WO2019096225A1

WO2019096225A1 - Coating slurries, separators, and methods for making the coating slurries and the separators thereof

Info

Publication number: WO2019096225A1
Application number: PCT/CN2018/115732
Authority: WO
Inventors: Alex Cheng; Lianjie WANG; Yongle Chen; Zhixue Wang; Chenbo LIAO
Original assignee: Shanghai Energy New Materials Technology Co., Ltd.
Priority date: 2017-11-16
Filing date: 2018-11-15
Publication date: 2019-05-23
Also published as: CN107955468B; CN107955468A

Abstract

A coating slurry consisting essentially of: from 1 to 5 parts by weight of polyacrylonitrile; from 20 to 40 parts by weight of at least one solvent; from 1 to 5 parts by weight of at least one filler; and from 50 to 75 parts by weight of a polymer solution, a method for preparing the coating slurry, a method for making a separator using the coating slurry, as well as separators prepared by the method.

Description

COATING SLURRIES, SEPARATORS, AND METHODS FOR MAKING THE COATING SLURRIES AND THE SEPARATORS THEREOF

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority to Chinese Application No. 201711133380.6, filed on November 16, 2017, the content of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to electrochemistry field, and especially relates to coating slurries, methods for preparing the coating slurries of separators, methods for preparing separators for electrochemical devices, as well as separators prepared by the methods.

BACKGROUND

With rapid growing market of energy storage, batteries and other forms of electrochemical devices are receiving more and more attentions. For example, lithium secondary batteries have been extensively used as energy sources in mobile phones, laptops, power tools, electrical vehicles, etc.

An electrode assembly of an electrochemical device usually comprises a positive electrode (i.e., cathode) , a negative electrode (i.e., anode) , and a permeable membrane (i.e., separator) interposed between the positive electrode and the negative electrode. The positive electrode and the negative electrode are prevented from being in direct contact with each other by the separator, thereby avoiding internal short circuit. In the meanwhile, ionic charge carriers (e.g., lithium ions) are allowed to pass through the separator so as to close the circuit during the passage of current. Separators are critical components in electrochemical devices because their structures and properties considerably affect the performances of the electrochemical devices, including, for example, internal resistance, energy density, power density, cycle life, and safety.

A separator is generally formed by a polymeric microporous membrane. For example, polyolefin-based microporous membrane has been widely used as separators in lithium secondary batteries because of its favorable chemical stability and excellent physical properties. However, polyolefin-based microporous membrane may not be sufficiently adhesive to bind the electrodes. A commonly-known method of manufacturing a battery comprises, for example, laminating a positive electrode, a negative electrode and a separator, winding up the laminate, charging the wound laminate into a battery container, injecting an electrolyte, and sealing the battery container. Strong adhesion between the separator and electrodes is therefore required to avoid dislocation motion between the separator and the electrodes during manufacturing or usage of the battery. The strong adhesion can further achieve a better interface contact between the separator and the electrodes, a higher peel strength of the separator, and a higher tensile strength of the battery, thereby further preventing short circuit and improving dimensional stability of an electrochemical device employing the separator. It has been disclosed that by placing a polyvinylidene fluoride (PVDF) coating on a polyolefin-based microporous membrane can enhance the adhesiveness of the separator, but such improvement may not be sufficient. Therefore, there exists a need for separators with stronger adhesiveness.

SUMMARY OF THE INVENTION

The present disclosure provides a coating slurry for preparing a coating layer for a separator, wherein the coating slurry consists essentially of: from 1 to 5 parts by weight of polyacrylonitrile (PAN) ; from 20 to 40 parts by weight of at least one solvent; from 1 to 5 parts by weight of at least one filler; and from 50 to 75 parts by weight of a polymer solution. Furthermore, the polymer solution may comprise, for example, from 5 wt%to 20 wt%of PVDF.

The present disclosure further provides a method for making a separator using the coating slurry, comprising: providing a microporous polyolefin-based membrane; coating at least one side of the membrane with the coating slurry of the present disclosure; washing the resulting coated membrane with water to remove the at least one solvent; and drying the coated membrane at a temperature ranging, for example, from 50 ℃ to 60 ℃ to form a coating layer on the membrane. Furthermore, the microporous coating layer has a thickness ranging, for example, from 1 μm to 4 μm on the membrane.

The present disclosure further provides a separator prepared by the method disclosed herein. The separator disclosed herein comprises a porous base membrane and a coating layer being formed on at least one side of the porous base membrane, wherein the coating layer is formed using the coating slurry disclosed herein.

DETAILED DESCRIPTION

In some embodiments, the present disclosure provides a coating slurry for preparing a coating layer for a separator, wherein the coating slurry consists essentially of:

(A) from 1 to 5 parts by weight of PAN;

(B) from 20 to 40 parts by weight of at least one solvent;

(C) from 1 to 5 parts by weight of at least one filler; and

(D) from 50 to 75 parts by weight of a polymer solution.

In some embodiments, the coating slurry consists essentially of:

(A) from 1 to 3 parts by weight of PAN;

(B) from 25 to 35 parts by weight of at least one solvent;

(C) from 1 to 2 parts by weight of at least one filler; and

(D) from 60 to 70 parts by weight of a polymer solution.

In some embodiments, PAN has a glass transition temperature ranging, for example, from 70 ℃ to 100 ℃, such as from 85 ℃ to 95 ℃. PAN may be dissolved in a solution before being mixed into the coating slurry. The PAN solution may have a solid content -the weight proportion of PAN in the PAN solution -ranging, for example, from 15 wt%to 40 wt%, such as from 20 wt%to 35 wt%. In some embodiments, PAN may be a PAN-based polymer, including PAN homopolymer and PAN copolymer. The solvent of the PAN solution may be one or more chosen, for example, from DMAC, N, N-dimethylformamide (DMF) , N-methyl pyrrolidone (NMP) , dmethyl sulfoxide (DMSO) , acetone, diethyl ether, propyl ether, cyclohexane, and tetrahydrofuran (THF) . In one embodiment, the solvent of the PAN solution is dimethyl acetamide (DMAC) . If PAN is mixed into the coating slurry in the form of PAN solution, the range of parts by weight refers to the PAN dissolved in the PAN solution.

Different types and amounts of the at least one filler in the coating slurry can affect the heat-resistance of the coating layer and the separator prepared from the coating slurry, thereby further preventing short circuit and improving dimensional stability of an electrochemical device employing the separator at a high temperature. Furthermore, the presence of the at least one filler may also affect, for example, the formation of pores in the coating layer and the increase of the physical strength of the coating layer. In some embodiments of the present disclosure, the at least one filler may comprise inorganic particles chosen, for example, from oxides, hydroxides, sulfides, nitrides, carbides, carbonates, sulfates, phosphates, titanates, and the like, comprising at least one of metallic and semiconductor elements, such as Al, Si, Ca, Ti, B, Sn, Mg, Li, Co, Ni, Sr, Ce, Zr, Y, Pb, Zn, Ba, and La. Specific examples of the particles include alumina (Al ₂O ₃) , boehmite (γ-AlOOH) , silica (SiO ₂) , zirconium dioxide (ZrO ₂) , titanium oxide (TiO ₂) , cerium oxide (CeO ₂) , calcium oxide (CaO) , zinc oxide (ZnO) , magnesium oxide (MgO) , lithium nitride (Li ₃N) , calcium carbonate (CaCO ₃) , barium sulfate (BaSO ₄) , lithium phosphate (Li ₃PO ₄) , lithium titanium phosphate (LTPO) , lithium aluminum titanium phosphate (LATP) , cerium titanate (CeTiO ₃) , calcium titanate (CaTiO ₃) , barium titanate (BaTiO ₃) and lithium lanthanum titanate (LLTO) . The particles disclosed herein may have an average particle size ranging, for example, from 5 nm to 1,000 nm, such as from 20 nm to 500 nm. The filler disclosed herein may be a powder that is among commercially available products.

Different types of the polymer in the coating slurry may affect the adhesion of the coating layer formed using the coating slurry. In some embodiments of the present disclosure, the polymer solution is a solution of one or more polymers chosen, for example, from polyvinylidene fluoride (PVDF) -based polymers, including PVDF homopolymer and/or PVDF copolymer. Examples of PVDF copolymer include polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP) , polyvinylidene fluoride-co-tetrafluoroethylene (PVDF-co-TFE) , and mixtures thereof. In some embodiments, the polymer solution is a PVDF solution that comprises, for example, from 5 wt%to 20 wt%, such as from 5 wt%to 10 wt%, of PVDF, wherein the PVDF has a weight average molecular weight ranging, for example, from 100,000 to 3,000,000, such as from 600,000 to 2,000,000.

In some embodiments of the present disclosure, the method for preparing a coating slurry for preparing a coating layer of a separator comprises:

(A) adding PVDF into a first solvent to obtain a first slurry;

(B) adding the at least one filler into a second solvent to obtain a second slurry;

(C) adding the PAN into a third solvent to obtain a third slurry; and

(D) mixing all the slurries to obtain the coating slurry for coating the separator.

The first, second, and third solvent in steps (A) - (C) may be the same or different. Each of the first, second, and third solvent may comprise one or more chosen, for example, from DMAC, DMF, NMP, DMSO, acetone, diethyl ether, propyl ether, cyclohexane, and THF. The first slurry comprises, for example, from 5 wt%to 20 wt%, such as from 5 wt%to 10 wt%, of PVDF, wherein the PVDF has a weight average molecular weight ranging, for example, from 100,000 to 1,000,000, such as from 200,000 to 500,000. The third slurry comprises, for example, from 15 wt%to 40 wt%, such as from 20 wt%to 35 wt%of PAN.

To enhance the solubility of PVDF, the at least one filler, and PAN in each of the first, second, and third solvent, respectively, or shorten the dissolution time, various techniques may be used, for example, agitation, raising the temperature of the at least one solvent (for example, the temperature of the at least one solvent may range from 5 ℃ to 80 ℃, such as from 20 ℃ to 50 ℃) , and/or adding at least one solubilizer into the solvent. The at least one solubilizer may be chosen, for example, from lithium chloride (LiCl) , calcium chloride (CaCl ₂) , and dodecylbenzene sulfonic acid (DBSA) .

In some embodiments of the present disclosure, the method for preparing a coating slurry for preparing a coating layer for a separator comprises:

(A) adding PVDF into a first solvent to obtain a first slurry;

(B) adding the at least one filler into a second solvent to obtain a second slurry; and

(C) adding PAN into a third solvent to obtain a third slurry;

(D) mixing the first and the second slurries until completely blended; and

(E) adding the third slurry to the mixture of the first slurry and the second slurry.

The present disclosure further provides coating slurries prepared by the method disclosed herein.

The present disclosure further provides a method for making a separator using the coating slurry prepared by the method disclosed herein, comprising:

(A) providing a base membrane;

(B) coating at least one side of the membrane with the coating slurry;

(C) washing the resulting coated membrane with water to remove the at least one solvent; and

(D) drying the coated membrane at a temperature ranging from 50 ℃ to about 60 ℃ to form a coating layer on the membrane.

In some embodiments of the present disclosure, the base membrane may have a thickness ranging, for example, from 5 μm to 25 μm, such as from 9 μm to 20 μm, and further such as from 12 μm to 16 μm. The base membrane may be a porous membrane that has numerous pores inside, through which gas, liquid, or ions can pass from one surface side to the other surface side of the base membrane.

In some embodiments of the present disclosure, the base membrane may be a microporous polyolefin-based membrane. The microporous polyolefin-based membrane may include, for example, polyethylene (PE) , polypropylene (PP) , polybutylene, polypentene, polymethylpentene (TPX) , copolymers thereof, and mixtures thereof. PE includes, for example, linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) . In some embodiments of the present disclosure, the base membrane is a microporous LLDPE membrane. The microporous polyolefin-based membrane disclosed herein may have an air permeability ranging, for example, from 50 to 400 sec/100cc, such as from 80 to 350 sec/100cc, and further such as from 150 to 300 sec/100cc. The polyolefin may have a weight average molecule weight (M _w) ranging, for example, from 400,000 to 3,000,000. The pores within the microporous polyolefin-based membrane may have an average pore size ranging, for example, from 0.02 μm to 0.1 μm. The microporous polyolefin-based membrane may have a porosity ranging, for example, from 30%to 60%. A microporous polyolefin-based membrane may have a single layer structure or a multiple-layer structure. A microporous polyolefin-based membrane of the multi-layer structure may include at least two laminated polyolefin-based layers containing different types of polyolefin or a same type of polyolefin having different molecular weights. The microporous polyolefin-based membrane disclosed herein can be prepared according to a conventional method known in the art or can be purchased directly in the market.

In some embodiments of the present disclosure, a coating layer is formed on at least one side of a porous base membrane. The “at least one side” disclosed herein means the coating layer is disposed on one side or both sides of the porous base membrane. In some embodiments, the separator may have a two-layer structure when only one surface of the porous base membrane is coated with the coating layer disclosed herein. In some other embodiments, the separator may have a three-layer structure when both surfaces of the porous base membrane are coated with the coating layer disclosed herein.

In some embodiments of the present disclosure, a coating slurry prepared according to the method disclosed herein may be applied onto the base membrane to form the coating layer using various techniques, such as roller coating, dip coating, or spin coating process. The coating may be either a continuous coating or a discontinuous coating.

The coating layer on at least one side of the base membrane may have a thickness ranging, for example, from 1 μm to 6 μm, such as from 2 μm to 4 μm. The average pore size of the pores within the coating layer may range, for example, from 10 to 500 μm, such as from 20 to 300 μm. The porosity of the coating layer may range, for example, from 20%to 70%, such as from 30%to 50%.

The coating layer disclosed herein comprises, for example, PVDF and PAN. The PAN may be present in the coating layer in an amount sufficient to improve the adhesion between the base membrane and the electrodes as compared to a membrane that is free of PAN in the coating layer. The ratio of PAN to PVDF may be controlled in a range to make sure that the resulting separator can have adhesiveness as high as possible, while maintaining acceptable level of the air permeability of the separator. In some embodiments, the coating slurry may comprise, for example, from 2.5 to 7.5 parts by weight of PVDF and from 1 to 5 parts by weight of PAN. In some embodiments, the coating layer may comprise, for example, from 4 to 7 parts by weight of PVDF and from 1 to 3 parts by weight of PAN. In some embodiments, the amount of PAN in the coating layer ranges, for example, from 0.01 to 0.3 mg/cm ², such as from 0.03 to 0.2 mg/cm ². In some embodiments, the amount of PVDF in the coating layer ranges, for example, from 0.03 to 0.45 mg/cm ², such as from 0.1 to 0.3 mg/cm ².

In steps (C) and (D) , the at least one solvent can be removed from the coating layer through a method known in the art, such as a thermal evaporation, a vacuum evaporation, a phase inversion process, or combinations thereof. In some embodiments, the at least one solvent may be removed through a phase inversion process. For example, a wet coating layer may be exposed to a poor solvent of PVDF and PAN, such as water, alcohols (e.g., ethanol) , or combinations thereof. The base membrane coated with the coating slurry may be immersed in water for a predetermined period ranging from 1 to 2 minutes, so that the at least one solvent may be transferred from the wet coating layer to water. The water used herein is, for example, deionized water. Residue of the at least one solvent and/or the poor solvent may be removed by, for example, thermal evaporation. As a result, a dry coating layer forms on the porous base membrane. In the instance where the at least one filler is included in the coating slurry, the inorganic particles are embedded in the porous coating layer, can assist in forming the pores in the coating layer, and can enhance the mechanical strength of the membrane.

In some embodiments of the present disclosure, drying the coated membrane in step (D) comprises using a three-section oven at temperatures ranging, for example, from 50℃ to 70℃, such as from 55℃ to 60℃. In some embodiments, the three-section oven has a first section having a temperature of 50℃, a second section having a temperature of 60℃, and a third section having a temperature of 55℃.

The present disclosure further provides a separator prepared by the method disclosed herein. The separator has excellent ion permeability and good adhesive strength. In some embodiments of the present disclosure, the separator is interposed between a positive electrode and a negative electrode of an electrochemical device. An electrolyte may be further included in the electrochemical device disclosed herein. The separator is sandwiched between the positive electrode and the negative electrode to prevent physical contact between the two electrodes and the occurrence of a short circuit. The porous structure of the separator ensures a passage of ionic charge carriers (e.g., lithium ions) between the two electrodes. In addition, the separator may also provide a mechanical support to the electrochemical device. The separator may be used in any electrochemical device in which electrochemical reactions occur, including, for example, primary batteries, secondary batteries, fuel cells, solar cells and capacitors. In some embodiments, the electrochemical device is a lithium secondary battery, such as a lithium ion secondary battery, a lithium polymer secondary battery, a lithium metal secondary battery, a lithium air secondary battery, or a lithium sulfur secondary battery. With the separator of the present disclosure inside, the electrochemical device can exhibit improved cycle life.

Reference is now made in detail to the following examples. It is to be understood that the following examples are illustrative only and the present disclosure is not limited thereto.

The following comparative example was conducted in comparison with Examples 1 to 3 that relate to the separates and the methods for preparing the separators according to the present disclosure.

Example 1:

0.2 kg of Al ₂O ₃ and 6 kg of DMAC were mixed to obtain a first slurry. 1.2 kg of PVDF with a Mw ranging from 700,000 to 2, 500,000 was mixed with 12 kg of DMAC to obtain a second slurry. The first slurry and the second slurry were mixed and then 0.8 kg 30 wt%of PAN was slowly added to obtain a coating slurry for preparing a separator.

The coating slurry was coated on a single-layer PE membrane having a thickness of 12 μm using gravure coating technique at a coating speed of 15 m/mins. The membrane was immersed in water for 1.5 minutes, and then passed through a three-section oven. The three-section oven had a first section having a temperature of 50℃, a second section having a temperature of 60℃, and a third section having a temperature of 55℃. A separator having a thickness of 15 μm was obtained. The coating layer on one side of the PE membrane had a thickness of 3 μm.

Example 2:

0.25 kg of boehmite and 6.5 kg of DMAC were mixed to obtain a first slurry. 1.2 kg of PVDF with a Mw ranging from 700,000 to 2,500,000 was mixed with 15 kg of DMAC to obtain a second slurry. The first slurry and the second slurry were mixed and then 1.8 kg 25 wt%of PAN was slowly added to obtain a coating slurry for preparing a separator.

The coating slurry was coated on a single-layer PE membrane having a thickness of 12 μm using gravure coating technique at a coating speed of 15 m/mins. The membrane was immersed in water for 2 minutes, and then passed through a three-section oven. The three-section oven had a first section having a temperature of 50℃, a second section having a temperature of 60℃, and a third section having a temperature of 55℃. A separator having a thickness of 15 μm was obtained. The coating layer on one side of the PE membrane had a thickness of 3 μm.

Example 3:

0.32 kg of Al ₂O ₃ and 7.5 kg of DMAC were mixed to obtain a first slurry. 1.2 kg of PVDF with a Mw ranging from 700,000 to 2, 500,000 was mixed with 15 kg of DMAC to obtain a second slurry. The first slurry and the second slurry were mixed and then 2.4 kg 30 wt%of PAN was slowly added to obtain a coating slurry for preparing a separator.

Comparative Example:

0.2 kg of Al ₂O ₃ and 6 kg of DMAC were mixed to obtain a first slurry. 1.2 kg of PVDF with a Mw ranging from 700,000 to 2, 500,000 was mixed with 12 kg of DMAC to obtain a second slurry. The first slurry and the second slurry were mixed to obtain a coating slurry for preparing a separator.

The coating slurry was coated on a single-layer PE membrane having a thickness of 12 μm using gravure coating technique at a coating speed of 15 m/mins. The membrane was immersed in water for a predetermined period, and then passed through a three-section oven. The three-section oven had a first section having a temperature of 50℃, a second section having a temperature of 60℃, and a third section having a temperature of 55℃. A separator having a thickness of 15 μm was obtained. The coating layer on one side of the PE membrane had a thickness of 3 μm.

The adhesiveness and air permeability of the separators prepared in Examples 1-3 and the Comparative Example were measured using the following methods.

Test 1: Adhesiveness

A separator sample was folded and hot pressed at 100℃ and 0.5 MPa for 10 seconds. The force required for separating the folded separator was measured using a tensile testing machine XJ 830 (Shanghai XiangJie, China) having a speed of 50 m/min. Three samples were tested for every separator and an average value was calculated.

Test 2: Air permeability

The Air permeability was measured using an air permeability testing machine (model of EGBO-55/65-1/1M R) . Three samples were tested for every separator and an average value was calculated.

Table 1 summarizes the results of Test 1 and Test 2 on the separators that were prepared according to Examples 1 to 3 and the Comparative Example.

The results in Table 1 show that the adhesive strength of the separators prepared in Examples 1 to 3 by the method of the present disclosure was much higher than that of the separator prepared in the Comparative Example. Even though the air permeability of the separators prepared in Examples 1 to 3 was slightly higher than that of the separator prepared in the Comparative Example, the difference is within the scope of regular fluctuations in manufacturing. Thus, the results in Table 1 show that the introduction of PAN to the coating layer of the separator resulted in significant improvement in adhesive strength of the separator, while maintaining similar level of the air permeability of the separator, and consequently made the separator disclosed herein suitable for a wider range of applications.

Claims

A coating slurry for preparing a coating layer for a separator, wherein the coating slurry consists essentially of:

(A) from 1 to 5 parts by weight of polyacrylonitrile;

(B) from 20 to 40 parts by weight of at least one solvent;

(C) from 1 to 5 parts by weight of at least one filler; and

(D) from 50 to 75 parts by weight of a polymer solution.
The coating slurry according to claim 1, wherein the coating slurry consists essentially of:

(A) from 1 to 3 parts by weight of polyacrylonitrile;

(B) from 25 to 35 parts by weight of at least one solvent;

(C) from 1 to 2 parts by weight of at least one filler; and

(D) from 60 to 70 parts by weight of a polymer solution.
The coating slurry according to claim 1 or 2, wherein the polymer solution comprises polyvinylidenefluoride.
The coating slurry according to claim 1 or 2, wherein the at least one solvent is chosen from N-methyl-2-pyrrolidone, dimethylacetamide, acetone, dimethylformamide, and dimethyl sulfoxide.
The coating slurry according to claim 3, wherein the polymer solution comprises from 5 wt%to 20 wt%of polyvinylidenefluoride that has a weight average molecular weight ranging from 100,000 to 3,000,000.
The coating slurry according to claim 5, wherein the polyvinylidenefluoride has a weight average molecular weight ranging from 700,000 to 2,500,000.
The coating slurry according to claim 1 or 2, wherein the at least one filler is chosen from alumina (Al2O3) , boehmite (γ-AlOOH) , silica (SiO2) , titanium oxide (TiO2) , cerium oxide (CeO2) , calcium oxide (CaO) , zinc oxide (ZnO) , magnesium oxide (MgO) , lithium nitride (Li3N) , calcium carbonate (CaCO3) , barium sulfate (BaSO4) , lithium phosphate (Li3PO4) , lithium titanium phosphate (LTPO) , lithium aluminum titanium phosphate (LATP) , cerium titanate (CeTiO3) , calcium titanate (CaTiO3) , barium titanate (BaTiO3) and lithium lanthanum titanate (LLTO) .
The coating slurry according to claim 7, wherein the at least one filler has a particle size ranging from 5 nm to 800 nm.
A method for preparing the coating slurry according to claim 1 or 2, comprising:

(A) adding the polyvinylidenfluoride into a first solvent to produce a first slurry;

(B) adding the at least one filler into a second solvent to produce a second slurry; and

(C) adding the polyacrylonitrile into a third solvent to produce a third slurry;

(D) stirring the mixture of the first and the second slurries until completely blended; and

(E) adding the third slurry to the mixture of the first slurry and the second slurry.
A method for preparing a coating layer for a separator using the coating slurry according to claim 5, comprising:

(A) providing a base membrane;

(B) coating at least one side of the membrane with the coating slurry;

(C) washing the resulting coated membrane with water to remove the at least one solvent; and

(D) drying the coated membrane at a temperature ranging from 50 ℃ to 60 ℃ to form a coating layer on the membrane, wherein the at least one filler is embedded in the coating layer.
The method according to claim 9, wherein:

(A) the membrane has a thickness ranging from 5 μm to 25 μm; and

(B) the coating layer has a thickness ranging from 1 μm to 4 μm.
The method according to claim 11, wherein:

(A) the amount of polyacrylonitrile ranges from 0.01 mg/cm ² to 0.3 mg/cm ²; and

(B) the amount of polyvinylidenefluoride ranges from 0.03 mg/cm ² to 0.45 mg/cm ².
The method according to claim 10, wherein:

(A) the membrane is a microporous polyethylene-based membrane having a thickness ranging from 5 μm to 25 μm; and

(B) the coating layer has a thickness ranging from 1 μm to 4 μm.
The method according to claim 13, wherein:

(A) the amount of polyacrylonitrile ranges from 0.01 mg/cm ² to 0.3 mg/cm ²; and

(B) the amount of polyvinylidenefluoride is ranges from 0.03 mg/cm ² to 0.45 mg/cm ².
A separator, comprising:

(A) a base membrane; and

(B) a coating layer on at least one side of the membrane, wherein the coating layer is prepared by coating the membrane with the coating slurry according to claim 1 or 2.
A separator, comprising:

(A) a microporous polyethylene-based membrane; and

(B) a coating layer on at least one side of the membrane, wherein the coating layer is prepared by coating the membrane with the coating slurry according to claim 1 or 2.
An electrochemical device, comprising the separator of claim 15 or 16 between an anode and a cathode in the device.