WO2023115625A1

WO2023115625A1 - Separator having large elastic deformation quantity and preparation method therefor

Info

Publication number: WO2023115625A1
Application number: PCT/CN2021/142772
Authority: WO
Inventors: 董秋春; 白耀宗; 刘杲珺; 张绪杰; 薛山; 刘志刚; 朱滕辉; 张影; 吴奇阳; 史新明; 马源; 甘珊珊
Original assignee: 中材锂膜有限公司
Priority date: 2021-12-23
Filing date: 2021-12-30
Publication date: 2023-06-29
Also published as: CN114243221A; CN114243221B

Abstract

The present invention relates to the technical field of separators. Provided are a separator having a large elastic deformation quantity and a preparation method therefor. The separator having a large elastic deformation quantity comprises: a base film, or a base film and a coating applied on at least one side of the base film; and the elastic deformation quantity of the separator having a large elastic deformation quantity satisfies: Δx/L > 0.2%. By means of the present invention, the technical problem of irreversible damage occurring in separator processing and modification processes is solved, and the technical effects of improving the physical property stability, especially the mechanical strength stability, of a product, enabling a battery cell having a modified separator or assembled using the separator to have an impact resistance capability under a stable physical property, and thereby improving the stability and safety of a lithium battery are achieved.

Description

Diaphragm with high elastic deformation and its preparation method

technical field

The invention relates to the technical field of diaphragms, in particular to a diaphragm with high elastic deformation and a preparation method thereof.

Background technique

As the key main material in the lithium-ion battery system, the diaphragm is crucial to the stability and safety of the battery.

In the prior art, mainly through inorganic, organic or inorganic-organic mixed coating and modification, the heat resistance of the diaphragm is improved, and the closed cell temperature is reduced, so as to improve the stability and safety of the battery. The publication number is JP6069677B2, which improves the heat resistance of the separator through organic and inorganic mixed coating, and the publication number is CN104185551B, which improves the safety of the battery by reducing the closed cell temperature of the separator through coating modification.

For deformation, at present, the main focus is on the elongation at break, and little attention is paid to elastic deformation. Elastic deformation is an important indicator for the stability of the diaphragm. The impact resistance of the diaphragm under stable physical properties can be judged by the size or presence of elastic deformation. After the diaphragm is changed, the elastic deformation rate is maintained to judge the damage degree of the change process.

In view of this, the present invention is proposed.

Contents of the invention

One of the objectives of the present invention is to provide a diaphragm with high elastic deformation to improve the stability of product properties, especially the stability of mechanical strength.

The second object of the present invention is to provide a method for preparing a diaphragm with high elastic deformation, so as to prepare a diaphragm whose elastic deformation meets specific requirements.

The third object of the present invention is to provide a lithium ion battery comprising the high elastic deformation diaphragm or the high elastic deformation diaphragm prepared by the preparation method.

In order to realize the above-mentioned purpose of the present invention, special adopt following technical scheme:

In a first aspect, the present invention provides a diaphragm with high elastic deformation, which includes: a base film, or a base film and a coating on at least one side of the base film;

The elastic deformation of the high elastic deformation diaphragm satisfies: Δx/L>0.2%, preferably 0.8%<Δx/L<10%, more preferably 1%<Δx/L<5%;

Among them, L is the original length, unit: meter; Δx is the elastic deformation, unit: meter.

In a second aspect, the present invention provides a method for preparing the high elastic deformation diaphragm, wherein the base film is prepared by a wet or dry process;

The wet process includes the following steps:

Mix liquid hydrocarbons and polyolefin resins for pretreatment according to the formula ratio, or directly transport them to the extrusion system, heat and melt to form a uniform mixture; the mixed melt is extruded to the casting roll to cool down, phase separation, cooling and molding, and the film is obtained Then heat the membrane to a temperature close to the melting point, carry out two-way synchronous or step-by-step stretching to make the molecular chain orientation, heat preservation, and finalization; the solvent elutes the residual liquid hydrocarbons, and after elution, the membrane is removed from the solvent, dried, and then horizontally Stretching, shaping, and retraction to prepare interpenetrating microporous membranes;

Among them, the wet preparation process needs to meet condition 1 and/or condition 2:

Condition 1: The solid content of polyolefin in the mixed slurry is less than 40%, the viscosity-average molecular weight of polyolefin (10,000)/drawing ratio>0.04, preferably>1, and the viscosity-average molecular weight of polyolefin (10,000)/MD stretching Ratio > 0.04; polyolefin viscosity-average molecular weight (10,000)/TD stretch ratio > 1, preferably > 10;

Condition 2: the shrinkage step controls the shrinkage area ratio > 1%;

Alternatively, the dry process includes the following steps:

The raw materials such as polyolefin resin and additives are pretreated according to the formula ratio, or directly transported to the extrusion system. In the extrusion system, the raw materials are melted and plasticized, and then the melt is extruded from the die to the casting roll to cool down, cooled and formed. Form a sheet (or base film) with a specific crystalline structure, heat-treat the sheet to obtain a hard elastic film, then perform cold stretching and hot stretching, retract and shape to form a base film;

Among them, the dry preparation process needs to meet condition 1' and/or condition 2':

Condition 1': viscosity-average molecular weight (10,000)/stretch ratio of polyolefin > 0.04, preferably > 1;

Condition 2': the shrinkage step controls the shrinkage area ratio > 1%.

In a third aspect, the present invention provides a lithium ion battery, comprising the high elastic deformation separator or the high elastic deformation separator prepared by the preparation method.

The technical solution of the present invention has the following beneficial effects:

The invention prepares a diaphragm with a certain amount of elastic deformation by controlling raw materials and processing technology, ensures that the diaphragm maintains a certain elastic deformation rate after changes and during processing, improves the stability of product properties, especially the stability of mechanical strength, and makes the diaphragm The modified or assembled batteries have impact resistance under stable physical properties, thereby improving the stability and safety of lithium batteries.

Description of drawings

In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the specific implementation or description of the prior art. Obviously, the accompanying drawings in the following description The drawings show some implementations of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

Fig. 1 is a flow chart of the preparation process of the high elastic deformation diaphragm provided by the embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

According to a first aspect of the present invention, a high elastic deformation diaphragm is provided, comprising: a base film, or, a base film and a coating placed on at least one side of the base film;

The elastic deformation of the high elastic deformation diaphragm satisfies: Δx/L>0.2%, such as 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3% %, 4%, 5%, 6%, 7%, 8%, 9%, 10%, preferably 0.8%<Δx/L<10%, more preferably 1%<Δx/L<5%;

Elastic deformation test method According to the test method of GB/1040.3-2006 to test tensile strength and elongation at break, according to Hooke's law (elastic law): F=k·Δx (where F is elastic force, the unit is N, k is The constant is the stiffness (stiffness) coefficient of the object, the unit is N/m, Δx is the deformation amount, the unit is m), and the elastic deformation amount is judged.

The separator satisfying the above elastic deformation rate has good stability of physical properties, especially stability of mechanical strength, good impact resistance, and high stability and safety of the prepared lithium battery.

The material of the base film is not particularly limited, and may be materials known in the art that can be used as the base film of a battery separator, including but not limited to polyethylene, polypropylene, polyethylene/polypropylene composite film, and the like.

The material of the coating is not particularly limited, and may be materials known in the art that can be used as a coating on the diaphragm base film, including but not limited to inorganic materials (such as ceramics), organic polymers (such as aramid fiber, etc.), Inorganic/organic composite materials, etc.

The thicknesses of the base film and the coating layer are not particularly limited as long as they are suitable for use as a separator of a battery. Preferably, the thickness of the base film is 3-20 μm; the thickness of the single-side coating is 0.1-6 μm.

According to the second aspect of the present invention, there is provided a method for preparing a diaphragm with high elastic deformation, as shown in FIG. 1 , including a wet process or a dry process.

The wet process includes the following steps:

Mix liquid hydrocarbons and polyolefin resins for pretreatment according to the formula ratio, or directly transport them to the extrusion system, heat and melt to form a uniform mixture; the mixed melt is extruded to the casting roll to cool down, phase separation, cooling and molding, and the film is obtained Then heat the membrane to a temperature close to the melting point, carry out two-way synchronous or step-by-step stretching to make the molecular chain orientation, heat preservation, and finalization; the solvent elutes the residual liquid hydrocarbons, and after elution, the membrane is removed from the solvent, dried, and then horizontally Stretching, shaping, and retraction to prepare interpenetrating microporous membranes.

The wet preparation process needs to meet condition 1 and/or condition 2:

Condition 1: The solid content of polyolefin in the mixed slurry (liquid hydrocarbon and polyolefin resin) is less than 40% (such as 35%, 30%, 25%), and the viscosity-average molecular weight of polyolefin (in tens of thousands)/stretch Ratio > 0.04, such as 0.05, 0.1, 0.2, 0.5, 0.8, 1.0, 2.0, 3.0, 5.0, 6.0, 7.0, 8.0, 10.0, preferably > 1, and the viscosity-average molecular weight of polyolefin (10,000)/MD draw ratio >0.04, such as 0.05, 0.1, 0.2, 0.5, 0.8, 1.0; polyolefin viscosity-average molecular weight (10,000)/TD draw ratio >1, such as 2.0, 3.0, 5.0, 6.0, 7.0, 8.0, 10.0, 12.0, 15.0, preferably>10;

Stretching in the wet process is biaxial stretching, including longitudinal stretching and transverse stretching. The stretching ratio refers to the product of the longitudinal stretching ratio (ie, MD stretching ratio) and the transverse stretching ratio (ie, TD stretching ratio).

MD or TD stretching ratio=length after stretching/length before stretching.

Condition 2: the shrinkage step controls the shrinkage area ratio > 1%, such as 2%, 3%, 5%;

Retraction area ratio = (area before retraction - area after retraction) / area before retraction

In a preferred embodiment, the wet preparation process also needs to meet condition 3:

Condition 3: Excluding the extrusion and stretching sections, other sections of the process control the longitudinal tension <500N/m by adjusting the roller speed ratio or speed difference, such as 100, 150, 200, 250, 300, 400, 450N/m, through The holding force of the shearing roller or pressing roller controls the lateral tension of the diaphragm to <100N/m, such as 10, 20, 50, 60, 80, 90N/m.

Ways that can be implemented in the wet process include: condition 1, condition 2, condition 1+2, condition 1+3, condition 2+3, and condition 1+2+3.

The dry process includes the following steps:

The raw materials such as PE or PP and additives are pretreated according to the formula ratio, or directly transported to the extrusion system. In the extrusion system, the raw materials are melted and plasticized, and then extruded from the die to the casting roll to cool down, cooled and formed. A sheet (or base film) with a specific crystalline structure is formed, and the sheet is heat-treated to obtain a hard elastic film, followed by cold stretching and hot stretching to form a nano-microporous membrane, that is, a diaphragm.

Condition 1': viscosity-average molecular weight (10,000)/stretch ratio of polyolefin > 0.04, such as 0.05, 0.1, 0.2, 0.5, 0.8, 1.0, 2.0, 3.0, 5.0, 6.0, 7.0, 8.0, 10.0, preferably > 1 ;

There is only unidirectional stretching in the dry process, and the stretching ratio refers to the unidirectional stretching ratio.

Condition 2': the shrinkage setting step controls the shrinkage area ratio > 1%, such as 2%, 3%, 5%.

In a preferred embodiment, the dry preparation process also needs to satisfy condition 3':

Condition 3': Excluding the extrusion and stretching sections, the longitudinal tension of the other sections is controlled by the roller speed ratio or speed difference <500N/m, such as 100, 150, 200, 250, 300, 400, 450N/m, The lateral tension of the diaphragm is controlled to be <100N/m, such as 10, 20, 50, 60, 80, 90N/m, by the holding force of the shearing roller or the pressing roller.

The ways that can be implemented in the dry process include: condition 1', condition 2', condition 1'+2', condition 1'+3', condition 2'+3', condition 1'+2'+3'.

As a further solution, the preparation method also includes: a step of adding a coating on one side or both sides of the base film: the coating slurry is coated on the surface of the base film, dried or dried after treatment, and the coating slurry is formed by One or a combination of inorganic ceramic particles and organic polymer materials;

Among them, the step of adding coating needs to meet condition 4:

When the weight ratio of inorganic ceramic particles is >80% (such as 85%, 90%, 95%), the inorganic ceramic particles are required to be 0.1μm≤D50≤2.0μm;

When the weight ratio of inorganic ceramic particles is 30%-80% (such as 40%, 50%, 60%, 70%), the inorganic ceramic particles are required to be 0.01μm≤D50≤4μm;

When the weight ratio of the inorganic ceramic particles is less than 30% (for example, 5%, 10%, 20%), the D50 of the inorganic ceramic particles is required to be ≤ 10 μm.

In a preferred embodiment, the step of adding the coating also needs to meet condition 5: control the longitudinal tension <150N/m during the coating, drying process or through the roller speed ratio or speed difference during the coating, treatment and drying process , such as 50, 100, 120N/m, the lateral tension is controlled to be less than 100N/m, such as 20, 50, 60, 80, 90N/m by the shearing or pressing roller holding force.

The ways that can be implemented in the step of adding the coating include: condition 4 or condition 4+5.

Preferably, the inorganic ceramic coating material in the coating slurry comprises the inorganic ceramic particles selected from alumina, boehmite, calcium carbonate, hydrotalcite, montmorillonite, spinel, mullite, titanium dioxide, di One or more of silicon oxide, zirconium dioxide, magnesium oxide, calcium oxide, beryllium oxide, magnesium hydroxide, boron nitride, silicon nitride, aluminum nitride, titanium nitride, boron carbide, silicon carbide, zirconium carbide kind;

Preferably, the organic polymer material in the coating slurry contains organic coating materials such as polyimide, polyetherimide, aramid fiber, polysulfone fiber, polyvinylidene fluoride, polymethyl methacrylate, poly One or more of organic powders or suspensions such as ethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, etc.

The base film or base film + coating diaphragm prepared by the above method meets the requirement of Δx/L>0.2%, which ensures that the diaphragm maintains a certain elastic deformation rate after changes and during processing, and improves the stability of product properties, especially The stability of mechanical strength enables the batteries modified or assembled with the diaphragm to have impact resistance under stable physical properties, thereby improving the stability and safety of lithium batteries.

According to a third aspect of the present invention, a lithium ion battery is provided, comprising the above-mentioned high elastic deformation separator or the high elastic deformation separator prepared by the above preparation method.

Lithium-ion batteries have the same advantages as the above-mentioned separators, so I won't repeat them here.

The present invention will be further described below in conjunction with the examples. It should be noted that the following examples are provided only for the purpose of illustration and do not constitute a limitation to the protection scope of the present invention.

Unless otherwise specified, the raw materials, reagents, and methods used in the examples are conventional raw materials, reagents, and methods in the art.

Example 1

The diluent in this embodiment is paraffin oil, the polyolefin resin in this embodiment is polyethylene with an average molecular weight of 900,000 (manufacturer: AsahiKASEI, model: UH650), and the equipment used is a wet-process diaphragm line from Sinoma Lithium Membrane Co., Ltd.

A diaphragm with high elastic deformation and a preparation method thereof, comprising mixing 75% by mass of paraffin oil and 25% by mass of polyethylene with an average molecular weight of 900,000, heating and melting to form a uniform mixture, and then cooling down Phase separation to obtain a membrane, and then heating the membrane to a temperature close to the melting point, and performing bidirectional simultaneous stretching (MD stretching 9 times, TD stretching 7 times) with a stretching ratio of 63 for the first time to orient the molecular chains, Then keep it warm for 3-15s, elute the residual liquid hydrocarbon with dichloromethane, a volatile solvent, and then dry it. Finally, after the second transverse stretching (TD stretching ratio 1.5 times), the area shrinks by 15% after setting, and the whole In the process, the speed difference between the front and rear rollers is controlled to be less than 0.2m/min, so that the maximum value of the tension in the longitudinal process is <300N/m, and the maximum value of the transverse tension of the diaphragm is controlled by the shearing roller or pressure roller to <90N/m, and the interpenetrating and Microporous membrane material with high elastic deformation. The elastic deformation of the obtained diaphragm satisfies Δx/L>1.2%, a thickness of 9 μm, a porosity of 40%, and an air permeability of 140 sec/100c.

Example 2

The diluent in this embodiment is paraffin oil, the polyolefin resin in this embodiment is polyethylene (manufacturer: Celanese, model: GURX223) with an average molecular weight of 1.5 million, and the equipment used is a wet-process diaphragm line from Sinoma Lithium Membrane Co., Ltd.

A diaphragm with high elastic deformation and a preparation method thereof, comprising mixing 82% paraffin oil with a mass proportion of 18% and polyethylene with an average molecular weight of 1.5 million, heating and melting to form a uniform mixture, and then cooling down Phase separation to obtain a membrane, and then heating the membrane to a temperature close to the melting point, and performing bidirectional simultaneous stretching (7 times MD stretching, 7 times TD stretching) with a stretching ratio of 49 for the first time to orient the molecular chains, Followed by heat preservation for a certain period of time, the residual liquid hydrocarbons were eluted with volatile solvent dichloromethane, then dried, and finally through the second transverse stretching (TD stretching ratio 1.4 times), the area retracted by 18% after setting, the whole process By controlling the speed difference between the front and rear rollers to be less than 0.3m/min, the maximum value of the tension in the longitudinal process is <400N/m, and the maximum value of the transverse tension of the diaphragm is controlled by the shearing roller or pressing roller to <100N/m, and the interpenetrating and high Microporous membrane material with elastic deformation. The elastic deformation of the obtained diaphragm satisfies Δx/L > 1.6%, a thickness of 7 μm, a porosity of 37%, and an air permeability of 135 sec/100c.

Example 3

The difference between this embodiment and embodiment 2 is that paraffin oil accounts for 80%, polyethylene accounts for 20%, and the second transverse stretching (TD stretching ratio is 1.45 times), the area shrinks back by 20% after setting. The elastic deformation of the obtained diaphragm satisfies Δx/L>1.3%, a thickness of 12 μm, a porosity of 40%, and an air permeability of 155 sec/100c.

In addition, the 3-20 μm diaphragm (base film) can be prepared through the process conditions of Examples 1-3, the elastic deformation of the diaphragm satisfies Δx/L>0.8%, the porosity is 25-70%, and the air permeability value is 50-400sec/ 100c.

Example 4

A diaphragm with high elastic deformation and its preparation method. The composition and content of the coating are: 92 parts of alumina with a D50 of 0.6 μm, 4.5 parts of modified polyacrylic acid, 2.5 parts of polyvinyl alcohol, and 1 part of ammonium polyacrylate. Stir to prepare a water-based coating slurry with a solid content of 30%, use the 9 μm prepared in Example 1 as the base film, and use the MCD type coater to gravure-coat the combined slurry of the above-mentioned water-based coating on the base film sheet. side, and finally after being baked in an oven, the coating thickness is 3 μm. The speed difference between the front and rear rollers is controlled to be less than 0.2m/min during the whole process, so that the maximum tension in the longitudinal process is less than 100N/m. The maximum value of the transverse tension is controlled by force <50N/m, and the microporous membrane material with interpenetration and high elastic deformation is prepared. The elastic deformation of the obtained diaphragm satisfies Δx/L>0.5%, the thickness is 12 μm, and the air permeability is 170 sec/100c.

Example 5

A high elastic deformation diaphragm and a preparation method thereof, 15 parts by weight of polyvinylidene fluoride glue solution (20% by mass fraction) and 20 parts by weight of polyimide glue solution (10% by mass fraction), are dissolved to 57 In the mixed liquid of dimethylacetamide and tripropylene glycol (wherein, the weight ratio of dimethylacetamide, tripropylene glycol and water is 15:70:30), add 20 parts by weight of silane coupling agent modified D50 is 0.64 μm alumina, 3 parts by weight of emulsion-type acrylate binder (solid content is 40%, viscosity is 20cps-200cps at 25°C), mixed and stirred at room temperature for 1 hour to obtain a white viscous coating slurry. The 7 μm prepared in Example 2 is used as the base film, and the above-mentioned coating slurry is coated on one side of the base film by means of gravure coating by an MCD type coater, and then immersed in a coagulation solution (dimethyl ethyl alcohol) at 22 ° C. The weight ratio of amide, tripropylene glycol and water is 28:12:60), and the wet film on the surface of the polyolefin porous membrane is first cured, washed with water and dried in turn to obtain a composite diaphragm. The thickness is 2μm, and the speed difference between the front and rear rollers is controlled to be less than 0.1m/min in the whole process, so that the maximum tension in the longitudinal process is <120N/m, and the maximum tension in the transverse direction is controlled by the shearing roller or pressing roller to <60N/m. A microporous membrane material with interpenetration and high elastic deformation. The elastic deformation of the obtained diaphragm satisfies Δx/L>1.0%, the thickness is 9 μm, and the air permeability is 180 sec/100c.

Example 6

A diaphragm with high elastic deformation and its preparation method, dispersing alumina powder with 0.1 times the mass of aramid fiber and D50 of 0.8 μm in the aramid fiber stock solution with a mass fraction of 1.5% and an apparent viscosity of 300cp, and passing it through a high-speed dispersing emulsifier Stir for 30 minutes, and obtain a uniform para-aramid slurry after filtering through a 1000-mesh filter. The 12 μm prepared in Example 3 is used as the base film, and the above-mentioned para-aramid slurry is coated on one side of the base film by means of gravure coating through an MCD type coating machine. Stay in the saturated steam atmosphere of RH for 30s, then wash in a pure water tank for 120s, and then dry in an oven at 75°C for 60s, with a coating thickness of 4μm. In the whole process, the speed difference between the front and rear rollers is controlled to be less than 0.15m/min, so that the maximum tension in the longitudinal process is less than 110N/m, and the maximum tension in the transverse direction is less than 80N/m through the holding force of the shearing roller or pressing roller. Microporous membrane material with elastic deformation. The elastic deformation of the obtained diaphragm satisfies Δx/L>0.8%, the thickness is 16 μm, and the air permeability is 260 sec/100c.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims

A high elastic deformation diaphragm, characterized in that the high elastic deformation diaphragm comprises: a base film, or a base film and a coating placed on at least one side of the base film;

The elastic deformation of the high elastic deformation diaphragm satisfies: Δx/L>0.2%;

Among them, L is the original length, unit: meter; Δx is the elastic deformation, unit: meter.
The high elastic deformation diaphragm according to claim 1, characterized in that, the thickness of the base film is 3-20 μm; and/or,

The thickness of the coating is 0.1-6 μm.
A method for preparing the high elastic deformation diaphragm according to claim 1 or 2, wherein the base film is prepared by a wet or dry process;

The wet process includes the following steps:

The liquid hydrocarbon and polyolefin resin are mixed according to the formula ratio and pretreated, or directly transported to the extrusion system, heated and melted to form a uniform mixture; the mixed melt is extruded to the casting roll to cool down, phase separated, cooled and formed, and obtained Diaphragm; then heat the membrane to a temperature close to the melting point, carry out two-way synchronous or step-by-step stretching to make the molecular chain orientation, heat preservation, and finalization; the solvent elutes the residual liquid hydrocarbons, and after elution, the membrane is removed from the solvent, dried, and then Transverse stretching, shaping, and retraction to prepare interpenetrating microporous membranes;

Among them, the wet preparation process needs to meet condition 1 and/or condition 2:

Condition 1: The solid content of polyolefin in the mixed slurry is less than 40%, the viscosity-average molecular weight (10,000)/stretch ratio of polyolefin>0.04, and the viscosity-average molecular weight (10,000)/MD stretch ratio of polyolefin>0.04; The viscosity-average molecular weight of polyolefin (10,000)/TD draw ratio>1;

Condition 2: the shrinkage step controls the shrinkage area ratio > 1%;

Alternatively, the dry process includes the following steps:

The polyolefin resin and additive raw materials are pretreated according to the formula ratio, or directly transported to the extrusion system. In the extrusion system, the raw materials are melted and plasticized, and then the melt is extruded from the die to the casting roll to cool down, cooled and formed, and formed For sheets with a specific crystalline structure, the sheet is heat-treated to obtain a hard elastic film, followed by cold stretching and hot stretching, retracting and shaping to form a base film;

Among them, the dry preparation process needs to meet condition 1' and/or condition 2':

Condition 1': viscosity-average molecular weight (10,000)/stretch ratio of polyolefin > 0.04;

Condition 2': the shrinkage step controls the shrinkage area ratio > 1%.
The preparation method according to claim 3, wherein the wet preparation process also needs to meet condition 3:

Condition 3: Excluding the process of extrusion and stretching, other processes control the longitudinal tension <500N/m, and the transverse tension <100N/m.
preparation method according to claim 3, is characterized in that, dry preparation process also needs to satisfy condition 3':

Condition 3': remove the process of extrusion and stretching, and control the longitudinal tension <1000N/m and transverse tension <100N/m in other processes.
The preparation method according to claim 3, characterized in that, the preparation method further comprises: the step of adding a coating on one side or both sides of the base film: the coating slurry is coated on the surface of the base film, dried or treated Formed after drying, the coating slurry is composed of one or a mixture of inorganic ceramic particles, organic polymer materials;

Among them, the step of adding coating needs to meet condition 4:

When the weight ratio of inorganic ceramic particles is >80%, the inorganic ceramic particles are required to be 0.1μm≤D50≤2.0μm;

When the weight ratio of inorganic ceramic particles is 30%-80%, the inorganic ceramic particles are required to be 0.01μm≤D50≤4μm;

When the weight ratio of the inorganic ceramic particles is less than 30%, the D50 of the inorganic ceramic particles is required to be less than or equal to 10 μm.
The preparation method according to claim 6, characterized in that the step of adding the coating also needs to meet condition 5: during the coating and drying process or during the coating, treatment and drying process, the longitudinal tension is controlled <150N/m, and the transverse tension is less than 150N/m. <100N/m.
The preparation method according to claim 6, wherein the inorganic ceramic particles include alumina, boehmite, calcium carbonate, hydrotalcite, montmorillonite, spinel, mullite, titanium dioxide, silicon dioxide, One or more of zirconia, magnesium oxide, calcium oxide, beryllium oxide, magnesium hydroxide, boron nitride, silicon nitride, aluminum nitride, titanium nitride, boron carbide, silicon carbide, and zirconium carbide.
The preparation method according to claim 6, wherein the organic polymer material comprises polyimide, polyetherimide, aramid fiber, polysulfone fiber, polyvinylidene fluoride, polymethyl methacrylate, One or more of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene organic powder or suspension.
A lithium-ion battery, characterized in that, the lithium-ion battery comprises the high elastic deformation diaphragm described in claim 1 or 2 or the high elastic deformation prepared by the preparation method described in any one of claims 3-9 diaphragm.