A method for reducing sodium ions in tricobalt tetraoxide by dialysis

Abstract

The application discloses a method for reducing sodium ions in tricobalt tetroxide by dialysis, and belongs to the technical field of tricobalt tetroxide processing. The method comprises the following steps: (1) dialysis bag pretreatment: selecting a dialysis bag with MW 3500-MW 14000, placing the dialysis bag in deionized water, heating and boiling for a period of time, then taking out the dialysis bag and soaking it in deionized water again; (2) powder slurry: mixing tricobalt tetroxide powder and deionized water to form a slurry; (3) dialysis: taking a certain amount of slurry into the dialysis bag, and performing dialysis after sealing; (4) process monitoring: replacing the deionized water outside the dialysis bag once every certain time until the sodium content is reduced to the target requirement, and obtaining impurity-removed tricobalt tetroxide. The method is simple in operation and low in cost, and does not need complex equipment and chemical reagents; and the process is mild, does not have adverse effects on the structure and performance of tricobalt tetroxide, can effectively reduce the sodium ion content in tricobalt tetroxide, and improves the product quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tricobalt tetraoxide processing, and particularly relates to a method for reducing sodium ions in tricobalt tetraoxide by dialysis. BACKGROUND

[0002] Tricobalt tetraoxide has a spinel structure of cubic crystal system Fd-3m space group. In this structure, oxygen atoms form a close-packed cubic dense structure, and cobalt ions occupy different positions. Tricobalt tetraoxide plays a very key role in the preparation of lithium cobaltate positive electrode materials, and lithium batteries made of lithium cobaltate are widely used in the battery field of 3C electronic products such as large-capacity mobile phones, notebook computers and digital cameras. 3C electronic products are favored by consumers because of their light and small characteristics, which requires the corresponding battery to have high energy density, thereby providing durable and stable power support for electronic products.

[0003] In the production and subsequent application of tricobalt tetraoxide, the problem of high sodium ion content has an adverse effect on its performance and safety that cannot be ignored. In terms of performance, too high sodium ion content may interfere with the crystal structure of tricobalt tetraoxide, thereby affecting the electrochemical performance of the lithium cobaltate positive electrode material made therefrom, such as reducing the charge and discharge efficiency of the battery, shortening the cycle life of the battery, etc. From the perspective of safety, too high sodium ion content may trigger side reactions inside the battery, and in some extreme cases may even cause the battery to overheat, bulge or catch fire and explode, etc. serious safety hazards.

[0004] Traditional methods for reducing sodium ions have many drawbacks. Some methods are inefficient, for example, some simple physical cleaning methods can only remove a small amount of sodium ions on the surface of tricobalt tetraoxide, and cannot remove more sodium ions inside the crystal, resulting in poor overall sodium removal effect. Although some chemical treatment methods can reduce the sodium ion content to some extent, the cost is too high, which undoubtedly increases the production and application cost of tricobalt tetraoxide, and reduces the competitiveness of the product in the market. In addition, some traditional methods may have other adverse effects on product quality during the sodium removal process, such as introducing new impurities or changing the crystal structure of tricobalt tetraoxide, etc., which will affect the performance of the lithium battery finally made. The common methods for reducing the content of sodium ions in the field at present include calcination method and centrifugal washing method.

[0005] Although calcination helps to remove sodium ions, it can also have some adverse effects that can damage the overall structure and performance of cobalt tetraoxide. During calcination, if the temperature is not properly controlled, cobalt tetraoxide can decompose or undergo phase transition, leading to the destruction of its spinel structure. High-temperature calcination can cause Co3O4 to partially transform into CoO, which not only changes the material's physical and chemical properties but also affects its performance. In addition, during high-temperature calcination, cobalt tetraoxide particles are prone to agglomeration and aggregation, especially during the initial stage of calcination when amorphous cobalt tetraoxide is formed. This agglomeration can lead to irregular particle shapes and reduced specific surface area, affecting its electrochemical performance and catalytic activity. During calcination, if the cooling rate is too fast or the calcination temperature fluctuates greatly, stress concentration areas can be generated within the cobalt tetraoxide, leading to microstructural defects. These defects can affect the material's electronic structure and magnetism. During rapid cooling, the internal crystals of Co3O4 can crack or defect due to uneven shrinkage, which can weaken its overall mechanical and functional properties. The length of calcination time and temperature can affect the size and morphology of cobalt tetraoxide crystals. Long-term high-temperature calcination can cause rapid grain growth, leading to a decrease in specific surface area and affecting its electrochemical performance.

[0006] Centrifugal washing method is to use the centrifugal force generated by high-speed rotation to make solid particles with higher density deposit at the bottom of the container, while liquid with lower density is thrown outside. By replacing the washing liquid and repeating the centrifugal process, impurity ions on the surface of solid particles can be gradually removed. During centrifugation, due to high-speed rotation, the component structure of cobalt tetraoxide may be affected by shear force, resulting in loss of activity or structure. Sodium ions in cobalt tetraoxide mainly move with the particles during centrifugal washing. Different settling speeds of cobalt tetraoxide particles can expose sodium ions when they are deposited, allowing them to be removed from the washing liquid. However, for sodium ions wrapped inside the particles, it is difficult to separate them by settling speed difference.

[0007] In summary, there is an urgent need to explore a new and effective method to reduce the sodium ion content in cobalt tetraoxide to ensure the performance and safety of cobalt tetraoxide and improve its applicability in the preparation of lithium cobaltate cathode materials, thereby promoting the optimized application of lithium batteries in 3C electronic products SUMMARY

[0008] In view of the above-mentioned defects of the prior art, in the first aspect of the present application, a method for efficiently, low-cost and mild process dialysis to reduce sodium ions in cobalt tetraoxide is provided, comprising the following steps:

[0009] (1) Dialysis bag pretreatment: select a dialysis bag with MW3500-MW14000, place the dialysis bag in deionized water, heat and boil for a period of time, then take out the dialysis bag and soak it in deionized water;

[0010] (2) Slurry the powder: Mix the tricobalt tetroxide powder with deionized water to form a slurry;

[0011] (3) Dialysis: Take a certain amount of slurry into the dialysis bag, and after packaging is completed, dialysis is carried out;

[0012] (4) Process monitoring: Replace the deionized water outside the dialysis bag every certain time until the sodium content is reduced to the target requirement, and obtain the impurity-removed tricobalt tetroxide.

[0013] The dialysis bag may contain trace amounts of sulfides, heavy metals and some impurities during production. Heating and boiling can effectively remove these harmful substances, reduce the pollution risk during dialysis, and ensure the safety and effectiveness of the dialysis process. Heating and boiling can expand the membrane pores of the dialysis bag, improve the dialysis efficiency, and also help remove the air bubbles that may exist inside the dialysis bag, avoiding the interference of air bubbles on the dialysis process, making the dialysis process faster and more effective, which is particularly critical to improve industrial production efficiency.

[0014] Preferably, in step (1), the dialysis bag is placed in deionized water and heated and boiled for 1-5 h.

[0015] Preferably, in step (2), the specific operation of slurry the powder is as follows: The tricobalt tetroxide powder and deionized water are stirred according to a certain solid-liquid ratio until a uniformly dispersed slurry is formed.

[0016] When the solid-liquid ratio of tricobalt tetroxide powder and deionized water is 1:20-30 g / g, the powder can be uniformly dispersed in the liquid to form a stable slurry. This ratio neither causes agglomeration due to too much powder nor makes the powder unable to disperse sufficiently due to too much liquid, which can ensure that the slurry has good flowability and is not prone to sedimentation or stratification, facilitating subsequent dialysis.

[0017] Further preferably, the solid-liquid ratio of the tricobalt tetroxide powder and deionized water is 1:20-30 g / g.

[0018] Similarly, when the stirring rate is controlled at 300-500 rpm, the tricobalt tetroxide powder is sufficiently dispersed in the deionized water. This speed range neither causes agglomeration due to too fast speed nor makes the powder unable to disperse uniformly due to too slow speed. Moderate stirring speed helps to break the agglomeration between the powders, making them uniformly distributed in the deionized water, thereby forming a uniform slurry. The stirring time is 3-5 h, which is long enough to ensure that the tricobalt tetroxide powder and deionized water are in sufficient contact and mixing. Within this time period, the powder has enough time to disperse in the liquid to form a uniform slurry. If the stirring time is too short, the powder may not be fully dispersed, affecting the uniformity of the slurry

[0019] Further preferably, the stirring speed is 300-500 rpm, and the stirring time is 3-5 h.

[0020] Industrial production is extremely sensitive to production efficiency per unit time. When the proportion of slurry volume to dialysis bag volume is between 40% and 80%, sufficient space is ensured for solute diffusion in the dialysis bag, and the solute concentration in the dialysis bag is also ensured not to be too high, thereby improving dialysis efficiency; appropriate slurry volume proportion can reduce the dialysis time, because in this range, the solute concentration in the dialysis bag changes rapidly, and the dialysis speed is also correspondingly increased. If the slurry volume proportion is too high, the dialysis bag may be ruptured due to excessive internal pressure; and if the proportion is too low, the solute concentration in the dialysis bag will change too slowly, affecting the dialysis effect.

[0021] Preferably, in the step (3), the proportion of slurry volume to dialysis bag volume is 40%-80%.

[0022] The dialysis of the present application can be carried out at room temperature without the need for heating and the like, and the process is mild, which has little effect on the product.

[0023] Preferably, in the step (3), the dialysis is carried out at room temperature.

[0024] Preferably, in the step (4), the deionized water outside the dialysis bag is replaced every 2-4 h.

[0025] According to different uses of the tricobalt tetroxide product, the dialysis time can be adjusted to obtain products with different degrees of reduction of sodium ion content. For the use of preparing lithium cobaltate positive electrode material, the sodium ion content is less than 50 ppm.

[0026] Preferably, in the step (4), the sodium ion content in the impurity-removed tricobalt tetroxide is less than 50 ppm.

[0027] The present application designs a dialysis process to reduce the sodium ion content in tricobalt tetroxide for the needs of industrial production, which utilizes the dialysis material to allow sodium ions to pass through, while preventing larger molecules or particles. Since the tricobalt tetroxide in the dialysis bag contains a high concentration of sodium ions, and the deionized water has a very low concentration of sodium ions, under the driving of the difference in ion concentration between the inside and outside, the sodium ions in the tricobalt tetroxide will gradually diffuse to the deionized water outside the dialysis bag, thereby realizing the precipitation of sodium ions.

[0028] Compared with calcination, the dialysis method of the present application does not require high temperature and will not change the structure of tricobalt tetraoxide, which helps to retain the grain integrity. In addition, compared with the centrifugal washing method, dialysis mainly moves sodium ions from high concentration areas to low concentration areas through the diffusion and convection of the dialysis bag semi-permeable membrane, thereby realizing the separation and purification of solutes. While centrifugal washing separates the solid particles in the mixture from the liquid by centrifugal force, and dissolves or dilutes the sodium ions in the solid particles into the liquid phase by the action of the washing liquid, thereby realizing solid-liquid separation. Centrifugal washing mainly relies on the different sedimentation speeds of different substances under the action of centrifugal force to realize solid-liquid separation. For sodium ions wrapped inside the crystal, the sedimentation speed is similar to that of the crystal itself, and they cannot be effectively separated. In the present application, due to the different driving forces of sodium ions, the selective permeation and concentration difference of dialysis drive the movement of sodium ions in the crystal, making them move from high concentration areas to low concentration areas, thereby effectively removing sodium ions wrapped inside the crystal. In addition, the stirring speed of the slurry of the powder in the present application is much lower than that of the centrifugal washing, and the influence of high-speed centrifugation on the component structure of tricobalt tetraoxide can also be avoided.

[0029] However, there are still many problems to be solved in the industrial production of dialysis method for reducing the content of sodium ions in tricobalt tetraoxide. Especially the selection of dialysis parameters needs to consider the crystal structure of tricobalt tetraoxide to ensure that it is not lost due to dialysis and maintains its integrity. At the same time, it is also necessary to more finely determine the cut-off range to screen sodium ions in the solution and improve the resolution and efficiency of dialysis. Based on the above technical solutions, the present application selects the range of MW3500-MW14000, which does not adsorb tricobalt tetraoxide material in this range and can effectively reduce the content of sodium ions. General dialysis operation is aimed at the dispersion liquid of tricobalt tetraoxide, and the dispersion liquid is a suspension, which may not be uniform in size and is prone to agglomeration. In the dialysis process, large particles in the powder dispersion liquid may block the pores of the dialysis membrane, affecting the dialysis efficiency. The dispersion liquid of tricobalt tetraoxide has poor stability and is prone to precipitation, and needs to be stirred frequently to maintain a uniform dispersion state, which is one of the reasons restricting the application of dialysis method. The present application uses slurry powder for dialysis. Compared with the dispersion liquid of tricobalt tetraoxide, the slurry powder is a uniform mixture of powder and liquid, which has good fluidity and stability. In the dialysis process, the slurry powder can pass through the dialysis membrane more easily because its particle size is relatively uniform and is not easy to block the pores of the dialysis membrane, and its dialysis efficiency is higher, which can quickly reach dialysis equilibrium and effectively solve the problem of time consumption of several days in current dialysis operation.

[0030] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0031] The application provides a dialysis method for reducing sodium ions in cobaltosic oxide, which is simple in operation, low in cost, and does not need complex equipment and chemical reagents. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A schematic diagram of the dialysis process of the application. DETAILED DESCRIPTION

[0033] The application will be further described by way of examples without limiting the application to the examples described. In the following examples, the experimental methods not specified in the specific conditions are selected according to the conventional methods and conditions or according to the product instructions.

[0034] Example 1

[0035] A dialysis method for reducing sodium ions in cobaltosic oxide, the steps are as follows:

[0036] (1) Dialysis bag pretreatment: select a dialysis bag with MW9000, ensure that it has no adsorption to cobaltosic oxide material and has good dialysis performance; place the dialysis bag in a beaker, add enough deionized water (submerge the dialysis bag), heat and boil for 1 h, then take out the dialysis bag and soak it in deionized water;

[0037] (2) Slurry of powder: put cobaltosic oxide powder and deionized water in a clean beaker according to the solid-liquid ratio of 1:25 g / g, stir for 4 h to uniformly disperse, and the stirring speed is 400 rmp;

[0038] (3) Dialysis: take a certain amount of slurry into the dialysis bag, the volume ratio of the slurry to the volume of the dialysis bag is 60%, and the dialysis bag containing cobaltosic oxide is placed in deionized water for dialysis. Since the dialysis bag contains a high concentration of sodium ions, and the concentration of sodium ions in deionized water is extremely low, the sodium ions in cobaltosic oxide will gradually diffuse to the deionized water outside the dialysis bag under the driving of the ion concentration difference, thereby realizing the precipitation of sodium ions;

[0039] (4) Process monitoring: replace the deionized water outside the dialysis bag every 2 hours, and send for sodium ion concentration test. The dialysis time of this embodiment is 4 h.

[0040] Example 2

[0041] This embodiment is basically the same as example 1, the difference is that the dialysis time of this embodiment is 8 h.

[0042] Example 3

[0043] This embodiment is basically the same as Example 1, the only difference is that the dialysis time of this embodiment is 12 h.

[0044] Example 4

[0045] This embodiment is basically the same as Example 1, the only difference is that the dialysis time of this embodiment is 14 h.

[0046] Example 5

[0047] This embodiment is basically the same as Example 1, the only difference is that the dialysis time of this embodiment is 20 h.

[0048] Example 6

[0049] This embodiment is basically the same as Example 1, the only difference is that the dialysis time of this embodiment is 24 h.

[0050] The sodium ion content in the product under different treatments was tested with cobaltosic oxide powder without dialysis treatment (regarded as the dialysis time of 0 h) as the blank control. The product was digested by strong acid, and then ICP was used to test the sodium ion content therein, and the results are shown in Table 1.

[0051] Table 1: Sodium ion content of the impurity-removed cobaltosic oxide obtained under different dialysis times

[0052]

[0053] From the above results, it can be seen that the present application can adjust the dialysis time according to the different uses of cobaltosic oxide product to obtain products with different degrees of reduction of sodium ion content. Dialysis for 24 h can make the sodium ion content less than 50 ppm, which is suitable for the subsequent preparation of lithium cobaltate positive electrode material. The processing time of the present application is lower than the time consumption of several days of traditional dialysis, and the dialysis efficiency is higher.

[0054] Example 7

[0055] A method for reducing sodium ions in cobaltosic oxide by dialysis, the steps are as follows:

[0056] (1) Dialysis bag pretreatment: select a dialysis bag with MW 3500, ensure that it has no adsorption to cobaltosic oxide material and has good dialysis performance; place the dialysis bag in a beaker, add enough deionized water (just enough to cover the dialysis bag), heat and boil for 1 h, then take out the dialysis bag and soak it in deionized water;

[0057] (2) Powder slurry: put cobaltosic oxide powder and deionized water in a clean beaker according to the solid-liquid ratio of 1:30 g / g, stir for 3 h to disperse uniformly, and the stirring speed is 500 rpm;

[0058] (3) Dialysis: Take a certain amount of slurry into the dialysis bag, the volume ratio of slurry to the volume of dialysis bag is 80%, and the dialysis bag packaged with cobaltosic oxide is placed in deionized water for dialysis. Since the dialysis bag contains a high concentration of sodium ions in cobaltosic oxide, and the concentration of sodium ions in deionized water is extremely low, the sodium ions in cobaltosic oxide will gradually diffuse to the deionized water outside the dialysis bag driven by the difference in ion concentration inside and outside, thereby realizing the precipitation of sodium ions;

[0059] (4) Process monitoring: replace the deionized water outside the dialysis bag every 2 hours, and send for sodium ion concentration test.

[0060] Example 8

[0061] A method for reducing sodium ions in cobaltosic oxide by dialysis, the steps are as follows:

[0062] (1) Dialysis bag pretreatment: select a dialysis bag with MW 14000, ensure that it has no adsorption to cobaltosic oxide material and has good dialysis performance; place the dialysis bag in a beaker, add enough deionized water (submerge the dialysis bag), heat and boil for 5 h, then take out the dialysis bag and soak it in deionized water;

[0063] (2) Powder slurry: Put cobaltosic oxide powder and deionized water in a clean beaker according to the solid-liquid ratio of 1:20 g / g, stir for 5 h until evenly dispersed, and the stirring speed is 300 rpm;

[0064] (3) Dialysis: Take a certain amount of slurry into the dialysis bag, the volume ratio of slurry to the volume of dialysis bag is 60%, and the dialysis bag packaged with cobaltosic oxide is placed in deionized water for dialysis. Since the dialysis bag contains a high concentration of sodium ions in cobaltosic oxide, and the concentration of sodium ions in deionized water is extremely low, the sodium ions in cobaltosic oxide will gradually diffuse to the deionized water outside the dialysis bag driven by the difference in ion concentration inside and outside, thereby realizing the precipitation of sodium ions;

[0065] (4) Process monitoring: replace the deionized water outside the dialysis bag every 4 hours, and send for sodium ion concentration test.

[0066] In the operation of the embodiments, the selection of the parameters should be controlled within the range defined by the present application. When the dialysis bag cut-off parameter is not within the above range, the dialysis bag exhibits adsorption to the cobaltosic cobalt material, deteriorating the degree of reduction of sodium ion content. The slurry is prepared in the process by using the solid-liquid ratio and stirring method of the present application, otherwise phenomena such as agglomeration between powders will occur, causing the powders to fail to be completely dispersed, resulting in stratification or sedimentation, reducing its stability, flowability. In addition, if the volume of the slurry occupies less than the selected value of the volume of the dialysis bag, the solute concentration will change too slowly; if it is higher than the selected value, there will be a phenomenon of rupture due to excessive internal pressure.

[0067] In summary, the dialysis method for reducing sodium ions in cobaltosic cobalt of the present application is simple to operate, low in cost, and does not require complex equipment and chemical reagents. The method uses ion concentration difference for dialysis, and the process is mild, without adversely affecting the structure and performance of cobaltosic cobalt, and can effectively reduce the sodium ion content in cobaltosic cobalt, improving product quality.

[0068] The above describes in detail the preferred embodiments of the present application. It should be understood that those skilled in the art can make many modifications and changes to the present application without creative labor, according to the concept of the present application. Therefore, any technical solution that can be obtained by logical analysis, reasoning or limited experiments by those skilled in the art on the basis of the prior art according to the concept of the present application shall be within the protection scope defined by the claims.

Claims

1. A method for reducing sodium ions in cobalt tetroxide using dialysis, characterized in that, Includes the following steps: (1) Pretreatment of dialysis bags: Select dialysis bags of MW3500-MW14000, place the dialysis bags in deionized water, heat and boil for a period of time, then take out the dialysis bags and soak them in deionized water again; (2) Powder slurry: Cobalt tetroxide powder and deionized water are stirred at a certain solid-liquid ratio until a uniformly dispersed slurry is formed; the solid-liquid ratio of cobalt tetroxide powder and deionized water is 1:20-30 g / g; the stirring speed is 300-500 rpm and the stirring time is 3-5 h. (3) Dialysis: Take a certain amount of slurry into the dialysis bag, seal it, and then perform dialysis; the volume of the slurry should be 40%-80% of the volume of the dialysis bag; dialysis should be performed at room temperature; (4) Process monitoring: Replace the deionized water outside the dialysis bag at regular intervals until the sodium content is reduced to the target level, thus obtaining impurity-free cobalt tetroxide.

2. The method for reducing sodium ions in cobalt tetroxide by dialysis according to claim 1, characterized in that: In step (1), the dialysis bag is placed in deionized water and heated to boiling for 1-5 hours.

3. The method for reducing sodium ions in cobalt tetroxide by dialysis according to claim 1, characterized in that: In step (4), the deionized water outside the dialysis bag is replaced every 2-4 hours.

4. The method for reducing sodium ions in cobalt tetroxide by dialysis according to claim 1, characterized in that: In step (4), the sodium ion content in the impurity-removed cobalt tetroxide is less than 50 ppm.

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