Lithium manganese iron phosphate positive electrode material and preparation method thereof, positive electrode sheet, and lithium-ion battery

Abstract

The present invention relates to the technical field of lithium-ion batteries, and more particularly to a lithium iron manganese phosphate positive electrode material and a preparation method thereof, a positive electrode plate, and a lithium-ion battery. The positive electrode material comprises a lithium iron manganese phosphate matrix and carbon coated on the surface of the lithium iron manganese phosphate matrix; the carbon coating coefficient k of the positive electrode material satisfies the following: 1000≤k≤3500; wherein k=(S×d×ρ) / (c), S represents the specific surface area of the positive electrode material, m 2 / g; d represents the average primary particle size of the positive electrode material, nm; ρ represents the true density of the positive electrode material, g / cm 3 c represents the carbon content of the positive electrode material, wt%. The positive electrode material not only has efficient carbon coating, but also has low specific surface area, low powder impedance, high electronic conductivity and high structural stability, thereby improving the processing performance of the positive electrode material and enabling it to exert better electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a lithium iron manganese phosphate positive electrode material and a preparation method thereof, a positive electrode sheet containing the positive electrode material, and a lithium-ion battery containing the positive electrode sheet. Background Art

[0002] Lithium-ion batteries are a new type of battery system featuring high capacity, long life, and a high voltage platform. In recent years, they have been widely used in the power and energy storage sectors, playing a vital role in electronic information, transportation, energy equipment, and national defense. Cathode materials are key components in lithium-ion battery systems, determining the battery's energy density, operating voltage range, cycle life, and other performance characteristics, making them particularly important in practical applications. Olivine-type phosphate materials and layered oxide ternary materials are currently the two most popular types of cathode materials on the market.

[0003] The commercial application of olivine-type phosphate materials has become increasingly mature in recent years, among which lithium iron phosphate (LiFePO4) and lithium iron manganese phosphate (LiMn x Fe 1-x PO4). Olivine-type phosphate materials have the characteristics of long cycle life and stable discharge platform, but compared with ternary materials (lithium nickel cobalt manganese oxide NCM and lithium nickel cobalt aluminum oxide NCA), their electronic conductivity is low and the powder impedance is relatively large. If used directly as a positive electrode material, the electrical performance is poor. Among them, lithium manganese iron phosphate (LiMn x Fe 1-x The introduction of Mn into lithium iron phosphate (LiFePO4) materials inevitably leads to the Jahn-Teller effect, creating a significant kinetic barrier for ion and electron transport at the interface during charge and discharge, resulting in lower electronic conductivity than lithium iron phosphate (LiFePO4). To address this issue with LiFePO4, the industry generally adopts carbon coating to improve the material's electronic conductivity and reduce impedance.

[0004] To address the low electronic conductivity of lithium manganese iron phosphate materials, multiple carbon coatings or the use of different types of carbon sources are currently being used to optimize and improve the carbon coating level of lithium manganese iron phosphate materials. For example, CN202211701878.9 achieves multiple carbon coatings on lithium manganese iron phosphate by multiple mixing and sintering of materials with organic carbon sources; CN202310363951.4 achieves uniformly coated graphene-coated lithium manganese iron phosphate by combining metal active sites with chemical vapor deposition, significantly improving the conductivity of the material; CN202311148714.2 effectively improves the conductivity of the lithium manganese iron phosphate material by sequentially providing a conductive agent coating layer and a solid electrolyte coating layer on the surface of a spherical lithium manganese iron phosphate material, wherein the conductive agent coating layer comprises sulfur-nitrogen dual-doped carbon nanotubes.

[0005] Although the above-mentioned existing technologies have improved the carbon coating level of lithium manganese iron phosphate to a certain extent, there are many types of carbon coating raw materials currently used, the amount of carbon source used is large, and the consistency of the coating effect is poor. It is impossible to ensure the uniform carbon coating of nano-scale primary particles at the microscopic scale. At the same time, a larger amount of carbon source added increases the specific surface area of the material, which has a negative impact on the processing performance of the material. Therefore, it is urgent to develop a more efficient carbon coating method and an effective carbon coating effect evaluation method to further improve the performance of lithium manganese iron phosphate (LiMn x Fe 1-x Electrochemical properties of PO4) materials. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned technical problems and provide a lithium iron manganese phosphate positive electrode material and a preparation method thereof, a positive electrode plate containing the positive electrode material, and a lithium ion battery containing the positive electrode plate. The positive electrode material not only has high-efficiency carbon coating, but also has low specific surface area, low powder impedance, high electronic conductivity and high structural stability, thereby improving the processing performance of the positive electrode material and enabling it to exert better electrochemical performance.

[0007] A first aspect of the present invention provides a lithium iron manganese phosphate positive electrode material, comprising a lithium iron manganese phosphate matrix and carbon coated on the surface of the lithium iron manganese phosphate matrix; the carbon coating coefficient k of the positive electrode material satisfies: 1000≤k≤3500;

[0008] Wherein, k = (S × d × ρ) / (c), S represents the specific surface area of the positive electrode material, m 2 / g; d represents the average primary particle size of the positive electrode material, nm; ρ represents the true density of the positive electrode material, g / cm 3 ; c represents the carbon content of the positive electrode material, wt%.

[0009] In the present invention, unless otherwise specified, the lithium manganese iron phosphate positive electrode material is referred to as the positive electrode material.

[0010] The inventors of the present invention have found that compared with lithium iron phosphate, the electronic conductivity of lithium manganese iron phosphate material is relatively low, and more carbon coating is required to ensure its electrical performance. However, the more conventional carbon material is coated, the larger the corresponding specific surface area. However, a larger specific surface area, on the one hand, makes the material itself easier to absorb water, and is more likely to produce jelly and gel during the battery slurry production process, thereby affecting normal coating and the subsequent pole piece rolling quality, thereby affecting the processing performance of the material; on the other hand, a larger specific surface area also makes it easier for manganese and iron elements to dissolve during the charge and discharge process of the material, resulting in the collapse of the structure of the lithium manganese iron phosphate material, seriously affecting the long-term performance of the material's electrical performance. Therefore, while maintaining efficient carbon coating, the specific surface area of the material needs to be reduced as much as possible to facilitate the structural stability of the material and the long-term performance of its electrical performance.

[0011] At the same time, many factors influence the performance of lithium manganese iron phosphate materials. Among them, there is a certain degree of intrinsic connection between the material's average primary particle size, specific surface area, carbon content, and true density. Specifically, if lithium manganese iron phosphate single crystal material is regarded as a single-particle sphere model, the material's average primary particle size and specific surface area reflect the particle size of the material itself; the material's carbon content represents the overall (surface + internal) carbon content of the material; and the material's true density represents the density level in terms of the material's intrinsic crystallographic structure. The product of the material's specific surface area, average primary particle size, and true density dimensionally reflects the material's effective electrochemical reaction quality per unit accessible area.

[0012] Therefore, in order to characterize the carbon coating level of the lithium manganese iron phosphate material, the carbon coating coefficient k is calculated by the specific surface area S, the average primary particle size d, the true density ρ and the carbon content c of the positive electrode material, that is, k = (S×d×ρ) / (c), and further limited to 1000≤k≤3500, indicating that the carbon coating effect of the positive electrode material is better. Under a certain amount of carbon content, the specific surface area is relatively low, and the optimal coating effect is achieved, so that the average primary particle size, carbon content and specific surface area of the positive electrode material have a better match, so that the positive electrode material can achieve excellent electrochemical performance, especially stable and efficient long-term electrochemical performance.

[0013] A second aspect of the present invention provides a method for preparing a lithium manganese iron phosphate positive electrode material, the preparation method comprising the following steps:

[0014] (1) mixing a Li source, a Mn source, a Fe source, a M source, a P source, a first carbon source, and water to obtain a first mixed slurry;

[0015] (2) subjecting the first mixed slurry to a first grinding and a first spray drying, and then to a first sintering in a protective atmosphere to obtain a lithium manganese iron phosphate matrix having the formula I;

[0016] (3) performing a second mixing of the lithium manganese iron phosphate matrix, a conductive polymer as a second carbon source, and water to obtain a second mixed slurry;

[0017] (4) subjecting the second mixed slurry to a second grinding and a second spray drying, and then to a second sintering in a protective atmosphere to obtain a lithium manganese iron phosphate positive electrode material;

[0018] Among them, Li a Mn 1-x Fe x M b (PO4) c (I) M is selected from at least one of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; 1≤a≤1.1; 0<x<1; 0≤b≤0.2; 1≤c≤1.1.

[0019] A third aspect of the present invention provides a positive electrode plate, which includes the positive electrode material provided by the first aspect, or the positive electrode material prepared by the preparation method provided by the second aspect.

[0020] A fourth aspect of the present invention provides a lithium-ion battery, comprising the positive electrode sheet provided in the third aspect.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The cathode material provided by the present invention, by limiting the carbon coating coefficient k to satisfy: 1000≤k≤3500, not only enables the cathode material to form a high-efficiency carbon coating with uniformity, effectiveness, dispersibility and anti-agglomeration properties, but also enables the cathode material to have excellent powder impedance, electronic conductivity and structural stability; in particular, the cathode material is able to reduce the specific surface area of the cathode material as much as possible while maintaining a certain carbon content, thereby improving the processing performance and long-term electrochemical performance of the cathode material, especially the long-term cycle life;

[0023] (2) The preparation method provided by the present invention forms a sufficient carbon coating network by adopting the technical means of double carbon addition and double sintering to achieve high-quality carbon coating; at the same time, a conductive polymer is introduced as a second carbon source for carbon coating to form a sufficient primary wrapping network for the lithium manganese iron phosphate matrix, so that the carbon coating coefficient k is 1000≤k≤3500, and high-quality carbon coating is formed without consuming too much carbon source;

[0024] (3) The preparation method provided by the present invention has a simple and clear process route, low operational difficulty, can be quickly introduced and applied based on existing mature equipment, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the XRD pattern of the lithium manganese iron phosphate matrix S1 prepared in Example 1;

[0026] Figure 2 is a TEM image of the positive electrode material P1 prepared in Example 1;

[0027] Figure 3 This is a TEM image of the positive electrode material DP1 prepared in Comparative Example 1;

[0028] Figure 4 Charge and discharge curves of the button cell assembled with the positive electrode material P1 prepared in Example 1 at the first cycle and the 80th cycle. DETAILED DESCRIPTION

[0029] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0030] In the present invention, unless otherwise specified, the terms "first" and "second" do not indicate a sequential order or limit the materials or steps involved. They are used only to distinguish or indicate that they are not the same materials or steps. For example, the terms "first" and "second" in "first mixed slurry" and "second mixed slurry" are used only to indicate that they are not the same mixed slurry; similarly, the terms "first" and "second" in "first sintering" and "second sintering" are used only to indicate that they are not the same sintering.

[0031] A first aspect of the present invention provides a lithium iron manganese phosphate positive electrode material, comprising a lithium iron manganese phosphate matrix and carbon coated on the surface of the lithium iron manganese phosphate matrix; the carbon coating coefficient k of the positive electrode material satisfies: 1000≤k≤3500;

[0032] Wherein, k = (S × d × ρ) / (c), S represents the specific surface area of the positive electrode material, m 2 / g; d represents the average primary particle size of the positive electrode material, nm; ρ represents the true density of the positive electrode material, g / cm 3 ; c represents the carbon content of the positive electrode material, wt%.

[0033] In the present invention, unless otherwise specified, the average primary particle size of the positive electrode material = the average primary particle size of the lithium iron manganese phosphate matrix + the carbon coating thickness; the carbon content of the positive electrode material = the sum of the carbon element content on the surface and inside the lithium iron manganese phosphate matrix.

[0034] In the present invention, unless otherwise specified, the specific surface area parameter is measured by a static adsorption method; the average primary particle size parameter is measured by a scanning electron microscope + particle recognition software; the true density parameter is measured by a true density meter; and the carbon content parameter is measured by a carbon-sulfur analyzer.

[0035] In the present invention, the specific surface area parameter is measured using the volumetric method for measuring the BET specific surface area of powders specified in GB / T 19587-2017 "Determination of the specific surface area of solid substances by gas adsorption BET method".

[0036] In this application, the true density parameter testing method includes: using an AccuPyc II 1345 true density meter, weighing a certain amount of sample and recording its mass, placing the sample cup into the instrument, and securing the sample cover and sealing cap. In the software interface, click "Sample analysis" to perform the sample analysis and obtain the sample's true density value.

[0037] In the present invention, the carbon content parameter is measured using the determination method specified in GB / T 20123-2006 “Determination of total carbon and sulfur content of steel - Infrared absorption method after combustion in a high-frequency induction furnace (conventional method)”.

[0038] In the present invention, the test method for the average primary particle size parameter includes: performing a scanning electron microscope test on the sample at a voltage of 30kV, selecting a 30k magnification photo, and calculating the average primary particle size value of the sample in the area using the "Nano Measurer" particle recognition software.

[0039] In some embodiments of the present invention, the carbon coating coefficient k of the positive electrode material satisfies: 1000≤k≤3500, for example, 1000, 1300, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2500, 2800, 3000, 3500, and any value in the range of any two numerical values, preferably satisfies: 1500≤k≤2500, more preferably satisfies: 1700≤k≤2200.

[0040] In the present invention, the carbon coating coefficient k satisfies the above range, so that the positive electrode material not only has efficient carbon coating, but also has excellent electronic conductivity, powder impedance and structural stability, thereby improving the processing performance of the positive electrode material and stable and efficient long-term electrochemical performance.

[0041] In some embodiments of the present invention, preferably, the specific surface area S of the positive electrode material is 5-25m 2 / g, for example, 5m 2 / g、8m2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g, and any value in the range of any two values, preferably 8-13m 2 The specific surface area meeting the above range enables the positive electrode material to have a lower specific surface area under the premise of a certain carbon content, thereby improving the processing performance and long-term cycle life of the positive electrode material.

[0042] In some embodiments of the present invention, preferably, the average primary particle size d of the positive electrode material is 50-200 nm, for example, 50 nm, 70 nm, 90 nm, 100 nm, 110 nm, 120 nm, 150 nm, 180 nm, 200 nm, and any value in the range consisting of any two values, preferably 70-120 nm.

[0043] In some embodiments of the present invention, preferably, the true density ρ of the positive electrode material is 4.2-4.4 g / cm 3 , for example, 4.3 g / cm 3 , 4.3g / cm 3 , 4.31g / cm 3 , 4.32g / cm 3 , 4.33g / cm 3 , 4.34g / cm 3 , 4.35g / cm 3 , 4.38g / cm 3 , 4.4g / cm 3 , and any value in the range of any two values, preferably 4.3-4.35 g / cm 3 .

[0044] In some embodiments of the present invention, the carbon content c of the positive electrode material is preferably 1-3 wt%, for example, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.3 wt%, 2.5 wt%, 3 wt%, and any value in a range consisting of any two values, preferably 1.2-2.3 wt%. In the present invention, the carbon content within the above range enables the positive electrode material to have high electronic conductivity and low powder resistance, thereby improving the electrochemical performance of the positive electrode material.

[0045] In some embodiments of the present invention, preferably, 0<the carbon coating thickness of the positive electrode material≤50nm, preferably 5-25nm. In the present invention, the carbon coating thickness refers to the absolute thickness of the carbon coating, which is measured using TEM images.

[0046] In some embodiments of the present invention, preferably, the lithium manganese iron phosphate matrix has a composition shown in Formula I: Li a Mn 1-x Fe x M b (PO4) c (I), wherein M is selected from at least one of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; 1≤a≤1.1; 0<x<1; 0≤b≤0.2; 1≤c≤1.1.

[0047] In the present invention, in Formula I, 1≤a≤1.1, for example, 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.1, and any value in a range consisting of any two values, preferably 1≤a≤1.05.

[0048] In the present invention, in Formula I, 0<x<1, for example, 0.1, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, and any value in the range consisting of any two values, preferably 0.1≤x≤0.5.

[0049] In the present invention, in Formula I, 0≤b≤0.2, for example, 0, 0.1, 0.12, 0.15, 0.18, 0.2, and any value in the range of any two values, preferably 0.1≤b≤0.2.

[0050] In the present invention, in Formula I, 1≤c≤1.1, for example, 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.08, 1.1, and any value in the range consisting of any two values, preferably 1≤c≤1.05.

[0051] In some embodiments of the present invention, further preferably, in Formula I, M is selected from at least one of Ti, W, Co, V and Mg.

[0052] In the present invention, by regulating a, x, b, c and M in formula I, the value of a is individually regulated within a certain range, thereby affecting the Li ratio in the positive electrode material, thereby affecting the capacity and compaction level of the positive electrode material; adjusting the value of x will affect the voltage platform of the positive electrode material; adjusting the values of b and M mainly affects the electrochemical kinetics and true density of the positive electrode material; adjusting the value of c will also affect the capacity and true density of the material by affecting the ratio of P in the material.

[0053] In some embodiments of the present invention, preferably, the average primary particle size of the lithium manganese iron phosphate matrix is 50-200 nm, for example, 50 nm, 70 nm, 90 nm, 100 nm, 110 nm, 120 nm, 150 nm, 180 nm, 200 nm, and any value in the range consisting of any two values, preferably selected from 70-120 nm.

[0054] In the present invention, the positive electrode material that meets the specific carbon coating coefficient k also has excellent powder impedance and electronic conductivity. Preferably, the powder impedance of the positive electrode material is 10-500Ω·cm, for example, 10Ω·cm, 20Ω·cm, 30Ω·cm, 40Ω·cm, 50Ω·cm, 100Ω·cm, 200Ω·cm, 300Ω·cm, 400Ω·cm, 500Ω·cm, and any value in the range of any two values, preferably 20-50Ω·cm. In the present invention, the powder impedance parameter is measured using a powder compactor.

[0055] In the present invention, the value of the powder impedance is inversely proportional to the value of the electronic conductivity. That is, the smaller the value of the powder impedance of the positive electrode material, the higher the value of the electronic conductivity of the positive electrode material.

[0056] A second aspect of the present invention provides a method for preparing a lithium manganese iron phosphate positive electrode material, the preparation method comprising the following steps:

[0057] (1) mixing a Li source, a Mn source, a Fe source, a M source, a P source, a first carbon source, and water to obtain a first mixed slurry;

[0058] (2) subjecting the first mixed slurry to a first grinding and a first spray drying, and then to a first sintering in a protective atmosphere to obtain a lithium manganese iron phosphate matrix having the formula I;

[0059] (3) performing a second mixing of the lithium manganese iron phosphate matrix, a conductive polymer as a second carbon source, and water to obtain a second mixed slurry;

[0060] (4) subjecting the second mixed slurry to a second grinding and a second spray drying, and then to a second sintering in a protective atmosphere to obtain a lithium manganese iron phosphate positive electrode material;

[0061] Among them, Li a Mn 1-x Fe x M b (PO4) c (I) M is selected from at least one of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; 1≤a≤1.1; 0<x<1; 0≤b≤0.2; 1≤c≤1.1.

[0062] Compared with the existing lithium iron phosphate and lithium manganese iron phosphate carbon coating systems, natural polysaccharides such as glucose and sucrose are mostly used as the main carbon source, with a small amount of small molecule alcohols, hydrocarbons (polyethylene glycol, polyvinyl alcohol, etc.) organic compounds as dispersants or adhesives for carbon coating; natural polysaccharides and small molecule alcohol hydrocarbon compound raw materials are easy to obtain and have low cost, but in actual use, it is found that the carbon coating effect of existing mainstream carbon sources is not good, especially for lithium manganese iron phosphate particles with smaller primary particles, there are more pores and adhesions between particles, and traditional natural polysaccharide carbon sources are difficult to achieve uniform carbon network coating between particles, and the carbon coating effect is poor.

[0063] Therefore, in order to improve the quality and effect of carbon coating, the present invention uses a conductive polymer, that is, a multiple composite polymer carbon source, for carbon coating, so that the material maintains a low specific surface area level at a certain carbon content level. At the same time, the present invention uses a conductive polymer for carbon coating, especially by limiting the average molecular weight of the conductive polymer to ≥10 4 g / mol, which gives it excellent particle wrapping ability and can add a dense conductive layer to the lithium manganese iron phosphate matrix, effectively coating primary particles while avoiding multi-particle agglomeration; at the same time, the conductive polymer also has a hydrophobic function, preventing the surface of tiny particles from absorbing water, and has a stronger anchoring ability for manganese, iron and the doping element M, showing obvious advantages in coating effectiveness, dispersibility, anti-agglomeration and other aspects.

[0064] In the present invention, unless otherwise specified, the protective atmosphere includes but is not limited to nitrogen atmosphere, helium atmosphere, argon atmosphere, etc., preferably nitrogen atmosphere.

[0065] In some embodiments of the present invention, preferably, in step (1), calculated as elements, the amounts of the Li source, Mn source, Fe source, M source, P source and the first carbon source satisfy n(Li):n(Mn):n(Fe):n(M):n(P):n(C), wherein, 1≤n(Li)≤1.1, 0<n(Mn)<1, 0<n(Fe)<1, 0≤n(M)≤0.2, 1≤n(P)≤1.1, 0<n(C)≤0.1; further preferably, 1≤n(Li)≤1.05, 0.5≤n(Mn)≤0.9, 0.1≤n(Fe)≤0.5, 0.1≤n(M)≤0.2, 1≤n(P)≤1.05, 0.01≤n(C)≤0.05.

[0066] In the present invention, unless otherwise specified, the Li source, Mn source, Fe source, M source and P source are each independently selected from soluble salts. In the present invention, soluble means readily soluble in water, or readily soluble in water under the action of an auxiliary agent.

[0067] In some embodiments of the present invention, preferably, the Li source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate and lithium chloride.

[0068] In some embodiments of the present invention, preferably, the Mn source is selected from at least one of trimanganese tetraoxide, manganese dioxide, manganese carbonate, manganese oxalate, manganese chloride, manganese sulfate and manganese nitrate.

[0069] In some embodiments of the present invention, preferably, the Fe source is selected from at least one of ferrous oxalate, ferrous oxalate, ferrous acetate, ferrous acetate, ferrous nitrate, ferric nitrate, ferric phosphate, ferric oxide, ferrous sulfate, ferric sulfate, ferrous chloride and ferric chloride.

[0070] In some embodiments of the present invention, preferably, the M source is selected from at least one of oxides, carbonates, and phosphides containing Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd, and is preferably selected from at least one of oxides, carbonates, and phosphides containing Ti, W, Co, V, and Mg.

[0071] In some embodiments of the present invention, preferably, the P source is selected from at least one of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate and sodium dihydrogen phosphate.

[0072] In some embodiments of the present invention, preferably, the first carbon source is selected from at least one of citric acid, glucose, sucrose, soluble starch, salicylic acid, tartaric acid, oxalic acid, and polyethylene glycol. In the present invention, the first carbon source acts as a reducing agent and is converted into a carbon-containing gas and volatilized after the first sintering.

[0073] In the present invention, the first mixing is to uniformly mix the Li source, Mn source, Fe source, M source, P source, first carbon source and water to obtain a first mixed slurry with a solid content of 40-60 wt%.

[0074] In the present invention, in step (2), the first grinding is intended to control the particle size of the first mixed slurry. Preferably, the particle size D of the first grinding is controlled. 50 1 is 0.2-0.6 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, and any value in the range of any two values, preferably 0.3-0.5 μm. In the present invention, the particle size D of the first grinding is adjusted. 50 1 That is, the particle size D of the first grinding material is 50 1 It is 0.2-0.6 μm, preferably 0.3-0.5 μm.

[0075] In the present invention, the first spray drying step refers to drying the first milled material. Preferably, the first spray drying step is performed under the following conditions: an inlet air temperature of 180-300°C, preferably 200-260°C; and an outlet air temperature of 85-115°C, preferably 95-105°C. In the present invention, meeting these conditions allows for rapid dehydration of the first milled material, yielding a uniform first spray-dried material.

[0076] In the present invention, the first sintering step is intended to sinter the first spray-dried material to obtain a lithium manganese iron phosphate matrix having Formula I and a carbon-containing gas. Preferably, the conditions for the first sintering step include: a temperature T1 of 350-650°C, preferably 400-600°C; a heating rate V1 of 0.5-10°C / min, preferably 1-5°C / min; and a time t1 of 0.1-10 hours, preferably 0.1-5 hours. Meeting the conditions for the first sintering step not only produces a lithium manganese iron phosphate matrix having Formula I, but also optimizes the material surface for efficient carbon coating.

[0077] In some embodiments of the present invention, preferably, the lithium manganese iron phosphate matrix is composed of primary particles, and the particle size of the primary particles is 50-200 nm.

[0078] In some embodiments of the present invention, preferably, in step (3), the average molecular weight of the second carbon source is ≥10 4 g / mol, preferably (1.5-3.5)×10 4 g / mol, for example, 10 4 g / mol, 1.5×10 4g / mol, 2×10 4 g / mol, 2.5×10 4 g / mol, 3×10 4 g / mol, 3.5×10 4 g / mol, any value in the range consisting of any two values.

[0079] In some embodiments of the present invention, the second carbon source is preferably selected from a substituted and / or unsubstituted polymer, and the polymer is selected from at least one of polyaniline, polypyrrole, polyacetylene, and polyvinyl alcohol, and the substituent group in the substituted polymer is selected from at least one of an amino group, a hydroxyl group, a thiol group, a C1-C5 alkyl group, a heteroatom, and a halogen. In the present invention, the C1-C5 alkyl group includes, but is not limited to, methyl, ethyl, and propyl groups; heteroatoms include, but are not limited to, S, N, and O; and halogens include, but are not limited to, F, Cl, Br, and I.

[0080] In the present invention, a specific second carbon source is used as the carbon coating raw material. Since the second carbon source is selected from a conductive polymer with a high molecular weight polymer structure, it not only has a chain extension effect, but also forms a sufficient carbon coating network to achieve high-quality carbon coating.

[0081] In some embodiments of the present invention, preferably, the mass ratio of the lithium manganese iron phosphate matrix and the second carbon source is 1:0.01-0.1, for example, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.08, 1:0.1, and any value in the range of any two values, preferably 1:0.03-0.08. When the amount of the second carbon source is small (i.e., the mass ratio of the lithium manganese iron phosphate matrix and the second carbon source is less than 1:0.01), a stable carbon coating network cannot be formed, and the conductivity of the material will be affected; when the amount of the second carbon source is too much (i.e., the mass ratio of the lithium manganese iron phosphate matrix and the second carbon source is greater than 1:0.1), the excess second carbon source will increase the coating layer on the surface of the material, which is not conducive to the dynamic performance of the material.

[0082] In the present invention, the second mixing is to uniformly mix the lithium manganese iron phosphate matrix, the second carbon source and water to obtain a second mixed slurry with a solid content of 40-60 wt%.

[0083] In the present invention, in step (4), the second grinding is intended to control the particle size of the second mixed slurry. Preferably, the particle size D of the second grinding is controlled. 50 2is 0.1-0.4 μm, for example, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.4 μm, and any value in the range of any two values, preferably 0.15-0.25 μm. In the present invention, the particle size D of the second grinding is adjusted. 50 2 That is, the particle size D of the second grinding material is 50 2 It is 0.1-0.4 μm, preferably 0.15-0.25 μm.

[0084] In the present invention, the second spray drying step is intended to remove water from the second milled material to obtain a second spray-dried material, that is, to uniformly coat the surface of the lithium manganese iron phosphate substrate with the second carbon source. Preferably, the second spray drying step is performed under the following conditions: an inlet air temperature of 180-300°C, preferably 200-245°C; and an outlet air temperature of 85-115°C, preferably 95-105°C.

[0085] In the present invention, the second sintering is intended to convert the second carbon source in the second spray-dried material into inorganic carbon to obtain a lithium manganese iron phosphate positive electrode material. Preferably, in step (4), the conditions of the second sintering include: a temperature T2 of 550-850°C, preferably 650-800°C; a heating rate V2 of 0.5-10°C / min, preferably 1-5°C / min; and a time t2 of 6-16 hours, preferably 8-12 hours.

[0086] In the present invention, the lithium manganese iron phosphate positive electrode material prepared by the preparation method provided by the second aspect meets the physical property parameter limitations of the positive electrode material provided by the first aspect, and the present invention will not be described in detail here.

[0087] A third aspect of the present invention provides a positive electrode plate, which includes the positive electrode material provided by the first aspect, or the positive electrode material prepared by the preparation method provided by the second aspect.

[0088] In some embodiments of the present invention, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer loaded on the surface of the positive electrode current collector, and the positive electrode active material layer includes: the positive electrode material provided by the present invention, a conductive agent and a binder, wherein the mass ratio of the positive electrode material, the conductive agent and the binder is 90-95:3-5:2-5.

[0089] In the present invention, the positive electrode current collector includes but is not limited to aluminum foil; the conductive agent includes but is not limited to acetylene black, graphite, etc.; the binder includes but is not limited to PVDF.

[0090] In a specific embodiment of the present invention, the positive electrode material, the conductive agent (acetylene black) and the binder (PVDF) are mixed with the solvent (NMP) in a mass ratio of 95:5:5 (temperature is 25°C, rotation speed is 1000 rpm, time is 40 min) to obtain a positive electrode slurry; the above-mentioned positive electrode slurry is coated on the surface of the aluminum foil to coat the positive electrode slurry coating on the surface of the aluminum foil, and after drying at 135°C, it is stamped with a pressure of 100 MPa to obtain a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm, and then the positive electrode sheet is placed in a vacuum drying oven and dried at 120°C for 12 hours.

[0091] A fourth aspect of the present invention provides a lithium-ion battery, comprising the positive electrode sheet provided in the third aspect.

[0092] The present invention will be described in detail below through examples.

[0093] Example 1

[0094] (1) a Li source (Li2CO3), a Mn source (Mn3O4), an Fe source (Fe2O3), a P source (NH4H2PO4) and a first carbon source (glucose) were first mixed in deionized water at a molar ratio of 1.03:0.6:0.4:1.01:0.05, calculated as elements, to obtain a first mixed slurry having a solid content of 50 wt%;

[0095] (2) The first mixed slurry is subjected to a first grinding to obtain a particle size D of the first grinding material. 50 1 The particle size of the ground material is 0.4 μm, and the ground material is subjected to a first spray drying (inlet air temperature 240° C., outlet air temperature 100° C.) to obtain a first spray-dried material;

[0096] In a nitrogen atmosphere, the first spray-dried material was subjected to a first sintering (T1 = 500 ° C, V1 = 5 ° C / min, t1 = 2h) to obtain a general formula of Li 1.03 Mn 0.6 Fe 0.4 (PO4) 1.01 The XRD pattern of the lithium iron manganese phosphate matrix S1 is as follows: Figure 1 As shown;

[0097] (3) The above-mentioned lithium manganese iron phosphate matrix S1 and the second carbon source (polypyrrole, average molecular weight 2.5×10 4 g / mol) in deionized water at a mass ratio of 1:0.05 to obtain a second mixed slurry with a solid content of 50 wt%;

[0098] (4) The second mixed slurry is subjected to a second grinding to obtain a second grinding material with a particle size D50 2 The second ground material was subjected to a second spray drying (inlet air temperature 220 ° C, outlet air temperature 95 ° C) to obtain a second spray-dried material;

[0099] In a nitrogen atmosphere, the second spray-dried material was subjected to a second sintering (T2=700° C., V1=5° C. / min, t2=10 h) to coat the surface of the lithium manganese iron phosphate substrate with carbon to obtain the positive electrode material P1.

[0100] Among them, the TEM image of the above-mentioned positive electrode material P1 is as follows Figure 2 As shown by Figure 2 It can be seen that the dark part is the surface of the positive electrode material, and the light part is the complete and uniform carbon coating, that is, the positive electrode material P1 includes a lithium iron manganese phosphate matrix, and carbon is uniformly coated on the surface of the lithium iron manganese phosphate matrix.

[0101] Example 2

[0102] The method of Example 1 is as follows, except that

[0103] In step (1), the molar ratio of the Li source (Li2CO3), Mn source (Mn3O4), Fe source (Fe2O3), P source (NH4H2PO4) and the first carbon source (glucose) was replaced with 1:0.5:0.5:1:0.05, calculated on an element basis, and the other conditions remained the same;

[0104] In step (2), the general formula is LiMn 0.5 Fe 0.5 PO4 lithium manganese iron phosphate matrix S2;

[0105] In step (4), the positive electrode material P2 is obtained.

[0106] Example 3

[0107] The method of Example 1 is as follows, except that

[0108] In step (1), the molar ratio of the Li source (Li2CO3), Mn source (Mn3O4), Fe source (Fe2O3), M source (TiO2), P source (NH4H2PO4) and the first carbon source (glucose) was adjusted to 1.05:0.7:0.3:0.01:1.03:0.05, calculated on an element basis, with the other conditions remaining the same;

[0109] In step (2), the general formula is Li 1.05 Mn 0.7 Fe 0.3 Ti 0.01 (PO4) 1.03 Lithium manganese iron phosphate matrix S3;

[0110] In step (4), the positive electrode material P3 is obtained.

[0111] Example 4

[0112] The method of Example 1 is as follows, except that

[0113] In step (1), the molar ratio of the Li source (Li2CO3), Mn source (Mn3O4), Fe source (Fe2O3), P source (NH4H2PO4) and the first carbon source (glucose) was replaced with 1.03:0.4:0.6:1.01:0.05, calculated on an element basis, and the other conditions remained the same;

[0114] In step (2), the general formula is Li 1.03 Mn 0.4 Fe 0.6 (PO4) 1.01 Lithium manganese iron phosphate matrix S4;

[0115] In step (4), positive electrode material P4 is obtained.

[0116] Example 5

[0117] The method of Example 1 is as follows, except that

[0118] In step (3), the second carbon source was replaced with a carbon source having an average molecular weight of 3.1×10 4 g / mol of amino-substituted polyvinylpyrrolidone, the other conditions being the same;

[0119] In step (4), the positive electrode material P5 is obtained.

[0120] Example 6

[0121] The method of Example 1 is as follows, except that

[0122] In step (3), the second carbon source is replaced with a carbon source having an average molecular weight of 1.5×10 4 g / mol of polyethylenedioxythiophene, the other conditions being the same;

[0123] In step (4), positive electrode material P6 is obtained.

[0124] Example 7

[0125] The method of Example 1 is as follows, except that

[0126] In step (3), the second carbon source is replaced with a carbon source having an average molecular weight of 0.9×10 4 g / mol of polypyrrole, the other conditions were the same;

[0127] In step (4), the positive electrode material P7 is obtained.

[0128] Example 8

[0129] The method of Example 1 is as follows, except that

[0130] In step (3), the mass ratio of the lithium manganese iron phosphate matrix S1 and the second carbon source is replaced with 1:0.02, and the other conditions remain the same;

[0131] In step (4), the positive electrode material P8 is obtained.

[0132] Example 9

[0133] The method of Example 1 is as follows, except that

[0134] In step (3), the mass ratio of the lithium manganese iron phosphate matrix S1 and the second carbon source is replaced with 1:0.2, and the other conditions are the same;

[0135] In step (4), the positive electrode material P9 is obtained.

[0136] Example 10

[0137] The method of Example 1 is as follows, except that

[0138] In step (4), the second sintering temperature T2 is replaced with 600°C, and the other conditions remain the same;

[0139] The positive electrode material P10 was obtained.

[0140] Example 11

[0141] The method of Example 1 is as follows, except that

[0142] In step (2), the particle size D of the first grinding material is regulated. 50 1 is 0.2μm, and the other conditions are the same;

[0143] The positive electrode material P11 was obtained.

[0144] Example 12

[0145] The method of Example 1 is as follows, except that

[0146] In step (4), the particle size D of the second grinding material is regulated. 50 2 is 0.4μm, and the other conditions are the same;

[0147] The positive electrode material P12 was obtained.

[0148] Comparative Example 1

[0149] (1) a Li source (Li2CO3), a Mn source (Mn3O4), an Fe source (Fe2O3), a P source (NH4H2PO4) and a first carbon source (glucose) were first mixed in deionized water at a molar ratio of 1.03:0.6:0.4:1.01:0.05, calculated as elements, to obtain a first mixed slurry having a solid content of 50 wt%;

[0150] (2) The first mixed slurry is subjected to a first grinding to obtain a particle size D of the first grinding material. 50 1 The particle size of the first grinding material is 0.4 μm, and the first grinding material is subjected to a first spray drying (inlet air temperature 240° C., outlet air temperature 100° C.) to obtain a first spray-dried material;

[0151] In a nitrogen atmosphere, the first spray-dried material was subjected to a first sintering (T1=700° C., V1=5° C. / min, t1=10 h) to obtain a positive electrode material DP1.

[0152] Among them, the TEM image of the above-mentioned positive electrode material DP1 is as follows Figure 3 As shown by Figure 3 It can be seen that the surface carbon coating layer of the positive electrode material DP1 is sparse, that is, the carbon coating quality is poor.

[0153] Comparative Example 2

[0154] The method of Example 1 is followed, except that the second carbon source is the same type of carbon source as the first carbon source.

[0155] In step (3), the second carbon source is replaced with glucose;

[0156] The other conditions were the same to obtain the positive electrode material DP2.

[0157] Table 1

[0158]

[0159] Note: 1- Mass ratio of lithium manganese iron phosphate matrix and the second carbon source.

[0160] Table 1

[0161]

[0162] Note: Carbon coating coefficient k = (S × d × ρ) / (c).

[0163] As can be seen from the results in Table 1, compared to Comparative Examples 1-2, the positive electrode material prepared using the method provided by the present invention not only has efficient carbon coating, that is, the carbon coating coefficient k satisfies 1000≤k≤3500, but also has a low specific surface area, low powder impedance, and high electronic conductivity. Furthermore, the present invention further optimizes the carbon coating coefficient of the positive electrode material by regulating the type, average molecular weight, and addition amount of the second carbon source, the temperature of the second sintering, and the particle size of the first and second grinding processes.

[0164] Test Example 1

[0165] Assemble the button cell battery:

[0166] The positive electrode materials prepared in the above examples and comparative examples, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in deionized water at a mass ratio of 90:5:5. The resulting positive electrode slurry was coated on aluminum foil and dried. The slurry was then stamped into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm using a pressure of 100 MPa. The positive electrode sheet was then placed in a vacuum drying oven and dried at 120° C. for 12 h.

[0167] The negative electrode uses a Li metal sheet with a diameter of 17 mm and a thickness of 1 mm; the diaphragm uses a polyethylene porous membrane with a thickness of 25 μm; and the electrolyte uses an equal mixture of 1 mol / L LiPF6, ethylene carbonate (EC) and diethyl carbonate (DEC).

[0168] The positive electrode sheet, separator, negative electrode sheet and electrolyte were assembled into a 2025 button cell in an Ar gas glove box with a water content and an oxygen content of less than 5 ppm. The cell at this time was regarded as an unactivated cell.

[0169] The performance evaluation of the button battery is defined as follows: after the button battery is made, it is placed for 2 hours. After the open circuit voltage stabilizes, the positive electrode is charged with a current density of 0.1C to a cutoff voltage of 4.25V, then charged at a constant voltage for 30 minutes, and then discharged with the same current density to a cutoff voltage of 2.5V; the same method is repeated once, and the battery at this time is regarded as an activated battery.

[0170] The cycle test is as follows: using activated batteries, the current density is 1C in the voltage range of 2.5-4.25V, and the temperature is 25℃, and the charge and discharge are continuously performed for 80 cycles. The changes in the average discharge voltage and specific energy of the material during the cycle are statistically analyzed. The test data are listed in Table 2.

[0171] The charge and discharge curves of the button cell assembled with the positive electrode material P1 of Example 1 before and after 80 cycles are as follows: Figure 4 As shown by Figure 4It can be seen that the average discharge voltage and specific capacity of the positive electrode material P1 of Example 1 in the first cycle and the 80th cycle are not much different, that is, the positive electrode material provided by the present invention has stable and efficient long-term electrochemical performance.

[0172] Table 2

[0173]

[0174] It can be seen from the results in Table 2 that, compared with Comparative Examples 1-2, the button-type batteries assembled with the positive electrode materials provided by the present invention have higher average discharge voltage after 80 cycles and higher specific energy after 80 cycles, that is, the button-type batteries assembled with the positive electrode materials provided by the present invention have excellent long-term electrochemical properties, especially long-term cycle life.

[0175] Test Example 2

[0176] The positive electrode materials prepared in the above embodiments and comparative examples were respectively subjected to structural stability tests. The specific test method is as follows: 1.00±0.01g of the positive electrode material sample was accurately weighed in a 150mL beaker, and then 100mL of 0.01mol / L hydrochloric acid was measured with a measuring cylinder. The beaker was sealed with a PE film, placed on a digital magnetic stirrer, adjusted to 850rmp / min, stirred for 30min, removed, and placed in an ultrasonic device for 2min. The ultrasonically treated sample was placed in a constant temperature water bath at 25±0.1℃ and taken out after 2h.

[0177] The sample solution was placed on a filtration device. After all the filtrates were completely filtered (filter membrane specification: 0.1 μm), the beaker was rinsed with 10 mL of water and the washing liquid was poured into the filtration bottle to continue filtration. Then 2 mL of concentrated nitric acid was added and all the filtrates were diluted to a 200 mL volumetric flask. The sample after the diluted volume was taken for ICP-Mn and Fe element content (ppm) test. The Mn and Fe dissolution test data are listed in Table 3.

[0178] Table 3

[0179] Mn element dissolution amount, ppm Fe element dissolution amount, ppm Example 1 55 23 Example 2 38 32 Example 3 72 19 Example 4 34 57 Example 5 43 24 Example 6 47 31 Example 7 78 64 Example 8 59 54 Example 9 63 59 Example 10 73 55 Example 11 75 64 Example 12 79 53 Comparative Example 1 372 256 Comparative Example 2 137 109

[0180] The results in Table 3 show that the cathode material provided by the present invention has lower Mn and Fe dissolution amounts than Comparative Examples 1-2. In other words, the cathode material provided by the present invention has higher structural stability.

[0181] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A lithium manganese iron phosphate positive electrode material, characterized in that: The positive electrode material includes a lithium manganese iron phosphate matrix and carbon coated on the surface of the lithium manganese iron phosphate matrix; the carbon coating coefficient k of the positive electrode material satisfies: 1800≤k≤3500; Wherein, k=(S×d×ρ) / (c), S represents the specific surface area of the positive electrode material, m 2 / g; d represents the average primary particle size of the positive electrode material, nm; ρ represents the true density of the positive electrode material, g / cm 3 ; c represents the carbon content of the positive electrode material, wt%; Wherein, the specific surface area S of the positive electrode material is 5-15m 2 / g; the average primary particle size d of the positive electrode material is 70-120nm; the true density ρ of the positive electrode material is 4.2-4.4g / cm 3 ; The carbon content c of the positive electrode material is 1.2-2.3wt%.

2. The positive electrode material according to claim 1, wherein The carbon coating coefficient k of the positive electrode material satisfies: 2000≤k≤3500.

3. The positive electrode material according to claim 2, wherein The carbon coating coefficient k of the positive electrode material satisfies: 2204≤k≤3140.

4. The positive electrode material according to claim 1, wherein The specific surface area S of the positive electrode material is 8-13m 2 / g; And / or, the true density ρ of the positive electrode material is 4.3-4.35 g / cm 3 ; And / or, 0<the carbon coating thickness of the positive electrode material≤50nm.

5. The positive electrode material according to claim 4, wherein The carbon coating thickness of the positive electrode material is 5-25 nm.

6. The positive electrode material according to claim 1, wherein The lithium manganese iron phosphate matrix has a composition shown in Formula I: Li a Mn 1-x Fe x M b (PO4) c (I), wherein M is selected from at least one of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd; 1≤a≤1.1; 0<x<1; 0≤b≤0.2; 1≤c≤1.1; And / or, the average primary particle size of the lithium manganese iron phosphate matrix is 50-200 nm.

7. The positive electrode material according to claim 6, wherein In Formula I, M is selected from at least one of Ti, W, Co, V and Mg; 1≤a≤1.05; 0.1≤x≤0.5; 0.1≤b≤0.2; 1≤c≤1.05; And / or, the average primary particle size of the lithium manganese iron phosphate matrix is 70-120 nm.

8. The positive electrode material according to any one of claims 1 to 7, wherein The powder impedance of the positive electrode material is 10-500 Ω·cm.

9. The positive electrode material according to claim 8, wherein The powder impedance of the positive electrode material is 20-50 Ω·cm.

10. A method for preparing the lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The preparation method comprises the following steps: (1) a Li source, a Mn source, a Fe source, a M source, a P source, a first carbon source, and water are first mixed to obtain a first mixed slurry; (2) subjecting the first mixed slurry to a first grinding and a first spray drying, and then to a first sintering in a protective atmosphere to obtain a lithium manganese iron phosphate matrix having the formula I; (3) performing a second mixing of the lithium manganese iron phosphate matrix, a conductive polymer as a second carbon source, and water to obtain a second mixed slurry; (4) subjecting the second mixed slurry to a second grinding and a second spray drying, and then to a second sintering in a protective atmosphere to obtain a lithium manganese iron phosphate positive electrode material; Among them, Li a Mn 1-x Fe x M b (PO4) c (I), M is at least one selected from the group consisting of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd; 1≤a≤1.1; 0<x<1; 0≤b≤0.2; 1≤c≤1.1; Wherein, the average molecular weight of the second carbon source is ≥10 4 g / mol.

11. The preparation method according to claim 10, wherein In step (1), Calculated as elements, the amounts of the Li source, Mn source, Fe source, M source, P source and first carbon source satisfy n(Li):n(Mn):n(Fe):n(M):n(P):n(C), wherein 1≤n(Li)≤1.1, 0<n(Mn)<1, 0<n(Fe)<1, 0≤n(M)≤0.2, 1≤n(P)≤1.1, 0<n(C)≤0.1; and / or, the Li source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate and lithium chloride; And / or, the Mn source is selected from at least one of manganese tetraoxide, manganese dioxide, manganese carbonate, manganese oxalate, manganese chloride, manganese sulfate and manganese nitrate; And / or, the Fe source is selected from at least one of ferrous oxalate, ferrous oxalate, ferrous acetate, ferric acetate, ferrous nitrate, ferric nitrate, ferric phosphate, ferric oxide, ferrous sulfate, ferric sulfate, ferrous chloride and ferric chloride; and / or, the M source is selected from at least one of oxides, carbonates, and phosphides containing Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd; and / or, the P source is at least one selected from phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate and sodium dihydrogen phosphate; and / or, the first carbon source is at least one selected from citric acid, glucose, sucrose, soluble starch, salicylic acid, tartaric acid, oxalic acid and polyethylene glycol; In step (2), And / or, regulating the particle size D of the first grinding 50 1 0.2-0.6μm And / or, the first spray drying conditions include: air inlet temperature of 180-300°C; air outlet temperature of 85-115°C; And / or, the first sintering conditions include: temperature T1 of 350-650° C.; heating rate V1 of 0.5-10° C. / min; time t1 of 0.1-10 h; And / or, the lithium manganese iron phosphate matrix is composed of primary particles, and the particle size of the primary particles is 50-200 nm.

12. The preparation method according to claim 11, wherein In step (1), 1≤n(Li)≤1.05, 0.5≤n(Mn)≤0.9, 0.1≤n(Fe)≤0.5, 0.1≤n(M)≤0.2, 1≤n(P)≤1.05, 0.01≤n(C)≤0.05; In step (2), And / or, regulating the particle size D of the first grinding 50 1 0.3-0.5μm; And / or, the first spray drying conditions include: air inlet temperature of 200-260°C; air outlet temperature of 95-105°C; And / or, the first sintering conditions include: temperature T1 of 400-600° C.; heating rate V1 of 1-5° C. / min; and time t1 of 0.1-5 h.

13. The preparation method according to claim 10, wherein In step (3), The average molecular weight of the second carbon source is (1.5-3.5)×10 4 g / mol; And / or, the second carbon source is selected from substituted and / or unsubstituted polymers, and the polymer is selected from at least one of polyaniline, polypyrrole, polyacetylene and polyvinyl alcohol, and the substituent group in the substituted polymer is selected from at least one of amino, hydroxyl, thiol, C1-C5 alkyl, heteroatom and halogen; And / or, the mass ratio of the lithium manganese iron phosphate matrix to the second carbon source is 1:0.01-0.1; In step (4), And / or, regulating the particle size D of the second grinding 50 2 0.1-0.4μm; And / or, the second spray drying conditions include: air inlet temperature of 180-300°C; air outlet temperature of 85-115°C; And / or, the second sintering conditions include: temperature T2 of 550-850° C.; heating rate V2 of 0.5-10° C. / min; and time t2 of 6-16 h.

14. The preparation method according to claim 13, wherein In step (3), And / or, the mass ratio of the lithium manganese iron phosphate matrix to the second carbon source is 1:0.03-0.08; In step (4), And / or, regulating the particle size D of the second grinding 50 2 0.15-0.25μm; And / or, the second spray drying conditions include: air inlet temperature of 200-245°C; air outlet temperature of 95-105°C; And / or, the second sintering conditions include: temperature T2 of 650-800° C.; heating rate V2 of 1-5° C. / min; and time t2 of 8-12 h.

15. A positive electrode plate, characterized in that: The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 9.

16. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 15.

Images