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

Abstract

The present application provides a cathode active material precursor, a cathode active material, a manufacturing method, and a secondary battery, the manufacturing method including the steps of: preparing a metal salt aqueous solution and a precipitant aqueous solution, the precipitant comprising one or more selected from oxalic acid and a water-soluble oxalate; mixing the precipitant aqueous solution and the metal salt aqueous solution at a shear rate of 10,000 r / min or more, and then carrying out a co-precipitation reaction; and washing and drying the mixture after the reaction to obtain the cathode active material precursor. The manufacturing method according to the present application can obtain a cathode 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 cathode active material and the secondary battery.

Description

[Technical field]

[0001] The present application belongs to the field of battery technology, and specifically relates to a positive electrode active material precursor, a positive electrode active material, a manufacturing method, and a secondary battery. [Background technology]

[0002] In recent years, secondary batteries have been widely used in many fields, such as energy storage power systems such as hydroelectric, thermal, wind and solar power plants, power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. The positive electrode active material is one of the important factors that affect the electrochemical performance of secondary batteries, and the positive electrode active material precursor, for example, the commonly used oxalate precursor, is one of the important factors that affect the performance of the positive electrode active material. However, the currently produced oxalate precursor has defects such as irregular morphology, large particle size, wide particle size distribution, poor batch stability and consistency, which affect the electrochemical performance of the positive electrode active material and secondary batteries. Summary of the Invention

[0003] An object of the present application is to provide a cathode active material precursor, a cathode active material, a manufacturing method, and a secondary battery that can improve the electrochemical performance of the cathode active material and secondary battery by obtaining a cathode active material precursor that has a regular morphology, a small particle size, a narrow particle size distribution, a single crystal phase, high purity, uniform element distribution, and high batch stability and consistency.

[0004] A first aspect of the present application provides a method for producing a positive electrode active material precursor, the method including: step S1 of preparing an aqueous metal salt solution and an aqueous precipitant solution, wherein the precipitant contains one or more selected from oxalic acid and a water-soluble oxalate; step S2 of mixing the aqueous precipitant solution and the aqueous metal salt solution at a shear rate of 10,000 r / min or more and then carrying out a co-precipitation reaction; and step S3 of washing and drying after the reaction to obtain the positive electrode active material precursor.

[0005] In the course of research, the inventors of the present application unexpectedly discovered that by using a high-speed homogenizer to mix the precipitant aqueous solution and the metal salt aqueous solution at a shear rate of 10,000 r / min or more and then carrying out a co-precipitation reaction, the production efficiency of the positive electrode active material precursor can be further improved, and the positive electrode active material precursor can be obtained with regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform element distribution, and high batch stability and consistency. The preparation method of the present application also has the advantages of simple process, high production efficiency, and easy large-scale industrialization. The preparation method of the present application can also realize low-cost and environmentally friendly production, and has high industrialization value. The preparation method of the present application also contributes to accurately controlling the particle size of the positive electrode active material precursor.

[0006] In any embodiment of the present application, in S2, the co-precipitation reaction is carried out in a high speed homogenizer.

[0007] In any embodiment of the present application, in S2, the shear rate is 10000r / min-28000r / min. Controlling the magnitude of the shear rate also contributes to obtaining a positive electrode active material precursor with different particle sizes. Therefore, the manufacturing method according to the present application also contributes to accurately controlling the particle size of the positive electrode active material precursor.

[0008] In any embodiment of the present application, in S2, the time of the co-precipitation reaction is 10 min-60 min.

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

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

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

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

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

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

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

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

[0017] In any embodiment of the present application, the metal salt comprises 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 the present application, the metal salt comprises at least a divalent Mn salt.

[0019] In any embodiment of the present application, the metal salt includes a divalent Mn salt, an Fe salt, and a selectable salt of another metal M1, where M1 represents a doping element of a manganese site and an iron site, and optionally the salt of another metal M1 includes one or more selected from a divalent Ni salt, a Co salt, an Mg salt, a Zn salt, a Ca salt, a Ti salt, a V salt, and a Cr salt, thereby making it possible to prepare a precursor of a lithium manganese iron phosphate positive electrode active material.

[0020] In any embodiment of the present application, the metal salt includes a divalent Mn salt, a Ni salt, a Co salt, and a selectable salt of another metal M2, where M2 represents a doping element of a manganese site, a nickel site, and a cobalt site, and optionally the salt of another metal M2 includes one or more selected from a divalent Fe salt, a Mg salt, a Zn salt, a Ca salt, a Ti salt, a V salt, and a Cr salt, thereby making it possible to prepare a precursor of a lithium nickel-cobalt manganese oxide positive electrode active material.

[0021] In any embodiment of the present application, the metal salt includes a divalent Mn salt, a Ni salt, and an optional salt of another metal M3, where M3 represents a doping element of a manganese site and a nickel site, and optionally the salt of another metal M3 includes one or more selected from a divalent Fe salt, a Co salt, a Mg salt, a Zn salt, a Ca salt, a Ti salt, a V salt, and a Cr salt, thereby making it possible to prepare a precursor of a lithium-rich manganese-based positive electrode active material.

[0022] In any embodiment of the present application, the metal salt aqueous solution further comprises a complexing agent, which contributes to improving the purity of the obtained positive electrode active material precursor and reducing the content of impurities, and also reduces the difference between the ratio of each metal ion in the obtained positive electrode active material precursor particles and the ratio of each metal ion in the raw material, and further allows for accurate control of the composition of the positive electrode active material precursor.

[0023] In any embodiment of the present application, the complexing agent includes one or more selected from aminocarboxylates, hydroxycarboxylates, and organic phosphonates. Optionally, the complexing agent includes one or more selected from ethylenediaminetetraacetates, gluconates, citrates, tartrates, metasilicates, tripolyphosphates, nitrilotriacetates, diethylenetriaminepentamethylenephosphonates, ethylenediaminetetrakis(methylenephosphonates), and hydroxyethanediphosphonates.

[0024] In any embodiment of the present application, the content of the complexing agent is 10 wt% or less (≦10 wt%) based on the total mass of the aqueous metal salt solution.

[0025] A second aspect of the present application has 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 for the manganese site and the iron site, and optionally includes 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 for the manganese site, the nickel site, and the cobalt site, and optionally includes 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 for the manganese site and the nickel site, and optionally includes one or more selected from Fe, Co, Mg, Zn, Ca, Ti, V, and Cr. Provided is a cathode active material precursor produced by the method according to the first aspect of the present application.

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

[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 manufacturing a positive electrode active material, including the step of mixing a positive electrode active material precursor manufactured by the method described in the first aspect of the present application or the positive electrode active material precursor of the second aspect of the present application with a lithium source and / or a phosphorus source at a predetermined ratio, and then performing a sintering process to obtain a positive electrode active material.

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

[0030] A fifth aspect of the present application provides a secondary battery including the positive electrode active material manufactured by the method described in the third aspect of the present application or the positive electrode active material of the fourth aspect of the present application.

[0031] The positive electrode active material precursor according to 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. Therefore, the electrochemical performance of the positive electrode active material and the secondary battery can be improved.

Brief Description of the Drawings

[0032] [Figure 1] It is a scanning electron microscope (SEM) image of the positive electrode active material precursor manufactured in Example 3. The magnification of FIG. 1(a) is 1000 times, and the magnification of FIG. 1(b) is 5000 times. [Diagram 2] It is a scanning electron microscope (SEM) image of the positive electrode active material precursor manufactured in Comparative Example 2. The magnification of FIG. 2(a) is 2000 times, and the magnification of FIG. 2(b) is 5000 times. [Diagram 3] It is a diagram of the first charge-discharge curves of the coin cells manufactured in Example 1, Example 2, and Comparative Example 1. Embodiments for Carrying Out the Invention

[0033] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the positive electrode active material precursor, positive electrode active material, manufacturing method, and secondary battery of the present application will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of already well-known matters and duplicated description of substantially the same configuration may be omitted. This is to avoid the following description becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the attached drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0034] The "ranges" disclosed in this application are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such a defined range may be an end value or an end value-free range, and may be combined in any way, i.e., any lower limit may be combined with any upper limit. For example, if ranges of 60-120 and 80-110 are recited for a particular parameter, then ranges of 60-110 and 80-120 are also contemplated. Also, if minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5 are recited, then ranges of 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be contemplated. In this application, unless otherwise stated, the numerical range "ab" is represented by the abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, with "0-5" being an abbreviation for combinations of these numerical values. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all the embodiments and optional embodiments of the present application may be combined with each other to form a new technical solution, and such technical solution should be considered to be included in the disclosure content of the present application.

[0036] Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form a new technical solution, and such technical solution should be considered as included in the disclosure content of the present application.

[0037] Unless otherwise specified, all steps in this application may be performed in sequence or randomly, but are preferably performed in sequence. For example, the method includes steps S1 and S2, which means that the method may include steps S1 and S2 performed in sequence, or steps S2 and S1 performed in sequence. For example, when it is mentioned that the method may further include step S3, it means that step S3 may be added to the method in any order. For example, the method may include steps S1, S2, and S3, or may include steps S1, S3, and S2, or may include steps S3, S1, and S2, etc.

[0038] Unless otherwise specified, the terms "comprise", "have", and "comprise" used herein mean open-ended and may also be closed-ended. For example, the terms "comprise", "have", and "comprise" may mean "comprise", "have", or "comprise" other components not listed, or "comprise", "have", or "comprise" only the listed components.

[0039] In this application, the term "or" is inclusive unless otherwise specified. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions are met: 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).

[0040] In this application, the terms "plurality" and "plurality" refer to two or more.

[0041] Co-precipitation is a common manufacturing process for producing a positive electrode active material precursor, but in the co-precipitation process, the growth rate of the crystal nuclei is fast, and it is difficult to control the size and morphology of the obtained crystals, so that the obtained positive electrode active material precursor usually has defects such as a large particle size (for example, the volume particle size Dv50 is usually 10 μm-40 μm), a wide particle size distribution, an irregular morphology, and poor batch stability and consistency. Furthermore, when the positive electrode active material is subsequently produced, it is necessary to perform ball milling for a long time to reduce the particle size, which is a time-consuming and energy-consuming process. In addition, it is difficult to achieve uniformity of the mixed materials when producing the positive electrode active material, which also affects the electrochemical performance of the positive electrode active material and secondary batteries.

[0042] In the course of research, the inventors of the present application unexpectedly discovered that by mixing and reacting an aqueous precipitant solution with an aqueous metal salt solution at a shear rate of 10,000 r / min or more, a positive electrode active material precursor having regular morphology, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform element distribution, and high batch stability and consistency can be obtained, thereby improving the electrochemical performance of the positive electrode active material and secondary battery.

[0043] Specifically, a first aspect of an embodiment of the present application provides a method for producing a positive electrode active material precursor, the method including: step S1 of preparing an aqueous metal salt solution and an aqueous precipitant solution, wherein the precipitant contains one or more selected from oxalic acid and a water-soluble oxalate; step S2 of mixing the aqueous precipitant solution and the aqueous metal salt solution at a shear rate of 10,000 r / min or more and then carrying out a co-precipitation reaction; and step S3 of washing and drying after the reaction to obtain the positive electrode active material precursor.

[0044] In S2, the co-precipitation reaction is carried out in a high speed homogenizer.

[0045] At present, in the prior art, when preparing a positive electrode active material precursor by coprecipitation, the stirring reaction is carried out in a normal stirrer at a stirring speed of 1200 r / min or less. In addition, in the past research, it has been concluded that after the stirring speed reaches a certain value, it cannot have a beneficial effect on the growth of crystals, for example, the particle size cannot be further refined. However, the inventors of the present application have found in the course of research that by mixing the precipitant aqueous solution and the metal salt aqueous solution at a shear rate of 10000 r / min or more using a high-speed homogenizer and then carrying out the coprecipitation reaction, it is possible to further improve the production efficiency of the positive electrode active material precursor, as well as 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.

[0046] The high-speed homogenizer has a unique stator and rotor structure, which can generate super strong shearing force, quickly reduce the size of the material, make the material finer, and make the dispersion degree more uniform, and can also circulate the material and complete the dispersion, emulsification, homogenization and mixing steps online.Normal agitators can only play a simple dispersion role to fully dissolve each reactant in the solvent even at high stirring speeds, but cannot play a shearing and fine-graining role.

[0047] In the preparation method of the present application, the shearing action of the high-speed homogenizer can instantly increase the initial concentration of the reaction system, and the metal salt and the precipitant can directly co-precipitate with each other. Therefore, the preparation method of the present application can further increase the formation rate of crystal nuclei, and the crystal particles can be rapidly nucleated and slowly grown, thereby achieving the effect of effectively controlling the particle size and particle size distribution of the positive electrode active material precursor.

[0048] In the co-precipitation reaction process, the high-speed homogenizer is used to suck the reactants into the working chamber, and the strong centrifugal force of the homogenizer is used to throw the reactants into the reasonably narrow gap between the rotor and the stator from the radial direction, and the positive active material precursor particles produced at this time are fully dispersed and crushed by the comprehensive action of strong liquid phase shear, liquid layer friction and tear collision, and can be ejected at high speed through the stator groove, and then the flow direction is changed by the action of the resistance force between the reactants themselves and the container wall, and at the same time, the action of the suction force in the upper and lower axial directions generated in the rotor area forms two strong upper and lower reverse turbulent flows, which greatly enhances the material transfer process. Therefore, after multiple cycles, the positive active material precursor particles with regular shape, small particle size, narrow particle size distribution, single crystal phase, high purity, uniform element distribution, and high batch stability and consistency can be obtained, and the positive active material produced therefrom has good batch stability and consistency and excellent electrochemical performance.

[0049] In addition, in the solid-phase ball mill process for producing a subsequent positive electrode active material using the positive electrode active material precursor obtained by the manufacturing method according to the present application as a raw material, it is possible to easily realize uniform mixing of multiple elements, which can significantly reduce the energy consumption and time of the ball mill process.

[0050] The production method according to the present application also has the advantages of being a simple process, having high production efficiency, and being amenable to large-scale industrial production.

[0051] The production method of the present application uses water (which may be, for example, pure water, distilled water, deionized water, etc.) as a solvent, has high efficiency in precipitation conversion of metal ions, and does not require the addition of organic solvents (e.g., alcohols, esters, etc.). This reduces process costs and the burden of pollution treatment for production wastewater, realizes low-cost and environmentally friendly production, and has high industrial value.

[0052] In S2, the shear rate is 10000 r / min or more. In some embodiments, in S2, the shear rate may be 10000 r / min-28000 r / min, such as 10000 r / min, 11000 r / min, 12000 r / min, 13000 r / min, 14000 r / min, 15000 r / min, 16000 r / min, 17000 r / min, 18000 r / min, 19000 r / min, 20000 r / min, 21000 r / min, 22000 r / min, 23000 r / min, 24000 r / min, 25000 r / min, 26000 r / min, 27000 r / min, 28000 r / min, or any range of values ​​above.

[0053] Controlling the magnitude of the shear rate also contributes to obtaining a positive electrode active material precursor with different particle sizes, and therefore the production method according to the present application also contributes to accurately controlling the particle size of the positive electrode active material precursor.

[0054] In S2, the order of adding the aqueous precipitant solution and the aqueous metal salt solution is not particularly limited, and for example, both may be added to the reaction vessel at the same time, or the aqueous metal salt solution may be added first and then the aqueous precipitant solution may be added. Optionally, in S2, the aqueous precipitant solution is added to the aqueous metal salt solution at a shear rate of 10,000 r / min or more, and mixed, and then the coprecipitation reaction is carried out, whereby the initial concentration of the reaction system is instantly increased by the shearing action of the high-speed homogenizer, and the metal salt and the precipitant can be directly co-precipitated.

[0055] In some embodiments, in S2, the time for the co-precipitation reaction may be 10 min-60 min.

[0056] In some embodiments, in S2, the temperature of the co-precipitation reaction may be 20°C-80°C.

[0057] In some embodiments, in S1, the concentration of the metal salt aqueous solution may be 0.5 mol / L-2 mol / L.

[0058] In some embodiments, in S1, the metal salt aqueous solution is prepared by a method in which a metal salt is dissolved in water to form a metal salt aqueous solution under a protective gas atmosphere including nitrogen gas, an inert gas, or a combination thereof.

[0059] In some examples, the metal salt may be a water-soluble metal salt known in the art for preparing a positive electrode active material precursor, and may include, for example, one or more selected from a sulfate, a nitrate, a hydrochloride, and an acetate of a metal.

[0060] In some examples, the metal salt may be a divalent metal salt.

[0061] According to the manufacturing method of the present application, a precursor of a lithium iron manganese phosphate positive electrode active material, a precursor of a lithium nickel cobalt manganese oxide positive electrode active material, and a precursor of a lithium-rich manganese-based positive electrode active material can be manufactured.

[0062] In some embodiments, the metal salt may include one or more selected from divalent Mn, Fe, Ni, Co, Mg, Zn, Ca, Ti, V, and Cr salts.

[0063] In some embodiments, the metal salt may include at least a divalent Mn salt.

[0064] In some embodiments, the metal salt may include a divalent Mn salt, an Fe salt, and an optional salt of another metal M1, where M1 represents a doping element of the manganese site and the iron site, and optionally the salt of another metal M1 includes one or more selected from a divalent Ni salt, a Co salt, an Mg salt, a Zn salt, a Ca salt, a Ti salt, a V salt, and a Cr salt, thereby producing a precursor of a lithium iron manganese phosphate positive electrode active material.

[0065] In some embodiments, the metal salt may include a divalent Mn salt, Ni salt, Co salt, and optionally another metal M2 salt, where M2 represents a doping element of the manganese site, the nickel site, and the cobalt site. Optionally, the other metal M2 salt may include one or more selected from a divalent Fe salt, an Mg salt, a Zn salt, a Ca salt, a Ti salt, a V salt, and a Cr salt. This allows the preparation of a precursor of a lithium nickel-cobalt manganese oxide positive electrode active material.

[0066] In some embodiments, the metal salt may include a divalent Mn salt, a Ni salt, and an optional salt of another metal M3, where M3 represents a doping element of the manganese site and the nickel site. Optionally, the salt of another metal M3 may include one or more selected from a divalent Fe salt, a Co salt, a Mg salt, a Zn salt, a Ca salt, a Ti salt, a V salt, and a Cr salt. This allows the preparation of a precursor of a lithium-rich manganese-based positive electrode active material.

[0067] In some embodiments, the concentration of the precipitant solution may be 0.5 mol / L-2 mol / L.

[0068] The precipitating agent comprises one or more selected from oxalic acid and a water-soluble oxalate. Optionally, in some embodiments, the water-soluble oxalate comprises one or more selected from lithium oxalate, sodium oxalate, potassium oxalate, and ammonium oxalate.

[0069] In some embodiments, the molar ratio of the amount of the precipitant to the amount of the metal salt may be 1:1-3:1. Adjusting the amount of the precipitant can contribute to improving the conversion efficiency of metal ions, reducing the difference in the precipitation rate of different metal ions in the reaction system, thereby contributing to uniform co-precipitation of metal ions, and furthermore, accurately controlling the composition of the positive electrode active material precursor, so that the actual content of each metal ion in the obtained positive electrode active material precursor is a predetermined value. Adjusting the amount of the precipitant can also contribute to making the degree of the co-precipitation reaction more complete, greatly reducing the content of metal ions in the reaction waste liquid, reducing the difficulty of the treatment process of the post-treatment waste liquid, reducing environmental pollution, and also contributing to improving the purity of the obtained positive electrode active material precursor and reducing the content of impurities.

[0070] In some embodiments, the aqueous metal salt solution may further comprise a complexing agent.

[0071] When preparing a positive electrode active material precursor by coprecipitation, due to the difference in the solubility product constants of different metal ions, the precipitation rates of different metal ions are different, and the uniform coprecipitation of metal ions cannot be realized. At the same time, the ratio of each metal ion in the obtained positive electrode active material precursor particles and the ratio of each metal ion in the raw material are also greatly different, which affects the performance and consistency of the product. The complexing agent can complex metal ions, achieve the purpose of controlling free metal ions, improve the precipitation conversion efficiency of metal ions, reduce the difference in the precipitation rates of different metal ions in the reaction system, realize the uniform coprecipitation of metal ions, and achieve the accurate control of 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 a predetermined value. Therefore, the addition of the complexing agent to the metal salt aqueous solution contributes to improving the purity of the obtained positive electrode active material precursor and reducing the content of impurities, and also reduces the difference between the ratio of each metal ion in the obtained positive electrode active material precursor particles and the ratio of each metal ion in the raw material, so that the composition of the positive electrode active material precursor can be accurately controlled.

[0072] In some embodiments, the complexing agent may include one or more selected from aminocarboxylates, hydroxycarboxylates, and organic phosphonates. Optionally, the complexing agent includes one or more selected from ethylenediaminetetraacetate, gluconate, citrate, tartrate, metasilicate, tripolyphosphate, nitrilotriacetate, diethylenetriaminepentamethylenephosphonate, ethylenediaminetetrakismethylenephosphonate, and hydroxyethanediphosphonate. More preferably, the complexing agent includes one or more selected from sodium ethylenediaminetetraacetate, sodium gluconate, sodium citrate, sodium tartrate, sodium metasilicate, sodium tripolyphosphate, nitrilotriacetate, sodium diethylenetriaminepentamethylenephosphonate, sodium ethylenediaminetetrakismethylenephosphonate, and sodium hydroxyethanediphosphonate.

[0073] In some embodiments, the content of the complexing agent is ≦10 wt %, and optionally 1 wt %-10 wt %, based on the total weight of the aqueous metal salt solution.

[0074] In some embodiments, in S3, the washing method may include one or more of water washing and alcohol washing, and may optionally include water washing and alcohol washing simultaneously. In the present application, the number of times of water washing and alcohol washing is not particularly limited, and may be, for example, 2-6 times. Optionally, the alcohol washing is washing with ethanol.

[0075] The present application does not have any particular limitations on the drying method, which can be adjusted according to actual circumstances. In some embodiments, in S3, the drying process can be either a spray drying process or a vacuum drying process.

[0076] In some embodiments, in S3, the drying process can include drying the washed material in a vacuum oven and then transferring it to a tube furnace for continued drying to obtain an anhydrous cathode active material precursor, which contributes to accurately adjusting the ratio of each element in the subsequently produced cathode active material.

[0077] Optionally, the drying temperature in the vacuum oven is 60°C-100°C, and the drying time in the vacuum oven is 6-24 hours. Optionally, the drying temperature in the tubular oven is 200°C-300°C, and the drying time in the tubular oven is 2h-8h.

[0078] Optionally, the atmosphere in the tube furnace is a protective gas atmosphere, the protective gas comprising nitrogen gas, an inert gas, or a combination thereof. Optionally, the inert gas is helium gas, argon gas, or a combination thereof.

[0079] In the method for producing a positive electrode active material precursor provided by the present application, unless otherwise specified, all of the raw materials and equipment used can be directly purchased.

[0080] A second aspect of the present application provides a positive electrode active material precursor produced by the method according to the first aspect of the present application.

[0081] The molecular formula of the positive electrode active material precursor is 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-qIt may be C2O4, where 0 < x < 1, 0 < y < 1, 0 ≤ 1 - x - y < 1. M1 represents a doping element for manganese sites and iron sites, and optionally contains one or more selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr, where 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≤ 1 - a - b - c < 1. M2 represents a doping element for manganese sites, nickel sites, and cobalt sites, and optionally contains one or more selected from Fe, Mg, Zn, Ca, Ti, V, and Cr, where 0 < p < 1, 0 < q < 1, 0 ≤ 1 - p - q < 1. M3 represents a doping element for manganese sites and nickel sites, and optionally contains one or more selected from Fe, Co, Mg, Zn, Ca, Ti, V, and Cr.

[0082] The cathode 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. Therefore, it can improve the electrochemical performance of the cathode active material and the secondary battery.

[0083] In some embodiments, the volume particle size Dv50 of the cathode active material precursor satisfies 0.3 μm ≤ Dv50 ≤ 3 μm.

[0084] In some embodiments, the volume particle sizes Dv90 and Dv50 of the cathode active material precursor satisfy 1 < Dv90 / Dv50 ≤ 1.5.

[0085] A third aspect of the embodiment of the present application provides a method for manufacturing a cathode active material, including mixing a cathode active material precursor manufactured by the method described in the first aspect of the embodiment of the present application or the cathode active material precursor of the second aspect of the embodiment 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 a cathode active material.

[0086] In some embodiments, the molecular formula of the cathode active material precursor is Fe x Mn y M1 1-x-yIt is C2O4, where 0 < x < 1, 0 < y < 1, 0 ≤ 1 - x - y < 1. M1 represents the doping elements of the manganese site and the iron site, and optionally includes one or more selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr. The method for manufacturing the positive electrode active material is Fe x Mn y M1 1-x-y After mixing C2O4 with a lithium source, a phosphorus source, and an optional carbon source in a predetermined ratio, and then performing a sintering treatment to obtain a positive electrode active material, the molecular formula of the positive electrode active material is LiFe x Mn y M1 1-x-y It may be PO4.

[0087] 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 It is C2O4, where 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≤ 1 - a - b - c < 1. M2 represents the doping elements of the manganese site, nickel site, and cobalt site, and optionally includes one or more selected from Fe, Mg, Zn, Ca, Ti, V, and Cr. The method for manufacturing the positive electrode active material is Ni a Co b Mn c M2 1-a-b-c After mixing C2O4 with a lithium source in a predetermined ratio, and then performing a sintering treatment to obtain a positive electrode active material, which may include the step. The molecular formula of the positive electrode active material is LiNi a Co b Mn c M2 1-a-b-c It may be O2.

[0088] In some embodiments, the molecular formula of the positive electrode active material precursor is Ni p Mn q M3 1-p-qIt is C2O4, 0 < p < 1, 0 < q < 1, 0 ≤ 1 - p - q < 1, M3 represents the doping elements of manganese sites and nickel sites, and optionally may contain one or more selected from Fe, Co, Mg, Zn, Ca, Ti, V and Cr. The method for manufacturing the positive electrode active material is Ni p Mn q M3 1-p-q It may include the step of obtaining a positive electrode active material by mixing C2O4 and a lithium source in a predetermined ratio and then performing a sintering treatment. The molecular formula of the positive electrode active material may be mLi2MnO3?(1 - m)LiMO2, where 0 < m < 1, and M includes one or more selected from Mn, Ni, Fe, Co, Mg, Zn, Ca, Ti, V and Cr.

[0089] The lithium source may be a lithium-containing compound that can be used in the manufacture of positive electrode active materials known in the art. For example, the lithium source may include those selected from Li2CO3, LiOH or combinations thereof.

[0090] The phosphorus source may be a phosphorus-containing compound that can be used in the manufacture of lithium manganese iron phosphate positive electrode active materials known in the art. For example, the phosphorus source may include one or more of (NH4)2HPO4, NH4H2PO4, (NH4)3PO4 and H3PO4.

[0091] The carbon source includes one or more of an organic carbon source and an inorganic carbon source, and optionally may include one or more of glucose, sucrose, starch, fructose, polyvinyl alcohol, polyethylene glycol and citric acid.

[0092] The fourth aspect of the embodiments of the present application provides a positive electrode active material manufactured 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.

[0093] A fifth aspect of the present application provides a secondary battery comprising a positive electrode active material produced by the method according to the third aspect of the present application or the positive electrode active material according to the fourth aspect of the present application. Working Example

[0094] The following examples are provided to more specifically illustrate the disclosure of the present application, and are merely illustrative, since it will be apparent to those skilled in the art that various modifications and variations may be made within the scope of the disclosure of the present application. Unless otherwise specified, all parts, percentages and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or can be synthesized according to conventional methods and can be used directly without further treatment. In addition, any equipment used in the examples can be obtained commercially. Example 1 S1. Preparation of metal salt and precipitant solutions

[0095] Under the protection of nitrogen gas, ferrous sulfate and manganese sulfate were mixed in a reaction vessel with a molar ratio of Fe:Mn of 4:6 and pure water to prepare a metal salt aqueous solution with a concentration of 0.5 mol / L, and 5 wt% sodium ethylenediaminetetraacetate was added as a complexing agent. The precipitant aqueous solution was prepared with oxalic acid and pure water to a concentration of 0.75 mol / L for use. S2. Coprecipitation reaction

[0096] After manually adjusting the rotation speed of the high-speed homogenizer to 12000 r / min, the precipitant solution was quickly added to the reaction vessel under the high-speed dispersion and shearing action of the high-speed homogenizer, and the suspension was obtained by shearing reaction for 30 minutes. The reaction temperature was room temperature (25°C), and the molar ratio of the metal salt to oxalic acid was 1:1.5. S3.Drying

[0097] The obtained suspension was washed multiple times with deionized water and ethanol, then centrifuged to collect the solid components. The collected solid components were then placed in a vacuum oven at 80 °C to dry, and the dried sample was placed in a tube furnace and heated at 200 °C for 2 hours in an argon gas atmosphere to remove the water of crystallization and obtain an anhydrous Mn 0.6 Fe 0.4 The C2O4 precursor was obtained. Example 2 S1. Preparation of metal salt and precipitant solutions

[0098] Under the protection of nitrogen gas, ferrous sulfate and manganese sulfate were mixed in a reaction vessel with a molar ratio of Fe:Mn of 4:6 and pure water to prepare a metal salt aqueous solution with a concentration of 0.5 mol / L, and 3 wt% sodium citrate was added as a complexing agent. The precipitant aqueous solution was prepared with oxalic acid and pure water to a concentration of 1.5 mol / L, and was prepared for use. S2. Coprecipitation reaction

[0099] After manually adjusting the rotation speed of the high-speed homogenizer to 28,000 r / min, the precipitant solution was quickly added to the reaction vessel under the high-speed dispersion and shearing action of the high-speed homogenizer, and the suspension was obtained by shearing reaction for 10 minutes. The reaction temperature was room temperature (25°C), and the molar ratio of the metal salt to oxalic acid was 1:3. S3.Drying

[0100] The obtained suspension was washed several times with deionized water and ethanol, and then centrifuged to collect the solid components. 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 in an argon gas atmosphere to remove the water of crystallization and obtain an anhydrous Mn 0.6 Fe 0.4 The C2O4 precursor was obtained. Example 3 S1. Preparation of metal salt and precipitant solutions

[0101] Under the protection of nitrogen gas, ferrous sulfate and manganese sulfate were mixed in a reaction vessel with a molar ratio of Fe:Mn of 3:7 and pure water to prepare a metal salt aqueous solution with a concentration of 0.5 mol / L, and 10 wt% of sodium diethylenetriaminepentamethylenephosphonate was added as a complexing agent. The precipitant sodium oxalate and pure water were mixed to prepare a precipitant aqueous solution with a concentration of 0.5 mol / L for use. S2. Coprecipitation reaction

[0102] After manually adjusting the rotation speed of the high-speed homogenizer to 10,000 r / min, the precipitant aqueous solution was quickly added to the reaction vessel under the high-speed dispersion and shearing action of the high-speed homogenizer, and the suspension was obtained by shearing reaction for 40 minutes. The reaction temperature was room temperature (25°C), and the molar ratio of the metal salt to sodium oxalate used was 1:1. S3.Drying

[0103] The obtained suspension was washed multiple times with deionized water and ethanol, then centrifuged to collect the solid components. The collected solid components were then placed in a vacuum oven at 80 °C to dry, and the dried sample was placed in a tube furnace and heated at 200 °C for 2 hours in an argon gas atmosphere to remove the water of crystallization and obtain an anhydrous Mn 0.7 Fe 0.3 The C2O4 precursor was obtained. Example 4 S1. Preparation of metal salt and precipitant solutions

[0104] Under the protection of nitrogen gas, nickel sulfate and manganese sulfate were mixed in a reaction vessel with a molar ratio of Ni:Mn of 3:7 and pure water to prepare a metal salt solution with a concentration of 0.5 mol / L, and 5 wt% of sodium ethylenediaminetetrakismethylenephosphonate was added as a complexing agent. The precipitant, oxalic acid, and pure water were mixed to prepare a precipitant solution with a concentration of 1 mol / L for use. S2. Coprecipitation reaction

[0105] After manually adjusting the rotation speed of the high-speed homogenizer to 15,000 r / min, the precipitant solution was quickly added to the reaction vessel under the high-speed dispersion and shearing action of the high-speed homogenizer, and the suspension was obtained by shearing reaction for 30 minutes. The reaction temperature was room temperature (25°C), and the molar ratio of the metal salt to oxalic acid was 1:2. S3.Drying

[0106] The obtained suspension was washed multiple times with deionized water and ethanol, then centrifuged to collect the solid components. The collected solid components were then placed in a vacuum oven at 80 °C to dry, and the dried sample was placed in a tube furnace and heated at 200 °C for 2 hours in an argon gas atmosphere to remove the water of crystallization and obtain an anhydrous Mn 0.7 Ni 0.3 The C2O4 precursor was obtained. Example 5 S1. Preparation of metal salt and precipitant solutions

[0107] Under the protection of nitrogen gas, nickel sulfate, cobalt sulfate, and manganese sulfate were prepared in a reaction vessel with a molar ratio of Ni:Co:Mn of 1:1:1 and pure water to prepare a metal salt aqueous solution with a concentration of 0.5 mol / L, and 5 wt% sodium gluconate was added as a complexing agent. The precipitant, ammonium oxalate, and pure water were used to prepare a precipitant aqueous solution with a concentration of 0.5 mol / L for use. S2. Coprecipitation reaction

[0108] After manually adjusting the rotation speed of the high-speed homogenizer to 20,000 r / min, the precipitant aqueous solution was quickly added to the reaction vessel under the high-speed dispersion and shearing action of the high-speed homogenizer, and the suspension was obtained by shearing reaction for 20 minutes. The reaction temperature was room temperature (25°C), and the molar ratio of the metal salt to ammonium oxalate was 1:1. S3.Drying

[0109] The obtained suspension was washed multiple times with deionized water and ethanol, then centrifuged to collect the solid components, which 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 in an argon gas atmosphere to remove the water of crystallization and produce anhydrous Ni0.33 Co 0.33 Mn 0.33 The C2O4 precursor was obtained. Comparative Example 1 S1. Preparation of metal salt and precipitant solutions

[0110] Under the protection of nitrogen gas, ferrous sulfate and manganese sulfate were mixed in a reaction vessel with a molar ratio of Fe:Mn of 4:6 and pure water to prepare a metal salt aqueous solution with a concentration of 0.5 mol / L, and 3 wt% sodium citrate was added as a complexing agent. The precipitant aqueous solution was prepared with oxalic acid and pure water to a concentration of 1.5 mol / L, and was prepared for use. S2. Coprecipitation reaction

[0111] The precipitant solution was added to the reaction vessel under the stirring action of a magnetic stirrer and stirred for 60 minutes to obtain a suspension. The reaction temperature was room temperature (25°C), the stirring speed was 800 r / min, and the molar ratio of the metal salt to oxalic acid was 1:3. S3.Drying

[0112] The obtained suspension was washed multiple times with deionized water and ethanol, then centrifuged to collect the solid components. The collected solid components were then placed in a vacuum oven at 80 °C to dry, and the dried sample was placed in a tube furnace and heated at 200 °C for 2 hours in an argon gas atmosphere to remove the water of crystallization and obtain an anhydrous Mn 0.6 Fe 0.4 The C2O4 precursor was obtained. Comparative Example 2 S1. Preparation of metal salt and precipitant solutions

[0113] Under the protection of nitrogen gas, ferrous sulfate and manganese sulfate were mixed in a reaction vessel with a molar ratio of Fe:Mn of 3:7 and purified water to prepare a metal salt aqueous solution with a concentration of 0.5 mol / L. The precipitant, sodium oxalate, and purified water were mixed to prepare a precipitant aqueous solution with a concentration of 0.5 mol / L for use. S2. Coprecipitation reaction

[0114] The precipitant solution was added to the reaction vessel under the stirring action of a magnetic stirrer and stirred for 60 minutes to obtain a suspension. The reaction temperature was room temperature (25°C), the stirring speed was 500 r / min, and the molar ratio of the metal salt to sodium oxalate was 1:1. S3.Drying

[0115] The obtained suspension was washed multiple times with deionized water and ethanol, then centrifuged to collect the solid components. The collected solid components were then placed in a vacuum oven at 80 °C to dry, and the dried sample was placed in a tube furnace and heated at 200 °C for 2 hours in an argon gas atmosphere to remove the water of crystallization and obtain an anhydrous Mn 0.7 Fe 0.3 The C2O4 precursor was obtained. Testing Part (1) Particle size test

[0116] The volumetric particle size of the prepared oxalate precursor was measured using a Malvern Master Size 3000 laser particle size analyzer. Dv50 and Dv90 are the particle sizes corresponding to the cumulative volume distribution percentage of the material reaching 50% and 90%. GB / T 19077-2016 can be referred to as the test standard.

[0117] The test results are shown in Table 1. (2) Metal element content test

[0118] Using a Plasma 3000 inductively coupled plasma optical emission spectrometer, the content of each metal element in the oxalate precursor prepared above was measured by ICP-OES, and the molar ratio was calculated.

[0119] The test results are shown in Table 2. (3) First cycle performance test of coin cells

[0120] The above prepared oxalate precursor (100mmol), Li2CO3 (50mmol), NH4H2PO4 (100mmol), and sucrose (15mmol) are placed in a ball mill tank, a small amount of ethanol and water are added as solvents, and ball milled at a rotation speed of 500r / min for 8 hours to obtain a slurry. The obtained slurry is transferred to a spray drying device and spray-dried and granulated to obtain a powder, and the drying temperature is set to 210°C. The obtained powder is placed in a muffle furnace and sintered at 400°C in an air atmosphere for 5 hours, and then naturally cooled to room temperature to obtain a pre-sintered material. The obtained pre-sintered material is placed in a ball mill tank, a small amount of ethanol and water are added as solvents, and ball milled at a rotation speed of 800r / min for 4 hours to obtain a slurry. The obtained slurry was transferred to a spray drying apparatus and spray-dried and granulated to obtain a powder of pre-sintered material. The drying temperature was set to 210°C, and the obtained pre-sintered material powder was placed in a muffle furnace and sintered at 700°C in a nitrogen gas atmosphere for 10 hours, naturally cooled to room temperature, and air-flow pulverized to obtain a lithium manganese iron phosphate positive electrode active material.

[0121] The above-prepared lithium manganese iron phosphate positive electrode active material, polyvinylidene fluoride (PVDF) as a binder, and acetylene black as a conductive agent were added to N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5, and the mixture was stirred in a drying chamber to prepare a slurry. The above slurry was applied to an aluminum foil, dried, and cold pressed to form a positive electrode sheet.

[0122] A lithium sheet was used as the negative electrode and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) with a volume ratio of 1:1:1 was used as the electrolyte, and assembled into a coin cell in a coin cell box together with the above prepared positive electrode sheet.

[0123] In a constant temperature environment of 25°C, the coin cell was charged to 4.3V at a constant current of 0.1C, then charged at a constant voltage of 4.3V until the current became 0.05mA or less. The charge capacity at this time was the initial charge capacity and was designated as C0. The coin cell was then left to stand for 2 minutes, after which it was discharged at a constant current of 0.1C to 2.0V. The discharge capacity at this time was the initial discharge capacity and was designated as D0.

[0124] Initial Coulombic Efficiency (%) of the coin cell = (D0 / C0) x 100%. Initial gram capacity (initial capacity per gram) of the coin cell (mAh / g) = D0 / m, where m represents the mass of the lithium manganese iron phosphate positive electrode active material.

[0125] The test results are shown in Table 3 and Figure 3.

[0126] [Table 1]

[0127] [Table 2]

[0128] [Table 3]

[0129] Fig. 1 is a scanning electron microscope (SEM) image of the positive electrode active material precursor prepared in Example 3, where Fig. 1(a) is a magnification of 1000 times and Fig. 1(b) is a magnification of 5000 times. Fig. 2 is a scanning electron microscope (SEM) image of the positive electrode active material precursor prepared in Comparative Example 2, where Fig. 2(a) is a magnification of 2000 times and Fig. 2(b) is a magnification of 5000 times.

[0130] Taking the measurement results in Tables 1 and 2 together with Figures 1 and 2, it can be seen that the positive electrode active material precursor produced by the production method according to the present application is characterized by regular morphology, small particle size, narrow particle size distribution, and uniform element distribution. Also, taking the test results in Examples 1-5 together, it can be seen that the higher the rotation speed (i.e., shear rate) of the high-speed homogenizer, the smaller the particle size and narrower the particle size distribution of the positive electrode active material precursor obtained.

[0131] In addition, taking the test results of Example 3 and Comparative Example 2 together, 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 accurately controlled, and the actual content of each metal ion in the obtained positive electrode active material precursor can reach a predetermined value.

[0132] Furthermore, taking the test results of Example 1, Example 2, and Comparative Example 1 together, it is also evident that, when a complexing agent is added to the metal salt aqueous solution, the production method according to the present application makes it possible to accurately control the composition of the positive electrode active material precursor, and also makes it possible to bring the actual content of each metal ion in the obtained positive electrode active material precursor closer to a predetermined value.

[0133] 3 is a graph showing the initial charge / discharge curves of the coin cells prepared in Example 1, Example 2, and Comparative Example 1. As can be seen from the test results in Table 3 and FIG. 3, the lithium manganese iron phosphate positive electrode active material prepared using the positive electrode active material precursor prepared in the present application as a raw material has a higher gram capacity and initial coulombic efficiency, which can better improve the electrochemical performance of the secondary battery.

[0134] The present application is not limited to the above-mentioned embodiment. The above-mentioned embodiment is merely illustrative, and any embodiment having substantially the same configuration as the technical idea within the technical scope of the present application and having similar effects is included within the technical scope of the present application. In addition, within the scope of the present application, various modifications conceived by a person skilled in the art and other forms constructed by combining some of the components in the embodiment are also included within the scope of the present application.

Claims

1. Step S1 of preparing an aqueous solution of a metal salt and an aqueous solution of a precipitant, the precipitant including one or more selected from oxalic acid and a water-soluble oxalate; Step S2 of mixing the precipitant aqueous solution and the metal salt aqueous solution at a shear rate of 10,000 r / min or more and then carrying out a coprecipitation reaction; Step S3 of obtaining the positive electrode active material precursor by washing and drying after the reaction is completed; A method for producing a positive electrode active material precursor comprising the steps of:

2. The method of claim 1 , wherein in S2, the co-precipitation reaction is carried out in a high speed homogenizer.

3. In S2, the shear rate is 10000 r / min-28000 r / min, and / or In S2, the time of the coprecipitation reaction is 10 min-60 min, and / or In S2, the temperature of the coprecipitation reaction is 20° C.-80° C.; The method according to claim 1 or 2.

4. The method according to any one of claims 1 to 3, wherein in S2, the molar ratio of the amount of the precipitating agent to the amount of the metal salt used is 1:1-3:

1.

5. In S1, the concentration of the metal salt aqueous solution is 0.5 mol / L-2 mol / L, and / or In S1, the concentration of the precipitant aqueous solution is 0.5 mol / L-2 mol / L; The method according to any one of claims 1 to 4.

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

7. In S1, the metal salt includes one or more selected from a sulfate, a nitrate, a hydrochloride, and an acetate of a metal, and / or The method according to any one of claims 1 to 6, wherein in step S1, the water-soluble oxalate comprises one or more selected from the group consisting of lithium oxalate, sodium oxalate, potassium oxalate, and ammonium oxalate.

8. The method according to any one of claims 1 to 7, wherein in S1, the metal salt is a divalent metal salt.

9. 9. The method of any one of claims 1 to 8, wherein the metal salt comprises one or more selected from divalent Mn, Fe, Ni, Co, Mg, Zn, Ca, Ti, V and Cr salts.

10. The method of any one of claims 1 to 9, wherein the metal salt comprises at least a divalent Mn salt.

11. The metal salts include divalent Mn salts, Fe salts, and optionally salts of other metals M1, where M1 represents a doping element of the manganese site and the iron site, and optionally the salts of other metals M1 include one or more selected from divalent Ni salts, Co salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts; Alternatively, the metal salts include divalent Mn salts, Ni salts, Co salts, and optionally salts of other metals M2, where M2 represents a doping element at the manganese site, the nickel site, and the cobalt site, and optionally the salts of other metals M2 include one or more selected from divalent Fe salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts; Or, the metal salts include divalent Mn salts, Ni salts, and optionally salts of other metals M3, where M3 represents a doping element for the manganese site and the nickel site, and optionally the salts of other metals M3 include one or more selected from divalent Fe salts, Co salts, Mg salts, Zn salts, Ca salts, Ti salts, V salts, and Cr salts; The method according to any one of claims 1 to 10.

12. The aqueous metal salt solution further comprises a complexing agent, and optionally the complexing agent comprises one or more selected from an aminocarboxylate, a hydroxycarboxylate, and an organic phosphonate; The method according to any one of claims 1 to 11.

13. The complexing agent comprises one or more selected from ethylenediaminetetraacetate, gluconate, citrate, tartrate, metasilicate, tripolyphosphate, nitrilotriacetate, diethylenetriaminepentamethylenephosphonate, ethylenediaminetetrakismethylenephosphonate and hydroxyethanediphosphonate; and / or The content of the complexing agent is 10 wt % or less based on the total mass of the metal salt aqueous solution. The method of claim 12.

14. A positive electrode active material precursor produced by the method according to any one of claims 1 to 13, Molecular formula is Fe ｘ Mn ｙ M1 １－ｘ－ｙ C ２ O ４ , Ni ａ Co ｂ Mn ｃ M2 １－ａ－ｂ－ｃ C ２ O ４ Or Ni ｐ Mn ｑ M3 １－ｐ－ｑ C ２ O ４ wherein 0<x<1, 0<y<1, 0≦1-x-y<1, M1 represents a doping element at the manganese site and the iron site, and optionally includes one or more selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr, and 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, and optionally includes one or more selected from Fe, Mg, Zn, Ca, Ti, V, and Cr, and 0<p<1, 0<q<1, 0≦1-p-q<1, M3 represents a doping element at the manganese site and the nickel site, and optionally includes one or more selected from Fe, Co, Mg, Zn, Ca, Ti, V, and Cr, Positive electrode active material precursor.

15. The volume particle size Dv50 of the positive electrode active material precursor satisfies 0.3 μm≦Dv50≦3 μm, and / or The positive electrode active material precursor according to claim 14 , wherein the volume particle diameters Dv90 and Dv50 of the positive electrode active material precursor satisfy 1 < Dv90 / Dv50 ≦ 1.

5.

16. A method for producing a positive electrode active material, comprising a step of mixing a positive electrode active material precursor produced by the method according to any one of claims 1 to 13 or the positive electrode active material precursor according to claim 14 or 15 with a lithium source and / or a phosphorus source in a predetermined ratio, and then sintering the mixture to obtain a positive electrode active material.

17. A positive electrode active material produced by the method of claim 16.

18. A secondary battery comprising a positive electrode active material produced by the production method according to claim 16 or the positive electrode active material according to claim 17.

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