WO2023005291A1

WO2023005291A1 - Composite separator, manufacturing method therefor, and secondary battery

Info

Publication number: WO2023005291A1
Application number: PCT/CN2022/088827
Authority: WO
Inventors: 马平川; 杜敬然; 甘珊珊; 刘杲珺; 白耀宗
Original assignee: 中材锂膜有限公司
Priority date: 2021-07-30
Filing date: 2022-04-24
Publication date: 2023-02-02

Abstract

Provided in the present disclosure are a composite separator, a manufacturing method therefor, and a secondary battery. The composite separator comprises a base membrane and a coating arranged on at least one surface of the base membrane, the coating comprising inorganic ceramic particles modified by a silane coupling agent, a polyvinylidene fluoride resin, a highly heat resistant polymer, and a binding agent. The composite separator of the present disclosure has superior bonding and heat resistance properties and low moisture content, and it can be ensured that a secondary battery has both a relatively high safety performance and a good electrochemical performance. Additionally, further provided in the present disclosure are a low moisture solvent-type PVDF coated separator and a manufacturing method therefor. The separator comprises a polyolefin substrate microporous membrane and a PVDF wet coated layer formed on one or two surfaces of the substrate. After the low moisture solvent-type PVDF coated separator of the present disclosure was hot pressed for 300 seconds at 80 °C and 1 MPa, a tensile force testing machine was used to evaluate adhesion strength, and the adhesion strength between a coating and an electrode piece of a battery was 5-30 N/m.

Description

Composite diaphragm, preparation method thereof, and secondary battery

Cross References to Related Applications

This disclosure requires that the Chinese patent application with the application number "CN 202110870431.3" titled "a low-moisture solvent-based PVDF coated diaphragm" be submitted to the Chinese Patent Office on July 30, 2021 and submitted to China on September 29, 2021. The priority of the Chinese patent application with the application number "CN 202111149816.7" titled "Composite Separator and Its Preparation Method, Secondary Battery" issued by the Patent Office, the entire contents of which are incorporated in this disclosure by reference.

technical field

The disclosure belongs to the technical field of batteries, and in particular relates to a composite diaphragm, a preparation method thereof, and a secondary battery.

Background technique

The separator is an electrically insulating film with a porous structure, which is an important part of the secondary battery, and is mainly used to separate the positive electrode and the negative electrode to prevent the internal short circuit of the secondary battery. Separators usually have a nanoscale pore structure that enables rapid transport of active ions (such as lithium ions) between positive and negative electrodes.

Traditional separators mainly use polyolefin porous membranes, such as single-layer membranes or multi-layer composite membranes of polyethylene (PE) and polypropylene (PP). However, the polyolefin separator has a lyophobic surface and low surface energy, resulting in poor wettability of the polyolefin separator to the electrolyte, which affects the transmission of active ions and the cycle life of the secondary battery. At the same time, the polyolefin separator has poor liquid absorption and liquid retention, which will also cause high internal resistance of the secondary battery. In addition, the melting point of the polyolefin separator is low, and severe heat shrinkage will occur when the temperature is too high. When the internal heat accumulates during the use of the secondary battery, the polyolefin separator is easily deformed and the positive and negative electrodes are in direct contact, causing secondary battery life. The internal short circuit of the battery may cause safety hazards such as fire or explosion.

Contents of the invention

The present disclosure provides a composite diaphragm, the composite diaphragm includes a base film and a coating provided on at least one surface of the base film, the coating includes inorganic ceramic particles modified by a silane coupling agent, polyylidene fluoride Vinyl resins, high heat resistant polymers and adhesives.

In some embodiments, the coating comprises:

Inorganic ceramic particles modified by silane coupling agent, 40-80 parts,

Polyvinylidene fluoride resin, 0.01 to 50 parts,

High heat-resistant polymer, 0.01-50 parts,

Binder, 0.1 to 15 parts.

In some embodiments, the coating comprises:

Inorganic ceramic particles modified by silane coupling agent, 40-70 parts,

Polyvinylidene fluoride resin, 8-40 parts,

High heat-resistant polymer, 8 to 40 parts,

Binder, 2 to 10 parts.

In some embodiments, the weight ratio of the polyvinylidene fluoride resin to the high heat-resistant polymer is 0.1:99.9˜99.9:0.1.

Optionally, the weight ratio of the polyvinylidene fluoride resin to the high heat-resistant polymer is 1:4˜4:1.

Optionally, the weight ratio of the polyvinylidene fluoride resin to the high heat-resistant polymer is 1:2˜3:2.

In some embodiments, the volume average particle diameter Dv50 of the inorganic ceramic particles modified by the silane coupling agent is 0.2 μm˜1.0 μm.

Optionally, the volume average particle diameter Dv50 of the inorganic ceramic particles modified by the silane coupling agent is 0.3 μm˜0.8 μm.

Optionally, the volume average particle diameter Dv50 of the inorganic ceramic particles modified by the silane coupling agent is 0.4 μm˜0.7 μm.

In some embodiments, the weight ratio of the silane coupling agent to the inorganic ceramic particles is 0.01:99.99˜2:98.

Optionally, the weight ratio of the silane coupling agent to the inorganic ceramic particles is 0.1:99.9˜1:99.

In some embodiments, the inorganic ceramic particles are selected from the group consisting of alumina, boehmite, calcium carbonate, hydrotalcite, montmorillonite, spinel, mullite, titania, silica, zirconia, magnesia, oxide One or more of calcium, beryllium oxide, magnesium hydroxide, boron nitride, silicon nitride, aluminum nitride, titanium nitride, boron carbide, silicon carbide, and zirconium carbide.

In some embodiments, the molecular formula of the silane coupling agent is Y-Si(OX) ₃ , wherein each X independently represents -CH ₃ , -C ₂ H ₅ , -(C=O)CH ₃ , or -( C=O)C ₂ H ₅ , Y represents C1~C10 alkyl, C1~C10 alkoxy, C2~C10 alkenyl, C2~C10 alkoxy, C2~C5 oxetanecycloalkyl, amino, methyl One or a combination of acryloyloxy and acryloyloxy.

Optionally, Y represents a C1-C10 alkyl group or a C1-C10 alkoxy group.

In some embodiments, the silane coupling agent is selected from methyltriethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, n-butyltriethoxysilane, isobutyltriethoxysilane, Ethoxysilane, (3,3-dimethylbutyl)triethoxysilane, n-hexyltriethoxysilane, n-octyltriethoxysilane, isooctyltriethoxysilane, n-decyl Triethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, isopropyltrimethoxysilane, butyltrimethoxysilane, isobutyltrimethoxysilane Silane, tert-butyltrimethoxysilane, n-pentyltrimethoxysilane, trimethoxy(1,1,2-trimethylpropyl)-silane, n-hexyltrimethoxysilane, n-octyltrimethoxy Silane, isooctyltrimethoxysilane, n-decyltrimethoxysilane, (methoxymethyl)triethoxysilane, (methoxymethyl)trimethoxysilane, trimethoxy(3-methoxy propyl)silane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidyl etheroxypropyltrimethoxysilane, γ-(methacryloyloxy)propane One of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane or several.

Optionally, the silane coupling agent is selected from methyltriethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, n-butyltriethoxysilane, isobutyltriethoxy ylsilane, (3,3-dimethylbutyl)triethoxysilane, n-hexyltriethoxysilane, n-octyltriethoxysilane, isooctyltriethoxysilane, n-decyltriethoxysilane, n-decyltriethoxysilane Ethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, isopropyltrimethoxysilane, butyltrimethoxysilane, isobutyltrimethoxysilane, tert-butyltrimethoxysilane, n-pentyltrimethoxysilane, trimethoxy(1,1,2-trimethylpropyl)-silane, n-hexyltrimethoxysilane, n-octyltrimethoxysilane, Isooctyltrimethoxysilane, n-decyltrimethoxysilane, (methoxymethyl)triethoxysilane, (methoxymethyl)trimethoxysilane, trimethoxy(3-methoxypropane One or more of the silanes.

In some embodiments, the polyvinylidene fluoride resin has a weight average molecular weight of 200,000-1.5 million and a melting point of 137°C-158°C.

Optionally, the polyvinylidene fluoride resin has a weight average molecular weight of 600,000-1.5 million and a melting point of 137°C-156°C.

Optionally, the polyvinylidene fluoride resin has a weight average molecular weight of 1 million to 1.5 million and a melting point of 137°C to 152°C.

In some embodiments, the high heat-resistant polymer is selected from one or more of polyimide, polyetherimide, aramid, and sulfone.

In some embodiments, the adhesive is selected from acrylate adhesives.

In some embodiments, the base film is selected from one or more of polyolefin porous films, non-woven fabrics, and glass fibers.

In some embodiments, the material of the base film is selected from polyethylene, polypropylene, polyimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyethylene terephthalate One or more of alcohol esters.

In some embodiments, the thickness of the base film is 4 μm-12 μm, and the porosity is 30%-50%. Optionally, the thickness of the base film is 7 μm-12 μm, and the porosity is 35%-45%.

In some embodiments, the coating has a thickness of 0.2 μm˜3 μm. Optionally, the coating has a thickness of 1 μm˜2 μm.

In some embodiments, the total thickness of the composite separator is 4 μm˜18 μm. Optionally, the total thickness of the composite separator is 9 μm˜16 μm.

In some embodiments, the air permeability of the composite membrane is ≤450s/100cc.

Optionally, the air permeability of the composite membrane is ≤300s/100cc.

Optionally, the air permeability of the composite membrane is ≤250s/100cc.

In some embodiments, the coating-coating bond strength of the composite separator is ≥3 N/m.

Optionally, the bonding strength between the coatings of the composite separator is ≥5N/m.

Optionally, the bonding strength between coatings of the composite separator is ≥10N/m.

In some embodiments, after the composite separator is kept at 130° C. for 60 minutes, the heat shrinkage rate in the longitudinal direction is ≤13%, and the heat shrinkage rate in the transverse direction is ≤13%.

Optionally, the heat shrinkage rate in the longitudinal direction is ≤7%, and the heat shrinkage rate in the transverse direction is ≤7%.

Optionally, the heat shrinkage rate in the longitudinal direction is ≤5%, and the heat shrinkage rate in the transverse direction is ≤5%.

In some embodiments, after the composite separator is kept at 110° C. for 10 minutes, the water mass percentage is ≤500 ppm.

Optionally, the water mass percentage is ≤300ppm.

In some embodiments, the air permeability of the composite membrane is ≤450s/100cc, optionally ≤300s/100cc, optionally ≤250s/100cc

The disclosure provides a method for preparing a composite diaphragm, comprising the following steps: dissolving polyvinylidene fluoride resin in a first organic solvent to prepare polyvinylidene fluoride glue, and dissolving a high heat-resistant polymer in a second organic solvent Prepare a high heat-resistant polymer glue solution; mix the inorganic ceramic particles modified by silane coupling agent, polyvinylidene fluoride glue solution, high heat-resistant polymer glue solution, and binder in the third organic solvent to obtain Slurry: coating the obtained slurry on at least one surface of the base film, and drying to obtain a composite diaphragm.

In some embodiments, the first organic solvent is selected from one or more of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, acetone, and dimethyl sulfoxide.

In some embodiments, the second organic solvent is selected from one or more of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, acetone, and dimethyl sulfoxide.

In some embodiments, the third organic solvent is a mixed solution of component 1 and component 2, and component 1 is selected from dimethylacetamide, dimethylformamide, N-methylpyrrolidone, acetone, di One or more of methyl sulfoxide, component 2 is selected from one or more of tripropylene glycol, propylene glycol, and ethanol, and the weight ratio of component 1 to component 2 is 10:90 to 40:60.

Optionally, the weight ratio of component 1 to component 2 is 20:80 to 30:70;

In some embodiments, the first organic solvent and the second organic solvent are the same.

In some embodiments, the method further includes the step of: reacting the silane coupling agent with the inorganic ceramic particles at 60° C. to 200° C. to obtain inorganic ceramic particles modified by the silane coupling agent.

The present disclosure also provides a secondary battery, including the above-mentioned composite separator or a composite separator prepared by the above-mentioned method.

The present disclosure also provides a low-moisture solvent-type PVDF coated diaphragm, which includes a polyolefin substrate microporous film and a PVDF coating layer formed on one or both sides of the substrate; the PVDF coating layer includes: silane coupling Inorganic particles, PVDF resin, and acrylic adhesive modified by the agent; the coated diaphragm was treated at 100-120°C for 5-15 minutes, and the moisture of the diaphragm was tested with a coulometric moisture tester, and the moisture value was lower than 500ppm.

In some embodiments, the coated surface of the separator is bonded to the battery pole piece, and after hot pressing at 1 MPa for 300s at 80°C, the bonding strength is tested using a tensile tester. The adhesion strength between the coating and the battery pole piece is 5- 30N/m.

In some embodiments, the polyolefin substrate microporous membrane is one of PE lithium battery separator and PE/PP lithium battery separator; the thickness of the microporous membrane is 5-12 μm.

In some embodiments, in the PVDF wet coating layer: 1-10 parts of PVDF resin, 5-15 parts of inorganic particles modified with silane coupling agent, and 0.1-5 parts of acrylic adhesive.

In some embodiments, the inorganic particles modified by the silane coupling agent are at least one of alumina, boehmite, silica, titania, hydrotalcite and montmorillonite.

In some embodiments, the silane coupling agent used is octyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ- Glycidyl ether oxypropyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethyl(ethyl)oxysilane, One or more of aminopropyltrimethyl(ethyl)oxysilane.

In some embodiments, the weight ratio of the silane chains in the modified inorganic particles is no higher than 2%.

In some embodiments, the preparation method of the PVDF wet coating layer is: dissolving the PVDF resin in the organic solvent 1 to prepare PVDF glue, and modifying the PVDF glue, silane coupling agent, inorganic particles, acrylate Adhesives and organic solvents 2 are mixed evenly to obtain a coating liquid, and the coating liquid is evenly coated on the surface of the polyethylene porous substrate, and the coated wet film is immersed in the coagulation liquid in turn, and washed with water in turn after the wet film is cured and drying to obtain a low-moisture solvent-based PVDF-coated separator.

In some embodiments, the organic solvent 1 is dimethylacetamide, and the organic solvent 2 is dimethylacetamide and tripropylene glycol in a volume ratio of 3-10:1-5;

The mass ratio of PVDF resin to organic solvent 1 is 1:3-8; the mass ratio of PVDF glue to organic solvent 2 is 1:3-8.

In some embodiments, the coagulation liquid is dimethylacetamide, tripropylene glycol and water in a mass ratio of 25-35:10-20:50-70.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the accompanying drawings required in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure. Those of ordinary skill in the art can also obtain other drawings based on these drawings without making creative efforts.

Fig. 1 is a structural schematic diagram of a composite diaphragm of the present disclosure;

Fig. 2 is the scanning electron microscope (SEM) picture of the composite membrane that embodiment 4 prepares;

Fig. 3 is the scanning electron microscope (SEM) picture of the composite membrane that comparative example 1 prepares;

Fig. 4 is the scanning electron microscope (SEM) picture of the composite membrane that comparative example 2 prepares;

Fig. 5 is the structural representation of inorganic particle modification process;

Fig. 6 is the structural schematic diagram of embodiment 19 low-moisture solvent type PVDF coating diaphragm;

Fig. 7 is embodiment 20 and prepares the topography figure of coating separator;

Fig. 8 is the topography figure of the coated diaphragm prepared in embodiment 21;

Fig. 9 is the topography figure of the coated diaphragm prepared in embodiment 22;

Fig. 10 is the topography figure of the coated diaphragm prepared by embodiment 23;

Fig. 11 is the topography diagram of the coated diaphragm prepared in comparative example 4;

FIG. 12 is a surface topography diagram of the coated separator prepared in Comparative Example 5. FIG.

Detailed ways

In order to make the purpose, technical solution and beneficial technical effects of the present disclosure clearer, the present disclosure will be described in detail below in conjunction with embodiments. It should be understood that the embodiments described in this specification are only for explaining the present disclosure, not for limiting the present disclosure.

For brevity, only certain numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with any other lower limit to form an unexpressed range, just as any upper limit can be combined with any other upper limit to form an unexpressed range. In addition, every point or individual value between the endpoints of a range is included within that range, although not expressly stated herein. Thus, each point or individual value may serve as its own lower or upper limit in combination with any other point or individual value or with other lower or upper limits to form a range not expressly recited.

In the description herein, it should be noted that, unless otherwise stated, "above" and "below" include the number, "one or more" and "one or more" in "multiple (a)" The meaning is two (one) or more.

The above disclosure of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The following description illustrates exemplary embodiments. At various places throughout the disclosure, guidance is provided through a series of examples, which examples can be used in various combinations. In various embodiments, the lists are presented as representative groups only and should not be construed as exhaustive.

Throughout this specification, substituents of compounds are disclosed as groups or ranges. It is expressly intended that this description include each individual subcombination of members of these groups and ranges. For example, the term "C1-C8 alkyl" is expressly intended to disclose individually C1, C2, C3, C4, C5, C6, C7, C8, C1-C8, C1-C7, C1-C6, C1-C5, C1- C4, C1～C3, C1～C2, C2～C8, C2～C7, C2～C6, C2～C5, C2～C4, C2～C3, C3～C8, C3～C7, C3～C6, C3～C5, C3-C4, C4-C8, C4-C7, C4-C6, C4-C5, C5-C8, C5-C7, C5-C6, C6-C8, C6-C7 and C7-C8 alkyl groups.

The term "alkyl" includes linear or branched saturated hydrocarbon groups, such as methyl, ethyl, propyl (such as n-propyl, isopropyl), butyl (such as n-butyl, isobutyl, sec-butyl, tert-butyl), pentyl (such as n-pentyl, isopentyl, neopentyl) and similar alkyl groups.

The term "alkenyl" includes straight chain or branched alkenyl groups such as ethenyl, propenyl (e.g. n-propenyl, isopropenyl), butenyl (e.g. 3-butenyl, 2-butenyl) and the like Alkenyl.

The term "alkoxy" refers to -O-alkyl. Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy (such as n-propoxy, isopropoxy), butoxy (such as n-butoxy, isobutoxy, sec-butoxy, oxy, tert-butoxy) and the like alkoxy.

The term "oxacycloalkyl" refers to a cycloalkyl group having one or more oxygen atoms in the ring. Examples of oxetanyl groups include, but are not limited to, oxiranyl, oxetanyl, and the like.

A first aspect of the present disclosure provides a composite separator and a method for preparing the same.

Composite diaphragm

One embodiment of the present disclosure provides a composite diaphragm, the composite diaphragm includes a base film and a coating disposed on at least one surface of the base film, the coating includes inorganic ceramic particles modified by a silane coupling agent, Polyvinylidene fluoride resins, high heat-resistant polymers, and adhesives. Referring to FIG. 1 , the composite diaphragm of the present disclosure includes a base film 101 and a coating 102 disposed on opposite surfaces of the base film 101, wherein the coating 102 includes inorganic ceramic particles modified by a silane coupling agent, polyvinylidene fluoride Vinyl resins, high heat resistant polymers and adhesives.

In the present disclosure, the term "polyvinylidene fluoride resin" includes both vinylidene fluoride homopolymer (PVDF) and vinylidene fluoride copolymer. As an example, the polyvinylidene fluoride resin includes vinylidene fluoride homopolymer (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trifluorochloroethylene copolymer One or more of compounds, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer.

Polyvinylidene fluoride resin has good electrolyte wettability because it contains polar groups. After polyvinylidene fluoride resin is dissolved in a solvent, it can form a more stable three-dimensional network structure during the gelation process, which in turn can The electrolyte is firmly locked inside the composite diaphragm, reducing the risk of electrolyte leakage and reducing the decomposition reaction between the electrolyte and the electrodes. The polyvinylidene fluoride resin can form a gel during the hot pressing process of the secondary battery, thereby improving the bonding performance between the electrode and the composite separator, increasing the hardness of the secondary battery, and improving the safety performance of the secondary battery.

Introducing a high heat-resistant polymer into the coating can improve the heat resistance of the coating and the composite separator.

Inorganic ceramic particles have high heat resistance, and when mixed with polyvinylidene fluoride resin and high heat-resistant polymers, they can improve the heat resistance and mechanical strength of coatings and composite diaphragms. However, after introducing inorganic ceramic particles into the coating, the compactness of the coating decreases, resulting in the ineffective improvement of the heat resistance of the composite separator. However, after the inorganic ceramic particles modified by the silane coupling agent are introduced into the coating, the heat resistance of the composite diaphragm can be effectively improved.

This is because the silane coupling agent contains two groups: one is an inorganic group, and the other is an organophilic group. Inorganophilic groups are easy to chemically react with inorganic ceramic particles to form covalent bonds, and organophilic groups can chemically react with polymers in the coating (such as polyvinylidene fluoride resins, high heat-resistant polymers) and base films Form covalent bonds or form interpenetrating network structures, etc. Therefore, the inorganic ceramic particles modified by the silane coupling agent have better compatibility with the polymer in the coating and the base film, and will not cause a decrease in the compactness of the coating, thereby effectively improving the heat resistance of the composite separator. performance. At the same time, introducing silane coupling agent-modified inorganic ceramic particles into the coating can also improve the bonding strength between the coating and the base film.

In addition, the surface of the inorganic ceramic particles has a large amount of -OH, and after introducing the inorganic ceramic particles into the coating, the moisture content of the coating and the composite separator is relatively high. The hydrolysis of the silane coupling agent can form -Si-OH, and -Si-OH forms a hydrogen bond with the -OH on the surface of the inorganic ceramic particles. Therefore, introducing the inorganic ceramic particles modified by the silane coupling agent into the coating can effectively Reduce the moisture content of the composite separator, so that the secondary battery has good electrochemical performance.

By mixing polyvinylidene fluoride resin with silane coupling agent-modified inorganic ceramic particles and high heat-resistant polymers, it can not affect the excellent bonding performance between the composite separator and the electrode and the good wettability between the composite separator and the electrolyte Under the premise, the heat resistance and mechanical strength of the composite separator can be effectively improved, and the moisture content of the composite separator can be effectively reduced, so that the secondary battery can have high safety performance and good electrochemical performance at the same time.

The composite diaphragm of the present disclosure has excellent bonding performance and heat resistance and low moisture content, and can ensure that the secondary battery has high safety performance and good electrochemical performance at the same time. At the same time, the composite diaphragm of the present disclosure has high mechanical strength, can withstand high expansion force and is not easily deformed, thereby further improving the safety performance of the secondary battery.

The composite diaphragm disclosed by the disclosure has excellent bonding performance, the coating is not easy to fall off from the base film, and the bonding strength between the coating and the electrode sheet is high, which can continuously improve the safety performance of the secondary battery.

The composite diaphragm of the present disclosure has excellent heat resistance, is not easily deformed after being heated, and can improve the safety performance of the secondary battery.

The composite diaphragm of the present disclosure has low moisture content and will not affect the electrochemical performance of the secondary battery.

In some embodiments, the coating comprises:

Inorganic ceramic particles modified by silane coupling agent, 40-80 parts, such as 40-80 parts, 40-80 parts or 40-80 parts,

Polyvinylidene fluoride resin, 0.01-50 parts, such as 1-55 parts, 10-50 parts or 15-40 parts,

High heat-resistant polymer, 0.01-50 parts, such as 1-45 parts, 5-35 parts or 10-25 parts,

Binder, 0.1-15 parts, such as 1-12 parts, 2-10 parts or 4-8 parts.

In some embodiments, the coating comprises:

Inorganic ceramic particles modified by silane coupling agent, 40-70 parts,

Polyvinylidene fluoride resin, 8-40 parts,

High heat-resistant polymer, 8 to 40 parts,

Binder, 2 to 10 parts.

When the content of each component in the coating is within an appropriate range, the composite separator can simultaneously have excellent bonding performance, excellent heat resistance performance, and lower moisture content.

In some embodiments, the weight ratio of the polyvinylidene fluoride resin to the high heat-resistant polymer is 0.1:99.9-99.9:0.1 such as 1:99-99:1, 5:90-90:5 or 15 :80～80:15.

When the weight ratio of the polyvinylidene fluoride resin to the high heat-resistant polymer is in an appropriate range, the composite separator can simultaneously have excellent bonding performance and excellent heat resistance performance.

The Dv50 of the inorganic ceramic particles modified by the silane coupling agent is within an appropriate range, and the compactness and uniformity of the coating are better.

In some embodiments, the weight ratio of the silane coupling agent to the inorganic ceramic particles is 0.01:99.99˜2:98. Optionally, the weight ratio of the silane coupling agent to the inorganic ceramic particles is 0.1:99.9˜1:99.

In some embodiments, the type of the inorganic ceramic particles is not particularly limited, and can be selected according to actual needs. As an example, the inorganic ceramic particles may be selected from alumina, boehmite, calcium carbonate, hydrotalcite, montmorillonite, spinel, mullite, titania, silica, zirconia, magnesia, oxide One or more of calcium, beryllium oxide, magnesium hydroxide, boron nitride, silicon nitride, aluminum nitride, titanium nitride, boron carbide, silicon carbide, and zirconium carbide.

In some embodiments, the molecular formula of the silane coupling agent is Y-Si(OX) ₃ , wherein each X independently represents -CH ₃ , -C ₂ H ₅ , -(C=O)CH ₃ , or -(C=O)C ₂ H ₅ , Y can represent C1～C10 alkyl, C1～C10 alkoxy, C2～C10 alkenyl, C2～C10 alkoxy, C2～C5 oxetanecycloalkyl, amino One or more of (-NH ₂ , -NH-), methacryloyloxy (CH ₃ (C=CH ₂ )-COO-), acryloyloxy (CH ₂ =CH-COO-) The combination. Y can be represented as one of the above-mentioned groups, and can also be represented as a combination of several of the above-mentioned groups. For example, Y represents the combination of C1~C10 alkyl (or alkylene) and amino (-NH ₂ , -NH-), the combination of C1~C10 alkyl (or alkylene) and methacryloyloxy (CH ₃ (C=CH ₂ )-COO-), the combination of C1～C10 alkyl (or alkylene) and acryloyloxy (CH ₂ ＝CH-COO-), the combination of C2～C10 alkoxy (or- O-alkylene) and the combination of C2～C5 oxetanecycloalkyl, etc.

Optionally, Y may represent a C1-C10 alkyl group, or a C1-C10 alkoxy group.

In some embodiments, as an example, the silane coupling agent can be selected from methyltriethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, n-butyltriethoxysilane Silane, isobutyltriethoxysilane, (3,3-dimethylbutyl)triethoxysilane, n-hexyltriethoxysilane, n-octyltriethoxysilane, isooctyltriethoxysilane Oxysilane, n-decyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, isopropyltrimethoxysilane, butyltrimethoxysilane, Isobutyltrimethoxysilane, tert-butyltrimethoxysilane, n-pentyltrimethoxysilane, trimethoxy(1,1,2-trimethylpropyl)-silane, n-hexyltrimethoxysilane, n-octyltrimethoxysilane, isooctyltrimethoxysilane, n-decyltrimethoxysilane, (methoxymethyl)triethoxysilane, (methoxymethyl)trimethoxysilane, trimethoxy (3-methoxypropyl)silane, γ-aminopropyltriethoxysilane (KH550), γ-aminopropyltrimethoxysilane (KH540), γ-glycidyl etheroxypropyltrimethoxy Silane (KH560), γ-(methacryloxy)propyltrimethoxysilane (KH570), N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (KH792), N-( One or more of β-aminoethyl)-γ-aminopropyltriethoxysilane (KH791).

Optionally, the silane coupling agent can be selected from methyltriethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, n-butyltriethoxysilane, isobutyl Triethoxysilane, (3,3-dimethylbutyl)triethoxysilane, n-hexyltriethoxysilane, n-octyltriethoxysilane, isooctyltriethoxysilane, n- Decyltriethoxysilane, Methyltrimethoxysilane, Ethyltrimethoxysilane, n-Propyltrimethoxysilane, Isopropyltrimethoxysilane, Butyltrimethoxysilane, Isobutyltrimethoxysilane butylsilane, tert-butyltrimethoxysilane, n-pentyltrimethoxysilane, trimethoxy(1,1,2-trimethylpropyl)-silane, n-hexyltrimethoxysilane, n-octyltrimethoxy ylsilane, isooctyltrimethoxysilane, n-decyltrimethoxysilane, (methoxymethyl)triethoxysilane, (methoxymethyl)trimethoxysilane, trimethoxy(3-methoxysilane One or more of oxypropyl) silanes.

In some embodiments, the weight average molecular weight of the polyvinylidene fluoride resin is 200,000-1.5 million, and the melting point is 137°C-158°C.

Optionally, the polyvinylidene fluoride resin has a weight average molecular weight of 600,000-1.5 million, such as 700,000-1.4 million, 800,000-1.3 million, or 900,000-1.2 million, and a melting point of 137°C-156°C, such as 140°C ~155°C, 142°C~152°C or 145°C~150°C.

The polyvinylidene fluoride resin with high molecular weight and low melting point is more likely to form a gel during the hot pressing process of the secondary battery, which can further improve the bonding performance between the electrode and the composite separator, increase the hardness of the secondary battery, and improve the secondary battery. The safety performance of secondary batteries.

In some embodiments, the high heat-resistant polymer is selected from one or more of polyimide, polyetherimide, aramid, and sulfone. The above-mentioned high heat-resistant polymer can further improve the heat resistance of the coating and the composite diaphragm. At the same time, the above-mentioned high heat-resistant polymer has higher compatibility with other components in the coating and the base film, and the uniformity of the coating and the composite diaphragm Sex is better.

In this disclosure, the term "aramid" refers to polyphenylene phthalamide. Optionally, the aramid fiber is para-aramid fiber, that is, polyparaphenylene terephthalamide.

In the present disclosure, the term "arylene sulfone" refers to polyphenylsulfone terephthalamide (PSA).

In some embodiments, the type of the binder is not particularly limited, and can be selected according to actual needs. As an example, the adhesive may be selected from acrylate adhesives (Acrylate adhesives). Optionally, the acrylic adhesive is a one-component acrylic adhesive or an emulsion-type acrylic adhesive, wherein the solid content of the emulsion-type acrylic adhesive can be 35% to 45% %, 25°C viscosity can be 20cps～200cps.

In some embodiments, the type of the base film is not particularly limited, and can be selected according to actual needs. Optionally, the base film is selected from one or more of polyolefin porous films, non-woven fabrics, and glass fibers. The base film can be a single-layer film or a multi-layer composite film. When the base film is a multilayer composite film, the materials of each layer are the same or different.

As an example, the material of the base film can be selected from polyethylene, polypropylene, polyimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyethylene terephthalate one or more of. Optionally, the material of the base film can be selected from polyethylene, polypropylene, or polypropylene/polyethylene/polypropylene composite material.

In some embodiments, the thickness of the base film is 4 μm-12 μm, and the porosity is 30%-50%.

Optionally, the base film has a thickness of 7 μm˜12 μm.

Optionally, the porosity of the base film is 35%-50%.

When the thickness and porosity of the base film are within an appropriate range, the composite separator can have sufficient mechanical strength while enabling the secondary battery to have low internal resistance and high ionic conductivity, and the overall performance of the secondary battery is better. .

In some embodiments, the coating has a thickness of 0.2 μm˜3 μm. Optionally, the coating has a thickness of 1 μm˜2 μm. In the present disclosure, the thickness of the coating refers to the thickness of the single-side coating of the base film.

When the thickness of the coating is in an appropriate range, the composite separator can make the secondary battery have low internal resistance and high ion conductivity while having excellent mechanical strength, bonding performance and heat resistance. The overall performance is better.

Optionally, the air permeability of the composite membrane is ≤300s/100cc.

Optionally, the air permeability of the composite membrane is ≤250s/100cc.

The total thickness and air permeability of the composite separator are within an appropriate range, and the composite separator can make the secondary battery have low internal resistance and high ion conductivity while having excellent mechanical strength, bonding performance and heat resistance , the overall performance of the secondary battery is better.

The higher the bonding strength between the coating and the coating of the composite separator, the better the bonding performance of the composite separator, the coating is less likely to fall off from the base film and the bonding strength between the coating and the electrode sheet is higher. The safety performance of the secondary battery is better.

In some embodiments, after the composite separator is kept at 130° C. for 60 minutes, the thermal shrinkage rate in the longitudinal direction (MD) is ≤13%, and the thermal shrinkage rate in the transverse direction (TD) is ≤13%.

Optionally, the heat shrinkage rate in the longitudinal direction (MD) is ≤7%, and the heat shrinkage rate in the transverse direction (TD) is ≤7%.

Optionally, the heat shrinkage rate in the longitudinal direction (MD) is ≤5%, and the heat shrinkage rate in the transverse direction (TD) is ≤5%.

The lower the heat shrinkage rate of the composite separator, the better the heat resistance of the composite separator, the less likely to be deformed after being heated, and the better the safety performance of the secondary battery.

In some embodiments, after the composite separator is kept at 110° C. for 10 minutes, the water mass percentage is ≤500 ppm. Optionally, the water mass percentage is ≤300ppm. The lower the moisture content of the composite separator, the better the electrochemical performance of the secondary battery.

The air permeability of the composite membrane is a well-known meaning in the art, and can be measured with instruments and methods known in the art. For example, referring to the determination of JIS P8117-2009 air permeability of paper and cardboard, the composite diaphragm is cut into a sample with a width ≥ 5cm along the TD direction, and the air permeability of the sample is tested using the Wangyan air permeability meter (when the width of the composite diaphragm in the TD direction is less than 5cm , a small measuring head can be used for testing), and the test time is set to 3s. In order to ensure the accuracy of the test results, multiple samples (for example, 10) can be taken for testing, and the average value is taken as the test result.

The bonding strength between the composite diaphragm coating and the coating is a well-known meaning in the art, and can be measured with instruments and methods known in the art. As an example, the test of the bonding strength between the composite diaphragm coating and the coating includes the steps of: providing two composite diaphragm samples, the sample size is 25mm × 100mm; After laminating the coating, place it inside two pieces of A4 paper, and use thermoplastic equipment SKY 325R6 to plastic seal at the gear "Speed 1" and temperature 100°C for 30s; then use a tensile testing machine to conduct a 180° peel test to obtain two The bonding strength between two coatings, wherein the tensile speed can be 300mm/min. In order to ensure the accuracy of the test results, multiple samples (for example, 10) can be taken for testing, and the average value is taken as the test result.

The heat shrinkage rate of the composite separator has a well-known meaning in the art, and can be measured with instruments and methods known in the art. As an example, the test of thermal shrinkage includes the steps of: cutting the composite diaphragm into a 15cm×15cm sample, drawing two mutually perpendicular line segments (for example, 10cm×10cm) according to the longitudinal direction (MD) and the transverse direction (TD), and using steel Measure the length of the sample in the longitudinal direction (MD) and the transverse direction (TD) with a ruler (or projector) respectively; place the sample flat on two sheets of A4 paper, and then place it in an oven at 130°C for 60 minutes; the heating is over Afterwards, the sample was taken out, and after returning to room temperature, the mark length in the longitudinal direction (MD) and transverse direction (TD) of the sample was measured again. Thermal shrinkage rate in MD direction = (length in MD direction before heating - length in MD direction after heating) / length in MD direction before heating × 100%, thermal shrinkage rate in TD direction = (length in TD direction before heating - length in TD direction after heating) / heating Front TD direction length × 100%. In order to ensure the accuracy of the test results, multiple samples (for example, 10) can be taken for testing, and the average value is taken as the test result.

The moisture content of the composite separator is a well-known meaning in the art, and can be measured with instruments and methods known in the art. For example, after keeping the composite diaphragm at 110°C for 10 minutes, test the moisture content of the composite diaphragm with reference to GB/T 26793-2011 coulometric moisture analyzer. In order to ensure the accuracy of the test results, multiple samples (for example, 10) can be taken for testing, and the average value is taken as the test result.

Preparation method of composite diaphragm

According to one embodiment of the present disclosure, a method for preparing a composite diaphragm is provided. The preparation method comprises the following steps: dissolving polyvinylidene fluoride resin in a first organic solvent to prepare a polyvinylidene fluoride glue, dissolving a high heat-resistant polymer in a second organic solvent to prepare a high heat-resistant polymer glue; mix the inorganic ceramic particles modified by silane coupling agent, polyvinylidene fluoride glue, high heat-resistant polymer glue, and binder in the third organic solvent to obtain slurry; the obtained slurry The material is coated on at least one surface of the base film, and the composite diaphragm is obtained after drying.

In some embodiments, the preparation method of the composite diaphragm further includes the step of: reacting the silane coupling agent with the inorganic ceramic particles at 60° C. to 200° C. to obtain the inorganic ceramic particles modified by the silane coupling agent.

Optionally, the reaction temperature is 70°C-150°C.

Optionally, the reaction temperature is 80°C to 120°C.

Optionally, the reaction time is 1h-3h.

In some embodiments, the preparation method of the inorganic ceramic particles modified by the silane coupling agent further includes the step of: performing activation pretreatment on the inorganic ceramic particles.

In some embodiments, the type of the first organic solvent is not particularly limited, and can be selected according to actual needs. As an example, the first organic solvent may be selected from one or more of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, acetone, and dimethylsulfoxide.

In some embodiments, the type of the second organic solvent is not particularly limited, and can be selected according to actual needs. As an example, the second organic solvent may be selected from one or more of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, acetone, and dimethylsulfoxide.

In some embodiments, the type of the third organic solvent is not particularly limited, and can be selected according to actual needs. As an example, the third organic solvent is a mixed solution of component 1 and component 2, and component 1 is selected from dimethylacetamide, dimethylformamide, N-methylpyrrolidone, acetone, dimethylmethylene One or more of sulfones, component 2 is selected from one or more of tripropylene glycol, propylene glycol, and ethanol.

In some embodiments, the weight ratio of component 1 to component 2 is 10:90˜40:60. Optionally, the weight ratio of component 1 to component 2 is 20:80˜30:70.

According to the method provided in one embodiment of the present disclosure, the composite diaphragm described in any one of the above can be used.

secondary battery

According to an embodiment of the present disclosure, there is provided a secondary battery. The secondary battery includes the above-mentioned composite separator or a composite separator prepared by the above-mentioned method.

The present disclosure has no special limitation on the type of the secondary battery, which can be selected according to actual needs. As an example, the secondary battery may be a lithium ion battery or a sodium ion battery.

The present disclosure also has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape.

The composite separator provided in the first aspect of the present disclosure has excellent bonding performance and heat resistance and low moisture content, which can ensure that the secondary battery has high safety performance and good electrochemical performance at the same time.

The second aspect of the present disclosure also provides a low moisture solventborne PVDF coated separator. Another embodiment of the present disclosure provides a low-moisture solvent-based PVDF coated diaphragm, which includes a polyolefin substrate microporous film and a PVDF wet coating layer formed on one or both sides of the substrate; the PVDF wet coating The layer includes: inorganic particles modified by silane coupling agent, PVDF resin, and acrylic adhesive; For 5 to 15 minutes (such as 7 to 14 minutes, 8 to 12 minutes or 9 to 11 minutes), use a coulometric moisture tester to test the moisture of the diaphragm, and the moisture value is lower than 500ppm.

In some embodiments, the coated surface of the separator is bonded to the battery pole piece. After hot pressing at 80°C and 1 MPa for 300s, the bonding strength is tested using a tensile tester. The adhesion strength between the coating and the battery pole piece is 5-30N/ m such as 8-25N/m, 10-20N/m or 12-18N/m.

In some embodiments, the organic solvent 1 is dimethylacetamide, and the organic solvent 2 is dimethylacetamide and tripropylene glycol with a volume ratio of 3-10:1-5; the mass ratio of PVDF resin to organic solvent 1 is 1 : 3-8; the mass ratio of PVDF glue and organic solvent 2 is 1:3-8.

In some embodiments, the method of modifying the inorganic particles by the silane coupling agent is to mix the silane coupling agent and the inorganic particles at a high speed at a temperature of 80-120° C., and dry to obtain the modified inorganic particles; wherein the inorganic particles and The mass ratio of the siloxane modified liquid is (98-99.99): (0.01-2);

Regarding the low-moisture solvent-based PVDF coated diaphragm provided in the second aspect of the present disclosure, the diaphragm has the following advantages:

The low-moisture solvent-type PVDF coating diaphragm provided by the present disclosure is a solvent-type lithium battery diaphragm with low water content and excellent adhesion to battery pole pieces, and the inorganic particles used are particles modified by a silane coupling agent.

The low-moisture solvent-type coated diaphragm provided by the present disclosure was treated at 110° C. for 10 minutes, and the moisture of the diaphragm was tested by a coulometric moisture tester, and the moisture value was lower than 300 ppm.

The low-moisture solvent-type PVDF coated diaphragm provided by the disclosure is hot-pressed at 80°C and 1 MPa for 300s, and the bonding strength is tested by a tensile testing machine. The bonding strength between the coating and the battery pole piece is 5-30N/m.

Example

The present disclosure is described in the following examples, which are provided for illustrative purposes only, since various modifications and changes within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods, and can be directly The instruments used without further processing, as well as in the examples, are commercially available.

For the first aspect of the present disclosure, the following Examples 1-18 and Comparative Examples 1-3 are provided for illustration and comparison.

Example 1

Preparation of Inorganic Ceramic Particles Modified by Silane Coupling Agent

React octyltriethoxysilane and alumina particles (Dv50: 0.64 μm) at a weight ratio of 1:99 at 80° C. to 120° C. for 1 hour to obtain silane coupling agent-modified alumina particles.

Preparation of Polyvinylidene Fluoride Glue

Add 20 parts by weight of polyvinylidene fluoride resin (PVDF, with a weight average molecular weight of 200,000 to 400,000 and a melting point of 154°C to 158°C) into 80 parts by weight of dimethylacetamide, and stir at room temperature for 3 hours to obtain light yellow or Colorless, clear and transparent polyvinylidene fluoride glue.

Preparation of High Heat Resistant Polymer Glue

Add 10 parts by weight of soluble polyimide (PI) to 90 parts by weight of dimethylacetamide, and stir at room temperature for 3 hours to obtain a light yellow or colorless clear and transparent polyimide glue solution.

Preparation of composite separator

Get 15 parts by weight of the above-mentioned polyvinylidene fluoride glue and 20 parts by weight of the above-mentioned polyimide glue, dissolve in 57 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, dimethylacetamide and tripropylene glycol The weight ratio is 70:30), and then add 6 parts by weight of the above-mentioned silane coupling agent modified alumina, 2 parts by weight of emulsion type acrylate adhesive (solid content is 40%, viscosity at 25°C is 20cps～ 200cps), mixed and stirred at room temperature for 1h to obtain a white viscous slurry.

The slurry prepared above is uniformly coated on both surfaces of a polyethylene porous membrane (porosity 42%) with a thickness of 5 μm, and then immersed in a coagulation solution (dimethylacetamide, tripropylene glycol and water) at 25 ° C. The weight ratio is 28:12:60), after the wet film on the surface of the polyolefin porous membrane is solidified, it is washed with water and dried in sequence to obtain a composite separator.

Example 2

Preparation of Inorganic Ceramic Particles Modified by Silane Coupling Agent

Preparation of Polyvinylidene Fluoride Glue

Add 20 parts by weight of polyvinylidene fluoride resin (PVDF, with a weight average molecular weight of 600,000 to 800,000 and a melting point of 151°C to 156°C) into 80 parts by weight of dimethylacetamide, and stir at room temperature for 3 hours to obtain light yellow or Colorless, clear and transparent polyvinylidene fluoride glue.

Preparation of High Heat Resistant Polymer Glue

Preparation of composite separator

The slurry prepared above is uniformly coated on both surfaces of a polyethylene porous membrane (porosity 42%) with a thickness of 7 μm, and then immersed in a coagulation solution (dimethylacetamide, tripropylene glycol and water) at 25 ° C. The weight ratio is 28:12:60), after the wet film on the surface of the polyolefin porous membrane is solidified, it is washed with water and dried in sequence to obtain a composite separator.

Example 3

Preparation of Inorganic Ceramic Particles Modified by Silane Coupling Agent

Preparation of Polyvinylidene Fluoride Glue

Add 20 parts by weight of polyvinylidene fluoride resin (PVDF, with a weight average molecular weight of 800,000 to 1 million, and a melting point of 147°C to 153°C) into 80 parts by weight of dimethylacetamide, and stir at room temperature for 3 hours to obtain light yellow or Colorless, clear and transparent polyvinylidene fluoride glue.

Preparation of High Heat Resistant Polymer Glue

Preparation of composite separator

The slurry prepared above is uniformly coated on both surfaces of a polyethylene porous membrane (porosity 42%) with a thickness of 12 μm, and then immersed in a coagulation solution (dimethylacetamide, tripropylene glycol and water) at 25 ° C. The weight ratio is 28:12:60), after the wet film on the surface of the polyolefin porous membrane is solidified, it is washed with water and dried in sequence to obtain a composite separator.

Example 4

Preparation of Inorganic Ceramic Particles Modified by Silane Coupling Agent

Preparation of Polyvinylidene Fluoride Glue

Add 20 parts by weight of polyvinylidene fluoride resin (PVDF, with a weight average molecular weight of 1 million to 1.5 million, and a melting point of 137°C to 152°C) into 80 parts by weight of dimethylacetamide, and stir at room temperature for 3 hours to obtain light yellow or Colorless, clear and transparent polyvinylidene fluoride glue.

Preparation of High Heat Resistant Polymer Glue

Preparation of composite separator

The slurry prepared above was uniformly coated on both surfaces of a polyethylene porous membrane (porosity 42%) with a thickness of 9 μm, and then immersed in a coagulation solution (dimethylacetamide, tripropylene glycol and water) at 25 ° C. The weight ratio is 28:12:60), after the wet film on the surface of the polyolefin porous membrane is solidified, it is washed with water and dried in sequence to obtain a composite separator.

Example 5

The preparation method is similar to that of Example 4, except that the composition of the coating slurry is adjusted.

Get the polyvinylidene fluoride glue solution prepared by 20 parts by weight of embodiment 4 and the polyimide glue solution prepared by 10 parts by weight of embodiment 4, dissolve in 62 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, The weight ratio of dimethylacetamide and tripropylene glycol is 70:30), then add the aluminum oxide modified by the silane coupling agent prepared by 6 parts by weight of embodiment 4, 2 parts by weight of emulsion type acrylate binder ( The solid content is 40%, the viscosity at 25°C is 20cps-200cps), and the mixture is stirred at room temperature for 1 hour to obtain a white viscous slurry.

Example 6

Get the polyvinylidene fluoride glue solution prepared by 5 parts by weight of embodiment 4 and the polyimide glue solution prepared by 40 parts by weight embodiment 4, dissolve in 47 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, The weight ratio of dimethylacetamide and tripropylene glycol is 70:30), then add the aluminum oxide modified by the silane coupling agent prepared by 6 parts by weight of embodiment 4, 2 parts by weight of emulsion type acrylate binder ( The solid content is 40%, the viscosity at 25°C is 20cps-200cps), and the mixture is stirred at room temperature for 1 hour to obtain a white viscous slurry.

Example 7

Get the polyvinylidene fluoride glue solution prepared by 15 parts by weight of embodiment 4 and the polyimide glue solution prepared by 20 parts by weight embodiment 4, dissolve in 55 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, The weight ratio of dimethylacetamide and tripropylene glycol is 70:30), then add the aluminum oxide modified by the silane coupling agent prepared by 8 parts by weight of embodiment 4, 2 parts by weight of emulsion type acrylate binder ( The solid content is 40%, the viscosity at 25°C is 20cps-200cps), and the mixture is stirred at room temperature for 1 hour to obtain a white viscous slurry.

Example 8

Get the polyvinylidene fluoride glue solution prepared by 15 parts by weight of embodiment 4 and the polyimide glue solution prepared by 20 parts by weight embodiment 4, dissolve in 51 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, The weight ratio of dimethylacetamide and tripropylene glycol is 70:30), then add the aluminum oxide modified by the silane coupling agent prepared by 12 parts by weight of embodiment 4, 2 parts by weight of emulsion type acrylate binder ( The solid content is 40%, the viscosity at 25°C is 20cps-200cps), and the mixture is stirred at room temperature for 1 hour to obtain a white viscous slurry.

Example 9

Get the polyvinylidene fluoride glue solution prepared by 25 parts by weight of embodiment 4 and the polyimide glue solution prepared by 8 parts by weight embodiment 4, dissolve in 62.5 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, The weight ratio of dimethylacetamide and tripropylene glycol is 70:30), then add 4 parts by weight of aluminum oxide modified by the above-mentioned silane coupling agent, 0.5 parts by weight of emulsion type acrylate binder (solid content is 40 %, the viscosity at 25°C is 20cps-200cps), mixed and stirred at room temperature for 1h to obtain a white viscous slurry.

Example 10

Get the polyvinylidene fluoride glue prepared by 4 parts by weight of embodiment 4 and the polyimide glue prepared by 50 parts by weight of embodiment 4, dissolve in 41.5 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, The weight ratio of dimethylacetamide and tripropylene glycol is 70:30), then add the aluminum oxide modified by the silane coupling agent prepared by 4 parts by weight of embodiment 4, 0.5 parts by weight of emulsion type acrylate binder ( The solid content is 40%, the viscosity at 25°C is 20cps-200cps), and the mixture is stirred at room temperature for 1 hour to obtain a white viscous slurry.

Example 11

Get the polyvinylidene fluoride glue solution prepared by 5 parts by weight of embodiment 4 and the polyimide glue solution prepared by 6 parts by weight embodiment 4, dissolve in 80 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, The weight ratio of dimethylacetamide and tripropylene glycol is 70:30), then add the aluminum oxide modified by the silane coupling agent prepared by 8 parts by weight of embodiment 4, 1 part by weight of emulsion type acrylate binder ( The solid content is 40%, the viscosity at 25°C is 20cps-200cps), and the mixture is stirred at room temperature for 1 hour to obtain a white viscous slurry.

Example 12

The preparation method is similar to that of Example 4, except that polyimide is replaced by polyetherimide, a high heat-resistant polymer.

Example 13

The preparation method is similar to that of Example 4, except that polyimide is replaced by para-aramid, a high heat-resistant polymer.

Example 14

The preparation method is similar to that of Example 4, except that polyimide is replaced by high heat-resistant polymer sulfonamide.

Example 15

The preparation method is similar to that of Example 4, except that the types of the silane coupling agent and the inorganic ceramic particles are different.

KH550 and boehmite particles (Dv50 is 0.40 μm) were reacted at 80° C. to 120° C. for 2 hours at a weight ratio of 1:99 to obtain boehmite particles modified by a silane coupling agent.

Example 16

React KH560 and silica particles (Dv50 is 0.20 μm) according to the weight ratio of 1:99 at 80°C to 120°C for 2 hours to obtain silica particles modified by silane coupling agent.

Example 17

KH570 and calcium carbonate particles (Dv50 is 0.6 μm) were reacted at 80°C to 120°C for 2 hours according to the weight ratio of 1:99 to obtain calcium carbonate particles modified by silane coupling agent.

Example 18

React KH791 and titanium dioxide particles (Dv50 is 0.9 μm) at a weight ratio of 1:99 at 80°C to 120°C for 2 hours to obtain titanium dioxide particles modified by silane coupling agent.

Comparative example 1

Preparation of Inorganic Ceramic Particles Modified by Silane Coupling Agent

Preparation of Polyvinylidene Fluoride Glue

Preparation of composite separator

Get 25 parts by weight of the above-mentioned polyvinylidene fluoride glue solution, dissolve it in 67 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, the weight ratio of dimethylacetamide and tripropylene glycol is 70:30), and then Add 6 parts by weight of the above-mentioned silane coupling agent-modified alumina, 2 parts by weight of emulsion-type acrylate binder (solid content: 40%, viscosity: 20cps-200cps at 25°C), and mix and stir at room temperature for 1 hour to obtain a white viscous Thick slurry.

Comparative example 2

Preparation of Inorganic Ceramic Particles Modified by Silane Coupling Agent

Preparation of High Heat Resistant Polymer Glue

Preparation of composite separator

Get 50 parts by weight of the above-mentioned polyimide glue solution, dissolve it in 42 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, the weight ratio of dimethylacetamide and tripropylene glycol is 70:30), and then Add 6 parts by weight of the above-mentioned silane coupling agent-modified alumina, 2 parts by weight of emulsion-type acrylate binder (solid content: 40%, viscosity: 20cps-200cps at 25°C), and mix and stir at room temperature for 1 hour to obtain a white viscous Thick slurry.

Comparative example 3

Preparation of Polyvinylidene Fluoride Glue

Preparation of High Heat Resistant Polymer Glue

Preparation of composite separator

Get 15 parts by weight of the above-mentioned polyvinylidene fluoride glue and 20 parts by weight of the above-mentioned polyimide glue, dissolve in 57 parts by weight of dimethylacetamide and tripropylene glycol mixed solution (wherein, dimethylacetamide and tripropylene glycol The weight ratio is 70:30), followed by adding 6 parts by weight of unmodified alumina particles and 2 parts by weight of emulsion-type acrylate binder (solid content is 40%, viscosity at 25°C is 20cps-200cps), Mix and stir at room temperature for 1 h to obtain a white viscous slurry.

test part

The performance tests of the composite diaphragms prepared in Examples 1-18 and Comparative Examples 1-3 include the air permeability test of the composite diaphragm, the bond strength test between the composite diaphragm coating and the coating, and the heat shrinkage of the composite diaphragm after being kept at 130°C for 60min. Rate test, moisture content test after the composite diaphragm is kept at 110°C for 10 minutes. The above-mentioned performance test can be carried out with reference to the test method described above in the disclosure specification.

Table 1 shows the test results of Examples 1-18 and Comparative Examples 1-3.

Table 1

From the test results in Table 1, it can be seen that by mixing polyvinylidene fluoride resin with inorganic ceramic particles modified by silane coupling agent and high heat-resistant polymer, the composite separators of Examples 1-18 all have high air permeability and low moisture content. content, high bond strength and high heat resistance, so as to ensure that the secondary battery has high safety performance and good electrochemical performance.

In Comparative Example 1, only PVDF with a weight average molecular weight of 1 million to 1.5 million was mixed with inorganic ceramic particles modified by a silane coupling agent, and the bond strength between the composite diaphragm coating and the coating could be as high as 30.5N/m, but , after the composite separator was kept at 130°C for 60min, the thermal shrinkage rates in the MD and TD directions were as high as 15% and 13%, respectively. In Comparative Example 2, only the high heat-resistant polymer PI was mixed with the inorganic ceramic particles modified by the silane coupling agent. After the composite separator was kept at 130°C for 60 minutes, the thermal shrinkage rates in the MD and TD directions were as low as 1% and 0.5% respectively. %, but the bonding strength between the composite diaphragm coating and the coating is only 0.5N/m. Referring to FIG. 2 to FIG. 4 , SEM images of Example 4, Comparative Example 1 and Comparative Example 2 are shown respectively.

It can also be seen from the test results of Example 4 and Comparative Example 3 that the moisture content of the composite separator can be effectively reduced after the inorganic ceramic particles modified by the silane coupling agent are introduced into the coating.

It can also be seen from the test results in Table 1 that the bonding strength between the composite separator coating and the coating increases with the increase of the weight average molecular weight of PVDF.

For the second aspect of the present disclosure, the following Examples 19-25 and Comparative Examples 4-5 are provided for illustration and comparison.

In the embodiment of the second aspect of the present disclosure, the modified inorganic particles used are obtained by mixing methyltriethoxysilane modifying solution and alumina at a high speed at a temperature of 100°C, and drying to obtain modified and oxidized particles. Aluminum; the mass ratio of alumina to methyltriethoxysilane is 99:1; the structure diagram of the alumina modification process is shown in Figure 5.

Example 19

A preparation method for a low-moisture solvent-based PVDF coating diaphragm, comprising the following steps:

1) Preparation of PVDF glue, 20 parts of PVDF was added to 80 parts of dimethylacetamide, stirred for 3 hours to obtain clear and transparent PVDF glue.

2) Dissolve 20 parts of the above-mentioned PVDF glue into 72 parts of dimethylacetamide and tripropylene glycol mixture (dimethylacetamide/tripropylene glycol=7/3), add 6 parts of modified alumina in turn, 2 Parts of acrylic adhesive (solid content 35-45%, viscosity 20-200cps) were mixed and stirred at room temperature for 1 hour to obtain a white viscous coating solution.

3) Apply the coating solution prepared above evenly on the surface of the polyethylene porous substrate, and sequentially immerse the coated wet film into the coagulation solution at 25°C (dimethylacetamide/tripropylene glycol/water=28: 12:60), after the wet film was solidified, it was washed with water and dried to obtain a low-moisture solvent-based PVDF-coated separator.

Example 20

1) Dissolve 20 parts of the above-mentioned PVDF glue (Example 19) into 70 parts of dimethylacetamide and tripropylene glycol mixture (dimethylacetamide/tripropylene glycol=7/3), and add 8 parts of modified Active alumina and 2 parts of acrylic adhesive were mixed and stirred at room temperature for 1 hour to obtain a white viscous coating solution.

2) Apply the coating solution prepared above evenly on the surface of the polyethylene porous substrate, and sequentially immerse the coated wet film into the 25°C coagulation solution (dimethylacetamide/tripropylene glycol/water=28: 12:60), after the wet film was solidified, it was washed with water and dried to obtain a low-moisture solvent-based PVDF-coated separator. See Figure 7 for the surface topography of the PVDF-coated separator.

Example 21

1) Dissolve 20 parts of the above-mentioned PVDF glue (Example 19) into 68 parts of dimethylacetamide and tripropylene glycol mixture (dimethylacetamide/tripropylene glycol=7/3), and add 10 parts of modified Active alumina and 2 parts of acrylic adhesive were mixed and stirred at room temperature for 1 hour to obtain a white viscous coating solution.

2) Apply the coating solution prepared above evenly on the surface of the polyethylene porous substrate, and sequentially immerse the coated wet film into the 25°C coagulation solution (dimethylacetamide/tripropylene glycol/water=28: 12:60), after the wet film was solidified, it was washed with water and dried to obtain a low-moisture solvent-based PVDF-coated separator. See Figure 8 for the surface topography of the PVDF-coated separator.

Example 22

1) Dissolve 20 parts of the above-mentioned PVDF glue (Example 19) into 66 parts of dimethylacetamide and tripropylene glycol mixture (dimethylacetamide/tripropylene glycol=7/3), and add 12 parts of modified Active alumina and 2 parts of acrylic adhesive were mixed and stirred at room temperature for 1 hour to obtain a white viscous coating solution.

2) Apply the coating solution prepared above evenly on the surface of the polyethylene porous substrate, and sequentially immerse the coated wet film into the 25°C coagulation solution (dimethylacetamide/tripropylene glycol/water=28: 12:60), after the wet film was solidified, it was washed with water and dried to obtain a low-moisture solvent-based PVDF-coated separator. See Figure 9 for the surface topography of the PVDF-coated separator.

Example 23

1) Dissolve 30 parts of the above-mentioned PVDF glue (Example 19) into 57 parts of dimethylacetamide and tripropylene glycol mixture (dimethylacetamide/tripropylene glycol=7/3), and add 9 parts of modified Active alumina and 2 parts of acrylic adhesive were mixed and stirred at room temperature for 1 hour to obtain a white viscous coating solution.

2) Apply the coating solution prepared above evenly on the surface of the polyethylene porous substrate, and sequentially immerse the coated wet film into the 25°C coagulation solution (dimethylacetamide/tripropylene glycol/water=28: 12:60), after the wet film was solidified, it was washed with water and dried to obtain a low-moisture solvent-based PVDF-coated separator. See Figure 10 for the surface topography of the PVDF-coated separator.

Example 24

1) Take 30 parts of the above-mentioned PVDF glue solution (Example 19) and dissolve it in 54 parts of dimethylacetamide and tripropylene glycol mixture (dimethylacetamide/tripropylene glycol=7/3), and add 12 parts in sequence The modified alumina and 2 parts of acrylic adhesive were mixed and stirred at room temperature for 1 hour to obtain a white viscous coating solution.

2) Apply the coating solution prepared above evenly on the surface of the polyethylene porous substrate, and sequentially immerse the coated wet film into the 25°C coagulation solution (dimethylacetamide/tripropylene glycol/water=28: 12:60), after the wet film was solidified, it was washed with water and dried to obtain a low-moisture solvent-based PVDF-coated separator.

Example 25

1) Dissolve 10 parts of the above-mentioned PVDF glue (Example 19) into 80 parts of dimethylacetamide and tripropylene glycol mixture (dimethylacetamide/tripropylene glycol=7/3), and add 8 parts of modified Active alumina and 2 parts of acrylic adhesive were mixed and stirred at room temperature for 1 hour to obtain a white viscous coating solution.

2) Apply the coating solution prepared above evenly on the surface of the polyethylene porous substrate, and sequentially immerse the coated wet film into the 25°C coagulation solution (dimethylacetamide/tripropylene glycol/water=28: 12:60), after the wet film is cured, it is washed with water and dried in turn to obtain a low-moisture solvent-based PVDF coated separator

Comparative example 4

1) Dissolve 20 parts of the above-mentioned PVDF glue (Example 19) into 72 parts of dimethylacetamide and tripropylene glycol mixture (dimethylacetamide/tripropylene glycol=7/3), and add 6 parts of untreated The modified alumina and 2 parts of acrylic adhesive were mixed and stirred at room temperature for 1 hour to obtain a white viscous coating solution.

2) Apply the coating solution prepared above evenly on the surface of the polyethylene porous substrate, and immerse the coated wet film in sequence at 25°C in the coagulation solution (dimethylacetamide/tripropylene glycol/water=28: 12:60), after the wet film was solidified, it was washed with water and dried to obtain a common solvent-based PVDF coated separator. See Figure 11 for the surface topography of the PVDF-coated separator.

Comparative example 5

1) Add 4 parts of PVDF, 6 parts of modified alumina, and 2 parts of acrylic adhesive to 88 parts of water, mix and stir evenly to obtain a white slurry

2) Coating the coating solution prepared above uniformly on the surface of the polyethylene porous substrate, and drying to obtain a water-based PVDF-coated separator.

Fig. 6 is a schematic diagram of a solvent-based PVDF-coated diaphragm in Example 19. PVDF is attached to both sides of the substrate in the form of a network, and ceramics are embedded in the network structure. Fig. 7-10 is the microstructure (embodiment 20-23) that uses the solvent-type PVDF coating membrane surface of silane coupling agent modified particle; Fig. 11 is the microstructure ( Comparative Example 4); Figure 12 is a microstructure diagram of a water-based PVDF-coated diaphragm (Comparative Example 5). The PVDF in Figure 7-10 forms a network structure, and the modified ceramic particles are embedded in the network structure, and the distribution is relatively uniform; when the overall solid content of the slurry increases or the PVDF content increases, the PVDF network on the coating surface The denser the structure; the conventional particles are used in Figure 11, the dispersion of ceramics in the slurry is poor, large-scale agglomeration occurs, and the network structure is poor; due to the use of organic solvents, PVDF is not dissolved, see Figure 12, PVDF is spherically accumulated on the base membrane surface.

Table 2: Comparison of coating film test results of Examples 19-25 and Comparative Examples 4-5

the	隔膜厚度Diaphragm thickness	涂层厚度Coating thickness	面密度Areal density	透气breathable	水分值Moisture value	粘接强度(N/m)Adhesive strength (N/m)
实施例19Example 19	12.212.2	3.23.2	9.039.03	170170	167167	8.58.5
实施例20Example 20	12.412.4	3.33.3	9.569.56	173173	174174	11.211.2
实施例21Example 21	12.612.6	3.63.6	10.5410.54	180180	145145	13.313.3
实施例22Example 22	12.512.5	3.53.5	9.749.74	192192	137137	14.614.6
实施例23Example 23	12.712.7	3.63.6	9.499.49	230230	153153	20.320.3
实施例24Example 24	12.812.8	3.83.8	9.689.68	280280	162162	25.625.6
实施例25Example 25	12.412.4	3.43.4	11.6211.62	163163	203203	4.64.6
对比例4Comparative example 4	12.312.3	3.23.2	9.109.10	184184	568568	6.36.3
对比例5Comparative example 5	12.512.5	3.43.4	10.8210.82	188188	193193	0.90.9

Note: The bonding strength between the low-moisture solvent-based PVDF-coated separator and the electrode is tested at 80°C and 1MPa for 300s, using a tensile tester to test the bonding strength. The bonding strength in Table 2 is the bonding strength between the low-moisture solvent-based PVDF-coated separator and the electrode.

See Table 2, the PVDF coated diaphragms in Examples 19-25 all adopted inorganic particles modified by silane coupling agent and the solvent used was dimethylacetamide; while the PVDF coated diaphragms in Comparative Example 4 used For conventional inorganic particles, the solvent used in Comparative Example 5 is water. The test and comparison results are as follows. The moisture value of the PVDF coated diaphragm prepared by using siloxane-modified inorganic particles is significantly lower than that of unmodified ceramics. The moisture values of Examples 21 and 22 are both lower than 150ppm, while the comparative example 5 The moisture value of the diaphragm is higher than 500ppm; in addition, the adhesive performance between the solvent-based PVDF-coated diaphragm and the electrode (> 8.5N/m) is much better than that of the traditional water-based PVDF-coated diaphragm (approximately 0.9N/m), and the adhesion between the separator and the electrode increases with the increase of PVDF content and slurry solid content (at the same PVDF content). Therefore, the low-moisture solvent-type PVDF coated diaphragm of the present application not only has the advantages of low air permeability of traditional coated diaphragms, but also reduces the moisture value in the diaphragm, improves the bonding performance of the coating and the electrode pole piece, and makes lithium The electrical performance and safety performance of the battery are better guaranteed.

The above are only some implementations of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any person skilled in the art can easily think of various equivalents within the technical scope of the present disclosure. Modifications or replacements should be covered within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be determined by the protection scope of the claims.

Industrial Applicability

The composite separator provided by the first aspect of the present disclosure has excellent bonding performance and heat resistance, and its moisture content is low, which can ensure that the secondary battery has high safety performance and good electrochemical performance at the same time, and can be widely used in lithium In the field of battery technology, it has excellent industrial application performance. At the same time, the second aspect of the present disclosure provides a low-moisture solvent-based PVDF coated diaphragm and a preparation method thereof. The low-moisture solvent-based PVDF coated diaphragm has the advantages of low water content and excellent adhesion to battery pole pieces, and can also be used Widely used in the field of lithium battery technology, it also has superior application performance and broad market prospects.

Claims

A composite diaphragm, comprising a base film and a coating disposed on at least one surface of the base film, characterized in that the coating includes inorganic ceramic particles modified by a silane coupling agent, polyvinylidene fluoride resin, high Heat resistant polymers and adhesives.
The composite diaphragm according to claim 1, characterized in that,

According to 100 parts based on the total weight of the coating, the coating comprises:

Inorganic ceramic particles modified by silane coupling agent, 40-80 parts,

Polyvinylidene fluoride resin, 0.01 to 50 parts,

High heat-resistant polymer, 0.01-50 parts,

Binder, 0.1 to 15 parts;

Optionally, based on the total weight of the coating as 100 parts, the coating includes:

Inorganic ceramic particles modified by silane coupling agent, 40-70 parts,

Polyvinylidene fluoride resin, 8-40 parts,

High heat-resistant polymer, 8 to 40 parts,

Binder, 2 to 10 parts.
The composite diaphragm according to claim 1 or 2, characterized in that the weight ratio of the polyvinylidene fluoride resin to the high heat-resistant polymer is 0.1:99.9-99.9:0.1, optionally 1:4 ~4:1, optionally 1:2~3:2.
The composite diaphragm according to claim 1, characterized in that,

The weight ratio of the silane coupling agent to the inorganic ceramic particles is 0.01:99.99 to 2:98, optionally 0.1:99.9 to 1:99, and/or,

The volume average particle diameter Dv50 of the inorganic ceramic particles modified by the silane coupling agent is 0.2 μm˜1.0 μm, optionally 0.3 μm˜0.8 μm, optionally 0.4 μm˜0.7 μm.
The composite diaphragm according to claim 1, characterized in that,

The inorganic ceramic particles are selected from alumina, boehmite, calcium carbonate, hydrotalcite, montmorillonite, spinel, mullite, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, calcium oxide, beryllium oxide , one or more of magnesium hydroxide, boron nitride, silicon nitride, aluminum nitride, titanium nitride, boron carbide, silicon carbide, zirconium carbide, and/or,

The molecular formula of the silane coupling agent is Y-Si(OX) 3 , wherein each X independently represents -CH 3 , -C 2 H 5 , -(C=O)CH 3 , or -(C=O) C 2 H 5 , Y represents C1～C10 alkyl, C1～C10 alkoxy, C2～C10 alkenyl, C2～C10 alkoxy, C2～C5 oxetanealkyl, amino, methacryloyloxy , acryloyloxy group or a combination of several, optionally, Y represents a C1~C10 alkyl group, or a C1~C10 alkoxy group,

Optionally, the silane coupling agent is selected from methyltriethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, n-butyltriethoxysilane, isobutyltriethoxysilane, Ethoxysilane, (3,3-dimethylbutyl)triethoxysilane, n-hexyltriethoxysilane, n-octyltriethoxysilane, isooctyltriethoxysilane, n-decyl Triethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, isopropyltrimethoxysilane, butyltrimethoxysilane, isobutyltrimethoxysilane Silane, tert-butyltrimethoxysilane, n-pentyltrimethoxysilane, trimethoxy(1,1,2-trimethylpropyl)-silane, n-hexyltrimethoxysilane, n-octyltrimethoxy Silane, isooctyltrimethoxysilane, n-decyltrimethoxysilane, (methoxymethyl)triethoxysilane, (methoxymethyl)trimethoxysilane, trimethoxy(3-methoxy propyl)silane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidyl etheroxypropyltrimethoxysilane, γ-(methacryloyloxy)propane One of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane or several,

Optionally, the silane coupling agent is selected from methyltriethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, n-butyltriethoxysilane, isobutyltriethoxysilane, Ethoxysilane, (3,3-dimethylbutyl)triethoxysilane, n-hexyltriethoxysilane, n-octyltriethoxysilane, isooctyltriethoxysilane, n-decyl Triethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, isopropyltrimethoxysilane, butyltrimethoxysilane, isobutyltrimethoxysilane Silane, tert-butyltrimethoxysilane, n-pentyltrimethoxysilane, trimethoxy(1,1,2-trimethylpropyl)-silane, n-hexyltrimethoxysilane, n-octyltrimethoxy Silane, isooctyltrimethoxysilane, n-decyltrimethoxysilane, (methoxymethyl)triethoxysilane, (methoxymethyl)trimethoxysilane, trimethoxy(3-methoxy One or more of propyl) silanes.
The composite diaphragm according to claim 1, characterized in that,

The polyvinylidene fluoride resin has a weight average molecular weight of 200,000 to 1.5 million and a melting point of 137°C to 158°C. Optionally, the polyvinylidene fluoride resin has a weight average molecular weight of 600,000 to 1.5 million and a melting point of 137°C to 156°C, optionally, the polyvinylidene fluoride resin has a weight average molecular weight of 1 million to 1.5 million and a melting point of 137°C to 152°C; and/or,

The high heat-resistant polymer is selected from one or more of polyimide, polyetherimide, aramid, and sulfonamide; and/or,

The adhesive is selected from acrylate adhesives.
The composite diaphragm according to claim 1, wherein the base film is selected from one or more of polyolefin porous membranes, non-woven fabrics, and glass fibers,

Optionally, the material of the base film is selected from polyethylene, polypropylene, polyimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyethylene terephthalate one or more of.
The composite diaphragm according to claim 1, characterized in that,

The base film has a thickness of 4 μm to 12 μm and a porosity of 30% to 50%, optionally, the base film has a thickness of 7 μm to 12 μm and a porosity of 35% to 45%; and/or,

The coating has a thickness of 0.2 μm to 3 μm, optionally 1 μm to 2 μm; and/or,

The total thickness of the composite separator is 4 μm˜18 μm, optionally 9 μm˜16 μm.
The composite diaphragm according to claim 1, characterized in that,

The bonding strength between coatings of the composite diaphragm is ≥3N/m, optionally ≥5N/m, optionally ≥10N/m;

After the composite diaphragm is kept at 130°C for 60 minutes, the heat shrinkage rate in the longitudinal direction is ≤13%, and the heat shrinkage rate in the transverse direction is ≤13%. Optionally, the heat shrinkage rate in the longitudinal direction is ≤7%, and the heat shrinkage rate in the transverse direction is rate≤7%, optionally, the heat shrinkage rate in the longitudinal direction is less than or equal to 5%, and the heat shrinkage rate in the transverse direction is less than or equal to 5%;

After the composite diaphragm is kept at 110°C for 10 minutes, the moisture mass percentage is ≤500ppm, optionally ≤300ppm;

The air permeability of the composite membrane is ≤450s/100cc, optionally ≤300s/100cc, optionally ≤250s/100cc.
A preparation method of a composite diaphragm, comprising the steps of:

dissolving polyvinylidene fluoride resin in a first organic solvent to prepare a polyvinylidene fluoride glue, and dissolving a high heat-resistant polymer in a second organic solvent to prepare a high heat-resistant polymer glue;

uniformly mixing inorganic ceramic particles modified by a silane coupling agent, polyvinylidene fluoride glue, high heat-resistant polymer glue, and a binder in a third organic solvent to obtain a slurry;

The obtained slurry is coated on at least one surface of the base film and dried to obtain a composite diaphragm.
The method according to claim 10, characterized in that,

The first organic solvent is selected from one or more of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, acetone, dimethyl sulfoxide, and/or,

The second organic solvent is selected from one or more of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, acetone, dimethyl sulfoxide, and/or,

The third organic solvent is a mixed solution of component 1 and component 2, and component 1 is selected from dimethylacetamide, dimethylformamide, N-methylpyrrolidone, acetone, dimethyl sulfoxide One or more, component 2 is selected from one or more of tripropylene glycol, propylene glycol, ethanol, the weight ratio of component 1 to component 2 is 10:90～40:60, optionally 20: 80～30:70;

Optionally, the first organic solvent and the second organic solvent are the same.
The method according to claim 10, further comprising the step of: reacting the silane coupling agent with the inorganic ceramic particles at 60° C. to 200° C. to obtain inorganic ceramic particles modified by the silane coupling agent.
A secondary battery, comprising the composite separator according to any one of claims 1-9 or the composite separator prepared according to the method according to any one of claims 10-12.
A low-moisture solvent-type PVDF coating diaphragm is characterized in that: the diaphragm includes a polyolefin substrate microporous film and a PVDF coating layer is formed on one or both sides of the substrate; the PVDF coating layer includes: a silane coupling agent Modified inorganic particles, PVDF resin, and acrylic adhesive; the coated diaphragm is treated at 100-120°C for 5-15 minutes, and the moisture of the diaphragm is tested by a coulometric moisture tester, and the moisture value is lower than 500ppm.
The low-moisture solvent-based PVDF-coated separator according to claim 14, characterized in that: the coated surface of the separator is bonded to the battery pole piece, and after hot pressing at 80°C and 1MPa for 300s, the bonding strength is tested using a tensile tester , The bonding strength between the coating and the battery pole piece is 5-30N/m.
The low-moisture solvent-type PVDF coating diaphragm according to claim 14 is characterized in that: the polyolefin substrate microporous film is a kind of in PE lithium battery diaphragm, PE/PP lithium battery diaphragm; The thickness of microporous film is 5-12 μm.
The low-moisture solvent-type PVDF coating diaphragm according to claim 14, characterized in that: in the PVDF wet coating layer: 1-10 parts of PVDF resin, 5-15 parts of inorganic particles modified by silane coupling agent parts, 0.1-5 parts for acrylic adhesives.
The low-moisture solvent-type PVDF coating diaphragm according to claim 14, characterized in that: the inorganic particles modified by the silane coupling agent are alumina, boehmite, silicon dioxide, titanium dioxide, hydrotalcite and montmorillonite at least one of the
The low-moisture solvent-type PVDF coating diaphragm according to claim 17, characterized in that: the silane coupling agent used is octyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane , γ-aminopropyltriethoxysilane, γ-glycidyl etheroxypropyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, N-(β-aminoethyl) -One or more of γ-aminopropyltrimethyl(ethyl)oxysilane and aminopropyltrimethyl(ethyl)oxysilane.
The low-moisture solvent-based PVDF-coated diaphragm according to claim 18, characterized in that the weight ratio of the silane chain in the modified inorganic particles is not higher than 2%.
The low-moisture solvent-type PVDF coating diaphragm according to claim 18, characterized in that: the preparation method of the PVDF wet coating layer is: dissolving the PVDF resin in the organic solvent 1 to prepare PVDF glue, and dissolving the PVDF glue , silane coupling agent modified inorganic particles, acrylic adhesive, and organic solvent 2 are mixed uniformly to obtain a coating liquid, and the coating liquid is evenly coated on the surface of the polyethylene porous substrate, and the coated wet film Immerse in the coagulation solution in sequence, and after the wet film solidifies, wash with water and dry in sequence to obtain a low-moisture solvent-type PVDF-coated separator.
The low-moisture solvent-type PVDF coating diaphragm according to claim 20 is characterized in that: the organic solvent 1 is dimethylacetamide, and the organic solvent 2 is dimethylacetamide and dimethylacetamide with a volume ratio of 3-10:1-5 Tripropylene glycol;

The mass ratio of PVDF resin to organic solvent 1 is 1:3-8; the mass ratio of PVDF glue to organic solvent 2 is 1:3-8.
The low-moisture solvent-type PVDF coated diaphragm according to claim 20, characterized in that the coagulation liquid is dimethylacetamide, tripropylene glycol and water with a mass ratio of 25-35:10-20:50-70.