Manganese tetraoxide with low specific surface area and preparation method thereof

Abstract

The invention belongs to the technical field of manganous-manganic oxide production, and particularly discloses low-specific-surface-area manganous-manganic oxide and a preparation method thereof.In the process of preparing manganous-manganic oxide through one-step oxidation, the oxygen introduction rate and the stirring linear speed at different reaction stages are accurately adjusted, so that the specific surface area of manganous-manganic oxide is increased, and the specific surface area of manganous-manganic oxide is increased. Furthermore, accurate cooperative control on crystal nucleation and growth processes is realized, so that a manganous-manganic oxide product with a low specific surface area can be stably obtained, and the requirement of a high-performance battery material on the low specific surface area is met. The method can be suitable for reaction equipment of different scales, and is beneficial for realizing large-scale production of products. In addition, the method is short in process, easy to operate, high in production efficiency and stable and controllable in product quality. And the obtained product is low in specific surface area, moderate in particle size, uniform in morphology and relatively high in tap density. The lithium manganate material adopting the product shows excellent cycle performance, the service life of the battery is remarkably prolonged, and the energy density of the battery is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a manganese-manganic oxide material, in particular to a manganese-manganic oxide with a low specific surface area and a preparation method thereof, belonging to the technical field of battery material production and preparation. Background Art

[0002] Lithium manganese oxide (LiMn2O4), an important cathode material for lithium-ion batteries, has been widely used in new energy vehicles, energy storage systems, portable electronic devices, and industrial applications due to its wide availability of raw materials, low cost, superior safety, and excellent rate and low-temperature performance. However, its low energy density and short cycle life have limited its further market adoption and application expansion.

[0003] As a precursor material for lithium manganate (LiMnO), manganese dioxide (Mn3O4) plays a decisive role in the electrochemical performance of cathode materials. In rapidly developing fields such as new energy vehicles and energy storage systems, the demand for battery materials with high energy density and long cycle life is increasingly urgent. The preparation of battery-grade manganese dioxide must meet requirements such as high purity, high tap density, suitable particle morphology, and low specific surface area. The specific surface area (BET), as one of the key parameters affecting battery cycling performance, has a significant impact on material properties.

[0004] Currently, the main methods for preparing manganese tetraoxide include the metal manganese method, the roasting method, and the manganese salt method. Among them, the metal manganese method is the main process for preparing battery-grade manganese tetraoxide in industry, and manganese tetraoxide is prepared from a suspension of manganese oxide powder. This method is mature and easy to operate, but the preparation cost is high, and the resulting product has a large specific surface area, which makes it difficult to meet the needs of high-performance battery materials. The roasting method is limited by its high energy consumption and high impurity content. In contrast, the manganese salt method for preparing manganese tetraoxide has attracted much attention due to its advantages such as low cost, wide raw material sources, easy control of grain morphology, and uniform particle size distribution. The traditional manganese salt method for preparing manganese tetraoxide is usually divided into two steps: first, an alkaline precipitant is added to the manganese salt to form a Mn(OH)2 precipitate, which is then filtered, washed, and slurried and oxidized to produce Mn3O4 particles. However, the traditional two-step oxidation method requires the use of inert gas protection throughout the preparation of Mn(OH)2, which leads to a complex process flow and limited control over product morphology and particle size, making it difficult to stably obtain low specific surface area manganese oxide materials. Summary of the Invention

[0005] In response to the problem that existing technologies are difficult to stably obtain low-specific surface area manganese tetraoxide, the present invention provides a low-specific surface area manganese tetraoxide and a preparation method thereof. Manganese tetraoxide is obtained by a direct one-step reaction using a divalent manganese salt and an ammonia solution as raw materials in an oxygen atmosphere. At the same time, according to the respective characteristics of the crystal nucleation and growth processes during the reaction, the oxygen introduction rate and the stirring linear velocity are precisely controlled to stably obtain a manganese tetraoxide product with a specific surface area of ​​less than 0.4 m² / g. The present invention can significantly shorten the preparation process while having a high direct manganese yield. The obtained manganese tetraoxide product also has the advantages of moderate particle size and high tap density. After calcination, the prepared lithium manganate material exhibits excellent cycle performance and has significant industrial application value.

[0006] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are specifically described as follows: According to a first embodiment of the present invention, there is provided a method for preparing manganese manganese tetroxide with low specific surface area: A method for preparing manganese tetraoxide with low specific surface area, the method is as follows: deionized water is added to a reaction vessel as a reaction base liquid, and a manganese salt solution and an ammonia solution are simultaneously added to the reaction base liquid under an oxygen atmosphere for reaction, wherein the reaction comprises: firstly, a first-stage reaction is carried out in an environment of a first oxygen introduction rate and a first stirring linear velocity. After the first-stage reaction is completed, a second-stage reaction is carried out in an environment of a second oxygen introduction rate and a second stirring linear velocity. After the second-stage reaction is completed, a third-stage reaction is finally carried out in an environment of a second oxygen introduction rate and a third stirring linear velocity. After the third-stage reaction is completed, a solid product is separated and washed and dried to obtain the target manganese tetraoxide product. Wherein, the second oxygen introduction rate is less than the first oxygen introduction rate, the second stirring linear velocity is less than the first stirring linear velocity, and the third stirring linear velocity is less than the second stirring linear velocity.

[0007] Preferably, a control model for obtaining the oxygen inlet rate is established with the volume of the reaction container as a variable, and the control model is as follows: (1).

[0008] In formula (1), Q is the oxygen inlet rate, L / min. V is the volume of the reaction vessel, L. A1 is the flow control coefficient, which ranges from 0.8 to 1.2 for the first stage reaction and from 0.2 to 0.3 for the second and third stages. C1 is the flow control constant, which ranges from -0.5 to 0.5.

[0009] Preferably, a control model for the stirring linear velocity is established with the volume of the reaction container as a variable. The control model is as follows: S=A2(1.1V+85.5)+C2 (2).

[0010] In formula (2), S is the stirring linear velocity, cm / s. V is the volume of the reaction vessel, L. A2 is the linear velocity control coefficient, which ranges from 0.9 to 1.1 for a one-stage reaction, from 0.25 to 0.35 for a two-stage reaction, and from 0.05 to 0.2 for a three-stage reaction. C1 is the linear velocity control constant, which ranges from -5 to 5.

[0011] Preferably, the manganese salt solution is one or more of manganese sulfate solution, manganese chloride solution, manganese nitrate solution, and manganese acetate solution, preferably manganese sulfate solution.

[0012] Preferably, the concentration of the manganese salt solution is 1-3 mol / L, preferably 1.2-2.5 mol / L, more preferably 1.5-2 mol / L.

[0013] Preferably, the concentration of the aqueous ammonia solution is 1.5-5 mol / L, preferably 2-4.5 mol / L, more preferably 3-4 mol / L.

[0014] Preferably, the manganese salt solution and the ammonia solution are added in such an amount that the ammonia-manganese ratio of the reaction system is 1.5-2.5, preferably 1.8-2.2.

[0015] Preferably, the amount of reaction base liquid added is 0.15 to 35 times, preferably 0.2 to 0.3 times, the total volume of the reaction container.

[0016] Preferably, the temperature during the reaction of the manganese salt solution and the ammonia solution is 50-90°C, preferably 55-85°C, more preferably 60-80°C.

[0017] Preferably, the duration of one reaction is 1 to 6 hours, preferably 2 to 4 hours.

[0018] Preferably, the duration of the second-stage reaction is 6 to 15 hours, preferably 8 to 12 hours.

[0019] Preferably, the three-stage reaction lasts for 1 to 6 hours, preferably 2 to 4 hours.

[0020] According to a second embodiment of the present invention, there is provided a manganese manganese oxide with a low specific surface area: A trimanganese tetraoxide with a low specific surface area is prepared according to the method described in the first embodiment.

[0021] Preferably, the specific surface area of ​​the trimanganese tetraoxide with low specific surface area is 0.2-0.4 m² / g. The tap density of the trimanganese tetraoxide with low specific surface area is 2.0-2.8 g / cm 3The D50 of the trimanganese tetraoxide with low specific surface area is 5-20 μm.

[0022] In the present invention, the manganese salt solutions used are prepared by mixing a soluble manganese salt with deionized water in a certain ratio. The ammonia solution used is prepared by adding a certain proportion of deionized water to concentrated ammonia water. The soluble manganese salts include, but are not limited to, manganese sulfate, manganese chloride, manganese nitrate, manganese acetate, and the like, and also include their respective hydrates. For example, manganese sulfate includes anhydrous manganese sulfate, manganese sulfate monohydrate, manganese sulfate tetrahydrate, and hydrated manganese sulfates of other water contents.

[0023] In the present invention, the formation of Mn3O4 particles follows the processes of nucleation, growth, agglomeration, and aggregation. Nucleation is the process of crystal precipitation from the liquid phase, and the growth process is the process of the formed crystal nucleus growing into a primary particle. Nucleation and growth are in a relationship of mutual growth and decline, and are also the key to controlling particle morphology. There are two ways for crystal growth. One is coagulation growth, that is, under the convection brought by stirring, collisions occur between the crystal nucleus and the particles, thereby agglomerating into larger particles; the other is that solute molecules, molecular clusters, etc. are adsorbed on the surface of larger crystals, thereby achieving stacking growth. Different growth stages of crystals have different characteristics, and experimental parameters have different effects on their growth in this process. Through research, it was found that: introducing a large amount of oxygen and increasing the stirring rate in the early stage of the reaction can help to increase the reaction rate, increase the supersaturation of the system, and induce a large amount of nucleation; appropriately reducing the oxygen intake and stirring rate in the middle and late stages of the reaction can slow down the nucleation rate, and reserving sufficient time can promote the full growth of the crystal nucleus. This crystallization process of explosive nucleation in the early stage and slow growth in the later stage can improve the sphericity and particle size distribution of the product, thereby reducing the specific surface area of ​​the product.

[0024] In the present invention, oxygen (oxygen volume concentration is generally not less than 20%) is used as the oxidant. After the reaction base solution is heated to the predetermined reaction temperature, oxygen is introduced while stirring. During the reaction, the entire system is kept in an oxygen atmosphere, thereby achieving the purpose of preparing manganese tetraoxide in a one-step process. The main reactions occurring during the preparation process are as follows: 6Mn 2+ +O2+12NH3·H2O=2Mn3O4+12NH4 + +6H2O.

[0025] During the reaction, Mn 2+ Under the action of oxygen oxidation, Mn3O4 and H + Ammonia has two main functions in the system. One is to neutralize the H generated in the solution. + , to avoid the system pH from continuously decreasing, affecting the product phase and reaction rate, and secondly, with Mn2+ Coordinate to form complexes and regulate the system Mn 2+ Supersaturation.

[0026] In the present invention, it is found through research that the oxygen introduction rate needs to be reasonably adjusted at different stages of the reaction, thereby making Mn 2+ While being directly oxidized to Mn3O4, it helps to stably obtain a manganese tetraoxide material with uniform particle size and morphology, high tap density and low specific surface area. In the present invention, after experimental research, it was found that if the process of obtaining manganese tetraoxide by reacting a manganese salt solution and an ammonia solution in a reaction vessel is divided into an early reaction (i.e., a one-stage reaction), an intermediate reaction (i.e., a two-stage reaction), and a late reaction (i.e., a three-stage reaction), and based on the difference in the volume of the reaction vessel at each stage, the oxygen introduction rate during the reaction at each stage is reasonably controlled and adjusted, thereby helping to obtain a manganese tetraoxide product with a smaller specific surface area. Generally, during the reaction process at each stage, the real-time oxygen introduction rate satisfies the following control model: (1).

[0027] In formula (1), Q is the oxygen introduction rate, L / min. V is the volume of the reaction vessel, L. A1 is the flow control coefficient. In the first stage of the reaction, A1 is 0.8-1.2 (the oxygen introduction rate calculated based on this A1 value is the oxygen introduction rate in the first stage of the reaction), and in the second and third stages of the reaction, A1 is 0.2-0.3 (the oxygen introduction rate calculated based on this A1 value is the oxygen introduction rate in the second and third stages of the reaction). C1 is the flow control constant, which is -0.5-0.5. In other words, when the operating conditions such as the reactor and process control remain basically unchanged, the flow control coefficient and flow control constant of the current operating conditions are also determined (calculated through empirical summary). Then, the optimal oxygen introduction rate for each stage of the reaction under the current operating conditions can be calculated according to formula (1).

[0028] Furthermore, by rationally controlling and adjusting the stirring speed during each stage of the reaction, it is further ensured that a manganese oxide product with a smaller specific surface area is obtained. Generally, during the reaction process of each stage, the real-time stirring speed of each stage satisfies the following control model: S=A2(1.1V+85.5)+C2 (2).

[0029] In formula (2), S is the stirring linear velocity, cm / s. V is the volume of the reaction vessel, L. A2 is the linear velocity control coefficient. In a single-stage reaction, A2 is 0.9–1.1 (the linear velocity calculated based on this A2 value is the stirring linear velocity in the single-stage reaction), in a two-stage reaction, A2 is 0.25–0.35 (the linear velocity calculated based on this A2 value is the stirring linear velocity in the single-stage reaction), and in a three-stage reaction, A2 is 0.05–0.2 (the linear velocity calculated based on this A2 value is the stirring linear velocity in the single-stage reaction). C1 is the linear velocity control constant, which is -5–5. In other words, when the operating conditions such as the reactor and process control remain essentially unchanged, the linear velocity control coefficient and linear velocity control constant for the current operating conditions are also determined (derived through empirical summary and deduction). The optimal linear velocity for each stage of the reaction under the current operating conditions can be deduced using formula (2).

[0030] That is to say, the present invention summarizes and formulates the corresponding process parameter control model according to the volume difference of different reaction vessels, thereby achieving low specific surface area manganese oxide products with similar physical properties in reaction vessels of different scales, providing process guidance for realizing large-scale production of products. Compared with the traditional step-by-step precipitation method, this process greatly shortens the preparation process and has a higher manganese direct yield. The obtained product not only has a moderate particle size, but also has a higher tap density. After roasting treatment, the prepared lithium manganate material shows excellent cycle performance and has significant industrial application value.

[0031] It should be noted that all formulas in the present invention are obtained by fitting by the inventors based on experiments and engineering applications, and all calculations are numerical values ​​converted according to prescribed units, and are obtained by substituting the converted numerical values ​​into the formulas (after converting the units, only the numerical values ​​are substituted into the formulas for calculation, without substituting the units; the units are only used to adjust the size of the numerical values).

[0032] Compared with the prior art, the beneficial technical effects of the present invention are as follows: 1: This method achieves precise coordinated control of crystal nucleation and growth during the one-step oxidation process to prepare manganese tetraoxide by precisely adjusting the oxygen inlet rate and stirring velocity at different stages of the reaction. This allows for the stable production of manganese tetraoxide with a low specific surface area (less than 0.4 m² / g), meeting the low specific surface area requirement for high-performance battery materials. This method is applicable to reactors of varying sizes, providing process guidance for achieving large-scale production.

[0033] The method of the present invention is simple, easy to operate, highly efficient, and produces stable and controllable product quality. The resulting manganese oxide product has a low specific surface area, a moderate particle size, uniform morphology, and a high tap density. The lithium manganate material prepared using this product exhibits excellent cycling performance, significantly improving the battery's lifespan and energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is an SEM image of manganese tetraoxide prepared in Example 1 of the present invention.

[0035] Figure 2 This is the isothermal adsorption-desorption curve of manganese tetraoxide prepared in Example 1 of the present invention.

[0036] Figure 3 This is the isothermal adsorption-desorption curve of manganese tetraoxide prepared in Example 2 of the present invention.

[0037] Figure 4 This is the isothermal adsorption-desorption curve of trimanganese tetraoxide prepared in Example 3 of the present invention.

[0038] Figure 5 This is the isothermal adsorption-desorption curve of trimanganese tetraoxide prepared in Comparative Example 1 of the present invention.

[0039] Figure 6 This is a cycle performance diagram of lithium manganate prepared using manganese tetraoxide according to Example 1 of the present invention. DETAILED DESCRIPTION

[0040] The technical solutions of the present invention are illustrated below with examples, and the scope of protection requested by the present invention includes but is not limited to the following embodiments. Example 1

[0041] First, prepare 1.5 mol / L manganese sulfate solution and 3.0 mol / L ammonia solution separately. Use a 5L reactor as the reaction vessel and 1.5L deionized water as the reaction base liquid. Under the current operating conditions: the flow control coefficient A1 is 0.89 for the first stage reaction, 0.22 for the second and third stages, and the flow control constant C1 is 0.01. The linear velocity control coefficient A2 is 0.99 for the first stage reaction, 0.33 for the second stage reaction, and 0.11 for the third stage reaction, and the linear velocity control constant C2 is 0. According to formula (1) and formula (2), the following is calculated: the first oxygen introduction rate in the first stage reaction is about 2.00 L / min, and the first stirring linear velocity is about 90 cm / s; the second oxygen introduction rate in the second stage reaction is about 0.50 L / min, and the second stirring linear velocity is about 30 cm / s; the third oxygen introduction rate in the third stage reaction is about 0.50 L / min, and the third stirring linear velocity is about 10 cm / s.

[0042] The specific preparation process is as follows: first, add 1.5L of deionized water as the reaction base liquid to a 5L reactor and heat it to a constant temperature of 70°C; then, introduce oxygen into the reactor and adjust the oxygen flow rate to 2.00L / min, adjust the stirring speed of the stirrer in the reactor to 90cm / s, then pump manganese sulfate solution into the reactor at a flow rate of 56mL / h, and introduce the corresponding amount of ammonia solution with an ammonia-manganese ratio of 2, and continue stirring and reacting for 2 hours; then adjust the oxygen flow rate to 0.50L / min, adjust the stirring speed to 30cm / s, and continue the reaction for 8 hours; finally, stop pumping the manganese sulfate solution and ammonia solution, maintain the oxygen flow rate at 0.50L / min, adjust the stirring speed to 10cm / s, and continue the reaction for 2 hours. After the reaction is completed, filter the reaction slurry, wash the resulting solid product with deionized water three times, and dry it to obtain the manganese tetraoxide product. Example 2

[0043] First, prepare 1.5 mol / L manganese sulfate solution and 3.0 mol / L ammonia solution, respectively, and use a 20 L reactor as the reaction vessel and 6 L of deionized water as the reaction base liquid. Under the current operating conditions: the flow control coefficient A1 is 0.89 for the first stage reaction, 0.22 for the second and third stages, and the flow control constant C1 is 0.02. The linear velocity control coefficient A2 is 1.02 for the first stage reaction, 0.33 for the second stage reaction, and 0.11 for the third stage reaction, with a linear velocity control constant C2 of 0.6. According to formula (1) and formula (2), the first oxygen introduction rate in the first stage reaction is about 4.00 L / min, and the first stirring linear velocity is about 110 cm / s; the second oxygen introduction rate in the second stage reaction is about 1.00 L / min, and the second stirring linear velocity is about 36 cm / s; the third oxygen introduction rate in the third stage reaction is about 1.00 L / min, and the third stirring linear velocity is about 12 cm / s.

[0044] The specific preparation process is as follows: First, add 6L of deionized water as the reaction base liquid to a 20L reactor and heat it to a constant temperature of 70°C; then, introduce oxygen into the reactor and adjust the oxygen flow rate to 4.00L / min. Adjust the stirring speed of the stirrer in the reactor to 110cm / s. Then, pump the manganese sulfate solution at a flow rate of 224mL / h, and introduce the corresponding amount of ammonia solution with an ammonia-manganese ratio of 2, and continue stirring for 2 hours; then adjust the oxygen flow rate to 1.00L / min, adjust the stirring speed to 36cm / s, and continue the reaction for 8 hours; finally, stop pumping the manganese sulfate solution and ammonia solution, maintain the oxygen flow rate at 1.00L / min, adjust the stirring speed to 12cm / s, and continue the reaction for 2 hours. After the reaction is completed, filter the reaction slurry, wash the resulting solid product with deionized water three times, and dry it to obtain the manganese tetraoxide product. Example 3

[0045] First, prepare 1.5 mol / L manganese sulfate solution and 3.0 mol / L ammonia solution separately. Use a 50 L reactor as the reaction vessel and 15 L of deionized water as the reaction base liquid. Under the current operating conditions: the flow control coefficient A1 is 0.89 for the first stage reaction, 0.23 for the second and third stages, and the flow control constant C1 is 0.01. The linear velocity control coefficient A2 is 1 for the first stage reaction, 0.30 for the second stage reaction, and 0.10 for the third stage reaction, and the linear velocity control constant C2 is 1. According to formula (1) and formula (2), the first oxygen introduction rate in the first stage reaction is about 6.31 L / min, and the first stirring linear velocity is about 141 cm / s; the second oxygen introduction rate in the second stage reaction is about 1.64 L / min, and the second stirring linear velocity is about 43 cm / s; the third oxygen introduction rate in the third stage reaction is about 1.64 L / min, and the third stirring linear velocity is about 15 cm / s.

[0046] The specific preparation process is as follows: First, add 15L of deionized water as the reaction base liquid to a 50L reactor and heat it to a constant temperature of 70°C; then, introduce oxygen into the reactor and adjust the oxygen flow rate to 6.31L / min. Adjust the stirring speed of the stirrer in the reactor to 141cm / s. Then, pump the manganese sulfate solution at a flow rate of 560mL / h, and introduce the corresponding amount of ammonia solution with an ammonia-manganese ratio of 2, and continue stirring for 2 hours. Then, adjust the oxygen flow rate to 1.64L / min, adjust the stirring speed to 43cm / s, and continue the reaction for 8 hours. Finally, stop pumping the manganese sulfate solution and ammonia solution, maintain the oxygen flow rate at 1.64L / min, adjust the stirring speed to 15cm / s, and continue the reaction for 2 hours. After the reaction is completed, filter the reaction slurry, wash the resulting solid product with deionized water three times, and dry it to obtain the manganese tetraoxide product. Example 4

[0047] First, prepare 1.5 mol / L manganese sulfate solution and 3.0 mol / L ammonia solution separately. Use a 5L reactor as the reaction vessel and 1.5L deionized water as the reaction base liquid. Under the current operating conditions: the flow control coefficient A1 is 0.89 for the first stage reaction, 0.22 for the second and third stages, and the flow control constant C1 is 0.5. The linear velocity control coefficient A2 is 0.99 for the first stage reaction, 0.33 for the second stage reaction, and 0.11 for the third stage reaction, and the linear velocity control constant C2 is 0. According to formula (1) and formula (2), the first oxygen introduction rate in the first stage reaction is about 2.49 L / min, and the first stirring linear velocity is about 90 cm / s; the second oxygen introduction rate in the second stage reaction is about 0.99 L / min, and the second stirring linear velocity is about 30 cm / s; the third oxygen introduction rate in the third stage reaction is about 0.99 L / min, and the third stirring linear velocity is about 10 cm / s.

[0048] The specific preparation process is as follows: first, add 1.5L of deionized water as the reaction base liquid to a 5L reactor and heat it to a constant temperature of 70°C; then, introduce oxygen into the reactor and adjust the oxygen flow rate to 2.49L / min. Adjust the stirring speed of the stirrer in the reactor to 90cm / s. Then, pump manganese sulfate solution at a flow rate of 56mL / h, and introduce the corresponding amount of ammonia solution with an ammonia-manganese ratio of 2, and continue stirring for 2 hours; then adjust the oxygen flow rate to 0.99L / min, adjust the stirring speed to 30cm / s, and continue the reaction for 8 hours; finally, stop pumping manganese sulfate solution and ammonia solution, maintain the oxygen flow rate at 0.99L / min, adjust the stirring speed to 10cm / s, and continue the reaction for 2 hours. After the reaction is completed, filter the reaction slurry, wash the resulting solid product with deionized water three times, and dry it to obtain the manganese tetraoxide product. Example 5

[0049] First, prepare 1.5 mol / L manganese sulfate solution and 3.0 mol / L ammonia solution separately. Use a 5L reactor as the reaction vessel and 1.5L deionized water as the reaction base liquid. Under the current operating conditions: the flow control coefficient A1 is 0.89 for the first stage reaction, 0.22 for the second and third stages, and the flow control constant C1 is 0.01. The linear velocity control coefficient A2 is 1.15 for the first stage reaction, 0.34 for the second stage reaction, and 0.08 for the third stage reaction, with a linear velocity control constant C2 of 5. According to formula (1) and formula (2), the first oxygen introduction rate in the first stage reaction is about 2.00 L / min, and the first stirring linear velocity is about 110 cm / s; the second oxygen introduction rate in the second stage reaction is about 0.50 L / min, and the second stirring linear velocity is about 36 cm / s; the third oxygen introduction rate in the third stage reaction is about 0.50 L / min, and the third stirring linear velocity is about 12 cm / s.

[0050] The specific preparation process is as follows: first, add 1.5L of deionized water as the reaction base liquid to a 5L reactor and heat it to a constant temperature of 70°C; then, introduce oxygen into the reactor and adjust the oxygen flow rate to 2.00L / min. Adjust the stirring speed of the stirrer in the reactor to 110cm / s. Then, pump the manganese sulfate solution at a flow rate of 56mL / h, and introduce the corresponding amount of ammonia solution with an ammonia-manganese ratio of 2, and continue stirring for 2 hours; then adjust the oxygen flow rate to 0.50L / min, adjust the stirring speed to 36cm / s, and continue the reaction for 8 hours; finally, stop pumping the manganese sulfate solution and ammonia solution, maintain the oxygen flow rate at 0.50L / min, adjust the stirring speed to 12cm / s, and continue the reaction for 2 hours. After the reaction is completed, filter the reaction slurry, wash the resulting solid product with deionized water three times, and dry it to obtain the manganese tetraoxide product. Example 6

[0051] Example 1 was repeated except that the reaction temperature was adjusted from 70°C to 75°C. Example 7

[0052] Example 1 was repeated except that a corresponding amount of aqueous ammonia solution was introduced during the reaction at an ammonia to manganese ratio of 2.2. Example 8

[0053] Example 1 was repeated except that a corresponding amount of aqueous ammonia solution was introduced during the reaction at an ammonia to manganese ratio of 2.5. Example 9

[0054] Example 1 was repeated except that a corresponding amount of aqueous ammonia solution was introduced during the reaction at an ammonia to manganese ratio of 1.8. Example 10

[0055] Example 1 was repeated except that a corresponding amount of aqueous ammonia solution was introduced during the reaction at an ammonia to manganese ratio of 1.5. Example 11

[0056] Example 1 was repeated except that the concentration of the manganese sulfate solution was 2 mol / L. Example 12

[0057] Example 1 was repeated except that the concentration of the ammonia solution was 4 mol / L.

[0058] Comparative Example 1 Example 1 was repeated, except that the first oxygen introduction rate was directly adjusted from 2 L / min to 0.6 L / min.

[0059] Comparative Example 2 Example 1 was repeated, except that the second oxygen introduction rate and the third oxygen introduction rate were both directly adjusted from 0.5 L / min to 2 L / min.

[0060] Comparative Example 3 Example 1 was repeated, except that the first stirring linear velocity was directly adjusted from 90 cm / s to 40 cm / s.

[0061] Comparative Example 4 Example 1 was repeated, except that the second stirring linear velocity was directly adjusted from 30 cm / s to 60 cm / s.

[0062] Comparative Example 5 Example 1 was repeated, except that the third stirring linear speed was directly adjusted from 10 cm / s to 30 cm / s.

[0063] Comparative Example 6 Example 1 was repeated, except that the second stirring linear speed and the third stirring linear speed were both directly adjusted to 90 cm / s.

[0064] Comparative Example 7 First, prepare 1.5 mol / L manganese sulfate solution and 3.0 mol / L ammonia solution, then add 1.5 L of deionized water to a 5 L reactor and heat to 70 ° C. Nitrogen is introduced into the reactor for 30 minutes, and the stirring speed of the stirrer in the reactor is adjusted to 90 cm / s. Then, manganese sulfate solution is pumped into the reactor at a flow rate of 56 mL / h under a nitrogen atmosphere, and the ammonia solution is introduced to maintain the ammonia-manganese ratio at 2. The reaction is stirred for 12 hours. After the reaction is completed, the addition of manganese sulfate solution and ammonia solution is stopped, the gas is changed to oxygen, and the reaction is continued for 8 hours. After the reaction is completed, the reaction slurry is filtered, and the solid product is washed three times with deionized water. Finally, it is dried to obtain a manganese tetraoxide product with a low specific surface area.

[0065] Table 1 is a comparison of the performance of the manganese tetraoxide products obtained in each embodiment and comparative example: Application Examples

[0066] The manganese tetraoxide prepared in each embodiment and comparative example was fully mixed with lithium carbonate, wherein the lithium content was 5%. The mixed powder was pre-calcined at 500°C for 4 hours and then calcined at 800°C for 12 hours to obtain the corresponding lithium manganate positive electrode materials. Then, button batteries were prepared using each lithium manganate positive electrode material as a raw material. The above-mentioned button batteries were subjected to cycle performance tests using an electrochemical charge and discharge tester from Wuhan Blue Electric. The voltage range was 3.0~4.3V, and the cycle process was: 0.1C activation for 5 cycles, and then 1C (148mAh / g) for 200 cycles. Their electrochemical properties were tested as follows: Table 2 is the comparison of the battery cycle performance test results

[0067] In the present invention, the specific surface area of ​​the product is tested in accordance with YB / T 4736-2019.

[0068] In the present invention, the tap density of the product is tested in accordance with YB / T 4736-2019.

[0069] In the present invention, the test of product D50 particle size is carried out in accordance with YB / T 4736-2019.

[0070] In the present invention, the test of manganese content in the product is carried out in accordance with YB / T 4736-2019.

[0071] In the present invention, the cycle performance test is carried out in accordance with GB / T 39861-2021.

[0072] In the present invention, the manganese sulfate used was purchased from Cangzhou Liding Chemical Products Co., Ltd.

[0073] In the present invention, the ammonia water used was purchased from Jinan Yifengyuan Biotechnology Co., Ltd.

Claims

1. A method for preparing manganese manganese tetroxide with low specific surface area, characterized in that: The method comprises the following steps: adding deionized water as a reaction base liquid into a reaction container, and simultaneously adding a manganese salt solution and an ammonia solution into the reaction base liquid under an oxygen atmosphere for reaction. The reaction comprises: firstly carrying out a first-stage reaction in an environment of a first oxygen introduction rate and a first stirring linear speed; after the first-stage reaction is completed, carrying out a second-stage reaction in an environment of a second oxygen introduction rate and a second stirring linear speed; after the second-stage reaction is completed, finally carrying out a third-stage reaction in an environment of a second oxygen introduction rate and a third stirring linear speed; after the third-stage reaction is completed, separating a solid product, washing the solid product, and drying the solid product to obtain a target trimanganese tetraoxide product; wherein the second oxygen introduction rate is lower than the first oxygen introduction rate, the second stirring linear speed is lower than the first stirring linear speed, and the third stirring linear speed is lower than the second stirring linear speed.

2. The method according to claim 1, wherein: Taking the volume of the reaction vessel as a variable, a control model for the oxygen inlet rate is established. The control model is as follows: （1）； In formula (1), Q is the oxygen introduction rate, L / min; V is the volume of the reaction vessel, L; A1 is the flow control coefficient, which is 0.8~1.2 in the first stage reaction and 0.2~0.3 in the second and third stage reactions; C1 is the flow control constant, which is -0.5~0.

5.

3. The method according to claim 1 or 2, characterized in that: Taking the volume of the reaction vessel as a variable, a control model for the stirring linear velocity is established. The control model is as follows: S=A2(1.1V+85.5)+C2 (2); In formula (2), S is the stirring linear velocity, cm / s; V is the volume of the reaction vessel, L; A2 is the linear velocity control coefficient, which is 0.9~1.1 in the first stage reaction, 0.25~0.35 in the second stage reaction, and 0.05~0.2 in the third stage reaction; C1 is the linear velocity control constant, which is -5~5.

4. The method according to any one of claims 1 to 3, characterized in that: The manganese salt solution is one or more of manganese sulfate solution, manganese chloride solution, manganese nitrate solution, and manganese acetate solution, preferably manganese sulfate solution.

5. The method according to any one of claims 1 to 4, characterized in that: The concentration of the manganese salt solution is 1-3 mol / L, preferably 1.2-2.5 mol / L, more preferably 1.5-2 mol / L; and / or The concentration of the ammonia solution is 1.5-5 mol / L, preferably 2-4.5 mol / L, and more preferably 3-4 mol / L.

6. The method according to any one of claims 1 to 5, characterized in that: The amount of the manganese salt solution and the ammonia solution added is such that the ammonia-manganese ratio of the reaction system is 1.5-2.5, preferably 1.8-2.

2.

7. The method according to any one of claims 1 to 6, characterized in that: The amount of reaction base liquid added is 0.15 to 0.4 times the total volume of the reaction container, preferably 0.2 to 0.3 times.

8. The method according to any one of claims 1 to 7, characterized in that: The temperature during the reaction of the manganese salt solution and the ammonia solution is 50 to 90°C, preferably 55 to 85°C, and more preferably 60 to 80°C.

9. The method according to any one of claims 1 to 8, characterized in that: The reaction time is 1 to 6 hours, preferably 2 to 4 hours; and / or The duration of the second stage reaction is 6 to 15 hours, preferably 8 to 12 hours; and / or The duration of the three-stage reaction is 1 to 6 hours, preferably 2 to 4 hours.

10. A manganese manganese oxide with a low specific surface area, characterized in that: The manganese manganese oxide with low specific surface area is prepared by the method according to any one of claims 1 to 9; Preferably, the specific surface area of ​​the trimanganese tetraoxide with low specific surface area is 0.2-0.4 m² / g; the tap density of the trimanganese tetraoxide with low specific surface area is 2.0-2.8 g / cm 3 ; The D50 of the low specific surface area manganese tetraoxide is 5~20μm.

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