Manganese iron oxide, method for preparing the same, and use thereof

Abstract

The application provides a manganese iron oxide and a preparation method and application thereof, and belongs to the technical field of secondary batteries. The molecular formula of the manganese iron oxide is Mn x Fe y A a B b O3, wherein A is a tetravalent metal, B is a divalent metal, 0.19<=x<=1.8, 0.19<=y<=1.8, 0<=a<=0.1, 0<=b<=0.1, 1.9<=x+y+3 / 2a+3b<=2.1, and the primary particles of the manganese iron oxide are in a sheet shape. The manganese iron oxide provided by the application is in a sheet structure, can provide more active sites to support efficient electrochemical reactions, and thus improves the electrochemical performance of a positive electrode material prepared by taking the manganese iron oxide as a precursor. The preparation method of the manganese iron oxide avoids the use of a complexing agent by precipitating and dissolving part of ferrous hydroxide under an overalkaline condition, so as to achieve a coprecipitation effect.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, and in particular relates to a manganese iron oxide, its preparation method and application. Background Technology

[0002] Lithium iron phosphate (LFP) batteries hold a significant position in the electric vehicle market due to their inherent safety, economic efficiency, and long cycle life, particularly in their application as batteries in new energy vehicles. However, as improvements to LFP technology approach their theoretical limits, these batteries struggle to meet the demands of extended driving ranges in electric vehicles in terms of energy density. To overcome this challenge, researchers have turned their attention to lithium manganese iron phosphate (LMFP). This material, by introducing manganese, not only improves the battery's voltage platform but also increases its energy density by approximately 10% to 20% compared to traditional LFP batteries. This means that, under the same volume conditions, batteries using LMFP can provide a longer driving range, thus offering a significant performance improvement for new energy vehicles.

[0003] Currently, the mainstream preparation processes for lithium manganese iron phosphate precursors include: ① solid-state method, ② high-temperature pyrolysis method, and ③ co-precipitation method. The solid-state method involves repeatedly grinding and mixing manganese and iron sources to obtain the lithium manganese iron phosphate precursor, manganese iron oxide, through calcination. However, since the solid-state method relies on chemical reactions between solids, improving the mixing uniformity of the raw materials is crucial to achieving the ideal reaction effect. The degree of mixing of manganese and iron elements depends entirely on the degree of grinding and mixing, thus requiring multiple and prolonged grinding and pulverization of the raw materials, resulting in long processing times, high energy consumption, and high manufacturing costs. The high-temperature pyrolysis method involves atomizing soluble manganese iron solution using ultrasonic spraying, followed by instantaneous pyrolysis at high temperatures to form manganese iron oxide. However, limited by the solubility of manganese iron salts, a large amount of water needs to be evaporated during pyrolysis, leading to excessively high energy consumption and costs, making industrialization difficult. The co-precipitation method involves adding a precipitant to a manganese iron solution for co-precipitation, followed by washing, drying, and calcination to obtain manganese iron oxide. However, due to the large difference in solubility products between ferrous hydroxide and manganese hydroxide, it is difficult to achieve a good co-precipitation effect. Existing technologies generally use complexing agents to complex the ferric ions of manganese hydroxide, thereby compensating for the difference in solubility products and achieving co-precipitation. However, complexing agents are organic substances, making the wastewater difficult to treat and hindering industrialization.

[0004] Therefore, it is necessary to propose a new manganese iron oxide and its preparation method to solve the technical problem that the existing co-precipitation method for producing manganese iron oxide requires the addition of a complexing agent to complex manganese iron ions, but the complexing agent is an organic substance, making the production wastewater difficult to treat and hindering industrialization. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a manganese iron oxide, its preparation method and application, aiming to solve the technical problem that the existing co-precipitation method for producing manganese iron oxide requires the addition of a complexing agent, but the complexing agent is an organic matter, the production wastewater is difficult to treat, and it is not conducive to industrialization.

[0006] In a first aspect, embodiments of this application provide a manganese iron oxide with the molecular formula Mn. x Fe y A a B b O3, where A is a tetravalent metal, B is a divalent metal, 0.19≤x≤1.8, 0.19≤y≤1.8, 0≤a≤0.1, 0≤b≤0.1, 1.9≤x+y+3 / 2a+3b≤2.1, and the primary particles of manganese iron oxide are in the form of flakes.

[0007] In the technical solution of this application embodiment, the primary particles of manganese iron oxide have a plate-like structure, which can provide more active sites to support efficient electrochemical reactions, thereby improving the electrochemical performance of the cathode material made with the above-mentioned manganese iron oxide as a precursor.

[0008] In some embodiments, the secondary particles of manganese iron oxide have a D50 particle size of 1.5~3.5 μm and a BET specific surface area of ​​12~20 m². 2 / g.

[0009] In this embodiment, when the D50 particle size of the manganese iron oxide meets the above-mentioned range, the particles are relatively small, avoiding adverse effects on the processing performance of lithium iron phosphate. If the D50 particle size of the manganese iron oxide is too large, it will lead to an increase in subsequent milling time. When the BET specific surface area of ​​the manganese iron oxide meets the above-mentioned range, sufficient active sites can be ensured to support efficient electrochemical reactions. If the specific surface area is too small, the particle size will be too large, thereby affecting the insertion and extraction of lithium ions; if the specific surface area is too large, there will be too many gaps between particles, thereby hindering the improvement of compaction density.

[0010] Secondly, embodiments of this application provide a method for preparing manganese iron oxide, comprising the following steps: Prepare a mixed metal salt solution, a precipitant solution, and a reaction base solution. The mixed metal salt solution contains manganese and iron elements, and the reaction base solution is an alkaline solution containing hydroxides. A co-precipitation reaction is carried out on a mixed metal salt solution, a precipitant solution, and a reaction substrate to obtain a reaction slurry; The reaction slurry was aged, filtered, rinsed, and oxidized and dehydrated to obtain basic manganese iron oxide; Basic ferromanganese oxide is calcined to obtain ferromanganese oxide; Among them, the molecular formula of manganese iron oxide is Mnx Fe y A a B b O3, where A is a tetravalent metal and B is a divalent metal, 0.19≤x≤1.8, 0.19≤y≤1.8, 0≤a≤0.1, 0≤b≤0.1, 1.9≤x+y+3 / 2a+3b≤2.1, and the primary particles of manganese iron oxide are in the form of flakes.

[0011] In the technical solution of this application embodiment, during the co-precipitation reaction of the metal mixed salt solution, precipitant solution, and reaction substrate, the amphoteric properties of iron are utilized to dissolve some ferrous hydroxide precipitate under superalkaline conditions, thereby increasing the solubility product of ferrous hydroxide. This compensates for the difference in solubility products between ferrous hydroxide and manganese hydroxide, achieving a co-precipitation effect and obtaining amorphous ferromanganese hydroxide. Subsequently, aging transforms the amorphous ferromanganese hydroxide into crystalline ferromanganese hydroxide, resulting in a reaction slurry containing crystalline ferromanganese hydroxide. The crystalline ferromanganese hydroxide is then converted into basic ferromanganese oxide through oxidation and dehydration, and the basic ferromanganese oxide is further converted into ferromanganese oxide through calcination. Compared with existing processes, the method of this application does not require the addition of a complexing agent, the treatment of production wastewater is relatively simple, it is conducive to industrialization, and it can also significantly reduce energy consumption. The above preparation process is beneficial for obtaining the ferromanganese oxide with the special morphology provided in this application, thereby improving the electrochemical performance of lithium manganese iron phosphate cathode materials prepared using the above-mentioned ferromanganese oxide as a precursor.

[0012] In some embodiments, the metal mixed salt solution includes soluble manganese salt and soluble ferrous salt; the total metal ion concentration of the metal mixed salt solution is 0.5~1.2 mol / L; the precipitant solution is sodium hydroxide solution and / or potassium hydroxide solution, and the concentration of the precipitant solution is 1~5 mol / L; the reaction base solution is sodium hydroxide solution and / or potassium hydroxide solution, and the concentration of the reaction base solution is 0.09~0.39 mol / L; the volume ratio of the metal mixed salt solution, the precipitant solution and the reaction base solution is 1:(0.5~3.1):(0.6~1.3).

[0013] In this embodiment, when the concentration of total metal ions in the mixed metal salt solution meets the above-mentioned range, high yield can be achieved while avoiding metal ion crystallization. If the total metal ion concentration is too low, the product yield will be too low for the same volume, easily leading to increased manufacturing costs; if the total metal ion concentration is too high, the mixed metal salt solution will be difficult to preserve and crystallization will easily occur. When the concentration of the precipitant solution meets the above-mentioned range, basic manganese ferrooxide with uniform particle size can be obtained and excessive wastewater treatment costs can be avoided. If the concentration of the precipitant solution is too low, wastewater treatment costs will increase and equipment utilization will decrease; if the concentration of the precipitant solution is too high, local overconcentration will occur, crystal nucleation rate will be too fast, and the generated crystal particles will be uneven in size. When the concentration of the reaction base liquid meets the above-mentioned range, co-precipitation of manganese ferro ions can be achieved and the yield of the target product can be improved. If the concentration of the reaction base liquid is too low, manganese ions cannot be completely precipitated, and the product yield will be low; if the concentration of the reaction base liquid is too high, Fe(OH)2 will redissolve at high pH values, resulting in excessive ferrous ions in the solution, while manganese ions will be completely precipitated, failing to achieve the co-precipitation effect. When the volume ratio of the mixed metal salt solution, the precipitant solution, and the reaction substrate meets the above range, the hydroxide concentration in the mixed solution will be consistent with the hydroxide concentration in the reaction substrate after the co-precipitation reaction is completed.

[0014] In some embodiments, the metal mixed salt solution further includes a doped metal source; the doped metal source includes at least one of soluble titanium salt and soluble magnesium salt; the molar ratio of the doped metal ions in the doped metal source to the total molar amount of metal ions in the metal mixed salt solution is (0.001~0.02):1.

[0015] In this embodiment, by doping manganese iron oxide with magnesium and titanium, the Jan Taylor effect can be suppressed, thereby further improving the product's capacity and cycle performance, and ultimately enhancing the battery's electrical performance. When the molar ratio of the doped metal ions in the metal source to the total molar amount of metal ions in the mixed metal salt solution meets the above-mentioned range, the crystal structure of manganese iron oxide can be stabilized, improving the effective capacity and charge / discharge capacity of lithium manganese iron phosphate cathode materials prepared using it as a precursor. If the proportion of doped metal ions in the metal source is too low, the product performance improvement will be insufficient. If the proportion of doped metal ions in the metal source is too high, the crystal structure distortion will be too large, which will reduce its effective capacity and charge / discharge capacity.

[0016] In some embodiments, the temperature of the coprecipitation reaction is 20~25℃, the time of the coprecipitation reaction is 100~150 min, and the atmosphere of the coprecipitation reaction is a protective atmosphere; the temperature of aging is 70~90℃, the time of aging is 1~3 h, and the atmosphere of aging is a protective atmosphere; the temperature of oxidation and dehydration is 70~80℃, the time of oxidation and dehydration is 8~12 h, and the atmosphere of oxidation and dehydration is air or oxygen.

[0017] In this embodiment, when the temperature of the co-precipitation reaction meets the above-mentioned range, the nucleation rate is slow, which helps to control crystal nucleation and growth, resulting in more uniform particle size. If the temperature of the co-precipitation reaction is too high, the nucleation rate will be too fast, and crystal growth and nucleation will occur simultaneously, resulting in uneven particle size. When the aging temperature meets the above-mentioned range, the crystal form of the slurry can be transformed. If the aging temperature is too low, a longer processing time is required, resulting in low production efficiency; if the aging temperature is too high, the crystal nucleation rate will be accelerated, which may cause inconsistencies in the morphology of the final product, thereby affecting the stability of the product. At the same time, since divalent manganese ions are easily oxidized under alkaline conditions, this application uses a protective atmosphere to avoid the problem of some divalent manganese combining with trivalent iron to form manganese ferrite as a byproduct instead of ferrous manganese hydroxide during the co-precipitation and aging reactions, thus reducing the purity of the product. When the temperature of oxidation and dehydration meets the above-mentioned range, crystalline ferrous manganese hydroxide can be converted into basic ferric manganese oxide. If the oxidation and dehydration temperature is too low, a longer processing time is required, resulting in low production efficiency; if the oxidation and dehydration temperature is too high, the external bound water will be lost prematurely, causing surface hardening and leading to an increase in product particle size.

[0018] In some embodiments, the calcination temperature is 600~700℃, the calcination time is 1~3h, the heating rate is 1~10℃ / min, and the calcination atmosphere is air.

[0019] In this embodiment, when the calcination temperature meets the above-mentioned range, basic manganese oxide can be converted into iron manganese oxide. If the calcination temperature is too low, a longer processing time is required, resulting in low production efficiency; if the calcination temperature is too high, some MnFeO3 in the phase will be converted into MnFe2O4, thereby reducing the purity of the product.

[0020] Thirdly, embodiments of this application provide a lithium manganese iron phosphate cathode material, which is prepared using manganese iron oxide as provided in the first aspect of this application as a precursor, or using manganese iron oxide prepared by the method for preparing manganese iron oxide provided in the second aspect of this application as a precursor.

[0021] In the technical solution of this application embodiment, the lithium manganese iron phosphate cathode material is prepared by using the above-mentioned manganese iron oxide as a precursor, and thus has good charge and discharge specific capacity, rate performance, energy density and cycle life.

[0022] Fourthly, embodiments of this application provide a positive electrode sheet, which includes the lithium manganese iron phosphate positive electrode material provided in the third aspect of this application.

[0023] In the technical solution of this application embodiment, the positive electrode sheet contains the above-mentioned lithium manganese iron phosphate positive electrode material, thus having good charge / discharge specific capacity, rate performance, energy density and cycle life.

[0024] Fifthly, embodiments of this application provide a secondary battery, which includes the positive electrode provided in the fourth aspect of this application.

[0025] In the technical solution of this application embodiment, the secondary battery includes the above-mentioned positive electrode sheet, and thus has good charge / discharge specific capacity, rate performance, energy density and cycle life.

[0026] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0028] Figure 1 This is a SEM image of magnesium-titanium-doped basic manganese iron oxide provided in Example 1 of this application; Figure 2 This is a SEM image of the doped magnesium-titanium-manganese-iron oxide provided in Example 1 of this application; Figure 3 This is a SEM image of magnesium-titanium-doped basic manganese iron oxide provided in Comparative Example 3 of this application; Figure 4 This is the XRD pattern of magnesium-titanium-doped basic manganese iron oxide provided in Example 1 of this application; Figure 5 This is the XRD pattern of the doped magnesium-titanium-manganese-iron oxide provided in Example 1 of this application; Figure 6 This is the XRD pattern of magnesium-titanium-doped basic manganese iron oxide provided in Comparative Example 1 of this application; Figure 7 This is the XRD pattern of the doped magnesium-titanium-manganese-iron oxide provided in Comparative Example 1 of this application; Figure 8 The 0.1C charge-discharge specific capacity test curve of a lithium manganese iron phosphate battery made using magnesium-titanium-manganese iron oxide as a precursor, as provided in Example 1 of this application. Detailed Implementation

[0029] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0031] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0034] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0035] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0036] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0037] the term Primary particle size: also known as original particle size, refers to the particle size of a single particle, reflecting the intrinsic size of particles when they do not interact in the early stages of formation.

[0038] Secondary particle size refers to the particle size of aggregates formed by the interaction between particles through agglomeration, coagulation, etc.

[0039] Coprecipitation is one of the mainstream processes for preparing lithium manganese iron phosphate precursors. The steps include adding a precipitant to a ferromanganese solution to induce a coprecipitation reaction, followed by washing, drying, and calcination to obtain ferromanganese oxide. However, due to the significant difference in solubility products between ferrous hydroxide and manganese hydroxide, achieving ideal coprecipitation results is difficult. Existing technologies generally use complexing agents to complex ferromanganese ions, compensating for the solubility product difference and achieving coprecipitation. However, complexing agents are often organic compounds, leading to difficult-to-treat wastewater and hindering industrialization.

[0040] To address the problem that existing co-precipitation methods for producing manganese iron oxide require the addition of complexing agents, which are organic compounds, leading to difficult-to-treat wastewater and hindering industrialization, this application provides a manganese iron oxide, its preparation method, and its applications. The manganese iron oxide provided in this application has a plate-like structure, offering more active sites to support efficient electrochemical reactions. The preparation method of the manganese iron oxide provided in this application achieves co-precipitation by dissolving part of the ferrous hydroxide precipitate under hyperalkaline conditions, thus avoiding the use of complexing agents. The electrochemical performance of cathode materials and secondary batteries containing lithium manganese iron phosphate cathode materials made from this manganese iron oxide as a precursor is also effectively improved.

[0041] In a first aspect, embodiments of this application provide a manganese iron oxide with the molecular formula Mn. x Fe y A a B bO3, where A is a tetravalent metal, B is a divalent metal, 0.19≤x≤1.8, 0.19≤y≤1.8, 0≤a≤0.1, 0≤b≤0.1, 1.9≤x+y+3 / 2a+3b≤2.1, and the primary particles of manganese iron oxide are in the form of flakes.

[0042] In the technical solution of this application embodiment, the primary particles of manganese iron oxide have a plate-like structure, which can provide more active sites to support efficient electrochemical reactions, thereby improving the electrochemical performance of the cathode material made with the above-mentioned manganese iron oxide as a precursor.

[0043] In this embodiment, in the molecular formula of manganese iron oxide, x, y, a, and b all represent stoichiometric ratios. Values ​​of x include, but are not limited to, 0.19, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, and 1.8; values ​​of y include, but are not limited to, 0.19, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, and 1.8; values ​​of a include, but are not limited to, 0, 0.001, 0.002, 0.004, 0.006, 0.008, 0.01, 0.5, and 0.1; and values ​​of b include, but are not limited to, 0, 0.005, 0.01, 0.02, 0.04, 0.06, 0.08, and 0.1.

[0044] Furthermore, in some embodiments, the tetravalent metal is titanium and the divalent metal is magnesium.

[0045] Lithium manganese iron phosphate (LFP) suffers from manganese leaching due to the Jan Taylor effect, which deposits on the negative electrode surface and damages the SEI film, thus adversely affecting battery performance. In the technical solution of this application, magnesium and titanium doping is performed on the manganese iron oxide to suppress the Jan Taylor effect, thereby further improving the product's capacity and cycle performance.

[0046] Furthermore, in some embodiments, the D50 particle size of the secondary particles of manganese iron oxide is 1.5~3.5μm, including but not limited to 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, etc.

[0047] In the technical solution of this application embodiment, when the D50 particle size of the manganese iron oxide meets the above-mentioned range, the particles are relatively small, thus avoiding adverse effects on the processing performance of lithium iron phosphate. If the D50 particle size of the manganese iron oxide is too large, it will lead to an increase in subsequent grinding time.

[0048] Furthermore, in some embodiments, the BET specific surface area of ​​the manganese iron oxide is 12-20 m². 2 / g, including but not limited to 12m 2 / g、14m 2 / g, 16m 2 / g、18m 2 / g、20m 2 / g etc.

[0049] In the technical solution of this application embodiment, when the BET specific surface area of ​​manganese iron oxide meets the above-mentioned range, sufficient active sites can be guaranteed to support efficient electrochemical reactions. If the specific surface area is too small, the particle size will be too large, thereby affecting the insertion and extraction of lithium ions; if the specific surface area is too large, there will be too many gaps between particles, thereby hindering the improvement of compaction density.

[0050] Furthermore, in some embodiments, the manganese oxide has a perovskite crystal structure.

[0051] In the technical solution of this application embodiment, the crystal form of manganese iron oxide is perovskite structure (ABO3 type), and the interaction force between ions is relatively weak, thereby giving it high ion mobility and chemical stability, and avoiding the problem of a large number of magnetic foreign objects in spinel structure manganese iron oxide when the reaction is insufficient due to its strong magnetism.

[0052] Secondly, embodiments of this application provide a method for preparing manganese iron oxide, comprising the following steps: Prepare a mixed metal salt solution, a precipitant solution, and a reaction base solution. The mixed metal salt solution contains manganese and iron elements, and the reaction base solution is an alkaline solution containing hydroxides. A co-precipitation reaction is carried out on a mixed metal salt solution, a precipitant solution, and a reaction substrate to obtain a reaction slurry; The reaction slurry was aged, filtered, rinsed, and oxidized and dehydrated to obtain basic manganese iron oxide; Basic ferromanganese oxide is calcined to obtain ferromanganese oxide; Among them, the molecular formula of manganese iron oxide is Mn x Fe y A a B b O3, where A is a tetravalent metal and B is a divalent metal, 0.19≤x≤1.8, 0.19≤y≤1.8, 0≤a≤0.1, 0≤b≤0.1, 1.9≤x+y+3 / 2a+3b≤2.1, and the primary particles of manganese iron oxide are in the form of flakes.

[0053] In the technical solution of this application embodiment, during the co-precipitation reaction of the metal mixed salt solution, precipitant solution, and reaction substrate, the amphoteric properties of iron are utilized to dissolve some ferrous hydroxide precipitate under superalkaline conditions, thereby increasing the solubility product of ferrous hydroxide. This compensates for the difference in solubility products between ferrous hydroxide and manganese hydroxide, achieving a co-precipitation effect and obtaining amorphous ferromanganese hydroxide. Subsequently, aging transforms the amorphous ferromanganese hydroxide into crystalline ferromanganese hydroxide, resulting in a reaction slurry containing crystalline ferromanganese hydroxide. The crystalline ferromanganese hydroxide is converted into basic ferromanganese oxide through oxidation and dehydration, and then converted into ferromanganese oxide through calcination. Compared with existing processes, the method of this application does not require the addition of a complexing agent, the treatment of production wastewater is relatively simple, it is conducive to industrialization, and it can also significantly reduce energy consumption. The above preparation process is beneficial for obtaining the ferromanganese oxide with the special morphology provided in this application, thereby improving the electrochemical performance of lithium manganese iron phosphate cathode materials prepared using the above-mentioned ferromanganese oxide as a precursor.

[0054] Furthermore, in some embodiments, the mixed metal salt solution includes soluble manganese salt and soluble ferrous salt.

[0055] Furthermore, soluble manganese salts include, but are not limited to, at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0056] Furthermore, soluble ferrous salts include, but are not limited to, at least one of ferrous chloride, ferrous sulfate, and ferrous nitrate.

[0057] Furthermore, in some embodiments, the total metal ion concentration of the metal mixed salt solution is 0.5~1.2 mol / L, including but not limited to 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, etc.

[0058] In the technical solution of this application embodiment, when the concentration of total metal ions in the metal mixed salt solution meets the above-mentioned range, high yield can be obtained while avoiding metal ion crystallization. If the total metal ion concentration is too low, the product yield is too low for the same volume, which can easily lead to increased manufacturing costs; if the total metal ion concentration is too high, the metal mixed salt solution is difficult to store and crystallization is likely to occur.

[0059] Furthermore, in some embodiments, in the metal mixed salt solution, manganese ions (Mn) 2+ ) and ferrous ions (Fe 2+ The molar ratio of ) is 1:9 to 9:1, including but not limited to 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, etc.

[0060] Furthermore, in some embodiments, the precipitant solution is a sodium hydroxide solution and / or a potassium hydroxide solution, and the concentration of the precipitant solution is 1~5 mol / L, including but not limited to 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, etc.

[0061] In the technical solution of this application embodiment, when the concentration of the precipitant solution meets the above-mentioned range, it is possible to obtain basic ferromanganese oxide with uniform particle size and avoid excessive wastewater treatment costs. If the concentration of the precipitant solution is too low, it will increase wastewater treatment costs and reduce equipment utilization; if the concentration of the precipitant solution is too high, it will lead to local overconcentration, excessively fast crystal nucleation rate, and uneven crystal particle size.

[0062] Furthermore, in some embodiments, the reaction substrate is a sodium hydroxide solution and / or a potassium hydroxide solution, and the concentration of the reaction substrate is 0.09~0.39 mol / L, including but not limited to 0.09 mol / L, 0.15 mol / L, 0.2 mol / L, 0.24 mol / L, 0.3 mol / L, 0.35 mol / L, 0.39 mol / L, etc.

[0063] In the technical solution of this application embodiment, when the concentration of the reaction substrate meets the above-mentioned range, co-precipitation of manganese and iron ions can be achieved and the yield of the target product can be improved. If the concentration of the reaction substrate is too low, manganese ions cannot be completely precipitated, and the product yield is not high; if the concentration of the reaction substrate is too high, Fe(OH)2 will redissolve at high pH values, resulting in an excessive amount of ferrous ions in the solution, while manganese ions will be completely precipitated, and the co-precipitation effect cannot be achieved.

[0064] Furthermore, in some embodiments, the volume ratio of the metal mixed salt solution, the precipitant solution, and the reaction base liquid is 1:(0.5~3.1):(0.6~1.3), including but not limited to 1:0.5:0.6, 1:0.5:0.8, 1:0.5:1, 1:0.5:1.3, 1:1.5:0.6, 1:1.5:0.8, 1:1.5:1, 1:1.5:1.3, 1:3.1:0.6, 1:3.1:0.8, 1:3.1:1, 1:3.1:1.3, etc.

[0065] In the technical solution of this application embodiment, when the volume ratio of the metal mixed salt solution, the precipitant solution and the reaction base liquid meets the above range, the hydroxide concentration in the mixed solution is consistent with the hydroxide concentration in the reaction base liquid after the co-precipitation reaction is completed.

[0066] Furthermore, in some embodiments, the metal mixed salt solution also includes a doped metal source.

[0067] Furthermore, in some embodiments, the doping metal source includes at least one of soluble titanium salt and soluble magnesium salt.

[0068] In the technical solution of this application embodiment, by doping manganese iron oxide with magnesium and titanium, the Jan Taylor effect can be suppressed, thereby further improving the capacity and cycle performance of the product, and thus improving the electrical performance of the battery.

[0069] Furthermore, soluble titanium salts include, but are not limited to, titanium oxysulfate.

[0070] Furthermore, soluble magnesium salts include, but are not limited to, at least one of magnesium sulfate, magnesium chloride, and magnesium nitrate.

[0071] Furthermore, in some embodiments, the molar ratio of the doped metal ions in the doped metal source to the total molar amount of metal ions in the mixed metal salt solution is (0.001~0.02):1, including but not limited to 0.001:1, 0.002:1, 0.004:1, 0.006:1, 0.008:1, 0.01:1, 0.012:1, 0.014:1, 0.016:1, 0.018:1, 0.02:1, etc.

[0072] In the technical solution of this application embodiment, when the molar ratio of the doped metal ions in the metal source to the total molar amount of metal ions in the mixed metal salt solution meets the above-mentioned range, the crystal structure of manganese iron oxide can be stabilized, improving the effective capacity and charge / discharge capacity of lithium manganese iron phosphate cathode material prepared using it as a precursor. If the proportion of doped metal ions in the metal source is too low, the product performance improvement will be insufficient. If the proportion of doped metal ions in the metal source is too high, the crystal structure distortion will be too large, which will reduce its effective capacity and charge / discharge capacity.

[0073] Furthermore, in some embodiments, the co-precipitation reaction is carried out by simultaneously adding a mixed metal salt solution and a precipitant solution to the reaction substrate.

[0074] In the technical solution of this application embodiment, by adopting a synchronous dropwise addition method, it not only helps to form a composite precipitate with uniform composition and reduce component segregation or stratification, but also helps to maintain the stability of hydroxide concentration in the reaction system, avoid the generation of impurity phases caused by drastic fluctuations, and improve product purity.

[0075] Furthermore, in some embodiments, the temperature of the coprecipitation reaction is 20~25℃, including but not limited to 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, etc., and the time of the coprecipitation reaction is 100~150min, including but not limited to 100min, 110min, 120min, 130min, 140min, 150min, etc., the atmosphere of the coprecipitation reaction is a protective atmosphere, and the coprecipitation reaction is carried out under stirring conditions.

[0076] In the technical solution of this application embodiment, when the temperature of the coprecipitation reaction meets the above-mentioned range, the nucleation rate is slow, which helps to control crystal nucleation and growth, resulting in more uniform particle size. If the temperature of the coprecipitation reaction is too high, the nucleation rate will be too fast, and crystal growth and nucleation will occur simultaneously, leading to uneven particle size. Simultaneously, since divalent manganese ions are easily oxidized under alkaline conditions, this application uses a protective atmosphere to avoid the problem of reduced product purity caused by some divalent manganese combining with trivalent iron to form manganese ferrite as a byproduct instead of ferrous manganese hydroxide during the coprecipitation reaction. This application does not limit the type of protective atmosphere; those skilled in the art can choose according to the actual situation. For example, the protective atmosphere can be nitrogen or argon, etc.

[0077] Furthermore, in some embodiments, after the coprecipitation reaction is completed, the hydroxide concentration in the mixed solution is the same as the hydroxide concentration in the reaction substrate.

[0078] In the technical solution of this application embodiment, maintaining the hydroxide concentration in the mixed solution after the co-precipitation reaction is consistent with the hydroxide concentration in the reaction substrate helps maintain the stability of the reaction system and makes the synthesized product highly stable. If the hydroxide concentration in the mixed solution is too low, manganese ions will not be completely precipitated, resulting in a low product yield; if the hydroxide concentration in the mixed solution is too high, Fe(OH)2 will redissolve at high pH, ​​resulting in an excessive amount of ferrous ions in the solution, while manganese ions will not be completely precipitated, thus failing to achieve the co-precipitation effect.

[0079] The formula for calculating the hydroxide concentration in the mixed solution is: Hydroxide concentration in the mixed solution = (Hydroxide content in the precipitant solution + Hydroxide content in the reaction base solution - Theoretical hydroxide content required for metal ion precipitation in the metal mixed salt solution) / (Volume of precipitant solution + Volume of reaction base solution + Volume of metal mixed salt solution).

[0080] Furthermore, in some embodiments, the aging temperature is 70~90℃, including but not limited to 70℃, 75℃, 80℃, 85℃, 90℃, etc., the aging time is 1~3h, including but not limited to 1h, 1.5h, 2h, 2.5h, 3h, the aging atmosphere is a protective atmosphere, and the aging is carried out under stirring conditions.

[0081] In the technical solution of this application embodiment, when the aging temperature meets the above-mentioned range, the crystal form of the slurry can be transformed. If the aging temperature is too low, a longer processing time is required, resulting in low production efficiency; if the aging temperature is too high, the crystal nucleus formation rate will be accelerated, which may cause inconsistencies in the morphology of the final product, thereby affecting the stability of the product. Meanwhile, since divalent manganese ions are easily oxidized under alkaline conditions, this application uses a protective atmosphere to avoid the problem of reduced product purity caused by some divalent manganese combining with trivalent iron to form manganese ferrite as a byproduct instead of ferrous manganese hydroxide during the aging reaction. This application does not limit the type of protective atmosphere; those skilled in the art can choose according to the actual situation. For example, the protective atmosphere can be nitrogen or argon, etc.

[0082] Furthermore, in some embodiments, the oxidation and dehydration temperature is 70~80°C, including but not limited to 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, etc., and the oxidation and dehydration time is 8~12h, including but not limited to 8h, 9h, 10h, 11h, 12h, and the oxidation and dehydration atmosphere is air or oxygen.

[0083] In the technical solution of this application embodiment, when the oxidation and dehydration temperature meets the above-mentioned range, crystalline ferrous manganese hydroxide can be converted into basic ferrous manganese oxide. If the oxidation and dehydration temperature is too low, a longer processing time is required, resulting in low production efficiency; if the oxidation and dehydration temperature is too high, the external bound water will be lost prematurely, causing surface hardening and leading to an increase in product particle size.

[0084] Furthermore, in some embodiments, the calcination temperature is 600~700℃, including but not limited to 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, etc., the calcination time is 1~3h, including but not limited to 1h, 1.5h, 2h, 2.5h, 3h, the heating rate is 1~10℃ / min, including but not limited to 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, and the calcination atmosphere is air.

[0085] In the technical solution of this application embodiment, when the calcination temperature meets the above-mentioned range, basic manganese oxide can be converted into iron manganese oxide. If the calcination temperature is too low, a longer processing time is required, resulting in low production efficiency; if the calcination temperature is too high, some MnFeO3 in the phase will be converted into MnFe2O4, thereby reducing the purity of the product.

[0086] Thirdly, embodiments of this application provide a lithium manganese iron phosphate cathode material, which is prepared using manganese iron oxide as provided in the first aspect of this application as a precursor, or using manganese iron oxide prepared by the method for preparing manganese iron oxide provided in the second aspect of this application as a precursor.

[0087] In the technical solution of this application embodiment, the lithium manganese iron phosphate cathode material is prepared by using the above-mentioned manganese iron oxide as a precursor, and thus has good charge and discharge specific capacity, rate performance, energy density and cycle life.

[0088] Furthermore, in some embodiments, the compaction density of the lithium manganese iron phosphate cathode material is 2.1~2.4 g / cm³. 3 including but not limited to 2.1g / cm 3 2.15g / cm 3 2.2g / cm 3 2.25g / cm 3 2.3g / cm 3 2.35g / cm 3 2.4g / cm 3 wait.

[0089] In the technical solution of this application embodiment, when the compaction density of the lithium manganese iron phosphate cathode material meets the above range, the particles have a good degree of compactness, which is beneficial to improving the charge and discharge specific capacity, rate performance, energy density and cycle life of the battery.

[0090] Fourthly, embodiments of this application provide a positive electrode sheet, which includes the lithium manganese iron phosphate positive electrode material provided in the third aspect of this application.

[0091] In the technical solution of this application embodiment, the positive electrode sheet contains the above-mentioned lithium manganese iron phosphate positive electrode material, thus having good charge / discharge specific capacity, rate performance, energy density and cycle life.

[0092] Fifthly, embodiments of this application provide a secondary battery, which includes the positive electrode provided in the fourth aspect of this application.

[0093] In the technical solution of this application embodiment, the secondary battery includes the above-mentioned positive electrode sheet, and thus has good charge / discharge specific capacity, rate performance, energy density and cycle life.

[0094] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0095] I. Preparation Method Example 1 (1) Prepare a 4 mol / L sodium hydroxide solution with pure water as a precipitant solution; prepare a 0.24 mol / L sodium hydroxide solution with pure water as a reaction base solution; mix 0.48 mol manganese sulfate, 0.32 mol ferrous sulfate, 0.00913 mol magnesium sulfate, and 0.001 mol titanium oxysulfate, and then add pure water to prepare a manganese iron magnesium titanium sulfate solution (800 mL volume) with a total metal ion concentration of about 1 mol / L as a mixed metal salt solution; (2) Purge the reactor with nitrogen gas. After the gas is replaced, ensure that the reactor is under positive pressure. Then, add 800 mL of mixed metal salt solution and 482.5 mL of precipitant solution dropwise to 500 mL of reaction base liquid at room temperature. The dropwise addition is completed in 120 min. Maintain the sodium hydroxide concentration in the reaction system at 0.24 mol / L to obtain the reaction slurry. (3) The reaction slurry was aged in a water bath at 80°C for 2 hours, filtered, and washed with pure water until the conductivity was ≤350us / cm. Then the manganese iron hydroxide filter cake was oxidized and dehydrated in a 70°C oven for 12 hours in an air atmosphere to obtain magnesium titanium doped basic manganese iron oxide. (4) Magnesium-titanium doped basic manganese iron oxide was calcined at 650℃ for 2 hours at a heating rate of 5℃ / min in an air atmosphere to obtain magnesium-titanium doped manganese iron oxide (Mn 1.185 Fe 0.79 Mg 0.0225 Ti 0.0025 O3).

[0096] Example 2 (1) Prepare a 4 mol / L sodium hydroxide solution with pure water as a precipitant solution; prepare a 0.09 mol / L sodium hydroxide solution with pure water as a reaction base solution; mix 0.08 mol manganese sulfate, 0.72 mol ferrous sulfate, 0.00913 mol magnesium sulfate, and 0.001 mol titanium sulfate, and then add pure water to prepare a manganese iron magnesium titanium sulfate solution (800 mL volume) with a total metal ion concentration of about 1 mol / L as a mixed metal salt solution; (2) Purge the reactor with nitrogen gas. After the gas is replaced, ensure that the reactor is under positive pressure. Then, add 800 mL of mixed metal salt solution and 433.4 mL of precipitant solution dropwise to 500 mL of reaction base liquid at room temperature. The dropwise addition is completed in 120 min. Maintain the sodium hydroxide concentration in the reaction system at 0.09 mol / L to obtain the reaction slurry. (3) The reaction slurry was aged in a water bath at 80°C for 2 hours, filtered, and washed with pure water until the conductivity was ≤350us / cm. Then the manganese iron hydroxide filter cake was oxidized and dehydrated in a 70°C oven for 12 hours in an air atmosphere to obtain magnesium titanium doped basic manganese iron oxide. (4) Magnesium-titanium doped basic manganese iron oxide was calcined at 650℃ for 2 hours at a heating rate of 5℃ / min in an air atmosphere to obtain magnesium-titanium doped manganese iron oxide (Mn 0.1975 Fe 1.7775 Mg 0.0225 Ti 0.0025 O3).

[0097] Example 3 (1) Prepare a 4 mol / L sodium hydroxide solution with pure water as a precipitant solution; prepare a 0.39 mol / L sodium hydroxide solution with pure water as a reaction base solution; mix 0.72 mol manganese sulfate, 0.08 mol ferrous sulfate, 0.00913 mol magnesium sulfate and 0.001 mol titanium sulfate, and then add pure water to prepare a manganese iron magnesium titanium sulfate solution (800 mL volume) with a total metal ion concentration of about 1 mol / L as a mixed metal salt solution; (2) Purge the reactor with nitrogen gas. After the gas is replaced, ensure that the reactor is under positive pressure. Then, add 800 mL of mixed metal salt solution and 536 mL of precipitant solution dropwise to 500 mL of reaction base liquid at room temperature. The dropwise addition is completed in 120 min. Maintain the sodium hydroxide concentration in the reaction system at 0.39 mol / L to obtain the reaction slurry. (3) The reaction slurry was aged in a water bath at 80°C for 2 hours, filtered, and washed with pure water until the conductivity was ≤350us / cm. Then the manganese iron hydroxide filter cake was oxidized and dehydrated in a 70°C oven for 12 hours in an air atmosphere to obtain magnesium titanium doped basic manganese iron oxide. (4) Magnesium-titanium doped basic manganese iron oxide was calcined at 650℃ for 2 hours at a heating rate of 5℃ / min in an air atmosphere to obtain magnesium-titanium doped manganese iron oxide (Mn 1.7775 Fe 0.1975 Mg 0.0225 Ti 0.0025 O3).

[0098] Example 4 (1) Prepare a 1 mol / L sodium hydroxide solution with pure water as a precipitant solution; prepare a 0.24 mol / L sodium hydroxide solution with pure water as a reaction base solution; mix 0.48 mol manganese sulfate, 0.32 mol ferrous sulfate, 0.013 mol magnesium sulfate, and 0.00265 mol titanium oxysulfate, and then add pure water to prepare a manganese iron magnesium titanium sulfate solution (800 mL volume) with a total metal ion concentration of about 1 mol / L as a mixed metal salt solution; (2) Purge the reactor with nitrogen gas. After the gas is replaced, ensure that the reactor is under positive pressure. Then, add 800 mL of mixed metal salt solution and 2408 mL of precipitant solution dropwise to 1000 mL of reaction base liquid at room temperature. The dropwise addition is completed in 120 min. Maintain the sodium hydroxide concentration in the reaction system at 0.24 mol / L to obtain the reaction slurry. (3) The reaction slurry was aged in a water bath at 80°C for 2 hours, filtered, and washed with pure water until the conductivity was ≤350us / cm. Then the manganese iron hydroxide filter cake was oxidized and dehydrated in a 70°C oven for 12 hours in an air atmosphere to obtain magnesium titanium doped basic manganese iron oxide. (4) Magnesium-titanium doped basic manganese iron oxide was calcined at 650℃ for 2 hours at a heating rate of 5℃ / min in an air atmosphere to obtain magnesium-titanium doped manganese iron oxide (Mn 1.177 Fe 0.7847 Mg 0.0319 Ti 0.0064 O3).

[0099] Example 5 (1) Prepare a 1 mol / L sodium hydroxide solution with pure water as a precipitant solution; prepare a 0.24 mol / L sodium hydroxide solution with pure water as a reaction base solution; mix 0.48 mol manganese sulfate, 0.32 mol ferrous sulfate, 0.00261 mol magnesium sulfate, and 0.0008 mol titanium oxysulfate, and then add pure water to prepare a manganese iron magnesium titanium sulfate solution (800 mL volume) with a total metal ion concentration of about 1 mol / L as a mixed metal salt solution; (2) Purge the reactor with nitrogen gas. After the gas is replaced, ensure that the reactor is under positive pressure. Then, add 800 mL of mixed metal salt solution and 2370 mL of precipitant solution dropwise to 1000 mL of reaction base liquid at room temperature. The dropwise addition is completed in 120 min. Maintain the sodium hydroxide concentration in the reaction system at 0.24 mol / L to obtain the reaction slurry. (3) The reaction slurry was aged in a water bath at 80°C for 2 hours, filtered, and washed with pure water until the conductivity was ≤350us / cm. Then the manganese iron hydroxide filter cake was oxidized and dehydrated in a 70°C oven for 12 hours in an air atmosphere to obtain magnesium titanium doped basic manganese iron oxide. (4) Magnesium-titanium doped basic manganese iron oxide was calcined at 650℃ for 2 hours at a heating rate of 5℃ / min in an air atmosphere to obtain magnesium-titanium doped manganese iron oxide (Mn 1.1949 Fe 0.7966 Mg 0.0065 Ti 0.002 O3).

[0100] Example 6 (1) Prepare a 4 mol / L sodium hydroxide solution with pure water as a precipitant solution; prepare a 0.24 mol / L sodium hydroxide solution with pure water as a reaction base solution; mix 0.48 mol manganese sulfate and 0.32 mol ferrous sulfate, and then add pure water to prepare a 1 mol / L manganese ferric sulfate solution (800 mL volume) as a mixed metal salt solution; (2) Purge the reactor with nitrogen gas. After the gas is replaced, ensure that the reactor is under positive pressure. Then, add 800 mL of mixed metal salt solution and 476.4 mL of precipitant solution dropwise to 500 mL of reaction base liquid at room temperature. The dropwise addition is completed in 120 min. Maintain the sodium hydroxide concentration in the reaction system at 0.24 mol / L to obtain the reaction slurry. (3) The reaction slurry was aged in a water bath at 80°C for 2 hours, filtered, and washed with pure water until the conductivity was ≤350us / cm. Then the manganese iron hydroxide filter cake was oxidized and dehydrated in a 70°C oven for 12 hours in an air atmosphere to obtain basic manganese iron oxide. (4) Basic ferromanganese oxide was calcined at 650℃ for 2 hours at a heating rate of 5℃ / min in an air atmosphere to obtain ferromanganese oxide (Mn). 1.2 Fe 0.8 O3).

[0101] Comparative Example 1 (1) Prepare a 4 mol / L sodium hydroxide solution with pure water as a precipitant solution; prepare a sodium hydroxide solution with a pH of 11-12 with pure water as a reaction base solution; mix 0.48 mol manganese sulfate, 0.32 mol ferrous sulfate, 0.00913 mol magnesium sulfate and 0.001 mol titanium sulfate, and then add pure water to prepare a manganese iron magnesium titanium sulfate solution (800 mL volume) with a total metal ion concentration of about 1 mol / L as a mixed metal salt solution; (2) Purge the reactor with nitrogen gas. After the gas is replaced, ensure that the reactor is under positive pressure. Then, add 800 mL of mixed metal salt solution and 407 mL of precipitant solution dropwise to 500 mL of reaction base liquid at room temperature. The dropwise addition is completed in 120 min. Maintain the pH value of the reaction system at 11~12 to obtain the reaction slurry. (3) The reaction slurry was aged in a water bath at 80°C for 2 hours, filtered, and washed with pure water until the conductivity was ≤350us / cm. Then the manganese iron hydroxide filter cake was oxidized and dehydrated in a 70°C oven for 12 hours in an air atmosphere to obtain magnesium titanium doped basic manganese iron oxide. (4) Magnesium-titanium doped basic manganese iron oxide was calcined at 650℃ for 2 hours at a heating rate of 5℃ / min in an air atmosphere to obtain magnesium-titanium doped manganese iron oxide (Mn 1.185 Fe 0.79 Mg 0.0225 Ti 0.0025 O3).

[0102] Comparative Example 2 (1) Prepare a 4 mol / L sodium hydroxide solution with pure water as a precipitant solution; prepare a 1 mol / L sodium hydroxide solution with pure water as a reaction base solution; mix 0.48 mol manganese sulfate, 0.32 mol ferrous sulfate, 0.00913 mol magnesium sulfate and 0.001 mol titanium oxysulfate, and then add pure water to prepare a manganese iron magnesium titanium sulfate solution (800 mL volume) with a total metal ion concentration of about 1 mol / L as a mixed metal salt solution; (2) Purge the reactor with nitrogen gas. After the gas is replaced, ensure that the reactor is under positive pressure. Then, add 800 mL of mixed metal salt solution and 810 mL of precipitant solution dropwise to 500 mL of reaction base liquid at room temperature. The dropwise addition is completed in 120 min. Maintain the sodium hydroxide concentration in the reaction system at 1 mol / L to obtain the reaction slurry. (3) The reaction slurry was aged in a water bath at 80°C for 2 hours, filtered, and washed with pure water until the conductivity was ≤350us / cm. Then the manganese iron hydroxide filter cake was oxidized and dehydrated in a 70°C oven for 12 hours in an air atmosphere to obtain magnesium titanium doped basic manganese iron oxide. (4) Magnesium-titanium doped basic manganese iron oxide was calcined at 650℃ for 2 hours at a heating rate of 5℃ / min in an air atmosphere to obtain magnesium-titanium doped manganese iron oxide (Mn 1.185 Fe 0.79 Mg 0.0225 Ti 0.0025 O3).

[0103] Comparative Example 3 Compared with Example 1, the only difference is that in step (2), 800 mL of mixed metal salt solution and 482.5 mL of precipitant solution are simultaneously added dropwise to 500 mL of reaction base solution at 80 °C.

[0104] Comparative Example 3: Magnesium-Titanium Doped Manganese Iron Oxide (Mn) was prepared 1.185 Fe 0.79 Mg 0.0225 Ti 0.0025 O3).

[0105] II. Testing Methods (I) Performance testing of basic ferromanganese oxide and ferromanganese oxide 1. SEM testing: The morphology of basic ferromanganese oxide and ferromanganese oxide was characterized using a field emission scanning electron microscope (Quanta200FEG) manufactured by Zeiss. The results are shown in the figure. Figures 1-3 .

[0106] 2. XRD Testing: The crystal structure of basic ferromanganese oxide and ferromanganese oxide was characterized using an X-ray diffractometer (SmartLab-SE) manufactured by Rigaku Corporation, Japan. The results are shown in [Figure number missing]. Figures 4-7 .

[0107] 3. Element content: The element content of manganese iron oxide was tested using an inductively coupled plasma optical emission spectrometer (ICP-OES), and the results are shown in Table 1.

[0108] 4. D10, D50, and D90 particle sizes of secondary particles: These were tested using a Malvern 3000 laser particle size analyzer, and the results are shown in Table 1.

[0109] 5. BET specific surface area: determined by gas adsorption BET method.

[0110] (II) Performance testing of lithium manganese iron phosphate 1. Preparation of lithium manganese iron phosphate: The manganese iron oxide, ammonium dihydrogen phosphate, lithium carbonate and glucose prepared in the above examples and comparative examples are mixed and ground evenly in a molar ratio of 1:1:1:0.05, with water as the solvent, to obtain a mixture; the mixture is spray-dried at a temperature of 110°C to obtain a lithium manganese iron phosphate precursor; the lithium manganese iron phosphate precursor is calcined under a nitrogen atmosphere at a temperature of 725°C for 12 hours to obtain a lithium manganese iron phosphate cathode material.

[0111] 2. Compacted density: The compaction density was tested using a compaction density meter. The test pressure was 3T and the compaction time was 30s. The test results are shown in Table 2.

[0112] (III) Properties of Secondary Batteries 1. Secondary battery assembly: The lithium manganese iron phosphate material prepared from the manganese iron oxide prepared in the above embodiments and comparative examples was mixed with conductive carbon black, PVDF binder, and NMP in a mass ratio of 18:1:20:17. The mixture was then coated onto a 12μm thick aluminum foil. The electrode was then dried in an oven at 110℃ for 10 hours. The dried electrode was then cut into positive electrode discs with a diameter of 15mm and compacted to a density of 1.8g / cm³. 3 Roll forming was performed using a 16mm diameter lithium sheet as the counter electrode. The electrolyte was obtained by dissolving LiPF6 in EC:EMC:DEC at a volume ratio of 1:1:1 with a concentration of 1mol / L. The cells were assembled in an LG2400 / 1000TS glove box manufactured by Wig Gas Purification Technology (Suzhou) Co., Ltd., to obtain coin half-cells.

[0113] 2. Secondary Battery Performance Testing: The battery performance testing system (model: CT3002A) from Wuhan Landian Electronics Technology Co., Ltd. was used for testing. The test temperature was 25℃, the voltage range was 2~4.35V, and the test rate was 0.1C. The test results are shown in Table 2 and... Figure 8 .

[0114] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 1

[0115] Table 2

[0116] Please see Figures 1-2 The magnesium-titanium-doped basic manganese iron oxide prepared in Example 1 of this application has a lamellar structure with a lateral dimension of 42.51~107.93 nm and a thickness of 8.38~18.21 nm. The particles are relatively large and uniformly distributed. Furthermore, the magnesium-titanium-doped manganese iron oxide formed by calcination of the above-mentioned magnesium-titanium-doped basic manganese iron oxide retains its lamellar structure very well. In contrast, the magnesium-titanium-doped basic manganese iron oxide prepared in Comparative Example 3 of this application has smaller particles and uneven particle size distribution. The above results show that, compared with Comparative Example 3, the magnesium-titanium-doped basic manganese iron oxide particles prepared by the method of this application are larger and more uniformly distributed.

[0117] Please see Figures 4-7 The crystal structure of the magnesium-titanium-doped basic manganese iron oxide prepared in Example 1 of this application is similar to that of (Fe 0.67 Mn 0.33The crystal structure of the magnesium-titanium manganese iron oxide prepared in Example 1 of this application is highly matched with that of FeMnO3 (PDF#14-0557). This indicates that the manganese iron oxide prepared in this application has a perovskite structure. Meanwhile, the crystal structure of the magnesium-titanium basic manganese iron oxide prepared in Comparative Example 1 of this application is highly matched with that of (FeMnO3) (PDF#75-0894), indicating that the manganese iron oxide prepared in this application has a perovskite structure. 0.67 Mn 0.33 The crystal structures of the doped magnesium-titanium manganese iron oxide prepared in Comparative Example 1 match those of FeMnO3 (PDF#14-0557) and MnO (PDF#75-0257), indicating that both the doped magnesium-titanium basic manganese iron oxide and the doped magnesium-titanium manganese iron oxide prepared by the method in Comparative Example 1 contain impurity phases. These results show that, compared to Comparative Example 1, the doped magnesium-titanium basic manganese iron oxide and the doped magnesium-titanium manganese iron oxide prepared by the method in this application have higher purity.

[0118] Please refer to Tables 1-2 and Figure 8 Through Tables 1-2 and Figure 8 It can be seen that the manganese-iron ratio of the manganese-iron oxide prepared in the embodiments of this application is very close to the theoretical value, which also indicates that the manganese-iron oxide prepared by the method of this application has high purity; at the same time, the D50 particle size of the manganese-iron oxide prepared in the embodiments of this application is 1.5~3.5μm, and the BET specific surface area is 12~20m². 2 / g indicates that the method of this application is beneficial to obtaining manganese iron oxide with more suitable particle size and BET specific surface area, thereby improving the electrochemical performance (such as charge / discharge specific capacity, coulombic efficiency, etc.) of batteries assembled from lithium manganese iron phosphate made from the above-mentioned manganese iron oxide as a precursor.

[0119] Compared with Example 1, the manganese iron oxide prepared in Example 6 of this application was not doped with magnesium and titanium. Although its manganese iron ratio was also very close to the theoretical value, the battery assembled from lithium manganese iron phosphate made from it as a precursor suffered from manganese dissolution due to the Jan Taylor effect, which deposited on the negative electrode surface and damaged the SEI film, resulting in a significant decrease in the electrochemical performance of the battery.

[0120] Compared with Example 1, the hydroxide concentration in the reaction substrate and the hydroxide concentration in the mixed solution after the coprecipitation reaction in Comparative Example 1 were both lower. Although the manganese-iron ratio of the prepared doped magnesium-titanium-manganese-iron oxide was similar to that in Example 1, XRD showed that it still contained high levels of impurities (Fe2O3, etc.). This indicates that the pH of the reaction substrate and the pH of the system after the coprecipitation reaction were too low, which would lead to a decrease in the final purity of the product and thus affect the electrochemical performance of the battery.

[0121] Compared with Example 1, the hydroxide concentration in the reaction substrate and the mixed solution after the co-precipitation reaction in Comparative Example 2 are both higher. When the hydroxide concentration is too high, a large amount of the generated Fe(OH)2 precipitate will dissolve and be lost during filtration, resulting in a higher final manganese-iron ratio and a decrease in final product purity, which in turn affects battery performance. In addition, when the hydroxide concentration is too high, the excess hydroxide in the system cannot be effectively utilized, which will also increase costs.

[0122] Compared to Example 1, the coprecipitation temperature in Comparative Example 3 was too high. When the coprecipitation temperature is too high, the nucleation rate is too fast, and crystal growth and nucleation occur simultaneously, resulting in a large number of small particles with uneven particle size distribution. Furthermore, due to insufficient atomic migration time during rapid crystal nucleation, the particles are difficult to arrange in an orderly manner, resulting in vacancies and grain boundary defects. Consequently, the electrochemical performance of the battery assembled from lithium manganese iron phosphate prepared by the above-mentioned doped magnesium, titanium, manganese iron oxide as a precursor is significantly reduced (such as charge / discharge specific capacity, coulombic efficiency, etc.).

[0123] 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 manganese iron oxide, characterized in that, Includes the following steps: Prepare a mixed metal salt solution, a precipitant solution, and a reaction base solution, wherein the mixed metal salt solution contains manganese and iron elements, and the reaction base solution is an alkaline solution containing hydroxides; The metal mixed salt solution, the precipitant solution and the reaction substrate are subjected to a co-precipitation reaction to obtain a reaction slurry; The reaction slurry was aged, filtered, rinsed, and oxidized and dehydrated to obtain basic manganese iron oxide; The basic ferromanganese oxide is calcined to obtain ferromanganese oxide; The molecular formula of the manganese iron oxide is Mn. x Fe y A a B b O3, where A is a tetravalent metal, B is a divalent metal, 0.19≤x≤1.8, 0.19≤y≤1.8, 0≤a≤0.1, 0≤b≤0.1, 1.9≤x+y+3 / 2a+3b≤2.1, and the primary particles of the manganese iron oxide are in the form of flakes; The mixed metal salt solution includes soluble manganese salt and soluble ferrous salt; The total metal ion concentration of the mixed metal salt solution is 0.5~1.2 mol / L; The precipitant solution is a sodium hydroxide solution and / or a potassium hydroxide solution, and the concentration of the precipitant solution is 1~5 mol / L; The reaction substrate is a sodium hydroxide solution and / or a potassium hydroxide solution, and the concentration of the reaction substrate is 0.09~0.39 mol / L; The volume ratio of the mixed metal salt solution, the precipitant solution, and the reaction substrate is 1:(0.5~3.1):(0.6~1.3). The temperature of the coprecipitation reaction is 20~25℃.

2. The method for preparing manganese iron oxide according to claim 1, characterized in that, The mixed metal salt solution further includes a doped metal source; wherein... The doped metal source includes at least one of soluble titanium salt and soluble magnesium salt; and / or, The molar ratio of the doped metal ions in the doped metal source to the total molar amount of metal ions in the mixed metal salt solution is (0.001~0.02):

1.

3. The method for preparing manganese iron oxide according to claim 1, characterized in that, The coprecipitation reaction takes 100-150 minutes, and the atmosphere for the coprecipitation reaction is a protective atmosphere; and / or, The aging temperature is 70~90℃, the aging time is 1~3 hours, and the aging atmosphere is a protective atmosphere; and / or, The oxidation and dehydration temperature is 70~80℃, the oxidation and dehydration time is 8~12h, and the oxidation and dehydration atmosphere is air or oxygen.

4. The method for preparing manganese iron oxide according to claim 1, characterized in that, The calcination temperature is 600~700℃, the calcination time is 1~3h, the heating rate is 1~10℃ / min, and the calcination atmosphere is air.

5. The method for preparing manganese iron oxide according to claim 1, characterized in that, The secondary particles of the manganese iron oxide have a D50 particle size of 1.5~3.5μm and a BET specific surface area of ​​12~20m². 2 / g.

6. A lithium iron phosphate cathode material, characterized in that, The manganese iron oxide was prepared using the manganese iron oxide preparation method described in any one of claims 1 to 5 as a precursor.

7. A positive electrode sheet, characterized in that, The positive electrode sheet includes the lithium manganese iron phosphate positive electrode material as described in claim 6.

8. A secondary battery, characterized in that, The secondary battery includes the positive electrode sheet as described in claim 7.

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