Positive electrode active material precursor, positive electrode active material, method for manufacturing, and secondary battery

Abstract

The application provides a positive electrode active material precursor, a positive electrode active material, a preparation method and a secondary battery. The preparation method comprises the following steps: S1, preparing a metal salt aqueous solution and a precipitant aqueous solution, wherein the precipitant comprises one or more selected from oxalic acid and a water-soluble oxalate; S2, performing a co-precipitation reaction after mixing the precipitant aqueous solution and the metal salt aqueous solution under a shearing speed of 10000 r / min or above; and S3, obtaining the positive electrode active material precursor after washing and drying after the reaction is completed. The preparation method provided by the application can obtain a positive electrode active material precursor with regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform element distribution and high batch stability and consistency, so as to improve the electrochemical performance of the positive electrode active material and the secondary battery.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a positive electrode active material precursor, a positive electrode active material, 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. The positive electrode active material is one of the key factors affecting the electrochemical performance of secondary batteries, and the precursor of the positive electrode active material, such as the commonly used oxalate precursor, is one of the key factors affecting the performance of the positive electrode active material itself. However, currently prepared oxalate precursors suffer from defects such as irregular morphology, large particle size, wide particle size distribution, and poor batch stability and consistency, thereby affecting the electrochemical performance of both the positive electrode active material and the secondary battery. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode active material precursor, a positive electrode active material, a preparation method, and a secondary battery, aiming to obtain a positive electrode active material precursor with regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform element distribution, and high batch stability and consistency, thereby improving the electrochemical performance of the positive electrode active material and the secondary battery.

[0004] The first aspect of this application provides a method for preparing a precursor of a positive electrode active material, comprising the following steps: S1, preparing an aqueous solution of a metal salt and an aqueous solution of a precipitant, wherein the precipitant includes one or more selected from oxalic acid and water-soluble oxalate; S2, mixing the aqueous solution of the precipitant and the aqueous solution of the metal salt at a shear rate of 10000 r / min or higher to carry out a co-precipitation reaction; S3, after the reaction is completed, washing and drying to obtain the precursor of the positive electrode active material.

[0005] The inventors of this application unexpectedly discovered during their research that by using a high-speed dispersion homogenizer to mix an aqueous solution of a precipitant and an aqueous solution of a metal salt at a shear rate exceeding 10,000 r / min for co-precipitation, not only can the production efficiency of cathode active material precursors be further improved, but also cathode active material precursors with regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform elemental distribution, and high batch stability and consistency can be obtained. The preparation method provided in this application also has the advantages of simple process, high production efficiency, and ease of large-scale industrial production. The preparation method provided in this application can also achieve low-cost and environmentally friendly production, possessing high industrial value. The preparation method provided in this application also helps to achieve precise control of the particle size of cathode active material precursors.

[0006] In any embodiment of this application, in S2, the coprecipitation reaction is carried out in a high-speed dispersion homogenizer.

[0007] In any embodiment of this application, the shear rate in S2 is 10000 r / min to 28000 r / min. Controlling the shear rate also helps to obtain cathode active material precursors with different particle sizes. Therefore, the preparation method provided in this application also helps to achieve precise control over the particle size of the cathode active material precursor.

[0008] In any embodiment of this application, in S2, the coprecipitation reaction time is 10 min to 60 min.

[0009] In any embodiment of this application, in S2, the temperature of the coprecipitation reaction is 20°C-80°C.

[0010] In any embodiment of this application, in step S2, the molar ratio of the precipitant to the metal salt is 1:1 to 3:1. Adjusting the amount of precipitant helps to improve the conversion efficiency of metal ions and also helps to make the co-precipitation reaction more complete.

[0011] In any embodiment of this application, in S1, the concentration of the metal salt aqueous solution is 0.5 mol / L-2 mol / L.

[0012] In any embodiment of this application, in S1, the concentration of the precipitant aqueous solution is 0.5 mol / L-2 mol / L.

[0013] In any embodiment of this application, the aqueous solution of the metal salt is prepared by dissolving the metal salt in water under a protective gas atmosphere to form an aqueous solution of the metal salt, wherein the protective gas includes nitrogen, an inert gas, or a combination thereof.

[0014] In any embodiment of this application, in S1, the metal salt includes one or more selected from metal sulfates, nitrates, hydrochlorides, and acetates.

[0015] In any embodiment of this application, in S1, the water-soluble oxalate includes one or more selected from lithium oxalate, sodium oxalate, potassium oxalate, and ammonium oxalate.

[0016] In any embodiment of this application, in S1, the metal salt is a divalent metal salt.

[0017] In any embodiment of this application, the metal salt includes one or more selected from divalent Mn salts, Fe salts, Ni salts, Co salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts.

[0018] In any embodiment of this application, the metal salt comprises at least a divalent Mn salt.

[0019] In any embodiment of this application, the metal salt includes divalent Mn salt, Fe salt, and optionally other metal M1 salt, where M1 represents the doping element at the manganese and iron sites. Optionally, the other metal M1 salt includes one or more selected from divalent Ni salt, Co salt, Mg salt, Zn salt, Ca salt, Ti salt, V salt, and Cr salt, thereby enabling the preparation of a precursor for lithium manganese iron phosphate cathode active material.

[0020] In any embodiment of this application, the metal salt includes divalent Mn salt, Ni salt, Co salt, and optionally other metal M2 salts, where M2 represents a doping element at the manganese, nickel, and cobalt sites. Optionally, the other metal M2 salts include one or more selected from divalent Fe salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts, thereby enabling the preparation of a precursor for lithium nickel cobalt manganese oxide cathode active material.

[0021] In any embodiment of this application, the metal salt includes divalent Mn salt, Ni salt, and optionally other metal M3 salt, where M3 represents the doping element at the manganese and nickel sites. Optionally, the other metal M3 salt includes one or more selected from divalent Fe salt, Co salt, Mg salt, Zn salt, Ca salt, Ti salt, V salt, and Cr salt, thereby enabling the preparation of a precursor for a lithium-rich manganese-based cathode active material.

[0022] In any embodiment of this application, the metal salt aqueous solution further includes a complexing agent. Adding a complexing agent to the metal salt aqueous solution helps improve the purity of the obtained positive electrode active material precursor, reduces the impurity content, and also makes the ratio of each metal ion in the obtained positive electrode active material precursor particles less different from the ratio of each metal ion in the raw material, thereby achieving precise control over the composition of the positive electrode active material precursor.

[0023] In any embodiment of this application, the complexing agent comprises one or more selected from aminocarboxylates, hydroxycarboxylates, and organophosphonates. Optionally, the complexing agent comprises one or more selected from ethylenediaminetetraacetic acid salt, gluconate, citrate, tartrate, metasilicate, tripolyphosphate, hypozoxytriacetic acid, diethylenetriaminepentamethylenephosphonate, ethylenediaminetetramethylenephosphonate, and hydroxyethylidene diphosphate.

[0024] In any embodiment of this application, the content of the complexing agent is ≤10wt%, based on the total mass of the aqueous solution of the metal salt.

[0025] A second aspect of the present application provides a positive electrode active material precursor prepared by the method described in the first aspect of the present application, with a molecular formula of Fe x Mn y M1 1-x-y C2O4, Ni a Co b Mn c M2 1-a-b-c C2O4 or Ni p Mn q M3 1-p-q C2O4, where 0<x<1, 0<y<1, 0≤1-x-y<1, M1 represents a doping element at the manganese site and the iron site, optionally including one or more selected from Ni, Co, Mg, Zn, Ca, Ti, V and Cr; 0<a<1, 0<b<1, 0<c<1, 0≤1-a-b-c<1, M2 represents a doping element at the manganese site, the nickel site and the cobalt site, optionally including one or more selected from Fe, Mg, Zn, Ca, Ti, V and Cr; 0<p<1, 0<q<1, 0≤1-p-q<1, M3 represents a doping element at the manganese site and the nickel site, optionally including one or more selected from Fe, Co, Mg, Zn, Ca, Ti, V and Cr.

[0026] In any embodiment of the present application, the volume particle size Dv50 of the positive electrode active material precursor satisfies 0.3μm≤Dv50≤3μm.

[0027] In any embodiment of the present application, the volume particle sizes Dv90 and Dv50 of the positive electrode active material precursor satisfy 1<Dv90 / Dv50≤1.5.

[0028] A third aspect of the present application provides a method for preparing a positive electrode active material, including the following steps: mixing the positive electrode active material precursor prepared by the method described in the first aspect of the present application or the positive electrode active material precursor according to the second aspect of the present application with a lithium source and / or a phosphorus source in a predetermined ratio, and then performing a sintering treatment to obtain the positive electrode active material.

[0029] A fourth aspect of the present application provides a positive electrode active material prepared by the method described in the third aspect of the present application.

[0030] A fifth aspect of the present application provides a secondary battery, comprising the positive electrode active material prepared by the method described in the third aspect of the present application or the positive electrode active material according to the fourth aspect of the present application.

[0031] The positive electrode active material precursor provided by the present application has the characteristics of regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform element distribution, and high batch stability and consistency, thereby being capable of improving the electrochemical performance of the positive electrode active material and the secondary battery. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope (SEM) image of the positive electrode active material precursor prepared in Example 3. Figure 1 (a) has a magnification of 1000x. Figure 1 (b) has a magnification of 5000.

[0033] Figure 2 This is a scanning electron microscope (SEM) image of the positive electrode active material precursor prepared in Comparative Example 2. Figure 2 (a) has a magnification of 2000 times. Figure 2 (b) has a magnification of 5000.

[0034] Figure 3 These are the first charge-discharge curves of the coin cells prepared in Examples 1, 2, and 1. Detailed Implementation

[0035] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material precursor, positive electrode active material, preparation method, and 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 the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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).

[0042] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0043] Coprecipitation is a common process for preparing precursors of cathode active materials. However, during coprecipitation, the rapid growth rate of crystal nuclei makes it difficult to control the size and morphology of the obtained crystals. Consequently, the resulting cathode active material precursors typically suffer from large particle sizes (e.g., volumetric particle size Dv50 is usually 10 μm-40 μm), wide particle size distribution, irregular morphology, and poor batch stability and consistency. This leads to the need for lengthy ball milling to reduce particle size during subsequent cathode active material preparation, a process that is both time-consuming and energy-intensive. Furthermore, achieving uniform mixing during cathode active material preparation is challenging, which also affects the electrochemical performance of the cathode active material and the secondary battery.

[0044] The inventors of this application made a surprising discovery during their research that by mixing and reacting the precipitant aqueous solution with the metal salt aqueous solution at a shear rate of over 10,000 r / min, they were able to obtain a positive electrode active material precursor with regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform element distribution, and high batch stability and consistency, thereby improving the electrochemical performance of the positive electrode active material and the secondary battery.

[0045] Specifically, the first aspect of this application provides a method for preparing a precursor of a positive electrode active material, comprising the following steps: S1, preparing an aqueous solution of a metal salt and an aqueous solution of a precipitant, wherein the precipitant includes one or more selected from oxalic acid and water-soluble oxalate; S2, mixing the aqueous solution of the precipitant and the aqueous solution of the metal salt at a shear rate of 10000 r / min or higher to carry out a co-precipitation reaction; S3, after the reaction is completed, washing and drying to obtain the precursor of the positive electrode active material.

[0046] In S2, the coprecipitation reaction is carried out in a high-speed dispersion homogenizer.

[0047] Currently, existing technologies for preparing cathode active material precursors via co-precipitation typically involve stirring in a conventional stirrer at a stirring speed not exceeding 1200 r / min. Furthermore, existing research generally suggests that once the stirring speed reaches a certain value, it no longer has a beneficial effect on crystal growth, such as failing to further refine particle size. However, the inventors of this application unexpectedly discovered during their research that by using a high-speed dispersion homogenizer to mix the precipitant aqueous solution and the metal salt aqueous solution at a shear rate exceeding 10000 r / min for co-precipitation, not only can the production efficiency of cathode active material precursors be further improved, but also cathode active material precursors with regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform elemental distribution, and high batch stability and consistency can be obtained.

[0048] High-speed dispersion homogenizers feature a unique stator and rotor structure that generates powerful shearing forces, rapidly reducing material size and resulting in finer, more uniformly dispersed materials. They can also circulate materials, completing online dispersion, emulsification, homogenization, and mixing processes. In contrast, conventional agitators, even at high stirring speeds, can only provide simple dispersion to ensure the reactants dissolve fully in the solvent, but they cannot achieve shearing and refining effects.

[0049] In the preparation method of this application, the shearing action of the high-speed dispersion homogenizer can instantly increase the initial concentration of the reaction system and enable the metal salt and precipitant to directly undergo a co-precipitation reaction. Therefore, the preparation method of this application can further increase the crystal nucleation rate and enable crystal particles to rapidly nucleate and slowly grow, thereby effectively controlling the particle size and particle size distribution of the positive electrode active material precursor.

[0050] In the coprecipitation reaction, the high-speed rotation of a high-speed dispersion homogenizer draws the reactants into the working chamber. The strong centrifugal force of the homogenizer propels the reactants radially into the narrow gap between the rotor and stator. Here, the generated cathode active material precursor particles are fully dispersed and broken up under the combined effects of intense liquid-phase shear, liquid-layer friction, and tearing collisions. They are then ejected at high speed through the stator slots. Subsequently, the flow direction changes due to the resistance of the reactants themselves and the container walls. Simultaneously, the axial suction force generated in the rotor region creates two strong turbulent flows, greatly enhancing the mass transfer process. Therefore, after multiple cycles, cathode active material precursor particles with regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform elemental distribution, and high batch stability and consistency can be obtained. Consequently, the cathode active material prepared from these particles exhibits good batch stability and consistency, as well as excellent electrochemical performance.

[0051] Furthermore, using the positive electrode active material precursor obtained by the preparation method provided in this application as raw material, the uniform mixing of multiple elements can be easily achieved in the subsequent solid-phase ball milling process for preparing positive electrode active materials, thereby greatly reducing the energy consumption and time of the ball milling process.

[0052] The preparation method provided in this application also has the advantages of simple process, high production efficiency and easy industrial-scale production.

[0053] The preparation method provided in this application uses water (e.g., pure water, distilled water, deionized water, etc.) as a solvent, which has high precipitation conversion efficiency of metal ions and does not require the addition of organic solvents (e.g., alcohols, esters, etc.). This can also reduce process costs and the pollution treatment burden of production wastewater, achieving low-cost and green environmentally friendly production, and has high industrialization value.

[0054] In S2, the shearing rate is 10,000 r / min or higher. In some embodiments, in S2, the shearing rate may be between 10,000 r / min and 28,000 r / min, for example, it may be a range consisting of any of the following values: 10,000 r / min, 11,000 r / min, 12,000 r / min, 13,000 r / min, 14,000 r / min, 15,000 r / min, 16,000 r / min, 17,000 r / min, 18,000 r / min, 19,000 r / min, 20,000 r / min, 21,000 r / min, 22,000 r / min, 23,000 r / min, 24,000 r / min, 25,000 r / min, 26,000 r / min, 27,000 r / min, 28,000 r / min, or higher.

[0055] By controlling the shear rate, it is also possible to obtain cathode active material precursors with different particle sizes. Therefore, the preparation method provided in this application also helps to achieve precise control over the particle size of cathode active material precursors.

[0056] In S2, there are no particular restrictions on the order of adding the precipitant aqueous solution and the metal salt aqueous solution. For example, both can be added to the reaction vessel simultaneously, or the metal salt aqueous solution can be added first, followed by the precipitant aqueous solution. Optionally, in S2, the precipitant aqueous solution is added to the metal salt aqueous solution at a shear rate of 10,000 r / min or higher for co-precipitation reaction. This allows the shear action of the high-speed dispersion homogenizer to instantly increase the initial concentration of the reaction system and enables the metal salt and precipitant to directly co-precipitate.

[0057] In some embodiments, the coprecipitation reaction in S2 can take 10 min to 60 min.

[0058] In some embodiments, in S2, the temperature of the coprecipitation reaction can be 20°C-80°C.

[0059] In some embodiments, in S1, the concentration of the metal salt aqueous solution may be 0.5 mol / L to 2 mol / L.

[0060] In some embodiments, in S1, the aqueous solution of the metal salt can be prepared by dissolving the metal salt in water under a protective gas atmosphere to form an aqueous solution of the metal salt, wherein the protective gas includes nitrogen, an inert gas, or a combination thereof.

[0061] In some embodiments, the metal salt may be a water-soluble metal salt known in the art for preparing precursors of positive electrode active materials, such as one or more selected from metal sulfates, nitrates, hydrochlorides, and acetates.

[0062] In some embodiments, the metal salt may be a divalent metal salt.

[0063] The preparation method of this application can be used to prepare precursors of lithium manganese iron phosphate cathode active materials, precursors of lithium nickel cobalt manganese oxide cathode active materials, and precursors of lithium-rich manganese-based cathode active materials.

[0064] In some embodiments, the metal salt may include one or more selected from divalent Mn salts, Fe salts, Ni salts, Co salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts.

[0065] In some embodiments, the metal salt may include at least a divalent Mn salt.

[0066] In some embodiments, the metal salt may include divalent Mn salts, Fe salts, and optionally other metal M1 salts, where M1 represents the doping element at the manganese and iron sites. Optionally, the other metal M1 salts may include one or more selected from divalent Ni salts, Co salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts, thereby enabling the preparation of a precursor for lithium manganese iron phosphate cathode active material.

[0067] In some embodiments, the metal salt may include divalent Mn salts, Ni salts, Co salts, and optionally other metal M2 salts, where M2 represents a doping element at the manganese, nickel, and cobalt sites. Optionally, the other metal M2 salts may include one or more selected from divalent Fe salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts, thereby enabling the preparation of a precursor for lithium nickel cobalt manganese oxide cathode active materials.

[0068] In some embodiments, the metal salt may include divalent Mn salts, Ni salts, and optionally other metal M3 salts, where M3 represents a doping element at the manganese and nickel sites. Optionally, the other metal M3 salts may include one or more selected from divalent Fe salts, Co salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts, thereby enabling the preparation of precursors for lithium-rich manganese-based cathode active materials.

[0069] In some embodiments, the concentration of the precipitant aqueous solution may be 0.5 mol / L to 2 mol / L.

[0070] The precipitant comprises one or more selected from oxalic acid and water-soluble oxalates. In some embodiments, the water-soluble oxalate may optionally comprise one or more selected from lithium oxalate, sodium oxalate, potassium oxalate, and ammonium oxalate.

[0071] In some embodiments, the molar ratio of the precipitant to the metal salt can be 1:1 to 3:1. Adjusting the amount of precipitant helps to improve the conversion efficiency of metal ions, reduce the difference in precipitation rates of different metal ions in the reaction system, thereby facilitating uniform co-precipitation of metal ions. This enables precise control over the composition of the cathode active material precursor and ensures that the actual content of each metal ion in the obtained cathode active material precursor reaches a predetermined value. Adjusting the amount of precipitant also helps to make the co-precipitation reaction more complete, thereby greatly reducing the metal ion content in the reaction waste liquid, reducing the difficulty of post-treatment waste liquid treatment processes, and reducing environmental pollution. In addition, it also helps to improve the purity of the obtained cathode active material precursor and reduce the content of impurity phases.

[0072] In some embodiments, the aqueous solution of the metal salt may further include a complexing agent.

[0073] When preparing cathode active material precursors via coprecipitation, the differences in solubility product constants of different metal ions lead to variations in their precipitation rates, hindering uniform coprecipitation. Furthermore, the proportions of metal ions in the obtained cathode active material precursor particles differ significantly from those in the raw materials, impacting product performance and consistency. Complexing agents can bind metal ions, controlling free metal ions to improve precipitation conversion efficiency, reduce the differences in precipitation rates among different metal ions in the reaction system, and achieve uniform coprecipitation. This allows for precise control over the composition of the cathode active material precursor, ensuring that the actual content of each metal ion in the obtained precursor reaches a predetermined value. Therefore, adding a complexing agent to a metal salt aqueous solution helps improve the purity of the obtained cathode active material precursor, reduces impurity phase content, and minimizes the difference in the proportions of metal ions in the obtained precursor particles compared to those in the raw materials, thus achieving precise control over the composition of the cathode active material precursor.

[0074] In some embodiments, the complexing agent may include one or more selected from aminocarboxylates, hydroxycarboxylates, and organophosphonates. Optionally, the complexing agent includes one or more selected from ethylenediaminetetraacetic acid (EDTA), gluconate, citrate, tartrate, metasilicate, tripolyphosphate, hypozinotriacetic acid, diethylenetriaminepentamethylenephosphonate, EDTA, and hydroxyethylidene diphosphate. More preferably, the complexing agent includes one or more selected from sodium ethylenediaminetetraacetic acid (EDTA), sodium gluconate, sodium citrate, sodium tartrate, sodium metasilicate, sodium tripolyphosphate, hypozinotriacetic acid, sodium diethylenetriaminepentamethylenephosphonate, sodium ethylenediaminetetramethylenephosphonate, and hydroxyethylidene diphosphate.

[0075] In some embodiments, the content of the complexing agent may be ≤10wt%, optionally 1wt%-10wt%, based on the total mass of the aqueous metal salt solution.

[0076] In some embodiments, in S3, the washing method may include one or more of water washing and alcohol washing, optionally including both water washing and alcohol washing. This application does not have a particular limitation on the number of water washing and alcohol washing cycles; for example, it may be 2-6 times. Optionally, the alcohol washing uses ethanol.

[0077] This application does not impose any particular restrictions on the drying method, which can be adjusted according to actual conditions. In some embodiments, in S3, the drying process can be either spray drying or vacuum drying.

[0078] In some embodiments, in S3, the drying process may include the following steps: transferring the washed material to a tubular furnace for further drying treatment after drying in a vacuum oven, so as to obtain an anhydrous positive electrode active material precursor, which facilitates precise adjustment of the proportion of each element in the subsequently prepared positive electrode active material.

[0079] Optionally, the drying temperature of the vacuum oven is 60°C to 100°C, and the drying time of the vacuum oven is 6h to 24h. Optionally, the drying temperature in the tubular furnace is 200°C to 300°C, and the drying time in the tubular furnace is 2h to 8h.

[0080] Optionally, the atmosphere in the tubular furnace is a protective gas atmosphere, and the protective gas may include nitrogen, an inert gas, or a combination thereof. Optionally, the inert gas is helium, argon, or a combination thereof.

[0081] In the preparation method of the positive electrode active material precursor provided in the present application, unless otherwise specified, all raw materials and instruments used are commercially available directly.

[0082] A second aspect of the embodiments of the present application provides a positive electrode active material precursor prepared by the method described in the first aspect of the embodiments of the present application.

[0083] The molecular formula of the positive electrode active material precursor may be Fe x Mn y M1 1-x-y C2O4, Ni a Co b Mn c M2 1-a-b-c C2O4 or Ni p Mn q M3 1-p-q C2O4, 0<x<1, 0<y<1, 0≤1-x-y<1, M1 represents a doping element at the manganese site and the iron site, optionally including one or more selected from Ni, Co, Mg, Zn, Ca, Ti, V and Cr, 0<a<1, 0<b<1, 0<c<1, 0≤1-a-b-c<1, M2 represents a doping element at the manganese site, the nickel site and the cobalt site, optionally including one or more selected from Fe, Mg, Zn, Ca, Ti, V and Cr, 0<p<1, 0<q<1, 0≤1-p-q<1, M3 represents a doping element at the manganese site and the nickel site, optionally including one or more selected from Fe, Co, Mg, Zn, Ca, Ti, V and Cr.

[0084] The positive electrode active material precursor of the present application has the characteristics of regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform element distribution, and high batch stability and consistency, which can improve the electrochemical performance of the positive electrode active material and the secondary battery.

[0085] In some embodiments, the volume particle size Dv50 of the positive electrode active material precursor satisfies 0.3μm≤Dv50≤3μm.

[0086] In some embodiments, the volume particle sizes Dv90 and Dv50 of the positive electrode active material precursor satisfy 1<Dv90 / Dv50≤1.5.

[0087] A third aspect of the embodiments of the present application provides a method for preparing a positive electrode active material, including the following steps: mixing the positive electrode active material precursor prepared by the method described in the first aspect of the embodiments of the present application or the positive electrode active material precursor of the second aspect of the embodiments of the present application with a lithium source and / or a phosphorus source in a predetermined ratio, followed by sintering treatment, to obtain the positive electrode active material.

[0088] In some embodiments, the molecular formula of the positive electrode active material precursor is Fe x Mn y M1 1-x-y C2O4, 0<x<1, 0<y<1, 0≤1-x-y<1, M1 represents a doping element at the manganese site and the iron site, optionally including one or more selected from Ni, Co, Mg, Zn, Ca, Ti, V and Cr, and the preparation method of the positive electrode active material may include the step of: mixing FexMnyM1 1-x-y C2O4 with a lithium source, a phosphorus source, and an optional carbon source in a predetermined ratio, followed by sintering treatment, to obtain the positive electrode active material, and the molecular formula of the positive electrode active material may be LiFe x Mn y M1 1-x-y PO4.

[0089] In some embodiments, the molecular formula of the positive electrode active material precursor is Ni a Co b Mn c M2 1-a-b-c C2O4, 0<a<1, 0<b<1, 0<c<1, 0≤1-a-b-c<1, M2 represents a doping element at the manganese site, the nickel site and the cobalt site, optionally including one or more selected from Fe, Mg, Zn, Ca, Ti, V and Cr, and the preparation method of the positive electrode active material may include the step of: mixing Ni a Co b Mn c M2 1-a-b-cAfter mixing C2O4 and a lithium source in a predetermined ratio, a sintering treatment is performed to obtain a positive electrode active material, and the molecular formula of the positive electrode active material may be LiNi a Co b Mn c M2 1-a-b-c O2.

[0090] In some embodiments, the molecular formula of the positive electrode active material precursor is Ni p Mn q M3 1-p-q C2O4, 0<p<1, 0<q<1, 0≤1-p-q<1, M3 represents a doping element at the manganese site and the nickel site, optionally including one or more selected from Fe, Co, Mg, Zn, Ca, Ti, V and Cr. The preparation method of the positive electrode active material may include the steps of: mixing Ni p Mn q M3 1-p-q C2O4 and a lithium source in a predetermined ratio, followed by a sintering treatment, to obtain the positive electrode active material. The molecular formula of the positive electrode active material may be mLi2MnO3·(1-m)LiM02, 0<m<1, and M includes one or more selected from Mn, Ni, Fe, Co, Mg, Zn, Ca, Ti, V and Cr.

[0091] The lithium source may be a lithium-containing compound known in the art that can be used for preparing a positive electrode active material, for example, the lithium source includes a member selected from Li2CO3, LiOH or a combination thereof.

[0092] The phosphorus source may be a phosphorus-containing compound known in the art that can be used for preparing a lithium manganese iron phosphate positive electrode active material, for example, the phosphorus source includes one or more of (NH4)2HPO4, NH4H2PO4, (NH4)3PO4 and H3PO4.

[0093] The carbon source includes one or more of an organic carbon source and an inorganic carbon source, optionally including one or more of glucose, sucrose, starch, fructose, polyvinyl alcohol, polyethylene glycol and citric acid.

[0094] A fourth aspect of the embodiments of the present application provides a positive electrode active material, which is prepared by the method described in the third aspect of the embodiments of the present application. The positive electrode active material may be a lithium manganese iron phosphate positive electrode active material, a lithium nickel cobalt manganese oxide positive electrode active material, or a lithium-rich manganese-based positive electrode active material.

[0095] A fifth aspect of the embodiments of the present application provides a secondary battery, comprising the positive electrode active material prepared by the method described in the third aspect of the embodiments of the present application or the positive electrode active material according to the fourth aspect of the embodiments of the present application.

[0096] Example

[0097] 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 weight, 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.

[0098] Example 1

[0099] S1, Preparation of aqueous solutions of metal salts and precipitants

[0100] Under nitrogen atmosphere, ferrous sulfate and manganese sulfate were mixed with pure water at a Fe:Mn molar ratio of 4:6 to prepare a 0.5 mol / L aqueous solution of the metal salt in a reaction vessel. Then, 5 wt% sodium ethylenediaminetetraacetate was added as a complexing agent. Oxalic acid, the precipitant, was mixed with pure water to prepare a 0.75 mol / L aqueous solution for later use.

[0101] S2, coprecipitation reaction

[0102] The speed of the high-speed dispersion homogenizer was manually adjusted to 12000 r / min. Then, under the high-speed dispersion and shearing action of the high-speed dispersion homogenizer, the aqueous solution of the precipitant was rapidly added to the reaction vessel and sheared for 30 min to obtain a suspension. The reaction temperature was room temperature (25℃), and the molar ratio of metal salt to oxalic acid was 1:1.5.

[0103] S3, Drying

[0104] The obtained suspension was washed multiple times with deionized water and ethanol, then the solid components were collected by centrifugation. The collected solid components were then dried in a vacuum oven at 80°C. Finally, the dried sample was placed in a tube furnace and heated at 200°C for 2 hours under an argon atmosphere to remove the water of crystallization, yielding anhydrous Mn. 0.6 Fe 0.4 C2O4 precursor.

[0105] Example 2

[0106] S1, Preparation of aqueous solutions of metal salts and precipitants

[0107] Under nitrogen atmosphere, ferrous sulfate and manganese sulfate were mixed with pure water at a Fe:Mn molar ratio of 4:6 to prepare a 0.5 mol / L aqueous solution of the metal salt in a reaction vessel. Then, 3 wt% sodium citrate was added as a complexing agent. Oxalic acid, the precipitant, was mixed with pure water to prepare a 1.5 mol / L aqueous solution for later use.

[0108] S2, coprecipitation reaction

[0109] The speed of the high-speed dispersion homogenizer was manually adjusted to 28,000 r / min. Then, under the high-speed dispersion and shearing action of the high-speed dispersion homogenizer, the aqueous solution of the precipitant was rapidly added to the reaction vessel and sheared for 10 min to obtain a suspension. The reaction temperature was room temperature (25℃), and the molar ratio of metal salt to oxalic acid was 1:3.

[0110] S3, Drying

[0111] The obtained suspension was washed multiple times with deionized water and ethanol, then the solid components were collected by centrifugation. The collected solid components were then dried in a vacuum oven at 80°C. Finally, the dried sample was placed in a tube furnace and heated at 200°C for 2 hours under an argon atmosphere to remove the water of crystallization, yielding anhydrous Mn. 0.6 Fe 0.4 C2O4 precursor.

[0112] Example 3

[0113] S1, Preparation of aqueous solutions of metal salts and precipitants

[0114] Under nitrogen atmosphere, ferrous sulfate and manganese sulfate were mixed with pure water at a Fe:Mn molar ratio of 3:7 to prepare a 0.5 mol / L aqueous solution of the metal salt in a reaction vessel. Then, 10 wt% sodium diethylenetriaminepentamethylphosphonate was added as a complexing agent. A 0.5 mol / L aqueous solution of sodium oxalate and pure water was prepared as a precipitant for later use.

[0115] S2, coprecipitation reaction

[0116] The speed of the high-speed dispersion homogenizer was manually adjusted to 10,000 r / min. Then, under the high-speed dispersion and shearing action of the high-speed dispersion homogenizer, the aqueous solution of the precipitant was rapidly added to the reaction vessel and sheared for 40 min to obtain a suspension. The reaction temperature was room temperature (25℃), and the molar ratio of metal salt to sodium oxalate was 1:1.

[0117] S3, Drying

[0118] The obtained suspension was washed multiple times with deionized water and ethanol, then the solid components were collected by centrifugation. The collected solid components were then dried in a vacuum oven at 80°C. Finally, the dried sample was placed in a tube furnace and heated at 200°C for 2 hours under an argon atmosphere to remove the water of crystallization, yielding anhydrous Mn. 0.7 Fe 0.3 C2O4 precursor.

[0119] Example 4

[0120] S1, Preparation of aqueous solutions of metal salts and precipitants

[0121] Under nitrogen atmosphere, nickel sulfate and manganese sulfate were mixed with pure water at a Ni:Mn molar ratio of 3:7 to prepare a 0.5 mol / L aqueous solution of the metal salts in a reaction vessel. Then, 5 wt% sodium ethylenediaminetetramethylene phosphate was added as a complexing agent. Oxalic acid was mixed with pure water to prepare a 1 mol / L aqueous solution of the precipitant for later use.

[0122] S2, coprecipitation reaction

[0123] The speed of the high-speed dispersion homogenizer was manually adjusted to 15000 r / min. Then, under the high-speed dispersion and shearing action of the high-speed dispersion homogenizer, the aqueous solution of the precipitant was rapidly added to the reaction vessel and sheared for 30 min to obtain a suspension. The reaction temperature was room temperature (25℃), and the molar ratio of metal salt to oxalic acid was 1:2.

[0124] S3, Drying

[0125] The obtained suspension was washed multiple times with deionized water and ethanol, then the solid components were collected by centrifugation. The collected solid components were then dried in a vacuum oven at 80°C. Finally, the dried sample was placed in a tube furnace and heated at 200°C for 2 hours under an argon atmosphere to remove the water of crystallization, yielding anhydrous Mn. 0.7 Ni 0.3 C2O4 precursor.

[0126] Example 5

[0127] S1, Preparation of aqueous solutions of metal salts and precipitants

[0128] Under nitrogen atmosphere, nickel sulfate, cobalt sulfate, and manganese sulfate were mixed with pure water in a Ni:Co:Mn molar ratio of 1:1:1 to prepare a 0.5 mol / L aqueous solution of the metal salts. Then, 5 wt% sodium gluconate was added as a complexing agent. Ammonium oxalate was also mixed with pure water to prepare a 0.5 mol / L aqueous solution of the precipitant for later use.

[0129] S2, coprecipitation reaction

[0130] The speed of the high-speed dispersion homogenizer was manually adjusted to 20,000 r / min. Then, under the high-speed dispersion and shearing action of the high-speed dispersion homogenizer, the aqueous solution of the precipitant was rapidly added to the reaction vessel and sheared for 20 min to obtain a suspension. The reaction temperature was room temperature (25℃), and the molar ratio of metal salt to ammonium oxalate was 1:1.

[0131] S3, Drying

[0132] The obtained suspension was washed multiple times with deionized water and ethanol, then the solid components were collected by centrifugation. The collected solid components were then dried in a vacuum oven at 80°C. Finally, the dried sample was placed in a tube furnace and heated at 200°C for 2 hours under an argon atmosphere to remove the water of crystallization, yielding anhydrous Ni. 0.33 Co 0.33 Mn 0.33 C2O4 precursor.

[0133] Comparative Example 1

[0134] S1, Preparation of aqueous solutions of metal salts and precipitants

[0135] Under nitrogen atmosphere, ferrous sulfate and manganese sulfate were mixed with pure water at a Fe:Mn molar ratio of 4:6 to prepare a 0.5 mol / L aqueous solution of the metal salt in a reaction vessel. Then, 3 wt% sodium citrate was added as a complexing agent. Oxalic acid, the precipitant, was mixed with pure water to prepare a 1.5 mol / L aqueous solution for later use.

[0136] S2, coprecipitation reaction

[0137] An aqueous solution of the precipitant was added to the reaction vessel and stirred for 60 minutes under the stirring action of a magnetic stirrer to obtain a suspension. The reaction temperature was room temperature (25℃), the stirring speed was 800 r / min, and the molar ratio of metal salt to oxalic acid was 1:3.

[0138] S3, Drying

[0139] The obtained suspension was washed multiple times with deionized water and ethanol, then the solid components were collected by centrifugation. The collected solid components were then dried in a vacuum oven at 80°C. Finally, the dried sample was placed in a tube furnace and heated at 200°C for 2 hours under an argon atmosphere to remove the water of crystallization, yielding anhydrous Mn. 0.6 Fe 0.4 C2O4 precursor.

[0140] Comparative Example 2

[0141] S1, Preparation of aqueous solutions of metal salts and precipitants

[0142] Under nitrogen atmosphere, ferrous sulfate and manganese sulfate were mixed with pure water in a reaction vessel at a Fe:Mn molar ratio of 3:7 to prepare a 0.5 mol / L aqueous solution of the metal salt. Sodium oxalate was also mixed with pure water to prepare a 0.5 mol / L aqueous solution of the precipitant, for later use.

[0143] S2, coprecipitation reaction

[0144] A precipitant aqueous solution was added to the reaction vessel and stirred for 60 minutes under the stirring action of a magnetic stirrer to obtain a suspension. The reaction temperature was room temperature (25℃), the stirring speed was 500 r / min, and the molar ratio of metal salt to sodium oxalate was 1:1.

[0145] S3, Drying

[0146] The obtained suspension was washed multiple times with deionized water and ethanol, then the solid components were collected by centrifugation. The collected solid components were then dried in a vacuum oven at 80°C. Finally, the dried sample was placed in a tube furnace and heated at 200°C for 2 hours under an argon atmosphere to remove the water of crystallization, yielding anhydrous Mn. 0.7 Fe 0.3 C2O4 precursor.

[0147] Test section

[0148] (1) Particle size test

[0149] The volumetric particle size of the oxalate precursor prepared above was measured using a Malvern Master Size 3000 laser particle size analyzer. Dv50 and Dv90 refer to the particle size corresponding to a cumulative volume distribution percentage of 50% and 90%, respectively. The testing standard can be found in GB / T 19077-2016.

[0150] The test results are shown in Table 1.

[0151] (2) Metal element content test

[0152] The contents of each metal element in the oxalate precursor prepared above were determined and their molar ratios were calculated using an ICP-OES method with a Plasma 3000 inductively coupled plasma atomic emission spectrometer.

[0153] The test results are shown in Table 2.

[0154] (3) First cycle performance test of button cell

[0155] The oxalate precursor (100 mmol) prepared above was placed in a ball mill jar with Li2CO3 (50 mmol), NH4H2PO4 (100 mmol) and sucrose (15 mmol), and a small amount of ethanol and water were added as solvents. The mixture was ball milled at 500 r / min for 8 h to obtain a slurry. The obtained slurry was transferred to a spray drying equipment for spray drying and granulation to obtain powder. The drying temperature was set at 210 °C. The obtained powder was placed in a muffle furnace and sintered at 400℃ in air atmosphere for 5 hours, and then naturally cooled to room temperature to obtain a pre-sintered material. The obtained pre-sintered material was placed in a ball mill jar, and a small amount of ethanol and water were added as solvents. The mixture was ball milled at 800 r / min for 4 hours to obtain a slurry. The obtained slurry was transferred to a spray drying equipment for spray drying and granulation to obtain pre-sintered material powder. The drying temperature was set to 210℃. The obtained pre-sintered material powder was placed in a muffle furnace and sintered at 700℃ in nitrogen atmosphere for 10 hours. After naturally cooling to room temperature, it was pulverized by airflow to obtain lithium manganese iron phosphate cathode active material.

[0156] The prepared lithium manganese iron phosphate positive electrode active material, along with the binder polyvinylidene fluoride (PVDF) and the conductive agent acetylene black, were added to N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5. The mixture was stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet.

[0157] A coin cell was assembled in a coin cell box using a lithium sheet as the negative electrode and a 1 mol / L LiPF6 solution in a 1:1:1 volume ratio of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) as the electrolyte.

[0158] In a constant temperature environment of 25℃, the coin cell battery is charged to 4.3V at a constant current of 0.1C, and then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. The charging capacity at this time is the initial charging capacity, denoted as C0. After the coin cell battery is left to stand for 2 minutes, it is discharged to 2.0V at a constant current of 0.1C. The discharge capacity at this time is the initial discharge capacity, denoted as D0.

[0159] The initial coulombic efficiency (%) of a coin cell is (D0 / C0) × 100%. The initial specific capacity (mAh / g) of a coin cell is D0 / m, where m represents the mass of the lithium manganese iron phosphate cathode active material.

[0160] The test results are shown in Table 3 and Figure 3 As shown.

[0161] Table 1

[0162] Example 1 1.5μm 2.1μm 1.40 Example 2 0.3μm 0.4μm 1.33 Example 3 1.7μm 2.5μm 1.47 Example 4 1.2μm 1.7μm 1.41 Example 5 0.8μm 1.1μm 1.37 Comparative Example 1 29.5μm 50.7μm 1.72 Comparative Example 2 35.8μm 64.7μm 1.81

[0163] Table 2

[0164]

[0165] Table 3

[0166] Example 1 98％ 150.4 Example 2 99％ 154.6 Example 3 97％ 149.5 Comparative Example 1 95％ 119.5 Comparative Example 2 92％ 115.3

[0167] Figure 1 This is a scanning electron microscope (SEM) image of the positive electrode active material precursor prepared in Example 3. Figure 1 (a) has a magnification of 1000x. Figure 1 (b) has a magnification of 5000. Figure 2 This is a scanning electron microscope (SEM) image of the positive electrode active material precursor prepared in Comparative Example 2. Figure 2 (a) has a magnification of 2000 times. Figure 2 (b) has a magnification of 5000.

[0168] Based on the test results in Tables 1 and 2, and Figure 1 and Figure 2 It can be seen that the positive electrode active material precursor prepared by the preparation method provided in this application has the characteristics of regular morphology, small particle size, narrow particle size distribution and uniform element distribution. The test results of Examples 1-5 also show that the higher the rotational speed (i.e., shear rate) of the high-speed dispersion homogenizer, the finer the particle size and the narrower the particle size distribution of the obtained positive electrode active material precursor.

[0169] Based on the test results of Example 3 and Comparative Example 2, it can be seen that by adding a complexing agent to the metal salt aqueous solution, the composition of the positive electrode active material precursor can be precisely controlled, and the actual content of each metal ion in the obtained positive electrode active material precursor can reach the predetermined value.

[0170] Based on the test results of Examples 1, 2 and Comparative Example 1, it can be seen that when a complexing agent is added to the metal salt aqueous solution, the preparation method provided in this application can achieve precise control over the composition of the positive electrode active material precursor, and make the actual content of each metal ion in the obtained positive electrode active material precursor closer to the predetermined value.

[0171] Figure 3 This is a graph showing the first charge-discharge curves of the coin cells prepared in Examples 1, 2, and Comparative Example 1. The test results in Table 3 are combined with... Figure 3 It can be seen that the lithium manganese iron phosphate cathode active material prepared using the cathode active material precursor prepared in this application as raw material has higher specific capacity and first coulombic efficiency, thereby better improving the electrochemical performance of secondary batteries.

[0172] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a precursor of a positive electrode active material, comprising the following steps: S1, preparing an aqueous solution of a metal salt and an aqueous solution of a precipitant, adding a complexing agent to the aqueous solution of the metal salt, wherein the complexing agent comprises one or more selected from aminocarboxylate, hydroxycarboxylate, and organophosphonate, and the precipitant comprises one or more selected from oxalic acid and water-soluble oxalate; S2, mixing the aqueous solution of the precipitant and the aqueous solution of the metal salt at a shear rate of 10000 r / min or higher and then performing a coprecipitation reaction, wherein the temperature of the coprecipitation reaction is 20℃-80℃; S3, after the reaction is completed, washing and drying to obtain the precursor of the positive electrode active material, wherein the volumetric particle size Dv50 of the precursor of the positive electrode active material satisfies 0.3 μm≤Dv50≤3 μm; and the volumetric particle sizes Dv90 and Dv50 of the precursor of the positive electrode active material satisfy 1<Dv90 / Dv50≤1.

5.

2. The method according to claim 1, wherein, In S2, the coprecipitation reaction is carried out in a high-speed dispersion homogenizer.

3. The method according to claim 1 or 2, wherein, In S2, the shearing rate is 10000 r / min - 28000 r / min; and / or, In S2, the coprecipitation reaction takes 10 min to 60 min.

4. The method according to claim 1 or 2, wherein, In S2, the molar ratio of the precipitant to the metal salt is 1:1 to 3:

1.

5. The method according to claim 1 or 2, wherein, In S1, the concentration of the aqueous metal salt solution is 0.5 mol / L - 2 mol / L; and / or, In S1, the concentration of the aqueous precipitant solution is 0.5 mol / L - 2 mol / L.

6. The method according to claim 1 or 2, wherein, The aqueous solution of the metal salt is prepared by dissolving the metal salt in water under a protective gas atmosphere to form an aqueous solution of the metal salt, wherein the protective gas includes an inert gas.

7. The method according to claim 6, wherein, The inert gas includes nitrogen.

8. The method according to claim 1 or 2, wherein, In S1, the metal salt includes one or more selected from metal sulfates, nitrates, hydrochlorides, and acetates; and / or, In S1, the water-soluble oxalate includes one or more selected from lithium oxalate, sodium oxalate, potassium oxalate, and ammonium oxalate.

9. The method according to claim 1 or 2, wherein, In S1, the metal salt is a divalent metal salt.

10. The method according to claim 1 or 2, wherein, The metal salt includes one or more selected from divalent Mn salts, Fe salts, Ni salts, Co salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts.

11. The method according to claim 1 or 2, wherein, The metal salt includes at least a divalent Mn salt.

12. The method according to claim 1, wherein, The metal salts include divalent Mn salts and Fe salts; Alternatively, the metal salt may include divalent Mn salts, Ni salts, or Co salts; Alternatively, the metal salt may include divalent Mn salts or Ni salts.

13. The method according to claim 12, wherein, The metal salt also includes salts of other metals M1, where M1 represents doping elements at manganese and iron sites.

14. The method according to claim 13, wherein, The other metal M1 salts include one or more selected from divalent Ni salts, Co salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts.

15. The method according to claim 12, wherein, The metal salt also includes salts of other metals M2, where M2 represents doping elements at manganese, nickel, and cobalt sites.

16. The method according to claim 15, wherein, The other metal M2 salts include one or more selected from divalent Fe salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts.

17. The method according to claim 12, wherein, The metal salt also includes salts of other metals M3, where M3 represents doping elements at manganese and nickel sites.

18. The method according to claim 17, wherein, The other metal M3 salts include one or more selected from divalent Fe salts, Co salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts.

19. The method according to any one of claims 12-18, wherein, The complexing agent comprises one or more selected from ethylenediaminetetraacetic acid (EDTA), gluconate, citrate, tartrate, metasilicate, tripolyphosphate, hypozinotriacetic acid, diethylenetriaminepentamethylphosphonate, EDTA, and hydroxyethylidene diphosphate; and / or, The content of the complexing agent is ≤10 wt%, based on the total mass of the aqueous solution of the metal salt.

20. A positive electrode active material precursor prepared by the method according to any one of claims 1-19, having the molecular formula Fe. x Mn y M1 1-x-y C2O4、Ni a Co b Mn c M2 1-a-b-c C2O4 or Ni p Mn q M3 1-p-q C2O4, 0 < x < 1, 0 < y < 1, 0 ≤ 1 - xy < 1, M1 represents the doping element at the manganese and iron sites, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≤ 1 - abc < 1, M2 represents the doping element at the manganese, nickel and cobalt sites, 0 < p < 1, 0 < q < 1, 0 ≤ 1 - pq < 1, M3 represents the doping element at the manganese and nickel sites.

21. The positive electrode active material precursor according to claim 20, wherein, M1 includes one or more selected from Ni, Co, Mg, Zn, Ca, Ti, V and Cr.

22. The positive electrode active material precursor according to claim 20, wherein, M2 includes one or more selected from Fe, Mg, Zn, Ca, Ti, V and Cr.

23. The positive electrode active material precursor according to claim 20, wherein, M3 includes one or more elements selected from Fe, Co, Mg, Zn, Ca, Ti, V, and Cr.

24. A method for preparing a positive electrode active material, comprising the following steps: The positive electrode active material precursor prepared by the method according to any one of claims 1-19 or the positive electrode active material precursor according to any one of claims 19-22 is mixed with a lithium source and / or a phosphorus source in a predetermined ratio, and then subjected to sintering treatment to obtain the positive electrode active material.

25. A positive electrode active material prepared by the method of claim 24.

26. A secondary battery comprising a positive electrode active material prepared by the method of claim 24 or the positive electrode active material of claim 25.

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