Preparation method and use of silicon-nitrogen-based silicon carbide ceramic membrane

Abstract

The application relates to a preparation method and application of a silicon-nitrogen-based silicon carbide ceramic membrane. The method comprises the following steps: 1. a silicon carbide ceramic cleaning and surface treatment step; 2. a high-temperature chlorination step of the ceramic membrane; 3. an amine grafting step of the ceramic membrane; and 4. a cooling liquid washing and deacidification step. The silicon-nitrogen-based ceramic membrane prepared by the method has excellent water removal and deacidification performance, high solvent flux, and is used for dehydrating and deacidifying an organic electrolyte. The silicon carbide ceramic membrane is stable in structure, resistant to acid and alkali, easy to regenerate, and capable of maintaining the stability of the ceramic membrane in dehydration and deacidification for a long time.

Description

Technical Field

[0001] This invention relates to the field of electrolyte treatment, and in particular to a method for preparing a ceramic membrane for electrolyte dehydration and deacidification. Background Technology

[0002] Lithium-ion batteries have the characteristics of high energy density, high specific power, good cycle performance, no memory effect, and no pollution.

[0003] It is now widely used in electronic digital products and is also an ideal energy choice for future electric vehicles.

[0004] Lithium-ion electrolytes consist of organic solvents and electrolytes. Commonly used electrolytes include lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), and lithium tetrafluoroborate (LiBF4). Among these, lithium hexafluorophosphate exhibits excellent conductivity and electrochemical stability, making it the mainstream electrolyte for lithium batteries. However, lithium hexafluorophosphate electrolytes suffer from poor thermal stability, easily decomposing into PF5, which leads to degradation and acidification of the organic solvent, resulting in increased color and affecting the performance of lithium-ion batteries.

[0005] Small amounts of additives are often added to electrolytes to remove water and acid, thereby improving the stability of lithium batteries. For example, common alkylsilazane compounds such as hexamethyldisilazane and heptamethyldisilazane utilize the reaction of alkylsilazane compounds with water to eliminate it. For instance, CN 107055574A uses silazane to remove free acids such as HF. However, the amount of silazane additives used is crucial to the performance of lithium battery products; therefore, lithium battery manufacturers need to test the amount of silazane additives to achieve quality control of their lithium battery products.

[0006] To address the aforementioned problems, heterogeneous separation technology shows great promise. For example, CN 106669440A proposes a modified ceramic membrane for seawater desalination and oil-water separation, exhibiting advantages such as high stability and strong acid and alkali resistance; CN107177226A proposes a surface-modified flat ceramic membrane for decomposing organic matter under photocatalytic conditions, demonstrating strong decontamination capabilities and easy regeneration. Therefore, using ceramic membranes as a substrate, modified with silicon-nitrogen groups, as a heterogeneous dehydration and acid removal separation method has practical significance. Summary of the Invention

[0007] To overcome the above technical problems, a method for preparing a silicon-nitrogen-based silicon carbide ceramic membrane for dehydration and acid removal of electrolytes is provided. The silicon carbide ceramic membrane prepared by this invention has excellent dehydration and acid removal performance, high solvent flux, and is suitable for dehydration and acid removal of organic electrolytes. Furthermore, the silicon carbide ceramic membrane has a stable structure, is resistant to acids and alkalis, is easy to regenerate, and can maintain the stability of dehydration and acid removal of the ceramic membrane for a long time.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a silicon nitride-based silicon carbide ceramic film includes the following steps:

[0010] (1) Optionally, the silicon carbide ceramic film is immersed in a low-boiling-point (boiling point <90°C) alcohol solvent, preferably ethanol, to clean and remove impurities from its surface, and then dried.

[0011] (2) Place the silicon carbide ceramic membrane in a tube furnace and pass nitrogen gas through it. After the temperature is raised to 800-1500°C, chlorine gas is introduced. After reacting for 1-4 hours, chlorinated silicon carbide ceramic membrane is obtained. Preferably, a low-boiling-point (boiling point <90°C) alcohol solvent is used for cleaning and drying.

[0012] (3) Place the ceramic membrane obtained in step (2) in a sealed reaction vessel, purge with nitrogen, and then introduce ammonia to react and obtain a crude silicon nitrogen-based ceramic membrane.

[0013] (4) The ceramic film obtained in step (3) is rinsed with a low-boiling-point (boiling point <90℃) alcohol solvent to dissolve the generated hydrogen chloride, and then dried to obtain a silicon nitride-based silicon carbide ceramic film.

[0014] As a preferred embodiment, the preparation method includes the following steps:

[0015] (1) Immerse the silicon carbide ceramic membrane in anhydrous ethanol to clean it and remove impurities from its surface, then dry it for later use.

[0016] (2) Place the dried silicon carbide ceramic membrane in step (1) into a tube furnace and pass nitrogen gas through it. After the temperature rises to 800-1500℃, chlorine gas is introduced. After reacting for 1-4 hours, the chlorinated silicon carbide ceramic membrane is taken out and cleaned and dried with ethanol.

[0017] (3) Place the ceramic membrane in a sealed reactor, purge with nitrogen, then introduce ammonia, keep the ammonia pressure in the reactor between 0.1 and 0.6 MPa, keep the temperature in the reactor between 40 and 50°C, and carry out the reaction for 0.5 to 4 hours. After cooling the reactor, remove the ceramic membrane.

[0018] (4) Rinse the ceramic membrane with ethanol to dissolve the generated hydrogen chloride, and dry it at 90-130°C to obtain a silicon nitride-based silicon carbide ceramic membrane.

[0019] Preferably, the reaction temperature in step (2) is 1200–1400℃, the amount of chlorine used is 0.5 kg–2 kg / kg silicon carbide, the partial pressure of chlorine is maintained at 0.02–0.1 MPa, and the space velocity is maintained at 0.02 m / s. 3 / h~2m 3 / h; More preferably, the chlorine usage is 0.6–0.8 kg / kg silicon carbide, the chlorine partial pressure is maintained at 0.02–0.04 MPa, and the space velocity is maintained at 0.02–0.06 m / h. 3 / h.

[0020] Preferably, the total pressure in step (3) is maintained at 0.2-0.4 MPa, the amount of ammonia used is 0.01-0.2 kg / kg silicon carbide ceramic membrane, and the reaction time is 2-4 h.

[0021] Preferably, the alcohols mentioned in steps (1), (2), and (4) include one or more of methanol, ethanol, or isopropanol. The washing solution used in step (4) is ethanol or methanol, the water content must be less than 100 ppm, and washing continues until the acidity is >6.

[0022] This invention uses silicon carbide as the ceramic membrane substrate. Through chlorination and amination processes on the ceramic membrane surface, silicon-nitrogen groups are grafted, thereby enabling the silicon carbide ceramic membrane to possess dehydration and acid removal functions. The principle of this invention is as follows:

[0023] Chlorination is carried out on a silicon carbide substrate, and the reaction produces chlorinated products. The reaction equation is as follows:

[0024]

[0025] Subsequently, chlorinated silicon carbide reacts with ammonia to produce silicon nitride-modified ceramics. The reaction equation is as follows:

[0026]

[0027] The -Si-NH-Si- groups are active groups for dehydration and acid removal, and their mechanism of action is as follows:

[0028]

[0029] Its dehydrated structure is [C-Si-OH, and the activation process is as in step (3). Ammonia gas is introduced to carry out the amination process, which has the advantages of convenient use and easy regeneration.

[0030] The advantages of this invention are that it prepares a heterogeneous silicon-nitrogen-modified silicon carbide ceramic membrane, which can effectively dehydrate and remove acid from electrolyte solutions without introducing soluble impurities and is easy to separate and recycle. Furthermore, this ceramic membrane can be activated and regenerated for reuse, reducing operating costs. Detailed Implementation

[0031] The technical solution of the present invention will be further described below through specific embodiments.

[0032] Unless otherwise specified, all raw materials and equipment used in this invention are commercially available or commonly used in the field.

[0033] Unless otherwise specified, the methods described in the embodiments are conventional methods in the art.

[0034] Example 1

[0035] (1) Immerse the silicon carbide ceramic membrane in anhydrous ethanol to clean it and remove impurities from its surface, and dry it at 70°C for later use.

[0036] (2) Place the dried silicon carbide ceramic membrane from step (1) into a tube furnace, purge it with nitrogen atmosphere, and maintain the reaction pressure at atmospheric pressure. After the temperature reaches 1400℃, introduce chlorine gas at a rate of 0.7 kg / kg silicon carbide, keeping the chlorine partial pressure at 0.03 MPa and the space velocity at 0.04 m / s. 3 / h, after reacting for 3h, remove the silicon carbide chloride ceramic membrane, clean it with ethanol and dry it at 70℃;

[0037] (3) Place the ceramic membrane in a sealed reactor, purge with nitrogen, then introduce ammonia to maintain the ammonia pressure in the reactor at 0.3 MPa, use 0.08 kg / kg silicon carbide, react at 40°C, react for 3 hours, then cool the reactor to 5°C and remove the ceramic membrane.

[0038] (4) The ceramic membrane is rinsed with methanol (water content is 10ppm), the generated hydrogen chloride is dissolved and washed until the acidity is greater than 6, and then dried at 120°C to obtain silicon nitride-modified silicon carbide ceramic membrane.

[0039] Example 2

[0040] (1) Immerse the silicon carbide ceramic membrane in anhydrous methanol to clean it and remove impurities from its surface, and dry it at 50°C for later use.

[0041] (2) The dried silicon carbide ceramic membrane (Dongqiang membrane, DQM, membrane element outer diameter: 30mm, channel diameter: 4mm, number of channels: 19, membrane area: 0.24m²) from step (1) is then dried. 2 The sample was placed in a tubular high-temperature furnace and purged with a nitrogen atmosphere. The reaction pressure was atmospheric pressure. After the temperature reached 1100℃, chlorine gas was introduced. The chlorine usage was 0.5 kg / kg silicon carbide, and the chlorine partial pressure was maintained at 0.02 MPa, while the space velocity was maintained at 0.02 m / s². 3 / h, after reacting for 2h, remove the silicon carbide chloride ceramic membrane, clean it with ethanol and dry it at 50℃;

[0042] (3) Place the ceramic membrane in a sealed reactor, purge with nitrogen, then introduce ammonia to maintain the ammonia pressure in the reactor at 0.2 MPa, use 0.06 kg / kg silicon carbide, react at 50°C, react for 2 hours, then cool the reactor to 10°C and remove the ceramic membrane.

[0043] (4) The ceramic membrane is rinsed with methanol (water content is 50ppm) to dissolve the generated hydrogen chloride. The washing is continued until the acidity is greater than 6. After drying at 90°C, the silicon nitride-based silicon carbide ceramic membrane is obtained.

[0044] Example 3

[0045] (1) Immerse the silicon carbide ceramic membrane in dehydrated isopropanol to clean it and remove impurities from its surface, and dry it at 90°C for later use.

[0046] (2) Place the dried silicon carbide ceramic membrane from step (1) into a tube furnace, purge it with nitrogen atmosphere, maintain the reaction pressure at atmospheric pressure, and after heating to 1500℃, introduce chlorine gas. The amount of chlorine used is 0.9 kg / kg silicon carbide, the partial pressure of chlorine is maintained at 0.05 MPa, and the space velocity is maintained at 0.06 m / s. 3 / h, after reacting for 4h, remove the silicon carbide chloride ceramic membrane, clean it with ethanol and dry it at 90℃;

[0047] (3) Place the ceramic membrane in a sealed reactor, purge with nitrogen, then introduce ammonia to maintain the ammonia pressure in the reactor at 0.5 MPa, use 0.1 kg / kg silicon carbide, react at 45°C, react for 4 hours, then cool the reactor to 10°C and remove the ceramic membrane.

[0048] (4) The ceramic membrane is rinsed with methanol (water content is 50ppm) to dissolve the generated hydrogen chloride. The washing is continued until the acidity is greater than 6. After drying at 120°C, the silicon nitride-based silicon carbide ceramic membrane is obtained.

[0049] Example 4

[0050] (1) Immerse the silicon carbide ceramic membrane in anhydrous ethanol to clean it and remove impurities from its surface, and dry it at 80°C for later use.

[0051] (2) Place the dried silicon carbide ceramic membrane from step (1) into a tube furnace, purge it with nitrogen atmosphere, and maintain the reaction pressure at atmospheric pressure. After the temperature reaches 800℃, introduce chlorine gas at a rate of 2 kg / kg silicon carbide, keeping the chlorine partial pressure at 0.02 MPa and the space velocity at 0.02 m / s. 3 / h, after reacting for 1h, remove the silicon carbide chloride ceramic membrane, clean it with ethanol and dry it at 80℃;

[0052] (3) Place the ceramic membrane in a sealed reactor, purge with nitrogen, then introduce ammonia to maintain the ammonia pressure in the reactor at 0.1 MPa, use 0.09 kg / kg silicon carbide, set the reaction temperature at 40°C, and set the reaction time at 4 h. Then cool the reactor to 5°C and remove the ceramic membrane.

[0053] (4) The ceramic membrane is rinsed with methanol (water content is 100ppm) to dissolve the generated hydrogen chloride. The washing is continued until the acidity is greater than 6. After drying at 100°C, the silicon nitride-based silicon carbide ceramic membrane is obtained.

[0054] Example 5

[0055] (1) Immerse the silicon carbide ceramic membrane in anhydrous methanol to clean it and remove impurities from its surface, and dry it at 90°C for later use.

[0056] (2) Place the dried silicon carbide ceramic membrane from step (1) into a tube furnace, purge it with nitrogen atmosphere, maintain the reaction pressure at atmospheric pressure, and after heating to 1500℃, introduce chlorine gas. The amount of chlorine used is 0.9 kg / kg silicon carbide, the partial pressure of chlorine is maintained at 0.05 MPa, and the space velocity is maintained at 0.06 m / s. 3 / h, after reacting for 4h, remove the silicon carbide chloride ceramic membrane, clean it with ethanol and dry it at 90℃;

[0057] (3) Place the ceramic membrane in a sealed reactor, purge with nitrogen, then introduce ammonia to maintain the ammonia pressure in the reactor at 0.2 MPa, use 0.06 kg / kg silicon carbide, react at 50°C for 2 hours, then cool the reactor to 5°C and remove the ceramic membrane.

[0058] (4) The ceramic membrane is rinsed with methanol (water content is 20ppm) to dissolve the generated hydrogen chloride. The washing is continued until the acidity is greater than 6. After drying at 110°C, the silicon nitride-based silicon carbide ceramic membrane is obtained.

[0059] Example 6

[0060] (1) Immerse the silicon carbide ceramic membrane in dehydrated isopropanol to clean it and remove impurities from its surface, and dry it at 110°C for later use.

[0061] (2) Place the dried silicon carbide ceramic membrane from step (1) into a tube furnace, purge it with nitrogen atmosphere, maintain the reaction pressure at atmospheric pressure, and after heating to 1300℃, introduce chlorine gas. The amount of chlorine used is 0.6 kg / kg silicon carbide, the partial pressure of chlorine is maintained at 0.05 MPa, and the space velocity is maintained at 0.07 m / s. 3 / h, after reacting for 4h, remove the silicon carbide chloride ceramic membrane, clean it with ethanol and dry it at 70℃;

[0062] (3) Place the ceramic membrane in a sealed reactor, purge with nitrogen, then introduce ammonia to maintain the ammonia pressure in the reactor at 0.6 MPa, use 0.08 kg / kg silicon carbide, react at 45°C, react for 4 hours, then cool the reactor to 5°C and remove the ceramic membrane.

[0063] (4) Rinse the ceramic membrane with methanol (water content of 10ppm) to dissolve the generated hydrogen chloride, wash until the acidity is greater than 6, and dry at 130°C to obtain silicon nitride-based silicon carbide ceramic membrane.

[0064] Example 7 - Regeneration

[0065] The ceramic membrane prepared in Example 6 was regenerated after being sampled and subjected to electrolyte dehydration and acid removal. The regeneration steps are as follows:

[0066] (1) Place the ceramic membrane in a sealed reactor, purge with nitrogen, then introduce ammonia to maintain the ammonia pressure in the reactor at 0.6 MPa, use 0.08 kg / kg silicon carbide, react at 45°C, react for 4 hours, then cool the reactor to 5°C and remove the ceramic membrane.

[0067] (2) The ceramic membrane is rinsed with methanol (water content is 10ppm) to dissolve the generated hydrogen chloride. The washing is continued until the acidity is greater than 6. After drying at 130℃, the silicon nitride-based silicon carbide ceramic membrane is obtained.

[0068] The ceramic membranes prepared in Examples 1-6 were subjected to dehydration and acid removal tests. The test object was a 20wt% LiPF6 / DMC solution with an initial acidity of 8000ppm and a water content of 12000ppm. The test pressure was 0.1MPa. Samples were taken for testing after the ceramic membrane had been running for 30 minutes.

[0069] For comparison, commercially available example anion exchange resin AmberLite HPR7000 (DuPont, weakly basic anion exchange resin) was used for testing. The test results (lower water content and acidity were considered better) are as follows:

[0070] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example Moisture content (ppm) 6 64 32 53 12 8 6 132 Acidity (ppm) 3 12 22 18 7 2 2 45

[0071] The test pressure was increased to 0.3 MPa, and after running for 24 hours, sampling tests were conducted. The test objects were the same as above, and the test results are as follows:

[0072]

Claims

1. A method for preparing a silicon nitride-based silicon carbide ceramic film, characterized in that, Includes the following steps: (1) Immerse the silicon carbide ceramic film in an alcohol solvent with a boiling point of <90℃ to clean and remove impurities from its surface, and then dry it. (2) Place the silicon carbide ceramic membrane in a tube furnace and pass nitrogen gas through it. After the temperature is raised to 800-1500℃, chlorine gas is introduced. After reacting for 1-4 hours, chlorinated silicon carbide ceramic membrane is obtained. (3) Place the ceramic membrane obtained in step (2) in a sealed reaction vessel, purge with nitrogen, and then introduce ammonia to react and obtain a crude silicon nitrogen-based ceramic membrane. (4) The ceramic membrane obtained in step (3) is rinsed with an alcohol solvent with a boiling point of <90℃ to dissolve the generated hydrogen chloride, and then dried to obtain a silicon nitride-based silicon carbide ceramic membrane.

2. The preparation method according to claim 1, characterized in that, The silicon carbide ceramic membrane obtained in step (2) is cleaned and dried using an alcohol solvent with a boiling point of <90°C.

3. The preparation method according to claim 1, characterized in that, In step (2), the amount of chlorine used is 0.5 kg to 2 kg / kg silicon carbide, the partial pressure of chlorine is maintained at 0.02 to 0.1 MPa, and the space velocity is maintained at 0.02 m3 / h to 2 m3 / h.

4. The preparation method according to claim 1, characterized in that, In step (3), the ammonia pressure in the reactor is maintained between 0.1 and 0.6 MPa, and the ammonia usage is 0.01 to 0.2 kg / kg.

5. The preparation method according to claim 4, characterized in that, In step (3), the total pressure is maintained between 0.2 and 1.2 MPa, the temperature in the reactor is maintained between 40 and 50°C, and the reaction is carried out for 0.5 to 4 hours.

6. The preparation method according to claim 5, characterized in that, In step (3), the reaction needs to be cooled to below 10°C, and the amination-treated silicon nitride-based silicon carbide ceramic film needs to be stored in a dry environment with an air humidity of less than 100 ppm.

7. The preparation method according to claim 2, characterized in that, The alcohol solvents mentioned in steps (1), (2), and (4) include one or more of methanol, ethanol, or isopropanol.

8. The preparation method according to claim 7, characterized in that, In step (4), the water content of the alcohol solvent is less than 100 ppm, and the washing continues until the acidity is >6.

9. The silicon nitride-based silicon carbide ceramic membrane obtained by any one of claims 1-8 is used for dehydration and acid removal of electrolyte.

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