CN113437438A

CN113437438A - Epoxy resin modified ceramic diaphragm and preparation method and application thereof

Info

Publication number: CN113437438A
Application number: CN202010151280.1A
Authority: CN
Inventors: 赵金保; 李航; 彭龙庆; 张鹏
Original assignee: Xiamen University
Current assignee: Xiamen University
Priority date: 2020-03-06
Filing date: 2020-03-06
Publication date: 2021-09-24

Abstract

The invention provides an epoxy resin modified ceramic diaphragm which comprises a porous base membrane, wherein epoxy resin is infiltrated into the ceramic diaphragm and cured, and epoxy resin protective layers are formed on the surfaces of inorganic ceramic particles of the ceramic diaphragm, the surfaces of the porous base membrane and the walls of micropores and among the surfaces of the inorganic ceramic particles, the surfaces of the porous base membrane and the walls of the micropores. Due to the properties of the epoxy resin itself, the protective layer is uniform and does not block the micropores of the porous base film. The epoxy resin protective layer can be formed by coating epoxy resin ceramic slurry on the single-layer or double-layer surface of the porous base film and curing, can also be formed by in-situ polymerization of epoxy resin on the ceramic-coated porous base film, and can also be formed by coating a layer of epoxy resin solution on the prepared ceramic diaphragm and curing.

Description

Epoxy resin modified ceramic diaphragm and preparation method and application thereof

Technical Field

The invention relates to a battery diaphragm, products such as a battery, a capacitor and the like, in particular to a high-temperature resistant ceramic diaphragm, a preparation method and an applied battery.

Background

The lithium ion battery is used as a chemical power system which has high energy density, high output voltage, no memory effect, excellent cycle performance and environmental friendliness, has good economic benefit, social benefit and strategic significance, is widely applied to various fields such as mobile communication, digital products and the like, and is most likely to become the most main power system in the fields of energy storage and electric automobiles.

The conventional lithium ion battery mainly comprises a positive electrode, a negative electrode, a diaphragm and electrolyte. Among them, the separator mainly plays a role in preventing the contact between the positive and negative electrodes and allowing ion conduction, and is an important component of the battery. At present, polyolefin diaphragm materials with a microporous structure, such as single-layer or multi-layer films of Polyethylene (PE) and Polypropylene (PP), are mainly used in commercial lithium ion batteries. Because the polyolefin diaphragm has low melting temperature and poor thermal stability (PE is about 130 ℃ and PP is about 160 ℃), although the polyolefin diaphragm can provide enough mechanical strength and chemical stability at normal temperature, the polyolefin diaphragm shows larger thermal shrinkage under the high-temperature condition, so that the contact short circuit of a positive electrode and a negative electrode is caused, thermal runaway is caused, heat accumulation is aggravated, high air pressure in the battery is generated, and the battery is burnt or exploded.

In order to meet the development requirement of high-capacity lithium ion batteries, the development of high-safety diaphragms is urgent. The excellent temperature resistance and high safety of the ceramic separator make it one of the main choices to replace the conventional polyolefin separator.

Ceramic Separators are safety functional Separators formed by coating a uniform protective layer made of Ceramic microparticles or the like on one or both surfaces of a conventional polyolefin microporous membrane substrate. On the basis of ensuring the original basic characteristics of the polyolefin microporous diaphragm, the high heat-resistant function of the diaphragm is given by the introduction of the ceramic layer, and the temperature difference between the closed pore temperature and the melting temperature of the diaphragm is pulled, so that the internal short circuit of the lithium ion battery is effectively reduced, and the thermal runaway of the battery caused by the internal short circuit of the battery is prevented.

However, existingCeramic membranes are also very limited in their thermal stability. Mainly because the inorganic ceramic particles are adhered to the surface of the base membrane of the polyolefin diaphragm through the adhesive, when the temperature reaches the melting point of the base membrane, the base membrane is melted, and the existence of the ceramic particles can not completely inhibit the shrinkage of the diaphragm although playing a certain role in hindering the shrinkage of the diaphragm. For example, Al based on PE₂O₃Ceramic diaphragm, PE-based film melts when the temperature rises to 130 deg.C due to Al₂O₃The shrinkage resistance of the ceramic particles is such that the ceramic diaphragm does not shrink, but Al does so when the temperature continues to rise above 150 deg.C₂O₃The ceramic coating layer shrinks along with the base film. And the mechanical property of the diaphragm is greatly reduced along with the melting of the base film, and the ceramic layer cannot be self-supported to form a film, so that the diaphragm is finally pulverized, and the contact short circuit of the anode and the cathode can still be caused. Obviously, a simple ceramic separator cannot meet the requirements of high-safety applications of batteries.

CN107785520A provides a lithium ion battery separator comprising a porous base film and a heat-resistant layer covering at least one side surface of the porous base film; the heat-resistant layer contains a high-temperature-resistant polymer and inorganic nanoparticles, and has a fiber network structure. The provided lithium ion battery diaphragm has good stability at high temperature (more than 160 ℃), small high-temperature heat shrinkage rate and good high-temperature mechanical strength, and is much better than the heat resistance and high-temperature mechanical strength of a composite diaphragm obtained by simply adopting high-temperature-resistant polymer spinning, and a Common Ceramic (CCL) diaphragm adopts a thermolabile polymer, so that the diaphragm has great heat shrinkage at high temperature or the phenomenon that the polymer melts and the ceramic particles are loosely connected at high temperature, thereby ensuring that the whole lithium ion battery diaphragm does not have high mechanical strength. The heat-resistant layer adopts a fiber mesh structure, the realization difficulty is high, and the preparation process is complex.

Disclosure of Invention

In order to solve the problems, the invention provides an epoxy resin modified ceramic diaphragm which is developed on the basis of a ceramic diaphragm. An object of the present invention is to provide an epoxy resin modified ceramic separator prepared by the inventive method, which can effectively suppress the thermal shrinkage of the base film and maintain the basic film form of the modified ceramic separator when the melting temperature of the base film is reached. The epoxy resin modified ceramic diaphragm provided by the invention has extremely excellent thermal stability and mechanical properties. Meanwhile, the invention has low cost and simple operation in the preparation process, and is suitable for large-scale production.

The invention also aims to provide a lithium ion battery containing the epoxy resin modified ceramic diaphragm prepared by the method.

The invention also aims to provide application of the ceramic modified diaphragm prepared by the method in a chemical power system, in particular application in a lithium ion battery.

In order to achieve the purpose, the invention adopts the following specific scheme:

the invention provides an epoxy resin modified ceramic diaphragm which comprises a porous base membrane, wherein epoxy resin is infiltrated into the ceramic diaphragm and cured, and epoxy resin protective layers are formed on the surfaces of inorganic ceramic particles of the ceramic diaphragm, the surfaces of the porous base membrane and the walls of micropores and among the surfaces of the inorganic ceramic particles, the surfaces of the porous base membrane and the walls of the micropores. Due to the properties of the epoxy resin itself, the protective layer is thin and uniform and does not block the micropores of the porous base film. The epoxy resin protective layer can be formed by coating epoxy resin ceramic slurry on the single-layer or double-layer surface of the porous base film and curing, can also be formed by in-situ polymerization of epoxy resin on the ceramic-coated porous base film, and can also be formed by coating a layer of epoxy resin solution on the prepared ceramic diaphragm and curing; the thickness of the single surface of the epoxy resin protective layer is 0.5 nm-40 nm, preferably 3-10 nm.

More specifically, epoxy resin and ceramic slurry can be mixed to prepare epoxy resin ceramic slurry, and then the epoxy resin ceramic slurry is coated on one side or two sides of the porous base membrane;

or coating ceramic slurry on the single-layer or double-layer surface of the porous base membrane to prepare a ceramic diaphragm, soaking the ceramic diaphragm in a mixed solution of epoxy resin polymerization monomers, and coating epoxy resin by in-situ polymerization; the ceramic diaphragm can also be prepared by coating ceramic slurry on the porous base film, coating the prepared epoxy resin solution on the ceramic diaphragm and then curing to form the epoxy modified ceramic diaphragm.

Further, the porous base film comprises at least one of polyolefin porous polymer (polyethylene, polypropylene and the like), polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polyethylene terephthalate, polybutylene terephthalate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyvinylpyrrolidone, polyethylene oxide, polyvinyl alcohol or a blending and copolymerization system derived from the above polymers.

Further, the size of the inorganic ceramic particles is 10-1000nm, preferably 50-500nm, and the thickness of the ceramic layer is 0.1-10 μm, preferably 2-5 μm.

Further, the ceramic slurry contains 5-80% of base materials by weight percentage and the balance of solvent. The base material comprises the following substances in parts by mass: 0.1-20 parts of binder and 80-99.9 parts of ceramic particles.

Further, the epoxy resin ceramic slurry contains 5-80% of base material by weight percentage and the balance of solvent. The base material comprises the following substances in parts by mass: 0.1-20 parts of binder, 60-99 parts of ceramic particles, 0.1-20 parts of epoxy resin, 0-5 parts of curing agent, 0-5 parts of curing accelerator, 0-5 parts of surfactant and 0-5 parts of modifier.

Further, the epoxy resin is an organic compound having two or more epoxy groups in its chemical structure, and is a high-molecular polymer that can form a thermosetting by a ring-opening reaction of the epoxy groups. The molecular weight of the epoxy resin is determined by gel permeation chromatography, and the weight average molecular weight is 100-5000.

Further, the epoxy resin polymerizable monomer is classified into a compound capable of introducing or forming an epoxy group (referred to as component a) and a compound, prepolymer or compound, prepolymer containing two or more unsaturated double bonds (referred to as component B) having two or more active hydrogens.

Furthermore, the mixed solution of the component A and the component B comprises, by weight, 0.1-40% of the component A, 0.1-40% of the component B, 0.01-8% of a catalyst, 0.01-5% of a curing agent, 0.01-5% of a curing accelerator, 0.01-5% of a surfactant, 0-5% of an additive, and the balance of a solvent.

Further, the catalyst includes, but is not limited to, sodium carbonate, potassium carbonate, pyridine, triethylamine, sodium acetate, sodium hydroxide, potassium hydroxide, quaternary ammonium salt, quaternary phosphonium salt, choline, and the like.

Further, the curing agent may be an addition polymerization type curing agent such as polyamine, acid anhydride, phenol, mercaptan, etc., or other obvious type curing agent such as a catalytic type curing agent, or a latent type curing agent such as imidazole, etc.

Further, the curing accelerator is selected according to the nucleophilic and electrophilic properties of the curing agent (the nucleophilic curing agent is matched with the electrophilic curing accelerator, and the electrophilic curing agent is matched with the nucleophilic curing accelerator). Commonly used curing accelerators are amines, phenols, acids, amides, and the like.

Further, the surfactant is at least one of stearic acid, sodium dodecyl benzene sulfonate, quaternary ammonium compound, sodium hexadecyl sulfonate, lecithin, amino acid type, betaine type, fatty glyceride, fatty sorbitan and polysorbate.

Further, the ceramic particles are at least one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride and magnesium nitride. The particle size of the ceramic particles is 5 nm-10 um.

Further, the binder is an aqueous binder or an organic binder;

the water system binder is at least one of sodium methyl cellulose, styrene-butadiene rubber, gelatin, polyvinyl alcohol and polyacrylate terpolymer latex;

the organic binder is at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene and polymethyl methacrylate.

Further, the solvent is one or more organic solvents such as methanol, ethanol, isopropanol, N-butanol, acetone, ethyl acetate, N-butyl acetate, xylene, acetonitrile, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, N-methylpyrrolidone, dichloromethane, trichloromethane and the like.

Further, the additive is not particularly limited, and is various additives capable of improving the properties of the epoxy resin.

The preparation scheme of the epoxy resin modified ceramic diaphragm provided by the invention is as follows:

the first scheme is as follows:

1. synthesizing an epoxy resin: according to mass percentage, mixing the component A: 1-40%, component B: 1-40 percent of mixed solution, 0.2-8 percent of alkaline catalyst and 10-95 percent of solvent react for 0.5-24h at 25-110 ℃ (the mixed solution can be reacted in sections at different temperatures, or the mixed solution can be reacted in sections at fixed temperature, or the alkaline catalyst can be added once or in batches), and the epoxy resin is obtained by separating, washing and drying.

2. Preparing a ceramic diaphragm: and uniformly mixing the ceramic particles and the binder according to a certain proportion to prepare ceramic slurry, coating one or two surfaces of the prepared ceramic slurry on the surface of the porous base membrane, drying and removing the solvent to obtain the ceramic diaphragm.

3. Preparing 1-10% of epoxy resin solution by mass, preferably 3-8%, adding 0.01-5% of curing agent, 0.01-5% of curing accelerator and 0-5% of additive. The ceramic diaphragm is fully soaked by the epoxy resin solution through the modes of spraying, soaking and the like, and is dried and cured for 0.5 to 24 hours at the temperature of between 25 and 110 ℃.

Scheme II:

1. and (2) preparing the ceramic diaphragm, namely uniformly mixing the ceramic particles and the binder according to a certain proportion to prepare ceramic slurry, coating one or two surfaces of the prepared ceramic slurry on the surface of the porous base membrane, and drying to remove the solvent to obtain the ceramic diaphragm.

2. Preparing an epoxy resin modified ceramic diaphragm: preparing a mixed solution of the component A and the component B with a certain concentration, and controlling the total mass fraction of the A, B two components to be a certain concentration value within 1-10%, preferably 3-8%, by adjusting the concentration. And (2) fully soaking the ceramic diaphragm prepared in the step (1) in the mixed solution of the component A and the component B, taking out, reacting at 25-110 ℃ for 0.5-24h (segmented reaction can be carried out at different temperatures, or segmented reaction can be carried out at a fixed temperature), washing and drying to obtain the epoxy resin modified ceramic diaphragm.

The coating mode of the invention is not limited, and comprises spraying, blade coating, roll coating and the like.

The invention also aims to provide an application of the epoxy ceramic diaphragm in the field of chemical power sources, in particular to a lithium ion battery.

Another object of the present invention is to provide a lithium ion battery, including a positive electrode material and a negative electrode material, wherein: the epoxy resin modified ceramic diaphragm provided by the invention is arranged between the anode material and the cathode material.

The positive electrode material generally used for lithium ion batteries can be used in the present invention. As the positive electrode active material of the positive electrode, a compound capable of reversibly inserting and extracting Li + can be used, and examples thereof include Li_xMO₂Or Li_yM₂O₄(wherein M is a transition metal, x is 0. ltoreq. x.ltoreq.1, and y is 0. ltoreq. y.ltoreq.2), a lithium-containing composite oxide, a spinel-like oxide, a metal chalcogenide having a layered structure, an olivine structure, or the like.

The negative electrode material generally used for lithium ion batteries can be used in the present invention. As the negative electrode active material for the negative electrode, a compound capable of inserting and extracting lithium metal or lithium may be used. For example, alloys of aluminum, silicon, tin, or the like, oxides, carbon materials, or the like can be used as the negative electrode active material. Examples of the oxide include titanium dioxide, and examples of the carbon material include graphite, pyrolytic carbons, cokes, glassy carbons, a fired product of an organic polymer compound, mesophase carbon microbeads, and the like.

For the negative electrode constituting the nonaqueous electrolyte secondary battery, for example, a conductive additive such as carbon black or acetylene black, or a binder such as polyvinylidene fluoride or polyethylene oxide is appropriately added to the negative electrode active material to prepare a negative electrode mixture, and the negative electrode mixture is applied to a tape-shaped molded body having a current collecting material such as a copper foil as a core material. However, the method for producing the negative electrode is not limited to the above example.

In the nonaqueous electrolyte secondary battery provided by the present invention, a nonaqueous solvent (organic solvent) is used as the nonaqueous electrolyte. The nonaqueous solvent includes carbonates, ethers, and the like.

In addition to the nonaqueous solvent, chain alkyl esters such as methyl propionate, chain phosphoric acid triesters such as trimethyl phosphate, and the like; nitrile solvents such as 3-methoxypropionitrile; a nonaqueous solvent (organic solvent) such as a branched compound having an ether bond typified by a dendrimer.

In addition, fluorine-based solvents can also be used.

As the electrolyte salt used in the nonaqueous electrolytic solution, lithium salts such as lithium perchlorate, organoboron lithium salt, lithium salt of fluorine-containing compound, and lithium imide salt are preferable.

The concentration of the electrolytic lithium salt in the nonaqueous electrolytic solution is, for example, preferably 0.3mol/L or more, more preferably 0.7mol/L or more, preferably 1.7mol/L or less, and more preferably 1.2mol/L or less. If the concentration of the electrolyte lithium salt is too low, the ionic conductivity is too low, and if it is too high, there is a fear that the electrolyte salt which is not completely dissolved may be precipitated.

The nonaqueous electrolytic solution may contain various additives for improving the performance of the battery using the nonaqueous electrolytic solution, and is not particularly limited.

The epoxy resin-modified ceramic separator and the nonaqueous electrolyte secondary battery using the same according to the present invention have excellent physical and chemical properties. Therefore, the nonaqueous electrolyte secondary battery of the present invention can be widely applied not only to secondary batteries for driving power sources of mobile information devices such as mobile phones and notebook personal computers, but also to power sources of various devices such as electric vehicles, by utilizing such characteristics.

By adopting the technical scheme, the invention has the beneficial effects that:

1. by coating the epoxy resin on the basis of the ceramic diaphragm, the ceramic particle layer, the surface of the porous base film and the hole wall can be bonded and connected into a whole through the epoxy resin, the curing shrinkage rate of the epoxy resin is low and is generally 1-2%, the epoxy resin and the ceramic particle layer form a three-dimensional composite protective layer, and the mechanical properties such as the tensile strength, the peeling strength and the like of the diaphragm are improved.

2. The three-dimensional composite protective layer composed of the epoxy resin and the ceramic particle layer improves the heat treatment stability of the diaphragm, still maintains strong mechanical strength at 200 ℃, can effectively prevent the contact of the anode and the cathode, and ensures the safety performance of the battery.

3. And fusing and closing the pores of the porous base membrane at the temperature of 130-140 ℃ to form a compact layer, cutting off a transmission channel of lithium ions in the diaphragm, and simultaneously keeping the dimensional stability of a three-dimensional protective layer consisting of the epoxy resin and the ceramic layer to prevent the negative electrode of the battery from contacting and short-circuiting. The synergistic effect of the epoxy resin protective layer, the ceramic layer and the porous base film endows the epoxy resin modified ceramic diaphragm with a heat blocking function, and prevents further thermal runaway of the battery at high temperature.

4. The epoxy resin material selected by the invention has O atoms capable of generating hydrogen bond interaction with H atoms on a porous base membrane such as pp and the like, the epoxy resin three-dimensional coating layer can be well adhered and combined on the base membrane through the hydrogen bond interaction of the epoxy resin and the base membrane, meanwhile, the O atoms and hydroxyl on the surface of ceramic particles can have similar interaction, and the interaction between the resin layer and the ceramic particle layer is enhanced.

5. The epoxy resin material selected by the invention can well permeate into micropores of a porous base membrane under the action of polar functional groups, and a thin and uniform polymer coating layer is preferentially adhered to the wall surface of the micropores of the diaphragm, the curing shrinkage rate of the epoxy resin is low, generally 1-2%, the micropores of the diaphragm can not be blocked, the influence on the porosity and the air permeability of the diaphragm is avoided, and enough ion conduction channels can be ensured on the thin coating, so that the negative influence on the performance of the battery is avoided.

6. The preparation method is simple and low in cost. Particularly, the epoxy resin is cheap and easy to obtain, can be cured at low temperature, has good electrochemical stability, can be directly applied to the battery without being cleaned, is easy to realize industrial production, is expected to replace the existing ceramic diaphragm, realizes industrial application and improves the safety performance of the lithium ion power battery.

Drawings

FIG. 1 comparative graph of example 1 (right) and comparative example 1 (left) after heat treatment at 160 ℃ for 30 min.

FIG. 2 comparative graph of tensile strength at different temperatures for example 2 and comparative example 2

FIG. 3 is a comparative graph of the heat-blocking function test of example 3 and comparative example 3.

FIG. 4 is a comparative scanning electron microscope image of example 1 and comparative example 1;

FIG. 5 is a histogram of the pore size distribution of the separators of example 1 and comparative example 1;

FIG. 6 is a graph showing the cycle performance test of example 7 and comparative example 5.

FIG. 7 comparative graph of example 4 before (left) and after (right) heat treatment at 160 ℃ for 30 min.

Table 1 table comparing air permeability and conductivity of example 1 with comparative examples 1 and 4;

table 2 table comparing the coating layer thicknesses of example 1 with those of example 4, example 5 and example 6.

Detailed Description

The following examples are given for the purpose of illustration and are not intended to limit the scope of the present invention.

The thickness of the coating or protective layer referred to in this specification means the thickness within the pores of the separator or the thickness at the plane of the coating or protective layer that is external to the ceramic layer of the separator. The calculation method in the specification is to estimate the thickness of the coating layer through the reduction of the average value of the pore diameter

Example 1:

preparing epoxy resin:

dissolving bisphenol A in epichlorohydrin according to the molar ratio of bisphenol A to epichlorohydrin of 1: 6, heating to 55 ℃ in nitrogen atmosphere, adding 50% (mass fraction) of NaOH aqueous solution (the addition is 0.08 times of bisphenol A molecules), reacting for 3h, vacuumizing, continuously dropwise adding 50% of NaOH aqueous solution for 1.5-3h, continuously reacting for 20min after dropwise adding of an alkaline catalyst, separating and purifying to obtain the liquid bisphenol A epoxy resin.

Preparing a ceramic diaphragm:

95 parts by mass of silicon dioxide ceramic particles with the particle size of about 300nm, 3 parts by mass of styrene butadiene rubber, 2 parts by mass of sodium carboxymethylcellulose and a water/ethanol mixed solution with the volume ratio of 1: 1 are prepared into ceramic slurry with the solid content of 11% (mass fraction), the ceramic slurry is coated on the single-layer surface of a commercial Polyethylene (PE) diaphragm, and the solvent is removed by drying, so that the silicon dioxide ceramic diaphragm is obtained.

Preparing an epoxy resin modified ceramic diaphragm:

dissolving the synthesized epoxy resin in an acetone solvent to prepare a solution with 5% mass dispersion, adding 0.5% curing agent diethylenetriamine and 0.1% curing accelerator resorcinol, coating the obtained epoxy resin solution on a silicon dioxide ceramic diaphragm, and drying and curing the silicon dioxide ceramic diaphragm in an oven at 45 ℃ for 12 hours. And obtaining the epoxy resin modified ceramic diaphragm.

Example 2

Preparing a ceramic diaphragm:

92 parts by mass of alumina ceramic particles with the particle size of about 400nm, 5 parts by mass of styrene butadiene rubber, 3 parts by mass of sodium carboxymethylcellulose and a water/ethanol mixed solution with the solvent in a volume ratio of 1: 1 are prepared into ceramic slurry with the solid content of 12% (mass fraction), the ceramic slurry is coated on the surface of a double layer of a commercial polypropylene (PP) diaphragm, and the solvent is dried to remove, so that the alumina ceramic diaphragm is obtained.

Preparing an epoxy resin modified ceramic diaphragm:

dissolving bisphenol F in epichlorohydrin according to the molar ratio of bisphenol F to epichlorohydrin of 1: 10, heating to 60 ℃ in nitrogen atmosphere, adding 50% (mass fraction) of NaOH aqueous solution (the addition amount is 0.01 times of bisphenol F molecules), reacting for 6h, and cooling. Adding 2 percent (mass fraction) of curing agent triethylenetetramine and 1 percent (mass fraction) of modifier, adding 20 percent of ethyl acetate as solvent (diluent) to dilute the concentration of the epoxy resin solution to 3 percent (mass fraction), immersing the prepared aluminum oxide ceramic diaphragm into the epoxy resin solution, fully infiltrating the ceramic diaphragm with the epoxy resin solution, taking out the diaphragm, and placing the diaphragm in an oven to be dried and cured for 24 hours at 50 ℃. And obtaining the epoxy resin modified ceramic diaphragm.

Example 3:

preparing epoxy resin:

dissolving bisphenol A in epichlorohydrin according to the molar ratio of bisphenol A to epichlorohydrin of 1: 8, heating to 55 ℃ in nitrogen atmosphere, adding 50% (mass fraction) of NaOH aqueous solution (the addition is 0.12 times of bisphenol A molecules), reacting for 6h, separating and purifying to obtain the liquid bisphenol A epoxy resin.

Preparing a ceramic diaphragm:

90 parts by mass of magnesia ceramic particles with the particle size of about 200nm, 6 parts by mass of styrene-butadiene rubber, 4 parts by mass of sodium carboxymethylcellulose and a water/acetone mixed solution with the solvent of the volume ratio of 2: 1 are prepared into ceramic slurry with the solid content of 10 percent (mass fraction), the ceramic slurry is coated on the single-layer surface of a commercial Polyethylene (PE) diaphragm, and the solvent is dried to remove, so that the magnesia ceramic diaphragm is obtained.

Preparing an epoxy resin modified ceramic diaphragm:

dissolving the synthesized epoxy resin in a xylene solvent to prepare a solution with the mass fraction of 5 percent, adding 4 percent of curing agent phthalic anhydride and 2 percent of curing accelerator quaternary ammonium salt, spraying the obtained epoxy resin solution on a silicon dioxide ceramic diaphragm, and placing the silicon dioxide ceramic diaphragm in an oven to be dried and cured for 48 hours at the temperature of 55 ℃. And obtaining the epoxy resin modified ceramic diaphragm.

Example 4

Preparing epoxy resin:

Preparing a ceramic diaphragm:

Preparing an epoxy resin modified ceramic diaphragm:

dissolving the synthesized epoxy resin in an acetone solvent to prepare a solution with the mass dispersion of 0.1%, adding 0.5% of curing agent diethylenetriamine and 0.1% of curing accelerator resorcinol, coating the obtained epoxy resin solution on a silicon dioxide ceramic diaphragm, and placing the silicon dioxide ceramic diaphragm in an oven to be dried and cured for 12 hours at the temperature of 45 ℃. And obtaining the epoxy resin modified ceramic diaphragm.

Example 5

Preparing epoxy resin:

Preparing a ceramic diaphragm:

Preparing an epoxy resin modified ceramic diaphragm:

dissolving the synthesized epoxy resin in an acetone solvent to prepare a solution with the mass dispersion of 3%, adding 0.5% of curing agent diethylenetriamine and 0.1% of curing accelerator resorcinol, coating the obtained epoxy resin solution on a silicon dioxide ceramic diaphragm, and drying and curing the silicon dioxide ceramic diaphragm in an oven at the temperature of 45 ℃ for 12 hours. And obtaining the epoxy resin modified ceramic diaphragm.

Example 6

Preparing epoxy resin:

Preparing a ceramic diaphragm:

Preparing an epoxy resin modified ceramic diaphragm:

dissolving the synthesized epoxy resin in an acetone solvent to prepare a solution with the mass dispersion of 10%, adding 0.5% of curing agent diethylenetriamine and 0.1% of curing accelerator resorcinol, coating the obtained epoxy resin solution on a silicon dioxide ceramic diaphragm, and drying and curing the silicon dioxide ceramic diaphragm in an oven at the temperature of 45 ℃ for 12 hours. And obtaining the epoxy resin modified ceramic diaphragm.

Example 7

A battery comprising a positive electrode material and a negative electrode material with the epoxy modified ceramic separator of example 1 therebetween.

Example 8

A battery comprising a positive electrode material and a negative electrode material with the epoxy modified ceramic separator of example 2 therebetween.

Example 9

A battery comprising a positive electrode material and a negative electrode material with the epoxy modified ceramic separator of example 3 therebetween.

Comparative example 1

Comparative example 2

Comparative example 3

90 parts by mass of magnesia ceramic particles with the particle size of about 200nm, 6 parts by mass of styrene-butadiene rubber, 4 parts by mass of sodium carboxymethylcellulose and a water/acetone mixed solution with the solvent of the volume ratio of 2: 1 are prepared into ceramic slurry with the solid content of 10 percent (mass fraction), the ceramic slurry is coated on the double-layer surface of a commercial Polyethylene (PE) diaphragm, and the solvent is dried to remove, so that the magnesia ceramic diaphragm is obtained.

Comparative example 4

Preparing epoxy resin:

Preparing a ceramic diaphragm:

Preparing an epoxy resin modified ceramic diaphragm:

dissolving the synthesized epoxy resin in an acetone solvent to prepare a solution with the mass fraction of 30%, adding 0.5% of curing agent diethylenetriamine and 0.1% of curing accelerator resorcinol, coating the obtained epoxy resin solution on a silicon dioxide ceramic diaphragm, and drying and curing the silicon dioxide ceramic diaphragm in an oven at the temperature of 45 ℃ for 12 hours. And obtaining the epoxy resin modified ceramic diaphragm.

Comparative example 5

A battery comprising a positive electrode material and a negative electrode material with the silica ceramic separator prepared in comparative example 1 therebetween.

And (3) analyzing a test result:

FIG. 1 is a comparison of example 1 (right) and comparative example 1 (left) after heat treatment at 160 ℃ for 30 min. As can be seen, the epoxy resin-modified ceramic separator of example 1 and the ceramic separator of comparative example 1 were heat-treated at 160 ℃ for 30 min. The epoxy modified membrane of example 1 did not shrink, whereas the ceramic membrane of comparative example 1 had shrunk significantly.

FIG. 2 is a graph of tensile strength properties at different temperatures for example 2 and comparative example 2. As can be seen, comparative example 2 rapidly lost its mechanical strength with an increase in temperature, and only 20MPa of tensile strength was obtained at 150 ℃ and when the temperature exceeded 180 ℃, it was completely melted and lost the mechanical strength. In contrast, example 2 maintained a tensile strength of over 35MPa at 150 ℃ and about 15MPa between 170 ℃ and 220 ℃.

Fig. 3 is a comparison of the heat-blocking function test of example 3 and comparative example 3. As can be seen, when the temperature is increased to 130 ℃, the PE-based film melts to block the pores, blocking the lithium ion channels in the battery, and the impedance is rapidly increased by 1 ten thousand times. When the temperature is continuously increased to 147 ℃, the ceramic diaphragm in the comparative example 3 shrinks, so that the contact short circuit of the anode and the cathode is caused, the impedance is rapidly reduced, and the epoxy resin modified ceramic diaphragm still keeps good dimensional stability, so that the contact short circuit of the anode and the cathode can be effectively prevented, and the battery is prevented from further thermal runaway.

Fig. 4 is a scanning electron microscope image of the uncoated ceramic slurry side of the epoxy resin-modified ceramic separator prepared in example 1 and the silica ceramic separator prepared in comparative example 1. As can be seen, the pores of the separator were not significantly reduced after coating with epoxy. This demonstrates that the epoxy resin has good film forming properties and that the thickness of the epoxy resin coating is thin under the parameters described in the examples.

Fig. 5 is a histogram of the pore size distribution of the epoxy resin-modified ceramic separator prepared in example 1 and the silica ceramic separator prepared in comparative example 1, both of which have pore size distributions conforming to the normal distribution, and it can be seen that the pore size of the pores of the epoxy resin-modified ceramic separator in example 1 as a whole is slightly smaller than that of the pores of the silica ceramic separator in comparative example 1. Statistically, the average pore diameter of example 1 is 103nm, the average pore diameter of comparative example 1 is 114nm, and the average thickness of the epoxy resin coating layer in example 1 is estimated to be about 5.5 nm.

FIG. 6 is a graph showing the cycle performance test of example 7 and comparative example 5. As can be seen, the cycle performance of example 7 and that of comparative example 5 are both good, and the cycle performance of example 7 is not significantly different from that of comparative example 5 for 100 cycles. The epoxy resin modified ceramic diaphragm prepared by the invention has no negative influence on the battery performance.

Table 1 shows a comparison of air permeability of example 1, comparative example 1 and comparative example 4, and it can be seen that the epoxy resin modified ceramic separator prepared in example 1 has reduced air permeability and electrical conductivity compared to the silica ceramic separator prepared in comparative example 1, but the reduction degree is very limited, and the epoxy resin coating layer of the epoxy resin modified separator is thin and uniform, has no problem of blocking pores of the separator, and does not have great influence on the air permeability and electrical conductivity of the separator. The gas permeability and the electrical conductivity of the high-concentration epoxy resin modified ceramic diaphragm in the comparative example 4 are both reduced sharply, which shows that, at a high concentration, the epoxy resin cannot form a thin and uniform epoxy resin layer on the ceramic diaphragm, but blocks the pores of the diaphragm, so that the gas permeability and the electrical conductivity of the diaphragm are seriously deteriorated. The above results show that. Under the control of proper parameters, the preferred epoxy resin coating material can form a coating layer with proper thickness on the ceramic diaphragm, and the key performances of the diaphragm, such as air permeability and electric conductivity, are hardly influenced.

Table 2 shows a comparison of the thicknesses of the pore coating layers in examples 1, 4, 5 and 6. Table 2 is intended to illustrate how different epoxy resin concentrations affect the average thickness of the epoxy resin layer coated over the separator pores. The average thickness of the epoxy coating layer was calculated by varying the average pore size of the epoxy-modified separator from that of the unmodified separator (the specific method is described in detail in the description of fig. 5). As can be seen from the table, as the concentration of the epoxy resin increases, the thickness of the epoxy resin coating layer increases, and when the concentration of the epoxy resin is low (example 4), the average thickness of the epoxy resin coating layer is correspondingly thin, which does not support the separator, and the high temperature resistance is limited, and the heat resistance test result is shown in fig. 7. When the epoxy concentration is higher, the average thickness of the epoxy resin coating is correspondingly relatively thicker. An excessively thin coating layer may affect the effect of the epoxy coating layer in inhibiting thermal shrinkage and improving mechanical strength of the ceramic separator, while an excessively thick coating layer may affect the air permeability of the ceramic separator and further reduce the electrical conductivity thereof.

Examples of the experiments	Example 1	Comparative example 1	Comparative example 4
				Air permeability (s/100ml)	280	260	2700
Conductivity (mS/cm)	0.81	0.95	0.06

TABLE 1

Examples of the experiments	Epoxy concentration (%)	Thickness of coating (nm)
			Example 4	0.1	＜0.5
Example 5	3	2.4
			Example 1	5	5.5
Example 6	10	32

TABLE 2

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention. It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition. In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims

1. An epoxy resin modified ceramic diaphragm comprises a porous base film and a single-layer or double-layer ceramic layer coated on the base film, and is characterized in that epoxy resin is coated or soaked or sprayed on at least one surface of the ceramic layer, and the thickness of the epoxy resin layer on one surface is 0.5-40 nm.

2. The epoxy-modified ceramic membrane of claim 1, wherein the epoxy resin is formulated to a weight concentration of 1% to 10%.

3. The epoxy resin modified ceramic separator according to claim 1, wherein the porous base film comprises at least one of polyolefin porous polymer, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polyethylene terephthalate, polybutylene terephthalate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyvinylpyrrolidone, polyethylene oxide, polyvinyl alcohol, or a blend or copolymer system derived from the above polymers.

4. The epoxy resin modified ceramic separator according to claim 1, wherein the average particle size of the ceramic particles is 10 to 1000nm, preferably 50 to 500nm, and the thickness of the ceramic layer is 0.1 to 10 μm, preferably 2 to 5 μm.

5. The epoxy resin-modified ceramic separator according to claim 1, wherein the epoxy resin is an organic compound having two or more epoxy groups in a chemical structure, and is a high-molecular polymer that can form a thermosetting by a ring-opening reaction of the epoxy groups; the molecular weight of the epoxy resin is determined by gel permeation chromatography, and the weight average molecular weight is 100-5000.

6. The epoxy resin-modified ceramic separator according to claim 1 or 2, wherein the epoxy resin polymerizable monomer is classified into a compound capable of introducing or generating an epoxy group, referred to as component a, and a compound having two or more active hydrogens, a prepolymer, or a compound having two or more unsaturated double bonds, referred to as component B.

7. The epoxy resin modified ceramic diaphragm of claim 6, wherein the mixed solution of the component A and the component B comprises, by weight, 0.1-40% of the component A, 0.1-40% of the component B, 0.01-8% of a catalyst, 0.01-5% of a curing agent, 0.01-5% of a curing accelerator, 0.01-5% of a surfactant, 0-5% of an additive, and the balance of a solvent.

8. The epoxy resin modified ceramic membrane of claim 7, wherein the catalyst comprises one of sodium carbonate, potassium carbonate, pyridine, triethylamine, sodium acetate, sodium hydroxide, potassium hydroxide, quaternary ammonium salt, quaternary phosphonium salt, and choline.

9. The epoxy resin modified ceramic membrane of claim 7, wherein the curing agent comprises polyamine, acid anhydride, phenolic aldehyde, thiol addition polymerization type curing agent, or catalytic type curing agent or other obvious type curing agent, or imidazole latent type curing agent.

10. An epoxy resin modified ceramic membrane according to claim 7, wherein the curing accelerator is selected according to the nucleophilic and electrophilic properties of the curing agent, the nucleophilic curing agent matches the electrophilic curing accelerator, and the electrophilic curing agent matches the nucleophilic curing accelerator.

11. The epoxy resin modified ceramic separator according to claim 7, wherein the surfactant is at least one of stearic acid, sodium dodecylbenzenesulfonate, quaternary ammonium compound, sodium hexadecylsulfonate, lecithin, amino acid type, betaine type, fatty acid glyceride, fatty acid sorbitan, and polysorbate.

12. An epoxy resin modified ceramic diaphragm comprises a porous base film and a single-layer or double-layer ceramic layer coated on the base film, and is characterized in that at least one surface of the ceramic layer is coated or soaked or sprayed with epoxy resin, and the porosity of the formed diaphragm is more than 40%; the epoxy resin is compounded with the ceramic layer, and the thickness of the epoxy resin is increased to be less than 40 nm.

13. The lithium battery separator according to claim 12, wherein the porous base film is coated with ceramic slurry on a surface of a single layer or a double layer to prepare a ceramic separator, and the ceramic separator is immersed in a mixed solution of epoxy resin polymerization monomers to be coated with epoxy resin by in-situ polymerization; or coating ceramic slurry on the porous base membrane to prepare a ceramic diaphragm, coating the prepared epoxy resin solution on the ceramic diaphragm, and curing to form the epoxy modified ceramic diaphragm.

14. The lithium battery separator as claimed in claim 13, wherein the epoxy resin is provided in an epoxy resin solution having a mass fraction of 1 to 10%.

15. A preparation method of a lithium battery diaphragm is characterized by comprising the following steps:

the epoxy resin polymerization monomer is divided into a compound which can introduce or generate epoxy groups and is called component A, a compound with two or more active hydrogen, a prepolymer or a compound containing two or more unsaturated double bonds, and a prepolymer is called component B;

step 1, synthesizing epoxy resin: according to mass percentage, mixing the component A: 1-40%, component B: 1-40 percent of mixed solution, 0.2-8 percent of alkaline catalyst and 10-95 percent of solvent react for 0.5-24 hours at the temperature of 25-110 ℃, and the epoxy resin is obtained after separation, washing and drying;

step 2, preparing a ceramic diaphragm: uniformly mixing ceramic particles and a binder according to a certain proportion to prepare ceramic slurry, coating one side or two sides of the prepared ceramic slurry on the surface of a porous base membrane, drying and removing a solvent to obtain a ceramic diaphragm; step 3, preparing an epoxy resin solution with the mass fraction of 1-10%, adding 0.01-5% of a curing agent, 0.01-5% of a curing accelerator and 0-5% of an additive; the ceramic diaphragm is soaked by the epoxy resin solution through spraying, soaking or other modes, and is dried and cured for 0.5 to 24 hours at the temperature of between 25 and 110 ℃.