A hot melt adhesive for lithium battery current collector coating and a method for preparing the same

Abstract

The present application relates to the technical field of lithium battery adhesive, and discloses a hot melt adhesive for coating lithium battery current collector and a preparation method thereof, wherein the hot melt adhesive for coating lithium battery current collector comprises the following components in parts by weight: polyolefin 20-45 parts, modified polyolefin 20-45 parts, tackifying resin 10-20 parts, wax 10-20 parts, coupling agent 0.1-1 part, and antioxidant 0.1-1 part.The hot melt adhesive has good adhesion to the current collector copper foil and aluminum foil, is resistant to electrolyte corrosion, is coated on the edges of the current collector copper and aluminum foil, has a coating thickness of 5-30 microns, a coating width of 1.5-5 mm, and a development time of less than 30 seconds, can effectively improve the tensile strength at break of the current collector, reduce cutting burrs, and improve the cutting speed and yield.

Description

Technical Field

[0001] This invention relates to the field of adhesives for lithium batteries, and more specifically to a hot melt 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 hot-melt adhesive 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 a hot melt adhesive for coating current collectors in lithium batteries, comprising the following components by weight: 20-45 parts of polyolefin, 20-45 parts of modified polyolefin, 10-20 parts of tackifying resin, 10-20 parts of wax, 0.1-1 parts of coupling agent, and 0.1-1 parts of antioxidant.

[0006] Furthermore, the polyolefin is an amorphous α-polyolefin (APAO), generally polymerized from three monomers (ethylene, propylene, and 1-butene), preferably APAO with a softening point of 90–130°C. Vestoplast series copolymers manufactured by Evonik, with a melt viscosity of 3000–10000 mPas at 190°C, can be used and are commercially available from Evonik. These amorphous α-olefin copolymers (APAO) possess low VOCs, low odor, excellent toughness and elasticity, good elongation and flexibility, and provide good adhesion.

[0007] Furthermore, the modified polyolefin is at least one of carboxyl- and / or anhydride-modified polyethylene, polypropylene, and ethylene-propylene-1-butene copolymer.

[0008] Furthermore, the modified polyolefin contains unsaturated carboxylic acid components. Considering factors such as superior adhesion to current collector materials, 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 polyolefin resin 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. The modified polyolefin is selected from at least one of ethylene-ethyl acrylate-maleic anhydride copolymer (BONDINE HX-8290 or LX-4110 manufactured by Arkem) and maleic anhydride modified polypropylene resin (Orevac 18722 or Orevac 18751 manufactured by Arkem).

[0009] Furthermore, the tackifying resin is a petroleum resin, hydrogenated petroleum resin, rosin resin, hydrogenated rosin resin, hydrogenated terpene resin, terpene phenolic resin, coumarone resin, etc., with a softening point of 80-125℃. Hydrogenated petroleum resin and hydrogenated terpene resin are preferred, as they have the characteristics of light color and good aging resistance. Options include ARKON series hydrogenated petroleum resins produced by Arakawa Chemical, TO series hydrogenated terpene resins produced by Yasuhara Chemical, and Escorez series hydrogenated petroleum resins produced by ExxonMobil. The addition of the tackifying resin helps improve the adhesion between the hot melt adhesive and the current collector and reduces viscosity. Hydrogenated C5-C9 petroleum resins have better compatibility with polyolefins.

[0010] Furthermore, the wax is one or a combination of two of polyethylene wax, polypropylene wax, and Fischer-Tropsch wax, preferably polyethylene wax and Fischer-Tropsch wax, with a melting point preferably of 80-110°C. Shell Fischer-Tropsch waxes (Sarawax SX80, Sarawax SX105) can be used. The addition of wax can significantly reduce the viscosity of the hot melt adhesive and shorten the open and cure times.

[0011] Furthermore, the coupling agent is a silane coupling agent or a titanate coupling agent, etc.

[0012] Furthermore, the antioxidant is a complex antioxidant of hindered phenols and phosphites.

[0013] The second objective of this invention is to provide a method for preparing the hot melt adhesive for coating current collectors of lithium batteries, characterized by the following steps: adding polyolefin, modified polyolefin, tackifying resin, wax, coupling agent, and antioxidant in a reaction vessel according to the mass fractions, heating to 170-180°C, and stirring and mixing evenly to obtain the hot melt adhesive for coating current collectors of lithium batteries.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention combines the properties of polyolefin, modified polyolefin and tackifying resin to obtain a hot melt adhesive for coating current collectors of lithium batteries. The hot melt adhesive has good adhesion to the copper foil and aluminum foil of the current collector, is resistant to electrolyte corrosion, and can be applied to the edges of the copper and aluminum foil of the current collector with a coating thickness of 5-30 μm and a coating width of 1.5-5 mm. The development time is <30s, which can effectively improve the tensile strength of the current collector at break, reduce cutting burrs, and improve the cutting rate and yield. Detailed Implementation

[0015] 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.

[0016] Example 1

[0017] The steps for applying a hot-melt adhesive to lithium battery current collectors are as follows:

[0018] In a 200L glass reactor equipped with an oil bath heating device and a stirring device, 35kg of polyolefin (Vestoplast 508 manufactured by Evonik), 35kg of modified polyolefin (Orevac 18722 manufactured by Arkema), 14kg of hydrogenated petroleum resin (ARKON P-125 manufactured by Arakawa Chemicals, with a softening point of 125℃), 14kg of Fischer-Tropsch wax (Sarawax SX80 manufactured by Shell), 1kg of silane coupling agent (KH-560), and 1kg of antioxidant (IRGANOX B215 manufactured by BASF) were added. The oil bath heating circulation device was turned on, the oil bath temperature was set to 180℃, and the mixture was stirred and melted for 3 hours. After cooling to room temperature, a hot melt adhesive was obtained.

[0019] Example 2 uses Vestoplast 703 manufactured by Evonik, and is otherwise the same as in Example 1.

[0020] Example 3 uses BONDINE HX-8290 manufactured by Arkema for the modified polyolefin, and is otherwise the same as in Example 1.

[0021] Example 4 uses Sarawax SX80 manufactured by Shell, and is otherwise the same as in Example 1.

[0022] Comparative Example 1

[0023] In a 200L glass reactor equipped with an oil bath heating device and a stirring device, 70kg of polyolefin (Vestoplast 508 manufactured by Evonik) was added; 14kg of hydrogenated petroleum resin (ARKON P-125 manufactured by Arakawa Chemicals, with a softening point of 125℃) was added; 14kg of Fischer-Tropsch wax (Sarawax SX80 manufactured by Shell) was added; 1kg of silane coupling agent (KH-560) was added; and 1kg of antioxidant (IRGANOX B215 manufactured by BASF) was added. The oil bath heating circulation device was turned on, and the oil bath temperature was set to 180℃. The mixture was stirred and fully melted for 3 hours, and then cooled to room temperature to obtain a hot melt adhesive.

[0024] Comparative Example 2

[0025] In a 200L glass reactor equipped with an oil bath heating device and a stirring device, 70kg of modified polyolefin, Orevac 18722 manufactured by Arkema, was added; 14kg of hydrogenated petroleum resin, ARKON P-125 (hydrogenated petroleum resin, softening point 125℃) manufactured by Arakawa Chemical was added; 14kg of Fischer-Tropsch wax, Sarawax SX80 manufactured by Shell was added; 1kg of silane coupling agent KH-560 was added; and 1kg of antioxidant, IRGANOX B215 manufactured by BASF was added. The oil bath heating circulation device was turned on, the oil bath temperature was set to 180℃, and the mixture was stirred for 3 hours to fully melt and stir. After cooling to room temperature, a hot melt adhesive was obtained.

[0026] Comparative Example 3

[0027] In a 200L glass reactor equipped with an oil bath heating device and a stirring device, 35kg of polyolefin (Vestoplast 508 manufactured by Evonik), 35kg of modified polyolefin (Orevac 18722 manufactured by Arkema), 14kg of Fischer-Tropsch wax (Sarawax SX80 manufactured by Shell), 1kg of silane coupling agent (KH-560), and 1kg of antioxidant (IRGANOX B215 manufactured by BASF) were added. The oil bath heating circulation device was turned on, the oil bath temperature was set to 180℃, and the mixture was stirred for 3 hours to fully melt and stir. After cooling to room temperature, a hot melt adhesive was obtained.

[0028] Comparative Example 4

[0029] In a 200L glass reactor equipped with an oil bath heating device and a stirring device, 35kg of polyolefin (Vestoplast 508 manufactured by Evonik), 35kg of modified polyolefin (Orevac 18722 manufactured by Arkema), 14kg of hydrogenated petroleum resin (ARKON P-125 manufactured by Arakawa Chemicals, with a softening point of 125℃), 1kg of silane coupling agent (KH-560), and 1kg of antioxidant (IRGANOX B215 manufactured by BASF) were added. The oil bath heating circulation device was turned on, the oil bath temperature was set to 180℃, and the mixture was stirred and melted for 3 hours. After cooling to room temperature, a hot melt adhesive was obtained.

[0030] Comparative Example 5 modified polyolefin used maleic anhydride-grafted polypropylene wax Licocene PPMA 6452 manufactured by Clariant, with a grafting rate of 7%, and other components were the same as in Example 1.

[0031] The performance of the hot melt adhesives used for coating lithium battery current collectors in Examples 1-4 and Comparative Examples 1-5 was tested using the following methods:

[0032] 1) Viscosity test: The viscosity at 170°C was tested using a Brookfield viscometer, model DV2T, rotor No. 27.

[0033] 2) Open time test: Tested in accordance with industry standard HG / T 3716-2003.

[0034] 3) Adhesive strength test: Apply hot melt adhesive to a 6μm thick copper foil. The hot melt adhesive thickness is 10μm. Adhede the hot melt adhesive with tape and perform peel strength test according to the national standard GB / T 2792-2014.

[0035] 4) Electrolyte immersion bonding strength test: Immerse the sample from step 3) in lithium battery electrolyte for 30 days. 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%. The peel strength test is carried out according to the method described in national standard GB / T 2792-2014.

[0036] 5) Tensile strength test: Tensile strength test shall be conducted in accordance with GB / T30776-2014.

[0037] The test data is shown in Table 1.

[0038] Table 1. Performance of the hot melt adhesives for coating lithium battery current collectors obtained in Examples 1-4

[0039]

[0040]

[0041] Table 2. Performance of hot melt adhesives for lithium battery current collector coating obtained in Comparative Examples 1-5

[0042]

[0043] 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.

[0044] As shown in Tables 1 and 2, Examples 1-4 exhibit moderate viscosity and excellent adhesion to copper foil, both after soaking in electrolyte, meeting the requirements for current collector protection. Comparative Example 1, which did not use modified polyolefin, showed low adhesion to metal and low adhesion after soaking in electrolyte; Comparative Example 2, which did not use polyolefin, had low electrolyte resistance; Comparative Example 3, which did not use hydrogenated petroleum resin, had high viscosity, making it unsuitable for coating processes; Comparative Example 4, which did not use Fischer-Tropsch wax, had high viscosity and a long open time, making it unsuitable for coating processes and subsequent winding; Comparative Example 5, which used modified polyolefin with a 7% maleic anhydride grafting rate, showed reduced electrolyte resistance.

[0045] It is evident that 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, thus demonstrating feasibility for industrial application.

[0046] 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 hot-melt adhesive for coating current collectors in lithium batteries, characterized in that, The preparation process includes: adding 35 kg of polyolefin (Vestoplast 508 manufactured by Evonik) to a 200 L glass reactor equipped with an oil bath heating device and a stirring device; adding 35 kg of modified polyolefin (Orevac 18722 manufactured by Arkema); adding 14 kg of hydrogenated petroleum resin (ARKON P-125 hydrogenated petroleum resin manufactured by Arakawa Chemicals, with a softening point of 125 °C); adding 14 kg of Fischer-Tropsch wax (Sarawax SX80 manufactured by Shell); adding 1 kg of silane coupling agent (KH-560); adding 1 kg of antioxidant (IRGANOX B215 manufactured by BASF); turning on the oil bath heating circulation device, setting the oil bath temperature to 180 °C, and stirring thoroughly for 3 hours, then cooling to room temperature to obtain the hot melt adhesive.

2. A hot-melt adhesive for coating current collectors in lithium batteries, characterized in that, The preparation process includes: adding 35 kg of polyolefin (Vestoplast 703 manufactured by Evonik) to a 200 L glass reactor equipped with an oil bath heating device and a stirring device; adding 35 kg of modified polyolefin (Orevac 18722 manufactured by Arkema); adding 14 kg of hydrogenated petroleum resin (ARKON P-125 hydrogenated petroleum resin manufactured by Arakawa Chemicals, with a softening point of 125 °C); adding 14 kg of Fischer-Tropsch wax (Sarawax SX80 manufactured by Shell); adding 1 kg of silane coupling agent (KH-560); adding 1 kg of antioxidant (IRGANOX B215 manufactured by BASF); turning on the oil bath heating circulation device, setting the oil bath temperature to 180 °C, and stirring thoroughly for 3 hours, then cooling to room temperature to obtain the hot melt adhesive.

3. A hot-melt adhesive for coating current collectors in lithium batteries, characterized in that, The preparation process includes: adding 35 kg of polyolefin (Vestoplast 508 manufactured by Evonik) to a 200 L glass reactor equipped with an oil bath heating device and a stirring device; adding 35 kg of modified polyolefin (BONDINE HX-8290 manufactured by Arkema); adding 14 kg of hydrogenated petroleum resin (ARKON P-125 manufactured by Arakawa Chemicals, with a softening point of 125℃); adding 14 kg of Fischer-Tropsch wax (Sarawax SX80 manufactured by Shell); adding 1 kg of silane coupling agent (KH-560); adding 1 kg of antioxidant (IRGANOX B215 manufactured by BASF); turning on the oil bath heating circulation device, setting the oil bath temperature to 180℃, and stirring thoroughly for 3 hours, then cooling to room temperature to obtain the hot melt adhesive.

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