Hot-melt adhesive for coating lithium battery current collector and preparation method of hot-melt adhesive

Abstract

The invention relates to the technical field of adhesives for lithium batteries, and discloses a hot-melt adhesive for coating a current collector of a lithium battery and a preparation method of the hot-melt adhesive, and the hot-melt adhesive for coating the current collector of the lithium battery comprises the following components in parts 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 part of a coupling agent and 0.1-1 part of an antioxidant. The hot-melt adhesive has good adhesion to the copper foil and the aluminum foil of the current collector and is resistant to electrolyte corrosion, the edges of the copper foil and the aluminum foil of the current collector are coated with the hot-melt adhesive, the coating thickness ranges from 5 micrometers to 30 micrometers, the coating width ranges from 1.5 mm to 5 mm, the development time is shorter than 30 s, the breaking tensile strength of the current collector can be effectively improved, cutting burrs are reduced, and the cutting speed and the yield are increased.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives for lithium batteries, and in particular to a hot melt adhesive for coating a lithium battery current collector and a preparation method thereof. Background Art

[0002] Lithium-ion battery is a rechargeable battery. It is widely used in mobile phones, notebooks, wearable electronic devices, power tools, drones and electric vehicles due to its advantages such as high operating voltage, small size, light weight, high energy, no memory effect, low self-discharge, long cycle life, and high unit density capacity. The positive pole ear of existing lithium-ion batteries generally uses aluminum pole ear (or other metals and alloys), and the current collector is aluminum foil; the negative pole ear uses nickel pole ear (or other metals and alloys), and the current collector is copper foil. The pole ear is connected to the current collector by welding (super welding, riveting, etc.). The ultra-thin copper foil of the current collector brings a series of problems: low tensile strength, poor coating continuity, easy to break; the thinner the copper foil, the easier it is for the copper foil pole ear to fold inward, and the lower the yield rate; the problem of burrs on the cutting edge of the copper foil, etc. Summary of the invention

[0003] The present invention aims to provide a hot melt adhesive for coating a lithium battery current collector and a preparation method thereof in view of the shortcomings of the existing lithium battery current collector.

[0004] To achieve the above objectives, the technical solutions adopted are:

[0005] One of the purposes of the present invention is to provide a hot melt adhesive for coating a lithium battery current collector, which comprises the following components, by weight: 20 to 45 parts of polyolefin, 20 to 45 parts of modified polyolefin, 10 to 20 parts of tackifying resin, 10 to 20 parts of wax, 0.1 to 1 part of coupling agent, and 0.1 to 1 part of antioxidant.

[0006] Further, the polyolefin is an amorphous α-polyolefin (APAO), which is generally polymerized from three monomers (ethylene, propylene and 1-butene), and preferably has a softening point of 90 to 130° C. The Vestoplast series produced by Evonik can be selected, and the copolymer with a melt viscosity of 3000 to 10000 mPas at 190° C. is commercially available from Evonik. The amorphous α-olefin copolymer (APAO) has the characteristics of low VOC, low odor, excellent toughness and elasticity, good elongation and bendability, and provides good bonding.

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

[0008] Furthermore, the modified polyolefin contains an unsaturated carboxylic acid component. Considering the factor of obtaining better adhesion to the current collector material, acrylic acid, methacrylic acid, maleic acid, and maleic anhydride are preferred, and acrylic acid and maleic anhydride are particularly preferred. The unsaturated carboxylic acid component in the polyolefin resin is contained by random copolymerization, block copolymerization, graft copolymerization (graft modification), etc. The mass content of the unsaturated carboxylic acid component in the modified polyolefin is 0.1% to 5%, preferably 0.8% to 3%. If the content of the unsaturated carboxylic acid component 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 component in the modified polyolefin is greater than 5%, the water resistance deteriorates and the electrolyte resistance performance is reduced. The modified polyolefin is at least one selected from 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] Further, 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 to 125°C, preferably hydrogenated petroleum resin and hydrogenated terpene resin, which have the characteristics of light color and good aging resistance. It can be selected from the ARKON series hydrogenated petroleum resin produced by Arakawa Chemical, the TO series hydrogenated terpene resin produced by Yasuhara Chemical, and the Escorez series hydrogenated petroleum resin produced by ExxonMobil. The addition of tackifying resin helps to improve the adhesion between the hot melt adhesive and the current collector and reduce the viscosity. The hydrogenated C5-C9 petroleum resin has better compatibility with polyolefins.

[0010] Furthermore, the wax is one of polyethylene wax, polypropylene wax, Fischer-Tropsch wax or a combination of any two of them, preferably polyethylene wax and Fischer-Tropsch wax, and the melting point is preferably 80-110° C. Fischer-Tropsch wax (Sarawax SX80, Sarawax SX105) produced by Shell can be used. The addition of wax can significantly reduce the viscosity of the hot melt adhesive and shorten the opening and curing time.

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

[0012] Furthermore, the antioxidant is a hindered phenol and phosphite composite antioxidant.

[0013] The second object of the present invention is to provide a method for preparing the hot melt adhesive for coating the lithium battery current collector, which is characterized in that it includes the following steps: adding polyolefin, modified polyolefin, tackifying resin, wax, coupling agent, and antioxidant in a reaction container according to mass fractions, heating to 170-180°C, stirring and mixing evenly, and obtaining the hot melt adhesive for coating the lithium battery current collector.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention combines the properties of polyolefins, modified polyolefins, and tackifying resins, and the obtained hot-melt adhesive for coating lithium battery current collectors has good adhesion to the current collector copper foil and aluminum foil, and is resistant to electrolyte corrosion. The hot-melt adhesive is coated on the edges of the current collector copper and aluminum foils, with a coating thickness of 5 to 30 μm, a coating width of 1.5 to 5 mm, and a development time of less than 30 s. It can effectively improve the tensile strength of the current collector at break, reduce cutting burrs, and improve the cutting rate and yield. DETAILED DESCRIPTION

[0015] The present invention is described below in conjunction with examples, which are only used to explain the present invention and are not used to limit the scope of the present invention.

[0016] Example 1

[0017] A hot melt adhesive for coating a lithium battery current collector comprises the following steps:

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

[0019] In Example 2, the polyolefin used was Vestoplast 703 produced by Evonik, and the rest was the same as in Example 1.

[0020] Example 3 The modified polyolefin used was BONDINE HX-8290 produced by Arkema, and the rest was the same as Example 1.

[0021] Example 4 The Fischer-Tropsch wax used was Sarawax SX80 produced by Shell, and the rest was 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 produced by Evonik, 14kg of hydrogenated petroleum resin, ARKON P-125 (hydrogenated petroleum resin, softening point 125°C) produced by Arakawa Chemical, 14kg of Fischer-Tropsch wax, Sarawax SX80 produced by Shell, 1kg of silane coupling agent KH-560, and 1kg of antioxidant, IRGANOX B215 produced by BASF were added; the oil bath heating circulation device was turned on, the oil bath temperature was set to 180°C, the mixture was fully melted and stirred for 3 hours, and 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 produced by Arkema, 14kg of hydrogenated petroleum resin, ARKON P-125 (hydrogenated petroleum resin, softening point 125°C) produced by Arakawa Chemical, 14kg of Fischer-Tropsch wax, Sarawax SX80 produced by Shell, 1kg of silane coupling agent KH-560, and 1kg of antioxidant, IRGANOX B215 produced by BASF were added; the oil bath heating circulation device was turned on, the oil bath temperature was set to 180°C, the mixture was fully melted and stirred for 3 hours, and cooled to room temperature to obtain a hot melt adhesive.

[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 produced by Evonik, 35kg of modified polyolefin, Orevac 18722 produced by Arkema, 14kg of Fischer-Tropsch wax, Sarawax SX80 produced by Shell, 1kg of silane coupling agent KH-560, and 1kg of antioxidant, IRGANOX B215 produced by BASF were added; the oil bath heating circulation device was turned on, the oil bath temperature was set to 180°C, the mixture was fully melted and stirred for 3 hours, and then cooled to room temperature to obtain a hot melt adhesive.

[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 produced by Evonik, 35kg of modified polyolefin, Orevac 18722 produced by Arkema, 14kg of hydrogenated petroleum resin, ARKON P-125 (hydrogenated petroleum resin, softening point 125°C) produced by Arakawa Chemical, 1kg of silane coupling agent KH-560, and 1kg of antioxidant, IRGANOX B215 produced by BASF were added; the oil bath heating circulation device was turned on, the oil bath temperature was set to 180°C, the mixture was fully melted and stirred for 3 hours, and cooled to room temperature to obtain a hot melt adhesive.

[0030] Comparative Example 5 The modified polyolefin used was maleic anhydride grafted polypropylene wax Licocene PPMA 6452 produced by Clariant, with a grafting rate of 7%. Other components were the same as those in Example 1.

[0031] The performance of the hot melt adhesive for coating lithium battery current collectors of Examples 1-4 and Comparative Examples 1-5 was tested by the following method:

[0032] 1) Viscosity test: Use a Brookfield viscometer, model DV2T, rotor No. 27 to test the viscosity at 170°C.

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

[0034] 3) Bonding strength test: Coat a hot melt adhesive on a 6 μm thick copper foil with a thickness of 10 μm, use tape to bond the hot melt adhesive, and perform a peel strength test according to the national standard GB / T 2792-2014 method;

[0035] 4) Adhesive strength test after immersion in electrolyte: The sample in step 3) was immersed in lithium battery electrolyte for 30 days. The mass ratio of the electrolyte was as follows: EC / PC / DEC / EP=30 / 10 / 30 / 30, and the mass ratio of 1M LiPF6 lithium salt was calculated as 12.5%. The peel strength test was performed according to the method described in the national standard GB / T 2792-2014;

[0036] 5) Tensile strength test: The tensile strength test was carried out in accordance with GB / T30776-2014.

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

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

[0039]

[0040]

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

[0042]

[0043] Note: a peel strength > 0.5N / mm means the tape cannot tear the coating off the foil. The force tested is the bonding strength between the tape and the hot melt adhesive coating.

[0044] From the results shown in Table 1 and Table 2, it can be seen that Examples 1-4 have moderate viscosity, excellent adhesion to copper foil and adhesion after electrolyte soaking, and meet the current collector protection requirements. Comparative Example 1 does not use modified polyolefin, has low adhesion to metal, and low adhesion after electrolyte soaking; Comparative Example 2 does not use polyolefin, and the electrolyte resistance of the body is low; Comparative Example 3 does not use hydrogenated petroleum resin, has high viscosity, and is not suitable for glue coating process; Comparative Example 4 does not use Fischer-Tropsch wax, has high viscosity, long open time, and is not suitable for glue coating process and subsequent winding molding; Comparative Example 5 uses modified polyolefin with a maleic anhydride grafting rate of 7%, and the electrolyte resistance is reduced.

[0045] It can be seen that the adhesive provided by the present invention has excellent adhesion to the current collector copper foil and aluminum foil, is resistant to electrolyte corrosion, improves the tensile strength of the current collector, can effectively protect the current collector, and is feasible for industrial use.

[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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A hot melt adhesive for coating a lithium battery current collector, characterized in that: The invention comprises the following components in parts by weight: 20 to 45 parts of polyolefin, 20 to 45 parts of modified polyolefin, 10 to 20 parts of tackifying resin, 10 to 20 parts of wax, 0.1 to 1 part of coupling agent and 0.1 to 1 part of antioxidant.

2. The hot melt adhesive for coating a lithium battery current collector according to claim 1, characterized in that: The polyolefin is an amorphous α-polyolefin.

3. The hot melt adhesive for coating a lithium battery current collector according to claim 2, characterized in that: The amorphous alpha-polyolefin is polymerized from ethylene, propylene and 1-butene and has a softening point of 90-130°C.

4. The hot melt adhesive for coating a lithium battery current collector according to claim 1, characterized in that: The modified polyolefin is at least one of polyethylene, polypropylene, and ethylene-propylene-1-butene copolymer modified by carboxyl and / or acid anhydride.

5. The hot melt adhesive for coating a lithium battery current collector according to claim 1, characterized in that: The modified polyolefin contains an unsaturated carboxylic acid component, and the mass content of the unsaturated carboxylic acid component in the modified polyolefin is 0.1% to 5%.

6. The hot melt adhesive for coating a lithium battery current collector according to claim 1, characterized in that: The modified polyolefin is at least one of ethylene-ethyl acrylate-maleic anhydride copolymer and maleic anhydride modified polypropylene resin.

7. The hot melt adhesive for coating a lithium battery current collector according to claim 1, characterized in that: The tackifying resin is one of petroleum resin, hydrogenated petroleum resin, rosin resin, hydrogenated rosin resin, hydrogenated terpene resin, terpene phenolic resin or coumarone resin with a softening point of 80-125° C., or a combination of any two thereof.

8. The hot melt adhesive for coating a lithium battery current collector according to claim 1, characterized in that: The wax is one of polyethylene wax, polypropylene wax and Fischer-Tropsch wax, or a combination of any two of them.

9. The hot melt adhesive for coating a lithium battery current collector according to claim 1, characterized in that: The coupling agent is a silane coupling agent or a titanate coupling agent, and the antioxidant is a hindered phenol and phosphite composite antioxidant.

10. A method for preparing a hot melt adhesive for coating a lithium battery current collector as claimed in any one of claims 1 to 9, characterized in that: The method comprises the following steps: adding polyolefin, modified polyolefin, tackifying resin, wax, coupling agent and antioxidant in proportion by mass into a reaction container, heating to 170-180° C., stirring and mixing evenly, and obtaining the hot melt adhesive for coating the lithium battery current collector.

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