TWI736318B - Polyvinyl alcohol graft copolymer and use thereof - Google Patents

Abstract

The present invention provides a polyvinyl alcohol graft copolymer comprising a polyvinyl alcohol main chain. The polyvinyl alcohol graft copolymer comprises branched chains comprising structure units derived from the following monomers: (a) a fluorine-containing ethylenically unsaturated monomer, and (b) an ethylenically unsaturated carboxylic acid monomer. The present invention also provides an aqueous binder composition and an electrode slurry composition comprising the polyvinyl alcohol graft copolymer. The electrode sheet manufactured by using the polyvinyl alcohol graft copolymer of the present invention has the advantageous properties such as good adhesion or low water absorption, and is not prone to brittle fracture.

Description

Polyvinyl alcohol graft copolymer and its use

The present invention relates to a polyvinyl alcohol graft copolymer and its use, especially a polyvinyl alcohol graft copolymer suitable as an aqueous binder in electrochemical devices.

In recent years, in the field of chemical energy storage systems, lithium-ion batteries have gained wide attention due to their relatively light weight and relatively high capacitance (ie, relatively high energy density), high operating voltage, and high Cycle life and other properties.

Lithium-ion batteries are mainly composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The lithium ions move in and out of the positive and negative electrodes to store or release electrical energy. When charging, lithium ions migrate out of the positive electrode and into the negative electrode; when discharging, lithium ions migrate out of the negative electrode and into the positive electrode.

The electrode sheet in a lithium-ion battery is a key component that plays an important role in battery performance. Specifically, it affects the energy density, discharge capacity, and cycle life of the battery. The electrode sheet is mainly composed of active materials (such as positive and negative materials), conductive materials (such as carbon black), binders and metal current collectors (such as copper foil, aluminum foil).

The conventionally used negative electrode materials are carbon-based materials, such as graphite, soft carbon, and hard carbon. However, in pursuit of higher energy density, silicon-based materials (such as silicon or silicon oxide) have been tried as anode materials for lithium-ion batteries. Compared with traditional carbon-based anode materials, silicon-based materials can greatly increase the energy density of lithium-ion batteries, but they will experience severe volume expansion (about 400%) during battery charging (the migration of lithium ions into the silicon-based materials) . During repeated charging and discharging, such severe volume expansion and contraction will destroy the structure of the negative electrode sheet, such as: the disintegration of the conductive network, and/or the electrode sheet peeling off, so that the negative electrode completely fails and has a very serious impact on the battery performance. negative effect.

In order to maintain the structure of the electrode sheet, the adhesive is used to bond the active material, the conductive material and the metal current collector together to form a structured electrode sheet. If the adhesion of the binder is not good, the aforementioned materials cannot be firmly bonded to each other. With repeated charging and discharging, they will fall off from the surface of the metal current collector, resulting in powdering of the electrode sheets and poor battery cycle life.

The binders commonly used in lithium-ion batteries mainly include polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC) polymers, acrylic polymers (PAA) and styrene-butadiene rubber (SBR). PVDF bonding agent is a more mature bonding agent in the current technology, with good bonding performance, but the use of this bonding agent to prepare electrode sheets requires a large amount of high boiling point organic solvents (such as N-methylpyrrolidone (NMP)), so PVDF The binder has disadvantages such as higher cost and easy pollution of the environment; in addition, PVDF binder is easy to swell in the commonly used electrolyte, which leads to the decrease of electrode stability. CMC and SBR are usually used together. This type of binder often uses water as a solvent, which has the advantages of low cost and not easy to pollute the environment. It is mostly used in graphite-based negative electrode active materials. It has good viscoelasticity and can make graphite have good dispersibility. However, the problem of volume expansion and contraction of silicon-based materials cannot be overcome. PAA has a carboxyl group, which can form a hydrogen bond force with the surface of the silicon-based material, thereby inhibiting the volume expansion of the silicon-based material, so it has attracted attention. However, PAA has the problem of easy moisture absorption, so it must be baked at a higher temperature and a longer time when making electrode sheets; in addition, PAA usually needs to be used together with CMC and/or SBR to avoid the easiness of pure PAA The problem of brittleness.

Nowadays, in response to the birth of high-capacity silicon-based anode materials, it is still necessary to develop a suitable bonding agent that can overcome the problem of volume expansion and contraction of silicon-based anode materials and avoid the disadvantages of conventional bonding agents described above.

In view of this, the inventor of the present case discovered a novel polyvinyl alcohol graft copolymer after research, which contains a polyvinyl alcohol backbone, and the branch of the polyvinyl alcohol graft copolymer contains a structure derived from the following monomers unit: (a) Fluorine-containing ethylenically unsaturated monomers; and (b) Ethylene unsaturated carboxylic acid monomers.

Another object of the present invention is to provide an aqueous adhesive composition comprising the above-mentioned polyvinyl alcohol graft copolymer.

Another object of the present invention is to provide an electrode slurry composition comprising the above-mentioned polyvinyl alcohol graft copolymer.

In the manufacture of electrode sheets, the polyvinyl alcohol graft copolymer of the present invention can be used as a single agent, which can replace CMC/SBR. It does not need to be used with other binders, which simplifies the manufacturing process and reduces the cost; even so, the polyvinyl alcohol of the present invention Vinyl alcohol graft copolymers can also be used with other binders (such as CMC/SBR). In addition, the polyvinyl alcohol graft copolymer of the present invention can avoid the problem of easy brittleness of pure PAA, and the produced electrode sheet has flexibility and is not easy to crack after winding, so it has good operability; in addition, the polyvinyl alcohol of the present invention Vinyl alcohol graft copolymer can improve PAA's easy moisture absorption problem, and the obtained electrode sheet is easy to dry, so it can reduce the energy consumption required for drying; in addition, the adhesion of the electrode sheet is improved, and it is not easy to depowder, thereby improving battery cycle life.

In order to facilitate the understanding of the disclosure stated in this article, a number of terms are defined below.

The term "about" means the acceptable error of a specific value as measured by a person familiar with the art, and the range of error depends on how the value is measured or measured.

In this article, unless specifically limited, the singular "一" and "the" also include the plural. The purpose of any and all of the examples and illustrative terms ("such as" and "such as") herein is only for highlighting the present invention more, and is not intended to limit the scope of the present invention. The terms in the specification of this case should not be regarded as implying any The requested method and conditions may constitute essential features when implementing the present invention.

The word "or" in a list of two or more than two items covers the interpretation of all the following words: any item in the list, all items in the list, and any combination of items in the list.

In the present invention, the term "structural unit" means that after monomers are polymerized to form a copolymer, the smallest unit with the same chemical composition in the copolymer is called a structural unit, also called a repeating unit.

In the present invention, the term "ethylenically unsaturated monomer" refers to a monomer having at least one -C=C- double bond.

In the present invention, the term "fluorine-containing ethylenically unsaturated monomer" refers to a monomer having at least one -C=C- double bond and at least one fluorine atom.

In the present invention, the term "alkyl" refers to a saturated linear or branched saturated hydrocarbon group, which may have 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms , Particularly preferably has 1 to 4 carbon atoms; examples include (but are not limited to) methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl And similar groups.

In the present invention, the term "aryl" is preferably a monocyclic or polycyclic aromatic carbocyclic group having 6 to 20 carbon atoms, and may also contain condensed rings, preferably containing 1, 2, 3 or 4 condensed rings. Ring or non-fused ring. Examples thereof include (but are not limited to): phenyl, indenyl, naphthyl, fluorenyl, anthracenyl, phenanthryl and the like. According to some preferred embodiments of the present invention, the aryl group is phenyl, biphenyl or naphthyl.

In the present invention, the term "aralkyl" refers to an alkyl group substituted with an aryl group, wherein the aryl group and the alkyl group have the above-mentioned definitions.

In the present invention, the term "ethylenically unsaturated carboxylic acid monomer" refers to a monomer having at least one -C=C- double bond and at least one carboxylic acid group.

In the present invention, the term "(meth)acrylic acid" refers to "acrylic acid or methacrylic acid"; the term "(meth)acrylic monomer" refers to "acrylic monomer or methacrylic monomer"; The rest of the related terms can be deduced by analogy.

The content of the present invention will be described in detail below. [ Polyvinyl Alcohol Graft Copolymer ]

The polyvinyl alcohol graft copolymer of the present invention uses polyvinyl alcohol as the main chain and uses fluorine-containing ethylenically unsaturated monomers, ethylenically unsaturated carboxylic acid monomers and other monomers as needed for graft copolymerization. Made.

The polyvinyl alcohol used in the present invention is not particularly limited, and preferably has a weight average molecular weight ranging from 10,000 to 400,000. The lower limit of the weight average molecular weight of polyvinyl alcohol may be 10,000, preferably 12,000 or 15,000. The upper limit of the weight average molecular weight of polyvinyl alcohol may be 400,000, preferably 350,000, 300,000, 250,000 or 200,000.

Specific implementation aspects of the polyvinyl alcohol used in the present invention, such as but not limited to: PVA 088-20 (Sinopec), GOHSENOL GL-05 (Japan Synthetic Chemical).

The fluorine-containing ethylenically unsaturated monomer (component (a)) used in the present invention can be, for example, but not limited to: fluoroalkyl (meth)acrylate, fluoroaryl (meth)acrylate , Fluorinated aralkyl (meth)acrylate, perfluoroalkyl (meth)acrylate, alkyl (fluoroalkyl)acrylate, aryl (fluoroalkyl)acrylate, or (fluoroalkyl) Alkyl) aralkyl acrylate; preferably fluoroalkyl (meth)acrylate or alkyl (fluoroalkyl)acrylate. Specific examples include, but are not limited to: trifluoromethyl (meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3-tetrafluoropropyl (meth)acrylate , 2,2,3,4,4,4-hexafluorobutyl (meth)acrylate, perfluorooctyl (meth)acrylate, methyl (trifluorometh)acrylate.

， 其中R ₁及R ₂中至少一者為經氟原子取代的基團，且R ₁及R ₂具有下述的定義： R ₁為H、C ₁-C ₄烷基、或經一或多個氟原子取代的C ₁-C ₄烷基；且 R ₂為H、C ₁-C ₁₂烷基、經一或多個氟原子取代的C ₁-C ₁₂烷基、芳基、經一或多個氟原子取代的芳基、芳烷基、或經一或多個氟原子取代的芳烷基。 According to a preferred embodiment of the present invention, the fluorine-containing ethylenically unsaturated monomer (component (a)) has the chemical formula (1):

, Wherein _{at least one of R 1} and R ₂ is a group substituted with a fluorine atom, and R ₁ and R ₂ have the following definitions: R ₁ is H, C ₁ -C ₄ alkyl, or one or more _{A C 1} -C ₄ alkyl group substituted with a fluorine atom; and R ₂ is H, a C ₁ -C _{12 alkyl group, a C 1} -C ₁₂ alkyl group substituted with one or more fluorine atoms, an aryl group, one or An aryl group substituted with multiple fluorine atoms, an aralkyl group, or an aralkyl group substituted with one or more fluorine atoms.

According to some embodiments of the present invention, R _{1 is} preferably H, C ₁ -C _{3 alkyl, or C 1} -C ₃ alkyl substituted with one or more fluorine atoms, more preferably H, methyl or Trifluoromethyl.

According to some aspects of embodiments of the present invention, R ₂ is preferably H, C ₁ -C ₈ alkyl, substituted with one or more fluorine atoms substituted with C ₁ -C ₈ alkyl, C ₆ -C ₂₀ aryl, _{C 6} -C ₂₀ aryl group substituted by one or more fluorine atoms _{, C 6} -C ₂₀ aryl group -C ₁ -C _{12 alkyl group, or C 6} -C ₂₀ aryl group substituted by one or more fluorine atoms- C ₁ -C ₁₂ alkyl.

According to some embodiments of the present invention, the fluorine-containing ethylenically unsaturated monomer has a chemical formula of formula (1), wherein R ₁ is H or C ₁ -C ₄ alkyl and R ₂ is through one or more fluorine atoms Substituted C ₁ -C ₁₂ alkyl. According to a preferred embodiment of the present invention, R ₁ is H or a C ₁ -C ₃ alkyl group and R _{2 is a C 1} -C ₈ alkyl group substituted with one or more fluorine atoms.

According to some embodiments of the present invention, per 100 parts by weight of polyvinyl alcohol, the content of component (a) is 20 parts by weight or more, preferably 25 parts by weight or more, and more preferably 30 parts by weight or more. If the content of component (a) is too low, the prepared electrode sheet will easily absorb moisture, resulting in excessively high water content and poor electrical properties. The upper limit of the content of component (a) is not particularly limited in theory. However, too high content of component (a) may cause the polyvinyl alcohol graft copolymer to precipitate due to poor water solubility, resulting in instability of the glue solution. , The dosage can be adjusted appropriately to avoid precipitation. According to some embodiments of the present invention, per 100 parts by weight of polyvinyl alcohol, the content of component (a) is preferably not more than 160 parts by weight, more preferably not more than 150 parts by weight, and particularly preferably not more than 140 parts by weight.

The ethylenically unsaturated carboxylic acid monomer (component (b)) used in the present invention can be, for example, but not limited to: (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, 2-Ethyl acrylic acid, isocrotonic acid, α-acetoxy acrylic acid, or β-trans-aryloxy acrylic acid.

(2) 其中R ₃為H或C ₁-C ₄烷基，較佳為甲基；且R ₄為-OH。 According to some embodiments of the present invention, the ethylenically unsaturated carboxylic acid monomer (component (b)) used in the present invention has the chemical formula (2):

(2) Wherein R ₃ is H or C ₁ -C ₄ alkyl, preferably methyl; and R ₄ is -OH.

According to some embodiments of the present invention, per 100 parts by weight of polyvinyl alcohol, the content of component (b) is 500 parts by weight to 3000 parts by weight, preferably 520 parts by weight to 2500 parts by weight, more preferably 530 parts by weight. Parts by weight to 1500 parts by weight, particularly preferably 550 parts by weight to 1200 parts by weight. If the content of component (b) is too low, the adhesive will not adhere well to the pole piece, and the active material will easily fall off from the pole piece; if the content of component (b) is too high, the adhesive will be made Too hard and brittle, it is easy to crack after winding, and the process operation is not easy.

According to some embodiments of the present invention, the branches of the polyvinyl alcohol graft copolymer of the present invention may further include structural units derived from ethylenically unsaturated carboxylic acid ester monomers (component (c)).

According to some embodiments of the present invention, the ethylenically unsaturated carboxylic acid ester monomer (component (c)) can be, for example, but not limited to: methyl (meth)acrylate, ethyl (meth)acrylate, Propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, n/isooctyl (meth)acrylate, isodecyl (meth)acrylate, laurel (meth)acrylate Ester, isobornyl (meth)acrylate, 2-phenoxyethyl acrylate, cumylphenoxyethyl acrylate, phenylphenoxyethyl acrylate or β-carboxyethyl acrylate .

(3) 其中R ₅為H或C ₁-C ₄烷基，較佳為H或C ₁-C ₃烷基，更佳為H或甲基；且R ₆為C ₁-C ₁₂烷氧基或芳氧基，較佳為C ₁-C ₈烷氧基或苯氧基。 According to some embodiments of the present invention, the ethylenically unsaturated carboxylic acid ester monomer (component (c)) used in the present invention has the formula (3):

(3) Wherein R ₅ is H or C ₁ -C ₄ alkyl, preferably H or C ₁ -C ₃ alkyl, more preferably H or methyl; and R ₆ is C ₁ -C ₁₂ alkoxy Or aryloxy, preferably C ₁ -C ₈ alkoxy or phenoxy.

According to some embodiments of the present invention, per 100 parts by weight of polyvinyl alcohol, the content of component (c) is 0 parts by weight to 80 parts by weight, 0 parts by weight to 70 parts by weight, and 0 parts by weight to 60 parts by weight. , 0 parts by weight to 50 parts by weight, 0 parts by weight to 40 parts by weight, 0 parts by weight to 30 parts by weight, 0 parts by weight to 20 parts by weight, or 0 parts by weight to 10 parts by weight, preferably 5 parts by weight to 75 parts by weight Parts by weight, more preferably 10 parts by weight to 70 parts by weight.

The inventor of the present case surprisingly found that using polyvinyl alcohol as the main chain and introducing structural units derived from fluorine-containing ethylenically unsaturated monomers, as well as ethylenically unsaturated carboxylic acid monomers and optionally ethylenic monomers, are introduced into the side chains. It is a structural unit of unsaturated carboxylic acid ester monomer. The graft copolymer obtained can have good adhesion with the surface of the material in contact. When applied to the bonding agent of the electrode sheet, it can solve the problem of easy moisture absorption or brittleness in the prior art Therefore, the performance and cycle life of the battery can be greatly improved.

In addition, compared with the prior art, the polyvinyl alcohol graft copolymer of the present invention is not easy to absorb water, so when used in the production of electrode sheets, the baking conditions can be reduced (for example, lower baking temperature and/or less Baking time), so as to achieve the beneficial effect of saving costs; when the polyvinyl alcohol graft copolymer of the present invention is used as a bonding agent, it can provide good adhesion without the problem of easy brittleness, and can be used alone as a bonding electrode No need to add additional carboxymethyl cellulose (CMC) polymer or styrene-butadiene rubber (SBR), so it can simplify the production process of the electrode sheet and reduce the cost. [ Preparation method of polyvinyl alcohol graft copolymer ]

The polyvinyl alcohol graft copolymer of the present invention can be prepared by any suitable method. In one embodiment of the present invention, the polyvinyl alcohol graft copolymer can be prepared by the following method: (1) Dissolve polyvinyl alcohol in a solvent to obtain a polyvinyl alcohol solution; (2) If necessary, pass inert gas into the polyvinyl alcohol solution of step (1) to remove oxygen in the solution; (3) Add fluorine-containing ethylenically unsaturated monomers, ethylenically unsaturated carboxylic acid monomers, optionally ethylenically unsaturated carboxylic acid esters or other monomers, and initiators to the solution obtained in step (2) ； (4) The polymerization reaction is carried out at elevated temperature, so that fluorine-containing ethylenic unsaturated monomers, ethylenic unsaturated carboxylic acid monomers and optionally ethylenic unsaturated carboxylic acid ester monomers are covalently grafted onto polyvinyl alcohol, Prepare polyvinyl alcohol graft copolymer.

The solvent used in the above step (1) is an aqueous solvent, such as but not limited to water or deionized water.

The initiator used in the above step (3) can be any suitable initiator known to those with ordinary knowledge in the technical field of the present invention, such as but not limited to: persulfate. Specific examples of persulfate include, but are not limited to, ammonium persulfate, potassium persulfate, sodium persulfate, lithium persulfate, potassium hydrogen persulfate or a combination of these, preferably ammonium persulfate or sodium persulfate.

In the above step (4), the initiator will decompose into free radicals at the reaction temperature, and the free radicals will be introduced into the polyvinyl alcohol molecular chain to initiate fluorine-containing ethylenic unsaturated monomers and ethylenic unsaturated carboxylic acid monomers. And optionally ethylenic unsaturated carboxylic acid ester monomer undergoes free radical polymerization reaction and is covalently grafted to polyvinyl alcohol. The reaction temperature is usually between about 30 to 100°C, such as 70°C; the time for completion of the polymerization reaction depends on the situation, and is usually between 0.5 to 12 hours, such as about 4 hours. [ Aqueous binder composition and its preparation method ]

The polyvinyl alcohol graft copolymer of the present invention has good compatibility with an aqueous solvent, and can be formulated with an aqueous solvent to prepare an aqueous binder composition. The solvent may be a solvent from the process of preparing the polyvinyl alcohol graft copolymer, or may be added after the preparation is completed to adjust the viscosity as needed. The above-mentioned aqueous solvents are obvious to those skilled in the art, such as but not limited to: water or deionized water.

Compared with the use of organic solvents, the cost of using water-based solvents is lower and less likely to pollute the environment, and the health risks to operators are also lower.

The aqueous binder composition of the present invention may optionally be added with any additives known to those with ordinary knowledge in the technical field of the present invention, such as but not limited to alkaline compounds (such as lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonium hydroxide). Or a mixture of them, preferably lithium hydroxide or sodium hydroxide) or a crosslinking agent. When the water-based adhesive is used for silicon-based materials, the pH value can be adjusted by adding alkaline compounds. By adjusting the pH value, the binding force of the adhesive on the silicon-based materials is increased.

In a preferred embodiment of the present invention, the pH can be adjusted to between 3 and 11 (for example, 3, 4, 5, 6, 7, 8, 9, 10 or 11), preferably adjusted to between 4 and 7.

According to one embodiment of the present invention, the aqueous binder composition of the present invention contains 1% to 10% by weight of polyvinyl alcohol graft copolymer (based on the total weight of the aqueous binder composition), for example, 1% by weight %, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight or 10% by weight of polyvinyl alcohol graft copolymer, preferably 2 Weight% to 8% by weight of polyvinyl alcohol graft copolymer, more preferably 3% to 7% by weight of polyvinyl alcohol graft copolymer.

The aqueous binder composition of the present invention can be prepared by any appropriate method. The polyvinyl alcohol graft copolymer, an aqueous solvent and optional additives are prepared after sufficient stirring.

The water-based adhesive of the present invention uses polyvinyl alcohol graft copolymer, which can be used as a single agent, and can provide the required softness without adding additional CMC/SBR. The manufactured electrode sheet has flexibility and is not easy to crack after winding. , Good operability, can improve the problem of easy brittleness of pure PAA; in addition, the fluorine-containing ethylenic unsaturated monomer in the main link branch effectively reduces the problem of easy moisture absorption for electrode sheets made of PAA or CMC/SBR. At the same time, the electrode sheet is easy to dry, and the energy consumption required for drying is reduced, and the performance of the battery is greatly improved. In addition, by grafting ethylenically unsaturated carboxylic acid monomers, the obtained graft copolymer can interact with the material in contact. The surface has good adhesion, which effectively improves the adhesion of the electrode sheet, and is not easy to depowder, thereby improving the cycle life of the battery. [ Electrode slurry composition and its preparation method ]

The present invention also provides an electrode slurry composition, which comprises: the polyvinyl alcohol graft copolymer of the present invention, an active material, a conductive material, an aqueous solvent, and additives as needed.

Relative to the total weight of the solid content of the electrode slurry composition, the polyvinyl alcohol graft copolymer of the present invention has the following content: 0.1 to 20% by weight, 0.2 to 15% by weight, 0.5 to 10% by weight, 0.8 to 8% by weight, or 1 to 5% by weight.

The above-mentioned active material is a negative electrode active material, including (but not limited to) graphite, hard carbon, soft carbon, silicon, silicon oxide (SiO _x ), silicon carbon, or a combination of the foregoing materials. Relative to the total weight of the solid content of the electrode slurry composition, the above-mentioned negative electrode active material has the following contents: 50 to 99% by weight, 60 to 99% by weight, 70 to 99% by weight, 80 to 99% by weight, 85% to 98% by weight, or 90 to 97% by weight.

The aforementioned conductive material includes (but is not limited to) conductive graphite, carbon black, carbon fiber, carbon nanotube, graphene, or a combination of the foregoing materials. Relative to the total weight of the solid content of the electrode slurry composition, the above-mentioned conductive material has the following content: 1 to 30% by weight, 1 to 20% by weight, 1 to 10% by weight, or 1 to 5% by weight, preferably 1 to 20% by weight, 1 to 10% by weight, or 2 to 5% by weight.

According to an embodiment of the present invention, the above-mentioned optional additives include basic compounds, such as (but not limited to) lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonium hydroxide or a mixture of them, preferably Lithium hydroxide or sodium hydroxide. In a preferred embodiment of the present invention, the pH can be adjusted to between 3 and 11 (for example, 3, 4, 5, 6, 7, 8, 9, 10 or 11), preferably adjusted to between 4 and 7.

According to an embodiment of the present invention, the aforementioned optional additive includes a dispersant.

The aforementioned aqueous solvent includes (but is not limited to) water or deionized water, preferably deionized water. Those with ordinary knowledge in the technical field to which the present invention pertains can add an appropriate amount of solvent according to the application requirements and according to the situation to adjust the viscosity to be suitable for use.

According to one embodiment of the present invention, the electrode slurry composition of the present invention may not contain carboxymethyl cellulose or styrene-butadiene rubber.

The electrode slurry of the present invention can be prepared by any appropriate method. The polyvinyl alcohol graft copolymer, active material, conductive material, aqueous solvent, and optional additives of the present invention are prepared after sufficient stirring.

The present invention will be further described with the following examples, but it should be understood that the following examples are only for illustrative purposes and should not be construed as limitations to the implementation of the present invention. Preparation Example Preparation of polyvinyl alcohol graft copolymer

Preparation examples 1 to 10: Dissolve polyvinyl alcohol (hereinafter referred to as "PVA") GOHSENOL GL-05 (Nippon Synthetic Chemicals) in 3000 ml of water, and stir thoroughly to obtain a uniform, transparent and viscous aqueous solution of polyvinyl alcohol. Continue to bubbling in nitrogen for about 60 minutes to remove the oxygen in the aqueous solution. Then added 2,2,2-trifluoroethyl (meth)acrylate (Sigma-Aldrich; purity 99%), (meth)acrylic acid (Sigma-Aldrich; purity 99%), hexyl (meth)acrylate ( Sigma-Aldrich; purity 99%) and 1% sodium persulfate aqueous solution, stir and mix uniformly, heat up to 70°C and continue to react for 4 hours to prepare polyvinyl alcohol graft copolymer (hereinafter referred to as "grafted PVA"), and then add 5 % Lithium hydroxide aqueous solution adjusts the pH to between 4 and 7, to obtain the aqueous binders of Preparation Examples 1 to 10 (solid content is 5.2 wt%). The amount of reactant for each grafted PVA is described in Table 1. Preparation of electrode slurry composition

Example 1-6 and Comparative Example 1-4: 38.46 grams of grafted PVA solution (solid content: 5.2% by weight) and 95 grams of silica/graphite negative electrode active material ( Model: BTR-500; Beterui New Energy Materials Co., Ltd.) and 3 grams of carbon black (Super P; Taiwan Boli Company), mix well at 25℃, and add appropriate amount of deionized water to adjust the viscosity to prepare negative electrode slurry material.

Comparative Example 5: 2 grams of CMC (Ashland Inc.; Bondwell™, BVH-8) was dissolved in 98 ml of water, and a 2% by weight CMC aqueous solution was prepared. Take 50 grams of 2% by weight CMC aqueous solution, add 95 grams of silicon oxide/graphite negative active material (model: BTR-500; Beiterui New Energy Materials Co., Ltd.) and 3 grams of carbon black (Super P; Taiwan Boli Company), After fully stirring, finally add 2.22 grams of 45% by weight styrene-butadiene rubber (JSR; TRD104A), and obtain a negative electrode slurry containing carboxymethyl cellulose/styrene-butadiene rubber after thorough stirring.

Comparative Example 6: Dissolve 2 g of PAA (Sigma-Aldrich, PAA450000) in 98 ml of water, prepare a 2% by weight PAA aqueous solution, take 50 g of 2% by weight PAA aqueous solution, and add 95 g of silica/graphite negative active material ( Model: BTR-500; Beterui New Energy Materials Co., Ltd.) and 3 grams of carbon black (Super P; Taiwan Boli Company), after fully stirring, finally add 2.22 grams of 45% by weight styrene-butadiene rubber ( JSR; TRD104A), after thorough stirring, a negative electrode slurry containing PAA/styrene-butadiene rubber is obtained.

The amount of relevant ingredients and the viscosity of the slurry are recorded in Table 2. Preparation of electrode pads

Use a doctor blade to coat the above-prepared electrode slurry composition on copper foil (Changchun copper foil for 10 µm batteries) [coating weight: 5~7 mg/cm ² ], dry at 100°C for 5 minutes and After cold pressing, it was cut into a circle with a 12 mm diameter cutting knife, and it was placed in a vacuum oven and heated at 100°C for 6 hours to obtain a negative electrode sheet. Preparation of button cell

The electrolyte components used include 2% ethylene carbonate (EC)/diethyl carbonate (DEC)-vinylene carbonate (VC), 8% fluoroethylene carbonate (FEC) and lithium hexafluorophosphorus (Formosa: LE ); The isolation film is a polypropylene film with a thickness of about 20 μm.

The above-mentioned negative electrode sheet and other components were assembled into a standard button battery (CR2032) in an inert environment by a conventional method, and its performance was tested. The assembly process is as follows: battery lower cover, lithium metal sheet (as the positive electrode), isolation film, negative electrode sheet, metal gasket, spring sheet and battery upper cover.

The assembled battery is allowed to stand for about 2 to 3 hours to allow the electrolyte to fully penetrate into the electrodes to improve conductivity. The open circuit voltage of the resulting battery is about 2.5 to 3 V. Test method 1. Detailed measurement

After stirring the water-based adhesive slurry, take an appropriate amount and drop it on the deepest part of the groove of the fineness meter (brand: PSIS-303-50), touch it vertically with the scraper, and pull the scraper from the largest scale to the smallest scale. Observe the significant position of the particles in the groove, and write down the corresponding scale value, which is the fineness. 2. Water content test

Use Coulomb-type Karl-Fischer moisture titrator (Karl-Fischer moisture titrator) to detect. Put the electrode sample into a sealed sample bottle and heat it to 130°C for 7 minutes to evaporate the moisture in the electrode sample. Then, let dry gas enter the electrolytic cell to participate in the reaction, and then determine the electrolysis process. Electricity, thereby determining the moisture content.

Take the electrode sheet of Comparative Example 5 using CMC/SBR as the adhesive as the control group (comparison standard). "◎" means that the moisture content is reduced by more than 20% compared to the electrode sheet of Comparative Example 5; "X" means that the moisture content is relatively low. Compared with Comparative Example 5, the reduction of electrode pads is less than 20%. The results obtained are recorded in Table 2. 3. Adhesion strength test

Use 3M 610 tape to closely fit the dried pole piece, and then use a tension meter (model: RX-100; Shengqun Technology) to perform a 180-degree tension test. 4. Pole piece cracking test

Take the pole piece with a coating weight greater than 7 mg/cm ² and wind it with a 3 mm cylindrical rod. After unwinding, observe whether there are cracks on the surface. 5. Capacitance maintenance rate test

The battery performance was measured using a charge and discharge machine (model: LBT21084) from Arbin Instruments.

Prerequisites: Charging: After the constant current section is charged with a constant current of 0.1C for 10 hours, the constant voltage section is charged with a constant voltage of 0.01 V for 1 hour; Discharge: Discharge with a current of 0.1C for 10 hours. The charge and discharge were repeated 3 times under the above conditions, and the first 3 cycles were used to form a solid-electrolyte interface (SEI).

The discharge capacity of the 1st circle and the 50th circle: Charging: After the constant current section is charged with a constant current of 0.5C for 2 hours, the constant voltage section is charged with a constant voltage of 0.01 V for 1 hour; Discharge: discharge with 0.5C current for 2 hours. The aforementioned 3 cycles for forming the solid electrolyte interface are included in the calculation, and the discharge capacity measured in the fourth cycle is regarded as the discharge capacity of the first cycle. After repeating the charge and discharge for 49 times under the above conditions, the discharge capacity measured at the 50th time is the discharge capacity at the 50th cycle.

Capacity retention rate=(discharge capacity of the 50th circle/discharge capacity of the first circle)×100%. Test Results

According to Table 1 and Table 2, it can be seen that the polyvinyl alcohol graft copolymer of the present invention is compared with CMC/SBR (Comparative Example 5) and PVA (Comparative Example 2) and PAA (Comparative Example 6), with significantly lower water content. This result indicates that the polyvinyl alcohol graft copolymer of the present invention is relatively difficult to absorb water, so when used in the production of electrode sheets, it can reduce baking energy consumption and save costs.

According to Examples 1-6, the battery using the polyvinyl alcohol graft copolymer of the present invention has a good capacity retention rate, and the capacity retention rate for 50 cycles is more than 80%, which is better than all comparative examples. In addition, the polyvinyl alcohol graft copolymer of the present invention can provide good adhesion, and the obtained electrode has flexibility even under high coating weight, and no cracks occur after winding. In addition, the electrode sheet prepared with the polyvinyl alcohol graft copolymer of the present invention has a lower moisture content.

The proportion of the main chain of the polyvinyl alcohol used in Comparative Example 1 is too high, so the number of branches is relatively insufficient, and the effect cannot be exerted. Therefore, the moisture content cannot be effectively reduced. The moisture content of the prepared electrode sheet is compared with that of CMC/SBR. The reduction of the electrode sheet is less than 20%, the battery capacity maintenance rate is not good, and the adhesion between the adhesive and the electrode sheet is also poor.

Comparative Example 2 did not use fluorine-containing ethylenically unsaturated monomers to form the branch of the polyvinyl alcohol copolymer, and the moisture content of the prepared electrode sheet was less than 20% lower than that of the electrode sheet made by CMC/SBR , And the battery capacity maintenance rate is not good.

Comparative Example 4 used too much ethylenically unsaturated carboxylic acid monomer, and the resulting battery negative electrode had poor flexibility, and cracks occurred after winding; Comparative Example 3 used too little ethylenically unsaturated carboxylic acid monomer, and the adhesion was poor. This results in poor battery capacity maintenance.

Those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the scope or spirit of the present invention. In view of the foregoing, the present invention intends to cover the modifications and changes of the present invention, and the limitation is that it falls within the scope of the following patent applications and their equivalents. Table I Preparation Example 1 Preparation Example 2 Preparation Example 3 Preparation Example 4 Preparation Example 5 Preparation Example 6 Preparation Example 7 Preparation Example 8 Preparation Example 9 Preparation Example 10 Grafted PVA (d) Polyvinyl alcohol (g) 15 15 15 18 18 20 40 15 20 3 (a) 2,2,2-trifluoroethyl (meth)acrylate (g) 6 12 20 6 10 15 6 0 10 2 (b) (Meth) acrylic acid (g) 138 132 127 138 127 115 113 138 90 160 (c) Hexyl (meth)acrylate (g) 6 6 3 3 10 15 6 12 45 0 water 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 [(a)+(b)+(c)]/(d) 10 10 10 8.2 8.2 7.25 3.125 10 7.25 54 Viscosity (cps) 6000 5200 4500 6500 6200 7500 20000 7000 6500 7600 pH value 5 5 5 5 5 5 5 5 5 5 Table II Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Comparative example 5 Comparative example 6 Preparation Example 1 Preparation Example 2 Preparation Example 3 Preparation Example 4 Preparation Example 5 Preparation Example 6 Preparation Example 7 Preparation Example 8 Preparation Example 9 Preparation Example 10 CMC/ SBR PAA/ SBR Grafted PVA (g) Solid content: 5.2 wt% 38.46 38.46 38.46 38.46 38.46 38.46 38.46 38.46 38.46 38.46 0 0 CMC (g) solid content: 2 wt% 0 0 0 0 0 0 0 0 0 0 50 0 SBR (g) Solid content: 45 wt% 0 0 0 0 0 0 0 0 0 0 2.22 2.22 PAA (g) Solid content: 2 wt% 0 0 0 0 0 0 0 0 0 0 0 50 Silica/graphite anode active material (g) 95 95 95 95 95 95 95 95 95 95 95 95 Super P (g) 3 3 3 3 3 3 3 3 3 3 3 3 Viscosity (CPs) 5500 5100 3800 4700 3500 4100 10000 6000 7500 6500 6200 NA Fineness (μm) 35 35 35 35 35 35 30 35 35 35 25 NA Capacity maintenance rate (%) 85 91 88 93 85 82 65 70 66 75 70 NA Adhesion (N) 7.0 6.2 5.5 8.5 8.2 7.7 3.0 6.5 3.7 3.0 8.2 NA High coating weight pole piece cracking slight without without slight without without without slight without Have without Have Moisture content ◎ ◎ ◎ ◎ ◎ ◎ X X ◎ X - X

Claims (10)

A polyvinyl alcohol graft copolymer comprising a polyvinyl alcohol main chain, wherein the branches of the polyvinyl alcohol graft copolymer comprise structural units derived from the following monomers: (1) fluorine-containing ethylenically unsaturated monomers Body; and (2) ethylenically unsaturated carboxylic acid monomer, wherein per 100 parts by weight of polyvinyl alcohol, the content of the fluorine-containing ethylenically unsaturated monomer is 20 parts by weight to 160 parts by weight, and the ethylenic The content of the unsaturated carboxylic acid monomer is 500 parts by weight to 3000 parts by weight. The polyvinyl alcohol graft copolymer of claim 1, wherein the fluorine-containing ethylenically unsaturated monomer has the structure of formula (1):

Wherein R ₁ is H, C ₁ -C ₄ alkyl, or with one or more fluorine atoms substituted with C ₁ -C ₄ alkyl; and R ₂ is H, C ₁ -C ₁₂ alkyl, substituted with one or more A C ₁ -C ₁₂ alkyl group substituted with one fluorine atom, an aryl group, an aryl group substituted with one or more fluorine atoms, an aralkyl group, or an aralkyl group substituted with one or more fluorine atoms; the restriction is R _{At least one of 1} and R ₂ is substituted with a fluorine atom. The polyvinyl alcohol graft copolymer of claim 2, wherein R ₁ is H or a C ₁ -C ₄ alkyl group and R _{2 is a C 1} -C ₁₂ alkyl group substituted with one or more fluorine atoms. The polyvinyl alcohol graft copolymer of claim 1, wherein the ethylenically unsaturated carboxylic acid monomer has a structure of formula (2):

Wherein R ₃ is H or C ₁ -C ₄ alkyl; and R ₄ is -OH. The polyvinyl alcohol graft copolymer of claim 1, wherein the branch of the polyvinyl alcohol graft copolymer further comprises a structural unit derived from an ethylenically unsaturated carboxylic acid ester monomer. The polyvinyl alcohol graft copolymer of claim 5, wherein the ethylenically unsaturated carboxylic acid ester monomer has a structure of formula (3):

Wherein R ₅ is H or C ₁ -C ₄ alkyl, and R ₆ is C ₁ -C ₁₂ alkoxy or aryloxy. The polyvinyl alcohol graft copolymer according to any one of claims 1 to 6, wherein the single systems are grafted to the polyvinyl alcohol main chain by free radical reaction. An aqueous binder composition comprising the polyvinyl alcohol graft copolymer according to any one of claims 1 to 7. The aqueous binder composition of claim 8, which further comprises a basic compound, wherein the basic compound comprises lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonium hydroxide or a mixture of them Things. An electrode slurry composition comprising the polyvinyl alcohol graft copolymer according to any one of claims 1 to 7.