Manganese iron oxide and its preparation method and application

Abstract

The present application provides a manganese iron oxide and its preparation method and application, which belongs to the field of lithium ion batteries. The preparation method of manganese iron oxide includes the following steps: providing a manganese iron solution, a complexing liquid and a base liquid, wherein the pH value of the base liquid is 11-12; mixing the manganese iron solution, the complexing liquid and the base liquid, and performing a first reaction treatment to obtain a first precursor; the first precursor is subjected to a second reaction treatment to obtain manganese iron oxide; wherein the manganese iron solution includes Fe 2+ and Mn 2+ The complexing liquid includes a first complexing agent, the first complexing agent and Fe 2+ The stability constant of the complex formed and the complexing agent and Mn 2+ The ratio of the stability constants of the complexes formed is 10 3 ~10 5 The technical solution of the embodiment of the present application can improve the co-precipitation effect of manganese and iron, thereby improving the product purity and other properties of manganese iron oxide.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a manganese iron oxide and a preparation method and application thereof. Background Art

[0002] Lithium manganese iron phosphate has gained widespread attention in the field of lithium-ion batteries due to its higher energy density than lithium iron phosphate. The current process flow for the preparation of lithium manganese iron phosphate mainly includes the manganese iron oxide route. Among them, the preparation methods of manganese iron oxide in the manganese iron oxide route include solid-phase method and liquid-phase co-precipitation method. In the liquid-phase co-precipitation method, a soluble manganese source and a ferrous source are usually dissolved as raw materials, and then the ferrous ions and manganese ions are co-precipitated by a chelating agent, and the precipitate is then calcined to obtain manganese iron oxide. In the traditional liquid-phase co-precipitation method, the co-precipitation effect of manganese and iron is poor, and it is easy to cause the prepared manganese iron oxide to be easily mixed with impurities. Summary of the Invention

[0003] In view of the technical problems existing in the background technology, the present application provides a method for preparing manganese iron oxide, which aims to solve the technical problems that the co-precipitation effect of manganese and iron in the traditional liquid phase co-precipitation method is poor, and the prepared manganese iron oxide is easily mixed with impurities.

[0004] In a first aspect, the present invention provides a method for preparing manganese iron oxide, comprising the following steps:

[0005] Providing a ferromanganese solution, a complexing solution, and a base solution, wherein the pH value of the base solution is 11-12;

[0006] The ferromanganese solution, the complexing solution and the base solution are mixed and subjected to a first reaction treatment to obtain a first precursor;

[0007] The first precursor is subjected to a second reaction treatment to obtain the manganese iron oxide;

[0008] Wherein, the ferromanganese solution includes Fe 2+ and Mn 2+ ;

[0009] The complexing liquid includes a first complexing agent, the first complexing agent and Fe 2+ The stability constant of the complex formed and the complexing agent with Mn 2+ The ratio of the stability constants of the complexes formed is 10 3 ~10 5 .

[0010] In the technical solution of the embodiment of the present application, the ferromanganese solution, the complexing liquid and the base liquid are mixed, and during the first reaction treatment, the first complexing agent and the Fe 2+ The stability constant of the complex formed and the first complexing agent with Mn2+ The ratio of the stability constants of the complexes formed is 10 3 ~10 5 , effectively making up for the nearly 3 orders of magnitude difference between the solubility product of Fe(OH)2 and the solubility product of Mn(OH)2; at the same time, the pH value of the bottom liquid is 11~12. During the first reaction treatment, the manganese ions and ferrous ions in the solution can be controlled by the chelating agent, so that the iron and manganese elements are evenly mixed, thereby achieving a better co-precipitation effect of manganese and iron, and obtaining a first precursor with high crystallization quality and less amorphous manganese-iron hydroxide impurities. It can be understood that the first precursor is a co-precipitation of manganese and ferrous hydroxide. The first precursor is then subjected to a second reaction treatment to obtain manganese iron oxide. The technical solution of the embodiment of the present application can improve the co-precipitation effect of manganese and iron, thereby improving the product purity and other properties of manganese iron oxide.

[0011] In some embodiments, the ferromanganese solution contains Mn 2+ and Fe 2+ The total concentration is 0.5mol / L~2mol / L.

[0012] In this embodiment, Mn in the ferromanganese solution 2+ and Fe 2+ When the total concentration of Mn is too high, the ferromanganese solution is difficult to store and is prone to crystallization. 2+ and Fe 2+ When the total concentration is too low, the amount of the first precursor and the manganese iron oxide product under the same volume is too small, which may easily lead to an increase in manufacturing costs.

[0013] In some embodiments, the ferromanganese solution contains Mn 2+ and Fe 2+ The molar ratio is (3~8): (2~7).

[0014] In this embodiment, Mn in the ferromanganese solution 2+ and Fe 2+ When the molar ratio of Mn is too high, the high proportion of manganese will affect the cycle performance of the subsequent prepared lithium manganese iron phosphate material. 2+ and Fe 2+ When the molar ratio is too low, it will affect the voltage platform and energy density of the subsequently prepared lithium manganese iron phosphate material.

[0015] In some embodiments, the concentration of the first complexing agent in the complexing solution is 0.5 mol / L to 4 mol / L.

[0016] In this embodiment, within the concentration range of the first complexing agent in the complexing solution, a better effect of co-precipitation of manganese ions and ferrous ions is achieved.

[0017] In some embodiments, the first complexing agent is selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

[0018] In some embodiments, the base solution includes a second complexing agent; the concentration of the second complexing agent in the base solution is 0.5 mol / L to 2 mol / L.

[0019] In this embodiment, by adding the second complexing agent in the base liquid, it is possible to prevent ferromanganese solution from adding rear manganese ion, ferrous ion and directly generating ferromanganese hydroxide with sodium hydroxide.After adding the second complexing agent in the base liquid, after ferromanganese solution adds the base liquid, complexing agent and manganese ion, ferrous ion first form a complex, and then along with the concentration of sodium hydroxide improves, manganese ion and ferrous ion are combined with hydroxide to generate ferromanganese hydroxide.When the concentration of the complexing agent in the base liquid is too low, ferromanganese solution is added to the base liquid, it is impossible to effectively complex manganese ion and ferrous ion, it is possible to directly generate ferromanganese hydroxide, there is a sequential precipitation order, it is difficult to achieve uniform coprecipitation effect.When the concentration of the complexing agent in the base liquid is too high, complexed iron ion is too much, causes manganese to precipitate first, is difficult to achieve uniform coprecipitation effect.

[0020] In some embodiments, the second complexing agent is selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

[0021] In this embodiment, ethylenediamine and Fe 2+ The stability constant of the complex formed and the stability constant of the complex with Mn 2+ The ratio of the stability constants of the complexes formed is about 10 4 , 2-methyl-8-hydroxyquinoline and Fe 2+ The stability constant of the complex formed and the stability constant of the complex with Mn 2+ The ratio of the stability constants of the complexes formed is about 10 3 Both ethylenediamine and 2-methyl-8-hydroxyquinoline can achieve good co-precipitation effects of manganese ions and ferrous ions.

[0022] In some embodiments, during the step of mixing the ferromanganese solution, the complexing solution, and the base solution and subjecting the mixture to a first reaction treatment to obtain a first precursor, a protective gas is continuously introduced into the base solution.

[0023] In this embodiment, because manganese is easily oxidized under alkaline conditions, it disproportionates into tiny particles of manganese dioxide, making it difficult for manganese and iron to coprecipitate. During the first reaction treatment step, continuously introducing a protective gas into the base liquid can reduce manganese oxidation and achieve a better coprecipitation effect.

[0024] In some embodiments, the step of mixing the ferromanganese solution, the complexing solution, and the base solution and subjecting the mixture to a first reaction treatment to obtain a first precursor comprises:

[0025] The ferromanganese solution, the complexing solution and the base solution are mixed and subjected to heat preservation treatment to obtain a slurry, wherein the slurry includes the first precursor;

[0026] The slurry is subjected to solid-liquid separation to obtain a solid material;

[0027] The solid material is purified to obtain the first precursor.

[0028] In this embodiment, the first reaction process to obtain the first precursor is as follows: the ferromanganese solution, the complexing solution, and the base solution are first mixed and heat-insulated to obtain a slurry containing the first precursor, which can convert amorphous ferromanganese hydroxide into crystalline ferromanganese hydroxide. The crystalline ferromanganese hydroxide then induces the growth of manganese ions and ferrous ions in the solution on crystal nuclei, thereby preventing excessive amorphous ferromanganese hydroxide. In other words, the first precursor can be purified.

[0029] In some embodiments, the ferromanganese solution, the complexing solution, and the base solution are mixed at 60° C. to 90° C. for 1 h to 3 h.

[0030] In this embodiment, within the above-mentioned mixing temperature and time range, the slurry crystal form can be transformed to obtain a first precursor with better stability. When the mixing temperature is too low, the required reaction time is relatively long. When the mixing temperature is too high, the upper limit of the supersaturation of the reaction system will decrease, and the nucleation rate of the crystal nucleus will easily be too fast, which will lead to inconsistent product morphology. Within the above-mentioned mixing time range, the morphology of the precursor can be regulated by the mixing time. When the mixing time is short, the nucleation rate is too fast, and the intermediate product during the second reaction treatment, the second precursor, basic manganese iron oxide, will have a spherical morphology; when the mixing treatment time is long, the nucleation rate is slow, and the second precursor basic manganese iron oxide has a more regular morphology and is flaky, which is more conducive to the formation of manganese iron oxide with improved purity, thereby obtaining a lithium manganese iron phosphate material with improved performance.

[0031] In some embodiments, the temperature of the heat preservation treatment of the slurry is 60°C~90°C.

[0032] In this embodiment, within the temperature range of the slurry insulation treatment, the slurry crystal form can be transformed to obtain a first precursor with better stability. If the temperature of the slurry insulation treatment is too low, the insulation treatment time is too long, affecting the product production efficiency. If the temperature of the slurry insulation treatment is too high, the upper limit of the supersaturation of the reaction system will decrease, and the nucleation rate of the crystal nucleus will be too fast, which will lead to inconsistent product morphology and affect the stability of the product.

[0033] In some embodiments, the slurry is kept warm for 1 hour to 3 hours.

[0034] In this embodiment, within the above-mentioned slurry heat treatment time range, the morphology of the precursor can be controlled by the heat treatment time of the slurry. If the heat treatment time is short, the crystal transformation of the precursor is difficult to fully proceed, and the morphology of the second precursor basic manganese ferrooxide will have a spherical morphology. If the heat treatment time is long, the crystal transformation of the precursor is more complete, and the morphology of the second precursor basic manganese ferrooxide is more regular and flaky.

[0035] In some embodiments, the first precursor is subjected to a second reaction treatment to obtain the manganese iron oxide, comprising the following steps:

[0036] The first precursor is subjected to oxidative dehydration treatment to obtain a second precursor;

[0037] The second precursor is calcined to obtain the manganese iron oxide.

[0038] In this embodiment, the first precursor is subjected to oxidative dehydration, that is, oxidative drying of manganese ferrohydroxide to convert it into basic manganese ferrohydroxide to obtain the second precursor.

[0039] In some embodiments, the preparation of the ferromanganese solution comprises the following steps:

[0040] Dissolve soluble manganese salt in pure water to prepare a manganese source solution;

[0041] Dissolve soluble ferrous salt in pure water to prepare a ferrous source solution;

[0042] The manganese source solution and the ferrous source solution are mixed in a molar ratio of manganese element to iron element of (3-8): (2-7) to obtain the ferromanganese solution.

[0043] In some embodiments, the soluble manganese salt includes at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0044] In some embodiments, the soluble ferrous salt includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0045] In some embodiments, the concentration of the manganese source solution is 0.5 mol / L to 2 mol / L.

[0046] In this embodiment, if the concentration of the manganese source solution is too high, the manganese source solution is difficult to store and crystallization is likely to occur. If the concentration of the manganese source solution is too low, the amount of the first precursor and manganese iron oxide produced per volume is too small, which can easily increase the manufacturing cost.

[0047] In some embodiments, the concentration of the ferrous source solution is 0.5 mol / L to 2 mol / L.

[0048] In this embodiment, when the concentration of the ferrous source solution is too high, the ferrous source solution is difficult to store and is prone to crystallization. When the concentration of the ferrous source solution is too low, the amount of the first precursor and ferromanganese oxide produced under the same volume is too small, which can easily increase the manufacturing cost.

[0049] In a second aspect, an embodiment of the present application provides a manganese iron oxide, which is prepared by any of the above-mentioned methods for preparing manganese iron oxide.

[0050] In the technical solution of the embodiment of the present application, the ferromanganese oxide is prepared by any of the above-mentioned methods for preparing ferromanganese oxide, and the manganese element and the iron element in the ferromanganese oxide are uniformly mixed.

[0051] In a third aspect, an embodiment of the present application provides a lithium manganese iron phosphate material, which is prepared using raw materials including the above-mentioned manganese iron oxide.

[0052] In this embodiment, the lithium manganese iron phosphate material is prepared using raw materials including the above-mentioned manganese iron oxide, and can have good cycle performance and high energy density.

[0053] In a fourth aspect, an embodiment of the present application provides a positive electrode plate, comprising a current collector and an active layer located on the surface of the current collector, wherein the active layer comprises the above-mentioned lithium manganese iron phosphate material.

[0054] In this embodiment, the active layer of the positive electrode plate includes the above-mentioned lithium manganese iron phosphate material, and thus has good electrochemical performance.

[0055] In a fifth aspect, an embodiment of the present application provides a secondary battery comprising the above-mentioned positive electrode plate.

[0056] In this embodiment, the secondary battery includes a positive electrode plate, and the active layer of the positive electrode plate includes the above-mentioned lithium iron manganese phosphate material. Therefore, when the positive electrode plate is applied to the secondary battery, the resulting secondary battery also has comprehensively improved electrochemical performance, so that it can be well applied in multiple usage scenarios.

[0057] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0059] Figure 1 A schematic flow chart of a method for preparing ferromanganese oxide provided in an embodiment of the present application;

[0060] Figure 2 The X-ray diffraction (XRD) results of the manganese iron oxides prepared in Examples 1 to 5 of the present application are shown;

[0061] Figure 3 This is the XRD result of the manganese iron oxide prepared in Comparative Example 1 of this application;

[0062] Figure 4 This is the XRD result of the manganese iron oxide prepared in Comparative Example 2 of this application;

[0063] Figure 5 This is a scanning electron microscope (SEM) image of the manganese iron oxide prepared in Example 1 of the present application;

[0064] Figure 6 This is the SEM result of the second precursor in Example 1 of the present application;

[0065] Figure 7 This is the SEM result of the second precursor in Example 4 of the present application;

[0066] Figure 8 This is the SEM result of manganese iron oxide in Comparative Example 1 of this application;

[0067] Figure 9 This is the SEM result of basic manganese iron oxide in Comparative Example 2 of this application. DETAILED DESCRIPTION

[0068] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0069] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0070] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0071] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0072] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0073] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0074] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0075] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0076] The current process flow for preparing lithium manganese iron phosphate mainly includes the manganese iron oxide route. Among them, the preparation methods of manganese iron oxide in the manganese iron oxide route include solid-phase method and liquid-phase co-precipitation method. In the liquid-phase co-precipitation method, a soluble manganese source and a ferrous source are usually dissolved as raw materials, and then the ferrous ions and manganese ions are co-precipitated by a complexing agent, and the precipitate is then calcined to obtain manganese iron oxide. In the traditional liquid-phase co-precipitation method, the co-precipitation effect of manganese and iron is poor, and the prepared manganese iron oxide has problems such as being easily mixed with impurities.

[0077] In order to solve the technical problems that the co-precipitation effect of manganese and iron is poor and the prepared manganese iron oxide is easily mixed with impurities, the present application provides a manganese iron oxide and a preparation method thereof, a lithium manganese iron phosphate material, a positive electrode sheet, a secondary battery and an electric device, wherein in the preparation method of manganese iron oxide, due to the first complexing agent and Fe 2+ The stability constant of the complex formed and the complexing agent and Mn 2+ The ratio of the stability constants of the complexes formed is 10 3 ~10 5 , effectively making up for the nearly three orders of magnitude difference between the solubility product of Fe(OH)2 and the solubility product of Mn(OH)2, which can improve the co-precipitation effect of manganese and iron, thereby improving the product purity and other properties of manganese iron oxide, and thus the cycle performance and energy density performance of lithium manganese iron phosphate materials, positive electrode sheets and secondary batteries are also improved.

[0078] First, refer to Figure 1 As shown, the present invention provides a method for preparing manganese iron oxide, comprising the following steps:

[0079] S10: providing a manganese iron solution, a complexing solution and a base solution, wherein the pH value of the base solution is 11-12;

[0080] S20: mixing the ferromanganese solution, the complexing solution and the base solution, and performing a first reaction treatment to obtain a first precursor;

[0081] S30: The first precursor is subjected to a second reaction treatment to obtain manganese iron oxide;

[0082] Among them, the ferromanganese solution includes Fe 2+ and Mn 2+ ;

[0083] The complexing liquid includes a first complexing agent, the first complexing agent and Fe 2+ The stability constant of the complex formed and the complexing agent and Mn 2+ The ratio of the stability constants of the complexes formed is 10 3 ~10 5 .

[0084] In the technical solution of the embodiment of the present application, the ferromanganese solution, the complexing liquid and the base liquid are mixed, and during the first reaction treatment, the first complexing agent and the Fe 2+ The stability constant of the complex formed and the complexing agent and Mn 2+ The ratio of the stability constants of the complexes formed is 10 3 ~10 5 , effectively making up for the nearly 3 orders of magnitude difference between the solubility product of Fe(OH)2 and the solubility product of Mn(OH)2; at the same time, the pH value of the bottom liquid is 11~12. During the first reaction treatment, the manganese ions and ferrous ions in the solution can be controlled by the complexing agent, so that the iron and manganese elements are evenly mixed, thereby achieving a better co-precipitation effect of manganese ions and ferrous ions, and obtaining a first precursor with higher crystallization quality and less amorphous manganese ferrohydroxide impurities. It can be understood that the first precursor is a co-precipitation of manganese and ferrous hydroxide. The first precursor is then subjected to a second reaction treatment to obtain manganese iron oxide. The technical solution of the embodiment of the present application can improve the co-precipitation effect of manganese and iron, thereby improving the product purity and other properties of manganese iron oxide.

[0085] Optionally, the first complexing agent and Fe 2+ The stability constant of the complex formed and the first complexing agent with Mn 2+ The ratio of the stability constants of the complexes formed is 10 3 , 2×10 3 , 4×10 3 , 6×10 3 , 8×10 3 , 10 4 , 2×10 4 , 4×10 4 , 6×10 4 , 8×10 4 or 10 5 Alternatively, the first complexing agent and Fe 2+ The stability constant of the complex formed and the first complexing agent with Mn 2+ The ratio of the stability constants of the formed complexes may also be within the range between any two of the above ratios.

[0086] Optionally, the pH value of the base liquid is 11, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9 or 12, or the pH value of the base liquid may be within the range between any two of the above pH values. It is understood that the pH values ​​in this application are all measured at 25°C.

[0087] In some embodiments, the ferromanganese solution contains Mn 2+ and Fe 2+The total concentration is 0.5mol / L~2mol / L.

[0088] In this embodiment, Mn in the ferromanganese solution 2+ and Fe 2+ When the total concentration of Mn is too high, the ferromanganese solution is difficult to store and is prone to crystallization. 2+ and Fe 2+ When the total concentration of Mn is too low, the amount of the first precursor and ferromanganese oxide products under the same volume is too small, which may easily lead to an increase in manufacturing costs. 2+ and Fe 2+ The total concentration of Mn in the ferromanganese solution is 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.7mol / L, 1.8mol / L, 1.9mol / L or 2mol / L, or 2+ and Fe 2+ The total concentration may also be within the range between any two of the above concentrations.

[0089] In some embodiments, the ferromanganese solution contains Mn 2+ and Fe 2+ The molar ratio is (3~8): (2~7).

[0090] In this embodiment, Mn in the ferromanganese solution 2+ and Fe 2+ When the molar ratio of Mn is too high, the high proportion of manganese will affect the cycle performance of the subsequent prepared lithium manganese iron phosphate material. 2+ and Fe 2+ When the molar ratio of Mn is too low, it will affect the voltage platform and energy density of the subsequent prepared lithium manganese iron phosphate material. 2+ and Fe 2+ The molar ratio of Mn in the ferromanganese solution is 8:2, 8:3, 8:4, 8:5, 8:6, 8:7, 3:2, 3:2.5, 3:3, 3:3.5, 3:4, 3:4.5, 3:5, 3:5.5, 3:6, 3:6.5 or 3:7. 2+ and Fe 2+ The molar ratio can also be within the range between any two of the above molar ratios.

[0091] In some embodiments, the concentration of the first complexing agent in the complexing solution is 0.5 mol / L to 4 mol / L.

[0092] In this embodiment, within the concentration range of the first complexing agent in the complexing solution, a good coprecipitation effect of manganese ions and ferrous ions is achieved. Optionally, the concentration of the first complexing agent in the complexing solution is 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, or 4 mol / L. Alternatively, the concentration of the first complexing agent in the complexing solution may be within a range between any two of the above concentrations.

[0093] In some embodiments, the base solution includes a second complexing agent; the concentration of the second complexing agent in the base solution is 0.5 mol / L to 2 mol / L. Alternatively, the concentration of the second complexing agent can be 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, or any concentration value between 0.5 mol / L and 2 mol / L.

[0094] In this embodiment, by adding the second complexing agent in the base liquid, it is possible to prevent ferromanganese solution from adding rear manganese ion, ferrous ion and directly generating ferromanganese hydroxide with sodium hydroxide.After adding the second complexing agent in the base liquid, after ferromanganese solution adds the base liquid, complexing agent and manganese ion, ferrous ion first form a complex, and then along with the concentration of sodium hydroxide improves, manganese ion and ferrous ion are combined with hydroxide to generate ferromanganese hydroxide.When the concentration of the complexing agent in the base liquid is too low, ferromanganese solution is added to the base liquid, it is impossible to effectively complex manganese ion and ferrous ion, it is possible to directly generate ferromanganese hydroxide, there is a sequential precipitation order, it is difficult to achieve uniform coprecipitation effect.When the concentration of the complexing agent in the base liquid is too high, complexed iron ion is too much, causes manganese to precipitate first, is difficult to achieve uniform coprecipitation effect. Optionally, the concentration of the second complexing agent in the base solution is 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2 mol / L, or the concentration of the second complexing agent in the base solution may be within the range between any two of the above concentrations.

[0095] In some embodiments, the base liquid further comprises at least one of sodium hydroxide and potassium hydroxide to adjust the pH value of the base liquid to 11-12.

[0096] In some embodiments, the first complexing agent is selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

[0097] In some embodiments, the second complexing agent is selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

[0098] In this embodiment, ethylenediamine and Fe 2+ The stability constant of the complex formed and the stability constant of the complex with Mn 2+ The ratio of the stability constants of the complexes formed is about 10 4 , 2-methyl-8-hydroxyquinoline and Fe 2+ The stability constant of the complex formed and the stability constant of the complex with Mn 2+ The ratio of the stability constants of the complexes formed is about 10 3 Both ethylenediamine and 2-methyl-8-hydroxyquinoline can achieve good co-precipitation effects of manganese ions and ferrous ions.

[0099] In some embodiments, during the step of mixing the ferromanganese solution, the complexing solution and the base solution and subjecting the mixture to a first reaction treatment to obtain the first precursor, a protective gas is continuously introduced into the base solution.

[0100] In this embodiment, because manganese is easily oxidized under alkaline conditions, it disproportionates into tiny particles of manganese dioxide, making it difficult for manganese and iron to coprecipitate. During the first reaction treatment step, continuously introducing a protective gas into the base liquid can reduce manganese oxidation and achieve a better coprecipitation effect.

[0101] In some embodiments, the protective gas includes at least one of nitrogen, helium, and argon.

[0102] In some embodiments, the steps of mixing the ferromanganese solution, the complexing solution, and the base solution and subjecting the mixture to a first reaction treatment to obtain a first precursor include:

[0103] The ferromanganese solution, the complexing liquid and the base liquid are mixed and subjected to heat preservation treatment to obtain a slurry, which includes a first precursor;

[0104] The slurry is subjected to solid-liquid separation to obtain solid material;

[0105] The solid material is purified to obtain a first precursor.

[0106] In this embodiment, the first reaction process to obtain the first precursor is as follows: the ferromanganese solution, the complexing solution, and the base solution are first mixed and heat-insulated. The mixing and heat-insulating process to obtain a slurry comprising the first precursor converts amorphous ferromanganese hydroxide into crystalline ferromanganese hydroxide. The crystalline ferromanganese hydroxide then induces the growth of manganese and ferrous ions in the solution on crystal nuclei, thereby preventing excessive amorphous ferromanganese hydroxide.

[0107] In some embodiments, the ferromanganese solution, the complexing liquid, and the base solution are mixed at 60°C to 90°C for 1 hour to 3 hours. Alternatively, the mixing time of the ferromanganese solution, the complexing liquid, and the base solution can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, or any time between 1 hour and 3 hours; the mixing of the ferromanganese solution, the complexing liquid, and the base solution can be carried out at 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, or any temperature between 60°C and 90°C.

[0108] In this embodiment, within the above-mentioned mixing temperature and time range, the slurry crystal form can be transformed to obtain a first precursor with better stability. When the mixing temperature is too low, the required reaction time is relatively long. When the mixing temperature is too high, the upper limit of the supersaturation of the reaction system will decrease, and the nucleation rate of the crystal nucleus will easily be too fast, which will lead to inconsistent product morphology. Within the above-mentioned mixing time range, the morphology of the precursor can be regulated by the mixing time. When the mixing time is short, the nucleation rate is too fast, and the intermediate product during the second reaction treatment, the second precursor, basic manganese iron oxide, will have a spherical morphology; when the mixing treatment time is long, the nucleation rate is slow, and the second precursor basic manganese iron oxide has a more regular morphology and is flaky, which is more conducive to the formation of manganese iron oxide with improved purity, thereby obtaining a lithium manganese iron phosphate material with improved performance.

[0109] For example, taking ethylenediamine as the complexing agent, during the mixing process, the ferrous ions and manganese ions are first complexed and then precipitated. The specific chemical equation of the reaction is as follows:

[0110] Fe 2+ +C2H8N2=[Fe(C2H8N2)] 2+

[0111] [Fe(C2H8N2)] 2+ +2OH - =Fe(OH)2

[0112] Mn 2+ +C2H8N2=[Mn(C2H8N2)] 2+

[0113] [Mn(C2H8N2)] 2+ +2OH - =Mn(OH)2

[0114] In some embodiments, during the steps of mixing the ferromanganese solution, the complexing solution, and the base solution and performing the heat preservation treatment, a pH adjuster is used to maintain the pH value of the slurry including the first precursor at 11-12.

[0115] In this embodiment, a pH adjuster is used during the mixing and heat preservation process to maintain the pH value of the slurry including the first precursor at 11-12, which can provide sufficient hydroxide, thereby achieving a good co-precipitation effect of manganese ions and ferrous ions. It is understood that the ferromanganese solution, the complexing solution, and the pH adjuster are added dropwise to the base solution at the same time.

[0116] In some embodiments, the steps of mixing the ferromanganese solution, the complexing solution and the base solution and subjecting the mixture to heat preservation to obtain the slurry include:

[0117] Heat the base liquid to 60℃~90℃;

[0118] Simultaneously, the ferromanganese solution, the complexing liquid and the pH regulator are added dropwise to the heated base liquid to obtain a slurry. The addition time is 1 h to 3 h, and the pH value of the slurry is maintained at 11 to 12.

[0119] After the dropwise addition is completed, the slurry is kept at 60°C to 90°C for 1 hour to 3 hours.

[0120] In some embodiments, the pH adjuster includes at least one of sodium hydroxide and potassium hydroxide.

[0121] In some embodiments, the temperature of the slurry insulation treatment is 60°C to 90°C.

[0122] In this embodiment, within the temperature range of the heat preservation treatment of the above-mentioned slurry, the crystal form of the slurry can be transformed to obtain a first precursor with better stability. When the temperature of the heat preservation treatment of the slurry is too low, the time required for heat preservation treatment is relatively long, which affects the production efficiency of the product. When the temperature of the heat preservation treatment of the slurry is too high, the upper limit of the supersaturation of the reaction system will decrease, and the nucleation rate of the crystal nucleus is likely to be too fast, which will lead to inconsistent product morphology and affect the stability of the product. Optionally, the temperature of the heat preservation treatment of the slurry is 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C or 90°C, or the temperature of the heat preservation treatment of the slurry may also be within the range between any two of the above temperatures.

[0123] In some embodiments, the slurry is kept warm for 1 hour to 3 hours.

[0124] In this embodiment, within the time range of the heat preservation treatment of the above-mentioned slurry, the morphology of the precursor can be regulated by the heat preservation time. When the time is short, the nucleation rate is too fast, and the second precursor basic manganese iron oxide morphology will have a spherical morphology. When the time is long, the nucleation rate is slow, and the second precursor basic manganese iron oxide morphology is more regular and flaky. Optionally, the heat preservation time is 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h, or the heat preservation time of the slurry can also be within the range between any two of the above times.

[0125] In some embodiments, the step of purifying the solid material to obtain the first precursor includes: washing the solid material with water until the conductivity of the washing water sampled after washing the solid material is less than or equal to 270 us / cm, thereby obtaining the first precursor.

[0126] Optionally, the conductivity of the cleaning water sampled after cleaning the solid material may be less than or equal to 250 us / cm, 252 us / cm, 254 us / cm, 256 us / cm, 258 us / cm, 260 us / cm, 262 us / cm, 264 us / cm, 266 us / cm, 268 us / cm or 270 us / cm.

[0127] In some embodiments, the first precursor is subjected to a second reaction treatment to obtain manganese iron oxide, comprising the following steps:

[0128] The first precursor is subjected to oxidative dehydration treatment to obtain a second precursor;

[0129] The second precursor is calcined to obtain manganese iron oxide.

[0130] In this embodiment, the first precursor is subjected to oxidative dehydration, that is, oxidative drying of manganese ferrohydroxide to convert it into basic manganese ferrohydroxide to obtain the second precursor.

[0131] In some embodiments, the temperature of the oxidative dehydration treatment is 90°C to 99°C.

[0132] Optionally, the temperature of the oxidative dehydration treatment is 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C or 99°C, or, the temperature of the oxidative dehydration treatment may be within the range between any two of the above temperatures.

[0133] In some embodiments, the oxidative dehydration treatment time is 6 hours to 12 hours.

[0134] Optionally, the time for the oxidative dehydration treatment is 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 11 h or 12 h, or the time for the oxidative dehydration treatment may also be within the range between any two of the above times.

[0135] In some embodiments, the oxidative dehydration treatment is performed under an air atmosphere.

[0136] In some embodiments, the calcination temperature is 700° C. to 850° C.

[0137] Optionally, the calcination temperature of the calcination treatment is 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C or 850°C, or the calcination temperature can also be within the range between any two of the above temperatures.

[0138] In some embodiments, the calcination time is 2 hours to 6 hours.

[0139] Optionally, the calcination time of the calcination treatment is 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, or the calcination time may also be within the range between any two of the above times.

[0140] In some embodiments, the calcination process is performed under an air atmosphere.

[0141] In some embodiments, after the second precursor is calcined, the resulting product is cooled to 25° C. to 50° C. before being discharged.

[0142] Optionally, after the second precursor is calcined, the resulting product is cooled to 25°C, 30°C, 35°C, 40°C, 45°C or 50°C before being discharged. Alternatively, the discharge temperature may be within the range between any two of the above temperatures.

[0143] In some embodiments, the preparation of the ferromanganese solution comprises the following steps:

[0144] Dissolve soluble manganese salt in pure water to prepare a manganese source solution;

[0145] Dissolve soluble ferrous salt in pure water to prepare a ferrous source solution;

[0146] The manganese source solution and the ferrous source solution are mixed in a molar ratio of manganese element to iron element of (3-8): (2-7) to obtain a manganese-ferromanganese solution.

[0147] In some embodiments, the soluble manganese salt includes at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0148] In some embodiments, the soluble ferrous salt includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0149] In some embodiments, the concentration of the manganese source solution is 0.5 mol / L to 2 mol / L.

[0150] In this embodiment, when the concentration of the manganese source solution is too high, the manganese source solution is difficult to store and is prone to crystallization. When the concentration of the manganese source solution is too low, the amount of the first precursor and manganese iron oxide produced under the same volume is too small, which can easily lead to increased manufacturing costs. Optionally, the concentration of the manganese source solution is 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2 mol / L, or the concentration of the manganese source solution can also be within the range between any two of the above concentrations.

[0151] In some embodiments, the concentration of the ferrous source solution is 0.5 mol / L to 2 mol / L.

[0152] In this embodiment, when the concentration of ferrous source solution is too high, the preservation of ferrous source solution is difficult and crystallization is easily produced. When the concentration of ferrous source solution is too low, the product amount of the first precursor and ferromanganese oxide under the same volume is too small, which easily causes the manufacturing cost to increase. Alternatively, the concentration of ferrous source solution is 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 1mol / L, 1.2mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.7mol / L, 1.8mol / L, 1.9mol / L or 2mol / L, or, the concentration of manganese source solution can also be in the range between any two of the above concentrations.

[0153] In a second aspect, embodiments of the present application provide manganese iron oxide, which is prepared by any of the above-mentioned methods for preparing manganese iron oxide.

[0154] In the technical solution of the embodiment of the present application, the ferromanganese oxide is prepared by any of the above-mentioned methods for preparing ferromanganese oxide, and the manganese element and the iron element in the ferromanganese oxide are uniformly mixed.

[0155] In a third aspect, an embodiment of the present application provides a lithium manganese iron phosphate material, which is prepared using raw materials including the above-mentioned manganese iron oxide.

[0156] In this embodiment, the lithium manganese iron phosphate material is prepared using raw materials including the above-mentioned manganese iron oxide, and can have good cycle performance and high energy density.

[0157] In some embodiments, the preparation method of lithium manganese iron phosphate material includes the following steps:

[0158] The phosphorus source, lithium source, carbon source and the above-mentioned manganese iron oxide are mixed and ground to obtain a mixed material;

[0159] The mixed material is spray-dried to obtain a lithium manganese iron phosphate precursor;

[0160] The lithium iron manganese phosphate precursor is calcined in a nitrogen atmosphere to obtain the lithium iron manganese phosphate material.

[0161] In this embodiment, the lithium iron manganese phosphate material is prepared by using the above-mentioned manganese iron oxide, phosphorus source, lithium source and carbon source, and the lithium iron manganese phosphate material with good cycle performance and high energy density can be prepared.

[0162] In some embodiments, the calcination temperature of the lithium manganese iron phosphate precursor in a nitrogen atmosphere is 650°C to 750°C, for example, it can be 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, or any temperature value between 650°C and 750°C.

[0163] In some embodiments, the phosphorus source includes at least one of ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium monohydrogen phosphate.

[0164] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium acetate.

[0165] In some embodiments, the carbon source comprises at least one of glucose, graphite, and sucrose.

[0166] In this embodiment, the phosphorus source, lithium source, and carbon source will not introduce impurity elements, which is conducive to the preparation of lithium manganese iron phosphate material with higher purity.

[0167] In a fourth aspect, an embodiment of the present application provides a positive electrode plate, comprising a current collector and an active layer located on the surface of the current collector, wherein the active layer comprises the above-mentioned lithium manganese iron phosphate material.

[0168] In this embodiment, the active layer of the positive electrode plate includes the above-mentioned lithium manganese iron phosphate material, and thus has good electrochemical performance.

[0169] In a fifth aspect, an embodiment of the present application provides a secondary battery comprising the above-mentioned positive electrode plate.

[0170] In this embodiment, the secondary battery includes a positive electrode plate, and the active layer of the positive electrode plate includes the above-mentioned lithium iron manganese phosphate material. Therefore, when the positive electrode plate is applied to the secondary battery, the resulting secondary battery also has comprehensively improved electrochemical performance, so that it can be well applied in multiple usage scenarios.

[0171] In a sixth aspect, an embodiment of the present application provides an electrical device comprising the above-mentioned secondary battery.

[0172] The electrical devices provided in the embodiments of the present application may be, but are not limited to, mobile phones, tablets, laptop computers, electric toys, electric tools, battery-powered vehicles, electric cars, ships, spacecraft, etc. The electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0173] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0174] 1. Preparation method

[0175] Example 1

[0176] Preparation method of manganese iron oxide:

[0177] 1. Raw material preparation:

[0178] (1) Preparation of manganese source solution: Prepare a 1.5 mol / L manganese sulfate solution by weighing manganese sulfate monohydrate and pure water and stirring to dissolve;

[0179] (2) Preparation of ferrous source solution: Prepare ferrous sulfate solution with a concentration of 1.5 mol / L by weighing ferrous sulfate heptahydrate and pure water and stirring to dissolve;

[0180] (3) Preparation of complexing solution: Prepare a first complexing agent solution with a concentration of 2 mol / L based on the total amount of synthesis, weigh ethylenediamine (first complexing agent) and pure water, and stir to dissolve;

[0181] (4) Preparation of sodium hydroxide solution: Prepare a sodium hydroxide solution with a concentration of 3 mol / L by weighing sodium hydroxide and pure water and stirring;

[0182] (5) Preparation of ferromanganese solution: According to Mn 2+ and Fe 2+ The molar ratio of Mn is 6:4. 2+ and Fe 2+ The total concentration is prepared to be 1 mol / L, and manganese sulfate solution and ferrous sulfate solution are weighed and stirred to mix.

[0183] 2. Synthesis:

[0184] (1) Preparation of base solution: pure water, second complexing agent, and sodium hydroxide solution were prepared into a base solution with a second complexing agent concentration of 1 mol / L and a pH value of 11.5. The second complexing agent was ethylenediamine.

[0185] (2) High-temperature hydrolysis synthesis: nitrogen was introduced into the reaction cauldron, and after the bottom liquid was heated to 80°C, ferromanganese solution, complex solution, and sodium hydroxide solution were simultaneously added to the bottom liquid using three tubes. The addition time of ferromanganese solution and complex solution was controlled to be 2h. Sodium hydroxide solution was used to adjust the synthesis pH value to maintain at 11-12 until the addition was completed. The temperature was kept for 1h to obtain the first precursor ferromanganese hydroxide slurry Mn. 0.6 Fe 0.4 (OH)2;

[0186] (3) Water washing: After the first precursor slurry is kept warm, the slurry is separated into solid and liquid and the solid material is washed with water until the end point conductivity is 260us / cm, and the first precursor manganese ferrohydroxide filter cake Mn is obtained. 0.6 Fe 0.4 (OH)2;

[0187] (4) Oxidation drying: The first precursor, ferromanganese hydroxide, was placed in an oven and oxidized and dried for 6 hours at 98°C in an air atmosphere to obtain the second precursor, basic ferromanganese oxide Mn 0.6 Fe 0.4 OOH;

[0188] (5) Calcination: The second precursor, basic manganese iron oxide, was calcined at 750°C in air atmosphere for 3 hours to obtain (Mn 0.6 Fe 0.4 )2O3.

[0189] Example 2

[0190] The preparation method of ferromanganese oxide in this embodiment is the same or similar to that in Example 1, with the only difference being that the first complexing agent and the second complexing agent in this embodiment are both 2-methyl-8-hydroxyquinoline. 2+ and Fe 2+ The molar ratio of calcined manganese iron oxide material is (Mn 0.7 Fe 0.3 )2O3.

[0191] Example 3

[0192] The preparation method of ferromanganese oxide in this embodiment is the same or similar to that in Example 1, with the only difference being that in the step of preparing the complexing agent solution in this embodiment, both the first complexing agent and the second complexing agent are 2-methyl-8-hydroxyquinoline, the concentration of the first complexing agent is 4 mol / L, and the concentration of the second complexing agent is 1 mol / L. The concentration of the sodium hydroxide solution is 4 mol / L. In the step of preparing the ferromanganese solution, Mn 2+ and Fe 2+ The molar ratio of Mn is 3:7. 2+ and Fe 2+ The total concentration is 1.5 mol / L. The material obtained by calcination is MnFeO3.

[0193] Example 4

[0194] The preparation method of ferromanganese oxide in this embodiment is the same or similar to that in Example 3, with the only difference being that in the step of preparing the ferromanganese sulfate solution, the manganese to iron ratio is 5:5. The material obtained by calcination is MnFeO3.

[0195] Example 5

[0196] The preparation method of ferromanganese oxide in this embodiment is the same or similar to that in Example 1, with the only difference being that in this embodiment, the concentration of manganese sulfate solution in the preparation of manganese source solution is 1 mol / L, the concentration of ferrous sulfate solution in the preparation of ferrous source solution is 1 mol / L, the first complexing agent and the second complexing agent are both 2-methyl-8-hydroxyquinoline, and the concentration of sodium hydroxide solution is 2 mol / L. In the step of preparing ferromanganese solution, Mn 2+ and Fe 2+ The molar ratio of Mn is 5:5. 2+ and Fe 2+ The total concentration is 0.5 mol / L. The material obtained by calcination is MnFeO3.

[0197] Example 6

[0198] The preparation method of ferromanganese oxide in this embodiment is the same or similar to that in embodiment 1, the only difference is that in the step of preparing ferromanganese solution, Mn 2+ and Fe 2+ The molar ratio of 4:6. The manganese iron oxide material obtained by calcination is (Mn 0.4 Fe 0.6 )2O3.

[0199] Example 7

[0200] The preparation method of ferromanganese oxide in this embodiment is the same or similar to that in Example 1, except that the concentration of manganese chloride solution in the preparation of manganese source solution is 0.5 mol / L, the concentration of ferrous chloride solution in the preparation of ferrous source solution is 0.5 mol / L, the concentration of the first complexing agent in the complexing solution is 0.5 mol / L, and the concentration of Mn in the ferromanganese solution is 0.5 mol / L. 2+ and Fe 2+ The total concentration is 0.5 mol / L. The pH of the base solution is 11, and the concentration of the second complexing agent in the base solution is 0.5 mol / L.

[0201] Example 8

[0202] The preparation method of ferromanganese oxide in this embodiment is the same or similar to that in Example 1, except that the concentration of manganese nitrate solution in the preparation of manganese source solution is 2 mol / L, the concentration of ferrous nitrate solution in the preparation of ferrous source solution is 2 mol / L, the concentration of the first complexing agent in the complexing solution is 4 mol / L, and the concentration of Mn in the ferromanganese solution is 2 mol / L. 2+ and Fe 2+ The total concentration of the base solution is 2 mol / L. The pH of the base solution is 12, and the concentration of the second complexing agent in the base solution is 2 mol / L.

[0203] Example 9

[0204] The preparation method of manganese iron oxide in this embodiment is the same or similar to that in Example 1, with the only difference being that in the high-temperature hydrolysis synthesis, the base liquid is heated to 60° C., the addition time is 3 h, and the temperature is kept for 3 h.

[0205] Example 10

[0206] The preparation method of manganese iron oxide in this embodiment is the same or similar to that in Example 1, with the only difference being that in the high-temperature hydrolysis synthesis, the base liquid is heated to 90° C., the addition time is 1 hour, and the temperature is kept at this temperature for 2 hours.

[0207] Example 11

[0208] Preparation method of lithium manganese iron phosphate material:

[0209] (1) The manganese iron oxide prepared in Example 1, ammonium dihydrogen phosphate, lithium carbonate and glucose were mixed in a molar ratio of 1:1:1:0.05, and ground and mixed until uniform;

[0210] (2) spray drying the mixed materials to remove moisture and obtain a lithium manganese iron phosphate precursor;

[0211] (3) The lithium manganese iron phosphate precursor is calcined in a nitrogen atmosphere to obtain the lithium manganese iron phosphate material.

[0212] Example 12

[0213] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Example 2 is used as a raw material in this embodiment.

[0214] Example 13

[0215] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Example 3 is used as a raw material in this embodiment.

[0216] Example 14

[0217] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Example 4 is used as a raw material in this embodiment.

[0218] Example 15

[0219] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Example 5 is used as a raw material in this embodiment.

[0220] Example 16

[0221] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Example 6 is used as a raw material in this embodiment.

[0222] Example 17

[0223] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Example 7 is used as a raw material in this embodiment.

[0224] Example 18

[0225] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Example 8 is used as a raw material in this embodiment.

[0226] Example 19

[0227] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Example 9 is used as a raw material in this embodiment.

[0228] Example 20

[0229] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Example 10 is used as a raw material in this embodiment.

[0230] Comparative Example 1

[0231] 1. Raw material preparation:

[0232] (1) Preparation of manganese solution: Prepare a 1 mol / L manganese sulfate solution by weighing manganese sulfate monohydrate and pure water and stirring to dissolve;

[0233] (2) Preparation of ferrous solution: Prepare ferrous sulfate solution with a concentration of 1 mol / L by weighing ferrous sulfate heptahydrate and pure water and stirring to dissolve;

[0234] (3) Preparation of sodium hydroxide solution: Prepare a sodium hydroxide solution with a concentration of 2 mol / L by weighing sodium hydroxide and pure water and stirring;

[0235] (4) Preparation of ferromanganese solution: According to Mn 2+ and Fe 2+ The molar ratio of Mn is 5:5. 2+ and Fe 2+ The total concentration is prepared to 0.5 mol / L, and manganese sulfate solution and ferrous sulfate solution are weighed and stirred to mix.

[0236] 2. Synthesis:

[0237] (1) Preparation of base solution: Prepare a base solution with a pH of 11.5 by taking pure water and sodium hydroxide solution;

[0238] (2) High-temperature hydrolysis synthesis: After heating the base liquid to 60°C, use a double-tube dropper to simultaneously add ferromanganese solution and sodium hydroxide solution to the base liquid. The dropping time of ferromanganese solution is controlled for 2 hours. Sodium hydroxide solution is used to adjust the synthesis pH value to maintain at 11-12 until the dropping is completed. Keep warm for 1 hour to obtain the first precursor slurry;

[0239] (3) Water washing: After the first precursor slurry is kept warm, it is washed with water until the end conductivity is 260 μs / cm to obtain the first precursor filter cake;

[0240] (4) Drying and calcining: The first precursor filter cake was placed in an oven, oxidized and dried at 98°C for 6 hours, and then calcined at 750°C for 3 hours to obtain manganese iron oxide MnFeO3.

[0241] Comparative Example 2

[0242] 1. Raw material preparation:

[0243] (1) Preparation of manganese solution: Prepare a 1 mol / L manganese sulfate solution by weighing manganese sulfate monohydrate and pure water and stirring to dissolve;

[0244] (2) Preparation of ferrous solution: Prepare ferrous sulfate solution with a concentration of 1 mol / L by weighing ferrous sulfate heptahydrate and pure water and stirring to dissolve;

[0245] (3) Preparation of sodium hydroxide solution: Prepare a sodium hydroxide solution with a concentration of 2 mol / L by weighing sodium hydroxide and pure water and stirring;

[0246] (4) Preparation of ferromanganese solution: According to Mn 2+ and Fe 2+ The molar ratio of Mn is 6:4. 2+ and Fe 2+ The total concentration is 1 mol / L, and manganese sulfate solution and ferrous sulfate solution are weighed and stirred;

[0247] (5) Preparation of complexing solution: Prepare ammonia water with a concentration of 1 mol / L. Weigh ammonia water and pure water and stir to mix.

[0248] 2. Synthesis:

[0249] (1) Preparation of base solution: pure water, complexing agent, and sodium hydroxide solution are prepared into a base solution with a complexing agent concentration of 1 mol / L and a pH value of 11.5;

[0250] (2) High-temperature hydrolysis synthesis: nitrogen was introduced into the reaction cauldron, and after the bottom liquid was heated to 90°C, ferromanganese solution, ammonia water, and sodium hydroxide solution were added to the bottom liquid simultaneously using three tubes. The addition time of ferromanganese solution and ammonia water was controlled to be 30 min. Sodium hydroxide solution was used to adjust the synthesis pH value to maintain at 11-12 until the addition was completed. The mixture was kept warm for 1 h to obtain a product with Mn 0.6 Fe 0.4 A first precursor manganese ferrohydroxide slurry of (OH)2;

[0251] (3) Water washing: After the first precursor slurry is kept warm, it is washed with water until the end conductivity is 260us / cm, and a slurry with Mn 0.6 Fe 0.4 a filter cake of ferromanganese hydroxide, the first precursor of (OH)2;

[0252] (4) Oxidative drying: The first precursor, ferromanganese hydroxide, was placed in an oven and oxidatively dried at 98°C in an air atmosphere for 6 hours to obtain the second precursor, basic ferromanganese oxide Mn 0.6 Fe 0.4 OOH;

[0253] (5) Calcination: The second precursor, basic manganese iron oxide, was calcined at 750°C in air atmosphere for 3 hours to obtain (Mn 0.6 Fe 0.4 )2O3.

[0254] Comparative Example 3

[0255] The preparation method of the lithium manganese iron phosphate material in this comparative example is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Comparative Example 1 is used as a raw material in this example.

[0256] Comparative Example 4

[0257] The preparation method of the lithium manganese iron phosphate material in this embodiment is the same as or similar to that in Example 11, the only difference being that the manganese iron oxide prepared in Comparative Example 2 is used as a raw material in this embodiment.

[0258] 2. Test Method

[0259] 1. In manganese iron oxide, the contents of manganese and iron are detected by redox titration, and other impurity elements are detected by inductively coupled plasma optical emission spectrometry.

[0260] 2. Property test of lithium manganese iron phosphate material

[0261] The compaction density of lithium manganese iron phosphate material is tested by tablet pressing method using a compaction density meter with a test pressure of 3T and a pressing time of 30s.

[0262] The test methods for charge specific capacity, discharge specific capacity and coulombic efficiency are as follows:

[0263] The lithium manganese iron phosphate materials prepared in Examples 11 to 20 and Comparative Examples 3 to 4 were mixed with conductive carbon black and PVDF binder in a mass ratio of 90:5:5, and coated on a 12 μm thick aluminum foil. The electrode was then placed in an oven at 110°C and dried for 10 hours. The dried electrode was punched into positive electrode discs with a diameter of 15 mm and pressed to a density of 1.8 g / cm 3 Roller pressing was performed, with a 16 mm diameter lithium sheet as the counter electrode and the electrolyte being 1 mol / L LiPF6 dissolved in EC:EMC:DEC with a volume ratio of 1:1:1. The battery was assembled in an LG2400 / 1000TS glove box produced by Weige Gas Purification Technology (Suzhou) Co., Ltd. to obtain a button half-cell, which was then subjected to rate performance testing.

[0264] The battery performance test system (model: CT3002A) of Wuhan Blue Electric Electronic Technology Co., Ltd. was used for testing. The test temperature was 25°C, the voltage range was 2V~3.75V, and the test rate was 0.1C.

[0265] 3. Analysis of test results of various embodiments and comparative examples

[0266] The contents of manganese, iron and other impurity elements in the ferromanganese oxides prepared in Examples 1 to 10 and Comparative Examples 1 to 2 are shown in Tables 1 and 2 below:

[0267] Table 1

[0268]

[0269] Table 2

[0270]

[0271] Reference Figure 2 As shown, Figure 2 The XRD patterns of the manganese iron oxides prepared in Examples 1 to 5 of the present application are shown. It can be seen that there are no impurity peaks of other phases in the test results of each embodiment. That is, by using the complexing agent in the present application, a better co-precipitation effect of manganese and iron can be achieved, and homogeneous precipitation of manganese and iron can be achieved, thereby obtaining manganese iron oxides with higher purity. Further, referring to Figure 6 and 7 It can be seen that, compared with Example 1, the concentration of the ferromanganese sulfate solution in Example 4 is higher, the dropping time is shorter, and the nucleation rate is faster, resulting in a more irregular morphology of the second precursor and the presence of particles with non-flaky morphology.

[0272] Reference Figure 3 As shown, in Comparative Example 1, since the precipitation reaction is carried out directly in an air atmosphere without using a complexing agent, the divalent manganese and iron ions will be partially oxidized in the air. Under high temperature conditions, the generated manganese ferrohydroxide will dehydrate to form a more stable manganese ferrite MnFe2O4, which is different from the product manganese ferrohydroxide generated under nitrogen protection; at the same time, since no complexing agent is used and only hydroxide is precipitated, the generated manganese ferrooxide has a clear manganese tetraoxide phase, indicating that the manganese ions and iron ions are heterogeneously precipitated, and the purity of the obtained manganese ferrooxide is low. Figure 8 As shown, in Comparative Example 1, since the precipitation reaction is directly carried out in an air atmosphere without using a complexing agent, and the precipitation is carried out only with hydroxide without using a complexing agent, the morphology of the obtained manganese iron oxide is irregular.

[0273] In Comparative Example 2, manganese ferrohydroxide was prepared using ammonia water as a complexing agent under a nitrogen atmosphere. The difference in the complexing ability of ammonia water was too small to effectively complex. Iron ions were first precipitated to form ferrous hydroxide, which ultimately resulted in the presence of ferric oxide in the product after drying, calcining, and oxidation. Figure 4 、 Figure 9 As shown, Figure 4This is the XRD pattern of the manganese iron oxide prepared in Comparative Example 2 of this application. It can be seen that in Comparative Example 2, ammonia water is a complexing agent, which causes the iron ions to precipitate first to form ferrous hydroxide, and finally ferric oxide exists in the product after drying, calcining and oxidation.

[0274] As can be seen from the results in Table 1 and Table 2, in the ferromanganese oxides obtained in Examples 1 to 10, the mass concentrations of elements such as Cd, Co, Cr, Cu, K, Na, Ni, Pb, Ti, and Zn are all at the ppm level, indicating that the ferromanganese oxides obtained in Examples 1 to 10 have few impurities and high purity.

[0275] The test results of the lithium manganese iron phosphate prepared in Examples 11 to 20 and Comparative Examples 3 to 4 are shown in Table 3 below:

[0276] Table 3

[0277]

[0278] From the data in Table 3, it can be seen that in Comparative Example 1, since no complexing agent is used, manganese ions and iron ions are heterogeneously precipitated, and an obvious manganese tetraoxide phase is present in the prepared manganese iron oxide, which leads to the compaction density, charge specific capacity, discharge specific capacity and first coulombic efficiency of the lithium manganese iron phosphate prepared in Comparative Example 3 using the manganese iron oxide prepared in Comparative Example 1 as a raw material. They are all lower than the lithium manganese iron phosphate materials prepared by using the manganese iron oxide obtained in Examples 1 to 10 as raw materials; in Comparative Example 2, ammonia water is used as a complexing agent to prepare manganese iron hydroxide. Since iron ions are first precipitated to form ferrous hydroxide, ferric oxide is present in the prepared manganese iron oxide, which leads to the compaction density, charge specific capacity and discharge specific capacity of the lithium manganese iron phosphate prepared by using the manganese iron oxide prepared in Comparative Example 4 as a raw material. The obtained manganese iron phosphate materials are prepared by using the manganese iron oxide as a raw material.

[0279] Examples 11 to 20, respectively, used the manganese iron oxides prepared in Examples 1 to 10 as raw materials to prepare lithium manganese iron phosphate materials, achieving significantly higher compaction density, charge specific capacity, and discharge specific capacity than Comparative Examples 3 to 4. Compared with Comparative Examples 1 and 2, Examples 1 to 10 used the method for preparing manganese iron oxide in the examples of the present application to prepare manganese iron oxide, which enabled uniform mixing of the iron and manganese elements, thereby achieving a better co-precipitation effect of manganese and iron, and obtaining a co-precipitation of manganese and ferrous hydroxide with high crystalline quality and less amorphous manganese iron hydroxide impurities, thereby improving the product purity and other properties of the manganese iron oxide. This facilitates the use of the manganese iron oxide prepared in the examples of the present application as a raw material to prepare the lithium manganese iron phosphate material, thereby simultaneously having a higher compaction density, charge specific capacity, discharge specific capacity, and first coulombic efficiency.

[0280] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing ferromanganese oxide, characterized in that: The steps include: Providing a ferromanganese solution, a complexing solution, and a base solution, wherein the pH value of the base solution is 11 to 12; The ferromanganese solution, the complexing solution and the base solution are mixed and subjected to a first reaction treatment to obtain a first precursor; The first precursor is subjected to a second reaction treatment to obtain the manganese iron oxide; Wherein, the ferromanganese solution includes Fe 2+ and Mn 2+ ; The complexing liquid includes a first complexing agent, the first complexing agent and Fe 2+ The stability constant of the complex formed and the complexing agent with Mn 2+ The ratio of the stability constants of the complexes formed is 10 3 ~10 5 ; The first complexing agent is selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

2. The method for preparing ferromanganese oxide according to claim 1, wherein The Mn in the ferromanganese solution 2+ and Fe 2+ The total concentration is 0.5 mol / L to 2 mol / L; and / or, The Mn in the ferromanganese solution 2+ and Fe 2+ The molar ratio is (3~8):(2~7).

3. The method for preparing ferromanganese oxide according to claim 1, wherein The concentration of the first complexing agent in the complexing solution is 0.5 mol / L to 4 mol / L; and / or, The base solution includes a second complexing agent; the concentration of the second complexing agent in the base solution is 0.5 mol / L to 2 mol / L; and / or, The second complexing agent is selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

4. The method for preparing ferromanganese oxide according to claim 1, wherein In the step of mixing the ferromanganese solution, the complexing solution and the base solution and subjecting the mixture to a first reaction treatment to obtain a first precursor, a protective gas is continuously introduced into the base solution; and / or, The step of mixing the ferromanganese solution, the complexing solution and the base solution and subjecting the mixture to a first reaction treatment to obtain a first precursor comprises: The ferromanganese solution, the complexing solution and the base solution are mixed and subjected to heat preservation treatment to obtain a slurry, wherein the slurry includes the first precursor; The slurry is subjected to solid-liquid separation to obtain a solid material; The solid material is purified to obtain the first precursor; and / or, The ferromanganese solution, the complexing solution and the base solution are mixed at 60° C. to 90° C. for 1 hour to 3 hours; and / or, The temperature of the heat preservation treatment of the slurry is 60°C to 90°C; and / or, The slurry is heat-insulated for 1 to 3 hours; and / or The first precursor is subjected to a second reaction treatment to obtain the manganese iron oxide, which comprises the following steps: The first precursor is subjected to oxidative dehydration treatment to obtain a second precursor; The second precursor is calcined to obtain the manganese iron oxide.

5. The method for preparing ferromanganese oxide according to claim 1, wherein: The preparation of the ferromanganese solution comprises the following steps: Dissolve soluble manganese salt in pure water to prepare a manganese source solution; Dissolve soluble ferrous salt in pure water to prepare a ferrous source solution; The manganese source solution and the ferrous source solution are mixed in a molar ratio of manganese element to iron element of (3-8): (2-7) to obtain the ferromanganese solution.

6. The method for preparing ferromanganese oxide according to claim 5, wherein: The soluble manganese salt includes at least one of manganese sulfate, manganese chloride and manganese nitrate; and / or, The soluble ferrous salt includes at least one of ferrous sulfate, ferrous chloride and ferrous nitrate; and / or, The concentration of the manganese source solution is 0.5 mol / L to 2 mol / L; and / or, The concentration of the ferrous source solution is 0.5 mol / L to 2 mol / L.

7. A manganese iron oxide, characterized in that The ferromanganese oxide is prepared by the method for preparing the ferromanganese oxide according to any one of claims 1 to 6.

8. A lithium manganese iron phosphate material, characterized in that: The method is prepared from raw materials comprising the manganese iron oxide according to claim 7.

9. A positive electrode plate, characterized in that: It comprises a current collector and an active layer located on the surface of the current collector, wherein the active layer comprises the lithium manganese iron phosphate material according to claim 8.

10. A secondary battery, characterized in that: Including the positive electrode sheet according to claim 9.

Images