CN114497880A - Diaphragm and lithium ion battery comprising same - Google Patents

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

Separator and lithium ion battery including the same

technical field

The present application relates to the field of battery technology, and in particular, to a separator and a lithium ion battery including the separator.

Background technique

With the wide application of consumer electronic products and electric vehicles, lithium-ion batteries with high energy density, excellent cycle performance and rapid charge and discharge performance are increasingly favored and valued by the market. Among them, fast charging can effectively reduce the charging time and frequency of lithium-ion batteries, improve the convenience of consumers, and relieve consumers' mileage anxiety.

Lithium-ion batteries are mainly composed of positive electrodes, negative electrodes, separators and electrolytes. Among them, the diaphragm is a layer of film used to separate the positive and negative electrodes to prevent the two from directly reacting in the electrolytic cell during the electrolysis reaction. In the structure of lithium ion battery, the separator is one of the key inner layer components. The performance of the separator determines the interface structure and internal resistance of the lithium ion battery, and directly affects the capacity, cycle performance and safety performance of the lithium ion battery. , the excellent performance of the separator is of great significance to improve the comprehensive performance of lithium-ion batteries.

The main materials of the existing separators are polyolefin base materials such as polyethylene and polypropylene. The polyolefin base material itself has strong chemical inertness and can effectively withstand harsh environments such as cathodic and anode oxidation reduction and electrolyte corrosion. At the same time, the electrolyte cannot effectively infiltrate and spread on the surface of the separator, resulting in the inability to efficiently transport lithium ions, thus limiting the fast charging performance of lithium ion batteries to a certain extent.

SUMMARY OF THE INVENTION

In view of this, the present application provides a separator, aiming at improving the problem that the existing separator cannot efficiently transport lithium ions.

The embodiments of the present application are implemented in this way, a separator includes a base film, the base film contains polyolefin and an additive, and the additive contains a polar group, and the polar group is in the range of 1000-1200 cm ^-1 There are infrared absorption peaks in any wavenumber range of 1600～1850cm ^-1 or 3000～3500cm ^-1 .

Optionally, in some embodiments of the present application, the polar group is selected from at least one of carboxyl group, hydroxyl group, etheroxy group and ester group.

Optionally, in some embodiments of the present application, the additive is selected from the group consisting of copolymers of olefins and organic acids, copolymers of olefins and esters, copolymers of olefins and alcohols, copolymers of olefins and organic acid salts, and inorganic at least one of the particles.

Optionally, in some embodiments of the present application, the copolymer of olefin and organic acid is selected from at least one of ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer and ethylene-vinyl acetate copolymer;

The copolymer of olefin and ester is selected from ethylene-methyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propyl acrylate copolymer and ethylene-butyl acrylate copolymer at least one of them;

The copolymer of olefin and alcohol is selected from ethylene-vinyl alcohol copolymer;

The copolymer of described olefin and organic acid salt is selected from at least one in ethylene-acrylic acid metal salt copolymer and ethylene-methacrylic acid metal salt copolymer;

The inorganic particles are selected from at least one of silica, alumina, magnesia, magnesium hydroxide, modified silica, modified alumina, modified magnesium oxide and modified magnesium hydroxide.

Optionally, in some embodiments of the present application, the particle size of the inorganic particles ranges from 1 nm to 1 um.

Optionally, in some embodiments of the present application, the polyolefin is selected from at least the group consisting of polyethylene, polypropylene, polyethylene-butene copolymer, polyethylene-propylene copolymer and polyethylene-octene copolymer A sort of.

Optionally, in some embodiments of the present application, in the base film, the mass percentage content of the polyolefin ranges from 50 to 99%, and the mass percentage content of the additive ranges from 1 to 50%.

Optionally, in some embodiments of the present application, the separator further includes a coating covering the surface of the base film, and the coating includes at least one of an inorganic coating and an organic coating.

Optionally, in some embodiments of the present application, the inorganic coating includes inorganic materials, and the inorganic materials are selected from aluminum oxide, silicon oxide, titanium oxide, calcium carbonate, magnesium oxide, magnesium hydroxide, boehm At least one of stone, silicon oxide, barium titanate and barium sulfate;

The organic coating contains an organic material, and the organic material is selected from the group consisting of polyacrylic resin, aramid, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene and polyvinylidene fluoride-hexafluoropropylene copolymer at least one of them.

Optionally, in some embodiments of the present application, the coating further includes a binder, and the binder is selected from polyacrylate, polybutadiene-styrene copolymer, polyacrylic acid, polypropylene At least one of cyano-acrylic acid copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polymethyl methacrylate and polyvinylidene fluoride-hexafluoropropylene copolymer.

Correspondingly, an embodiment of the present application further provides a lithium-ion battery, and the lithium-ion battery includes the above-mentioned separator.

The polar group is included in the base film of the separator described in the present application, and the polar group can couple and dissociate with lithium ions, thereby reducing the migration resistance of lithium ions in the base film. When the separator is used in a lithium ion battery, the wetting ability of the separator to the electrolyte can be effectively improved, and the migration ability of lithium ions in the separator can be improved, thereby improving the rapid conduction ability of lithium ions, thereby improving the lithium ion battery. fast charging performance.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art under the premise of no creative work shall fall within the protection scope of this application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, but not to limit the present application.

In the description of this application, the term "including" means "including but not limited to". The terms first, second, third, etc. are used merely as designations and do not impose numerical requirements or establish an order. The term "plurality" means "two or more".

Various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation to the scope of the present application; therefore, the described range should be considered The description has specifically disclosed all possible subranges as well as individual numerical values within that range. For example, a description of a range from 1 to 6 should be considered to have 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., and Single numbers within the stated range, such as 1, 2, 3, 4, 5, and 6, apply regardless of the range. Additionally, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

An embodiment of the present application provides a separator, including a base film, the base film includes polyolefin and an additive, the additive includes a polar group, and the polar group is 1000-1200 cm ^-1 or 1600-1850 cm There are infrared absorption peaks in any wavenumber range of ^-1 or 3000～3500cm ^-1 .

The polar group may be selected from, but not limited to, at least one of carboxyl (-COOH), hydroxyl (-OH), etheroxy and ester groups. The polar groups can couple and dissociate with lithium ions, thereby reducing the migration resistance of lithium ions in the base film.

The additive may be selected from, but not limited to, at least one of copolymers of olefins and organic acids, copolymers of olefins and esters, copolymers of olefins and alcohols, copolymers of olefins and organic acid salts, and inorganic particles.

The copolymer of olefin and 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, ethylene-methyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propyl acrylate copolymer, and ethylene- At least one of butyl acrylate copolymers.

The copolymer of olefin and alcohol may be selected from, but not limited to, ethylene-vinyl alcohol copolymers.

The copolymer of olefin and organic acid salt may be selected from, but not limited to, at least one of ethylene-acrylic acid metal salt copolymer and ethylene-methacrylic acid metal salt 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 magnesium oxide and modified magnesium hydroxide . It can be understood that hydroxyl groups are attached to the surfaces of the silica, alumina, magnesia, and magnesium hydroxide. At least one of the above-mentioned polar groups is connected to the surface of the modified silica, modified alumina, modified magnesium oxide and modified magnesium hydroxide. In at least one embodiment, the surfaces of the modified silica, modified alumina, modified magnesium oxide and modified magnesium hydroxide are connected with etheroxy groups.

The particle size of the inorganic particles ranges from 1 nm to 1 um. In at least some embodiments, the inorganic particles range in size from 5 to 100 nm.

The polyolefin may be selected from, but not limited to, at least one of polyethylene (PE), polypropylene (PP), polyethylene-butene 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 2 million g/mol.

In the base film, the mass percentage content of the polyolefin is in the range of 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 transport of lithium ions can be promoted.

In some embodiments, the thickness of the base film is 3-30 μm. If the thickness of the base film is too thick, the migration resistance of lithium ions will increase, resulting in a decrease in the discharge rate and cycle performance of the lithium ion battery.

It can be understood that the base film has a porous structure. In some embodiments, the base film has a porosity of 20-60%.

In some embodiments, the puncture strength of the basement membrane is 100-1000 g.

It will be appreciated that the base film may be prepared by wet or dry methods known in the art for base film preparation.

In some embodiments, the base film is prepared by a wet process, and the additives in the base film are selected from the group consisting of the copolymer of the olefin and an organic acid, the copolymer of the olefin and the ester, the olefin and the alcohol At least one of the copolymer and the copolymer of the olefin and the organic acid salt, at this time, in the base film, the mass percentage content of the additive is 1-50%.

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. In this case, the mass percentage of the additive in the base film is 1 to 20%.

In some embodiments, the base film is prepared by a dry process, and the additive in the base film is selected from the group consisting of the copolymer of the olefin and an organic acid, the copolymer of the olefin and the ester, the olefin and the alcohol At least one of the copolymer and the copolymer of the olefin and the organic acid salt, at this time, in the base film, the mass percentage content of the additive is 1-20%.

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. In this case, the mass percentage of the additive in the base film is 1 to 10%.

In some embodiments, the separator further includes a coating on the surface of the base film. The coating includes at least one of an inorganic coating and an organic coating. The coating can improve the thermal stability, mechanical strength, puncture resistance, wettability and liquid retention of the separator.

The inorganic coating contains inorganic materials, and the inorganic materials can be selected from but not limited to aluminum oxide, silicon oxide, titanium oxide, calcium carbonate, magnesium oxide, magnesium hydroxide, boehmite, silicon oxide, barium titanate and At least one of barium sulfate.

The organic coating contains organic materials, and the organic materials can be selected from, but not limited to, polyacrylic resin, aramid, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, and polyvinylidene fluoride-hexafluoroethylene At least one of the copolymers of fluoropropylene.

In some embodiments, the coating further includes a binder, in other words, the inorganic coating includes an inorganic material and a binder, and the organic coating includes an organic material and a binder.

The binder may be selected from, but not limited to, polyacrylate, polybutadiene-styrene copolymer, polyacrylic acid, polyacrylonitrile-acrylic acid copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polymethacrylic acid At least one of methyl ester and polyvinylidene fluoride-hexafluoropropylene copolymer.

It can be understood that when the organic coating is selected from polyvinylidene fluoride, polytetrafluoroethylene or polyvinylidene fluoride-hexafluoropropylene copolymer, because the above three substances are inherently viscous, no binder can be added. .

In some embodiments, in the inorganic coating, the mass percentage of the inorganic material ranges from 90 to 99.5%, and the mass percentage of the binder ranges from 0.5 to 10%. Within the range, the inorganic coating can be better adhered to the surface of the base film.

In some embodiments, in the organic coating, the mass percentage content of the organic material is in the range of 80-100%, and the mass percentage content of the binder is in the range of 0-20%. Within the range, the organic coating can be better adhered to the surface of the base film.

The polar group is included in the base film of the separator described in the present application, and the polar group can couple and dissociate with lithium ions, thereby reducing the migration resistance of lithium ions in the base film. When the separator is used in a lithium ion battery, the wetting ability of the separator to the electrolyte can be effectively improved, and the migration ability of lithium ions in the separator can be improved, thereby improving the rapid conduction ability of lithium ions, thereby improving the lithium ion battery. fast charging performance.

It will be appreciated that the separators of the present application can be used in any electrochemical device where electrochemical reactions can occur. The electrochemical device can 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, and the lithium ion secondary battery may be, but is 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 present application also provides a preparation method of the diaphragm, comprising the following steps:

Step S01: provide polyolefin and additives, and mix them according to a certain ratio to obtain a mixture;

Step S02: preparing the mixture into a base film;

Step S03: coating a coating material on the surface of the base film to form a coating.

In the step S01:

The types and ratios of the polyolefin and the additive are as described above, and will not be repeated here.

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, eg, wet and dry methods, and the like.

In some embodiments, the mixture is prepared into a base film by a wet method, specifically: extruding the mixture at a high temperature of 180-20° C. through a T-die to obtain a sheet-like film, which is then stretched, extracted, heated Shape and cut to obtain a base film. Wherein, the temperature range of the heat setting is 110-130°C.

In other embodiments, the mixture is prepared into a base film by a dry method, specifically: extruding the mixture at a high temperature of 200-250°C through a T-die to obtain a sheet-like film, which is then stretched and heat-set , and cut to obtain a basement membrane. Wherein, the temperature range of the heat setting is 140-160°C.

It can be understood that the stretching can be uniaxial stretching or biaxial stretching.

In the step S03:

The coating material can be an organic coating material or an inorganic coating material, the organic coating material includes an organic material and a binder, and the inorganic coating material includes 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 will not be repeated here.

Embodiments of the present application further provide an electrochemical device, the electrochemical device including the separator.

The embodiment of the present application also provides a lithium ion battery, comprising a positive electrode piece, a negative electrode piece, an electrolyte and the separator. Wherein, the separator is located between the positive electrode and the negative electrode, and the electrolyte is filled in the gap between the positive electrode and the separator, and between the negative electrode and the separator.

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material combined on the surface of the positive electrode current collector. The material of the positive electrode current 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 graphite-based carbon materials, non-graphite-based carbon materials, metallic lithium, alloy lithium, silicon-based alloys, tin-based alloys, conductive oxides, and conductive polymers. Wherein, the conductive oxide can be selected from but not limited to Li _x Fe ₂ O ₃ , Li _x WO ₂ , SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , At least one of Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ and Bi ₂ O ₅ ; the conductive polymer may be selected from but not limited to polyacetylene, polyacetylene At least one of aniline and polythiophene. where 0<y<1.

The negative electrode plate includes 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 current collector may be selected from, but not limited to, at least one of aluminum and nickel. The negative electrode active material may be selected from, but not limited to, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _c )O ₂ , LiNi _y Co _1-y O ₂ , LiCo _y Mn _{1 - y} O ₂ , LiCo _y Al _1-y O ₂ , LiCo _y B _1-y O ₂ , LiCo _y Mg _1-y O ₂ , LiCo _y Ti _1-y O ₂ , LiCo _y Mo _1-y O ₂ , LiCo _y Sn _1-y O ₂ , LiCo _y Ca _1-y O ₂ , LiCo _y C μ _1-y O ₂ , LiCo _y V _1-y O ₂ , LiCo _y Zr _1-y O ₂ , LiCo _y Si _{1 -y} O ₂ , LiCo _y W _1-y O ₂ , LiCo _y Y _1-y O ₂ , LiCo _y La _1-y O ₂ , LiCo _y Mn _1-y O ₂ , LiNi _y Mn _1-y O ₂ , At least one of LiCoPO ₄ and LiFePO ₄ . Wherein, 0<a<1, 0<b<1, a+b+c=1; 0<y<1.

The electrolyte solution includes solvent, cation and anion. The solvent may be selected from, but not limited to, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, dimethyl sulfoxide, acetonitrile, tetrahydrofuran, N-methylpyrrolidone, ethyl methyl carbonate and γ - at least one of butyrolactone. The cation may be selected from, but not limited to, at least one of Li ⁺ , Na ⁺ and K ⁺ . The anion can be selected from, but not limited to, PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N(CF ₃ At least one of SO ₂ ) ₂ ^- and C(CF ₂ SO ₂ ) ₃ ^- .

The lithium ion battery can 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 rolled structure, a laminated structure or a folded structure.

The lithium ion battery includes the separator, and the base film of the separator includes the polar group, and the polar group can be coupled and dissociated with lithium ions, thereby reducing lithium ions in the Migration resistance in basement membranes. When the separator is used in a lithium ion battery, the wetting ability of the separator to the electrolyte can be effectively improved, and the migration ability of lithium ions in the separator can be improved, thereby improving the rapid conduction ability of lithium ions, thereby improving the lithium ion battery. fast charging performance.

The present application will be specifically described below through specific examples, and the following examples are only partial examples of the present application, and are not intended to limit the present application.

Example 1

Preparation of the diaphragm:

Mix and extrude high molecular PE, ethylene acrylic acid copolymer and paraffin oil with a weight average molecular weight of 800,000, wherein the mass ratio of PE and ethylene acrylic acid copolymer is 70:30, and the total mass of PE and ethylene acrylic acid copolymer is the same as the paraffin wax. The mass ratio of oil is 3:7. The sheet-like film is extruded through a T-shaped die at a high temperature of 200 °C, and then cooled by a casting roll, and then subjected to biaxial stretching, extraction and heat-setting in the MD (longitudinal) and TD (transverse) directions. , and slitting to obtain a base film, wherein the stretching ratio corresponding to the MD direction and the TD direction is 7*7 times, and the heat setting temperature is 130°C.

Preparation of the coating:

In parts by weight, 90 parts of ceramic particles and 10 parts of acrylate binder were added to deionized water, mixed uniformly to prepare a slurry, and then the slurry was uniformly coated on the surface of the base film by microgravure coating. After drying in the oven, polyvinylidene fluoride is sprayed to obtain a base film comprising an inorganic coating layer and an organic coating layer, and a separator is obtained.

Preparation of positive electrode sheet:

In parts by weight, 94 parts of active material lithium cobaltate, 3 parts of conductive carbon, and 3 parts of binder polyvinylidene fluoride were fully stirred and mixed in N-methylpyrrolidone solvent system, and then coated on aluminum foil. Drying, cold pressing and slitting to obtain a positive pole piece.

Preparation of negative pole piece:

By weight, 97.5 parts of active material artificial graphite, 1.5 parts of binder styrene-butadiene rubber, and 1 part of thickener sodium carboxymethyl cellulose are fully stirred and mixed in deionized water, and then coated on copper foil. After drying, cold pressing and slitting, the negative pole piece is obtained.

Preparation of lithium-ion batteries:

Stack the above-mentioned positive pole piece, separator film, and negative pole piece in order so that the diaphragm is in the middle of the positive pole and the negative pole to play a role of isolation, and roll it to obtain a bare cell, place the bare cell in the casing, and inject the electrolyte. And encapsulated to obtain a lithium ion battery.

Example 2

This embodiment is basically the same as Embodiment 1, the difference is that the preparation method of the base film of this embodiment is:

The polymer PP and ethylene acrylic acid copolymer with a weight average molecular weight of 300,000 are melted and kneaded by an extruder according to a mass ratio of 90:10, and a sheet-like film is extruded through a T-die at a high temperature of 210 °C, and then cooled by a casting roll. After rewinding, multi-layer composite, and then uniaxially stretched in the MD direction by a stretching machine, heat-set at 140° C., layered, and slit to obtain a base film, wherein the MD direction stretching ratio is 2.3.

Example 3

This embodiment is basically the same as Embodiment 1, the difference is that the preparation method of the base film of this embodiment is:

The polymer PE, ethylene acrylic acid copolymer and silica with a weight average molecular weight of 800,000 are mixed and extruded, wherein the mass ratio of PE, ethylene acrylic acid copolymer and silica is 75:20:5. The sheet film was extruded at a high temperature of 200 °C in a die, and then cooled by a casting roll, and then subjected to biaxial stretching, extraction, heat setting, and slitting in the MD and TD directions to obtain a base film, wherein the stretching corresponding to the MD direction and the TD direction The ratio is 7*7 times, and the heat setting temperature is 130℃.

Example 4

This example is basically 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 basically 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 embodiment is basically the same as embodiment 2, except that the mass ratio of PP and ethylene acrylic acid copolymer in this embodiment is 80:20.

Example 7

This embodiment is basically the same as embodiment 2, except that the mass ratio of PP and ethylene acrylic acid copolymer in this embodiment is 99:1.

Example 8

This example is basically 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 basically the same as Example 1, except that in this example, the ethylene-propylene copolymer is replaced by an ethylene-vinyl acetate copolymer.

Example 10

This example is basically the same as Example 1, except that in this example, the ethylene propylene copolymer is replaced by an ethylene-vinyl alcohol copolymer.

Example 11

This embodiment is basically the same as Embodiment 1, except that the ethylene-propylene copolymer is replaced by ethylene-methyl acrylate in this embodiment.

Example 12

This example is basically the same as Example 1, the difference is that this example replaces the ethylene propylene copolymer with silica.

Example 13

This example is basically the same as Example 1, except that in this example, the ethylene propylene copolymer is replaced with hydrophobic silica, and the surface of the hydrophobic silica is connected with etheroxy groups.

Examples 14-17

Examples 14-17 are basically the same as Example 1, except that the thicknesses of the base films of Example 1 and Examples 14-17 are different, see Table 1 for details.

Comparative Example 1

This comparative example is basically the same as Example 1, the difference is that the preparation method of the base film of this comparative example is:

Mix and extrude polymer PE with a weight average molecular weight of 800,000 and paraffin oil (mass ratio 3:7), extrude a sheet-like film through a T-die at 220 °C at a high temperature, and then cool it through a casting roll and pass through MD and TD. Directional stretching, extraction, heat setting, and slitting were performed to obtain a base film, wherein the stretching ratio corresponding to the MD direction and the TD direction was 7*7 times, and the temperature of the heat setting section was 130°C.

Comparative Example 2

This comparative example is basically the same as Example 2, the difference is that the preparation method of the base film of this comparative example is:

The polymer PP with a weight-average molecular weight of 300,000 is melted and kneaded through an extruder, extruded into a sheet-like film through a T-die at 220°C, and then cooled by a casting roll, rolled up, multi-layered, and then drawn The base film was obtained by stretching in the MD direction with a stretching machine, heat-setting at 145° C., layering, and slitting, wherein the stretching ratio in the MD direction was 2.3.

The base film thickness test, porosity test and infrared absorption peak position test were performed on the base films of Examples 1-17 and Comparative Examples 1-2. The test results are shown in Table 1.

Base film thickness test: Take the base film with a length * width of 500*100mm in the TD direction of the base film, evenly take 5 points, use a ten thousand point thickness gauge to test the thickness of the base film at different positions, and then calculate the thickness of the above 5 points. The average value was taken as the thickness of the base film.

Porosity test: Take 5 pieces of base film with a size of 100*100mm, measure the weight and take the average value as its weight value M (mg), use the calculation formula of porosity: X=1-M/T*S*ρ Calculate The porosity is obtained, where T is the thickness of the base film, S is the area of the base film, and ρ is the density of the polyolefin raw material of the base film.

Infrared absorption peak position test: use the infrared spectrometer to test the infrared absorption peak position of the base film by the total reflection method.

Table I:

The lithium ion batteries of Examples 1-17 and Comparative Examples 1-2 were subjected to a discharge rate test and a 25°C cycle performance test. The test results are shown in Table 2.

Discharge rate test: Take 3 lithium-ion batteries of Example 1-17 and Comparative Example 1-2, charge them to 4.4V at a constant current rate of 0.5C at room temperature, and then charge them with a constant voltage at a voltage of 4.4V to 0.05C, and then discharge at a discharge current of 2C to test its discharge capacity, and record the ratio of the discharge capacity to the capacity obtained at a discharge current of 0.5C as its 2C discharge rate.

25°C cycle performance (capacity retention rate) test: take 3 lithium-ion batteries of Example 1-17 and Comparative Example 1-2, charge them to 4.4V at a constant current rate of 3C at 25°C, and then charge at 4.4 Under the voltage condition of V, the battery was charged to 0.05C under constant voltage, and the initial capacity of the cell was obtained. The cycle process is as follows: discharge at a discharge current of 1C to 3.0V, then charge at a constant current rate of 3C to 4.4V, and then charge at a constant voltage to 0.05C at a voltage of 4.4V, and then repeat the above process 1000 times, the 3 The remaining capacity of each lithium-ion battery is averaged to obtain the final capacity, and then divided by the initial capacity to obtain the capacity retention rate.

Table II:

It can be seen from Table 2 that:

Compared with the lithium ion battery of Comparative Example 1, the lithium ion batteries of Examples 1, 3-5 and 8-17 have higher discharge rates and better capacity retention rates. Among them, the thickness of the base film in Example 17 was too large, resulting in a lower discharge rate.

Compared with the lithium ion battery of Comparative Example 2, the lithium ion batteries of Examples 2, 6 and 7 have higher discharge rates and better capacity retention rates.

It can be seen that when the separator described in the present application is used in a lithium ion battery, the fast charging performance of the lithium ion battery can be effectively improved.

The separators and lithium-ion batteries provided by the embodiments of the present application have been introduced in detail above. The principles and implementations of the present application are described in this article by using specific examples. The descriptions of the above embodiments are only used to help understand the methods of the present application. and its core idea; at the same time, for those skilled in the art, according to the idea of the application, there will be changes in the specific implementation and application scope. In summary, the content of this description should not be construed as a reference to the application. limit.

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.