CN114497880A - Diaphragm and lithium ion battery comprising same - Google Patents
Diaphragm and lithium ion battery comprising same Download PDFInfo
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- CN114497880A CN114497880A CN202210104178.5A CN202210104178A CN114497880A CN 114497880 A CN114497880 A CN 114497880A CN 202210104178 A CN202210104178 A CN 202210104178A CN 114497880 A CN114497880 A CN 114497880A
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- copolymer
- ethylene
- base film
- diaphragm
- olefin
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
Abstract
The application discloses diaphragm reaches lithium ion battery including the diaphragm. The diaphragm comprises a base film, wherein the base film comprises polyolefin and an additive, the additive comprises a polar group, and the polar group is 1000-1200 cm‑1Or 1600 to 1850cm‑1Or 3000-3500 cm‑1Has an infrared absorption peak in any wavenumber range. The base film of the separator contains the polar group, and the polar group can be coupled with and dissociated from lithium ions, so that the migration resistance of the lithium ions in the base film is reduced. When the diaphragm is used in a lithium ion battery, the wetting capacity of the diaphragm to electrolyte can be effectively improved, the migration capacity of lithium ions in the diaphragm is improved,therefore, the quick conductivity of the lithium ions is improved, and the quick charging performance of the lithium ion battery is further improved.
Description
Technical Field
The application relates to the technical field of batteries, in particular to a diaphragm and a lithium ion battery comprising the diaphragm.
Background
With the wide application of consumer electronic products and electric vehicles, lithium ion batteries with high energy density, excellent cycle performance and fast charge and discharge performance are increasingly popular and appreciated in the market. The quick charging can effectively reduce the charging time and times of the lithium ion battery, improve the use convenience of consumers and relieve the mileage anxiety of the consumers.
The lithium ion battery mainly comprises an anode, a cathode, a diaphragm and electrolyte. Wherein, the diaphragm is a layer of film which is used for separating the anode and the cathode when in electrolytic reaction so as to prevent the anode and the cathode from directly reacting in the electrolytic cell. In the structure of the lithium ion battery, the diaphragm is one of the key inner layer components, the performance of the diaphragm determines the interface structure, the internal resistance and the like of the lithium ion battery, the characteristics of the capacity, the cycle performance, the safety performance and the like of the lithium ion battery are directly influenced, and the diaphragm with excellent performance has important significance for improving the comprehensive performance of the lithium ion battery.
The existing diaphragm is mainly made of polyolefin base materials such as polyethylene and polypropylene, the polyolefin base materials have strong chemical inertness and can effectively resist adverse environments such as cathode and anode oxidation reduction, electrolyte corrosion and the like, but the electrolyte cannot be effectively soaked and spread on the surface of the diaphragm, so that lithium ions cannot be efficiently transmitted, and the quick charging performance of the lithium ion battery is limited to a certain extent.
Disclosure of Invention
In view of the above, the present application provides a separator, which aims to solve the problem that the conventional separator cannot efficiently transfer lithium ions.
The embodiment of the application is realized by that the diaphragm comprises a base film, the base film comprises polyolefin and an additive, the additive comprises a polar group, and the polar group is 1000-1200 cm-1Or 1600 to 1850cm-1Or 3000-3500 cm-1Has an infrared absorption peak in any wave number range.
Optionally, in some embodiments herein, the polar group is selected from at least one of a carboxyl group, a hydroxyl group, an ether oxygen group, and an ester group.
Optionally, in some embodiments herein, the additive is selected from at least one of a copolymer of an olefin and an organic acid, a copolymer of an olefin and an ester, a copolymer of an olefin and an alcohol, a copolymer of an olefin and an organic acid salt, and inorganic particles.
Optionally, in some embodiments herein, the copolymer of an olefin and an organic acid is selected from at least one of an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, and an ethylene-vinyl acetate copolymer;
the copolymer of olefin and ester is at least one selected from ethylene-methyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propyl acrylate copolymer and ethylene-butyl acrylate copolymer;
the copolymer of an olefin and an alcohol is selected from ethylene-vinyl alcohol copolymers;
the copolymer of olefin and organic acid salt is at least one selected from ethylene-metal acrylate copolymer and ethylene-metal methacrylate copolymer;
the inorganic particles are at least one selected from silica, alumina, magnesia, magnesium hydroxide, modified silica, modified alumina, modified magnesia and modified magnesium hydroxide.
Optionally, in some embodiments of the present application, the inorganic particles have a particle size ranging from 1nm to 1 um.
Optionally, in some embodiments herein, the polyolefin is selected from at least one of polyethylene, polypropylene, polyethylene-butene copolymer, polyethylene-propylene copolymer, and polyethylene-octene copolymer.
Optionally, in some embodiments of the present application, in the base film, the mass percentage of the polyolefin is in a range of 50 to 99%, and the mass percentage of the additive is in a range of 1 to 50%.
Optionally, in some embodiments of the present application, the separator further includes a coating layer coated on a surface of the base film, and the coating layer includes at least one of an inorganic coating layer and an organic coating layer.
Optionally, in some embodiments of the present application, the inorganic coating layer comprises an inorganic material selected from at least one of alumina, silica, titania, calcium carbonate, magnesium oxide, magnesium hydroxide, boehmite, silica, barium titanate, and barium sulfate;
the organic coating comprises an organic material, and the organic material is selected from at least one of polyacrylic resin, aramid fiber, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene and a copolymer of polyvinylidene fluoride and hexafluoropropylene.
Optionally, in some embodiments of the present application, the coating further comprises a binder selected from at least one of polyacrylate, polybutadiene-styrene copolymer, polyacrylic acid, polyacrylonitrile-acrylic acid copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polymethyl methacrylate, and polyvinylidene fluoride-hexafluoropropylene copolymer.
Correspondingly, the embodiment of the application also provides a lithium ion battery, and the lithium ion battery comprises the diaphragm.
The base film of the separator described herein includes the polar group, and the polar group can be coupled with and dissociated from lithium ions, thereby reducing migration resistance of lithium ions in the base film. When the diaphragm is used in a lithium ion battery, the wetting capacity of the diaphragm to electrolyte can be effectively improved, and the migration capacity of lithium ions in the diaphragm is improved, so that the rapid conduction capacity of the lithium ions is improved, and the rapid charging performance of the lithium ion battery is further improved.
Detailed Description
The technical solutions in the embodiments of the present application are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application. Furthermore, it should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the invention, are given by way of illustration and explanation only, and are not intended to limit the scope of the invention.
In the description of this application, the term "including" means "including but not limited to". The terms first, second, third and the like are used merely as labels, and do not impose numerical requirements or an established order. The term "plurality" means "two or more".
Various embodiments of the present application may exist in a range of forms; it is to be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the application; accordingly, the described range descriptions should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, it is contemplated that the description of a range from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the stated range, such as 1, 2, 3, 4, 5, and 6, as applicable regardless of the range. Additionally, whenever a numerical range is indicated herein, it is meant to include any number (fractional or whole) recited within the indicated range.
The embodiment of the application provides a diaphragm, including the basement membrane, contain polyolefin and additive in the basement membrane, include polar group in the additive, polar group is in 1000 ~ 1200cm-1Or 1600 to 1850cm-1Or 3000-3500 cm-1Has an infrared absorption peak in any wave number range.
The polar group may be selected from, but not limited to, at least one of a carboxyl group (-COOH), a hydroxyl group (-OH), an ether oxy group, and an ester group. The polar group can be coupled with and dissociated from lithium ions, thereby reducing migration resistance of the lithium ions in the base film.
The additive may be selected from, but not limited to, at least one of a copolymer of an olefin and an organic acid, a copolymer of an olefin and an ester, a copolymer of an olefin and an alcohol, a copolymer of an olefin and an organic acid salt, and inorganic particles.
The copolymer of the olefin and the organic acid may be selected from, but not limited to, at least one of ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, and ethylene-vinyl acetate copolymer.
The copolymer of olefin and ester may be selected from, but not limited to, at least one of ethylene-methyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propyl acrylate copolymer, and ethylene-butyl acrylate copolymer.
The copolymer of an olefin and an alcohol may be selected from, but is not limited to, ethylene-vinyl alcohol copolymers.
The copolymer of the olefin and the organic acid salt may be selected from, but not limited to, at least one of an ethylene-metal acrylate copolymer and an ethylene-metal methacrylate copolymer.
The inorganic particles may be selected from, but not limited to, at least one of silica, alumina, magnesia, magnesium hydroxide, modified silica, modified alumina, modified magnesia, and modified magnesium hydroxide. It is understood that the surface of the silica, alumina, magnesia, magnesium hydroxide has hydroxyl groups attached. The surfaces of the modified silicon dioxide, the modified aluminum oxide, the modified magnesium oxide and the modified magnesium hydroxide are connected with at least one of the polar groups. In at least one embodiment, the surfaces of the modified silica, the modified alumina, the modified magnesia and the modified magnesium hydroxide are connected with ether oxygen groups.
The particle size range of the inorganic particles is 1 nm-1 um. In at least some embodiments, the inorganic particles have a particle size in the range of 5 to 100 nm.
The polyolefin may be selected from, but not limited to, at least one of Polyethylene (PE), polypropylene (PP), polyethylene-butadiene copolymer, polyethylene-propylene copolymer, and polyethylene-octene copolymer. In some embodiments, the polyolefin has a weight average molecular weight in the range of 20 to 200 ten thousand g/mol.
In the base film, the mass percentage content range of the polyolefin is 50-99%, and the mass percentage content of the additive is 1-50%. Within the content range, the wettability of the base film can be effectively improved, and the effective transmission of lithium ions is promoted.
In some embodiments, the base film has a thickness of 3 to 30 μm. If the thickness of the base film is too thick, the migration resistance of lithium ions is increased, and the discharge rate and the cycle performance of the lithium ion battery are reduced.
It is understood that the base film has a porous structure. In some embodiments, the porosity of the base film is 20 to 60%.
In some embodiments, the base film has a puncture strength of 100 to 1000 g.
It is understood that the base film may be prepared by a wet process or a dry process known in the art for base film preparation.
In some embodiments, the base film is prepared by a wet method, and the additive in the base film is at least one selected from the group consisting of a copolymer of olefin and organic acid, a copolymer of olefin and ester, a copolymer of olefin and alcohol, and a copolymer of olefin and organic acid salt, wherein the additive is 1-50% by mass of the base film.
In still other embodiments, the base film is prepared by a wet method, and the additive in the base film is selected from the inorganic particles, and in this case, the additive is 1-20% by mass in the base film.
In some embodiments, the base film is prepared by a dry method, and the additive in the base film is selected from at least one of the copolymer of olefin and organic acid, the copolymer of olefin and ester, the copolymer of olefin and alcohol, and the copolymer of olefin and organic acid salt, and in this case, the additive is 1-20% by mass in the base film.
In still other embodiments, the base film is prepared by a dry method, and the additive in the base film is selected from the inorganic particles, and in this case, the mass percentage of the additive in the base film is 1-10%.
In some embodiments, the separator further comprises a coating layer coated on a surface of the base film. The coating includes at least one of an inorganic coating and an organic coating. The coating can improve the performances of the diaphragm such as thermal stability, mechanical strength, puncture resistance, wettability, liquid retention and the like.
The inorganic coating layer includes an inorganic material, which may be selected from, but not limited to, at least one of alumina, silica, titania, calcium carbonate, magnesium oxide, magnesium hydroxide, boehmite, silica, barium titanate, and barium sulfate.
The organic coating comprises an organic material, and the organic material can be selected from at least one of polyacrylic resin, aramid fiber, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene and a copolymer of polyvinylidene fluoride and hexa-fluoropropylene.
In some embodiments, the coating further comprises a binder, in other words, the inorganic coating comprises an inorganic material and a binder, and the organic coating comprises an organic material and a binder.
The binder may be selected from, but not limited to, at least one of polyacrylate, polybutadiene-styrene copolymer, polyacrylic acid, polyacrylonitrile-acrylic acid copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polymethyl methacrylate, and polyvinylidene fluoride-hexafluoropropylene copolymer.
It will be appreciated that when the organic coating is selected from polyvinylidene fluoride, polytetrafluoroethylene or a copolymer of polyvinylidene fluoride-hexafluoropropylene, no binder may be added due to the inherent tackiness of the three materials.
In some embodiments, in the inorganic coating layer, the inorganic material is present in an amount ranging from 90 to 99.5% by mass, and the binder is present in an amount ranging from 0.5 to 10% by mass. Within the range, the inorganic coating layer can be made to adhere well to the surface of the base film.
In some embodiments, in the organic coating, the organic material is contained in an amount ranging from 80 to 100% by mass, and the binder is contained in an amount ranging from 0 to 20% by mass. Within the range, the organic coating layer can be made to adhere well to the surface of the base film.
The base film of the separator described herein includes the polar group, and the polar group can be coupled with and dissociated from lithium ions, thereby reducing migration resistance of lithium ions in the base film. When the diaphragm is used in a lithium ion battery, the wetting capacity of the diaphragm to electrolyte can be effectively improved, and the migration capacity of lithium ions in the diaphragm is improved, so that the rapid conduction capacity of the lithium ions is improved, and the rapid charging performance of the lithium ion battery is further improved.
It is to be understood that the separator of the present application may be used in any electrochemical device in which electrochemical reactions may occur. The electrochemical device may be, but is not limited to, a primary lithium ion battery, a secondary lithium ion battery, a fuel lithium ion battery, a solar lithium ion battery, a capacitor, and the like. The secondary lithium ion battery may be a lithium secondary battery, which may be, but not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer battery, or a lithium ion polymer secondary battery.
The embodiment of the application also provides a preparation method of the diaphragm, which comprises the following steps:
step S01: providing polyolefin and an additive, and mixing the polyolefin and the additive according to a certain proportion to obtain a mixture;
step S02: preparing the mixture into a base film;
step S03: and coating a coating material on the surface of the base film to form a coating.
In the step S01:
the types and proportions of the polyolefin and the additive are as described above and will not be described herein.
In the step S02:
the method of preparing the mixture into a base film is a method known in the art for preparing a base film, for example, a wet method, a dry method, and the like.
In some embodiments, the mixture is prepared as a base film by a wet process, in particular: extruding the mixture through a T-shaped neck mold at a high temperature of 180-20 ℃ to obtain a flaky film, and then stretching, extracting, heat setting and cutting to obtain the base film. Wherein the temperature range of the heat setting is 110-130 ℃.
In other embodiments, the mixture is prepared into a base film by a dry process, in particular: extruding the mixture at a high temperature of 200-250 ℃ through a T-shaped neck mold to obtain a flaky film, and then stretching, heat setting and slitting to obtain the base film. Wherein the temperature range of the heat setting is 140-160 ℃.
It is understood that the stretching may be unidirectional or bidirectional.
In the step S03:
the coating material can be an organic coating material or an inorganic coating material, the organic coating material comprises an organic material and a binder, and the inorganic coating material comprises an inorganic material and a binder. The types and proportions of the organic material, the inorganic material and the binder are as described above, and are not repeated herein.
Embodiments also provide an electrochemical device including the separator.
The embodiment of the application also provides a lithium ion battery, which comprises a positive pole piece, a negative pole piece, electrolyte and the diaphragm. Wherein the separator is located between the positive electrode and the negative electrode, and the electrolyte is filled in gaps between the positive electrode and the separator and between the negative electrode and the separator.
The positive electrode piece comprises a positive electrode current collector and a positive electrode active substance combined on the surface of the positive electrode current collector. The material of the positive electrode collector may be selected from, but not limited to, at least one of copper, nickel, stainless steel, and titanium. The positive active material may be selected from, but not limited to, at least one of a graphite-based carbon material, a non-graphite-based carbon material, metallic lithium, alloy lithium, a silicon-based alloy, a tin-based alloy, a conductive oxide, and a conductive polymer. Wherein the conductive oxide may be selected from, but not limited to, LixFe2O3、LixWO2、SnO、SnO2、 PbO、PbO2、Pb2O3、Pb3O4、Sb2O3、Sb2O4、Sb2O5、GeO、GeO2、Bi2O3、Bi2O4And Bi2O5At least one of; the conductive polymer may be selected from, but not limited to, at least one of polyacetylene, polyaniline, and polythiophene. Wherein y is more than 0 and less than 1.
The negative electrode plate comprises a negative electrode current collector and a negative electrode active material combined on the surface of the negative electrode current collector. The material of the negative electrode collector may be selected from, but not limited to, at least one of aluminum and nickel. The negative active material may be selected from, but not limited to, LiCoO2、LiNiO2、LiMnO2、LiMn2O4、 Li(NiaCobMnc)O2、LiNiyCo1-yO2、LiCoyMn1- yO2、LiCoyAl1-yO2、LiCoyB1-yO2、 LiCoyMg1-yO2、LiCoyTi1-yO2、LiCoyMo1-yO2、LiCoySn1-yO2、LiCoyCa1-yO2、LiCoyC μ1-yO2、LiCoyV1-yO2、LiCoyZr1-yO2、LiCoySi1-yO2、LiCoyW1-yO2、LiCoyY1-yO2、 LiCoyLa1-yO2、LiCoyMn1-yO2、LiNiyMn1-yO2、LiCoPO4And LiFePO4At least one of (1). Wherein a is more than 0 and less than 1, b is more than 0 and less than 1, and a + b + c is 1; y is more than 0 and less than 1.
The electrolyte comprises a solvent, cations and anions. The solvent may be selected from, but not limited to, at least one of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl sulfoxide, acetonitrile, tetrahydrofuran, N-methylpyrrolidone, ethyl methyl carbonate, and γ -butyrolactone. The cation may be selected from, but is not limited to, Li+、Na+And K+At least one of (1). The anion may be selected from, but is not limited to, PF6 -、 BF4 -、Cl-、Br-、I-、ClO4 -、AsF6 -、CH3CO2 -、CF3SO3 -、N(CF3SO2)2 -And C (CF)2SO2)3 -At least one of (1).
The lithium ion battery may be, but is not limited to, a primary lithium ion battery, a secondary lithium ion battery, a fuel lithium ion battery, and a solar lithium ion battery.
The lithium ion battery may have a wound structure, a laminated structure, or a folded structure.
The lithium ion battery comprises the diaphragm, a base film of the diaphragm comprises the polar group, and the polar group can be coupled and dissociated with lithium ions, so that the migration resistance of the lithium ions in the base film is reduced. When the diaphragm is used in a lithium ion battery, the wetting capacity of the diaphragm to electrolyte can be effectively improved, and the migration capacity of lithium ions in the diaphragm is improved, so that the rapid conduction capacity of the lithium ions is improved, and the rapid charging performance of the lithium ion battery is further improved.
The present application will be described in detail with reference to specific examples, which are intended to be part of the present application and are not intended to limit the present application.
Example 1
Preparing a diaphragm:
mixing and extruding high polymer PE with the weight-average molecular weight of 80 ten thousand, ethylene acrylic acid copolymer and paraffin oil, wherein the mass ratio of the PE to the ethylene acrylic acid copolymer is 70:30, the mass ratio of the total mass of the PE to the ethylene acrylic acid copolymer to the paraffin oil is 3:7, extruding a sheet-shaped film through a T-shaped neck die at the high temperature of 200 ℃, cooling the film through a casting roll, and performing bidirectional stretching, extraction, heat setting and cutting in the MD (longitudinal) direction and the TD (transverse) direction to obtain a base film, wherein the stretching ratio corresponding to the MD direction and the TD direction is 7 x 7 times, and the heat setting temperature is 130 ℃.
Preparing a coating:
adding 90 parts by weight of ceramic particles and 10 parts by weight of acrylate binder into deionized water, uniformly mixing to prepare slurry, uniformly coating the slurry on the surface of the base film by micro gravure coating, drying by an oven, and spraying polyvinylidene fluoride to obtain the base film containing the inorganic coating and the organic coating, thereby obtaining the diaphragm.
Preparing a positive pole piece:
according to the weight portion, 94 portions of active material lithium cobaltate, 3 portions of conductive carbon and 3 portions of adhesive polyvinylidene fluoride are fully stirred and uniformly mixed in an N-methyl pyrrolidone solvent system, and then the mixture is coated on an aluminum foil, and the positive pole piece is obtained through drying, cold pressing and splitting.
Preparing a negative pole piece:
according to the weight portion, 97.5 portions of active substance artificial graphite, 1.5 portions of binder styrene butadiene rubber and 1 portion of thickener carboxymethylcellulose sodium are fully stirred and mixed evenly in deionized water, coated on a copper foil, and subjected to drying, cold pressing and stripping to obtain the negative pole piece.
Preparing a lithium ion battery:
and (3) stacking the positive pole piece, the isolating membrane and the negative pole piece in sequence, so that the membrane is positioned between the positive pole and the negative pole to play an isolating role, winding to obtain a naked electric core, placing the naked electric core in a shell, injecting electrolyte and packaging to obtain the lithium ion battery.
Example 2
This example is substantially the same as example 1 except that the base film of this example was prepared by the method comprising:
the preparation method comprises the steps of melting and mixing high-molecular PP with the weight-average molecular weight of 30 ten thousand and ethylene acrylic acid copolymer by an extruder according to the mass ratio of 90:10, extruding a sheet-shaped film at the high temperature of 210 ℃ through a T-shaped die, cooling by a casting roll, rolling, compounding in a multi-layer mode, performing unidirectional stretching in the MD direction through a stretching machine, performing heat setting at 140 ℃, layering and cutting to obtain the base film, wherein the stretching ratio in the MD direction is 2.3.
Example 3
This example is substantially the same as example 1, except that the base film of this example was prepared by the method comprising:
mixing and extruding high polymer PE with the weight-average molecular weight of 80 ten thousand, ethylene acrylic acid copolymer and silicon dioxide, wherein the mass ratio of the PE to the ethylene acrylic acid copolymer to the silicon dioxide is 75:20:5, extruding a sheet-shaped film at the high temperature of 200 ℃ through a T-shaped die, cooling the film through a casting roller, and performing biaxial stretching, extraction, heat setting and cutting in the MD direction and the TD direction to obtain a base film, wherein the stretching ratio corresponding to the MD direction and the TD direction is 7 x 7 times, and the heat setting temperature is 130 ℃.
Example 4
This example is substantially the same as example 1, except that the mass ratio of PE to ethylene acrylic acid copolymer in this example is 99: 1.
example 5
This example is substantially the same as example 1, except that the mass ratio of PE to ethylene acrylic acid copolymer in this example is 80: 20.
example 6
This example is substantially the same as example 2 except that the mass ratio of PP to ethylene acrylic acid copolymer in this example is 80: 20.
Example 7
This example is essentially the same as example 2, except that the mass ratio of PP to ethylene acrylic acid copolymer in this example is 99: 1.
Example 8
This example is essentially the same as example 1, except that this example replaces the ethylene propylene copolymer with an ethylene-methacrylic acid copolymer.
Example 9
This example is essentially the same as example 1, except that the ethylene propylene copolymer was replaced with an ethylene vinyl acetate copolymer.
Example 10
This example is essentially the same as example 1, except that this example replaces the ethylene propylene copolymer with an ethylene vinyl alcohol copolymer.
Example 11
This example is essentially the same as example 1, except that this example replaces the ethylene propylene copolymer with ethylene methyl acrylate.
Example 12
This example is essentially the same as example 1, except that this example replaces the ethylene propylene copolymer with silica.
Example 13
This example is essentially the same as example 1, except that it replaces the ethylene propylene copolymer with hydrophobic silica having ether oxy groups attached to the surface.
Examples 14 to 17
Examples 14 to 17 were substantially the same as example 1 except that the thicknesses of the base films in examples 1 and 14 to 17 were different, and are shown in table one.
Comparative example 1
This comparative example is substantially the same as example 1 except that the base film of this comparative example is prepared by:
mixing and extruding macromolecular PE with the weight-average molecular weight of 80 ten thousand and paraffin oil (the mass ratio is 3:7), extruding a flaky film at the high temperature of 220 ℃ through a T-shaped die, cooling the film by a casting roller, and stretching, extracting, heat setting and cutting the film in the MD and TD directions to obtain a base film, wherein the stretching ratio corresponding to the MD direction and the TD direction is 7 x 7 times, and the temperature of a heat setting section is 130 ℃.
Comparative example 2
This comparative example is substantially the same as example 2 except that the base film of this comparative example is prepared by:
the method comprises the steps of melting and mixing high polymer PP with the weight-average molecular weight of 30 ten thousand through an extruder, extruding a flaky film at the high temperature of 220 ℃ through a T-shaped die, cooling through a casting roller, rolling, compounding in a multi-layer mode, stretching in the MD direction through a stretching machine, heat setting at 145 ℃, layering and slitting to obtain a base film, wherein the stretching ratio in the MD direction is 2.3.
The base films of examples 1 to 17 and comparative examples 1 to 2 were subjected to a base film thickness test, a porosity test and an infrared absorption peak position test. The test results are shown in Table I.
Testing the thickness of the base film: taking a base film with the length and the width of 500 and 100mm in the TD direction of the base film, uniformly taking 5 points, testing the thickness of the base film at different positions by adopting a ten-thousandth thickness tester, and then calculating the average value of the thicknesses at the 5 points to be used as the thickness of the base film.
And (3) porosity testing: taking 5 pieces of base membrane with the size of 100mm, testing the weight of the base membrane, taking the average value as the weight value M (mg), and utilizing the calculation formula of the porosity: and calculating the porosity by X-1-M/T S rho, wherein T is the thickness of the base film, S is the area of the base film, and rho is the density of the polyolefin raw material of the base film.
And (3) testing infrared absorption peak position: and (3) carrying out infrared absorption peak position test on the base film by using an infrared spectrometer and adopting a total reflection method.
Table one:
the lithium ion batteries of examples 1 to 17 and comparative examples 1 to 2 were subjected to a discharge rate test and a 25 ℃ cycle performance test. The test results are shown in Table II.
And (3) testing discharge rate: taking 3 lithium ion batteries of examples 1 to 17 and comparative examples 1 to 2, charging the batteries to 4.4V at a constant current of 0.5C at normal temperature, then charging the batteries to 0.05C at a constant voltage under the condition of 4.4V, then discharging the batteries at a discharge current of 2C, testing the discharge capacity of the batteries, and recording the ratio of the discharge capacity to the capacity obtained by the discharge current of 0.5C as the discharge rate of 2C.
Cycle performance (capacity retention) test at 25 ℃:3 lithium ion batteries of examples 1 to 17 and comparative examples 1 to 2 were each charged at 25 ℃ to 4.4V at a constant current at a rate of 3C and then charged at a constant voltage of 0.05C at a voltage of 4.4V to obtain an initial capacity of a cell. The circulation process is as follows: discharging to 3.0V by using 1C discharge current, then charging to 4.4V by using 3C multiplying factor constant current, then charging to 0.05C under the voltage condition of 4.4V at constant voltage, then repeating the process for 1000 times, averaging the residual capacities of 3 lithium ion batteries to obtain the final capacity, and then dividing the final capacity by the initial capacity to obtain the capacity retention ratio.
Table two:
as can be seen from Table II:
the lithium ion batteries of examples 1, 3 to 5, and 8 to 17 had higher discharge rates and better capacity retention rates than the lithium ion battery of comparative example 1. Among them, the thickness of the base film of example 17 is too large, resulting in a low discharge rate.
The lithium ion batteries of examples 2, 6, and 7 had higher discharge rates and better capacity retention rates than the lithium ion battery of comparative example 2.
Therefore, when the diaphragm is used for the lithium ion battery, the quick charging performance of the lithium ion battery can be effectively improved.
The diaphragm and the lithium ion battery provided in the embodiments of the present application are described in detail above, and specific examples are applied herein to explain the principles and embodiments of the present application, and the description of the embodiments is only used to help understand the method and the core idea of the present application; meanwhile, for those skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.
Claims (11)
1. A separator comprising a base film, characterized in that: the base film comprises polyolefin and an additive, wherein the additive comprises a polar group, and the polar group is 1000-1200 cm-1Or 1600 to 1850cm-1Or 3000-3500 cm-1Has an infrared absorption peak in any wave number range.
2. A diaphragm according to claim 1, wherein: the polar group is selected from at least one of carboxyl, hydroxyl, ether oxygen and ester group.
3. A diaphragm according to claim 1, wherein: the additive is at least one selected from the group consisting of a copolymer of an olefin and an organic acid, a copolymer of an olefin and an ester, a copolymer of an olefin and an alcohol, a copolymer of an olefin and an organic acid salt, and inorganic particles.
4. A diaphragm according to claim 3, wherein: the copolymer of olefin and organic acid is at least one selected from ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer and ethylene-vinyl acetate copolymer;
the copolymer of olefin and ester is selected from at least one of ethylene-methyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propyl acrylate copolymer and ethylene-butyl acrylate copolymer;
the copolymer of an olefin and an alcohol is selected from ethylene-vinyl alcohol copolymers;
the copolymer of olefin and organic acid salt is at least one selected from ethylene-metal acrylate copolymer and ethylene-metal methacrylate copolymer;
the inorganic particles are at least one selected from silica, alumina, magnesia, magnesium hydroxide, modified silica, modified alumina, modified magnesia and modified magnesium hydroxide.
5. A diaphragm according to claim 3, wherein: the particle size range of the inorganic particles is 1 nm-1 um.
6. A diaphragm according to claim 1, wherein: the polyolefin is at least one selected from polyethylene, polypropylene, polyethylene-butylene copolymer, polyethylene-propylene copolymer and polyethylene-octene copolymer.
7. A diaphragm according to claim 1, wherein: in the base film, the mass percentage content range of the polyolefin is 50-99%, and the mass percentage content of the additive is 1-50%.
8. A diaphragm according to claim 1, wherein: the diaphragm also comprises a coating coated on the surface of the base film, and the coating comprises at least one of an inorganic coating and an organic coating.
9. The septum of claim 8, wherein: the inorganic coating comprises an inorganic material, and the inorganic material is selected from at least one of alumina, silica, titanium oxide, calcium carbonate, magnesium oxide, magnesium hydroxide, boehmite, silica, barium titanate and barium sulfate;
the organic coating comprises an organic material, and the organic material is selected from at least one of polyacrylic resin, aramid fiber, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene and a copolymer of polyvinylidene fluoride and hexafluoropropylene.
10. A diaphragm according to claim 8, wherein: the coating also comprises a binder, wherein the binder is selected from at least one of polyacrylate, polybutadiene-styrene copolymer, polyacrylic acid, polyacrylonitrile-acrylic acid copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polymethyl methacrylate and polyvinylidene fluoride-hexafluoropropylene copolymer.
11. A lithium ion battery, characterized by: the lithium ion battery comprises the separator according to any one of claims 1 to 10.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115347324A (en) * | 2022-09-19 | 2022-11-15 | 武汉微美新材料科技有限公司 | Ceramic coating, and diaphragm and lithium ion battery comprising same |
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