WO2019088698A2 - Separator without separator substrate and electrochemical device comprising same - Google Patents

Abstract

The present invention relates to a separator for an electrochemical device for securing electrical insulation between an anode and a cathode, wherein the separator for an electrochemical device does not comprise a polyolefin substrate but comprises inorganic particles, a binder for binding between the inorganic particles, and a cross-linking agent.

Description

Membrane without membrane substrate and electrochemical device containing the same

This application claims the benefit of priority based on Korean Patent Application No. 2017-0143690, filed on October 31, 2017, the entire contents of which are incorporated herein by reference.

The present invention relates to a separator without a separator substrate and an electrochemical device including the separator, and more particularly to a separator which does not contain a polyolefin substrate used as a separator substrate and includes inorganic particles, a binder for binding between the inorganic particles, To a separation membrane for an electrochemical device.

Research on various power generation technologies such as nuclear power, solar power, wind power, and tidal power is continuing. Research on batteries for more efficient use of the produced energy is also being carried out steadily.

The demand for lithium secondary batteries is increasing in line with the rapid growth of the market related to mobile devices. Electric vehicles (EV) and hybrid electric vehicles (HEV).

The lithium secondary battery is a battery case in which an electrode assembly capable of charging / discharging with a positive electrode / separator / negative electrode structure is mounted on a battery case. The positive electrode and the negative electrode are formed by applying a slurry containing an electrode active material or the like on one side or both sides of a metal current collector, followed by drying and rolling.

Membranes are one of the most important factors determining the performance and lifetime of secondary batteries. The ion permeability should be high so that the electrolyte can pass through while electrically insulating the anode and the cathode. Mechanical strength and stability at high temperatures are also required.

Conventional separators composed of a separator substrate and an inorganic coating layer are weak in adhesion to electrodes and are partially raised or wrinkled at the interface. Polyolefins used as a separator substrate have a problem of being melted at a high temperature.

In order to eliminate the root cause, a new membrane composed of an inorganic coating layer without a polyolefin membrane substrate was constructed. The new separator was very low in insulation and internal short-circuiting was easy to occur. The separator is easily torn due to low tensile strength to low elongation. This easily causes a minute short circuit within the electrode assembly.

Patent Document 1 discloses a separator composed of a microporous polymer layer composed of an organic modified aluminum boehmite and an organic polymer. And does not provide a concrete solution for improving the strength of these.

Non-Patent Document 1 refers to the crosslinking of PVdF-HFP / PEGDMA (polyethylene glycol dimethacrylate) as a method of increasing the strength of a new separation membrane. Non-Patent Document 1 does not apply the above material to a separator, but applies only to a polymer electrolyte.

Non-Patent Document 2 discloses boehmite nanoparticles and polyvinylidene fluoride polymers as separators for lithium secondary batteries. It is inappropriate to apply it to a stress cell cell assembly process.

Non-Patent Document 3 discloses a porous ceramic membrane based on magnesium aluminate as a separation membrane of a lithium secondary battery having flexibility and thermal stability. A specific method for improving the strength has not been disclosed.

As described above, there has not been proposed a technology for a separator which does not have a polyolefin substrate, which has high stability against a high-temperature environment, has excellent insulation, and has improved dimensional stability and can solve the above problems.

- Prior art literature

(Patent Document 1) U.S. Patent No. 8883354

(Non-Patent Document 1) Thermal shrinking behavior of PVdF-HFP based polymer electrolytes is disclosed in J. Power Sources 144, 2005

(Non-Patent Document 2) Boehmite-based ceramic separator for lithium-ion batteries, Journal of Applied Electrochemistry, 2016, 69

(Non-Patent Document 3) Thin, flexible and thermally stable ceramic membranes as separator for lithium-ion batteries, Journal of Membrane Science, 2014, 103

It is an object of the present invention to provide a technique capable of preventing a short circuit due to damage of a separation membrane and a separation membrane to which the technology is applied. Specifically, the present invention aims to provide a separator having a tensile strength and a high elongation while having insulating properties of the conventional separator.

In order to achieve the above object, the present invention provides a separation membrane for an improved electrochemical device, which does not include a polyolefin substrate, and which comprises i) inorganic particles and ii) a binder for bonding between the inorganic particles.

The separation membrane according to the present invention is a separation membrane for an electrochemical device for securing electrical insulation between a cathode and a cathode.

The improved separator does not comprise a polyolefin substrate and may be composed of i) inorganic particles, ii) a binder for binding between the inorganic particles, and iii) compounds further comprising a crosslinking agent.

Compared with the conventional separator of the present invention, the separator of the present invention is a structure without a separator base of a polyolefin series. The conventional separation membrane is a polyolefin-based separation membrane base, and further, at least one surface thereof is coated with an inorganic layer composed of an inorganic material and a binder. The present invention is a separation membrane composed of only the substances constituting the remaining inorganic layer without the separator substrate.

As a separator similar to the present invention, there is a separator composed of only an inorganic layer. Such a conventional separation membrane has a low overall strength of the separation membrane because the polyolefin separation membrane substrate is omitted. If an electrode assembly is made of a low-strength separator, the separator is damaged and is likely to be short-circuited.

The present invention uses i) a linear polymer having a plurality of branches or ii) a polymer having two or more functional groups capable of reacting at a specific temperature as a crosslinking agent in a separation membrane to form a three-dimensional network structure. Due to the nature of the network structure, the physical properties and dimensional stability related to stiffness are improved as the density is increased, and a separator having reduced resistance can be provided.

When the initiator is injected, the three-dimensional network structure is formed more strongly so that the tensile strength of the separator itself is improved while maintaining dimensional stability, and the risk of damage to the separator is reduced.

The present invention can remarkably lower a fine short circuit due to tearing of the separator in the process of manufacturing an electrochemical device. In addition, the rate of dimensional change with respect to the electrolytic solution is reduced, and wrinkles caused by swelling when the electrolytic solution is impregnated can be prevented.

a) inorganic particles

In the separator according to the present invention, the inorganic particles serve as a kind of spacer capable of forming micropores through the formation of void spaces between inorganic particles and maintaining physical shape. The inorganic particles used in the separator generally do not change their physical properties even when the temperature is higher than 200 ° C.

Such inorganic particles are not particularly limited as long as they are electrochemically stable. The inorganic particles usable in the present invention are not particularly limited as long as oxidation and / or reduction reaction does not occur in the operating voltage range of the applied battery (for example, 0 to 5 V based on Li / Li +). When inorganic particles having a high electrolyte ion transporting ability are used, the performance of the electrochemical device can be improved, so that it is preferable that the electrolyte ion transporting ability is as high as possible. When the inorganic particles have a high density, they are not only difficult to disperse when forming the separator, but also have a problem of increasing the weight of the battery. Therefore, it is preferable that the density is small. In the case of an inorganic substance having a high dielectric constant, the dissociation of an electrolyte salt, for example, a lithium salt in the liquid electrolyte, can also contribute to enhance the ionic conductivity of the electrolyte.

For the above reasons, the inorganic particles may be selected from the group consisting of high-permittivity inorganic particles having a dielectric constant of 1 or more, preferably 10 or more, inorganic particles having piezoelectricity, inorganic particles having lithium ion transferring ability, ≪ / RTI >

Examples of the inorganic particles having a dielectric constant of 1 or more include SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, But is not limited thereto.

The piezoelectricity inorganic particle means a non-conductive material at normal pressure, or a material having electrical conductivity due to a change in internal structure when a certain pressure is applied. The inorganic particles have a high dielectric constant value with a dielectric constant of 100 or more. In addition, when tension or compression is applied by applying a certain pressure, charges are generated. One side is charged positively and the other side is negatively charged, resulting in a potential difference between both sides.

In the case of using the inorganic particles having the above-mentioned characteristics, when the internal short-circuit of both electrodes occurs due to an external impact such as local crush or nail, the anode and the cathode are not in direct contact with each other due to the inorganic particles coated on the separator , The electric potential difference in the particle is generated due to the piezoelectricity of the inorganic particles. As a result, the electrons move between the electrodes, that is, the minute electric current flows, so that the voltage of the battery can be smoothly reduced and the safety can be improved.

Examples of the inorganic particles having the piezoelectricity is _{BaTiO 3, Pb (Zr, Ti} ) O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), Pb (Mg 1/3 Nb 2 _{/ 3} ) O ₃ -PbTiO ₃ (PMN-PT) hafnia (HfO ₂ ), or mixtures thereof.

The inorganic particles having the lithium ion transferring ability include inorganic particles containing a lithium element but having a function of not transferring lithium but moving lithium ions. The inorganic particles having lithium ion transferring ability can transfer and move lithium ions due to a kind of defect existing in the particle structure, so that the lithium ion conductivity in the battery is improved and the battery performance is improved thereby .

Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li (LiAlTiP) _x O _y series glass (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5) such as _3.25 Ge _0.25 P _0.75 S ₄ , lithium nitride such as _{Li 3 N (Li x N y} , 0 <x <4, 0 <y <2), Li 3 PO 4 -Li 2 S-SiS 2 SiS 2 based glass (Li _x Si _y S, such as _{z, 0 <x <3,} 0 <y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 as P ₂ S ₅ based _{glass (Li x P y S z} , 0 <x <3 , such , 0 <y <3, 0 <z <7), or a mixture thereof, but are not limited thereto.

The alumina hydrate is classified as crystalline and gelatinous depending on the preparation method. The crystalline alumina hydrate contains the gib ZUID ¡-Al (OH) _3, via light Al (OH) _3, Dyer Spore ¡-AlOOH, bohe 4 paper, and the gel form of the alumina hydrate has a boehmite aluminum ion ¡-AlOOH Aluminum hydroxide precipitated by ammonia, and preferably boehmite? -AlOOH can be used.

When the inorganic particles having a high dielectric constant, the inorganic particles having piezoelectricity, the inorganic particles having lithium ion transporting ability, and alumina hydrates are mixed, the synergistic effect of these can be doubled.

The size of the inorganic particles is not limited, but is preferably in the range of 0.001 탆 to 10 탆 in order to form a film having a uniform thickness and a proper porosity. When the thickness is less than 0.001 μm, the dispersibility of the separator is deteriorated and it is difficult to control the physical properties of the separator. When the thickness is more than 10 μm, the thickness of the separator formed with the same solid content is increased to decrease the mechanical properties. The probability of an internal short circuit occurring during discharge increases.

b) binder

The binder is gelled upon impregnation with a liquid electrolyte and can exhibit a high degree of swelling of the electrolyte. In the case of a polymer having an excellent electrolyte impregnation rate, the electrolyte injected after assembling the cell is impregnated with the polymer, and the polymer having the absorbed electrolyte has electrolytic ion conduction capability. The wetting of the electrolyte for a battery is improved as compared with the conventional hydrophobic polyolefin-based separator, and it is also possible to apply a polar electrolyte for a battery, which has been difficult to be used conventionally. The solubility index is preferably 15 MPa ^1/2 to 45 MPa ^1/2 , preferably 15 MPa ^1/2 to 25 MPa ^1/2 and more preferably 30 MPa ^1/2 to 45 MPa ^1/2, . When the solubility index exceeds 15 MPa ^1/2 and exceeds 45 MPa ^1/2 , it is difficult to swell by a common liquid electrolyte for a battery.

Specifically, the binder is selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichlorethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate , Polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl (EPDM), sulphonated EPDM, styrene butylene rubber (SBR), fluorine-containing polymers such as fluorine-containing polymers such as ethylene-propylene-diene monomers Rubber and polyimide. Or two or more.

c) Crosslinking agent

The cross-linking agent is not particularly limited as long as it is a cross-linking reaction at a specific temperature and is formed of a polymer having a three-dimensional network structure. For example, a cross-linking agent may be used for a polymer material containing two to ten functional groups.

Specifically, it may be polyethylene glycol dimethacrylate (PEGDMA) or a polymer substance represented by the following formulas (1) to (2).

Formula 1

X is an integer of 1 to 100, y is an integer of 0 to 30, and z is an integer of 1 to 1,000. The weight average molecular weight of the formula (1) is 1,000 to 100,000 and the p value is a dependent variable.

(2)

In the above formula (2), a and c are integers of 1 to 30, and b is an integer of 1 to 1000. The weight average molecular weight of the formula (2) is 1,000 to 100,000 and the d value is a dependent variable.

The reaction temperature of the crosslinking agent may be in the range of 120 ° C to 160 ° C, more preferably 130 ° C to 150 ° C. At a low temperature before reaching the temperature range, As the temperature is reached, the reaction takes place and a three-dimensional network is formed by crosslinking.

When the reaction temperature of the crosslinking agent is lower than 120 ° C, the crosslinking sites of the crosslinking agent are not broken and the crosslinking reaction is difficult to occur. When the reaction temperature is higher than 160 ° C, the binder or crosslinking agent used may be melted.

In addition, since the separator according to the present invention has a structure in which a crosslinking agent is added to a separator composed of inorganic particles and a binder, a breakdown voltage is high even if the separator substrate is omitted.

Specifically, when a foreign substance such as iron (Fe), which is a conductive material, is applied to the separator of the present invention, it is confirmed that the separator has a substantially similar breakdown voltage value as compared with a separator including a separator substrate applied to a secondary battery for an automobile , And the decrease of the breakdown voltage before and after the application of the conductive material hardly occurs.

d) reaction initiator

In one specific example, the separation membrane may further include a reaction initiator for the crosslinking agent in order to enhance the effect of improving the physical properties by the crosslinking reaction.

The type of the reaction initiator is not particularly limited and may be specifically an azo compound or a peroxide compound. For example, the azo compound may be 2,2'-azobis ( (2-methylbutyronitrile), 2,2'-azobis (isobutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile) and 2,2'-azobis Methoxy-2,4-dimethylvaleronitrile), and preferably at least one of 2,2'-azobis (isobutyronitrile) or 2,2'-azobis (2,4- Ronitril).

The peroxide compound may be at least one selected from the group consisting of tetramethyl butyl peroxyneodecanoate, bis (4-butylcyclohexyl) peroxydicarbonate, di (2-ethylhexyl) peroxycarbonate, butyl peroxyneodecanoate, Diisopropylperoxy dicarbonate, diethoxyhexyl peroxydicarbonate, diethoxyhexyl peroxydicarbonate, hexyl peroxy dicarbonate, dimethoxy butyl peroxy dicarbonate, bis (3-methoxy-3 -Methoxybutyl) peroxy dicarbonate, dibutyl peroxy dicarbonate, dicetyl peroxy dicarbonate, dimyristyl peroxy dicarbonate, 1,1,3,3-tetramethyl butyl peroxide Peroxypivalate, hexyl peroxypivalate, butyl peroxypivalate, trimethylhexanoyl peroxide, dimethylhydroxybutyl peroxyneodecanoate, amyl peroxy Butyl peroxyneodecanoate, neodecanoate, Atofina, butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate, amyl peroxypivalate, t-butyl peroxypivalate, t-amyl peroxy-2-ethylhexanoate And may be at least one or more selected from the group consisting of lauryl peroxide, dilauroyl peroxide, didecanoyl peroxide, benzoyl peroxide and dibenzoyl peroxide.

e) Composition of membrane

Since the separation membrane according to the present invention has a structure without a separation membrane substrate compared to a conventional separation membrane, the strength of the separation membrane itself may be a problem, so that the separation membrane may have a relatively thick thickness. &Lt; / RTI &gt;

When the thickness of the separator is less than 5 탆, the separator may have a weak strength and may be easily damaged. When the separator is more than 30 탆, the thickness of the entire electrode assembly may increase and the capacity may decrease.

The content of the crosslinking agent in the separator may be greater than 0 wt% to less than 15 wt% based on the total weight of the solid content. When the content of the crosslinking agent is more than 15 wt% based on the total weight of the solid content, And the local crosslinking agent acts as a plasticizer since it does not occur, and the tensile strength is remarkably reduced, which is not preferable.

The air permeability of the separator may range from 50 sec / 100cc to 4,000 sec / 100cc. When the air permeability is less than 50 sec / 100cc, the insulation characteristics are very poor. When the air permeability is more than 4,000 sec / 100cc, And the ionic conductivity is lowered.

The physical properties of the separation membrane are influenced by the reaction temperature and reaction time. As the reaction time becomes longer and the reaction temperature increases, the degree of crosslinking reaction increases.

For example, in the case of polyethylene glycol dimethacrylate (PEGDMA) used as a crosslinking agent, when the reaction time increases from 10 minutes to 30 minutes and when the reaction temperature is increased from 120 ° C to 150 ° C, the degree of crosslinking .

f) electrochemical devices

The present invention also provides an electrochemical device comprising a positive electrode and a negative electrode, the separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the electrochemical device may be a lithium secondary battery.

The positive electrode is prepared by applying a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, followed by drying. If necessary, a filler may be further added.

The cathode current collector is generally made to have a thickness of 3 m or more to 500 m or less. Such a positive electrode collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Carbon, nickel, titanium, silver, or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The conductive material is usually added in an amount of 1 wt% to 30 wt% based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is manufactured by applying a negative electrode material on an anode current collector, and drying the anode current collector. Optionally, the above-described components may be optionally included.

The negative electrode current collector is generally made to have a thickness of 3 mu m or more and 500 mu m or less. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, And Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The present invention can also provide a battery pack including the electrochemical device.

Specifically, the battery pack may be used as a power source for devices requiring high-temperature safety, long cycle characteristics, and high rate characteristics. Examples of such devices include a mobile device, a wearable device A power tool powered by an electric motor; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And an energy storage system, but the present invention is not limited thereto.

The structure of these devices and their fabrication methods are well known in the art, and a detailed description thereof will be omitted herein.

1 is a graph showing the results of measurement of physical properties depending on the presence of a crosslinking agent and an initiator.

2 is a graph showing the results of measurement of physical properties of the crosslinking agent according to the reaction temperature.

Hereinafter, the present invention will be described in further detail with reference to the following examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

Specific methods for measuring the physical properties of the separator prepared in the following Examples and the like are as follows.

Volumetric Insulation Resistance Measurement

Ten sheets of 6 cm * 6 cm cut membranes were prepared and the separator was stored in a dryer for two days before measuring the insulation resistance.

For the volume insulation resistance measurement, the SM7120 manufactured by HIOKI Co., Ltd. was used and measured under the Rv mode condition. Volumetric insulation resistance was measured for 10 membranes and the average value was calculated. The values listed in Table 1 below are average values.

The specific measurement condition setting is as follows.

- Measurement time: 3s

- Average: off

- voltage: 100V

- speed: slow2

- range: auto

- Delay: 0ms

- SEQ: ON: 0

- DCHG 1: 0

- CHG: 0

- DCHG 2: 0

Tensile strength and elongation measurement

Six separation membranes cut to a size of 15 mm * 150 mm were prepared, and each of the separation membranes was adhered so as to correspond to the short axis direction and the long axis direction of the slide glass.

The one end portion of the separation membrane located on the slide glass and the other end portion of the separation membrane not yet attached to the slide glass were mounted on a universal testing machine, and then the strength of the separation membrane was measured while being pulled in opposite directions. At this time, the measurement speed of the UTM apparatus was 500 mm / min, and the length of the measurement section was 100 mm.

Each of the experiments was carried out on the six membranes, and the average values of tensile strength and elongation were calculated. The values listed in Table 1 below are average values.

Measuring rate of dimensional change

6 membranes cut to a size of 10 cm * 10 cm and ethyl carbonate / ethyl methyl carnobate / dimethylcarbonate in a ratio of 3: 3 :: 4, and a lithium salt , An electrolyte solution containing 1.0 M of LiPF ₆ was prepared.

The membrane was impregnated with 10 ml of the electrolyte solution for 1 hour, and then the length of the membrane was measured to calculate the dimensional change ratio. The average values were calculated for each of the six membranes, and the values shown in Table 1 are average values.

Electrical resistance measurement

A coin cell of 2016 size containing only the separator and electrolyte was prepared without electrodes.

Using the Cell Test System 1470E from Solatron and the Frequency Response Analyzer 1255B from Solatron, the impedance at a specific frequency in the range of 10,000 Hz to 100,000 Hz was measured, and the impedance at each frequency The section was taken as the resistance of the membrane.

&Lt; Example 1 >

The content of solid content of boehmite (AlO (OH)) as inorganic particles, polyvinylidene fluoride (PVdF) as a binder and polyethylene glycol dimethacrylate (PEGDMA) as a crosslinking agent in a weight ratio of 78: 20: 2 The slurry was made to be 18% by weight based on the total weight of the slurry.

Specifically, 28.08 g of boehmite (AlO (OH)), 7.2 g of PVdF and 0.72 g of PEGDMA were added to 164 g of acetone, and then a slurry was prepared. The slurry was formed into a separator and reacted at 150 ° C for 30 minutes to prepare a separator. After completion of the crosslinking reaction, the membrane was further dried at room temperature.

&Lt; Example 2 >

A separation membrane was prepared in the same manner as in Example 1, except that 0.0072 g of 2,2'-azobis (isobutyronitrile) as an initiator was added to the slurry of Example 1.

&Lt; Comparative Example 1 &

Except that a solid content of boehmite (AlO (OH)) and polyvinylidene fluoride (PVdF) mixed at a ratio of 78:22 was used so as not to include polyethylene glycol dimethacrylate (PEGDMA) as a crosslinking agent. 1, a separator was prepared.

<Experimental Example 1>

Measurement of physical properties according to presence of crosslinking agent and initiator

Volumetric resistivity, tensile strength, and dimensional change (swelling) were measured using the separator prepared in Examples 1 and 2 and Comparative Example 1, and the results are shown in Tables 1 and 2 Respectively.

	Example 1	Example 2	Comparative Example 1
Volumetric Insulation Resistance (GΩ · cm) (100V, 3S)	4.2	270,000	11
Tensile strength (kgf / cm 2 )	138	149	135
Dimensional change ratio (%)	3	3	4

Referring to Table 1 and FIG. 1, in Example 1 in which the initiator was not added, the volume insulation resistance was as low as 4.2 GΩ · cm, while in Example 2 in which the initiator was added, Comparative Example 1 As compared with the control. When the volume insulation resistance is low, insulation is insufficient and a minute current flows. On the other hand, when the volume insulation resistance is high, insulation is secured so that no current flows. Therefore, it is understood that when the initiator is added, the insulating property is remarkably improved. When the initiator is added, the crosslinking degree is improved, the content of the unreacted crosslinking agent is reduced, and the proportion of the polymer reacted with the crosslinking agent is increased. Therefore, it is presumed that the addition of the initiator improves the insulation resistance.

In the case of Examples 1 and 2 including a crosslinking agent changing into a three-dimensional network structure, the tensile strength is increased and the strength of the separator is improved, and the dimensional change rate is decreased and the dimensional stability is increased.

That is, in the case of a separator prepared by adding a crosslinking agent such as PEGDMA, a three-dimensional network structure due to crosslinking is formed through drying at 150 ° C., so that the tensile strength increases and the dimensional change rate decreases.

Further, when Example 1 in which no initiator was added and Example 2 in which an initiator was added was compared with Example 2, it was found that the initiator was effective for crosslinking for forming a three-dimensional network structure as the tensile strength was further increased have.

&Lt; Example 3 >

A separation membrane was prepared in the same manner as in Example 1, except that the reaction temperature was changed from 150 캜 to 130 캜.

&Lt; Comparative Example 2 &

The separation membrane was prepared in the same manner as in Example 1, except that the reaction temperature of the slurry was changed to 100 캜.

&Lt; Comparative Example 3 &

A separation membrane was prepared in the same manner as in Example 1 except that the reaction temperature of the slurry was changed to 170 캜.

<Experimental Example 2>

Measurement of physical properties according to reaction temperature of initiator

Volumetric resistivity, tensile strength and swelling were measured using the separator prepared in Example 1, Example 3, Comparative Example 2 and Comparative Example 3, The results are shown in Table 2 and FIG.

	Comparative Example 2 (100 ° C)	Example 3 (130 < 0 > C)	Example 1 (150 < 0 > C)	Comparative Example 3 (170 DEG C)
Volumetric Insulation Resistance (GΩ · cm) (100V, 3S)	1.20	3.43	5.91	5.50
Tensile strength (kgf / cm 2 )	97	118	136	132
Dimensional change ratio (%)	3	2	2	2

Referring to Table 2 and FIG. 2, the physical properties of Example 1 having a crosslinking temperature of 150 占 폚 increase in volume insulation resistance and tensile strength as compared with Example 3 where the crosslinking temperature is 130 占 폚. It can be seen that the rate of dimensional change remains the same.

In addition, in Comparative Example 2 in which the crosslinking temperature was 100 캜 and Example 3 in which the crosslinking temperature was 130 캜, the volume insulation resistance, the tensile strength, and the dimensional change were all found to be in the inferior state.

In the case of Comparative Example 3 in which the crosslinking temperature was 170 占 폚, the dimensional change ratio was kept at the same value as compared with Example 1, but the volume insulation resistance and the tensile strength were measured to decrease.

Therefore, it can be confirmed that the crosslinking agent of the present invention is capable of producing a separating membrane having a desired physical property by progressively proceeding a crosslinking reaction at a temperature of 120 ° C to 160 ° C. When the crosslinking temperature is 150 ° C, It is estimated that a membrane can be produced.

<Example 4>

A separator was prepared in the same manner as in Example 1 except that the content ratio of the binder in Example 1 was changed from 20% by weight to 15% by weight based on the total solid content weight, and the amount of the crosslinking agent was changed from 2% by weight to 7% by weight .

&Lt; Example 5 >

A separator was prepared in the same manner as in Example 1 except that the content ratio of the binder in Example 1 was changed from 20% by weight to 11% by weight based on the total solid weight, and the amount of the crosslinking agent was changed from 2% by weight to 11% by weight .

&Lt; Comparative Example 4 &

A separator was prepared in the same manner as in Example 1 except that the content ratio of the binder in Example 1 was changed from 20% by weight to 7% by weight based on the total solid content weight, and the amount of the crosslinking agent was changed from 2% by weight to 15% .

<Experimental Example 3>

Measurement of physical properties according to the content of crosslinking agent

Electrical resistance and elongation of the separator prepared in Examples 1, 4, 5 and 4 were measured. The results are shown in Table 3 below.

	Example 1 (2 wt% PEGDMA)	Example 4 (7 wt% PEGDMA)	Example 5 (11 wt% PEGDMA)	Comparative Example 4 (15 wt% of PEGDMA)
Tensile strength kgf / cm 2 )	136	88	79	10
Elongation (%)	46	41	15	3

Referring to Table 3, Examples 1, 4 and 5, in which less than 15 wt% of crosslinking agent was contained, were measured to have increased both tensile strength and elongation as compared with Comparative Example 4 containing 15 wt% of crosslinking agent.

That is, when the cross-linking agent is added in an excessive amount, the tensile strength is remarkably weakened.

Therefore, it was confirmed that the present invention can obtain a separation membrane capable of cell assembly by maintaining a constant tensile strength and elongation only when the content of the crosslinking agent increases within a certain range.

&Lt; Example 7 >

Instead of polyethylene glycol dimethacrylate (PEGDMA) as a crosslinking agent in Example 2, the compound of Formula 1 having 6 functional groups was used, and 2,2'-azobis (isobutyronitrile) instead of initiator 2,2'-azobis '-Azobis (2,4-dimethylvaleronitrile) was used instead of the azobis (2,4-dimethylvaleronitrile).

&Lt; Example 8 >

Instead of polyethylene glycol dimethacrylate (PEGDMA) as a crosslinking agent in Example 2, the compound of Formula 2 having 10 functional groups was used, and 2,2'-azobis (isobutyronitrile) instead of initiator 2,2'-azobis '-Azobis (2,4-dimethylvaleronitrile) was used instead of the azobis (2,4-dimethylvaleronitrile).

<Experimental Example 4>

Measurement of physical properties according to the number of functional groups and the content of crosslinking agent

Volumetric insulation resistance, electrical resistance, tensile strength, and numerical rate of change were measured using the separator prepared in Example 2, Example 7, and Example 8. The results are shown in Table 4 below.

	Number of cross-linker functional groups	Volumetric insulation resistance (TΩ · cm, 100V, 3S, 6 * 6cm)	Electrical Resistance (Ω)	Tensile strength (kgf / cm 2 )	Dimensional change ratio (%)
Example 2 (2 wt% of crosslinking agent)	2 functional group	21.5	1.96	147	3
Example 7 (2 wt% of crosslinking agent)	6 functional groups	54	1.76	170	2.5
Example 8 (2 wt% of crosslinking agent)	10 functional groups	53.4	1.98	179	2.3

Referring to Table 4, in Example 7 using a crosslinking agent having 6 functional groups and Example 8 using a crosslinking agent having 10 functional groups in comparison with the separation membrane of Example 2 containing a crosslinking agent having a functional group number of 2, . This is presumed to be due to more cross-linking.

Analysis of the change in tensile strength shows that tensile strength decreases as the number of functional groups increases.

When the content of the cross-linking agent is the same, the dimensional change rate tends to increase as the number of functional groups increases.

As described above, the separation membrane according to the present invention does not include a polyolefin substrate, and includes a cross-linking agent as an element of the separation membrane, and optionally an initiator. The cross-linking agent has from 2 to 10 functional groups, The volume insulation resistance is remarkably increased to ensure insulation and improve dimensional stability.

It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

As described above, the separation membrane for an electrochemical device according to the present invention does not include a polyolefin substrate used as a separation membrane substrate, unlike a conventional separation membrane, and is made of a material including inorganic particles, a binder and a crosslinking agent. The problem of low thermal stability can be overcome and the insulating property of the separator can be remarkably improved as the crosslinking compound forms a three-dimensional network structure.

Also, as the crosslinking agent is transformed from a linear structure to a three-dimensional network structure, the tensile strength of the separating membrane itself is increased, so that the possibility of damage to the separating membrane is lowered and short-circuiting within the cell can be prevented. Further, as the number of functional groups of the crosslinking agent increases, the dimensional stability of the separating membrane is improved, and wrinkling or deformation of the separating membrane can be prevented.

Claims (13)

1. A separation membrane for an electrochemical device for securing electrical insulation between an anode and a cathode,

   Wherein the separator does not include a polyolefin substrate, and includes inorganic particles, a binder for binding between the inorganic particles, and a crosslinking agent.
2. The method according to claim 1,

   Wherein the inorganic particles are high-k inorganic particles having a dielectric constant of 1 or more, inorganic particles having piezoelectricity, inorganic particles having lithium ion-transferring ability, alumina hydrate, or a mixture of two or more thereof.
3. The method according to claim 1,

   The binder may be selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichlorethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyacryl Polyvinyl pyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, (EPDM), sulfonated EPDM, styrene butylene rubber (SBR), fluorocarbon rubber, and poly (polybutylene terephthalate) rubber. Examples of the thermoplastic elastomer include, but are not limited to, polyethylene terephthalate, polyethylene terephthalate, polyethylene terephthalate, &Lt; / RTI &gt; and &lt; RTI ID = 0.0 &gt; Separation membranes for chemical elements.
4. The method according to claim 1,

   Wherein the cross-linking agent is a polymer material containing 2 to 10 functional groups.
5. 5. The method of claim 4,

   Wherein the crosslinking agent is polyethylene glycol dimethacrylate, or a polymeric substance represented by any one of the following formulas (1) to (2).

   Formula 1

   

   X is an integer of 1 to 100, y is an integer of 0 to 30, and z is an integer of 1 to 1,000. The weight average molecular weight of the formula (1) is 1,000 to 100,000 and the p value is a dependent variable.

   (2)

   

   In the above formula (2), a and c are integers of 1 to 30, and b is an integer of 1 to 1000. The weight average molecular weight of the formula (2) is 1,000 to 100,000 and the d value is a dependent variable.
6. The method according to claim 1,

   Wherein the cross-linking agent has a reaction temperature of 120 ° C to 160 ° C.
7. The method according to claim 1,

   Wherein the separation membrane further comprises a reaction initiator for the crosslinking agent.
8. 8. The method of claim 7,

   Wherein the reaction initiator is an azo-based compound or a peroxide-based compound.
9. 9. The method of claim 8,

   The azo compound may be at least one selected from the group consisting of 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (isobutyronitrile), 2,2'-azobis Nitrile) and 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile).
10. 10. The method of claim 9,

    Wherein the azo-based compound is 2,2'-azobis (isobutyronitrile) or 2,2'-azobis (2,4-dimethylvaleronitrile).
11. 9. The method of claim 8,

    The peroxide compound may be at least one selected from the group consisting of tetramethyl butyl peroxyneodecanoate, bis (4-butylcyclohexyl) peroxydicarbonate, di (2-ethylhexyl) peroxycarbonate, butyl peroxyneodecanoate, Diisopropylperoxy dicarbonate, diethoxyhexyl peroxydicarbonate, diethoxyhexyl peroxydicarbonate, hexyl peroxy dicarbonate, dimethoxy butyl peroxy dicarbonate, bis (3-methoxy-3 -Methoxybutyl) peroxy dicarbonate, dibutyl peroxy dicarbonate, dicetyl peroxy dicarbonate, dimyristyl peroxy dicarbonate, 1,1,3,3-tetramethyl butyl peroxide Peroxypivalate, hexyl peroxypivalate, butyl peroxypivalate, trimethylhexanoyl peroxide, dimethylhydroxybutyl peroxyneodecanoate, amyl peroxy Butyl peroxyneodecanoate, neodecanoate, Atofina, butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate, amyl peroxypivalate, t-butyl peroxypivalate, t-amyl peroxy-2-ethylhexanoate Wherein at least one of dicumyl peroxide, dicumyl peroxide, lauryl peroxide, dilauroyl peroxide, didecanoyl peroxide, benzoyl peroxide and dibenzoyl peroxide is selected.
12. The method according to claim 1,

    Wherein the content of the crosslinking agent in the separator is in the range of more than 0 wt% to 15 wt% or less based on the total weight of the solid content.
13. An electrochemical device comprising a separation membrane for an electrochemical device according to any one of claims 1 to 12.

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