CN110323391B

CN110323391B - Polymer diaphragm and preparation method thereof, dispersion, lithium ion battery and preparation method thereof

Info

Publication number: CN110323391B
Application number: CN201810290696.4A
Authority: CN
Inventors: 曹晓东; 金丽娜; 宣博文; 吴金祥; 单军
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2018-03-30
Filing date: 2018-03-30
Publication date: 2022-01-07
Anticipated expiration: 2038-03-30
Also published as: CN110323391A

Abstract

The invention discloses a polymer diaphragm and a preparation method thereof, and a lithium ion battery adopting the diaphragm and a preparation method thereof. The polymer separator of the present invention comprises a porous base material and a polymer particle layer attached to at least one surface of the porous base material, wherein the polymer particle layer contains polymer particles, a binder, a polyoxyethylene ether, a fluorine-containing organic compound, and an additive selected from a cellulose compound and/or an acrylate-based polymer, and the polymer particles are polyvinylidene fluoride particles and/or vinylidene fluoride-hexafluoropropylene copolymer particles. The polymer diaphragm of the invention not only has high porosity, but also maintains the porous characteristic after the polymer diaphragm is manufactured into a lithium ion battery and is subjected to a pressure formation step. The lithium ion battery prepared by the polymer diaphragm has good rate discharge performance, normal-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance.

Description

Polymer diaphragm and preparation method thereof, dispersion, lithium ion battery and preparation method thereof

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a polymer diaphragm and a preparation method thereof, and also relates to a dispersion body, and the invention further relates to a lithium ion battery and a preparation method thereof.

Background

Currently, the polymer matrix applied in the lithium ion battery is mainly polyethers (such as polyethylene oxide PEO), Polyacrylonitriles (PAN), polyacrylates (such as polymethyl methacrylate PMMA and its copolymer), polyvinylidene fluoride (including polyvinylidene fluoride PVDF and vinylidene fluoride-hexafluoropropylene copolymer P (VDF-HFP)), and the like. These polymer matrices can absorb electrolyte in a lithium ion battery, and reach a swelling state to form a gel structure, and have good lithium ion conductivity, and are called gel electrolytes. The polyacrylate and polyvinylidene fluoride are mainly researched and applied, and the polyacrylate and polyvinylidene fluoride can be used as an ideal polymer matrix of the polymer gel electrolyte mainly due to low interface impedance and good interface stability with a metal lithium electrode.

Many patent documents report the use of acrylate polymers as Gel Polymer Electrolyte (GPE) matrices in lithium ion batteries. The CN103633367A discloses a gel polymer electrolyte, which is formed by swelling a polymer film after absorbing the electrolyte, wherein the polymer film is formed by thermosetting and self-crosslinking a polymer mixed solution, the polymer mixed solution contains a pure acrylic emulsion and hydrated ammonia water, and the glass transition temperature of the pure acrylic emulsion is-30 ℃ to 50 ℃. However, the rate performance of the lithium ion battery prepared by the gel polymer electrolyte is poor, and the polarization is large when the lithium ion battery is charged and discharged under high rate, so that the performance of the lithium ion battery is influenced.

The root cause of the above problems is: the low porosity of the gel polymer electrolyte results in a large bulk impedance. In order to avoid this problem and increase the ionic conductivity, researchers have proposed pore-forming for GPE, and there are two main approaches: 1) solvent evaporation precipitation phase separation method, 2) immersion precipitation phase separation method.

CN101062987A reports a porous gel polymer electrolyte film, which contains 33-54% of polyvinylidene fluoride, 3-15% of acrylonitrile-methyl ether methacrylate copolymer and 43-52% of 1M lithium hexafluorophosphate carbonate electrolyte by mass percentage. The electrolyte film is prepared by adopting an immersion precipitation phase separation method, and specifically comprises the following steps:

1) blending and dissolving polyethylene glycol methyl ether methacrylate and acrylonitrile in an ethanol solvent, wherein the mass ratio of the polyethylene glycol methyl ether methacrylate to the acrylonitrile is 1: 1 to 1: 2.2, preparing a blending monomer solution with the concentration of 0.3g/mL, adding an initiator azobisisobutyronitrile, wherein the dosage of the azobisisobutyronitrile is 0.7 percent of the mass of the blending monomer, stirring until the azobisisobutyronitrile is completely dissolved, introducing nitrogen or argon, reacting at 70-80 ℃ to obtain semitransparent viscous liquid, evaporating to remove an ethanol solvent, and drying to obtain an acrylonitrile-methacrylic acid polyethylene glycol monomethyl ether ester copolymer;

2) weighing acrylonitrile-polyethylene glycol monomethylether methacrylate copolymer and polyvinylidene fluoride according to mass percentage, blending and dissolving in N, N-dimethylacetamide solvent, stirring and mixing uniformly at 50 ℃, preparing polymer solution with concentration of 0.15-0.2g/mL, cooling to room temperature, coating the polymer solution on a glass plate, then dipping the glass plate into deionized water to obtain a porous film, drying, dipping the porous film into 1M lithium hexafluorophosphate carbonate electrolyte solution, adsorbing and gelling to obtain the porous gel polymer electrolyte film, wherein the 1M lithium hexafluorophosphate carbonate electrolyte solution is prepared from dimethyl carbonate, diethyl carbonate and ethylene carbonate according to mass ratio: diethyl carbonate: ethylene carbonate ═ 1: 1: 1 are mixed.

In view of the above disadvantages of complicated pore-forming techniques or pore-forming schemes and many control conditions, researchers desire to develop schemes that do not require pore-forming or special pore-forming techniques.

CN105552277A reports a PVDF coated lithium ion battery diaphragm, which is composed of a basal membrane and a coating coated on one side or two sides of the basal membrane, wherein the coating is obtained by coating and drying slurry, the thickness of the coating is 0.1-0.5 μm, and the coating contains regularly arranged PVDF spherical particles. The slurry is low-solid-content aqueous PVDF slurry, the slurry contains 1-2.5% of base material according to weight percentage, and the balance is deionized water, and the base material comprises the following substances in parts by mass: 65-75 parts of PVDF resin powder, 3-7 parts of aqueous binder, 1.5-3 parts of surfactant and 8-15 parts of dispersing agent, wherein the dispersing agent is triethyl phosphate. However, the method necessarily adopts triethyl phosphate as a dispersing agent, does not completely abandon the use of an oil phase solvent, and also brings certain dangerousness, and the long drying time of the coating causes low productivity and low efficiency of industrialization.

CN105576175A discloses a preparation method of a polymer coating composite diaphragm, which comprises the step of coating one or two surfaces of a base film with aqueous slurry to form a polymer coating, wherein the aqueous slurry takes deionized water as a solvent and is formed by dispersing polymer particles, a surfactant and an aqueous binder in the deionized water, the aqueous slurry also contains a suspending agent, the dosage of the suspending agent is 3-25% of the total weight of the aqueous slurry, and the suspending agent is at least one of potassium chloride, sodium chloride, dichloroacetic acid, ethylene dibromide, 3-bromopyridine, 4, 5-dichloro 1, 3-dioxolane-2-one, dichloroethane, ethylene dichloride and 1, 3-butanediol sulfite. However, the battery diaphragm prepared by the method has reduced air permeability, so that the internal resistance of the lithium ion battery is increased, and the performance of the lithium ion battery is not improved.

Disclosure of Invention

Aiming at the defects that the existing polymer coating battery diaphragm still needs to use an oil-soluble organic solvent on one hand, and the prepared battery diaphragm has insufficient air permeability to cause the increase of the internal resistance of a lithium ion battery on the other hand, the inventor of the invention carries out intensive research.

The existing preparation process of the polymer coating battery diaphragm takes the improvement of the dispersion degree of polymer particles in polymer slurry for coating as a starting point, and takes corresponding measures to inhibit the polymer particles from agglomerating in aqueous dispersion. However, the inventors of the present invention found in the course of their studies that: the polymer particles and at least one of polyoxyethylene ether, a fluorine-containing organic compound, a binder and a cellulose compound and/or an acrylate polymer are dispersed in water to form a dispersion, the polymer particles generate a certain degree of agglomeration in the water, but the dispersion is coated on the surface of a porous substrate and dried to form a polymer diaphragm with a polymer particle layer attached to the surface, so that the polymer diaphragm not only has high air permeability, but also has high bonding strength to a positive electrode and a negative electrode when used for preparing a lithium ion battery, so that the positive electrode, the negative electrode and the diaphragm are ensured to be always in close contact in the circulating process of the battery, the capacity loss is reduced, the cycle performance of the battery is improved, and the service life of the battery is prolonged. The present invention has been completed based on the above findings.

According to a first aspect of the present invention, there is provided a polymer separator comprising a porous substrate and a polymer particle layer attached to at least one surface of the porous substrate, wherein the polymer particle layer comprises polymer particles, a binder, a polyoxyethylene ether, a fluorine-containing organic compound, and an additive, the additive is one or more selected from a cellulose-based compound and/or an acrylate-based polymer, and the polymer particles are polyvinylidene fluoride particles and/or vinylidene fluoride-hexafluoropropylene copolymer particles.

According to a second aspect of the present invention, there is provided a composition comprising polymer particles, a binder, polyoxyethylene ether, a fluorine-containing organic compound, and an additive, wherein the additive is one or more selected from a cellulose-based compound and/or an acrylate-based polymer, the polymer particles are polyvinylidene fluoride particles and/or vinylidene fluoride-hexafluoropropylene copolymer particles, and the content of the binder is 0.5 to 25 parts by weight relative to 100 parts by weight of the polymer particles; the content of the polyoxyethylene ether is 0.1-5 parts by weight; the content of the fluorine-containing organic compound is 0.1 to 10 parts by weight; the content of the additive is 0.1-10 parts by weight.

According to a third aspect of the invention, there is provided a dispersion formed by dispersing the components of the composition of the second aspect of the invention in water.

According to a fourth aspect of the present invention, there is provided a method of preparing a polymer separator, the method comprising:

s1, applying the dispersion of the third aspect of the present invention on at least one surface of a porous substrate to obtain a porous substrate with a coating;

and S2, drying the coating to form a polymer particle layer.

According to a fifth aspect of the present invention, there is provided a polymer separator produced by the method according to the fourth aspect of the present invention.

According to a sixth aspect of the present invention, the present invention provides a lithium ion battery, which includes a positive electrode plate, a negative electrode plate and a polymer diaphragm, wherein the polymer diaphragm is the polymer diaphragm according to the first aspect or the fifth aspect of the present invention.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a lithium ion battery, the method comprising:

s1, preparing the polymer diaphragm by adopting the method of the fourth aspect of the invention;

and S2, arranging the polymer diaphragm between the positive pole piece and the negative pole piece to form a battery pole core, and then packaging.

The polymer diaphragm disclosed by the invention has high porosity, and the polymer diaphragm can still keep porous characteristics after being prepared into a lithium ion battery through a pressurization formation step, so that normal transmission and migration of lithium ions in the working process of the battery can be ensured; in addition, the polymer diaphragm has higher bonding strength with the positive electrode and the negative electrode, and can tightly bond the positive and negative pole pieces together. Therefore, the lithium ion battery prepared by the polymer diaphragm has good rate discharge performance, normal-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance.

According to the preparation method of the dispersion and the polymer diaphragm, the polymer particles, the polyoxyethylene ether, the fluorine-containing organic compound, the cellulose compound and the binder are dispersed in water to form the dispersion, the polymer particles form slight agglomeration in the dispersion, and when the dispersion is coated on the surface of the porous base material, the polymer coating is formed by taking the agglomerated particles in the dispersion as units, so that the prepared polymer diaphragm has high porosity.

According to the dispersion and the method for preparing the polymer separator of the present invention, a stable dispersion can be obtained without using an oil-soluble organic solvent such as triethyl phosphate, etc., and without using a suspending agent such as potassium chloride, sodium chloride, dichloroacetic acid, ethylene dibromide, 3-bromopyridine, 4, 5-dichloro-1, 3-dioxolan-2-one, dichloroethane, dichloroethylene, 1, 3-butanediol sulfite.

Drawings

Fig. 1A and 1B are surface SEM topography pictures of the polymer separator prepared in example 1, fig. 1A is a photograph magnified 500 times, and fig. 1B is a photograph magnified 5000 times.

Fig. 2A and 2B are surface SEM topography pictures of the polymer separator prepared in comparative example 3, fig. 2A is a photograph magnified 500 times, and fig. 2B is a photograph magnified 5000 times.

FIG. 3 is a graph showing a particle size distribution of solid particles in the dispersion prepared in example 3, measured by a Zeta potentiometer.

Fig. 4 is a graph showing peel strength test curves of the positive electrode and the polymer separator of the lithium ion batteries prepared in example 1 and comparative example 1.

Fig. 5 is a graph showing a peel strength test of the negative electrode and the polymer separator of the lithium ion batteries prepared in example 1 and comparative example 1.

Fig. 6 is an SEM topography picture (magnification: 10000 times) of the surface of the polymer separator after the lithium ion battery prepared in example 1 is pressurized.

Fig. 7 is an SEM topography picture (magnification: 10000 times) of the surface of the polymer separator after the lithium ion battery prepared in comparative example 3 is pressurized.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

According to a first aspect of the present invention, there is provided a polymer separator comprising a porous substrate and a polymer particle layer attached to at least one surface of the porous substrate, wherein the polymer particle layer comprises polymer particles, a binder, a polyoxyethylene ether, a fluorine-containing organic compound, and an additive, and the additive is one or more selected from a cellulose-based compound and/or an acrylate-based polymer.

The polymer particles are polyvinylidene fluoride particles and/or vinylidene fluoride-hexafluoropropylene copolymer particles. In the vinylidene fluoride-hexafluoropropylene copolymer, the content of the structural unit formed from vinylidene fluoride and the content of the structural unit formed from hexafluoropropylene may be conventionally selected. In general, the content of the structural unit formed from hexafluoropropylene may be 1 to 30% by weight, preferably 1 to 20% by weight, based on the total amount of the vinylidene fluoride-hexafluoropropylene copolymer.

From the viewpoint of further improving the performance of the lithium ion battery prepared by the polymer separator and prolonging the service life of the battery, the melting point of the polymer particles is preferably 110-170 ℃, and more preferably 130-160 ℃. The melting point of the polymer particles is determined using Differential Scanning Calorimetry (DSC).

The binder may be a substance sufficient to bind the polymer particles together into a unitary structure and to bond the polymer particles to the porous matrix. In a preferred embodiment, the binder is an oil soluble binder. The lithium ion battery prepared using the polymer separator according to the preferred embodiment shows more excellent performance, which may be due to: the oil-soluble binder readily coats the surface of the polymer particles, thereby better binding the polymer particles together into a unitary structure and bonding the polymer particles to the porous substrate. According to this preferred embodiment, the binder is more preferably one or two or more of a polyacrylate type binder, a polyacrylonitrile type binder, an acrylate-acrylonitrile copolymer type binder, and a polyamide type binder. The polyacrylate type binder may be a polymer formed by addition polymerization of one or more kinds of acrylates (also referred to as a pure acrylic polymer), or may be a polymer formed by addition polymerization of one or more kinds of acrylates with styrene (also referred to as a styrene-acrylic polymer). When the binder is a pure acrylic polymer and a styrene-acrylic polymer, the content of the styrene-acrylic polymer may be 30 to 70% by weight, preferably 40 to 60% by weight, based on the total amount of the binder.

According to the polymer separator of the present invention, the amount of the binder may be selected according to the amount of the polymer particles. Generally, the binder may be contained in an amount of 0.5 to 25 parts by weight, preferably 2 to 20 parts by weight, and more preferably 5 to 18 parts by weight, relative to 100 parts by weight of the polymer particles.

According to the polymer separator of the present invention, the number average molecular weight of the polyoxyethylene ether is preferably 200-. In the present invention, the number average molecular weight of the polyoxyethylene ether is measured by gel permeation chromatography, wherein polystyrene is used as a standard.

The polyoxyethylene ether is preferably one or more of polyoxyethylene saturated alcohol ether, polyoxyethylene unsaturated alcohol ether and polyoxyethylene aryl ether, and the saturated alcohol is preferably C₁-C₂₀More preferably C₈-C₁₆The fatty alcohol of (1). The unsaturated alcohol is preferably C₂-C₂₀Unsaturated alcohol, more preferably C₁₀-C₂₀The unsaturated alcohol is preferably a compound containingAn alcohol having an ethylenic bond. The aryl group is preferably an alkyl-substituted aryl group, more preferably C₇-C₂₀Alkyl-substituted aryl of (1). Preferred examples of the polyoxyethylene ether include, but are not limited to: one or more of polyoxyethylene-octyl phenyl ether, polyoxyethylene-nonyl phenyl ether, polyoxyethylene ether-dodecanol and polyoxyethylene ether-octadeca-9-enol.

In a more preferred embodiment, the polyoxyethylene ether is a polyoxyethylene aryl ether. According to this preferred embodiment, both end groups of the polyoxyethylene ether may be aryl groups. Preferably, one side end group of the polyoxyethylene ether is aryl, and the other side end group is hydroxyl. According to this more preferred embodiment, the aryl group is more preferably C₅-C₁₂Alkyl-substituted phenyl of (a). The polyoxyethylene ether according to a more preferred embodiment may be, for example, polyoxyethylene-octylphenyl ether and/or polyoxyethylene-nonylphenyl ether.

According to the polymer separator of the present invention, the polyoxyethylene ether may be contained in an amount of 0.1 to 5 parts by weight, preferably 0.2 to 4 parts by weight, and more preferably 0.5 to 3 parts by weight, relative to 100 parts by weight of the polymer particles.

According to the polymer separator of the present invention, the fluorine-containing organic compound may be C₂-C₁₈Preferably C₄-C₁₂More preferably C₆-C₁₀The fluorine-containing organic compound of (1). Preferably, the fluorine-containing compound is a perfluoroorganic compound.

In a preferred embodiment, the fluorine-containing organic compound is a fluorine-containing organic acid salt, such as one or two or more of a fluorine-containing carboxylate, a fluorine-containing sulfonate, a fluorine-containing phosphate, and a fluorine-containing sulfate. According to this preferred embodiment, the fluorine-containing organic compound is a perfluoroorganic acid salt. According to the preferred embodiment, specific examples of the fluorine-containing organic compound may include, but are not limited to: one or more of sodium perfluorooctanoate, sodium perfluorooctane sulfonate, ammonium perfluorooctanoate and potassium perfluorohexylsulfonate.

According to the polymer separator of the present invention, the content of the fluorine-containing organic compound may be 0.1 to 10 parts by weight, preferably 1 to 8 parts by weight, and more preferably 2 to 7 parts by weight, relative to 100 parts by weight of the polymer particles.

According to the polymer separator of the present invention, the cellulose-based compound is preferably a cellulose ether and/or a cellulose salt. The cellulose salt is preferably an alkali metal salt of cellulose, such as the sodium or potassium salt. Specific examples of the cellulose-based compound may include, but are not limited to, one or more of methyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose, and hydroxyethyl cellulose.

According to the polymer separator of the present invention, the acrylic acid salt-based polymer may be an alkali metal salt and/or an ammonium salt of an acrylic acid polymer, preferably an alkali metal salt such as a sodium salt or a potassium salt. The number average molecular weight of the acrylate-based polymer may be 200000-2000000. The acrylate polymer may be a polyacrylate polymer.

The polymer separator according to the present invention may contain the additive in an amount of 0.1 to 10 parts by weight, preferably 1 to 8 parts by weight, and more preferably 2 to 6 parts by weight, relative to 100 parts by weight of the polymer particles.

The polymer separator according to the present invention preferably further contains polyvinyl alcohol. The number average molecular weight of the polyvinyl alcohol may be 2000-. The content of the polyvinyl alcohol may be 0.1 to 5 parts by weight, preferably 1 to 4 parts by weight, and more preferably 2 to 3 parts by weight, relative to 100 parts by weight of the polymer particles.

According to the polymer separator of the present invention, the thickness of the polymer particle layer may vary within a wide range, thereby satisfying the requirements of different applications. Generally, according to the polymer separator of the present invention, the thickness of the polymer particle layer may be 0.1 to 5 μm, preferably 0.3 to 3 μm, more preferably 0.4 to 2 μm, and further preferably 0.5 to 1.5 μm. In the present invention, the thickness of the polymer particle layer is measured by a film thickness gauge.

According to the polymer diaphragm of the invention, in the polymer particle layer, the primary particle size of the polymer particles is generally 50-500nm, preferably 100-400nm, and more preferably 200-300 nm. In the present invention, the primary particle size of the polymer particles refers to the average primary particle size, and is determined by a Scanning Electron Microscope (SEM) method, and the specific test method is as follows: the particle diameters of all primary particles appearing in the eyepiece region were measured at a magnification of 5000 times, and the average value was calculated as the primary particle diameter.

According to the polymer separator of the present invention, the porous substrate may contain a porous polymer layer and optionally a ceramic layer.

The porous polymer layer may be used to swell the liquid electrolyte and transport lithium ions, and may be a porous material commonly used in the field of polymer separators, and is preferably a porous polyolefin layer, such as one or more of a porous Polyethylene (PE) layer, a Porous Polypropylene (PP) layer, a porous polyethylene and polypropylene composite layer. The porous polyethylene and porous polypropylene composite layer can be a PE/PP/PE composite substrate layer. The thickness of the porous polymer layer may be 1 to 50 μm, preferably 3 to 20 μm, more preferably 5 to 15 μm, and further preferably 6 to 12 μm.

The ceramic layer is used for improving the thermal stability, the mechanical property and the electrolyte adsorption capacity of the porous polymer layer. The ceramic particles in the ceramic layer may be made of Al₂O₃、SiO₂、SnO₂、ZrO₂、TiO₂、SiC、Si₃N₄、CaO、MgO、ZnO、BaTiO₃、LiAlO₂And BaSO₄One or more than two of the ceramic particles are formed by sintering. Generally, the thickness of the ceramic layer may be 1 to 5 μm, preferably 1.5 to 3 μm.

The polymer membrane has good air permeability. Generally, the gurley number of the polymer membrane according to the present invention may be 100-300s/100mL, preferably 150-280s/100mL, and more preferably 180-260s/100 mL.

The polymer membrane according to the present invention has good resistance to thermal shrinkage. Generally, the polymer separator according to the present invention has a longitudinal shrinkage of not more than 1% at 120 ℃ and a transverse shrinkage of not more than 0.5% at 120 ℃.

The polymer separator according to the invention has a high porosity, which may generally be between 30 and 60%, preferably between 35 and 60%. The polymer diaphragm prepared by the invention can still maintain the porous structure after being formed into a lithium ion battery. The porosity of the polymer separator according to the present invention after formation may be 25 to 55%, preferably 30 to 50%, more preferably 35 to 45%.

According to a second aspect of the present invention, there is provided a composition comprising polymer particles, a binder, a polyoxyethylene ether, a fluorine-containing organic compound, and an additive, wherein the additive is one or more selected from a cellulose-based compound and/or an acrylate-based polymer.

The average particle diameter of the polymer particles may be 50 to 500nm, preferably 100-400nm, more preferably 200-300 nm. In the present invention, the average particle size of the polymer particles is determined by a laser particle sizer and is a volume average particle size.

From the viewpoint of further improving the performance of the lithium ion battery prepared by the polymer separator and prolonging the service life of the battery, the melting point of the polymer particles is preferably 110-170 ℃, and more preferably 130-160 ℃.

The binder may be a substance sufficient to bind the polymer particles together into a unitary structure and to bond the polymer particles to the porous matrix. In a preferred embodiment, the binder is an oil soluble binder. The lithium ion battery prepared using the polymer separator according to the preferred embodiment shows more excellent performance, which may be due to: the oil-soluble binder readily coats the surface of the polymer particles, thereby better binding the polymer particles together into a unitary structure and bonding the polymer particles to the porous substrate. According to this preferred embodiment, the binder is more preferably one or two or more of a polyacrylate type binder, a polyacrylonitrile type binder, an acrylate-acrylonitrile copolymer type binder, and a polyamide type binder. The polyacrylate type binder may be a polymer formed by addition polymerization of one or more kinds of acrylates (also referred to as a pure acrylic polymer), or may be a polymer formed by addition polymerization of one or more kinds of acrylates with styrene (also referred to as a styrene-acrylic polymer). When the binder is a pure acrylic polymer and a styrene-acrylic polymer, the content of the styrene-acrylic polymer may be 30 to 70% by weight, preferably 40 to 60% by weight, based on the total amount of the binder. The binder may be provided in a variety of forms as is common, and in a preferred embodiment, the binder is provided in the form of an emulsion. When the binder is provided in the form of an emulsion, the solids content of the emulsion may be from 30 to 70% by weight, preferably from 40 to 60% by weight.

The amount of binder used may be selected according to the amount of polymer particles in the composition according to the invention. Generally, the binder may be contained in an amount of 0.5 to 25 parts by weight, preferably 2 to 20 parts by weight, and more preferably 5 to 18 parts by weight, relative to 100 parts by weight of the polymer particles.

According to the composition of the invention, the polyoxyethylene ether is coated on the surface of the polymer particles and is used for promoting the wetting of the polymer particles and water. The number average molecular weight of the polyoxyethylene ether is preferably 200-.

The polyoxyethylene ether may be one that is sufficient to increase the wettability of the surface of the polymer particles, thereby promoting wetting of the polymer particles with water. In a preferred embodiment, the polyoxyethylene ether is preferably one or more of a polyoxyethylene saturated alcohol ether, a polyoxyethylene unsaturated alcohol ether, and a polyoxyethylene aryl ether. In this preferred embodiment, the saturated alcohol is preferably C₁-C₂₀More preferably fatty alcohol of (2)Is C₈-C₁₆The fatty alcohol of (1). In this preferred embodiment, the unsaturated alcohol is preferably C₂-C₂₀Unsaturated alcohol, more preferably C₁₀-C₂₀Unsaturated alcohols, preferably alcohols containing ethylenic bonds. In this preferred embodiment, the aryl group is preferably an aryl group substituted with an alkyl group, more preferably C₇-C₂₀Alkyl-substituted aryl of (1).

Preferred examples of the polyoxyethylene ether include, but are not limited to: one or more of polyoxyethylene-octyl phenyl ether, polyoxyethylene-nonyl phenyl ether, polyoxyethylene ether-dodecanol and polyoxyethylene ether-octadeca-9-enol.

In a more preferred embodiment, the polyoxyethylene ether is a polyoxyethylene aryl ether. According to this preferred embodiment, both end groups of the polyoxyethylene ether may be aryl groups. Preferably, one side end group of the polyoxyethylene ether is aryl, and the other side end group is hydroxyl. According to this more preferred embodiment, the aryl group is more preferably substituted by C₅-C₁₂Alkyl-substituted phenyl of (a). The polyoxyethylene ether according to a more preferred embodiment may be, for example, polyoxyethylene-octylphenyl ether and/or polyoxyethylene-nonylphenyl ether, such as triton.

According to the composition of the present invention, the content of the polyoxyethylene ether may be selected according to the amount of the polymer particles. Generally, the polyoxyethylene ether may be contained in an amount of 0.1 to 5 parts by weight, preferably 0.2 to 4 parts by weight, and more preferably 0.5 to 3 parts by weight, relative to 100 parts by weight of the polymer particles.

According to the composition of the invention, the fluorine-containing organic compound acts as an emulsifier and may be C₂-C₁₈Preferably C₄-C₁₂More preferably C₆-C₁₀The fluorine-containing organic compound of (1). Preferably, the fluorine-containing compound is a perfluoroorganic compound.

The composition according to the present invention may contain the fluorine-containing organic compound in an amount of 0.1 to 10 parts by weight, preferably 1 to 8 parts by weight, more preferably 2 to 7 parts by weight, relative to 100 parts by weight of the polymer particles.

According to the composition of the present invention, the additive acts to inhibit settling of the polymer particles when the components of the composition are dispersed in water.

The cellulose-based compound is preferably a cellulose ether and/or a cellulose salt. The cellulose salt is preferably an alkali metal salt of cellulose, such as the sodium or potassium salt. Specific examples of the cellulose-based compound may include, but are not limited to, one or more of methyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose, and hydroxyethyl cellulose. The acrylate-based polymer may be an alkali metal salt and/or ammonium salt of an acrylic polymer, preferably an alkali metal salt such as a sodium or potassium salt. The number average molecular weight of the acrylate-based polymer may be 200000-1000000. The acrylate polymer may be a polyacrylate polymer, such as an LD thickener.

The composition according to the invention may contain the additive in an amount of 0.1 to 10 parts by weight, preferably 1 to 8 parts by weight, more preferably 2 to 6 parts by weight, relative to 100 parts by weight of the polymer particles.

The compositions according to the invention preferably contain polyvinyl alcohol. The polyvinyl alcohol serves to promote the dispersibility of the polymer particles in water when the components of the composition are dispersed in water. The number average molecular weight of the polyvinyl alcohol is preferably 2000-.

The content of the polyvinyl alcohol may be 0.1 to 5 parts by weight, preferably 1 to 4 parts by weight, and more preferably 2 to 3 parts by weight, relative to 100 parts by weight of the polymer particles.

The components of the composition according to the second aspect of the present invention may be dispersed in water by conventional means to form a dispersion. In one embodiment, the components of the composition according to the second aspect of the invention may be mixed with water and the mixture sonicated to obtain a dispersion. In the ultrasonic treatment, the frequency of the ultrasonic wave may be 15 to 60kHz, preferably 20 to 50 kHz. The duration of the ultrasonic treatment may be 0.1 to 1 hour, preferably 0.2 to 0.5 hour. In this embodiment, the polymer particles are preferably dispersed in water and then the remaining components are added and mixed before being sonicated.

According to the dispersion of the present invention, the average particle diameter of the solid particles in the dispersion may be 200-5000nm, preferably 300-3000nm, more preferably 500-2500nm, further preferably 800-2000nm, and still further preferably 900-1400 nm. In the present invention, the average particle diameter of solid particles in the dispersion is measured by a Zeta potential analyzer. The ratio of the average particle size of the polymer particles in the dispersion according to the third aspect of the invention to the average particle size of the polymer particles in the composition according to the second aspect of the invention is generally from 2 to 10, preferably from 3 to 7, more preferably from 3 to 5, indicating that the polymer particles in the dispersion exhibit slight agglomeration.

The dispersions according to the invention show a higher stability despite the slight agglomeration of the polymer particles in the dispersion. According to the dispersion of the present invention, the thickness of a clear layer measured after the dispersion is left to stand for 2 hours at 35 ℃ under 1 atm is not more than 8mm, preferably not more than 5mm, more preferably 1 to 3mm, by placing the dispersion in a round-bottom type sample cell of 2.5cm (diameter) × 5.5cm (height). In the invention, the thickness of the clarification layer is measured by adopting an all-around near-infrared stability analyzer.

and S2, drying the coating to form a polymer particle layer.

According to the method of the fourth aspect of the invention, the porous substrate may contain a porous polymer layer and optionally a ceramic layer.

The porous polymer layer may be a porous material commonly used in the field of polymer separators, and is preferably a porous polyolefin layer, such as one or more of a porous Polyethylene (PE) layer, a Porous Polypropylene (PP) layer, a porous polyethylene and polypropylene composite layer. The porous polyethylene and polypropylene composite layer can be a PE/PP/PE composite substrate layer. The thickness of the porous polymer layer may be 1 to 50 μm, preferably 3 to 20 μm, more preferably 5 to 15 μm, and further preferably 6 to 12 μm.

The ceramic particles in the ceramic layer may be made of Al₂O₃、SiO₂、SnO₂、ZrO₂、TiO₂、SiC、Si₃N₄、CaO、MgO、ZnO、BaTiO₃、LiAlO₂And BaSO₄One or more than two of the ceramic particles are formed by sintering. Generally, the thickness of the ceramic layer may be 1 to 5 μm, preferably 1.5 to 3 μm.

In step S1, the dispersion may be applied to at least one surface of the porous substrate using conventional methods, such as: one or a combination of two or more of spray coating, extrusion coating, gravure coating, dip coating, screen printing, and transfer coating.

In step S1, the coating amount of the dispersion on the surface of the porous substrate may be selected according to the thickness of the polymer particle layer to be formed on the surface of the porous substrate, so that the thickness of the polymer particle layer can meet the requirement. Generally, the dispersion is applied to the surface of the porous substrate in such an amount that the thickness of the finally formed polymer particle layer is 0.1 to 5 μm, preferably 0.3 to 3 μm, more preferably 0.4 to 2 μm, and further preferably 0.5 to 1.5 μm.

According to the method of the fourth aspect of the present invention, in step S2, the drying is performed so that the coating layer is solidified to form the polymer particle layer. In particular, the drying may be carried out at a temperature of 30 to 70 ℃, preferably 40 to 60 ℃. The duration of the drying may be selected according to the temperature at which the drying is carried out. In general, the duration of the drying can be from 0.2 to 5 hours, preferably from 2 to 4 hours.

The polymer membrane prepared by the method of the fourth aspect of the present invention has good air permeability. Generally, the gurley number of the polymer membrane according to the present invention may be 100-300s/100mL, preferably 150-280s/100mL, and more preferably 180-260s/100 mL.

The polymer membrane produced by the method according to the fourth aspect of the present invention has good resistance to thermal shrinkage. Generally, the polymer separator prepared by the method according to the fourth aspect of the present invention has a longitudinal shrinkage of not more than 1% at 120 ℃ and a transverse shrinkage of not more than 0.5% at 120 ℃.

The polymer separator prepared by the method of the fourth aspect of the present invention has a high porosity, which may be generally 30 to 60%, preferably 35 to 60%. The porous structure of the lithium ion battery made of the polymer separator prepared by the method of the fourth aspect of the invention is still maintained after formation. The porosity of the polymer separator according to the present invention after formation may be 25 to 55%, preferably 30 to 50%, more preferably 35 to 45%.

According to a sixth aspect of the present invention, the present invention provides a lithium ion battery, which includes a positive electrode plate, a negative electrode plate and a polymer diaphragm, wherein the polymer diaphragm is the polymer diaphragm according to the fourth or fifth aspect of the present invention.

The positive pole piece is prepared by mixing a positive pole material for the lithium ion battery, a conductive agent and a binder into slurry and coating the slurry on an aluminum foil. The positive electrode material used includes any positive electrode material that can be used in lithium ion batteries, for example, lithium cobalt oxide (LiCoO)₂) Lithium nickel oxide (LiNiO)₂) Lithium manganese oxide (LiMn)₂O₄) And lithium iron phosphate (LiFePO)₄) One or more than two of them. The negative pole piece is prepared by mixing a negative pole material for the lithium ion battery, a conductive agent and a binder into slurry and coating the slurry on a copper foil. The negative electrode material used includes any negative electrode material usable for lithium ion batteries, for example, one or two or more of graphite, soft carbon, and hard carbon.

The lithium ion battery of the present invention may or may not contain an electrolyte solution. The electrolyte is well known to those skilled in the art and contains a lithium salt and an organic solvent. The lithium salt may be a dissociable lithium salt, and may be, for example, selected from lithium hexafluorophosphate (LiPF)₆) Lithium perchlorate (LiClO)₄) And lithium tetrafluoroborate (LiBF)₄) One or more than two of them. The organic solvent may be one or more selected from Ethylene Carbonate (EC), Propylene Carbonate (PC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) and Vinylene Carbonate (VC). Preferably, the concentration of the lithium salt in the electrolyte may be 0.8 to 1.5 mol/L.

Step S2 can be performed by a conventional method in the technical field of lithium ion battery preparation, and the present invention is not particularly limited thereto. In step S2, the battery pole core may be filled with the electrolyte, or may be directly packaged without being filled with the electrolyte.

The present invention will be described in detail with reference to examples, but the scope of the present invention is not limited thereto.

In the following examples and comparative examples, the number average molecular weight was measured on a gel permeation chromatograph; monodispersed polystyrene was used as a standard.

In the following examples and comparative examples, the volume average particle diameter of polymer particles was measured using a laser particle sizer.

Examples 1-10 serve to illustrate the invention.

Example 1

(1) Polyvinylidene fluoride-hexafluoropropylene copolymer particles are dispersed in water at ambient temperature (25 ℃) with stirring, and then triton, polyvinyl alcohol, sodium perfluorooctanoate, sodium carboxymethylcellulose and polyacrylic acid as a binder are added and stirred uniformly. The resulting mixture was subjected to sonication at a frequency of 20kHz for a time of 0.4 hours to give a dispersion according to the invention. The contents of the components, the average particle diameter of the solid particles in the prepared dispersion, and the stability of the prepared dispersion (thickness of the clear layer after standing for 2 hours) are shown in Table 1.

(2) And (2) coating the dispersion prepared in the step (1) on two sides of the porous substrate by a gravure roll transfer coating method to obtain the porous substrate with the coating. And drying the porous base material with the coating in a forced air drying box to obtain the polymer diaphragm with the polymer particle layers on both sides of the porous base material. Among them, the kind of the porous base material used, the drying conditions, and the thickness of the polymer particle layer in the prepared polymer separator are listed in table 2.

(3) In a drying room, LiCoO is added₂Preparing the SL454187 LiCoO model by winding the positive plate, the graphite negative plate and the polymer diaphragm prepared in the step (2)₂Filling electrolyte into the graphite soft-package polymer lithium ion battery pole core, and then packaging to obtain the lithium ion battery; wherein, the original ceramic surface faces the anode, the electrolyte in the electrolyte is lithium hexafluorophosphate, the concentration of the lithium hexafluorophosphate is 1mol/L, and the organic solvent is EC, EMC and DEC according to the weight ratio of 1: 1: 1 mixing the obtained mixed solution.

Examples 2 to 10

A dispersion, a polymer separator, and a lithium ion battery were prepared in the same manner as in example 1, except that the contents of the components in step (1), the average particle diameter of solid particles in the prepared dispersion were listed in table 1, and the kind of porous base material used in step (2), the ultrasonic conditions, and the drying conditions were listed in table 2. FIG. 3 shows a spectrum of the particle size distribution of solid particles in the dispersion prepared in example 3, measured using a Zeta potentiometer.

Comparative example 1

(1) 1040, 1005 and S601 were mixed at a solids content of 9: 1: 10, and adding a proper amount of water to make the total solid content be 1 weight percent. After being stirred uniformly, mixed slurry is formed.

(2) A polymer separator was prepared in the same manner as in step (1) of example 1, except that the mixed slurry prepared in step (1) of comparative example 1 was applied to both side surfaces of the porous substrate.

(3) A polymer separator was prepared in the same manner as in step (1) of example 1, except that the polymer separator prepared in step (2) of comparative example 1 was used.

Comparative example 2

(2) A polymer separator was prepared in the same manner as in example 3, except that the mixed slurry prepared in step (1) of comparative example 2 was applied to both side surfaces of the porous substrate.

(3) A polymer separator was prepared in the same manner as in step (1) of example 3, except that the polymer separator prepared in step (2) of comparative example 2 was used.

Comparative example 3

(1) Polyvinylidene fluoride-hexafluoropropylene copolymer particles (Co.) were stirred at ambient temperature (25 deg.C.) with stirring

Example 1) was dispersed in water, and then polyvinyl alcohol (same as example 1), sodium polyacrylate, sodium carboxymethyl cellulose (same as example 1) and polyacrylic acid (same as example 1) as a binder were added and stirred uniformly. The resulting mixture was subjected to ultrasonic treatment at a frequency of 12kHz for 0.3 hour to obtain a dispersion. The contents of the components and the average particle diameter of the solid particles in the prepared dispersion are shown in Table 1.

(2) A polymer separator was prepared in the same manner as in example 1, except that the mixed slurry prepared in step (1) of comparative example 3 was applied to both side surfaces of the porous substrate.

(3) A polymer separator was prepared in the same manner as in step (1) of example 1, except that the polymer separator prepared in step (2) of comparative example 3 was used.

Comparative examples 4 to 8

A dispersion, a polymer separator, and a lithium ion battery were prepared in the same manner as in example 1, except that the contents of the components in step (1), and the average particle diameter of solid particles in the prepared dispersion were as listed in table 1.

Comparative example 9

A dispersion, a polymer separator, and a lithium ion battery were prepared in the same manner as in example 1, except that, in the step (1), polyvinylidene fluoride-hexafluoropropylene copolymer particles were dispersed in a mixed liquid of water and triethyl phosphate with stirring at an ambient temperature (25 ℃), and then the remaining components were added and subjected to ultrasonic treatment, wherein the content of triethyl phosphate in the mixed liquid was 0.15% by weight.

Table 1 (content of each component in weight percent based on the total amount of the dispersion)

¹: 2751: commercially available from arkema, is a copolymer of polyvinylidene fluoride and hexafluoropropylene having a hexafluoropropylene content of 10-15 wt%, a melting point of 131 ℃, and a polymer particle volume average particle size of 300 nm.

²: LBG: from Akema as polyvinylidene fluorideAn ethylene-hexafluoropropylene copolymer, wherein the copolymer has a hexafluoropropylene-forming structural unit content of more than 0 and not more than 5 wt%, a melting point of 155 ℃, and a volume average particle diameter of 250 nm.

³: LBG: 2751 the mass ratio is 3: 7.

⁴: purchased from Ashland investment Limited under the designation HB-9.

⁵: from Shanghai Pasteur New materials, Inc.

⁶: 1005: is a pure acrylic emulsion which is purchased from Shanghai Aigao chemical Co., Ltd, has a glass transition temperature of 22 ℃ and a solid content of 50 wt%.

⁷: 1040: is a pure acrylic emulsion which is purchased from Shanghai Aigao chemical Co., Ltd, has a glass transition temperature of 54 ℃ and a solid content of 50 wt%.

⁸: 1005: 1040: the weight ratio of S601 is 9: 1: 10, S601 was purchased from Shanghai-Chemicals, Ltd, and was a styrene-acrylic emulsion having a glass transition temperature of 22 ℃ and a solid content of 50% by weight.

TABLE 2

¹: CCL is high-temperature resistant Al₂O₃Ceramic layer

²: PE thickness + CCL thickness

³: CCL thickness + PE thickness + CCL thickness

Test example

1. And (3) observing the surface appearance:

the microscopic morphology of the polymer separators prepared in examples and comparative examples was observed using a scanning electron microscope (SEM, JEOL, JSM-7600 FE). The scanning electron microscope observation showed that the pores in the polymer particle layer of the polymer separator prepared in example were uniform, the number of secondary particles was small, and most of the polymer particles were present in the form of primary particles.

Fig. 1A and 1B show surface SEM morphology photographs of polymer particle layers of the polymer separator prepared in example 1. As can be seen from fig. 1A and 1B, in the polymer particle layer of the polymer separator prepared in example 1, the pores are uniform, the number of secondary particles is small, and most of the polymer particles exist in the form of primary particles. Fig. 2A and 2B show surface SEM morphology photographs of the polymer separator prepared in comparative example 3, and as shown in fig. 2A and 2B, in the polymer particle layer of the polymer separator prepared in comparative example 3, the particle agglomeration was very severe, and most of the polymer particles agglomerated into a sheet. Comparative examples 3-9 were too severe to reduce the coating areal density due to the agglomeration of solid particles in the dispersion, as shown in table 3.

2. Polymer membrane gas permeability (Gurley value) and apparent porosity test

The test was carried out using an air permeability apparatus of type Gurley 4110N. The time for 100mL of air to pass through a 1.0 square inch area of a polymeric septum at 1 standard atmosphere was tested. The results of the test for the gas permeability of the polymer separator are shown in table 3. As can be seen from the results of table 3, the polymer separator according to the present invention showed better gas permeability.

3. Polymer membrane heat shrinkage test

Isothermal heat treatment is carried out on the polymer diaphragm (the area is 5mm multiplied by 5mm) for 2h and 1h by utilizing a constant temperature oven at the temperature of 90 ℃ and 120 ℃ respectively, and the temperature resistance of the polymer diaphragm is represented. The experimental results are shown in table 3, and it can be understood from the results of table 3 that the polymer separator according to the present invention has a lower thermal shrinkage rate.

4. Tensile Strength test of Polymer membranes

Measured using a universal mechanical tester according to the method specified in GB/T13022-. The experimental results are shown in table 3, and it can be understood from the results of table 3 that the polymer separator according to the present invention has a high tensile strength.

5. Polymer membrane puncture strength test

The diameter of the steel needle was 1 mm as determined by the method specified in GB/T1004-. The results of the experiment are shown in table 3, and it can be seen from table 3 that the polymer membrane according to the present invention has a high puncture strength.

TABLE 3

6. Polymer membrane porosity test

Cutting the polymer diaphragm into a wafer with the diameter of 17mm, measuring the thickness, weighing the mass, soaking the wafer in n-butyl alcohol for 2h, taking out the wafer, sucking the liquid on the surface of the membrane by using filter paper, and weighing the mass at the moment. The porosity was calculated according to the following formula:

p is the porosity of the porous material,

M₀the mass of the dry film is,

m is the mass after soaking in n-butanol for 2 hours,

r is the radius of the film,

d is the thickness of the film.

For the formed polymer diaphragm, after the polymer diaphragm is stripped from the battery, the polymer diaphragm is dried at 60 ℃ for 24 hours to remove electrolyte and other moisture, and then the porosity of the dried formed diaphragm is measured by adopting the method.

As can be seen from the data of table 4, the polymer separator according to the present invention has a high porosity, and the formed separator also maintains the high porosity.

7. Polymer diaphragm imbibition test

The prepared polymer separator was cut into a 17 mm-diameter wafer, dried at 60 ℃ for 12 hours, weighed, immersed in an electrolyte LB65 (a mixture of lithium hexafluorophosphate as an electrolyte having a concentration of 1mol/L and EC, EMC, and DEC mixed at a weight ratio of 1: 1: 1) for 24 hours, taken out, and the surface of the membrane was blotted with filter paper and weighed to obtain the mass, which was all performed in a glove box filled with argon gas. The liquid absorption rate was calculated according to the following formula:

w is the mass of the dry film;

wi is the mass of the dry film after being soaked in the electrolyte for 24 hours.

As can be seen from the data of table 4, the polymer separator according to the present invention shows improved liquid absorption rate.

8. Polymer membrane ionic conductivity test

The test is carried out by adopting an alternating current impedance method, and the specific operation steps are as follows.

Cutting a polymer diaphragm into a wafer with the diameter of 17mm, drying, overlapping three layers, placing between two Stainless Steel (SS) electrodes, absorbing enough electrolyte (lithium hexafluorophosphate is used as electrolyte, the concentration of the lithium hexafluorophosphate is 1mol/L, organic solvent is mixed liquid obtained by mixing EC, EMC and DEC according to the weight ratio of 1: 1: 1), sealing in a 2016 type button cell, performing an alternating current impedance experiment by adopting an electrochemical workstation (CHI 660C), wherein the frequency range of an alternating current signal is 0.01Hz to 1MHz, the amplitude of a sine wave potential is 5mV, the intersection point of a linear axis and a real axis is the bulk resistance of the polymer diaphragm, and calculating the ionic conductivity of the polymer diaphragm by adopting the following formula:

σ＝L/(A·R)，

wherein L represents the thickness of the gel polymer electrolyte,

a is the contact area of the stainless steel plate and the polymer diaphragm,

r is the bulk resistance of the polymer electrolyte.

The bulk impedance and ionic conductivity of the polymer separator are shown in table 2.

As can be seen from table 4, the polymer separator according to the present invention exhibited excellent ionic conductivity.

TABLE 4

Serial number	Porosity (%)	Porosity of formed separator (%)	Liquid absorption Rate (%)	Conductivity (mS/cm)
					Example 1	54	42	198	1.29
Example 2	57	43	158	1.32
					Example 3	43	39	276	1.17
Example 4	39	35	227	1.12
					Example 5	52	45	220	1.22
Example 6	47	37	287	1.20
					Example 7	37	31	157	1.14
Example 8	42	35	166	1.17
					Example 9	45	37	158	1.18
Example 10	48	38	164	1.21
					Comparative example 1	37	27	108	0.98
Comparative example 2	31	27	149	0.76
					Comparative example 3	32	28	127	0.75
Comparative example 4	37	30	134	0.98
					Comparative example 5	31	25	145	0.46
Comparative example 6	42	29	141	0.57
					Comparative example 7	31	24	124	0.34
Comparative example 8	34	25	118	0.52
					Comparative example 9	35	28	123	0.64

9. Adhesion and peel strength testing of polymer separators to positive and negative electrodes:

the lithium ion batteries obtained in the examples and the comparative examples are dissected under a full-power state after being pressurized and formed (85 ℃, 4h and 1MPa), the peeling mechanical strength of the lithium ion batteries is measured by adopting a universal mechanical testing machine, and the test method of the standard reference GBT 2792-2014 adhesive tape peeling strength is measured. Fig. 4 and 5 show graphs of peel strength tests of the positive and negative electrodes and the polymer separator of the lithium ion batteries prepared in example 1 and comparative example 1, respectively. As shown in fig. 4 and 5, the polymer separator according to the present invention exhibited higher peel strength to the positive electrode and the negative electrode, indicating that the polymer separator according to the present invention had higher adhesion to both the witness and the negative electrode.

Fig. 6 and 7 are surface morphology photographs obtained by observing the surface morphology of the polymer separators obtained by peeling the lithium ion batteries subjected to pressure chemical conversion, prepared in example 1 and comparative example 3, respectively, by SEM. As can be seen from fig. 6 and 7, the polymer separator according to the present invention still maintains a good porous morphology after the pressurization formation step, such that the ionic conductivity is not affected, and the cycle stability of the lithium ion battery is ensured.

10. Testing of Normal and high temperature hardness of Battery

The prepared lithium ion battery was subjected to a hardness test in a half-electric state (SOC: 50%) after being pressurized (85 ℃, 4h, 1MPa), and the results are listed in table 5. As can be seen from the results of table 5, the lithium ion battery prepared from the polymer separator of the present invention showed higher hardness at both normal temperature (25 ℃) and high temperature (60 ℃).

TABLE 5

11. Test of battery rate performance

And (BK 6016) a lithium ion battery performance test cabinet (Guangzhou Lanqi) is adopted to test the rate discharge performance of the polymer lithium ion battery after capacity grading.

The multiplying power discharge test method comprises the following steps: the cell was charged to 4.40V with a constant current and voltage of 0.5C (1C 2830mA), the cutoff current was 0.02C, left for 5min, discharged to 3.0V with 0.2C/0.5C/1C/2C/3C/4C, and the discharge capacity was recorded. Each example and comparative example were subjected to 3 sets of parallel experiments. The results of the rate discharge test are shown in Table 6. The test result shows that: the lithium ion battery according to the present invention shows improved high-rate discharge performance due to the improved conductivity, which can reduce polarization during charge and discharge, and is advantageous for lithium ion migration.

TABLE 6

12. Testing of normal temperature cycle performance of battery

And (BK 6016) a lithium ion battery performance test cabinet (Guangzhou Lanqi) is adopted to test the 25 ℃ circulation performance of the polymer lithium ion battery after capacity grading. The test method comprises the following steps: charging the battery to 4.40V at 1C, and cutting off at 0.1C; after standing for 10min, the mixture was discharged to 3.0V at 1C, and the cycle was repeated, and the charge-discharge cycle performance data are shown in Table 7. The test result shows that: the lithium ion battery according to the present invention shows more excellent cycle performance, which may be due to: lithium ions migrate slowly in the polymer separator prepared in comparative example 1, so that the polarization of the battery of the polymer separator is large during charging and discharging, lithium dendrites are generated in the charging step of each cycle to consume lithium, and the capacity decay is fast; however, the shape of the hollow hole of the polymer diaphragm adopting the invention is still intact, the migration of lithium ions is not influenced, the generated polarization is small, and the cycle performance is greatly improved.

TABLE 7

13. Testing of high temperature cycle performance of battery

And (BK 6016) a lithium ion battery performance test cabinet (Guangzhou Lanqi) is adopted to test the cycle performance of the polymer lithium ion battery after capacity grading at 45 ℃. The test method comprises the following steps: charging the battery to 4.40V at 1C, and cutting off at 0.1C; standing for 10min, and cooling to 3.0V at 1C, and circulating. The charge-discharge cycle performance data are shown in table 8. The test result shows that: the lithium ion battery according to the present invention shows better high temperature cycle performance.

TABLE 8

14. Battery high temperature storage performance test

And (4) carrying out storage performance test on the lithium ion battery at 85 ℃ for 4 h. The test method is as follows:

1) the battery was charged to 4.40V at 0.5C with a (guangzhou langqi, BK6016) li-ion battery performance test cabinet, cut-off at 0.02C; standing for 5min, discharging to 3.0V at 0.2C, and recording the discharge capacity before discharge;

2) the cell was charged to 4.40V at 0.5C, cut off at 0.02C; testing the voltage, the internal resistance and the thickness before standing for 1 h;

3) the battery is placed into an oven at 85 ℃ for storage for 4 h;

4) testing the thickness immediately after storage, and testing the cooling thickness, the post-voltage and the post-internal resistance after placing for 2 hours at normal temperature;

5) discharging the battery to 3.0V at 0.2C, recording the remaining capacity, and calculating the capacity remaining rate (remaining capacity divided by previous discharge capacity);

6) fully charged at 0.5C, left stand for 5min, discharged to 3.0V at 0.2C, the recovered capacity was recorded, and the capacity recovery ratio (recovered capacity divided by previous capacity) was calculated.

The test results are shown in Table 9. As can be seen from Table 9: the lithium ion battery according to the present invention shows improved high temperature storage performance.

TABLE 9

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. A dispersion for forming a polymer coating in a polymer separator, the dispersionIs prepared by dispersing each component of a composition in water, wherein the composition contains polymer particles, a binder, polyoxyethylene ether, a fluorine-containing organic compound and an additive, and the fluorine-containing organic compound is C₂-C₁₈The perfluorinated organic compound of (A) is one or more of fluorine-containing carboxylate, fluorine-containing sulfonate, fluorine-containing phosphate and fluorine-containing sulfate, the binder is an oil-soluble binder, the additive is one or more selected from cellulose compounds and/or acrylate polymers, the number average molecular weight of the acrylate polymers is 200000- & lt 2000000 & gt, the polymer particles are polyvinylidene fluoride particles and/or vinylidene fluoride-hexafluoropropylene copolymer particles, relative to 100 parts by weight of the polymer particles, the content of the binder is 0.5-25 parts by weight, the content of the polyoxyethylene ether is 0.1-5 parts by weight, the content of the fluorine-containing organic compound is 0.1-10 parts by weight, and the content of the additive is 0.1-10 parts by weight;

the ratio of the average particle size of the polymer particles in the dispersion to the average particle size of the polymer particles in the composition is from 3 to 7.

2. The dispersion of claim 1, wherein the ratio of the average particle size of the polymer particles in the dispersion to the average particle size of the polymer particles in the composition is from 3 to 5.

3. The dispersion of claim 1, wherein the composition comprises, relative to 100 parts by weight of the polymer particles, 2 to 20 parts by weight of the binder, 0.2 to 4 parts by weight of the polyoxyethylene ether, 1 to 8 parts by weight of the fluorine-containing organic compound, and 1 to 8 parts by weight of the additive.

4. The dispersion according to claim 3, wherein the composition contains 5 to 18 parts by weight of the binder, 0.5 to 3 parts by weight of the polyoxyethylene ether, 2 to 7 parts by weight of the fluorine-containing organic compound, and 2 to 6 parts by weight of the additive, relative to 100 parts by weight of the polymer particles.

5. The dispersion as claimed in claim 1, wherein the number average molecular weight of the polyoxyethylene ether in the composition is 200-10000.

6. The dispersion as claimed in claim 5, wherein the number average molecular weight of the polyoxyethylene ether in the composition is 200-5000.

7. The dispersion according to any one of claims 1 and 3 to 6, wherein the polyoxyethylene ether in the composition is one or more than two of polyoxyethylene saturated alcohol ether, polyoxyethylene unsaturated alcohol ether and polyoxyethylene aryl ether.

8. The dispersion of claim 7, wherein in the composition, the saturated alcohol is C₁-C₂₀The unsaturated alcohol is C₂-C₂₀Unsaturated alcohol, the aryl group is alkyl substituted aryl group.

9. The dispersion of claim 7, wherein in the composition, the saturated alcohol is C₈-C₁₆The unsaturated alcohol is C₁₀-C₂₀Unsaturated alcohol, the aryl group being C₇-C₂₀Alkyl-substituted aryl of (1).

10. The dispersion according to any one of claims 1 and 3 to 6, wherein in the composition, the polyoxyethylene ether is one or more of polyoxyethylene-octylphenyl ether, polyoxyethylene-nonylphenyl ether, polyoxyethylene ether-dodecanol, and polyoxyethylene ether-octadeca-9-enol.

11. The dispersion of any one of claims 1,3 and 4, wherein in the composition the fluorine-containing organic compound is C₄-C₁₂The fluorine-containing organic compound of (1).

12. The dispersion of claim 11, wherein in said composition said fluorine-containing organic compound is C₆-C₁₀The fluorine-containing organic compound of (1).

13. The dispersion according to any one of claims 1,3 and 4, wherein the fluorine-containing organic compound in the composition is one or more of sodium perfluorooctanoate, sodium perfluorooctane sulfonate, ammonium perfluorooctanoate and potassium perfluorohexyl sulfonate.

14. The dispersion of claim 1, wherein in the composition, the binder is one or more of a polyacrylate-based binder, a polyacrylonitrile-based binder, an acrylate-acrylonitrile copolymer-based binder, and a polyamide-based binder.

15. A dispersion according to any one of claims 1,3 and 4, wherein in said composition said cellulose-based compound is a cellulose ether and/or a cellulose salt;

in the composition, the acrylate polymer is an alkali metal salt and/or an ammonium salt of an acrylic polymer.

16. The dispersion according to any one of claims 1,3 and 4, wherein in the composition, the cellulose-based compound is one or more of methylcellulose, hydroxypropylmethylcellulose, sodium carboxymethylcellulose, and hydroxyethylcellulose;

in the composition, the acrylate polymer is an alkali metal salt of an acrylic polymer.

17. The dispersion of any one of claims 1,3 and 4, wherein the composition further comprises polyvinyl alcohol in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the polymer particles.

18. The dispersion as claimed in claim 17, wherein the number average molecular weight of the polyvinyl alcohol in the composition is 2000-100000.

19. The dispersion as claimed in claim 18, wherein the number average molecular weight of the polyvinyl alcohol in the composition is 3000-50000.

20. The dispersion as claimed in claim 19, wherein the number average molecular weight of the polyvinyl alcohol in the composition is 5000-.

21. The dispersion of claim 17, wherein the polyvinyl alcohol is present in the composition in an amount of 1 to 4 parts by weight per 100 parts by weight of the polymer particles.

22. A dispersion as claimed in claim 21 wherein said polyvinyl alcohol is present in said composition in an amount of from 2 to 3 parts by weight per 100 parts by weight of polymer particles.

23. A dispersion according to any one of claims 1,3 and 4 wherein the average particle size of the polymer particles in the composition is from 50 to 500 nm.

24. The dispersion as claimed in claim 23, wherein the average particle size of the polymer particles in the composition is 100-400 nm.

25. The dispersion as claimed in claim 24, wherein the average particle size of the polymer particles in the composition is 200-300 nm.

26. The dispersion as claimed in claim 1, wherein the dispersion has an average particle diameter of 200-5000 nm.

27. The dispersion as claimed in claim 26, wherein the average particle size of the solid particles in the dispersion is 300-3000 nm.

28. The dispersion as claimed in claim 27, wherein the average particle size of the solid particles in the dispersion is 500-2500 nm.

29. The dispersion as claimed in claim 28, wherein the average particle size of the solid particles in the dispersion is 800-2000 nm.

30. The dispersion as claimed in claim 29, wherein the dispersion has an average particle size of 900-1400 nm.

31. A method of making a polymeric separator, the method comprising:

s1, applying the dispersion of any one of claims 1 to 30 to at least one surface of a porous substrate to obtain a porous substrate having a coating;

and S2, drying the coating to form a polymer particle layer.

32. The production method according to claim 31, wherein the dispersion is applied to the surface of the porous substrate in such an amount that the thickness of the finally-formed polymer particle layer is 0.1 to 5 μm.

33. The production method according to claim 32, wherein the dispersion is applied to the surface of the porous substrate in such an amount that the thickness of the finally-formed polymer particle layer is 0.3 to 3 μm.

34. The production method according to claim 33, wherein the dispersion is applied to the surface of the porous substrate in such an amount that the thickness of the finally-formed polymer particle layer is 0.4 to 2 μm.

35. The production method according to claim 34, wherein the dispersion is applied to the surface of the porous substrate in such an amount that the thickness of the finally-formed polymer particle layer is 0.5 to 1.5 μm.

36. A polymer separator made by the method of any one of claims 31-35.

37. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, and a polymer separator, wherein the polymer separator is the polymer separator of claim 36.

38. A method of making a lithium ion battery, the method comprising:

s1, preparing a polymer separator using the method of any one of claims 31-35;