KR102309876B1 - Separator using lithium ion battery and manufacturing method of the same - Google Patents

Abstract

The present invention is a porous polymer substrate; and two or more dissimilar metal oxide layers formed on the surface of the porous polymer substrate, wherein the dissimilar metal oxide layer relates to a separator for a lithium secondary battery formed by an ALD film forming method.

Description

Separator using lithium ion battery and manufacturing method of the same

The present invention relates to a separator for a lithium secondary battery and a method for manufacturing the same. Another object of the present invention is to provide a new separator for a lithium secondary battery that exhibits high heat resistance and excellent wettability with an electrolyte. Another object of the present invention is to provide a new separator for a lithium secondary battery that significantly increases the high heat resistance and provides a battery with a high capacity at the same time.

Polyolefin microporous film is widely used as a separator for various batteries, a separation filter, and a microfiltration membrane due to its chemical stability and excellent physical properties.

Recently, in line with the trend of high capacity and high output of secondary batteries, there is a growing demand for characteristics improvement of separators for high strength, high permeability, thermal stability and electrical safety of secondary batteries during charging and discharging. In the case of a lithium secondary battery, high mechanical strength is required to improve safety during the battery manufacturing process and use, and high transmittance is required to improve capacity and output. In addition, high thermal stability is required.

For example, if the thermal stability of the separator is lowered, a short circuit between electrodes may occur due to damage or deformation of the separator caused by an increase in temperature in the battery, thereby increasing the risk of overheating or fire of the battery. In addition, as the range of use of secondary batteries is expanded to hybrid vehicles, etc., securing the safety of the battery due to overcharging has become an important requirement, and the characteristics of the separator capable of withstanding the electrical pressure caused by overcharging are required.

High strength is required to prevent short circuit between electrodes by preventing damage to the separator that may occur during the battery manufacturing process and damage to the separator that may be caused by dendrites generated in the electrode during the charging/discharging process of the battery. In addition, if the strength of the separator is weakened at a high temperature, a short circuit due to membrane breakage may also occur. In this case, heat generation/ignition/explosion due to a short circuit between the electrodes occurs.

High permeability is required to improve the capacity and output of the lithium secondary battery. The demand for high-permeability separators is increasing in the trend that high-capacity and high-output lithium secondary batteries are required.

The thermal stability of the battery is affected by the closing temperature of the separator, the melt rupture temperature, and the rate of thermal contraction. Among them, the lateral thermal contraction rate at high temperature has a large effect on the thermal stability of the battery. If the transverse thermal contraction rate is large, when the inside of the battery becomes high temperature, the edge of the electrode is exposed in the transverse direction during the contraction process, resulting in a short circuit between the electrodes, which causes heat generation/ignition/explosion.

Even if the melt-rupture temperature of the separator is high, if the transverse thermal contraction rate is large, the edge of the electrode is exposed during the temperature increase of the separator, which may cause a short circuit between the electrodes.

In order to solve the safety problem of the electrochemical device as described above, Korean Patent Laid-Open Publication Nos. 2006-0072065 (Patent Document 1), 2007-0000231, etc. disclose inorganic filler particles and a polymer binder on one or both sides of a porous polymer substrate. A separation membrane formed with a porous coating layer of a mixture of The inorganic filler particles of the microporous coating layer formed on the porous polymer substrate act as a kind of passivation that can maintain the physical shape, thereby suppressing the thermal contraction of the porous polymer substrate during overheating due to malfunction of the electrochemical device. An empty space exists between the inorganic filler particles together with the binder to form micropores.

Lithium secondary batteries are charged and discharged in such a way that lithium ions from the positive electrode material are released and inserted into the carbon layer of the negative electrode during charging, and lithium ions from the negative electrode carbon layer are released and inserted into the positive electrode active material during discharge. Since the electrolyte serves as a medium for moving lithium ions between the negative electrode and the positive electrode, wettability to the non-aqueous electrolyte plays a very important role in the efficiency of charging and discharging. Therefore, in order to improve the battery efficiency, which determines the charge/discharge efficiency, it is required to be made thinner, to have sufficient strength, and to have excellent wettability to the non-aqueous electrolyte.

Republic of Korea Patent Publication 10-2006-0072065 (June 27, 2006)

Accordingly, the present inventors minimize the problem of increasing the thickness of the separator by forming a separate metal compound layer according to the use of the slurry coating and the binder in order to solve the problems pointed out in the background art, thereby minimizing the path of lithium ions, and at the same time, the electrolyte solution An object of the present invention is to provide a novel separator for lithium secondary battery, which significantly improves the charge/discharge efficiency by improving the wettability, and in which the safety of the battery is sufficiently secured by ensuring sufficient heat resistance and mechanical strength, and a method for manufacturing the same.

In addition, the present invention improves the heat resistance of the separator and the wettability of the non-aqueous electrolyte by forming a dissimilar metal compound layer using an atomic layered deposition (ALD) process, and a novel separator having high-efficiency charge/discharge characteristics and excellent battery safety, and a method for manufacturing the same will provide

Another object of the present invention is to provide a separator for an electrochemical device capable of high-density charging for high-capacity as well as improved thermal stability.

Another object of the present invention is to provide an electrochemical device such as a lithium secondary battery using the novel separator.

The present invention relates to a separator for a lithium secondary battery and a method for manufacturing the same.

One aspect of the present invention is a porous polymer substrate; and two or more dissimilar metal compound layers formed on the surface of the porous polymer substrate, the dissimilar metal compound layer relates to a separator for a lithium secondary battery formed by an ALD film forming method.

Another aspect of the present invention is

(a) introducing and contacting the first inorganic precursor on the surface of the porous polymer substrate;

(b) purging with a non-reactive gas;

(c) introducing and contacting a gas comprising a first reactant;

(d) purging with a non-reactive gas;

(e) introducing a second inorganic precursor;

(f) purging with a non-reactive gas;

(g) introducing and contacting a gas comprising a second reactant; and

(h) purging with a non-reactive gas;

A method for manufacturing a separator for a lithium secondary battery comprising a dissimilar metal compound layer prepared including , steps (a) to (h) may be performed twice or in more than two cycles, in another case after repeating steps (a) to (d) two or more times, only steps (e) to (h) are performed in 2 cycles. It relates to a method for manufacturing a separator for a lithium secondary battery, characterized in that the manufacturing is repeated more than once.

The separator for a lithium secondary battery according to the present invention is excellent in high capacity and charge/discharge through minimization of increase in thickness due to the formation of a metal compound layer capable of high-density charging, and excellent safety through introduction of an inorganic metal compound having excellent heat resistance and mechanical strength. A separator capable of manufacturing a battery can be manufactured.

In addition, the present invention can provide a separator for a secondary battery having excellent ionic conductivity characteristics due to excellent wettability with a non-aqueous electrolyte.

1 shows an electron micrograph of the surface of the separator prepared in Example 1 of the present invention, and the magnification is 20,000 times.
Figure 2 shows an electron micrograph of the surface of the separator prepared in Example 3, and the magnification is 20,000 times.
Figure 3 shows an electron micrograph of the surface of the separator prepared in Comparative Example 2, the magnification is 20,000 times.
4 shows a method for measuring the shrinkage ratio of separators prepared in Examples and Comparative Examples.

Hereinafter, a separator for a secondary battery and a manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings. The drawings introduced below are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. Also, like reference numerals refer to like elements throughout.

At this time, if there is no other definition in the technical terms and scientific terms used, it has the meaning commonly understood by those of ordinary skill in the technical field to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Descriptions of known functions and configurations that may be unnecessarily obscure will be omitted.

The present invention is a porous polymer substrate; and a heterogeneous or homogeneous metal precursor by atomic layer lamination (ALD) on a porous polymer substrate, and after laminating the metal precursor, laminated in multiple layers using a heterogeneous or homogeneous reactant to form a single metal oxide layer. Thereafter, by repeating this to form two or more metal compound layers, a new separator and a method thereof are provided, which have remarkably excellent charge/discharge efficiency, excellent heat resistance and mechanical strength, and minimize an increase in thickness due to lamination.

In addition, the present invention improves the adhesion between the porous polymer substrate and the metal precursor and the metal compound layer by forming a metal compound layer after corona discharge treatment or plasma discharge treatment or surface modification using a compound on the surface of the porous polymer substrate, and also By forming two or more heterogeneous metal compound layers formed on a polymer substrate layer, a separation membrane having more excellent wettability and a method for manufacturing the same are provided.

The porous polymer substrate, for example, a polyolefin porous polymer substrate, may be used without limitation as long as it has a high porosity capable of movement of lithium ions between both electrodes. Such a porous polymer substrate is commonly used in the art, and most of it includes a polyolefin porous polymer substrate represented by polyethylene or polypropylene, and other porous polymer substrates of various materials may be used. Specifically, polyethylene (high density polyethylene, low density polyethylene, linear low density polyethylene, high molecular weight polyethylene, etc.), polypropylene, polypropylene terephthalate, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate , polyimide, polyamide imide, polyether imide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide and polyethylene naphthalate may be at least one selected from the group consisting of, but is not limited thereto.

In the present invention, the thickness of the porous polymer substrate is not particularly limited, but may be exemplified by a thickness of 5 to 80 μm, and preferably, a range of 7 to 30 μm is most used, but is not limited thereto. In addition, the porosity of the porous polymer substrate is not particularly limited, but in this technical field, it is common to have a porosity of 10 to 80%, preferably 40 to 70%, and the pore size is 10 nm to 2 μm, preferably may be used in a range of 10 nm to 1 μm.

Nano-thick inorganic compounds formed by the atomic layer lamination method of the present invention include tantalum oxide, tantalum nitride, zirconium oxide, silicon oxide, silicon nitride, silicon carbide, vanadium oxide, zinc oxide, zinc sulfide, aluminum oxide, aluminum hydroxide, It may be at least one selected from the group consisting of aluminum nitride, titanium oxide, titanium nitride, hafnium oxide, hafnium nitride, and the like, but is not limited thereto. The thickness of the atomic laminate is preferably in the form of a thin film of 1 to 200 nm, more preferably 5 to 50 nm.

According to the ALD film forming method of the present invention, the metal compound layer may be formed not only on the surface of the porous polymer substrate but also on the surface of holes (pores) passing through the first and second surfaces of the porous polymer substrate.

In the present invention, the method of coating the inorganic compound on the porous polymer substrate may be formed by atomic layer deposition (ALD), and the dissimilar metal compound layer may be formed using a dissimilar metal precursor or a dissimilar reactant. possible. A metal compound layer is formed at the atomic level by atomic lamination of a dissimilar metal precursor, and then one or more reactants such as water, oxygen, ozone, hydrogen peroxide, oxygen plasma, and NH ₃ plasma are added to form a metal compound layer different from the first inorganic precursor. A separation membrane, which is a composite porous membrane in which a dissimilar metal compound is laminated at an atomic level, may be manufactured by re-stacking the provided second metal precursor or using a second reactant different from the first reactant. In addition, in the present invention, by performing multiple cycles with the lamination of the first metal precursor and the step of contacting the first reactant as one cycle, a laminate in which the first metal compound is atomicly laminated in multiple layers is obtained, and then the second metal precursor is laminated and the second metal precursor is A method in which a second metal compound is atomically stacked in multiple layers to form a dissimilar metal compound by performing a plurality of cycles using the contacting step of the two reactants as one cycle It may proceed to form a dissimilar metal compound.

When a metal compound is introduced into a polymer substrate by the atomic layer deposition method, a film with a low density or a high surface roughness of the metal compound formed due to the low density of functional groups on the surface of the polymer substrate capable of being reacted by stacking a metal precursor may be formed. In this case, substantial improvement in heat resistance and mechanical strength is not achieved. In order to solve this problem, a metal precursor that is easy to stack on a polymer substrate having a low density of functional groups is introduced at the beginning of the atomic layer deposition cycle, or a reactant capable of introducing functional groups to the surface of the polymer substrate is used in the initial cycle. It is possible to form a metal compound layer of high and excellent morphology.

In the present invention, in the ALD method, plasma ALD method or thermal ALD method can be used in order to promote the reaction of inorganic precursors, but when heat is applied, the porous polymer substrate may be damaged, so it is recommended to adopt plasma ALD, but limited to this it's not going to be

Hereinafter, the ALD film forming method will be examined in detail.

First, placing a porous polymer substrate film in a reactive chamber, and then in a predetermined vacuum atmosphere (a) introducing and contacting the first inorganic precursor on the surface of the porous polymer substrate;

(b) purging with a non-reactive gas;

(c) introducing and contacting a gas comprising a first reactant;

(d) purging with a non-reactive gas;

(e) introducing a second inorganic precursor;

(f) purging with a non-reactive gas;

(g) introducing and contacting a gas comprising a second reactant; and

(h) purging with a non-reactive gas;

can be manufactured including

In this case, the first inorganic precursor and the second inorganic precursor are the same or different from each other, and the first reactant and the second reactant are the same or different from each other, and steps (a) to (h) are performed twice or more than twice. It may proceed as a cycle, and in another case, after repeating steps (a) to (d) two or more times, it may include manufacturing by repeating only steps (e) to (h) two or more times.

Here, in the ALD film formation method of the present invention, for example, first, a porous polymer substrate is introduced into an ALD chamber, a gaseous metal precursor is introduced into the chamber, and a non-reactive gas such as arcon, krypton, nitrogen, hydrogen, etc. is used to After purging, a gas containing one or more reactants such as water, oxygen, ozone, hydrogen peroxide, oxygen plasma, and NH ₃ plasma is introduced and purged with the same or different non-reactive gas. Nano-sized metal A compound thin film is formed.

As a metal precursor that can be used in the present invention, for example, AlCl ₃ , TMA (Tri-methyl-Aluminum), Al(CH ₃ ) ₂ Cl, Al(C ₂ H ₅ ) ₃ , Al(OC ₂ H ₅ ) ₃ , Al(N(C ₂ H ₅ ) ₂ ) ₃ , Al(N(CH ₃ ) ₂ ) ₃ , SiCl ₄ , SiCl ₂ H ₂ , Si ₂ Cl ₆ , Si(C ₂ H ₅ )H ₂ , Si ₂ H ₆ , TiF ₄ , TiCl ₄ , TiI ₄ , Ti(OCH ₃ ) ₄ , Ti(OC ₂ H ₅ ) ₄ , Ti(N(CH ₃ ) ₂ ) ₄ , Ti(N(C ₂ H ₅ ) ₂ ) ₄ , Ti(N(CH ₃ )(C ₂ H ₅ )) ₄ , VOCl ₃ , Zn, ZnCl ₂ , Zn(CH ₃ ) ₂ , Zn(C ₂ H ₅ ) ₂ , ZnI ₂ , ZrCl ₄ , ZrI ₄ , Zr(N(CH ₃ ) ₂ ) ₄ , Zr(N(C ₂ H ₅ ) ₂ ) ₄ , Zr(N(CH ₃ )(C ₂ H ₅ )) ₄ , HfCl ₄ , HfI ₄ , Hf(NO _{3 ) ) 4, Hf (N (CH} 3) (C 2 H 5)) 4, Hf (N (CH 3) 2) 4, Hf (N (C 2 H 5) 2) 4, TaCl 5, TaF 5, TaI ₅ , Ta(O(C ₂ H ₅ )) ₅ , Ta(N(CH ₃ ) ₂ ) ₅ , Ta(N(C ₂ H ₅ ) ₂ ) ₅ , TaBr ₅ , but may be selected from the group consisting of It is not limited.

As a reactant that can be used in the present invention, for example, water, oxygen, ozone, hydrogen peroxide, alcohol, NO ₂ , N ₂ O, NH ₃ , N ₂ , N ₂ H ₄ , C ₂ H ₄ , HCOOH, CH ₃ COOH, H ₂ S, (C ₂ H ₅ ) ₂ S ₂ , N ₂ O plasma, hydrogen plasma, oxygen plasma, CO ₂ plasma, NH _{3 It} may be selected from the group consisting of plasma, but is not limited thereto.

In the present invention, before forming the ALD layer, the surface of the porous polymer substrate is subjected to plasma treatment containing oxygen or gas such as water or nitrogen, surface treatment by plasmaizing organic compound monomers, corona discharge treatment, UV irradiation treatment, ozone treatment, etc. It is better for adhesion, and in particular, it is possible to form a metal compound layer with high density and excellent morphology by increasing the density of functional groups on the surface of the polymer substrate.

In the present invention, since a metal oxide layer or a ceramic layer is additionally formed on more than one surface of the surface and inside the microporous membrane on the porous polymer substrate, the pores of the existing porous polymer substrate are blocked, thereby reducing the permeability. In particular, when the transmittance exceeds 300s due to the formation of the composite membrane, even a composite membrane with high heat resistance is not an efficient separator because battery output and battery cycle characteristics are remarkably reduced. In the present invention, as a result of forming a composite membrane using a porous polymer substrate having various transmittances, it was found that the transmittance range at a level that is the most stable and does not interfere with the battery behavior is 300 s or less.

In the case of the porous polymer substrate referred to in the present invention, since it is usually manufactured through a stretching process, shrinkage occurs at a high temperature. Shrinkage occurring at high temperature basically causes contraction in the X and Y directions in the case of biaxial stretching. doesn't happen

TMA is an experimental method that shows the thermal behavior of a specimen at a high temperature, and measures the degree of shrinkage and elongation of the specimen while the temperature rises at a constant rate by attaching a weight to a 6 mm × 10 mm specimen. TMA measurement is not only an item that can evaluate the high-temperature stability of the separator itself, but is also one of the methods that can predict the thermal stability of a battery. Therefore, the TMA maximum shrinkage temperature and TMA meltdown temperature can be said to be the criteria for predicting the high-temperature stability of the separator and the thermal stability of the battery. In the case of a normal polyethylene-based microporous membrane, the maximum shrinkage temperature of TMA is about 135℃, and the maximum shrinkage and shrinkage temperature are sometimes determined due to process variables, but the maximum shrinkage of TMA is about 0 to 60%, and the TMA meltdown temperature is approximately 144°C or less. In some cases, the maximum shrinkage is negative, but the TMA meltdown temperature is usually low, below 140°C. On the other hand, in the case of the composite membrane manufactured using the conditions presented in the present invention, the maximum shrinkage rate at the TMA maximum shrinkage temperature is 5% or less, and the meltdown temperature is 150°C or more simultaneously.

The separator according to the present invention provides high ionic conductivity, high discharge efficiency, and excellent battery efficiency while maintaining excellent heat resistance and mechanical properties of the conventional composite separator having an inorganic compound layer, thereby having an unexpected effect that high capacity is possible.

The present invention may also provide a lithium secondary battery manufactured including a separator. In addition, the present invention may provide a primary or secondary cell including a separator, a fuel cell, a solar cell, or an electrochemical device including a capacitor. As a specific example, the present invention is particularly suitable for a lithium secondary battery, and has a structure including a negative electrode, a positive electrode, an electrolyte, and the separator of the present invention.

The negative active material provided in the negative electrode may be any type of negative active material used in conventional secondary batteries, and as an example of a lithium ion secondary battery, the negative active material provided in the negative electrode is graphite, amorphous carbon, lithium titanate (Lithium). Titanate, Li ₄ Ti ₅ O ₁₂ ), titanium dioxide (TiO ₂ ), Si, an Si alloy (alloy), Sn, a Sn alloy (alloy), or a mixture thereof.

The positive electrode may be prepared by applying and drying a slurry containing a positive electrode active material on each of the two opposite surfaces of the positive electrode current collector, followed by pressing, and in this case, the outermost positive electrode is a positive electrode active material on one surface of the positive electrode current collector, preferably It can be prepared by coating and drying the slurry containing the positive electrode active material, applying and drying the slurry containing the negative electrode active material, inorganic particles that do not react with the positive electrode active material, or a mixture thereof on the other side, and then rolling.

Like the positive electrode, the negative electrode may also be prepared by applying and drying a slurry containing the negative electrode active material on each of two opposing surfaces of the negative electrode current collector, followed by rolling. In this case, the slurry for preparing the electrode active material coating layer or the outermost coating layer may further include an additive including a conventional binder such as polyvinylidene fluoride.

In addition, each of the above-described positive electrode active material is prepared by using a positive electrode current collector, that is, a foil produced by aluminum, nickel, or a combination thereof, and a negative electrode current collector, that is, copper, gold, nickel or a copper alloy or a combination thereof. It goes without saying that the positive electrode can be configured in the form of binding to the manufactured foil.

The electrolyte may include a liquid electrolyte used in a conventional secondary battery, for example, a lithium ion secondary battery, and the electrolyte may be a liquid electrolyte in which a lithium salt including lithium perchlorate and lithium borofluoride is dissolved in a solvent. An example of the solvent included in the electrolyte may include an ester-based solvent including propylene carbonate, ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate.

Hereinafter, the present invention will be described in more detail by way of Examples. However, the following examples are merely illustrative of the invention, and the content of the present invention is not limited by the examples.

The physical properties of the specimens prepared in Examples were measured as follows.

(1) film thickness

A contact-type thickness gauge having a thickness accuracy of 0.1 μm was used.

(2) average pore diameter

The pore size was measured by a half-dry method according to ASTM F316-03 using a porometer (Porometer: PMI).

(3) porosity

A rectangular sample of A cm x B cm was cut out and calculated from Equation (1). Both A/B were cut and measured in a range of 5 to 20 cm, respectively.

[Equation 1]

Space factor = {(A×B×T)-(M÷ρ)÷(A×B×T)}×100

where T = thickness of the separator (cm)

M = sample weight (g)

ρ = resin density (g/cm 3 )

(4) gas permeability (Gurley densometer)

The gas permeability was measured with a porometer (Gurley densometer: Toyoseiki). It is the time it takes for a ^{certain volume (100 ml) of gas to pass through a certain area (1 in 2} ) at a certain pressure (about 1 to 2 psig), in seconds.

(5) deposition thickness

In the case of the inorganic metal compound deposition thickness on the composite microporous film by the ALD film formation method, the thickness was measured through a reflectometer after depositing the inorganic metal compound on the Si wafer under the same deposition conditions.

(6) shrinkage

Put a Teflon sheet between the glass plates and apply a force of 7.5 mg/mm² to the composite microporous membrane to be measured. After leaving it in an oven at 200 ° C for 1 hour, measure the contraction in the longitudinal and lateral directions to calculate the final area shrinkage in % did. A detailed drawing is shown in FIG. 4 .

(11) TMA maximum shrinkage and melt rupture temperature

Using METTLER TOLEDO's TMA (Thermo-mechanical analysis) equipment, a weight of 0.015 N is attached to a 6 mm × 10 mm specimen, and the temperature is raised at a rate of 5° C./min. In the case of a specimen manufactured through the stretching process, contraction occurs at a certain temperature, and when Tg and Tm are exceeded, the specimen is stretched due to the weight of the weight. In the case of TMA maximum shrinkage, it is defined as a value expressed as a percentage of the length of shrinkage deformation compared to the initial measured length at the maximum shrinkage point occurring at a constant temperature, and it starts to stretch by the weight of the weight. At this time, the initial length (zero point) of the specimen is defined as The temperature at which it begins to exceed is defined as the melt rupture temperature. Also, in the case of a sample in which no shrinkage occurs, it is defined as the temperature where it meets the x-axis when the slope is maximum.

(11) Heat exposure measurement (Hot box test)

A battery was assembled using a polyolefin-based composite microporous membrane as a separator. A positive electrode using lithium cobalt oxide (LiCoO ₂ ) as an active material and a negative electrode using graphite carbon as an active material are wound together with the prepared separator and put into an aluminum pack, and then ethylene carbonate and diethylene carbonate An electrolyte solution in which lithium hexafluorophosphate (LiPF6) was dissolved at a 1 molar concentration in a 1:1 solution was injected and sealed to assemble a battery.

The assembled battery was placed in an oven, heated at 5°C/min, reached 150°C, and left to stand for 30 minutes to measure the change in the battery.

(12) Measurement of nail penetration

A battery was assembled using a polyethylene-based composite microporous membrane as a separator. A positive electrode using lithium cobalt oxide (LiCoO ₂ ) as an active material and a negative electrode using graphite carbon as an active material are wound together with the prepared separator and put into an aluminum pack, and then ethylene carbonate and diethylene carbonate An electrolyte solution in which lithium hexafluorophosphate (LiPF6) was dissolved at a 1 molar concentration in a 1:1 solution was injected and sealed to assemble a battery. The assembled battery was fixed, and the behavior of the battery was observed by penetrating it at a speed of 80 mm/sec using a nail having a diameter of 2.5 mm.

Example 1

For the preparation of the polyolefin microporous membrane, high-density polyethylene having a weight average molecular weight of 3.8 × 10 ⁵ was used, and as diluent, dibutyl phthalate and paraffin oil having a kinematic viscosity of 160 cSt at 40°C were mixed in 1:2. The contents of polyethylene and diluent were 30% by weight and 70% by weight, respectively. The composition was extruded at 240° C. using a twin screw compounder equipped with a T-die, passed through a section set at 180° C. to induce phase separation, and a sheet was prepared using a casting roll. The draw ratio was 7.5 times each of MD and TD, and the stretching temperature was 131 ° C., which was manufactured through sequential biaxial stretching, the heat setting temperature was 130 ° C, and the heat setting width was 1-1.3-1.1. The final thickness of the prepared separator was 25 μm, the gas permeability (Gurley) was 100 sec, and the shrinkage at 130° C. was 25% and 28% in the vertical and horizontal directions, respectively.

After mounting the prepared porous polymer substrate in a chamber at 100 ° C., trimethylaluminum (Al(CH ₃ ) ₃ ), argon (Ar), ammonia (NH ₃ ) plasma, and argon (Ar) were exposed to 0.5, 10, 5, and 10 sec, respectively. It was sequentially introduced to the surface of the porous polymer substrate with time, and this was repeated 10 times to deposit an aluminum nitride (AlN) film, which is a first metal compound film, on the surface of the porous polymer substrate.

Then, trimethylaluminum (Al(CH ₃ ) ₃ ), argon (Ar), moisture (H ₂ O), and argon (Ar) were deposited with the inorganic metal compound at an exposure time of 5, 5, 5, and 5 sec, respectively, to the porous polymer substrate It was sequentially introduced to the surface, and this was repeated 50 times to form an _{aluminum oxide (Al 2} O _{3 ) film as a second metal compound film.} The sum of the thicknesses of the prepared aluminum nitride and aluminum oxide was 15 nm.

Example 2

Except that in Example 1, the porous polymer substrate was treated with an in-line oxygen plasma equipment under the conditions of 1.9 kW, plasma slit distance 3 mm, plasma slit gap 2 mm, and line speed 3 m/min. The same was carried out. The results are shown in Table 1.

Example 3

In Example 1, the first metal compound film was trimethylaluminum (Al(CH ₃ ) ₃ ), argon (Ar), ozone (O ₃ ), and argon (Ar) were porous with exposure times of 0.2, 10, 2, and 10 sec, respectively. It was sequentially introduced to the surface of the polymer substrate and repeated 100 times, except that it was formed as _{an aluminum oxide (Al 2} O _{3 ) film.} The results are shown in Table 1.

Comparative Example 1

In Example 1, the porous polymer substrate was used without any inorganic metal compound deposition. The results are shown in Table 1.

Comparative Example 2

In Example 1, after the porous polymer substrate was mounted in a chamber at 100° C., trimethylaluminum (Al(CH ₃ ) ₃ ), argon (Ar), moisture (H ₂ O), and argon (Ar) were respectively 5, 5, 5, The inorganic metal compound was sequentially introduced onto the surface of the deposited porous polymer substrate with an exposure time of 5 sec, and this was repeated 75 times to form an aluminum oxide (Al ₂ O ₃ ) film. The thickness of the prepared aluminum oxide film was 15 nm. The results are shown in Table 1.

Comparative Example 3

After carrying out in the same manner as in Comparative Example 2, the same process was repeated again except that 75 cycles were added. As a result, the thickness of the aluminum oxide film was 30 nm. The results are shown in Table 1.

Referring to Table 1, compared with Comparative Examples 1 and 2, Example 1 in which a dissimilar metal compound was introduced showed excellent shrinkage and TMA properties, and the shrinkage and TMA properties were improved through plasma surface treatment of the porous polymer substrate. could check On the other hand, in the case of Example 3 in which the same type of metal compound was used but different types of first and second reactants were used, it was found that excellent shrinkage rate and TMA characteristics were exhibited.

[Table 1]

Examples 4 to 6 and Comparative Examples 3 to 5

The battery characteristics were investigated using the separators prepared in Examples 1 to 4 and Comparative Examples 1 to 3 in the following manner.

Preparation of anode

N-methyl-2 pyrrolidone (NMP) as a solvent in which 92 wt% of lithium cobalt composite oxide is used as a cathode active material, 4 wt% of carbon black is used as a conductive material, and 4 wt% of polyvinylidene fluoride (PVdF) is used as a binder. ) to prepare a positive electrode mixture slurry. The positive electrode active material slurry was coated on an aluminum (Al) thin film, dried to prepare a positive electrode, and then roll-pressed.

Preparation of the cathode

Graphite carbon as an anode active material, PVdF as a binder, and carbon black as a conductive material in 96 wt%, 3 wt%, and 1 wt%, respectively, were added to NMP as a solvent to prepare an anode mixture slurry. . The negative electrode active material slurry was coated on a copper (Cu) thin film and dried to prepare a negative electrode, followed by roll-pressing.

manufacture of batteries

After the positive electrode and the negative electrode prepared by the above method were wound together with the prepared separator and put into an aluminum pack, 1 mole of lithium hexafluorophosphate (LiPF6) was added to a 1:1 solution of ethylene carbonate and diethylene carbonate. A battery was assembled by injecting an electrolyte solution dissolved in concentration and sealing it.

The results are listed in Table 2 below.

Battery safety evaluation

In Examples 4 to 6 and Comparative Examples 3 to 4, the batteries having a positive and negative electrode capacity of 4 mAh were charged at 0.2C and then discharged at 0.2C. Table 2 below. Heat exposure measurement (Hot box test) The assembled battery was placed in an oven, the temperature was raised at 5°C/min to reach 150°C, and then left for 30 minutes to measure the change in the battery. Measurement of nail penetration The assembled battery was fixed, and the behavior of the battery was observed by penetrating it at a speed of 80 mm/sec using a nail having a diameter of 2.5 mm. The measurement results are shown in Table 2.

[Table 2]

Referring to Table 2, as compared with Comparative Examples 1 and 2, Example 1 introducing a dissimilar metal compound introducing a dissimilar metal compound, Example 2 introducing a plasma surface treatment to a porous polymer substrate, and depositing a homogeneous metal compound However, in the case of Example 3 using heterogeneous first and second reactants, it was found that excellent performance was shown in heat exposure and cell penetration measurement.

Claims (12)

porous polymer substrate; and
As a separator for a lithium secondary battery comprising a dissimilar metal compound layer formed on the surface of the porous polymer substrate,
The dissimilar metal compound layer includes a first metal compound layer and a second metal compound layer, and the first and second metal compound layers are ALD-formed using different dissimilar metal precursors or different dissimilar reactants. The separator has a TMA maximum shrinkage of 5% or less and a meltdown temperature of 150°C or higher for lithium secondary batteries. The method of claim 1,
In the separator, the transmittance (Gurley) of the entire separator including the dissimilar metal compound layer is 300 sec or less, and the shrinkage rate for 1 hour at 200° C. is 0 to 10% in both the longitudinal and transverse directions. The method of claim 1,
The porous polymer substrate is a separator for a lithium secondary battery having a pore size of 0.01 to 1 μm. The method of claim 1,
The porous polymer substrate is a separator for a lithium secondary battery having a porosity of 40 to 70%. The method of claim 1,
The porous polymer substrate is polyethylene, polypropylene, polypropylene terephthalate, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyamideimide, polyetherimide, polyether A separator for lithium secondary batteries at least one selected from the group consisting of ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide and polyethylene naphthalate. The method of claim 1,
Each of the first metal compound layer and the second metal compound layer has a thickness of 5 to 50 nm a separator for a lithium secondary battery. delete delete The method of claim 1,
The dissimilar metal compound layer is tantalum oxide, tantalum nitride, zirconium oxide, silicon oxide, silicon nitride, silicon carbide, vanadium oxide, zinc oxide, zinc sulfide, aluminum oxide, aluminum hydroxide, aluminum nitride, titanium oxide, titanium nitride, hafnium oxide, A separator for a lithium secondary battery, characterized in that at least one selected from the group consisting of hafnium nitride. delete delete The method of claim 1,
A separator for a lithium secondary battery wherein any one layer selected from the porous polymer substrate and the dissimilar metal compound layer is surface-treated by corona or plasma discharge.

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