A low-sulfur, high-purity manganese tetraoxide and its preparation method and application

Abstract

The invention discloses a low-sulfur high-purity manganese tetraoxide and its preparation method and application, and relates to the technical field of positive electrode materials. The method comprises: mixing a high-sulfur manganese tetraoxide raw material with a sulfur content of ≥100ppm with a strong oxidant; oxidizing and heat-keeping the mixture at 350-600℃ air atmosphere for 3-8h to obtain a low-sulfur manganese oxide; treating at 250-550℃ for 2-4h under reducing gas conditions to obtain a low-sulfur high-purity manganese tetraoxide with a doped phase purity of 100% and a sulfur content of ≤50ppm. The present invention can achieve complete decomposition of sulfur residues during oxidation by oxidizing and then reducing the high-sulfur manganese tetraoxide raw material, thereby improving the treatment efficiency of sulfur residues. During the reduction process, other oxides of manganese are converted into Mn3O4, which is conducive to preventing the generated Mn3O4 from further reacting, and keeping the crystal form unchanged, and the obtained product has high purity, high tap density and good activity.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode materials, and in particular to low-sulfur high-purity manganese tetraoxide and a preparation method and application thereof. Background Art

[0002] In the field of material processing, manganese tetraoxide is an important material, especially in the positive electrode materials of lithium batteries. There are many methods for preparing manganese tetraoxide, among which the metal manganese oxidation method and the co-precipitation of manganese sulfate and alkaline substances are the most common. However, in this process, a large amount of sulfur residues are often produced. The sulfur residues are mostly sulfur impurities in the catalyst ammonium sulfate and raw materials. If these sulfur residues are not handled in time, they will affect the performance of manganese tetraoxide and material processing equipment.

[0003] Current solution: Existing technologies mainly use water washing and high temperature decomposition methods to remove sulfur residues in the process of hydrolysis of metallic manganese or sulfate co-precipitation to synthesize manganese tetraoxide. Specifically, the obtained manganese tetraoxide with high sulfur content is first washed with water to remove most of the water and sulfur residues, or the material is decomposed at a high temperature greater than 850°C to remove the remaining sulfur residues.

[0004] However, the existing technology has some problems in removing sulfur residues. First, water washing will waste a lot of water and cause pollution to the environment. Secondly, although high temperature decomposition can effectively remove sulfur residues, high temperature will destroy the crystal form of manganese tetraoxide, and the crystal form of manganese tetraoxide will be converted from tetragonal phase to cubic phase, affecting its activity. In addition, the existing technology is less efficient in removing sulfur residues, requiring a long time and high temperature conditions, which not only increases production costs, but also limits the production efficiency of manganese tetraoxide. Therefore, the problems or shortcomings of the existing technology in this field limit its scope of application and effect.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a low-sulfur high-purity manganese tetraoxide and a preparation method and application thereof.

[0007] The present invention is achieved in that:

[0008] In a first aspect, the present invention provides a method for preparing low-sulfur high-purity manganese tetraoxide, which comprises:

[0009] Mixing a high-sulfur manganese tetraoxide raw material having a sulfur content of ≥100 ppm with a strong oxidant to obtain a mixture;

[0010] The mixture is oxidized and kept at 350-600° C. in an air atmosphere for 3-8 hours to obtain low-sulfur manganese oxide;

[0011] The low-sulfur manganese oxide is treated under reducing gas conditions at 250-550° C. for 2-4 hours to obtain doped low-sulfur high-purity trimanganese tetroxide, wherein the trimanganese tetroxide has a physical purity of 100% and a sulfur content of ≤50ppm.

[0012] In an optional embodiment, the strong oxidant includes at least one of titanium dioxide, niobium pentoxide, vanadium pentoxide, chromium trioxide, manganese heptoxide, iron trioxide and hydrogen peroxide.

[0013] In an optional embodiment, the strong oxidizing agent is niobium pentoxide.

[0014] In an optional embodiment, the strong oxidant is added in an amount of 1000-8000 ppm.

[0015] In an optional embodiment, the reducing gas includes at least one of methane, hydrogen and carbon monoxide. In a second aspect, the present invention provides a low-sulfur high-purity trimanganese tetraoxide, which is prepared by the method for preparing low-sulfur high-purity trimanganese tetraoxide as described in any of the above embodiments.

[0016] In a third aspect, the present invention provides the use of the low-sulfur and high-purity manganese manganese tetroxide described in the aforementioned embodiment in the preparation of lithium electric materials, sodium electric materials or magnetic materials.

[0017] In a fourth aspect, the present invention provides a positive electrode material, which includes the low-sulfur and high-purity manganese manganese tetroxide material as described in the above embodiment.

[0018] In a fifth aspect, the present invention provides a lithium battery comprising the positive electrode material as described in the above embodiment.

[0019] The present invention has the following beneficial effects:

[0020] The preparation method of low-sulfur high-purity manganese tetraoxide provided by the present invention is to add a strong oxidant to a high-sulfur manganese tetraoxide raw material, and the strong oxidant oxidizes the low-valent sulfur in the high-sulfur manganese tetraoxide raw material into SO2 gas or SO3 gas at 350-600°C, and ammonium sulfate can be completely decomposed during this temperature, and the complete decomposition of sulfur residues can be achieved, thereby improving the treatment efficiency of sulfur residues, but at the same time, manganese tetraoxide will also be partially oxidized into other oxides of manganese. Therefore, the present invention continues to reduce the low-sulfur manganese oxide at 250-550°C, at which time, the manganese oxide can be converted into Mn3O4, and it is beneficial to prevent the generated Mn3O4 from further reacting, and keep the crystal form unchanged. Therefore, the obtained product has a higher purity, a high tap density, and good activity. The low reaction temperature can reduce the crystal form transformation during the sintering process, and the phase purity of the manganese tetraoxide obtained by the method is 100%, and the sulfur content is ≤50ppm. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 This is the X-ray powder diffraction (XRD) pattern of the low-sulfur, high-purity manganese tetraoxide provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0024] The invention provides a method for preparing low-sulfur high-purity trimanganese tetraoxide, which comprises: mixing a high-sulfur trimanganese tetraoxide raw material with a strong oxidant to obtain a mixture; oxidizing and heat-keeping the mixture in an air atmosphere at 350-600° C. for 3-8 hours to obtain low-sulfur manganese oxide; treating the low-sulfur manganese oxide under reducing gas conditions at 250-550° C. for 2-4 hours to obtain doped low-sulfur high-purity trimanganese tetraoxide.

[0025] The sulfur content of the high-sulfur trimanganese tetraoxide raw material of the present invention is ≥100ppm. By combining a strong oxidant with a temperature of 350-600°C, the strong oxidant can be used to oxidize the low-valent sulfur in the high-sulfur trimanganese tetraoxide raw material into SO2 gas or SO3 gas at low temperature, and ammonium sulfate can be completely decomposed during this temperature period, and the complete decomposition of sulfur residues can be achieved, thereby improving the treatment efficiency of sulfur residues, but trimanganese tetraoxide can also be partially oxidized into other oxides of manganese. Therefore, the present invention continues to reduce the low-sulfur manganese oxide at 250-550°C, at which time, the oxide of manganese can be converted into Mn3O4, and the reduction gas and low temperature conditions are conducive to preventing the generated Mn3O4 from further reacting, and the crystal form is kept unchanged. Therefore, the obtained product has a higher purity, a high tap density, and good activity. The low reaction temperature can reduce the crystal form transformation of the sintering process, and the trimanganese tetraoxide obtained by the method has a phase purity of 100% and a sulfur content of ≤50ppm.

[0026] Specifically, in the present invention, the strong oxidant should satisfy the requirement of not introducing harmful elements or substances that can be decomposed at low temperatures. In some embodiments, the strong oxidant includes at least one of titanium dioxide, niobium pentoxide, vanadium pentoxide, chromium trioxide, manganese heptoxide, ferric oxide and hydrogen peroxide. Preferably, the strong oxidant is niobium pentoxide. When the strong oxidant is niobium pentoxide, the low-sulfur high-purity manganese tetraoxide doped with niobium is finally prepared. Niobium can improve the electrical conductivity of the material, enhance the structural stability of the positive electrode material, reduce the structural changes during the charge and discharge process, improve the diffusion channel of lithium ions, reduce the diffusion energy barrier of lithium ions, and make the migration of lithium ions in the material easier, thereby improving the rate performance and charge and discharge efficiency of the battery, and providing excellent performance for the later synthesis of lithium battery positive electrode materials.

[0027] In some embodiments, the amount of the strong oxidant added is 1000-8000 ppm, for example, any one of 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000 ppm or a range between any two thereof, preferably 2000 ppm. In the present invention, by controlling the amount of the strong oxidant added, it is possible to ensure that the low-valent sulfur in the high-sulfur trimanganese tetraoxide raw material is fully oxidized without introducing other harmful elements.

[0028] In some embodiments, the reducing gas includes but is not limited to at least one of methane, hydrogen and carbon monoxide. Preferably, the reducing gas is methane. When methane is used as a reducing gas, the reaction temperature is lower than that of other reducing gases (hydrogen, carbon monoxide). At 350°C, manganese oxide can be converted into Mn3O4, which is beneficial to prevent the generated Mn3O4 from further reacting and keep the crystal form unchanged.

[0029] The preparation method of low-sulfur high-purity manganese tetraoxide provided by the present invention avoids water washing and high-temperature decomposition, which not only saves water resources and reduces environmental pollution, but also improves production efficiency and reduces production costs. The processing process of the present invention is simple, easy to operate, suitable for large-scale production, and has good industrial application prospects. The phase purity of the prepared low-sulfur high-purity manganese tetraoxide is 100%, and the sulfur content is ≤50ppm. Compared with the prior art, the present invention not only improves the purity and performance of manganese tetraoxide, but also saves resources, reduces environmental pollution, improves production efficiency, reduces production costs, and has significant advantages. The low-sulfur high-purity manganese tetraoxide obtained by the method can be applied to the fields of lithium electricity, sodium electricity, magnetic materials, etc.

[0030] Correspondingly, the present invention also provides a positive electrode material, which includes the above-mentioned low-sulfur high-purity manganese manganese tetroxide material. In addition, the present invention also provides a lithium battery, which includes the above-mentioned positive electrode material.

[0031] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0032] Example 1

[0033] The present embodiment provides a method for preparing low-sulfur high-purity trimanganese tetraoxide, which comprises: mixing a high-sulfur trimanganese tetraoxide raw material with a sulfur content of 7536 ppm with a strong oxidant (niobium pentoxide) to obtain a mixture, wherein the amount of the strong oxidant added is 2000 ppm; oxidizing the mixture in an air atmosphere at 500° C. for 3 hours to obtain low-sulfur manganese oxide; treating the low-sulfur manganese oxide at 350° C. for 3 hours under reducing gas (methane) conditions to obtain doped low-sulfur high-purity trimanganese tetraoxide.

[0034] The crystal structure of the low-sulfur high-purity manganese tetraoxide doped with the sample obtained in Example 1 was determined using a D / MAX-2500VL / PC X-ray diffractometer from Rigaku Corporation, with a Cu target Kα ray, a wavelength of λ=0.154 06 nm, a 2θ angle scanning range of 5°~90°, and a scanning rate of 5 (°) / min. Figure 1 It can be seen from the XRD diffraction peaks that the diffraction characteristic peaks of Example 1 are consistent with the standard characteristic diffraction peaks of Mn3O4, all of which are cubic spinel structures of the Fd-3m space group. The corresponding PDF card is 80-0382, without impurity peaks, and the unit cell parameters are calculated according to the Bragg equation: 2dsinθ=nλ. The axial ratio c / a is used to determine that the tetramanganese in Example 1 is γ-Mn3O4.

[0035] Example 2

[0036] The present embodiment provides a method for preparing low-sulfur high-purity trimanganese tetraoxide, which comprises: mixing a high-sulfur trimanganese tetraoxide raw material with a sulfur content of 7536 ppm with a strong oxidant (niobium pentoxide) to obtain a mixture, wherein the amount of the strong oxidant added is 1000 ppm; oxidizing the mixture in an air atmosphere at 500° C. for 3 hours to obtain low-sulfur manganese oxide; treating the low-sulfur manganese oxide at 350° C. for 3 hours under reducing gas (methane) conditions to obtain doped low-sulfur high-purity trimanganese tetraoxide.

[0037] Example 3

[0038] The present embodiment provides a method for preparing low-sulfur high-purity trimanganese tetraoxide, which comprises: mixing a high-sulfur trimanganese tetraoxide raw material with a sulfur content of 7536 ppm with a strong oxidant (niobium pentoxide) to obtain a mixture, wherein the amount of the strong oxidant added is 8000 ppm; oxidizing the mixture in an air atmosphere at 500° C. for 3 hours to obtain low-sulfur manganese oxide; treating the low-sulfur manganese oxide at 350° C. for 3 hours under reducing gas (methane) conditions to obtain doped low-sulfur high-purity trimanganese tetraoxide.

[0039] Example 4

[0040] The present embodiment provides a method for preparing low-sulfur and high-purity trimanganese tetraoxide, which comprises: mixing a high-sulfur trimanganese tetraoxide raw material having a sulfur content of 7536 ppm with a strong oxidant (chromium trioxide) to obtain a mixture, wherein the amount of the strong oxidant added is 2000 ppm; oxidizing the mixture in an air atmosphere at 500° C. for 3 hours to obtain low-sulfur manganese oxide; treating the low-sulfur manganese oxide at 350° C. for 3 hours under reducing gas (methane) conditions to obtain doped low-sulfur and high-purity trimanganese tetraoxide.

[0041] Example 5

[0042] The present embodiment provides a method for preparing low-sulfur and high-purity trimanganese tetraoxide, which comprises: mixing a high-sulfur trimanganese tetraoxide raw material with a sulfur content of 7536 ppm with a strong oxidant (titanium dioxide) to obtain a mixture, wherein the amount of the strong oxidant added is 2000 ppm; oxidizing the mixture in an air atmosphere at 500° C. for 3 hours to obtain low-sulfur manganese oxide; treating the low-sulfur manganese oxide at 350° C. for 3 hours under reducing gas (methane) conditions to obtain doped low-sulfur and high-purity trimanganese tetraoxide.

[0043] Example 6

[0044] The present embodiment provides a method for preparing low-sulfur and high-purity trimanganese tetraoxide, which comprises: mixing a high-sulfur trimanganese tetraoxide raw material with a sulfur content of 7536 ppm with a strong oxidant (vanadium pentoxide) to obtain a mixture, wherein the amount of the strong oxidant added is 2000 ppm; oxidizing the mixture in an air atmosphere at 500° C. for 3 hours to obtain low-sulfur manganese oxide; treating the low-sulfur manganese oxide at 350° C. for 3 hours under reducing gas (methane) conditions to obtain doped low-sulfur and high-purity trimanganese tetraoxide.

[0045] Example 7

[0046] The present embodiment provides a method for preparing low-sulfur high-purity trimanganese tetraoxide, which comprises: mixing a high-sulfur trimanganese tetraoxide raw material with a sulfur content of 7536 ppm with a strong oxidant (niobium pentoxide) to obtain a mixture, wherein the amount of the strong oxidant added is 2000 ppm; oxidizing the mixture in an air atmosphere at 500° C. for 3 hours to obtain low-sulfur manganese oxide; treating the low-sulfur manganese oxide at 300° C. for 3 hours under reducing gas (hydrogen) conditions to obtain doped low-sulfur high-purity trimanganese tetraoxide.

[0047] Example 8

[0048] The present embodiment provides a method for preparing low-sulfur high-purity trimanganese tetraoxide, which comprises: mixing a high-sulfur trimanganese tetraoxide raw material with a sulfur content of 7536 ppm with a strong oxidant (niobium pentoxide) to obtain a mixture, wherein the amount of the strong oxidant added is 2000 ppm; oxidizing the mixture in an air atmosphere at 500° C. for 3 hours to obtain low-sulfur manganese oxide; treating the low-sulfur manganese oxide at 550° C. for 5 hours under reducing gas (carbon monoxide) conditions to obtain doped low-sulfur high-purity trimanganese tetraoxide.

[0049] Comparative Example 1

[0050] This comparative example is substantially the same as Example 1, except that the amount of strong oxidant added in this comparative example is 10000 ppm.

[0051] Comparative Example 2

[0052] This comparative example is substantially the same as Example 1, except that the insulation temperature in this comparative example is 700° C. in an air atmosphere.

[0053] Comparative Example 3

[0054] This comparative example is substantially the same as Example 1, except that in this comparative example, niobium pentoxide is replaced by sodium dichromate.

[0055] Comparative Example 4

[0056] This comparative example is substantially the same as Example 1, except that the insulation temperature in this comparative example under the reducing gas atmosphere is 700°C.

[0057] Comparative Example 5

[0058] In this comparative example, the high-sulfur manganese tetraoxide raw material is directly washed with water. Specifically, the high-sulfur manganese tetraoxide is washed with deionized water. During the washing process, multi-stage washing and filtering equipment (such as filter press, vacuum filter, etc.) is used to remove impurities and solid particles in the solution. The solution is filtered and stirred at each stage of washing to ensure that impurities are fully removed. The washed manganese tetraoxide solution needs to be dried to remove the moisture therein. Commonly used drying equipment includes rotary dryers, fluidized bed dryers, etc. The dried product is a manganese tetraoxide powder with a higher purity.

[0059] Comparative Example 6

[0060] In this comparative example, the high-sulfur manganese tetraoxide raw material was directly decomposed at 850° C. for 5 h.

[0061] Experimental Example 1

[0062] The trimanganese tetraoxide prepared in the above Examples 1-8 and Comparative Examples 1-6 was tested for axial ratio c / a, tap density, trimanganese tetraoxide phase purity and sulfur content, and the testing method was as follows:

[0063] (1) Axial ratio c / a: The crystal structure of the sample was determined using a Rigaku D / MAX-2500VL / PC X-ray diffractometer. The unit cell parameters were calculated based on the Bragg equation: 2dsinθ=nλ to obtain the lattice constants a, b, and c, and then the axial ratio c / a was obtained.

[0064] (2) Tap density: measured in accordance with the provisions of GB / T 5162-2021.

[0065] (3) Phase purity of manganese tetraoxide: The crystal structure of the sample was determined using Rigaku's D / MAX-2500VL / PC X-ray diffractometer. The crystal structure ratio of the material can be obtained through refinement.

[0066] (4) Sulfur content: Agilent 5800 ICP-OES inductively coupled optical emission spectrometer and inductively coupled plasma optical emission spectrometry were used. The high temperature of inductively coupled plasma was used to atomize the elements in the sample, excite them and emit characteristic spectra. The sulfur content in the sample was determined by detecting the intensity and wavelength of these characteristic spectra.

[0067] Please refer to Table 1 for the test results.

[0068] Table 1. Statistical table of performance test results of manganese tetraoxide in different examples

[0069]

[0070] As can be seen from the above table, Examples 1-8 can obtain low-sulfur (less than 43ppm), high-tap (greater than 2.39 g / cm³), high-purity manganese tetraoxide materials, which contain doping elements that help stabilize the structure of manganese tetraoxide, and the crystal form is relatively good, with an axial ratio c / a between 1.562 and 1.641, representing that the corresponding material is γ-Mn3O4, and the manganese tetraoxide of this configuration is a hexagonal closest packing structure. In Comparative Example 1, although the sulfur content is lower than that of Example 1, due to the excessive amount of strong oxidant, other elements are easily introduced, resulting in a decrease in the purity of manganese tetraoxide. In Comparative Example 2, the insulation temperature in the air atmosphere is too large, which will cause the axial ratio c / a to decrease, the crystal form to change, and the purity of manganese tetraoxide to be significantly reduced, and the sulfur content to increase. In Comparative Example 3, sodium dichromate is selected as a strong oxidant, and the ionic radius of sodium is relatively large at 1.02Å. The unit cell parameter a of the material to which sodium ions are added will increase, resulting in a significant decrease in its axial ratio c / a, poor radial direction, and a significant decrease in the purity of manganese tetraoxide, and an increase in sulfur content. In Comparative Example 4, when the holding temperature under reducing gas exceeds the scope of the present invention, it will cause a violent reduction and be difficult to control, thereby causing the crystal form to change, and the axial ratio c / a will be significantly reduced. In Comparative Example 5, the high-sulfur manganese tetraoxide raw material is directly washed with water. Although washing with water avoids changes in the crystal form, it cannot effectively remove sulfur. It can be seen that the sulfur content of Comparative Example 5 is significantly higher than that of other embodiments and comparative examples. In Comparative Example 6, by decomposing at high temperature, this will cause the crystal form to change, and the axial ratio c / a is only 0.634316. At the same time, although the sulfur content is reduced to a certain extent, it is still significantly higher than that of other embodiments and comparative examples.

[0071] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing low-sulfur high-purity manganese tetraoxide, characterized in that: It includes: Mixing a high-sulfur manganese tetraoxide raw material having a sulfur content of ≥100 ppm with a strong oxidant to obtain a mixture, wherein the strong oxidant comprises at least one of titanium dioxide, niobium pentoxide, vanadium pentoxide, chromium trioxide, manganese heptoxide, ferric oxide and hydrogen peroxide, and the addition amount of the strong oxidant is 1000-8000 ppm; The mixture is oxidized and kept at 350-600° C. in an air atmosphere for 3-8 hours to obtain low-sulfur manganese oxide; The low-sulfur manganese oxide is treated under reducing gas conditions at 250-550° C. for 2-4 hours to obtain doped low-sulfur high-purity trimanganese tetroxide, wherein the trimanganese tetroxide has a physical purity of 100% and a sulfur content of ≤50ppm.

2. The method for preparing low-sulfur high-purity trimanganese tetraoxide according to claim 1, characterized in that: The strong oxidant is niobium pentoxide.

3. The method for preparing low-sulfur high-purity trimanganese tetraoxide according to claim 1, characterized in that: The reducing gas includes at least one of methane, hydrogen and carbon monoxide.

4. A low-sulfur, high-purity manganese tetraoxide, characterized in that: The product is prepared by the method for preparing low-sulfur and high-purity manganese tetraoxide as described in any one of claims 1 to 3.

5. Use of the low-sulfur, high-purity manganese tetraoxide as claimed in claim 4 in the preparation of lithium electric materials, sodium electric materials or magnetic materials.

6. A positive electrode material, characterized in that It includes the low-sulfur high-purity manganese manganese tetroxide material as claimed in claim 4.

7. A lithium battery, characterized in that: It comprises the positive electrode material as claimed in claim 6.

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