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

Abstract

This application provides a continuous reaction system, a manganese iron oxalate precursor, lithium manganese iron phosphate, a preparation method, and a secondary battery. The preparation method of the manganese iron oxalate precursor provided in this application is a continuous preparation method, which can improve production efficiency, simplify the production process, and obtain a manganese iron oxalate precursor with small particle size, narrow particle size distribution, uniform elemental distribution, high crystallinity, regular morphology, and high batch stability and consistency.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a continuous reaction system, a manganese iron oxalate precursor, lithium manganese iron phosphate, a 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 vehicles, 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. Ferric manganese oxalate, as one of the important raw materials for preparing LFP, has a crucial impact on the performance of LFP and secondary batteries. However, the current intermittent preparation method for LFP suffers from problems such as 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 manganese iron oxalate precursor, lithium manganese iron phosphate, a preparation method, and a secondary battery, aiming to improve the production efficiency of the manganese iron oxalate precursor, simplify the production process of the manganese iron oxalate precursor, and obtain a manganese iron oxalate precursor with small particle size, narrow particle size distribution, uniform element distribution, high crystallinity, regular morphology, and high batch stability and consistency.

[0004] This application provides a continuous reaction system for preparing a precursor of manganese ferric manganese oxalate, comprising a first melting vessel, a second melting vessel, a first reaction vessel, a second reaction vessel, a storage vessel, and an ultrasonic reactor; the first melting vessel is used to contain a metal salt solution required for preparing the precursor of manganese ferric manganese oxalate, and the second melting vessel is used to contain a precipitant solution required for preparing the precursor of manganese ferric manganese oxalate; the first reaction vessel has a first inlet and a first overflow outlet, the first inlet of the first reaction vessel being connected to the first outlet of the first melting vessel and the second outlet of the second melting vessel via two pipes respectively, so that the first reaction vessel contains the metal salt solution and the precipitant solution and mixes them to react and generate a first reaction solution; the second reaction vessel has a second inlet and a second overflow outlet, the second inlet of the second reaction vessel... The feed inlet is connected to the first overflow port of the first reactor via a pipe, so that the second reactor can contain the first reaction liquid from the first reactor and allow it to continue reacting to generate the second reaction liquid. The storage tank includes a third feed inlet, a fourth feed inlet, a third discharge port, and a third overflow port. The third feed inlet of the storage tank is connected to the second overflow port of the second reactor via a pipe, so that the storage tank can contain the second reaction liquid from the second reactor and allow it to continue reacting to generate the third reaction liquid. The third discharge port and the fourth feed inlet of the storage tank are circulated to the ultrasonic reactor via a circulation pipe and a circulation pump, so that the third reaction liquid in the storage tank is refined under the action of ultrasonic cavitation. When the liquid level of the third reaction liquid is higher than the third overflow port of the storage tank, the third reaction liquid flows out through the third overflow port of the storage tank.

[0005] In any embodiment of this application, the continuous reaction system further includes a first metering pump and a second metering pump. The two ends of the first metering pump are respectively connected to the first outlet of the first melting vessel and the first inlet of the first reaction vessel via pipelines to adjust the flow rate of the metal salt solution. The two ends of the second metering pump are respectively connected to the second outlet of the second melting vessel and the first inlet of the first reaction vessel via pipelines to adjust the flow rate of the precipitant solution.

[0006] In any embodiment of this application, the continuous reaction system further includes a cooling water circulation pipe disposed outside the ultrasonic reactor.

[0007] The second aspect of this application provides a method for preparing a manganese ferric oxalate precursor using the continuous reaction system of the first aspect of this application, comprising at least the following steps: S1, adding a metal salt solution required for preparing the manganese ferric oxalate precursor to a first melting vessel, and adding a precipitant solution required for preparing the manganese ferric oxalate precursor to a second melting vessel; S2, conveying the metal salt solution in the first melting vessel and the precipitant solution in the second melting vessel to a first reaction vessel through different pipelines to mix and react to generate a first reaction liquid; when the liquid level of the first reaction liquid is higher than the overflow port of the first reaction vessel, the first reaction liquid is automatically conveyed to the second reaction vessel, and then the reaction continues to generate a second reaction liquid; when the liquid level of the second reaction liquid is higher than the overflow port of the second reaction vessel... When the overflow port of the reactor is reached, the second reaction liquid is automatically transported to the storage tank to continue the reaction and generate the third reaction liquid. At the same time, the third reaction liquid is pumped into the ultrasonic reactor through the circulation pipe and circulation pump. Under the ultrasonic cavitation effect of the ultrasonic reactor, the crystal particles in the third reaction liquid are refined and then pumped back into the storage tank. When the liquid level of the third reaction liquid is higher than the overflow port of the storage tank, the third reaction liquid automatically flows out through the overflow port of the storage tank. During the reaction process, the first solvent tank, the second solvent tank, the first reaction tank, the second reaction tank and the storage tank are all under a protective gas atmosphere and each tank is kept in a stirring state. S3, the third reaction liquid obtained from the overflow port of the storage tank is centrifuged, washed and dried to obtain the manganese ferric oxalate precursor.

[0008] The method for preparing the manganese iron oxalate precursor provided in this application is a continuous preparation method, which has the advantages of high production efficiency, high energy efficiency, simple process, easy operation, and low labor cost, and is particularly suitable for large-scale industrial production. The manganese iron oxalate precursor obtained by the preparation method provided in this application has the advantages of small particle size, narrow particle size distribution, uniform elemental distribution, high crystallinity, regular morphology, and high batch stability and consistency. Therefore, when it is used as a raw material to prepare lithium manganese iron phosphate by solid-state sintering, it can achieve uniform mixing of lithium and various metal elements, resulting in faster lithium-ion diffusion and easier embedding into the lithium manganese iron phosphate precursor, thus enabling the prepared lithium manganese iron phosphate to have excellent electrochemical performance. The method for preparing the manganese iron oxalate precursor provided in this application also has good production flexibility, and can control the crystal growth rate and adjust the size and morphology of crystal particles, thereby meeting different production needs to prepare lithium manganese iron phosphate with different particle sizes.

[0009] 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 ethylenediaminetetramethylene phosphate, sodium ethylenediaminetetraacetate, sodium gluconate, and sodium citrate. This allows for the acquisition of high-purity (e.g., purity ≥99.7%) manganese oxalate precursor particles with uniform metal element distribution. Furthermore, the molar ratio of each metal element in the obtained manganese oxalate precursor particles differs little from the molar ratio of each metal element in the raw material, enabling precise control of the metal element content.

[0010] 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 storage vessel is lower than that of the second reactor. This not only allows for adjustment of the particle size of the obtained ferromanganese oxalate precursor, but also helps to obtain ferromanganese oxalate precursor particles with narrow particle size distribution, uniform elemental distribution, high crystallinity, and regular morphology.

[0011] In any embodiment of this application, the reaction temperature of the first reactor is 20°C to 30°C.

[0012] In any embodiment of this application, the reaction temperature of the second reactor is 40°C to 90°C, and can be selected as 40°C to 60°C.

[0013] In any embodiment of this application, the reaction temperature of the storage vessel is 20°C to 30°C.

[0014] In any embodiment of this application, the flow rate of the metal salt solution is 0.5 L / min to 6 L / min, and can be selected as 2 L / min to 6 L / min.

[0015] In any embodiment of this application, the flow rate of the precipitant solution is 0.5 L / min to 6 L / min, and can be selected as 2 L / min to 6 L / min.

[0016] In any embodiment of this application, the flow rates of the metal salt solution and the precipitant solution are the same, which helps to improve the consistency of the obtained manganese iron oxalate precursor particles.

[0017] In any embodiment of this application, the residence time of the manganese ferric oxalate precursor in the first reactor during growth is 10 min to 2 h, and can be selected as 10 min to 30 min.

[0018] In any embodiment of this application, the residence time of the manganese ferric oxalate precursor in the second reactor during growth is 10 min to 10 h, optionally 30 min to 6 h, and more preferably 30 min to 90 min.

[0019] In any embodiment of this application, the residence time of the manganese ferric oxalate precursor in the storage tank during growth is 10 min to 10 h, optionally 30 min to 6 h, and more preferably 30 min to 90 min.

[0020] 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 to 5), and more preferably 1:3. This helps to give the obtained manganese ferric oxalate precursor particles a higher degree of crystallinity.

[0021] In any embodiment of this application, the volume of the first reaction vessel is less than or equal to the volume of the storage vessel. Optionally, the ratio of the volume of the first reaction vessel to the volume of the storage vessel is 1:(1 to 5), and more preferably 1:3. This helps to obtain manganese ferric oxalate precursor particles with smaller particle size.

[0022] In any embodiment of this application, the volume of the second reactor is the same as the volume of the storage reactor.

[0023] In any embodiment of this application, the frequency of the ultrasonic reactor is 15 kHz to 60 kHz, and can be selected as 30 kHz to 60 kHz. This is beneficial for preparing nanoscale manganese iron oxalate precursors.

[0024] In any embodiment of this application, the metal salt required for preparing the manganese iron oxalate precursor includes a water-soluble divalent iron salt, a water-soluble divalent manganese salt, and a divalent 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.

[0025] In any embodiment of this application, optionally, the water-soluble divalent ferric salt includes one or more of ferrous chloride, ferrous bromide, ferrous nitrate, ferrous sulfate, ferrous acetate, ferrous fluorosilicate, and ferrous perchlorate.

[0026] In any embodiment of this application, optionally, the water-soluble divalent manganese salt includes one or more of manganese chloride, manganese bromide, manganese nitrate, manganese sulfate, manganese acetate, and manganese perchlorate.

[0027] In any embodiment of this application, optionally, the divalent 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.

[0028] In any embodiment of this application, the precipitant includes one or more of oxalic acid and water-soluble oxalate. Optionally, the water-soluble oxalate includes one or more of lithium oxalate, sodium oxalate, potassium oxalate, and ammonium oxalate.

[0029] 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.

[0030] In any embodiment of this application, the concentration of the precipitant 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 molar ratio of the metal salt to the precipitant is 1:1 to 1:5.

[0032] In any embodiment of this application, the stirring speed of the first melting vessel is 300 r / min to 600 r / min.

[0033] In any embodiment of this application, the stirring speed of the second melting vessel is 300 r / min to 600 r / min.

[0034] In any embodiment of this application, the stirring speed of the first reactor is 300 r / min to 600 r / min.

[0035] In any embodiment of this application, the stirring speed of the second reactor is 300 r / min to 600 r / min.

[0036] In any embodiment of this application, the stirring speed of the storage tank is 300 r / min to 600 r / min.

[0037] In any embodiment of this application, the protective gas includes nitrogen, an inert gas, or a combination thereof.

[0038] A third aspect of this application provides a manganese iron oxalate precursor prepared by the method of the second aspect of this application, which has the chemical formula Fe. x Mn y M 1-x-y C2O4·2H2O, 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, 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, and the manganese iron oxalate precursor is electrically neutral.

[0039] The manganese iron oxalate precursor provided in this application has the advantages of small particle size, narrow particle size distribution, uniform element distribution, high crystallinity, and regular morphology.

[0040] In any embodiment of this application, the volumetric particle sizes Dv90 and Dv50 of the manganese oxalate precursor satisfy 1 < Dv90 / Dv50 ≤ 2, and optionally, 1.3 ≤ Dv90 / Dv50 ≤ 1.7.

[0041] In any embodiment of this application, the volumetric particle size Dv50 of the manganese oxalate precursor is 200 nm to 600 nm, and can be selected as 230 nm to 510 nm.

[0042] In any embodiment of this application, the volumetric particle size Dv90 of the manganese iron oxalate precursor is 260 nm to 800 nm, and can be selected as 320 nm to 730 nm.

[0043] The fourth aspect of this application provides a method for preparing lithium manganese iron phosphate, comprising at least the following steps: S10, mixing the ferromanganese oxalate precursor prepared by the method of the second aspect of this application or the ferromanganese oxalate precursor of the third aspect of this application with a lithium source, a phosphorus source, a source of optional dopant element N, a source of optional dopant element Q, 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; Q represents a phosphorus-site dopant element, optionally including one or more of B, S, Si, and N; 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 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.

[0044] The lithium manganese iron phosphate obtained by the above preparation method of this application can achieve a uniform mixture of lithium and various metal elements, thereby enabling lithium ions to diffuse faster and be more easily embedded in the lithium manganese iron phosphate precursor, thus enabling the prepared lithium manganese iron phosphate to have excellent electrochemical performance.

[0045] 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.

[0046] The fifth aspect of this application provides a lithium manganese iron phosphate prepared by the method of the fourth aspect of this application, which has excellent electrochemical performance.

[0047] The sixth aspect of this application provides a secondary battery comprising lithium manganese iron phosphate prepared by the method of the fourth aspect of this application. Attached Figure Description

[0048] 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.

[0049] Figure 1 A continuous reaction system for preparing manganese iron oxalate precursors is shown.

[0050] Figure 2 The image shown is a scanning electron microscope (SEM) image of the manganese iron oxalate precursor prepared in Example 1. Figure 2 (a) has a magnification of 20,000. Figure 2 (b) has a magnification of 50,000.

[0051] Figure 3 The image shows a scanning electron microscope (SEM) image of the manganese iron oxalate precursor prepared in Comparative Example 3 at a magnification of 5000x.

[0052] Figure 4 The X-ray diffraction (XRD) pattern of the manganese iron oxalate precursor prepared in Example 1 is shown.

[0053] 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 Storage vessel; 6 Ultrasonic reactor; 7 First feed inlet; 8 First overflow port; 9 First discharge port; 10 Second discharge port; 11 Second feed inlet; 12 Second overflow port; 13 Third feed inlet; 14 Fourth feed inlet; 15 Third discharge port; 16 Third overflow port; 17 Circulation pump; 18 First metering pump; 19 Second metering pump; 20 Cooling water circulation pipe; 21 First shut-off valve; 22 Second shut-off valve; 23 Third shut-off valve; 24 Fourth shut-off valve; 25 Fifth shut-off valve. Detailed Implementation

[0054] The following detailed description, with appropriate reference to the accompanying drawings, discloses the continuous reaction system, manganese iron oxalate precursor, lithium manganese iron phosphate, 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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).

[0061] 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.

[0062] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0063] The first aspect of this application provides a continuous reaction system for preparing manganese iron oxalate precursors.

[0064] like Figure 1 As 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, a storage vessel 5, and an ultrasonic reactor 6. The first melting vessel 1 contains the metal salt solution required for preparing the manganese ferric oxalate precursor, and the second melting vessel 2 contains the precipitant solution required for preparing the manganese ferric oxalate precursor. The first reaction vessel 3 has a first inlet 7 and a first overflow 8. The first inlet 7 of the first reaction vessel is connected to the first outlet 9 of the first melting vessel and the second outlet 10 of the second melting vessel via two pipes, respectively, so that the first reaction vessel 3 contains the metal salt solution and the precipitant solution, and after mixing, they react to generate the first reaction liquid. The second reaction vessel 4 has a second inlet 11 and a second overflow 12. The second inlet 11 of the second reaction vessel is connected to the first reaction vessel via a pipe. The first overflow port 8 is connected to the second reactor 4 so that the first reaction liquid from the first reactor 3 can be contained in the second reactor 4 and continue to react to generate the second reaction liquid. The storage vessel 5 includes a third inlet 13, a fourth inlet 14, a third outlet 15 and a third overflow port 16. The third inlet 13 of the storage vessel is connected to the second overflow port 12 of the second reactor through a pipe so that the storage vessel 5 can contain the second reaction liquid from the second reactor 4 and continue to react to generate the third reaction liquid. The third outlet 15 and the fourth inlet 14 of the storage vessel are circulated to the ultrasonic reactor 6 through a circulation pipe and a circulation pump 17 so that the third reaction liquid in the storage vessel 5 is refined under the action of ultrasonic cavitation. When the liquid level of the third reaction liquid is higher than the third overflow port 16 of the storage vessel, the third reaction liquid flows out through the third overflow port 16 of the storage vessel.

[0065] In some embodiments, the continuous reaction system further includes a first metering pump 18 and a second metering pump 19. The two ends of the first metering pump 18 are respectively connected to the first outlet 9 of the first melting vessel and the first inlet 7 of the first reaction vessel via pipes to adjust the flow rate of the metal salt solution. The two ends of the second metering pump 19 are respectively connected to the second outlet 10 of the second melting vessel and the first inlet 7 of the first reaction vessel via pipes to adjust the flow rate of the precipitant solution.

[0066] In some embodiments, the ultrasonic reactor 6 includes an ultrasonic reaction vessel, an ultrasonic generator, and an ultrasonic transducer. In this application, the ultrasonic reactor operates by using an ultrasonic generator to emit a high-frequency oscillation signal, which is then converted into a high-frequency mechanical oscillation by the ultrasonic transducer and propagated into a third reaction liquid that continuously flows through the ultrasonic reaction vessel, thereby refining the crystal particles (i.e., manganese ferric oxalate precursor particles) in the third reaction liquid.

[0067] In some embodiments, the continuous reaction system further includes a cooling water circulation pipe 20 disposed outside the ultrasonic reactor 6. When using the ultrasonic reactor, some energy may cause the body of the ultrasonic reactor to heat up. By setting up a cooling water circulation pipe, the body temperature of the ultrasonic reactor can be reduced, thereby protecting the equipment.

[0068] In some embodiments, a first shut-off valve 21 is also provided on the pipeline between the first outlet 9 of the first melting vessel and the first metering pump 18.

[0069] In some embodiments, a second shut-off valve 22 is also provided on the pipeline between the first outlet 9 of the first melting vessel and the second metering pump 19.

[0070] In some embodiments, a third shut-off valve 23 is also provided on the pipeline between the first overflow port 8 of the first reactor and the second feed port 11 of the second reactor.

[0071] In some embodiments, a fourth shut-off valve 24 is also provided on the pipeline between the second overflow port 12 of the second reactor and the third feed port 13 of the storage vessel.

[0072] In some embodiments, a fifth shut-off valve 25 is also provided on the circulation pipe between the third discharge port 15 of the storage vessel and the circulation pump 17.

[0073] When preparing the manganese ferric oxalate precursor, the first shut-off valve 21, the second shut-off valve 22, the third shut-off valve 23, the fourth shut-off valve 24, and the fifth shut-off valve 25 can all be kept open, thereby ensuring continuous feeding and continuous discharging, allowing multiple reactors to react simultaneously.

[0074] 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 storage vessel 5.

[0075] In some embodiments, heating devices may also be provided in the first melting vessel 1, the second melting vessel 2, the first reaction vessel 3, the second reaction vessel 4, and the storage vessel 5 to adjust the temperature of each vessel as needed.

[0076] In some embodiments, the first overflow port 8 is disposed at the top of the first reactor 3, the second overflow port 12 is disposed at the top of the second reactor 4, and the third overflow port 16 is disposed at the top of the storage vessel 5.

[0077] The second aspect of this application provides a method for preparing a manganese ferric oxalate precursor using a continuous reaction system according to the first aspect of this application, comprising at least the following steps: S1, adding a metal salt solution required for preparing the manganese ferric oxalate precursor to a first solvent vessel, and adding a precipitant solution required for preparing the manganese ferric oxalate precursor to a second solvent vessel; S2, conveying the metal salt solution in the first solvent vessel and the precipitant solution in the second solvent vessel to the first reaction vessel through different pipelines to mix and react to generate a first reaction liquid; when the liquid level of the first reaction liquid is higher than the overflow port of the first reaction vessel, the first reaction liquid is automatically conveyed to the second reaction vessel, and then the reaction continues to generate a second reaction liquid; when the liquid level of the second reaction liquid... When the overflow level of the second reaction vessel is higher than the overflow port of the second reaction vessel, the second reaction liquid is automatically transported to the storage vessel to continue the reaction and generate the third reaction liquid. At the same time, the third reaction liquid is pumped into the ultrasonic reactor through the circulation pipe and circulation pump. Under the ultrasonic cavitation effect of the ultrasonic reactor, the crystal particles in the third reaction liquid are refined and then pumped back into the storage vessel. When the liquid level of the third reaction liquid is higher than the overflow port of the storage vessel, the third reaction liquid automatically flows out through the overflow port of the storage vessel. During the reaction process, the first melting vessel, the second melting vessel, the first reaction vessel, the second reaction vessel, and the storage vessel are all under a protective gas atmosphere and each vessel is kept in a stirring state. S3, the third reaction liquid obtained from the overflow port of the storage vessel is centrifuged, washed, and dried to obtain the manganese ferric oxalate precursor.

[0078] Existing reaction systems for preparing lithium manganese iron oxalate 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.

[0079] This application employs a continuous reaction system to prepare ferromanganese oxalate precursors. In this continuous reaction system, the first reaction vessel, the second reaction vessel, and the storage vessel are connected in series, thereby ensuring continuous feeding and discharging, allowing multiple vessels to react simultaneously. Therefore, the method for preparing ferromanganese oxalate precursors provided by 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.

[0080] The preparation method for ferromanganese oxalate precursors is typically a co-precipitation method. During precipitation, the crystal nuclei grow rapidly, making it difficult to control the size and morphology of the resulting crystals. Consequently, ferromanganese oxalate precursors obtained through existing intermittent preparation methods suffer from large particle sizes (e.g., volumetric particle size Dv50 typically ranges from 10 μm to 40 μm), wide particle size distribution, and uneven elemental distribution. Therefore, when using ferromanganese oxalate precursors obtained through existing intermittent preparation methods as raw materials for the preparation of lithium iron manganese phosphate, a lengthy ball milling process is required to reduce the particle size, which is both time-consuming and energy-intensive. Furthermore, achieving uniform mixing during the preparation of lithium iron manganese phosphate is challenging. In addition, lithium iron manganese oxalate precursors obtained through existing intermittent preparation methods also suffer from large fluctuations in product quality and poor batch stability and consistency.

[0081] The method for preparing the ferromanganese oxalate precursor provided in this application is a continuous preparation method. In this continuous preparation process, the residence time of each ferromanganese oxalate precursor particle in the first reactor, the second reactor, and the storage reactor is consistent, and all particles undergo ultrasonic cavitation at the same frequency. This allows for particle size refinement under the strong shear force generated by ultrasonic cavitation. Therefore, compared with lithium iron oxalate precursors obtained through existing intermittent preparation methods, the ferromanganese oxalate precursors obtained by the continuous preparation method provided in this application have advantages such as small particle size, narrow particle size distribution, uniform elemental distribution, high crystallinity, regular morphology, and high batch stability and consistency. Furthermore, when used as a raw material to prepare lithium iron manganese phosphate via solid-state sintering, it enables uniform mixing of lithium and various metal elements, resulting in faster lithium-ion diffusion and easier embedding into the lithium iron manganese phosphate precursor, thus enabling the prepared lithium iron manganese phosphate to exhibit excellent electrochemical performance.

[0082] In the preparation method of manganese oxalate ferric precursor provided in this application, parameters such as the flow rate of the metal salt solution and the precipitant solution, the residence time of the manganese oxalate ferric precursor in each reactor during growth, the reaction temperature of each reactor, and the frequency of the ultrasonic reactor can all be precisely adjusted. Therefore, the preparation method of manganese oxalate ferric precursor provided in this application also has good production flexibility.

[0083] The residence time of the ferromanganese oxalate precursor in each reactor (first reactor, second reactor, and storage reactor) during growth is negatively correlated with the flow rates of the metal salt solution and precipitant solution, and positively correlated with the volume of each reactor. When the flow rates of the metal salt solution and precipitant solution are high, the residence time of the ferromanganese oxalate precursor 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 and morphology of the ferromanganese oxalate precursor can be adjusted by regulating the flow rates of the metal salt solution and precipitant solution, as well as the volume of each reactor.

[0084] The reaction temperature also affects the particle size of the obtained manganese ferric oxalate precursor. Therefore, the particle size and morphology of the manganese ferric oxalate precursor can be adjusted by regulating the reaction temperature of each reactor within different ranges.

[0085] The frequency of the ultrasonic reactor also affects the particle size of the obtained manganese ferric oxalate precursor. Therefore, by adjusting the frequency of the ultrasonic reactor, different degrees of particle refinement can be achieved, thereby adjusting the particle size of the manganese ferric oxalate precursor.

[0086] Therefore, the preparation method of manganese iron oxalate precursor provided in this application can also control the crystal growth rate and adjust the size and morphology of crystal particles, thereby meeting different production needs and facilitating the preparation of lithium manganese iron phosphate with different particle sizes.

[0087] In some embodiments, a complexing agent may also be added to the first melting vessel.

[0088] In the preparation of ferromanganese oxalate precursors via coprecipitation, uniform coprecipitation cannot be achieved due to the differences in precipitation rates of different metal ions. Furthermore, the molar ratios of the metal elements in the obtained ferromanganese oxalate precursor particles differ significantly from those in the raw materials, thus affecting the product's performance and consistency. In the preparation method of ferromanganese oxalate precursors provided in this application, a complexing agent can be added to the first dissolving vessel. The complexing agent can complex metal ions, thereby controlling the free metal ions, improving the precipitation conversion efficiency of metal ions, reducing the difference in precipitation rates of different metal ions in the reaction solution, and achieving uniform coprecipitation. Therefore, when a complexing agent is added to the first dissolving vessel, the preparation method of ferromanganese oxalate precursors provided in this application can obtain ferromanganese oxalate precursor particles with high purity (e.g., purity ≥99.7%) and uniform metal element distribution. Moreover, the molar ratios of the metal elements in the obtained ferromanganese oxalate precursor particles differ less from those in the raw materials, enabling precise control of the metal element content.

[0089] Optionally, the complexing agent comprises one or more of aminocarboxylates, hydroxycarboxylates, and organophosphonates. More preferably, the complexing agent comprises one or more of sodium ethylenediaminetetramethylene phosphate, sodium ethylenediaminetetraacetate, sodium gluconate, and sodium citrate.

[0090] 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.

[0091] In some embodiments, the reaction temperature of the first reactor is lower than that of the second reactor, and the reaction temperature of the storage vessel is lower than that of the second reactor.

[0092] In the preparation method of the manganese ferric oxalate precursor provided in this application, the first reaction vessel, the second reaction vessel, and the storage vessel are connected in series, and the reaction temperatures of the first reaction vessel and the storage vessel are set lower than those of the second reaction vessel. This allows the different vessels in the continuous reaction system to perform different functions. The lower reaction temperature of the first reaction vessel enables pre-mixing and rapid pre-nucleation of the metal salt solution and the precipitant solution. Furthermore, the lower reaction temperature inhibits the aggregation and growth of crystal nuclei in the first reaction solution, allowing metal ions and oxalate ions to co-precipitate and form a large number of uniformly sized and elementally distributed crystal nuclei, which is beneficial for better growth and crystallization of the nuclei in the second reaction vessel. The higher reaction temperature of the second reaction vessel provides sufficient energy to promote crystal growth and crystallization when the reaction solution flows from the first reaction vessel to the second reaction vessel, and also improves the crystallinity of the formed crystals while avoiding the aggregation and growth of crystal nuclei. The lower reaction temperature in the storage vessel allows for further crystallization and growth of the crystals, improving their crystallinity, uniformity, and consistency. Simultaneously, the lower reaction temperature also prevents the reaction liquid from overheating, thus avoiding overheating of the ultrasonic reactor and affecting the lifespan of the ultrasonic transducer. Furthermore, the lower reaction temperature in the storage vessel compared to the second reaction vessel allows for cooling of the reaction liquid as it flows from the second reaction vessel into the storage vessel.

[0093] Therefore, by adjusting the reaction temperature of each reactor, not only can the particle size of the obtained manganese ferric oxalate precursor be adjusted, but it also helps to obtain manganese ferric oxalate precursor particles with narrow particle size distribution, uniform element distribution, high crystallinity, and regular morphology.

[0094] In some embodiments, the reaction temperature of the first reactor is optionally 20°C to 30°C.

[0095] In some embodiments, the reaction temperature of the second reactor is optionally 40°C to 90°C, and more preferably 40°C to 60°C.

[0096] In some embodiments, the reaction temperature of the storage vessel is optionally 20°C to 30°C.

[0097] In some embodiments, the flow rate of the metal salt solution (or the pumping speed of the first metering pump) is 0.5 L / min to 6 L / min, and can be selected as 2 L / min to 6 L / min.

[0098] In some embodiments, the flow rate of the precipitant solution (or the pumping speed of the second metering pump) is 0.5 L / min to 6 L / min, and can be selected as 2 L / min to 6 L / min.

[0099] In some embodiments, the flow rates of the metal salt solution and the precipitant 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 ferric oxalate precursor particles.

[0100] In some embodiments, the residence time of the manganese ferric oxalate precursor in the first reactor during growth is 10 min to 2 h, and can be selected as 10 min to 30 min.

[0101] In some embodiments, the residence time of the manganese ferric oxalate precursor in the second reactor during growth is 10 min to 10 h, optionally 30 min to 6 h, and more preferably 30 min to 90 min.

[0102] In some embodiments, the residence time of the manganese ferric oxalate precursor in the storage tank during growth is 10 min to 10 h, optionally 30 min to 6 h, and more preferably 30 min to 90 min.

[0103] 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 ferro oxalate precursor particles to remain in the second reactor for a longer period, which helps to achieve higher crystallinity in the obtained manganese ferro oxalate precursor particles. Optionally, the ratio of the volume of the first reactor to the volume of the second reactor is 1:(1 to 5), more preferably 1:3.

[0104] In some embodiments, the volume of the first reaction vessel is less than or equal to the volume of the storage vessel, thereby allowing the generated manganese ferro oxalate precursor particles to remain in the storage vessel for a longer period, which helps to result in smaller particle sizes of the obtained manganese ferro oxalate precursor particles. Optionally, the ratio of the volume of the first reaction vessel to the volume of the storage vessel is 1:(1 to 5), and more preferably 1:3.

[0105] In some embodiments, the volume of the second reactor is optionally the same as the volume of the storage vessel.

[0106] In some embodiments, the frequency of the ultrasonic reactor is optionally 15 kHz to 60 kHz, and optionally 30 kHz to 60 kHz. This is advantageous for preparing nanoscale manganese iron oxalate precursors.

[0107] In some embodiments, the metal salt required for preparing the manganese iron oxalate precursor includes a water-soluble divalent iron salt, a water-soluble divalent manganese salt, and an optional divalent 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.

[0108] The water-soluble ferrous salt can be any existing water-soluble compound containing ferrous ions. Optionally, the water-soluble ferrous salt includes one or more of ferrous chloride, ferrous bromide, ferrous nitrate, ferrous sulfate, ferrous acetate, ferrous fluorosilicate, and ferrous perchlorate.

[0109] The water-soluble divalent manganese salt can be any existing water-soluble compound containing divalent manganese ions. Optionally, the water-soluble divalent manganese salt includes one or more of manganese chloride, manganese bromide, manganese nitrate, manganese sulfate, manganese acetate, and manganese perchlorate.

[0110] The water-soluble divalent salt of dopant element M can be any existing compound containing divalent M ions that is soluble in water. Optionally, the water-soluble divalent salt of dopant element M includes one or more of the following: hydrochloride, nitrate, sulfate, and acetate of dopant element M.

[0111] In some embodiments, the precipitant may optionally include one or more of oxalic acid and water-soluble oxalate. Optionally, the water-soluble oxalate may include one or more of lithium oxalate, sodium oxalate, potassium oxalate, and ammonium oxalate.

[0112] 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 ferric oxalate precursor with deionized water.

[0113] In some embodiments, the precipitant solution is an aqueous solution of the precipitant, for example, obtained by uniformly mixing the precipitant with deionized water.

[0114] In some embodiments, the concentration of the metal salt solution is optionally 0.5 mol / L to 2 mol / L, and more preferably 0.5 mol / L to 1 mol / L.

[0115] In some embodiments, the concentration of the precipitant solution is optionally 0.5 mol / L to 2 mol / L, and more preferably 0.5 mol / L to 1 mol / L.

[0116] In some embodiments, the molar ratio of the metal salt to the precipitant is optionally 1:1 to 1:5.

[0117] During the reaction, the first melting vessel, the second melting vessel, the first reaction vessel, the second reaction vessel, and the storage vessel are all kept under stirring. In some embodiments, optionally, the stirring speed of the first melting vessel is 300 r / min to 600 r / min. In some embodiments, optionally, the stirring speed of the second melting vessel is 300 r / min to 600 r / min. In some embodiments, optionally, the stirring speed of the first reaction vessel is 300 r / min to 600 r / min. In some embodiments, optionally, the stirring speed of the second reaction vessel is 300 r / min to 600 r / min. In some embodiments, optionally, the stirring speed of the storage vessel is 300 r / min to 600 r / min.

[0118] 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 storage 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.

[0119] In the preparation method of the manganese iron oxalate precursor provided in this application, unless otherwise specified, all raw materials can be purchased directly.

[0120] A third aspect of this application provides a ferromanganate precursor, which is prepared by the method of a second aspect of this application. The ferromanganate precursor has the chemical formula Fe. x Mn y M 1-x-y C2O4·2H2O, 0<x<1, 0<y<1, 0≤1-xy<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, and the manganese iron oxalate precursor is electrically neutral.

[0121] The manganese iron oxalate 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, uniform element distribution, high crystallinity and regular morphology.

[0122] In some embodiments, the volumetric particle sizes Dv90 and Dv50 of the manganese oxalate precursor satisfy 1 < Dv90 / Dv50 ≤ 2, and optionally, 1.3 ≤ Dv90 / Dv50 ≤ 1.7.

[0123] In some embodiments, the volumetric particle size Dv50 of the manganese iron oxalate precursor is 200 nm to 600 nm, and optionally 230 nm to 510 nm.

[0124] In some embodiments, the volumetric particle size Dv90 of the manganese iron oxalate precursor is 260 nm to 800 nm, and optionally 320 nm to 730 nm.

[0125] In some embodiments, optionally, 0.2 ≤ x ≤ 0.5.

[0126] In some embodiments, optionally, 0.5 ≤ y ≤ 0.8.

[0127] In some embodiments, 1-xy = 0; in other embodiments, 0 < 1-xy ≤ 0.05.

[0128] The fourth aspect of this application provides a method for preparing lithium manganese iron phosphate, comprising at least the following steps: S10, mixing the ferromanganese oxalate precursor prepared by the method of the second aspect of this application or the ferromanganese oxalate precursor of the third aspect of this application with a lithium source, a phosphorus source, a source of optional dopant element N, a source of optional dopant element Q, 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; Q represents a phosphorus-site dopant element, optionally including one or more of B, S, Si, and N; 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.

[0129] The lithium manganese iron phosphate obtained by the above preparation method of this application can achieve a uniform mixture of lithium and various metal elements, thereby enabling lithium ions to diffuse faster and be more easily embedded in the lithium manganese iron phosphate precursor, thus enabling the prepared lithium manganese iron phosphate to have excellent electrochemical performance.

[0130] 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.

[0131] In some embodiments, the phosphorus source may be a phosphorus-containing compound known in the art that can be used to prepare lithium manganese iron phosphate cathode active materials. For example, the phosphorus source includes one or more of (NH4)2HPO4, NH4H2PO4, (NH4)3PO4 and H3PO4.

[0132] 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.

[0133] In some embodiments, the source of the dopant element Q includes one or more of the following: sulfate, borate, nitrate, and silicate of the dopant element Q.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] In the above preparation method, the amount of each of the doping elements N, Q, and R added depends on the target doping amount; the amounts of lithium and phosphorus sources added conform to the stoichiometry of lithium manganese iron phosphate. In some embodiments, the amount of lithium source added can be slightly excessive, for example, it can 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 according to the stoichiometry of lithium manganese iron phosphate.

[0139] Unless otherwise specified, all raw materials used in the above preparation method can be purchased directly.

[0140] The fifth aspect of this application provides a lithium manganese iron phosphate prepared by the method of the fourth aspect of this application.

[0141] 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.

[0142] In some embodiments, the lithium manganese iron phosphate is further coated with carbon, thereby improving the conductivity of the lithium manganese iron phosphate.

[0143] 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.

[0144] Example

[0145] 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.

[0146] Example 1

[0147] use Figure 1 The continuous reaction system shown is used to prepare the manganese iron oxalate precursor.

[0148] A 1 mol / L metal salt solution was prepared by adding water-soluble divalent manganese chloride, water-soluble divalent ferrous chloride, the complexing agent sodium ethylenediaminetetramethylene phosphate, 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 7:3, and the mass concentration of the complexing agent was 5 wt%. A 1 mol / L precipitant solution was prepared by adding ammonium oxalate and deionized water to the second solvent vessel.

[0149] 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 storage vessel. During the reaction, the stirring speed in each vessel is 400 r / min. The reaction temperature in the first reaction vessel and the storage vessel is controlled at room temperature (25℃), the reaction temperature in the second reaction vessel is controlled at 40℃, and the frequency of the ultrasonic reactor is 60 kHz.

[0150] The metal salt solution and the precipitant solution are continuously transported from the first and second solvent vessels to the first reaction vessel through two inlet pipes, respectively, so that they are mixed and react to generate the first reaction solution. The flow rates of the metal salt solution and the precipitant solution are both 6 L / min.

[0151] After 10 minutes 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.

[0152] After the reaction continues for 30 minutes, the liquid level of the second reaction liquid is higher than the second overflow port, and then it automatically flows out from the second overflow port into the storage tank to continue the reaction and generate the third reaction liquid.

[0153] The third reaction liquid in the storage vessel is continuously pumped into the ultrasonic reactor through a circulation pipeline and a circulation pump. Under the ultrasonic cavitation effect of the ultrasonic reactor, the manganese iron oxalate precursor particles in the third reaction liquid are refined and then pumped back into the storage vessel.

[0154] After the reaction continued for 30 minutes, the liquid level of the third reaction solution was higher than the third overflow port, and then it automatically flowed out from the third overflow port.

[0155] The obtained third reaction solution was centrifuged and washed multiple times, then transferred to a desiccator and dried at 120°C for 6 hours to obtain the manganese iron oxalate precursor.

[0156] Example 2

[0157] use Figure 1 The continuous reaction system shown is used to prepare the manganese iron oxalate precursor.

[0158] A 1 mol / L metal salt solution was prepared by adding water-soluble divalent manganese nitrate (manganese nitrate), water-soluble divalent ferrous nitrate (ferrous nitrate), sodium ethylenediaminetetraacetate (EDTA) 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 7:3, and the mass concentration of the complexing agent was 3 wt%. A 1 mol / L precipitant solution was then prepared by adding oxalic acid as a precipitant and deionized water to the second solvent vessel.

[0159] 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 storage vessel, and the stirring speed of each vessel is 600 r / min during the reaction. The reaction temperature of the first reaction vessel and the storage vessel is controlled at room temperature (25℃), the reaction temperature of the second reaction vessel is controlled at 60℃, and the frequency of the ultrasonic reactor is 30KHz.

[0160] The metal salt solution and the precipitant solution are continuously transported from the first and second solvent vessels to the first reaction vessel through two inlet pipes, respectively, so that they are mixed and react to generate the first reaction solution. The flow rates of the metal salt solution and the precipitant solution are both 2 L / min.

[0161] After 30 minutes 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.

[0162] After the reaction continues for 90 minutes, the liquid level of the second reaction liquid is higher than the second overflow port, and then it automatically flows out from the second overflow port into the storage tank to continue the reaction and generate the third reaction liquid.

[0163] The third reaction liquid in the storage vessel is continuously pumped into the ultrasonic reactor through a circulation pipeline and a circulation pump. Under the ultrasonic cavitation effect of the ultrasonic reactor, the manganese iron oxalate precursor particles in the third reaction liquid are refined and then pumped back into the storage vessel.

[0164] After the reaction continued for 90 minutes, 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.

[0165] The obtained third reaction solution was centrifuged and washed multiple times, then transferred to a desiccator and dried at 120°C for 6 hours to obtain the manganese iron oxalate precursor.

[0166] Example 3

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

[0168] A 0.5 mol / L metal salt solution was prepared by adding water-soluble divalent manganese sulfate, water-soluble divalent ferrous sulfate, sodium gluconate (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 10 wt%. A 0.5 mol / L precipitant solution was then prepared by adding oxalic acid (a precipitant) and deionized water to the second solvent vessel.

[0169] 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 storage vessel, and the stirring speed of each vessel is 300 r / min during the reaction. The reaction temperature of the first reaction vessel and the storage vessel is controlled at room temperature (25℃), the reaction temperature of the second reaction vessel is controlled at 50℃, and the frequency of the ultrasonic reactor is 50KHz.

[0170] The metal salt solution and the precipitant solution are continuously transported from the first and second solvent vessels to the first reaction vessel through two inlet pipes, respectively, so that they are mixed and react to generate the first reaction solution. The flow rates of the metal salt solution and the precipitant solution are both 3 L / min.

[0171] After 20 minutes 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 continues for 60 minutes, the liquid level of the second reaction liquid is higher than the second overflow port, and then it automatically flows out from the second overflow port into the storage tank to continue the reaction and generate the third reaction liquid.

[0173] The third reaction liquid in the storage vessel is continuously pumped into the ultrasonic reactor through a circulation pipeline and a circulation pump. Under the ultrasonic cavitation effect of the ultrasonic reactor, the manganese iron oxalate precursor particles in the third reaction liquid are refined and then pumped back into the storage vessel.

[0174] After the reaction continued for 60 minutes, 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.

[0175] The obtained third reaction solution was centrifuged and washed multiple times, then transferred to a desiccator and dried at 120°C for 6 hours to obtain the manganese iron oxalate precursor.

[0176] Example 4

[0177] use Figure 1 The continuous reaction system shown is used to prepare the manganese iron oxalate precursor.

[0178] A 1 mol / L metal salt solution was prepared by adding water-soluble divalent manganese acetate, water-soluble divalent ferrous acetate, water-soluble divalent cobalt acetate, sodium citrate (a complexing agent), and deionized water to a first dissolving vessel. In the prepared metal salt solution, the molar ratio of divalent manganese ions, divalent ferrous ions, and divalent cobalt ions was 6.9:3:0.1, and the mass concentration of the complexing agent was 5 wt%. A 1 mol / L precipitant solution was prepared by adding ammonium oxalate (a precipitant), oxalic acid, and deionized water to a second dissolving vessel. The molar ratio of ammonium oxalate to oxalic acid was 1:1.

[0179] 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 storage vessel, and the stirring speed of each vessel is 400 r / min during the reaction. The reaction temperature of the first reaction vessel and the storage vessel is controlled at room temperature (25℃), the reaction temperature of the second reaction vessel is controlled at 60℃, and the frequency of the ultrasonic reactor is 40KHz.

[0180] The metal salt solution and the precipitant solution are continuously transported from the first and second solvent vessels to the first reaction vessel through two inlet pipes, respectively, so that they are mixed and react to generate the first reaction solution. The flow rates of the metal salt solution and the precipitant solution are both 4 L / min.

[0181] After 15 minutes 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.

[0182] After the reaction continues for 45 minutes, the liquid level of the second reaction liquid is higher than the second overflow port, and then it automatically flows out from the second overflow port into the storage tank to continue the reaction and generate the third reaction liquid.

[0183] The third reaction liquid in the storage vessel is continuously pumped into the ultrasonic reactor through a circulation pipeline and a circulation pump. Under the ultrasonic cavitation effect of the ultrasonic reactor, the manganese iron oxalate precursor particles in the third reaction liquid are refined and then pumped back into the storage vessel.

[0184] After the reaction continued for 45 minutes, the liquid level of the third reaction solution was higher than the third overflow port, and then it automatically flowed out from the third overflow port.

[0185] The obtained third reaction solution was centrifuged and washed multiple times, then transferred to a desiccator and dried at 120°C for 6 hours to obtain the manganese iron oxalate precursor.

[0186] Example 5

[0187] The preparation method of the manganese iron oxalate precursor is the same as in Example 1, except that no complexing agent is added.

[0188] Comparative Example 1

[0189] A 1 mol / L metal salt solution was prepared by mixing water-soluble manganese chloride (divalent manganese salt), water-soluble ferrous chloride (divalent ferric salt), and deionized water. The molar ratio of divalent manganese ions to divalent ferric ions in the prepared metal salt solution was 7:3. A 1 mol / L precipitant solution was prepared by mixing oxalic acid (precipitant) and deionized water.

[0190] The metal salt solution and precipitant solution were simultaneously injected into the reactor, and rapid stirring was started at a speed of 400 r / min. The reaction temperature was controlled at 60℃, and the reaction time was 40 min. After the reaction, the mixture was allowed to cool naturally to room temperature to obtain a slurry. The obtained slurry was discharged from the outlet at the bottom of the reactor, centrifuged and washed multiple times, and then transferred to a dryer and dried at 120℃ for 6 h to obtain the manganese ferric oxalate precursor.

[0191] Comparative Example 2

[0192] A 1 mol / L metal salt solution was prepared by mixing water-soluble divalent manganese chloride, water-soluble divalent ferrous chloride, a complexing agent (sodium ethylenediaminetetramethylene phosphate), and deionized water. In the prepared metal salt solution, the molar ratio of divalent manganese ions to divalent ferrous ions was 7:3, and the mass concentration of the complexing agent was 5 wt%. A 1 mol / L precipitant solution was prepared by mixing oxalic acid and deionized water.

[0193] The metal salt solution and precipitant solution were simultaneously injected into the reactor, and rapid stirring was started at a speed of 400 r / min. The reaction temperature was controlled at 60℃, and the reaction time was 40 min. After the reaction, the mixture was allowed to cool naturally to room temperature to obtain a slurry. The obtained slurry was discharged from the outlet at the bottom of the reactor, centrifuged and washed multiple times, and then transferred to a dryer and dried at 120℃ for 6 h to obtain the manganese ferric oxalate precursor.

[0194] Comparative Example 3

[0195] A 1 mol / L metal salt solution was prepared by mixing water-soluble manganese chloride (divalent manganese salt), water-soluble ferrous chloride (divalent ferric salt), and deionized water. The molar ratio of divalent manganese ions to divalent ferric ions in the prepared metal salt solution was 7:3. A 1 mol / L precipitant solution was prepared by mixing oxalic acid (precipitant) and deionized water.

[0196] The metal salt solution and precipitant solution were simultaneously injected into the reactor, and rapid stirring was started at a speed of 400 r / min. The reaction temperature was controlled at 60℃, and the reaction time was 40 min. After the reaction, the mixture was allowed to cool naturally to room temperature to obtain a slurry. The obtained slurry was discharged from the outlet at the bottom of the reactor and introduced into an ultrasonic reactor for refining treatment. After reacting for 30 min, the slurry was centrifuged and washed multiple times, then transferred to a desiccator and dried at 120℃ for 6 h to obtain the manganese ferric oxalate precursor.

[0197] Test section

[0198] (1) Particle size test

[0199] The volumetric particle size of the prepared manganese ferrooxatate precursor was measured using a Malvern Master Size 3000 laser particle size analyzer. Dv50 and Dv90 refer to the particle size corresponding to a cumulative volumetric distribution percentage of 50% and 90%, respectively. The testing standards can be found in GB / T 19077-2016.

[0200] (2) Mn / Fe molar ratio test

[0201] The contents of manganese and iron in the prepared manganese oxalate iron precursor were determined and their molar ratio was calculated using an ICP-OES method with a Plasma 3000 inductively coupled plasma atomic emission spectrometer.

[0202] Table 1

[0203]

[0204]

[0205] Figure 2The image shown is a scanning electron microscope (SEM) image of the manganese iron oxalate precursor prepared in Example 1. Figure 2 (a) has a magnification of 20,000. Figure 2 (b) has a magnification of 50,000. Figure 3 The image shows a scanning electron microscope (SEM) image of the manganese iron oxalate precursor prepared in Comparative Example 3 at a magnification of 5000x. Figure 4 The X-ray diffraction (XRD) pattern of the manganese iron oxalate precursor prepared in Example 1 is shown.

[0206] Based on the test results in Table 1 and Figure 2 It can be seen that the manganese iron oxalate precursor prepared by the continuous preparation method provided in this application has the advantages of small particle size, narrow particle size distribution, uniform element distribution and regular morphology.

[0207] Based on the test results in Table 1 and Figure 3 It can be seen that the precursor of manganese iron oxalate prepared by the existing intermittent preparation method has large particle size, wide particle size distribution and uneven element distribution.

[0208] from Figure 4 It is also known that the manganese iron oxalate precursor prepared by the continuous preparation method provided in this application has the advantages of high purity and high crystallinity.

[0209] Based on the test results of Example 1 and Comparative Example 2, and Example 5 and Comparative Example 1, it can be seen that the difference between the Mn / Fe molar ratio in the manganese iron oxalate 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.

[0210] Based on the test results of Example 1 and Comparative Example 2, and Example 5 and Comparative Example 1, it can be seen that when a complexing agent is added to the first melting vessel, it helps to further precisely control the manganese and iron content in the prepared manganese ferric oxalate precursor particles.

[0211] 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 continuous reaction system for preparing manganese iron oxalate precursor, wherein, the continuous reaction system comprises a first dissolving tank, a second dissolving tank, a first reaction tank, a second reaction tank, a storage tank and an ultrasonic reactor; the first dissolving tank is used for containing metal salt solution required for preparing manganese iron oxalate precursor, and the second dissolving tank is used for containing precipitant solution required for preparing manganese iron oxalate precursor; the first reaction tank has a first inlet and a first overflow, and the first inlet of the first reaction tank is communicated with the first outlet of the first dissolving tank and the second outlet of the second dissolving tank through two pipes respectively, so that the first reaction tank contains and mixes the metal salt solution and the precipitant solution to generate a first reaction liquid; the second reaction tank has a second inlet and a second overflow, and the second inlet of the second reaction tank is communicated with the first overflow of the first reaction tank through a pipe, so that the second reaction tank contains and continues to react the first reaction liquid from the first reaction tank to generate a second reaction liquid; the storage tank comprises a third inlet, a fourth inlet, a third outlet and a third overflow, the third inlet of the storage tank is communicated with the second overflow of the second reaction tank through a pipe, so that the storage tank contains and continues to react the second reaction liquid from the second reaction tank to generate a third reaction liquid, and the third outlet and the fourth inlet of the storage tank are communicated with the ultrasonic reactor through a circulation pipe and a circulation pump, so that the third reaction liquid in the storage tank is refined under ultrasonic cavitation; when the liquid level of the third reaction liquid is higher than the third overflow of the storage tank, the third reaction liquid flows out through the third overflow of the storage tank; in the preparation process of manganese iron oxalate precursor, the first reaction tank, the second reaction tank and the storage tank are communicated in series, and the reaction temperature of the first reaction tank is lower than that of the second reaction tank, and the reaction temperature of the storage tank is lower than that of the second reaction tank, the low reaction temperature in the first reaction tank can inhibit the aggregation and growth of crystal nucleus in the first reaction liquid, the high reaction temperature of the second reaction tank promotes the growth of crystal nucleus and crystallization, and the low reaction temperature of the storage tank further promotes the crystallization and growth of crystal.

2. The continuous reaction system of claim 1, wherein, the continuous reaction system further comprises a first metering pump and a second metering pump, two ends of the first metering pump are communicated with the first outlet of the first dissolving tank and the first inlet of the first reaction tank through pipes respectively, so as to adjust the flow rate of the metal salt solution, and two ends of the second metering pump are communicated with the second outlet of the second dissolving tank and the first inlet of the first reaction tank through pipes respectively, so as to adjust the flow rate of the precipitant solution.

3. The continuous reaction system of claim 1, wherein, the continuous reaction system further comprises a cooling water circulation pipe arranged outside the ultrasonic reactor. 4.A method for preparing manganese iron oxalate precursor by the continuous reaction system of claim 1, at least comprising the following steps: S1, adding metal salt solution required for preparing manganese iron oxalate precursor into the first dissolving tank, and adding precipitant solution required for preparing manganese iron oxalate precursor into the second dissolving tank; S2, the metal salt solution in the first dissolving kettle and the precipitant solution in the second dissolving kettle are respectively transported to the first reaction kettle through different pipes to mix and react to generate a first reaction liquid, when the liquid level of the first reaction liquid is higher than the overflow port of the first reaction kettle, the first reaction liquid is automatically transported to the second reaction kettle, and then the reaction continues to generate a second reaction liquid, when the liquid level of the second reaction liquid is higher than the overflow port of the second reaction kettle, the second reaction liquid is automatically transported to the storage kettle to continue the reaction to generate a third reaction liquid, at the same time, the third reaction liquid is pumped into the ultrasonic reactor through the circulating pipe and the circulating pump, and under the ultrasonic cavitation effect of the ultrasonic reactor, the crystal particles in the third reaction liquid are refined and then pumped back into the storage kettle, when the liquid level of the third reaction liquid is higher than the overflow port of the storage kettle, the third reaction liquid automatically flows out through the overflow port of the storage kettle, wherein, in the reaction process, the first dissolving tank, the second dissolving tank, the first reaction tank, the second reaction tank and the storage tank are all in a protective gas atmosphere and are kept in a stirred state. S3, the third reaction solution obtained from the overflow port of the storage kettle is centrifuged, washed and dried to obtain the manganese iron oxalate precursor; In the preparation process of the manganese iron oxalate precursor, the first reaction kettle, the second reaction kettle and the storage kettle are connected in series, the reaction temperature of the first reaction kettle is lower than that of the second reaction kettle, and the reaction temperature of the storage kettle is lower than that of the second reaction kettle. The low reaction temperature in the first reaction kettle can inhibit the aggregation and growth of the crystal nucleus in the first reaction solution, the high reaction temperature of the second reaction kettle promotes the growth of the crystal nucleus and crystallization, and the low reaction temperature of the storage kettle further promotes the crystallization and growth of the crystal.

5. The method of claim 4, wherein, The first solution kettle also adds a complexing agent.

6. The method of claim 5, wherein, The complexing agent includes one or more of aminocarboxylate, hydroxycarboxylate and organic phosphonate.

7. The method of claim 5, wherein, The complexing agent includes one or more of ethylenediamine tetramethylene phosphonic acid sodium, ethylenediamine tetraacetic acid sodium, sodium grape acid and sodium citrate.

8. The method of claim 4, wherein, the reaction temperature of the first reaction kettle is 20-30℃; and / or, the reaction temperature of the second reaction kettle is 40-90℃; and / or, the reaction temperature of the storage kettle is 20-30℃.

9. The method of claim 4, wherein, the reaction temperature of the second reaction kettle is 40-60℃.

10. The method of claim 4, wherein, the flow rate of the metal salt solution is 0.5-6 L / min; and / or, the flow rate of the precipitant solution is 0.5-6 L / min; and / or, the flow rates of the metal salt solution and the precipitant solution are the same.

11. The method of claim 10, wherein, the flow rate of the metal salt solution is 2-6 L / min; and / or, the flow rate of the precipitant solution is 2-6 L / min.

12. The method of claim 4, wherein, the residence time of the manganese iron oxalate precursor in the first reaction kettle is 10 min-2 h; and / or, the residence time of the manganese iron oxalate precursor in the second reaction kettle is 10 min-10 h; and / or, the residence time of the manganese iron oxalate precursor in the storage kettle is 10 min-10 h.

13. The method of claim 12, wherein, the residence time of the manganese iron oxalate precursor in the first reaction kettle is 10 min-30 min; and / or, the residence time of the manganese iron oxalate precursor in the second reaction kettle is 30 min-6 h; and / or, the residence time of the manganese iron oxalate precursor in the storage kettle is 30 min-6 h.

14. The method of claim 12, wherein, the method, wherein, the residence time of the manganese iron oxalate precursor in the second reaction kettle is 30 min-90 min; and / or, the residence time of the manganese iron oxalate precursor in the storage kettle is 30 min-90 min.

15. The method of claim 4, wherein, the volume of the first reaction kettle is less than or equal to the volume of the second reaction kettle; and / or, the volume of the first reaction kettle is less than or equal to the volume of the storage kettle; and / or, the volume of the second reaction kettle is the same as the volume of the storage kettle. ​ 16. The method of claim 15, wherein, a ratio of a volume of the first reactor to a volume of the second reactor is 1: (1-5); and / or, a ratio of a volume of the first reactor to a volume of the storage tank is 1: (1-5).

17. The method of claim 15, wherein, a ratio of a volume of the first reactor to a volume of the second reactor is 1:3; and / or, a ratio of a volume of the first reactor to a volume of the storage tank is 1:

3.

18. The method of claim 4, wherein, a frequency of the ultrasonic reactor is 15 KHz-60 KHz.

19. The method of claim 18, wherein, a frequency of the ultrasonic reactor is 30 KHz-60 KHz.

20. The method of claim 4, wherein, The metal salt required for preparing the manganese iron oxalate precursor includes a water-soluble divalent iron salt, a water-soluble divalent manganese salt, and a water-soluble divalent salt of a doping element M, M representing a doping element of the manganese site and the iron site.

21. The method of claim 20, wherein, M includes one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr.

22. The method of claim 20, wherein, The water-soluble divalent iron salt includes one or more of ferrous chloride, ferrous bromide, ferrous nitrate, ferrous sulfate, ferrous acetate, ferrous fluosilicate, and ferrous perchlorate.

23. The method of claim 20, wherein, The water-soluble divalent manganese salt includes one or more of manganous chloride, manganous bromide, manganous nitrate, manganous sulfate, manganous acetate, and manganous perchlorate.

24. The method of claim 20, wherein, The water-soluble divalent salt of the doping element M includes one or more of hydrochloride, nitrate, sulfate, and acetate of the doping element M.

25. The method of any one of claims 4-20, wherein, The precipitant includes one or more of oxalic acid and a water-soluble oxalate.

26. The method of claim 25, wherein, The water-soluble oxalate includes one or more of lithium oxalate, sodium oxalate, potassium oxalate, and ammonium oxalate.

27. The method of claim 4, wherein, a concentration of the metal salt solution is 0.5 mol / L-2 mol / L; and / or, a concentration of the precipitant solution is 0.5 mol / L-2 mol / L; and / or, a molar ratio of the metal salt to the precipitant is 1:1-1:

5.

28. The method of claim 27, wherein, a concentration of the metal salt solution is 0.5 mol / L-1 mol / L; and / or, a concentration of the precipitant solution is 0.5 mol / L-1 mol / L.

29. The method of claim 4, wherein, a stirring speed of the first dissolving tank is 300 r / min-600 r / min; and / or, a stirring speed of the second dissolving tank is 300 r / min-600 r / min; and / or, a stirring speed of the first reactor is 300 r / min-600 r / min; and / or, a stirring speed of the second reactor is 300 r / min-600 r / min; and / or, a stirring speed of the storage tank is 300 r / min-600 r / min.

30. The method of claim 4, wherein, The protective gas includes nitrogen, an inert gas, or a combination thereof.

31. A manganese iron oxalate precursor having the chemical formula FeMnC2O4-2H2O, 0 < x < 1, M represents manganese site and iron site dopant elements, and the manganese iron oxalate precursor is charge neutral, prepared by the method of claim 4. x Mn y M 1-x-y C2O4-2H2O, 0 < x < 1, M represents manganese site and iron site dopant elements, and the manganese iron oxalate precursor is charge neutral.

32. The manganese iron oxalate precursor of claim 31, wherein, 0.2≤x≤0.5, 0 33. The manganese iron oxalate precursor of claim 31, wherein, 0.5≤y≤0.8, 0≤1-x-y<1.

34. The manganese iron oxalate precursor of claim 31, wherein, 0 35. The manganese iron oxalate precursor of claim 31, wherein, M includes one or more of Co, Mg, Zn, Ca, Ti, V, Ni, and Cr.

36. The manganese iron oxalate precursor of claim 31, wherein, the volume particle size Dv90 and Dv50 of the manganese iron oxalate precursor satisfy 1 the volume particle size Dv50 of the manganese iron oxalate precursor is 200 nm to 600 nm; and / or the volume particle size Dv90 of the manganese iron oxalate precursor is 260 nm to 800 nm.

37. The manganese iron oxalate precursor according to claim 36, wherein, the volume particle size Dv90 and Dv50 of the manganese iron oxalate precursor satisfy 1.3 the volume particle size Dv50 of the manganese iron oxalate precursor is 230 nm to 510 nm; and / or the volume particle size Dv90 of the manganese iron oxalate precursor is 320 nm to 730 nm.

38. A method for preparing lithium manganese iron phosphate, comprising at least the following steps: S10, mixing the manganese iron oxalate precursor prepared by the method of any one of claims 4-30 or the manganese iron oxalate precursor of any one of claims 31-36 with a lithium source, a phosphorus source, a source of doping element N, a source of doping element Q, and a source of doping element R in predetermined proportions to obtain a mixed raw material, wherein, N represents a doping element at a lithium site, Q represents a doping element at a phosphorus site, and R represents a doping element at an oxygen site; S20, performing sintering treatment on the mixed raw material obtained in S10 to obtain lithium manganese iron phosphate, The lithium manganese iron phosphate has a chemical formula of Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n , M represents a doping element of manganese and iron, N represents a doping element of lithium, Q represents a doping element of phosphorus, R represents a doping element of oxygen, 0.9≤a≤1.1, 0≤b≤0.1, and the lithium manganese iron phosphate is electrically neutral.

39. The method of claim 38, wherein, N includes one or more of Zn, Al, Na, K, Mg, Nb, Mo and W, Q includes one or more of B, S, Si and N, and R includes one or more of S, F, Cl and Br.

40. The method of claim 38, wherein, M includes one or more of Co, Mg, Zn, Ca, Ti, V, Ni and Cr, N includes one or more of Zn, Al, Na, K, Mg, Nb, Mo and W, Q includes one or more of B, S, Si and N, and R includes one or more of S, F, Cl and Br.

41. The method of claim 38, wherein, 0 42. The method of claim 38, wherein, 0.2 43. The method of claim 38, wherein, 0.5 44. The method of claim 38, wherein, 0 45. The method of claim 38, wherein, 0 46. The method of claim 38, wherein, 0＜n≤0.05。 47. The method of claim 38, wherein, In S10, a carbon source is further added to the mixed raw material.

48. Lithium manganese iron phosphate prepared by the method of claim 38 or 47.

49. A secondary battery comprising lithium manganese iron phosphate prepared by the method of claim 38 or 47.

Images