Manganese tetraoxide material as well as preparation method and application thereof

Abstract

The invention provides a manganous-manganic oxide material as well as a preparation method and application thereof, and belongs to the technical field of battery materials. The manganous-manganic oxide material has a sunflower-like structure, and the sunflower-like structure is characterized in that the interior of a manganous-manganic oxide particle is formed by orderly assembling sheet-shaped or columnar primary crystal grains which are arranged in the radial direction, and the section of the particle presents a sunflower-like morphology which radiates outwards from the center. The manganous-manganic oxide with the sunflower-like structure provided by the invention can maintain a relatively excellent capacity retention ratio at normal temperature and high temperature, and provides a powerful material support for the development of high-performance lithium ion batteries.

Description

Technical Field

[0001] This application relates to the field of battery materials, and in particular to a manganese tetroxide material, its preparation method, and its application. Background Technology

[0002] LiMn2O4 has low preparation cost, a mature and simple production process, and good safety. Unlike layered oxides and olivine-type lithium iron phosphate, spinel-type LiMn2O4 has become an ideal cathode material for energy storage devices due to its environmental friendliness, unique structure, good electrochemical stability, and high theoretical capacity. Currently, the precursors for lithium manganese oxide cathode materials used in the market are mainly electrolytic manganese dioxide and manganese tetroxide. The manganese in the latter is in a low valence state and has high chemical activity, so the temperature for completing the synthesis of lithium manganese oxide is relatively low. This saves energy consumption and can effectively inhibit excessive grain growth and manganese volatilization caused by high temperature, thereby obtaining products with more uniform particle size and more suitable specific surface area, which is conducive to rapid lithium ion insertion and extraction and improves rate performance. In addition, manganese tetroxide and lithium manganese oxide both have a spinel structure. During sintering, this structural similarity makes it easier for atomic rearrangement to develop into regular spinel LiMn2O4, which helps to form cathode materials with higher crystallinity and fewer lattice defects.

[0003] Currently, the use of manganese tetroxide in the synthesis of lithium manganese oxide cathode materials encounters the following problems: ① The Mn content in lithium manganese oxide... 3+ A disproportionation reaction (Mn) will occur in the electrolyte. 3+ → Mn 2+ + Mn 4+ ), generating Mn 2+ It will dissolve into the electrolyte. This directly leads to the loss of active materials and damages the material structure. The larger the particle specific surface area, the larger the contact area with the electrolyte, and the more severe the manganese dissolution will be. ② In high valence state Mn³ + (Especially under high temperature or deep discharge) the crystal lattice of the material will be distorted, transforming from a cubic crystal system to a tetragonal crystal system, which will induce structural stress and generate microcracks, thereby aggravating capacity decay.

[0004] Document CN119637941A discloses a method for preparing and applying modified "sea urchin-type" manganese tetroxide. It involves using ammonia as a precipitant and aminocarboxylic acids as complexing agents, introducing elements such as Al, Mg, Ti, and Zn through liquid-phase doping to form a coating layer on the surface. By controlling parameters such as pH, temperature, and solid content, modified manganese tetroxide is obtained. This document can improve the cycling performance of lithium manganese oxide; however, the cycling performance of this structure of manganese tetroxide is poor under high-temperature conditions. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a manganese tetroxide material, its preparation method and application, which improves the structural stability of lithium manganese oxide and accelerates the lithium ion diffusion rate by preparing a sunflower-like manganese tetroxide product, thereby achieving a significant improvement in high-temperature cycling performance.

[0006] Specifically, the first aspect of this application provides a manganese tetroxide material, which has a sunflower-like structure. The sunflower-like structure refers to the fact that the manganese tetroxide particles are composed of radially arranged plate-like or columnar primary grains that are orderly assembled, and the cross-section of the particles exhibits a sunflower-like morphology that radiates outward from the center.

[0007] Furthermore, the average particle size D50 of the manganese tetroxide material is 5–13 μm.

[0008] The second aspect of this application provides a method for preparing manganese tetroxide material, comprising the following steps: S1. Preparation of manganese tetroxide seed crystals: Soluble manganese salt, precipitant, and complexing agent are added to the bottom liquid in a co-current flow and reacted in the presence of an oxidant to obtain manganese tetroxide seed crystals with an average particle size D50 of 2-5 μm. S2. Synthesis of sunflower-like structure of manganese tetroxide: Soluble manganese salt, precipitant and complexing agent are added concurrently to a system containing the manganese tetroxide seed crystals. The reaction continues in the presence of an oxidant. The amount of oxidant, pH value and concentration of complexing agent in the reaction system are controlled to make the manganese tetroxide crystals grow radially in an orderly manner to form a sunflower-like structure. S3. Post-processing steps: After the reaction is completed, solid-liquid separation, washing and drying are performed to obtain sunflower-shaped manganese tetroxide material.

[0009] Furthermore, in step S2, the amount of oxidant used is 3 to 10 times the theoretical amount, where the theoretical amount refers to the amount of Mn... 2+ The amount of oxidant required for complete oxidation to Mn3O4.

[0010] Furthermore, the concentration of the complexing agent in the reaction system in step S2 is 1–3 mol / L.

[0011] Furthermore, the pH value of the reaction system in step S2 is 8.5–9.9.

[0012] Further, step S2 controls the amount of oxidant O, the pH value P, and the concentration of the complexing agent C to ensure that the S value, as defined by the following formula, is ≥0.68: S = [0.35 F(O) + 0.4 G(P) + 0.25 H(C)] Φ(O, P, C) in:

[0013] When the oxidant ratio O is in the range of 3 to 10, F(O) is the normalized function of the oxidant dosage.

[0014] When the pH value P is in the range of 8.5 to 9.9, G(P) is the normalization function of the pH value.

[0015] When the concentration of the complexing agent C is in the range of 1–3 mol / L, H(C) is the normalized function of the concentration of the complexing agent. Φ(O,P,C) is a constraint function. When O, P, and C are all within the above range, Φ=1; otherwise, Φ=0.

[0016] The third aspect of this application provides the application of manganese tetroxide material in the preparation of lithium manganese oxide cathode material.

[0017] The fourth aspect of this application provides a method for preparing lithium manganese oxide cathode material, comprising the following steps: mixing manganese tetroxide material with a lithium source and calcining it at 750-800°C for 12-24 hours in an air or oxygen atmosphere to obtain lithium manganese oxide cathode material.

[0018] The present invention has the following beneficial effects: The manganese tetroxide (MnO) grain structure provided by this invention exhibits a unique sunflower-like shape. The interior of the MnO particles is composed of plate-like or columnar primary grains arranged radially in an orderly assembly. This orderly arrangement allows for clear observation of the particle cross-section, where the primary grains extend and distribute radially outward from the central region of the particle, resembling sunflower petals, thus forming a cross-sectional morphology similar to a sunflower head.

[0019] This unique microstructure endows the material with numerous advantages. First, the abundant gaps and channels formed between the radially arranged lamellar or columnar primary grains provide efficient diffusion paths for lithium ion migration, significantly accelerating the lithium ion transport rate within the material and contributing to improved rate performance. Second, the ordered assembly structure gives the material high overall structural stability, effectively buffering stress caused by volume changes during charging and discharging, reducing microcrack formation, and thus minimizing manganese ion dissolution. Furthermore, this sunflower-like structure provides the particles with a relatively suitable specific surface area, avoiding excessive contact with the electrolyte due to an excessively large specific surface area, which would exacerbate manganese dissolution, while ensuring sufficient reactive sites for the full electrochemical reaction. When the material lattice is influenced by Mn... 3+ When distortion occurs, the strong inter-grain bonding of the ordered arrangement can resist structural transformation to a certain extent, thereby enhancing the structural stability of lithium manganese oxide cathode material, significantly improving its high-temperature cycling performance, effectively alleviating capacity decay problems, and providing strong material support for the development of high-performance lithium-ion batteries. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 The image shows the morphology of manganese tetroxide prepared in Example 1. Figure 2 The morphology of manganese tetroxide prepared in Example 2 is shown in the image. Figure 3 The image shows the morphology of manganese tetroxide prepared in Example 3. Figure 4 The image shows the morphology of manganese tetroxide prepared in Comparative Example 1. Figure 5 The image shows the morphology of manganese tetroxide prepared in Comparative Example 2. Figure 6 The image shows the morphology of manganese tetroxide prepared in Comparative Example 3.

[0022] The purpose, features, and advantages of this accompanying drawing will be further explained in conjunction with the embodiments and with reference to the accompanying drawing. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0024] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0025] An embodiment of the first aspect of this application provides a manganese tetroxide material having a sunflower-like structure. The sunflower-like structure refers to the fact that the manganese tetroxide particles are composed of radially arranged plate-like or columnar primary grains that are orderly assembled, and the cross-section of the particles exhibits a sunflower-like morphology radiating outward from the center.

[0026] The manganese tetroxide (MnO) grain structure provided by this invention exhibits a unique sunflower-like shape. The interior of the MnO particles is composed of radially arranged, ordered primary grains of lamellar or columnar form. This ordered arrangement allows for a clear view of the primary grains radiating outwards from the center of the particle, like sunflower petals, creating a sunflower-like morphology in the cross-section. This unique microstructure provides the material with numerous advantages. First, the abundant gaps and channels between the radially arranged lamellar or columnar primary grains provide efficient diffusion paths for lithium ion migration, significantly accelerating the lithium ion transport rate within the material and contributing to improved rate performance. Second, the ordered assembly structure gives the material high overall structural stability, effectively buffering stress caused by volume changes during charging and discharging, reducing microcrack formation, and thus minimizing manganese ion dissolution. Furthermore, this sunflower-like structure gives the particles a relatively suitable specific surface area, which avoids excessive contact with the electrolyte due to an excessively large specific surface area, thus preventing the aggravation of manganese dissolution, while ensuring sufficient reactive sites, which is conducive to the full progress of the electrochemical reaction. When the material lattice is influenced by Mn... 3+When distortion occurs, the strong inter-grain bonding of the ordered arrangement can resist structural transformation to a certain extent, thereby enhancing the structural stability of lithium manganese oxide cathode material, significantly improving its high-temperature cycling performance, effectively alleviating capacity decay problems, and providing strong material support for the development of high-performance lithium-ion batteries.

[0027] Preferably, the average particle size D50 of the manganese tetroxide material is 5–13 μm.

[0028] An embodiment of the second aspect of this application provides a method for preparing manganese tetroxide material, comprising the following steps: S1. Preparation of manganese tetroxide seed crystals: Soluble manganese salt, precipitant, and complexing agent are added to the bottom liquid in a co-current flow and reacted in the presence of an oxidant to obtain manganese tetroxide seed crystals with an average particle size D50 of 2-5 μm. S2. Synthesis of sunflower-like structure of manganese tetroxide: Soluble manganese salt, precipitant and complexing agent are added concurrently to a system containing the manganese tetroxide seed crystals. The reaction continues in the presence of an oxidant. The amount of oxidant, pH value and concentration of complexing agent in the reaction system are controlled to make the manganese tetroxide crystals grow radially in an orderly manner to form a sunflower-like structure. S3. Post-processing steps: After the reaction is completed, solid-liquid separation, washing and drying are performed to obtain sunflower-shaped manganese tetroxide material.

[0029] Specifically, in step S1, the soluble manganese salt is a 0.5-3 mol / L manganese sulfate solution, the precipitant concentration is 2-12 mol / L, and the precipitant is one or more of sodium hydroxide, potassium hydroxide, ammonia, and barium hydroxide; the complexing agent is one or more of citric acid, ethylenediamine, ammonia, ammonium sulfate, ammonium chloride, nitrogenous triacetic acid, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, aminotriacetic acid, and ethylene glycol diethyl ether diaminetetraacetic acid; and the oxidizing agent is one or more of air, oxygen, hydrogen peroxide, and ozone.

[0030] Preparation of manganese tetroxide seed crystals: Using pure water as the base liquid, manganese sulfate, precipitant, and complexing agent were added to the reactor in a molar ratio of 1:(1.8-3):(0.5-2) in parallel flow. Oxidant was introduced according to the theoretical dosage. The reaction temperature was controlled at 60-70℃, the reaction time was 0.5-2h, and the product was aged for 1-4h. The product D50 was controlled to be 2-5μm to obtain manganese tetroxide seed crystals.

[0031] Excessive saturation can lead to explosive nucleation, which is not conducive to the production of ordered structures. Under these conditions, the manganese tetroxide particles are all disordered. If the crystal nucleus D50 is too large, it is not conducive to the continued growth of subsequent layered ordered structures on this basis.

[0032] In this embodiment, the synthesis of sunflower-like manganese tetroxide in step S2 involves adding manganese sulfate, a precipitant, and a complexing agent in a parallel stream to the solution containing manganese tetroxide crystal nuclei, wherein the reaction temperature is 60-90℃ and the reaction time is 10-40h.

[0033] The amount of oxidant used is 3 to 10 times the theoretical amount, where the theoretical amount refers to the amount of Mn... 2+ The molar amount of oxidant required for complete oxidation to Mn3O4. Higher concentrations of oxidant are beneficial for the formation of sunflower-like ordered structures, but excessive use of oxidant will increase costs and may also lead to over-oxidation.

[0034] In step S2, the concentration of the complexing agent in the reaction system is 1–3 mol / L. If the complexing agent concentration is too low, the reaction rate cannot be effectively controlled, and the explosive nucleation of the system is not conducive to the formation of an ordered structure. If the complexing agent concentration is too high, a large number of metal ions are "locked" by the complexing agent, resulting in an excessively low concentration of free metal ions in the solution. This leads to insufficient driving force (supersaturation) for the precipitation reaction, making the reaction slow and difficult to control, thus affecting crystal growth kinetics. Excessively high concentrations will disrupt this delicate balance, preventing the crystal from growing in the expected sunflower-like or layered direction in an orderly manner.

[0035] The pH of the reaction system in step S2 is 8.5–9.9. A higher pH environment affects the complexation-dissociation equilibrium and supersaturation of Mn ions. This can change the surface energy of different crystal planes and promote the formation of primary grains. However, if the pH is too high, the complexation effect weakens, and the explosive nucleation results in a disordered growth process, which is not conducive to the formation of an ordered sunflower-like structure.

[0036] The average particle size D50 of the manganese tetroxide seeds prepared in step S1 is 2–5 μm. Seeds within this particle size range can provide stable core support for the subsequent growth of sunflower-like structures. If the seed particle size is too small, it is easy to agglomerate during the subsequent growth process, resulting in disordered structural growth; if the particle size is too large, it is difficult to achieve radially ordered arrangement of primary grains on its surface, which is not conducive to the formation of a regular sunflower-like morphology.

[0037] Under the condition that the D50 of the seed crystal meets the 2-5 μm requirement described in step two, the probability of forming a sunflower-like structure can be calculated according to the formula. That is, step S2 controls the amount of oxidant O, the pH value P, and the concentration of the complexing agent C to ensure that the S value, defined by the following formula, is ≥0.68: S = [0.35 F(O) + 0.4 G(P) + 0.25 H(C)] Φ(O, P, C) in:

[0038] When the oxidant ratio O is in the range of 3 to 10, F(O) is the normalized function of the oxidant dosage.

[0039] When the pH value P is in the range of 8.5 to 9.9, G(P) is the normalization function of the pH value.

[0040] When the concentration of the complexing agent C is in the range of 1–3 mol / L, H(C) is the normalized function of the concentration of the complexing agent. Φ(O,P,C) is a constraint function. When O, P, and C are all within the above range, Φ=1; otherwise, Φ=0.

[0041] Φ = 0, resulting in S = 0 (completely infeasible) when any of the following conditions occur: O is in the range [3, 10]; P is in the range [8.5, 9.9]; C is in the range [1, 3]. Analysis of the experimental data revealed that the value of S needs to be ≥0.68 to guarantee the formation of the sunflower-like structure of manganese tetrahydropalmatine. S≥0.68 forms sunflower-like manganese tetroxide; When S≤0.68, it cannot form and will eventually accumulate.

[0042] The third aspect of this application provides the application of manganese tetroxide material in the preparation of lithium manganese oxide cathode material.

[0043] The fourth aspect of this application provides a method for preparing lithium manganese oxide cathode material, comprising the following steps: adding manganese tetroxide and lithium carbonate in a molar ratio of Li / Mn of 0.55:1, and calcining at 750-800°C for 12-24 hours in an air or oxygen atmosphere to obtain lithium manganese oxide cathode material.

[0044] Example The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0045] Example 1 Step 1: Raw material preparation. 1 mol / L manganese sulfate solution, 3 mol / L sodium hydroxide as the precipitant, 2 mol / L ammonia water as the complexing agent, and air as the oxidizing agent; Step 2: Preparation of manganese tetroxide seed crystals. Using pure water as the base liquid, manganese sulfate, precipitant, and complexing agent were added to the reactor in a molar ratio of 1:2:0.8 in parallel flow. Oxidant was introduced according to the theoretical dosage. The reaction temperature was controlled at 66℃, the reaction time was 1 hour, and the product was aged for 1.5 hours. The product D50 was 2.75 μm, thus obtaining manganese tetroxide seed crystals. Step 3: Synthesis of manganese tetroxide with a sunflower-like structure. Manganese sulfate, a precipitant, and a complexing agent were added concurrently to the solution containing manganese tetroxide crystal nuclei. The reaction temperature was 60°C; the amount of oxidant used was 6.5 times the theoretical amount; the pH was 9.05; the concentration of the complexing agent in the system was 2 mol / L; the reaction time was 28 h. After the reaction, the product was filtered, washed, and dried. The final particle size was 11.5 μm. Morphology diagram is shown below. Figure 1 .

[0046] Work out:

[0047] This is the theoretically optimal value, and this example ultimately yields a sunflower-like structure of manganese tetroxide. Step 4: Preparation of lithium manganese oxide material. Manganese tetroxide with an internal morphology resembling a sunflower was added to lithium carbonate at a molar ratio of Li / Mn of 0.55:1. The mixture was calcined at 770℃ for 18 hours in air, and then crushed and graded to obtain the lithium manganese oxide cathode material product.

[0048] Example 2 Step 1: Raw material preparation. 2.5 mol / L manganese sulfate, a mixed solution of 8 mol / L sodium hydroxide and potassium hydroxide as precipitants, a mixed solution of 1.9 mol / L ammonium sulfate and ammonia as complexing agents, and oxygen and air as oxidants; Step 2: Preparation of manganese tetroxide seed crystals. Using pure water as the base liquid, manganese sulfate, precipitant, and complexing agent were added to the reactor in a molar ratio of 1:2.5:1.2 in parallel flow. Oxidant was introduced according to the theoretical dosage. The reaction temperature was controlled at 68℃, the reaction time was 2 hours, and the product was aged for 3 hours. The product D50 was controlled to be 3.5 μm to obtain manganese tetroxide seed crystals.

[0049] Step 3: Synthesis of manganese tetroxide with a sunflower-like structure. Manganese sulfate, a precipitant, and a complexing agent were added concurrently to the solution containing manganese tetroxide crystal nuclei. The reaction temperature was 75℃; the amount of oxidant used was 7 times the theoretical amount; the pH was 9; the concentration of the complexing agent in the system was 1.9 mol / L; the reaction time was 12 h. After the reaction, the product was filtered, washed, and dried. The final particle size was 8.9 μm, and the morphology is shown in the figure. Figure 2 .

[0050] Work out:

[0051] This example ultimately yielded a sunflower-like structure of manganese tetroxide.

[0052] Step 4: Preparation of lithium manganese oxide material. Manganese tetroxide with an internal morphology resembling a sunflower was added to lithium carbonate at a molar ratio of Li / Mn of 0.55:1. The mixture was calcined at 770℃ for 18 hours in air, and then crushed and graded to obtain the lithium manganese oxide cathode material product.

[0053] Example 3 Step 1: Raw material preparation. The raw materials include 1.5 mol / L manganese sulfate, 5 mol / L sodium hydroxide as the precipitant, a mixed solution of 1.6 mol / L ethylenediamine and aminotriacetic acid as the complexing agent, and oxygen and ozone as the oxidizing agents.

[0054] Step 2: Preparation of manganese tetroxide seed crystals. Using pure water as the base liquid, manganese sulfate, precipitant, and complexing agent were added to the reactor in a molar ratio of 1:2.8:1.8 in parallel flow. Oxidant was introduced according to the theoretical dosage. The reaction temperature was controlled at 70℃, the reaction time was 0.5 h, and the product was aged for 1 h. The D50 of the product was controlled to be 2.2 μm to obtain manganese tetroxide seed crystals. Step 3: Synthesis of manganese tetroxide with a sunflower-like structure. Manganese sulfate, a precipitant, and a complexing agent were added concurrently to the solution containing manganese tetroxide crystal nuclei. The reaction temperature was 90°C; the amount of oxidant used was 9.8 times the theoretical amount; the pH was 8.96; the concentration of the complexing agent in the system was 1.35 mol / L; the reaction time was 38 h. After the reaction, the product was filtered, washed, and dried. The final particle size was 12.7 μm. Morphology diagram is shown below. Figure 3 .

[0055] Work out:

[0056] This example ultimately yielded a sunflower-like structure of manganese tetroxide.

[0057] Step 4: Preparation of lithium manganese oxide material. Manganese tetroxide with an internal morphology resembling a sunflower was added to lithium carbonate at a molar ratio of Li / Mn of 0.55:1. The mixture was calcined at 770℃ for 18 hours in air, and then crushed and graded to obtain the lithium manganese oxide cathode material product.

[0058] Comparative Example 1 Step 1: Raw material preparation. The raw materials are: 1 mol / L manganese sulfate, 1 mol / L sodium hydroxide as the precipitant, 0.5 mol / L ammonia as the complexing agent, and air and hydrogen peroxide as the oxidizing agents. Step 2: Preparation of manganese tetroxide seed crystals. Using pure water as the base liquid, manganese sulfate, precipitant, and complexing agent were added to the reactor in a molar ratio of 1:2.6:1.3 in parallel flow. Oxidant was introduced according to the theoretical dosage. The reaction temperature was controlled at 60℃, the reaction time was 1 hour, and the product was aged for 1 hour. The D50 of the product was controlled to be 6.3 μm to obtain manganese tetroxide seed crystals. Step 3: Synthesis of manganese tetroxide with a sunflower-like structure. Manganese sulfate, a precipitant, and a complexing agent were added concurrently to the solution containing manganese tetroxide crystal nuclei. The reaction temperature was 80°C; the amount of oxidant used was 7 times the theoretical amount; the pH was 9.05; the concentration of the complexing agent in the system was 2 mol / L; the reaction time was 25 h. After the reaction, the product was filtered, washed, and dried. The final particle size was 14.2 μm. Morphology diagram is shown below. Figure 4 .

[0059] The final calculation is as follows:

[0060] Although The value meets the requirements, but because the preconditions are not met, the D50 of the seed crystal is too large, which causes the particle size of the final product to exceed the range. In this example, the final product forms a stacked manganese tetroxide. Step 4: Preparation of lithium manganese oxide material. Manganese tetroxide and lithium carbonate were added at a molar ratio of Li / Mn of 0.55:1, and calcined at 770℃ for 18 hours in air. After crushing and grading, the lithium manganese oxide cathode material product was obtained.

[0061] Comparative Example 2 Step 1: Raw material preparation. A mixed solution of 2.5 mol / L manganese sulfate, 1 mol / L potassium hydroxide as the precipitant, 1.5 mol / L ammonium chloride as the complexing agent, ammonium sulfate, and citric acid; oxidizing agents are oxygen and air. Step 2: Preparation of manganese tetroxide seed crystals. Using pure water as the base liquid, manganese sulfate, precipitant, and complexing agent were added to the reactor in a molar ratio of 1:2.4:1.5 in parallel flow. Oxidant was introduced according to the theoretical dosage. The reaction temperature was controlled at 65℃, the reaction time was 0.5 h, and the product was aged for 3 h. The D50 of the product was controlled to be 3.3 μm to obtain manganese tetroxide seed crystals. Step 3: Synthesis of manganese tetroxide with a sunflower-like structure. Manganese sulfate, a precipitant, and a complexing agent were added concurrently to the solution containing manganese tetroxide crystal nuclei. The reaction temperature was 85°C; the amount of oxidant used was 5 times the theoretical amount; the pH was 8.7; the concentration of the complexing agent in the system was 1.3 mol / L; the reaction time was 18 h. After the reaction, the product was filtered, washed, and dried. The final particle size was 10.8 μm. Morphology diagram is shown below. Figure 5 .

[0062] The final calculation is as follows:

[0063] Since S < 0.68, this example ultimately forms a stacked manganese tetroxide.

[0064] Step 4: Preparation of lithium manganese oxide material. Manganese tetroxide and lithium carbonate were added at a molar ratio of Li / Mn of 0.55:1, and calcined at 770℃ for 18 hours in air. After crushing and grading, the lithium manganese oxide cathode material product was obtained.

[0065] Comparative Example 3 Step 1: Raw material preparation. 1.5 mol / L manganese sulfate, a precipitant of 9 mol / L sodium hydroxide and barium hydroxide mixed solution, and a complexing agent of 3 mol / L ethylenediamine and ethylenediaminetetraacetic acid mixed solution; Step 2: Preparation of manganese tetroxide seed crystals. Using pure water as the base liquid, manganese sulfate, precipitant, and complexing agent were added to the reactor in a molar ratio of 1:1.8:0.6 in parallel flow. Oxidant was introduced according to the theoretical dosage. The reaction temperature was controlled at 67℃, the reaction time was 2 hours, and the product was aged for 1 hour. The product D50 was controlled to be 4.5 μm to obtain manganese tetroxide seed crystals.

[0066] Step 3: Synthesis of manganese tetroxide with a sunflower-like structure. Manganese sulfate, a precipitant, and a complexing agent were added concurrently to the solution containing manganese tetroxide crystal nuclei. The reaction temperature was 65°C; the amount of oxidant used was three times the theoretical amount; the pH was 8.35; the concentration of the complexing agent in the system was 1.5 mol / L; the reaction time was 18 h. After the reaction, the product was filtered, washed, and dried. The final particle size was 12.3 μm, and the morphology is shown in the figure. Figure 6 .

[0067] Because the pH during the reaction is 8.35, which is smaller than the pH range of 8.5-9.9, and S=0, this embodiment also ultimately forms a stacked structure of manganese tetroxide.

[0068] Step 4: Preparation of lithium manganese oxide material. Manganese tetroxide and lithium carbonate were added at a molar ratio of Li / Mn of 0.55:1, and calcined at 770℃ for 18 hours in air. After crushing and grading, the lithium manganese oxide cathode material product was obtained.

[0069] Table 1 summarizes the oxidant dosage O, pH value P, and complexing agent concentration C in Examples 1-3 and Comparative Examples 1-3.

[0070] Table 1. Summary of component dosages for Examples 1-3 and Comparative Examples 1-3

[0071] Electrochemical performance testing: Using lithium foil as the negative electrode and lithium manganese oxide cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 as the positive electrode, secondary button batteries, model CR2025, were prepared. Tests were conducted at 4.2V voltage and temperatures of 55°C (high temperature) and room temperature (25°C). First, a 0.2C charge / discharge cycle was performed, followed by a 1C charge / discharge cycle test to measure the initial charge / discharge efficiency and the initial 1C discharge capacity. The test results are shown in Tables 2 and 3.

[0072] Table 2 Test results under high temperature conditions

[0073]

[0074] From the two tables above, it can be seen that in Examples 1-3 of this application, when S≥0.68, a special sunflower-like structure was formed, and the capacity retention rate after room temperature and high temperature cycling both exceeded 98%. In Comparative Example 1, due to the failure to meet the seed size requirement, a stacked manganese tetroxide was formed, and the capacity retention rate after room temperature cycling was about 2% lower than that of the sunflower-like manganese tetroxide, and the capacity retention rate after high temperature cycling was nearly 4% lower than that of the sunflower-like manganese tetroxide. In Comparative Examples 2 and 3, when S<0.68, the formation of the internal sunflower-like structure was affected, and the morphology was stacked, resulting in a 1-3% lower capacity retention rate at room temperature and a 5-6% lower capacity retention rate at high temperature compared to the formed examples.

[0075] Therefore, for manganese tetroxide, the sunflower-like structure can maintain a better capacity retention rate at both room temperature and high temperature, while the stacked structure is generally worse than the sunflower-like structure. The capacity retention rate is better at room temperature, but poor at high temperature, and can no longer meet the requirements of lithium manganese oxide cathode materials.

[0076] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A manganese tetroxide material, characterized in that, The manganese tetroxide material has a sunflower-like structure, which means that the manganese tetroxide particles are composed of radially arranged plate-like or columnar primary grains that are orderly assembled, and the cross-section of the particles shows a sunflower-like morphology radiating outward from the center.

2. The manganese tetroxide material according to claim 1, characterized in that, The average particle size D50 of the manganese tetroxide material is 5–13 μm.

3. A method for preparing manganese tetroxide material, characterized in that, The method for preparing manganese tetroxide according to claim 1 or 2 includes the following steps: S1. Preparation of manganese tetroxide seed crystals: Soluble manganese salt, precipitant, and complexing agent are added to the bottom liquid in a co-current flow and reacted in the presence of an oxidant to obtain manganese tetroxide seed crystals with an average particle size D50 of 2-5 μm. S2. Synthesis of sunflower-like structure of manganese tetroxide: Soluble manganese salt, precipitant and complexing agent are added concurrently to a system containing the manganese tetroxide seed crystals. The reaction continues in the presence of an oxidant. The amount of oxidant, pH value and concentration of complexing agent in the reaction system are controlled to make the manganese tetroxide crystals grow radially in an orderly manner to form a sunflower-like structure. S3. Post-processing steps: After the reaction is completed, solid-liquid separation, washing and drying are performed to obtain sunflower-shaped manganese tetroxide material.

4. The method for preparing manganese tetroxide material according to claim 3, characterized in that, In step S2, the amount of oxidant used is 3 to 10 times the theoretical amount, where the theoretical amount refers to the amount of Mn... 2+ The molar amount of oxidant required for complete oxidation to Mn3O4.

5. The method for preparing manganese tetroxide material according to claim 3, characterized in that, The concentration of the complexing agent in the reaction system in step S2 is 1–3 mol / L.

6. The method for preparing manganese tetroxide material according to claim 3, characterized in that, The pH value of the reaction system in step S2 is 8.5 to 9.

9.

7. The method for preparing manganese tetroxide material according to claim 3, characterized in that, Step S2 controls the amount of oxidant O, pH value P, and complexing agent concentration C to ensure that the S value, as defined by the following formula, is ≥0.68: S =[0.35 F(O) + 0.4 G(P) + 0.25 H(C) ] Φ(O, P, C) in: When the oxidant ratio O is in the range of 3 to 10, F(O) is the normalized function of the oxidant dosage. When the pH value P is in the range of 8.5 to 9.9, G(P) is the normalization function of the pH value. When the concentration of the complexing agent C is in the range of 1–3 mol / L, H(C) is the normalized function of the concentration of the complexing agent. Φ(O,P,C) is a constraint function. When O, P, and C are all within the above range, Φ=1; otherwise, Φ=0.

8. The application of a manganese tetroxide material as described in claim 1 or 2, or a manganese tetroxide material prepared by the method described in any one of claims 3-7, in the preparation of lithium manganese oxide cathode materials.

9. A method for preparing a lithium manganese oxide cathode material, characterized in that, The process includes the following steps: mixing the manganese tetroxide material as described in claim 1 or 2 or the manganese tetroxide material prepared by the method described in any one of claims 3-7 with a lithium source, and calcining it at 750-800°C for 12-24 hours in an air or oxygen atmosphere to obtain a lithium manganese oxide cathode material.

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