CN115799764A

CN115799764A - Electrode assembly using two-stage ceramic coating diaphragm and lithium ion secondary battery comprising same

Info

Publication number: CN115799764A
Application number: CN202211099727.0A
Authority: CN
Inventors: 徐正现; 黄正泰; 李笑美; 崔株宁
Original assignee: SK On Co Ltd
Current assignee: SK On Co Ltd
Priority date: 2021-09-13
Filing date: 2022-09-09
Publication date: 2023-03-14
Also published as: KR20230038979A

Abstract

The present invention relates to an electrode assembly using a two-stage ceramic coating separator and a lithium ion secondary battery including the same. And more particularly, to an electrode assembly including an anode, a cathode, and a separator interposed between the anode and the cathode, in which an inorganic coating layer is formed on a separator extension portion of the separator not in contact with the anode and the cathode, and a lithium ion secondary battery including the same.

Description

Electrode assembly using two-stage ceramic coating diaphragm and lithium ion secondary battery comprising same

Technical Field

The present invention relates to a lithium ion secondary battery, and more particularly, to a lithium ion secondary battery using a two-stage ceramic coating separator.

Background

Recently, as the application range of lithium secondary batteries is expanded to medium and large-sized batteries applied to Electric Vehicles (EVs), energy Storage Systems (ESS), and the like, the lithium secondary batteries are required to have high-capacity, high-power characteristics.

Following this trend, attempts have been made to reduce the thickness of the separator to increase the electrode reaction area and reduce the distance between the anode and the cathode, but as the thickness of the separator is reduced, there is a problem in that the mechanical strength and thermal stability are reduced. In particular, as the thermal stability is reduced, there is also a problem that the risk in terms of safety, such as low voltage of the cell, fire, etc., increases.

In order to solve such a problem, a technique of improving the characteristics of the separator itself by providing functional layers such as a ceramic coating, a heat-resistant polymer coating, and a crosslinked polymer coating on the polymer separator itself has been disclosed. However, when the ceramic coating layer is formed or applied thick, thermal stability can be improved, but the problem of a decrease in permeability occurs, and when the ceramic coating layer is coated with a heat-resistant polymer or a crosslinked polymer, thermal stability is still decreased, and therefore, the problem of shrinkage of the separator occurs, and the like, and thus, a low voltage, ignition, and the like actually occur.

Accordingly, there is a need for an electrode assembly having excellent heat resistance and mechanical strength to suppress thermal shrinkage of a separator, to suppress short-circuiting of electrodes, and to significantly reduce the risk of fire, and a lithium ion secondary battery including the same.

[ Prior art documents ]

[ patent document ]

(patent document 1) korean laid-open patent No. 10-2017-0055038 (2017.05.19.)

Disclosure of Invention

Technical problem

An aspect of the present invention is directed to provide an electrode assembly capable of realizing large capacity and high power including a separator having improved heat resistance and permeability, and a lithium ion secondary battery including the same. And more particularly, to an electrode assembly having a structure in which an anode, a cathode, and a separator interposed between the anode and the cathode are formed at edges (extension portions) of the separator with a two-stage ceramic coating layer to suppress thermal shrinkage, low voltage, ignition, etc. from occurring due to a short circuit between the cathode and the anode (tabs of the anode), thereby securing user safety.

And, an aspect of the present invention is directed to provide a lithium ion secondary battery in which an inorganic coating layer formed on an edge (extension) of a separator and a central portion where a cathode and an anode meet is formed of different compositions to suppress thermal shrinkage, to have excellent gas permeability, to thereby improve operational stability, and to improve battery performance.

Technical scheme

An electrode assembly according to the present invention is an electrode assembly including an anode, a cathode, and a separator interposed between the anode and the cathode, characterized in that: the separator has a separator extension portion extending from one side of the anode and the cathode in the longitudinal direction, and the separator extension portion includes a first extension portion having substantially the same thickness as the separator and a second extension portion having a first inorganic coating layer formed on one or both sides thereof and thicker than the thickness of the separator.

In the electrode assembly according to one embodiment of the present invention, the length of the second extension part in the length direction may be greater than the length of the first extension part.

In the electrode assembly according to one embodiment of the present invention, one or both sides of the separator may further include a second inorganic coating layer.

In the electrode assembly according to one embodiment of the present invention, the first inorganic coating layer may be formed on the second inorganic coating layer.

In the electrode assembly according to one embodiment of the present invention, the composition of the inorganic compound of the first inorganic coating layer may be different from the composition of the inorganic compound of the second inorganic coating layer.

In the electrode assembly according to one embodiment of the present invention, a concentration of the binder per unit volume of the first inorganic coating layer may be higher than a concentration of the binder per unit volume of the second inorganic coating layer.

In the electrode assembly according to one embodiment of the present invention, the inorganic compound of the first inorganic coating layer may include fibrous or plate-shaped inorganic particles having an aspect ratio of 1.

In the electrode assembly according to one embodiment of the present invention, the second inorganic coating layer may further include an inorganic compound, organic particles, and a binder.

In the electrode assembly according to an embodiment of the present invention, the first inorganic coating layer of the second extension part of the separator is formed at one side of the separator opposite to the cathode, and the thickness of the first inorganic coating layer may be in the range of 40 to 100% of the thickness of the cathode.

In the electrode assembly according to one embodiment of the present invention, the permeability of the separator is 250 seconds/100 cc or more, and the heat shrinkage rate at 150 ℃ may be less than 1%.

The lithium ion secondary battery according to the present invention includes the above-described electrode assembly.

Technical effects

In the electrode assembly according to the present invention, one or more sides of the separator interposed between the anode and the cathode in the longitudinal direction may have a separator extension part extended from one side of the anode and the cathode in the longitudinal direction, and an additional inorganic coating layer may be formed on the separator extension part to suppress thermal shrinkage of the separator, thereby having an effect of suppressing an electrode short circuit, a low voltage, and a fire.

In particular, the inorganic coating layer (first inorganic coating layer) additionally formed on the separator extension is formed of a composition different from that of the inorganic coating layer (second inorganic coating layer) of the separator, and not only effectively suppresses shrinkage of the edge of the separator (separator extension), but also the first inorganic coating layer formed on one or both surfaces of the central portion of the separator in contact between the anode and the cathode has excellent Air permeability (Air permeability), and thus an electrode assembly having a thin separator and improved cell energy density can be provided, and thus, a lithium ion secondary battery having significantly improved battery life and performance can be obtained.

In particular, the short circuit due to the thermal contraction of the separator is suppressed to prevent the danger of fire or explosion, thereby further improving the safety of users and the operational stability of the electrode assembly.

Drawings

FIG. 1 is an isolated perspective view of an electrode assembly according to one embodiment of the present invention;

FIG. 2 is an isolated perspective view of an electrode assembly according to another embodiment of the present invention;

fig. 3 is a result of a thermal stability test of the electrode assemblies manufactured in comparative examples 1 and 2 of the present invention.

Detailed Description

Terms used in the present invention have the same meaning as commonly understood by one of ordinary skill in the art without other definitions. Furthermore, the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

The use of the singular in the description of the invention and in the appended claims is also meant to include the plural unless otherwise indicated herein.

Throughout the specification of the present invention, unless otherwise specified, the term "includes" or "including" a certain component means that other components may be included, but not excluded.

The present inventors have conducted extensive studies to solve the above problems, and as a result, they have found that, in an electrode assembly having a structure including an anode, a cathode, and a separator interposed between the anode and the cathode, when a two-stage ceramic coating is formed on a separator extension portion extending from the anode and the cathode to be left as a remaining portion, the remaining portion of the separator can be prevented from being thermally shrunk to cause an electrode short circuit, and thus the present invention has been finally achieved.

Also, the ceramic coating layer formed on the separator extension part and the inorganic coating layer formed on the central portion of the separator contacting between the cathode and the anode in the electrode assembly according to one embodiment of the present invention are formed of different compositions, so that thermal shrinkage is effectively suppressed without reducing permeability of the separator, thereby enabling realization of an electrode assembly capable of further improving battery performance.

In particular, the secondary battery pack according to an embodiment of the present invention has the above-described characteristics, thereby having the effect of preventing short-circuiting of electrodes due to thermal contraction, and preventing accidents such as fire or explosion to ensure user safety.

The respective configurations of the present invention will be described below in more detail with reference to the drawings. This is by way of example only and the invention is not limited to the specific embodiments illustrated.

The term 'electrode' as used in the present invention is used in a meaning including 'anode' and 'electrode'.

An electrode assembly according to an embodiment of the present invention includes an anode, a cathode, and a separator interposed between the anode and the cathode, wherein one or more sides of the separator in a longitudinal direction have a separator extension portion extending further than one side of the anode and the cathode in the longitudinal direction, and the separator extension portion may be formed of a first extension portion having substantially the same thickness as the separator and a second extension portion having a first inorganic coating layer formed on one or both sides thereof and thicker than the thickness of the separator.

The separator has a separator extension portion which is not in contact with the anode and the cathode and extends to both sides of the length of the anode and the length of the cathode with respect to the longitudinal direction of the separator, the separator extension portion has one or more side surfaces of an electrode tab, and the separator extension portion has a first extension portion having a thickness substantially the same as the thickness of the separator and a second extension portion having a thickness larger than the thickness of the separator and having a first inorganic coating layer formed on one or both of the two side surfaces.

Fig. 1 shows an electrode assembly 1 according to one embodiment of the present invention.

Referring to fig. 1, again with the electrode assembly 1 as described above, the electrode assembly 1 includes an anode 10, a cathode 30, and a separator 50 interposed between the anode 10 and the cathode 30, the separator 50 including an opposite portion 51 opposite to the anode 10 or the cathode 30, and a separator extension portion 53 extending from at least one side edge of the opposite portion 51. The diaphragm extension portion 53 includes a first extension portion 53a extending with the same thickness as the opposing portion 51, and a second extension portion 53b having at least one surface on which a first inorganic coating layer is formed so as to be thicker than the first extension portion 53 a.

Specifically, the facing portion 51 of the separator 50 is a region of the separator facing the cathode 30 or the anode 10, and when the area facing one of the electrodes is larger than the area facing the other electrode, the facing portion 51 may be formed with reference to the region facing the electrode having a larger area. As an example, as shown in the drawing, when the cathode 30 is larger than the anode 10, the area of the separator 50 facing the cathode 30, that is, the area corresponding to the facing portion 51 may be used.

The separator extension 53 extending to one or more sides of the length of the anode and the cathode may have a size of 1 to 15% in the longitudinal direction based on the length of the separator 50, but is not limited thereto.

The diaphragm extension 53, as shown in fig. 1, includes a first extension 53a on which the first inorganic coating is not formed and a second extension 53b on which at least one side is coated with the first inorganic coating, and the second extension 53b is also formed with the first inorganic coating compared to the first extension 53a, and thus may have a thickness thicker than the first extension 53a by an amount corresponding to the first inorganic coating.

The length of the second extension 53b in the longitudinal direction of the diaphragm extension 53 may be equal to or greater than the length of the first extension 53a, and preferably, may be greater than the length of the first extension 53 a. The provision of the first extending portion 53a is preferable because, when the separator thermally contracts, the first inorganic coating layer protruding in the electrode direction of the second extending portion 53b is caught by the end portion of the cathode 30 or the anode 10 or the end portions of the cathode 30 and the anode 10, and an effect of preventing the electrode from being short-circuited due to the contraction of the separator 50 can be achieved.

The separator 50 may be a known separator without limitation, specifically, a polymer substrate such as a polymer film may be used, and preferably, a microporous membrane having a porous structure including a plurality of pores may be used.

The size and degree of pores present in the microporous membrane are not particularly limited, but may be about 0.01 μm to about 50 μm and about 10% to about 95%, respectively. The polymer substrate includes a polymer material, which is not particularly limited as long as it is generally used as a separator material in the art, but examples of the polymer material include polyethylene (polyethylene), polypropylene (polypropylene), polyethylene terephthalate (polyethylene terephthalate), polybutylene terephthalate (polybutylene terephthalate), polyester (polyester), polyacetal (polyacetal), polyamide (polyamide), polycarbonate (polycarbonate), polyimide (polyimide), polyether ether ketone (polyether ketone), polyaryletherketone (polyaryletherketone), polyetherimide (polyetherimide), polyamideimide (polyamide), polybenzimidazole (polybenzazole), polyethersulfone (polyethersulfone), polyphenylene oxide (polyphenylene oxide), cyclic olefin copolymer (cyclic olefin copolymer), polyphenylene sulfide (polyphenylene sulfide), and polyethylene naphthalate (polyethylene naphthalate) and mixtures thereof. Preferably, the polymer material of the microporous membrane may be polyolefin, specifically, polyethylene.

The method for producing the polyolefin microporous membrane may be a wet process, but this is merely an example, and any known method for producing a microporous membrane is not limited. Specifically, the wet process may manufacture the microporous membrane through a process of kneading and extruding a polyolefin resin and a diluent, a sheet forming process, a stretching process, and the like, and may further include a diluent extraction process and a heat treatment process.

Fig. 2 illustrates an electrode assembly according to another embodiment of the present invention.

Referring to fig. 2, as a preferred embodiment, the separator may be a porous separator having/inorganic composite including a second inorganic coating layer 70 on one or both sides of the separator.

As a non-limiting example, in the case of using a composite porous separator, the first inorganic coating layer may be formed on the second inorganic coating layer 70. In this case, the first inorganic coating layer and the second inorganic coating layer 70 may each independently include an inorganic compound and a binder.

The second inorganic coating layer 70 of the organic/inorganic composite porous separator may be formed of a composition containing a known inorganic compound and a binder, and preferably may contain an inorganic compound, organic particles and a binder. The second inorganic coating layer is formed on the porous separator to improve heat resistance and permeability, and more preferably, the composition may be configured to improve gas permeability, but is not limited thereto.

The gas permeability of the organic/inorganic composite porous separator having the second inorganic coating layer formed thereon at a thickness of 15 μm may be 200 seconds/100 cc or more, specifically 250 seconds/100 cc or more, with no upper limit, but may have a value of 700 seconds/100 cc or less, specifically 500 seconds/100 cc or less. And, the heat shrinkage rate at 150 ℃ may be less than 3%, preferably less than 2%, and more preferably less than 1%, and the tensile strength may be 500 to 2,000kgf/cm ² Specifically 700 to 1,500kgf/cm ² 。

The inorganic compound and the binder forming the second inorganic coating layer are not limited as long as they are known, but as a preferred embodiment, the inorganic compound forming the second inorganic coating layer may be any one or two or more inorganic particles selected from Alumina (Aluminum), boehmite (Boehmite), aluminum Hydroxide (Aluminum Hydroxide), titanium Oxide (Titanium Oxide), barium Titanium Oxide (Barium Oxide), magnesium Oxide (Magnesium Oxide), magnesium Hydroxide (Magnesium Hydroxide), silica (Silica), clay (Clay), glass powder (Glass powder), and the like, and preferably, an Aluminum-based Oxide selected from a mixture of any one or two or more of high-purity Alumina (Aluminum), boehmite (Boehmite), aluminum Hydroxide (Aluminum Hydroxide), and the like, which have a small impurity content, may be used. The inorganic compound may be an inorganic compound having an average size ranging from 10nm to 5 μm, preferably from 100nm to 2 μm, more preferably from 200nm to 500 nm. The inorganic particles may be in the form of spheres (sphere), plates (plate), fibers (fiber), or the like, but are not limited thereto, and any form may be used in the art.

The organic particles function as a filler, can be coated with a uniform film as compared with an inorganic filler, and are advantageous in terms of air permeability and insulation. Specifically, the organic particles may act as a support within the membrane. For example, when the separator is intended to shrink at high temperature, the presence of organic particles between the inorganic fillers suppresses the shrinkage of the separator. Also, the coating layer disposed on the separator includes organic particles, so that sufficient porosity can be secured and heat resistance can be improved. Therefore, it is preferable that the content of the binder be reduced so that the filler is relatively contained in a larger amount, and the effects of improving the gas permeability and also improving the heat resistance can be achieved.

The organic particles may have an average particle diameter of 0.15 to 0.35 μm, and preferably 0.2 to 0.3 μm, and in the case of having a particle diameter within the range, a thin film coating layer having a uniform thickness may be formed to reduce the thickness of the separator, enabling appropriate porosity.

The organic particles may have an aspect ratio (aspect ratio) of 1 to 0.5 to 1, preferably 1 to 0.7 to 1.5, more preferably 1 to 0.8 to 1.2. When the aspect ratios of the second organic particles are within the ranges, the miscibility with the non-uniform inorganic particles is increased, and thus a thin film coating having a uniform thickness can be formed to reduce the thickness of the separator, and appropriate porosity and heat resistance characteristics can be provided.

The organic particles may be crosslinked polymers (cross-linked polymers), and the thermal decomposition temperature (thermal decomposition temperature) may be 300 ℃ or higher, specifically 300 ℃ to 500 ℃, and may include, as specific examples, acrylate crosslinked polymers and derivatives thereof, vinyl crosslinked polymers and derivatives thereof, diallyl phthalate crosslinked polymers and derivatives thereof, polyimide crosslinked polymers and derivatives thereof, polyurethane crosslinked polymers and derivatives thereof, copolymers thereof, or combinations thereof, but is not limited thereto, as long as it can be used as a filler in the art. For example, the organic particles may be crosslinked polystyrene particles, crosslinked polymethylmethacrylate particles.

The binder is preferably a polymer resin which has a melting temperature of 150 ℃ or higher than the melting temperature of the polymer base material or a glass transition temperature, is electrochemically stable, and is insoluble in a dielectric substance. Specific examples of the polymer resin may be selected from the group consisting of Polyphenylsulfone (Polyphenylsulfone), polysulfone (polysulfonone), polyimide (Polyimide), polyamideimide (Polyamideimide), polyaramide (Polyarylamide), polyarylate (Polyarylate), polycarbonate (Polycarbonate), polyvinylidene fluoride (Polyvinyldenefluoride), and copolymers thereof, but are not limited thereto.

The weight ratio of the binder and the organic particles in the second inorganic coating may be from 30. In the above range, the heat resistance is excellent, and the interface resistance is reduced by increasing the electrode adhesion force, so that the cell performance can be improved.

The content of the inorganic particles in the second inorganic coating layer may be 20 to 80wt%, and preferably, the content may be 40 to 60wt%. In the above range, the heat resistance is excellent, and the electrode adhesion force is increased to reduce the interface resistance, thereby improving the cell performance.

The thickness of the second inorganic coating layer may be 0.3 to 5.0 μm, preferably 0.3 to 4.0 μm, and may be more preferably 0.3 to 2.0 μm. In the case where the thickness of the coating layer satisfies the range, the separator including the same may provide improved electrode adhesion force and heat resistance and insulation. In particular, a coating layer of 1 μm or less may be formed on one side, so that it is possible to minimize not only the thickness of the entire separator but also the thickness of the electrode assembly, thereby enabling the capacity per unit volume of the battery to be maximized.

Further, by limiting the average particle size and the weight ratio of the organic particles and the inorganic particles to the above ranges, not only the electrode adhesion force of the coating layer but also the coagulation force to the substrate are improved, so that uniform coating and thinning of the coating layer can be achieved.

The first inorganic coating layer is a ceramic coating layer formed on the separator extension part of the present invention, contains an inorganic compound and a binder, and may be formed of a component different from that of the second inorganic coating layer, and preferably may be configured to improve heat resistance from the viewpoint of suppressing thermal shrinkage of the separator.

The ratio of the thickness of the second inorganic coating layer to the thickness of the first inorganic coating layer may be 1 to 1, 20, specifically 1 to 2 to 1, and more specifically 1 to 3 to 1.

As a non-limiting example, the composition forming the first inorganic coating layer may include a first form of a binder including components different from the binder forming the second inorganic coating layer, and a second form of a binder including a content ratio higher than that of the binder of the composition forming the second inorganic coating layer, that is, a concentration of the binder per unit volume of the first inorganic coating layer is higher than that of the binder per unit volume of the second inorganic coating layer.

More specifically, in the first embodiment of the composition for forming the first inorganic coating layer, the binder for forming the first inorganic coating layer may be any one or more selected from the group consisting of 1) a mixed binder including an inorganic composite sol and an organic polymer, 2) a mixed binder including an organic heat-resistant binder and an organic adhesive binder, and 3) an Interpenetrating Polymer Network (IPN) type binder.

The mixed binder will be specifically described below.

1) Mixed adhesive containing inorganic composite sol and organic polymer

The organic-inorganic composite sol can be prepared by adding yttrium salt after reacting alumina sol with epoxy silane. The epoxysilane refers to an epoxy resin containing a silane group that can form a covalent bond with the surface of the alumina sol to form a coating on the surface of the alumina sol. The alumina sol and the epoxy silane may be mixed and reacted in a weight ratio of 10 to 1.

And the organic polymerMay be polyvinyl alcohol (PVA), polyvinyl alcohol/maleic acid (PVA/MA), polyethylene glycol (PEG), or alkoxysilane-substituted derivatives of the organic polymer. The alkoxysilane-substituted derivative is obtained by substituting 0.1 to 5mol% of hydroxyl groups of the organic polymer with alkoxysilane to form a structure represented by x-L-Si (OR) ₃ Substituted with the substituent(s) of (1). L of the substituent can be substituted or unsubstituted C1-C6 alkylene (alkylene), and R can be C1-C3 alkyl or hydrogen.

The mixed binder of the organic composite sol and the organic polymer may be used in a weight ratio of 1.

2) Mixed adhesive of organic heat-resistant adhesive and organic adhesive

The organic heat-resistant adhesive is a first organic material having a glass transition temperature (Tg) of 130 to 200 ℃, and for example, one or more selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, carboxymethylcellulose, polyamide, polyacrylic acid, and poly N-vinylacetamide (PNVA), and the organic adhesive may be a polymer having a glass transition temperature of-40 ℃ or less, for example-80 ℃ to-40 ℃, for example-80 ℃ to-50 ℃, for example-80 ℃ to-65 ℃, and specifically, one or more selected from the group consisting of polymethyl methacrylate, polybutyl methacrylate, polyethyl methacrylate, and poly-2-ethylhexyl acrylate.

The mixed binder of the organic heat-resistant binder and the organic adhesive binder may be mixed in a weight ratio of 6. In the above range, the inorganic coating layer on the separator substrate is excellent in the coagulation force and the heat resistance characteristics are improved, which may be preferable.

3) Interpenetrating Polymer Network (IPN) type adhesives

The interpenetrating polymer network type adhesive may be an adhesive which does not have a melting point at 300 ℃ and is thermally decomposed at 300 ℃ or higher. Specifically, the interpenetrating polymer network type adhesive may have a thermal decomposition temperature of 300 ℃ or more, preferably 350 ℃ or more. Specifically, the temperature may be 300 to 500 ℃, preferably 350 to 500 ℃. When the thermal decomposition temperature is in the above range, the shrinkage of the separator base material is effectively suppressed, and short-circuiting between the electrodes is prevented, so that heat generation, ignition, explosion, or the like can be prevented, which is preferable. And the flexibility of the separator is prevented from being reduced, so that the effect of easily maintaining the form can be achieved.

The interpenetrating polymer network type adhesive may be manufactured by a method for manufacturing a substrate described in korean laid-open patent No. 2016-0079623, but is not limited thereto, and may be preferably a polymer network in which an acrylic resin is interpenetrating or a cellulose-based polymer is impregnated into an acrylic resin network. Specifically, the polymer network type adhesive with which the acrylic resin is interpenetrated may be an interpenetrating polymer network polymer including and prepared from any one or more acrylic monomers selected from acrylamide, acrylonitrile, N- (isobutoxymethyl) acrylamide, acrylic acid, methacrylic acid, sulfonic acid acrylate, N-benzyl acrylamide, methyl methacrylate, ethyl acrylate, hydroxyethyl acrylate, methyl acrylate, ethyl methacrylate, and the like, but is not limited thereto. And the polymer network type binder in which the cellulose-based polymer penetrates into the acrylic resin network may be a polymer network polymer or a semi-interpenetrating polymer network (semi-IPN) polymer in which carboxymethyl cellulose penetrates into a polymer network made of the acrylic monomer as described above.

In the second form of the composition for forming the above-mentioned first inorganic coating layer, the first inorganic coating layer may be in an amount of 10 to 70wt%, preferably 30 to 60wt%, and the binder may be in an amount of 30 to 90wt%, preferably 40 to 70wt%, with respect to 100wt% of the total amount of the coating layer. The second inorganic coating layer may be in an amount of 80wt% to 99.5wt% and the binder in an amount of 0.5wt% to 20wt%, with respect to 100wt% of the total amount of the coating layer. More specifically, the content of the binder contained in the first inorganic coating layer and the content of the binder contained in the second inorganic coating layer may be 1. That is, as shown in the above range, the content of the binder forming the first inorganic coating layer is preferably higher than the content of the binder forming the second inorganic coating layer, so that the adhesion of the inorganic compound to the separator is improved, and the heat resistance is improved, and thus the effect of effectively suppressing the heat shrinkage of the separator can be achieved.

Also, the inorganic compound forming the first inorganic coating layer may be the same as the above inorganic compound, and preferably, the inorganic particles may have a plate shape or a fiber shape. In this case, the aspect ratio (aspect ratio) of the inorganic particles may be from about 1.

In the flat surface of the plate-like inorganic particle, the length ratio of the major axis to the minor axis may be 1 to 3, preferably 1 to 2, and more preferably 1 to 1.1. The aspect ratio and the length ratio of the long axis to the short axis may represent values obtained by measuring the lengths of the long axis and the short axis after arbitrarily selecting 100 particles by a Scanning Electron Microscope (SEM) and averaging. The aspect ratio and the length range of the short axis relative to the long axis can suppress the contraction of the separator.

When the inorganic particles have a plate-like shape, the average angle of the flat plate surface of the inorganic particles with respect to one surface of the porous substrate may be 0 to 30 degrees, and preferably, the angle may converge to 0 degree. That is, one surface of the porous substrate and the flat surface of the inorganic particles may be parallel. For example, when the average angle of the flat surface of the inorganic particles with respect to one surface of the porous substrate is within the above range, thermal shrinkage of the porous substrate can be effectively prevented, and therefore a separator having a reduced shrinkage rate can be provided.

The electrode assembly according to one embodiment of the present invention may include a first form in which the first inorganic coating layer of the second extension portion of the separator is formed on one side of the separator opposite to the cathode or the anode, and a second form in which the first inorganic coating layer of the second extension portion of the separator is formed on both sides of the separator opposite to the anode and the cathode, wherein the thickness of the first inorganic coating layer may be 40 to 100% of the thickness of the cathode or the anode.

An embodiment of the present invention may provide a lithium ion secondary battery accommodating the electrode assembly and an electrolyte as described above. Here, the electrode assembly may have a form selected from a jelly-roll type (J/L) electrode assembly, a stack (stack) folding type (folding) electrode assembly that is rolled in one direction, a Z-stack & folding type electrode assembly that is rolled in a zigzag direction, and the like, but is not limited thereto.

The present invention will be described in more detail below based on examples and comparative examples. However, the examples and comparative examples are only examples for illustrating the present invention in more detail, and the present invention is not limited to the examples and comparative examples below.

The following physical properties were measured as follows.

1) Gas permeability

The gas permeability of the separator was in accordance with the JIS P8117 specification, and 100ml of air was recorded in seconds to pass through the separator 1inch ² The time required for the area of (a) was compared.

2) Heat resistance

The separators according to the examples and comparative examples were cut into pieces of TD + MD =100 mm + 100 mm, and marked at intervals of 20 mm in the width Direction (TD, transverse Direction)/Machine Direction (MD, machine Direction) by knonus (nonius). The membrane was sandwiched between teflon plates and held in a thermostatic bath at 150 ℃ for 60 minutes. After that, the separator was taken out, and the mark interval of each TD/MD was read by nonius, and the heat shrinkage was calculated by the following equation. The results of the obtained heat shrinkage evaluations are shown in Table 1 below.

Heat shrinkage (%) = ((20-interval after heating)/20) × 100

3) Thermal stability

After the electrode assembly manufactured in the example was fully charged to SOC (charging rate) 100%, the temperature and time at the time point of ignition were measured while increasing the temperature and shown in the graph.

Production example 1 production of an inorganic-organic composite separator having a second inorganic coating layer formed thereon

A second inorganic coating layer-forming composition was prepared by mixing 23 parts by weight of crosslinked polymethylmethacrylate (PMMA, nippon Shokubai) having an average particle diameter (D50) of 0.25 μm as organic particles, 65 parts by weight of boehmite (AlOOH, nabaltec) having an average particle diameter (D50) of 0.7 μm as inorganic particles, and 12 parts by weight of polystyrene. The slurry of the prepared coating layer forming composition was applied to both sides of a polyethylene-based porous substrate (SK innovation, ENPASS) having a Gurley permeability of 150 seconds/100 cc and a thickness of 9 μm at a speed of 10 m/min using a slot coating die (slot coating die), left to stand for 2 minutes, and then dried by passing through a dryer having a length of 6m discharging 60 ℃ hot air, thereby manufacturing a separator provided with a coating layer. The thickness of the coating was 2.0 μm on one side. Here, the time required for 100cc of air to pass through the polyethylene porous substrate was 172 seconds (sec).

Production example 2

A separator was prepared according to the above production example 1, except that a polyethylene-based porous substrate having a thickness of 11 μm (SK innovation, ENPASS) was used, and the thickness of the coating layer was 5.0 μm on one side.

[ example 1]

(formation of the first inorganic coating layer)

After adding 39g of a 5wt% acetic acid solution to 130g of 3-Glycidyloxypropyltrimethoxysilane (GPS) and stirring at room temperature for 1 hour, 377.2g of an alumina sol having a solid content of 10wt% was added while heating to 70 ℃ and heating was continued for 4 hours, and after adding 2.71g of a 5wt% acetic acid solution, 21.79g of methyltriethoxysilane was added dropwise and heating was continued for 4 hours. Adding Y (NO) at ambient temperature after the heated mixture is cooled ₃ ) _3.6 H ₂ O2.74 g and stirring to prepare an inorganic composite sol.

Boehmite (Dispal 10F-4, sasol, average particle size 40 nm) powder was slowly added to distilled water to be dispersed, and the prepared inorganic composite sol was added, and after stirring at room temperature for 60 minutes, PVA was added to prepare a first inorganic coating layer forming slurry.

The prepared slurry was respectively coated on 2/3 position portions at 1cm of end portions of both side surfaces in the length direction of the separator manufactured in manufacturing example 1, and then oven-dried at 90 ℃ for 30 minutes to further form a first inorganic coating layer having a thickness of 2 μm. The end portion is a portion not in contact with the electrode.

(production of cathode)

97wt% of graphite particles (C1 SR, japanese carbon) having an average particle size of 25 μm, 1.5wt% of styrene-butadiene rubber (SBR) binder (Zeon) and 1.5wt% of carboxymethyl cellulose (CMC, NIPPON A & L) were mixed, and then poured into distilled water and stirred for 60 minutes using a mechanical stirrer to prepare a cathode active material slurry. The slurry was coated on a copper current collector of 10 μm thickness using a doctor blade and dried at 100c for 0.5 hour in a hot air dryer, and then dried again at 120 c for 4 hours under vacuum and rolled (roll press) to manufacture a cathode plate.

(production of Anode)

Hybrid LiCoO ₂ 97wt%, 1.5wt% of carbon black powder as a conductive material, and 1.5wt% of polyvinylidene fluoride (PV dF, SOLVAY) were put in an N-methyl-2-pyrrolidone solvent, and then stirred for 30 minutes using a mechanical stirrer to prepare an anode active material slurry. The slurry was coated on an aluminum current collector of 20 μm thickness using a doctor blade and dried at 100c for 0.5 hour in a hot air dryer, and then dried again at 120 c for 4 hours under vacuum and rolled (roll press) to manufacture an anode plate.

(electrode Assembly)

An electrode assembly jelly roll was manufactured by disposing the separator formed with the first inorganic coating between the anode plate and the cathode plate manufactured as above and then winding. The jelly roll is inserted into a pouch and the pouch is vacuum sealed after injecting an electrolyte.

LiPF using 1.3M ₆ And an electrolyte dissolved in a 2/4/4 mixed solvent of Ethylene Carbonate (EC)/Ethyl Methyl Carbonate (EMC)/diethyl carbonate (DEC).

Applying 250kgf/cm to jelly roll inserted into bag ² While heat softening (thermo softening) at a temperature of 70 ℃ for 1 hour, while at the same time initially charging (pre-charging) to 70% of the SOC.

Thereafter, removing gas from the bag (evacuation),applying 200kgf/cm to the jelly roll ² The pressure was charged to 4.3V at a constant current at a rate of 0.2C at a temperature of 45C while maintaining the constant voltage at 4.3V until the current reached 0.05C. Thereafter, the cycle of discharging at a constant current of 0.2C until the discharge-time voltage reached 3.0V was repeated five times to perform the formation step.

[ example 2]

A first inorganic coating layer forming slurry was prepared using polyvinylpyrrolidone (PVP) as an organic heat-resistant binder and poly (2-ethylhexyl acrylate) as an organic adhesive binder in a weight ratio of 7.

The first inorganic coating layer was formed to have a thickness of 2 μm in the same manner as in example 1 except that the prepared slurry was used. After which the electrode assembly is manufactured and a formation step is performed.

[ example 3]

A composite adhesive composition was prepared by mixing a particulate polymer binder solution in which 12 parts by weight of an acrylic particulate polymer binder (Tg: -52 ℃ C., average particle diameter 380nm, 20wt% BM900B solids) was dispersed in 100 parts by weight of water, and an IPN-type binder (Td: 385 ℃, cross-linked permeability: 18.5, solids 14.1wt%, viscosity 1, 560cps) in which a network acrylic polymer and carboxymethyl cellulose were interpenetrated, which was prepared from a mixture of acrylic acid and methyl methacrylate monomers, was dispersed in 100 parts by weight of water, and then 100 parts by weight of boehmite (γ (Nabaltec, apyral AOH 60) having an average particle diameter of 500nm was added to 100 parts by weight of the composite adhesive composition, followed by stirring to prepare a uniform slurry.

Performed in the same manner as in example 1 except for using the prepared slurry, the thickness of the first inorganic coating layer was 2 μm. After which the electrode assembly is manufactured and subjected to a formation step.

[ example 4]

The first inorganic coating layer was formed to have a thickness of 2 μm, which was performed in the same manner as in example 1, except that the second inorganic coating layer-forming composition used in production example 1 was used. After which the electrode assembly is manufactured and a formation step is performed.

Comparative example 1

Using the separator manufactured in the manufacturing example 1 alone, electrodes were formed and an electrode assembly was manufactured in the same manner as in example 1, and then a formation step was performed.

Comparative example 2

Using the separator manufactured in the manufacturing example 2 alone, electrodes were formed and an electrode assembly was manufactured in the same manner as in example 1, and then a formation step was performed.

The gas permeability and the heat shrinkage rate of the separators manufactured in the examples and comparative example 1 were measured, as shown in table 1 below. Also, the thermal stability of the electrode assemblies manufactured in comparative examples 1 and 2 was measured, as shown in fig. 3.

[ TABLE 1]

As shown in table 1 above, it was confirmed that the separators manufactured in examples 1 to 4 had a gas permeability of 250 seconds/100 cc or more and a heat shrinkage rate of less than 1%, and the heat shrinkage rate was low at 300 ℃, and thus the form of the membrane was maintained, whereas comparative example 1 had a gas permeability of 100 seconds/100 cc, performance decreased by two times or more, and a heat shrinkage rate of 10% was high, and thus the form of the film was not maintained. As shown in fig. 3, it was confirmed that the thickness of the separator as the porous base material and the thickness of the second inorganic coating layer formed on the separator were increased, and therefore, the thermal stability was excellent, and thus it was confirmed that the example could realize excellent thermal stability without increasing the thicknesses of the separator and the second inorganic coating layer as in comparative example 2, and particularly, had more excellent gas permeability with a thin overall thickness. In particular, it was confirmed that the electrode assemblies of examples 1 to 4 of the present invention were ignited at a higher temperature than the ignition temperature of the electrode assembly manufactured in comparative example 2, specifically, at a temperature of 200 ℃.

That is, it can be confirmed that the electrode assembly according to the present invention not only suppresses thermal shrinkage, but also suppresses short-circuiting of the electrodes due to contraction of the separator because the first inorganic coating layer of the second extension portion is caught by the electrodes even if it contracts, thereby suppressing occurrence of fire. Further, since the first inorganic coating layer is formed on the extension portion of the separator, the gas permeability of the separator itself is not reduced, and therefore, the lithium ion secondary battery having improved heat resistance and battery performance can be provided as compared with the conventional one.

Therefore, the spirit of the present invention should not be limited to the above-described embodiments, and the scope of the appended claims and all equivalents or equivalent variations thereof should be construed to include the scope of the spirit of the present invention.

Claims

1. An electrode assembly comprising an anode, a cathode, and a separator between the anode and the cathode, characterized in that:

one or more sides of the separator in the longitudinal direction have a separator extension portion extending further than one side of the anode and the cathode in the longitudinal direction,

the diaphragm extension portion includes a first extension portion having substantially the same thickness as the diaphragm, and a second extension portion having a first inorganic coating layer formed on one or both sides thereof and thicker than the thickness of the diaphragm.

2. The electrode assembly of claim 1, wherein:

the length of the second extension part along the length direction is larger than that of the first extension part.

3. The electrode assembly of claim 1, wherein:

the separator is a composite porous separator having a second inorganic coating layer on one or both surfaces thereof.

4. The electrode assembly of claim 3, wherein:

the first inorganic coating layer is formed on the second inorganic coating layer.

5. The electrode assembly of claim 3, wherein:

the composition of the inorganic compound of the first inorganic coating layer is different from the composition of the inorganic compound of the second inorganic coating layer.

6. The electrode assembly of claim 3, wherein:

the first inorganic coating layer has a higher concentration of binder per unit volume than the second inorganic coating layer.

7. The electrode assembly of claim 3, wherein:

the inorganic compound of the first inorganic coating layer includes fibrous or plate-like inorganic particles having an aspect ratio of 1.

8. The electrode assembly of claim 3, wherein:

the second inorganic coating layer also includes an inorganic compound, organic particles, and a binder.

9. The electrode assembly of claim 3, wherein:

the first inorganic coating layer of the second extension of the separator is formed on a side of the separator opposite to the cathode,

the first inorganic coating layer has a thickness of 40 to 100% of the thickness of the cathode.

10. The electrode assembly of claim 1, wherein:

the permeability of the separator is 250 seconds/100 cc or more, and the heat shrinkage rate at 150 ℃ is less than 1%.

11. A lithium ion secondary battery, characterized in that:

comprising an electrode assembly according to any of claims 1 to 10.