Low-swelling low-dissolution adhesive for lithium ion battery and preparation method of low-swelling low-dissolution adhesive

Abstract

The invention relates to a low-swelling low-dissolution adhesive for a lithium ion battery and a preparation method of the low-swelling low-dissolution adhesive. The adhesive for the lithium ion battery has the characteristics of low swelling and low dissolution. The preparation method of the adhesive comprises the following steps: mixing a monomer, a cross-linking agent and a photoinitiator to prepare a solution, and carrying out ultraviolet radiation to prepare the adhesive for the lithium ion battery. The preparation process disclosed by the invention is simple and efficient, does not use an organic solvent, is low in cost, safe and environment-friendly, is easy to realize large-scale efficient preparation of the adhesive, and has remarkable social benefits and economic benefits.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, relates to an adhesive for lithium ion batteries and a preparation method thereof, and particularly relates to an adhesive for lithium ion batteries with low swelling and low dissolution and a preparation method thereof. Background Art

[0002] In the complex system of lithium-ion batteries, binders, while not a significant component, play a crucial role. Like "invisible glue," they are responsible for tightly connecting the electrode active material and conductive agent to the electrode current collector, ensuring overall connectivity among the electrode components, thereby effectively reducing electrode impedance and playing a crucial role in battery performance. With the widespread application of lithium-ion batteries in electric vehicles, energy storage systems, and other fields, the requirements for their performance are also constantly increasing.

[0003] The main types of adhesives for lithium-ion batteries are:

[0004] Polyvinylidene fluoride (PVDF): The most commonly used oil-based adhesive, it is a non-polar, chain-like polymer material with outstanding redox resistance, excellent thermal stability, and easy dispersion. However, PVDF requires N-methylpyrrolidone (NMP) as a solvent, which has a high evaporation temperature, posing environmental risks and being relatively expensive.

[0005] Styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na): widely used water-based adhesives, easily soluble in water and polar solvents, with good mechanical stability and operability, but low bonding strength, especially when used in silicon-based negative electrode materials, serious material and current collector peeling will occur.

[0006] Polyacrylic acid (PAA): It hardly swells in the carbonate solvent of the electrolyte, which can ensure the stability of the electrode structure during the charge and discharge process; its carboxyl group can form strong hydrogen bonds with the surface groups of the active material, promoting a more uniform coating on the electrode surface; it can form a dense film in the electrode sheet, enhancing the electrical contact between the active material and the current collector, but the hard and brittle characteristics of the PAA film lead to poor processing performance of the electrode, limiting its application.

[0007] Natural extract binder sodium alginate: a natural polysaccharide extracted from brown seaweed, with properties similar to CMC, and possesses the viscosity, solubility, stability and safety required for lithium-ion battery binders.

[0008] Although the above-mentioned adhesives can meet the performance requirements of lithium-ion batteries to a certain extent, there is still a gap from the ideal state. For example, under high voltage and high rate charge and discharge conditions, the electrochemical stability of some adhesives in the electrolyte is insufficient, which will lead to accelerated battery capacity decay and shortened cycle life; for some new high-specific capacity electrode materials, existing adhesives are difficult to fully adapt to their huge volume changes and cannot effectively maintain the long-term stability of the electrode structure. Furthermore, with the increase in environmental awareness and the increasingly stringent relevant regulations, the environmental performance of adhesives has attracted much attention. The organic solvent NMP used in traditional adhesives has potential hazards to the environment and human health. Although water-based adhesives have improved in this regard, other pollutants may still be generated during the production process, and some water-based adhesives are not biodegradable. The development of greener, more environmentally friendly, and solvent-free adhesives has become an important challenge facing the sustainable development of the industry.

[0009] To address these issues, CN108203482A discloses a negative electrode binder and its preparation method. This patent adds an acrylate monomer to an aqueous solution at a mass ratio of 1:1 to 1:5. An initiator is then added to initiate a polymerization reaction, resulting in a binder emulsion with a solid content of 35 to 55 wt%. When preparing the negative electrode sheet, the aforementioned negative electrode binder and crosslinker are added to the negative electrode slurry. After the binder cures, the binder and the polymer in the crosslinker crosslink to form a network structure unit. This prevents the electrolyte from being in a free state, thereby providing more storage space for the electrolyte, increasing the electrolyte retention capacity, and achieving high ionic conductivity. This enables high-rate rapid charge and discharge in lithium-ion batteries, improving the power performance and cycle performance of lithium-ion batteries. However, this patent still has the problem that the binder's composition and ratio need to be further optimized to improve its conductivity and ion diffusion coefficient. CN118255925A discloses an additive for increasing the peel strength of a PAA binder for lithium-ion batteries and its preparation method. This patent utilizes a free radical polymerization reaction of specific raw materials to produce an additive with a specific structure. This additive incorporates siloxane segments that crosslink with acrylic functional groups at high temperatures to improve adhesion. The addition of styrene inhibits crosslinking of the siloxane segments at room temperature, making the adhesive less prone to gelling during storage and easier to store and use. However, this patent still raises the issue of the additive's chemical structure requiring further optimization to enhance its ability to enhance the adhesion, flexibility, and dispersibility of the PAA adhesive.

[0010] Therefore, there is an urgent need to develop a new adhesive for lithium-ion batteries that can address the problems of existing adhesives while meeting the performance requirements of lithium-ion batteries in the new energy vehicle and energy storage industries. This adhesive should have good bonding strength, good resistance to high temperature and humidity, and low swelling and dissolution properties to improve the overall performance and service life of lithium-ion batteries. Summary of the Invention

[0011] Aiming at the problems of poor swelling and dissolution performance and low bonding strength of adhesives for lithium ion batteries in the prior art, the present invention provides a low swelling and low dissolution adhesive for lithium ion batteries and a preparation method thereof.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0013] The present invention provides a method for preparing a low-swelling and low-dissolution adhesive for lithium-ion batteries, characterized by comprising steps S1 and S2, wherein in step S1, acrylic acid monomer, hydroxyethyl acrylate monomer, crosslinking agent and photoinitiator are fully mixed to form a solution; and in step S2, the above solution is polymerized under ultraviolet light irradiation to prepare the adhesive for lithium-ion batteries. In step S1, the mass ratio of acrylic acid monomer to hydroxyethyl acrylate monomer is generally 5:95 to 90:10, preferably 20:80 to 70:30; the cross-linking agent is selected from one of polyethylene glycol diacrylate (PEGDA), triethylene glycol dimethacrylate (TEGDMA), trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTMA) and triallyl isocyanurate (TAIC). The present invention has no particular restriction on the content of the cross-linking agent, but considering that too low a content is not conducive to providing a cross-linking degree, too high a content leads to an excessively high cross-linking density and loss of toughness, the amount of the cross-linking agent added is generally 1 to 20 parts by mass relative to 100 parts by mass of the monomer, preferably 1 to 10 parts by mass, and most preferably 2 to 5 parts by mass. The photoinitiator of the present invention is one or more selected from 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173), benzophenone (BP), (2,4,6-trimethylbenzoyl)-diphenylphosphine oxide (TPO), ethyl p-dimethylaminobenzoate (EDB), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (2959), 2-isopropylthioxanthone (ITX), 1-hydroxycyclohexylphenyl ketone (184) and benzoin diethyl ether (651). Preferably, it is one or more of benzophenone (BP), (2,4,6-trimethylbenzoyl)-diphenylphosphine oxide (TPO), ethyl p-dimethylaminobenzoate (EDB), and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (2959); relative to 100 parts by mass of monomer, the amount of photoinitiator added is 0.5 to 5 parts by mass. If it is too high, the degree of polymerization will be too low and affect the mechanical properties; if it is too low, the polymerization rate will be too low and it will not be conducive to improving the efficiency. Therefore, it is preferably 1 to 3 parts by mass.

[0014] The wavelength of the ultraviolet light in step S2 of the preparation method provided by the present invention is 365nm or 395nm. Considering the preparation efficiency, 365nm is preferred. The intensity of the ultraviolet light is generally 200-2000mw / cm 2Too low will affect the polymerization and curing efficiency, while too high will easily lead to violent polymerization. It is further preferably 500-1000 mw / cm 2 The present invention does not impose any restrictions on the UV irradiation time. Considering the efficiency and the degree of polymerization and cross-linking, the UV irradiation time is generally 1 to 200 seconds, preferably 1 to 40 seconds.

[0015] The present invention also provides a low swelling and low dissolution adhesive for lithium ion batteries, wherein the swelling of the adhesive in the electrolyte is 0-10%; the dissolution of the adhesive in the electrolyte is 0-5%.

[0016] The principle of the present invention is as follows: To address the technical difficulties of existing lithium-ion battery adhesives such as poor swelling and dissolution performance in electrolyte, low strength, and low preparation efficiency, the present invention uses polar monomers such as hydroxyethyl acrylate and acrylic acid to reduce the compatibility of the adhesive with the electrolyte, thereby fundamentally reducing the swelling of the adhesive in the electrolyte; hydroxyethyl acrylate and acrylic acid are copolymerized to improve strength and toughness; and photopolymerization / curing technology is used to improve the preparation efficiency of the adhesive on the one hand, and the conversion rate of hydroxyethyl acrylate to acrylic acid on the other hand, thereby reducing the dissolution of the adhesive in the electrolyte, ensuring the stability of the adhesive and the battery.

[0017] Beneficial effects of the present invention: First, the present invention prepares a solution by fully mixing acrylic acid monomer, hydroxyethyl acrylate monomer, crosslinking agent and photoinitiator, and polymerizes the solution under ultraviolet light irradiation. The obtained adhesive has excellent bonding strength, which effectively solves the problem that the existing water-based adhesive is prone to peeling between the material and the current collector in silicon-based negative electrode materials. Secondly, the present invention significantly improves the crosslinking degree of the adhesive and improves the spreading performance of the molecular chain on the adherend by optimizing the mass ratio of acrylic acid monomer to hydroxyethyl acrylate monomer, as well as the addition amount of the crosslinking agent, and effectively solves the problem of insufficient peeling force caused by insufficient crosslinking degree of the existing adhesive. Furthermore, the adhesive prepared by the present invention has good high temperature and high humidity resistance. By reasonably selecting the wavelength, light intensity and irradiation time of the photoinitiator and ultraviolet light, the stability of the adhesive during long-term use is ensured, which effectively solves the problem that the existing ultraviolet light-curing composition is prone to performance degradation in high temperature and high humidity environments. Furthermore, the adhesive produced by the present invention has a controlled swelling of 0-10% in the electrolyte and a controlled dissolution of 0-5%, significantly improving the electrolyte retention of the battery, thereby increasing the energy density and service life of the lithium-ion battery. In summary, the preparation method of the present invention is simple and controllable, with readily available raw materials and moderate cost, making it suitable for industrial production and having good economic benefits and practical value. DETAILED DESCRIPTION

[0018] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0019] The raw materials used in the examples and their sources are summarized in Table 1.

[0020] Table 1. Types and sources of raw materials

[0021]

[0022] Swelling determination:

[0023] The calculation formula is: Swelling Ratio (SR) is the ratio of (swelling mass minus dry mass) to dry mass, specifically:

[0024]

[0025] Where W s is the mass of the adhesive after swelling equilibrium, W d is the initial mass in dry state

[0026] Dissolution assay:

[0027] The calculation formula is: Dissolution rate (%) is the ratio of the mass of dissolved substance to the mass of total substance, specifically:

[0028]

[0029] Example 1:

[0030] A low-swelling, low-dissolution adhesive for lithium-ion batteries and a preparation method thereof. The preparation comprises the following steps:

[0031] Step 1: Weigh 5 parts of acrylic acid monomer, 95 parts of hydroxyethyl acrylate monomer, 5 parts by mass of crosslinker polyethylene glycol diacrylate (PEGDA), and 2 parts by mass of photoinitiator benzophenone BP, mix them thoroughly to form a solution, take a portion and pour it into a culture dish until the solution depth reaches 2 mm, and then let it stand to remove bubbles for 3 hours.

[0032] Step 2: The defoamed solution was irradiated at a wavelength of 365 nm and a light intensity of 2000 mw / cm 2 The adhesive was prepared by irradiating the adhesive for 200 seconds under an ultraviolet LED surface light source. The adhesive was measured to have a strength of 0.3 MPa, a swelling rate of 10% in the electrolyte, and a dissolution rate of 2.5%.

[0033] Example 2:

[0034] A low-swelling, low-dissolution adhesive for lithium-ion batteries and a preparation method thereof. The preparation comprises the following steps:

[0035] Step 1. Weigh 90 parts of acrylic acid monomer, 10 parts of hydroxyethyl acrylate monomer, 20 parts by mass of a mixture of crosslinking agents triethylene glycol dimethacrylate (TEGDMA) and polyethylene glycol diacrylate (PEGDA), and 3 parts by mass of a mixture of photoinitiators oxetanes and ethyl p-dimethylaminobenzoate, mix them thoroughly to form a solution, take a portion and pour it into a culture dish until the solution depth reaches 2 mm, and then let it stand for 3 hours to remove bubbles.

[0036] Step 2: The defoamed solution was irradiated at a wavelength of 395 nm and a light intensity of 800 mw / cm 2 The adhesive was prepared by irradiating the adhesive for 1 second under an ultraviolet LED surface light source. The results showed that the adhesive had a strength of 0.35 MPa, a swelling rate of 8% in the electrolyte, and a dissolution rate of 3%.

[0037] Example 3:

[0038] A low-swelling, low-dissolution adhesive for lithium-ion batteries and a preparation method thereof. The preparation comprises the following steps:

[0039] Step 1. Weigh 50 parts of acrylic acid monomer, 50 parts of hydroxyethyl acrylate monomer, 1 part by mass of crosslinking agent trimethylolpropane triacrylate (TMPTA), and 0.5 parts by mass of a mixture of photoinitiator (2,4,6-trimethylbenzoyl)-diphenylphosphine oxide (TPO) and ethyl p-dimethylaminobenzoate (EDB), mix them thoroughly to form a solution, take a portion and pour it into a culture dish until the solution depth reaches 2 mm, and then let it stand for 3 hours to remove bubbles.

[0040] Step 2: The defoamed solution was irradiated at a wavelength of 395 nm and a light intensity of 500 mw / cm 2 The adhesive was prepared by irradiating the adhesive for 3 seconds under an ultraviolet LED surface light source. The adhesive was measured to have a strength of 0.33 MPa, a swelling rate of 6% in the electrolyte, and a dissolution rate of 5%.

[0041] Example 4:

[0042] A low-swelling, low-dissolution adhesive for lithium-ion batteries and a preparation method thereof. The preparation comprises the following steps:

[0043] Step 1. Weigh 50 parts by mass of an acrylic acid monomer, 50 parts by mass of a hydroxyethyl acrylate monomer, 1 part by mass of a crosslinking agent trimethylolpropane triacrylate (TMPTA), and 3 parts by mass of a mixture of a photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (2959) benzoin diethyl ether (651), mix them thoroughly to form a solution, take a portion and pour it into a culture dish until the solution depth reaches 2 mm, and then let it stand for 3 hours to remove bubbles.

[0044] Step 2: The defoamed solution was irradiated at a wavelength of 365 nm and a light intensity of 1200 mw / cm 2 The adhesive was prepared by irradiating the adhesive under an ultraviolet LED surface light source for 30 seconds. The results showed that the adhesive had a strength of 2 MPa, a swelling rate of 2% in the electrolyte, and a dissolution rate of 1.8%.

[0045] Embodiment 5:

[0046] A low-swelling, low-dissolution adhesive for lithium-ion batteries and a preparation method thereof. The preparation comprises the following steps:

[0047] Step 1. Weigh 40 parts of acrylic acid monomer, 60 parts of hydroxyethyl acrylate monomer, 10 parts by mass of a mixture of a crosslinking agent trimethylolpropane trimethacrylate (TMPTMA) and triallyl isocyanurate (TAIC), and 5 parts by mass of a mixture of a photoinitiator phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (819) 2-isopropylthioxanthone (ITX), mix them thoroughly to form a solution, take a portion and pour it into a culture dish until the solution depth reaches 2 mm, and then let it stand for 3 hours to remove bubbles.

[0048] Step 2: The defoamed solution was irradiated at a wavelength of 365 nm and a light intensity of 800 mw / cm 2 The adhesive was prepared by irradiating the adhesive under an ultraviolet LED surface light source for 30 seconds. The adhesive was measured to have a strength of 2.5 MPa, a swelling rate of 6% in the electrolyte, and a dissolution rate of 3.4%.

Claims

1. A method for preparing a low-swelling and low-dissolution adhesive for lithium-ion batteries, characterized in that: The steps include: Step S1: fully mixing acrylic acid monomer, hydroxyethyl acrylate monomer, crosslinking agent and photoinitiator to form a solution; Step S2: polymerizing the above solution under ultraviolet light to obtain a binder for lithium-ion batteries.

2. The method for preparing a low swelling and low dissolution adhesive for lithium ion batteries according to claim 1, wherein: The mass ratio of the acrylic acid monomer to the hydroxyethyl acrylate monomer in step S1 is 5:95 to 90:

10.

3. The method for preparing a low swelling and low dissolution adhesive for lithium ion batteries according to claim 1, wherein: The cross-linking agent in step S1 is selected from one of polyethylene glycol diacrylate (PEGDA), triethylene glycol dimethacrylate (TEGDMA), trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTMA) and triallyl isocyanurate (TAIC); the amount of the cross-linking agent added is 1 to 20 parts by mass relative to 100 parts by mass of the monomer.

4. The method for preparing a low swelling and low dissolution adhesive for lithium ion batteries according to claim 1, wherein: The photoinitiator in step S1 is selected from one of 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173), benzophenone (BP), (2,4,6-trimethylbenzoyl)-diphenylphosphine oxide (TPO), ethyl p-dimethylaminobenzoate (EDB), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (2959), 2-isopropylthioxanthone (ITX), 1-hydroxycyclohexylphenyl ketone (184) and benzoin diethyl ether (651); the amount of the photoinitiator added is 0.5 to 5 parts by mass relative to 100 parts by mass of the monomer.

5. The method for preparing a low swelling and low dissolution adhesive for lithium ion batteries according to claim 1, wherein: The wavelength of the ultraviolet light in step S2 is 365 nm or 395 nm.

6. The method for preparing a low swelling and low dissolution adhesive for lithium ion batteries according to claim 1, wherein: The intensity of the ultraviolet light in step S2 is 200-2000 mw / cm 2 .

7. The method for preparing a low swelling and low dissolution adhesive for lithium ion batteries according to claim 1, wherein: The irradiation time of the ultraviolet light in step S2 is 1 to 200 seconds.

8. A low swelling and low dissolution adhesive for lithium ion batteries prepared by the preparation method of the adhesive for lithium ion batteries according to any one of claims 1 to 7.

9. The low swelling and low dissolution adhesive for lithium ion batteries according to claim 8, characterized in that: Its swelling in the electrolyte is 0 to 10%.

10. The low swelling and low dissolution adhesive for lithium ion batteries according to claim 8, characterized in that: Its dissolution in the electrolyte is 0 to 5%.

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