Spherical-like ferromanganese phosphate as well as preparation method and application thereof

Abstract

The invention provides sphere-like ferromanganese phosphate and a preparation method and application thereof, and belongs to the field of lithium ion batteries, the chemical formula of the sphere-like ferromanganese phosphate is MnxFe1-xPO4, x = 0.3-0.7; the sphere-like iron phosphate has the following particle size distribution: D50 is 1.97 to 5.16 [mu] m, and D100 is 32.53 to 43.40 [mu] m. According to the present invention, the diffusion path of the lithium ions in the positive electrode active material particles can be shortened so as to improve the rate capability of the positive electrode material, such that the electrochemical performance of the secondary battery prepared from the positive electrode material can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a quasi-spherical ferromanganese phosphate and a preparation method and application thereof. Background Art

[0002] As new energy vehicles require longer driving range, the development of existing lithium iron phosphate battery materials has basically reached the bottleneck of lithium iron phosphate material energy density, and there is little room for subsequent improvement. A material with the same safety and higher energy density is needed. Currently, research on lithium manganese iron phosphate is quite popular. Lithium manganese iron phosphate and lithium iron phosphate have the same crystal structure and both belong to olivine-type phosphate positive electrode materials. When both are used on high-voltage platforms, the energy density of lithium manganese iron phosphate batteries is about 10% to 20% higher than that of lithium iron phosphate batteries, which means that with the same volume and weight, it can store more electrical energy, thereby achieving longer driving time.

[0003] At present, the mainstream process routes for preparing lithium iron manganese phosphate are solid phase method and liquid phase method. Among them, the liquid phase method is mainly based on the co-precipitation route, in which manganese sulfate, ferrous sulfate, ammonium dihydrogen phosphate and other materials are co-precipitated to generate a manganese iron phosphate precursor, and then a lithium source and a carbon source are added to grind and calcine it. In this method, impurity elements such as Al, Zn, Ca and S are easily co-precipitated with manganese iron phosphate during the co-precipitation process, resulting in a higher impurity content in the prepared lithium iron manganese phosphate, which in turn affects the electrochemical properties of the lithium iron manganese phosphate. Summary of the invention

[0004] In view of the technical problems existing in the background technology, the present application provides a quasi-spherical ferromanganese phosphate and its preparation method and application, aiming to solve the technical problems of high impurity content and poor electrochemical performance of existing ferromanganese phosphate.

[0005] In the first aspect, the present invention provides a quasi-spherical ferromanganese phosphate material, wherein the chemical formula of the quasi-spherical ferromanganese phosphate is Mn x Fe 1-x PO4, x=0.3~0.7; the quasi-spherical iron phosphate has the following particle size distribution: D50 is 1.97~5.16μm, and D100 is 32.53~43.40μm.

[0006] In the technical solution of the embodiment of the present application, the present invention provides a quasi-spherical ferromanganese phosphate, which has a low impurity content and a small particle size, and can significantly reduce the diffusion path of lithium ions inside the positive electrode active material particles, so as to efficiently deintercalate and improve the rate performance of the material. At the same time, because the ferromanganese phosphate particles have a small particle size, the specific surface area of ​​the active particles can be increased, that is, the reaction active area with the electrolyte is increased, thereby improving the electrochemical performance of the secondary battery prepared using the quasi-spherical ferrophosphate.

[0007] In a second aspect, an embodiment of the present application provides a method for preparing a quasi-spherical ferromanganese phosphate material, comprising the following steps: adding an iron source and a manganese source to a phosphoric acid solution, and obtaining a dihydrogen ferromanganese phosphate solution through solid-liquid separation; adding hydrogen peroxide to the dihydrogen ferromanganese phosphate solution to obtain a ferromanganese phosphate slurry; subjecting the ferromanganese phosphate slurry to a primary aging treatment to obtain a first ferromanganese phosphate precursor; mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry and subjecting the mixture to a secondary aging treatment to obtain a second ferromanganese phosphate precursor; washing, drying and sintering the second ferromanganese phosphate precursor in sequence to obtain a quasi-spherical ferromanganese phosphate; wherein the ratio of the sum of the amounts of iron and manganese elements in the iron source and the manganese source to the amount of phosphorus element in the phosphoric acid solution is 10:(22~30), the ratio of the amount of manganese element in the manganese source to the amount of phosphorus element in the phosphoric acid solution is (3~7):(22~30), and the ratio of the amount of iron element in the iron source to the amount of phosphorus element in the phosphoric acid solution is (3~7):(22~30).

[0008] In the technical scheme of the embodiment of the present application, first, a ferromanganese dihydrogen phosphate solution is prepared by increasing the addition ratio of phosphoric acid in the reaction, wherein excess phosphoric acid can avoid the generation of black precipitates in the intermediate state of ferrous phosphate and ferric phosphate, thereby avoiding the consumption of iron and phosphorus in the solution by the black precipitate. Secondly, in the present application, ferromanganese dihydrogen phosphate and hydrogen peroxide are oxidized to prepare amorphous ferromanganese phosphate slurry, and part of the ferromanganese phosphate slurry is subjected to an aging treatment, and during the aging process, the ferromanganese phosphate slurry undergoes a crystal transformation to obtain a first ferromanganese phosphate precursor, and thereafter, the first ferromanganese phosphate precursor is mixed with the ferromanganese phosphate slurry that has not been subjected to an aging treatment and subjected to a secondary aging treatment to obtain a second ferromanganese phosphate precursor, and finally, by high-temperature sintering the second ferromanganese phosphate precursor, a quasi-spherical ferromanganese phosphate can be prepared. In the present application, the prepared quasi-spherical ferromanganese phosphate has a small primary particle size, a low impurity content, and better electrochemical performance. In addition, the process conditions of the present invention are simple, the reaction system is a pure water system, the by-products are only phosphoric acid and hydrogen, and the intermediate by-product phosphoric acid can be reused, thereby reducing the wastewater treatment cost of the existing ferromanganese phosphate preparation process and being suitable for large-scale industrial production.

[0009] In some embodiments, the step of adding an iron source and a manganese source to a phosphoric acid solution and obtaining a dihydrogen manganese ferrophosphate solution by solid-liquid separation comprises: adding an iron source and a manganese source to the phosphoric acid solution at a temperature of 40 to 90° C. and performing dispersion treatment until the pH value of the obtained slurry is 1 to 2; performing solid-liquid separation on the slurry to obtain a dihydrogen manganese ferrophosphate solution; wherein the concentration of the phosphoric acid solution is 10 to 50 wt %.

[0010] In this embodiment, if the concentration of phosphoric acid is higher than 50 wt %, phosphoric acid will be wasted, and if the concentration of phosphoric acid is lower than 10 wt %, the reaction time will be prolonged.

[0011] In some embodiments, the step of adding hydrogen peroxide to a ferromanganese phosphate solution to obtain a ferromanganese phosphate slurry comprises: diluting the ferromanganese phosphate solution with water until the total concentration of iron and manganese elements in the ferromanganese phosphate solution is 0.1-1 mol / kg; and dropwise adding hydrogen peroxide to the diluted ferromanganese phosphate solution to obtain a ferromanganese phosphate slurry; wherein the molar ratio of hydrogen peroxide contained in the hydrogen peroxide to the total concentration of iron and manganese elements in the ferromanganese phosphate solution is (1.2-2):1.

[0012] In this embodiment, the dihydrogen manganese ferrophosphate solution is diluted with water to reduce the concentrations of manganese ions and iron ions in the synthesis, so that the manganese ions and iron ions can nucleate and grow grains within a suitable range. If the total concentration of iron ions and manganese ions is higher than 1 mol / kg, the nucleation and growth of grains are carried out simultaneously, resulting in the problem of different sizes of the formed grains. If the total concentration of iron and manganese is lower than 0.1 mol / kg, the number of formed grains is small and the production efficiency is low.

[0013] Furthermore, the reaction system is a high-temperature synthesis system, and both manganese ions and iron ions have a catalytic effect on hydrogen peroxide. By increasing the amount of hydrogen peroxide, that is, the ratio of the total molar amount of iron and manganese elements in the dihydrogen manganese ferrophosphate solution is (1.2~2):1, thereby ensuring that the manganese ions and iron ions can be completely oxidized.

[0014] In some embodiments, in the step of adding hydrogen peroxide to the diluted ferromanganese phosphate solution to obtain ferromanganese phosphate slurry, the reaction temperature is 20~80°C and the reaction time is 30~60min; and / or, in the step of subjecting the ferromanganese phosphate slurry to an aging treatment to obtain a first ferromanganese phosphate precursor, the aging treatment comprises: heating the ferromanganese phosphate slurry to 70~98°C within 5~20min, and then aging the ferromanganese phosphate slurry for 150~240min.

[0015] In this embodiment, the reaction temperature of adding hydrogen peroxide to the dihydrogen manganese ferrophosphate solution is 20-80° C. and the reaction time is 30-60 min, so that the grains grow normally, thereby ensuring the yield of the product.

[0016] Furthermore, in the process of aging the ferromanganese phosphate slurry, the system temperature is raised to 70-98°C within 5-20 minutes, and the aging and heat preservation is carried out for 150-240 minutes, which can ensure that the crystal form of the ferromanganese phosphate slurry can be transformed from an amorphous form to a dihydrate ferromanganese phosphate phase, that is, the first ferromanganese phosphate precursor is obtained.

[0017] In some embodiments, the step of mixing a first ferromanganese phosphate precursor with a ferromanganese phosphate slurry and subjecting it to a secondary aging treatment to obtain a second ferromanganese phosphate precursor includes: mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry to obtain a mixed slurry; heating the mixed slurry to 70-100°C, subjecting it to a first insulation aging, and then subjecting it to a second insulation aging; wherein the mass ratio of the first ferromanganese phosphate precursor to the ferromanganese phosphate slurry is (1-3): (7-9); the first insulation aging time is 60-90 min, and the second insulation aging time is 30-120 min.

[0018] In this embodiment, the un-crystallized ferromanganese phosphate slurry is induced to crystallize by using a partially crystallized material, i.e., the first ferromanganese phosphate precursor, so that the morphology of the un-crystallized material can be changed to a spherical shape, thereby reducing the primary particle size of the second ferromanganese phosphate precursor. At the same time, after heat preservation and induction of crystallization and filtration, the second ferromanganese phosphate precursor and the filtrate are obtained, wherein the filtrate can be used as the phosphoric acid solution in the preparation step of the dihydrogen manganese ferrophosphate solution when the filtrate is evaporated to a phosphorus content of 3-10wt%, thereby realizing the recycling and reuse of the filtrate.

[0019] In some embodiments, after the second ferromanganese phosphate precursor is washed, dried and sintered in sequence, in the step of obtaining spherical ferromanganese phosphate, the drying temperature is 90~110°C, and the drying time is 4~6h; and / or the sintering temperature is 550~650°C, and the sintering time is 3~4h.

[0020] In this embodiment, free water of the product is removed by drying, so that excessive water can be prevented from evaporating during the calcination process and damaging the calcination equipment. If the drying time is less than 4 hours, the free water is not completely evaporated, resulting in a large amount of water evaporating during the calcination process, affecting the calcination equipment. If the drying time is more than 6 hours, part of the bound water in the calcined material will be detached, thereby aggravating the particle agglomeration phenomenon during the sintering process.

[0021] Furthermore, from the perspective of the temperature range, 550~650℃ is a relatively narrow range, which means that the temperature control needs to be very precise to ensure the consistency and stability of the sintering effect. As for the sintering time, 3~4h is also of great significance. If the sintering time is too short, it may lead to incomplete sintering and uneven internal structure of the prepared quasi-spherical manganese ferrophosphate material; if the sintering time is too long, it will not only lead to energy waste, but also may cause over-sintering, affecting the electrochemical properties of the prepared quasi-spherical manganese ferrophosphate material.

[0022] In a third aspect, an embodiment of the present application provides a positive electrode material, which includes lithium iron manganese phosphate prepared using quasi-spherical manganese phosphate as a raw material, or includes lithium iron manganese phosphate prepared using quasi-spherical manganese phosphate obtained by the above-mentioned preparation method as a raw material.

[0023] In this embodiment, the positive electrode material includes the above-mentioned spherical manganese iron phosphate material, so it has the technical effects of uniform particle dispersion, low impurity content and good electrochemical performance.

[0024] In a fourth aspect, an embodiment of the present application provides a positive electrode plate, which is prepared using the above-mentioned positive electrode material.

[0025] In this embodiment, the positive electrode plate includes the above-mentioned positive electrode material, and thus also has the advantages of low impurity content and better electrochemical performance.

[0026] In a fifth aspect, an embodiment of the present application provides a secondary battery, comprising the above-mentioned positive electrode plate.

[0027] In this embodiment, the secondary battery includes the above-mentioned positive electrode plate, and thus has the advantage of better electrochemical performance.

[0028] 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

[0029] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 The figure is a schematic diagram of the preparation process of the quasi-spherical ferromanganese phosphate according to the present invention.

[0031] Figure 2This is the SEM spectrum of the quasi-spherical manganese ferrophosphate prepared in Example 1.

[0032] Figure 3 This is the XRD diffraction pattern of the quasi-spherical manganese iron phosphate prepared in Example 1.

[0033] Figure 4 This is the SEM spectrum of the ferromanganese phosphate prepared in Comparative Example 1.

[0034] Figure 5 This is the XRD diffraction pattern of the quasi-spherical ferromanganese phosphate prepared in Example 2.

[0035] Figure 6 This is the SEM spectrum of the quasi-spherical manganese ferrophosphate prepared in Example 2.

[0036] Figure 7 This is the XRD diffraction pattern of the quasi-spherical manganese iron phosphate prepared in Example 3.

[0037] Figure 8 This is the SEM spectrum of the quasi-spherical manganese iron phosphate prepared in Example 3.

[0038] Fig. 9 This is the XRD diffraction pattern of the quasi-spherical manganese iron phosphate prepared in Example 4.

[0039] Fig.10 This is the SEM spectrum of the quasi-spherical manganese ferrophosphate prepared in Example 4.

[0040] Fig.11 This is the XRD diffraction pattern of the quasi-spherical manganese iron phosphate prepared in Example 5.

[0041] Fig.12 This is the SEM spectrum of the quasi-spherical manganese ferrophosphate prepared in Example 5.

[0042] Fig.13 This is the XRD diffraction pattern of the ferromanganese phosphate prepared in Comparative Example 1.

[0043] Fig.14 This is the XRD diffraction pattern of the ferromanganese phosphate prepared in Comparative Example 2.

[0044] Fig.15 This is the SEM spectrum of the ferromanganese phosphate prepared in Comparative Example 2.

[0045] Fig.16 This is the XRD diffraction pattern of the ferromanganese phosphate prepared in Comparative Example 3.

[0046] Fig.17 This is the SEM spectrum of the ferromanganese phosphate prepared in Comparative Example 3. DETAILED DESCRIPTION

[0047] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field 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" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0049] 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 clearly and specifically defined.

[0050] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0051] 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, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0052] 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).

[0053] 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. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which 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 referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0054] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0055] In the prior art, in the process of preparing a ferromanganese phosphate precursor, after manganese powder and iron powder are dissolved in a phosphoric acid solution respectively, an oxidant is added to react, and at the same time, the pH is controlled during the reaction to obtain a ferromanganese phosphate precursor. Manganese powder and iron powder are dissolved in a phosphoric acid solution respectively to generate dihydrogen manganese phosphate and dihydrogen ferrous phosphate, wherein the dihydrogen ferrous phosphate solution is easily oxidized to generate a black precipitate that is an intermediate between ferrous phosphate and ferric phosphate, and the black precipitate consumes iron and phosphorus in the solution, thereby increasing the product loss.

[0056] In order to solve the technical problems that the ferromanganese phosphate prepared by the existing preparation method of ferromanganese phosphate has high impurity content and poor electrochemical performance, the present application provides a quasi-spherical ferromanganese phosphate and its preparation method and application, wherein by increasing the proportion of phosphoric acid in the reaction, the oxidation of ferrous dihydrogen phosphate can be avoided, thereby preparing a quasi-spherical ferromanganese phosphate with low impurity content and better electrochemical performance, and then the electrochemical performance of the positive electrode material and secondary battery prepared by using the aforementioned quasi-spherical ferromanganese phosphate is also improved.

[0057] In the first aspect, the present invention provides a quasi-spherical ferromanganese phosphate material, wherein the chemical formula of the quasi-spherical ferromanganese phosphate is Mn x Fe 1-x PO4, x=0.3~0.7; the quasi-spherical iron phosphate has the following particle size distribution: D50 is 1.97~5.16μm, and D100 is 32.53~43.40μm.

[0058] The spherical ferromanganese phosphate prepared by the present invention has lower impurities and smaller particle size, and can significantly reduce the diffusion path of lithium ions inside the positive electrode active material particles, so as to efficiently deintercalate and improve the rate performance of the material, and also can increase the specific surface area of ​​the active particles. When the spherical ferromanganese phosphate is used as a positive electrode material, the reaction active area between the positive electrode material and the electrolyte is increased, thereby improving the electrochemical performance of the secondary battery prepared by using the positive electrode material.

[0059] Furthermore, in some embodiments, the quasi-spherical manganese ferrophosphate is Mn 0.3 Fe 0.7 PO4、Mn 0.5 Fe 0.5 PO4、Mn 0.6 Fe 0.4 PO4 and Mn 0.7 Fe 0.3 One or more of PO4.

[0060] In a second aspect, the present application provides a method for preparing a quasi-spherical ferromanganese phosphate material, comprising the following steps: S1. Adding an iron source and a manganese source to a phosphoric acid solution, and obtaining a dihydrogen manganese ferrophosphate solution by solid-liquid separation; S2, adding hydrogen peroxide to the ferromanganese dihydrogen phosphate solution to obtain ferromanganese phosphate slurry; S3, subjecting the ferromanganese phosphate slurry to an aging treatment to obtain a first ferromanganese phosphate precursor; S4, mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry and performing a secondary aging treatment to obtain a second ferromanganese phosphate precursor; S5, washing, drying and sintering the second ferromanganese phosphate precursor in sequence to obtain quasi-spherical ferromanganese phosphate; Among them, the ratio of the sum of the amounts of iron and manganese elements in the iron source and manganese source to the amount of phosphorus element in the phosphoric acid solution is 10:(22~30), the ratio of the amount of manganese element in the manganese source to the amount of phosphorus element in the phosphoric acid solution is (3~7):(22~30), and the ratio of the amount of iron element in the iron source to the amount of phosphorus element in the phosphoric acid solution is (3~7):(22~30).

[0061] Specifically, the main chemical reaction corresponding to step S1 is as follows: xMn+yFe+2H3PO4→Mn x Fe y (H2PO4)2+H2↑(x=0.3~0.7,y=1-x) In the present application, a dihydrogen manganese ferrophosphate solution is prepared by increasing the addition ratio of phosphoric acid in the reaction, wherein excess phosphoric acid can avoid the generation of a black precipitate intermediate between ferrous phosphate and ferric phosphate, thereby avoiding the consumption of iron and phosphorus in the solution by the black precipitate.

[0062] Specifically, the ratio of the sum of the amounts of iron and manganese elements in the iron source and the manganese source to the amount of phosphorus element in the phosphoric acid solution is 10:22, 10:24, 10:26, 10:28, 10:30 or any value between 10: (22 and 30); wherein the ratio of the amount of manganese element in the manganese source to the amount of phosphorus element in the phosphoric acid solution can be 3:22, 5:22, 6:22, 7:22, 3:24, 5:24, 6:24, 7:24, 3:26, 5:26, 6:26, 7:26, 3:28, 5:28, 6:28, 7:22. 8. 3:30, 5:30, 6:30, 7:30 or any value between (3-7): (22-30); the molar ratio of the iron element in the iron source to the phosphorus element in the phosphoric acid solution can be 3:22, 5:22, 6:22, 7:22, 3:24, 5:24, 6:24, 7:24, 3:26, 5:26, 6:26, 7:26, 3:28, 5:28, 6:28, 7:28, 3:30, 5:30, 6:30, 7:30 or any value between (3-7): (22-30).

[0063] Further, in some embodiments, step S1 adds an iron source and a manganese source to a phosphoric acid solution, and obtains a dihydrogen manganese ferrophosphate solution by solid-liquid separation, comprising: S10, adding an iron source and a manganese source to the phosphoric acid solution at a temperature of 40 to 90° C. and performing dispersion treatment until the pH value of the obtained slurry is 1 to 2; S11, performing solid-liquid separation on the slurry to obtain a dihydrogen manganese ferrophosphate solution; Wherein, the concentration of the phosphoric acid solution is 10~50wt%.

[0064] In the present application, the concentration of the phosphoric acid solution is maintained between 10 and 50wt%, so that the extraction of manganese and iron can be achieved in a short time, and the utilization rate of phosphoric acid is improved. Understandably, limited by the solubility of manganese phosphate and iron phosphate, if the phosphoric acid concentration is higher than 50wt%, phosphoric acid will be wasted, and if the phosphoric acid concentration is lower than 10wt%, the time required for the reaction will be prolonged. Among them, in the step of adding an iron source and a manganese source to the phosphoric acid solution and dispersing the treatment, the purpose of dispersion can be achieved by stirring.

[0065] Specifically, the concentration of the phosphoric acid solution may be 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, or any value between 10 and 50 wt%.

[0066] Furthermore, the main chemical reaction corresponding to step S2 is as follows: 2Mn x Fe y (H2PO4)2+H2O2+2H2O→2Mn x Fe y PO4·2H2O↓+2H3PO4 (x=0.3~0.7, y=1-x) It should be noted that under the action of high temperature and oxidant, the divalent manganese ions and iron ions in the dihydrogen manganese ferrophosphate solution are oxidized to trivalent manganese ions and iron ions, and the solubility product of the trivalent manganese ions and iron ions with phosphate is small. When there are too many trivalent manganese ions and iron ions and phosphate ions in the solution, the trivalent manganese ions and iron ions will form an amorphous ferromanganese phosphate precipitate with the phosphate, and after a primary aging treatment and crystallization, a first ferromanganese phosphate precursor is formed. The first ferromanganese phosphate precursor after crystallization is used as a seed, and the ferromanganese phosphate slurry is subjected to a secondary aging treatment, so that spherical ferromanganese phosphate with a primary particle size of about 50nm can be prepared. If the primary aging treatment is not followed by a secondary aging treatment, the generated first ferromanganese phosphate precursor will have a flaky morphology after calcination, rather than a spherical shape.

[0067] In the present application, ferromanganese phosphate slurry with an amorphous structure can be prepared by an oxidation reaction between ferromanganese phosphate and hydrogen peroxide. A portion of the ferromanganese phosphate slurry is subjected to a primary aging treatment. During the primary aging process, the ferromanganese phosphate slurry undergoes a crystal transformation to obtain a first ferromanganese phosphate precursor. Thereafter, the first ferromanganese phosphate precursor is mixed with the ferromanganese phosphate slurry that has not undergone a crystal transformation and subjected to a secondary aging treatment to obtain a second ferromanganese phosphate precursor. Finally, quasi-spherical ferromanganese phosphate is prepared by high-temperature sintering the second ferromanganese phosphate precursor. The prepared quasi-spherical ferromanganese phosphate has a small primary particle size, a low impurity content and good electrochemical properties.

[0068] At the same time, the process conditions of the present invention are simple, the reaction system is a pure water system, the by-products are only phosphoric acid and hydrogen, and the intermediate by-product phosphoric acid can be reused, thereby reducing the wastewater treatment cost of the existing ferromanganese phosphate preparation process and being suitable for large-scale industrial production.

[0069] Further, in some embodiments, step S2, adding hydrogen peroxide to the ferromanganese dihydrogen phosphate solution to obtain ferromanganese phosphate slurry, comprises: S20, diluting the ferromanganese dihydrogen phosphate solution with water until the total concentration of iron and manganese in the ferromanganese dihydrogen phosphate solution is 0.1-1 mol / kg; S21, adding hydrogen peroxide dropwise to the diluted ferromanganese dihydrogen phosphate solution to obtain ferromanganese phosphate slurry; Among them, the molar ratio of hydrogen peroxide contained in hydrogen peroxide to the sum of iron and manganese elements in dihydrogen manganese ferrophosphate solution is (1.2~2):1; the mass fraction of hydrogen peroxide in hydrogen peroxide is 27.5%.

[0070] In the present application, the ferromanganese dihydrogen phosphate solution is diluted with water to reduce the concentrations of manganese ions and iron ions during the oxidation reaction, so that the concentrations of manganese ions and iron ions are within a suitable range for nucleation and growth of grains. If the total concentration of iron ions and manganese ions is higher than 1 mol / kg, the nucleation and growth of grains proceed simultaneously, resulting in the problem of different sizes of the formed grains. If the total concentration of iron ions and manganese ions is lower than 0.1 mol / kg, a small number of grains are formed, resulting in low production efficiency.

[0071] Specifically, in the solution diluted with water, the total concentration of iron ions and manganese ions can be 0.1 mol / kg, 0.2 mol / kg, 0.3 mol / kg, 0.4 mol / kg, 0.5 mol / kg, 0.6 mol / kg, 0.7 mol / kg, 0.8 mol / kg, 0.19 mol / kg, 1 mol / kg or any value within the range of 0.1~1 mol / kg.

[0072] Understandably, in the preparation process of ferromanganese phosphate slurry, the reaction system is a high-temperature synthesis system, and both manganese ions and iron ions have a catalytic effect on hydrogen peroxide. When the ratio of hydrogen peroxide in hydrogen peroxide to the total molar amount of iron and manganese elements in dihydrogen manganese phosphate ferromanganese solution is (1.2~2):1, it can ensure that manganese ions and iron ions can be completely oxidized. In addition, the mass fraction of hydrogen peroxide in hydrogen peroxide is 27.5%, and hydrogen peroxide of this concentration is easy to purchase, reducing the cost of raw materials.

[0073] Further, in the present application, the hydrogen peroxide is added dropwise within 5 to 30 minutes, which can avoid the simultaneous nucleation and growth of grains due to the too fast addition speed, thereby effectively controlling the size and morphology of the grains, so that the prepared quasi-spherical manganese ferrophosphate has a consistent particle size distribution. Understandably, if the addition speed is too fast, the metal cations may be entrained into the grains, thereby affecting the purity of the prepared quasi-spherical manganese ferrophosphate. Therefore, in the present application, controlling the dropwise addition speed of hydrogen peroxide helps to reduce the introduction of impurities during the growth of the grains, thereby improving the purity of the prepared quasi-spherical manganese ferrophosphate.

[0074] Further, in step S21, hydrogen peroxide is added dropwise to the diluted ferromanganese phosphate solution to obtain ferromanganese phosphate slurry, the reaction temperature is 20-80° C., and the reaction time is 30-60 min.

[0075] In the present application, hydrogen peroxide is added to the dihydrogen manganese ferrophosphate solution and reacted at 20-80° C. for 30-60 minutes, which can make the synthesized grains grow, thereby ensuring the yield of the product.

[0076] Further, in step S3, the ferromanganese phosphate slurry is subjected to an aging treatment to obtain a first ferromanganese phosphate precursor, and the aging treatment includes: heating the ferromanganese phosphate slurry to 70-98° C. within 5-20 minutes, and then aging the ferromanganese phosphate slurry for 150-240 minutes.

[0077] In the present application, the system temperature is raised to 70-98°C within 5-20 minutes, and the aging and heat preservation are carried out for 150-240 minutes, which can ensure that the crystal form of the ferromanganese phosphate slurry is transformed from an amorphous state to a dihydrate ferromanganese phosphate phase, that is, the first precursor of ferromanganese phosphate.

[0078] Further, in step S4, the first ferromanganese phosphate precursor is mixed with the ferromanganese phosphate slurry and subjected to secondary aging treatment to obtain a second ferromanganese phosphate precursor, which includes: S40, mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry to obtain a mixed slurry; S41, heating the mixed slurry to 70-100°C, performing a first heat preservation aging, and then performing a second heat preservation aging; Among them, the mass ratio of the first ferromanganese phosphate precursor to the ferromanganese phosphate slurry is (1~3): (7~9); the first insulation aging time is 60~90min, and the second insulation aging time is 30~120min.

[0079] In the present application, the first ferromanganese phosphate precursor is used to induce the untransformed ferromanganese phosphate slurry to transform into a spherical shape, thereby reducing the particle size of the primary particles of the second ferromanganese phosphate precursor. Furthermore, after the mixed slurry is filtered after the heat preservation and induction of crystallization, the second ferromanganese phosphate precursor and the filtrate can be obtained. The filtrate is evaporated to a phosphorus content of 3 to 10wt%, which can be used as a phosphoric acid solution in the preparation step of the dihydrogen manganese ferrophosphate solution, thereby realizing the recycling and reuse of the filtrate.

[0080] Specifically, the first ferromanganese phosphate precursor and the ferromanganese phosphate slurry can be mixed in any mass ratio within the range of (1-3): (7-9) or 1:7, 1:8, 1:9, 2:7, 2:8, 2:9, 3:7, 3:8, 3:9.

[0081] Further, in step S5, the second ferromanganese phosphate precursor is washed, dried and sintered in sequence to obtain quasi-spherical ferromanganese phosphate, the drying temperature is 90-110° C., and the drying time is 4-6 hours; and / or, The sintering temperature is 550~650℃, and the sintering time is 3~4h.

[0082] In the technical solution of the embodiment of the present application, free water of the product is removed by drying to prevent excessive water from evaporating during the calcination process and damaging the calcination equipment. If the drying time is less than 4 hours, the free water is not completely evaporated, and if the drying time is more than 6 hours, part of the bound water in the product is separated, thereby aggravating the agglomeration of product particles during the sintering process.

[0083] From the temperature range, 550~650℃ is a relatively narrow range, which means that the temperature control needs to be very precise to ensure the consistency and stability of the sintering effect. As for the sintering time, 3~4h is also of great significance. Understandably, if the sintering time is too short, it may lead to incomplete sintering, which in turn leads to uneven internal structure of the sintered material; if the sintering time is too long, it may not only lead to energy waste, but also cause over-sintering, thus affecting the electrochemical properties of the sintered material.

[0084] Specifically, the drying temperature can be 90°C, 100°C, 110°C or any value in the range of 90~110°C, the drying time can be 4h, 5h, 6h or any value in the range of 4~6h, the sintering temperature can be 550°C, 600°C, 650°C or any value in the range of 550~650°C, and the sintering time can be 3h, 4h or any value in the range of 3~4h.

[0085] In a third aspect, an embodiment of the present application provides a positive electrode material, which includes lithium iron manganese phosphate prepared using quasi-spherical manganese phosphate as a raw material, or includes lithium iron manganese phosphate prepared using quasi-spherical manganese phosphate obtained by the above-mentioned preparation method as a raw material.

[0086] In the present application, the positive electrode material includes the above-mentioned spherical manganese iron phosphate material, and thus has the technical effects of uniform particle dispersion, low impurity content and good electrochemical performance.

[0087] In a fourth aspect, an embodiment of the present application provides a positive electrode plate, which includes the above-mentioned positive electrode material.

[0088] In the present application, the positive electrode plate contains the above-mentioned positive electrode material, and thus also has the advantages of low impurity content and better electrochemical performance.

[0089] In a fifth aspect, an embodiment of the present application provides a secondary battery, and the secondary battery includes the above-mentioned positive electrode plate.

[0090] In the present application, the secondary battery includes the above-mentioned positive electrode plate, and thus has the advantage of better electrochemical performance.

[0091] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained commercially.

[0092] 1. Preparation method Example 1 A method for preparing quasi-spherical ferromanganese phosphate, comprising the following steps: (1) adding an appropriate amount of pure water to phosphoric acid to prepare a dilute phosphoric acid solution with a mass fraction of 25%; adding iron powder and manganese powder to the phosphoric acid solution, stirring, heating to 80° C. and reacting at this temperature, wherein the molar ratio of manganese, iron and phosphorus is 6:4:24, and stopping heating when the pH value of the slurry is 1, filtering the slurry obtained by the reaction, and obtaining a dihydrogen manganese iron phosphate solution; 0.6Mn+0.4Fe+2H3PO4→Mn 0.6 Fe 0.4 (H2PO4)2+H2↑ (2) preparing a clear iron-manganese solution with a total iron and manganese concentration of 0.5 mol / kg by mixing a dihydrogen manganese phosphate solution with pure water, and dripping hydrogen peroxide (the molar ratio of hydrogen peroxide to the total iron and manganese in the hydrogen peroxide is 1.2:1, and the concentration of hydrogen peroxide is 27.2%) into the manganese iron solution at 20°C while stirring for 20 minutes to obtain a manganese iron phosphate slurry; heating the manganese iron phosphate slurry for aging, the heating time is controlled within 20 minutes, the insulation temperature is 85°C, and after the reaction slurry crystal form changes (the crystal form changes after 2 hours of reaction), continue to heat for 60 minutes to obtain a first manganese iron phosphate precursor; 2Mn 0.6 Fe 0.4 (H2PO4)2+H2O2+2H2O→2Mn 0.6 Fe 0.4 PO4·2H2O↓+2H3PO4; (3) Mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry described in step (2) in a mass ratio of 2:8, and keeping the mixture at 85° C. After the reaction slurry undergoes a crystal transformation (the crystal transformation is completed after 1 h of reaction), the mixture is kept warm for 60 min, and filtered to obtain the second ferromanganese phosphate precursor and mother liquor. The filtered mother liquor is collected, evaporated and concentrated to a phosphorus content of 5 wt%, which can be used as an aqueous solution to dilute the phosphoric acid in step (1), thereby completing the mother liquor phosphoric acid cycle; (4) The second precursor of manganese ferrophosphate was dried at 98°C for 4 hours and then sintered at 600°C for 3 hours to prepare spherical manganese ferrophosphate (theoretical chemical formula is Mn 0.6Fe 0.4 PO4).

[0093] The manganese and iron contents in the product were detected by redox titration. The quasi-spherical manganese ferrophosphate prepared in this embodiment contained 14.77% Fe and 21.85% Mn. Therefore, the actual structural formula of the quasi-spherical manganese ferrophosphate obtained by conversion is: Mn 0.6 Fe 0.4 PO4, the ratio of manganese to iron in the resulting spherical manganese ferrophosphate is basically consistent with the theoretical value of 6:4.

[0094] Example 2 A method for preparing quasi-spherical ferromanganese phosphate, comprising the following steps: (1) adding an appropriate amount of pure water to phosphoric acid to prepare a dilute phosphoric acid solution with a mass fraction of 25%; adding iron powder and manganese powder to the phosphoric acid solution, stirring, heating to 80° C. and reacting at this temperature, wherein the molar ratio of manganese, iron and phosphorus is 7:3:24, and the phosphoric acid is in excess of 20%. When the pH value of the slurry is 1, the heating is stopped, and the slurry obtained by the reaction is filtered to obtain a dihydrogen manganese iron phosphate solution; 0.7Mn+0.3Fe+2H3PO4→Mn 0.7 Fe 0.3 (H2PO4)2+H2↑ (2) preparing a clear iron-manganese solution with a total iron and manganese concentration of 0.5 mol / kg by mixing a dihydrogen manganese phosphate solution with pure water, and dripping hydrogen peroxide (the molar ratio of hydrogen peroxide to the total iron and manganese in the hydrogen peroxide is 1.2:1, and the concentration of hydrogen peroxide is 27.2%) into the manganese iron solution at 40°C while stirring within 20 minutes to obtain a manganese iron phosphate slurry; heating the manganese iron phosphate slurry for aging, the heating time is controlled within 20 minutes, the insulation temperature is 85°C, and after the reaction slurry crystal form changes (the crystal form changes after 2 hours of reaction), continue to heat for 60 minutes to obtain a first manganese iron phosphate precursor; 2Mn 0.7 Fe 0.3 (H2PO4)2+H2O2+2H2O→2Mn 0.7 Fe 0.3 PO4·2H2O↓+2H3PO4; (3) Mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry described in step (2) in a mass ratio of 2:8, and keeping the mixture at 85° C. After the reaction slurry undergoes a crystal transformation (the crystal transformation is completed after 1 h of reaction), the mixture is kept warm for 60 min, and filtered to obtain the second ferromanganese phosphate precursor and mother liquor. The filtered mother liquor is collected, evaporated and concentrated to a phosphorus content of 5 wt%, which can be used as an aqueous solution to dilute the phosphoric acid in step (1), thereby completing the mother liquor phosphoric acid cycle; (4) The second precursor of manganese ferrophosphate was dried at 98°C for 5 hours and then sintered at 600°C for 3 hours to prepare spherical manganese ferrophosphate (theoretical chemical formula is Mn 0.7 Fe 0.3 PO4).

[0095] The manganese and iron contents in the product were detected by redox titration. The quasi-spherical manganese ferrophosphate prepared in this embodiment contained 11.07% Fe and 25.47% Mn. Therefore, the actual structural formula of the quasi-spherical manganese ferrophosphate obtained by conversion is: 0.7 Fe 0.3 PO4, the ratio of manganese to iron in the resulting spherical manganese ferrophosphate is basically consistent with the theoretical value of 7:3.

[0096] Example 3 A method for preparing quasi-spherical ferromanganese phosphate, comprising the following steps: (1) adding an appropriate amount of pure water and a mother liquor (the mother liquor filtered in step (3) of Example 1 is collected and evaporated to concentrate to a phosphorus content of 5%) to a phosphoric acid solution having a concentration of 85 wt% to prepare a dilute phosphoric acid solution having a mass fraction of 25%; adding iron powder and manganese powder to the dilute phosphoric acid solution, stirring, heating to 80° C. and reacting at this temperature, wherein the molar ratio of manganese, iron and phosphorus is 6:4:24, and the phosphoric acid is in excess of 20%. When the pH value of the slurry is 1, the heating is stopped, and the slurry obtained by the reaction is filtered to obtain a dihydrogen manganese ferrophosphate solution; 0.6Mn+0.4Fe+2H3PO4→Mn 0.6 Fe 0.4 (H2PO4)2+H2↑ (2) preparing a clear iron-manganese solution with a total iron and manganese concentration of 0.5 mol / kg by mixing a dihydrogen manganese phosphate solution with pure water, and dripping hydrogen peroxide (the molar ratio of hydrogen peroxide to the total iron and manganese in the hydrogen peroxide is 1.2:1, and the concentration of hydrogen peroxide is 27.2%) into the manganese iron solution at 80°C while stirring for 20 minutes to obtain a manganese iron phosphate slurry; heating the manganese iron phosphate slurry for aging, the heating time is controlled within 20 minutes, the insulation temperature is 85°C, and after the reaction slurry crystal form changes (the crystal form changes after 3 hours of reaction), continue to heat for 60 minutes to obtain a first manganese iron phosphate precursor; 2Mn 0.6 Fe 0.4 (H2PO4)2+H2O2+2H2O→2Mn 0.6 Fe 0.4 PO4·2H2O↓+2H3PO4; (3) Mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry described in step (2) in a mass ratio of 2:8, and keeping the mixture at 85° C. After the reaction slurry undergoes a crystal transformation (the crystal transformation is completed after 90 minutes of reaction), the mixture is kept warm for 60 minutes, and filtered to obtain the second ferromanganese phosphate precursor and mother liquor. The filtered mother liquor is collected, evaporated and concentrated to a phosphorus content of 5wt%, which can be used as an aqueous solution to dilute the phosphoric acid in step (1), thereby completing the mother liquor phosphoric acid cycle; (4) The second precursor of manganese ferrophosphate was dried at 98°C for 6 hours and then sintered at 600°C for 4 hours to prepare spherical manganese ferrophosphate (theoretical chemical formula is Mn 0.6 Fe 0.4 PO4).

[0097] The manganese and iron contents in the product were detected by redox titration. The quasi-spherical manganese ferrophosphate prepared in this embodiment contained 14.72% Fe and 21.75% Mn. Therefore, the actual structural formula of the quasi-spherical manganese ferrophosphate obtained by conversion is: Mn 0.6 Fe 0.4 PO4, the ratio of manganese to iron in the resulting spherical manganese ferrophosphate is basically consistent with the theoretical value of 6:4.

[0098] Example 4 A method for preparing quasi-spherical ferromanganese phosphate, comprising the following steps: (1) adding an appropriate amount of pure water to phosphoric acid to prepare a dilute phosphoric acid solution with a mass fraction of 25%; adding iron powder and manganese powder to the phosphoric acid solution, stirring, heating to 80° C. and reacting at this temperature, wherein the molar ratio of manganese, iron and phosphorus is 3:7:24, and the phosphoric acid is in excess of 20%. When the pH value of the reaction slurry reaches 1, the heating is stopped, and the slurry obtained by the reaction is filtered to obtain a dihydrogen manganese iron phosphate solution; 0.3Mn+0.7Fe+2H3PO4→Mn 0.3 Fe 0.7 (H2PO4)2+H2↑ (2) preparing a ferromanganese phosphate solution with pure water to prepare a clear ferromanganese solution with a total iron and manganese concentration of 0.5 mol / kg, and dripping hydrogen peroxide (the molar ratio of hydrogen peroxide to the total iron and manganese in the hydrogen peroxide is 1.2:1, and the concentration of hydrogen peroxide is 27.2%) into the ferromanganese solution at 50°C while stirring within 20 minutes to obtain ferromanganese phosphate slurry; heating the ferromanganese phosphate slurry for aging, the heating time is controlled within 20 minutes, the insulation temperature is 85°C, and after the reaction slurry crystal form changes (the crystal form changes after 150 minutes of reaction), continue to heat for 60 minutes to obtain the first ferromanganese phosphate precursor; 2Mn 0.3 Fe 0.7 (H2PO4)2+H2O2+2H2O→2Mn0.3 Fe 0.7 PO4·2H2O↓+2H3PO4; (3) Mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry described in step (2) in a mass ratio of 2:8, and keeping the mixture at 85° C. After the reaction slurry undergoes a crystal transformation (the crystal transformation is completed after 1 hour of reaction), the mixture is kept warm for 60 minutes, and filtered to obtain the second ferromanganese phosphate precursor and mother liquor. The filtered mother liquor is collected, evaporated and concentrated to a phosphorus content of 5%, and can be used as an aqueous solution to dilute the phosphoric acid in step (1), thereby completing the mother liquor phosphoric acid cycle; (4) The second precursor of manganese ferrophosphate was dried at 98°C for 5 hours and then sintered at 600°C for 3 hours to prepare spherical manganese ferrophosphate (theoretical chemical formula is Mn 0.3 Fe 0.7 PO4).

[0099] The manganese and iron contents in the product were detected by redox titration. The quasi-spherical manganese ferrophosphate prepared in this embodiment contained 25.96% Fe and 10.88% Mn. Therefore, the actual structural formula of the quasi-spherical manganese ferrophosphate obtained by conversion is: 0.3 Fe 0.7 PO4, the ratio of manganese to iron in the resulting spherical manganese ferrophosphate is basically consistent with the theoretical value of 3:7.

[0100] Example 5 A method for preparing quasi-spherical ferromanganese phosphate, comprising the following steps: (1) adding an appropriate amount of pure water to phosphoric acid to prepare a dilute phosphoric acid solution with a mass fraction of 25%; adding iron powder and manganese powder to the phosphoric acid solution, stirring, heating to 80° C. and reacting at this temperature, wherein the molar ratio of manganese, iron and phosphorus is 5:5:24, and the phosphoric acid is in excess of 20%. When the pH value of the slurry is 1, the heating is stopped, and the slurry obtained by the reaction is filtered to obtain a dihydrogen manganese iron phosphate solution; 0.5Mn+0.5Fe+2H3PO4→Mn 0.5 Fe 0.5 (H2PO4)2+H2↑ (2) preparing a clear iron-manganese solution with a total iron and manganese concentration of 0.5 mol / kg by mixing a dihydrogen manganese phosphate solution with pure water, and dripping hydrogen peroxide (the molar ratio of hydrogen peroxide to the total iron and manganese in the hydrogen peroxide is 1.2:1, and the concentration of hydrogen peroxide is 27.2%) into the manganese iron solution at 70°C while stirring for 20 minutes to obtain a manganese iron phosphate slurry; heating the manganese iron phosphate slurry for aging, the heating time is controlled within 20 minutes, the insulation temperature is 85°C, and after the reaction slurry crystal form changes (the crystal form changes after 2 hours of reaction), continue to heat for 60 minutes to obtain a first manganese iron phosphate precursor; 2Mn0.5 Fe 0.5 (H2PO4)2+H2O2+2H2O→2Mn 0.5 Fe 0.5 PO4·2H2O↓+2H3PO4; (3) Mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry described in step (2) in a mass ratio of 2:8, and keeping the mixture at 85° C. After the reaction slurry undergoes a crystal transformation (the crystal transformation is completed after 1 hour of reaction), the mixture is kept warm for 60 minutes, and filtered to obtain the second ferromanganese phosphate precursor and mother liquor. The filtered mother liquor is collected, evaporated and concentrated to a phosphorus content of 5%, and can be used as an aqueous solution to dilute the phosphoric acid in step (1), thereby completing the mother liquor phosphoric acid cycle; (4) The second precursor of manganese ferrophosphate was dried at 98°C for 4 hours and then sintered at 600°C for 4 hours to prepare spherical manganese ferrophosphate (theoretical chemical formula is Mn 0.5 Fe 0.5 PO4).

[0101] The manganese and iron contents in the product were detected by redox titration. The quasi-spherical manganese ferrophosphate prepared in this embodiment contained 18.19% Fe and 18.55% Mn. Therefore, the actual structural formula of the quasi-spherical manganese ferrophosphate obtained by conversion is: 0.5 Fe 0.5 PO4, the ratio of manganese to iron in the resulting spherical manganese ferrophosphate is basically consistent with the theoretical value of 5:5.

[0102] Comparative Example 1 A method for preparing ferromanganese phosphate, comprising the following steps: (1) adding an appropriate amount of pure water to phosphoric acid to prepare a dilute phosphoric acid solution with a mass fraction of 25%; adding iron powder and manganese powder to the phosphoric acid solution, stirring, heating to 80° C. and reacting at this temperature, wherein the molar ratio of manganese, iron and phosphorus is 6:4:24, and the phosphoric acid is in excess of 20%. When the pH value of the slurry is 1, the heating is stopped, and the slurry obtained by the reaction is filtered to obtain a dihydrogen manganese iron phosphate solution; 0.6Mn+0.4Fe+2H3PO4→Mn 0.6 Fe 0.4 (H2PO4)2+H2↑ (2) preparing a clear iron-manganese solution with a total iron and manganese concentration of 0.5 mol / kg by mixing a dihydrogen manganese phosphate solution with pure water, and dripping hydrogen peroxide (the molar ratio of hydrogen peroxide to the total iron and manganese in the hydrogen peroxide is 1.2:1, and the concentration of hydrogen peroxide is 27.2%) into the manganese iron solution at 20°C while stirring for 40 minutes to obtain a manganese iron phosphate slurry; heating the manganese iron phosphate slurry for aging, the heating time is controlled within 20 minutes, the insulation temperature is 85°C, and after the reaction slurry crystal form changes (the crystal form changes after 2 hours of reaction), continue to heat for 60 minutes to obtain a first manganese iron phosphate precursor; 2Mn 0.6 Fe 0.4 (H2PO4)2+H2O2+2H2O→2Mn 0.6 Fe 0.4 PO4·2H2O↓+2H3PO4; (3) The first precursor of manganese ferrophosphate is dried at 98°C for 4 hours, and then sintered at 600°C for 3 hours to prepare the anhydrous manganese ferrophosphate (theoretical chemical formula is Mn 0.6 Fe 0.4 PO4).

[0103] Compared with Example 1, the difference is that the dropping time of the hydrogen peroxide solution in step (2) is changed from 20 min to 40 min, and at the same time, the step of inducing crystallization is removed.

[0104] The manganese and iron contents in the product were detected by redox titration. The manganese iron phosphate prepared in this embodiment contained 14.81% Fe and 21.89% Mn. Therefore, the actual structural formula of the manganese iron phosphate obtained by conversion is: 0.6 Fe 0.4 PO4, the ratio of manganese to iron in the resulting ferromanganese phosphate is basically consistent with the theoretical value of 6:4.

[0105] Comparative Example 2 A method for preparing ferromanganese phosphate, comprising the following steps: (1) adding an appropriate amount of pure water to phosphoric acid to prepare a dilute phosphoric acid solution with a mass fraction of 25%; adding iron powder and manganese powder to the phosphoric acid solution, stirring, heating to 80° C. and reacting at this temperature, wherein the molar ratio of manganese, iron and phosphorus is 6:4:20, at which time the phosphoric acid is not excessive, and stopping heating when the pH value of the slurry reaches 1, filtering the slurry obtained by the reaction, and obtaining a dihydrogen manganese iron phosphate solution; 0.6Mn+0.4Fe+2H3PO4→Mn 0.6 Fe 0.4 (H2PO4)2+H2↑ (2) preparing a clear iron-manganese solution with a total iron and manganese concentration of 0.5 mol / kg by mixing a dihydrogen manganese phosphate solution with pure water, and dripping hydrogen peroxide (the molar ratio of hydrogen peroxide to the total iron and manganese in the hydrogen peroxide is 1.2:1, and the concentration of hydrogen peroxide is 27.2%) into the manganese iron solution at 20°C while stirring for 20 minutes to obtain a manganese iron phosphate slurry; heating the manganese iron phosphate slurry for aging, the heating time is controlled within 20 minutes, the insulation temperature is 85°C, and after the reaction slurry crystal form changes (the crystal form changes after 2 hours of reaction), continue to heat for 60 minutes to obtain a first manganese iron phosphate precursor; 2Mn 0.6 Fe 0.4 (H2PO4)2+H2O2+2H2O→2Mn 0.6 Fe 0.4 PO4·2H2O↓+2H3PO4; (3) Mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry described in step (2) in a mass ratio of 2:8, and keeping the mixture at 85° C. After the reaction slurry undergoes a crystal transformation (the crystal transformation is completed after 1 hour of reaction), the mixture is kept warm for 60 minutes, and filtered to obtain the second ferromanganese phosphate precursor and mother liquor. The filtered mother liquor is collected, evaporated and concentrated to a phosphorus content of 5%, and can be used as an aqueous solution to dilute the phosphoric acid described in step (1), thereby completing the mother liquor phosphoric acid cycle; (4) The second precursor of ferromanganese phosphate was dried at 98°C for 4 hours and then sintered at 600°C for 3 hours to prepare ferromanganese phosphate (theoretical chemical formula is Mn 0.6 Fe 0.4 PO4).

[0106] The manganese and iron contents in the product were detected by redox titration. The manganese iron phosphate prepared in this embodiment contained 12.77% Fe and 23.26% Mn. Therefore, the actual structural formula of the manganese iron phosphate obtained by conversion is: 0.65 Fe 0.35 PO4. This is because the phosphoric acid is not excessive. In the actual reaction process, due to the increase in the pH value of the reaction system and the decrease in the hydrogen ion concentration of the system, the subsequent reaction is difficult, resulting in the inability to completely extract manganese and iron ions. In addition, manganese is more active than iron, and the manganese extraction rate is higher. Ultimately, the manganese:iron ratio in the generated manganese iron phosphate is significantly different from the theoretical value of 6:4.

[0107] Comparative Example 3 A method for preparing ferromanganese phosphate, comprising the following steps: (1) preparing a ferromanganous sulfate solution: mixing FeSO4·7H2O, MnSO4·H2O and pure water under stirring conditions at a molar ratio of Mn:Fe of 6:4 to prepare a ferromanganous sulfate solution with a concentration of 0.5 mol / L; (2) preparing ammonium phosphate solution: under stirring, mix monoammonium phosphate (MAP), pure water and hydrogen peroxide (the concentration of hydrogen peroxide is 27.2%) to prepare a 1 mol / L ammonium phosphate solution; (3) Synthesis: The ferromanganese sulfate solution in step (1) is used as a base solution, and an ammonium phosphate solution is added dropwise thereto, wherein the ratio of the total molar number of ferromanganese elements in the ferromanganese sulfate solution to the molar number of phosphorus elements in the ammonium phosphate solution is 1:1.02, and the dropping time is controlled within 30 minutes. After the dropping is completed, the pH is adjusted to 6 by adding ammonia water to obtain a ferromanganese phosphate slurry; (4) Filtration and washing: The ferromanganese phosphate slurry obtained in step (3) is filtered and washed until the conductivity of the washing water is 260 us / cm to obtain a ferromanganese phosphate filter cake; (5) Drying and calcining: The ferromanganese phosphate filter cake obtained in step (4) is first dried in an oven at 98°C for 4 h, and then calcined in a muffle furnace at 600°C for 3 h to obtain ferromanganese phosphate.

[0108] 2. Test Method Particle size test: The particle size of the ferromanganese phosphate materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 was tested by laser particle size analysis. The results are shown in Table 1.

[0109] Impurity test: The impurity composition and corresponding content of the ferromanganese phosphate materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were tested by inductively coupled plasma emission spectroscopy. The results are shown in Table 1.

[0110] Table 1 Statistics of impurity contents of various embodiments and comparative examples

[0111] III. Analysis of test results of various embodiments and comparative examples According to the statistical results in Table 1, we can see that the ferromanganese phosphate prepared in Examples 1 to 5 of the present invention has the advantages of low impurities and small particle size relative to the ferromanganese phosphate formed in the system of Comparative Example 1. Further, by comparing Example 1 with Comparative Example 1, it can be seen that the hydrogen peroxide in Comparative Example 1 is added for a longer time, so that the amount of metal cations entrained into the product is less, which is manifested as the content of Ca in the comparative example is less than that in Example 1, but since Comparative Example 1 does not perform induced crystallization, the particle size of the product finally prepared is larger.

[0112] Further, Example 1 is compared with Comparative Example 2. In Comparative Example 2, since phosphoric acid is not excessive, in the actual reaction process, due to the increase in the pH value of the reaction system, the decrease in the hydrogen ion concentration of the system, the subsequent reaction is difficult, resulting in manganese and iron ions cannot be completely extracted, and manganese is more active than iron, and the extraction rate of manganese is higher, which ultimately leads to a large difference between the ratio of manganese and iron in the generated anhydrous manganese iron phosphate and the theoretical value.

[0113] Furthermore, by comparing Comparative Example 3 with Examples 1 to 5, it can be seen that the method provided by the present invention can prepare ferromanganese phosphate with small particle size and uniform distribution. At the same time, the types and contents of impurities contained in the ferromanganese phosphate prepared by the present application are significantly reduced compared with those in Comparative Example 3, which fully demonstrates that the preparation method provided by the present invention is a significant improvement over the conventional preparation method of ferromanganese phosphate.

[0114] Further, Figure 2 This is the SEM spectrum of the quasi-spherical ferromanganese phosphate prepared in Example 1 of the present invention. Figure 2 It can be seen that the manganese iron phosphate prepared in the present application is spherical particles with a primary particle size of about 50 nm.

[0115] Further, Figure 3 The XRD diffraction pattern of the quasi-spherical ferromanganese phosphate prepared in Example 1 of the present invention is as follows: Figure 3 It can be seen that the XRD diffraction pattern of the quasi-spherical manganese iron phosphate prepared in Example 1 is consistent with the standard card 70-1555 (Fe 0.65 Mn 0.35 The main peak positions and main peak intensities of PO4 are basically the same, which indicates that ferromanganese phosphate was prepared in Example 1. It should be noted that for the case of lithium ferromanganese phosphate, which can have a continuously changing composition ratio, the standard card library cannot contain material data of all possible composition ratios. Usually, a representative or widely studied ratio is selected as the standard. 0.65 Mn 0.35 PO4 is standard.

[0116] Further, Figure 4 This is the SEM spectrum of the ferromanganese phosphate prepared in Comparative Example 1 of the present invention. Figure 4 It can be seen that the microscopic morphology of the ferromanganese phosphate prepared in Comparative Example 1 is flake-like. Figure 1 , Figure 6 , Figure 8 , Fig.10 and Fig.12 It can be seen from the content that the ferromanganese phosphate obtained after the induced crystallization treatment has a quasi-spherical structure, while the ferromanganese phosphate without the induced crystallization treatment, that is, the ferromanganese phosphate prepared in Comparative Example 1, is in the form of flakes. It can be understood that the quasi-spherical ferromanganese phosphate has a more uniform particle size distribution and a higher specific surface area than the flake-like ferromanganese phosphate, which is conducive to the penetration of the electrolyte and the diffusion of lithium ions, thereby possibly improving the charge and discharge rate capability of the battery.

[0117] Further, Figure 5 The XRD diffraction pattern of the quasi-spherical ferromanganese phosphate prepared in Example 2 is as follows: Figure 5It can be seen that the XRD diffraction pattern of the quasi-spherical ferromanganese phosphate prepared in Example 2 is consistent with the standard card 70-1555 (Fe 0.65 Mn 0.35 The main peak position and main peak intensity of PO4 are basically consistent, indicating that ferromanganese phosphate was prepared in Example 2. Figure 6 This is the SEM spectrum of the quasi-spherical ferromanganese phosphate prepared in Example 2. Figure 6 It can be seen that the ferromanganese phosphate prepared in Example 2 is spherical particles with a primary particle size of about 50 nm.

[0118] Further, Figure 7 The XRD diffraction pattern of the quasi-spherical ferromanganese phosphate prepared in Example 3 is as follows: Figure 7 It can be seen that the XRD diffraction pattern of the quasi-spherical ferromanganese phosphate prepared in Example 3 is consistent with the standard card 70-1555 (Fe 0.65 Mn 0.35 The main peak position and main peak intensity of PO4 are basically consistent, indicating that ferromanganese phosphate was prepared in Example 3. Figure 8 This is the SEM spectrum of the quasi-spherical ferromanganese phosphate prepared in Example 3. Figure 8 It can be seen that the ferromanganese phosphate prepared in Example 3 is spherical particles with a primary particle size of about 50 nm.

[0119] Further, Fig. 9 The XRD diffraction pattern of the quasi-spherical ferromanganese phosphate prepared in Example 4 is as follows: Fig. 9 It can be seen that the XRD diffraction pattern of the quasi-spherical ferromanganese phosphate prepared in Example 4 is consistent with the standard card 70-1555 (Fe 0.65 Mn 0.35 The main peak position and main peak intensity of PO4 are basically consistent, indicating that ferromanganese phosphate was prepared in Example 4. Fig.10 This is the SEM spectrum of the spherical ferromanganese phosphate prepared in Example 4. Fig.10 It can be seen that the ferromanganese phosphate prepared in Example 4 is a spherical particle with a primary particle size of about 80 nm, and the particles are agglomerated into flakes. Understandably, because the drying time in Example 4 is longer than that in Example 1, part of the bound water in the second precursor particles of the ferromanganese phosphate is separated during the drying stage, and the agglomeration of the particles in the subsequent sintering process is aggravated.

[0120] Further, Fig.11 The XRD diffraction pattern of the quasi-spherical ferromanganese phosphate prepared in Example 5 is as follows: Fig.11 It can be seen that the XRD diffraction pattern of the quasi-spherical manganese ferrophosphate prepared in Example 5 is consistent with the standard card 70-1555 (Fe 0.65 Mn 0.35 The main peak position and main peak intensity of PO4 are basically consistent, indicating that ferromanganese phosphate was prepared in Example 5. Fig.12 This is the SEM spectrum of the quasi-spherical ferromanganese phosphate prepared in Example 5. Fig.12 It can be seen that the ferromanganese phosphate prepared in Example 5 is spherical particles with a primary particle size of about 50 nm.

[0121] Further, Fig.13 The XRD diffraction pattern of the ferromanganese phosphate prepared in Comparative Example 1 of the present invention is as follows: Fig.13 It can be seen that the XRD diffraction pattern of the ferromanganese phosphate prepared in Comparative Example 1 is consistent with the standard card 70-1555 (Fe 0.65 Mn 0.35 The main peak position and main peak intensity of PO4 are basically consistent, indicating that ferromanganese phosphate was prepared in Comparative Example 1.

[0122] Further, Fig.14 The XRD diffraction pattern of the ferromanganese phosphate prepared in Comparative Example 2 of the present invention is as follows: Fig.14 It can be seen that the XRD diffraction pattern of the ferromanganese phosphate prepared in Comparative Example 2 is consistent with the standard card 70-1555 (Fe 0.65 Mn 0.35 The main peak position and main peak intensity of PO4 are basically consistent, indicating that ferromanganese phosphate was prepared in Comparative Example 2. Fig.15 The SEM spectrum of the ferromanganese phosphate prepared in Comparative Example 2 is as follows: Fig.15 It can be seen that the ferromanganese phosphate prepared in Comparative Example 2 is spherical particles with a primary particle size of about 50 nm.

[0123] Further, Fig.16 The XRD diffraction pattern of the ferromanganese phosphate prepared in Comparative Example 3 of the present invention is as follows: Fig.16 It can be seen that the XRD diffraction pattern of the ferromanganese phosphate prepared in Comparative Example 3 is consistent with the standard card 70-1555 (Fe 0.65 Mn 0.35 The main peak position and main peak intensity of PO4 are basically consistent, indicating that ferromanganese phosphate was prepared in Comparative Example 3. Fig.17 This is the SEM spectrum of the ferromanganese phosphate prepared in Comparative Example 3 of the present invention. Fig.17 It can be seen that the microscopic morphology of the ferromanganese phosphate prepared in Comparative Example 3 is a stack of thin sheets. Figure 2 and Figure 4 It can be clearly seen that the product obtained by Comparative Example 1, which is only different from the preparation method of the present invention in the step of "induced crystallization", also has a flaky morphology, but its stacking number is much less than that of Comparative Example 3, and the stacking is more disordered. It can be seen that different preparation methods and specific preparation processes have a greater impact on the microscopic morphology of the product.

[0124] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A quasi-spherical ferromanganese phosphate, characterized in that: The chemical formula of the quasi-spherical manganese iron phosphate is Mn x Fe 1-x PO4, x=0.3~0.7; the quasi-spherical iron phosphate has the following particle size distribution: D50 is 1.97~5.16μm, and D100 is 32.53~43.40μm.

2. A method for preparing quasi-spherical ferromanganese phosphate as claimed in claim 1, characterized in that: The steps include: Adding an iron source and a manganese source into a phosphoric acid solution, and obtaining a dihydrogen manganese ferrophosphate solution through solid-liquid separation; adding hydrogen peroxide to the ferromanganese dihydrogen phosphate solution to obtain ferromanganese phosphate slurry; Performing an aging treatment on the ferromanganese phosphate slurry to obtain a first ferromanganese phosphate precursor; The first ferromanganese phosphate precursor is mixed with the ferromanganese phosphate slurry and subjected to secondary aging treatment to obtain a second ferromanganese phosphate precursor; The second ferromanganese phosphate precursor is sequentially washed, dried and sintered to obtain the quasi-spherical ferromanganese phosphate; Among them, the ratio of the sum of the amounts of iron and manganese elements in the iron source and the manganese source to the amount of phosphorus element in the phosphoric acid solution is 10: (22-30), the ratio of the amount of manganese element in the manganese source to the amount of phosphorus element in the phosphoric acid solution is (3-7): (22-30), and the ratio of the amount of iron element in the iron source to the amount of phosphorus element in the phosphoric acid solution is (3-7): (22-30).

3. The method for preparing quasi-spherical ferromanganese phosphate according to claim 2, characterized in that: The step of adding an iron source and a manganese source to a phosphoric acid solution and obtaining a dihydrogen manganese ferrophosphate solution by solid-liquid separation comprises: Under the condition of a temperature of 40-90° C., adding the iron source and the manganese source to the phosphoric acid solution and performing a dispersion treatment until the pH value of the obtained slurry is 1-2; The slurry is subjected to solid-liquid separation to obtain the dihydrogen manganese ferrophosphate solution; Wherein, the concentration of the phosphoric acid solution is 10~50wt%.

4. The method for preparing quasi-spherical ferromanganese phosphate according to claim 2, characterized in that: The step of adding hydrogen peroxide to the ferromanganese phosphate dihydrogen solution to obtain ferromanganese phosphate slurry comprises: The dihydrogen manganese ferrophosphate solution is diluted with water until the total concentration of iron and manganese in the dihydrogen manganese ferrophosphate solution is 0.1-1 mol / kg; Adding hydrogen peroxide dropwise to the diluted ferromanganese dihydrogen phosphate solution to obtain ferromanganese phosphate slurry; Wherein, the molar ratio of the hydrogen peroxide contained in the hydrogen peroxide to the sum of the iron element and the manganese element in the dihydrogen manganese ferrophosphate solution is (1.2-2):

1.

5. The method for preparing quasi-spherical ferromanganese phosphate according to claim 4, characterized in that: In the step of adding hydrogen peroxide to the diluted ferromanganese phosphate solution to obtain ferromanganese phosphate slurry, the reaction temperature is 20-80° C. and the reaction time is 30-60 min; and / or In the step of subjecting the ferromanganese phosphate slurry to an aging treatment to obtain a first ferromanganese phosphate precursor, the aging treatment comprises: heating the ferromanganese phosphate slurry to 70-98° C. within 5-20 minutes, and then subjecting the ferromanganese phosphate slurry to an aging treatment for 150-240 minutes.

6. The method for preparing quasi-spherical ferromanganese phosphate according to claim 2, characterized in that: The step of mixing the first ferromanganese phosphate precursor with the ferromanganese phosphate slurry and performing a secondary aging treatment to obtain a second ferromanganese phosphate precursor comprises: Mixing the first ferromanganese phosphate precursor with ferromanganese phosphate slurry to obtain a mixed slurry; The mixed slurry is heated to 70-100° C. for a first heat preservation aging, and then a second heat preservation aging; Among them, the mass ratio of the first ferromanganese phosphate precursor to the ferromanganese phosphate slurry is (1-3): (7-9); the first insulation aging time is 60-90 minutes, and the second insulation aging time is 30-120 minutes.

7. The method for preparing quasi-spherical ferromanganese phosphate according to claim 2, characterized in that: In the step of washing, drying and sintering the second ferromanganese phosphate precursor in sequence to obtain the quasi-spherical ferromanganese phosphate, the drying temperature is 90-110° C. and the drying time is 4-6 hours; and / or The sintering temperature is 550-650° C., and the sintering time is 3-4 hours.

8. A positive electrode material, characterized in that The positive electrode material includes lithium manganese iron phosphate prepared using the quasi-spherical manganese iron phosphate described in claim 1 as a raw material, or includes lithium manganese iron phosphate prepared using the quasi-spherical manganese iron phosphate obtained by the preparation method described in claims 2-7 as a raw material.

9. A positive electrode sheet, characterized in that: The positive electrode material is prepared using the positive electrode material described in claim 8.

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

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