A membrane adhesive, a membrane, and a battery

Abstract

In order to overcome the problem of low adhesion between the diaphragm and the pole piece in the prior art, the application provides a diaphragm adhesive, a diaphragm and a battery. The diaphragm adhesive is a core-shell structure, comprising a core and a shell layer arranged on the outer surface of the core and at least partially covering the core, the core comprising a first polymer, and the shell layer comprising a second polymer; the glass transition temperature of the first polymer is-60~20℃, and the glass transition temperature of the second polymer is 40~110℃; the first polymer comprises a first structural unit containing a polar functional group, and the polar functional group is selected from at least one of carboxyl, sulfonic acid group, phosphate group, amide group and cyano group; the mass percentage of the first structural unit in the first polymer is 1%~10%. When the diaphragm adhesive provided by the application is applied to the diaphragm, the shell layer of the diaphragm adhesive is broken after the diaphragm is pressurized at room temperature, and the core is exposed, so that the diaphragm is bonded with the pole piece under room temperature pressure, but self-bonding does not occur after the diaphragm is wound.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a separator adhesive, a separator, and a battery. Background Technology

[0002] Lithium-ion batteries have advantages such as high voltage, high specific energy, stable discharge voltage, good cycle performance, good safety performance, and long service life, and are widely used in electric vehicles, energy storage and other fields.

[0003] Lithium-ion batteries typically consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. The separator, as a crucial inner component, primarily functions to separate the positive and negative electrodes, preventing short circuits caused by contact. Currently, most separators used in existing technology are polyolefin porous membranes. Because these polyolefin porous membranes have a melting point below 200°C, when the battery temperature rises due to internal or external factors, the membrane shrinks or melts, causing direct contact between the positive and negative electrodes, leading to a short circuit and potentially resulting in battery combustion or explosion.

[0004] To address the aforementioned issues, existing technologies attempt to use binders to coat ceramic particles onto the surface of the separator substrate to create a ceramic / polymer composite separator. The heat resistance of the ceramic particles is utilized to reduce the thermal shrinkage rate of the separator, while the polymer is used to improve the adhesion between the separator and the electrode interface, thereby preventing short circuits and increasing cell rigidity. However, the adhesion between the composite separator and the electrode is relatively low, and misalignment between the separator and the electrode is prone to occur.

[0005] Therefore, there is an urgent need for an adhesive that can improve the adhesion between the diaphragm and the electrode. Summary of the Invention

[0006] The technical problem to be solved by the present invention is the low adhesion between the existing separator and the electrode. The present invention provides a separator adhesive, a separator, and a battery.

[0007] To solve the above-mentioned technical problems, the present invention provides a diaphragm adhesive, wherein the diaphragm adhesive has a core-shell structure, including a core and a shell layer disposed on the outer surface of the core and at least partially covering the core, wherein the core comprises a first polymer and the shell layer comprises a second polymer;

[0008] The glass transition temperature of the first polymer is -60 to 20°C, and the glass transition temperature of the second polymer is 40 to 110°C.

[0009] The first polymer includes a first structural unit containing a polar functional group, wherein the polar functional group is selected from at least one of carboxyl, sulfonic acid, phosphate, hydroxyl, and cyano groups; the mass percentage of the first structural unit in the first polymer is 1% to 10%.

[0010] Preferably, the first structural unit is a structural unit formed by the polymerization of a first monomer, the first monomer including at least one of acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, β-carboxyethyl acrylate, cinnamic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, succinic acid, alkenyl sulfonic acid compounds, sodium allyloxyhydroxypropyl methanesulfonate, acrylate sulfonate salts, acrylamide alkyl sulfonic acid compounds, acryloyloxyethyl phosphate compounds, allyl phosphate, acrylamide compounds, methacrylamide compounds, acrylonitrile compounds, methacrylonitrile compounds, and 2-cyanoethyl acrylate.

[0011] Preferably, the first polymer further includes cross-linked structural units, wherein the mass percentage of the cross-linked structural units in the first polymer is 0.1% to 3%.

[0012] Preferably, the crosslinked structural unit is a structural unit obtained by polymerization of a crosslinked monomer, and the crosslinked monomer contains at least two polymerizable double bonds;

[0013] The crosslinking monomers include at least one of acrylate compounds, methacrylate compounds, aromatic vinyl compounds, acrylamide compounds, and allyl compounds.

[0014] Preferably, the first polymer further includes a second structural unit, which includes at least one of vinyl structural units, acrylate structural units, methacrylate structural units, maleate structural units, itaconic acid ester structural units, maleimide structural units, acrylamide structural units, and methacrylamide structural units.

[0015] And / or, the second polymer comprises at least one of vinyl structural units, acrylate structural units, methacrylate structural units, maleate structural units, itaconic acid ester structural units, maleimide structural units, acrylamide structural units, and methacrylamide structural units.

[0016] Preferably, the mass ratio of the first polymer to the second polymer is (30:70) to (80:20).

[0017] Preferably, the dissolution rate of the diaphragm adhesive in the electrolyte is <3%;

[0018] And / or, the average particle size of the diaphragm adhesive is 0.2~6μm.

[0019] Secondly, this application provides a diaphragm, including a base membrane and an adhesive layer, the adhesive layer being disposed on at least one side of the base membrane, the adhesive layer including a diaphragm adhesive as described in any of the above claims.

[0020] Preferably, the areal density of the membrane adhesive in each of the adhesive layers is 0.1-0.6 g / m³. 2 ;

[0021] And / or, at 25~30℃ and 2~10MPa, the peel strength between the adhesive layer and the negative electrode sheet is ≥1N / m.

[0022] Thirdly, this application provides a lithium-ion battery, including the separator described above.

[0023] The diaphragm adhesive provided in this application has a core-shell structure. When applied to the diaphragm, the shell layer of the adhesive ruptures after the diaphragm is pressurized at room temperature with the electrode, exposing the core. The glass transition temperature of the first polymer in the core is between -60°C and 20°C, thus achieving adhesion between the diaphragm and the electrode under room temperature and pressure. This results in good adhesion, reduced energy consumption, and cost savings. Furthermore, self-adhesion does not occur after the diaphragm is wound up. The carboxyl, sulfonic acid, and phosphate groups in the first polymer have strong intermolecular forces with the negative electrode, resulting in good adhesion between the diaphragm and the electrode. Cyano groups or amide groups can form hydrogen bonds and polar interactions with hydroxyl groups, nitrogen, and other elements in the negative electrode, increasing the adhesion between the diaphragm and the electrode. By limiting the mass percentage of the first structural unit in the first polymer to 1% to 10%, the adhesion between the diaphragm adhesive and the electrode is controlled, while simultaneously controlling the glass transition temperature of the first polymer to between -60°C and 20°C. Detailed Implementation

[0024] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] One embodiment of this application provides a diaphragm adhesive, the diaphragm adhesive having a core-shell structure, including a core and a shell layer disposed on the outer surface of the core and at least partially covering the core, the core comprising a first polymer and the shell layer comprising a second polymer;

[0026] The glass transition temperature (Tg) of the first polymer is -60~20℃, and the glass transition temperature of the second polymer is 40~110℃.

[0027] The first polymer includes a first structural unit containing a polar functional group, wherein the polar functional group is selected from at least one of carboxyl, sulfonic acid, phosphate, amide, and cyano groups; the mass percentage of the first structural unit in the first polymer is 1% to 10%.

[0028] The diaphragm adhesive provided in this application has a core-shell structure. When applied to the diaphragm, the shell layer of the adhesive ruptures after the diaphragm is pressurized with the electrode at room temperature (25~30℃), exposing the core. The glass transition temperature of the first polymer in the core is between -60~20℃, thus achieving adhesion between the diaphragm and the electrode under room temperature and pressure. This results in good adhesion, reduced energy consumption, and cost savings. Furthermore, self-adhesion does not occur after the diaphragm is wound up. The carboxyl groups, sulfonic acid groups, and phosphate ester groups in the first polymer have strong intermolecular forces with the negative electrode, resulting in good adhesion between the diaphragm and the electrode. Cyano groups or amide groups can form hydrogen bonds and polar interactions with hydroxyl groups, nitrogen, and other elements in the negative electrode, increasing the adhesion between the diaphragm and the electrode. By limiting the mass percentage of the first structural unit in the first polymer to 1%~10%, the adhesion between the diaphragm adhesive and the electrode is controlled, while simultaneously controlling the glass transition temperature of the first polymer to between -60~20℃.

[0029] Intermolecular interactions between polar functional groups can enhance the cohesive force of the first polymer. However, if the content of the first structural unit is greater than 10%, the cohesive strength of the first polymer is too high while its toughness is insufficient. This leads to an increase in the glass transition temperature and a decrease in elasticity, making it impossible for the diaphragm to bond with the electrode under room temperature and pressure. If the content of the first structural unit is less than 1%, the intermolecular forces between the polar functional groups in the diaphragm adhesive and the electrode weaken, resulting in a decrease in the adhesion between the diaphragm and the electrode.

[0030] Specifically, the mass percentage of the first structural unit in the first polymer includes, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0031] The glass transition temperatures of both the first and second polymers were obtained by differential scanning calorimetry (DSC).

[0032] In some embodiments, the first structural unit is a structural unit formed by polymerization of a first monomer, the first monomer including at least one of acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, β-carboxyethyl acrylate, cinnamic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, succinic acid, alkenyl sulfonic acid compounds, sodium allyloxyhydroxypropyl methanesulfonate, acrylate sulfonate salts, acrylamide alkyl sulfonic acid compounds, acryloyloxyethyl phosphate compounds, allyl phosphate, acrylamide compounds, methacrylamide compounds, acrylonitrile compounds, methacrylonitrile compounds, and 2-cyanoethyl acrylate.

[0033] Specifically, alkenyl sulfonic acid compounds include at least one of vinyl sulfonic acid, allyl sulfonic acid, methyl allyl sulfonic acid, methyl vinyl sulfonic acid, styrene sulfonic acid, and α-methylstyrene sulfonic acid.

[0034] Acrylate sulfonates include at least one of propyl 3-sulfonate acrylate, propyl 3-sulfonate methacrylate, 2-ethanesulfonate acrylate, and 2-ethanesulfonate methacrylate.

[0035] Acrylamidoalkyl sulfonic acid compounds include at least one of acrylamido-2-methylpropanesulfonic acid, acrylamido-2-hydroxypropanesulfonic acid, methacrylamido-2-methylpropanesulfonic acid, and methacrylamido-2-hydroxypropanesulfonic acid.

[0036] Acryloyloxyethyl phosphate compounds include at least one of acryloyloxyethyl phosphate, methacryloyloxyethyl phosphate, 2-hydroxyethylacryloyl phosphate, 2-hydroxyethylmethacryloyl phosphate, phenyl-2-acryloyloxyethyl phosphate, and di[2-(methacryloyloxy)ethyl] phosphate.

[0037] Acrylamide compounds and methacrylamide compounds include at least one of acrylamide, methacrylamide, C1-C12 alkyl-substituted acrylamide, C1-C12 alkyl-substituted methacrylamide, C6-C18 aryl-substituted acrylamide, and C6-C18 aryl-substituted methacrylamide.

[0038] Acrylonitrile compounds include at least one of acrylonitrile and methacrylonitrile.

[0039] In some embodiments, the first polymer further includes cross-linked structural units, wherein the mass percentage of the cross-linked structural units in the first polymer is 0.1% to 3%.

[0040] The first polymer has a low glass transition temperature and may dissolve in high-temperature electrolytes. Once the first polymer dissolves, an electrochemical reaction will occur at the positive or negative electrode, causing a decrease in battery cycle performance. Therefore, to reduce the electrolyte dissolution rate of the first polymer, cross-linked structural units are introduced into the first polymer to prevent the core from flowing and causing blockage of the separator pores during use, thereby improving battery cycle performance.

[0041] Furthermore, if the crosslinking monomer content is below 0.1%, the flow of the first polymer during use cannot be completely suppressed, leading to blockage of the separator pores and affecting lithium-ion transport during battery use, thus reducing battery cycle performance. If the crosslinking monomer content is above 3%, the cohesive strength of the first polymer is too high while its toughness is insufficient, i.e., its elasticity decreases, making it impossible for the separator to bond with the electrode under room temperature and pressure.

[0042] In some embodiments, the crosslinked structural unit is a structural unit obtained by polymerization of a crosslinked monomer, wherein the crosslinked monomer contains at least two polymerizable double bonds;

[0043] The crosslinking monomers include at least one of acrylate compounds, methacrylate compounds, aromatic vinyl compounds, acrylamide compounds, and allyl compounds.

[0044] Specifically, acrylate compounds and methacrylate compounds include at least one of ethylene glycol diacrylate, polyethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, dipropylene glycol diacrylate, trimethylolpropane triacrylate, glycerol triacrylate, pentaerythritol triacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, propylene glycol dimethacrylate, dipropylene glycol dimethacrylate, dipropylene glycol dimethacrylate, tripropylene glycol dimethacrylate, trimethylolpropane trimethacrylate, glycerol trimethacrylate, pentaerythritol trimethacrylate, allyl acrylate, and allyl methacrylate.

[0045] Aromatic vinyl compounds include divinylbenzene.

[0046] Acrylamide compounds include N,N-methylenebisacrylamide.

[0047] Allyl compounds include at least one of diallyl phthalate, glycerol diallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, diallyl adipate, allyl acrylate, and allyl methacrylate.

[0048] To suppress the dissolution of the first polymer in the electrolyte, in a preferred embodiment, the crosslinking monomer is selected from at least one of N,N-methylenebisacrylamide, polyethylene glycol diacrylate, and polyethylene glycol dimethacrylate.

[0049] In some embodiments, the first polymer further includes a second structural unit, which includes at least one of vinyl structural units, acrylate structural units, methacrylate structural units, maleate structural units, itaconic acid ester structural units, maleimide structural units, acrylamide structural units, and methacrylamide structural units. The glass transition temperature and adhesive strength of the first polymer are controlled through the synergistic effect of the above structural units, crosslinking units, and the first structural unit.

[0050] In some embodiments, the second polymer includes at least one of vinyl structural units, acrylate structural units, methacrylate structural units, maleate structural units, itaconic acid ester structural units, maleimide structural units, acrylamide structural units, and methacrylamide structural units.

[0051] Specifically, the second structural unit and the vinyl structural unit in the second polymer are structural units obtained by the participation of vinyl monomers in the polymer. The vinyl monomers include at least one of aliphatic vinyl compounds, alicyclic vinyl compounds, aromatic vinyl compounds, allyl compounds, and vinyl compounds containing heteroatoms.

[0052] The aliphatic vinyl compounds include, but are not limited to, at least one of the following: C2-C12 olefins, C3-C24 α-olefins, and C4-C12 dienes. C2-C12 olefins include, but are not limited to, at least one of ethylene, propylene, butene, isobutene, pentene, hepten, diisobutene, octene, dodecene, and octadecene. C4-C12 dienes include, but are not limited to, at least one of butadiene, isoprene, 1,4-pentadiene, 1,6-hexadiene, and 1,7-octadiene.

[0053] The alicyclic vinyl hydrocarbons include, but are not limited to, at least one of C6-C15 monocyclic or bicyclic alkenes, C5-C12 monocyclic or bicyclic dienes, and terpenoids. C6-C15 monocyclic or bicyclic alkenes include, but are not limited to, at least one of cyclohexene, vinylcyclohexene, and ethimide-bicyclic heptene. C5-C12 monocyclic or bicyclic dienes include, but are not limited to, at least one of cyclopentadiene, cycloheptadiene, dicyclopentadiene, and dicycloheptadiene. Terpenoids include, but are not limited to, at least one of limonene and indene.

[0054] The aromatic vinyl hydrocarbon compounds include, but are not limited to, styrene and substituted styrene, wherein the substituted styrene includes, but is not limited to, at least one of α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotonylstyrene, divinylbenzene, divinyltoluene, divinyldimethylbenzene, trivinylbenzene, vinylnaphthalene, and p-tert-butylstyrene.

[0055] Vinyl compounds containing heteroatoms include, but are not limited to, at least one of vinyl (thio) ethers, vinyl sulfones, acrylonitrile, methacrylonitrile, cyanostyrene, 4-vinylpyridine, 2-vinylpyridine, vinylimidazole, N-vinylpyrrole, and N-vinylthiopyrrolidone.

[0056] The acrylate or methacrylate structural unit in the second structural unit and the second polymer is a structural unit obtained by polymerization of acrylate monomers or methacrylate monomers, including but not limited to methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, isobornyl acrylate, phenoxyethyl acrylate, dicyclopentenyl acrylate, cyclohexyl acrylate, benzyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, carboxyethyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, phenoxyethyl methacrylate, dicyclopentenyl ... Cyclopentenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, polyethylene glycol mono[(meth)acrylate] ester, glycidyl (meth)acrylate, tetrahydrofuran (meth)acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, ethoxylated ethylene glycol diacrylate, ethoxylated ethylene glycol dimethacrylate, allyl methacrylate, diallyl phthalate, diallyl adipate At least one of the following: ester, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol diacrylate, pentaerythritol dimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, urethane acrylate, urethane acrylate, dimethyl urethane acrylate, dimethyl urethane acrylate, diethyl urethane acrylate, diethyl urethane methacrylate, and tert-butyl urethane acrylate.

[0057] The second structural unit and the maleate ester structural unit in the second polymer are structural units obtained by polymerization of maleate ester monomers. The maleate ester monomers include at least one of C1-C12 monoalkyl esters or C1-C12 dialkyl esters of maleic acid. C1-C12 indicates that the number of carbon atoms is 1-12. Specifically, the maleate ester monomers include at least one of monomethyl maleate, dimethyl maleate, monoethyl maleate, diethyl maleate, monopropyl maleate, dipropyl maleate, monobutyl maleate, dibutyl maleate, monooctyl maleate, and dioctyl maleate.

[0058] The itaconic acid ester structural unit in the second structural unit and the second polymer is a structural unit obtained by polymerization of itaconic acid ester monomers, which include at least one of itaconic acid C1-C12 monoesters and itaconic acid C1-C12 diesters. Specifically, the itaconic acid ester monomers include at least one of itaconic acid monomethyl ester, itaconic acid dimethyl ester, itaconic acid monoethyl ester, itaconic acid diethyl ester, itaconic acid monobutyl ester, itaconic acid dibutyl ester, itaconic acid monooctyl ester, and itaconic acid dioctyl ester.

[0059] The maleimide structural unit in the second structural unit and the second polymer is a structural unit obtained by polymerization of maleimide monomers, wherein the maleimide monomers include at least one of maleimide, C1-C12 alkyl-substituted maleimide, and C6-C16 aryl-substituted maleimide.

[0060] The acrylamide-type structural unit or methacrylamide-type structural unit in the second structural unit and the second polymer is a structural unit obtained by polymerization of acrylamide monomers or methacrylamide monomers, including at least one of (meth)acrylamide, N-methyl(meth)acrylamide, N-butylacrylamide, acetylacetone acrylamide, N-hydroxymethyl(meth)acrylamide, N,N'-methylenebis[(meth)acrylamide], cinnamamide, N,N-dimethylacrylamide, N,N-dibenzylacrylamide, methacryloylformamide, N-methylN-vinylacetamide, and N-vinylpyrrolidone.

[0061] In some embodiments, the mass ratio of the first polymer to the second polymer is (30:70) to (80:20). By limiting the mass ratio of the first polymer to the second polymer within the above range, the thickness of the shell layer is limited, thereby ensuring that the thickness of the shell layer of the diaphragm adhesive can rupture under pressure, while ensuring the integrity of the shell layer during winding.

[0062] Specifically, the mass ratio of the first polymer to the second polymer includes, but is not limited to, 30:70, 40:60, 50:50, 60:40, 70:30, or 80:20.

[0063] Furthermore, the mass content of the first polymer in the core-shell structure is 30%-80%, and the mass content of the second polymer is 20%-70%.

[0064] In some embodiments, the dissolution rate of the membrane binder in the electrolyte is <3%. By limiting the dissolution rate of the membrane binder in the electrolyte, electrochemical reactions of the membrane binder at the positive or negative electrode sites are avoided, which could lead to a decrease in battery cycle performance.

[0065] In some embodiments, the average particle size of the membrane adhesive is 0.2~6 μm. Limiting the average particle size of the membrane adhesive limits the thickness of the adhesive layer formed on the membrane, thereby achieving high bonding strength between the membrane and the electrode. Specifically, the average particle size of the membrane adhesive in this embodiment can be obtained by measuring the membrane adhesive using equipment such as a laser particle size analyzer. After the membrane is prepared, the membrane adhesive in the adhesive layer of the membrane can be tested using the following steps: the membrane is tested using SEM, measuring the average particle size of at least 20 particles, and then the average value is taken as the final measurement result.

[0066] The average particle size of the diaphragm binder includes, but is not limited to, 0.2μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm or 6μm.

[0067] The particle size is the volume average particle size. When using SEM to calculate the particle size, the particles can be considered as spherical for calculation.

[0068] Furthermore, one embodiment of this application provides a method for preparing a diaphragm adhesive, comprising the following steps:

[0069] Preparation of nuclei:

[0070] Deionized water, emulsifier, and a monomer mixture of the first polymer are added to an emulsification vessel and stirred to emulsify, thereby obtaining a monomer pre-emulsion of the first polymer. The amount of emulsifier used is 0.01%-1% of the weight of the monomer mixture.

[0071] In another reaction vessel, deionized water was added, nitrogen gas was introduced and the temperature was raised, an initiator was added, and then the monomer pre-emulsion of the first polymer was added dropwise to carry out the reaction and obtain the first polymer emulsion.

[0072] If the particle size of the first polymer to be prepared is greater than 1 μm, it can be prepared by methods such as suspension polymerization, dispersion polymerization, and precipitation polymerization.

[0073] Taking suspension polymerization as an example: a monomer mixture of the first polymer, an initiator, and an aqueous solution containing a dispersant are added to a reactor to obtain an oil-water mixture. The mixture is homogenized to the required particle size using a homogenizer, and polymerization is carried out at a higher temperature to obtain the first polymer with the required particle size.

[0074] When prepared by suspension polymerization, the particle size of the polymer is mainly related to the rotation speed of the homogenizer, and the particle size can be adjusted by changing the rotation speed of the homogenizer. For specific preparation procedures, please refer to patent CN117060010A.

[0075] Preparation of diaphragm adhesive:

[0076] The first polymer emulsion is heated, an initiator is added, and then a mixture of monomers of the second polymer is added dropwise to react and obtain a core-shell structured granular polymer, i.e., a membrane binder.

[0077] As those skilled in the art know, the reactions in the above steps are conventional free radical polymerization, and the specific methods and reaction conditions are common free radical polymerization methods in the prior art, which will not be described in detail in this invention.

[0078] In this application, the mass fraction of monomers in the core and shell is not limited, as long as the glass transition temperature of the first polymer is -60 to 20°C, the glass transition temperature of the second polymer is 40 to 110°C, and the mass ratio of the first polymer to the second polymer is (30:70) to (80:20).

[0079] There are no particular limitations on the initiator; any commonly used initiator for free radical polymerization can be used. These are typically persulfate, azo, and peroxide initiators, including but not limited to sodium persulfate, ammonium persulfate, potassium persulfate, tert-butyl hydroperoxide, azobisisobutyronitrile, benzoyl peroxide / sucrose, tert-butyl hydroperoxide / sodium sodium metabisulfite, tert-butyl hydroperoxide / sodium metabisulfite, benzoyl peroxide / N,N-dimethylaniline, ammonium persulfate / sodium bisulfite, potassium persulfate / sodium bisulfite, hydroperoxide / tartaric acid, hydroperoxide / sodium formaldehyde sulfoxylate, ammonium persulfate / ferrous sulfate, hydroperoxide / ferrous sulfate, benzoyl peroxide / N,N-diethylaniline, benzoyl peroxide / ferrous pyrophosphate, potassium persulfate / silver nitrate, persulfate / thiol, cumene hydroperoxide / ferrous chloride, potassium persulfate / ferrous chloride, hydroperoxide / ferrous chloride, cumene hydroperoxide / tetraethyleneimine, and lauroyl peroxide, among one or more of these.

[0080] The emulsifier can be any type of emulsifier currently available on the market.

[0081] In this invention, each of the aforementioned structural units represents the structural portion of the corresponding monomer present in the resulting polymer after the monomer participates in the polymerization reaction. The mass ratio of each structural unit is based on the mass content of the corresponding monomer in the total amount of monomers participating in the polymerization.

[0082] This application also provides a diaphragm, including a base membrane and an adhesive layer, wherein the adhesive layer is disposed on at least one side of the base membrane or the coated diaphragm, and the adhesive layer includes a diaphragm adhesive as described in any of the above claims.

[0083] In some embodiments, the areal density of the membrane adhesive in each adhesive layer is 0.1~0.6 g / m³. 2 By limiting the coating density of the diaphragm adhesive and the amount of diaphragm adhesive used in the adhesive layer, a high bonding strength between the diaphragm and the electrode can be ensured.

[0084] Specifically, the surface density of the diaphragm adhesive coating in the adhesive layer on one side of the diaphragm includes, but is not limited to, 0.1 g / m³. 2 0.2g / m 2 0.3g / m 2 0.4g / m 2 0.5g / m 2 or 0.6g / m 2 .

[0085] In some embodiments, the separator further includes a non-conductive particulate coating disposed on at least one side of the base membrane, the non-conductive particulate coating having a thickness of 0.5~4 μm. When the thickness of the non-conductive particulate coating is less than 0.5 μm, the heat resistance of the separator decreases, and the prepared battery has a significant safety risk. When the thickness of the non-conductive particulate coating is greater than 4 μm, the separator thickness increases, and the prepared battery has a lower energy density.

[0086] Preferably, the thickness of the non-conductive particle coating is 0.5~3μm.

[0087] Specifically, the non-conductive particle coating and the adhesive layer exist together, with the adhesive layer located on the side of the diaphragm facing the electrode, and the adhesive layer can be disposed on the non-conductive particle coating.

[0088] In some embodiments, the non-conductive particulate coating includes non-conductive particles, a ceramic binder, and selectively added rheology modifiers, dispersants, and wetting agents.

[0089] Non-conductive particles include, but are not limited to, at least one of the following: hydrated alumina, aluminum oxide, boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, calcium carbonate, barium titanate, barium sulfate, and heat-resistant organic polymer particles. When the above-mentioned materials are selected as non-conductive particles, they can better improve the mechanical strength and thermal stability of the separator, further reduce the thermal shrinkage rate of the separator, and thus further improve the safety of the battery.

[0090] The ceramic binder in this embodiment can be any commercially available ceramic binder, and ceramic binders with the required particle size and glass transition temperature can be obtained directly by purchasing them.

[0091] The wetting agent can be any existing wetting agent, such as at least one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether and polyether-modified polysiloxane.

[0092] The dispersant can be any existing dispersant, such as sodium polyacrylate or sodium carboxymethyl cellulose.

[0093] In some embodiments, the weight ratio of non-conductive particles, ceramic binder, sodium carboxymethyl cellulose, dispersant, and wetting agent in the non-conductive particle coating is (88~96.3):(3~15):(0~3):(0~2):(0~2).

[0094] Preferably, in the non-conductive particle coating, the weight ratio of non-conductive particles, ceramic binder, rheology modifier, dispersant, and wetting agent is (88~96.3):(3~15):(0.5~3):(0.1~2):(0.1~2).

[0095] In some embodiments, the average particle size of the non-conductive particles is 0.1 to 2 μm. The average particle size of the non-conductive particles is smaller than the thickness of the non-conductive particle coating. When the thickness of the non-conductive particle coating is 0.5 to 4 μm, if the average particle size of the non-conductive particles exceeds 2 μm, the thermal shrinkage rate of the diaphragm will increase significantly.

[0096] Specifically, the average particle size of the non-conductive particles includes, but is not limited to, 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1.1 μm, 1.4 μm, 1.7 μm or 2 μm.

[0097] In some embodiments, the base film is selected from at least one of polyethylene base film, polypropylene base film, polypropylene-polyethylene-polypropylene laminated base film, or nonwoven base film.

[0098] In some embodiments, the thickness of the base film is 5-12 μm.

[0099] In some embodiments, at 25~30℃ and 2~10MPa, the peel strength between the adhesive layer and the negative electrode sheet is ≥1N / m to avoid relative displacement between the separator and the adhesive.

[0100] An embodiment of this application also provides a lithium-ion battery, including the separator described above.

[0101] The present invention will be further illustrated by the following examples.

[0102] Specifically, this invention discloses the separator binder, positive electrode composition, negative electrode sheet, and lithium-ion battery thereof.

[0103] Example 1

[0104] 1) Preparation of diaphragm adhesive

[0105] The monomers of the first polymer include the following components: 368 parts butyl acrylate, 16 parts styrene, 4 parts divinylbenzene, and 12 parts acrylic acid.

[0106] The second polymer comprises 95 parts styrene and 5 parts butyl acrylate.

[0107] The preparation of the diaphragm binder includes the following steps: (1) adding the monomer of the core body, deionized water, and emulsifier to an emulsification vessel, and stirring to emulsify to obtain a monomer pre-emulsion of the first polymer. The amount of emulsifier is 0.1% of the monomer weight.

[0108] (2) Add deionized water to another emulsification vessel, heat to 80°C by purging with nitrogen, add sodium persulfate as an initiator, and then dropwise add the monomer pre-emulsion of the first polymer. After adding the pre-emulsion for 3 hours, keep the reaction at the temperature for 3 hours to obtain the first polymer emulsion with an average particle size of 0.21 μm.

[0109] (3) The first polymer emulsion was heated to 80°C, and after adding ammonium persulfate initiator, the monomer mixture of the second polymer was added dropwise. After the addition was completed in 3 hours, the reaction was continued for another 3 hours to obtain a core-shell structured membrane binder with an average particle size of 0.23 μm.

[0110] The solid weight ratio of the first polymer to the second polymer is 80:20.

[0111] In the diaphragm binder, the glass transition temperature of the first polymer is -48℃, and the glass transition temperature of the second polymer is 86℃; the dissolution rate of the diaphragm binder in the electrolyte is 1.5%.

[0112] 2) Preparation of the diaphragm:

[0113] A non-conductive particle slurry was prepared by mixing 93.4 parts of non-conductive boehmite powder, 6 parts of ceramic binder (HD2126 from Shenzhen Haodian Technology Co., Ltd.), 0.3 parts of dispersant sodium polyacrylate, 1 part of sodium carboxymethyl cellulose, and 0.3 parts of wetting agent alkylphenol polyoxyethylene ether. The non-conductive particle slurry was coated on one surface of a polyethylene base film with a thickness of 9 μm. After drying in an oven at 50℃, a non-conductive particle coating was formed on the base film surface.

[0114] The diaphragm adhesive was applied to the side of the base membrane free of non-conductive particles using a roller coating method, with a coating density of 0.2 g / m². 2 After drying, an adhesive layer is obtained.

[0115] 3) Preparation of the negative electrode:

[0116] A negative electrode composition is prepared by mixing 1.5% styrene-butadiene latex (SBR), 96% graphite (negative electrode active material), 1% conductive carbon black (negative electrode conductive agent), and 1.5% sodium carboxymethyl cellulose (CMC) (thickener), and then adding deionized water and stirring. The negative electrode composition is then coated onto both surfaces of a Cu foil (negative electrode current collector), and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0117] The negative electrode active material, graphite, has a particle size of 20 μm.

[0118] 4) Preparation of the positive electrode:

[0119] 97.8% of the positive electrode active material lithium cobalt oxide, 1% of the positive electrode conductive agent conductive carbon black, and 1.2% of the binder PVDF were added to N-methylpyrrolidone and stirred to prepare a positive electrode slurry. The positive electrode slurry was then coated on both surfaces of the positive electrode current collector Al foil, and after drying, cold pressing, and slitting, a separator was obtained.

[0120] 5) Lithium-ion battery manufacturing:

[0121] The separator, positive electrode, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator, thus forming an electrode assembly. The electrode assembly is then placed in an outer package, injected with commercially available electrolyte, and sealed. After processes such as electrolyte injection, formation, and degassing, a lithium-ion battery is obtained.

[0122] Examples 2 to 11

[0123] Examples 2 to 11 are largely the same as Example 1, except that the monomers of the first polymer in the diaphragm adhesive are different, as shown in Table 1.

[0124] Table 1

[0125]

[0126] Example 12

[0127] Most of the steps in Example 12 are the same as those in Example 1, except that the second polymer comprises 75 parts styrene and 25 parts butyl acrylate.

[0128] The Tg of the second polymer is 45℃.

[0129] Example 13

[0130] Most of the steps in Example 1 are the same as in Example 2, except that the second polymer comprises 100 parts of styrene.

[0131] The Tg of the second polymer is 104℃.

[0132] Example 14

[0133] Most of the steps in Example 14 are the same as those in Example 1, except that the mass ratio of the first polymer to the second polymer is 30:70.

[0134] Example 15

[0135] Most of the steps in Example 15 are the same as those in Example 1, except that the mass ratio of the first polymer to the second polymer is 60:40.

[0136] Example 16

[0137] Most of the steps in Example 16 are the same as those in Example 1, except that the mass ratio of the first polymer to the second polymer is 20:80.

[0138] Example 17

[0139] Most of the steps in Example 17 are the same as those in Example 1, except that the mass ratio of the first polymer to the second polymer is 90:10.

[0140] Example 18

[0141] Most of the steps in Example 18 are the same as those in Example 1, except that the particle size of the diaphragm binder is 3 μm.

[0142] Example 19

[0143] Most of the steps in Example 19 are the same as those in Example 1, except that the particle size of the diaphragm binder is 0.1 μm.

[0144] Example 20

[0145] Most of the steps in Example 20 are the same as those in Example 1, except that the particle size of the diaphragm binder is 6 μm.

[0146] Example 21

[0147] Most of the steps in Example 21 are the same as those in Example 1, except that the particle size of the diaphragm binder is 10 μm.

[0148] Example 22

[0149] Example 22 is largely the same as Example 1, except that the surface density of the membrane adhesive coating is 0.1 g / m³ during membrane preparation. 2 .

[0150] Example 23

[0151] Example 23 is largely the same as Example 1, except that the surface density of the membrane adhesive coating is 0.3 g / m³ during membrane preparation. 2 .

[0152] Example 24

[0153] Example 24 is largely the same as Example 1, except that the surface density of the membrane adhesive coating is 0.6 g / m³ during membrane preparation. 2 .

[0154] Example 25

[0155] Example 25 is largely the same as Example 1, except that the surface density of the membrane adhesive coating is 0.7 g / m³ during membrane preparation. 2 .

[0156] Example 26

[0157] Example 26 is largely the same as Example 1, except that the surface density of the membrane adhesive coating is 0.08 g / m³ during membrane preparation. 2 .

[0158] Comparative Examples 1 to 3

[0159] The steps of Comparative Examples 1 to 3 are mostly the same as those of Example 1, except that the monomer composition of the first polymer added to the diaphragm adhesive is different, as shown in Table 1.

[0160] Comparative Example 4

[0161] Comparative Example 4 and Example 1 share most of the same steps, except that the membrane adhesive does not have a core-shell structure. The specific preparation method is as follows:

[0162] (1) Mix the monomers of the core, add the additives, and stir while heating to obtain the first polymer;

[0163] (2) After the monomers of the shell layer are mixed evenly, potassium persulfate is added and stirred while heating to obtain the second polymer;

[0164] (3) The first polymer and the second polymer are mixed and then spray-dried to obtain a membrane adhesive.

[0165] Comparative Example 5

[0166] Comparative Example 5 is similar to Example 1 in most steps, except that the membrane adhesive used is existing PVDF.

[0167] Comparative Example 6

[0168] Comparative Example 6 follows most of the same steps as Example 1, except that the second polymer comprises 70 parts styrene and 30 parts α-methylstyrene (Tg: 119°C).

[0169] Comparative Example 7

[0170] Comparative Example 7 followed most of the steps of Example 1, except that the second polymer comprised 70 parts styrene and 30 parts butyl acrylate. (Tg: 35°C)

[0171] Electrical performance testing:

[0172] The separators and lithium-ion batteries prepared in the above embodiments and comparative examples were tested as follows.

[0173] 1) 25℃ room temperature peel strength test: Cut the diaphragm and the negative electrode sheet into strips of 20mm*100mm respectively. Under the conditions of 25℃ and 2MPa, press the side of the diaphragm containing the diaphragm adhesive against the negative electrode sheet for 60s. Use an electronic tensile testing machine to perform a 180° peel strength test. The test result is the average of 3 samples.

[0174] 2) Electrolyte dissolution rate test: The membrane adhesive was dried at 70℃ to form a membrane with a weight of m1; it was then immersed in a lithium-free carbonate solvent (EC:DEC:EMC=3:2:5) at 60℃ for 72 hours, and dried to a weight of m2. The electrolyte dissolution rate is [(m1-m2) / m1]*100%.

[0175] 3) Diaphragm unwinding self-adhesion verification: A 9μm base film was used, with a 2μm ceramic coating on both sides, and then 0.6g / m 2 The membrane adhesive is coated on both sides with a surface density of 2000 meters. After storing it at 25°C for 3 days, the membrane is unwound and observed for self-adhesion.

[0176] 4) 30℃ 1MPa Diaphragm Self-Adhesion Simulation Test: Diaphragms coated with diaphragm adhesive on both sides are pressed together at 30℃ and 1MPa for 60 seconds, and the peel strength between the diaphragms is tested. An adhesion force ≤0.5N / m is considered as no self-adhesion between the diaphragms.

[0177] 5) Room temperature cycling test

[0178] After placing the battery in a constant temperature test chamber at 25℃±2℃ for 1 hour, charge it to 4.45V with a constant current and constant voltage of 1C and cut off the current at 0.05C; discharge it to 3V with a constant current of 1C and record the discharge capacity; repeat the above steps 500 times and calculate the capacity retention rate.

[0179] Fill the test results obtained from the examples and comparative examples into Table 2.

[0180] Table 2

[0181]

[0182] Continued from Table 2

[0183]

[0184] As shown in Table 2, the first structural unit in the first polymer has a significant impact on the adhesion. The test results of Examples 1 and 3 show that when the first polymer does not contain the first structural unit, the adhesion between the separator and the electrode is extremely low. Because the first structural unit in the first polymer has excellent water solubility, when its content exceeds the upper limit, the polymerization process becomes unstable or even demulsifies. Controlling the first structural unit content to below 10% is more suitable. The test results of Examples 1 and 4-7 show that the crosslinking structural unit in the first polymer has a significant impact on dissolution and adhesion. When no crosslinking structural unit is present, dissolution exceeds 3%, negatively impacting battery cycle performance. When the crosslinking structural unit content exceeds 3%, the room temperature adhesion of the separator adhesive decreases significantly. The glass transition temperature of the first polymer also affects the room temperature adhesion of the adhesive; a lower glass transition temperature results in better room temperature adhesion. The test results of Examples 1, 12, 13, Comparative Example 6, and Comparative Example 7 show that the glass transition temperature of the second polymer mainly affects the room temperature adhesion and the self-adhesion of the separator. If the glass transition temperature of the second polymer is too high, it is difficult to break, and the first polymer in the core cannot contact the electrode, resulting in insufficient adhesion. If the glass transition temperature of the second polymer is too low, the separator is prone to self-adhesion. The test results of Examples 1 and Examples 14-17 show that the ratio of the first polymer to the second polymer has a significant impact on the room temperature adhesion and the self-adhesion of the separator. The lower the proportion of the first polymer, the worse the room temperature adhesion; below the lower limit, adhesion is almost negligible. Conversely, the higher the proportion of the first polymer, the worse the coating effect of the second polymer on the first polymer, leading to self-adhesion of the separator. The test results of Examples 1 and Examples 18-21 show that the particle size of the separator adhesive mainly affects the adhesion and battery performance. Smaller particle size results in a larger contact area and better adhesion. When the particle size is smaller than the lower limit, the binder will clog the membrane pores, leading to a decrease in battery cycle performance. When the particle size is larger than the upper limit, the binder is difficult to adhere to the membrane and will detach, resulting in a decrease in adhesion. When the membrane binder has no core-shell structure and is simply mixed, the first polymer is directly exposed, and although the membrane has relatively good room temperature adhesion, it will also exhibit significant self-adhesion. The test results of Examples 1 and 22-26 show that the surface area density of the membrane binder coating mainly affects the adhesion; a high surface area density results in strong adhesion, while a low surface area density results in weak adhesion. If the surface area density is too high, the membrane pores will be clogged, causing a decrease in battery performance. If the surface area density is too low, insufficient adhesion will also easily lead to a decrease in battery performance.

[0185] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A separator binder characterized by, The diaphragm adhesive is a core-shell structure, comprising a core and a shell layer arranged on the outer surface of the core and at least partially covering the core, the core comprising a first polymer, and the shell layer comprising a second polymer; The glass transition temperature of the first polymer is -60~20℃, and the glass transition temperature of the second polymer is 40~110℃; The first polymer comprises a cross-linking structural unit and a first structural unit containing a polar functional group selected from at least one of carboxyl, sulfonic acid group, phosphate group, amide group, and cyano group; the mass percentage of the first structural unit in the first polymer is 1%~10%, and the mass percentage of the cross-linking structural unit is 0.1%~3%; the cross-linking structural unit is a structural unit obtained by polymerization of a cross-linking monomer, and the cross-linking monomer contains at least two polymerizable double bonds; The mass ratio of the first polymer to the second polymer is (30:70)~(80:20); The average particle size of the diaphragm adhesive is 0.2~6μm; The first structural unit is a structural unit formed by polymerization of a first monomer, and the first monomer comprises at least one of acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, β-carboxyethyl acrylate, cinnamic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, alkenyl sulfonic acid compound, acrylamido alkyl sulfonic acid compound, acryloyloxyethyl phosphate compound, allyl phosphate, acrylamide compound, methacrylamide compound, acrylonitrile compound, methacrylonitrile compound, and 2-cyanoethyl acrylate; The second polymer comprises at least one of a vinyl compound, an acrylate compound, and a methacrylate compound.

2. The separator binder according to claim 1, characterized in that, The cross-linking monomer comprises at least one of an acrylate compound, a methacrylate compound, an aromatic vinyl compound, an acrylamide compound, and an allyl compound.

3. The separator binder of claim 1, wherein, The first polymer further comprises a second structural unit, and the second structural unit comprises at least one of a vinyl compound, an acrylate compound, a methacrylate compound, a maleate compound, an itaconate compound, a maleimide compound, an acrylamide compound, and a methacrylamide compound.

4. The separator binder of claim 1, wherein The dissolution rate of the diaphragm adhesive in electrolyte is <3%.

5. A diaphragm characterized by, The diaphragm comprises a base film and a bonding layer arranged on at least one side of the base film, and the bonding layer comprises the diaphragm adhesive according to any one of claims 1~4; The coating area density of the separator binder of each of the adhesive layers is 0.1-0.6 g / m 2 .

6. The diaphragm of claim 5, wherein The peeling strength between the bonding layer and the negative electrode sheet is ≥1N / m under 25~30℃ and 2~10MPa.

7. A lithium-ion battery, characterized by The diaphragm comprises the diaphragm according to claim 5 or 6.

Images