KR101543055B1 - Stack and Folding-Typed Electrode Assembly Having Improved Safety Property and Method for preparation of the same - Google Patents

Abstract

The present invention relates to a stacked / folded lithium secondary battery having improved safety and a method of manufacturing the stacked / folded lithium secondary battery. More particularly, the present invention relates to a stack / folding type lithium secondary battery, And a stack / folding type electrode assembly in which gas or the like can be easily discharged from the inside of the stack / folding type electrode assembly to the outside, and a method of manufacturing the same. The present invention relates to a stack / folding type lithium secondary battery, in which a breaking groove is formed at the edge of a folding separator sheet of a stacked / foldable lithium secondary battery, thereby providing a passage for the electrolyte during the activation process of the battery, The speed is remarkably improved. In addition, when an abnormal phenomenon such as high temperature and overcharging occurs, the vaporized electrolyte and gas can be quickly discharged to the outside of the electrode assembly, thereby improving the safety and performance of the battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a stacked / folded lithium secondary battery having improved safety and a method of manufacturing the stacked / folded lithium secondary battery.

The present invention relates to a stacked / folded lithium secondary battery having improved safety and a method of manufacturing the stacked / folded lithium secondary battery. More particularly, the present invention relates to a stack / folding type lithium secondary battery, And a stack / folding type electrode assembly in which gas or the like can be easily discharged from the inside of the stack / folding type electrode assembly to the outside, and a method of manufacturing the same.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as an energy source has been increasing rapidly. Many researches have been conducted on lithium secondary batteries having high energy density and high discharge voltage among such secondary batteries. Widely used.

The secondary battery may be classified according to how the electrode assembly having the anode / separator / cathode structure is formed. Typically, the jelly-roll (cathode) structure is a structure in which the anode and the cathode of the long sheet type are wound with the separator interposed therebetween (Stacked) electrode assembly in which a plurality of positive electrodes and negative electrodes cut in units of a predetermined size are sequentially stacked with a separator interposed therebetween, a stacked (stacked) electrode assembly in which a predetermined unit of positive and negative electrodes are stacked A stack / folding type electrode assembly having a structure in which stacked bi-cells or full cells are wound.

Such conventional jelly-roll type electrode assemblies in the electrode assemblies are formed into a cylindrical or elliptical structure by winding the elongated sheet-like positive electrode and negative electrode in a tight state so that the stress caused by the expansion and contraction of the electrode during charging and discharging When the stress accumulation exceeds a certain limit, deformation of the electrode assembly occurs. As a result of the deformation of the electrode assembly, the gap between the electrodes becomes uneven and the performance of the battery is rapidly deteriorated. As a result, The safety of the device is threatened.

Further, since the long sheet-like positive electrode and the negative electrode are required to be wound, it is difficult to rapidly wind the positive electrode and the negative electrode while maintaining a constant distance between the positive electrode and the negative electrode.

On the other hand, since the stacked electrode assembly requires a plurality of anode and cathode unit members to be sequentially stacked, a process of transferring the electrode plate for manufacturing the unit pieces is separately required, and a time and effort are required for the sequential stacking process, I have.

In order to solve these problems, an electrode assembly of advanced structure which is a mixed type of jelly roll type and stacked type is used. The electrode assembly includes a bi-cell or a full cell stacked with a separator interposed between a positive electrode and a negative electrode, a stack / folding type electrode assembly having a structure in which a long separator sheet is used to wind the electrodes is developed.

Figures 1-4 illustrate a schematic diagram of one exemplary full-cell and bi-cell that can be preferably used as a unit cell in such a stack / foldable electrode assembly.

In addition, Fig. 5 schematically shows an exemplary structure of such a stack / folding type electrode assembly.

5, a plurality of pull cells 140 in which an anode 120, a separator 130, and a cathode 110 are sequentially disposed as unit cells are overlapped, and a separator sheet 150 is stacked in each of the overlaps, Respectively. The separator sheet 150 has a unit length that can wrap around the pull cells and has a structure in which each pull cell is folded inward and wrapped around the pull cells continuously from the center pull cell to the outermost pull cell, have. In addition, the distal end of the separation sheet 150 is finished by heat-sealing or attaching an adhesive tape 60 or the like.

The stack / folding type electrode assembly can solve the disadvantages of the jelly-roll type or stack type electrode assembly as described above. However, when the electrolyte cell is impregnated with the electrolytic solution completely or the impregnation rate is low There are slow drawbacks. Further, when the electrolyte is vaporized in an emergency such as high temperature or overcharge, or when gas is generated in the electrode assembly, it is difficult for the vaporized electrolyte or gas to be discharged and easily discharged to the outside due to the multiple- The swelling is relatively high.

At this time, the vaporized electrolytic solution or gas may be discharged in a direction perpendicular to the winding direction (direction in which the electrode tabs protrude) that is not clogged with the separator sheet, but such gas or the like may be discharged from the central portion of the stack / There is a limit in that the gas generated at the center is discharged in both directions in which the electrode tabs protrude. Therefore, the swelling phenomenon that the battery swells due to the gas and the vaporized electrolyte in the central portion of the stack / folding type electrode assembly is more likely to occur, and accordingly, the anode and the cathode of a unit cell such as a full cell or a bi- When the battery is in a high temperature or an overcharged state, the separator interposed in the unit cell may be worn or shrunk, and when the battery is in an emergency state of high temperature or overcharge, The electrodes of the cell are bent and the shrinkage or abrasion of the separator may occur at the same time. As a result, the anode and the cathode may come into contact with each other at the end edge of the unit cell, resulting in a short circuit.

Such interelectrode short circuit generates a lot of heat, so that ignition or explosion of the battery may occur, which may seriously lower the safety of the secondary battery.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a stack / folding type warp assembly, which is capable of easily discharging a vaporized electrolyte or gas generated in the electrode assembly to the outside, Folded electrode assembly in which a breaking groove is formed in a certain portion of the sheet.

It is another object of the present invention to provide a method of manufacturing such an electrode assembly.

It is still another object of the present invention to provide a lithium secondary battery including the electrode assembly.

According to an aspect of the present invention,

An electrode assembly comprising a plurality of stacked unit cells stacked and a continuous folding separator sheet interposed between the stacked unit cells, wherein a plurality of split grooves The electrode assembly includes a first electrode and a second electrode.

In this case, the predetermined portion is formed on both sides of the folding separator sheet with respect to the upper side where the electrode tab protrudes.

Further, the breaking grooves are semicircular or elliptical.

The stacked unit cell may be a full cell or a bi-cell.

The positive electrode or the negative electrode of the stacked unit cell is formed with a depressed portion recessed inward at a position corresponding to a position where the breaking groove is formed on the folding separator sheet.

In this case, the size of the indentation is 0.5 to 2 mm deeper than the depth of the fracture groove, and is formed to be 0.5 to 2 mm apart from the outermost fracture groove.

The indentation may be formed in a triangular, quadrangular, semicircular or oval shape.

The present invention also provides a secondary battery comprising the electrode assembly.

The secondary battery is a lithium ion secondary battery.

The present invention also provides a middle- or large-sized battery module characterized by including a secondary battery as a unit cell.

Meanwhile, the present invention provides a method of manufacturing the electrode assembly,

(a) laminating a cathode current collector and an anode current collector in a state in which a separator is interposed therebetween, and cutting the cathode current collector and the anode current collector to a predetermined size to manufacture a plurality of pull cells or bi cells;

(b) placing the unit cells (central unit cells) manufactured in the step (a) at the first end of the long folding separator sheet and continuously positioning the unit cells in the same electrode orientation manner at predetermined intervals ;

(c) winding the central unit cell once with the long folding separator sheet, folding the folding separator sheet outward where the adjacent unit cells are located, and folding each unit cell by folding; And

(d) forming a breaking groove on both sides of the separator sheet based on a direction in which the electrode tab protrudes after the folding of the folding separator sheet is completed by the step (c); Folded electrode assembly according to the present invention.

In this case, the positive electrode current collector or the negative electrode current collector is formed with a depressed portion recessed inward at a position corresponding to a position where the breaking groove is formed on the separator sheet.

The indentation may be formed in a triangular, quadrangular, semicircular or oval shape.

The breaking groove is formed by partially cutting a corresponding portion of the separator sheet with a needle-shaped body having a predetermined diameter.

The present invention relates to a stack / folding type lithium secondary battery, in which a breaking groove is formed at the edge of a folding separator sheet of a stacked / foldable lithium secondary battery, thereby providing a passage for the electrolyte during the activation process of the battery, The speed is remarkably improved. In addition, when an abnormal phenomenon such as high temperature and overcharging occurs, the vaporized electrolyte and gas can be quickly discharged to the outside of the electrode assembly, thereby improving the safety and performance of the battery.

1 to 4 are schematic diagrams of one exemplary pull cell and bi-cells that can be preferably used as a unit cell of a stack / folding type electrode assembly.
FIG. 5 shows a stack / folding type secondary battery folded from a center of a unit cell to a separator sheet according to a related art.
6 is a perspective view of a stack / folding type electrode assembly according to a preferred embodiment of the present invention.
7 to 10 are various embodiments of electrode current collectors according to a preferred embodiment of the present invention.
11 is a view illustrating a method of manufacturing a stack / folding type electrode assembly according to a preferred embodiment of the present invention.

In order to achieve the above object, an electrode assembly of the present invention includes a plurality of electrochemical cells having a predetermined unit cell made of a full cell or a bi-cell as a basic unit, A stacked / folded electrode assembly having a structure in which a continuous folding separator sheet is interposed,

And a folding groove is formed in the folding separator sheet wound by winding the stacked electrochemical cells.

The present invention also provides a method of manufacturing the stack / folding type electrode assembly and a lithium secondary battery including the stack / folding type electrode assembly.

Hereinafter, the present invention will be described in detail with reference to the drawings.

It is to be understood that the drawings are only for the purpose of illustrating the present invention and that the scope of the present invention is not limited to the above drawings and may be suitably modified or applied by those skilled in the art to which the present invention belongs .

6 is a schematic diagram showing a top view of a stack / folding type electrode assembly according to an embodiment of the present invention.

Referring to FIG. 6, the stack / folding type electrode assembly according to the present invention is a stack / folding type electrode assembly formed by winding a plurality of pull cells or unit cells in a long sheet-like folding separator sheet, And a breaking groove is formed on the folding sheet separating sheet.

The size of the fracture groove is not particularly limited. However, if the size of the fracture groove is too large, the function of the folding separator sheet may be deteriorated or the damage of the folding separator sheet may be promoted, On the contrary, when the size of the fracture groove is too small, it is difficult to sufficiently exhibit the effects such as improvement of impregnation of the electrolyte solution and easy discharge of gas, which is expected in the present invention.

Therefore, the size of the rupture groove can be adjusted to a suitable size by a person skilled in the art in order to achieve the above-mentioned object, and more specifically, it can be formed to have a size of 0.1 to 2 mm according to a preferred embodiment of the present invention.

However, according to the results of experiments conducted by the inventors of the present application, the swelling phenomenon of the center portion of the battery cell is most likely to occur during overcharging of the battery cell, Generally, a portion where the electrolyte or gas evaporated in an emergency, such as a high temperature or an overcharge, is well formed is a central portion of the electrode assembly. In the direction in which the electrode tab protrudes, gas or vaporized electrolyte is easily discharged. Because it is easy. Therefore, it is most preferable that the break groove is formed in the central portion of the electrode assembly, and also on the lateral sides of both sides of the large-area portion of the electrode assembly.

The central portion of the electrode assembly is less likely to discharge the generated gas and to impregnate the electrolyte, and furthermore, there is a higher probability that the gas is accumulated on the side B than on the side A in FIG.

Also, the number of the break grooves formed on the folding separator sheet of the stack / folding type electrode assembly is not particularly limited, and the number of the break grooves formed may vary depending on the use or size of the secondary battery. In this case, the number of the rupture grooves is related to the size of the rupture grooves. When the size of the rupture grooves is small, many rupture grooves can be formed from the center of the electrode assembly, and when the rupture grooves are relatively large, By reducing the number of broken grooves, it is possible to control the gas emission direction and the speed direction. According to a preferred embodiment of the present invention, about 5 to about 40 break grooves may be formed per corner in the B direction. In this case, the spacing of the formed break grooves may be adjusted depending on the size and application of the secondary battery, and preferably, the equal intervals are maintained.

On the other hand, the shape of the fracture groove is formed in a circular or elliptic curved shape which does not support the angle. In the case where the breaking groove is not formed in such a curved shape and is formed as a mocking or an angled shape, stress may concentrate on the angled portion, which may easily damage or deteriorate the folding separator sheet .

The folding separator sheet or separator may be a polyethylene film containing micropores, a polypropylene film, or a multilayer film produced by a combination of these films, and a layered film made of polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene Fluorinated hexafluoropropylene copolymer, and polymer film for a polymer electrolyte of a fluorinated hexafluoropropylene copolymer, and may be a single layer or a multi-layered folding separator sheet or separator film .

In one preferred embodiment, the folding separator sheet has a unit length that can wrap around a battery chemical cell, and the folding separator sheet may be folded inward for each unit length to continuously wrap the unit cell of the central pull cell or bi- have.

Generally, when the interfacial contact between the electrode and the folding separator sheet is not maintained as the battery is repeatedly charged and discharged, the capacity and performance of the battery are drastically lowered, and the pressure for stably maintaining the contact by continuously pressing the interface is maintained need.

Therefore, the electrode assembly having the above-described structure can efficiently utilize the electrodes among the unit cells by interposing the separator sheet while stacking the unit cells, and the tensile force generated when the separator sheet is wound by the electrodes is formed in all the cells The interface between the separator sheets can be squeezed, which is very excellent in terms of battery performance and capacity.

The structure of the pull cell or the bi-cell as a basic unit chain is not particularly limited and a well-known pull cell or unit cell can be used. Preferably, the pull cell or the bi- ) Anode / separator / cathode / separator / anode / separator / cathode laminate structure.

The number of unit cells such as a pull cell or a bi-cell wound on the folding separation membrane may be determined by various factors such as the structure of each unit cell such as a pull cell or a bi-cell, Preferably 6 to 30 carbon atoms.

The folding separator sheet may have an extended length to wrap the electrode assembly once after winding, and the outermost end of the folding separator sheet may be thermally fused or tape-fixed. For example, the folding separator sheet itself can be melted by heat and adhered and fixed by bringing a heat welding machine or a hot plate into contact with the folding separator sheet to be finished. As a result, .

The breaking groove according to the present invention is formed by winding unit cells by a folding separator sheet and fixing the outermost end of the folding separator sheet by heat welding or adhesive tape to form a stack / folding type electrode assembly, Folded electrode assembly is preferably formed on both sides of the stack / folding type electrode assembly.

In this case, the method of forming the fracture groove is not particularly limited, but according to a preferred embodiment, the folding groove can be formed by partially breaking the corresponding portion of the folding membrane sheet with a needle-like body having a predetermined diameter.

In addition, at least one indentation may be formed on the sides of the anode or cathode forming the electrode groups of the positive and negative electrodes forming the stack / folding type electrode assembly of the present invention, Thereby making it possible to prevent the risk of being damaged in the process of forming the fracture groove. When the anode or the cathode is damaged by the step of forming the breaking groove in the folding separator sheet, the effect of improving the performance or the life of the battery is hardly obtained.

The shape, position, and size of the indent formed on the electrode current collector are not particularly limited, but may be determined by taking into consideration the position where the break groove is formed on the folding separator sheet and the size and number of the break groove, .

FIGS. 7 to 10 schematically show a preferred embodiment of the negative electrode or the positive electrode current collector 310 in which the indentations 312 are formed in various shapes.

As shown in the drawing, the indent of the electrode current collector may be formed in the shape of a square, a circle, an ellipse, or a triangle. Since the electrode groove is formed at the center of the electrode assembly, It is preferable that the entire depressed portion is formed in the center portion of both side edges of the electrode current collector so as to correspond to the position where the breaking groove is formed.

At this time, the length of the indentation and the depth of the indentation are not particularly limited and may be changed depending on the expected position, size, and number of the rupture grooves, and may be appropriately changed so that the electrode collector is not damaged by the rupture groove forming process Of course.

However, in a preferred embodiment, the size of the indented portion may be formed to be at least 0.5 to 2 mm deeper than the depth of the rupture groove, and may be at least 0.5 to 2 mm or more apart from the outermost rupture groove Can be formed.

The electrode current collector may be generally made to have a thickness of 3 to 500 탆, such as other known electrodes, except that the indented portion can be formed as described above. Preferably, the positive electrode is an electrode coated with a positive electrode material on both surfaces of a positive electrode collector, and the negative electrode is an electrode coated with a negative electrode material on both surfaces of the negative electrode collector. The positive electrode may include a separator interposed between the positive electrode and the negative electrode Bonded to each other.

The positive electrode is prepared, for example, by applying a mixture of a positive electrode active material, a conductive material and a binder to both surfaces of a positive electrode current collector in which an indentation portion of a predetermined size is formed in advance, followed by drying and pressing, Additional fillers may be added. The cathode current collector generally has a thickness of 3 to 500 mu m. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and examples thereof include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum, Surface-treated with carbon, nickel, titanium, silver, or the like may be used.

On the other hand, the current collector may form fine irregularities on its surface to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

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

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, 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 metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

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

On the other hand, the negative electrode is manufactured by applying, drying and pressing an anode active material on an anode current collector, and may optionally further include a conductive material, a binder, a filler, and the like as described above. The negative electrode current 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 electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a 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, as in the case of the positive electrode current 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 active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{LixFe 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': Al , B, P, Si, Group 1, Group 2 and Group 3 elements of the periodic table, Halogen, 0 <x <1> 1 <y> 3, 1 <z <8); 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 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi 2 O 5 A conductive polymer such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The present invention also includes a secondary battery including a stack / folding type electrode assembly having the above characteristics. The secondary battery is preferably a lithium secondary battery.

The present invention also provides a middle- or large-sized battery module including the lithium secondary battery as a unit cell.

Hereinafter, a method of manufacturing the stack / folding type electrode assembly will be described in detail.

A method of manufacturing a stack / folding type electrode assembly according to the present invention comprises:

(a) a step of laminating a cathode current collector and a cathode current collector in a state in which a separator is interposed, and cutting the anode current collector and the anode current collector to a predetermined size to manufacture a plurality of unit cells of pull cells or bi-cells. There is no particular limitation on the method of manufacturing such a unit cell, and the unit cell can be manufactured by using a known manufacturing method.

In this case, the positive electrode or the negative electrode current collector may be a negative electrode and a positive electrode current collector having the above-mentioned indentation portion. In this case, the process of forming the indentation portion may depend on the number, The positive electrode or the negative electrode current collector may be cut according to the size and shape of the predetermined indentation, and then the current collector may be included in the unit cells such as the pull cell or the bi-cell.

(b) Thereafter, the unit cells of the pull cell or the bi-cell manufactured by the above method are placed on the first end of the long folding separator sheet and the unit cells are successively positioned in the same electrode orientation manner at predetermined intervals .

(c) After the unit cells are wound once with the folding separator sheet, the folding separator sheet is folded outward where the adjacent unit cells are located, and each of the unit cells is folded and overlapped.

(d) After the stack / folding type electrode assembly is formed in the same manner as described above, a fracture groove is formed on both sides of the folding separator sheet with reference to the protruding direction of the electrode tabs of the stack / folding type electrode assembly Groove forming step.

The method of forming the fracture groove on the folding separator sheet is not particularly limited, but it is possible to use a method of partially forming the folded separator sheet by partially cutting the folded sheet with a needle having a predetermined diameter, It is not.

The present invention also provides a secondary battery and a middle- or large-sized battery module including the stack / folding type electrode assembly manufactured by the above-described method. The manufacturing method of the secondary battery and the middle- or large-sized battery module is not particularly limited and can be manufactured by a known method.

The stack / folding type secondary battery of the present invention includes the electrode assembly formed by the above-described method, and the gas or the vaporized electrolyte that can be generated in an emergency can be easily discharged from the inside to the outside of the battery, Can be greatly increased.

100: stack / folding type electrode assembly,
110: negative electrode, 120: positive electrode, 130: separator, 140: unit cell, 150: folding separator sheet,
200a: Stack / folding type electrode assembly, 210, 210a: anode, 220, 220a: cathode,
230, 230a: Folding separator sheet 240a: Breaking groove 10, 300, 300a to 300c: Unit cell,
310: electrode collector,
312, 312a to 312c: indentations,
320: electrode tab, 330: separator.

Claims (14)

An electrode assembly having a structure in which a plurality of stacked unit cells are stacked and a continuous folding separator sheet is interposed in each of the stacked units,
A plurality of folded grooves are formed on both sides of the folded sheet separator sheet on the basis of an upper end of the folded sheet separator sheet on which the electrode tabs protrude from the stacked electrochemical cells,
The positive electrode or negative electrode of the laminated unit cell is formed with a recessed portion inwardly at a position corresponding to a position where a fracture groove is formed on the folding separation membrane sheet. The recessed portion is semicircular or elliptical, Is 0.5 to 2 mm deeper than the depth of the outermost break groove and is 0.5 to 2 mm apart from the outermost break groove. delete The electrode assembly of claim 1, wherein the fracture groove is semicircular or elliptical. The electrode assembly according to claim 1, wherein the stacked unit cell is a full cell or a bi-cell. delete delete delete A secondary battery comprising the electrode assembly according to claim 1. The secondary battery according to claim 8, wherein the secondary battery is a lithium ion secondary battery. The middle- or large-sized battery module according to claim 8, wherein the secondary battery comprises a unit cell. delete delete delete delete

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