Lithium manganese iron phosphate positive electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and provides a lithium iron manganese phosphate positive electrode material and a preparation method thereof, the lithium iron manganese phosphate positive electrode material comprises a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source; the carbon source is prepared by the following steps: adding activated carbon into deionized water, stirring and dispersing uniformly, adding ethylenediamine tetraacetic acid, heating, continuously stirring and reacting, naturally cooling, centrifugally separating, washing and drying to obtain the carbon source. The preparation method comprises the following steps: S1, adding a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source into pure water according to a molar ratio, and uniformly stirring to obtain mixed slurry; s2, sanding the mixed slurry, and performing spray drying on the sanded mixed slurry to obtain powder; and S3, calcining the powder under the protection of inert gas, cooling, grinding and sieving to finally obtain the lithium manganese iron phosphate positive electrode material which has the advantage of uniform thickness of a carbon coating layer, and is excellent in electrochemical performance and stable in cycle performance.

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] As a new energy source, lithium-ion batteries have become a hot topic for research in industry and academia. The positive electrode material is one of the four important components of lithium-ion batteries. It plays a vital role in the electrochemical performance and safety performance of lithium-ion batteries. Its cost is also close to half of the total cost of lithium-ion batteries. The development of positive electrode materials has largely restricted the development of lithium-ion batteries. There are many types of positive electrode active materials for lithium-ion batteries, among which lithium cobalt oxide, lithium manganese oxide, ternary materials, lithium iron phosphate, etc. are widely used. Lithium manganese iron phosphate and lithium iron phosphate are both phosphate-based positive electrode active materials for lithium-ion batteries. Their theoretical specific capacity can reach 170mAh·g -1 , with the advantages of good cycle performance, excellent safety performance, wide source of raw materials, low cost, and environmental friendliness. In addition, compared with lithium iron phosphate, lithium manganese iron phosphate has a higher discharge voltage, and has certain advantages in specific energy and specific power. Therefore, the development of lithium manganese iron phosphate with excellent electrochemical performance as a positive electrode active material has become one of the hot spots in lithium-ion battery research. However, due to the poor conductivity of lithium manganese iron phosphate, the reversibility of the material during the charge and discharge process is also poor, and it is more prone to polarization. Therefore, the actual specific capacity of lithium manganese iron phosphate is difficult to reach its theoretical value.

[0003] The Chinese patent application document with patent application number CN102738465A discloses a method for preparing a lithium iron manganese phosphate-carbon composite material, which comprises the following steps: (1) lithium source, trivalent iron source, manganese dioxide, phosphorus source and carbon source are prepared according to the stoichiometric ratio of each element in lithium iron manganese phosphate, and a dispersant and a complexing agent are added for ball milling; (2) the slurry obtained by ball milling is dried, and then subjected to secondary ball milling to obtain a precursor powder; (3) the precursor powder is placed in a calcining furnace for sintering, and an inert gas is introduced as a protective gas to obtain a lithium iron manganese phosphate-carbon composite material. This preparation method reduces the particle size of the insoluble raw material and improves the uniformity of the elemental composition by solid-liquid mixing and mechanical grinding. However, the disadvantage of this type of method is that solid-liquid mixing cannot achieve uniform mixing at the atomic level, and the slurry obtained by mechanical grinding has a large viscosity and is easy to segregate. Therefore, it has limited effect on improving the uniformity of multiple components (especially solid phase components), and the product quality and performance are unstable, and it is difficult to obtain a lithium iron manganese phosphate-carbon composite material that meets product requirements. In addition, manganese dissolution is also one of the reasons why the conductivity of lithium iron manganese phosphate cathode materials cannot be well exerted. The Chinese patent application document with patent application number CN104852037A discloses a precursor with rich iron on the surface and rich manganese in the core and a method for preparing a carbon-coated lithium iron manganese phosphate material using the precursor as a raw material. Although this method can reduce manganese dissolution, it cannot synthesize a lithium iron manganese material with uniform distribution of iron and manganese, and there are places where manganese is more distributed with low conductivity and places where iron is more distributed with high conductivity, resulting in low overall conductivity of the lithium iron manganese phosphate material.

[0004] Therefore, developing a method for preparing lithium manganese iron phosphate positive electrode material with high production efficiency, low cost and excellent electrochemical performance is a technical problem that needs to be solved urgently. Summary of the invention

[0005] In order to improve the electrochemical performance of lithium iron manganese phosphate positive electrode material, the present invention provides a lithium iron manganese phosphate positive electrode material and a preparation method thereof.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The first aspect of the present invention provides a lithium iron manganese phosphate positive electrode material, wherein the lithium iron manganese phosphate positive electrode material comprises a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source; the carbon source is prepared by the following steps:

[0008] Add activated carbon into deionized water, stir and disperse it evenly, add ethylenediaminetetraacetic acid, raise the temperature to 65-75°C, continue stirring and reacting for 6-8h, cool naturally and centrifuge, wash and dry to obtain a carbon source.

[0009] In some embodiments of the present invention, the usage ratio of activated carbon, deionized water and ethylenediaminetetraacetic acid is 10.0-10.5 g:100 mL:2.0-2.2 g.

[0010] In some embodiments of the present invention, the molar ratio of the lithium source, iron source, manganese source, phosphorus source and carbon source is 1.0-1.1:x:(1-x):y:(1-y), wherein 0.50≤x≤0.65, 0.85≤y≤1.

[0011] In some embodiments of the present invention, the lithium source is at least one of lithium benzoate, lithium tartrate, lithium carbonate, lithium nitrate, lithium hydroxide and lithium acetate.

[0012] In some embodiments of the present invention, the iron source is at least one of ferrous lactate, ferrous citrate, ferrous sulfate, ferrous chloride, ferrous nitrate and ferrous acetate.

[0013] In some embodiments of the present invention, the manganese source is at least one of manganous sulfate, manganous nitrate, manganous citrate, and manganous acetate. The addition of manganese source can effectively improve the energy density, structural stability, rate performance and other properties of the positive electrode material.

[0014] In some embodiments of the present invention, the phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and dipotassium hydrogen phosphate. The phosphorus source can not only improve the diffusion coefficient and conductivity of lithium ions, but also improve the morphology and structure of the material by in-situ growth, thereby significantly improving its large current discharge capacity and cycle life. Among them, ammonium dihydrogen phosphate and diammonium hydrogen phosphate are selected as phosphorus sources, which can provide a stable supply of phosphorus and help form a uniform olivine structure, thereby improving the cycle stability and safety of the material.

[0015] A second aspect of the present invention provides a method for preparing a lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0016] S1. Adding a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source into pure water according to a molar ratio, stirring until uniform, and obtaining a mixed slurry;

[0017] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry to obtain a powder;

[0018] S3, calcining the powder obtained in S2 under the protection of inert gas, grinding and sieving after cooling, and finally obtaining lithium manganese iron phosphate positive electrode material.

[0019] In some embodiments of the present invention, the spray air inlet temperature of the spray drying in S2 is 200-280°C, and the air outlet temperature is 90-120°C.

[0020] In some embodiments of the present invention, the calcination temperature in S3 is 550-650°C, the calcination time is 6-8h, and the heating rate is 1-2°C / min. The lithium manganese iron phosphate material prepared by calcining at a temperature of 550-650°C can exhibit the best electrochemical performance, with the smallest impedance and good kinetic performance.

[0021] In some embodiments of the present invention, the particle size D50 after grinding and sieving in S3 is 1 to 30 μm.

[0022] Beneficial effects of the present invention:

[0023] The lithium iron manganese phosphate positive electrode material of the present invention is prepared by mixing a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source, and then sintering at a high temperature to obtain the lithium iron manganese phosphate positive electrode material. The carbon coating layer of the prepared lithium iron manganese phosphate positive electrode material has a uniform thickness, excellent electrochemical performance and stable cycle performance.

[0024] In the present invention, manganese is introduced into the lithium iron phosphate positive electrode material for improvement, but the improvement method easily leads to the poor conductivity of the lithium iron manganese phosphate positive electrode material, the dissolution of manganese affects the cycle life and the generation of new problems of stability. In order not to affect the preparation of the lithium iron manganese phosphate positive electrode material, weaken and improve the impact of new problems on battery performance, the present invention adopts the addition of a carbon source to achieve carbon coating to improve the performance of the lithium iron manganese phosphate battery. Carbon coating can effectively enhance the electrical conductivity of the material, improve the electrochemical activity of the material, improve the electrochemical performance of the material, and inhibit the growth of material particles, improve the conductivity between material particles, so that the active material is fully utilized.

[0025] Furthermore, in the present invention, the carbon source is prepared by modifying the surface of activated carbon by the hydroxyl and amine groups in ethylenediaminetetraacetic acid with the hydroxyl groups of activated carbon through hydrogen bonding and the like; on the one hand, activated carbon has the advantages of developed internal pores, large specific surface area and high rate charge and discharge, and adding it as a carbon source to the preparation process of lithium iron manganese phosphate positive electrode material is beneficial to Li + The formation of electron transfer and conductive network effectively improves the electronic conductivity and compaction density of the material, further improving the cycle performance of lithium-ion batteries. On the other hand, EDTA can form a strong complex with metal ions, and then adsorb manganese ions dissolved in lithium iron manganese phosphate materials, thereby inhibiting the dissolution of manganese, stabilizing the structure of lithium iron manganese phosphate cathode materials, and further improving the electrochemical performance of lithium iron manganese phosphate cathode materials.

[0026] The lithium manganese iron phosphate positive electrode material prepared by the present invention not only has good electrical conductivity and excellent electrochemical performance, but also has the advantages of low resistivity, high specific capacity of the first discharge, excellent cycle characteristics, etc.

[0027] The preparation method of the lithium iron manganese phosphate positive electrode material provided by the present invention is simple, has a short process flow, has low equipment requirements, and is suitable for application in large-scale industrial production. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Obviously, the following descriptions are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios without creative work. In addition, it can also be understood that although the efforts made in this development process may be complicated and lengthy, for ordinary technicians in the field related to the content disclosed in this application, some changes in design, manufacturing or production based on the technical content disclosed in this application are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

[0030] However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present application and is not intended to limit the subject matter described in the claims.

[0031] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0032] Example 1

[0033] This embodiment provides a carbon source, and the preparation steps are as follows:

[0034] Add 10.0 g of activated carbon to 100 mL of deionized water, stir until evenly dispersed, add 2.0 g of ethylenediaminetetraacetic acid, heat to 65 ° C and continue stirring to react for 8 hours, cool naturally and then centrifuge, wash with anhydrous ethanol and deionized water for multiple times, and finally place in a 60 ° C oven to dry for 24 hours to obtain a carbon source.

[0035] Example 2

[0036] This embodiment provides a carbon source, and the preparation steps are as follows:

[0037] Add 10.3 g of activated carbon to 100 mL of deionized water, stir until evenly dispersed, add 2.1 g of ethylenediaminetetraacetic acid, heat to 65 ° C and continue stirring to react for 8 hours, cool naturally and then centrifuge, wash with anhydrous ethanol and deionized water for multiple times, and finally dry in a 60 ° C oven for 24 hours to obtain a carbon source.

[0038] Example 3

[0039] This embodiment provides a carbon source, and the preparation steps are as follows:

[0040] Add 10.5 g of activated carbon to 100 mL of deionized water, stir until uniformly dispersed, add 2.2 g of ethylenediaminetetraacetic acid, heat to 65 ° C and continue stirring to react for 8 hours, cool naturally and then centrifuge, wash with anhydrous ethanol and deionized water for multiple times, and finally place in a 60 ° C oven to dry for 24 hours to obtain a carbon source.

[0041] Example 4

[0042] This embodiment provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof:

[0043] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0044] Lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid and the carbon source in Example 1;

[0045] The molar ratio of the lithium source, the iron source, the manganese source, the phosphorus source and the carbon source in Example 1 is 1.0:0.50:0.50:0.85:0.15.

[0046] The preparation steps are as follows:

[0047] S1, adding the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 1 into pure water according to the molar ratio, stirring until uniform, to obtain a mixed slurry;

[0048] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 200° C. and the outlet air temperature is 90° C., to obtain a powder;

[0049] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 550°C, a calcination time of 8h, a heating rate of 1°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0050] Example 5

[0051] This embodiment provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof:

[0052] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0053] Lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid and the carbon source in Example 2;

[0054] The molar ratio of the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 2 is 1.0:0.50:0.50:0.85:0.15.

[0055] The preparation steps are as follows:

[0056] S1, adding the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 2 into pure water according to the molar ratio, stirring until uniform, to obtain a mixed slurry;

[0057] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 200° C. and the outlet air temperature is 90° C., to obtain a powder;

[0058] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 550°C, a calcination time of 8h, a heating rate of 1°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0059] Example 6

[0060] This embodiment provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof:

[0061] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0062] Lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid and the carbon source in Example 3;

[0063] The molar ratio of the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 3 is 1.0:0.50:0.50:0.85:0.15.

[0064] The preparation steps are as follows:

[0065] S1, adding the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 3 into pure water according to the molar ratio, stirring until uniform, to obtain a mixed slurry;

[0066] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 200° C. and the outlet air temperature is 90° C., to obtain a powder;

[0067] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 550°C, a calcination time of 8h, a heating rate of 1°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0068] Example 7

[0069] This embodiment provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof:

[0070] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0071] Lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid and the carbon source in Example 1;

[0072] The molar ratio of the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 1 is 1.0:0.60:0.40:0.85:0.15.

[0073] The preparation steps are as follows:

[0074] S1, adding the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 1 into pure water according to the molar ratio, stirring until uniform, to obtain a mixed slurry;

[0075] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 280° C. and the outlet air temperature is 120° C., to obtain a powder;

[0076] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 650°C, a calcination time of 6 hours, a heating rate of 1°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5 μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0077] Example 8

[0078] This embodiment provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof:

[0079] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0080] Lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid and the carbon source in Example 1;

[0081] The molar ratio of the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 1 is 1.1:0.50:0.50:0.85:0.15.

[0082] The preparation steps are as follows:

[0083] S1, adding the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 1 into pure water according to the molar ratio, stirring until uniform, to obtain a mixed slurry;

[0084] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 260° C. and the outlet air temperature is 100° C., to obtain a powder;

[0085] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 600°C, a calcination time of 6.5h, a heating rate of 2°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0086] Example 9

[0087] This embodiment provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof:

[0088] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0089] Lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid and the carbon source in Example 1;

[0090] The molar ratio of the lithium source, the iron source, the manganese source, the phosphorus source and the carbon source in Example 1 is 1.0:0.50:0.50:0.95:0.05.

[0091] The preparation steps are as follows:

[0092] S1, adding the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 1 into pure water according to the molar ratio, stirring until uniform, to obtain a mixed slurry;

[0093] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 200° C. and the outlet air temperature is 90° C., to obtain a powder;

[0094] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 650°C, a calcination time of 6 hours, a heating rate of 2°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5 μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0095] Example 10

[0096] This embodiment provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof:

[0097] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0098] Lithium benzoate, ferrous citrate, manganese citrate, phosphoric acid and the carbon source in Example 2;

[0099] The molar ratio of the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 2 is 1.0:0.50:0.50:0.85:0.15.

[0100] The preparation steps are as follows:

[0101] S1, adding the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 2 into pure water according to the molar ratio, stirring until uniform, to obtain a mixed slurry;

[0102] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 200° C. and the outlet air temperature is 90° C., to obtain a powder;

[0103] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 550°C, a calcination time of 8h, a heating rate of 1°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0104] Comparative Example 1

[0105] This comparative example provides a lithium iron manganese phosphate positive electrode material and a preparation method thereof, wherein no carbon source is added to the raw materials for preparing the lithium iron manganese phosphate positive electrode material:

[0106] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0107] Lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid;

[0108] The molar ratio of the lithium source, the iron source, the manganese source and the phosphorus source is 1.0:0.50:0.50:1.

[0109] The preparation steps are as follows:

[0110] S1. Adding a lithium source, an iron source, a manganese source and a phosphorus source into pure water according to a molar ratio, stirring until uniform, to obtain a mixed slurry;

[0111] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 200° C. and the outlet air temperature is 90° C., to obtain a powder;

[0112] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 550°C, a calcination time of 8h, a heating rate of 1°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0113] Comparative Example 2

[0114] This comparative example provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof, wherein the carbon source in the raw material for preparing the lithium manganese iron phosphate positive electrode material is activated carbon:

[0115] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0116] lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid, and activated carbon;

[0117] The molar ratio of the lithium source, the iron source, the manganese source, the phosphorus source and the activated carbon is 1.0:0.50:0.50:0.85:0.15.

[0118] The preparation steps are as follows:

[0119] S1. Adding a lithium source, an iron source, a manganese source, a phosphorus source and activated carbon into pure water according to a molar ratio, stirring until uniform, and obtaining a mixed slurry;

[0120] S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 200° C. and the outlet air temperature is 90° C., to obtain a powder;

[0121] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 550°C, a calcination time of 8h, a heating rate of 1°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0122] Comparative Example 3

[0123] The only difference compared with Example 4 is:

[0124] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0125] Lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid and the carbon source in Example 1;

[0126] The molar ratio of the lithium source, iron source, manganese source, phosphorus source and the carbon source in Example 1 is 1.0:0.40:0.60:0.85:0.15.

[0127] Comparative Example 4

[0128] The only difference compared with Example 4 is:

[0129] A lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material comprising:

[0130] Lithium benzoate, ferrous lactate, manganous nitrate, phosphoric acid and the carbon source in Example 1;

[0131] The molar ratio of the lithium source, the iron source, the manganese source, the phosphorus source and the carbon source in Example 1 is 1.0:0.50:0.50:0.75:0.25.

[0132] Comparative Example 5

[0133] The only difference compared with Example 4 is:

[0134] S2. Sand-grind the mixed slurry obtained in S1, and then spray-dry the sand-grinded mixed slurry, wherein the spray inlet air temperature of the spray drying is 180° C. and the outlet air temperature is 90° C., to obtain a powder.

[0135] Comparative Example 6

[0136] The only difference compared with Example 4 is:

[0137] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 500°C, a calcination time of 8h, a heating rate of 0.5°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 5μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0138] Comparative Example 7

[0139] The only difference compared with Example 4 is:

[0140] S3. The powder obtained in S2 is calcined under the protection of inert gas at a calcination temperature of 550°C, a calcination time of 8h, a heating rate of 1°C / min, and then ground and sieved after cooling. The particle size D50 after grinding and sieving is 40μm, and finally, lithium manganese iron phosphate positive electrode material is obtained.

[0141] The application and performance tests of the lithium iron manganese phosphate positive electrode materials prepared in Examples 4 to 10 and Comparative Examples 1 to 7 were performed:

[0142] Assembly of lithium manganese iron phosphate button battery: The lithium manganese iron phosphate positive electrode material obtained in the embodiment and the comparative example: SP (carbon black conductive agent): PVDF (polyvinylidene fluoride binder) was homogenized according to a mass ratio of 90:5:5, and then coated on a 20 μm thick aluminum foil, dried, and a positive electrode sheet was prepared; the obtained positive electrode sheet was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the PE-PP composite film was used as the battery separator, and 1 mol·L -1 LiPF6 / (EC+DMC) was used as the electrolyte, in which the volume ratio of EC to DMC was 1:1, and assembled into CR2032 button batteries.

[0143] 1C cycle performance test at 25°C: The lithium manganese iron phosphate button cells in the embodiments and comparative examples were tested using a blue electric tester, and the prepared button cells were placed in a high-temperature oven at 25°C for charge and discharge tests, with a voltage range of 2.0V-4.35V, 0.1C charge and discharge activation for one cycle, and then charged at 0.5C constant current and constant voltage, with a cut-off current of 0.05C, and discharged at 1C current for 100 cycles to obtain relevant data of 0.1C, 1C first discharge capacity, and 100th cycle discharge capacity. The test results are shown in Table 1:

[0144] Table 1

[0145]

[0146]

[0147] It can be seen from Table 1 that, compared with Comparative Examples 1-7, the lithium iron manganese phosphate positive electrode materials prepared in Examples 4-10 have good electrochemical properties, high capacity retention rate, better cycle performance, and better compaction density. It can be seen that the preparation method of the lithium iron manganese phosphate positive electrode material provided by the present invention can significantly improve the specific capacity, high rate performance and compaction density of the lithium iron manganese phosphate positive electrode material.

[0148] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0149] It should be understood that in the various embodiments of the present application, the size of the serial number of each process does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0150] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0151] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium manganese iron phosphate positive electrode material, characterized in that: The lithium manganese iron phosphate positive electrode material comprises a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source; the carbon source is prepared by the following steps: Add activated carbon into deionized water, stir and disperse it evenly, add ethylenediaminetetraacetic acid, raise the temperature to 65-75°C, continue stirring and reacting for 6-8h, cool naturally and centrifuge, wash and dry to obtain a carbon source.

2. A lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The usage ratio of activated carbon, deionized water and ethylenediaminetetraacetic acid is 10.0-10.5 g:100 mL:2.0-2.2 g.

3. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The molar ratio of the lithium source, iron source, manganese source, phosphorus source and carbon source is 1.0-1.1:x:(1-x):y:(1-y), wherein 0.50≤x≤0.65, 0.85≤y≤1.

4. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The lithium source is at least one of lithium benzoate, lithium tartrate, lithium carbonate, lithium nitrate, lithium hydroxide and lithium acetate.

5. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The iron source is at least one of ferrous lactate, ferrous citrate, ferrous sulfate, ferrous chloride, ferrous nitrate and ferrous acetate.

6. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The manganese source is at least one of manganous sulfate, manganous nitrate, manganous citrate and manganous acetate.

7. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and dipotassium hydrogen phosphate.

8. A method for preparing a lithium iron manganese phosphate positive electrode material according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Adding a lithium source, an iron source, a manganese source, a phosphorus source and a carbon source into pure water according to a molar ratio, stirring until uniform, and obtaining a mixed slurry; S2, sand-grinding the mixed slurry obtained in S1, and then spray-drying the sand-grinded mixed slurry to obtain a powder; S3, calcining the powder obtained in S2 under the protection of inert gas, grinding and sieving after cooling, and finally obtaining lithium manganese iron phosphate positive electrode material.

9. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 8, characterized in that: The spray inlet air temperature of the spray drying in S2 is 200-280°C, and the outlet air temperature is 90-120°C.

10. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 8, characterized in that: In S3, the calcination temperature is 550-650°C, the calcination time is 6-8h, and the heating rate is 1-2°C / min; And / or, the particle size D50 after grinding and sieving in S3 is 1 to 30 μm.

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