron phosphate positive electrode material, characterized in that: The following steps are involved: (1) mixing manganese acetylacetonate, ferric acetylacetonate, a phosphorus source and an organic solvent to obtain an organic solution, wherein the manganese in the manganese acetylacetonate is trivalent manganese and the iron in the ferric acetylacetonate is trivalent iron; (2) heating the organic solution obtained in step (1) and evaporating it to dryness to obtain a solid gel; (3) mixing a lithium source, a carbon source, and water with the solid gel obtained in step (2), drying, calcining under an inert gas, and cooling to obtain the lithium manganese iron phosphate positive electrode material; in step (1), the phosphorus source is phosphoric acid, the organic solvent is at least one of toluene, methanol, n-butanol, glacial acetic acid and ethylene glycol, and the mixing method is to first mix manganese acetylacetonate and iron acetylacetonate to obtain a mixture, then dissolve the mixture in the organic solvent, and then add phosphoric acid dropwise to mix.

2. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: In step (1), the manganese acetylacetonate, the iron acetylacetonate and the phosphorus source are mixed in a molar ratio of (Fe+Mn) to P of 1:(1-1.1).

3. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: In step (1), manganese acetylacetonate and iron acetylacetonate are mixed in a molar ratio of iron to manganese of (0.1-5):1 to obtain a mixture.

4. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: In step (1), the mixture is dissolved in the organic solvent at a ratio of (3-15) g / 100 g.

5. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: In step (3), the solid gel is mixed with a lithium source and a carbon source according to a molar ratio of (Fe+Mn):Li:carbon source=1:(1.0-1.2):(0.3-0.5).

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