Lithium manganese iron phosphate material and preparation method therefor, positive electrode sheet and secondary battery

Abstract

The present application relates to the technical field of lithium ion batteries, and in particular to a lithium manganese iron phosphate material and a preparation method therefor, a positive electrode sheet, a secondary battery and an electric device. The lithium manganese iron phosphate material comprises a core, and the core comprises a core material of general formula LixMgyMnzFeaAlbPO4, wherein x is 1.008-1.05, y is 0-0.006, z is 0.4-0.6, a is 0.388-0.6, and b is 0-0.012.

Description

Lithium manganese iron phosphate material and preparation method thereof, positive electrode sheet and secondary battery

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202311097874.9, filed on August 28, 2023, entitled “A Method for Preparing Lithium Manganese Iron Phosphate,” the entire text of which is incorporated herein by reference. Technical Field

[0003] The present application relates to the technical field of lithium-ion batteries, and in particular to a lithium iron manganese phosphate material and a preparation method thereof, a positive electrode sheet, and a secondary battery. Background Art

[0004] Lithium iron manganese phosphate (LFP) and lithium iron phosphate (LFP) are both phosphate-based materials, differing only in the addition of manganese and the reduction of iron. In terms of performance, LFP retains the advantages of LFP, such as long cycle life, high thermal stability, and strong safety, while increasing the voltage platform from 3.4-3.5V to 4.3V, compared to LFP, and increasing energy density by 15-20%. Regarding cost, manganese is widely present in nature and is a plentiful resource. Increasing the proportion of manganese in the cathode material significantly reduces battery costs.

[0005] At present, the preparation processes of lithium manganese iron phosphate include solid-phase method and hydrothermal method. Among them, the solid-phase method uses manganese salt, iron salt (oxide, phosphate, oxalate, etc.) and lithium carbonate, phosphate to grind after adding water slurry, and then spray-dry and calcined to obtain lithium manganese iron phosphate. The lithium manganese iron phosphate prepared by the solid-phase method has the problem of segregation of manganese iron materials. Because the conductivity of lithium manganese phosphate is extremely low, if there is a separate lithium manganese phosphate phase, it will cause very low capacity. The hydrothermal method uses lithium salt, iron salt, manganese salt, and phosphate to mix and add them to water, and then react under high temperature and high pressure. The lithium manganese iron phosphate obtained thereby has the problem of low crystallinity.

[0006] In view of this, this application is hereby filed.

[0007] Summary of the Invention

[0008] According to at least some embodiments of the present application, a lithium iron manganese phosphate material is provided. Also provided are a method for preparing the lithium iron manganese phosphate material, a positive electrode sheet containing the lithium iron manganese phosphate material, a secondary battery, and an electrical device.

[0009] In a first aspect, a lithium manganese iron phosphate material is provided, wherein the lithium manganese iron phosphate material comprises a core, wherein the core comprises a general formula of Li x Mg y Mn z Fe a Alb The core material of PO4, wherein x is 1.002 to 1.05, y is 0 to 0.009, z is 0.4 to 0.6, a is 0.388 to 0.6, and b is 0 to 0.012.

[0010] Optionally, the lithium manganese iron phosphate material further includes a coating layer coated on the surface of the core, and the material of the coating layer includes a carbon material;

[0011] Wherein, the mass fraction of the carbon material is 1.5% to 2.5%, and / or the coverage rate of the carbon material is 98.0% to 99.9%.

[0012] Optionally, the lithium manganese iron phosphate material satisfies at least one of the following conditions:

[0013] (1) The sphericity of lithium manganese iron phosphate material is 0.7 to 1.0;

[0014] (2) The average primary particle size of the lithium manganese iron phosphate material is 170nm to 220nm;

[0015] (3) The secondary particle size of the lithium manganese iron phosphate material meets the following requirements: D10 is 0.2 μm to 0.6 μm, D50 is 1.5 μm to 3 μm, and D90 is 5 μm to 15 μm;

[0016] (4) The compacted density of lithium manganese iron phosphate material is 2.35 g / mL to 2.45 g / mL;

[0017] (5) The tap density of lithium manganese iron phosphate material is 1.1g / mL to 1.2g / mL;

[0018] (6) The specific surface area of ​​lithium manganese iron phosphate material is 13.5m 2 / g~15.5m 2 / g;

[0019] (7) The powder resistivity of lithium manganese iron phosphate material is less than 15Ω.cm;

[0020] (8) The manganese dissolution rate of the lithium manganese iron phosphate material is less than or equal to 0.05% of the manganese content in the lithium manganese iron phosphate material;

[0021] (9) The specific capacity of lithium manganese iron phosphate material is 160mAh / g~169mAh / g.

[0022] In a second aspect, a method for preparing a lithium manganese iron phosphate material is provided, comprising the following steps:

[0023] Mixing a mixed solution I with a phosphoric acid solution to obtain a mixed solution II; wherein the mixed solution I comprises a first manganese salt, a first iron salt, and a first lithium salt, and the first manganese salt, the first iron salt, and the first lithium salt are all soluble salts;

[0024] The mixed solution II is spray-dried, calcined and pulverized in sequence to obtain the lithium manganese iron phosphate material;

[0025] The lithium manganese iron phosphate material includes a core, and the core includes a general formula of Li x Mg y Mn z Fe a Al b The core material of PO4, wherein x is 1.002 to 1.05, y is 0 to 0.009, z is 0.4 to 0.6, a is 0.388 to 0.6, and b is 0 to 0.012.

[0026] Optionally, the mixed solution I further includes a first magnesium salt and a first aluminum salt, and the first magnesium salt and the first aluminum salt are both soluble salts.

[0027] Optionally, in the mixed solution II, the molar ratio of manganese element, iron element, lithium element and phosphorus element is (0.4-0.6):(0.4-0.6):(1.02-1.05):1.

[0028] Optionally, in the mixed solution II, the molar ratio of aluminum element, magnesium element and manganese element is (0.01-0.02):(0.005-0.01):1.

[0029] Optionally, the lithium manganese iron phosphate material further includes a coating layer coated on the surface of the core, and the material of the coating layer includes a carbon material; in the step of mixing the mixed solution I and the phosphoric acid solution to obtain the mixed solution II, the preparation method further includes:

[0030] The soluble organic carbon source is mixed with the mixed solution I and the phosphoric acid solution.

[0031] Optionally, the soluble organic carbon source includes a first carbon source and a second carbon source;

[0032] and / or, the first carbon source comprises m-phenylenediamine and / or p-hydroxyaniline;

[0033] and / or, the second carbon source comprises at least one of glucose, sucrose, polyethylene glycol and starch;

[0034] And / or, the mass ratio of the first carbon source to the second carbon source is (5-10):(90-95).

[0035] Optionally, the carbon content in the lithium manganese iron phosphate material is 1.5 wt% to 2.5 wt%.

[0036] Optionally, a method for preparing the mixed solution I comprises: reacting a mixture containing iron powder, manganese powder and lithium carbonate with an acetic acid solution, and obtaining the mixed solution I after solid-liquid separation;

[0037] And / or, the mixed material further includes magnesium powder and aluminum powder.

[0038] Optionally, the inlet air temperature of the spray drying is 250-350°C;

[0039] And / or, after spray drying, a spray material is obtained, the particle size of the spray material is 3 to 8 μm, and the water content in the spray material is less than 0.8 wt %.

[0040] Optionally, the calcination includes: heating to 650-690° C. under an inert atmosphere, maintaining the temperature for 9-13 hours, and cooling.

[0041] Optionally, the pulverizing includes: pulverizing the calcined material obtained after calcination to a particle size of 1.5 to 3 μm.

[0042] In a third aspect, a positive electrode plate is provided, comprising: a current collector and a positive electrode material arranged on at least one side of the current collector along its thickness direction; the positive electrode material comprises the lithium manganese iron phosphate material as described in the first aspect.

[0043] In a fourth aspect, a secondary battery is provided, comprising: a positive electrode sheet, a separator, and a negative electrode sheet stacked together; the positive electrode sheet is the positive electrode sheet as described in the third aspect.

[0044] In a fifth aspect, an electrical device is provided, comprising: a plurality of batteries connected in series and / or in parallel, at least one battery being a secondary battery as described in the fourth aspect.

[0045] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0047] FIG1 is a manganese (Mn) element distribution diagram of the lithium manganese iron phosphate material provided in an embodiment of the present application analyzed by EDS;

[0048] FIG2 is a distribution diagram of the iron (Fe) element of the lithium iron manganese phosphate material provided in an embodiment of the present application analyzed by EDS;

[0049] FIG3 is an SEM image of the lithium manganese iron phosphate material of Example 12 of the present application.

[0050] FIG4 is a TEM image of the lithium manganese iron phosphate material of Example 12 of the present application.

[0051] FIG5 is a 0.1C charge-discharge curve of the lithium manganese iron phosphate material of Example 12 of the present application.

[0052] FIG6 is a 1C charge-discharge curve of the lithium manganese iron phosphate material of Example 12 of the present application. DETAILED DESCRIPTION

[0053] The technical scheme of the present application 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 the present application's embodiments, rather than all of the embodiments, and are only used to illustrate the present application, and should not be considered as limiting the scope of the present application. Based on the embodiments in the present application, 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 application. Those who do not specify specific conditions in the embodiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified as manufacturers are conventional products that can be purchased commercially.

[0054] In the first aspect, the embodiment of the present application provides a lithium iron manganese phosphate material, which includes a core, the core including a general formula of Li x Mg y Mn z Fe a Al b The core material of PO4, wherein x is 1.002 to 1.05, y is 0 to 0.009, z is 0.4 to 0.6, a is 0.388 to 0.6, and b is 0 to 0.012.

[0055] Wherein, x can be 1.003, 1.007, 1.008, 1.01, 1.015, 1.02, 1.025, 1.03, 1.035, 1.04, 1.045 or 1.05; y can be 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008 or 0.0 09; z can be 0.4, 0.5 or 0.6 for example; a can be 0.388, 0.4, 0.45, 0.5, 0.55 or 0.6 for example; b can be 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011 or 0.012 for example.

[0056] The lithium manganese iron phosphate material may not be doped with magnesium and aluminum. In this case, the general formula of the lithium manganese iron phosphate is Li x Mn zFe a PO4, x is 1.02 to 1.05, z is 0.4 to 0.6, and a is 0.4 to 0.6. Alternatively, the lithium manganese iron phosphate can be doped with magnesium and aluminum. In this case, magnesium is doped in Li + Aluminum doped in Fe 3+ At this time, the values ​​of x, y, z, a and b can be obtained by calculation. In the case of doping with magnesium and aluminum, ion doping can be formed to further improve the ionic conductivity of the lithium manganese iron phosphate. At the same time, magnesium doping can significantly reduce manganese dissolution and improve cycle performance. Aluminum doping can further improve the compaction density and rate performance of lithium manganese iron phosphate.

[0057] When the lithium manganese iron phosphate material is not doped with magnesium and aluminum, the above x may be 1.02, 1.03, 1.04 or 1.05, z may be 0.4, 0.5 or 0.6, and a may be 0.4, 0.5 or 0.6.

[0058] Among them, through EDS testing, it was found that the manganese and iron in the lithium manganese iron phosphate material provided in the embodiment of the present application are distributed relatively evenly, and manganese and iron segregation almost does not occur. The specific test results are shown in Figures 1 and 2.

[0059] In response to the problems of low crystallinity of lithium iron manganese phosphate materials and the occurrence of manganese segregation phase in lithium iron manganese phosphate materials in related technologies, in the lithium iron manganese phosphate material provided in the embodiments of the present application, the crystallinity of the lithium iron manganese phosphate material can reach more than 97%, and the manganese segregation phase of the lithium iron manganese phosphate material is less, which can reduce manganese segregation, thereby improving the capacity and conductivity of the lithium iron manganese phosphate material.

[0060] In some optional embodiments, y:b:z is (0.01-0.02):(0.005-0.01):1; further, (0.012-0.018):(0.007-0.009):1.

[0061] Wherein, y:b:z is (0.01~0.02):(0.005~0.01):1, which means that y:b:z can be 0.01:0.005:1, or y:b:z can be 0.02:0.005:1, or y:b:z can be 0.015:0.005:1, or y:b:z can be 0.012:0.005:1, or y:b:z can be 0.01:0.01:1, or y:b:z can be 0.01:0.006:1, or y:b:z can be 0.01:0.007:1, or y:b:z can be 0.01:0.008:1, or y:b:z can be 0.01:0.009:1, or y:b:z can be 0.012:0.006:1 , or, y:b:z can be 0.012:0.007:1, or, y:b:z can be 0.012:0.008:1, or, y:b:z can be 0.012:0.009:1, or, y:b:z can be 0.018:0.006:1, or, y:b:z can be 0.018:0.007:1, or, y:b:z can be 0.018:0.008:1, or, y:b:z can be 0.018:0.009:1, or, y:b:z can be 0.015:0.006:1, or, y:b:z can be 0.015:0.007:1, or, y:b:z can be 0.015:0.008:1, or, y:b:z can be 0.015:0.009:1.

[0062] In these embodiments, if the magnesium and aluminum are doped too much, the capacity of the lithium manganese iron phosphate material will be low and the cycle performance will be reduced.

[0063] In some embodiments, the surface of the lithium manganese iron phosphate material is further coated with a carbon material; wherein the mass fraction of the carbon material is 1.5 wt% to 2.5 wt%, and / or the coverage of the carbon material is 98.0% to 99.9%.

[0064] Wherein, the mass fraction of the carbon material is 1.5% to 2.5%, which means that the mass fraction of the carbon material can be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4% or 2.5%. The coverage rate of the carbon material is 98.0% to 99.9%, which means that the coverage rate of the carbon material can be 98.0%, 98.1%, 98.2%, 98.3%, 98.4%, 98.5%, 98.6%, 98.7%, 98.8%, 98.9%, 99.0%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8% or 99.9%.

[0065] In these embodiments, the carbon material covers the surface of the lithium manganese iron phosphate material more completely, which can further improve the conductivity of the lithium manganese iron phosphate material and reduce the manganese dissolution rate.

[0066] In some embodiments, the lithium manganese iron phosphate material satisfies at least one of the following conditions:

[0067] (1) The sphericity of lithium manganese iron phosphate material is 0.7 to 1.0;

[0068] (2) The average primary particle size of the lithium manganese iron phosphate material is 170nm to 220nm;

[0069] (3) The secondary particle size of the lithium manganese iron phosphate material meets the following requirements: D10 is 0.2 μm to 0.6 μm, D50 is 1.5 μm to 3 μm, and D90 is 5 μm to 15 μm;

[0070] (4) The compacted density of lithium manganese iron phosphate material is 2.35 g / mL to 2.45 g / mL;

[0071] (5) The tap density of lithium manganese iron phosphate material is 1.1g / mL to 1.2g / mL;

[0072] (6) The specific surface area of ​​lithium manganese iron phosphate material is 13.5m 2 / g~15.5m 2 / g;

[0073] (7) The powder resistivity of lithium manganese iron phosphate material is less than 15Ω.cm;

[0074] (8) The manganese dissolution rate of the lithium manganese iron phosphate material is less than or equal to 0.05% of the manganese content in the lithium manganese iron phosphate material;

[0075] (9) The specific capacity of lithium manganese iron phosphate material is 160mAh / g~169mAh / g.

[0076] The sphericity of the lithium manganese iron phosphate material is 0.7 to 1.0, which means that the sphericity of the lithium manganese iron phosphate material can be 0.7, 0.8, 0.9, 1.0, or any value between 0.7 and 1.0.

[0077] The average primary particle size of the lithium manganese iron phosphate material is 170nm~220nm, which means that the average primary particle size of the lithium manganese iron phosphate material can be 170nm, 175nm, 780nm, 185nm, 190nm, 195nm, 200nm, 205nm, 210nm, 215nm, 220nm or any value between 170nm and 220nm.

[0078] The secondary particle size of the lithium iron manganese phosphate material satisfies the following requirements: D10 particle size is 0.2 μm to 0.6 μm, D50 particle size is 1.5 μm to 3 μm, and D90 particle size is 5 μm to 15 μm, which means that the D10 particle size can be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or 0.6 μm, etc., the D50 particle size can be 1.5 μm, 2.0 μm, 2.5 μm, or 3 μm, etc., and the D90 particle size can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, etc. The D10 particle size, D50 particle size, and D90 particle size can be measured by a laser particle size analyzer.

[0079] The compacted density of the lithium manganese iron phosphate material is 2.35 g / mL to 2.45 g / mL, which means that the compacted density of the lithium manganese iron phosphate material can be 2.35 g / mL, 2.36 g / mL, 2.37 g / mL, 2.38 g / mL, 2.39 g / mL, 2.40 g / mL, 2.41 g / mL, 2.42 g / mL, 2.43 g / mL, 2.44 g / mL, 2.45 g / mL, etc.

[0080] The tap density of the lithium manganese iron phosphate material is 1.1 g / mL to 1.2 g / mL, which means that the tap density of the lithium manganese iron phosphate material is 1.1 g / mL, 1.11 g / mL, 1.12 g / mL, 1.13 g / mL, 1.14 g / mL, 1.15 g / mL, 1.16 g / mL, 1.17 g / mL, 1.18 g / mL, 1.19 g / mL, 1.2 g / mL, etc.

[0081] The specific surface area of ​​the lithium manganese iron phosphate material is 13.5m 2 / g~15.5m 2 / g, which means that the specific surface area of ​​the lithium manganese iron phosphate material can be 13.5m 2 / g, 13.6m 2 / g, 13.7m 2 / g, 13.8m 2 / g, 13.9m 2 / g, 14.0m 2 / g, 14.1m 2 / g, 14.2m 2 / g, 14.3m 2 / g, 14.4m 2 / g, 14.5m 2 / g, 14.6m 2 / g, 14.7m 2 / g, 14.8m 2 / g, 14.9m 2 / g, 15.0m2 / g, 15.1m 2 / g, 15.2m 2 / g, 15.3m 2 / g, 15.4m 2 / g, 15.5m 2 / g, etc.

[0082] The powder resistivity of the lithium iron manganese phosphate material is less than 15Ω.cm, which means that the powder resistivity of the lithium iron manganese phosphate material can be 14Ω.cm, 14.1Ω.cm, 14.2Ω.cm, 14.3Ω.cm, 14.4Ω.cm, 14.5Ω.cm, 14.6Ω.cm, 14.7Ω.cm, 14.8Ω.cm, 14.9Ω.cm, 13Ω.cm, 13.1Ω.cm, 13.2Ω.cm, 13.3Ω.cm, 13.4Ω.cm, 13.5Ω.cm, 13.6Ω.cm, 13.7Ω.cm, 13.8Ω.cm, 13.9Ω.cm or 12Ω.cm, etc.

[0083] The manganese dissolution rate of the lithium iron manganese phosphate material is less than or equal to 0.05% of the manganese content in the lithium iron manganese phosphate material, which means that the manganese dissolution rate of the lithium iron manganese phosphate material accounts for 0.05%, 0.04%, 0.03%, 0.02% or 0.01% of the manganese content in the lithium iron manganese phosphate material.

[0084] The specific capacity of the lithium iron manganese phosphate material is 160mAh / g to 169mAh / g, which means that the specific capacity of the lithium iron manganese phosphate material can be 160mAh / g, 161mAh / g, 162mAh / g, 163mAh / g, 164mAh / g, 165mAh / g, 166mAh / g, 167mAh / g, 168mAh / g or 169mAh / g, etc.

[0085] In these embodiments, the particles of the lithium manganese iron phosphate material have high sphericity, small particle size, small specific surface area, high compaction density and tap density, low powder resistivity, high density when made into positive electrode sheets, and excellent performance in electrical properties such as specific capacity.

[0086] In a second aspect, some embodiments of the present application provide a method for preparing a lithium manganese iron phosphate material, comprising the following steps:

[0087] Step 10. Mixing the mixed solution I with the phosphoric acid solution to obtain a mixed solution II, wherein the mixed solution I includes a first manganese salt, a first iron salt, and a first lithium salt, and the first manganese salt, the first iron salt, and the first lithium salt are all soluble salts;

[0088] Step 20. The mixed solution II is spray-dried, calcined and crushed in sequence to obtain a lithium manganese iron phosphate material; the lithium manganese iron phosphate material includes a core, and the core includes a general formula of Li x Mg y Mn z Fe a Al b The core material of PO4, wherein x is 1.008 to 1.05, y is 0 to 0.006, z is 0.4 to 0.6, a is 0.388 to 0.6, and b is 0 to 0.012.

[0089] Wherein, x can be 1.003, 1.007, 1.008, 1.01, 1.015, 1.02, 1.025, 1.03, 1.035, 1.04, 1.045 or 1.05; y can be 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008 or 0.0 09; z can be 0.4, 0.5 or 0.6 for example; a can be 0.388, 0.4, 0.45, 0.5, 0.55 or 0.6 for example; b can be 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011 or 0.012 for example.

[0090] In an embodiment of the present application, to improve the poor electrical performance of lithium manganese iron phosphate obtained by the preparation method of lithium manganese iron phosphate, the present application provides a wet process for preparing lithium manganese iron phosphate. Specifically, a mixed solution I containing a first manganese salt, a first iron salt, and a first lithium salt is uniformly mixed with a phosphoric acid solution to obtain a mixed solution II; the mixed solution II is then spray-dried, calcined, and pulverized to obtain the lithium manganese iron phosphate material.

[0091] In the conventional solid-phase method, the mixing size is limited by the particle size, and the mixing scale is large, making it difficult to ensure uniform mixing of manganese iron, resulting in segregation. In places where manganese is enriched, the capacity is low, resulting in relatively poor capacity of the entire product, poor cycle performance, and obvious manganese dissolution. Compared with the conventional solid-phase method, the preparation method of the lithium manganese iron phosphate material provided in the embodiment of the present application is mixed and dispersed in the aqueous solution in an ionic state. The mixing size is very small, reaching the ionic scale, ensuring uniform mixing of manganese iron, reducing manganese segregation, and reducing manganese dissolution, thereby improving the cycle performance and capacity of the product.

[0092] In addition, the present application reduces the calcination temperature of the subsequent calcination process because the raw materials are mixed at the ion level before spray drying. At a lower calcination temperature, the ion migration distance is very short, the reaction fusion is very fast, and a higher compaction density can be obtained. Moreover, because it is not calcined at a high temperature, the generation of large particles is avoided, and the capacity will also be higher. Compared with the solid-phase method prepared lithium manganese iron phosphate materials in the related art, there is the problem of segregation of manganese iron materials, and the co-precipitation of manganese iron has a long process flow and the co-precipitation effect is difficult to ensure. Compared with the hydrothermal method in the related art, which is difficult to achieve carbon coating and large-scale production application, it is convenient for carbon coating to be carried out simultaneously and can achieve large-scale production application.

[0093] In some embodiments, the first manganese salt includes at least one of manganese acetate, manganese chloride, and manganese nitrate; and / or the first iron salt includes at least one of ferrous acetate and ferrous chloride; and / or the first lithium salt includes at least one of lithium acetate and lithium carbonate.

[0094] In these embodiments, during the spray drying process, due to the volatility of acetic acid, hydrochloric acid, and nitric acid, the acetate, chloride, and nitrate in the mixed solution II will be preferentially volatilized with the hydrogen ions (i.e., acetic acid, hydrochloric acid, and nitric acid). That is, when prepared using a high-boiling-point acid, it will be evaporated and volatilized together with water at a high temperature. The anions in the mixed solution II are volatilized due to their low boiling point, and the remaining materials form a spray precursor; and then calcined to obtain a high-performance lithium manganese iron phosphate material.

[0095] In some embodiments, the mixed solution I further includes a first magnesium salt and a first aluminum salt, and the first magnesium salt and the first aluminum salt are both soluble salts.

[0096] In these embodiments, the first magnesium salt and the first aluminum salt in the mixed solution I serve as dopants, introducing aluminum and magnesium to form ion doping, thereby further improving ionic conductivity. At the same time, magnesium doping can significantly reduce manganese dissolution and improve cycle performance. Furthermore, aluminum doping can further improve the compaction density and rate performance of the lithium manganese iron phosphate material.

[0097] In some embodiments, the first magnesium salt comprises at least one of magnesium acetate, magnesium chloride, and magnesium nitrate; and / or the first aluminum salt comprises at least one of aluminum acetate, aluminum chloride, and aluminum nitrate.

[0098] In these embodiments, during the spray drying process, due to the volatility of acetic acid, hydrochloric acid, and nitric acid, the acetate, chloride, and nitrate in the mixed solution II will be preferentially volatilized with the hydrogen ions (i.e., acetic acid, hydrochloric acid, and nitric acid). That is, when prepared using a high-boiling-point acid, it will be evaporated and volatilized together with water at a high temperature. The anions in the mixed solution II will be volatilized due to the low boiling point, and the remaining material will form a spray precursor; and then calcined to obtain high-performance magnesium-aluminum-doped lithium manganese iron phosphate.

[0099] In some embodiments, the lithium manganese iron phosphate material further includes a coating layer coated on the surface of the core, and the material of the coating layer includes a carbon material; in the step of mixing the mixed solution I and the phosphoric acid solution to obtain the mixed solution II, the preparation method further includes:

[0100] The soluble organic carbon source is mixed with the mixed solution I and the phosphoric acid solution.

[0101] In some embodiments, the soluble organic carbon source comprises a first carbon source and a second carbon source; the first carbon source comprises m-phenylenediamine and / or p-hydroxyaniline; and the second carbon source comprises at least one of glucose, sucrose, polyethylene glycol, and starch.

[0102] In some embodiments, the mass ratio of the first carbon source to the second carbon source is (5-10):(90-95); typically but not limiting, for example, the mass ratio of the first carbon source to the second carbon source can be 5:95, 6:94, 7:93, 8:92, 9:91, 10:90 or a range consisting of any two thereof.

[0103] The first carbon source contains both benzene rings and amine groups (i.e., nitrogen). The carbon source generated by the benzene rings has a high degree of graphitization, resulting in good conductivity and low powder resistivity. The presence of the amine groups also introduces nitrogen doping, further improving the conductivity of the carbon. The second carbon source provides the carbon source for coating.

[0104] If the content of the first carbon source in the present application is too high, the carbon content will be too high, the specific surface area of ​​the product will be too large, and the processing performance of the final product will be poor.

[0105] In some embodiments, in the mixed solution II, the molar ratio of manganese element, iron element, lithium element and phosphorus element is (0.4-0.6): (0.4-0.6): (1.02-1.05):1. For example, the molar ratio of manganese element, iron element, lithium element and phosphorus element may be 0.4:0.4:1.02:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element may be 0.6:0.4:1.02:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element may be 0.5:0.4:1.02:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element may be 0.4:0.6:1.02:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element may be 0.4:0.5:1.02:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element may be 0.4:0.4:1.05:1, Alternatively, the molar ratio of manganese element, iron element, lithium element and phosphorus element can be 0.4:0.4:1.03:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element can be 0.4:0.4:1.04:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element can be 0.6:0.4:1.05:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element can be 0.5:0.4:1.04:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element can be 0.5:0.6:1.05:1, or the molar ratio of manganese element, iron element, lithium element and phosphorus element can be 0.5:0.5:1.04:1.

[0106] In some embodiments, in the mixed solution II, the molar ratio of aluminum element, magnesium element and manganese element is (0.01-0.02):(0.005-0.01):1; optionally, it is (0.012-0.018):(0.007-0.09):1. For example, the molar ratio of the aluminum element, the magnesium element, and the manganese element may be 0.01:0.005:1, or the molar ratio of the aluminum element, the magnesium element, and the manganese element may be 0.02:0.005:1, or the molar ratio of the aluminum element, the magnesium element, and the manganese element may be 0.015:0.005:1, or the molar ratio of the aluminum element, the magnesium element, and the manganese element may be 0.01:0.01:1, or the molar ratio of the aluminum element, the magnesium element, and the manganese element may be 0.01:0.006:1, or the molar ratio of the aluminum element, the magnesium element, and the manganese element may be 0.01:0.007:1, or the molar ratio of the aluminum element, the magnesium element, and the manganese element may be 0.01:0.008:1, or the molar ratio of the aluminum element, the magnesium element, and the manganese element may be 0.01:0.009:1, or the molar ratio of the aluminum element, the magnesium element, and the manganese element may be 0. The molar ratio of the aluminum element, the magnesium element and the manganese element may be 0.02:0.006:1, or the molar ratio of the aluminum element, the magnesium element and the manganese element may be 0.02:0.007:1, or the molar ratio of the aluminum element, the magnesium element and the manganese element may be 0.02:0.008:1, or the molar ratio of the aluminum element, the magnesium element and the manganese element may be 0.02:0.009:1, or the molar ratio of the aluminum element, the magnesium element and the manganese element may be 0.015:0.01:1, or the molar ratio of the aluminum element, the magnesium element and the manganese element may be 0.015:0.006:1, or the molar ratio of the aluminum element, the magnesium element and the manganese element may be 0.015:0.007:1, or the molar ratio of the aluminum element, the magnesium element and the manganese element may be 0.015:0.008:1, or the molar ratio of the aluminum element, the magnesium element and the manganese element may be 0.015:0.009:1.

[0107] Excessive doping of magnesium and aluminum in this application will result in a low capacity of the lithium manganese iron phosphate material and a reduction in cycle performance.

[0108] In some embodiments, the carbon content in the lithium manganese iron phosphate material is 1.5wt% to 2.5wt%, that is, the mass fraction of the carbon element is 1.5% to 2.5%; typically but not limitatively, for example, the carbon content in the lithium manganese iron phosphate material can be 1.5wt%, 1.7wt%, 1.9wt%, 2wt%, 2.2wt%, 2.4wt%, 2.5wt% or a range consisting of any two of them.

[0109] In some embodiments, the above step 10 further comprises the following steps for preparing the mixed solution I:

[0110] A mixture containing iron powder, manganese powder and lithium carbonate is reacted with an acetic acid solution, and a mixed solution I is obtained after solid-liquid separation.

[0111] In some embodiments, in the preparation method of the mixed solution I, the molar ratio of iron powder, manganese powder, lithium carbonate and acetic acid in the acetic acid solution is (0.4-0.6): (0.4-0.6): (0.501-0.51): (3.3-3.5). For example, the molar ratio of acetic acid in the iron powder, manganese powder, lithium carbonate and acetic acid solution is 0.4:0.4:0.501:3.3, or the molar ratio of acetic acid in the iron powder, manganese powder, lithium carbonate and acetic acid solution is 0.4:0.6:0.501:3.3, or the molar ratio of acetic acid in the iron powder, manganese powder, lithium carbonate and acetic acid solution is 0.4:0.5:0.51:3.3, or the molar ratio of acetic acid in the iron powder, manganese powder, lithium carbonate and acetic acid solution is 0.4:0.5:0.505:3.5, or the molar ratio of acetic acid in the iron powder, manganese powder, lithium carbonate and acetic acid solution is 0.4:0.6:0.51:3.4.

[0112] In some embodiments, in the method for preparing the mixed solution I, the concentration of the acetic acid solution is 3 to 5 mol / L. For example, the concentration of the acetic acid solution can be 3 mol / L, 4 mol / L, or 5 mol / L.

[0113] In some embodiments, in the method for preparing the mixed solution I, the temperature for reacting the mixed material with the acetic acid solution is 30-50° C. For example, the temperature for reacting the mixed material with the acetic acid solution can be 30° C., 32° C., 35° C., 37° C., 38° C., 40° C., 41° C., 43° C., 44° C., 46° C., 48° C., 49° C., or 50° C.

[0114] In some embodiments, in the preparation method of mixed liquid I, the mixed material also includes magnesium powder and aluminum powder; optionally, the molar ratio of magnesium powder, aluminum powder and manganese powder is (0.01~0.02): (0.005~0.01): 1; further optionally, it is (0.012~0.018): (0.007~0.09): 1. For example, the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.01:0.005:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.01:0.01:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.02:0.005:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.02:0.01:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.01:0.008:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.012:0.007:1, or magnesium powder The molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.012:0.008:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.015:0.005:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.015:0.008:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.018:0.005:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.018:0.007:1, or the molar ratio of magnesium powder, aluminum powder and manganese powder can be 0.018:0.009:1.

[0115] In some embodiments, the concentration of the phosphoric acid solution is 5 to 8 mol / L. For example, the concentration of the phosphoric acid solution can be 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, or any value between 5 and 8 mol / L.

[0116] In some embodiments, the temperature for mixing the mixed solution I and the phosphoric acid solution is room temperature.

[0117] In some embodiments, the spray material obtained after spray drying has a particle size of 3 to 8 μm and a moisture content of less than 0.8 wt %. For example, the particle size of the spray material is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or any value between 3 and 8 μm.

[0118] In some embodiments, spray drying comprises using a pressure spray dryer; the inlet air temperature of the spray drying is 250-350° C., typically but not limited to, for example, 250° C., 270° C., 290° C., 310° C., 330° C., 350° C., or a range consisting of any two thereof.

[0119] During the spray drying process, due to the volatility of acetic acid, the acetate radical in the mixed solution II will be volatilized preferentially with the hydrogen ions (i.e., acetic acid). The embodiment of the present application can completely volatilize the acetic acid and water by adjusting the temperature value of the spray drying, and will not cause excessive evaporation of the remaining material. Among them, liquid II enters the spray dryer for spray drying to obtain a spray material and exhaust gas, which are separated by a cyclone dust collector and a dust collecting bag. The dust collecting bag adopts a high-temperature resistant 800-1200 mesh dust collection bag. The exhaust gas is cooled by a cooling coil. There is pure water in the cooling coil. The heated pure water is returned to prepare the phosphoric acid solution. The condensed water is a dilute acetic acid solution. The obtained dilute acetic acid is added to glacial acetic acid to adjust the concentration and then returned for dissolution and use.

[0120] In addition, most of the water and acetic acid in the mixed liquid II are condensed and recovered, and then returned to dissolve the mixed material, thereby forming a closed loop and realizing the circulation method for preparing lithium manganese iron phosphate material; this saves costs and basically no waste is generated during the preparation process.

[0121] In some embodiments, calcination comprises: heating to 650-690° C. for 9-13 hours under an inert atmosphere, followed by cooling; typically, but not limited to, the calcination temperature is 650° C., 660° C., 670° C., 680° C., 690° C., or any two thereof; and the holding time is 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, or any two thereof. Preferably, the inert atmosphere comprises nitrogen.

[0122] Compared with the calcination temperature of 700°C in the solid-phase method for preparing lithium manganese iron phosphate material in the related art, the calcination temperature of the calcination process in the embodiment of the present application is lower. Since the calcination is carried out at a lower temperature, the ion migration distance is shortened and the reaction fusion is accelerated, the compaction density of the lithium manganese iron phosphate material can be further improved. Moreover, because the calcination is not carried out at a high temperature, the generation of large particles is avoided, which can further improve the capacity of the lithium manganese iron phosphate material.

[0123] In some embodiments, the heating rate during the calcination process is 2-4°C / h. For example, the heating rate during the calcination process is 2°C / h, 3°C / h, 4°C / h, or any value between 2-4°C / h.

[0124] In some embodiments, the material is discharged after cooling to a temperature of ≤100°C. The spray material is first loaded into a graphite sagger by a loader and then placed in a roller hearth furnace for calcination. During the heating stage, an induced draft port is provided, which is connected to an induced draft fan. Nitrogen is introduced into the roller hearth furnace to maintain the oxygen content in the rotary kiln below 5 ppm and the pressure in the rotary kiln is maintained 30 to 60 Pa higher than the external pressure.

[0125] In some embodiments, the pulverizing includes pulverizing the calcined material obtained after calcination to a particle size (D50) of 1.5 to 3 μm.

[0126] In some embodiments, the pulverization includes pulverizing using a fluidized bed jet mill. The fluidized bed jet mill uses nitrogen at 110-140°C and a nitrogen pressure of 6-8 kg. The nitrogen is injected into a pulverizing chamber through a Laval nozzle at a flow rate of Mach 3-5. The calcined material is finally pulverized to a particle size of 1.5-3 μm using a classifying wheel.

[0127] In some embodiments, after crushing, screening and iron removal are also included; preferably, screening uses a 100-200 mesh screen, and iron removal uses an electromagnetic iron remover.

[0128] In a third aspect, a positive electrode plate is provided, comprising: a current collector and a positive electrode material arranged on at least one side of the current collector along its thickness direction; the positive electrode material comprises the lithium manganese iron phosphate material as described in the first aspect.

[0129] In the positive electrode plate provided in the embodiment of the present application, the positive electrode plate contains the above-mentioned lithium iron manganese phosphate material, and thus has the advantages of the lithium iron manganese phosphate material.

[0130] In a fourth aspect, a secondary battery is provided, comprising: a positive electrode sheet, a separator, and a negative electrode sheet stacked together; the positive electrode sheet is the positive electrode sheet as described in the third aspect.

[0131] In the secondary battery provided in the embodiment of the present application, the secondary battery includes the above-mentioned positive electrode sheet, and thus has the advantages of the positive electrode sheet.

[0132] In a fifth aspect, an electrical device is provided, comprising: a plurality of batteries connected in series and / or in parallel, at least one battery being a secondary battery as described in the fourth aspect.

[0133] In the electric device provided in the embodiment of the present application, the electric device includes the aforementioned secondary battery, and thus has the advantages of a secondary battery.

[0134] The embodiments of the present application will be described in detail below in conjunction with Examples and Comparative Examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be construed as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0135] Example 1

[0136] The method for preparing the lithium manganese iron phosphate material provided in this embodiment includes the following steps:

[0137] S1. Mix iron powder, manganese powder, and lithium carbonate to obtain a mixed material, then add acetic acid solution with a concentration of 4.2 mol / L, react at 40°C until the manganese powder, iron powder, and lithium carbonate are completely dissolved, and then filter to obtain a mixed solution I; the molar ratio of the iron powder, manganese powder, lithium carbonate, and acetic acid in the acetic acid solution is 0.5:0.5:0.5035:3.4.

[0138] S2. Add a phosphoric acid solution with a concentration of 7 mol / L and a soluble organic carbon source to the mixed solution I, stir and mix evenly to obtain a mixed solution II; the molar ratio of phosphoric acid to manganese powder in the phosphoric acid solution is 1:0.5, and the soluble organic carbon source is added so that the carbon content in the prepared lithium manganese iron phosphate material is 1.97 wt%, and the soluble organic carbon source is sucrose and glucose with a mass ratio of 8:92.

[0139] S3 and the mixed solution II are spray-dried in a pressure spray dryer to obtain a spray material and exhaust gas having an average particle size (D50) of 4.8 μm and a moisture content of less than 0.8 wt%. During the spray drying process, the inlet air temperature is maintained at 290-310°C. The spray material and exhaust gas are separated by a cyclonic dust collector and a high-temperature resistant 1000-mesh dust bag. The exhaust gas is cooled by a cooling coil containing pure water. The heated pure water is returned to prepare the phosphoric acid solution. The exhaust gas is condensed to obtain dilute acetic acid. Glacial acetic acid is added to the dilute acetic acid to adjust the concentration, and the dilute acetic acid is returned to step S1 to react with the mixed material. The recovery rate of acetic acid in the exhaust gas is 88%, the recovery rate of water is 75%, and the temperature of the pure water is increased from room temperature to above 75°C.

[0140] S4. The spray material is loaded into a graphite sagger through a loader, and then placed in a roller furnace for calcination to obtain a calcined material; nitrogen is introduced during the calcination process, and the temperature is raised to 680°C at a rate of 3°C / h and kept warm for 12 hours, and then the temperature is lowered to below 100°C for discharge; an induced draft port is provided during the heating stage, and the induced draft port is connected to the induced draft fan, and nitrogen is introduced into the roller furnace to maintain the oxygen content in the rotary kiln below 5ppm, and the pressure in the rotary kiln is maintained at 50±2Pa higher than the external pressure.

[0141] S5. The calcined material is pulverized by a fluidized bed air flow mill. The air intake is 130±2°C nitrogen with a nitrogen pressure of 7.2kg. The air is sprayed into the pulverizing chamber through a Laval nozzle. The air flow rate entering the pulverizing chamber is 4.2 Mach. The calcined material is then classified by a classifying wheel. Finally, the calcined material is pulverized to an average particle size (D50) of 1.9μm. After the calcined material is pulverized, it is screened with a 120-mesh sieve in turn, and iron is removed by an electromagnetic iron remover to obtain lithium manganese iron phosphate material.

[0142] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 1.

[0143] Table 1

[0144] Example 2

[0145] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 1, except that, in step S1, the iron powder, manganese powder, and lithium carbonate are mixed to obtain a mixed material; and the molar ratio of the iron powder, manganese powder, lithium carbonate, and acetic acid in the acetic acid solution is 0.4:0.6:0.501:3.3.

[0146] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 2.

[0147] Table 2

[0148] Example 3

[0149] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 1, except that, in step S1, the iron powder, manganese powder, and lithium carbonate are mixed to obtain a mixed material; and the molar ratio of the iron powder, manganese powder, lithium carbonate, and acetic acid in the acetic acid solution is 0.6:0.4:0.51:3.5.

[0150] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 3.

[0151] Table 3

[0152] Example 4

[0153] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 1, except that, in step S1, the iron powder, manganese powder, lithium carbonate, magnesium powder and aluminum powder are mixed to obtain a mixed material; the molar ratio of the iron powder, manganese powder, lithium carbonate and acetic acid in the acetic acid solution is 0.5:0.5:0.5035:3.4, and the molar ratio of the magnesium powder, aluminum powder and manganese powder is 0.015:0.008:1.

[0154] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 4.

[0155] Table 4

[0156] Example 5

[0157] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 4, except that the molar ratio of magnesium powder, aluminum powder and manganese powder is 0.012:0.009:1.

[0158] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 5.

[0159] Table 5

[0160] Example 6

[0161] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 4, except that the molar ratio of magnesium powder, aluminum powder and manganese powder is 0.018:0.007:1.

[0162] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 6.

[0163] Table 6

[0164] Example 7

[0165] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 4, except that the molar ratio of magnesium powder, aluminum powder and manganese powder is 0.01:0.005:1.

[0166] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 7.

[0167] Table 7

[0168] Example 8

[0169] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 4, except that the molar ratio of magnesium powder, aluminum powder and manganese powder is 0.02:0.01:1.

[0170] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 8.

[0171] Table 8

[0172] Example 9

[0173] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 4, except that the molar ratio of magnesium powder, aluminum powder and manganese powder is 0.025:0.01:1.

[0174] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 9.

[0175] Table 9

[0176] Example 10

[0177] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 4, except that the molar ratio of magnesium powder, aluminum powder and manganese powder is 0.02:0.012:1.

[0178] Example 11

[0179] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 4, except that the molar ratio of magnesium powder, aluminum powder and manganese powder is 0.05:0.015:1.

[0180] Example 12

[0181] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 4, except that in step S2, sucrose is replaced by m-phenylenediamine.

[0182] The properties of the lithium manganese iron phosphate product prepared in this example are shown in Table 10.

[0183] Table 10

[0184] Example 13

[0185] The preparation method of the lithium iron manganese phosphate material provided in this embodiment refers to Example 12, except that in step S1, the molar ratio of magnesium powder, aluminum powder and manganese powder is 0.03:0.008:1.

[0186] Example 14

[0187] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 12, except that, in step S2, the mass ratio of m-phenylenediamine to glucose is 15:85.

[0188] Example 15

[0189] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 12, except that, in step S4, the temperature is raised to 650° C. at a rate of 4° C. / h and kept at this temperature for 13 hours.

[0190] Example 16

[0191] The preparation method of lithium manganese iron phosphate provided in this embodiment refers to Example 12, except that, in step S4, the temperature is raised to 690° C. at a rate of 2° C. / h and kept at this temperature for 9 hours.

[0192] Example 17

[0193] The preparation method of the lithium manganese iron phosphate material provided in this embodiment refers to Example 12, except that, in step S4, the temperature is raised to 700° C. at a rate of 3° C. / h and kept at this temperature for 13 hours.

[0194] Comparative Example 1

[0195] The preparation method of the lithium manganese iron phosphate material provided in this comparative example comprises the following steps:

[0196] Red iron oxide, manganese tetraoxide, lithium dihydrogen phosphate, and glucose are added to pure water to form a slurry with a solid content of 32wt%. The molar ratio of red iron oxide, manganese tetraoxide, lithium dihydrogen phosphate, and glucose is 1:0.667:4.06:0.07. The slurry is ground with a sand mill to a particle size of 335nm, and then spray-dried, calcined, crushed, sieved, and iron-removed in sequence to obtain a lithium manganese iron phosphate material; wherein, the processes of spray drying, calcining, crushing, sieving, and iron-removal refer to Example 12.

[0197] The properties of the lithium manganese iron phosphate product prepared in this comparative example are shown in Table 11.

[0198] Table 11

[0199] Comparative Example 2

[0200] The preparation method of the lithium manganese iron phosphate material provided in this comparative example comprises the following steps:

[0201] Ferrous sulfate, manganese sulfate, lithium hydroxide and ammonium monohydrogen phosphate are added to pure water, then added to a hydrothermal reactor, and then stirred and dispersed to a solid content of 25wt%. The temperature is then raised to 190°C and a pressure of 11.5MPa under stirring. The reaction is carried out under these conditions for 16 hours. The material is then taken out, filtered and washed. The obtained material is slurried in pure water, glucose is added, and then sand-milled to a particle size of 330nm. The material is then spray-dried, calcined, crushed, sieved and iron-removed to obtain lithium manganese iron phosphate material.

[0202] The molar ratio of ferrous sulfate, manganese sulfate, lithium hydroxide, ammonium monohydrogen phosphate and glucose is 1:1:2.03:1.01:0.035; the processes of spray drying, calcination, crushing, screening and iron removal are referred to Comparative Example 1.

[0203] The properties of the lithium manganese iron phosphate product prepared in this comparative example are shown in Table 12.

[0204] Table 12

[0205] Test Case

[0206] 1. The properties of the lithium iron manganese phosphate products in Examples 1 to 12 and Comparative Examples 1 to 2 were tested as follows: Fe content was determined by potentiometric titration, phosphorus content was determined by quinoline phosphomolybdate weighing, lithium, sodium, potassium, calcium, magnesium, nickel, and aluminum content was determined by inductively coupled plasma atomic emission spectrometry, and free lithium content was determined by automatic potentiometric titration. The moisture content in the lithium iron manganese phosphate material was determined by the KF method; magnetic foreign matter in the lithium iron manganese phosphate material can be collected by a magnet, dissolved in aqua regia, and tested on an atomic absorption spectrometer; the pH value of the lithium iron manganese phosphate material was determined by acid-base potentiometric titration and a pH meter. Specific test results can be found in Tables 1 to 12 above. No additional magnesium and aluminum were added in Examples 1 to 3, so the magnesium and aluminum contents obtained in the final test were both trace amounts, i.e., at the ppm level.

[0207] 2. The sphericity of the lithium iron manganese phosphate material directly affects its flowability and stacking properties. The lithium iron manganese phosphate product prepared in Example 12 was subjected to scanning electron microscopy testing, and the results are shown in Figure 3. As can be seen from Figure 3, the particles of the lithium iron manganese phosphate material prepared in this application have high sphericity, with an average primary particle size of 186 nm.

[0208] In addition, the sphericity of the lithium manganese iron phosphate material can be measured by combining microscopic measurement methods and image processing technology. The particle image is processed and analyzed by image analysis software to obtain the particle size and shape information of each particle. The particle size and shape information of each particle are then statistically analyzed to obtain the particle size (D50) and particle size distribution, average major diameter and aspect ratio distribution, average circularity and circularity distribution, etc. Here, the average circularity is used to represent the sphericity of the lithium manganese iron phosphate material. It can be obtained that the sphericity of the lithium manganese iron phosphate material provided in the embodiment of the present application is above 86%, and the average primary particle size is in the range of 170nm to 220nm. The specific test results are shown in Table 13 below.

[0209] Table 13

[0210] 3. The lithium manganese iron phosphate product prepared in Example 12 was tested by transmission electron microscopy, and the results are shown in Figure 4. As can be seen from Figure 4, the surface of the lithium manganese iron phosphate is coated with a carbon layer, and the coating is very complete and uniform.

[0211] The thickness of the coating layer is measured using a transmission electron microscope. The coating rate of the coating layer is defined as the percentage of the coverage area of ​​the coating layer on the surface of the particle (i.e., the lithium manganese iron phosphate of Examples 1 to 17 above) to the total surface area of ​​the particle. The coating amount of the coating layer is measured using diffuse reflectance infrared Fourier transform spectroscopy. The coating rate can be calculated based on the coating amount and the cross-sectional area (also called the cross-sectional area) of the coating layer. The calculation formula is: Where n represents the coating ratio, M represents the coating amount, q represents the molecular weight of the coating layer material, NA is a constant (6.023×1023), a0 represents the cross-sectional area of ​​the coating layer, and Sw represents the specific surface area of ​​the particle.

[0212] According to the above measurements and calculations, the content of the carbon material on the surface of the lithium manganese iron phosphate provided in this application is 1.5wt% to 2.5wt%, and the coverage rate is above 98.0%. The specific test results are shown in Table 14 below.

[0213] Table 14

[0214] 4. The particle size distribution and specific surface area of ​​the lithium manganese iron phosphate products provided in Examples 1-2, Examples 4-5, Examples 12 and 17, and Comparative Examples 1-2 were tested, and the results are shown in Table 15.

[0215] Table 15

[0216] In Table 15, the specific surface area of ​​the lithium manganese iron phosphate material is obtained by using a BET specific surface area determination method, such as a nitrogen adsorption multi-point BET method; the D50 particle size, D90 particle size and D10 particle size in the particle size distribution of the lithium manganese iron phosphate material can be obtained by using a laser particle size analyzer, which can be a Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd., UK; wherein the D50 particle size indicates the particle size corresponding to when the cumulative volume distribution percentage of the lithium manganese iron phosphate material reaches 50%, the D10 particle size indicates the particle size corresponding to when the cumulative volume distribution percentage of the lithium manganese iron phosphate material reaches 10%, and the D90 particle size indicates the particle size corresponding to when the cumulative volume distribution percentage of the lithium manganese iron phosphate material reaches 90%.

[0217] As shown in Table 15, Examples 1-2, 4-5, and 12 of the present application have a smaller D90 particle size and a more concentrated and uniform particle size distribution. Simultaneously, their specific surface area is larger, thereby effectively increasing the density of the positive electrode sheet while effectively improving the compaction density. When the spray material is calcined at 700°C, as shown in Example 17, the D90 particle size of the lithium manganese iron phosphate material significantly increases, while the specific surface area significantly decreases. This indicates that lower calcination temperatures can shorten ion migration distances and accelerate reaction fusion speeds, thereby avoiding the formation of large particles and improving the compaction density of the lithium manganese iron phosphate material.

[0218] 5. The powder resistivity, PD (compacted density), AD (tapped density) and manganese dissolution rate of the lithium manganese iron phosphate products provided in Example 1, Example 4, Example 12, Examples 14 to 17 and Comparative Examples 1 to 2 were tested. The test results are shown in Table 16 below.

[0219] Table 16

[0220] Among them, in Table 16, powder resistivity test: adopts the four-probe method, and the test pressure is 10MPa.

[0221] PD (compaction density) test: measured using an electronic powder compactor with a test pressure of 3T.

[0222] AD (tap density) test: Take 100.00g of material and place it in a standard 100mL graduated cylinder. Vibrate it 1000 times with an amplitude of 2cm. The density obtained by calculating mass / volume is the tap density.

[0223] Manganese dissolution test method: 10g of lithium manganese iron phosphate product is added to 90g of 0.1mol / L hydrochloric acid solution, stirred at 25°C for 30 minutes, and then filtered. The manganese element in the filtrate is measured by ICP-OES to obtain manganese dissolution data.

[0224] From Figure 3, Table 13, and Table 16, it can be seen that the particles of the lithium manganese iron phosphate material prepared in the present application have high sphericity, an average primary particle size of 170 nm to 220 nm, and good density. Although the particles are not large, the compaction density can reach more than 2.30 g / mL, while maintaining small particles, ensuring the compaction density and capacity.

[0225] This application achieves a significant reduction in the ion diffusion distance during high-temperature calcination by mixing manganese, iron, lithium, and phosphorus ions at the ionic level, while also avoiding the segregation of manganese and iron, thereby ensuring the capacity of the product. Furthermore, this application introduces aluminum, which can improve the density of the particles to a certain extent, thereby maintaining a higher compaction density at a lower sintering temperature.

[0226] In addition, the doping of magnesium and aluminum can improve ionic conductivity. At the same time, magnesium doping can significantly reduce manganese dissolution and improve cycle performance, while aluminum doping can improve compaction density and rate performance.

[0227] 6. The positive electrode material formula is lithium manganese iron phosphate: SP: CNT: PVDF = 83:8:2:7. The electrochemical properties of the lithium manganese iron phosphate materials prepared in Example 1, Example 4, Examples 12-17, and Comparative Examples 1-2 were tested, and the results are shown in Table 17. The 0.1C charge-discharge curve of the lithium manganese iron phosphate material of Example 12 is shown in Figure 5, and the 1C charge-discharge curve is shown in Figure 6.

[0228] The 0.1C charge capacity, 0.1C discharge capacity, and initial discharge efficiency were all measured using a battery-drop test system. The 1C discharge capacity and capacity retention after 1000 cycles at 1C at room temperature were both measured using a soft-pack test line; the soft-pack capacity was 0.5Ah.

[0229] Table 17

[0230] It can be seen from Figures 5, 6 and Table 17 that the manganese capacity of the lithium manganese iron phosphate material of the present application is relatively good during the discharge process (i.e., the capacity at 3.75 to 4.6 V), and the manganese capacity is basically exerted, indicating that the manganese iron eutectic of the present application is relatively good and there is basically no manganese segregation phenomenon.

[0231] As shown in Table 17, compared to the lithium manganese iron phosphate material prepared by the solid phase method in Comparative Example 1, Examples 1 to 17 of the present application disperse the raw materials in an ionic state into the aqueous solution, effectively improving the degree of mixing uniformity, reducing manganese segregation and manganese dissolution, and significantly improving the charge specific capacity, discharge specific capacity, and capacity retention rate after 1000 cycles of the resulting lithium manganese iron phosphate material when used in batteries, indicating its improvement in electrochemical properties such as cycle performance and capacity performance. At the same time, because the raw materials have been mixed at the ionic level before spray drying, while reducing the calcination temperature and avoiding the generation of large particles, a lithium manganese iron phosphate material with improved cycle performance and capacity performance is obtained.

[0232] With reference to Tables 1 to 17 above, compared with Comparative Example 2, a carbon layer is formed on the surface of the lithium manganese iron phosphate in Examples 1 to 17.

[0233] Combining Example 1 with Examples 4 to 17, it can be seen that the use of magnesium and aluminum doping in the lithium manganese iron phosphate material further improves the compaction density, cycle performance, and rate performance of the lithium manganese iron phosphate material. At the same time, controlling the molar ratio of manganese, iron, lithium, and phosphorus in the raw materials for synthesizing the lithium manganese iron phosphate material to be (0.4 to 0.6): (0.4 to 0.6): (1.02 to 1.05): 1, and the molar ratio of aluminum, magnesium, and manganese to be (0.01 to 0.02): (0.005 to 0.01): 1 is conducive to obtaining a lithium manganese iron phosphate material with better cycle performance, rate performance, and higher capacity.

[0234] It can be seen from the data in Tables 16 and 17 of Example 12 that when m-phenylenediamine is used as the soluble organic carbon source, the phenylenediamine structure contains both benzene rings and amino groups, and the formed coating layer has a high degree of graphitization, which reduces the powder resistivity of the lithium manganese iron phosphate material and improves the conductivity of the lithium manganese iron phosphate material; at the same time, due to the introduction of nitrogen elements, the conductivity of the lithium manganese iron phosphate material is further improved.

[0235] Although the present application has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features therein may be replaced by equivalents, without departing from the spirit and scope of the present application. These modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present application. Therefore, this means that all such replacements and modifications within the scope of the present application are included in the appended claims.

[0236] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0237] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A lithium manganese iron phosphate material, wherein: The lithium iron manganese phosphate material includes a core, and the core includes a general formula of Li x Mg y Mn z Fe a Al b The core material of PO4, wherein x is 1.002 to 1.05, y is 0 to 0.009, z is 0.4 to 0.6, a is 0.388 to 0.6, and b is 0 to 0.

012.

2. The lithium iron manganese phosphate material according to claim 1, wherein: The lithium iron manganese phosphate material further includes a coating layer coated on the surface of the core, and the material of the coating layer includes a carbon material; The mass fraction of the carbon material is 1.5% to 2.5%, and / or the coverage rate of the carbon material is 98.0% to 99.9%.

3. The lithium iron manganese phosphate material according to claim 1 or 2, wherein: The lithium iron manganese phosphate material meets at least one of the following conditions: (1) The sphericity of the lithium manganese iron phosphate material is 0.7 to 1.0; (2) The average primary particle size of the lithium manganese iron phosphate material is 170nm to 220nm; (3) The secondary particle size of the lithium manganese iron phosphate material meets the following requirements: D10 is 0.2 μm to 0.6 μm, D50 is 1.5 μm to 3 μm, and D90 is 5 μm to 15 μm; (4) The compaction density of the lithium manganese iron phosphate material is 2.35 g / mL to 2.45 g / mL; (5) The tap density of the lithium manganese iron phosphate material is 1.1 g / mL to 1.2 g / mL; (6) The specific surface area of ​​the lithium manganese iron phosphate material is 13.5 m2 / g to 15.5 m2 / g; (7) The powder resistivity of the lithium iron manganese phosphate material is less than 15Ω.cm; (8) The manganese dissolution rate of the lithium manganese iron phosphate material is less than or equal to 0.05% of the manganese content in the lithium manganese iron phosphate material; (9) The specific capacity of the lithium manganese iron phosphate material is 160 mAh / g to 169 mAh / g.

4. A method for preparing lithium manganese iron phosphate material, wherein: The steps include: Mixing a mixed solution I and a phosphoric acid solution to obtain a mixed solution II; wherein the mixed solution I comprises a first manganese salt, a first iron salt and a first lithium salt, and the first manganese salt, the first iron salt and the first lithium salt are all soluble salts; The mixed solution II is spray-dried, calcined and crushed in sequence to obtain the lithium manganese iron phosphate material; The lithium iron manganese phosphate material includes a core, and the core includes a general formula of Li x Mg y Mn z Fe a Al b The core material of PO4, wherein x is 1.002 to 1.05, y is 0 to 0.009, z is 0.4 to 0.6, a is 0.388 to 0.6, and b is 0 to 0.

012.

5. The method for preparing lithium iron manganese phosphate material according to claim 4, wherein: The mixed solution I also includes a first magnesium salt and a first aluminum salt, and the first magnesium salt and the first aluminum salt are both soluble salts.

6. The method for preparing lithium manganese iron phosphate material according to claim 4 or 5, wherein in the mixed solution II, the molar ratio of manganese element, iron element, lithium element and phosphorus element is (0.4-0.6): (0.4-0.6): (1.02-1.05):

1.

7. The method for preparing lithium iron manganese phosphate material according to claim 6, wherein in the mixed solution II, the molar ratio of aluminum element, magnesium element and manganese element is (0.01-0.02): (0.005-0.01):

1.

8. The method for preparing lithium iron manganese phosphate material according to any one of claims 4 to 7, wherein: The lithium manganese iron phosphate material also includes a coating layer coated on the surface of the core, and the material of the coating layer includes a carbon material; in the step of mixing the mixed solution I and the phosphoric acid solution to obtain the mixed solution II, the preparation method also includes: The soluble organic carbon source is mixed with the mixed solution I and the phosphoric acid solution.

9. The method for preparing lithium iron manganese phosphate material according to claim 8, wherein: The soluble organic carbon source includes a first carbon source and a second carbon source; and / or, the first carbon source comprises m-phenylenediamine and / or p-hydroxyaniline; and / or, the second carbon source comprises at least one of glucose, sucrose, polyethylene glycol and starch; And / or, the mass ratio of the first carbon source to the second carbon source is (5-10):(90-95).

10. The method for preparing the lithium iron manganese phosphate material according to claim 8 or 9, wherein the lithium iron manganese phosphate material has a carbon content of 1.5 wt% to 2.5 wt%.

11. The method for preparing lithium manganese iron phosphate material according to any one of claims 4 to 10, wherein: The preparation method of the mixed solution I comprises: reacting a mixed material containing iron powder, manganese powder and lithium carbonate with an acetic acid solution, and obtaining the mixed solution I after solid-liquid separation; And / or, the mixture further includes magnesium powder and aluminum powder.

12. The method for preparing lithium iron manganese phosphate material according to any one of claims 4 to 11, wherein: The inlet air temperature of the spray drying is 250-350°C; And / or, after the spray drying, a spray material is obtained, the particle size of the spray material is 3 to 8 μm, and the water content of the spray material is less than 0.8 wt %.

13. The method for preparing lithium iron manganese phosphate material according to any one of claims 4 to 12, wherein: The calcination comprises: heating to 650-690° C. under an inert atmosphere, maintaining the temperature for 9-13 hours, and cooling.

14. The method for preparing lithium manganese iron phosphate material according to any one of claims 4 to 13, wherein: The pulverization comprises: The calcined material obtained after the calcination is crushed to a particle size of 1.5 to 3 μm.

15. A positive electrode sheet, wherein: include: A current collector and a positive electrode material arranged on at least one side of the current collector along the thickness direction thereof; the positive electrode material comprises the lithium manganese iron phosphate material according to any one of claims 1 to 3.

16. A secondary battery, wherein: include: A positive electrode sheet, a separator and a negative electrode sheet are stacked; the positive electrode sheet is the positive electrode sheet as claimed in claim 15.

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