CN117837015A

CN117837015A - Separator for electrochemical device and electrochemical device including the same

Info

Publication number: CN117837015A
Application number: CN202280055030.5A
Authority: CN
Inventors: 金凤泰; 李柱成; 文星植; 李娥英; 郑吉安; 韩诚宰
Original assignee: LG Chem Ltd
Current assignee: LG Chem Ltd
Priority date: 2021-07-20
Filing date: 2022-07-20
Publication date: 2024-04-05
Also published as: KR20230013981A

Abstract

The present disclosure relates to a separator for an electrochemical device including an inorganic-containing porous layer on at least one surface of a porous polymer support and including an inorganic filler and a binder polymer, wherein the binder polymer includes a first binder polymer, and the first binder polymer is poly (vinylidene fluoride-co-hexafluoropropylene) having a tan delta peak at-18 ℃ to-5 ℃ when measured by dynamic mechanical analysis, and an electrochemical device including the same. The separator for an electrochemical device according to one embodiment of the present disclosure has improved adhesion characteristics with an electrode and safety at high temperature.

Description

Separator for electrochemical device and electrochemical device including the same

Technical Field

One embodiment of the present disclosure relates to a separator for an electrochemical device and an electrochemical device including the same.

The present application claims priority from korean patent application nos. 2021-0095122, 2021-0095123 and 2021-0095124, filed in korea at 7.20 of 2021, the disclosures of which are incorporated herein by reference.

Background

Recently, energy storage technology has received increasing attention. As the application field of energy storage technology expands to mobile phones, camcorders, notebook computers, and even electric vehicles, the demand for high energy density of batteries used as power sources for electronic devices is increasing. Lithium secondary batteries are the best electrochemical devices to meet the demand, and many researches on lithium secondary batteries are underway.

In the manufacture and use of lithium secondary batteries, it is a challenge to ensure the safety of lithium secondary batteries. In particular, separators commonly used for lithium secondary batteries exhibit severe heat shrinkage behavior under high temperature conditions due to material characteristics and process characteristics thereof, thereby causing safety problems such as internal short circuits.

To solve this safety problem, separators comprising a porous polymer support coated with a mixture of an inorganic filler and a binder polymer have been proposed. However, in this case, since the melting temperature Tm value of the binder polymer used is about 120 ℃, the separator still exhibits heat shrinkage behavior at a high temperature of, for example, 150 ℃. Additionally, when the separator and the electrode are stacked to form an electrode assembly, the electrode and the separator are separated from each other due to insufficient interlayer adhesion, and thus the separated inorganic filler may act as a partial defect in the electrochemical device.

Disclosure of Invention

Technical problem

The present disclosure is directed to providing a separator for an electrochemical device having improved adhesive characteristics with an electrode and safety at high temperature, and an electrochemical device including the same.

Technical proposal

In order to solve the above-described problems, according to one aspect of the present disclosure, there is provided a separator for an electrochemical device of the following embodiments.

The first embodiment relates to a separator for an electrochemical device, the separator for an electrochemical device including:

a porous polymer support; and

an inorganic-containing porous layer on at least one surface of the porous polymer support and comprising an inorganic filler and a binder polymer,

wherein the binder polymer comprises a first binder polymer, and

the first binder polymer is poly (vinylidene fluoride-co-hexafluoropropylene) having a tan delta peak at-18 ℃ to-5 ℃ when measured by dynamic mechanical analysis.

According to a second embodiment, in the first embodiment,

the amount of hexafluoropropylene repeating units in the first binder polymer may be 4 to 22 wt% based on the total of the amount of vinylidene fluoride repeating units and the amount of hexafluoropropylene repeating units of 100 wt%.

According to a third embodiment, in the first embodiment or the second embodiment,

the binder polymer may also comprise a second binder polymer, and

the second binder polymer may be poly (vinylidene fluoride-co-chlorotrifluoroethylene) having a tan delta peak at-11 ℃ to 0 ℃ when measured by dynamic mechanical analysis.

According to a fourth embodiment, in a third embodiment,

the second binder polymer may have a melting temperature of 155 ℃ or more.

According to a fifth embodiment, in the third or fourth embodiment,

the amount of chlorotrifluoroethylene repeating units in the second binder polymer may be 10 to 30 wt% based on the sum of the amount of vinylidene fluoride repeating units and the amount of chlorotrifluoroethylene repeating units of 100 wt%.

According to a sixth embodiment, in any one of the third to fifth embodiments,

the weight ratio between the first binder polymer and the second binder polymer may be 50:50 to 95:5.

According to a seventh embodiment, in any one of the first to sixth embodiments,

the thickness of the inorganic substance-containing porous layer may be 10 μm or less.

According to an eighth embodiment, in any one of the first to seventh embodiments,

after the separator for an electrochemical device is left to stand at 130 ℃ for 1 hour, the heat shrinkage rate in each of the Machine Direction (MD) and the Transverse Direction (TD) may be 25% or less.

According to a ninth embodiment, in any one of the first to eighth embodiments,

after the separator for an electrochemical device is left to stand at 150 ℃ for 30 minutes, the heat shrinkage rate in each of the Machine Direction (MD) and the Transverse Direction (TD) may be 55% or less.

According to a tenth embodiment, in any one of the first to ninth embodiments,

the separator for an electrochemical device may have an electrode adhesion characteristic of 40gf/25mm or more.

According to an eleventh embodiment, in any one of the first to tenth embodiments,

the first binder polymer may be poly (vinylidene fluoride-co-hexafluoropropylene) having a gamma-crystal form.

According to a twelfth embodiment, in any one of the first to eleventh embodiments,

the melting temperature of the first binder polymer may be 155 ℃ or higher.

In order to solve the above-described problems, according to one aspect of the present disclosure, there is provided an electrochemical device of the following embodiments.

A thirteenth embodiment relates to an electrochemical device, including:

positive and negative electrodes, a separator for an electrochemical device interposed between the positive and negative electrodes,

wherein a separator for an electrochemical device is defined in any one of the first to twelfth embodiments.

Advantageous effects

A separator for an electrochemical device according to one embodiment of the present disclosure includes poly (vinylidene fluoride-co-hexafluoropropylene) having a tan delta peak at-18 ℃ to-5 ℃ when measured by dynamic mechanical analysis, thereby improving adhesive characteristics with an electrode and reducing thermal shrinkage at high temperature.

The separator for an electrochemical device according to one embodiment of the present disclosure includes poly (vinylidene fluoride-co-hexafluoropropylene) having a tan delta peak at-18 ℃ to-5 ℃ when measured by dynamic mechanical analysis and poly (vinylidene fluoride-co-chlorotrifluoroethylene) having a tan delta peak at-11 ℃ to 0 ℃ when measured by dynamic mechanical analysis, thereby improving adhesive characteristics with an electrode and reducing thermal shrinkage at high temperature.

A separator for an electrochemical device according to one embodiment of the present disclosure includes a first binder polymer for adhesive properties with an electrode and a second binder polymer for adhesive properties between a porous polymer support and an inorganic-containing porous layer, thereby improving adhesive properties with an electrode.

Drawings

The accompanying drawings illustrate one embodiment of the present disclosure and, together with the foregoing disclosure, serve to provide a further understanding of the technical features of the present disclosure. However, the present disclosure should not be construed as being limited to the accompanying drawings.

Fig. 1 is a graph showing the relationship between the temperature of the first binder polymer used in examples 1 to 3 and comparative example 1 and tan δ measured by Dynamic Mechanical Analysis (DMA).

Fig. 2 is a graph showing a relationship between the temperature of the second binder polymer used in example 1 and tan δ measured by Dynamic Mechanical Analysis (DMA).

Fig. 3 is a graph showing a crystal form of the first binder polymer used in example 1, measured by wide angle X-ray diffraction (WAXS).

Fig. 4 is a graph showing a crystal form of the first binder polymer used in example 2, measured by wide angle X-ray diffraction (WAXS).

Fig. 5 is a graph showing a crystal form of the first binder polymer used in example 3, measured by wide angle X-ray diffraction (WAXS).

Fig. 6 is a graph showing a crystal form of the first binder polymer used in comparative example 1, measured by wide angle X-ray diffraction (WAXS).

Detailed Description

Hereinafter, one exemplary embodiment of the present disclosure will be described in detail. Before the description, it is to be understood that the terms or words used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation.

Thus, the disclosure in the embodiments of the present disclosure is only one exemplary embodiment of the present disclosure, but is not intended to fully describe the technical aspects of the present disclosure, so it should be understood that various other equivalents and modifications may be made thereto at the time of filing the application.

Terms such as "first," "second," and the like are used to distinguish one element from another element, and the elements are not limited by terms.

A separator for an electrochemical device according to one aspect of the present disclosure includes:

a porous polymer support; and

wherein the binder polymer comprises a first binder polymer, and

A separator for an electrochemical device according to one embodiment of the present disclosure includes a porous polymer support.

In general, the porous polymer support may comprise any type of material for a separator of an electrochemical device without limitation. The porous polymeric support is a film comprising a polymeric material, and non-limiting examples of the polymeric material include olefin polymers, ethylene terephthalate polymers, butylene terephthalate polymers, acetal polymers, amide polymers, carbonate polymers, imide polymers, ether ketone polymers, ether sulfone polymers, phenylene ether polymers, phenylene sulfide polymers, ethylene naphthalene polymers. Additionally, the porous polymeric support may comprise a nonwoven fabric or porous polymeric membrane made from the polymeric materials described above or a stack of two or more of them. Specifically, the porous polymer support may be any one of the following a) to e):

a) A porous film formed by melting and extruding a polymer material,

b) A multilayer film formed by stacking a) a porous film in two or more layers,

c) A nonwoven web made of filaments obtained by melting/spinning a polymeric material,

d) A multilayer film formed by stacking the c) nonwoven web in two or more layers,

e) A porous membrane comprising a multilayer structure of at least two of a) to d).

In order to ensure high air permeability and porosity from the above materials, the porous polymer support may be manufactured by forming pores through a common method known in the art (e.g., a wet method using a solvent, a diluent, or a pore-forming agent, or a dry method using stretching).

In one embodiment of the present disclosure, there is no limitation on the thickness of the porous polymer support, but the thickness of the porous polymer support may be 1 μm to 100 μm or 1 μm to 30 μm. When the thickness of the porous polymer support is within the above range, it is possible to prevent damage of the separator during use of the battery and to secure energy density.

In the specification, the thickness of the porous polymer support may be measured using, for example, a thickness measuring instrument (Mitutoy, VL-50S-B).

In this case, there is no limitation on the average pore size and porosity of the porous polymer support, and the porous polymer support may have an optimal average pore size and porosity for electrochemical device applications. The average pore size may be 0.01 μm to 50 μm or 0.1 μm to 20 μm, and the porosity may be 5% to 95%. When the pore size and the porosity are within the above ranges, it is possible to easily prevent the porous polymer support from acting as resistance and maintain the mechanical properties of the porous polymer support.

The average pore size and porosity of the porous polymer support can be measured by a 6-point BET method according to the nitrogen adsorption flow method using a Scanning Electron Microscope (SEM) image, mercury porosimeter, capillary flow porosimeter, or porosimetry analyzer (Bell Japan Inc, belsorp-II mini).

Alternatively, the porosity of the porous polymeric support may be measured by: the net density of the porous support is calculated from the density (apparent density) of the porous support, the composition ratio of materials contained in the porous support, and the density of each component, and the porosity of the porous support is calculated from the difference between the apparent density and the net density. For example, the porosity may be calculated by the following equation.

[ equation 1]

Porosity (volume%) = {1- (apparent density/net density) } ×100

In equation 1 above, the apparent density may be calculated from equation 2 below.

[ equation 2]

Apparent density (g/m) ³ ) = (weight of porous support (g))/(thickness of porous support (cm))× (area of porous support (cm)) ² ))}

A separator for an electrochemical device according to one embodiment of the present disclosure includes an inorganic-containing porous layer on at least one surface of a porous polymer support. The inorganic-containing porous layer may be on one or both surfaces of the porous polymer support.

The inorganic-containing porous layer may contain an inorganic filler and a binder polymer for binding the inorganic filler so that they are held together (i.e., the binder polymer connects the inorganic filler and holds the inorganic filler together), and the inorganic filler and the porous polymer support may be held together by the binder polymer.

The inorganic filler may include, but is not limited to, electrochemical stabilizationAny type of inorganic filler. That is, inorganic fillers that may be used in the present disclosure may include, but are not limited to, those that are in the operating voltage range of the applied electrochemical device (e.g., relative to Li/Li ⁺ 0V to 5V) of any type of inorganic filler that does not cause oxidation and/or reduction reactions. In particular, the use of a high dielectric constant inorganic filler may facilitate an increase in the degree of dissociation of the electrolyte salt in a liquid electrolyte such as a lithium salt, thereby improving the ionic conductivity of the electrolyte solution.

For the above reasons, in one embodiment of the present disclosure, the inorganic filler may include a high dielectric constant inorganic filler having a dielectric constant of 5 or more, and preferably 10 or more. Non-limiting examples of the inorganic filler having a dielectric constant of 5 or more may include at least one of: baTiO ₃ 、Pb(Zr,Ti)O ₃ (PZT)、Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT，0<x<1，0<y<1)、Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), hafnium oxide (HfO) ₂ )、SrTiO ₃ 、SnO ₂ 、CeO ₂ 、MgO、Mg(OH) ₂ 、NiO、CaO、ZnO、ZrO ₂ 、SiO ₂ 、Y ₂ O ₃ 、Al ₂ O ₃ 、AlOOH、Al(OH) ₃ SiC, or TiO ₂ 。

Additionally, in another embodiment of the present disclosure, the inorganic filler may include an inorganic filler capable of transporting lithium ions, i.e., an inorganic filler that contains lithium but does not store lithium and has a function of moving lithium ions. Non-limiting examples of the inorganic filler capable of transporting lithium ions may include at least one of: lithium phosphate (Li) ₃ PO ₄ ) The method comprises the steps of carrying out a first treatment on the surface of the Lithium titanium phosphate (Li) _x Ti _y (PO ₄ ) ₃ ，0<x<2，0<y<3) The method comprises the steps of carrying out a first treatment on the surface of the Lithium aluminum titanium phosphate (Li) _x Al _y Ti _z (PO ₄ ) ₃ ，0<x<2，0<y<1，0<z<3) The method comprises the steps of carrying out a first treatment on the surface of the Based on (LiAlTiP) _x O _y Glass (0)<x<4，0<y<13 For example 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ The method comprises the steps of carrying out a first treatment on the surface of the Lanthanum lithium titanate (Li) _x La _y TiO ₃ ，0<x<2，0<y<3) The method comprises the steps of carrying out a first treatment on the surface of the Lithium germanium thiophosphate (Li) _x Ge _y P _z S _w ，0<x<4，0<y<1，0<z<1，0<w<5) For example Li _3.25 Ge _0.25 P _0.75 S ₄ The method comprises the steps of carrying out a first treatment on the surface of the Lithium nitride (Li) _x N _y ，0<x<4，0<y<2) For example Li ₃ N; siS-based ₂ Glass (Li) _x Si _y S _z ，0<x<3，0<y<2，0<z<4) For example Li ₃ PO ₄ -Li ₂ S-SiS ₂ The method comprises the steps of carrying out a first treatment on the surface of the Or based on P ₂ S ₅ Glass (Li) _x P _y S _z ，0<x<3，0<y<3，0<z<7) For example LiI-Li ₂ S-P ₂ S ₅ 。

In one embodiment of the present disclosure, the inorganic filler may have an average particle size of 0.01 μm to 1.5 μm. When the average particle size of the inorganic filler satisfies the above range, the inorganic-containing porous layer having a uniform thickness and optimal porosity can be easily formed, and good dispersion of the inorganic filler and desired energy density can be provided.

In this case, the average particle size of the inorganic filler as used herein refers to the D50 particle size, and "D50 particle size" refers to the particle size at 50% in the cumulative particle size distribution. Particle size can be measured using laser diffraction. Specifically, after dispersing the powder to be measured in a dispersion medium and introducing a commercially available laser diffraction particle size measuring instrument (e.g., microtrac S3500), the particle size distribution is calculated by measuring the diffraction pattern difference according to the particle size when the particles pass through a laser beam. D50 particle size can be measured by calculating the particle size at 50% of the cumulative particle size distribution in the measuring device.

In general, in the case of poly (vinylidene fluoride-co-hexafluoropropylene), as the amount of hexafluoropropylene repeating units increases, the adhesion properties increase, but the heat resistance decreases.

The inventors found that when poly (vinylidene fluoride-co-hexafluoropropylene) has a tan δ peak in a specific temperature range, both adhesion characteristics and heat resistance can be improved regardless of the amount of hexafluoropropylene repeating units, and based on the finding, the inventors completed the present disclosure.

In the specification, for example, the amount of the poly (vinylidene fluoride-co-hexafluoropropylene) repeating unit can be measured by measuring the amount of Hexafluoropropylene (HFP) functional groups in the inorganic-containing porous layer. For example, the amount of poly (vinylidene fluoride-co-hexafluoropropylene) repeating units can be measured by determining the HFP content in the inorganic-containing porous layer via atomic fluorine Nuclear Magnetic Resonance (NMR) spectroscopy.

In one embodiment of the present disclosure, for example, the measurement may be performed by using a 19F NMR (Bruker DRX-300) analyzer and a reference material CFCl as follows ₃ Is performed by fluorine atom NMR spectroscopy. For example, first, the target sample is dissolved in deuterated acetone at a concentration of 8 wt%. The weight average molecular weight was determined by gel permeation chromatography (GPC, high temperature PL 220, waters) equipped with a refractive index detector and two PLgel-10 μm Mixed-B columns (Polymer Laboratory). For the mobile phase solvent, dimethylformamide with 0.1M LiBr was used, and the measurement conditions included 80 ℃ and a flow rate of 1.0 mL/min. The standard sample may be, for example, polystyrene having an average molecular weight of from 2,000g/mol to 2,000,000 g/mol.

In another embodiment of the present disclosure, for example, fluorine atom NMR spectroscopy can be performed at 376.3MHz using a Unity 400 spectrometer. For example, the spectrum may be obtained by: an excitation pulse width of 8.0 microseconds and a recycling delay of 10 seconds in deuterated dimethylformamide at 50 ℃, or an excitation pulse width of 6.0 microseconds and a recycling delay of 5 seconds in deuterated dimethyl sulfoxide at 50 ℃, or an excitation pulse width of 8.0 microseconds and a recycling delay of 20 seconds in deuterated acetone at 50 ℃.

The binder polymer comprises a first binder polymer, for example, poly (vinylidene fluoride-co-hexafluoropropylene) having a tan delta peak at-18 ℃ to-5 ℃ when measured by dynamic mechanical analysis.

In the specification, tan δ refers to the ratio of the loss modulus E "to the storage modulus E', and the size of the tan δ peak refers to the amount of amorphous region in the sample.

"tan δ peak" is an inflection point indicating that the tangential slope of a graph showing the relationship between the temperature on the x-axis and tan δ on the y-axis changes from positive (+) to negative (-). Alternatively, "tan δ peak" is a point where the tangential slope of the pointer to the graph is 0. In this case, the tan δ peak may refer to the second peak of the plurality of tan δ peaks.

Since the first binder polymer has a tan delta peak in the above temperature range, the adhesive property and heat resistance at high temperature are good. For example, heat resistance may be good regardless of the amount of hexafluoropropylene repeating units. Even if the amount of hexafluoropropylene repeating unit increases, heat resistance may be good.

Accordingly, the separator for an electrochemical device including the first binder polymer according to one embodiment of the present disclosure may have improved safety at high temperature. For example, after the separator is left to stand at 130 ℃ for 1 hour, the heat shrinkage of the separator in each of the Machine Direction (MD) and the Transverse Direction (TD) may be 25% or less, or 20% or less, or 15% or less, or 10% or less, or 5% or less.

Additionally, after the separator is left standing at 150 ℃ for 30 minutes, the heat shrinkage of the separator in each of the Machine Direction (MD) and the Transverse Direction (TD) may be 55% or less, or 50% or less, or 45% or less, or 40% or less, or 35% or less, or 30% or less, or 25% or less, or 20% or less, or 15% or less, or 10% or less, or 5% or less.

Here, "machine direction" refers to a traveling direction when the separator is continuously produced or a longitudinal direction in which the length of the separator is long in the winding direction of the manufactured separator, and "transverse direction" refers to an orthogonal direction to the machine direction, that is, a direction perpendicular to the traveling direction when the separator is continuously produced or a direction perpendicular to the longitudinal direction in which the length of the separator is long in the winding direction of the manufactured separator.

In the case where the first binder polymer does not have a tan delta peak in the above temperature range, for example, in the case where the first binder polymer has a tan delta peak at 17 to 28 ℃, as the amount of hexafluoropropylene repeating unit increases, the adhesion property increases, but the heat resistance decreases.

In one embodiment of the present disclosure, the first binder polymer may have a tan delta peak at-15 ℃ or higher, or-13 ℃ or higher, or-12.12 ℃ or higher, or-12 ℃ or higher, or-10 ℃ or higher, or-9.68 ℃ or higher, or-9 ℃ or higher, or-8.74 ℃, and-6 ℃ or lower, or-7 ℃ or lower, or-8 ℃ or lower, or-8.74 ℃ or lower, or-9 ℃ or lower, or-9.68 ℃ or lower, or-12 ℃ or lower, or-12.12 ℃ or lower, as measured by dynamic mechanical analysis.

Dynamic mechanical analysis is an analytical method for measuring the elastic modulus (modulus) and energy loss (damping) as a function of temperature or frequency by applying vibratory forces or deformations to a polymer sample.

In one embodiment of the present disclosure, after applying pressure to the first binder polymer at 190 ℃ to make a binder sample having a thickness of 0.5mm, and further maintaining the binder sample at-80 ℃ for 10 minutes, the tan delta value may be measured by measuring the ratio between the storage modulus E' and the loss modulus E "using dynamic mechanical analysis while increasing the temperature to 140 ℃ at a rate of 5 ℃/minute.

In one embodiment of the present disclosure, the measurement may be made by dynamic mechanical analysis using TA Instruments DMA Q800.

In one embodiment of the present disclosure, the melting temperature of the first binder polymer may be 155 ℃ or higher, or 160 ℃ or higher, or 165 ℃ or higher, or 165.36 ℃ or higher, or 166 ℃ or higher, or 166.31 ℃ or higher, or 166.37 ℃ or higher. Additionally, the first binder polymer may have a melting temperature of 200 ℃ or less, 190 ℃ or less, or 180 ℃ or less, or 170 ℃ or less, or 166.37 ℃ or less, or 166.31 ℃ or less, or 166 ℃ or less, or 165.36 ℃ or less. The first binder polymer may have a tan delta peak at-18 ℃ to-5 ℃ when measured by dynamic mechanical analysis and may have the above-described range of melting temperatures. When the melting temperature of the first binder polymer satisfies the above range, the separator for an electrochemical device including the first binder polymer according to one embodiment of the present disclosure may have improved heat resistance at high temperature. For example, the separator may have a reduced thermal shrinkage at high temperatures.

In the specification, the melting temperature of the binder polymer may be measured using a Differential Scanning Calorimeter (DSC). Differential scanning calorimeters are thermal analysis techniques that measure the difference in heat required to raise the temperature of a sample and a reference material as a function of temperature.

In one embodiment of the present disclosure, when the binder polymer is heated from 25 ℃ to 200 ℃ at a rate of 10 ℃/min, allowed to stand at 200 ℃ for 10 minutes, cooled to 25 ℃ at 10 ℃/min, allowed to stand at 25 ℃ for 10 minutes, and re-heated to 200 ℃ at 10 ℃/min, the melting temperature of the binder polymer can be calculated from the temperature of the differential scanning calorimetric peak in the range of 155 ℃ to 180 ℃.

In one embodiment of the present disclosure, the amount of hexafluoropropylene repeating units in the first binder polymer may be 4 wt% or more, 7 wt% or more, or 9 wt% or more, or 10 wt% or more, or 11 wt% or more, or 13 wt% or more, or 15 wt% or more, or 17 wt% or more, or 18 wt% or more, or 18.1 wt% or more, or 18.5 wt% or more, and 22 wt% or less, or 20 wt% or less, or 19 wt% or less, or 18.5 wt% or less, or 18.1 wt% or less, or 18 wt% or less, or 17 wt% or less, or 15 wt% or 13 wt% or less, or 11 wt% or less, or 10 wt% or less, based on the sum of the amount of vinylidene fluoride repeating units and the amount of hexafluoropropylene repeating units. When the first binder polymer contains hexafluoropropylene repeating units in the above amount, the adhesion property to an electrode can be improved.

In one embodiment of the present disclosure, the first binder polymer may have a gamma-crystal form.

In the specification, the γ -crystal form refers to a crystal form having a trans-trans-trans-bystander structure (trans-trans-trans-gauche). When the first binder polymer has a γ -crystal form, the first binder polymer may have improved heat resistance due to having a trans-bystander structure. That is, the first binder polymer may have a tan delta peak at-18 ℃ to-5 ℃ when measured by dynamic mechanical analysis and may have a gamma-crystal form.

Wide angle X-ray diffraction (WAXS) may be used to determine whether the first binder polymer has a gamma-crystal form. When the first binder polymer has a gamma-crystal form, a diffraction peak wider than the alpha-crystal form or the beta-crystal form is observed adjacent to a 2θ position of about 20.73 °, and a shoulder is found adjacent to a 2θ position of about 20.73 °, as measured by wide angle X-ray diffraction (WAXS). Additionally, the relative ratios of diffraction peaks at the 2θ positions of 17.7 °, 18.44 °, 20.04 °, 20.73 °, 26.72 °, 27.70 ° were 46, 62, 100, 52, 15, 8, respectively. Here, the relative ratio of diffraction peaks indicates the degree of crystallization of the first binder polymer.

In one embodiment of the present disclosure, the binder polymer may further comprise a second binder polymer in addition to the first binder polymer.

The second binder polymer may be poly (vinylidene fluoride-co-chlorotrifluoroethylene) having a tan delta peak at-11 ℃ or higher, or-9 ℃ or higher, or-7 ℃ or higher, or-6.26 ℃ or higher, and 0 ℃ or lower, or-2 ℃ or lower, or-4 ℃ or lower, or-6 ℃ or lower, or-6.26 ℃ or lower, as measured by dynamic mechanical analysis. In this case, the tan δ peak may be the second peak of the many tan δ peaks. When the second binder polymer has a tan delta peak in the above temperature range, heat resistance at high temperature can be improved.

Accordingly, the separator for an electrochemical device according to one embodiment of the present disclosure may have improved safety at high temperature when the first binder polymer and the second binder polymer are simultaneously included.

Additionally, in one embodiment of the present disclosure, when both the first binder polymer and the second binder polymer are included, the first binder polymer moves to the separator-electrode interface, thereby securing the electrode adhesive property of the separator for an electrochemical device, and the second binder polymer may function in securing the adhesive property between the porous polymer support and the inorganic-containing porous layer.

Due to the different phase separation rates of poly (vinylidene fluoride-co-hexafluoropropylene) and poly (vinylidene fluoride-co-chlorotrifluoroethylene), the first binder polymer moves to the separator-electrode interface, thereby ensuring the electrode adhesion characteristics of the separator for an electrochemical device, and the second binder polymer may play a role in ensuring the adhesion characteristics between the porous polymer support and the inorganic-containing porous layer.

In the process of applying the separator including the binder polymer in the inorganic-containing porous layer to the battery, the binder polymer included in the inorganic-containing porous layer may be released through the electrolyte solution, resulting in loss of the binder polymer. In particular, when the temperature in the battery increases, the release of the binder polymer through the electrolyte solution becomes more serious, and generally, after the battery is manufactured, aging occurs under a temperature condition of 60 ℃ or more, and during aging, the binder polymer in the inorganic-containing porous layer is released through the electrolyte solution, resulting in a decrease in the bonding strength of the inorganic-containing porous layer, and the inorganic-containing porous layer may be peeled off from the porous polymer support or the inorganic filler in the inorganic-containing porous layer may be separated.

Since the separator for an electrochemical device according to one embodiment of the present disclosure includes the second binder polymer, release of the binder polymer may be reduced. Therefore, separation of the inorganic filler can be easily prevented.

In one embodiment of the present disclosure, the second binder polymer may have a melting temperature of 155 ℃ or more, or 160 ℃ or more, or 165 ℃ or more, or 166 ℃ or more, or 166.6 ℃ or more. Additionally, the second binder polymer may have a melting temperature of 200 ℃ or less, 190 ℃ or less, or 180 ℃ or less, or 170 ℃ or less, or 166.6 ℃ or less. The second binder polymer may have a tan delta peak at-11 ℃ to 0 ℃ and the above melting temperature range when measured by dynamic mechanical analysis. When the melting temperature of the second binder polymer satisfies the above range, the separator for an electrochemical device including the second binder polymer according to one embodiment of the present disclosure may have improved heat resistance at high temperature. For example, a separator for an electrochemical device may have a reduced thermal shrinkage rate at high temperatures.

In one embodiment of the present disclosure, the amount of chlorotrifluoroethylene repeating units in the second binder polymer may be 10 wt% or more, or 15 wt% or more, or 17 wt% or more, or 20 wt% or more, and 30 wt% or less, or 25 wt% or less, or 22 wt% or less, or 20 wt% or less, based on the sum of the amount of vinylidene fluoride repeating units and the amount of chlorotrifluoroethylene repeating units of 100 wt%. The second binder polymer may comprise poly (vinylidene fluoride-co-chlorotrifluoroethylene) having a tan delta peak at-11 ℃ to 0 ℃ and chlorotrifluoroethylene repeating units in the amounts described above when measured by dynamic mechanical analysis. When the second binder polymer contains the repeating unit in the above amount, the adhesion property with the electrode can be improved.

In one embodiment of the present disclosure, the weight ratio between the first binder polymer and the second binder polymer may be 50:50 to 95:5, or 86:14 to 80:20, or 84:16 to 80:20, or 82:18 to 80:20. When the weight ratio between the first binder polymer and the second binder polymer satisfies the above range, it is possible to easily secure the adhesion property with the electrode and suppress the release of the binder at high temperature when immersed in the electrolyte solution. Additionally, micro-voids may be reduced.

In one embodiment of the present disclosure, the weight ratio between the inorganic filler and the binder polymer may be determined in consideration of the thickness, pore size, and porosity of the inorganic-containing porous layer, and may be 50:50 to 99.9:0.1, or 50:50 to 80:20, or 80:20 to 99.9:0.1, or 95:5 to 99.9:0.1. When the weight ratio between the inorganic filler and the binder polymer is within the above range, a sufficient empty space between the inorganic filler can be ensured, thereby making it easy to ensure the pore size and porosity of the inorganic-containing porous layer. Additionally, adhesion characteristics between the inorganic fillers and the porous polymer support can be easily ensured.

In one embodiment of the present disclosure, the inorganic-containing porous layer may further comprise additives such as dispersants and/or thickeners. In one embodiment of the present disclosure, the additive may include at least one of the following: citric acid, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethyl hydroxyethyl cellulose (EHEC), methyl Cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose or acrylonitrile polyvinyl alcohol.

In one embodiment of the present disclosure, the inorganic-containing porous layer has such a structure: wherein the inorganic fillers are tightly compacted in contact with each other and held together by the binder polymer to form interstitial volumes between the inorganic fillers, and the interstitial volumes between the inorganic fillers become empty spaces to be pores.

The inorganic substance-containing porous layer may be formed by: preparing an inorganic-containing porous layer forming slurry comprising an inorganic filler, a first binder polymer, and a solvent for the first binder polymer, and coating and drying the inorganic-containing porous layer forming slurry on at least one surface of the porous polymer support.

In view of further comprising a second binder polymer, the solvent for the first binder polymer may act as a solvent for the second binder polymer.

In one embodiment of the present disclosure, the solvent for the first binder polymer may include at least one of N-methyl-2-pyrrolidone, acetone, methyl ethyl ketone, dimethylformamide, or dimethylacetamide.

The inorganic-containing porous layer forming slurry may be prepared by dissolving or dispersing the first binder polymer or the first binder polymer and the second binder polymer in a solvent for the first binder polymer, adding and dispersing the inorganic filler, but the method for preparing the slurry is not limited thereto.

In one embodiment of the present disclosure, the phase separation may be performed after the inorganic-containing porous layer forming slurry is coated on at least one surface of the porous polymer support by a general method known in the art using a non-solvent for the first binder polymer. Phase separation may be performed to form a pore structure in the inorganic-containing porous layer. Phase separation may be performed by wet phase separation or impregnation phase separation processes.

The following is a description of wet phase separation.

First, the wet phase separation may be performed under a temperature condition in the range of 15 to 70 ℃ or 20 to 50 ℃ and a relative humidity condition in the range of 15 to 80% or 30 to 50%. The inorganic-containing porous layer forming slurry may undergo phase transition by a phase separation (vapor-induced phase separation) phenomenon known in the corresponding technical field through a drying process.

For wet phase separation, the non-solvent for the first binder polymer may be introduced in a gaseous state. The non-solvent for the first binder polymer may include, but is not limited to, any type of non-solvent that does not dissolve the first binder polymer and is partially compatible with the solvent for the first binder polymer, and may include, for example, a non-solvent having a solubility of less than 5 wt% of the first binder polymer at 25 ℃.

The non-solvent for the first binder polymer may also be a non-solvent for the second binder polymer, and for example, may include a non-solvent that does not dissolve the second binder polymer and has a solubility of less than 5 wt% at 25 ℃.

For example, the non-solvent for the first binder polymer may be at least one of: water, methanol, ethanol, isopropanol, butanol, butanediol, ethylene glycol, propylene glycol or tripropylene glycol.

The following is a description of the separation of the impregnated phases.

The inorganic-containing porous layer forming slurry is coated on at least one surface of the porous polymer support and immersed in a coagulant solution containing a non-solvent for the first binder polymer for a predetermined time. Thus, phase separation occurs in the coated inorganic-containing porous layer slurry to solidify the first binder polymer. In this process, a porous layer containing an inorganic substance is formed. Subsequently, washing is performed to remove the coagulant solution, and then drying is performed. The drying may be performed using a known method, and may be performed by a batch or continuous process using an oven or a heater type chamber in a temperature range in consideration of vapor pressure of a solvent used for the first binder polymer. Drying is performed to remove a substantial portion of the solvent for the first binder polymer from the slurry. From the viewpoint of productivity, the shorter the better, and for example, drying may be performed for 1 minute or less or 30 seconds or less.

For the coagulant solution, a single non-solvent for the first binder polymer or a mixed solvent of a non-solvent for the first binder polymer and a solvent for the first binder polymer may be used. The mixed solvent of the non-solvent for the first binder polymer and the solvent for the first binder polymer forms a good pore structure, and the non-solvent for the first binder polymer may be present in an amount of 50% by weight or more based on 100% by weight of the coagulant solution from the viewpoint of productivity.

In one embodiment of the present disclosure, the average pore size of the inorganic-containing porous layer may be 0.001 μm to 10 μm. The average pore size of the inorganic-containing porous layer can be measured by capillary flow porosimetry. Capillary flow porosimetry measures the diameter of the smallest hole in the thickness direction. Therefore, in order to measure the average pore size of the inorganic-containing porous layer by capillary flow porosimetry, the inorganic-containing porous layer must be separated from the porous polymer support and covered with a nonwoven fabric to support the separated inorganic-containing porous layer, and in this case, the pore size of the nonwoven fabric is much larger than that of the inorganic-containing porous layer.

In one embodiment of the present disclosure, the porosity of the inorganic-containing porous layer may be 5% to 95%, or 10% to 95%, or 20% to 90%, or 30% to 80%. The porosity corresponds to a value obtained by subtracting the volume converted from the weight and density of each component of the inorganic substance-containing porous layer from the volume calculated using the thickness of the inorganic substance-containing porous layer and the horizontal and vertical dimensions.

The porosity of the inorganic-containing porous layer can be measured by a 6-point BET method according to a nitrogen adsorption flow method using SEM images, mercury porosimetry, capillary flow porosimetry, or porosimetry analyzer (Bell Japan Inc, belsorp-II mini).

In one embodiment of the present disclosure, the thickness of the inorganic-containing porous layer may be 10 μm or less, or 8 μm or less, or 6 μm or less, or 5 μm or less, or 4 μm or less, and 3 μm or more, or 4 μm or more. Here, the thickness of the inorganic substance-containing porous layer means the sum of the thicknesses of the inorganic substance-containing porous layers on each of the two surfaces of the porous polymer support. When the thickness of the inorganic substance-containing porous layer satisfies the above range, the adhesion characteristics with the electrode and the cell strength of the battery can be improved.

Since the separator for an electrochemical device according to one embodiment of the present disclosure includes the first binder polymer having a tan delta peak at-18 ℃ to-8 ℃ when measured by dynamic mechanical analysis, safety at high temperature and adhesion characteristics with an electrode can be improved.

In one embodiment of the present disclosure, after the separator for an electrochemical device is left to stand at 130 ℃ for 1 hour, the separator may have a heat shrinkage rate in each of the Machine Direction (MD) and the Transverse Direction (TD) of 25% or less, or 20% or less.

Additionally, after the separator is left to stand at 150 ℃ for 30 minutes, the heat shrinkage rate of the separator in each of the Machine Direction (MD) and the Transverse Direction (TD) may be 55% or less, or 50% or less.

In one embodiment of the present disclosure, the separator for an electrochemical device may have an electrode adhesive property of 40gf/25mm or more, or 50gf/25mm or more, or 60gf/25mm or more, and 70gf/25mm or less.

In one embodiment of the present disclosure, 1000kg at a temperature of 60 ℃ is achieved after inserting the separator and electrode between 100 μmPET films and using a horizontal laminator _f After pressing for 1 second under pressure to adhere them, a force may be applied to the adhered separator in a direction of 180 ° at a measurement speed of 300 mm/min, and the electrode adhesion characteristics may be measured from the force required to separate the separator.

For example, one separator and one electrode may be stacked facing each other, then interposed between 100 μm PET films, and at 1000kg _f /cm ² The electrodes and separators adhered to each other may be attached to the glass having the double-sided tape such that the electrode surfaces are attached, the ends of the separators may be mounted on the UTM apparatus (LLOYD Instrument LF Plus), a force may be applied in a direction of 180 ° at a measuring speed of 300 mm/min, and the electrode adhesion characteristics of the separators may be measured by the force required to separate the adhered separators while they are adhered to each other by a horizontal laminator at 60 ℃.

A separator for an electrochemical device may be interposed between the positive electrode and the negative electrode to manufacture the electrochemical device.

Electrochemical devices of the present disclosure may include any type of device that utilizes an electrochemical reaction, and specific examples may include primary and secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitors.

In particular, the electrochemical device may be a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The electrode to be applied together with the separator for an electrochemical device of the present disclosure is not limited to a specific type, and may be manufactured by bonding an electrode active material layer including an electrode active material, a conductive material, and a binder to an electrode current collector via a general method known in the corresponding technical field.

Non-limiting examples of positive electrode active materials may include layered compounds or compounds having one or more transition metals, such as lithium cobalt composite oxide (LiCoO) ₂ ) Lithium nickel oxide (LiNiO) ₂ ) The method comprises the steps of carrying out a first treatment on the surface of the Lithium manganese oxides, e.g. Li _1+x Mn _2-x O ₄ (x=0 to 0.33), liMnO ₃ 、LiMn ₂ O ₃ 、LiMnO ₂ The method comprises the steps of carrying out a first treatment on the surface of the Lithium copper oxide (Li) ₂ CuO ₂ ) The method comprises the steps of carrying out a first treatment on the surface of the Vanadium oxides, e.g. LiV ₃ O ₅ 、LiV ₃ O ₄ 、V ₂ O ₅ 、Cu ₂ V ₂ O ₇ The method comprises the steps of carrying out a first treatment on the surface of the From LiNi _1-x M _x O ₂ (m= Co, mn, al, cu, fe, mg, B or Ga, x=0.01 to 0.3); from LiMn _2-x M _x O ₂ (m= Co, ni, fe, cr, zn or Ta, x=0.01 to 0.1) or Li ₂ Mn ₃ MO ₅ (m= Fe, co, ni, cu or Zn); liMn in which alkaline earth metal ions partially replace Li ₂ O ₄ The method comprises the steps of carrying out a first treatment on the surface of the A disulfide compound; and Fe (Fe) ₂ (MoO ₄ ) ₃ But is not limited thereto.

Non-limiting examples of the negative electrode active material may include any negative electrode active material commonly used for a negative electrode of an electrochemical device, and in particular, may include lithium adsorption materials such as lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite, or other carbon.

Non-limiting examples of positive electrode current collectors may include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of negative electrode current collectors may include foils made of copper, gold, nickel, or copper alloys, or combinations thereof.

In one embodiment of the present disclosure, the conductive materials used in the negative electrode and the positive electrode may be generally added in amounts of 1 to 30 wt%, respectively, based on the total weight of the active material layer. The conductive material may include, but is not limited to, any particular type of conductive material having conductive properties while not causing a chemical change to the corresponding cell, and may include, for example: graphite, such as natural graphite or artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers or metal fibers; a fluorocarbon compound; metal powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives.

In one embodiment of the present disclosure, the binder used in the negative electrode and the positive electrode helps to bond the active material and the conductive material and to bond the active material and the current collector, and in general, the binder used in the negative electrode and the positive electrode may be added in an amount of 1 to 30 wt%, respectively, based on the total weight of the active material layer. Examples of the binder may include polyvinylidene fluoride (PVdF), polyacrylic acid (PAA), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various types of copolymers.

In one embodiment of the present disclosure, the electrochemical device includes an electrolyte solution, and the electrolyte solution may include an organic solvent and a lithium salt. Alternatively, the electrolyte solution may contain an organic solid electrolyte or an inorganic solid electrolyte.

For example, the organic solvent may include aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma butyrolactone, 1, 2-dimethoxyethane, tetrahydroxy flange g (tetrahydroxy franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphotriester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

Lithium salts are materials that readily dissolve in organic solvents and may include, for example LiCl, liBr, liI, liClO ₄ 、LiBF ₄ 、LiB ₁₀ Cl ₁₀ 、LiPF ₆ 、LiCF ₃ SO ₃ 、LiCF ₃ CO ₂ 、LiAsF ₆ 、LiSbF ₆ 、LiAlCl ₄ 、CH ₃ SO ₃ Li、CF ₃ SO ₃ Li、(CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenyl borate, and imides.

Additionally, in order to improve charge/discharge characteristics and flame retardancy, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-glyme, triamide hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted can be added to the electrolyte solutionOxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol and aluminum trichloride. In some cases, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be added to impart incombustibility, and carbon dioxide gas may be added to improve high-temperature storage characteristics.

For example, the organic solid electrolyte may include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, poly stirring lysines (poly agitation lysine), polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, and polymers containing ionic dissociation groups.

For example, the inorganic solid electrolyte may include nitrides, halides, and sulfates of Li, such as Li ₃ N、LiI、Li ₅ NI ₂ 、Li ₃ N-LiI-LiOH、LiSiO ₄ 、LiSiO ₄ -LiI-LiOH、Li ₂ SiS ₃ 、Li ₄ SiO ₄ 、Li ₄ SiO ₄ -LiI-LiOH、Li ₃ PO ₄ -Li ₂ S-SiS ₂ 。

The injection of the electrolyte solution may be performed in any suitable step of the battery manufacturing process, depending on the manufacturing process of the final product and the desired characteristics. That is, the injection of the electrolyte solution may be performed before the battery assembly or in the final step of the battery assembly.

In one embodiment of the present disclosure, the process of applying the separator for an electrochemical device to the battery may include a winding process, which is generally used, and lamination or stacking and folding processes of the separator and the electrode.

In one embodiment of the present disclosure, a separator for an electrochemical device may be interposed between a positive electrode and a negative electrode of the electrochemical device, and when a plurality of cells or electrodes are assembled to form an electrode assembly, a separator for an electrochemical device may be interposed between adjacent cells or electrodes. The electrode assembly may have various structures, such as a simple stack type, a roll type (jelly-roll type), a stack-fold type, and a laminate-stack type.

Hereinafter, embodiments of the present disclosure will be described in detail to aid in understanding the present disclosure. However, the embodiments of the present disclosure may be modified in many other forms, and the scope of the present disclosure should not be construed as being limited to the following embodiments. Embodiments of the present disclosure are provided to fully and thoroughly describe the present disclosure to one of ordinary skill in the art to which the present disclosure pertains.

Alternatively, hereinafter, in examples and comparative examples, HFP content was measured at 376.3MHz using a Unity 400 spectrometer, and the spectra showed values obtained by excitation pulse width of 8.0 microseconds and recirculation delay of 10 seconds in deuterated dimethylformamide at 50 ℃.

Example 1

For the porous polymer support, a porous vinyl film 9 μm thick was prepared.

Al to be used as inorganic filler ₂ O ₃ (D50: 300 nm), poly (vinylidene fluoride-co-hexafluoropropylene) as the first binder polymer (Kynar 3121-50, tm:166.31 ℃ C., HFP content 10% by weight as measured by DSC), and poly (vinylidene fluoride-co-chlorotrifluoroethylene) (Solvay, sol 32008, tm:166.6 ℃ C., CTFE content 20% by weight as measured by DSC) as the second binder polymer were added to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 80:16:4, and the inorganic filler was ground and dispersed using a ball milling method to prepare an inorganic-containing porous layer forming slurry.

An inorganic-containing porous layer forming slurry was coated on at least two surfaces of a porous polymer support and immersed in a coagulant solution containing water and NMP in a weight ratio of 6:4 to cause separation of the impregnated phases. Subsequently, washing with water is performed through a multi-step process, and then drying is performed to prepare the separator.

Example 2

A separator was produced by the same method as in example 1 except that poly (vinylidene fluoride-co-hexafluoropropylene) (Kynar 3031-10, tm measured by DSC: 166.37 ℃, HFP content of 18.5 wt%) was used instead of poly (vinylidene fluoride-co-hexafluoropropylene) (Kynar 3121-50) for the first binder polymer.

Example 3

A separator was produced by the same method as in example 1 except that poly (vinylidene fluoride-co-hexafluoropropylene) (Kynar 3031-50), tm measured by DSC: 165.36 ℃, HFP content of 18.1 wt%) was used instead of poly (vinylidene fluoride-co-hexafluoropropylene) (Kynar 3121-50) for the first binder polymer.

Comparative example 1

A separator was produced by the same method as in example 1 except that poly (vinylidene fluoride-co-hexafluoropropylene) (Solef 20808, tm measured by DSC: 151.53 ℃, HFP content of 8 wt%) was used instead of poly (vinylidene fluoride-co-hexafluoropropylene) (Kynar 3121-50) for the first binder polymer.

Evaluation example 1: tan delta peak temperature analysis of binder polymers

Fig. 1 shows the relationship between the temperature and tan δ of the first binder polymer used in examples 1 to 3 and comparative example 1.

Pressure was applied to the first binder polymers used in examples 1 to 3 and comparative example 1 at 190 ℃ to prepare 0.5mm thick binder samples, the temperature of the binder samples was maintained at-80 ℃ for 10 minutes, then raised to 140 ℃ at a rate of 5 ℃/min, and the ratio between storage modulus E' and loss modulus E "was measured using TA Instruments DMA Q800 to measure tan delta values.

Additionally, fig. 2 shows the relationship between the temperature and tan δ of the second binder polymer used in example 1.

Pressure was applied to the second binder polymer used in example 1 at 190 ℃ to prepare a 0.5mm thick binder sample, the temperature of the binder sample was maintained at-80 ℃ for 10 minutes, then raised to 140 ℃ at a rate of 5 ℃/min, and the ratio between storage modulus E' and loss modulus E "was measured using TA Instruments DMA Q800 to measure tan delta value.

As can be seen from fig. 1, it can be seen that the first binder polymer used in example 1 has a second tan delta peak at-12.12 ℃. Additionally, it can be seen that the first binder polymer used in example 2 has a second tan delta peak at-9.68 ℃. It can be seen that the first binder polymer used in example 3 has a second tan delta peak at-8.74 ℃.

In contrast, it can be seen that the first binder polymer used in comparative example 1 has a second tan delta peak at about 20 ℃.

Additionally, as can be seen from fig. 2, the second binder polymer used in example 1 was found to have a second tan delta peak at-6.26 ℃.

Evaluation example 2: analysis of the Crystal form of the first Binder Polymer

The crystal forms of the first binder polymers used in examples 1 to 3 and comparative example 1 were measured using wide angle X-ray diffraction (WAXS) and the results are shown in fig. 3 to 6, respectively.

In fig. 3 to 5, the first binder polymers used in examples 1 to 3 show relative ratios of diffraction peak intensities of 46, 62, 100, 52, 15, 8 at 2θ positions of 17.7 °, 18.44 °, 20.04 °, 20.73 °, 26.72 °, 27.70 °, respectively, when measured by wide angle X-ray diffraction (WAXS). Additionally, it can be seen that a relatively broad diffraction peak was observed adjacent to the 20.73 ° 2θ position and a shoulder was found adjacent to 20.73 °.

Thus, it can be seen that the first binder polymer used in examples 1 to 3 has a γ -crystal form.

In contrast, in fig. 6, the relative ratios of the diffraction peak intensities at the 2θ positions of 17.65 °, 18.43 °, 19.93 °, 21.29 °, 26.75 °, 32.05 ° were 52, 64, 100, 17, 70, 41, respectively, when measured by wide angle X-ray diffraction. Additionally, it can be seen that a relatively narrow diffraction peak was observed adjacent to the 20.73 ° 2θ position and no shoulder was found adjacent to 20.73 °.

Thus, it can be seen that the first binder polymer used in comparative example 1 does not have a γ -crystal form.

Claims

1. A separator for an electrochemical device, comprising:

a porous polymer support; and

wherein the binder polymer comprises a first binder polymer, and

wherein the first binder polymer is poly (vinylidene fluoride-co-hexafluoropropylene) having a tan delta peak at-18 ℃ to-5 ℃ when measured by dynamic mechanical analysis.

2. The separator for an electrochemical device according to claim 1, wherein the amount of hexafluoropropylene repeating unit in the first binder polymer is 4 to 22 wt% based on the sum of the amount of vinylidene fluoride repeating units and the amount of hexafluoropropylene repeating units of 100 wt%.

3. The separator for an electrochemical device according to claim 1, wherein the binder polymer further comprises a second binder polymer, and

wherein the second binder polymer is a poly (vinylidene fluoride-co-chlorotrifluoroethylene) having a tan delta peak at-11 ℃ to 0 ℃ when measured by dynamic mechanical analysis.

4. The separator for an electrochemical device according to claim 3, wherein the second binder polymer has a melting temperature of 155 ℃ or higher.

5. The separator for an electrochemical device according to claim 3, wherein the amount of chlorotrifluoroethylene repeating unit in the second binder polymer is 10 to 30 wt% based on the sum of the amount of vinylidene fluoride repeating units and the amount of chlorotrifluoroethylene repeating units of 100 wt%.

6. The separator for an electrochemical device according to claim 3, wherein a weight ratio between the first binder polymer and the second binder polymer is 50:50 to 95:5.

7. The separator for an electrochemical device according to claim 1, wherein the thickness of the inorganic substance-containing porous layer is 10 μm or less.

8. The separator for an electrochemical device according to claim 1, wherein after the separator for an electrochemical device is left standing at 130 ℃ for 1 hour, a heat shrinkage rate in each of a Machine Direction (MD) and a Transverse Direction (TD) is 25% or less.

9. The separator for an electrochemical device according to claim 1, wherein after the separator for an electrochemical device is left standing at 150 ℃ for 30 minutes, a heat shrinkage rate in each of a Machine Direction (MD) and a Transverse Direction (TD) is 55% or less.

10. The separator for an electrochemical device according to claim 1, wherein the separator for an electrochemical device has an electrode adhesion characteristic of 40gf/25mm or more.

11. The separator for an electrochemical device according to claim 1, wherein the first binder polymer is poly (vinylidene fluoride-co-hexafluoropropylene) having a γ -crystal form.

12. The separator for an electrochemical device according to claim 1, wherein the first binder polymer has a melting temperature of 155 ℃ or higher.

13. An electrochemical device comprising:

a positive electrode and a negative electrode, a separator for an electrochemical device interposed between the positive electrode and the negative electrode,

wherein the separator for an electrochemical device is defined in any one of claims 1 to 12.