Preparation method of high-purity phase battery-grade trimanganese tetraoxide

Abstract

The application discloses a preparation method of high-purity-phase battery-grade trimanganese tetraoxide. Pure water is firstly added into a reaction kettle and stirring is started, then ammonium salt and an additive are added and oxidation gas is introduced, then manganese powder is continuously added into the reaction kettle, the pH of the reaction liquid is controlled to be 7-9 during the feeding process, and high-purity-phase battery-grade trimanganese tetraoxide is obtained after treatment. In the application, the manganese powder is continuously added and the pH is controlled to be 7-9 during the whole reaction process, and the two technologies are combined, so that the prepared trimanganese tetraoxide does not contain needle-shaped heterogeneous phases, and pure-phase trimanganese tetraoxide is obtained.

Description

Technical Field

[0001] This invention belongs to the field of energy materials technology, and in particular relates to a battery-grade manganese tetroxide and its preparation method. Background Technology

[0002] As a new generation of green energy, the performance of cathode materials is crucial for lithium-ion batteries. Among them, spinel-type lithium manganese oxide (LiMn2O4) has become one of the important cathode materials in the fields of power batteries and energy storage batteries due to its abundant raw materials, low cost, high safety, and environmental friendliness. The synthesis methods of LiMn2O4 mainly include high-temperature solid-state method, microwave synthesis method, melt impregnation method, hydrothermal synthesis method, co-precipitation method, and sol-gel method. Among these, the solid-state reaction method, which involves mixing a lithium source (such as lithium carbonate or lithium hydroxide) with a manganese source precursor in a certain proportion and then calcining at high temperature, has the advantages of simple operation, large-scale production capability, and low cost, and is widely used in the industry. The physicochemical properties of the manganese source precursor, such as purity, particle size distribution, morphology, and tap density, directly determine the electrochemical performance, processing performance, and consistency of the final LiMn2O4 product. Among the many manganese sources, manganese tetroxide (Mn3O4) is the ideal precursor for preparing high-performance LiMn2O4 because its manganese valence state is closest to that of spinel LiMn2O4. During calcination, the oxygen stoichiometry is stable, and both have regular spinel structures, which reduces phase structure changes and improves structural integrity.

[0003] The mainstream industrial method for preparing battery-grade Mn3O4 is the manganese powder oxidation method (referred to as the "manganese powder method"). This method uses high-purity electrolytic manganese as raw material. After crushing and pulverizing, the manganese is mixed with water to form a suspension. The suspension is then subjected to an oxidation reaction at 50-80°C in the presence of a catalyst (such as ammonium salt) and air or oxygen-containing gas is introduced to ultimately obtain Mn3O4. The advantage of this method is that it starts with high-purity electrolytic manganese, theoretically possessing the potential to produce high-purity products. Furthermore, the process is simple, the conditions are mild, and the yield is high, making it suitable for large-scale continuous production. However, the manganese powder method has an unresolved problem: the product generally contains a large number of needle-like heterogeneous impurities. Analysis has identified the main components as γ-MnOOH, Mn2O3, and Mn3O4. The presence of these impurities means that the product is not pure Mn3O4; its chemical composition is heterogeneous, forming irregular morphologies within the material. This severely affects the structural uniformity and stability of manganese tetroxide, failing to meet the stringent high-quality requirements for battery cathode materials. These highly reactive impurity phases can trigger uncontrollable side reactions during the subsequent LiMn2O4 sintering process, affecting the integrity of the spinel structure and becoming a potential cause of electrochemical performance degradation. When needle-like heterogeneous impurity phases are embedded inside Mn3O4 secondary particles, they hinder the close packing of primary particles, generating numerous voids and defects within the particles and significantly reducing the tap density of the material. When needle-like heterogeneous impurity phases exist between secondary particles, they act as "bridges," connecting multiple secondary particles together to form agglomerates. This macroscopically manifests as a wider particle size distribution and an increase in large particles, which not only hinders subsequent sieving and classification but also leads to uneven reactions during LiMn2O4 sintering, affecting product consistency.

[0004] The battery-grade Mn3O4 preparation methods disclosed in Chinese patent applications CN118239521A and CN120698506A produce needle-like heterogeneous impurities, but their formation mechanism is not analyzed in depth. Chinese patent application CN110040783A discloses a method for preparing needle-like / rod-like nano-Mn3O4, which is a hydrothermal reaction at temperatures above 100℃, significantly different from the conditions of the traditional manganese powder method. Furthermore, existing research on the manganese powder method regarding needle-like heterogeneous impurities is minimal. Summary of the Invention

[0005] To overcome the problem of numerous needle-like heterogeneous phases in existing manganese tetroxide products, this invention provides a high-purity phase battery-grade manganese tetroxide and its preparation method. By precisely controlling the feeding method of manganese powder and the pH of the synthesis process, high-purity phase battery-grade manganese tetroxide is obtained.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] This invention provides a method for preparing high-purity phase-cell battery-grade manganese tetroxide, comprising the following steps: S1. Add pure water to the reactor and start stirring. Add ammonium salt and additives and introduce oxidizing gas. S2. Manganese powder is added to the reaction vessel in step S1 by continuous feeding, and the pH of the reaction solution is controlled to be 7-9 during the feeding process. S3. After the reaction is completed, the manganese tetroxide slurry is aged and then processed to obtain high-purity battery-grade manganese tetroxide.

[0008] In existing technologies, the one-time addition of manganese powder causes a sharp increase in the pH of the environment to around 10. Furthermore, the slow mass transfer of large amounts of manganese powder in a large-capacity reactor leads to localized pH inconsistencies. This unstable pH fluctuation results in significant differences in the size, morphology, and zeta potential of primary particles, further causing secondary particles to become coarse and irregular, and the presence of needle-like heterogeneous phases in the product, severely impacting the electrochemical performance of the material. Moreover, even if the pH is controlled in the later stages of the reaction, needle-like heterogeneous phases still appear because the initial pH fluctuations have already had an irreversible effect. Therefore, this invention employs a continuous addition of manganese powder, while precisely controlling the pH of the reaction solution to 7–9 throughout the reaction process. This significantly suppresses side reaction pathways such as disproportionation, improving the selectivity of the conversion of divalent manganese ions to the target manganese tetroxide. On the other hand, the continuous addition of manganese powder and the specific pH environment effectively regulate the generation and growth rate of crystal nuclei, suppressing the formation of needle-like heterogeneous phases from the crystallographic source, ultimately yielding impurity-free, high-purity battery-grade manganese tetroxide.

[0009] As an optional implementation, in the preparation method provided by the present invention, in step S3, the pH of the solution is controlled to be 7-9 during the aging process and in the manganese tetroxide slurry.

[0010] In this invention, even during the aging process after the reaction is completed and the manganese tetroxide slurry is not separated into dry and wet states in time, the pH needs to be controlled at 7 to 9. If the pH is not controlled, a large number of needle-like heterogeneous phases will still be generated.

[0011] As an optional implementation method, in the preparation method provided by the present invention, in step S2, for a small-scale test of 5-10 L, the manganese powder is added at a rate of 1.0-3.0 g / min; for a small-scale test of 6-20 m... 3 In the pilot test, the manganese powder was added at a rate of 2.5–6 kg / min.

[0012] In this invention, the addition rate of manganese powder in the small-scale test is 1.0~3.0 g / min, and the addition rate of manganese powder in the pilot-scale test is 2.5~6 kg / min.

[0013] As an optional implementation, in the preparation method provided by the present invention, in step S2, the purity of the manganese powder is >99.9 wt.%, and the sieving rate through a 100-mesh sieve is 100%.

[0014] As an optional implementation, in the preparation method provided by the present invention, in step S2, one or more of ammonia solution, sodium hydroxide solution or potassium hydroxide solution are used to adjust the pH of the solution.

[0015] As an optional implementation, in the preparation method provided by the present invention, in step S2, the temperature of the solution during the reaction process is 50-80°C.

[0016] Furthermore, the preferred temperature is 60–70°C.

[0017] As an optional implementation, in the preparation method provided by the present invention, in step S2, the pH of the reaction solution is controlled to be 7.7 to 8.8 during the feeding process.

[0018] As an optional implementation, in the preparation method provided by the present invention, in step S1, the ammonium salt is selected from one or more of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium formate, and ammonium acetate, and the concentration of the ammonium salt is 13-16 g / L.

[0019] As an optional implementation, in the preparation method provided by the present invention, in step S1, the additive is selected from one or more of polyvinylpyrrolidone, ammonium polyacrylate, sodium carboxymethyl cellulose, sodium polystyrene sulfonate, and polyethylene glycol.

[0020] As an optional implementation, in the preparation method provided by the present invention, step S3 includes filtration, washing and drying, washing until the conductivity of the filtrate is <100 µs / cm, drying at 110°C and drying in a vacuum drying oven for 20 h.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In this invention, by continuously adding manganese powder and controlling the pH to be 7-9 throughout the reaction process, the two technologies work together to prepare manganese tetroxide without needle-like heterogeneous impurities, thus obtaining pure phase manganese tetroxide.

[0022] (2) Based on the already large-scale industrialized and technologically mature metal manganese oxidation method, this invention achieves a leapfrog improvement in product quality simply by improving the way manganese powder is added and the precise pH monitoring and control technology during the reaction process. This improvement does not require complex and expensive additional equipment, does not change the core architecture of the existing production process, is easy to operate, has minimal cost increase, is highly compatible with the process, and is easy to promote. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a scanning electron microscope image of the manganese tetroxide product prepared in Example 1; Figure 2 This is a scanning electron microscope image of the manganese tetroxide product prepared in Example 2; Figure 3 This is a scanning electron microscope image of the manganese tetroxide product prepared in Example 3; Figure 4 This is a scanning electron microscope image of the manganese tetroxide product prepared in Example 4; Figure 5 This is a scanning electron microscope image of the manganese tetroxide product prepared in Comparative Example 1; Figure 6 This is a scanning electron microscope image of the manganese tetroxide product prepared in Comparative Example 2; Figure 7 This is a scanning electron microscope image of the manganese tetroxide product prepared in Comparative Example 3; Figure 8 The images are scanning electron microscope (SEM) images of the manganese tetroxide products prepared in Comparative Example 4. The left image is an SEM image of the product after aging with pH controlled, and the right image is an SEM image of the product after aging without pH controlled. Figure 9 This is a transmission electron microscope (TEM) image and a diffraction pattern analysis of the needle-like heterogeneous phase obtained in Comparative Example 2. Detailed Implementation

[0025] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0026] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0027] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0028] Example 1 Add 1.5 L of pure water to a 5 L reactor, along with 15 g of ammonium acetate, 0.15 g of polyvinylpyrrolidone, and 0.15 g of ammonium polyacrylate. Start stirring at 1200 rpm, with an oxygen flow rate of 2 L / min. Maintain the reactor temperature at 55±5℃. Weigh 200 g of manganese powder (purity >99.9 wt.%, 100% sieve pass rate through a 100-mesh sieve) and add it at a rate of 1.0 g / min. Simultaneously add 8% ammonia water, maintaining the pH range at 7.7–7.8. After the manganese powder is added, continue adding ammonia water to maintain the pH within this range. Aging is completed after 1 h. During aging and before filtration and washing, maintain the pH range at 7.7–7.8 to obtain a manganese tetroxide slurry. Filter and wash the slurry, dry it in a vacuum oven at 110℃ for 20 h, and then grind it to obtain manganese tetroxide powder.

[0029] The scanning electron microscope image of the manganese tetroxide product prepared in this example is shown below. Figure 1 As shown, from Figure 1 It can be seen that there are no needle-like foreign phases in the product.

[0030] Example 2 Add 1.5 L of pure water to a 5 L reactor, along with 13 g of ammonium sulfate, 0.15 g of polyvinylpyrrolidone, and 0.15 g of ammonium polyacrylate. Start stirring at 1200 rpm, with an oxygen flow rate of 2 L / min. Maintain the reactor temperature at 55±5℃. Weigh 200 g of manganese powder (purity >99.9 wt.%, 100% sieve pass rate through a 100-mesh sieve) and add it at a rate of 2.0 g / min. Simultaneously add a mixed alkaline solution containing 8% ammonia and 3% sodium hydroxide, maintaining the pH range at 8.2–8.3. After the manganese powder is added, continue adding the mixed alkaline solution while maintaining the pH within this range. Aging is completed after 1 h. During aging and before filtration and washing, the pH range is maintained at 8.2–8.3 to obtain a manganese tetroxide slurry. Filter and wash the slurry, dry it in a vacuum oven at 110℃ for 20 h, and then grind it to obtain manganese tetroxide powder.

[0031] The scanning electron microscope image of the manganese tetroxide product prepared in this example is shown below. Figure 2 As shown, from Figure 2 It can be seen that there are no needle-like foreign phases in the product.

[0032] Example 3 Add 1.5 L of pure water to a 5 L reactor, along with 16 g of ammonium nitrate, 0.15 g of polyvinylpyrrolidone, and 0.15 g of ammonium polyacrylate. Start stirring at 1200 rpm, with an oxygen flow rate of 2 L / min. Maintain the reactor temperature at 55±5℃. Weigh 200 g of manganese powder (purity >99.9 wt.%, 100% sieve pass rate through 100 mesh), and add it at a rate of 3.0 g / min. Simultaneously add a mixed alkaline solution containing 8% ammonia and 5% potassium hydroxide, maintaining the pH range at 8.7–8.8. After the manganese powder is added, continue adding the mixed alkaline solution while maintaining the pH within this range. Aging is completed after 1 h. During aging and before filtration and washing, the pH range is maintained at 8.7–8.8 to obtain a manganese tetroxide slurry. Filter and wash the slurry, dry it in a vacuum oven at 110℃ for 20 h, and then grind it to obtain manganese tetroxide powder.

[0033] The scanning electron microscope image of the manganese tetroxide product prepared in this example is shown below. Figure 3 As shown, from Figure 3 It can be seen that there are no needle-like foreign phases in the product.

[0034] Example 4 towards 6 m 3 4.8 m were added to the reactor. 3 Add pure water, along with 48 kg of ammonium acetate, 0.3 kg of polyvinylpyrrolidone, and 0.3 kg of ammonium polyacrylate. Start stirring at 240 rpm and introduce air at a rate of 240 m³ / min. 3 The temperature inside the reactor was controlled at 65±5℃. 1000 kg of manganese powder was weighed and fed at a rate of 2.5 kg / min, while simultaneously adding ammonia water containing 8% ammonia, maintaining the pH range at 7.7–7.8. After the manganese powder was added, ammonia water was continued to be added to maintain the pH within this range. The process was completed after 8 hours of aging, yielding a manganese tetroxide slurry. The slurry was filtered, washed, and dried in a vacuum oven at 110℃ for 20 hours. After grinding, manganese tetroxide powder was obtained.

[0035] The scanning electron microscope image of the manganese tetroxide product prepared in this example is shown below. Figure 4 As shown, from Figure 4 It can be seen that there are no needle-like foreign phases in the product.

[0036] Comparative Example 1 Add 1.5 L of pure water to a 5 L reactor, along with 15 g of ammonium acetate, 0.15 g of polyvinylpyrrolidone, and 0.15 g of ammonium polyacrylate. Start stirring at 1200 rpm, with an oxygen flow rate of 2 L / min. Maintain the reactor temperature at 55±5℃. Weigh 200 g of manganese powder and add it at a rate of 1.0 g / min. After the manganese powder is added, continue aging for 1 hour to obtain a manganese tetroxide slurry. Filter and wash the slurry, dry it in a vacuum oven at 110℃ for 20 hours, and then grind it to obtain manganese tetroxide powder.

[0037] In the small-scale experiment, the pH was not controlled during the reaction process. The scanning electron microscope image of the manganese tetroxide product prepared in this example is shown below. Figure 5 As shown, from Figure 5 It can be seen that the product contains a large number of needle-like heterogeneous phases.

[0038] Comparative Example 2 towards 6 m 3 4.8 m were added to the reactor. 3 Add pure water, along with 48 kg of ammonium acetate, 0.3 kg of polyvinylpyrrolidone, and 0.3 kg of ammonium polyacrylate. Start stirring at 240 rpm and introduce air at a rate of 240 m³ / min. 3 The temperature inside the reactor was controlled at 65±5℃. 1000 kg of manganese powder was weighed and fed at a rate of 2.5 kg / min. After the manganese powder was added, the reactor was aged for another 8 hours to obtain manganese tetroxide slurry. The slurry was filtered, washed, and dried in a vacuum oven at 110℃ for 20 hours. After grinding, manganese tetroxide powder was obtained.

[0039] In the pilot-scale experiment, the pH was not controlled during the reaction process. The scanning electron microscope image of the manganese tetroxide product prepared in this example is shown below. Figure 6 As shown, from Figure 6 It can be seen that the product contains a large number of needle-like heterogeneous impurities. The transmission electron microscopy and diffraction pattern phase analysis images of the manganese tetroxide product prepared in this example are shown below. Figure 9 As shown, the needle-like structures are composed of γ-MnOOH, Mn2O3, and Mn3O4, and are mostly heterogeneous phases.

[0040] Comparative Example 3 The difference from Example 3 is that the manganese powder is not added continuously, but is added all at once after the bottom liquid is mixed. During the reaction, a mixed alkaline solution containing 8% ammonia and 5% potassium hydroxide is added to control the pH range of 8.7 to 8.8.

[0041] The scanning electron microscope image of the manganese tetroxide product prepared in this example is shown below. Figure 7 As shown, from Figure 7It can be seen that the product contains needle-like heterogeneous phases.

[0042] Comparative Example 4 The difference from Example 4 is that the pH was no longer controlled after aging, and the reaction was stopped after stirring continued until the pH dropped naturally to around 5.8.

[0043] The scanning electron microscope image of the manganese tetroxide product prepared in this example is shown below. Figure 8 As shown, from Figure 8 It can be seen that when pH is controlled after aging, the product does not contain needle-like heterogeneous phases; when pH is not controlled after aging, the product contains a large number of needle-like heterogeneous phases.

[0044] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity battery-grade manganese tetroxide, characterized in that, Includes the following steps: S1. Add pure water to the reactor and start stirring. Add ammonium salt and additives and introduce oxidizing gas. S2. Manganese powder is added to the reaction vessel in step S1 by continuous feeding, and the pH of the reaction solution is controlled to be 7-9 during the feeding process. S3. After the reaction is completed, the manganese tetroxide slurry is aged and then processed to obtain high-purity battery-grade manganese tetroxide.

2. The method for preparing high-purity battery-grade manganese tetroxide according to claim 1, characterized in that, In step S2, for small-scale tests of 5–10 L, the manganese powder is added at a rate of 1.0–3.0 g / min; for tests of 6–20 m... 3 In the pilot test, the manganese powder was added at a rate of 2.5–6 kg / min.

3. The method for preparing high-purity phase-cell battery-grade manganese tetroxide according to claim 1, characterized in that, In step S3, the pH of the solution is controlled to be 7-9 during the aging process and in the manganese tetroxide slurry.

4. The method for preparing high-purity battery-grade manganese tetroxide according to claim 1, characterized in that, In step S2, the purity of the manganese powder is >99.9 wt.%, and the sieving rate through a 100-mesh sieve is 100%.

5. The method for preparing high-purity phase-cell battery-grade manganese tetroxide according to claim 1, characterized in that, In step S2, the pH of the solution is adjusted using one or more of the following: ammonia solution, sodium hydroxide solution, or potassium hydroxide solution.

6. The method for preparing high-purity phase-cell battery-grade manganese tetroxide according to claim 1, characterized in that, In step S2, the temperature of the solution during the reaction is 50–80°C.

7. The method for preparing high-purity phase-cell battery-grade manganese tetroxide according to claim 1, characterized in that, In step S2, the pH of the reaction solution is controlled to be 7.7 to 8.8 during the feeding process.

8. The method for preparing high-purity phase-phase battery-grade manganese tetroxide according to claim 1, characterized in that, In step S1, the ammonium salt is selected from one or more of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium formate, and ammonium acetate, and the concentration of the ammonium salt is 13-16 g / L.

9. The method for preparing high-purity phase-cell battery-grade manganese tetroxide according to claim 1, characterized in that, In step S1, the additive is selected from one or more of polyvinylpyrrolidone, ammonium polyacrylate, sodium carboxymethyl cellulose, sodium polystyrene sulfonate, and polyethylene glycol.

10. The method for preparing high-purity phase-cell battery-grade manganese tetroxide according to claim 1, characterized in that, In step S3, the process includes filtration, washing and drying. The filtrate is washed until the conductivity is <100 µs / cm, and the drying temperature is 110℃. The filtrate is dried in a vacuum drying oven for 20 h.

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