Aqueous adhesive for battery separators, method of preparation and use thereof in lithium-ion batteries

Abstract

The application provides a water-based adhesive for a battery separator, a preparation method and application thereof in a lithium ion battery, the preparation method comprising a pre-emulsification stage, a polymerization stage and a post-treatment stage; wherein a lithium hydroxide aqueous solution is added in the post-treatment stage to adjust the pH of the intermediate emulsion to 6.5-7.5, and a water-based adhesive for a battery separator is obtained through filtration. The adhesive of the application takes vinyl acetate monomers as the main body, and cyano monomers, organic silicon monomers and carboxyl or sulfonic acid monomers are added for copolymerization, and finally the pH of the system is adjusted by lithium hydroxide, so that the functional groups are introduced while the adhesion or intermolecular force of polyvinyl acetate is maintained, the solvation of Li is participated, the coordination number of EC is reduced, the influence of by-products is reduced, an effective solid electrolyte interface layer is formed on the electrode surface, and the cycle stability and service life of the lithium ion battery are improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and in particular relates to an aqueous adhesive for battery separators, a preparation method thereof, and its application in lithium-ion batteries. Background Technology

[0002] In recent years, with the rapid advancement of lithium-ion battery technology, lithium-ion batteries have become the mainstream power batteries used in 3C devices (communication products, computer products, consumer electronics), new energy vehicles, and large-scale energy storage devices. The separator, as a crucial component of lithium-ion batteries, plays a vital role in their performance. Currently, commercially available lithium-ion battery separator materials are mainly polyolefin separators, including polyethylene (PE), polypropylene (PP), and PP / PE / PP three-layer composite films. Polyolefin separators possess excellent mechanical properties, good electrochemical stability, and safe thermal pore-closing temperature. However, inherent shortcomings such as poor thermal dimensional stability and insufficient hydrophilicity limit the development of electrochemical performance and safety of lithium-ion batteries. To address these issues, commercial improvements are made using inorganic and organic coatings such as polyvinylidene fluoride, ceramic particles, and acrylic. Binders are essential in these processes, but currently used water-based binders only provide adhesion, offering a limited and singular function. Summary of the Invention

[0003] In view of this, the present invention aims to overcome the defects in the prior art and proposes an aqueous adhesive for battery separators, a preparation method thereof, and its application in lithium-ion batteries.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a water-based adhesive for a battery separator, comprising the following steps: S1, Pre-emulsification stage: Deionized water, emulsifier, and buffer are mixed and stirred until the emulsifier is completely dissolved; then mixed monomers are added and stirring is continued for 30-40 minutes to form a uniform, stable, milky white pre-emulsion. The mixed monomers include vinyl acetate, carboxyl or sulfonic acid monomers, organosilicon monomers, and cyano polymeric monomers. S2, Aggregation Phase: S21. Take a portion of the total pre-emulsion and heat it to 80-85℃. Stir and wait for the system to show blue light. Add a portion of the initiator aqueous solution and keep it warm for 10-15 minutes. S22. The reaction temperature is maintained at 80-85℃ during the dropwise addition, while the remaining pre-emulsion and the remaining initiator aqueous solution are added dropwise. S23. After the addition is complete, heat to 85-90℃ and keep warm for 30-40 minutes to completely polymerize and obtain the intermediate emulsion. S3, Post-processing stage: The intermediate emulsion was cooled to below 40°C, and an aqueous lithium hydroxide solution was added to adjust the pH of the intermediate emulsion to 6.5-7.5. The mixture was then filtered to obtain an aqueous adhesive for the battery separator.

[0005] Preferably, the mass fractions of each component in the mixed monomers in step S1 are: 95-105 parts vinyl acetate monomer, 2.5-10 parts monomers containing carboxyl or sulfonic acid groups, 2.5-5 parts organosilicon monomers, and 5-20 parts cyano monomers.

[0006] Preferably, the monomers containing carboxyl or sulfonic acid groups include, but are not limited to, one or a mixture of two or more of acrylic acid (AA), methacrylic acid (MAA), itaconic acid (IA), maleic anhydride (MAH), sodium styrene sulfonate (SSS), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), vinyl sulfonic acid (VS), and p-styrene sulfonic acid (PSSA).

[0007] Preferably, the organosilicon monomer is a silicon-containing monomer containing an olefinically unsaturated functional group, including but not limited to one or a mixture of two or more of vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, propenyltrimethoxysilane, propenyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and methacryloyloxypropyltri(isopropoxy)silane.

[0008] Preferably, the cyano monomer is, but is not limited to, acrylonitrile and / or 2-methyl-2-butenonitrile.

[0009] Preferably, the emulsifier in step S1 is one or more of dodecyl sulfonate, dodecyl sulfonate, and alkylphenol polyoxyethylene ether emulsifiers.

[0010] Preferably, the amount of emulsifier added in step S1 is 3% to 5% of the total mass of vinyl acetate, carboxyl or sulfonic acid monomers, organosilicon monomers and cyano polymeric monomers.

[0011] Preferably, the buffer is sodium bicarbonate.

[0012] Preferably, the amount of buffer added is 1% to 3% of the total mass of vinyl acetate, carboxyl or sulfonic acid monomers, organosilicon monomers and cyano polymeric monomers.

[0013] Preferably, the initiator is one or more of persulfate, hydrogen peroxide, and azobisisobutyronitrile, and the mass percentage of the aqueous initiator solution is 1%-5%.

[0014] Preferably, the amount of the initiator added is 0.5% to 1% of the total mass of vinyl acetate, carboxyl or sulfonic acid monomers, organosilicon monomers and cyano polymeric monomers.

[0015] Preferably, in step S22, an antifoaming agent is added during the process of adding the remaining pre-emulsion and the remaining initiator aqueous solution.

[0016] The reaction of this invention belongs to free radical polymerization. The core is a synergistic process of "emulsifier stabilization + multi-monomer free radical copolymerization + in-situ generation of siloxane bonds". Functional group embedding and emulsion preparation are achieved through three key reactions, as follows: 1. Pre-emulsification stage: Constructing a stable monomer dispersion system. In this stage, the emulsifier provides a uniform monomer environment for subsequent copolymerization: After the emulsifier dissolves in water, it forms micelles and adsorption layers, which encapsulate the copolymer monomers inside the micelles or adsorb them onto the surface of the droplets, preventing monomer stratification and aggregation.

[0017] 2. Copolymerization stage: Functional group insertion initiated by free radicals. Through free radical polymerization, the segments of the four monomers and the functional groups (cyano groups) are simultaneously incorporated into the polymer backbone. The initiator (such as ammonium persulfate) decomposes upon heating to generate free radicals, which diffuse into the micelles and preferentially initiate the double bond breakage of monomers with higher reactivity (such as acrylic acid > acrylonitrile > vinyl acetate > silicon-containing monomers) to form active segments.

[0018] Initiators (such as ammonium persulfate) decompose upon heating in an aqueous phase, generating initial free radicals, such as (S₂O₈). 2- →2SO4 - These initial free radicals react with monomers such as vinyl acetate (VAc), carboxylic acid or sulfonic acid units, and cyano units in the aqueous phase, breaking the carbon-carbon double bonds of the monomers to form monomeric free radicals, such as (SO₄)₂. · 4 - +CH2=CHCOOCH3→CH · 2-CHCOOCH3). By controlling the monomer dropping rate and reaction temperature, the distribution ratio of the four monomers in the main chain can be adjusted to ensure uniform insertion of functional groups such as cyano groups.

[0019] 3. Silicon-oxygen bond formation stage: The hydrolysis-condensation reaction of silicon-containing segments occurs in an aqueous environment, forming in-situ silicon-oxygen bonds (Si-O-Si): the alkoxy groups (-Si(OC2H5)3) on the organosilicon segments react with acidic substances (such as H2O) produced by the decomposition of the initiator in the aqueous phase (or trace amounts of water generated in the reaction). +Under catalysis, a hydrolysis reaction occurs: -Si(OC2H5)3 + 3H2O → -Si(OH)3 + 3C2H5OH, generating silanol groups (-SiOH). The silanol groups on the surface of adjacent polymer segments or latex particles further undergo a condensation reaction: -SiOH + HOSi- → -Si-O-Si- + H2O, forming a cross-linked silicon-oxygen bond network.

[0020] 4. Post-treatment stage: Adjust the pH with lithium hydroxide to neutralize the carboxyl or sulfonic acid groups, turning them into lithium carboxylate or lithium sulfonate, thereby improving the storage stability and ionic conductivity of the emulsion and preventing excessive hydrolysis of organosilicon units under acidic conditions.

[0021] Secondly, the present invention provides an aqueous adhesive for battery separators prepared by the above-described preparation method.

[0022] Thirdly, the present invention provides the application of the water-based adhesive from the above-mentioned battery separator in the preparation of lithium-ion batteries.

[0023] Compared with the prior art, the present invention has the following advantages: (1) The binder of the present invention is based on vinyl acetate monomer, and cyano monomers, organosilicon monomers and monomers containing carboxyl (-COOH) or sulfonic acid (-SO3H) are added to copolymerize it. Finally, lithium hydroxide (LiOH) is used to adjust the pH of the system. In this way, while maintaining the adhesion or intermolecular forces of polyvinyl acetate, functional groups are introduced to participate in the solvation of Li, reduce the number of EC coordinations, reduce the influence of by-products, and form an effective solid electrolyte interface layer on the electrode surface, thereby improving the cycle stability and life of lithium-ion batteries.

[0024] (2) Based on the deficiencies of existing technologies, this invention introduces functional groups such as cyano (-CN), silicon-oxygen bonds (-Si-O-), and lithium carboxylate (-COOLi) / lithium sulfonate (-SO3Li) as binders for the separator coating. These polar groups improve the wettability of the polyolefin separator to the electrolyte. Furthermore, the unique properties of cyano-containing polymers, such as high dielectric constant, strong electron-withdrawing effect, low LUMO, and high electrochemical stability over a wide electrochemical window, are utilized. Additionally, -CN participates in the formation of the CEI and SEI layers. The resulting SEI layer contains a higher proportion of LiF, Li2O, and -CN. -CN promotes the diffusion of Li ions to the anode through electrostatic interactions, synergistically reducing lithium dendrite formation with LiF and Li2O, thereby improving the performance of the lithium-ion battery. The introduced silicon-oxygen bonds (Si-O) can bind to acidic products, slowing their corrosion of the cathode material, thus further extending the lifespan of the lithium-ion battery. Introducing lithium ion carrier groups lithium carboxylate (-COOLi) / lithium sulfonate (-SO3Li) enables the binder itself to have ion conduction capabilities, eliminating the need for electrolyte wetting, making it particularly suitable for high-rate battery scenarios. Attached Figure Description

[0025] Figure 1 The infrared spectrum of the battery separator prepared in Example 1 using an aqueous adhesive; Figure 2 The infrared spectrum of the battery separator prepared in Example 2 using an aqueous adhesive; Figure 3 A comparison chart of the cycle performance of the experimental and control groups of batteries using a ternary / graphite system at 0.5C rate; Figure 4 The graph shows a comparison of the cycle performance of the batteries in the experimental and control groups using the ternary / graphite system. Detailed Implementation

[0026] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0027] In this document, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0028] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0029] In this article, the terms "multiple" or "more than" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0030] In this document, the terms "preferred" and "more preferred" are used only to describe implementation methods or embodiments with better effects, and should be understood as not constituting a limitation on the scope of protection of this invention.

[0031] In this document, terms such as "further" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0032] In this article, the term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0033] In this document, the term "about" means a specified value of + / - 10%, preferably + / - 5%, and more preferably + / - 1%.

[0034] In this article, the terms “include,” “including,” “have,” “contain,” etc., are all open-ended terms, meaning that they include but are not limited to.

[0035] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0036] The present invention will be described in detail below with reference to the embodiments.

[0037] Example 1 A method for preparing a water-based adhesive for a battery separator includes the following steps: S1. Pre-emulsification stage (preparation of stable monomer emulsions) Add 120g of deionized water, compound emulsifier (2g sodium dodecylbenzenesulfonate and 3g OP-10 mixed by mass), and buffer (NaHCO3, 1.2g) to a pre-emulsification tank, and stir (200 rpm) until the emulsifier is completely dissolved; then slowly add mixed monomers (96g vinyl acetate VAc, 7.2g acrylic acid AA, 4.8g vinyltrimethoxysilane (Momentive A-171) and 12g acrylonitrile AN mixed by mass), and continue stirring for 30 min to form a uniform, stable milky white pre-emulsion (no layering, no floating oil).

[0038] S2. Aggregation Phase S21: For the initial initiation, add 50g of milky white pre-emulsion to the reactor, heat to 80℃, and stir (200rpm); when the system shows blue light, slowly add part of the initiator ammonium persulfate APS aqueous solution (total amount of ammonium persulfate is 0.8g, dissolved in 15.2g of deionized water), keep warm for 15min, and observe that the viscosity of the system increases slightly, confirming the start of polymerization.

[0039] S22: During the dropwise addition reaction, maintain the reactor temperature at 80-85℃, and simultaneously add the remaining pre-emulsion and the remaining APS aqueous solution slowly, controlling the dropping rate (the pre-emulsion is added in 3 hours, and the APS solution is added slightly slower than the pre-emulsion).

[0040] S23: After the addition is complete, heat to 90℃ and keep warm for 40 minutes to allow unreacted monomers to polymerize completely.

[0041] S3. Post-processing stage Cool the emulsion to below 40°C, add lithium hydroxide aqueous solution (1% mass concentration) to adjust the pH to 6.5; filter (using a 100-mesh filter) to remove a small amount of coagulations, and obtain the water-based adhesive for the battery separator.

[0042] Measurements showed that the adhesive prepared in this embodiment had a solid content of 30.1% (measured by weight loss method), a viscosity of 2.4 Pa·s (measured by NDJ-1 viscometer), and an infrared spectrum containing ~2250 cm⁻¹ -1 ~1730cm -1 , ~1550-1610cm -1 , ~1400-1450cm -1 , ~1220-1260cm -1 ~1000-1100cm -1 This indicates that the obtained product was modified by organosilicon, acrylonitrile, and lithium carboxylate. The infrared spectrum is as follows: Figure 1 As shown.

[0043] Example 2 The preparation method of the battery separator using the water-based adhesive in this embodiment is basically the same as that in Example 1, except that: The total amount of initiator is 1.0g, vinyltrimethoxysilane is 2.5g, vinyl acetate is 95g, acrylonitrile is 20g, and styrene sulfonic acid is 2.5g.

[0044] Measurements showed that the adhesive prepared in this embodiment had a solid content of 33.5% (measured by weight loss method), a viscosity of 3.0 Pa·s (measured by NDJ-1 viscometer), and still contained ~3000-3100 cm⁻¹ in its infrared spectrum. -1 ~2230cm -1 ~1740cm -1 , ~1220-1260cm-1 ~1000-1100cm -1 This indicates that the obtained product was modified by organosilicon, acrylonitrile, and lithium carboxylate. The infrared spectrum is as follows: Figure 2 As shown.

[0045] Example 3 The preparation method of the battery separator using the water-based adhesive in this embodiment is basically the same as that in Example 1, except that: Replace the organosilicon monomer with 5g of γ-methacryloyloxypropyltrimethoxysilane, replace the cyanopolymer monomer with 7.5g of 2-methyl-2-butenonitrile, 2.5g of acrylic acid, and 105g of vinyl acetate.

[0046] Measurements showed that the adhesive prepared in this embodiment had a solid content of 32.1% (measured by weight loss method), a viscosity of 2.8 Pa·s (measured by NDJ-1 viscometer), and an infrared spectrum containing ~2250 cm⁻¹ -1 ~1730cm -1 , ~1550-1610cm -1 , ~1400-1450cm -1 , ~1220-1260cm -1 ~1000-1100cm -1 This indicates that the obtained product was modified by organosilicon, 2-methyl-2-butenonitrile, and lithium carboxylate.

[0047] Example 4 The preparation method of the battery separator using the water-based adhesive in this embodiment is basically the same as that in Example 1, except that: Vinyl acetate 100g, itaconic acid 5g, γ-methacryloxypropyltrimethoxysilane 5g, 2-methyl-2-butenonitrile 5g; compound emulsifier 3.6g; buffer 2.0g; initiator 0.6g. Add lithium hydroxide aqueous solution (1% mass concentration) to adjust the pH of the emulsion to 7.5.

[0048] Example 5 The preparation method of the battery separator using the water-based adhesive in this embodiment is basically the same as that in Example 1, except that: 100g vinyl acetate, 10g sodium styrene sulfonate, 5g vinyltris(β-methoxyethoxy)silane, 5g 2-methyl-2-butenonitrile; 6g compound emulsifier; 3.6g buffer; 1.2g initiator. Adjust the pH of the emulsion to 7.0 by adding a 1% (w / w) lithium hydroxide aqueous solution.

[0049] Comparative Example 1 The preparation method of the battery separator in this comparative example using an aqueous adhesive is basically the same as that in Example 1, except that: In this comparative example, sodium bicarbonate aqueous solution (1% mass concentration) was added in S3 to adjust the pH of the emulsion, and the remaining steps were the same as in Example 1.

[0050] The ionic conductivity of the adhesive prepared in this comparative example and the adhesive prepared in Example 1 were tested. The results showed that the ionic conductivity of the adhesive prepared in Example 1 was 3.5 × 10⁻⁶. -4 S / cm. The adhesive prepared in Comparative Example 1 has an ionic conductivity of 2.8 × 10⁻⁶. -4 S / cm. The results above show that introducing lithium ions can improve the ionic conductivity of the binder.

[0051] Application examples The adhesive prepared in Example 1 (experimental group) and Dow EAA3440 adhesive (control group) were used to coat a diaphragm (base membrane: Enjie 9μm diaphragm; coating: acrylic, ceramic). The prepared diaphragm was tested, and the test results were as follows:

[0052] The separators prepared in the experimental and control groups were assembled into a 1Ah pouch cell using a ternary / graphite system. The battery performance was tested, and the results are as follows: Figure 3 and Figure 4 As shown, the battery assembled with the binder of this invention exhibits better rate discharge performance and cycle performance.

[0053] 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 method for preparing a water-based adhesive for a battery separator, characterized in that: Includes the following steps: S1, Pre-emulsification stage: Deionized water, emulsifier, and buffer are mixed and stirred until the emulsifier is completely dissolved; then mixed monomers are added and stirring is continued for 30-40 minutes to form a uniform, stable, milky white pre-emulsion. The mixed monomers include vinyl acetate, carboxyl or sulfonic acid monomers, organosilicon monomers, and cyano polymeric monomers. S2, Aggregation Phase: S21. Take a portion of the pre-emulsion and heat it to 80-85℃. Stir and wait for the system to show blue light. Add a portion of the initiator aqueous solution and keep it warm for 10-15 minutes. S22. The reaction temperature is maintained at 80-85℃ during the dropwise addition, while the remaining pre-emulsion and the remaining initiator aqueous solution are added dropwise. S23. After the addition is complete, heat to 85-90℃ and keep warm for 30-40 minutes to completely polymerize and obtain the intermediate emulsion. S3, Post-processing stage: The intermediate emulsion was cooled to below 40°C, and an aqueous lithium hydroxide solution was added to adjust the pH of the intermediate emulsion to 6.5-7.

5. The mixture was then filtered to obtain an aqueous adhesive for the battery separator.

2. The method for preparing the battery separator using an aqueous adhesive according to claim 1, characterized in that: The mass fractions of each component in the mixed monomers in step S1 are as follows: 95-105 parts vinyl acetate monomer, 2.5-10 parts monomers containing carboxyl or sulfonic acid groups, 2.5-5 parts organosilicon monomers, and 5-20 parts cyano monomers.

3. The method for preparing the battery separator with an aqueous adhesive according to claim 1, characterized in that: The monomers containing carboxyl or sulfonic acid groups include, but are not limited to, one or more of acrylic acid, methacrylic acid, itaconic acid, maleic anhydride, sodium styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, vinyl sulfonic acid, and p-styrene sulfonic acid.

4. The method for preparing the battery separator with an aqueous adhesive according to claim 1, characterized in that: The organosilicon monomers are silicon-containing monomers containing olefinic unsaturated functional groups, including but not limited to one or more of vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, propenyltrimethoxysilane, propenyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and methacryloyloxypropyltri(isopropoxy)silane.

5. The method for preparing the battery separator with an aqueous adhesive according to claim 1, characterized in that: The cyano monomers include, but are not limited to, acrylonitrile and / or 2-methyl-2-butenonitrile.

6. The method for preparing the battery separator with an aqueous adhesive according to claim 1, characterized in that: The emulsifier in step S1 is one or more of dodecyl sulfonate, dodecyl sulfonate, and alkylphenol polyoxyethylene ether emulsifiers. The amount of emulsifier added in step S1 is 3% - 5% of the total mass of vinyl acetate, carboxyl or sulfonic acid monomers, organosilicon monomers and cyano polymer monomers.

7. The method for preparing the battery separator with an aqueous adhesive according to claim 1, characterized in that: The buffer is sodium bicarbonate; the amount of the buffer added is 1% to 3% of the total mass of vinyl acetate, carboxyl or sulfonic acid monomers, organosilicon monomers and cyano polymer monomers.

8. The method for preparing the battery separator with an aqueous adhesive according to claim 1, characterized in that: The initiator is one or more of persulfate, hydrogen peroxide, and azobisisobutyronitrile, and the mass percentage of the aqueous solution of the initiator is 1%-5%; the amount of the initiator added is 0.5%-1% of the total mass of vinyl acetate, carboxyl or sulfonic acid monomers, organosilicon monomers and cyano polymer monomers.

9. The battery separator prepared by the preparation method according to any one of claims 1-8 is an aqueous adhesive.

10. The application of the water-based adhesive for the battery separator according to claim 9 in the preparation of lithium-ion batteries.

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