Cleaning composition and application thereof

Abstract

The invention discloses a cleaning composition and application thereof, and belongs to the technical field of lithium battery diaphragm coating film recovery. The cleaning composition comprises a cationic surface active agent, an ester solvent and mineral oil, wherein the viscosity of the mineral oil is 30-80 cP, and the mineral oil can effectively remove an organic / inorganic coating, an aluminum oxide ceramic coating, a boehmite coating and PMMA and PVDF organic coatings coated on the surface of the coating film. And the residual amount of the coating elements is only ppm level. The cleaning composition provided by the invention not only improves the recycling rate of resources and reduces the production cost, but also has the advantages of environmental protection, no toxicity and low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium battery diaphragm recovery, and specifically relates to a cleaning composition and application thereof. Background Art

[0002] The diaphragm is an important component of lithium-ion batteries. Its performance has a direct impact on the battery's interface structure, electrolyte retention performance and internal resistance, and thus has a great impact on the overall performance of the battery (such as charge and discharge rate, cycle life). The diaphragm is a layer of microporous membrane material between the positive and negative electrodes. Its main function is to effectively isolate the electrode material and prevent short circuits in the battery caused by direct contact between the positive and negative electrodes. In addition, sufficient electrolyte is retained to allow lithium ions to freely conduct between the positive and negative electrodes through the diaphragm. In order to improve the mechanical properties and ion transport conductivity of lithium battery diaphragms, it is necessary to coat inorganic or organic coatings on their surfaces. The inorganic coating materials are mainly alumina, boehmite, etc., and the organic coatings include PMMA, PVDF, etc., to form a coating film for lithium batteries. At present, the edge materials cut off from the base film of the production line after winding are generally sold directly to downstream plastic product manufacturers at a low price, or used for granulation and recycling. However, because the coating film contains inorganic coatings and adhesives on the surface, the edge materials after cutting are of no good use and cannot be used for granulation, resulting in waste of resources and increased production costs. At present, most manufacturers adopt the method of selling at low prices to deal with the recycling of coating film scraps, but this method will cause waste of resources, energy cannot be maximized, and the production costs of enterprises will increase.

[0003] The prior art discloses a lithium battery diaphragm cleaning agent, including nonionic surfactants and anionic surfactants, glycol ether, methyl pyrrolidone, methyl siloxane, alkaline additives, acidic additives, preservatives, and water, but only for organic and inorganic dirt mechanically attached to the diaphragm, but not enough to remove the coating film coated and bonded on the diaphragm. The prior art discloses a method for recovering a resin coated with a coating film, specifically, contacting a thermoplastic resin coated with a coating film decomposing agent in a molten state to decompose the coating film, and the coating film decomposing agent includes primary amines, secondary amines, tertiary amines or quaternary ammonium compounds, but the cleaning and recovery process is complicated, and melting removal requires energy consumption.

[0004] Therefore, developing a cleaning composition that can effectively remove the organic or inorganic coating on the surface of the coating film has important research significance and application value. Summary of the invention

[0005] In order to solve the challenge that cleaning agents in the prior art are difficult to effectively remove the coating film of the lithium battery separator, the primary purpose of the present invention is to provide a cleaning composition.

[0006] Another object of the present invention is to provide a cleaning agent comprising the above cleaning composition.

[0007] Another object of the present invention is to provide a method for cleaning a lithium battery separator coating film.

[0008] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0009] A cleaning composition comprising a cationic surfactant, an ester solvent, and mineral oil.

[0010] Wherein, the viscosity of the mineral oil is 30-80 cP.

[0011] The cleaning composition provided by the invention aims to clean and remove the coating of the lithium battery diaphragm coating film, and comprises a cationic surfactant, an ester solvent and mineral oil.

[0012] Among them, the role of cationic surfactants is to effectively improve the wetting and penetration ability of the cleaning composition to the coating by reducing the surface tension of the oily coating, enhancing permeability, improving dispersibility and wetting. It can also effectively neutralize the charge of the coating, making the coating easier to decompose and peel off. Specifically, cationic surfactants can reduce the surface tension of the oily coating, making it easier for it and other cleaning composition components to penetrate into the tiny gaps between the diaphragm and the coating, thereby enhancing the wetting and penetration ability of the cleaning composition to the coating, allowing the cleaning composition to reach and decompose the coating components, and improving the cleaning efficiency; after the coating is detached from the surface of the diaphragm, the cationic surfactant disperses it into the cleaning liquid to prevent the coating from being re-deposited on the substrate.

[0013] Ester solvents: They have good solubility and are conducive to the dissolution and stripping of coating components. Esters usually have mild cleaning ability and are suitable for cleaning grease and certain organic matter (acrylic resins in membrane coating adhesives and PMMA / PVDF are both non-polar oily coatings). They can be used on a variety of surfaces, including metals, plastics and textiles. Due to their biodegradability, esters have relatively little impact on the environment. At the same time, ester solvents are oily solvents that can better infiltrate the membrane surface, play a wetting and penetration effect, increase the contact area between the solvent and the membrane coating, make the oily coating easier to strip and dissolve, better play the similar solubility effect, and play a synergistic role with mineral oil, so that the coating removal effect is better, which is significantly improved compared to when it exists alone.

[0014] Mineral oil is a non-polar oily substance with a similar polarity to the coating adhesive, and it is easy to infiltrate and penetrate the oily coating layer. In addition, choosing a mineral oil with appropriate viscosity can also reduce friction during the cleaning process and avoid damage to the base film.

[0015] More specifically, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent, and the mineral oil satisfies

[0016] Cationic surfactant: ester solvent: mineral oil = 1-3: 2-5: 10-30.

[0017] That is to say, when the mass fraction of the cationic surfactant is 1 to 3 parts, based on the mass of the cationic surfactant, the mass fraction of the ester solvent is 2 to 5 parts, and the relative mass fraction of the mineral oil is 10 to 30 parts.

[0018] Preferably, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent and the mineral oil satisfies

[0019] Cationic surfactant: ester solvent: mineral oil = 1-2: 2-4: 15-25.

[0020] Preferably, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent and the mineral oil satisfies

[0021] Cationic surfactant: ester solvent: mineral oil = 1-1.5: 2-3: 18-22.

[0022] Preferably, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent and the mineral oil satisfies

[0023] Cationic surfactant: ester solvent: mineral oil = 1:2:20.

[0024] Preferably, the viscosity of the mineral oil is 50 to 65 cP. More preferably, the viscosity of the mineral oil is 60 cP.

[0025] Viscosity test method for mineral oil: Using a cone and plate rotational viscometer:

[0026] In the present invention, the viscosity of mineral oil refers to the value measured under the conditions of 25° C., 200 rpm, and 60 seconds according to GB / T 265-1988 “Method for determination of kinematic viscosity and calculation of dynamic viscosity of petroleum products”.

[0027] Preferably, the cationic surfactant is a quaternary ammonium salt cationic surfactant.

[0028] Preferably, the cationic surfactant is one or more of dodecyldimethylbenzyl ammonium chloride, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, methyl ditallowylethyl-2-hydroxyethylammonium methyl sulfate, N-methyl-N-tallowamidoethyl-2-tallow imidazoline methyl sulfate or polyquaternium-16.

[0029] Preferably, the cleaning composition further comprises alcohol.

[0030] Preferably, the alcohol is selected from one or more of methanol, ethanol, butanol or propanol. The alcohol is preferably ethanol.

[0031] Preferably, the cleaning composition further comprises water, and the water is preferably deionized water.

[0032] More specifically, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent, the mineral oil, and the alcohol satisfies 1-3:2-5:10-30:0-10:0-60.

[0033] More preferably, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent, the mineral oil, and the alcohol satisfies 1-3:2-5:10-30:0-5:0-30.

[0034] More preferably, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent, the mineral oil, and the alcohol satisfies 1-2:2-4:15-25:0-5:0-30.

[0035] More preferably, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent, the mineral oil, and the alcohol satisfies 1-1.5:2-3:18-22:0-5:0-30.

[0036] More preferably, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent, the mineral oil, and the alcohol satisfies 1-1.5:2-3:18-22:1-5:1-30.

[0037] More preferably, in the cleaning composition, the mass ratio of the cationic surfactant, the ester solvent, the mineral oil, and the alcohol satisfies 1:2:20:5:30.

[0038] The present invention also protects a cleaning agent, comprising the above cleaning composition.

[0039] A method for cleaning a lithium battery separator coating film is also within the protection scope of the present invention, comprising the step of soaking the lithium battery separator coating film with the above-mentioned cleaning composition or the above-mentioned cleaning agent.

[0040] Preferably, the method for cleaning the lithium battery separator coating film further comprises the step of peeling off the surface coating of the lithium battery separator coating film by a physical method.

[0041] Preferably, the method for cleaning the lithium battery separator coating film further comprises a step of organic solvent extraction.

[0042] Preferably, the organic solvent is at least one of dichloromethane, ethyl ether, petroleum ether or carbon tetrachloride.

[0043] More preferably, the organic solvent is dichloromethane.

[0044] Specifically, the extraction step is as follows: the completely cleaned coating film is completely immersed in an extraction tank filled with an organic solvent, and a clamp weight is dropped under the coating film to keep the coating film in a vertical state.

[0045] The purpose of the extraction step is to remove the pore-blocking substances in the micropores of the lithium ion channels of the coating membrane and to more thoroughly remove the residual slurry. Generally, the principle of similar miscibility between dichloromethane and other alternative extractants and the pore-blocking substances in the micropores is used to extract and remove the pore-blocking substances. The pore-blocking substances include: residual slurry, oily impurities, and small molecules of detergents. This avoids the influence of the pore-blocking substances in the pores of the coating membrane on the subsequent processing technology (such as the granulation process), and at the same time improves the recycling rate of the coating membrane edge materials.

[0046] Preferably, the soaking time is 3 to 5 minutes.

[0047] Preferably, the cleaning time is 10 to 15 minutes.

[0048] Preferably, the extraction time is 5 to 10 minutes.

[0049] Preferably, the mass concentration of the cleaning agent dilution solution is 25-50%.

[0050] Preferably, the lithium battery separator coating film is a lithium battery separator surface coated with one or more of alumina, boehmite (γ-AlOOH), PMMA or PVDF.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] The cleaning composition provided by the present invention comprises components including a cationic surfactant, an ester solvent and a mineral oil, and can effectively clean a lithium battery diaphragm coating film and an organic / inorganic coating coated on the surface. After cleaning, the residual amount of coating elements is only at the ppm level, and the removal performance is excellent. The lithium battery diaphragm coating film cleaned by the cleaning composition of the present invention can be directly used for granulation, saving production costs, being environmentally friendly, non-toxic and low-cost. DETAILED DESCRIPTION

[0053] The present invention is further described below in conjunction with examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are usually carried out according to conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets. Any non-substantial changes and substitutions made by those skilled in the art on the basis of the present invention belong to the scope of protection claimed by the present invention.

[0054] The cleaning compositions of the embodiments and comparative examples of the present invention are used in the following steps for cleaning the corresponding coating films:

[0055] S1: 20 g of the cleaning agent dilution; placed in a watch glass with a diameter of 10 cm;

[0056] S2: Cut the coating film into 31.5 cm × 5 cm size and immerse it completely in the cleaning solution for 5 minutes;

[0057] S3: Take out the coating film and place it flat on a test bench covered with a dust-free cloth. Pour an appropriate amount of cleaning solution on the coating repeatedly and rub the coating surface repeatedly with four fingers. Do not use too much force to cause damage to the film surface. Rinse repeatedly with deionized water until there is no obvious coating residue observed by naked eye.

[0058] S4: Place the cleaned membrane in a 45°C oven and dry for 30 minutes to remove moisture from the membrane surface;

[0059] S5: Extraction: After cleaning, rinsing and drying the membrane surface, immerse the cleaned coating membrane completely in a dichloromethane extraction tank. Place a clamp weight under the coating membrane to allow the coating membrane to be vertically immersed in the extraction tank filled with dichloromethane. The extraction time is 10 minutes.

[0060] In Tables 2 to 5, the cleaning test results without special description include the extraction step of S5 described above.

[0061] The performance testing methods and standards of the cleaning compositions of the embodiments and comparative examples of the present invention are as follows:

[0062] The coating film samples in each example and comparative example were characterized before cleaning, after cleaning, and after extraction.

[0063] (1) Observe and record the surface condition of the coating;

[0064] (2) ICP characterization: focus on elements Al, Ca, K, Fe, Mg, Na, Si, Ti, and Zn;

[0065] (3) SEM characterization: characterize the surface state of the coating film, surface and cross section;

[0066] (4) Air permeability value: s / 100mL. The test instrument is Wangyan air permeability tester, EGOI-55-IMR, Asahi Seiko Co., Ltd., Japan. The air resistance of the battery diaphragm is tested by the air permeability tester to characterize the permeability performance of the diaphragm. The air permeability value refers to the time required for a certain volume of gas to pass through a fixed area of ​​diaphragm under a certain pressure difference. The quality of the diaphragm permeability is determined by the length of the passing time. The larger the air permeability value, the worse the permeability of the diaphragm. The air permeability value in this article refers to the area of ​​6.45cm2 that 100mL of air passes through under a pressure of 1.21KPa. 2 The time required for the diaphragm, also known as the Gurley value;

[0067] (5) X-ray fluorescence spectrometry (XRF), the cleaning effect of PVDF coating is characterized by measuring the F content, and the cleaning effect of PMMA coating is characterized by measuring the O content;

[0068] (6) The viscosity of mineral oil refers to the value measured at 25°C, 200 rpm, and 60 seconds in accordance with GB / T 265-1988 “Method for determination of kinematic viscosity and calculation of dynamic viscosity of petroleum products”.

[0069] Table 1 Cleaning compositions of various embodiments and comparative examples

[0070]

[0071]

[0072]

[0073] Table 2 Characterization of the coating film of single-sided alumina ceramic coating 3μm before and after cleaning and comparative experimental results

[0074]

[0075]

[0076]

[0077] Table 3 Cleaning test results of the cleaning composition of Example 1

[0078]

[0079] Table 4 Cleaning test results of cleaning composition of Example 2

[0080]

[0081]

[0082] Table 5 Experimental results of cleaning the single-sided alumina ceramic coating 3 μm coating film by the cleaning compositions of Examples 3 to 9

[0083]

[0084]

[0085] It can be seen from Tables 3 to 5 that among the cleaning compositions prepared in Examples 1 to 11 of the present invention, Example 1 has the best comprehensive performance. Table 3 shows the cleaning effect of the cleaning composition of Example 1 applied to different inorganic or organic lithium battery separator coating films, Table 4 shows the cleaning effect of the cleaning composition of Example 2 applied to different inorganic or organic lithium battery separator coating films, and Table 5 shows the cleaning effect of the cleaning composition of Examples 3 to 11 applied to a coating film with a single-sided alumina ceramic coating of 3 μm.

[0086] For 6 different types of coatings on the diaphragms (single-sided 3μm alumina ceramic coating, single-sided 4μm boehmite coating, double-sided 2μm alumina and boehmite coating, single-sided 2μm PMMA organic coating, single-sided 2μm PVDF organic coating), after a certain period of time and concentration cleaning, there was no obvious coating residue on the membrane surface, and the Al element residue was 78.38ppm. This cleaning agent has a high coating removal rate and low cost. The ingredients used are all environmentally friendly, and it can achieve high-efficiency recycling of coating membrane scraps.

[0087] In Comparative Example 1, no cationic surfactant is added to the cleaning composition, and the cleaning agent components are insoluble in each other, resulting in stratification and cannot be used normally; in Comparative Example 2, an anionic surfactant is used, and the membrane hole channels are blocked by the cleaning agent components, the air permeability value is very poor, and the aluminum content exceeds the detection limit, indicating that the anionic surfactant cannot disperse the cleaning components and play the role of removing the coating; Comparative Example 3 uses a nonionic surfactant and Comparative Example 4 uses a zwitterionic surfactant, both of which cannot replace the role of the cationic surfactant; Comparative Example 5 does not use an ester solvent, and the cleaning composition is difficult to fully disperse and work without a proper solvent; In Example 6, only anhydrous ethanol was used to clean the coating, which only dissolved a small amount of polar substances to a certain extent and had almost no effect; in Comparative Example 7, acetone was used, which had no synergistic cleaning effect with other components; in Comparative Example 8, no paraffin oil was added, and it was difficult to remove non-polar substances on the coating, such as acrylic resin, PVDF or PMMA; in Comparative Example 9, paraffin oil with a viscosity of less than 30 cP was used, resulting in excessive friction when cleaning the coating film, which easily caused the film cloth to break and was difficult to recycle; in Comparative Example 10, paraffin oil with a viscosity of more than 80 cP was used, which was not conducive to uniform dispersion of the cleaning composition, and was difficult to completely remove during the extraction process, and was prone to residue.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A cleaning composition, characterized in that Including cationic surfactants, ester solvents, mineral oil; Wherein, the viscosity of the mineral oil is 30-80 cP.

2. The cleaning composition according to claim 1, characterized in that The cationic surfactant is a quaternary ammonium salt cationic surfactant.

3. The cleaning composition according to claim 1 or 2, characterized in that Alcohol and / or water are also included.

4. The cleaning composition according to claim 3, characterized in that The alcohol is selected from one or more of methanol, ethanol, butanol or propanol.

5. The cleaning composition according to any one of claims 1 to 3, characterized in that The mineral oil is paraffin oil and / or white oil.

6. A cleaning agent, characterized in that: The cleaning composition comprises the cleaning composition according to any one of claims 1 to 5.

7. A method for cleaning a lithium battery separator coating film, characterized in that: include The step of soaking the lithium battery separator coating film with the cleaning composition according to any one of claims 1 to 5 or the cleaning agent according to claim 6.

8. The cleaning method according to claim 7, characterized in that: The method also includes a step of peeling off the surface coating of the lithium battery separator coating film by physical methods.

9. The cleaning method according to claim 8, characterized in that: The method further comprises the step of applying the cleaning composition according to any one of claims 1 to 5 or the cleaning agent according to claim 6 to the coating surface.

10. The cleaning method according to claim 7, characterized in that: The method also includes an organic solvent extraction step.

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