A binder for lithium battery current collector and a method for preparing the same

Abstract

The present application relates to the technical fields of adhesive and adhesive for lithium battery, and specifically relates to a kind of lithium battery current collector coating binder and preparation method thereof.The lithium battery current collector coating binder includes the following components according to weight parts: polyvinylidene fluoride 10-20 parts, maleic anhydride grafting modified styrene-ethylene / butene-styrene 10-20 parts, modified polyolefin 1-10 parts, ceramic powder 50-70 parts, coupling agent 0.1-1 part, antioxidant 0.1-3 parts, solvent 300-500 parts.The binder of the present application has good adhesion to current collector copper foil and aluminum foil, is resistant to electrolyte corrosion, and improves the tensile strength of current collector fracture.

Description

Technical Field

[0001] This invention relates to the field of adhesives for lithium batteries, and more specifically to an adhesive for coating current collectors in lithium batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries widely used in mobile phones, laptops, wearable electronic devices, power tools, drones, and electric vehicles due to their advantages such as high operating voltage, small size, light weight, high energy density, no memory effect, low self-discharge, long cycle life, and high capacity per unit density. Currently, lithium-ion batteries typically use aluminum tabs (or other metals and alloys) for the positive electrode and aluminum foil as the current collector; and nickel tabs (or other metals and alloys) for the negative electrode and copper foil as the current collector. The tabs are connected to the current collector using welding methods (such as super-welding and riveting). However, the ultra-thinning of the copper foil current collector brings a series of problems: low tensile strength, poor coating continuity, and easy breakage; thinner copper foil makes the copper foil tabs more prone to inward folding, reducing yield; and there are also issues with burrs on the cut edges of the copper foil. Summary of the Invention

[0003] This invention addresses the shortcomings of existing lithium battery current collectors by providing a binder for coating lithium battery current collectors and its preparation method.

[0004] To achieve the above objectives, the technical solution adopted is:

[0005] One of the objectives of this invention is to provide an adhesive for coating current collectors in lithium batteries, comprising the following components by weight: 10-20 parts of polyvinylidene fluoride, 10-20 parts of maleic anhydride-grafted modified styrene-ethylene / butene-styrene, 1-10 parts of modified polyolefin, 50-70 parts of ceramic powder, 0.1-1 parts of coupling agent, 0.1-3 parts of antioxidant, and 300-500 parts of solvent.

[0006] The polyvinylidene fluoride (PVDF) mentioned therein, specifically PVDF homopolymers and copolymers with a weight-average molecular weight of 500,000 to 1,100,000, can be selected from those manufactured by Solvay. Arkema's Kynar HSV 1800 / 900 uses polyvinylidene fluoride (PVDF), which has properties such as anti-aging, chemical resistance, weather resistance, and UV radiation resistance. It is chemically inert and does not react with electrolytes or lithium.

[0007] Furthermore, the maleic anhydride-grafted modified styrene-ethylene / butene-styrene (SEBS-g-MAH) can be selected with a styrene content of 13% to 30 wt% and a maleic anhydride grafting rate of 0.5% to 3.0%. Optional materials include Asahi Kasei's TUFTEC M1911 and TUFTEC M1941 from Japan, and Kraton's FG1901 and FG1924 from the United States. Maleic anhydride-grafted modified styrene-ethylene / butene-styrene is a polar thermoplastic elastomer with excellent compatibility and low-temperature flexibility, and can be used as a compatibilizer and adhesive for different engineering plastics, enhancing adhesion to metal substrates.

[0008] Furthermore, the modified polyolefin is a chlorinated, carboxyl, anhydride, or amino-modified polyethylene, polypropylene, or ethylene-propylene-1-butene copolymer. The modified polyolefin contains unsaturated carboxylic acid components. Considering the superior adhesion to the current collector material, acrylic acid, methacrylic acid, maleic acid, and maleic anhydride are preferred, with acrylic acid and maleic anhydride being particularly preferred. The unsaturated carboxylic acid components in the modified polyolefin are obtained through random copolymerization, block copolymerization, graft copolymerization (graft modification), etc. The mass content of the unsaturated carboxylic acid components in the modified polyolefin is 0.1% to 5%, preferably 0.8% to 3%. If the content of the unsaturated carboxylic acid components in the modified polyolefin is less than 0.1%, the adhesion to the metal substrate is low; if the content of the unsaturated carboxylic acid components in the modified polyolefin is greater than 5%, the water resistance deteriorates, and the electrolyte resistance decreases. Ethylene-ethyl acrylate-maleic anhydride copolymer (BONDINE HX-8290 or LX-4110 manufactured by Arkem) can be used, as can maleic anhydride-modified polypropylene resin (Orevac 18722 or Orevac 18751 manufactured by Arkem), amorphous α-polyolefin Vestoplast 308 manufactured by Evonik, or ADMER manufactured by Mitsui. TM It is a modified polyolefin composed of modified polyethylene and modified polypropylene, which can act as a coupling agent to increase the compatibility between filler and polyolefin.

[0009] Furthermore, the ceramic powder is at least one of high-purity alumina and boehmite, wherein the high-purity alumina has a purity of 99.99% or higher and a particle size D50 of 0.1–1.0 μm. Submicron-grade boehmite (grade: LSB-2-2L) produced by Zhengzhou Nonferrous Metals Research Institute Co., Ltd. of China Aluminum Corporation can be used, with a particle size D50 of 0.5–0.8 μm. Alternatively, high-purity alumina ZTL-WAO-030 produced by Yangzhou Zhongtianli can be used, with a particle size D50 ≤ 1.0 μm. The addition of ceramic powder is beneficial for improving the heat resistance of the adhesive and also facilitates heat conduction, thereby solving the problem of poor thermal conductivity of the adhesive.

[0010] Furthermore, the coupling agent is a titanate coupling agent, etc.

[0011] Furthermore, the antioxidant is a complex antioxidant of hindered phenols and phosphites.

[0012] Furthermore, the solvent is N-methylpyrrolidone.

[0013] A second objective of this invention is to provide a method for preparing the binder for coating lithium battery current collectors, comprising the following steps:

[0014] In a reaction vessel, polyvinylidene fluoride, maleic anhydride-grafted modified styrene-ethylene / butene-styrene, modified polyolefin, ceramic powder, coupling agent, antioxidant, and solvent are added in parts by mass. The mixture is heated to 60-80°C, dissolved, stirred, and mixed evenly. The mixture in the reaction vessel is then cooled to room temperature to obtain the binder for coating lithium battery current collectors.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention combines the properties of polyvinylidene fluoride, maleic anhydride grafted modified styrene-ethylene / butene-styrene and modified polyolefin, and the resulting adhesive has good adhesion to copper foil and aluminum foil of current collector, is resistant to electrolyte corrosion, and improves the tensile strength of current collector at break. Detailed Implementation

[0016] The present invention will be described below with reference to examples. These examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0017] Example 1

[0018] The steps for applying an adhesive to lithium battery current collectors are as follows:

[0019] In a 100L glass reactor equipped with an oil bath heating device and a stirring device, 80kg of N-methylpyrrolidone (NMP) solvent was added, and the mixture was heated to 70℃ and held at that temperature. Then, 13kg of ceramic powder (submicron-grade boehmite, LSB-2-2L, produced by China Aluminum Zhengzhou Nonferrous Metals Research Institute Co., Ltd.) was added sequentially; followed by 3kg of polyvinylidene fluoride (PVDF, produced by Solvay). 5130; Add 3 kg of maleic anhydride-grafted modified styrene-ethylene / butene-styrene (Kraton FG1901, USA); add 0.8 kg of modified polyolefin resin (BONDINE HX-8290, Arkema); add 0.13 kg of coupling agent (TTS titanate coupling agent, Ajinomoto); add 0.5 kg of antioxidant (IRGANOX B215, BASF); stir the solvent thoroughly for 3 hours, cool to room temperature, and obtain the binder with a solid content of 20%.

[0020] Example 2 uses high-purity alumina ZTL-WAO-030 produced by Yangzhou Zhongtianli as the ceramic powder, and the rest is the same as in Example 1.

[0021] Example 3 uses Kynar HSV 900 manufactured by Arkema for polyvinylidene fluoride, and is otherwise the same as in Example 1.

[0022] Example 4 Maleic anhydride grafted modified styrene-ethylene / butene-styrene used TUFTEC M1911 produced by Asahi Kasei, and was otherwise the same as in Example 1.

[0023] Example 5 uses Arkema's LX-4110 modified polyolefin, and is otherwise the same as in Example 1.

[0024] Comparative Example 1

[0025] In a 100L glass reactor equipped with an oil bath heating device and a stirring device, 80kg of N-methylpyrrolidone (NMP) solvent was added, and the mixture was heated to 70℃ and held at that temperature. Then, 13kg of ceramic powder (submicron-grade boehmite, LSB-2-2L, produced by Zhengzhou Nonferrous Metals Research Institute Co., Ltd. of Aluminum Corporation of China) was added sequentially; 3kg of maleic anhydride-grafted modified styrene-ethylene / butene-styrene (Kraton FG1901, USA) was added; 0.8kg of modified polyolefin resin (BONDINE HX-8290, produced by Arkema) was added; 0.13kg of coupling agent (TTS titanate coupling agent produced by Ajinomoto) was added; and 0.5kg of antioxidant (IRGANOX B215, produced by BASF) was added. The solvent was stirred thoroughly for 3 hours and then cooled to room temperature to obtain a binder with a solid content of 20%.

[0026] Comparative Example 2

[0027] In a 100L glass reactor equipped with an oil bath heating device and a stirring device, 80kg of N-methylpyrrolidone (NMP) solvent was added, and the mixture was heated to 70℃ and held at that temperature. Then, 13kg of ceramic powder (submicron-grade boehmite, LSB-2-2L, produced by China Aluminum Zhengzhou Nonferrous Metals Research Institute Co., Ltd.) was added sequentially; followed by 3kg of polyvinylidene fluoride (PVDF, produced by Solvay). 5130; Add 0.8 kg of modified polyolefin resin, BONDINE HX-8290 manufactured by Arkema; ​​Add 0.13 kg of coupling agent, TTS titanate coupling agent manufactured by Ajinomoto; Add 0.5 kg of antioxidant, IRGANOX B215 manufactured by BASF; Stir the solvent thoroughly for 3 hours, cool to room temperature, and obtain the binder with a solid content of 20%.

[0028] Comparative Example 3

[0029] In a 100L glass reactor equipped with an oil bath heating device and a stirring device, 80kg of N-methylpyrrolidone (NMP) solvent was added, and the mixture was heated to 70℃ and held at that temperature. Then, 13kg of ceramic powder (submicron-grade boehmite, LSB-2-2L, produced by China Aluminum Zhengzhou Nonferrous Metals Research Institute Co., Ltd.) was added sequentially; followed by 3kg of polyvinylidene fluoride (PVDF, produced by Solvay). 5130; Add 3 kg of maleic anhydride-grafted modified styrene-ethylene / butene-styrene, Kraton FG1901 (USA); Add 0.13 kg of coupling agent, titanate coupling agent TTS (Ajinomoto); Add 0.5 kg of antioxidant, IRGANOX B215 (BASF); Stir the solvent thoroughly for 3 hours, cool to room temperature, and obtain the binder with a solid content of 20%.

[0030] Comparative Example 4

[0031] Replace BONDINE HX-8290 with an equal amount of unmodified polyolefin Vestoplast 703, otherwise the same as in Example 1.

[0032] Comparative Example 5

[0033] The modified polyolefin was replaced with maleic anhydride-grafted polypropylene wax Licocene PP MA 6452 manufactured by Clariant, with a grafting rate of 7%, and the rest was the same as in Example 1.

[0034] The performance of the binders used for coating lithium battery current collectors in Examples 1-5 and Comparative Examples 1-5 was tested using the following methods:

[0035] 1) Viscosity test: Brookfield viscometer, model TC550, water bath temperature control, CP-42# rotor was used to test the viscosity at 25℃;

[0036] 2) Adhesion strength test: Adhesive is applied to a 6μm thick copper foil with a thickness of 10μm, and hot melt adhesive is bonded with tape. Peel strength test is performed according to the national standard GB / T 2792-2014.

[0037] 3) Electrolyte immersion bonding strength test: Immerse the sample from step 2) in lithium battery electrolyte at 85℃ for 6 hours. The electrolyte mass ratio is as follows: EC / PC / DEC / EP=30 / 10 / 30 / 30, and the mass ratio of 1M LiPF6 lithium salt is calculated as 12.5%. After cooling to room temperature, the peel strength test is carried out according to the method described in national standard GB / T 2792-2014.

[0038] 4) Swelling thickness change rate test: The sample thickness is 4-7mm. Soak in electrolyte (85℃ for 14d). Cool the aged electrolyte to room temperature, take the sample out of the electrolyte, wipe the electrolyte off the sample surface with a lint-free cloth, and then measure the thickness with vernier calipers and calculate the thickness change rate.

[0039] 5) Dissolution rate test: Weigh the sample before and after aging, soak it in electrolyte (85℃ for 14 days), cool the aging electrolyte to room temperature, take the sample out of the electrolyte, wipe the electrolyte off the sample surface with a lint-free cloth, and then weigh it for testing.

[0040] Table 1. Performance of the binders for coating lithium battery current collectors obtained in Examples 1-5

[0041]

[0042] Table 2. Performance of binders for lithium battery current collector coating obtained in Comparative Examples 1-5

[0043]

[0044]

[0045] Note: a. Peel strength > 0.5 N / mm indicates that the tape cannot peel the coating off the foil. The force tested is the adhesive force between the tape and the hot melt adhesive coating.

[0046] As shown in Tables 1 and 2, the adhesion and electrolyte resistance of Examples 1-5, as well as the adhesion strength and swelling / dissolution after electrolyte immersion, all meet customer requirements. Comparative Example 1, which did not use polyvinylidene fluoride, showed deterioration in the adhesive's resistance to electrolyte swelling and dissolution. Comparative Examples 2-4, which did not use maleic anhydride-grafted modified styrene-ethylene / butene-styrene, modified polyolefin resin, or unmodified polyolefin respectively, showed deterioration in metal adhesion and electrolyte resistance. Comparative Example 5, which used a 7% grafted polyolefin, showed deterioration in electrolyte resistance.

[0047] The adhesive provided by this invention has excellent adhesion to copper and aluminum foil current collectors, is resistant to electrolyte corrosion, improves the tensile strength of the current collector at break, and can effectively protect the current collector, making it feasible for industrial application.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A binder for lithium battery current collector coating, characterized by, By weight parts, including the following components: polyvinylidene fluoride 10~20 parts, maleic anhydride grafted modified styrene-ethylene / butylene-styrene 10~20 parts, modified polyolefin 1~10 parts, ceramic powder 50~70 parts, coupling agent 0.1~1 parts, antioxidant 0.1~3 parts, solvent 300~500 parts; the modified polyolefin contains unsaturated carboxylic acid component, and the mass content of the unsaturated carboxylic acid component is 0.1%~5%.

2. The binder for lithium battery current collector coating according to claim 1, characterized by, The polyvinylidene fluoride is a homopolymer and a copolymer with a weight average molecular weight of 500,000~1,100,000.

3. The binder for lithium battery current collector coating according to claim 1, wherein The grafting rate of maleic anhydride in the maleic anhydride grafted modified styrene-ethylene / butylene-styrene is 0.5-2.0%.

4. The binder for lithium battery current collector coating according to claim 1, wherein The modified polyolefin is at least one of ethylene-ethyl acrylate-maleic anhydride copolymer and maleic anhydride modified polypropylene resin.

5. The binder for lithium battery current collector coating according to claim 4, characterized by, The ceramic powder is at least one of high-purity alumina and boehmite, and the particle size D50 is 0.1~1.0μm.

6. The binder for lithium battery current collector coating according to claim 5, wherein The coupling agent is a titanate coupling agent.

7. The binder for lithium battery current collector coating according to claim 6, wherein The antioxidant is a hindered phenol and phosphite composite antioxidant.

8. A method for producing a binder for coating a lithium battery current collector as claimed in any one of claims 1 to 7, characterized by, The method comprises the following steps: In a reaction vessel, polyvinylidene fluoride, maleic anhydride grafted modified styrene-ethylene / butylene-styrene, modified polyolefin, ceramic powder, coupling agent, antioxidant, solvent are added by mass fraction, heated to 60-80℃, dissolved and stirred to mix uniformly, and the mixture in the reaction vessel is cooled to room temperature to obtain the binder for lithium battery current collector coating.

Images