Manganese iron phosphate precursor, preparation method therefor, positive electrode material, electrode sheet and battery

Abstract

A manganese iron phosphate precursor, a preparation method therefor, a positive electrode material, an electrode sheet, and a battery. The formula of the manganese iron phosphate precursor is (NH4)(3-2x-2y)FexMnyPO4•H2O, wherein 0 < x < 1, and 0 < y < 1. The manganese iron phosphate precursor satisfies the following conditions: the average particle size is 2.0μm to 2.5μm, the D50 particle size is 1.6μm to 2.0μm, and the span is 0.4-0.7.

Description

Manganese iron phosphate precursor, preparation method thereof, positive electrode material, electrode sheet and battery

[0001] Related applications

[0002] The present application claims priority to the Chinese patent application No. 2024107263923, filed on June 5, 2024, entitled "A lithium manganese iron phosphate positive electrode material precursor, a preparation method thereof and a positive electrode material", the contents of which are hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of battery materials, in particular to a manganese iron phosphate precursor, a preparation method thereof, a positive electrode material, an electrode sheet and a battery. BACKGROUND

[0004] The large-scale use of traditional fossil fuels has led to increasingly serious problems such as resource shortage and environmental pollution, and accelerating the transformation of energy structure has become an important goal. Among them, developing energy storage devices with high efficiency, high energy density and low cost to help the electrification of automobiles is a key measure to achieve this goal.

[0005] At present, lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP) with olivine structure have attracted widespread attention in the market due to their high safety, good electrochemical performance and relatively low cost. Compared with LFP, LMFP has higher energy density and higher voltage platform. In addition, the cost of manganese raw material is low, and LMFP has more advantages in terms of price. In addition, compared with another ternary material, LMFP has long cycle life, good thermal stability, high safety and no explosion risk.

[0006] The preparation method of LMFP is similar to that of LFP. Common preparation methods include solid phase method, sol-gel method, hydrothermal method and co-precipitation method. The steps of co-precipitation method for preparing LMFP are generally as follows: first, mix manganese source and iron source, add precipitator and complexing agent for co-precipitation reaction to obtain precipitate, then wash and dry the precipitate to obtain a precursor, and finally mix the precursor with lithium source and calcine to obtain LMFP positive electrode material. This method mainly includes two steps of liquid phase co-precipitation (crystal nucleation and growth) and high temperature calcination. The morphology and structure characteristics of the precursor and the positive electrode material ultimately affect the electrochemical properties of the positive electrode material. The advantages of this method are simple operation, low equipment requirement and short reaction time, which is suitable for large-scale preparation. However, the technical difficulty lies in how to control the operation conditions during the co-precipitation preparation process to make Fe and Mn metal ions reach atomic or molecular level mixing, so as to obtain a manganese iron phosphate precursor with regular and uniform morphology and excellent performance, and thus obtain an LMFP positive electrode material with excellent performance.

[0007] Therefore, there is an urgent need to provide a preparation method capable of preparing manganese iron phosphate precursors with regular and uniform morphology and excellent performance.

[0008] SUMMARY

[0009] Based on this, according to various embodiments of the present application, a manganese iron phosphate precursor and a preparation method thereof, a positive electrode material, a pole piece and a battery are provided, and the technical solutions are as follows:

[0010] In a first aspect, the embodiments of the present application provide a manganese iron phosphate precursor, and the expression of the manganese iron phosphate precursor is (NH4) (3-2x-2y) Fe x Mn y PO4·H2O, wherein 0 < x < 1 and 0 < y < 1.

[0011] The manganese iron phosphate precursor satisfies: the average particle size is 2.0 μm to 2.5 μm, the D50 particle size is 1.6 μm to 2.0 μm, and the span is 0.4 to 0.7.

[0012] In some embodiments, the primary particles of the manganese iron phosphate precursor have an olivine morphology, and the length to width ratio of the manganese iron phosphate precursor is (2 to 2.5) : (1 to 1.5).

[0013] In some embodiments, the tap density of the manganese iron phosphate precursor is 1.4 g / cm 3 to 1.8 g / cm 3 , the specific surface area is 25 m 2 / g to 30 m 2 / g.

[0014] In a second aspect, the embodiments of the present application provide a preparation method of a manganese iron phosphate precursor, including the following steps:

[0015] providing a first mixed solution, a second mixed solution, a precipitant solution and a buffer base solution; and

[0016] adding the first mixed solution, the second mixed solution and the precipitant solution into the buffer base solution at the same time to perform a co-precipitation reaction, and performing aging treatment, washing treatment and drying treatment to prepare the manganese iron phosphate precursor;

[0017] wherein the pH value in the co-precipitation reaction is greater than 3.5 and less than 5;

[0018] The first mixed solution contains ferrous salt, manganese salt and a first complexing agent;

[0019] The second mixed solution contains a second complexing agent and a first precipitant;

[0020] The precipitant solution contains a second precipitant;

[0021] The buffer solution contains a third precipitant and a third complexing agent;

[0022] The first complexing agent and the second complexing agent are different from each other;

[0023] The third complexing agent comprises one or more of the first complexing agent and the second complexing agent.

[0024] In some embodiments, the ferrous salt comprises one or more of ferrous sulfate, ferrous nitrate, ferrous oxalate, and ferrous chloride.

[0025] In some embodiments, the manganese salt comprises one or more of manganese sulfate, manganese nitrate, manganese acetate, manganese oxalate, and manganese chloride.

[0026] In some embodiments, the first complexing agent comprises one or more of citric acid, sodium citrate, ascorbic acid, lactic acid, and malic acid.

[0027] In some embodiments, the second complexing agent comprises one or more of ammonia, ethylenediaminetetraacetic acid, diisopropylamino tetraacetic acid, and tris(2-aminoethyl)triacetic acid.

[0028] In some embodiments, the third complexing agent comprises one or more of citric acid, sodium citrate, ammonia, ascorbic acid, lactic acid, and malic acid.

[0029] In some embodiments, the first precipitant, the second precipitant, and the third precipitant each independently comprises one or more of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0030] In some embodiments, the total concentration of manganese ions and ferrous ions is 10 g / L to 120 g / L.

[0031] In some embodiments, the molar ratio of ferrous ions to manganese ions is 1:(0.01 to 100).

[0032] In some embodiments, the concentration of the first complexing agent is 2 g / L to 10 g / L.

[0033] In some embodiments, the concentration of the second complexing agent is 5 g / L to 120 g / L.

[0034] In some embodiments, the mass ratio of the second complexing agent to the first precipitant is 1:(0.2 to 0.6).

[0035] In some embodiments, the concentration of the second precipitant in the precipitant solution is 10 g / L to 120 g / L.

[0036] In some embodiments, the concentration of the third complexing agent is 2 g / L-10 g / L.

[0037] In some embodiments, the concentration of the third precipitant is 6 g / L-80 g / L.

[0038] In some embodiments, the molar ratio of the third complexing agent to the third precipitant is 1:(1-8).

[0039] In some embodiments, the pH value of the buffer stock solution is 2-6.

[0040] In some embodiments, the volume ratio of the first mixed solution, the second mixed solution, the second mixed solution to the buffer stock solution is (1-3):(2-9):(2-9):1.

[0041] In some embodiments, the temperature of the co-precipitation reaction is 50°C-60°C, and the time of the co-precipitation reaction is 2 h-24 h.

[0042] In some embodiments, the temperature of the aging treatment is 50°C-60°C, and the time of the aging treatment is 1 h-6 h.

[0043] In a third aspect, the embodiments of the present application provide a lithium iron manganese phosphate positive electrode material, and an expression of the lithium iron manganese phosphate positive electrode material is LiFe x Mn 1-x PO4 / C, wherein 0 < x < 1.

[0044] The lithium iron manganese phosphate positive electrode material satisfies: the average particle size is 1.5 μm-1.7 μm, the D50 particle size is 1.5 μm-1.7 μm, and the span is 1.9-2.3.

[0045] In some embodiments, the primary particles of the lithium iron manganese phosphate positive electrode material have irregular spherical morphology.

[0046] In some embodiments, the tap density of the lithium iron manganese phosphate positive electrode material is 2.0 g / cm 3 -2.2 g / cm 3 .

[0047] In some embodiments, the specific surface area of the lithium iron manganese phosphate positive electrode material is 12 m 2 / g-23 m 2 / g.

[0048] In a fourth aspect, the embodiments of the present application provide a positive electrode sheet, which comprises the lithium iron manganese phosphate positive electrode material provided in the third aspect of the present application.

[0049] In a fifth aspect, the embodiments of the present application provide a secondary battery, which comprises the positive electrode sheet provided in the fourth aspect of the present application.

[0050] The details of one or more embodiments of the application are set forth in the description below, and other features, objects, and advantages of the application will be apparent from the description and the claims. BRIEF DESCRIPTION OF DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort based on the disclosed drawings.

[0052] FIG. 1 is a process flow diagram of an embodiment of the preparation method of the manganese iron phosphate precursor provided by the embodiments of the present application;

[0053] FIG. 2 is a scanning electron microscope (SEM) morphology result diagram of the manganese iron phosphate precursor obtained in Example 1 of the present application;

[0054] FIG. 3 is a scanning electron microscope (SEM) morphology result diagram of the manganese iron phosphate precursor obtained in Example 4 of the present application;

[0055] FIG. 4 is a scanning electron microscope (SEM) morphology result diagram of the manganese iron phosphate precursor obtained in Comparative Example 1 of the present application;

[0056] FIG. 5 is a scanning electron microscope (SEM) morphology result diagram of the manganese iron phosphate precursor obtained in Comparative Example 7 of the present application;

[0057] FIG. 6 is a scanning electron microscope (SEM) morphology result diagram of the manganese iron phosphate precursor obtained in Comparative Example 8 of the present application;

[0058] FIG. 7 is a scanning electron microscope (SEM) morphology result diagram of the manganese iron phosphate precursor obtained in Comparative Example 9 of the present application;

[0059] FIG. 8 is a scanning electron microscope (SEM) morphology result diagram of the LMFP positive electrode material obtained in Example 1 of the present application;

[0060] FIG. 9 is a scanning electron microscope (SEM) morphology result diagram of the LMFP positive electrode material obtained in Example 4 of the present application;

[0061] FIG. 10 is a scanning electron microscope (SEM) morphology result diagram of the LMFP positive electrode material obtained in Comparative Example 1 of the present application;

[0062] Fig. 11 is a scanning electron microscope (SEM) morphology result diagram of the LMFP positive electrode material obtained in Comparative Example 7 of the present application;

[0063] Fig. 12 is a scanning electron microscope (SEM) morphology result diagram of the LMFP positive electrode material obtained in Comparative Example 8 of the present application;

[0064] Fig. 13 is a scanning electron microscope (SEM) morphology result diagram of the LMFP positive electrode material obtained in Comparative Example 9 of the present application;

[0065] Fig. 14 is an X-ray diffraction (XRD) result diagram of the manganese iron phosphate precursor obtained in Example 4 of the present application;

[0066] Fig. 15 is an X-ray diffraction (XRD) result diagram of the LMFP positive electrode material obtained in Example 4 of the present application;

[0067] Fig. 16 is the rate performance of the LMFP positive electrode material obtained in Example 1 of the present application at 2-4.35V;

[0068] Fig. 17 is the rate performance of the LMFP positive electrode material obtained in Example 4 of the present application at 2-4.35V;

[0069] Fig. 18 is the rate performance of the LMFP positive electrode material obtained in Comparative Example 1 of the present application at 2-4.35V. DETAILED DESCRIPTION

[0070] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0071] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The use of the terms "including," "comprising," or "having" and any variations thereof in the specification and in the claims are not intended to imply or create any limitations on the contents of the application. The use of the term "or" in the

[0072] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0073] Reference to an "embodiment" herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase that the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. As will be apparent to those of ordinary skill in the art, embodiments described herein can be combined with one another.

[0074] In the description of the embodiments of the present application, the term "and / or" is merely an association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0075] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0076] The term

[0077] Unless otherwise stated or contradictory, the terms or phrases used in the present application have the following meanings:

[0078] Particle size: for spherical particles, the particle size refers to the diameter of the spherical particles. For non-spherical particles, such as particles with olivine morphology, the particle size generally refers to the equivalent particle size (generally referred to as particle size) of the non-spherical particles, and the particle size measured by the laser particle size analyzer is the equivalent diameter of the particle. Among them, the equivalent particle size refers to that the physical property of a particle is the same or similar to that of a homogeneous spherical particle, and the diameter of the spherical particle is used to represent the diameter of the actual particle. Unless otherwise stated or contradictory, the particle size in the present application represents the equivalent particle size.

[0079] Particle size distribution parameter: in the particle size distribution curve of the particles, the particle size corresponding to the cumulative particle size distribution percentage reaching N% is called DN particle size, which means that the particles smaller than the particle size account for N% of all particles, wherein N = 0-100. When N = 100, D100 particle size represents the particle size corresponding to the cumulative particle size distribution percentage reaching 100%. When N = 50, D50 particle size is the particle size corresponding to the cumulative particle size distribution percentage reaching 50%, which represents the median particle size or median diameter, indicating that the particles smaller and larger than the particle size each account for 50%. For example, D50 particle size = 1mm, which means that the particles with particle size smaller than 1mm and the particles with particle size larger than 1mm each account for 50% of all particles.

[0080] Span: also known as span, the calculation formula is: span=(D90-D10)÷D50. The smaller the span, the more concentrated the particle size distribution of the particles; the larger the span, the greater the difference in particle size, the more dispersed the distribution.

[0081] The co-precipitation method is a commonly used method for preparing positive electrode materials, and high-performance LMFP positive electrode materials can be prepared by this method. The steps of preparing LMFP by co-precipitation method are generally as follows: first, mix manganese source, iron source, etc., then add precipitants and complexing agents for co-precipitation reaction, and finally wash, dry the precipitate, mix with lithium source and calcine to obtain LMFP positive electrode material. In the process of preparing lithium manganese iron phosphate by co-precipitation method, the operating conditions in the co-precipitation preparation process need to be controlled to make Fe and Mn two kinds of metal ions reach atomic or molecular level mixing, so as to obtain manganese iron phosphate precursor with regular and uniform morphology and excellent performance, thereby obtaining LMFP positive electrode material with excellent performance.

[0082] In order to solve the technical problems of the product morphology being non-uniform and the performance being poor of the manganese iron phosphate precursor prepared by the co-precipitation method in the prior art, the present application provides a manganese iron phosphate precursor, a preparation method thereof, a positive electrode material, a pole piece and a battery. The manganese iron phosphate precursor provided by the present application has the advantages of regular morphology, uniform particle size distribution and uniform distribution of metal elements in the crystal lattice; the manganese iron phosphate precursor is prepared by co-precipitation method, and the addition mode of salt, precipitant and complexing agent and the reaction pH value in the co-precipitation process are adjusted to control the morphology of the precursor, so that the morphology of the precursor is regular, the particle size distribution is uniform, and the metal elements are uniformly distributed in the crystal lattice; the LMFP positive electrode material prepared from the manganese iron phosphate precursor has high specific capacity and good rate performance, and the specific capacity and rate performance of the positive electrode pole piece and the secondary battery are also improved.

[0083] In a first aspect, the embodiments of the present application provide a manganese iron phosphate precursor, the expression of the manganese iron phosphate precursor is (NH4) (3-2x-2y) Fe x Mn y PO4·H2O, wherein 0

[0084] The manganese iron phosphate precursor satisfies: the average particle size is 2.0 μm-2.7 μm, the D50 particle size is 1.6 μm-2.0 μm, and the span is 0.4-0.7.

[0085] The manganese iron phosphate precursor provided in the application has the advantages of regular morphology, uniform particle size distribution and uniform distribution of metal elements in the crystal lattice. Compared with the irregular and fragmented manganese iron phosphate precursor, the manganese iron phosphate precursor provided in the application has more excellent performance, is beneficial to the preparation of lithium manganese iron phosphate positive electrode material with higher specific discharge capacity and higher rate performance, and is suitable for large-scale industrial application.

[0086] In the application, the value of x includes but is not limited to 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, etc., and the value of y includes but is not limited to 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, etc.

[0087] Further, in some embodiments, 0<3-2x-2y≤1, including but not limited to 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 1, etc.

[0088] In the application, the average particle size of the manganese iron phosphate precursor is 2.0 μm to 2.5 μm, including but not limited to 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, etc. In some embodiments, the average particle size of the manganese iron phosphate precursor is further preferably 2.0 μm to 2.4 μm.

[0089] In the application, the D50 particle size of the manganese iron phosphate precursor is 1.6 μm to 2.0 μm, including but not limited to 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, etc. In some embodiments, the D50 particle size of the manganese iron phosphate precursor is further preferably 1.7 μm to 1.9 μm.

[0090] Further, in some embodiments, the D10 particle size of the manganese iron phosphate precursor is 1.2 μm to 1.7 μm, including but not limited to 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, etc. In some embodiments, the D10 particle size of the manganese iron phosphate precursor is further preferably 1.4 μm to 1.7 μm.

[0091] Further, in some embodiments, the D90 particle size of the manganese iron phosphate precursor is 2.2 μm to 2.8 μm, including but not limited to 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, etc. In some embodiments, the D90 particle size of the manganese iron phosphate precursor is further preferably 2.4 μm to 2.7 μm.

[0092] In the present application, the span of the manganese iron phosphate precursor is 0.4-0.7, including but not limited to 0.4, 0.42, 0.45, 0.48, 0.5, 0.52, 0.55, 0.58, 0.6, 0.62, 0.65, 0.68, 0.7, etc. In some embodiments, the span of the manganese iron phosphate precursor is further preferably 0.42-0.67.

[0093] In the technical scheme of the embodiments of the present application, the span of the manganese iron phosphate precursor is controlled in the range of 0.4-0.7, so that the particle size distribution concentration of the manganese iron phosphate precursor is high, which is beneficial to improve the processing performance and enhance the performance stability.

[0094] Further, in some embodiments, the primary particles of the manganese iron phosphate precursor have an olivine morphology, and the ratio of the length to the width of the manganese iron phosphate precursor is (2-2.5):(1-1.5), including but not limited to 2:1, 2:1.2, 2:1.5, 2.2:1, 2.2:1.2, 2.2:1.5, 2.4:1, 2.4:1.2, 2.4:1.5, 2.5:1, 2.5:1.2, 2.5:1.5, etc.

[0095] In the technical scheme of the embodiments of the present application, the primary particles of the manganese iron phosphate precursor all exhibit uniform and regular olivine morphology, and the ratio of the length to the width is controlled in the range of (2-2.5):(1-1.5), so that the lithium ion migration path is shortened, which is beneficial to the extraction and embedding of lithium ions, thereby improving the electrochemical performance of the material.

[0096] In some embodiments, the length and width of the manganese iron phosphate precursor can be obtained after morphology characterization by SEM.

[0097] Further, in some embodiments, the tap density of the manganese iron phosphate precursor is 1.4 g / cm 3 -1.8 g / cm 3 , including but not limited to 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , etc. In some embodiments, the tap density of the manganese iron phosphate precursor is further preferably 1.587 g / cm 3 -1.752 g / cm 3 .

[0098] In the technical scheme of the embodiments of the present application, the manganese iron phosphate precursor has a high compaction density. On the one hand, the high compaction density of the precursor plays a decisive role in preparing a LMFP positive electrode material with high compaction density, thereby being conducive to improving the specific discharge capacity, rate performance and energy density of the material. On the other hand, the delivery amount can be increased without increasing the transportation volume, the material transportation and feeding efficiency can be improved, and the operation cost can be saved.

[0099] Further, in some embodiments, the specific surface area of the manganese iron phosphate precursor is 25 m 2 / g to 30 m 2 / g, including but not limited to 25 m 2 / g, 26 m 2 / g, 27 m 2 / g, 28 m 2 / g, 29 m 2 / g, 30 m 2 / g, etc. In some embodiments, the specific surface area of the manganese iron phosphate precursor is further preferably 25.43 m 2 / g to 29.88 m 2 / g.

[0100] In the technical scheme of the embodiments of the present application, the manganese iron phosphate precursor has a moderate specific surface area. The specific surface area is not too large to cause too many gaps between particles, thereby hindering the improvement of the compaction density. The specific surface area is not too small to cause the particle size to be too large, thereby affecting the embedding and de-embedding of lithium ions.

[0101] The primary particles of the manganese iron phosphate precursor provided in the present application exhibit an olivine morphology, have the advantages of regular morphology, uniform particle size distribution, and uniform distribution of metal elements in the crystal lattice. Compared with the manganese iron phosphate precursor with irregular morphology and in the form of fragments, the manganese iron phosphate precursor provided in the present application has smaller particle size, moderate specific surface area, and higher compaction density, and therefore has more excellent electrochemical performance. It is conducive to preparing a LMFP positive electrode material with higher specific discharge capacity and higher rate performance, and is suitable for large-scale industrial application.

[0102] Referring to FIG. 1, in a second aspect, the present application provides a preparation method of a manganese iron phosphate precursor, comprising the following steps:

[0103] S1, providing a first mixed solution, a second mixed solution, a precipitant solution, and a buffer base solution; and,

[0104] S2, simultaneously adding the first mixed solution, the second mixed solution and the precipitant solution into the buffer base solution to perform a co-precipitation reaction, and performing aging treatment, washing treatment and drying treatment to prepare a manganese iron phosphate precursor;

[0105] The pH value in the coprecipitation reaction is greater than 3.5 and less than 5.

[0106] The first mixed solution contains ferrous salt, manganese salt and a first complexing agent;

[0107] The second mixed solution contains a second complexing agent and a first precipitant;

[0108] The precipitant solution contains a second precipitant;

[0109] The buffer base solution contains a third precipitant and a third complexing agent;

[0110] The first complexing agent and the second complexing agent are different from each other;

[0111] The third complexing agent comprises one or more of the first complexing agent and the second complexing agent.

[0112] In addition to the control of the conventional reaction conditions (reaction time, reaction temperature and rotation speed), the present application focuses on the matching of "salt solution-complexing agent-precipitant" and its coordination with the pH value of the reaction process. Specifically, by pre-mixing the salt with the complexing agent, the present application stabilizes the precipitation and crystallization process of manganese and iron elements; by pre-mixing different complexing agents with precipitants and using them as the second mixed solution and the buffer base solution respectively, the present application quickly stabilizes the pH value of the reaction system and has complexing effect, realizes the steady state of the precipitation reaction process and the liquid phase mass transfer process, and has good control over the morphology of the precipitate after the reaction, solves the problems of uneven particle composition and particle morphology in the coprecipitation process, and successfully prepares a manganese iron phosphate precursor with uniform distribution of Mn / Fe in the crystal lattice, regular particle morphology, uniform particle size distribution and excellent performance. At the same time, by washing and drying the aged material, the residual metal ions, ammonium ions and sulfate ions and other impurity ions on the surface of the material can be removed to avoid their influence on the subsequent lithium content and the formation of the LMFP positive electrode material. In addition, the present application has the advantages of simple operation, easy control of reaction conditions, low cost and the like, and is suitable for large-scale industrial production.

[0113] Further, in some embodiments, in step S1, the ferrous salt comprises one or more of ferrous sulfate, ferrous nitrate, ferrous oxalate and ferrous chloride; typical but non-limiting combinations include a combination of ferrous sulfate and ferrous nitrate, a combination of ferrous sulfate and ferrous oxalate, a combination of ferrous sulfate and ferrous chloride, a combination of ferrous sulfate, ferrous nitrate, ferrous oxalate and ferrous chloride.

[0114] Further, in some embodiments, in step S1, the manganese salt comprises one or more of manganese sulfate, manganese nitrate, manganese acetate, manganese oxalate, and manganese chloride; typical but non-limiting combinations include a combination of manganese sulfate and manganese nitrate, a combination of manganese sulfate and manganese acetate, a combination of manganese sulfate and manganese oxalate, a combination of manganese sulfate and manganese chloride, a combination of manganese nitrate and manganese acetate, a combination of manganese nitrate and manganese oxalate, a combination of manganese nitrate and manganese chloride, a combination of manganese acetate and manganese oxalate, a combination of manganese acetate and manganese chloride, a combination of manganese oxalate and manganese chloride, a combination of manganese sulfate, manganese nitrate, and manganese acetate, or a combination of manganese sulfate, manganese nitrate, manganese acetate, manganese oxalate, and manganese chloride.

[0115] Further, in some embodiments, in step S1, the first complexing agent comprises one or more of citric acid, sodium citrate, ascorbic acid, lactic acid, and malic acid; typical but non-limiting combinations include a combination of citric acid and sodium citrate, a combination of citric acid and ascorbic acid, a combination of citric acid and lactic acid, and a combination of citric acid and malic acid.

[0116] In the technical solution of the embodiments of the present application, by selecting the above-mentioned first complexing agent, the ferrous ions can be preferentially complexed instead of manganese ions, thereby inhibiting the oxidation of ferrous ions.

[0117] Further, in some embodiments, in step S1, the total concentration of manganese ions and ferrous ions in the first mixed solution is 10 g / L to 120 g / L, including but not limited to any one of 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, or 120 g / L, or a range value between any two of them.

[0118] In the technical solution of the embodiments of the present application, by selecting the above-mentioned concentration range of manganese ions and ferrous ions, the co-precipitation of manganese and iron can be achieved, and too high ion concentration can easily cause partial oxidation of ferrous ions, resulting in element segregation, and too low ion concentration can cause reduced precipitation efficiency.

[0119] The present application does not limit the molar ratio of ferrous ions to manganese ions in the first mixed solution, and those skilled in the art can adjust it according to the actual process. Further, in some embodiments, the molar ratio of ferrous ions to manganese ions is 1:(0.01 to 100), including but not limited to any one of 1:0.01, 1:0.1, 1:1, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, or a range value between any two of them.

[0120] Further, in some embodiments, in step S1, the concentration of the first complexing agent in the first mixed solution is 2-10 g / L, including but not limited to any one of 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L or a range value between any two of them.

[0121] In the technical scheme of the embodiments of the present application, by selecting the concentration range of the first complexing agent, the ferrous ions can be effectively complexed to prevent the ferrous ions from being oxidized before participating in the reaction. If the concentration of the first complexing agent is too high, the precipitation rate of part of the ferrous ions in the co-precipitation process will be reduced, and if the concentration is too low, it is not conducive to protecting the ferrous ions in the first mixed solution.

[0122] Further, in some embodiments, in step S1, the second complexing agent includes one or more of ammonia, ethylenediaminetetraacetic acid (EDTA), diisopropylamino tetraacetic acid (DTPA) and tris (2-aminoethyl) triacetic acid (TTHA); typical but non-limiting combinations include combinations of ammonia and EDTA, combinations of ammonia and DTPA, combinations of ammonia and TTHA.

[0123] In the technical scheme of the embodiments of the present application, by selecting the above-mentioned second complexing agent, the co-complexing of manganese and iron can be achieved.

[0124] Further, in some embodiments, in step S1, in the second mixed solution, the concentration of the second complexing agent is 5-20 g / L, including but not limited to any one of 5 g / L, 7 g / L, 9 g / L, 11 g / L, 13 g / L, 15 g / L, 17 g / L, 20 g / L, and the concentration of the first precipitant is 1-12 g / L, including but not limited to any one of 1 g / L, 3 g / L, 5 g / L, 7 g / L, 9 g / L, 12 g / L or a range value between any two of them.

[0125] In the technical scheme of the embodiments of the present application, by selecting the concentration range of the second complexing agent, the effective complexing of manganese and iron ions can be achieved. If the concentration of the second complexing agent is too high, the precipitation reaction rate will be reduced, and if the concentration is too low, a heterogeneous manganese-iron co-precipitation precursor is easy to form.

[0126] Further, in some embodiments, in step S1, in the second mixed solution, the mass ratio of the second complexing agent to the first precipitant is 1:(0.2-0.6), including but not limited to any one of 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6 or a range value between any two of them.

[0127] In the technical scheme of the embodiment of the present application, by controlling the ratio of the second complexing agent to the first precipitant in the second mixed solution within the above range, the pH value of the coprecipitation reaction process can be stabilized, and the manganese-iron co-complexing and coprecipitation can be realized. If the ratio is too low, the second mixed solution cannot adjust the pH value. If the ratio is too high, the complexing ability of the second mixed solution to manganese-iron ions is easily reduced, which is not conducive to the homogeneous precipitation of the precursor.

[0128] Further, in some embodiments, in step S1, the concentration of the second precipitant in the precipitant solution is 10 g / L to 120 g / L, including but not limited to any one of 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L or 120 g / L, or a range value between any two of them.

[0129] In the technical scheme of the embodiment of the present application, by selecting the concentration range of the second precipitant in the precipitant solution, uniform nucleation of manganese-iron ions can be realized. If the concentration of the second precipitant is too high, the precursor particles will be large. If the concentration is too low, the coprecipitation reaction rate will be reduced.

[0130] Further, in some embodiments, in step S1, the third complexing agent includes one or more of citric acid, sodium citrate, ammonia, ascorbic acid, lactic acid and malic acid. Typical but non-limiting combinations include combinations of citric acid and sodium citrate, combinations of citric acid and ascorbic acid, combinations of citric acid and lactic acid, and combinations of citric acid and malic acid.

[0131] In the technical scheme of the embodiment of the present application, by selecting the third complexing agent, manganese-iron in the system can be quickly complexed to prevent phase segregation.

[0132] Further, in some embodiments, in step S1, in the buffer base solution, the concentration of the third complexing agent is 2 g / L to 10 g / L, including but not limited to any one of 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, or a range value between any two of them; and the concentration of the third precipitant is 6 g / L to 80 g / L, including but not limited to any one of 6 g / L, 12 g / L, 18 g / L, 24 g / L, 30 g / L, 36 g / L, 42 g / L, 48 g / L, 54 g / L, 60 g / L, 66 g / L, 72 g / L, 78 g / L or 80 g / L, or a range value between any two of them.

[0133] Further, in some embodiments, in step S1, the pH value of the buffer base solution is 2-6, including but not limited to any one of 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 or a range value between any two of them.

[0134] In the technical scheme of the embodiments of the present application, by controlling the pH value of the buffer base solution in the above range, the pH value in the reaction process can be stabilized, and the precipitation of manganese iron in different proportions can be easily realized. Both too high and too low pH values of the buffer base solution will cause crystal phase segregation.

[0135] Further, in some embodiments, in step S1, the molar ratio of the third complexing agent to the third precipitant in the buffer base solution is 1:(1-8), including but not limited to any one of 1:1, 1:3, 1:5, 1:7, 1:8 or a range value between any two of them.

[0136] In the technical scheme of the embodiments of the present application, by controlling the ratio of the third complexing agent to the third precipitant in the buffer base solution in the above range, the pH value required for the reaction can be controlled in the range in which manganese iron can be precipitated, and both too high and too low ratios of the third complexing agent to the third precipitant are not conducive to the rapid stabilization of the pH value in the coprecipitation reaction.

[0137] Further, in some embodiments, in step S1, the first precipitant, the second precipitant and the third precipitant each independently includes one or more of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate and ammonium phosphate; typical but non-limiting combinations include combinations of phosphoric acid and diammonium hydrogen phosphate, combinations of phosphoric acid and ammonium dihydrogen phosphate, combinations of phosphoric acid and diammonium hydrogen phosphate, combinations of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate and ammonium phosphate.

[0138] In the technical scheme of the embodiments of the present application, by selecting the above precipitants, the coprecipitation of manganese iron can be realized, and the pH value in the reaction process can be stabilized to obtain a manganese iron phosphate coprecipitation precursor.

[0139] Further, in some embodiments, in step S1, the process of preparing the first mixed solution includes dissolving the ferrous salt, the manganese salt and the first complexing agent into water to prepare the first mixed solution; the process of preparing the second mixed solution includes dissolving the second complexing agent and the first precipitant into water to prepare the second mixed solution; the process of preparing the precipitant solution includes dissolving the second precipitant into water to prepare the precipitant solution; and the process of preparing the buffer base solution includes dissolving the third complexing agent and the third precipitant into water to prepare the buffer base solution.

[0140] In the present application, during the co-precipitation reaction of step S2, the pH value of the reaction system is greater than 3.5 and less than 5, including but not limited to 3.51, 3.55, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.8, 4.8, 4.9, 4.95, 4.99, etc., which are not limited in the present application.

[0141] Further, in some embodiments, during the co-precipitation reaction of step S2, the pH value of the reaction system is 4-4.5, including but not limited to any one of 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, or a range value between any two of them, and the pH value fluctuation range during the reaction is controlled to be not more than ±0.01.

[0142] In the technical scheme of the embodiments of the present application, by controlling the pH value of the co-precipitation reaction process in this range, different proportions of manganese and iron can be stably co-precipitated; if the pH value is too low, too much iron will be precipitated and too little manganese will be precipitated; if the pH value is too high, too much manganese will be precipitated and too little iron will be precipitated.

[0143] Further, in some embodiments, in step S2, during the co-precipitation reaction, the temperature of the reaction system is 50-60℃, including but not limited to any one of 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, or a range value between any two of them.

[0144] In the technical scheme of the embodiments of the present application, by controlling the temperature of the co-precipitation reaction process in this range, the co-precipitation reaction rate can be accelerated; if the temperature is too low, the reaction rate will be too slow and the reaction degree will be low; if the temperature is too high, the pH meter equipment will be damaged and the precursor will be oxidized.

[0145] In the technical scheme of the embodiments of the present application, during the entire co-precipitation reaction process, the temperature is kept constant and the pH value in the reaction kettle is stable to ensure that the reaction in the solution is fully carried out.

[0146] Further, in some embodiments, in step S2, during the co-precipitation reaction, the time of the co-precipitation reaction is 2-24h, including but not limited to any one of 2h, 6h, 10h, 14h, 18h or 24h, or a range value between any two of them.

[0147] Further, in some embodiments, in step S2, the co-precipitation reaction is carried out under stirring.

[0148] The stirring speed for the coprecipitation reaction is 200 rpm to 1000 rpm, including but not limited to any one of 200 rpm, 400 rpm, 600 rpm, 800 rpm, and 1000 rpm, or any range between two of them.

[0149] In the technical solution of this application embodiment, by controlling the stirring speed of the coprecipitation reaction within this range, it is beneficial to achieve uniform precursor particle size. If the stirring speed is too low, the precursor particles will be difficult to grow, and if the stirring speed is too high, the secondary particle structure of the precursor will be destroyed.

[0150] Furthermore, in some embodiments, in step S2, the coprecipitation reaction is carried out under a protective gas.

[0151] Furthermore, in some embodiments, the protective gas includes nitrogen, helium, neon, argon, xenon, etc.

[0152] Furthermore, in some embodiments, step S2, in which a first mixture, a second mixture, and a precipitant solution are simultaneously added to the buffer base liquid to carry out a coprecipitation reaction, includes: adding the buffer base liquid to the reaction vessel, and then injecting the first mixture, the second mixture, and the precipitant solution in parallel into the reaction vessel, which has been preheated to the coprecipitation reaction temperature and filled with protective gas, using a peristaltic pump, while continuously stirring.

[0153] Parallel-flow injection refers to the simultaneous injection of all solutions into the reactor at identical times, ensuring that all components participate in the reaction at every stage and guaranteeing the homogeneity of the mixed slurry. However, during parallel-flow injection, the flow rates of each component can be the same or different, depending on the specific requirements.

[0154] In the technical solution of this application embodiment, by adopting the above-described injection method, the feeding speed can be controlled more precisely and the pH value in the solution can be stabilized.

[0155] Furthermore, in some embodiments, in step S2, during the co-precipitation reaction, the co-injection time is 2h to 24h, including but not limited to any one of 2h, 6h, 10h, 14h, 18h or 24h, or any range between two of them.

[0156] In the technical solution of this application embodiment, by controlling the injection time within this range, element segregation can be reduced, which is beneficial to the homogenization of the precursor morphology. If the injection time is too short (i.e., the flow rate is too fast), it is difficult to achieve effective co-complexation of manganese and iron. If the injection time is too long (i.e., the flow rate is too slow), the synthesis efficiency will be reduced.

[0157] Further, in some embodiments, in step S2, during the co-precipitation reaction, the flow rate of the first mixed solution is 0.5 mL / min to 5 mL / min, including but not limited to any one of 0.5 mL / min, 1 mL / min, 1.5 mL / min, 2 mL / min, 2.5 mL / min, 3 mL / min, 3.5 mL / min, 4 mL / min, 4.5 mL / min or 5 mL / min, or a range value between any two of them; the flow rate of the second mixed solution is 1 mL / min to 15 mL / min, including but not limited to any one of 1 mL / min, 2 mL / min, 4 mL / min, 6 mL / min, 8 mL / min, 10 mL / min, 12 mL / min, 14 mL / min, 15 mL / min, or a range value between any two of them; the flow rate of the precipitant solution is 1 mL / min to 15 mL / min, including but not limited to any one of 1 mL / min, 2 mL / min, 4 mL / min, 6 mL / min, 8 mL / min, 10 mL / min, 12 mL / min, 14 mL / min, 15 mL / min, or a range value between any two of them.

[0158] Further, in some embodiments, in step S2, during the aging process, the temperature of the aging is 50℃ to 60℃, including but not limited to any one of 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, or a range value between any two of them; the time of the aging is 1h to 6h, including but not limited to any one of 1h, 2h, 3h, 4h, 5h or 6h, or a range value between any two of them; the pH value of the reaction system is 4 to 4.5, including but not limited to any one of 4, 4.1, 4.2, 4.3, 4.4, 4.5, or a range value between any two of them.

[0159] Further, in some embodiments, the aging process is carried out under stirring and protective gas.

[0160] Further, in some embodiments, the stirring speed of the aging process is 200rpm to 1000rpm, including but not limited to any one of 200rpm, 400rpm, 600rpm, 800rpm or 1000rpm, or a range value between any two of them.

[0161] In the technical scheme of the embodiments of the present application, by controlling the stirring speed of the aging process in this range, the precursor particle morphology can be regularized and the particle size is uniform, and too low stirring speed is not conducive to regularizing the particle morphology, and too high stirring speed is not conducive to the aggregation and growth of the precipitated particles.

[0162] Further, in some embodiments, the protective gas includes nitrogen, helium, neon, argon, xenon, and the like.

[0163] Further, in some embodiments, the deionized water used for washing the precipitate obtained after the aging process has a conductivity of 50 μS / cm to 150 μS / cm, including but not limited to any one of 50 μS / cm, 60 μS / cm, 70 μS / cm, 80 μS / cm, 90 μS / cm, 100 μS / cm, 110 μS / cm, 120 μS / cm, 130 μS / cm, 140 μS / cm, or 150 μS / cm, or a range value between any two of them.

[0164] Further, in some embodiments, the drying process is performed at a temperature of 60°C to 120°C, including but not limited to any one of 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, or 120°C, or a range value between any two of them; and the drying process is performed for a time period of 6h to 12h, including but not limited to any one of 6h, 7h, 8h, 9h, 10h, 11h, 12h, or a range value between any two of them.

[0165] Further, in some embodiments, in step S2, the volume ratio of the buffer base solution to the first mixed solution is 1:(1-3), including but not limited to any one of 1:1, 1:1.5, 1:2, 1:2.5, 1:3, or a range value between any two of them; the volume ratio of the buffer base solution to the second mixed solution is 1:(2-9), including but not limited to any one of 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or a range value between any two of them; and the volume ratio of the buffer base solution to the precipitant solution is 1:(2-9), including but not limited to any one of 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9.

[0166] In a third aspect, the embodiments of the present application provide a lithium manganese iron phosphate positive electrode material, which is prepared from the lithium manganese iron phosphate precursor provided in the first aspect of the present application or the lithium manganese iron phosphate precursor prepared by the preparation method provided in the second aspect of the present application.

[0167] The LMFP positive electrode material of the present application is prepared from the lithium manganese iron phosphate precursor described above. Thanks to the advantages of regular morphology, uniform particle size distribution, and uniform distribution of metal elements in the crystal lattice of the precursor, the LMFP positive electrode material has the advantages of high specific capacity and good rate performance.

[0168] In some embodiments, the expression of the LMFP positive electrode material is LiFe x Mn 1-xPO4 / C, wherein 0 < x < 1;

[0169] The LMFP positive electrode material satisfies: an average particle size of 1.5 μm to 1.7 μm, a D50 particle size of 1.5 μm to 1.7 μm, and a span of 1.9 to 2.3.

[0170] In the present application, the value of x includes but is not limited to 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, etc.

[0171] In the present application, the average particle size of the LMFP positive electrode material is 1.5 μm to 1.7 μm, including but not limited to 1.5 μm, 1.55 μm, 1.6 μm, 1.65 μm, 1.7 μm, etc. In some embodiments, the average particle size of the LMFP positive electrode material is further preferably 1.599 μm to 1.689 μm.

[0172] In the present application, the D50 particle size of the LMFP positive electrode material is 1.5 μm to 1.7 μm, including but not limited to 1.5 μm, 1.55 μm, 1.6 μm, 1.65 μm, 1.7 μm, etc. In some embodiments, the D50 particle size of the LMFP positive electrode material is further preferably 1.548 μm to 1.689 μm.

[0173] Further, in some embodiments, the D10 particle size of the LMFP positive electrode material is 0.2 μm to 0.5 μm, including but not limited to 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, etc. In some embodiments, the D10 particle size of the LMFP positive electrode material is further preferably 0.309 μm to 0.477 μm.

[0174] Further, in some embodiments, the D90 particle size of the LMFP positive electrode material is 3.2 μm to 4.5 μm, including but not limited to 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.4 μm, 4.5 μm, etc. In some embodiments, the D90 particle size of the LMFP positive electrode material is further preferably 3.336 μm to 4.101 μm.

[0175] In the present application, the span of the LMFP positive electrode material is 1.9 to 2.3, including but not limited to 1.9, 1.95, 2, 2.05, 2.1, 2.15, 2.2, 2.25, 2.3, etc. In some embodiments, the span of the LMFP positive electrode material is further preferably 1.93 to 2.21.

[0176] Further, in some embodiments, the primary particles of the LMFP positive electrode material have an irregular spherical morphology.

[0177] In the technical scheme of the embodiments of the present application, the primary particles of the LMFP positive electrode material all have irregular spherical morphology, and the situation of coexistence of rod-shaped, fragment-shaped, spherical and other different morphologies does not occur, and the overall morphology is uniform and regular. At the same time, the diameter distance of the LMFP positive electrode material is controlled in the range of 1.9-2.3, indicating that the particle size distribution concentration of the LMFP positive electrode material is high, which on the one hand improves its dispersibility in the electrode slurry, is beneficial to form a more flat electrode coating, and on the other hand can optimize the lithium ion transmission performance and increase the structural stability, so as to play the purpose of improving the electrochemical performance.

[0178] Further, in some embodiments, the tap density of the LMFP positive electrode material is 2.0 g / cm 3 -2.2 g / cm 3 , including but not limited to 2.0 g / cm 3 , 2.02 g / cm 3 , 2.05 g / cm 3 , 2.08 g / cm 3 , 2.1 g / cm 3 , 2.12 g / cm 3 , 2.15 g / cm 3 , 2.18 g / cm 3 , 2.2 g / cm 3 , etc. In some embodiments, the tap density of the LMFP positive electrode material is further preferably 2.036 g / cm 3 -2.159 g / cm 3 .

[0179] In the technical scheme of the embodiments of the present application, the LMFP positive electrode material has a high tap density, which can improve the discharge specific capacity and rate performance, and is beneficial to reduce the amount of positive electrode material and reduce the preparation cost of the battery.

[0180] Further, in some embodiments, the specific surface area of the LMFP positive electrode material is 12 m 2 / g-23 m 2 / g, including but not limited to 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 17 m 2 / g, 18 m 2 / g, 19 m 2 / g, 20 m 2 / g, 21 m 2 / g, 22 m 2 / g, 23 m2 / g, etc. In some embodiments, the specific surface area of the LMFP positive electrode material is further preferably 12.11 m 2 / g~22.59 m 2 / g.

[0181] In the technical solutions of the embodiments of the present application, the LMFP positive electrode material has a relatively moderate specific surface area, which means that it has more active sites for electrochemical reactions to occur, and at the same time can improve the transmission rate of lithium ions, so that the battery can exhibit higher discharge specific capacity and better rate performance.

[0182] Further, in some embodiments, the discharge specific capacity of the LMFP positive electrode material at 0.1C is 143 mAh / g~158 mAh / g, including but not limited to 143 mAh / g, 145 mAh / g, 148 mAh / g, 150 mAh / g, 152 mAh / g, 155 mAh / g, 158 mAh / g, etc.

[0183] Further, in some embodiments, the discharge specific capacity of the LMFP positive electrode material at 2C is 120 mAh / g~142 mAh / g, including but not limited to 120 mAh / g, 125 mAh / g, 130 mAh / g, 135 mAh / g, 140 mAh / g, 142 mAh / g, etc.

[0184] Further, in some embodiments, the 2C / 0.1C rate of the LMFP positive electrode material is 83%~91%, including but not limited to 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, etc.

[0185] In the technical solutions of the embodiments of the present application, the LMFP positive electrode material has very high rate performance, exhibits excellent rapid charge and discharge capacity, and is suitable for high-power output application scenarios.

[0186] The primary particles of the LMFP positive electrode material provided in the present application exhibit irregular spherical morphology, have the advantages of small particle size, uniform particle size distribution, moderate specific surface area, and high compaction density, and therefore exhibit higher discharge specific capacity and higher rate performance, and exhibit excellent electrochemical performance.

[0187] Further, in some embodiments, the LMFP positive electrode material is prepared by uniformly mixing a manganese iron phosphate precursor with a lithium source and then using a high-temperature solid phase method, wherein the manganese iron phosphate precursor is the manganese iron phosphate precursor provided in the first aspect of the present application, or is a manganese iron phosphate precursor prepared by the preparation method of the manganese iron phosphate precursor provided in the second aspect of the present application.

[0188] Further, in some embodiments, the molar ratio of the manganese iron phosphate precursor to the lithium source is 1:(1-1.03), including but not limited to 1:1, 1:1.01, 1:1.02, 1:1.03, etc.

[0189] Further, in some embodiments, the lithium source is lithium carbonate.

[0190] Further, in some embodiments, the manganese iron phosphate precursor is mixed with the lithium source uniformly, and a carbon source is further added.

[0191] Further, in some embodiments, the molar ratio of the manganese iron phosphate precursor to the carbon source is 1:(0.01-0.2), including but not limited to 1:0.01, 1:0.02, 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.15, 1:0.18, 1:0.2, etc., which are not limited in the present application.

[0192] Further, in some embodiments, the carbon source is selected from one or more of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0193] Further, in some embodiments, the manganese iron phosphate precursor is mixed with the lithium source uniformly by means of grinding.

[0194] Further, in some embodiments, the high-temperature solid-phase method is a high-temperature gradient calcination.

[0195] Further, in some embodiments, during the high-temperature gradient calcination, the calcination temperature of the first stage is 350-450 DEG C, including but not limited to any one of 350 DEG C, 370 DEG C, 390 DEG C, 410 DEG C, 430 DEG C, 450 DEG C, or a range value between any two of them; the holding time of the first stage is 2-6 h, including but not limited to any one of 2 h, 3 h, 4 h, 5 h, 6 h, or a range value between any two of them; the calcination temperature of the second stage is 760-790 DEG C, including but not limited to any one of 760 DEG C, 770 DEG C, 780 DEG C, 790 DEG C, or a range value between any two of them; the holding time of the second stage is 2-6 h, including but not limited to any one of 2 h, 3 h, 4 h, 5 h, 6 h, or a range value between any two of them; the calcination temperature of the third stage is 600-700 DEG C, including but not limited to any one of 600 DEG C, 620 DEG C, 640 DEG C, 660 DEG C, 680 DEG C, 700 DEG C, or a range value between any two of them; the holding time of the third stage is 2-6 h, including but not limited to any one of 2 h, 3 h, 4 h, 5 h, 6 h, or a range value between any two of them; the heating rate and the cooling rate of each stage during the calcination of the material are both 3-5 DEG C / min.

[0196] Further, in some embodiments, the high-temperature gradient calcination is carried out under a protective gas.

[0197] Further, in some embodiments, the protective gas includes nitrogen, helium, neon, argon, xenon, etc.

[0198] Further, in some embodiments, after the high-temperature gradient calcination, the method further includes: cooling the calcination product and then fully grinding and sieving.

[0199] In a fourth aspect, the embodiments of the present application provide a positive electrode tab, which includes the lithium manganese iron phosphate positive electrode material provided in the third aspect of the present application.

[0200] The positive electrode tab of the present application includes the above-mentioned LMFP positive electrode material, and thus has the advantages of high specific capacity and good rate performance.

[0201] In a fifth aspect, the embodiments of the present application provide a secondary battery, which includes the positive electrode tab provided in the fourth aspect of the present application.

[0202] The secondary battery of the present application includes the above-mentioned positive electrode tab, and thus has the advantages of high specific capacity and good rate performance.

[0203] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are used only to explain the present application and cannot be understood as a limitation of the present application. If a specific technology or condition is not specified in the examples, the technology or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained on the market.

[0204] Example 1

[0205] The preparation method of the iron-manganese phosphate precursor and the LMFP positive electrode material of the present embodiment is as follows:

[0206] (1) Preparation of the first mixed solution: dissolve the ferrous salt, manganese salt and the first complexing agent in deionized water to prepare the first mixed solution; wherein the ferrous salt is ferrous sulfate, the manganese salt is manganese sulfate, the total concentration of the two metal ions is 80 g / L, and the molar ratio of manganese to iron is 6:4; the first complexing agent is citric acid with a concentration of 4 g / L.

[0207] (2) Preparation of the second mixed solution: dissolve the first precipitant and the second complexing agent in deionized water to prepare the second mixed solution; wherein the first precipitant is ammonium dihydrogen phosphate with a concentration of 3.2 g / L; the second complexing agent is ammonia water with a concentration of 8 g / L.

[0208] (3) Preparation of the precipitant solution: dissolve the second precipitant in deionized water to prepare the precipitant solution; wherein the second precipitant is phosphoric acid and diammonium hydrogen phosphate with a molar ratio of 1:1, and the total concentration is 80 g / L.

[0209] (4) Preparation of the buffer base solution: dissolve the third complexing agent and the third precipitant in deionized water to prepare the buffer base solution; wherein the third complexing agent is citric acid, the third precipitant is ammonium dihydrogen phosphate, the molar ratio of citric acid to ammonium dihydrogen phosphate is 1:3, the concentration of ammonium dihydrogen phosphate is 6 g / L, and the pH value of the buffer base solution is 4.

[0210] (5) Preparation of the iron manganese phosphate precursor: take the first mixed solution, the second mixed solution, the precipitant solution and the buffer base solution in a volume ratio of 0.5:1:1:0.5; in order to ensure uniform stirring at the initial stage of the reaction, 500 mL of the buffer base solution is added to a double-layer glass reaction kettle, and the temperature in the reaction process is controlled to be constant at 50°C through water bath heating; 500 mL of the first mixed solution, 1 L of the second mixed solution and 1 L of the precipitant solution are simultaneously slowly pumped into the reaction kettle through a peristaltic pump for co-precipitation reaction; the feeding speed of the second mixed solution is controlled to maintain the pH value of the co-precipitation reaction at 4; during the process of pumping the three solutions into the reaction kettle, the stirring speed is controlled to be 800 rpm, N2 is continuously introduced for protection, and the duration of the co-precipitation reaction is controlled to be 6 h; after the reaction is completed, the precursor slurry is obtained after aging at 50°C for 1 h; the precursor slurry is washed with deionized water to remove impurities in the precursor slurry until the conductivity of the deionized water removed by washing is 120 μS / cm, and then the washed precursor slurry is placed in a blast drying oven at 110°C for drying for 10 h to obtain the iron manganese phosphate precursor.

[0211] (6) Preparation of the LMFP positive electrode material: according to a molar ratio of 1:1.03:0.09, the iron manganese phosphate precursor, lithium carbonate and glucose are added to a mortar and ground until they are uniformly mixed, and then the mortar is loaded into a crucible; the crucible is sent into a tube furnace, high-purity nitrogen is pre-introduced, and when the oxygen content in the tube furnace is 8 ppm, the following staged calcination program is started:

[0212] First calcination stage: sintering at 400°C for 5 h;

[0213] Second calcination stage: sintering at 760°C for 5 h;

[0214] Third calcination stage: sintering at 700°C for 4 h;

[0215] The heating rate and the cooling rate in the staged calcination program are both controlled to be 5°C / min;

[0216] After the staged calcination program is completed, the furnace is cooled to room temperature, and sieving treatment is performed using a 300-mesh sieve to obtain the LMFP positive electrode material.

[0217] Example 2

[0218] The preparation method of the iron manganese phosphate precursor and the LMFP positive electrode material in this example is as follows:

[0219] (1) Preparation of the first mixed solution: dissolve the ferrous salt, the manganese salt and the first complexing agent in deionized water to prepare the first mixed solution; wherein the ferrous salt is selected from ferrous sulfate, the manganese salt is selected from manganese nitrate, the total concentration of the two metal ions is 60 g / L, and the molar ratio of manganese to iron is 7:3; the first complexing agent is selected from citric acid, and the concentration is 3 g / L.

[0220] (2) Preparation of the second mixed solution: the first precipitant and the second complexing agent are dissolved in deionized water to prepare the second mixed solution; wherein the first precipitant is ammonium dihydrogen phosphate with a concentration of 4 g / L; the second complexing agent is ammonia water with a concentration of 8 g / L.

[0221] (3) Preparation of the precipitant solution: the second precipitant is dissolved in deionized water to prepare the precipitant solution; wherein the second precipitant is di-ammonium hydrogen phosphate with a concentration of 60 g / L.

[0222] (4) Preparation of the buffer base solution: the third complexing agent and the third precipitant are dissolved in deionized water to prepare the buffer base solution; wherein the third complexing agent is ammonia water, the third precipitant is phosphoric acid and ammonium dihydrogen phosphate with a mass ratio of 1:3, the molar ratio of ammonia water to ammonium dihydrogen phosphate is 1:1, the concentration of ammonium dihydrogen phosphate is 8 g / L, and the pH value of the buffer base solution is 4.5.

[0223] (5) Preparation of the iron-manganese phosphate precursor: take the first mixed solution, the second mixed solution, the precipitant solution and the buffer base solution with a volume ratio of 1:3:3:0.5; in order to ensure uniform stirring at the initial stage of the reaction, 500 mL of the buffer base solution is added to a double-layer glass reaction kettle, and the temperature in the reaction process is controlled to be constant at 50°C through water bath heating; 1 L of the first mixed solution, 3 L of the second mixed solution and 3 L of the precipitant solution are simultaneously and slowly pumped into the reaction kettle for co-precipitation reaction by using a peristaltic pump; the feeding speed of the second mixed solution is adjusted to maintain the pH value of the co-precipitation reaction at 4.5; during the process of pumping the three solutions into the reaction kettle, the stirring speed is controlled at 900 rpm, N2 is continuously introduced for protection, and the duration of the co-precipitation reaction is controlled for 4 h; after the reaction is completed, the precursor slurry is aged at 50°C for 1 h, then washed with deionized water to remove impurities in the precursor slurry until the conductivity of the deionized water removed by washing is 128 μS / cm, and then the washed precursor slurry is placed in a blast drying oven at 110°C for drying for 8 h to obtain the iron-manganese phosphate precursor.

[0224] (6) Preparation of the LMFP positive electrode material: according to a molar ratio of 1:1.02:0.1, the iron-manganese phosphate precursor, lithium carbonate and glucose are added to a mortar and ground until mixed uniformly, and then loaded into a crucible; the crucible is sent into a tube furnace, high-purity nitrogen is pre-introduced, and when the oxygen content in the tube furnace is 8 ppm, the following staged calcination program is started:

[0225] First calcination stage: sintering at 400°C for 4 h;

[0226] Second calcination stage: sintering at 770°C for 4 h;

[0227] Third calcination stage: sintering at 700°C for 5 h;

[0228] The temperature rising rate and the temperature falling rate in the staged calcination procedure are both controlled at 4℃ / min.

[0229] After the staged calcination procedure, the furnace is cooled to room temperature, and sieving treatment is performed using a 300-mesh sieve to obtain the LMFP positive electrode material.

[0230] Example 3

[0231] The preparation method of the iron-manganese phosphate precursor and the LMFP positive electrode material of the present example is as follows:

[0232] (1) Preparation of the first mixed solution: ferrous salt, manganese salt and the first complexing agent are dissolved in deionized water to prepare the first mixed solution; wherein the ferrous salt is ferrous nitrate, the manganese salt is manganese nitrate, the total concentration of the two metal ions is 100g / L, and the molar ratio of manganese to iron is 7:3; the first complexing agent is lactic acid and sodium citrate with a mass ratio of 1:1, and the total concentration is 4.5g / L.

[0233] (2) Preparation of the second mixed solution: the first precipitating agent and the second complexing agent are dissolved in deionized water to prepare the second mixed solution; wherein the first precipitating agent is diammonium hydrogen phosphate, and the concentration is 9g / L; the second complexing agent is ethylenediaminetetraacetic acid, and the concentration is 15g / L.

[0234] (3) Preparation of the precipitating agent solution: the second precipitating agent is dissolved in deionized water to prepare the precipitating agent solution; wherein the second precipitating agent is phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate and ammonium phosphate with a molar ratio of 1:1:1:1, and the total concentration is 90g / L.

[0235] (4) Preparation of the buffer base solution: the third complexing agent and the third precipitating agent are dissolved in deionized water to prepare the buffer base solution; wherein the third complexing agent is citric acid, the third precipitating agent is ammonium dihydrogen phosphate, the molar ratio of citric acid to ammonium dihydrogen phosphate is 1:5, the concentration of ammonium dihydrogen phosphate is 12g / L, and the pH value of the buffer base solution is 4.3.

[0236] (5) Preparation of iron manganese phosphate precursor: take the first mixed solution, the second mixed solution, the precipitant solution and the buffer bottom solution with a volume ratio of 1:2:2:1; in order to ensure uniform stirring at the beginning of the reaction, 1L of buffer bottom solution is added in a double-layer glass reaction kettle, and the temperature in the reaction process is controlled to be constant at 55°C through water bath heating; 1L of the first mixed solution, 2L of the second mixed solution and 2L of the precipitant solution are simultaneously slowly pumped into the reaction kettle for coprecipitation reaction by using a peristaltic pump; the feeding speed of the second mixed solution is controlled to maintain the pH value of the coprecipitation reaction at 4.3; during the process of pumping the three solutions into the reaction kettle, the stirring speed is controlled at 600 rpm, N2 is continuously introduced for protection, and the duration of the coprecipitation reaction is controlled for 4h; after the reaction is completed, the precursor slurry is obtained by aging at 55°C for 2h; the impurities in the precursor slurry are removed by washing with deionized water until the conductivity of the deionized water removed by washing is 136μS / cm, and then the washed precursor slurry is placed in a blast drying oven at 120°C for drying for 6h to obtain the iron manganese phosphate precursor.

[0237] (6) Preparation of LMFP positive electrode material: according to the molar ratio of 1:1.02:0.12, iron manganese phosphate precursor, lithium carbonate and glucose are added in a mortar and ground until uniformly mixed, and then loaded into a crucible; the crucible is sent into a tube furnace, high-purity nitrogen is pre-pumped, and when the oxygen content in the tube furnace is 6ppm, the following staged calcination program is started:

[0238] First calcination stage: sintering at 350°C for 4h;

[0239] Second calcination stage: sintering at 790°C for 3h;

[0240] Third calcination stage: sintering at 650°C for 6h;

[0241] The heating rate and the cooling rate in the staged calcination program are both controlled at 5°C / min;

[0242] After the staged calcination program is completed, the furnace is cooled to room temperature, and sieving treatment is performed using a 300 mesh sieve to obtain the LMFP positive electrode material.

[0243] Example 4

[0244] This example is basically the same as Example 1, except that the pH value of the coprecipitation reaction is 4.5.

[0245] Example 5

[0246] This example is basically the same as Example 2, except that the buffer bottom solution in step (4) is different.

[0247] The preparation method of the buffer stock solution in step (4) is as follows: the third complexing agent and the third precipitating agent are dissolved in deionized water to prepare the buffer stock solution; wherein the third complexing agent is ascorbic acid with a concentration of 2 g / L; the third precipitating agent is phosphoric acid and ammonium phosphate with a mass ratio of 1:4, and the concentration of ammonium phosphate is 8 g / L; and the pH value of the buffer stock solution is 4.5.

[0248] Example 6

[0249] This example is basically the same as example 3, and the only difference is that the second mixed solution in step (2) is different.

[0250] The preparation method of the second mixed solution in step (2) is as follows: the first precipitating agent and the second complexing agent are dissolved in deionized water to prepare the second mixed solution; wherein the first precipitating agent is diammonium hydrogen phosphate with a concentration of 4.8 g / L; and the second complexing agent is ammonia and tris(2-aminoethyl)triacetic acid with a concentration of 8 g / L.

[0251] Examples 7-13

[0252] Examples 7-13 are basically the same as example 1, and the only difference is that the molar ratio of manganese to iron in the first mixed solution is different.

[0253] Example 7: the molar ratio of manganese to iron is 9:1;

[0254] Example 8: the molar ratio of manganese to iron is 8:2;

[0255] Example 9: the molar ratio of manganese to iron is 5:5;

[0256] Example 10: the molar ratio of manganese to iron is 4:6;

[0257] Example 11: the molar ratio of manganese to iron is 3:7;

[0258] Example 12: the molar ratio of manganese to iron is 2:8;

[0259] Example 13: the molar ratio of manganese to iron is 1:9.

[0260] Comparative examples 1-9

[0261] Comparative examples 1-9 are basically the same as example 1, and the only difference is that:

[0262] Comparative example 1: no first complexing agent is added to the first mixed solution;

[0263] Comparative example 2: no second complexing agent is added to the second mixed solution;

[0264] Comparative example 3: no first precipitating agent is added to the second mixed solution;

[0265] Comparative Example 4: No second precipitant was added to the precipitant solution, i.e. the precipitant solution in the co-precipitation reaction was replaced with an equal volume of deionized water;

[0266] Comparative Example 5: No third complexing agent was added to the buffer solution;

[0267] Comparative Example 6: No third precipitant was added to the buffer solution;

[0268] Comparative Example 7: The pH value of the co-precipitation reaction was 3.5;

[0269] Comparative Example 8: The pH value of the co-precipitation reaction was 5;

[0270] Comparative Example 9: The pH value of the co-precipitation reaction was 5.5.

[0271] Test Example

[0272] (I) Test Items:

[0273] 1. SEM Test: The MERLIN Compact field emission scanning electron microscope (Model: Quanta 200FEG) produced by Zeiss was used to perform SEM tests on the manganese iron phosphate precursor and the LMFP positive electrode material, and the results are shown in Tables 1-2 and Figures 2-13. Among them, Figures 2-7 are SEM result graphs of the manganese iron phosphate precursor of Example 1, Example 4, Comparative Example 1 and Comparative Examples 7-9, and Figures 8-13 are SEM result graphs of the LMFP positive electrode material of Example 1, Example 4, Comparative Example 1 and Comparative Examples 7-9.

[0274] 2. EDS Test: The energy dispersive X-ray diffractometer of Oxford was used to perform element ratio analysis on the manganese iron phosphate precursor and the LMFP positive electrode material, and the molar ratio (Mn:Fe) of manganese element and iron element was calculated, and the results are shown in Tables 1-2.

[0275] 3. XRD Test: The Bruker D8 Advance model X-ray diffractometer produced by Germany Brüker was used to perform phase analysis on the manganese iron phosphate precursor and the LMFP positive electrode material, and the molar ratio (Mn:Fe) of manganese element and iron element was calculated, and the results are shown in Tables 1-2 and Figures 14-15.

[0276] 4. Particle Size Test: The Mastersizer 2000 laser particle size instrument produced by Malvern Instruments Ltd. in the United Kingdom was used to perform particle size analysis on the manganese iron phosphate precursor and the LMFP positive electrode material, and the results are shown in Tables 1-2.

[0277] 5. Compaction density: The compaction density of the manganese iron phosphate precursor and the LMFP positive electrode material was tested by using the UTM7305 battery powder compaction density instrument provided by Shenzhen Sansi Zongheng Technology Co., Ltd., and the results are shown in Tables 1-2.

[0278] 6. Specific surface area: The specific surface area of the manganese iron phosphate precursor and the LMFP positive electrode material was tested by using the BELSORP Max II type specific surface area analyzer produced by Japan-Macchi Kibei, and the results are shown in Tables 1-2.

[0279] 7. Performance test of secondary battery

[0280] The LMFP positive electrode material was mixed with conductive carbon black and PVDF binder in a mass ratio of 90:5:5 to obtain a positive electrode slurry; the positive electrode slurry was coated on an aluminum foil with a thickness of 12 μm to form a positive electrode slurry layer with a thickness of 80 μm; then it was dried in an oven at 110°C for 10 h, and after drying, it was punched into a circular electrode with a diameter of 15 mm, and it was pressed to a compaction density of 1.8 g / cm 3 rolled to obtain a positive electrode sheet.

[0281] Lithium hexafluorophosphate (LiPF6) was used as a lithium salt, and ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 1:1:1 were used as organic solvents, and the lithium salt was dissolved in the organic solvents to prepare an electrolyte with a concentration of 1M; a lithium sheet with a diameter of 16 mm was used as a counter electrode, and the positive electrode sheet and the electrolyte were assembled in an LG2400 / 1000TS glove box produced by Weige Gas Purification Technology (Suzhou) Co., Ltd. to obtain a button-type half battery.

[0282] The button-type half battery was tested for rate performance by using a battery performance test system (model: CT3002A) of Wuhan Landian Electronics Technology Co., Ltd., the test temperature was 25°C, the voltage range was 2-4.35V, and the rate range was 0.1C-3C, and the results are shown in Table 3 and Figs. 16-18.

[0283] (II) Analysis of results

[0284] Please refer to Tables 1, Figs. 2-3 and Fig. 14, the primary particles of the manganese iron phosphate precursors prepared in Examples 1-13 all have an olivine-like morphology, the morphology is very uniform and regular, and they exhibit the characteristics of small particle size, uniform particle size distribution, moderate specific surface area and high compaction density. In addition, the Mn:Fe molar ratio of the manganese iron phosphate precursors prepared in Examples 1-13 is between 91:9 and 11:89, the distribution span of the Mn:Fe molar ratio is large, and Mn / Fe is uniformly distributed in the lattice, and the Mn:Fe of the precursor can be arbitrarily adjusted according to actual production needs.

[0285] As can be seen from the comparison of FIG. 2 and FIG. 4, compared with Example 1, no first complexing agent is added in the first mixed solution of Comparative Example 1, resulting in that the manganese iron phosphate precursor prepared in Comparative Example 1 presents a fragment shape and cannot form an olivine morphology; the average particle size, D10 particle size, D50 particle size and D90 particle size of the manganese iron phosphate precursor prepared in Comparative Example 1 are obviously higher than those of Example 1, the specific surface area is also greatly improved, but the compaction density is obviously reduced, which shows the defects of large particle size, uneven particle size, too high specific surface area and low compaction density. This shows that the addition of the first complexing agent in the first mixed solution can effectively pre-complex the divalent iron ions in the solution, so as to realize the co-precipitation of manganese and iron elements and form an olivine-shaped precursor; if no first complexing agent is added in the first mixed solution, the divalent iron ions therein are easy to be oxidized into trivalent iron ions, which are difficult to co-precipitate with manganese ions in the co-precipitation reaction, so that a precursor with regular and uniform morphology cannot be formed.

[0286] Similarly, compared with Example 1, no complexing agent or precipitant is pre-added in the second mixed solution, precipitant solution or buffer base solution of Comparative Examples 2-6, which all result in that the manganese iron phosphate precursor cannot form an olivine morphology and shows the defects of large particle size, too wide particle size distribution, too high specific surface area and low compaction density. This is because the different complexing agents are mixed with the precipitant in advance and are respectively used as the second mixed solution and the buffer base solution, which can quickly and stably control the pH value of the reaction system and have a complexing effect, realize the steady state of the precipitation reaction process and the liquid phase mass transfer process and good control of the morphology of the precipitate after the reaction, so that the manganese iron phosphate precursor with uniform Mn / Fe distribution in the crystal lattice, regular particle morphology, uniform particle size distribution and excellent performance is successfully prepared.

[0287] The pH value of the reaction system in the co-precipitation reaction process of Examples 1-13 is controlled in the range of 4-4.5, and the manganese iron phosphate precursor with regular morphology, uniform size and olivine morphology is obtained. As can be seen from the comparison of FIG. 2 and FIG. 5, compared with Example 1, the pH value of Comparative Example 7 is not more than 3.5, which makes the material nucleation rate too slow, the thickness of the growth layer is thin, and the crystal growth rate is slow, so that the precursor presents a fragment shape; as can be seen from the comparison of FIG. 2 and FIG. 6-7, compared with Example 1, the pH value of Comparative Examples 8-9 is not less than 5, which makes the material nucleation rate too fast, and the precursor cannot grow orderly and uniformly, which shows that the material synthesis becomes difficult to control under this condition, so that the precursor presents the characteristics of coexistence of fragment and rod.

[0288] Referring to Table 2, FIGS. 8-9 and 15, the primary particles of the LMFP positive electrode materials prepared in Examples 1-13 all exhibit irregular spherical morphology, regular morphology, small particle size, uniform particle size distribution, moderate specific surface area and high tap density, and the molar ratio of Mn to Fe of the LMFP positive electrode materials is basically consistent with the molar ratio of Mn to Fe of the manganese iron phosphate precursor, and the molar ratio of Mn to Fe of the LMFP positive electrode material can be arbitrarily adjusted according to actual production needs.

[0289] As can be seen from the comparison of FIGS. 8 and 10, compared with Example 1, the LMFP positive electrode material prepared in Comparative Example 1 exhibits a flaky shape, irregular morphology; the average particle size, D10 particle size, D50 particle size, D90 particle size and span of the LMFP positive electrode material prepared in Comparative Example 1 are all significantly higher than those of Example 1, and the specific surface area is close to twice that of Example 1, but the tap density is greatly reduced, which shows defects of large particle size, uneven particle size distribution, excessively high specific surface area and low tap density. This shows that the addition of the first complexing agent in the first mixed solution in Example 1 effectively realizes the co-precipitation of manganese and iron elements, so that the manganese iron phosphate precursor has an olivine morphology with regular morphology, uniform size and moderate specific surface area, thereby preparing the LMFP positive electrode material with regular morphology, uniform size and irregular spherical morphology.

[0290] Similarly, compared with Example 1, the second mixed solution, the precipitator solution or the buffer base solution of Comparative Examples 2-6 does not pre-add a complexing agent or a precipitator, resulting in the formation of irregular flaky morphology of the LMFP positive electrode material, and large particle size, excessively wide particle size distribution, excessively high specific surface area and low tap density. This shows that pre-mixing different complexing agents with precipitators and using them as the second mixed solution and the buffer base solution is also crucial for preparing the LMFP positive electrode material with regular morphology, uniform size and irregular spherical morphology.

[0291] The pH value of the reaction system in the co-precipitation reaction process of Examples 1-13 is controlled in the range of 4-4.5, and the LMFP positive electrode material with regular morphology, uniform size and irregular spherical morphology can be obtained. As can be seen from the comparison of FIGS. 8 and 11, compared with Example 1, the pH value of Comparative Example 7 does not exceed 3.5, so that the manganese iron phosphate precursor exhibits a large flaky morphology, and thus the synthesized LMFP positive electrode material exhibits a thicker flaky morphology after mixing with lithium salt; as can be seen from the comparison of FIGS. 2 and 12-13, compared with Example 1, the pH value of Comparative Examples 8-9 is not lower than 5, so that the manganese iron phosphate precursor has a morphology of coexistence of fragments and rods, resulting in the synthesized LMFP positive electrode material exhibiting the characteristics of coexistence of flaky and irregular spherical morphology.

[0292] Please refer to Table 3 and FIGS. 16-17, the discharge specific capacity of the LMFP cathode material prepared in Examples 1-13 is 143-158 mAh / g at 0.1C and 120-143 mAh / g at 2C, and the 2C / 0.1C rate reaches 83-91%, which has a high discharge specific capacity and good rate performance.

[0293] In the above examples, the pH value of the co-precipitation reaction in Example 1 is 4, the discharge specific capacity of the LMFP cathode material is 145 mAh / g at 0.1C and 126 mAh / g at 2C. The pH value of the co-precipitation reaction in Example 4 is 4.5, the discharge specific capacity of the LMFP cathode material is 158 mAh / g at 0.1C and 142 mAh / g at 2C, which is superior to Example 1 in terms of discharge specific capacity and rate performance. The pH value of the co-precipitation reaction in Comparative Example 7 is not more than 3.5, and the pH value of the co-precipitation reaction in Comparative Examples 8-9 is not less than 5, which will cause the discharge specific capacity and rate performance of the LMFP cathode material to decrease significantly. Therefore, the co-precipitation reaction at a suitable pH value can maintain the LMFP cathode material with a higher discharge specific capacity and better rate performance.

[0294] As can be seen from the comparison of FIGS. 16 and 18, compared with Example 1, no first complexing agent is added in the first mixed solution of Comparative Example 1, and the LMFP cathode material prepared has irregular morphology, large particle size, uneven particle size distribution, too high specific surface area, and low tap density, which ultimately leads to poor rate performance of the LMFP cathode material, with a discharge specific capacity of only 105 mAh / g at 2C and a 2C / 0.1C rate of only 75%. Similarly, compared with Example 1, no complexing agent or precipitant is added in advance in the second mixed solution, precipitant solution or buffer solution of Comparative Examples 2-6, which also leads to poor rate performance of the LMFP cathode material.

[0295] In summary, the manganese iron phosphate precursor is prepared by the co-precipitation method, so that the manganese iron phosphate precursor has regular and uniform morphology, and has the advantages of small particle size, uniform particle size distribution, moderate specific surface area, and high tap density. The cathode material prepared from the precursor has a higher discharge specific capacity and a higher rate performance, and has excellent electrochemical performance.

[0296] Table 1. Related parameters of manganese iron phosphate precursor

[0297] Table 2. Related parameters of LMFP cathode material

[0298] Table 3. Electrical performance of LMFP cathode material

[0299] Each technical feature of the above-described embodiments can be combined with any other technical feature, and for the sake of brevity, not all possible combinations are described, but it is understood that the scope of the present disclosure encompasses all such possible combinations.

[0300] The above-described embodiments are merely illustrative of several embodiments of the present application, and the description is relatively specific and detailed, but should not be construed as limiting the scope of the patent application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims.

Claims

1. A manganese iron phosphate precursor, characterized in that, The manganese iron phosphate precursor has an expression of (NH4) (3-2x-2y) Fe x Mn y PO4·H2O, wherein 0 < x < 1, 0 < y < 1. The manganese iron phosphate precursor satisfies: an average particle size of 2.0-2.5 μm, a D50 particle size of 1.6-2.0 μm, and a span of 0.4-0.

7.

2. The manganese iron phosphate precursor of claim 1, wherein, The primary particles of the manganese iron phosphate precursor have an olivine morphology, and the ratio of length to width of the manganese iron phosphate precursor is (2-2.5):(1-1.5).

3. The manganese iron phosphate precursor of claim 1, wherein, The compaction density of the manganese iron phosphate precursor is 1.4 g / cm 3 ~1.8 g / cm 3 The specific surface area is 25 m 2 / g~30 m 2 / g.

4. A method of producing a manganese iron phosphate precursor, characterized by, The method comprises the following steps: a first mixed solution, a second mixed solution, a precipitant solution, and a buffer base solution are provided; and, the first mixed solution, the second mixed solution, and the precipitant solution are simultaneously added to the buffer base solution to perform a co-precipitation reaction, and the manganese iron phosphate precursor is prepared through aging treatment, washing treatment, and drying treatment; wherein the pH value in the co-precipitation reaction is greater than 3.5 and less than 5; the first mixed solution contains a ferrous salt, a manganese salt, and a first complexing agent; the second mixed solution contains a second complexing agent and a first precipitant; the precipitant solution contains a second precipitant; the buffer base solution contains a third precipitant and a third complexing agent; the first complexing agent and the second complexing agent are different from each other; the third complexing agent comprises one or more of the first complexing agent and the second complexing agent.

5. The method for preparing the manganese iron phosphate precursor according to claim 4, characterized in that, One or more of the following conditions are satisfied: (1) the ferrous salt comprises one or more of ferrous sulfate, ferrous nitrate, ferrous oxalate, and ferrous chloride; (2) the manganese salt comprises one or more of manganese sulfate, manganese nitrate, manganese acetate, manganese oxalate, and manganese chloride; (3) the first complexing agent comprises one or more of citric acid, sodium citrate, ascorbic acid, lactic acid, and malic acid; (4) the second complexing agent comprises one or more of ammonia, ethylenediaminetetraacetic acid, diisopropylamino tetraacetic acid, and tris(2-aminoethyl)triacetic acid; (5) the third complexing agent comprises one or more of citric acid, sodium citrate, ammonia, ascorbic acid, lactic acid, and malic acid; (6) the first precipitant, the second precipitant, and the third precipitant each independently comprise one or more of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

6. The method for preparing the manganese iron phosphate precursor according to claim 4, characterized in that, One or more of the following conditions are satisfied for the first mixed solution: (1) the total concentration of manganese ions and ferrous ions is 10-120 g / L; (2) the molar ratio of ferrous ions to manganese ions is 1:(0.01-100); (3) the concentration of the first complexing agent is 2-10 g / L.

7. The method for preparing the manganese iron phosphate precursor according to claim 4, characterized in that, One or more of the following conditions are satisfied for the second mixed solution: (1) the concentration of the second complexing agent is 5-120 g / L; (2) the mass ratio of the second complexing agent to the first precipitant is 1:(0.2-0.6).

8. The method for preparing the manganese iron phosphate precursor according to claim 4, characterized in that, In the precipitant solution, the concentration of the second precipitant is 10-120 g / L.

9. The method for preparing the manganese iron phosphate precursor according to claim 4, characterized in that, One or more of the following conditions are satisfied for the buffer base solution: (1) the concentration of the third complexing agent is 2-10 g / L; (2) the concentration of the third precipitant is 6-80 g / L; (3) the molar ratio of the third complexing agent to the third precipitant is 1:(1-8); (4) the pH value of the buffer base solution is 2-6.

10. The method of producing a manganese iron phosphate precursor according to any one of claims 4 to 9, characterized in that, The volume ratio of the first mixed solution, the second mixed solution, the second mixed solution and the buffer base solution is (1-3):(2-9):(2-9):

1.

11. The method of claim 10, wherein the manganese iron phosphate precursor is prepared by the steps of: One or more of the following conditions are met: ​ (1) the temperature of the co-precipitation reaction is 50-60 DEG C, and the time of the co-precipitation reaction is 2-24 hours; (2) the temperature of the aging treatment is 50-60 DEG C, and the time of the aging treatment is 1-6 hours.

12. A lithium iron manganese phosphate cathode material, characterized in that, The expression of the lithium iron manganese phosphate positive electrode material is LiFe x Mn 1-x PO4 / C, wherein 0 < x < 1; The lithium iron manganese phosphate positive electrode material meets the following conditions:

13. The lithium iron manganese phosphate cathode material of claim 12, wherein, (1) the primary particles of the lithium iron manganese phosphate positive electrode material have irregular spherical morphology; The secondary battery includes the positive electrode sheet of claim 14. (2) the compaction density of the lithium iron manganese phosphate positive electrode material is 2.0 g / cm 3 ~ 2.2 g / cm 3 ; (3) the specific surface area of the lithium iron manganese phosphate positive electrode material is 12 m 2 / g~23 m 2 / g.

14. A positive electrode sheet characterized by comprising: The secondary battery includes the positive electrode sheet of claim 14.

15. A secondary battery characterized by comprising: ​

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