KR20160015769A - A stack/folding type electrode assembly with safety improvement and a electrochemical cell comprising the same - Google Patents

Abstract

The present invention relates to a stack/folding type electrode assembly with improved safety and battery performance, and an electrochemical cell comprising the same and, more specifically, to an electrode assembly and an electrochemical cell comprising the same, wherein the electrode assembly comprises a separator included in an unit electrode assembly and an outer separator covering the unit electrode assembly which have different properties. In particular, the separator included in an unit electrode assembly has improved heat resistance of a battery and electrolyte wettability by being formed into a non-woven fabric web comprising a heat-resistant polymer resin. The outer separator has an effect of preventing a short circuit which is spread to entire cells in the case of generating the short circuit of an inner separator.

Description

[0001] The present invention relates to a stack / folding type electrode assembly having improved safety and battery performance, and an electrochemical cell including the stack / folding type electrode assembly,

The present invention relates to a stack / folding type electrode assembly having improved safety and an electrochemical cell including the same. More particularly, the separator interposed in a unit cell includes a nonwoven web, and a separator interposed between the unit cells includes a porous film The present invention relates to an electrochemical cell.

Due to the development of technology and demand for mobile devices, the demand for secondary batteries is also rapidly increasing. Of these, lithium secondary batteries, which have high energy density and high operating voltage and excellent storage and life characteristics, Is widely used as an energy source.

Generally, a secondary battery includes a unit cell composed of a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, or is embedded in a battery case of a metal can or a laminate sheet in a state of being wound using a separator, .

One of the major research tasks in such secondary batteries is to improve safety. For example, a secondary battery can have a high temperature and / or high temperature inside the battery that can be caused by an abnormal operating condition of the battery, such as an internal short circuit, an overcharged condition exceeding an allowable current and voltage, exposure to a high temperature, The explosion of the battery may be caused by high pressure.

As one of the problems of safety, an internal short circuit due to shrinkage or breakage of the separator caused when the battery is exposed to high temperature may cause very serious consequences. Generally, a porous polymer film such as polyethylene or polypropylene is used as a separator. Such a separator is advantageous in that it is inexpensive and excellent in chemical resistance and is suitable for operation of a battery, but is liable to shrink in a high temperature environment. Therefore, in order to overcome the thermal instability of the separator in the secondary battery, a nonwoven fabric separator having a small heat shrinkage ratio may be used. However, the separator of the nonwoven fabric type has poor mechanical properties such as tensile stress and causes many problems in manufacturing the electrode assembly.

The secondary battery is classified into a cylindrical battery, a prismatic battery, and a pouch-shaped battery according to the external and internal structural characteristics. Among them, the secondary battery can be stacked with a high degree of integration and the prismatic battery and the pouch- Especially noteworthy.

The electrode assembly of the anode / separator / cathode structure constituting the secondary battery is largely classified into a jelly-roll type (winding type) and a stack type (laminate type) depending on its structure. In the jelly-roll type electrode assembly, an electrode active material or the like is coated on a metal foil used as a current collector, dried and pressed, cut in a band shape having a desired width and length, dielectrically divided into a negative electrode and a positive electrode using a separator, . Although such a jelly-roll type electrode assembly can be preferably used for a cylindrical battery, when applied to a rectangular or pouch type battery, the electrode active material is concentrated locally and the electrode active material is peeled off or repeatedly shrunk and expanded, And the like. On the other hand, the stacked electrode assembly has a structure in which a plurality of positive electrode and negative electrode unit cells are sequentially stacked and has a merit that it is easy to obtain a rectangular shape. However, when the manufacturing process is troublesome and impact is applied, .

In order to solve such a problem, an electrode assembly of advanced structure which is a mixed type of jelly-roll type and stack type, and which has a positive electrode / separator / negative structure full cell or a positive electrode / A stack / folding type electrode assembly having a structure in which a bicell of a negative electrode (positive electrode) / separator / positive electrode (negative electrode) structure is folded by using a first separator having a long length is developed, Korean Patent Application Laid-Open Nos. 2001-82058, 2001-82059, 2001-82060, etc.

Generally, in a stack / folding type electrode assembly, a first separator interposed between unit cells such as a full-cell or a bi-cell, and a second separator interposed between an anode of each unit cell and a cathode are made of the same material . The first separator and the second separator both function as transfer paths of ions while maintaining an insulated state between the positive electrode and the negative electrode in the electrochemical cell. However, since the applied regions are different, the required physical properties are not the same, A method of providing predetermined safety using another material may be considered.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a stack / folding type electrode assembly in which a separator included in a unit cell and a separator interposed between unit cells are electrochemically and physically An electrode assembly and an electrochemical cell including the electrode assembly, wherein the electrode assembly is improved in safety and battery performance. Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The present invention provides a stack / folding type electrode assembly including two or more different types of separators.

The electrode assembly is a stack / folding type electrode assembly having a structure in which a plurality of unit cells are stacked with a first separator interposed between unit cells, wherein the first separator is a film- And may be bent and / or wound one or more times in such a manner as to surround at least a part of the outer surface of the unit cell and / or the electrode assembly, and the unit cell may include a second separator And the second separator includes a nonwoven web.

The porous membrane includes a polyolefin-based polymer resin.

In the first separator, an inorganic coating layer including inorganic particles and a binder polymer resin may be formed on at least one side of the porous film.

The first separator may have an adhesive layer formed on one side or both sides of the outermost surface.

The nonwoven web may have a fiber diameter of 200 nm to 800 nm and a pore size of 0.05 to 1 μm.

The second separator may have an adhesive layer formed on one side or both sides of the outermost surface.

The second separator may be formed with an inorganic coating layer including inorganic particles and a binder polymer resin on at least one side of the nonwoven web.

The nonwoven web may be formed by electrospinning.

The nonwoven web may include a high heat resistant polymer resin.

The present invention also provides an electrochemical cell including the above-described electrode assembly.

The stack / folding type electrode assembly according to the present invention has an effect of preventing performance deterioration in a large-area or high-output cell because the electrolyte impregnability and wettability are improved by interposing a separator including a nonwoven web on the unit cell. Also, as the separator surrounding the outer surface of the electrode assembly, a film-like porous film produced by extrusion / molding of a polymer may be used to shut down the battery when the temperature of the battery rises, thereby blocking the current.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. On the other hand, the shape, size, scale or ratio of the elements in the drawings incorporated herein can be exaggerated to emphasize a clearer description.
1 is a schematic diagram of an electrode assembly according to one embodiment of the present invention.
FIGS. 2A-2E are schematic diagrams of one exemplary full-cell and bi-cells that can be preferably used as a unit electrode assembly in the electrode assembly of FIG.
FIG. 3 is a schematic view of an electrode assembly in which a plurality of unit electrode assemblies are folded by a first separator as a modification of FIG. 1;

The present invention will now be described in detail with reference to the accompanying drawings. The terms or words used in the present specification and claims should not be construed to be limited to ordinary or dictionary terms and the inventor shall properly define the concept of the term in order to best explain its invention The present invention should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

In the present invention, "porosity" means a ratio of the volume occupied by the pores to the volume of the separator, and is used in terms of porosity, porosity, etc., Typically, the pores in a secondary cell must be sized to prevent internal shorting. The term "permeability " used in the separator of the present invention means the time for 100 cc of air to permeate the separator, and as a unit thereof, the unit is used in seconds / 100 cc. And is usually indicated by a Gurely value or the like. As used herein, the term "puncture strength" refers to the resistance of the separator from outside, for example, the penetration of an external object, and gf is used as its unit, and interchangeability with penetration strength, The higher the value, the lower the internal short-circuit defect rate of the separator.

The present invention provides an electrode assembly applicable to an electrochemical device such as a secondary battery, preferably a lithium secondary battery. The electrode assembly according to the present invention is a stack / folding type electrode assembly and has a structure in which a plurality of unit cells are stacked with a first separator interposed between unit cells. In the present invention, different kinds of separators are used as the first separator and the separator included in the unit cell. The first separator may include a porous membrane formed by extruding / molding a polymer resin, and may be bent and / or wound one or more times in such a manner as to cover at least a part of the outer surface of the unit cell and / have. Also, the unit cell includes a second separator interposed between electrodes having different polarities, and the second separator includes a nonwoven web.

According to a specific embodiment of the present invention, the stack / folding type electrode assembly is formed by bending or winding the first separator in a state where a plurality of unit cells are bonded to one or both surfaces of a first separator having a length longer than the width, And the unit cells may be stacked in a state where the first separator is interposed between the unit cells.

Generally, the stack / folding type electrode assembly includes a first separator for externally surrounding an electrode assembly and / or a unit cell, and a second separator included in a unit cell constituting an electrode assembly. The first separator and the second separator may be the same, but the micro environmental conditions such as the temperature and the electrolyte distribution may be different depending on the positions where the separators are disposed in the electrode assembly. According to the present invention, there is provided a battery in which safety is improved by disposing a separator having different characteristics according to the difference in the micro environment.

1 schematically illustrates a specific embodiment of a stack / folding type electrode assembly according to the present invention. According to Fig. 1, a second separator is interposed between electrodes having opposite polarities in each unit cell, and each unit cell is surrounded by at least a part of the outer surface by the first separator, Thereby forming a laminated structure. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The first separator

In the stack / folding type electrode assembly according to the present invention, the first separator is disposed to surround each unit cell from the outside, and is interposed between the cathode of one unit cell and the anode of another unit cell, And insulates the electrodes of the opposite polarity from each other. The structure of the electrode assembly will be described later in detail.

The first separator includes a porous film in the form of a film as a separator base. In the present invention, the porous membrane includes a polyolefin-based polymer resin. The polyolefin-based polymer resin is selected from the group consisting of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), polypropylene, polybutene, polymethylpentene, Or mixtures thereof.

According to a specific embodiment of the present invention, the polyolefin-based polymer resin may include at least one polypropylene-based resin. Examples of the polypropylene resin include homopolymers of propylene homopolymers and copolymers of propylene with at least one of ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, , 1-undecene, 1-dodecene and the like, or a propylene copolymer such as a graft copolymer or a block copolymer, but the present invention is not limited thereto.

According to a specific embodiment of the present invention, the porous membrane can be produced according to a dry preparation method. As the dry manufacturing method, a method which is generally performed in the technical field of the present invention can be used. In the dry type manufacturing method, micro-cracks are generated in the polymer thin film by stretching, and there are a substrate opening method and a fine particle opening method.

In the substrate opening method, a polyolefin is extracted in a sheet form under a high orientation condition, annealed to increase the degree of crystallization, and then stretched to form a crack at the crystal interface, followed by further stretching at a high temperature to form micropores. If the length of the molecule is sufficient, it is possible to connect the same molecules to each other. For example, the above-mentioned polypropylene-based polymer resin is melt-extruded at a high temperature and is formed into a sheet form and stretched to form pores in the thin film. The stretching may be a cold stretching or a hot stretching, and an annealing process may be further performed before the stretching process is performed. Further, in the above-mentioned dry production method, a method of promoting pore formation by incorporating a polymer resin having semi crystalline characteristics may be applied.

The particulate reclamation method is to obtain a porous substrate by mixing fine particles with a molten polymer resin, melting and extruding the resultant to prepare a sheet, and then stretching the sheet. According to this method, by stretching, the interfacial bond between the polymer and the fine particles is broken by the stretching force applied to the sheet, and pores are formed in the separator base.

In addition to the above method, the porous film can be produced by a method of preparing a composition containing a polypropylene resin and a beta crystal nucleating agent, and extruding the composition to melt-extrud the beta-crystallized sheet. The beta-crystallized polypropylene undrawn sheet is subjected to stretching at the same time as heat is applied. Beta crystals are transferred to alpha crystals to reduce the volume, thereby forming voids between the crystals and the crystals, Can be formed. The beta crystal nucleating agent can be used without any particular limitation as long as it can induce beta crystallization of the polypropylene resin.

In the dry production method, the sheet may be uniaxially stretched in machine direction, simultaneous biaxial stretching or sequential biaxial stretching, and a heat fixing step after the stretching process may be additionally performed.

The detailed process conditions and methods such as temperature condition, time, elongation ratio, and stretching method in the above-mentioned dry-type manufacturing method are not limited to the final manufacturing process, the type of polymer resin, the content, the sheet thickness, uniformity, dimensional stability, It is obvious that an appropriate range can be selected depending on the physical properties of the product to be used.

In one embodiment of the present invention, the porous membrane can be produced by a wet manufacturing method. When a porous film is formed by a wet production method, it is preferable that a polyethylene-based polymer resin such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene is included. As the wet production method, a method commonly used in the technical field of the present invention can be used. For example, in the above-mentioned wet production method, a polyethylene resin is kneaded with a pore-forming agent at a high temperature to prepare a single phase, the polyolefin and pore-forming agent are phase-separated in a cooling process, . The film produced therefrom is thin and uniform in thickness, and has excellent physical properties such as mechanical strength by the stretching process.

Also, the method of producing a porous membrane by the wet method can be classified into a high-liquid phase separation method and a liquid-liquid phase separation method depending on the phase of the pore-forming agent which is kneaded with the base material constituting the membrane, have. In the case of solid-liquid phase separation, only the solidification of the base material proceeds until the base material is crystallized and solidified through the cooling process, and the remaining pore formers are removed from the solid phase of the base material, It happens. That is, as the molecular chains of the base material are crystallized, the pore-forming agent is pushed out to the outside of the base material crystal to cause phase separation, so that the size of the phase-separated phase generated at this time has a size corresponding to the crystal size of the base material molecule.

On the other hand, in the case of liquid-liquid phase separation, the base material exists in a uniform single phase at a temperature not lower than the phase separation temperature, and a liquid different from the base material in a liquid state at a temperature above the temperature at which the base material crystallizes and solidifies, Phase separation occurs due to the thermodynamic instability. As a result, the shape and size of the separated droplets vary depending on the phase separation condition.

The detailed process conditions and methods such as the temperature condition, time, stretching ratio, and stretching method in the above-mentioned wet production method are not limited to the final production method, the type of polymer resin, the content, the sheet thickness, uniformity, dimensional stability, An appropriate range may be selected depending on the properties of the product used.

In one specific embodiment of the present invention, the first separator may have a single-layer structure composed of one porous membrane or a multi-layer structure in which a porous membrane is stacked in two or more layers. In the case of a multi-layer structure, And may have different characteristics with respect to the porous membrane within the above-described characteristic range. The first separator of the multi-layered structure may be formed by separately forming each layer and sequentially stacking the layers or by simultaneously forming two or more layers by a method such as co-extrusion.

In the present invention, the first separator has a smaller pore structure than the separator substrate of the nonwoven web material and has a uniform shutdown characteristic. Therefore, the stability of the battery can be ensured under high temperature use conditions, And the mechanical strength is excellent. In one embodiment of the present invention, the first separator has a porosity of 30% to 80%, an air permeability of 50 sec / 100 cc to 500 sec / 100 cc, and a puncture strength of about 150 gf or more.

The second separator

In the present invention, the second separator is interposed between the opposite electrodes in the unit cell to electrically insulate the two electrodes. The second separator has better wettability than the first separator and improves electrolyte wettability into the unit cell .

In the present invention, the second separator includes a nonwoven web as a separator base. According to an embodiment of the present invention, the average diameter of the fibers of the nonwoven web is about 200 nm to about 800 μm, and the long diameter (pore diameter of the pores) of formed pores is within a range of about 0.05 μm to about 1 μm. When the pore size falls within the above-mentioned range, it is possible to manufacture a separator suitable for a high-capacity secondary battery, which is excellent in insulating property and excellent in wettability to an electrolyte solution.

In one specific embodiment of the present invention, the nonwoven web comprises a polyolefin-based polymer resin and / or a high-heat-resistant polymer resin. The polyolefin-based polymer resin is selected from the group consisting of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), polypropylene, polybutene, polymethylpentene, (Propylene homopolymer) such as ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1- , Propylene copolymers such as random copolymers or graft copolymers or block copolymers of alpha-olefins having 4 to 12 carbon atoms such as 1-undecene and 1-dodecene, or mixtures thereof But is not limited thereto.

On the other hand, the high heat-resistant polymer resin is specifically exemplified by polyethylene terephthalate (PET), polyacrylonitrile (PAN), polyimide (PI), and aramid resin. And preferably polyethylene terephthalate.

In one specific embodiment of the present invention, the nonwoven web is known in the art or may be prepared from the polymeric resins described above by conventional methods. For example, a method of making a porous nonwoven web comprises the steps of preparing a spinning solution, spinning the fibers, and forming a nonwoven web. First, the above-mentioned polymer resin is melted or dissolved in a solvent to form a spinning solution. As the solvent, it is preferable that the solubility index is similar to that of the polymer resin used and the boiling point is low. The spinning solution is spun into a collector, for example, by spinning methods known in the art, such as melt spinning, solution spinning, electro-spinning, and the like. The fibers thus spun on the collector can be formed according to the requirements of the final nonwoven web by a web forming process known in the art such as dry laid, wet laid, spun bonded, spun lace laced, melt blown or the like to form a nonwoven web. The nonwoven web is thermally fused at a high temperature. Here, the temperature of the nonwoven fabric web refers to the temperature at which the high heat-resistant polymer of the nonwoven web partially melts and is capable of melt-bonding with the surface of the adjacent nonwoven web, particularly other high-temperature resistant polymer or other portion. And the temperature range thereof is not particularly limited if it exists under such a condition. Such thermal fusion bonding is performed by heat fusion bonding through a conventional thermal fusion bonding method such as thermocompression bonding in the related art. The heat fusion is performed by fusing the fibers under conditions such as heating temperature, heating time, pressure and the like suitable for fusing the fibers, whereby the fibers are entirely or partially fused (bonded) to each other. Such nonwoven webs can also reinforce the bonds between the fibers through methods known in the art, such as needle punching, mechanical processes, use of adhesives, etc., to form nonwoven webs with better tensile strength . The thus formed nonwoven web has a porous structure having a plurality of pores, and the bonding force between the fibers is greatly increased by fusion, thereby increasing the tensile strength of the entire nonwoven web. The thickness of the nonwoven web thus formed ranges from about 9 to about 30 Mu m.

In one specific embodiment of the present invention, the thickness of the second separator is 15 占 퐉 to 45 占 퐉, preferably 30 占 퐉 or less, more preferably 25 占 퐉 or less. The second separator has an air permeability ranging from 1 sec / 100cc to 200s / 100cc.

Inorganic coating layer

According to a specific embodiment of the present invention, the first separator and / or the second separator may further include an inorganic coating layer on one side and / or both sides thereof. The inorganic coating layer includes inorganic particles and a polymeric binder resin.

The inorganic particles form an interstitial volume between inorganic particles to provide micropores. It also serves as a kind of spacer capable of maintaining the physical form. In addition, since the inorganic particles generally have a characteristic that their physical properties do not change even at a high temperature of 200 DEG C or more, the separator has excellent heat resistance by the formed inorganic coating layer.

The inorganic particles 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 an operating voltage range of the applied battery (for example, 0 to 5 V based on Li / Li +). Particularly, when inorganic particles having an ion transporting ability are used, the ion conductivity in the electrochemical device can be increased to improve the performance, so that it is preferable that the ionic conductivity is as high as possible. In addition, when the inorganic particles have a high density, it is difficult to disperse the particles at the time of coating. Also, in the case of an inorganic substance having a high dielectric constant, the dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte can be increased, and the ion conductivity of the electrolyte can be improved. For the above-mentioned reasons, the inorganic particles are preferably high-permittivity inorganic particles having a dielectric constant of 5 or more, preferably 10 or more.

The size of the inorganic particles is not limited. However, it is preferable that the size of the inorganic particles is in the range of 0.001 to 10 mu m for the formation of the film having a uniform thickness and the appropriate porosity, and the porosity of the substrate (porous film or nonwoven web) Can be adjusted appropriately. When the particle size is less than 0.001 탆, the dispersibility is lowered and the physical properties of the inorganic coating layer are difficult to control. When the particle size exceeds 10 탆, the thickness of the inorganic coating layer is increased and the mechanical properties are deteriorated. The probability of an internal short circuit occurring during charging and discharging increases.

The content of the inorganic particles is preferably in the range of 50% by weight to 99% by weight, more preferably 60% by weight to 95% by weight, based on 100% by weight of the mixture of the inorganic particles constituting the inorganic coating layer and the binder polymer resin.

The binder polymer resin may be a polymer resin conventionally used in the art. Particularly, it is possible to use a glass transition temperature (Tg) as low as possible, preferably in the range of -200 to 200 ° C. This is because the mechanical properties such as flexibility and elasticity of the final film can be improved. The polymer resin faithfully performs a binder function to connect and stably fix the inorganic particles and the particles, thereby contributing to prevention of deterioration of the mechanical properties of the finally formed inorganic coating layer.

According to one embodiment of the present invention, the inorganic coating layer is prepared by mixing an inorganic particle and a binder polymer resin with an appropriate solvent to prepare a slurry for an inorganic coating layer, and then coating the surface of the inorganic coating layer with a known method such as a dip coating method or a doctor blade coating method By applying the slurry and drying the slurry. For example, the inorganic coating layer can be formed on the surface of the porous film in the case of the first separator and on the surface of the nonwoven web in the case of the second separator.

Adhesive layer

In the present invention, the first and / or second separator may further include an adhesive layer including a binder polymer on one side or both sides of the outermost surface. For example, in the case of the first separator, if the inorganic coating layer is not formed, the adhesive layer may be further formed on the inorganic coating layer if the inorganic coating layer is formed on the surface of the porous film. The binder polymer provides a binding force between one component of the electrode assembly that is in contact with each separator. Examples of the binder polymer resin include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, poly Polymethylmethacrylate, and the like, and various kinds of binder polymer resins may be used singly or in combination of two or more.

The adhesive layer is formed by coating the at least a part of the surface of the outermost surface of the separator with the binder polymer.

Unit cell

According to one embodiment of the present invention, the unit cell may be a bi-cell having the same electrode structure on both sides and / or a full-cell having a different electrode structure on both sides. have.

Specifically, the full-cell has a unit structure of a positive electrode / a separator / a negative electrode, and the positive electrode and the negative electrode are located on both sides of the unit cell. Such a full-cell includes a unit cell which is the anode / separator / cathode having the most basic structure, and an anode / separator / cathode / separator / anode / separator / cathode unit cell. 2A, a full-cell structure of a positive electrode / separator / negative electrode structure is shown in FIG. 2A. In order to construct an electrochemical cell including such a secondary cell by using such full-cells, A plurality of full-cells must be stacked so that the anode and the cathode face each other.

The bi-cell as a unit cell is a cell in which the same electrode is located on both sides of a unit cell, such as a unit structure of a cathode / separator / cathode / separator / anode and a unit structure of a cathode / separator / anode / separator / cathode. 2B shows a schematic view of a bi-cell of a positive electrode / separator / negative electrode / separator / positive electrode structure, and a schematic view of a bi-cell of a negative electrode / separator / positive electrode / separator / negative electrode structure is shown in FIG. 2C In order to construct the electrochemical cell including the secondary cell by using such bi-cells, the bi-cell of the positive electrode / separator / negative electrode / separator / positive electrode structure and the negative electrode / separator / A plurality of bi-cells must be stacked such that the bi-cells of the separator / negative electrode structure face each other.

As shown in FIG. 2D, the bi-cells of the positive electrode / separator / negative electrode / separator / positive electrode / separator / negative electrode / separator / And a schematic view of a bi-cell having a negative electrode / separator / positive electrode / separator / negative electrode / separator / positive electrode / separator / negative electrode structure is shown in FIG.

Electrode assembly

1 is a schematic view of an electrode assembly according to an embodiment of the present invention.

1, the electrode assembly 100 includes a plurality of bi-cells 200, 201, 202,... With a second separator 300 interposed between a cathode 210 and an anode 220, (Not shown). The electrode assembly 100 is formed such that the second separator 400 surrounds the outer surface of the first bi-cell 200 at the center and forms a second bi-cell 200 at the upper and lower portions of the first bi- 201, 202, ... with a structure in which the outer surfaces of the first and second bi-cells 201, 201 and the third bi-cell 202 are positioned.

The second separator 300 has a structural characteristic that it is fixed by electrodes and lamination, and the high heat-resistant polymer material exhibits low heat shrinkability, so that the shrinkage phenomenon is small even when high heat is applied. Therefore, short-circuiting of the cathode 210 and the anode 220 due to contraction of the separator in the unit cells 200, 201, 202, etc. including the second separator is not caused, The penetration of the electrolytic solution into the unit cell is easy.

Further, since the first separator 400 exhibits a relatively high heat shrinkability as compared with the second separator 300, shrinkage occurs upon application of a high temperature. However, in the direction of folding (winding) the unit cells 200, 201, and 202 as shown in the drawing, the occurrence of contraction is limited by a large frictional force with the unit cells 200, 201, and 202. Accordingly, contraction of the first separator 400 in the folding direction having a relatively large length can be greatly suppressed, so that a short circuit between the unit cells 200, 201, and 202 can be prevented.

In a specific embodiment of the present invention, the first separator 400 is configured to have a relatively larger surplus portion in the width direction than the second separator 300 in consideration of the above-described heat shrinkage, Can be compensated. Here, the remainder refers to a portion where the first separator 400 or the second separator 300 protrudes from the outer surface of the cathode 210 or the anode 220.

3, a first separator 400 is folded in a Z-shape from the lowermost bipolar cell 204 to the uppermost bipolar cell 203, . Heat shrinkage and mechanical properties of the separator inside the first separator 400 bipolar cells 203 and 203 in the electrode assembly 101 of FIG. 3 are substantially the same as those of the electrode assembly 100 of FIG. 1 .

The present invention also provides an electrochemical cell comprising the electrode assembly.

The electrochemical cell is preferably a lithium secondary battery, preferably a lithium ion secondary battery. The secondary battery has a structure in which a chargeable and dischargeable electrode assembly is embedded in a battery case while being impregnated with an ion-containing electrolytic solution. Particularly, since the mechanical strength of the battery case is low, The electrode assembly according to the present invention can be preferably used for a secondary battery using a plate-shaped battery case.

The secondary battery is preferably a lithium secondary battery having a high energy density, a discharge voltage, and an output safety. Among these, a lithium ion secondary battery having low possibility of electrolyte leakage, low weight and low manufacturing cost, Is most preferable. Other components and manufacturing methods of the lithium secondary battery are well known in the art, and a detailed description thereof will be omitted in this specification.

100, 101 ... electrode assembly
200, 201, 202, 203, 204 ... bi-
210 cathode 211 anode active material layer 212 cathode collector
220 Positive electrode 221 Positive electrode active material layer 222 Positive electrode collector
300 second separator
400 first separator

Claims (11)

A stack / folding type electrode assembly having a structure in which a plurality of unit cells are stacked with a first separator interposed between unit cells,
Here, the first separator includes a porous film in the form of a film including a polymer resin, and may be bent and / or wound one or more times in such a manner as to cover at least a part of the outer surface of the unit cell and / or the electrode assembly ,
Wherein the unit cell comprises a second separator interposed between electrodes having different polarities, and the second separator comprises a nonwoven web.
The method according to claim 1,
Wherein the porous membrane comprises a polyolefin-based polymer resin.
The method according to claim 1,
Wherein the first separator has an inorganic coating layer formed on at least one side of the porous membrane, the inorganic coating layer including inorganic particles and a binder polymer resin.
The method according to claim 1,
Wherein the first separator has an adhesive layer formed on one side or both sides of the outermost surface.
The method according to claim 1,
Wherein the nonwoven web has a fiber diameter of 200 nm to 800 nm.
The method according to claim 1,
Wherein the nonwoven web has a major axis of pore size of 0.05 to 1 占 퐉.
The method according to claim 1,
Wherein the second separator has an adhesive layer formed on one side or both sides of the outermost surface.
The method according to claim 1,
Wherein the second separator has an inorganic coating layer formed on at least one side of the nonwoven web, the inorganic coating layer including inorganic particles and a binder polymer resin.
The method according to claim 1,
Wherein the nonwoven web is formed by electrospinning.
The method according to claim 1,
Wherein the nonwoven web comprises a high heat resistant polymer resin.
An electrochemical cell comprising an electrode assembly according to any one of claims 1 to 10.

Images