Continuous reaction system, manganese iron phosphate precursor, lithium manganese iron phosphate, and preparation method thereof, and secondary battery

Abstract

The application provides a continuous reaction system, a manganese iron phosphate precursor, lithium manganese iron phosphate, a preparation method of the lithium manganese iron phosphate, and a secondary battery. The preparation method of the manganese iron phosphate precursor provided by the application is a continuous preparation method, so that the production efficiency can be improved, and the manganese iron phosphate precursor with small particle size, narrow particle size distribution, high crystallinity, single crystal phase, regular morphology, high tap density, high batch stability and consistency can be obtained.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a continuous reaction system, a manganese iron phosphate precursor, lithium manganese iron phosphate, its preparation method, and a secondary battery. Background Technology

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the application and promotion of secondary batteries, their safety performance has received increasing attention. Lithium manganese iron phosphate (LFP) has become one of the most popular cathode active materials due to its advantages such as high capacity, good safety performance, and abundant raw material sources. As one of the important raw materials for preparing LFP, the performance of iron manganese phosphate is crucial to the performance of LFP and secondary batteries. However, currently, iron manganese phosphate is obtained using intermittent preparation methods, which suffer from low production efficiency, cumbersome processes, difficulty in controlling the production process, large fluctuations in product quality, and poor batch stability and consistency. Summary of the Invention

[0003] The purpose of this application is to provide a continuous reaction system, a precursor of manganese iron phosphate, lithium manganese iron phosphate, a preparation method thereof, and a secondary battery, aiming to improve the production efficiency of the precursor of manganese iron phosphate and obtain a precursor of manganese iron phosphate with small particle size, narrow particle size distribution, high crystallinity, single crystal phase, regular morphology, high tap density, and high batch stability and consistency.

[0004] This application provides a continuous reaction system for preparing ferromanganese phosphate precursor, comprising a first melting vessel, a second melting vessel, a first reaction vessel, a second reaction vessel, and an aging vessel, wherein the first reaction vessel, the second reaction vessel, and the aging vessel are connected in series via pipelines; the first melting vessel is used to contain a metal salt solution required for preparing the ferromanganese phosphate precursor, and the second melting vessel is used to contain an oxidant and a phosphorus source solution required for preparing the ferromanganese phosphate precursor; the first reaction vessel has a first inlet and a first overflow outlet, and the first inlet of the first reaction vessel is connected to the first melting vessel and the second melting vessel via a first pipeline and a second pipeline respectively, so that the first reaction vessel contains the metal salt solution and the phosphorus source solution, and after mixing them, a reaction occurs to generate a first reaction solution; a first shut-off valve and a first metering valve are provided on the first pipeline. A pump is used to regulate the flow rate of the metal salt solution. A second shut-off valve and a second metering pump are installed on the second pipeline to regulate the flow rate of the phosphorus source solution. The second reactor has a second inlet and a second overflow. The second inlet of the second reactor is connected to the first overflow of the first reactor through a third pipeline, so that the second reactor can contain the first reaction liquid from the first reactor and allow it to continue to react to generate the second reaction liquid. The aging reactor includes a third inlet and a third overflow. The third inlet of the aging reactor is connected to the second overflow of the second reactor through a fourth pipeline, so that the aging reactor can contain the second reaction liquid from the second reactor and allow it to continue to react to generate the third reaction liquid. When the liquid level of the third reaction liquid is higher than the third overflow of the aging reactor, the third reaction liquid flows out through the third overflow of the aging reactor.

[0005] The second aspect of this application provides a method for preparing a manganese ferric phosphate precursor, comprising at least the following steps: S1, connecting a first reactor, a second reactor, and an aging reactor in series via pipelines; the first reactor having a first inlet and a first overflow; the first inlet of the first reactor being connected to a first dissolving vessel via a first pipeline; the first inlet of the first reactor being connected to the second dissolving vessel via a second pipeline; the first pipeline being equipped with a first shut-off valve and a first metering pump; the second pipeline being equipped with a second shut-off valve and a second metering pump; the second reactor having a second inlet and a second overflow; the second inlet of the second reactor being connected to the first overflow of the first reactor via a third pipeline; the aging vessel including a third inlet and a third overflow; the third inlet of the aging vessel being connected to the second overflow of the second reactor via a fourth pipeline; S2, adding a metal salt solution required for preparing the manganese ferric phosphate precursor to the first dissolving vessel; adding an oxidant and a phosphorus source solution required for preparing the manganese ferric phosphate precursor to the second dissolving vessel; and discharging the metal salt solution in the first dissolving vessel through a first shut-off valve. A valve and a first metering pump pump into the first pipeline, and the phosphorus source solution in the second dissolving vessel is pumped into the second pipeline through the second shut-off valve and the second metering pump. This allows the metal salt solution and the phosphorus source solution to mix and react in the first reaction vessel to generate a first reaction liquid. When the liquid level of the first reaction liquid is higher than the first overflow port of the first reaction vessel, the first reaction liquid is automatically transferred to the second reaction vessel to continue the reaction and generate a second reaction liquid. When the liquid level of the second reaction liquid is higher than the second overflow port of the second reaction vessel, the second reaction liquid is automatically transferred to the aging vessel to continue the reaction. A third reaction liquid should be generated. When the liquid level of the third reaction liquid is higher than the third overflow port of the aging kettle, the third reaction liquid will automatically flow out through the third overflow port of the aging kettle. During the reaction process, the first solvent kettle, the second solvent kettle, the first reaction kettle, the second reaction kettle and the aging kettle are all under a protective gas atmosphere and each kettle is kept in a stirring state. Optionally, the protective gas includes nitrogen, inert gas or a combination thereof; S3, after filtering, washing and drying the third reaction liquid obtained from the third overflow port of the aging kettle, manganese iron phosphate precursor is obtained.

[0006] The method for preparing the ferromanganese phosphate precursor provided in this application has advantages such as high production efficiency, high energy efficiency, simple process, ease of operation, and low labor costs, making it particularly suitable for large-scale industrial production. The method for preparing the ferromanganese phosphate precursor provided in this application is a continuous preparation method. The ferromanganese phosphate precursor obtained by this continuous preparation method has advantages such as small particle size, narrow particle size distribution, high crystallinity, single crystal phase, regular morphology, high tap density, and high batch stability and consistency. The method for preparing the ferromanganese phosphate precursor provided in this application can also adjust the crystal particle growth rate and the size and morphology of the crystal particles, thereby meeting different production needs and facilitating the preparation of lithium ferromanganese phosphate with different particle sizes.

[0007] In any embodiment of this application, a complexing agent is also added to the first melting vessel. Optionally, the complexing agent includes one or more of aminocarboxylate, hydroxycarboxylate, and organophosphonate, and more preferably one or more of sodium triacetate, disodium ethylenediaminetetraacetate, sodium gluconate, and sodium citrate. This allows for the production of spherical manganese-iron phosphate precursor particles with high purity and uniform metal element distribution, exhibiting a high tap density; it also enables precise control of the metal element content.

[0008] In any embodiment of this application, a surfactant is also added to the first melting vessel. Optionally, the surfactant includes one or more of hexadecyltrimethylammonium bromide, sodium dodecyl sulfonate, and polyvinylpyrrolidone. This helps to better adjust the morphology of the manganese iron phosphate precursor particles.

[0009] In any embodiment of this application, the reaction temperature of the first reactor is lower than that of the second reactor, and the reaction temperature of the aging reactor is lower than that of the second reactor. This not only allows for adjustment of the particle size of the obtained ferromanganese phosphate precursor, but also helps to obtain ferromanganese phosphate precursor particles with narrow particle size distribution, high crystallinity, single crystal phase, regular morphology, and high tap density.

[0010] In any embodiment of this application, the reaction temperature of the first reactor is 70°C to 90°C.

[0011] In any embodiment of this application, the reaction temperature of the second reactor is 150°C to 250°C.

[0012] In any embodiment of this application, the reaction temperature of the aging kettle is 20°C to 30°C.

[0013] In any embodiment of this application, the flow rate of the metal salt solution in the first pipe is 0.2 L / min to 2 L / min, and optionally 0.25 L / min to 1 L / min.

[0014] In any embodiment of this application, the flow rate of the phosphorus source solution in the second pipe is 0.2 L / min to 2 L / min, and can be optionally 0.25 L / min to 1 L / min.

[0015] In any embodiment of this application, the flow rates of the metal salt solution and the phosphorus source solution are the same, which helps to improve the consistency of the obtained manganese iron phosphate precursor particles.

[0016] In any embodiment of this application, the residence time of the manganese iron phosphate precursor in the first reactor during growth is 1 h to 4 h.

[0017] In any embodiment of this application, the residence time of the manganese iron phosphate precursor in the second reactor during growth is 1 h to 16 h, and can be selected as 4 h to 16 h.

[0018] In any embodiment of this application, the residence time of the manganese iron phosphate precursor in the aging reactor during growth is 1 h to 48 h, and can be selected as 12 h to 48 h.

[0019] In any embodiment of this application, the volume of the first reactor is less than or equal to the volume of the second reactor. Optionally, the ratio of the volume of the first reactor to the volume of the second reactor is 1:(1~4), and more preferably 1:(2~4). This helps to give the obtained manganese ferric phosphate precursor particles a higher degree of crystallinity.

[0020] In any embodiment of this application, the volume of the first reaction vessel is less than or equal to the volume of the aging vessel. Optionally, the ratio of the volume of the first reaction vessel to the volume of the aging vessel is 1:(1~12), and more preferably 1:(4~12). This helps to obtain a larger particle size in the obtained manganese iron phosphate precursor.

[0021] In any embodiment of this application, the volume of the second reaction vessel is less than or equal to the volume of the aging vessel. Optionally, the ratio of the volume of the second reaction vessel to the volume of the aging vessel is 1:(1~3), and more preferably 1:(2~3). This helps to obtain a larger particle size in the obtained manganese iron phosphate precursor.

[0022] In any embodiment of this application, the metal salt required for preparing the manganese iron phosphate precursor includes a water-soluble iron salt, a water-soluble manganese salt, and a salt of an optional water-soluble dopant element M, where M represents a dopant element at the manganese and iron sites, and optionally includes one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr.

[0023] In any embodiment of this application, the water-soluble iron salt includes one or more of ferrous chloride, ferrous nitrate, ferrous sulfate, ferrous acetate, ferric chloride, ferric nitrate, ferric sulfate, and ferric acetate.

[0024] In any embodiment of this application, the water-soluble manganese salt includes one or more of manganese chloride, manganese nitrate, manganese sulfate, and manganese acetate.

[0025] In any embodiment of this application, the salt of the water-soluble dopant element M includes one or more of the following: hydrochloride, nitrate, sulfate, and acetate of the dopant element M.

[0026] In any embodiment of this application, the phosphorus source required for preparing the manganese iron phosphate precursor includes one or more of phosphoric acid and water-soluble phosphates. Optionally, the water-soluble phosphates include one or more of trisodium phosphate, tripotassium phosphate, monoammonium hydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

[0027] In any embodiment of this application, the phosphorus source required for preparing the manganese iron phosphate precursor further includes a source of a water-soluble dopant element Q, where Q represents the dopant element at the phosphorus site, and optionally includes one or more of B, S, Si, and N. Optionally, the source of the dopant element Q includes one or more of the sulfate, borate, nitrate, and silicate of the dopant element Q.

[0028] In any embodiment of this application, the oxidant includes one or more of hydrogen peroxide, nitric acid, sodium hypochlorite, potassium hypochlorite, sodium chlorate, and potassium chlorate, and may be selected as hydrogen peroxide.

[0029] In any embodiment of this application, the molar ratio of the metal salt to the oxidant is 1:(0.1~1.2), and optionally 1:(0.5~0.6).

[0030] In any embodiment of this application, the concentration of the metal salt solution is 0.5 mol / L to 2 mol / L, and may be 0.5 mol / L to 1 mol / L.

[0031] In any embodiment of this application, the concentration of the phosphorus source solution is 0.5 mol / L to 2 mol / L, and may be 0.5 mol / L to 1 mol / L.

[0032] In any embodiment of this application, the molar ratio of the metal salt to the phosphorus source is 1:1 to 1:3.

[0033] In any embodiment of this application, the stirring speed of the first melting vessel is 100 r / min ~ 500 r / min.

[0034] In any embodiment of this application, the stirring speed of the second melting vessel is 100 r / min ~ 500 r / min.

[0035] In any embodiment of this application, the stirring speed of the first reaction vessel is 100 r / min ~ 500 r / min.

[0036] In any embodiment of this application, the stirring speed of the second reactor is 100 r / min ~ 500 r / min.

[0037] In any embodiment of this application, the stirring speed of the aging kettle is 100 r / min ~ 500 r / min.

[0038] In any embodiment of this application, in step S3, the drying temperature is 200°C to 300°C.

[0039] In any embodiment of this application, the drying time in S3 is 3 h to 8 h.

[0040] In any embodiment of this application, in S3, the dry atmosphere is a protective gas atmosphere, which includes nitrogen, an inert gas, or a combination thereof.

[0041] A third aspect of this application provides a manganese iron phosphate precursor prepared by the preparation method of the second aspect of this application, which has the chemical formula Fe. x Mn y M 1-x-y P 1-m Q m O4, 0 < x < 1, optionally, 0.2 ≤ x ≤ 0.5, 0 < y < 1, optionally, 0.5 ≤ y ≤ 0.8, 0 ≤ 1 - xy < 1, optionally, 0 < 1 - xy ≤ 0.05, 0 ≤ m ≤ 0.1, optionally, 0 < m ≤ 0.05, M represents the doping element at the manganese and iron sites, optionally including one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr, Q represents the doping element at the phosphorus site, optionally including one or more of B, S, Si, and N, and the manganese iron phosphate precursor is electrically neutral.

[0042] The manganese iron phosphate precursor provided in this application has the advantages of small particle size, narrow particle size distribution, high crystallinity, single crystal phase, regular morphology, high tap density, and high batch stability and consistency.

[0043] In any embodiment of this application, the manganese iron phosphate precursor has a spherical morphology.

[0044] In any embodiment of this application, the manganese iron phosphate precursor is orthorhombic with space group pmnb.

[0045] In any embodiment of this application, the volumetric particle sizes Dv90 and Dv50 of the manganese iron phosphate precursor satisfy 1 < Dv90 / Dv50 ≤ 2, and optionally, 1.1 ≤ Dv90 / Dv50 ≤ 1.7.

[0046] In any embodiment of this application, the volumetric particle size Dv50 of the manganese iron phosphate precursor is from 1 μm to 10 μm, and optionally from 2.5 μm to 6 μm.

[0047] This application provides a method for preparing lithium manganese iron phosphate, comprising at least the following steps: S10, mixing the lithium manganese iron phosphate precursor prepared by the method of the second aspect of this application or the lithium manganese iron phosphate precursor of the third aspect of this application with a lithium source, a source of optional dopant element N, and a source of optional dopant element R in a predetermined ratio to obtain a mixed raw material, wherein N represents a lithium site dopant element, optionally including one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W, and R represents an oxygen site dopant element, optionally including one or more of S, F, Cl, and Br; S20, sintering the mixed raw material obtained in S10 to obtain lithium manganese iron phosphate, wherein the lithium manganese iron phosphate has the chemical formula Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n M represents the doping element at the manganese and iron sites, optionally including one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr; N represents the doping element at the lithium site, optionally including one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W; Q represents the doping element at the phosphorus site, optionally including one or more of B, S, Si, and N; and R represents the doping element at the oxygen site, optionally including one of S, F, Cl, and Br. Or multiple, 0.9≤a≤1.1, 0≤b≤0.1, optionally, 0<b≤0.05, 0<x<1, optionally, 0.2≤x≤0.5, 0<y<1, optionally, 0.5≤y≤0.8, 0≤1-xy<1, optionally, 0<1-xy≤0.05, 0≤m≤0.1, optionally, 0<m≤0.05, 0≤n≤0.1, optionally, 0<n≤0.05, and the lithium manganese iron phosphate is electrically neutral.

[0048] The preparation method described in this application helps to obtain lithium manganese iron phosphate with spherical morphology and uniform distribution of elements.

[0049] In any embodiment of this application, in S10, a carbon source is also added to the mixed raw materials, thereby enabling the preparation of carbon-coated lithium manganese iron phosphate. Furthermore, the preparation method described above in this application helps to form a complete, uniform, and robust carbon coating layer, thereby improving the conductivity of the obtained lithium manganese iron phosphate.

[0050] The fifth aspect of this application provides a lithium manganese iron phosphate prepared by the preparation method of the fourth aspect of this application, which has excellent electrochemical performance.

[0051] The sixth aspect of this application provides a secondary battery comprising lithium manganese iron phosphate prepared by the preparation method of the fourth aspect of this application. Attached Figure Description

[0052] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort. In the drawings, the drawings may not be drawn to actual scale.

[0053] Figure 1 A continuous reaction system for preparing manganese iron phosphate precursors is shown.

[0054] Figure 2 The X-ray diffraction (XRD) pattern of the manganese iron phosphate precursor prepared in Example 1 is shown.

[0055] Figure 3 The image shown is a scanning electron microscope (SEM) image of the manganese iron phosphate precursor prepared in Example 1. Figure 3 (a) has a magnification of 1000x. Figure 3 (b) has a magnification of 20,000.

[0056] Figure 4 The image shows a scanning electron microscope (SEM) image of the manganese iron phosphate precursor prepared in Comparative Example 1 at 1000x magnification.

[0057] Figure 5 The image shows a scanning electron microscope (SEM) image of the manganese iron phosphate precursor prepared in Comparative Example 2 at 1000x magnification.

[0058] The reference numerals in the attached drawings are explained as follows: 1 First melting vessel; 2 Second melting vessel; 3 First reaction vessel; 4 Second reaction vessel; 5 Aging vessel; 6 First feed inlet; 7 First overflow port; 8 First shut-off valve; 9 First metering pump; 10 Second shut-off valve; 11 Second metering pump; 12 Second feed inlet; 13 Second overflow port; 14 Third feed inlet; 15 Third overflow port; 16 Third shut-off valve; 17 Fourth shut-off valve. Detailed Implementation

[0059] The following detailed description, with appropriate reference to the accompanying drawings, discloses the continuous reaction system, manganese iron phosphate precursor, lithium manganese iron phosphate, its preparation method, and embodiments of the secondary battery of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0060] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0062] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0063] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps S1 and S2, indicating that the method may include steps S1 and S2 performed sequentially, or it may include steps S2 and S1 performed sequentially. For example, the method may also include step S3, indicating that step S3 may be added to the method in any order. For example, the method may include steps S1, S2, and S3, or it may include steps S1, S3, and S2, or it may include steps S3, S1, and S2, etc.

[0064] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0065] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0066] Unless otherwise specified, in this application, the terms "first," "second," "third," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0067] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0068] The first aspect of this application provides a continuous reaction system for preparing manganese iron phosphate precursors.

[0069] like Figure 1As shown, the continuous reaction system includes a first melting vessel 1, a second melting vessel 2, a first reaction vessel 3, a second reaction vessel 4, and an aging vessel 5. The first reaction vessel 3, the second reaction vessel 4, and the aging vessel 5 are connected in series via pipelines. The first melting vessel 1 is used to contain the metal salt solution required for preparing the manganese iron phosphate precursor, and the second melting vessel 2 is used to contain the oxidant and the phosphorus source solution required for preparing the manganese iron phosphate precursor. The first reaction vessel 3 has a first inlet 6 and a first overflow 7. The first inlet 6 of the first reaction vessel is connected to the first melting vessel 1 and the second melting vessel 2 via a first pipeline and a second pipeline, respectively, so that the first reaction vessel 3 can contain the metal salt solution and the phosphorus source solution and mix them to react and generate a first reaction solution. A first shut-off valve 8 and a first metering pump 9 are installed on the first pipeline to regulate the flow rate of the metal salt solution. A second shut-off valve 10 and a second metering pump 11 are installed on the pipeline to regulate the flow rate of the phosphorus source solution; the second reactor 4 has a second inlet 12 and a second overflow 13. The second inlet 12 of the second reactor is connected to the first overflow 7 of the first reactor through a third pipeline, so that the second reactor 4 can contain the first reaction liquid from the first reactor 3 and allow it to continue to react to generate the second reaction liquid; the aging reactor 5 includes a third inlet 14 and a third overflow 15. The third inlet 14 of the aging reactor is connected to the second overflow 13 of the second reactor through a fourth pipeline, so that the aging reactor 5 can contain the second reaction liquid from the second reactor 4 and allow it to continue to react to generate the third reaction liquid; when the liquid level of the third reaction liquid is higher than the third overflow 15 of the aging reactor, the third reaction liquid flows out through the third overflow 15 of the aging reactor.

[0070] In some embodiments, a stirring device is provided in the first melting vessel 1, the second melting vessel 2, the first reaction vessel 3, the second reaction vessel 4, and the aging vessel 5.

[0071] In some embodiments, heating devices may also be provided in the first reaction vessel 3, the second reaction vessel 4, and the aging vessel 5 to adjust the reaction temperature of each vessel according to actual needs.

[0072] In some embodiments, a third shut-off valve 16 is also provided on the third pipeline, and a fourth shut-off valve 17 is also provided on the fourth pipeline.

[0073] When preparing the manganese iron phosphate precursor, the first shut-off valve 8, the second shut-off valve 10, the third shut-off valve 16, and the fourth shut-off valve 17 can all be kept open, thereby ensuring continuous feeding and continuous discharging, allowing multiple reactors to react simultaneously.

[0074] The second aspect of this application provides a method for preparing a manganese iron phosphate precursor using a continuous reaction system according to the first aspect of this application. For example... Figure 1 As shown, the method includes at least the following steps: S1, the first reactor 3, the second reactor 4, and the aging reactor 5 are connected in series via pipelines. The first reactor 3 has a first inlet 6 and a first overflow 7. The first inlet 6 of the first reactor is connected to the first melting reactor 1 via a first pipeline. The first inlet 6 of the first reactor is connected to the second melting reactor 2 via a second pipeline. A first shut-off valve 8 and a first metering pump 9 are installed on the first pipeline. A second shut-off valve 10 and a second metering pump 11 are installed on the second pipeline. The second reactor 4 has a second inlet 12 and a second overflow 13. The second inlet 12 of the second reactor is connected to the first overflow 7 of the first reactor via a third pipeline. The aging reactor 5 includes a third inlet 14 and a third overflow 15. The third inlet 14 of the aging reactor is connected to the second overflow 13 of the second reactor via a fourth pipeline. S2, the metal salt solution required for preparing the manganese iron phosphate precursor is added to the first solvent vessel 1, and the oxidant and the phosphorus source solution required for preparing the manganese iron phosphate precursor are added to the second solvent vessel 2. The metal salt solution in the first solvent vessel 1 is pumped into the first pipeline through the first shut-off valve 8 and the first metering pump 9, and the phosphorus source solution in the second solvent vessel 2 is pumped into the second pipeline through the second shut-off valve 10 and the second metering pump 11, so that the metal salt solution and the phosphorus source solution are mixed and reacted in the first reaction vessel 3 to generate the first reaction liquid. When the liquid level of the first reaction liquid is higher than the first overflow port 7 of the first reaction vessel... The first reaction liquid is automatically transported to the second reaction vessel 4 to continue the reaction and generate the second reaction liquid. When the liquid level of the second reaction liquid is higher than the second overflow port 13 of the second reaction vessel, the second reaction liquid is automatically transported to the aging vessel 5 to continue the reaction and generate the third reaction liquid. When the liquid level of the third reaction liquid is higher than the third overflow port 15 of the aging vessel, the third reaction liquid flows out automatically through the third overflow port 15 of the aging vessel. During the reaction process, the first solvent vessel 1, the second solvent vessel 2, the first reaction vessel 3, the second reaction vessel 4 and the aging vessel 5 are all under a protective gas atmosphere and each vessel is kept in a stirring state. S3, after filtering, washing and drying the third reaction liquid obtained from the third overflow port 15 of the aging kettle, the manganese iron phosphate precursor is obtained.

[0075] Existing reaction systems for preparing lithium manganese iron phosphate precursors mostly employ intermittent production processes using a single reactor or multiple reactors connected in parallel. This results in low production efficiency. Furthermore, when multiple reactors are connected in parallel, it is necessary to switch between different reactors periodically, which leads to cumbersome production processes and high labor costs.

[0076] This application adopts Figure 1The continuous reaction system shown in this application prepares ferromanganese phosphate precursors. In this continuous reaction system, the first reactor, the second reactor, and the aging reactor are connected in series, thereby ensuring continuous feeding and discharging, allowing multiple reactors to react simultaneously. Therefore, the method for preparing ferromanganese phosphate precursors provided in this application has advantages such as high production efficiency, high energy efficiency, simple process, ease of operation, and low labor costs, making it particularly suitable for large-scale industrial production.

[0077] Existing intermittent preparation methods for obtaining manganese iron phosphate precursors still suffer from defects such as large particle size, wide particle size distribution, irregular morphology, and low tap density. These defects affect the flowability, dispersibility, and processability of the product, and greatly hinder the practical application of manganese iron phosphate precursors in lithium manganese iron phosphate.

[0078] The method for preparing the ferromanganese phosphate precursor provided in this application is a continuous preparation method. In the continuous preparation process, the residence time of the ferromanganese phosphate precursor particles in the first reactor, the second reactor, and the aging reactor is consistent. Therefore, compared with the lithium iron phosphate precursor obtained by the existing intermittent preparation method, the ferromanganese phosphate precursor obtained by the continuous preparation method provided in this application has the advantages of small particle size, narrow particle size distribution, high crystallinity, single crystal phase, regular morphology, high tap density, and high batch stability and consistency.

[0079] The method for preparing the ferromanganese phosphate precursor provided in this application is a hydrothermal method, and the ferromanganese phosphate precursor obtained by the method has a regular spherical morphology. The spherical morphology of the ferromanganese phosphate precursor ensures that lithium ions can uniformly and synchronously penetrate into the center of the ferromanganese phosphate precursor from all directions through the micropores on the surface of the spherical particles during the subsequent lithium iron phosphate sintering process, and contributes to obtaining lithium iron phosphate with a spherical morphology and uniform elemental distribution. Furthermore, compared to the irregularly shaped ferromanganese phosphate precursor prepared by existing technologies, the spherical ferromanganese phosphate precursor particles obtained by the continuous preparation method of this application can also form a complete, uniform, and robust carbon coating layer during the subsequent lithium iron phosphate sintering process, thereby improving the conductivity of the obtained lithium iron phosphate.

[0080] In the preparation method of manganese iron phosphate precursor provided in this application, parameters such as the flow rate of metal salt solution and phosphorus source solution, the residence time of manganese iron phosphate precursor particles in each reactor during growth, and the reaction temperature of each reactor can be precisely adjusted. Therefore, the preparation method provided in this application also has good production flexibility.

[0081] The residence time of ferromanganese phosphate precursor particles during growth in each reactor (first reactor, second reactor, and aging reactor) is negatively correlated with the flow rates of the metal salt solution and phosphorus source solution, and positively correlated with the volume of each reactor. When the flow rates of the metal salt solution and phosphorus source solution are high, the residence time of the ferromanganese phosphate precursor particles in each reactor is short; when the flow rates are low, the residence time is long; when the volume of each reactor is small, the residence time is short; when the volume of each reactor is large, the residence time is long. Therefore, the particle size of ferromanganese phosphate precursor can be adjusted by regulating the flow rates of the metal salt solution and phosphorus source solution, as well as the volume of each reactor.

[0082] The reaction temperature also affects the particle size and morphology of the obtained manganese ferric phosphate precursor. Therefore, the particle size and morphology of the manganese ferric phosphate precursor can be adjusted by regulating the reaction temperature of each reactor within different ranges.

[0083] Therefore, the preparation method of the manganese iron phosphate precursor provided in this application can also adjust the crystal particle growth rate and the size and morphology of the crystal particles, thereby meeting different production needs and facilitating the preparation of lithium manganese iron phosphate with different particle sizes.

[0084] In some embodiments, a complexing agent may also be added to the first melting vessel.

[0085] Existing technologies for preparing ferromanganese phosphate precursors via conventional co-precipitation methods suffer from limitations. Due to the varying precipitation rates of different metal ions, uniform precipitation cannot be achieved. Furthermore, the molar ratios of the metal elements in the obtained ferromanganese phosphate precursor particles differ significantly from those in the raw materials, impacting product performance and consistency. Moreover, the ferromanganese phosphate precursor particles prepared by conventional co-precipitation methods are typically irregularly shaped flakes or blocks, resulting in low tap density. This negatively affects the product's flowability, dispersibility, and processability, significantly hindering the practical application of ferromanganese phosphate precursors in lithium iron phosphate.

[0086] The preparation method of the manganese ferric phosphate precursor provided in this application is a hydrothermal method, and a complexing agent is added to the first melting vessel in this preparation method. The complexing agent can complex metal ions to control free metal ions, thereby improving the conversion efficiency of metal ions and reducing the difference in reaction rate between different metal ions in the reaction solution, thus achieving uniform deposition and crystallization. Therefore, when a complexing agent is added to the first melting vessel, the preparation method of this application can obtain spherical manganese ferric phosphate precursor particles with high purity and uniform metal element distribution, which have a high tap density; at the same time, the molar ratio of each metal element in the spherical manganese ferric phosphate precursor particles obtained by the preparation method of this application is less different from the molar ratio of each metal element in the raw material, thereby enabling precise control of the metal element content.

[0087] Optionally, the complexing agent comprises one or more of aminocarboxylates, hydroxycarboxylates, and organophosphonates. More preferably, the complexing agent comprises one or more of sodium triacetate, disodium ethylenediaminetetraacetate, sodium gluconate, and sodium citrate.

[0088] Optionally, the mass concentration of the complexing agent is below 10 wt%, more preferably 1 wt% to 10 wt%, based on the total mass of the metal salt solution.

[0089] In some embodiments, a surfactant may also be added to the first melting vessel, thereby helping to better adjust the morphology of the manganese iron phosphate precursor particles.

[0090] Optionally, the surfactant includes one or more of hexadecyltrimethylammonium bromide, sodium dodecyl sulfonate, and polyvinylpyrrolidone.

[0091] Optionally, the mass concentration of the surfactant is below 5 wt%, and can be selected as 1 wt% to 5 wt%, based on the total mass of the metal salt solution.

[0092] In some embodiments, the reaction temperature of the first reactor is lower than that of the second reactor, and the reaction temperature of the aging reactor is lower than that of the second reactor.

[0093] In the preparation method of the manganese iron phosphate precursor provided in this application, the first reactor, the second reactor, and the aging reactor are connected in series, and the reaction temperatures of the first reactor and the aging reactor are set lower than those of the second reactor. This allows the different reactors in the continuous reaction system to play different functions. The lower reaction temperature of the first reactor allows for pre-mixing and pre-nucleation of the metal salt solution and the phosphorus source solution. At this temperature, metal ions and phosphate ions tend to form a large number of crystal nuclei, which is beneficial for better crystallization and particle size distribution control in the second reactor. The higher reaction temperature of the second reactor provides sufficient energy to promote crystal growth and crystallization when the reaction solution flows from the first reactor to the second reactor, and also improves the crystallinity of the crystal nuclei while avoiding crystal aggregation. The lower reaction temperature of the aging reactor allows for cooling when the reaction solution flows from the second reactor to the aging reactor, enabling unreacted raw materials to continue crystallizing on the surface of the already formed crystal particles, thus increasing the size of the crystal particles and narrowing their particle size distribution.

[0094] Therefore, by adjusting the reaction temperature of each reactor, not only can the particle size of the obtained manganese ferric phosphate precursor be adjusted, but it also helps to obtain manganese ferric phosphate precursor particles with narrow particle size distribution, high crystallinity, single crystal phase, regular morphology, and high tap density.

[0095] In some embodiments, the reaction temperature of the first reactor is optionally 70°C to 90°C.

[0096] In some embodiments, the reaction temperature of the second reactor is optionally 150°C to 250°C.

[0097] In some embodiments, the reaction temperature of the aging reactor is optionally 20°C to 30°C.

[0098] In some embodiments, the flow rate of the metal salt solution in the first pipeline (or the pumping speed of the first metering pump) is 0.2 L / min to 2 L / min, and optionally 0.25 L / min to 1 L / min.

[0099] In some embodiments, the flow rate of the phosphorus source solution in the second pipeline (or the pumping speed of the second metering pump) is 0.2 L / min to 2 L / min, and optionally 0.25 L / min to 1 L / min.

[0100] In some embodiments, the flow rates of the metal salt solution and the phosphorus source solution are the same (i.e., the pumping speeds of the first metering pump and the second metering pump are the same), which helps to improve the consistency of the obtained manganese iron phosphate precursor particles.

[0101] In some embodiments, the residence time of the manganese iron phosphate precursor in the first reactor during growth is 1 h to 4 h.

[0102] In some embodiments, the residence time of the manganese iron phosphate precursor in the second reactor during growth is 1 h to 16 h, optionally 4 h to 16 h.

[0103] In some embodiments, the residence time of the manganese iron phosphate precursor in the aging reactor during growth is 1 h to 48 h, optionally 12 h to 48 h.

[0104] In some embodiments, the volume of the first reactor is less than or equal to the volume of the second reactor, thereby allowing the manganese ferrophosphate precursor to remain in the second reactor for a longer period during growth, which helps to achieve higher crystallinity in the obtained manganese ferrophosphate precursor particles. Optionally, the ratio of the volume of the first reactor to the volume of the second reactor is 1:(1~4), more preferably 1:(2~4).

[0105] In some embodiments, the volume of the first reactor is less than or equal to the volume of the aging reactor, thereby allowing the manganese ferrophosphate precursor to remain in the aging reactor for a longer period during growth, which helps to produce a larger particle size in the obtained manganese ferrophosphate precursor. Optionally, the ratio of the volume of the first reactor to the volume of the aging reactor is 1:(1~12), more preferably 1:(4~12).

[0106] In some embodiments, the volume of the second reactor is less than or equal to the volume of the aging reactor, thereby allowing the ferromanganese phosphate precursor to remain in the aging reactor for a longer period during growth, which helps to produce a larger particle size of the obtained ferromanganese phosphate precursor. Optionally, the ratio of the volume of the second reactor to the volume of the aging reactor is 1:(1~3), more preferably 1:(2~3).

[0107] In some embodiments, in S3, optionally, the drying temperature is 200 °C ~ 300 °C.

[0108] In some embodiments, in S3, optionally, the drying time is 3 h to 8 h.

[0109] In some embodiments, in S3, drying can be carried out in a dryer, and the drying atmosphere can be a protective gas atmosphere, including nitrogen, an inert gas, or a combination thereof. Optionally, the inert gas includes helium, argon, or a combination thereof.

[0110] In some embodiments, the metal salt required for preparing the manganese iron phosphate precursor includes a water-soluble iron salt, a water-soluble manganese salt, and optionally a salt of a water-soluble dopant element M, where M represents a dopant element at the manganese and iron sites, and optionally includes one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr.

[0111] The water-soluble iron salt can be any existing compound containing iron ions (e.g., ferrous ions, ferric ions) that is soluble in water. Optionally, the water-soluble iron salt includes one or more of ferrous chloride, ferrous nitrate, ferrous sulfate, ferrous acetate, ferric chloride, ferric nitrate, ferric sulfate, and ferric acetate.

[0112] The water-soluble manganese salt can be any existing water-soluble manganese ion-containing compound (e.g., divalent manganese ion). Optionally, the water-soluble manganese salt includes one or more of manganese chloride, manganese nitrate, manganese sulfate, and manganese acetate.

[0113] The salt of the water-soluble dopant element M can be any existing water-soluble compound containing M ions. Optionally, the salt of the water-soluble dopant element M includes one or more of the following: hydrochloride, nitrate, sulfate, and acetate of the dopant element M.

[0114] In some embodiments, the phosphorus source required for preparing the manganese iron phosphate precursor includes one or more of phosphoric acid and water-soluble phosphates. Optionally, the water-soluble phosphate includes one or more of trisodium phosphate, tripotassium phosphate, monoammonium hydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

[0115] In some embodiments, the phosphorus source required for preparing the manganese iron phosphate precursor may further include a source of a water-soluble dopant element Q, where Q represents the dopant element at the phosphorus site, optionally including one or more of B, S, Si, and N. In some embodiments, the source of the dopant element Q may optionally include one or more of the sulfate, borate, nitrate, and silicate of the dopant element Q.

[0116] In some embodiments, the metal salt solution is an aqueous solution of a metal salt, for example, obtained by uniformly mixing the metal salt required for preparing the manganese iron phosphate precursor with deionized water.

[0117] In some embodiments, the phosphorus source solution is an aqueous solution of a phosphorus source, for example, obtained by uniformly mixing an oxidant, a phosphorus source, and deionized water.

[0118] In some embodiments, the oxidant includes one or more of hydrogen peroxide, nitric acid, sodium hypochlorite, potassium hypochlorite, sodium chlorate, and potassium chlorate, and may be selected as hydrogen peroxide.

[0119] In some embodiments, the concentration of the metal salt solution is 0.5 mol / L to 2 mol / L, and may be 0.5 mol / L to 1 mol / L.

[0120] In some embodiments, the concentration of the phosphorus source solution is 0.5 mol / L to 2 mol / L, and may be 0.5 mol / L to 1 mol / L.

[0121] The amount of phosphorus source added can be excessive compared to the metal salt. In some embodiments, the molar ratio of the metal salt to the phosphorus source is 1:1 to 1:3.

[0122] The amount of oxidant added can be excessive compared to the metal salt. In some embodiments, the molar ratio of the metal salt to the oxidant is 1:(0.1~1.2), optionally 1:(0.5~0.6).

[0123] During the reaction, the first melting vessel, the second melting vessel, the first reaction vessel, the second reaction vessel, and the aging vessel are all kept under stirring. In some embodiments, the stirring speed of the first melting vessel is 100 r / min to 500 r / min. In some embodiments, the stirring speed of the second melting vessel is 100 r / min to 500 r / min. In some embodiments, the stirring speed of the first reaction vessel is 100 r / min to 500 r / min. In some embodiments, the stirring speed of the second reaction vessel is 100 r / min to 500 r / min. In some embodiments, the stirring speed of the aging vessel is 100 r / min to 500 r / min.

[0124] During the reaction, a protective gas is introduced into the first melting vessel, the second melting vessel, the first reaction vessel, the second reaction vessel, and the aging vessel. In some embodiments, the protective gas includes nitrogen, an inert gas, or a combination thereof. Optionally, the inert gas includes helium, argon, or a combination thereof.

[0125] In the preparation method of the manganese iron phosphate precursor provided in this application, unless otherwise specified, all raw materials can be purchased directly.

[0126] A third aspect of this application provides a manganese iron phosphate precursor, which is prepared by the preparation method of the second aspect of this application. The manganese iron phosphate precursor has the chemical formula Fe. x Mn y M 1-x-y P 1-m Q mO4, 0 < x < 1, 0 < y < 1, 0 ≤ 1 - xy < 1, 0 ≤ m ≤ 0.1, M represents the doping element at the manganese and iron sites, optionally including one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr, Q represents the doping element at the phosphorus site, optionally including one or more of B, S, Si, and N, and the manganese iron phosphate precursor is electrically neutral.

[0127] The manganese iron phosphate precursor provided in this application is prepared by the method of the second aspect of the embodiments of this application, and therefore has the advantages of small particle size, narrow particle size distribution, high crystallinity, single crystal phase, regular morphology, high tap density, and high batch stability and consistency.

[0128] In some embodiments, the manganese iron phosphate precursor has a spherical morphology.

[0129] In some embodiments, the manganese iron phosphate precursor is orthorhombic with space group pmnb.

[0130] In some embodiments, the volumetric particle sizes Dv90 and Dv50 of the manganese iron phosphate precursor satisfy 1 < Dv90 / Dv50 ≤ 2, and optionally, 1.1 ≤ Dv90 / Dv50 ≤ 1.7.

[0131] In some embodiments, the volumetric particle size Dv50 of the manganese iron phosphate precursor is 1 μm to 10 μm, and optionally 2.5 μm to 6 μm.

[0132] In some embodiments, 0.2 ≤ x ≤ 0.5.

[0133] In some embodiments, 0.5 ≤ y ≤ 0.8.

[0134] In some embodiments, 1-xy = 0; in other embodiments, 0 < 1-xy ≤ 0.05.

[0135] In some embodiments, m = 0; in other embodiments, 0 < m ≤ 0.05.

[0136] The fourth aspect of this application provides a method for preparing lithium manganese iron phosphate, comprising at least the following steps: S10, mixing the lithium manganese iron phosphate precursor prepared by the method of the second aspect of this application or the lithium manganese iron phosphate precursor of the third aspect of this application with a lithium source, a source of optional dopant element N, and a source of optional dopant element R in a predetermined ratio to obtain a mixed raw material, wherein N represents a lithium site dopant element, optionally including one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W, and R represents an oxygen site dopant element, optionally including one or more of S, F, Cl, and Br; S20, sintering the mixed raw material obtained in S10 to obtain lithium manganese iron phosphate, wherein the lithium manganese iron phosphate has the chemical formula Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n M represents the doping element at the manganese and iron sites, optionally including one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr; N represents the doping element at the lithium site, optionally including one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W; Q represents the doping element at the phosphorus site, optionally including one or more of B, S, Si, and N; and R represents the doping element at the oxygen site, optionally including one of S, F, Cl, and Br. Or multiple, 0.9≤a≤1.1, 0≤b≤0.1, optionally, 0<b≤0.05, 0<x<1, optionally, 0.2≤x≤0.5, 0<y<1, optionally, 0.5≤y≤0.8, 0≤1-xy<1, optionally, 0<1-xy≤0.05, 0≤m≤0.1, optionally, 0<m≤0.05, 0≤n≤0.1, optionally, 0<n≤0.05, and the lithium manganese iron phosphate is electrically neutral.

[0137] When preparing lithium manganese iron phosphate using the aforementioned ferromanganese phosphate precursor of this application, during the sintering process, lithium ions can uniformly and synchronously penetrate into the center of the ferromanganese phosphate precursor from all directions through the micropores on the surface of the spherical ferromanganese phosphate precursor particles, which helps to obtain lithium manganese iron phosphate with spherical morphology and uniform distribution of elements. Therefore, the preparation method of this application enables the obtained lithium manganese iron phosphate to have excellent electrochemical performance.

[0138] In some embodiments, the lithium source may be a lithium-containing compound known in the art that can be used to prepare lithium manganese iron phosphate cathode active materials. For example, the lithium source may include one or more of Li2CO3, LiOH, Li3PO4 and LiH2PO4.

[0139] In some embodiments, the source of the dopant element N includes one or more of the following: hydrochloride, nitrate, sulfate, and acetate of the dopant element N.

[0140] In some embodiments, the source of the dopant element R includes one or more of the elemental form of dopant element R and an ammonium salt.

[0141] By selecting the sources of the aforementioned doping elements, the uniformity of their distribution can be improved, thereby enhancing the electrochemical performance of lithium manganese iron phosphate.

[0142] In some embodiments, in S10, a carbon source may be added to the mixed raw materials, thereby enabling the preparation of carbon-coated lithium manganese iron phosphate. When preparing lithium manganese iron phosphate using the above-described iron manganese phosphate precursor of this application, a complete, uniform, and robust carbon coating layer can also be formed on the surface of the lithium manganese iron phosphate to improve the conductivity of the obtained lithium manganese iron phosphate.

[0143] In some embodiments, the carbon source includes one or more of organic carbon sources and inorganic carbon sources, and optionally includes one or more of glucose, sucrose, starch, fructose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0144] In the above preparation method, the amount of each of the doping elements N and R added depends on the target doping amount; the amount of lithium source added conforms to the stoichiometry of lithium manganese iron phosphate. In some embodiments, the amount of lithium source added may be slightly excessive, for example, it may be 100% to 110% of the theoretical mass of the lithium source, where the theoretical mass of the lithium source refers to the mass of the lithium source calculated based on the stoichiometry of lithium manganese iron phosphate.

[0145] Unless otherwise specified, all raw materials used in the above preparation method can be purchased directly.

[0146] The fifth aspect of this application provides a lithium manganese iron phosphate prepared by the method of the fourth aspect of this application.

[0147] The lithium manganese iron phosphate has the chemical formula Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R nM represents the doping element at the manganese and iron sites, optionally including one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr; N represents the doping element at the lithium site, optionally including one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W; Q represents the doping element at the phosphorus site, optionally including one or more of B, S, Si, and N; and R represents the doping element at the oxygen site, optionally including one of S, F, Cl, and Br. Or multiple, 0.9≤a≤1.1, 0≤b≤0.1, optionally, 0<b≤0.05, 0<x<1, optionally, 0.2≤x≤0.5, 0<y<1, optionally, 0.5≤y≤0.8, 0≤1-xy<1, optionally, 0<1-xy≤0.05, 0≤m≤0.1, optionally, 0<m≤0.05, 0≤n≤0.1, optionally, 0<n≤0.05, and the lithium manganese iron phosphate is electrically neutral.

[0148] In some embodiments, the lithium manganese iron phosphate is further coated with carbon, thereby improving the conductivity of the lithium manganese iron phosphate.

[0149] A sixth aspect of this application provides a secondary battery comprising lithium manganese iron phosphate prepared by the method of a fourth aspect of this application. The lithium manganese iron phosphate can be used as a positive electrode active material in the secondary battery and also helps to improve the electrochemical performance of the secondary battery.

[0150] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0151] Example 1 use Figure 1 The continuous reaction system shown is used to prepare the manganese iron phosphate precursor.

[0152] Water-soluble manganese chloride (divalent manganese salt), water-soluble ferrous chloride (divalent ferric salt), and deionized water were added to the first dissolving vessel to prepare a 1 mol / L metal salt solution. In the prepared metal salt solution, the molar ratio of divalent manganese ions to divalent ferric ions was 5:5. Hydrogen peroxide (oxidant), phosphoric acid (phosphoric acid source), and deionized water were added to the second dissolving vessel to prepare a 1 mol / L phosphorus source solution, with the molar ratio of hydrogen peroxide to the metal salt controlled at (0.5~0.6):1.

[0153] like Figure 1 As shown, nitrogen gas is introduced into the first melting vessel, the second melting vessel, the first reaction vessel, the second reaction vessel, and the aging vessel, and the stirring speed of each vessel is 200 r / min during the reaction. The reaction temperature of the first reaction vessel is controlled at 90℃, the reaction temperature of the second reaction vessel is controlled at 160℃, and the reaction temperature of the aging vessel is controlled at 25℃.

[0154] The metal salt solution and phosphorus source solution are continuously pumped from the first and second dissolving vessels into the first reaction vessel through a shut-off valve and a metering pump, respectively, so that they are mixed and react to generate the first reaction solution. The flow rates of the metal salt solution and the phosphorus source solution are both 0.5 L / min.

[0155] After 2 hours of reaction, the liquid level of the first reaction liquid is higher than the first overflow port, and then it automatically flows out from the first overflow port into the second reaction vessel to continue the reaction and generate the second reaction liquid.

[0156] After the reaction continued for 8 hours, the liquid level of the second reaction liquid was higher than that of the second overflow port, and then it automatically flowed out from the second overflow port into the aging kettle to continue the reaction and generate the third reaction liquid.

[0157] After the reaction continued for 24 hours, the liquid level of the third reaction solution was higher than that of the third overflow port, and then it automatically flowed out from the third overflow port.

[0158] The obtained third reaction solution was filtered and washed by a filter press, then transferred to a desiccator and dried at 200 °C for 6 h in a nitrogen atmosphere to remove water of crystallization, finally yielding the manganese iron phosphate precursor.

[0159] Example 2 use Figure 1 The continuous reaction system shown is used to prepare the manganese iron phosphate precursor.

[0160] A 0.5 mol / L metal salt solution was prepared by adding water-soluble divalent manganese nitrate (manganese nitrate), water-soluble divalent ferrous nitrate (ferrous nitrate), sodium triacetate (sodium aminotriacetate) as a complexing agent, and deionized water to the first solvent vessel. In the prepared metal salt solution, the molar ratio of divalent manganese ions to divalent ferrous ions was 6:4, and the mass concentration of the complexing agent was 1 wt%. A 0.5 mol / L phosphorus source solution was prepared by adding hydrogen peroxide (oxidant), phosphoric acid (phosphoric acid source), and deionized water to the second solvent vessel, with the molar ratio of hydrogen peroxide to the metal salt controlled at (0.5~0.6):1.

[0161] like Figure 1As shown, nitrogen gas is introduced into the first melting vessel, the second melting vessel, the first reaction vessel, the second reaction vessel, and the aging vessel, and the stirring speed of each vessel is 250 r / min during the reaction. The reaction temperature of the first reaction vessel is controlled at 80℃, the reaction temperature of the second reaction vessel is controlled at 180℃, and the reaction temperature of the aging vessel is controlled at 25℃.

[0162] The metal salt solution and phosphorus source solution are continuously transported from the first and second dissolving vessels to the first reaction vessel through a shut-off valve and a metering pump, respectively, so that they are mixed and react to generate the first reaction solution. The flow rates of the metal salt solution and the phosphorus source solution are both 0.25 L / min.

[0163] After 4 hours of reaction, the liquid level of the first reaction liquid is higher than the first overflow port, and then it automatically flows out from the first overflow port into the second reaction vessel to continue the reaction and generate the second reaction liquid.

[0164] After the reaction continued for 16 hours, the liquid level of the second reaction liquid was higher than that of the second overflow port, and then it automatically flowed out from the second overflow port into the aging kettle to continue the reaction and generate the third reaction liquid.

[0165] After the reaction continued for 48 hours, the liquid level of the third reaction solution was higher than that of the third overflow port, and then it automatically flowed out from the third overflow port.

[0166] The obtained third reaction solution was filtered and washed by a filter press, then transferred to a desiccator and dried at 200 °C for 6 h in a nitrogen atmosphere to remove water of crystallization, finally yielding the manganese iron phosphate precursor.

[0167] Example 3 use Figure 1 The continuous reaction system shown is used to prepare the manganese iron phosphate precursor.

[0168] A 1 mol / L metal salt solution was prepared by adding water-soluble divalent manganese sulfate, water-soluble divalent ferrous sulfate, water-soluble divalent chromium sulfate, disodium ethylenediaminetetraacetate (EDTA) complexing agent, and deionized water to the first solvent vessel. In the prepared metal salt solution, the molar ratio of divalent manganese ions, divalent ferrous ions, and divalent chromium ions was 6.9:3:0.1, and the mass concentration of the complexing agent was 5 wt%. A 1 mol / L phosphorus source solution was prepared by adding hydrogen peroxide (oxidant), trisodium phosphate (phosphorus source), and deionized water to the second solvent vessel, with the molar ratio of hydrogen peroxide to the metal salt controlled at (0.5~0.6):1.

[0169] like Figure 1As shown, nitrogen gas is introduced into the first melting vessel, the second melting vessel, the first reaction vessel, the second reaction vessel, and the aging vessel, and the stirring speed of each vessel during the reaction is 150 r / min. The reaction temperature of the first reaction vessel is controlled at 90℃, the reaction temperature of the second reaction vessel is controlled at 160℃, and the reaction temperature of the aging vessel is controlled at 25℃.

[0170] The metal salt solution and phosphorus source solution are continuously transported from the first and second dissolving vessels to the first reaction vessel through a shut-off valve and a metering pump, respectively, so that they are mixed and react to generate the first reaction solution. The flow rates of the metal salt solution and the phosphorus source solution are both 1 L / min.

[0171] After 1 hour of reaction, the liquid level of the first reaction liquid is higher than the first overflow port, and then it automatically flows out from the first overflow port into the second reaction vessel to continue the reaction and generate the second reaction liquid.

[0172] After the reaction continued for 4 hours, the liquid level of the second reaction liquid was higher than that of the second overflow port, and then it automatically flowed out from the second overflow port into the aging kettle to continue the reaction and generate the third reaction liquid.

[0173] After the reaction continued for 12 hours, the liquid level of the third reaction solution was higher than that of the third overflow port, and then it automatically flowed out from the third overflow port.

[0174] The obtained third reaction solution was filtered and washed by a filter press, then transferred to a desiccator and dried at 200 °C for 6 h in a nitrogen atmosphere to remove water of crystallization, finally yielding the manganese iron phosphate precursor.

[0175] Comparative Example 1 Water-soluble manganese nitrate (divalent manganese salt), water-soluble ferrous nitrate (divalent ferrous salt), and deionized water were added to the first dissolving vessel to prepare a 0.5 mol / L metal salt solution. In the prepared metal salt solution, the molar ratio of divalent manganese ions to divalent ferrous ions was 6:4. Hydrogen peroxide (oxidant), phosphoric acid (phosphorus source), and deionized water were added to the second dissolving vessel to prepare a 0.5 mol / L phosphorus source solution, with the molar ratio of hydrogen peroxide to the metal salt controlled at (0.5~0.6):1.

[0176] The metal salt solution and phosphorus source solution were simultaneously pumped into the reactor at a metering pump speed of 0.25 L / min. Nitrogen gas was introduced into the reactor, and rapid stirring was started at a speed of 250 r / min. The reactor temperature was controlled at 180 °C, and the reaction time was 20 h. After the reaction, the reactor was allowed to cool naturally from 180 °C to room temperature to obtain a slurry. The obtained slurry was discharged from the reactor outlet, filtered and washed using a filter press, and then transferred to a dryer and dried at 200 °C for 6 h in a nitrogen atmosphere to remove water of crystallization, finally obtaining the manganese iron phosphate precursor.

[0177] Comparative Example 2 A 0.5 mol / L metal salt solution was prepared by adding water-soluble divalent manganese nitrate (manganese nitrate), water-soluble divalent ferrous nitrate (ferrous nitrate), sodium triacetate (sodium aminotriacetate) as a complexing agent, and deionized water to the first solvent vessel. In the prepared metal salt solution, the molar ratio of divalent manganese ions to divalent ferrous ions was 6:4, and the mass concentration of the complexing agent was 1 wt%. A 0.5 mol / L phosphorus source solution was prepared by adding hydrogen peroxide (oxidant), phosphoric acid (phosphoric acid source), and deionized water to the second solvent vessel, with the molar ratio of hydrogen peroxide to the metal salt controlled at (0.5~0.6):1.

[0178] The metal salt solution and phosphorus source solution were simultaneously pumped into the reactor at a metering pump speed of 0.25 L / min. Nitrogen gas was introduced into the reactor, and rapid stirring was started at a speed of 250 r / min. The reactor temperature was controlled at 180 °C, and the reaction time was 20 h. After the reaction, the reactor was allowed to cool naturally from 180 °C to room temperature to obtain a slurry. The obtained slurry was discharged from the reactor outlet, filtered and washed using a filter press, and then transferred to a dryer and dried at 200 °C for 6 h in a nitrogen atmosphere to remove water of crystallization, finally obtaining the manganese iron phosphate precursor.

[0179] Test section (1) Particle size test: The volumetric particle size of the prepared manganese iron phosphate precursor was tested using a Malvern Master Size 3000 laser particle size analyzer. Dv50 and Dv90 refer to the particle size corresponding to a cumulative volume distribution percentage of 50% and 90%, respectively. The test standard can be found in GB / T 19077-2016.

[0180] (2) Mn / Fe molar ratio test: The contents of manganese and iron in the prepared manganese iron phosphate precursor were tested and the molar ratio was calculated using a Plasma 3000 inductively coupled plasma optical emission spectrometer (ICP-OES).

[0181] Table 1 Figure 2 The X-ray diffraction (XRD) pattern of the manganese iron phosphate precursor prepared in Example 1 is shown. Figure 3 The image shown is a scanning electron microscope (SEM) image of the manganese iron phosphate precursor prepared in Example 1. Figure 3 (a) has a magnification of 1000x. Figure 3 (b) has a magnification of 20,000. Figure 4 The image shows a scanning electron microscope (SEM) image of the manganese iron phosphate precursor prepared in Comparative Example 1 at 1000x magnification. Figure 5 The image shows a scanning electron microscope (SEM) image of the manganese iron phosphate precursor prepared in Comparative Example 2 at 1000x magnification.

[0182] Based on the test results in Table 1 and Figures 2 to 3 It can be seen that the manganese iron phosphate precursor prepared by the continuous preparation method provided in this application has the advantages of small particle size, narrow particle size distribution, high crystallinity, single crystal phase, and regular morphology.

[0183] Based on the test results in Table 1 and Figures 4 to 5 It can be seen that the precursor of manganese iron phosphate prepared by the existing intermittent preparation method has large particle size, wide particle size distribution, and low morphological regularity.

[0184] Based on the test results of Example 2, Comparative Example 1, and Comparative Example 2, it can be seen that the difference between the Mn / Fe molar ratio in the manganese iron phosphate precursor particles prepared by the continuous preparation method provided in this application and the Mn / Fe molar ratio in the metal salt solution is smaller, thereby enabling precise control of the manganese and iron content.

[0185] Based on the test results of Example 2, Comparative Example 1 and Comparative Example 2, it can be seen that the complexing agent helps to further precisely control the content of manganese and iron in the prepared manganese iron phosphate precursor particles.

[0186] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a manganese iron phosphate precursor, comprising at least the following steps: S1, the first reactor, the second reactor, and the aging reactor are connected in series via pipelines. The first reactor has a first inlet and a first overflow. The first inlet of the first reactor is connected to the first melting vessel via a first pipeline. The first inlet of the first reactor is connected to the second melting vessel via a second pipeline. A first shut-off valve and a first metering pump are installed on the first pipeline. A second shut-off valve and a second metering pump are installed on the second pipeline. The second reactor has a second inlet and a second overflow. The second inlet of the second reactor is connected to the first overflow of the first reactor via a third pipeline. The aging reactor includes a third inlet and a third overflow. The third inlet of the aging reactor is connected to the second overflow of the second reactor via a fourth pipeline. S2, the metal salt solution required for preparing the manganese iron phosphate precursor is added to the first solvent vessel, and the oxidant and the phosphorus source solution required for preparing the manganese iron phosphate precursor are added to the second solvent vessel. The metal salt solution in the first solvent vessel is pumped into the first pipeline through the first shut-off valve and the first metering pump, and the phosphorus source solution in the second solvent vessel is pumped into the second pipeline through the second shut-off valve and the second metering pump. This allows the metal salt solution and the phosphorus source solution to mix and react in the first reactor to generate a first reaction liquid. When the liquid level of the first reaction liquid is higher than the first overflow port of the first reactor, the first reaction liquid is automatically transferred to the second reactor to continue the reaction and generate a second reaction liquid. When the liquid level of the second reaction liquid is higher than the second overflow port of the second reactor, the second reaction liquid is automatically transferred to the aging reactor to continue the reaction and generate a third reaction liquid. When the liquid level of the third reaction liquid is higher than the third overflow port of the aging reactor, the third reaction liquid automatically flows out through the third overflow port of the aging reactor. During the reaction, the first melting vessel, the second melting vessel, the first reaction vessel, the second reaction vessel, and the aging vessel are all under a protective gas atmosphere and each vessel is kept under stirring. S3 involves filtering, washing, and drying the third reaction liquid obtained from the third overflow port of the aging reactor to obtain the manganese iron phosphate precursor. The reaction temperature in the first reactor is 70℃ ~ 90℃, the reaction temperature in the second reactor is 150℃ ~ 250℃, and the reaction temperature in the aging reactor is 20℃ ~ 30℃.

2. The preparation method according to claim 1, wherein, A complexing agent was also added to the first melting vessel.

3. The preparation method according to claim 2, wherein, The complexing agent includes one or more of aminocarboxylate, hydroxycarboxylate, and organophosphonate.

4. The preparation method according to claim 3, wherein, The complexing agent includes one or more of sodium triacetate, disodium ethylenediaminetetraacetate, sodium gluconate, and sodium citrate.

5. The preparation method according to any one of claims 1-4, wherein, Surfactants were also added to the first melting vessel.

6. The preparation method according to claim 5, wherein, The surfactant includes one or more of hexadecyltrimethylammonium bromide, sodium dodecyl sulfonate, and polyvinylpyrrolidone.

7. The preparation method according to claim 1, wherein, The flow rate of the metal salt solution in the first pipe is 0.2 L / min ~ 2 L / min; and / or, The flow rate of the phosphorus source solution in the second pipe is 0.2 L / min ~ 2 L / min; and / or, The flow rates of the metal salt solution and the phosphorus source solution are the same.

8. The preparation method according to claim 1, wherein, The flow rate of the metal salt solution in the first pipe is 0.25 L / min ~ 1 L / min; and / or, The flow rate of the phosphorus source solution in the second pipe is 0.25 L / min ~ 1 L / min.

9. The preparation method according to claim 1, wherein, The residence time of the manganese iron phosphate precursor in the first reactor during growth is 1 h to 4 h; and / or, The residence time of the manganese iron phosphate precursor in the second reactor during growth is 1 h to 16 h; and / or, The residence time of the manganese iron phosphate precursor in the aging reactor during growth is 1 h to 48 h.

10. The preparation method according to claim 9, wherein, The residence time of the manganese iron phosphate precursor in the second reactor during growth is 4 h to 16 h; and / or, The residence time of the manganese iron phosphate precursor in the aging reactor during growth is 12 h to 48 h.

11. The preparation method according to claim 1, wherein, The volume of the first reactor is less than or equal to the volume of the second reactor; and / or, The volume of the first reaction vessel is less than or equal to the volume of the aging vessel; and / or, The volume of the second reaction vessel is less than or equal to the volume of the aging vessel.

12. The preparation method according to claim 11, wherein, The volume ratio of the first reactor to the second reactor is 1:(1~4); and / or, The volume ratio of the first reaction vessel to the aging vessel is 1:(1~12); and / or, The ratio of the volume of the second reaction vessel to the volume of the aging vessel is 1:(1~3).

13. The preparation method according to claim 12, wherein, The volume ratio of the first reactor to the second reactor is 1:(2~4); and / or, The volume ratio of the first reaction vessel to the aging vessel is 1:(4~12); and / or, The ratio of the volume of the second reaction vessel to the volume of the aging vessel is 1:(2~3).

14. The preparation method according to claim 1, wherein, The metal salts required for preparing the manganese iron phosphate precursor include water-soluble iron salts, water-soluble manganese salts, and optional water-soluble dopant element M, where M represents the dopant element at the manganese and iron sites.

15. The preparation method according to claim 14, wherein, M includes one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr.

16. The preparation method according to claim 14, wherein, The water-soluble iron salt includes one or more of ferrous chloride, ferrous nitrate, ferrous sulfate, ferrous acetate, ferric chloride, ferric nitrate, ferric sulfate, and ferric acetate.

17. The preparation method according to claim 14, wherein, The water-soluble manganese salt includes one or more of manganese chloride, manganese nitrate, manganese sulfate, and manganese acetate.

18. The preparation method according to claim 14, wherein, The salts of the water-soluble dopant element M include one or more of the following: hydrochloride, nitrate, sulfate, and acetate of the dopant element M.

19. The preparation method according to claim 1, wherein, The phosphorus source required for preparing the manganese iron phosphate precursor includes one or more of phosphoric acid and water-soluble phosphates.

20. The preparation method according to claim 19, wherein, The water-soluble phosphates include one or more of trisodium phosphate, tripotassium phosphate, monoammonium hydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

21. The preparation method according to claim 19, wherein, The phosphorus source required for preparing the manganese iron phosphate precursor also includes a source of water-soluble dopant element Q, where Q represents the dopant element at the phosphorus site.

22. The preparation method according to claim 21, wherein, Q includes one or more of B, S, Si, and N.

23. The preparation method according to claim 21, wherein, The source of the dopant element Q includes one or more of the following: sulfate, borate, nitrate, and silicate of the dopant element Q.

24. The preparation method according to claim 1, wherein, The oxidizing agent includes one or more of hydrogen peroxide, nitric acid, sodium hypochlorite, potassium hypochlorite, sodium chlorate, and potassium chlorate.

25. The preparation method according to claim 24, wherein, The oxidant is hydrogen peroxide.

26. The preparation method according to claim 24, wherein, The molar ratio of the metal salt to the oxidant is 1:(0.1~1.2).

27. The preparation method according to claim 26, wherein, The molar ratio of the metal salt to the oxidant is 1:(0.5~0.6).

28. The preparation method according to claim 1, wherein, The concentration of the metal salt solution is 0.5 mol / L to 2 mol / L; and / or, The concentration of the phosphorus source solution is 0.5 mol / L to 2 mol / L; and / or, The molar ratio of the metal salt to the phosphorus source is 1:1 to 1:

3.

29. The preparation method according to claim 28, wherein, The concentration of the metal salt solution is 0.5 mol / L to 1 mol / L; and / or, The concentration of the phosphorus source solution is 0.5 mol / L to 1 mol / L.

30. The preparation method according to claim 1, wherein, The stirring speed in the first melting vessel is 100 r / min ~ 500 r / min; and / or, The stirring speed in the second melting vessel is 100 r / min ~ 500 r / min; and / or, The stirring speed of the first reaction vessel is 100 r / min ~ 500 r / min; and / or, The stirring speed of the second reaction vessel is 100 r / min ~ 500 r / min; and / or, The stirring speed of the aging kettle is 100 r / min ~ 500 r / min.

31. The preparation method according to claim 1, wherein, The protective gas includes nitrogen, an inert gas, or a combination thereof.

32. The preparation method according to claim 1, wherein, In S3, the drying temperature is 200 ℃ ~ 300 ℃; and / or, In S3, the drying time is 3 h ~ 8 h; and / or, In S3, the dry atmosphere is a protective gas atmosphere, which includes nitrogen, an inert gas, or a combination thereof.

33. A manganese iron phosphate precursor prepared by any one of claims 1-32, having the chemical formula Fe x Mn y M 1-x-y P 1-m Q m O4, 0 < x < 1, 0 < y < 1, 0 ≤ 1 - xy < 1, 0 ≤ m ≤ 0.1, where M represents the doping element at the manganese and iron sites, Q represents the doping element at the phosphorus site, and the manganese iron phosphate precursor is electrically neutral.

34. The manganese iron phosphate precursor according to claim 33, wherein, 0.2≤x≤0.5。 35. The manganese iron phosphate precursor according to claim 33, wherein, 0.5≤y≤0.8。 36. The manganese iron phosphate precursor according to claim 33, wherein, 0 < 1 - xy ≤ 0.

05.

37. The manganese iron phosphate precursor according to claim 33, wherein, 0＜m≤0.05。 38. The manganese iron phosphate precursor according to claim 33, wherein, M includes one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr.

39. The manganese iron phosphate precursor according to claim 33, wherein, Q includes one or more of B, S, Si, and N.

40. The manganese iron phosphate precursor according to claim 33, wherein, The manganese iron phosphate precursor has a spherical morphology; and / or, The manganese iron phosphate precursor is orthorhombic with space group pmnb.

41. The manganese iron phosphate precursor according to claim 33, wherein, The volumetric particle sizes Dv90 and Dv50 of the manganese iron phosphate precursor satisfy 1 < Dv90 / Dv50 ≤ 2; and / or, The volumetric particle size Dv50 of the manganese iron phosphate precursor is 1 μm to 10 μm.

42. The manganese iron phosphate precursor according to claim 41, wherein, The volumetric particle sizes Dv90 and Dv50 of the manganese iron phosphate precursor satisfy 1.1 ≤ Dv90 / Dv50 ≤ 1.7; and / or, The volumetric particle size Dv50 of the manganese iron phosphate precursor is 2.5 μm to 6 μm.

43. A method for preparing lithium manganese iron phosphate, comprising at least the following steps: S10, mixing the lithium manganese iron phosphate precursor prepared by any one of claims 1-32 or the lithium manganese iron phosphate precursor prepared by any one of claims 33-42 with a lithium source, a source of optional doping element N, and a source of optional doping element R in a predetermined ratio to obtain a mixed raw material, wherein, N represents the doping element at the lithium site, and R represents the doping element at the oxygen site; S20, the mixed raw material obtained in S10 is sintered to obtain lithium manganese iron phosphate, wherein the lithium manganese iron phosphate has the chemical formula Li a N b Fe x Mn y M 1-x- y P 1-m Q m O 4-n R n M represents the doping element at the manganese and iron sites, N represents the doping element at the lithium site, Q represents the doping element at the phosphorus site, R represents the doping element at the oxygen site, 0.9≤a≤1.1, 0≤b≤0.1, 0<x<1, 0<y<1, 0≤1-xy<1, 0≤m≤0.1, 0≤n≤0.1, and the lithium manganese iron phosphate is electrically neutral.

44. The preparation method according to claim 43, wherein, In S10, N includes one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W.

45. The preparation method according to claim 43, wherein, In S10, R includes one or more of S, F, Cl and Br.

46. ​​The preparation method according to claim 43, wherein, In S20, M includes one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr.

47. The preparation method according to claim 43, wherein, In S20, N includes one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W.

48. The preparation method according to claim 43, wherein, In S20, Q includes one or more of B, S, Si, and N.

49. The preparation method according to claim 43, wherein, In S20, R includes one or more of S, F, Cl and Br.

50. The preparation method according to claim 43, wherein, In S20, 0 < b ≤ 0.

05.

51. The preparation method according to claim 43, wherein, In S20, 0.2 ≤ x ≤ 0.

5.

52. The preparation method according to claim 43, wherein, In S20, 0.5≤y≤0.

8.

53. The preparation method according to claim 43, wherein, In S20, 0 < 1 - xy ≤ 0.

05.

54. The preparation method according to claim 43, wherein, In S20, 0 < m ≤ 0.

05.

55. The preparation method according to claim 43, wherein, In S20, 0 < n ≤ 0.

05.

56. The preparation method according to claim 43, wherein, In S10, a carbon source is also added to the mixed raw materials.

57. A lithium manganese iron phosphate prepared by any one of claims 43-56.

58. A secondary battery comprising lithium manganese iron phosphate prepared by any one of claims 43-56.

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