Manganese iron oxide, preparation method therefor, and use thereof

Abstract

The present application belongs to the field of lithium-ion batteries and provides a manganese iron oxide, a preparation method therefor, and a use thereof. The preparation method for the manganese iron oxide comprises the following steps: providing a manganese iron solution, a complexing solution, and a base solution, the pH of the base solution being 11-12; mixing the manganese iron solution, the complexing solution, and the base solution, and performing a first reaction treatment to obtain a first precursor; and subjecting the first precursor to a second reaction treatment to obtain a manganese iron oxide. The manganese iron solution comprises Fe2+ and Mn2+. The complexing solution comprises a first complexing agent, and the ratio of a stability constant of a complex formed by the first complexing agent and the Fe2+ to a stability constant of a complex formed by the complexing agent and the Mn2+ is 103-105. The technical solution of the embodiments of the present application can improve the co-precipitation effect of manganese and iron, thereby improving properties such as the product purity of the manganese iron oxide.

Description

Manganese iron oxide, preparation method and application thereof TECHNICAL FIELD

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

[0002] Manganese iron lithium phosphate has attracted extensive attention in the field of lithium ion batteries due to its higher energy density than lithium iron phosphate. The current process flow for preparing manganese iron lithium phosphate mainly includes a manganese iron oxide route. In the manganese iron oxide route, the preparation method of manganese iron oxide includes a solid phase method and a liquid phase coprecipitation method. In the liquid phase coprecipitation method, a soluble manganese source and a ferrous source are usually used as raw materials to be dissolved, and then the ferrous ions and manganese ions are co-precipitated by a complexing agent, and the precipitate is calcined to obtain manganese iron oxide. In the traditional liquid phase coprecipitation method, the co-precipitation effect of manganese and iron is poor, and the prepared manganese iron oxide is prone to mix with impurities.

[0003] SUMMARY

[0004] In view of the technical problems in the background art, the present application provides a preparation method of manganese iron oxide, aiming to solve the technical problems that in the traditional liquid phase coprecipitation method, the co-precipitation effect of manganese and iron is poor, and the prepared manganese iron oxide is prone to mix with impurities.

[0005] In a first aspect, the embodiments of the present application provide a preparation method of manganese iron oxide, comprising the following steps:

[0006] providing a manganese iron solution, a complexing solution and a bottom solution, wherein the pH value of the bottom solution is 11-12;

[0007] mixing the manganese iron solution, the complexing solution and the bottom solution, and performing a first reaction treatment to obtain a first precursor;

[0008] performing a second reaction treatment on the first precursor to obtain the manganese iron oxide;

[0009] wherein the manganese iron solution comprises Fe 2+ and Mn 2+ ;

[0010] the complexing solution comprises a first complexing agent, and the ratio of the stability constant of the complex formed by the first complexing agent and Fe 2+ to the stability constant of the complex formed by the complexing agent and Mn 2+ is 10 3 -10 5 .

[0011] In the technical scheme of the embodiment, the manganese-iron solution, the complexing solution and the base solution are mixed, and in the first reaction process, the first complexing agent and Fe 2+ form a complex with a stability constant, and the first complexing agent and Mn 2+ form a complex with a stability constant, and the ratio of the stability constant of the complex formed by the first complexing agent and Fe 3 to the stability constant of the complex formed by the first complexing agent and Mn 5 is 10 2+ ~10 2+ , effectively compensating for the difference of nearly 3 orders of magnitude 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 base solution is 11~12, and in the first reaction process, the complexing agent can control the manganese ions and ferrous ions in the solution, so that the iron element and the manganese element are uniformly mixed, and then a better co-precipitation effect of manganese and iron is realized, and a first precursor with high crystallization quality and less mixed amorphous manganese-iron hydroxide impurities is obtained. It can be understood that the first precursor is a co-precipitate of manganese and ferrous hydroxide. The first precursor is further subjected to a second reaction process to obtain a manganese-iron oxide. The technical scheme of the embodiment can improve the co-precipitation effect of manganese and iron, thereby improving the product purity and other properties of the manganese-iron oxide.

[0012] In some embodiments, the total concentration of Mn 2+ and Fe 2+ in the manganese-iron solution is 0.5 mol / L~2 mol / L.

[0013] In this embodiment, when the total concentration of Mn 2+ and Fe 2+ in the manganese-iron solution is too high, the manganese-iron solution is difficult to store and is prone to crystallization. When the total concentration of Mn 2+ and Fe 2+ in the manganese-iron solution is too low, the product amount of the first precursor and the manganese-iron oxide under the same volume is too small, which is prone to increase the manufacturing cost.

[0014] In some embodiments, the molar ratio of Mn 2+ to Fe 2+ in the manganese-iron solution is (3~8):(2~7).

[0015] In this embodiment, when the molar ratio of Mn 2+ to Fe 2+ in the manganese-iron solution is too high, the high proportion of manganese will affect the cycle performance of the subsequently prepared lithium manganese iron phosphate material. When the molar ratio of Mn 2+ to Fe 2+ in the manganese-iron solution is too low, it will affect the voltage platform and energy density of the subsequently prepared lithium manganese iron phosphate material.

[0016] In some embodiments, the concentration of the first complexing agent in the complexing solution is 0.5 mol / L~4 mol / L.

[0017] In this embodiment, within the concentration range of the first complexing agent in the complexing solution, the co-precipitation effect of manganese ions and ferrous ions is better achieved.

[0018] In some embodiments, the first complexing agent is selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

[0019] In some embodiments, the base liquid includes a second complexing agent; the concentration of the second complexing agent in the base liquid is 0.5 mol / L to 2 mol / L.

[0020] In this embodiment, adding a second complexing agent to the base solution prevents manganese and ferrous ions from directly reacting with sodium hydroxide to form ferric manganese hydroxide after the ferric manganese solution is added. After adding the second complexing agent to the base solution, the complexing agent first forms a complex with the manganese and ferrous ions. Then, as the concentration of sodium hydroxide increases, the manganese and ferrous ions combine with hydroxide ions to form ferric manganese hydroxide. If the concentration of the complexing agent in the base solution is too low, adding the ferric manganese solution will not effectively complex the manganese and ferrous ions, leading to the direct formation of ferric manganese hydroxide, resulting in a sequential precipitation and making it difficult to achieve a uniform co-precipitation effect. If the concentration of the complexing agent in the base solution is too high, too many ferric ions are complexed, causing manganese to precipitate first, making it difficult to achieve a uniform co-precipitation effect.

[0021] In some embodiments, the second complexing agent is selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

[0022] In this embodiment, ethylenediamine and Fe 2+ The stability constant of the formed complex and its relationship with Mn 2+ The ratio of the stability constants of the formed complexes is approximately 10. 4 2-Methyl-8-hydroxyquinoline and Fe 2+ The stability constant of the formed complex and its relationship with Mn 2+ The ratio of the stability constants of the formed complexes is approximately 10. 3 Both ethylenediamine and 2-methyl-8-hydroxyquinoline can achieve good co-precipitation effects of manganese ions and ferrous ions.

[0023] In some embodiments, during the step of mixing the manganese-iron solution, the complexing liquid, and the base liquid, and then performing a first reaction treatment to obtain a first precursor, a protective gas is continuously introduced into the base liquid.

[0024] In this embodiment, manganese is easily oxidized under alkaline conditions, and after oxidation, it disproportionates into tiny manganese dioxide particles, making it difficult for manganese and iron to co-precipitate. In the first reaction treatment step, a protective gas is continuously introduced into the bottom liquid to reduce manganese oxidation and achieve a better co-precipitation effect.

[0025] In some embodiments, the step of mixing the manganese-iron solution, the complexing solution and the base solution, and subjecting to a first reaction treatment to obtain the first precursor includes:

[0026] The step of mixing the manganese-iron solution, the complexing solution and the base solution, and subjecting to a first reaction treatment to obtain the first precursor includes:

[0027] The step of mixing the manganese-iron solution, the complexing solution and the base solution, and subjecting to a first reaction treatment to obtain the first precursor includes:

[0028] The step of mixing the manganese-iron solution, the complexing solution and the base solution, and subjecting to a first reaction treatment to obtain the first precursor includes:

[0029] In this embodiment, the step of subjecting to a first reaction treatment to obtain the first precursor includes: mixing the manganese-iron solution, the complexing solution and the base solution, and subjecting to a heat preservation treatment to obtain a slurry including the first precursor, so that the amorphous manganese-iron hydroxide is converted into crystalline manganese-iron hydroxide, and the crystalline manganese-iron hydroxide induces the manganese ions and ferrous ions in the solution to grow on the crystal nucleus, thereby avoiding excessive amorphous manganese-iron hydroxide. That is, the first precursor can be purified.

[0030] In some embodiments, the manganese-iron solution, the complexing solution and the base solution are mixed at 60-90°C for 1-3h.

[0031] In this embodiment, within the above temperature and time range of mixing, the crystal form of the slurry is converted, and the first precursor with good stability is obtained. If the temperature of mixing is too low, the reaction time required is relatively long. If the temperature of mixing is too high, the upper limit of the supersaturation degree of the reaction system will decrease, the nucleation rate of the crystal nucleus is prone to be too fast, and thus the product morphology is inconsistent. Within the above time range of mixing, the morphology of the precursor can be controlled by the mixing time. If the mixing time is short, the nucleation rate is too fast, and the second precursor, i.e., the basic manganese-iron oxide, in the second reaction treatment has a spherical morphology. If the mixing time is long, the nucleation rate is slow, the second precursor, i.e., the basic manganese-iron oxide, has a more regular and flaky morphology, which is more conducive to the formation of manganese-iron oxide with improved purity, and thus the lithium manganese-iron phosphate material with improved performance is obtained.

[0032] In some embodiments, the heat preservation treatment of the slurry is performed at 60-90°C.

[0033] In this embodiment, within the above temperature range of heat preservation treatment of the slurry, the crystal form of the slurry is converted, and the first precursor with good stability is obtained. If the temperature of 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. If the temperature of heat preservation treatment of the slurry is too high, the upper limit of the supersaturation degree of the reaction system will decrease, the nucleation rate of the crystal nucleus is prone to be too fast, and thus the product morphology is inconsistent, which affects the stability of the product.

[0034] In some embodiments, the holding treatment of the slurry is performed for 1-3 hours.

[0035] In this embodiment, the holding treatment time of the slurry can control the morphology of the precursor within the range of the holding treatment time of the slurry. When the holding treatment time is short, the crystal transformation of the precursor is difficult to fully proceed, and the morphology of the second precursor of the basic manganese-iron oxide may be spherical. When the holding treatment time is long, the crystal transformation of the precursor is more fully, and the morphology of the second precursor of the basic manganese-iron oxide is more regular and presents a sheet shape.

[0036] In some embodiments, the first precursor is subjected to a second reaction treatment to obtain the manganese-iron oxide.

[0037] The first precursor is subjected to an oxidation and dehydration treatment to obtain a second precursor.

[0038] The second precursor is subjected to a calcination treatment to obtain the manganese-iron oxide.

[0039] In this embodiment, the first precursor is subjected to an oxidation and dehydration treatment, i.e., the manganese-iron hydroxide is dried to be oxidized to the basic manganese-iron oxide, to obtain the second precursor.

[0040] In some embodiments, the preparation of the manganese-iron solution includes the following steps:

[0041] A soluble manganese salt is dissolved in pure water to prepare a manganese source solution;

[0042] A soluble ferrous salt is dissolved in pure water to prepare a ferrous source solution;

[0043] The manganese source solution and the ferrous source solution are mixed at a molar ratio of manganese element to iron element of (3-8):(2-7) to obtain the manganese-iron solution.

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

[0045] In some embodiments, the soluble ferrous salt includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0046] In some embodiments, the concentration of the manganese source solution is 0.5-2 mol / L.

[0047] 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 product amount of the first precursor and the manganese-iron oxide under the same volume is too small, which is prone to increase the manufacturing cost.

[0048] In some embodiments, the concentration of the ferrous source solution is 0.5-2 mol / L.

[0049] In the embodiment, when the concentration of the ferrous source solution is too high, the ferrous source solution is difficult to store and crystallization is prone to occur. When the concentration of the ferrous source solution is too low, the product amount of the first precursor and the manganese-iron oxide under the same volume is too small, which is prone to cause the manufacturing cost to increase.

[0050] In a second aspect, the embodiment of the present application provides a manganese-iron oxide prepared by the preparation method of the manganese-iron oxide.

[0051] In the technical solution of the embodiment of the present application, the manganese-iron oxide is prepared by any one of the preparation methods of the manganese-iron oxide, and the manganese element and the iron element in the manganese-iron oxide are uniformly mixed.

[0052] In a third aspect, the embodiment of the present application provides a lithium manganese iron phosphate material prepared by using the raw material including the manganese-iron oxide.

[0053] In the embodiment, the lithium manganese iron phosphate material is prepared by using the raw material including the manganese-iron oxide, and the lithium manganese iron phosphate material can have good cycle performance and high energy density.

[0054] In a fourth aspect, the embodiment of the present application provides a positive electrode sheet including a current collector and an active layer on the surface of the current collector, and the active layer includes the lithium manganese iron phosphate material.

[0055] In the embodiment, the active layer of the positive electrode sheet includes the lithium manganese iron phosphate material, and thus the positive electrode sheet has good electrochemical performance.

[0056] In a fifth aspect, the embodiment of the present application provides a secondary battery including the positive electrode sheet.

[0057] In the embodiment, the secondary battery includes the positive electrode sheet, the active layer of the positive electrode sheet includes the lithium manganese iron phosphate material, and thus the secondary battery has overall improved electrochemical performance when the positive electrode sheet is applied to the secondary battery, and the secondary battery can be well applied to multiple use scenarios.

[0058] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, the specific embodiments of the present application can be implemented according to the content of the description, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0059] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0060] Fig. 1 is a flowchart of a preparation method of manganese iron oxide provided by an embodiment of the present application;

[0061] Fig. 2 is an X-ray diffraction (XRD) result diagram of the manganese iron oxide prepared by Examples 1-5 of the present application;

[0062] Fig. 3 is an XRD result diagram of the manganese iron oxide prepared by Comparative Example 1 of the present application;

[0063] Fig. 4 is an XRD result diagram of the manganese iron oxide prepared by Comparative Example 2 of the present application;

[0064] Fig. 5 is a scanning electron microscope (SEM) result diagram of the manganese iron oxide prepared by Example 1 of the present application;

[0065] Fig. 6 is a SEM result diagram of the second precursor in Example 1 of the present application;

[0066] Fig. 7 is a SEM result diagram of the second precursor in Example 4 of the present application;

[0067] Fig. 8 is a SEM result diagram of the manganese iron oxide in Comparative Example 1 of the present application;

[0068] Fig. 9 is a SEM result diagram of the basic manganese iron oxide in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0069] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0070] 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 the present application belongs; the terms used herein are only for the purpose of describing specific embodiments of the present application, and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0071] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise explicitly specified and limited.

[0072] Reference herein to "embodiments" means that the particular features, structures, or characteristics described in connection with the embodiments can 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 all refer to the same embodiment, nor is it necessarily a separate or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0073] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0074] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two), and similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0075] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0076] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "connection", "fixing", and the like should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0077] Currently, the process flow of lithium manganese iron phosphate preparation mainly includes a manganese iron oxide route. In the manganese iron oxide route, the preparation method of the manganese iron oxide includes a solid phase method and a liquid phase coprecipitation method. In the liquid phase coprecipitation method, a soluble manganese source and a ferrous source are usually used as raw materials to be dissolved, and then the ferrous ions and the manganese ions are co-precipitated through a complexing agent, and then the precipitate is calcined to obtain the manganese iron oxide. In the traditional liquid phase coprecipitation method, the co-precipitation effect of manganese and iron is poor, and the manganese iron oxide prepared has problems such as easy mixing with impurities.

[0078] In order to solve the technical problems that the co-precipitation effect of manganese and iron is poor, and the manganese iron oxide prepared has problems such as easy mixing 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 the manganese iron oxide, the ratio of the stability constant of the complex formed by the first complexing agent and Fe 2+ to the stability constant of the complex formed by the complexing agent and Mn 2+ is 10 3 ~ 10 5 , which effectively makes up for the difference of nearly 3 orders of magnitude between the solubility product of Fe(OH)2 and the solubility product of Mn(OH)2, improves the co-precipitation effect of manganese and iron, and thus improves the product purity and other properties of the manganese iron oxide, and further improves the cycle performance and energy density performance of the lithium manganese iron phosphate material, the positive electrode sheet and the secondary battery.

[0079] In a first aspect, referring to FIG. 1, the present application provides a preparation method of a manganese iron oxide, including the following steps:

[0080] S10: providing a manganese iron solution, a complexing solution and a bottom solution, the pH value of the bottom solution being 11-12;

[0081] S20: mixing the manganese iron solution, the complexing solution and the bottom solution, and obtaining a first precursor through a first reaction treatment;

[0082] S30: obtaining the manganese iron oxide through a second reaction treatment of the first precursor;

[0083] The manganese iron solution includes Fe 2+ and Mn 2+ ;

[0084] The complexing solution includes a first complexing agent, and the ratio of the stability constant of the complex formed by the first complexing agent and Fe 2+ to the stability constant of the complex formed by the complexing agent and Mn 2+ is 10 3 ~ 10 5 .

[0085] In the technical scheme of the embodiments of the present application, the manganese-iron solution, the complexing solution and the base solution are mixed, and in the process of the first reaction treatment, the first complexing agent and Fe 2+ form a complex with a stability constant, and the first complexing agent and Mn 2+ form a complex with a stability constant, and the ratio of the stability constant of the complex formed by the first complexing agent and Fe 3 to the stability constant of the complex formed by the first complexing agent and Mn 5 is 10 2+ ~ 10 2+ . The difference between the solubility product of Fe(OH)2 and the solubility product of Mn(OH)2 is nearly 3 orders of magnitude, which is effectively made up; at the same time, the pH value of the base solution is 11 ~ 12, and in the process of the first reaction treatment, the manganese ions and ferrous ions in the solution can be controlled by the complexing agent, so that the iron element and the manganese element are uniformly mixed, and then a better co-precipitation effect of the manganese ions and the ferrous ions is realized, and a first precursor with higher crystallization quality and less mixed amorphous manganese-iron hydroxide impurities is obtained. It can be understood that the first precursor is a co-precipitate of manganese and ferrous hydroxide. The first precursor is further subjected to a second reaction treatment to obtain a manganese-iron oxide. The technical scheme of the embodiments of the present application can improve the co-precipitation effect of manganese and iron, thereby improving the product purity and other performances of the manganese-iron oxide.

[0086] Optionally, the ratio of the stability constant of the complex formed by the first complexing agent and Fe 2+ to the stability constant of the complex formed by the first complexing agent and Mn 2+ is 10 3 , 2x10 3 , 4x10 3 , 6x10 3 , 8x10 3 , 10 4 , 2x10 4 , 4x10 4 , 6x10 4 , 8x10 4 or 10 5 . Alternatively, the ratio of the stability constant of the complex formed by the first complexing agent and Fe 2+ to the stability constant of the complex formed by the first complexing agent and Mn 2+ may also be within a range between any two of the above values.

[0087] Optionally, the pH value of the base solution 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 solution may also be within a range between any two of the above pH values. It can be understood that the pH values in the present application are all measured at 25℃.

[0088] In some embodiments, the Mn 2+ and Fe 2+The total concentration is 0.5 mol / L to 2 mol / L.

[0089] In this embodiment, Mn in the manganese-iron solution 2+ and Fe 2+ When the total concentration of Mn in a manganese-iron solution is too high, it becomes 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 manganese iron oxide produced in the same volume is too small, which can easily lead to increased manufacturing costs. Optionally, the Mn in the manganese iron solution... 2+ and Fe 2+ The total concentration is 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 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, in the manganese-iron solution, Mn 2+ and Fe 2+ The total concentration can also be within the range between any two of the above concentrations.

[0090] In some embodiments, Mn in manganese-iron solution 2+ and Fe 2+ The molar ratio is (3-8):(2-7).

[0091] In this embodiment, Mn in the manganese-iron solution 2+ and Fe 2+ When the molar ratio is too high, the excessive manganese content will affect the cycling performance of the subsequently prepared lithium manganese iron phosphate material. The Mn content in the manganese iron solution... 2+ and Fe 2+ When the molar ratio of Mn is too low, it will affect the voltage plateau and energy density of the subsequently prepared lithium manganese iron phosphate material. Optionally, the Mn content in the manganese iron solution... 2+ and Fe 2+ The molar ratios are 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, or, in the manganese-iron solution, Mn 2+ and Fe 2+ The molar ratio can also be within the range between any two of the above molar ratios.

[0092] In some embodiments, the concentration of the first complexing agent in the complexing solution is 0.5 mol / L to 4 mol / L.

[0093] In the embodiment, the concentration of the first complexing agent in the complexing solution is in the range of 0.5-2 mol / L. Optionally, the concentration of the first complexing agent in the complexing solution can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or the concentration of the first complexing agent in the complexing solution can be in the range between any two of the above concentrations.

[0094] In some embodiments, the base solution comprises a second complexing agent, and the concentration of the second complexing agent in the base solution is 0.5-2 mol / L. Optionally, 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 the concentration of the second complexing agent can be any concentration value in the range between 0.5 mol / L and 2 mol / L.

[0095] In the embodiment, by adding the second complexing agent to the base solution, the direct formation of manganese ferrite hydroxide from manganese ions and ferrous ions after the addition of the manganese-iron solution can be prevented. After the addition of the second complexing agent to the base solution, the complexing agent first forms a complex with the manganese ions and ferrous ions after the addition of the manganese-iron solution to the base solution, and then, as the concentration of sodium hydroxide increases, the manganese ions and ferrous ions combine with hydroxide ions to form manganese ferrite hydroxide. If the concentration of the complexing agent in the base solution is too low, the manganese-iron solution cannot effectively complex the manganese ions and ferrous ions after being added to the base solution, which can result in the direct formation of manganese ferrite hydroxide and the difficulty in achieving uniform co-precipitation. If the concentration of the complexing agent in the base solution is too high, too many iron ions are complexed, which can result in the precipitation of manganese first and the difficulty in achieving uniform co-precipitation. 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 can be in the range between any two of the above concentrations.

[0096] In some embodiments, the base solution further comprises at least one of sodium hydroxide and potassium hydroxide to adjust the pH of the base solution to 11-12.

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

[0098] In some embodiments, the second complexing agent is selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

[0099] In this embodiment, ethylenediamine and Fe 2+ The ratio of the stability constants of the complexes formed with Mn 2+ The ratio of the stability constants of the complexes formed with Mn 4 In this embodiment, 2-methyl-8-hydroxyquinoline and Fe 2+ The ratio of the stability constants of the complexes formed with Mn 2+ The ratio of the stability constants of the complexes formed with Mn 3 Both ethylenediamine and 2-methyl-8-hydroxyquinoline can achieve good co-precipitation effects of manganese ions and ferrous ions.

[0100] In some embodiments, in the step of mixing the manganese-iron solution, the complexing solution, and the base solution, and performing first reaction treatment to obtain the first precursor, protective gas is continuously introduced into the base solution.

[0101] In this embodiment, since manganese is easily oxidized under alkaline conditions, after oxidation, it is disproportionated into fine particles of manganese dioxide, thereby making it difficult for manganese and iron elements to be co-precipitated. In the step of first reaction treatment, protective gas is continuously introduced into the base solution, which can reduce the oxidation of manganese to achieve good co-precipitation effects.

[0102] In some embodiments, the protective gas includes at least one of nitrogen, helium, and argon.

[0103] In some embodiments, the step of mixing the manganese-iron solution, the complexing solution, and the base solution, and performing first reaction treatment to obtain the first precursor includes:

[0104] The manganese-iron solution, the complexing solution, and the base solution are mixed and subjected to heat preservation treatment to obtain slurry, and the slurry includes the first precursor;

[0105] The slurry is subjected to solid-liquid separation to obtain solid material;

[0106] The solid material is subjected to purification treatment to obtain the first precursor.

[0107] In this embodiment, the step of first reaction treatment to obtain the first precursor is as follows: the manganese-iron solution, the complexing solution, and the base solution are first mixed and subjected to heat preservation treatment. The slurry including the first precursor obtained by first mixing and heat preservation treatment can convert amorphous manganese-iron hydroxide into crystalline manganese-iron hydroxide, and then induce manganese ions and ferrous ions in the solution to grow on the crystal nucleus, thereby avoiding excessive amorphous manganese-iron hydroxide.

[0108] In some embodiments, the manganese-iron solution, the complexing solution, and the base solution are mixed at 60-90 °C for 1-3 hours. Optionally, the manganese-iron solution, the complexing solution, and the base solution can be mixed for 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 period between 1 hour and 3 hours; the manganese-iron solution, the complexing solution, and the base solution can be mixed 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.

[0109] In this embodiment, within the above-mentioned temperature and time range of mixing, the slurry crystal form can be changed to obtain a first precursor with good stability. If the temperature of mixing is too low, the reaction time required is relatively long. If the temperature of mixing 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. Within the above-mentioned time range of mixing, the morphology of the precursor can be controlled by the mixing time. If the mixing time is short, the nucleation rate will be too fast, and the intermediate product, the second precursor, the basic manganese-iron oxide, will have a spherical morphology. If the mixing time is long, the nucleation rate will be slow, and the second precursor, the basic manganese-iron oxide, will have a more regular morphology and a sheet shape, 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.

[0110] For example, when the complexing agent is ethylenediamine, in the mixing process, both the ferrous ions and the manganese ions are first complexed and then precipitated. The specific chemical equation of the reaction is as follows:

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

[0112] [Fe(C2H8N2)] 2+ +2OH - =Fe(OH)2

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

[0114] [Mn(C2H8N2)] 2+ +2OH - =Mn(OH)2

[0115] In some embodiments, in the step of mixing the manganese-iron solution, the complexing solution, and the base solution and the heat preservation treatment, a pH adjuster is used to maintain the pH value of the slurry including the first precursor at 11-12.

[0116] In this embodiment, the pH value of the slurry including the first precursor is maintained at 11-12 during the mixing and the heat preservation process by using the pH adjuster, so that sufficient hydroxyl ions are provided, and the co-precipitation effect of manganese ions and ferrous ions is better. It can be understood that the manganese-iron solution, the complexing solution and the pH adjuster are added dropwise into the base solution in the same time period.

[0117] In some embodiments, the step of mixing the manganese-iron solution, the complexing solution and the base solution, and performing heat preservation to obtain a slurry includes:

[0118] heating the base solution to 60-90°C;

[0119] simultaneously adding dropwise the manganese-iron solution, the complexing solution and the pH adjuster into the heated base solution to obtain a slurry, and the dropwise adding time is 1-3 hours, so that the pH value of the slurry is maintained at 11-12;

[0120] after the dropwise adding is completed, the slurry is subjected to heat preservation at 60-90°C for 1-3 hours.

[0121] In some embodiments, the pH adjuster includes at least one of sodium hydroxide and potassium hydroxide.

[0122] In some embodiments, the heat preservation temperature of the slurry is 60-90°C.

[0123] In this embodiment, within the temperature range of the heat preservation of the slurry, the crystal form of the slurry can be changed, and the first precursor with good stability can be obtained. If the heat preservation temperature of the slurry is too low, the heat preservation time is relatively long, which affects the production efficiency. If the heat preservation temperature of the slurry is too high, the upper limit of the supersaturation of the reaction system will decrease, the nucleation rate of the crystal nucleus will be too fast, and then the product morphology will be inconsistent, which affects the stability of the product. Alternatively, the heat preservation temperature 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 heat preservation temperature of the slurry can also be within the range between any two of the above temperatures.

[0124] In some embodiments, the heat preservation time of the slurry is 1-3 hours.

[0125] In this embodiment, the time of the heat preservation treatment of the slurry can be used to control the morphology of the precursor within the time range of the heat preservation treatment of the slurry. When the time is short, the nucleation rate is too fast, and the morphology of the second precursor of the basic manganese-iron oxide can have a spherical morphology. When the time is long, the nucleation rate is slow, and the morphology of the second precursor of the basic manganese-iron oxide is more regular and presents a flaky shape. Alternatively, the time of the heat preservation treatment can be 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, or 3 h, or the time of the heat preservation treatment of the slurry can also be within a range between any two of the above times.

[0126] In some embodiments, the step of obtaining the first precursor by purifying the solid material includes: performing a water washing treatment on the solid material until the conductivity of a sample of the washing water after washing the solid material is less than or equal to 270 us / cm, thereby obtaining the first precursor.

[0127] Alternatively, the conductivity of the sample of the washing water after washing the solid material can 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.

[0128] In some embodiments, the first precursor is subjected to a second reaction treatment to obtain a manganese-iron oxide, including the following steps:

[0129] The first precursor is subjected to an oxidative dehydration treatment to obtain a second precursor;

[0130] The second precursor is subjected to a calcination treatment to obtain a manganese-iron oxide.

[0131] In this embodiment, the first precursor is subjected to an oxidative dehydration treatment, i.e., the manganese-iron hydroxide is oxidized and dehydrated to be dried, to be converted into a basic manganese-iron oxide, thereby obtaining the second precursor.

[0132] In some embodiments, the temperature of the oxidative dehydration treatment is 90°C to 99°C.

[0133] Alternatively, the temperature of the oxidative dehydration treatment can be 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 can also be within a range between any two of the above temperatures.

[0134] In some embodiments, the time of the oxidative dehydration treatment is 6 h to 12 h.

[0135] Optionally, the time for the oxidative dehydration treatment is 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 11h or 12h, or the time for the oxidative dehydration treatment can also be within a range between any two of the above.

[0136] In some embodiments, the oxidative dehydration treatment is performed under an air atmosphere.

[0137] In some embodiments, the calcination temperature for the calcination treatment is 700℃-850℃.

[0138] Optionally, the calcination temperature for the calcination treatment is 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃ or 850℃, or the temperature for the calcination treatment can also be within a range between any two of the above.

[0139] In some embodiments, the calcination time for the calcination treatment is 2h-6h.

[0140] Optionally, the calcination time for the calcination treatment is 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, or the time for the calcination treatment can also be within a range between any two of the above.

[0141] In some embodiments, the calcination treatment is performed under an air atmosphere.

[0142] In some embodiments, after the second precursor is subjected to the calcination treatment, the obtained product is discharged after being cooled to 25℃-50℃.

[0143] Optionally, after the second precursor is subjected to the calcination treatment, the obtained product is discharged after being cooled to 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃, or the discharge temperature can also be within a range between any two of the above.

[0144] In some embodiments, the preparation of the manganese-iron solution comprises the following steps:

[0145] Dissolving a soluble manganese salt in pure water to prepare a manganese source solution;

[0146] Dissolving a soluble ferrous salt in pure water to prepare a ferrous source solution;

[0147] Mixing the manganese source solution and the ferrous source solution in a molar ratio of manganese element to iron element of (3-8):(2-7) to obtain a manganese-iron solution.

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

[0149] In some embodiments, the soluble ferrous salt includes at least one of ferrous sulfate, ferrous chloride and ferrous nitrate.

[0150] In some embodiments, the concentration of the manganese source solution is 0.5 mol / L-2 mol / L.

[0151] In this embodiment, when the concentration of the manganese source solution is too high, the manganese source solution is difficult to preserve and is easy to crystallize. When the concentration of the manganese source solution is too low, the product amount of the first precursor and the manganese-iron oxide under the same volume is too small, which is easy to cause the manufacturing cost to increase. Alternatively, 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.

[0152] In some embodiments, the concentration of the ferrous source solution is 0.5 mol / L-2 mol / L.

[0153] In this embodiment, when the concentration of the ferrous source solution is too high, the ferrous source solution is difficult to preserve and is easy to crystallize. When the concentration of the ferrous source solution is too low, the product amount of the first precursor and the manganese-iron oxide under the same volume is too small, which is easy to cause the manufacturing cost to increase. Alternatively, the concentration of the ferrous 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.

[0154] In the second aspect, the embodiments of the present application provide a manganese-iron oxide, which is prepared by the preparation method of the manganese-iron oxide according to any one of the above.

[0155] In the technical scheme of the embodiments of the present application, the manganese-iron oxide is prepared by the preparation method of the manganese-iron oxide according to any one of the above, and the manganese element and the iron element in the manganese-iron oxide are uniformly mixed.

[0156] In the third aspect, the embodiments of the present application provide a lithium manganese iron phosphate material, which is prepared by using the raw material including the manganese-iron oxide according to the above.

[0157] In this embodiment, the lithium manganese iron phosphate material is prepared by using the raw material including the manganese-iron oxide according to the above, and can have good cycle performance and high energy density.

[0158] In some embodiments, the method for preparing the lithium manganese iron phosphate material comprises the following steps:

[0159] The phosphorus source, the lithium source, the carbon source, and the manganese iron oxide are mixed and ground to obtain a mixture;

[0160] The mixture is dried by spray drying to obtain a lithium manganese iron phosphate precursor;

[0161] The lithium manganese iron phosphate precursor is calcined under a nitrogen atmosphere to obtain the lithium manganese iron phosphate material.

[0162] In this embodiment, the lithium manganese iron phosphate material is prepared from the manganese iron oxide, the phosphorus source, the lithium source, and the carbon source described above, and a lithium manganese iron phosphate material with good cycle performance and high energy density can be prepared.

[0163] In some embodiments, the calcination temperature of the lithium manganese iron phosphate precursor under a nitrogen atmosphere is 650-750 DEG C, for example, it can be 660 DEG C, 670 DEG C, 680 DEG C, 690 DEG C, 700 DEG C, 710 DEG C, 720 DEG C, 730 DEG C, 740 DEG C, or any temperature value between 650 DEG C and 750 DEG C.

[0164] In some embodiments, the phosphorus source comprises at least one of ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium monohydrogen phosphate.

[0165] In some embodiments, the lithium source comprises at least one of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium acetate.

[0166] In some embodiments, the carbon source comprises at least one of glucose, graphite, and sucrose.

[0167] In this embodiment, the phosphorus source, the lithium source, and the carbon source described above do not introduce impurity elements, which is conducive to the preparation of a lithium manganese iron phosphate material with high purity.

[0168] In a fourth aspect, the embodiments of the present application provide a positive electrode tab, comprising a current collector and an active layer on the surface of the current collector, wherein the active layer comprises the lithium manganese iron phosphate material described above.

[0169] In this embodiment, the active layer of the positive electrode tab comprises the lithium manganese iron phosphate material described above, and thus has good electrochemical performance.

[0170] In a fifth aspect, the embodiments of the present application provide a secondary battery comprising the positive electrode tab described above.

[0171] In this embodiment, the secondary battery comprises the positive electrode tab, the active layer of the positive electrode tab comprises the lithium manganese iron phosphate material described above, and thus the secondary battery also has overall improved electrochemical performance when the positive electrode tab is applied to the secondary battery, so that the secondary battery can be well applied to multiple use scenarios.

[0172] In a sixth aspect, the embodiments of the present application provide a power consumption device, comprising the secondary battery.

[0173] The power consumption device provided by the embodiments of the present application can be, but is not limited to, a mobile phone, a tablet computer, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric automobile, a ship, a spacecraft, etc. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric automobile toy, an electric ship toy, an electric aircraft toy, etc. The spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, etc.

[0174] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are used only to explain the present application, and cannot be understood as a limitation of the present application. If a specific technology or condition is not specified in the examples, the technology or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained from the market.

[0175] I. Preparation method

[0176] Example 1

[0177] Preparation method of manganese iron oxide:

[0178] 1. Preparation of raw materials:

[0179] (1) Preparation of manganese source solution: manganese sulfate solution with a concentration of 1.5 mol / L is prepared, and manganese sulfate monohydrate and pure water are weighed and stirred to dissolve;

[0180] (2) Preparation of ferrous source solution: ferrous sulfate solution with a concentration of 1.5 mol / L is prepared, and ferrous sulfate heptahydrate and pure water are weighed and stirred to dissolve;

[0181] (3) Preparation of complexing solution: the first complexing agent solution with a concentration of 2 mol / L of the total synthesis amount is prepared, and ethylenediamine (the first complexing agent) and pure water are weighed and stirred to dissolve;

[0182] (4) Preparation of sodium hydroxide solution: sodium hydroxide solution with a concentration of 3 mol / L is prepared, and sodium hydroxide and pure water are weighed and stirred to mix;

[0183] (5) Preparation of manganese iron solution: the molar ratio of Mn 2+ and Fe 2+ is 6:4, and the total concentration of Mn 2+ and Fe 2+ is 1 mol / L, and manganese sulfate solution and ferrous sulfate solution are weighed and stirred to mix.

[0184] 2. Synthesis:

[0185] (1) Base solution preparation: pure water, second complexing agent, sodium hydroxide solution are taken to prepare a base solution with a second complexing agent concentration of 1 mol / L and a pH value of 11.5, and the second complexing agent is ethylenediamine;

[0186] (2) High-temperature hydrolysis synthesis: nitrogen is introduced into the reaction kettle, and the base solution is heated to 80°C. Manganese-iron solution, complexing solution, and sodium hydroxide solution are added simultaneously by using a three-tube dropping method. The dropping time of manganese-iron solution and complexing solution is controlled to be 2h. The pH value of the synthesis is adjusted to be maintained at 11-12 by using sodium hydroxide solution until the dropping is completed. After 1h of heat preservation, the first precursor manganese-iron hydroxide slurry Mn 0.6 Fe 0.4 (OH)2 is obtained.

[0187] (3) Water washing: after the heat preservation of the first precursor slurry is completed, the slurry is solid-liquid separated, and the solid material is washed until the final point conductivity is 260us / cm, and the first precursor manganese-iron hydroxide filter cake Mn 0.6 Fe 0.4 (OH)2 is obtained.

[0188] (4) Oxidation and drying: the first precursor manganese-iron hydroxide filter cake is placed in an oven and oxidized and dried at 98°C in an air atmosphere for 6h to obtain the second precursor basic manganese-iron oxide Mn 0.6 Fe 0.4 OOH.

[0189] (5) Calcination: the second precursor basic manganese-iron oxide is calcined at 750°C in an air atmosphere for 3h to obtain (Mn 0.6 Fe 0.4 )2O3.

[0190] Example 2

[0191] In this embodiment, the preparation method of manganese-iron oxide is the same as or similar to that of Example 1, and the only difference is that in this embodiment, the first complexing agent and the second complexing agent are both 2-methyl-8-hydroxyquinoline. In the step of preparing the manganese-iron solution, the molar ratio of Mn 2+ to Fe 2+ is 7:3. The manganese-iron oxide material obtained by calcination is (Mn 0.7 Fe 0.3 )2O3.

[0192] Example 3

[0193] The preparation method of the manganese iron oxide in this example is the same as or similar to that in Example 1, except that in the step of preparing the complexing agent solution, the first complexing agent and the second complexing agent are both 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 manganese iron solution, the molar ratio of Mn 2+ and Fe 2+ is 3:7, and the total concentration of Mn 2+ and Fe 2+ is 1.5 mol / L. The obtained material after calcination is MnFeO3.

[0194] Example 4

[0195] The preparation method of the manganese iron oxide in this example is the same as or similar to that in Example 3, except that in the step of preparing the manganese iron sulfate solution, the manganese iron ratio is 5:5. The obtained material after calcination is MnFeO3.

[0196] Example 5

[0197] The preparation method of the manganese iron oxide in this example is the same as or similar to that in Example 1, except that in this example, the concentration of the manganese sulfate solution in the preparation of the manganese source solution is 1 mol / L, the concentration of the ferrous sulfate solution in the preparation of the 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 the sodium hydroxide solution is 2 mol / L. In the step of preparing the manganese iron solution, the molar ratio of Mn 2+ and Fe 2+ is 5:5, and the total concentration of Mn 2+ and Fe 2+ is 0.5 mol / L. The obtained material after calcination is MnFeO3.

[0198] Example 6

[0199] The preparation method of the manganese iron oxide in this example is the same as or similar to that in Example 1, except that in the step of preparing the manganese iron solution, the molar ratio of Mn 2+ and Fe 2+ is 4:6. The obtained manganese iron oxide material after calcination is (Mn 0.4 Fe 0.6 )2O3.

[0200] Example 7

[0201] The preparation method of the manganese iron oxide in this embodiment is the same as or similar to that in embodiment 1, and the only difference is that the concentration of the manganese chloride solution in the manganese source solution preparation is 0.5 mol / L, the concentration of the ferrous chloride solution in the ferrous source solution preparation is 0.5 mol / L, the concentration of the first complexing agent in the complexing solution is 0.5 mol / L, and the total concentration of Mn 2+ and Fe 2+ in the manganese iron solution is 0.5 mol / L. The pH of the bottom solution is 11, and the concentration of the second complexing agent in the bottom solution is 0.5 mol / L.

[0202] Embodiment 8

[0203] The preparation method of the manganese iron oxide in this embodiment is the same as or similar to that in embodiment 1, and the only difference is that the concentration of the manganese nitrate solution in the manganese source solution preparation is 2 mol / L, the concentration of the ferrous nitrate solution in the ferrous source solution preparation is 2 mol / L, the concentration of the first complexing agent in the complexing solution is 4 mol / L, and the total concentration of Mn 2+ and Fe 2+ in the manganese iron solution is 2 mol / L. The pH of the bottom solution is 12, and the concentration of the second complexing agent in the bottom solution is 2 mol / L.

[0204] Embodiment 9

[0205] The preparation method of the manganese iron oxide in this embodiment is the same as or similar to that in embodiment 1, and the only difference is that, in the high-temperature hydrolysis synthesis, the bottom solution is heated to 60°C, the dropping time is 3 h, and the holding time is 3 h.

[0206] Embodiment 10

[0207] The preparation method of the manganese iron oxide in this embodiment is the same as or similar to that in embodiment 1, and the only difference is that, in the high-temperature hydrolysis synthesis, the bottom solution is heated to 90°C, the dropping time is 1 h, and the holding time is 2 h.

[0208] Embodiment 11

[0209] The preparation method of the manganese iron lithium phosphate material is as follows:

[0210] (1) The manganese iron oxide obtained in embodiment 1, ammonium dihydrogen phosphate, lithium carbonate, and glucose are mixed in a molar ratio of 1:1:1:0.05, and then ground and mixed uniformly;

[0211] (2) The uniformly mixed material is dried by spray drying to obtain a manganese iron lithium phosphate precursor.

[0212] (3) The manganese iron lithium phosphate precursor is calcined in a nitrogen atmosphere to obtain a manganese iron lithium phosphate material.

[0213] Embodiment 12

[0214] The preparation method of the lithium manganese iron phosphate material in this example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Example 2 is used as the raw material in this example.

[0215] Example 13

[0216] The preparation method of the lithium manganese iron phosphate material in this example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Example 3 is used as the raw material in this example.

[0217] Example 14

[0218] The preparation method of the lithium manganese iron phosphate material in this example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Example 4 is used as the raw material in this example.

[0219] Example 15

[0220] The preparation method of the lithium manganese iron phosphate material in this example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Example 5 is used as the raw material in this example.

[0221] Example 16

[0222] The preparation method of the lithium manganese iron phosphate material in this example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Example 6 is used as the raw material in this example.

[0223] Example 17

[0224] The preparation method of the lithium manganese iron phosphate material in this example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Example 7 is used as the raw material in this example.

[0225] Example 18

[0226] The preparation method of the lithium manganese iron phosphate material in this example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Example 8 is used as the raw material in this example.

[0227] Example 19

[0228] The preparation method of the lithium manganese iron phosphate material in this example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Example 9 is used as the raw material in this example.

[0229] Example 20

[0230] The preparation method of the lithium manganese iron phosphate material in this example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Example 10 is used as a raw material in this example.

[0231] Comparative Example 1

[0232] 1. Raw material preparation:

[0233] (1) Manganese solution preparation: manganese sulfate solution with a concentration of 1 mol / L is prepared by weighing manganese sulfate monohydrate and pure water and stirring to dissolve;

[0234] (2) Ferrous solution preparation: ferrous sulfate solution with a concentration of 1 mol / L is prepared by weighing ferrous sulfate heptahydrate and pure water and stirring to dissolve;

[0235] (3) Sodium hydroxide solution preparation: sodium hydroxide solution with a concentration of 2 mol / L is prepared by weighing sodium hydroxide and pure water and stirring to mix;

[0236] (4) Manganese iron solution preparation: manganese iron solution is prepared according to a molar ratio of Mn 2+ and Fe 2+ of 5:5 and a total concentration of Mn 2+ and Fe 2+ of 0.5 mol / L by weighing manganese sulfate solution and ferrous sulfate solution and stirring to mix.

[0237] 2. Synthesis:

[0238] (1) Base solution preparation: pure water and sodium hydroxide solution are used to prepare a base solution with a pH value of 11.5;

[0239] (2) High-temperature hydrolysis synthesis: after heating the base solution to 60°C, manganese iron solution and sodium hydroxide solution are added to the base solution using a double-tube dropping method, the dropping time of manganese iron solution is controlled for 2 h, and sodium hydroxide solution is used to adjust the synthesis pH value to maintain at 11-12, until the dropping is completed, and the first precursor slurry is obtained after 1 h of insulation;

[0240] (3) Water washing: after the insulation of the first precursor slurry is completed, water washing is performed until the final point conductivity is 260 us / cm, and the first precursor filter cake is obtained;

[0241] (4) Drying and calcination: the first precursor filter cake is placed in an oven, oxidized and dried at 98°C for 6 h, and then calcined at 750°C for 3 h to obtain manganese iron oxide MnFeO3.

[0242] Comparative Example 2

[0243] 1. Raw material preparation:

[0244] (1) Manganese solution preparation: manganese sulfate solution with a concentration of 1 mol / L is prepared, manganese sulfate monohydrate and pure water are weighed and stirred to dissolve;

[0245] (2) Ferrous solution preparation: ferrous sulfate solution with a concentration of 1 mol / L is prepared, ferrous sulfate heptahydrate and pure water are weighed and stirred to dissolve;

[0246] (3) Sodium hydroxide solution preparation: sodium hydroxide solution with a concentration of 2 mol / L is prepared, sodium hydroxide and pure water are weighed and stirred to mix;

[0247] (4) Manganese-iron solution preparation: the molar ratio of Mn 2+ and Fe 2+ is 6:4, and the total concentration of Mn 2+ and Fe 2+ is 1 mol / L, manganese sulfate solution and ferrous sulfate solution are weighed and stirred to mix;

[0248] (5) Complexing solution preparation: ammonia water with a concentration of 1 mol / L is prepared, ammonia water and pure water are weighed and stirred to mix.

[0249] 2. Synthesis:

[0250] (1) Base solution preparation: pure water, complexing agent, and sodium hydroxide solution are prepared to form a base solution with a complexing agent concentration of 1 mol / L and a pH value of 11.5;

[0251] (2) High-temperature hydrolysis synthesis: nitrogen is introduced into the reaction kettle, the base solution is heated to 90°C, and manganese-iron solution, ammonia water, and sodium hydroxide solution are added simultaneously using a three-tube dropping method. The dropping time of manganese-iron solution and ammonia water is controlled for 30 minutes, and sodium hydroxide solution is used to adjust the synthesis pH value to maintain at 11-12 until the end of dropping. After 1h of incubation, a first precursor manganese-iron hydroxide slurry with Mn 0.6 Fe 0.4 (OH)2 is obtained;

[0252] (3) Water washing: after the incubation of the first precursor slurry is completed, water washing is performed until the final point conductivity is 260 us / cm, obtaining a first precursor manganese-iron hydroxide filter cake with Mn 0.6 Fe 0.4 (OH)2;

[0253] (4) Oxidation and drying: the first precursor manganese-iron hydroxide filter cake is placed in an oven and oxidized and dried at 98°C in an air atmosphere for 6h to obtain a second precursor basic manganese-iron oxide Mn 0.6 Fe 0.4 OOH;

[0254] (5) Calcination: the second precursor basic manganese iron oxide was calcined at 750°C under air atmosphere for 3h to obtain (Mn 0.6 Fe 0.4 )2O3.

[0255] Comparative Example 3

[0256] The preparation method of the lithium manganese iron phosphate material in the present comparative example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Comparative Example 1 is used as the raw material in the present example.

[0257] Comparative Example 4

[0258] The preparation method of the lithium manganese iron phosphate material in the present example is the same as or similar to that in Example 11, and the only difference is that the manganese iron oxide prepared in Comparative Example 2 is used as the raw material in the present example.

[0259] II. Test Methods

[0260] 1. The content of manganese and iron elements in the manganese iron oxide was detected by redox titration, and other impurity elements were detected by inductively coupled plasma emission spectrometry.

[0261] 2. Property test of lithium manganese iron phosphate material

[0262] The compaction density of the lithium manganese iron phosphate material was tested by tabletting method using a compaction density instrument, and the test pressure was 3T and the pressing time was 30s.

[0263] The test methods of charge specific capacity, discharge specific capacity and coulombic efficiency are as follows:

[0264] The lithium manganese iron phosphate materials prepared in Examples 11-20 and Comparative Examples 3-4 were mixed with conductive carbon black and PVDF binder according to a mass ratio of 90:5:5, coated on a 12μm thick aluminum foil, and then the electrode sheet was dried in an oven at 110°C for 10h. The dried electrode sheet was punched into a 15mm diameter positive electrode disc, and was pressed to a compaction density of 1.8g / cm 3 Rolling, using a 16mm diameter lithium sheet as the counter electrode, and the electrolyte was 1mol / L LiPF6 dissolved in EC:EMC:DEC with a volume ratio of 1:1:1, and the battery was assembled in a LG2400 / 1000TS glove box produced by WIGAS Purification Technology (Suzhou) Co., Ltd. to obtain a button-type half cell, and the rate performance test was carried out.

[0265] The battery performance test system (model: CT3002A) of Wuhan Blue Electric 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.

[0266] III. Analysis of test results of each embodiment and comparative example

[0267] The contents of manganese, iron and other impurity elements in the manganese-iron oxides prepared in Examples 1-10 and Comparative Examples 1-2 are shown in Table 1 and Table 2 as follows:

[0268] Table 1

[0269] Table 2

[0270] Referring to FIG. 2, which is an XRD pattern of the manganese-iron oxides prepared in Examples 1-5 of the present application, it can be seen that there are no other phase impurity peaks 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 is realized, thereby obtaining manganese-iron oxides with higher purity. Further, referring to FIGS. 6 and 7, it can be seen that, compared with Example 1, the concentration of the manganese-iron 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, with particles having a non-flaky morphology.

[0271] Referring to FIG. 3, in Comparative Example 1, since the precipitation reaction is directly carried out without using a complexing agent under an air atmosphere, the divalent manganese and iron ions will be partially oxidized in the air. Under high temperature conditions, the generated manganese-iron hydroxide will dehydrate to generate more stable manganese ferrite MnFe2O4, which is different from the product manganese-iron hydroxide generated under nitrogen protection. At the same time, since no complexing agent is used, only hydroxyl ions are used for precipitation, and the generated manganese-iron oxide has obvious trimanganese tetroxide phase, indicating that the manganese ions and iron ions are not homogeneously precipitated, and the obtained manganese-iron oxide has lower purity. Referring to FIG. 8, in Comparative Example 1, since the precipitation reaction is directly carried out without using a complexing agent under an air atmosphere, and no complexing agent is used, only hydroxyl ions are used for precipitation, resulting in an irregular morphology of the obtained manganese-iron oxide.

[0272] In Comparative Example 2, manganese-iron hydroxide is prepared under a nitrogen atmosphere using ammonia as a complexing agent. The difference in the complexing ability of ammonia is small, and effective complexing is difficult, which may result in the precipitation of iron ions to generate ferrous hydroxide first, and ultimately lead to the presence of iron trioxide in the product after drying and calcination oxidation. Referring to FIGS. 4 and 9, which is an XRD pattern of the manganese-iron oxide prepared in Comparative Example 2 of the present application, it can be seen that, in Comparative Example 2, using ammonia as a complexing agent will result in the precipitation of iron ions to generate ferrous hydroxide first, and ultimately lead to the presence of iron trioxide in the product after drying and calcination oxidation.

[0273] The results in Table 1 and Table 2 show that the mass concentrations of Cd, Co, Cr, Cu, K, Na, Ni, Pb, Ti, Zn and other elements in the manganese iron oxides obtained in Examples 1-10 are in ppm level, indicating that the manganese iron oxides obtained in Examples 1-10 have less impurities and high purity.

[0274] The test results of the lithium manganese iron phosphate prepared in Examples 11-20 and Comparative Examples 3-4 are shown in Table 3.

[0275] Table 3

[0276] As can be seen from the data in Table 3, in Comparative Example 1, since no complexing agent is used, the manganese ions and iron ions are precipitated heterogeneously, and the manganese iron oxide prepared has obvious trimanganese tetroxide phase, which further leads to that the lithium manganese iron phosphate prepared in Comparative Example 3 using the manganese iron oxide prepared in Comparative Example 1 as raw material has lower tap density, charge specific capacity, discharge specific capacity and first coulombic efficiency than the lithium manganese iron phosphate prepared using the manganese iron oxides obtained in Examples 1-10 as raw material; in Comparative Example 2, the manganese iron hydroxide is prepared using ammonia as complexing agent, and since the iron ions are first precipitated to form ferrous hydroxide, the manganese iron oxide prepared has iron trioxide, which further leads to that the lithium manganese iron phosphate prepared in Comparative Example 4 using the manganese iron oxide prepared as raw material has lower tap density, charge specific capacity and discharge specific capacity than the lithium manganese iron phosphate prepared using the manganese iron oxides obtained in Examples 1-10 as raw material.

[0277] The lithium manganese iron phosphate materials prepared in Examples 11-20 using the manganese iron oxides prepared in Examples 1-10 as raw material have obviously higher tap density, charge specific capacity and discharge specific capacity than Comparative Examples 3-4. Compared with Comparative Examples 1 and 2, the manganese iron oxides are prepared using the preparation method of the manganese iron oxides in the examples, which can make the uniform mixing of iron and manganese elements, and further realize the better co-precipitation effect of manganese and iron, obtain the co-precipitate of manganese and ferrous hydroxide with higher crystalline quality and less mixed manganese iron hydroxide impurities, and improve the product purity and other properties of the manganese iron oxide, so that the lithium manganese iron phosphate material prepared using the manganese iron oxide prepared in the examples as raw material can have higher tap density, charge specific capacity, discharge specific capacity and first coulombic efficiency.

[0278] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art, without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A method for producing a manganese iron oxide, characterized by, The method comprises the following steps: providing a manganese-iron solution, a complexing solution, and a bottom solution with a pH value of 11-12; mixing the manganese-iron solution, the complexing solution, and the bottom solution, and performing a first reaction treatment to obtain a first precursor; performing a second reaction treatment on the first precursor to obtain the manganese-iron oxide; wherein the manganese iron solution comprises Fe 2+ and Mn 2+ ; The complexing solution includes a first complexing agent that forms a complex with Fe 2+ a ratio of a stability constant of a complex formed by the complexing agent and Mn 2+ to a stability constant of a complex formed by the complexing agent and Fe is 10 3 ~ 10 5 .

2. The method of producing a manganese iron oxide according to claim 1, characterized by, Mn in manganese-iron solution 2+ and Fe 2+ The total concentration is 0.5 mol / L to 2 mol / L; and / or, The molar ratio of Mn 2+ and Fe 2+ in the manganese-iron solution is (3-8):(2-7).

3. The method of producing a manganese iron oxide according to claim 1, characterized by, the concentration of the first complexing agent in the complexing solution is 0.5-4 mol / L; and / or, the bottom solution comprises a second complexing agent, and the concentration of the second complexing agent in the bottom solution is 0.5-2 mol / L; and / or, the first complexing agent and the second complexing agent are each independently selected from at least one of ethylenediamine and 2-methyl-8-hydroxyquinoline.

4. The method of producing a manganese iron oxide according to claim 1, characterized by, In the step of mixing the manganese-iron solution, the complexing solution, and the bottom solution, and performing a first reaction treatment to obtain a first precursor, protective gas is continuously introduced into the bottom solution; and / or, the step of mixing the manganese-iron solution, the complexing solution, and the bottom solution, and performing a first reaction treatment to obtain a first precursor comprises: mixing the manganese-iron solution, the complexing solution, and the bottom solution, and performing a heat preservation treatment to obtain a slurry, wherein the slurry comprises the first precursor; performing a solid-liquid separation on the slurry to obtain a solid material; performing a purification treatment on the solid material to obtain the first precursor; and / or, the manganese-iron solution, the complexing solution, and the bottom solution are mixed at 60-90°C for 1-3 hours; and / or, the temperature of the heat preservation treatment of the slurry is 60-90°C; and / or, the time of the heat preservation treatment of the slurry is 1-3 hours; and / or, the step of performing a second reaction treatment on the first precursor to obtain the manganese-iron oxide comprises the following steps: performing an oxidative dehydration treatment on the first precursor to obtain a second precursor; performing a calcination treatment on the second precursor to obtain the manganese-iron oxide.

5. The method of producing a manganese iron oxide according to claim 1, characterized by, The preparation of the manganese-iron solution comprises the following steps: dissolving a soluble manganese salt in pure water to prepare a manganese source solution; dissolving a soluble ferrous salt in pure water to prepare a ferrous source solution; mixing the manganese source solution and the ferrous source solution at a molar ratio of manganese element to iron element of (3-8):(2-7) to obtain the manganese-iron solution.

6. The method of producing a manganese iron oxide according to claim 5, characterized by, the soluble manganese salt comprises at least one of manganese sulfate, manganese chloride, and manganese nitrate; and / or, the soluble ferrous salt comprises at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate; and / or, the concentration of the manganese source solution is 0.5-2 mol / L; and / or, the concentration of the ferrous source solution is 0.5-2 mol / L.

7. A manganese iron oxide characterized in that, obtained by the method for preparing a manganese-iron oxide according to any one of claims 1-6.

8. A lithium iron manganese phosphate material, characterized in that, obtained by using a raw material comprising the manganese-iron oxide according to claim 7.

9. A positive electrode sheet characterized by comprising: comprising a current collector and an active layer 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 by comprising: comprising the positive electrode sheet according to claim 9.

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