KR20160120509A - Stacked and folded type electrode assembly with improved safety and Lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a stack-folding type electrode assembly having enhanced safety, and to a lithium secondary battery comprising the same. A folding separator and a unit cell separator comprise a porous coating layer prepared by including a mixture of inorganic particles and a binder polymer. The porous coating layer, in one separator of the folding separator and the unit cell separator, uses an organic-based binder polymer as a binder polymer, and, in the porous coating layer of the other separator, uses a water-based binder polymer. Thus, safety during nail penetration, a volumetric decrease of an electrode assembly, and eco-friendly effects are secured.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a stack-folding type electrode assembly and a lithium secondary battery including the same,

The present invention relates to a stack-folding type electrode assembly having improved safety and a lithium secondary battery including the same. More particularly, the present invention relates to a stack-folding type electrode assembly having improved safety, Folded electrode assembly and a lithium secondary battery including the same.

Recently, interest in energy storage technology is increasing. As cell phones, camcorders, notebook PCs, and even electric vehicles' energy are being expanded, efforts are being made to research and develop batteries. BACKGROUND ART Electrochemical devices have been attracting the most attention in this respect. Especially in recent years, with the trend toward miniaturization and light weight of electronic devices, the development of secondary batteries as a battery which can be charged and discharged with small size and high capacity has become a focus of attention.

Also, the secondary battery is classified according to the structure of the electrode assembly having the positive electrode / separator / negative electrode structure. Typically, the positive electrode, the separator, and the negative electrode have a structure in which long- A roll (wound type) electrode assembly, and stacked (stacked) electrode assemblies formed by sequentially stacking a plurality of positive electrodes and negative electrode units cut out in units of a predetermined size, and unit cells formed with a separator interposed therebetween.

However, such conventional electrode assemblies have some problems.

First, since the jelly-roll electrode assembly is formed into a cylindrical or elliptical structure by winding a long sheet-like anode and cathode in a densified state, the stress caused by the expansion and contraction of the electrode during charging and discharging is accumulated in the electrode assembly When such a stress accumulation exceeds a certain limit, deformation of the electrode assembly occurs. As a result of the deformation of the electrode assembly, the spacing between the electrodes becomes uneven, resulting in a sudden drop in the performance of the battery and a risk of the safety of the battery being damaged due to an internal short circuit. In addition, since the long sheet-like positive electrode and negative electrode must be wound up, it is difficult to rapidly wind up while keeping the distance between the positive electrode and the negative electrode constant, and the productivity is lowered.

Secondly, since the stacked electrode assembly requires a lot of time and effort to sequentially stack a plurality of unit cells, the stacked electrode assembly has a problem of low productivity.

In order to solve such a problem, an electrode assembly having an advanced structure of the jelly-roll type and the stack type mixed type is used. The electrode assembly includes a bi-cell or a pull cell Stacked electrode assemblies having a structure in which full cells are wound by using a separator for folding sheets of a long length has been developed and disclosed in Korean Patent Application Laid-Open Nos. 2001-0082058A, 2001-0082059, 2001-0082060 and the like.

1 to 3 are sectional views schematically showing the structure of a stack-folding type electrode assembly. In the drawings, the same reference numerals denote the same members.

1 to 3, the electrode assembly includes cathodes 1a, 1b and 1c and positive electrodes 5a, 5b and 5c located on both sides of the separators 3a, 3b and 3c and the separators 3a, 3b and 3c, It includes a plurality of unit cell _{(7a, 7b, 7c 1,} 7c 2) respectively provided. The positive electrodes 5a, 5b and 5c have a structure in which a positive electrode active material layer is formed on both surfaces of a positive electrode collector and negative electrodes 1a, 1b and 1c have a structure in which a negative electrode active material layer is formed on both surfaces of the negative electrode collector. As shown in Figs. 1 to 3, the unit cells may have the structure of one of the pull cells 7a and 7b in which one anode 5a and one anode 5b are located on both sides of the separators 3a and 3b, The separator 3c is positioned on both sides of the cathode 5c or the cathode 1c and the structure of the bielses 7c ₁ and 7c _{2 in} which the cathode 1c or the anode 5c is respectively disposed on the respective separators 3c A structure of anode / separator / cathode / separator / anode, or a structure of cathode / separator / anode / separator / cathode). Hereinafter, a separator interposed between an anode and a cathode in a unit cell is referred to as a " unit cell separator ".

In the electrode assembly 10, 20, 30, each of the unit cells 7a, 7b, 7c ₁ , 7c ₂ exists in a laminated form. At this time, each of the unit cells adjacent to correspond to each other _{(7a, 7b, 7c 1,} 7c 2) to include a, a series of single batch so as to surround each of the unit cells _{(7a, 7b, 7c 1,} 7c 2) between of folding the separator (9a, 9b, 9c) for being interposed in a variety of forms as shown in Figures 1 to 3 performs the separator function between each unit cell _{(7a, 7b, 7c 1,} 7c 2).

The separator for a unit cell and the folding separator may have a structure in which a porous coating layer is formed on at least one surface of a porous polymer substrate by coating or applying a slurry containing a mixture of inorganic particles and a binder polymer on at least one surface of the porous polymer substrate to improve heat resistance It is also manufactured. The stack-folding type electrode assembly formed from such a separator exhibits excellent safety in evaluation items such as heat resistance and nail penetration, and has a structure in which a porous coating layer is further formed on the porous polymer base material. Therefore, There is a tendency that it can not meet the current tendency to pursue miniaturization or thinning of the battery. In addition, since the process involves dispersing the binder polymer in an organic solvent at the time of preparing the slurry, it is expensive and environmentally unfavorable.

Accordingly, it is an object of the present invention to provide a stack-folding type electrode assembly having a small volume and improved safety.

Another problem to be solved by the present invention is to provide a method of manufacturing a stack-folding type electrode assembly at a lower cost by a more environmentally friendly method.

In order to solve the above-mentioned technical problem, in one aspect of the present invention, a plurality of unit cells including a positive electrode, a negative electrode, and a separator for a unit cell interposed between the positive electrode and the negative electrode are stacked (stacked) A stack-folding type electrode assembly in which an aqueous binder polymer is used for one of the separator for a unit cell and a separator for folding, and an organic binder polymer is used for another separator, is used as the electrode assembly having a structure in which a continuous folding separator is interposed / RTI >

Wherein the separator for a unit cell comprises: a porous polymer base; And a porous coating layer formed on at least one surface of the porous polymer substrate and including a mixture of inorganic particles and organic binder polymer, wherein the folding separator comprises a porous polymer substrate; And an aqueous binder polymer layer formed on at least one surface of the porous polymer base material.

Alternatively, the separator for a unit cell comprises a porous polymer substrate; And an aqueous binder polymer layer formed on at least one surface of the porous polymer base material, wherein the folding separator comprises a porous polymer base material; And a porous coating layer formed on at least one surface of the porous polymer substrate and including a mixture of inorganic particles and organic binder polymer.

Between the porous polymer base material and the aqueous binder polymer layer, a porous coating layer comprising a mixture of an aqueous binder polymer and inorganic particles may be further formed.

The aqueous binder polymer may be a binder polymer dispersible in water, and the organic binder polymer may be a binder polymer dispersible or soluble in an organic solvent.

The aqueous binder polymer may be one or a mixture of two or more selected from the group consisting of styrene-butadiene rubber, carboxymethyl cellulose, acrylate-based polymer, and polyvinylidene fluoride-based copolymer.

The organic binder polymer may include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, Polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyvinyl alcohol, ethylene-vinyl acetate copolymer (polyethylene-co) polyvinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullate, Cyanoethylpullulan, Furnace can be a polyvinyl alcohol-acetate (cyanoethylpolyvinylalcohol), cyanoethyl cellulose (cyanoethylcellulose), cyanoethyl sucrose (cyanoethylsucrose) and pullulan alone or in combination of two or more thereof selected from the group consisting of (pullulan).

The porous coating layer containing the water-based binder polymer may have a thickness of 2 to 20 mu m.

The porous coating layer containing the organic binder polymer may have a thickness of 4 to 20 mu m.

The inorganic particles may be inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transporting ability, or a mixture thereof.

The porous coating layer is attached to the inorganic particles by a binder polymer so that the inorganic particles can be held together. The inorganic particles are packed in contact with each other to form an interstitial An interstitial volume may be formed, and pores may be formed in the porous coating layer by the interstitial volume.

According to another aspect of the present invention, there is provided a lithium secondary battery including the above stack-folding type electrode assembly.

In the stack-folding type electrode assembly according to an embodiment of the present invention, the organic binder polymer is used as the binder polymer in one of the folding separator and the separator for the unit cell, and the aqueous binder polymer is used in the other separator, The volume reduction of the electrode assembly and the eco-friendly effect can be ensured.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, serve to further the understanding of the technical idea of the invention, It should not be interpreted.
1 is a schematic cross-sectional view of one embodiment of a stack-folded electrode assembly.
Figure 2 is a schematic cross-sectional view of another embodiment of a stack-folding electrode assembly
3 is a schematic cross-sectional view of another embodiment of a stack-folded electrode assembly.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the constitutions described in the drawings are merely the most preferred embodiments, and not all of the technical ideas of the present invention are described. Therefore, various equivalents which can be substituted at the time of the present application It should be understood that variations can be made.

In the present invention, a plurality of unit cells including a positive electrode, a negative electrode, and a separator for a unit cell interposed between the positive electrode and the negative electrode are stacked (stacked), and a continuous folding separator is interposed in each of the overlapping portions. A stack-folding type electrode assembly in which an aqueous binder polymer is used as a binder polymer in one of the separator for a unit cell and a separator for folding, and an organic binder polymer is used as a binder polymer in another separator.

More specifically, in one aspect of the present invention, a plurality of unit cells including a positive electrode, a negative electrode, and a separator for a unit cell interposed between the positive electrode and the negative electrode are stacked (stacked) An electrode assembly having a separator interposed therebetween, wherein the separator for a unit cell comprises: a porous polymer base; And a porous coating layer formed on at least one surface of the porous polymer substrate and including a mixture of inorganic particles and organic binder polymer, wherein the folding separator comprises a porous polymer substrate; And an aqueous binder polymer layer formed on at least one surface of the porous polymer substrate.

In another embodiment of the present invention, a plurality of unit cells including a positive electrode, a negative electrode, and a separator for a unit cell interposed between an anode and a cathode are stacked (stacked), and a continuous folding separator is interposed in each of the overlapping portions Wherein the separator for a unit cell comprises: a porous polymer substrate; And an aqueous binder polymer layer formed on at least one surface of the porous polymer base material, wherein the folding separator comprises a porous polymer base material; And a porous coating layer formed on at least one surface of the porous polymer substrate and including a mixture of inorganic particles and organic binder polymer.

The porous coating layer may further include a mixture of an aqueous binder polymer and inorganic particles between the porous polymer substrate and the aqueous binder polymer layer.

As used herein, the term 'separator for unit cell' is understood to mean a separator interposed between an anode and a cathode in order to prevent an anode and a cathode from coming into contact with each other to prevent internal short-circuiting.

The term 'folding separator' in the present specification means a separator for wrapping the stacked unit cells so that the electrode assembly has improved stability. In this case, when the folding separator surrounds the unit cell, Non-limiting examples are shown in Figures 1-3, but are not limited thereto. The fixing of the folding separator to the electrode assembly can be accomplished using a tape at the longitudinal end. In addition to finishing with tape, thermal fusion can also be used to finish the ends. That is, the heat-welding machine or the heat plate or the like may be brought into contact with the folding separator for finishing so that the folding separator itself is melted and fixed by heat.

The unit cell that can be used in the present invention is not particularly limited and may be a full cell or a bicell as a non-limiting example. The number of stacked pull cells or bixes is determined by the desired capacity of the final cell.

Herein, the term "full cell" means that the electrodes at both ends, such as a separator / cathode for an anode / a unit cell, a separator / a cathode / a separator for a unit cell, a separator / Means an electrode assembly laminated to form a cathode.

The term "bicell" as used herein refers to an electrode assembly in which electrodes at both ends are formed so as to form the same electrode. The electrode assembly includes a separator / negative electrode / separator for unit cell / And a positive electrode bi-cell composed of a negative electrode / separator for unit cell / positive electrode / separator for unit cell / negative electrode.

The porous polymer base material usable in each of the separator for a unit cell and the folding separator may be a porous polymer base material having a plurality of pores so as to have a desired porosity and air permeability. However, when the temperature rises above a certain range due to an external factor or an internal factor such as a short circuit, the inside of the pores forming the membrane is melted and collapsed to block the passage of the membrane. (Shutdown) to prevent further temperature rise of the battery.

The porous polymer base material of each of the separator for a unit cell and the porous separator for a folding separator may be at least one of polyolefin, Sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, but the present invention is not limited thereto.

The porous substrate of each of the separator for a unit cell and the porous separator for a folding separator may have a thickness different from each other, and may preferably have a thickness of 1 to 100 μm or 3 to 30 μm. Further, it may have pores having a diameter of 0.01 to 10 탆.

Depending on the required function, the porous polymer substrate may be composed of a layer structure of the above polymers such as polypropylene / polyethylene / polypropylene.

Herein, the 'porous coating layer' may be formed on at least one surface of the porous polymer substrate, and the inorganic particles are attached to each other by a binder polymer so that the inorganic particles can be maintained in a state of being bonded to each other, Means an interstitial volume formed between the inorganic particles over the entire porous coating layer and a pore formed on the entire porous coating layer by the interstitial volume. do. The separator having such a porous coating layer is excellent in heat resistance and can have improved safety.

The term 'binder polymer layer' as used herein is understood to mean a layer formed on at least one surface of the porous polymer substrate or formed on the surface of the porous coating layer and substantially composed of a binder polymer.

In the present specification, the term 'aqueous binder polymer' is understood to mean a binder polymer dispersible in water. Nonlimiting examples of such an aqueous binder polymer include, but are not limited to, styrene-butadiene rubber, carboxymethyl cellulose, acrylate-based polymer, and polyvinylidene fluoride-based copolymer.

Non-limiting examples of the acrylate-based polymer include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, (meth) acrylate, 2-ethylbutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate and tetradecyl And may be a polymer containing at least one kind of polymer.

Non-limiting examples of the polyvinylidene fluoride-based copolymer include polyvinylidene fluoride, polyvinylidene fluoride-chlorotrifluoroethylene, polyvinylidene fluoride-hexafluoropropylene or polyvinylidene fluoride- Trichlorethylene, and the like, but are not limited thereto.

The term "organic binder polymer" as used herein refers to an organic binder polymer as used in the present invention, such as acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, Refers to a binder polymer that can be dissolved or dispersed in an organic solvent such as N-methyl-2-pyrrolidone (NMP) or cyclohexane. Non-limiting examples of such organic binder polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, But are not limited to, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyvinyl alcohol, ethylene vinyl acetate, Polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, , Cyanoethylpull (Cyanoethylpullulan), cyanoethyl polyvinyl alcohol (cyanoethylpolyvinylalcohol), cyanoethyl cellulose (cyanoethylcellulose), cyanoethyl sucrose (cyanoethylsucrose), pullulan (pullulan), but the like, and the like.

Some of the binder polymers may be dispersed in water and used as an aqueous binder polymer, while they may be dissolved in an organic solvent and used as an organic binder polymer. In this case, even when the same binder polymer is dispersed in water and used as an aqueous dispersion, the binder polymer has a particle form, whereas in an organic solvent it is dissolved or swollen and used in a dispersed form.

Also, the organic binder polymer is used together with the inorganic particles to form a porous coating layer of the separator. The porous coating layer must satisfy both of the requirements for securing the adhesion with the electrode and minimizing the electrical resistance due to the binder polymer. The porous coating layer prepared to satisfy both is formed to have a relatively thick thickness. On the other hand, the aqueous binder polymer is dispersed in water and exists in the form of particles, so that it can be formed separately as a separator electrode adhesive layer. Accordingly, in the porous coating layer, the binder polymer is used in a minimum amount necessary for binding inorganic particles, and an electrode bonding layer substantially formed of an aqueous binder polymer on at least one surface of the porous coating layer or the porous polymer substrate is further formed . The separator manufactured using the aqueous binder polymer may be made thinner, for example, about a half of the thickness of the separator manufactured using the organic binder polymer in the porous coating layer. That is, a porous coating layer using an organic binder polymer can be produced to a thickness of at least 4 μm, whereas a porous coating layer using an aqueous binder polymer can be formed to a thickness of about 2 to 3 μm or about 2 μm.

On the other hand, when the entire cell is manufactured using only the water-based binder polymer, there is a great advantage in reducing the thickness of the cell and reducing the resistance. However, since a small amount of the binder polymer is used and the porous coating layer is also formed thin, It is disadvantageous in that the shut down effect is weakened because the amount of the binder to help the shut down function is small when heat is generated after penetration. On the other hand, according to one aspect of the present invention, compared with the mode in which a battery cell is manufactured using only an organic binder polymer, a cell thickness / cell resistance is reduced and a battery cell is manufactured using only an aqueous binder polymer. A stack-folding type electrode assembly having improved safety such as penetration can be provided.

The thickness of the porous coating layer may vary depending on the inorganic particles used, the binder polymer and the coating method, and the porous coating layer in which the aqueous binder polymer is used may have a thickness of 1 to 20 占 퐉 or 2 to 20 占 퐉 or 2 to 3 占 퐉 , And the porous coating layer in which the organic binder polymer is used may have a thickness of 4 to 20 탆. In this case, the lower limit of the thickness of the porous coating layer including the water-based binder polymer and the organic binder polymer is important. Each of the separator for unit cell and the folding separator is not used only once in the electrode assembly, The difference in thickness causes a larger thickness difference in the electrode assembly dimension, and in this respect, the difference in thickness of the lower limit value is significant because it is interposed between the cathodes and surrounds all of the unit cell overlapping portions. The porous coating layer including the water-based binder polymer under the same conditions may be formed, for example, as a thin film having a thickness of 2 탆, whereas the porous coating layer including the organic binder polymer requires a certain thickness for securing the electrode adhesion, It may be difficult to form a layer having a thickness of 4 탆 or less. Such securing of the electrode adhesion is particularly important in the case of a large-sized battery cell for an automobile, so that when a separator using an organic-based binder polymer is used for a large-sized battery cell, it becomes difficult to manufacture a thin-film battery cell.

In addition, since water-based binder polymer uses water as a solvent, it is eco-friendly and has a relatively low process ratio.

In the present invention, the determination as to which of the separator for a unit cell and the folding separator to employ an organic binder polymer (or an aqueous binder polymer) can be made, for example, in consideration of the following: (Length) of the separator for folding, the water-based binder polymer is used as a separator for a unit cell in the case where a battery cell requires an electrode assembly of a 'thin film' preference in a higher priority, In the case of 'improved safety', an organic binder polymer may be employed for the separator for a unit cell.

The inorganic particles used in the porous coating layer are not particularly limited as long as they are electrochemically stable. That is, 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 electrochemical device (for example, 0 to 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having ion transfer ability are used, the ion conductivity in the electrochemical device can be increased to improve the performance. When inorganic particles having a high dielectric constant are used as the inorganic particles, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte is also increased, and ion conductivity of the electrolyte can be improved. For the reasons stated above, it is preferable that the inorganic particles include high-permittivity inorganic particles having a dielectric constant of 5 or more, preferably 10 or more, inorganic particles having lithium ion transferring ability, or a mixture thereof.

The dielectric constant of about 5 or more inorganic _{particles, BaTiO 3, Pb (Zr x} , Ti 1 -x) O 3 (PZT, 0 <x <1), Pb 1 - x LaxZr 1 -y Ti y O 3 (PLZT , 0 <x <1, 0 <y <1), (1-x) Pb (Mg 1/3 Nb 2/3) O 3 -x PbTiO 3 (PMN-PT, 0 <x <1), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC and TiO ₂ . And mixtures of two or more thereof.

The inorganic particles having lithium ion transferring ability include, but are not limited to, lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x < lithium aluminum titanium phosphate _{(Li x Al y Ti z (} PO 4) 3, 0 <x <2, 0 <y <1, 0 <z <3) (LiAlTiP) x O y series glass (glass), (0 < x <4, 0 <y < 13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2,0 <y <3), lithium germanium thiophosphate Mani Titanium (Li _x Ge _y P _z S _{w, 0 <x <4,} 0 <y <1, 0 <z <1, 0 <w <5), lithium nitrides _{(Li x N y, 0 <} x <4, 0 <y <2), SiS _{2 (Li x Si y S z} , 0 <x <3,0 <y <2,0 <z <4) based glass, and _{P 2 S 5 (Li x P} y S z, 0 <x <3, 0 < y <3, 0 <z <7) series glass, or a mixture of two or more thereof.

The average particle size of the inorganic particles is not particularly limited, but may range from about 0.001 탆 to about 10 탆 for the formation of a porous coating layer of uniform thickness and proper porosity. When the average particle diameter of the inorganic particles satisfies the above range, the dispersibility of the inorganic particles can be prevented from lowering, and a porous coating layer having an appropriate thickness can be formed.

In the porous coating layer, the inorganic particles to binder polymer may be used in a weight ratio of 10:90 to 99: 1.

A method of manufacturing a separator for a unit cell or a separator for folding comprising an organic binder polymer includes the steps of providing a porous polymer substrate (S1), preparing a slurry (S2) for forming a porous coating layer, and coating the slurry ).

(S1), a porous polymer substrate having a plurality of pores as a separator substrate is provided. A description of such a porous polymer substrate is as described above.

In step (S2), a slurry for forming a porous coating layer is prepared. At this time, after the organic binder polymer is dissolved or dispersed in an organic solvent, the inorganic particles are mixed and dispersed to obtain a slurry for forming the porous coating layer. 0.5 to 20 parts by weight of an organic binder polymer and 5 to 50 parts by weight of an inorganic particle are used based on 100 parts by weight of the organic solvent. In addition to the inorganic particles and the organic binder polymer, the slurry may further include conventional additives known in the art. The inorganic particles, the organic binder polymer, and the solvent are as described above. In addition, the solvent is preferably a solvent having a similar solubility index to the binder to be used and a low boiling point. This is because the mixing and dissolution can be made uniform, and then the solvent can be easily removed by drying.

In step (S3), the slurry formed in step (S2) is coated on at least one surface of the porous polymer substrate provided in step (S1). The coating method is not particularly limited, and for example, an offset coating method, a hard roll-gravure coating method or a roll-plate coating method may be used. The offset coating method may be a reverse offset coating method, a gravure offset coating method, a plate-plate offset coating method, or the like. The solvent is then removed from the slurry layer. For example, solvent removal is possible by batchwise or continuous drying using an oven or a heated chamber or the like at a temperature range that takes into account the vapor pressure of the solvent used.

The method for producing a separator for a unit cell or a separator for folding comprising a water-based binder polymer layer according to another aspect of the present invention comprises the steps of: (S1) providing a porous polymer base material; And then coating the aqueous polymer binder dispersion on at least one side of the porous polymer base material. In this case, the water-based binder polymer may be used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of water. In addition, the above-mentioned contents are referred to for the porous polymer base material, the kind of the aqueous binder polymer and coating method.

A method of manufacturing a separator for a unit cell or a separator for folding comprising a porous coating layer comprising an aqueous binder polymer according to another embodiment of the present invention comprises the steps of providing a porous polymer substrate (S1), dispersing the aqueous binder polymer in water, (S3) of coating the slurry on at least one surface of the porous polymer base material (S3), and dispersing the aqueous binder polymer in water to prepare a slurry for preparing an aqueous binder polymer dispersion And then coating the surface of the porous coating layer after the preparation. Here, the above-mentioned contents are referred to for the porous polymer substrate, the kind of the aqueous binder polymer, the kind of the inorganic particle, and the coating method. However, when preparing the slurry for forming the porous coating layer, 10 parts by weight and inorganic particles 5 to 50 parts by weight are used.

The anode of the unit cell constituting the electrode assembly according to an embodiment of the present invention is manufactured, for example, by applying a mixture of a cathode active material, a conductive agent and a binder on a cathode current collector, and drying the mixture, , A filler may be further added to the mixture.

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; A lithium manganese oxide (LiMnO ₂ ) such as LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, etc. represented by the formula Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33); Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Nickel type lithium nickel oxide represented 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) oxide); 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 part of the lithium in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) _3, or a composite oxide formed of a combination of these materials, and the like, and are not limited thereto.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with 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 conductive agent is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive agent is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite and 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 oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in binding of the active material and the conductive agent and bonding to the current collector, and is usually added in an amount of 1 to 50% by weight 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 terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing 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, and examples thereof 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 the negative electrode collector and drying the same, and if necessary, the above-described components may further be included.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an 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.

The negative electrode material may be, for example, carbon such as non-graphitized carbon or 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 and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The electrochemical device of the present invention is preferably a lithium secondary battery in which a lithium salt-containing nonaqueous electrolyte is contained in the electrode structure.

The lithium salt-containing non-aqueous electrolyte is composed of a nonaqueous electrolyte and lithium. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, But are not limited to, lactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, Nitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives , Tetrahydrofuran derivatives, ether, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving charge / discharge characteristics, flame retardancy, etc., non-aqueous electrolytes may be used in the form of, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like are added It is possible. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

Claims (13)

A plurality of unit cells including a positive electrode, a negative electrode, and a separator for a unit cell interposed between the positive electrode and the negative electrode are overlapped (stacked), and a continuous folding separator is interposed in each of the overlapping portions,
An aqueous binder polymer is used for one of the separator for a unit cell and a folding separator, and an organic binder polymer is used for another separator
Stack-folding electrode assembly.
The method according to claim 1,
Wherein the separator for a unit cell comprises: a porous polymer base; And a porous coating layer formed on at least one surface of the porous polymer substrate and including a mixture of inorganic particles and organic binder polymer,
Wherein the folding separator comprises a porous polymer substrate; And an aqueous binder polymer layer formed on at least one surface of the porous polymer substrate.
The method according to claim 1,
Wherein the separator for a unit cell comprises: a porous polymer base; And an aqueous binder polymer layer formed on at least one surface of the porous polymer base material,
Wherein the folding separator comprises a porous polymer substrate; And a porous coating layer formed on at least one surface of the porous polymer substrate and including a mixture of inorganic particles and organic binder polymer.
The method according to claim 2 or 3,
Wherein a porous coating layer including a mixture of an aqueous binder polymer and inorganic particles is further formed between the porous polymer substrate and the aqueous binder polymer layer.
4. The method according to any one of claims 1 to 3,
Wherein the aqueous binder polymer is a binder polymer dispersible in water.
4. The method according to any one of claims 1 to 3,
Wherein the organic binder polymer is a binder polymer capable of being dispersed or dissolved in an organic solvent.
4. The method according to any one of claims 1 to 3,
Wherein the aqueous binder polymer is one or a mixture of two or more selected from the group consisting of styrene-butadiene rubber, carboxymethyl cellulose, acrylate-based polymer and polyvinylidene fluoride-based copolymer. .
4. The method according to any one of claims 1 to 3,
Wherein the organic binder polymer is selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, Polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyvinyl alchol, ethylene-vinyl acetate copolymer (polyethylene-co polyvinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullate, Cyanoethylpullulan, Wherein the mixture is one or a mixture of two or more selected from the group consisting of cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose and pullulan. Type electrode assembly.
The method according to claim 2 or 3,
Wherein the porous coating layer comprising the water-based binder polymer has a thickness of 1 to 20 占 퐉.
The method according to claim 2 or 3,
Wherein the porous coating layer comprising the organic binder polymer has a thickness of 4 to 20 占 퐉.
The method according to claim 2 or 3,
Wherein the inorganic particles are inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transferring ability, or mixtures thereof.
The method according to claim 2 or 3,
The porous coating layer is attached to the inorganic particles by a binder polymer so that the inorganic particles can be held together. The inorganic particles are packed in contact with each other to form an interstitial Wherein the interstitial volume forms an interstitial volume and pores are formed throughout the porous coating layer by the interstitial volume.
A lithium secondary battery comprising the stack-folding type electrode assembly according to any one of claims 1 to 3.

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