KR102261649B1 - Electrode Assembly Comprising Electrode Having Different Porosity Depending on Position of Unit-cell - Google Patents

Abstract

The present invention is an electrode assembly having a structure in which a plurality of unit cells are stacked. In the unit cell stacked structure, the unit cells located on the outer side have a porosity of the electrode assembly layer coated on the electrode plate, compared to the unit cells located on the inner side. It relates to an electrode assembly, characterized in that relatively low.

Description

Electrode Assembly Comprising Electrode Having Different Porosity Depending on Position of Unit-cell}

The present invention relates to an electrode assembly including an electrode having a different porosity depending on the position of a unit cell.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate. has been commercialized and widely used.

In addition, as interest in environmental issues grows, research on electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, is being conducted. . Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, research using lithium secondary batteries with high energy density and discharge voltage is being actively conducted, and some are in the commercialization stage.

According to the shape of the battery case, these secondary batteries are classified into cylindrical batteries and prismatic batteries in which the electrode assembly is embedded in a cylindrical or prismatic metal can, and pouch-type batteries in which the electrode assembly is embedded in a pouch-type case of an aluminum laminate sheet. do.

In addition, secondary batteries are classified according to the structure of the electrode assembly consisting of a positive electrode, a negative electrode, and a separator. Typically, a jelly having a structure in which a long sheet-shaped positive electrode and negative electrode are wound with a separator interposed therebetween. -Roll (winding type) electrode assembly, stacked (stacked type) electrode assembly in which a plurality of positive and negative electrodes cut in units of a predetermined size are sequentially stacked with a separator interposed therebetween, positive and negative electrodes of a predetermined unit are interposed with a separator A stack-folding electrode assembly having a structure in which bicells or full cells, which are unit cells stacked in one state, are disposed on a separation film and then wound, or bicell or full cell ) in a stacked state with a separator interposed therebetween, and a lamination-stack type electrode assembly.

Recently, a secondary battery including an electrode assembly including a bi-cell or full-cell having high structural applicability in response to various types of devices as well as a simple manufacturing process, low manufacturing cost, and various types of devices is attracting attention.

However, in the case of a unit cell positioned inside the stack-type (stacked-type) electrode assembly, the stack-folding-type electrode assembly, or the lamination-stack-type electrode assembly, the unit cells positioned on the outer side and the electrodes constituting each unit cell Due to the plate and the separator, it is true that it is relatively difficult to be impregnated with the electrolyte, and there is a problem that it takes a long time to manufacture all of the unit cells.

In addition, if the unit cell located inside the electrode assembly is not properly impregnated with the electrolyte, there is a region where the SEI (Solid Electrolyte Interface) film is not formed on the surface of the active material of the electrode plate, and in the case of the negative plate, lithium is precipitated in the region. As a result, it causes great problems in performance and safety, such as reduction of cycles and induction of micro-shorts by lithium dendrites.

Therefore, there is a high need for a technology capable of improving the impregnation of the electrolyte up to the unit cell located inside the electrode assembly.

An object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

Specifically, an object of the present invention is to provide an electrode assembly capable of reducing the cell manufacturing time by improving the electrolyte impregnation property of the electrode located inside the electrode assembly.

The present invention for achieving this object,

As an electrode assembly having a structure in which a plurality of unit cells are stacked, the unit cells located on the outer side in the unit cell stack structure have a relatively low porosity of the electrode assembly layer coated on the electrode plate compared to the unit cells located on the inner portion. characterized in that

As the demand for high-capacity batteries increases, the number of unit cells constituting the electrode assembly increases. However, when the electrolyte is injected after packaging the electrode assembly in the battery case, the impregnation rate is slow due to the high viscosity of the electrolyte, There was a disadvantage in that it was difficult for the electrolyte to reach the unit cell located inside the electrode assembly.

In particular, when the electrolyte does not reach the inner unit cell, an unreacted active material region is formed in the electrode plate constituting the unit cell, and there is a problem in that lithium dendrites are generated.

However, in the electrode assembly according to the present invention, the electrode porosity of the unit cells located in the inner portion is higher than that of the unit cells located in the outer portion, and thus the electrolyte impregnability of the electrode located in the inner portion can be improved overall, resulting in lithium den It is possible to secure the safety of the battery by reducing the occurrence of dry.

The electrode assembly can be applied to any structure as long as it has a structure in which unit cells are stacked, but one example thereof may be a stack-type structure, a stack-folding structure, or a lamination-stack-type structure.

The unit cells may be formed of a bi-cell, or a full cell, or a combination of a bi-cell and a full cell, and the bi-cell is an A-type bi-cell in which a positive electrode, a negative electrode and a positive electrode are sequentially stacked with a separator interposed therebetween, or a negative electrode, a positive electrode and a At least one of C-type bicells in which the negative electrode is sequentially stacked with a separator interposed therebetween may be used.

The structure and the effect of a specific electrode assembly for achieving this will be described in detail through non-limiting examples to be described in detail below.

In one specific example, the total number of unit cells constituting the electrode assembly is n (4≤n≤50);

The unit cells located in the outer portion are the outermost unit cells, or a combination of the outermost unit cell and the unit cells adjacent to the outermost unit cells, in the range of 10% to 60% of the total number of unit cells, ;

The unit cells located in the inner portion may be the remaining unit cells from all unit cells except for the unit cells located in the outer portion.

If the number of unit cells located in the outer portion is less than 10% of the total number of unit cells, the electrode mixture layer having a high porosity occupies most of the electrode assembly. At this time, in order to keep the amount of energy of the electrode assembly the same as before, since the content of the electrode mixture is more input than before, the area or thickness of the electrode assembly may be increased, and thus the energy density of the battery may be reduced.

When the number of unit cells located in the outer portion exceeds 60% of the total number of unit cells, it means that the unit cell with a low porosity exceeds 60% of the electrode assembly, so the unit cells present in the outer portion of the electrode assembly Their electrolyte impregnability may be insufficient.

In addition, the difference between the average porosity of the unit cells located in the outer portion and the average porosity of the unit cells located in the inner portion is in the range of 0.1% to 20%, specifically, may be in the range of 1% to 10%. When the difference in average porosity is less than 0.1%, the difference in porosity between the inner region and the outer region is not large, so it is difficult to affect the electrolyte impregnation property of the battery cell in the inner region. When it exceeds 20%, the unit cells located in the inner region contain Since the amount of the electrode mixture becomes insufficient, the energy density and output characteristics of the battery may be deteriorated.

k number of unit cells located in the outer part sequentially adjacent to the outermost unit cell and the outermost unit cell (0≤k≤13, provided that k is smaller than n and the range satisfying the conditions of 10% to 60% ), the porosity may all be the same from the outermost unit cell to the k-th unit cell in some cases.

In another specific example, k number (0≤k≤13, provided that k is smaller than n and the 10% to the outermost unit cell and the outermost unit cell sequentially adjacent to the unit cells located in the outer part When defined as unit cells of a range that satisfies the condition of 60%), the porosity may sequentially increase from the outermost unit cell to the k-th unit cell.

The unit cells classified as being present at the position of the outer part may also decrease the impregnation property of the electrolyte as they are stacked closer to the center of the electrode assembly, so the porosity from the outermost unit cell to the k-th unit cell is sequentially It is possible to further improve the impregnability of the electrode assembly while increasing the .

On the other hand, in the electrode assembly, the unit cells located at the k-th position from the outermost unit cell exist by two regardless of the structure of the electrode assembly, except for the unit cell located at the center when the unit cells are stacked in odd numbers, The two unit cells may have the same or different porosity, but if the porosity of each of the two unit cells is set to be lower than that of the adjacent k+1-th unit cell, there is no problem in manufacturing.

In another specific example, in order to uniformly improve the electrolyte impregnation of the unit cells located in the inner portion, the unit cells in the inner portion may all have the same porosity.

In another specific example, in the unit cells located in the inner portion, the porosity of the unit cell located in the center is the highest, and the porosity of the unit cell is sequentially decreased according to the distance from the unit cell located in the center. can

The electrolyte is generally injected from the end of the battery case for smooth sealing of the battery, and is often impregnated in the order close to the outermost unit cell and the outermost unit cell, so the unit cell located in the center of the electrode assembly is an electrode. Since it is farthest from the outermost unit cell of the assembly, an area that cannot be impregnated with the electrolyte may be formed more widely, or the time for being impregnated with the electrolyte may be further increased. That is, since each unit cell is not easily impregnated with the electrolyte as the distance from the nearest outermost unit cells increases, the porosity of the unit cell is greatly adjusted as the distance from the unit cell located in the center increases as described above, and the electrode It is possible to further increase the electrolyte impregnability of the assembly.

The porosity can be adjusted by the rolling rate when the electrode assembly is coated on the electrode plate and then rolled, and in this case, the porosity is set by adjusting the thickness after using the same amount of the electrode mixture for the electrode plates of each unit cell. , it is possible to design the porosity for each unit cell and/or electrode, so that the quality of the unit cell included in the electrode assembly can be uniformly produced.

The present invention also provides a secondary battery in which an electrode assembly is built in a battery case together with a non-aqueous electrolyte. The secondary battery is not particularly limited, but as a specific example, high energy density, discharge voltage, output stability, etc. It may be a lithium secondary battery such as a lithium ion (Li-ion) secondary battery, a lithium polymer (Li-polymer) secondary battery, or a lithium ion polymer (Li-ion polymer) secondary battery having advantages.

In general, a lithium secondary battery refers to a battery composed of a positive electrode, a negative electrode, a separator, and a lithium salt-containing non-aqueous electrolyte, which are the components of the electrode assembly.

The positive electrode, for example, is prepared by coating a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector and/or an extended current collector and then drying, and, if necessary, further adding a filler to the mixture do.

The positive electrode current collector and/or the extended current collector is generally made to have a thickness of 3 to 500 micrometers. The positive electrode current collector and the extended current collector are not particularly limited as long as they have high conductivity without causing a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum. A stainless steel surface treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector and the extended current collector may form fine irregularities on the surface thereof to increase the adhesive force of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwovens are possible.

The positive active material may _{include 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; Lithium manganese oxides such as Formula 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 ;} Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (wherein 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, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, lithium manganese composite oxide represented by Ni, 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; And the like Fe ₂ (MoO _{4) 3,} but is not limited to these.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive active material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or 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 fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive 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 butadiene rubber, fluororubber, various copolymers, and the like.

The filler is optionally used as a component for inhibiting the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. For example, an olipine-based polymer such as polyethylene or polypropylene; A fibrous material such as glass fiber or carbon fiber is used.

The negative electrode is manufactured by coating and drying the negative electrode active material on the negative electrode current collector and/or the extended current collector, and if necessary, the above-described components may be optionally further included.

The negative current collector and/or the extended current collector is generally made to have a thickness of 3 to 500 micrometers. Such a negative current collector and/or extended current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, Copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven body.

Examples of the negative electrode active material include carbon such as non-graphitizable carbon and graphitic 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 composite oxides such as Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloys; tin-based alloys; 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 metal oxides such as _{Bi 2} O _{5 ;} conductive polymers such as polyacetylene; A Li-Co-Ni-based material or the like can be used.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 micrometers, and the thickness is generally 5 to 300 micrometers. As such a separation membrane, For example, olefin polymers, such as chemical-resistant and hydrophobic polypropylene; A sheet or nonwoven fabric made of glass fiber or polyethylene is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The electrolyte may be a lithium salt-containing non-aqueous electrolyte, and includes a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc. are used, but are not limited thereto.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dime ethoxyethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyropion An aprotic organic solvent such as methyl acid or ethyl propionate may be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymer containing an ionic dissociation group or 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, sulfates, etc. of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS _{2 and the like may be used.}

The lithium salt is a material easily 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.

In addition, for the purpose of improving charge/discharge characteristics, flame retardancy, etc. in the nonaqueous electrolyte, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. have. In some cases, in order to impart incombustibility, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate) ), PRS (propene sultone), and the like may be further included.

In one specific example, LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ Lithium salt such as a cyclic carbonate of EC or PC and a low-viscosity solvent of DEC, DMC or EMC A lithium salt-containing non-aqueous electrolyte may be prepared by adding it to a mixed solvent of linear carbonate.

As described above, in the electrode assembly according to the present invention, the electrode porosity of the unit cells located in the inner portion is higher than that of the unit cells located in the outer portion, thereby improving the electrolyte impregnation property of the electrode located in the inner portion, resulting in By reducing lithium dendrites, it is possible to secure battery safety and cycle characteristics together.

1 is a schematic diagram of a conventional stack-folding electrode assembly;
2 is a schematic diagram of an electrode assembly according to an embodiment of the present invention;
3 is a schematic diagram of an electrode assembly according to another embodiment of the present invention;
4 is a schematic diagram of an electrode assembly according to another embodiment of the present invention;
5 is a schematic diagram of an electrode assembly according to another embodiment of the present invention;
6 is a schematic diagram of an electrode assembly according to another embodiment of the present invention;
7 is a schematic diagram of an electrode assembly according to another embodiment of the present invention.

Hereinafter, although described with reference to the drawings according to the embodiment of the present invention, this is for easier understanding of the present invention, and the scope of the present invention is not limited thereto.

1 schematically shows the general structure of a conventional stack-folding type electrode assembly.

Referring to FIG. 1 , the electrode assembly 100 is composed of a combination of unit cells of a cathode-separator-anode-separator-cathode structure and unit cells of a cathode-separator-cathode-separator-anode structure, and each of the electrode assembly The separation film 150 interposed between the unit cells surrounds each side of the unit cells 111 , 112 , 113 , 114 , 115 , 116 and 117 in which electrode terminals are not formed, and the unit All electrodes constituting the cells have the same porosity. On the other hand, the direct structure of the unit cell is not shown for the sake of simplification of the drawing.

2 schematically shows the structure of an electrode assembly according to an embodiment of the present invention.

Referring to FIG. 2 , the electrode assembly 200 includes unit cells 211 , 212 , 221 , 222 positioned on the outer part 210 , 220 and unit cells 231 , 232 , 233 positioned on the inner part 220 . ) and a separation film 250, and the unit cell located in the outer portion is a combination of the outermost unit cells 211 and 221 and the unit cells 212 and 222 adjacent to the outermost unit cells. made, the electrode mixture layer coated on the electrode plate has a relatively lower porosity than the unit cells (231, 232, 233) located in the inner portion.

3 schematically shows the structure of an electrode assembly according to another embodiment of the present invention.

Referring to FIG. 3 , the electrode assembly 300 includes unit cells 311 , 312 , 313 , 314 positioned in the outer part 310 and unit cells 331 , 332 , 333 positioned in the inner part 330 and It is composed of the separation film 350, and the unit cells located in the outer portion have the same porosity, and have a lower porosity than the unit cells 331, 332, 333 located in the inner portion.

4 schematically shows the structure of an electrode assembly according to another embodiment of the present invention.

Referring to FIG. 4 , the unit cells 411 , 412 , 421 , and 422 located in the outer portions 410 and 420 of the electrode assembly 400 sequentially have higher porosity as they are positioned closer to the center of the electrode assembly. Specifically, the unit cell 412 has a higher porosity than the unit cell 411 , and the unit cell 422 has a higher porosity than the unit cell 421 .

5 schematically shows the structure of an electrode assembly according to another embodiment of the present invention.

Referring to FIG. 5 , the unit cells 531 , 532 , 533 located in the inner portion 530 of the electrode assembly 500 are unit cells 511 , 512 , 521 , 522 located in the outer portions 510 and 520 of the electrode assembly 500 . ), and the unit cells 531 , 532 , and 533 located in the inner portion have the same porosity.

6 schematically shows the structure of an electrode assembly according to another embodiment of the present invention.

Referring to FIG. 6 , the unit cells 631 , 632 , and 633 located in the inner portion 630 of the electrode assembly 600 are greater than the unit cells 611 , 612 , 613 and 614 located in the outer portion 610 . The unit cells 611 , 612 , 613 , and 614 have a high porosity, and the unit cells 611 , 612 , 613 , and 614 located in the outer region all have the same porosity, and the unit cells 631 , 632 , 633 located in the inner region have the same porosity, respectively.

7 schematically shows the structure of an electrode assembly according to another embodiment of the present invention.

Referring to FIG. 7 , in the battery cells constituting the electrode assembly 700 , the unit cell 741 located at the center has the highest porosity, and the unit cells 731 and 732 located closest to the unit cell 741 . ) has the next highest porosity. As described above, the further away from the unit cell 741 located in the center, the lower the porosity, and as a result, the porosity of the unit cells 711 and 712 located at the outermost part of the electrode assembly is the lowest.

Those of ordinary skill in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (17)

As an electrode assembly having a structure in which a plurality of unit cells are stacked, the unit cells located on the outer side in the unit cell stack structure have a relatively low porosity of the electrode assembly layer coated on the electrode plate compared to the unit cells located on the inner portion ,
the total number of unit cells constituting the electrode assembly is n (4≤n≤50);
The unit cells located in the outer portion are the outermost unit cells, or a combination of the outermost unit cell and the unit cells adjacent to the outermost unit cells, in the range of 10% to 60% of the total number of unit cells, ;
The unit cells located in the inner portion are the remaining unit cells except for the unit cells located in the outer portion of all unit cells,
The unit cells located in the outer portion are placed in the outermost unit cell and the outermost unit cell.
When defined as k sequentially adjacent unit cells (0≤k≤13, where k is smaller than n and satisfies the conditions of 10% to 60%) of unit cells,
The porosity sequentially increases from the outermost unit cell to the k-th unit cell,
An electrode assembly, characterized in that all unit cells located in the inner portion have the same porosity. The electrode assembly according to claim 1, wherein the electrode assembly has a stacked structure, a stack-folding structure, or a lamination-stacked structure. The electrode assembly according to claim 1, wherein the unit cells are formed of a bi-cell, a full cell, or a combination of a bi-cell and a full cell. The method according to claim 3, wherein the bicell is an A-type bicell in which a positive electrode, a negative electrode, and a positive electrode are sequentially stacked with a separator interposed therebetween, or a C-type bicell in which a negative electrode, a positive electrode and a negative electrode are sequentially stacked with a separator interposed therebetween. Electrode assembly characterized in that. delete The electrode assembly according to claim 1, wherein a difference between the average porosity of the unit cells located in the outer portion and the average porosity of the unit cells located in the inner portion is in the range of 0.1% to 20%. The electrode assembly according to claim 1, wherein a difference between the average porosity of the unit cells located in the outer portion and the average porosity of the unit cells located in the inner portion is in the range of 1% to 10%. The method of claim 1,
k number of unit cells located in the outer portion sequentially adjacent to the outermost unit cell and the outermost unit cell (0≤k≤13, provided that k is smaller than n and the range satisfying the conditions of 10% to 60% When it is defined as unit cells of
Electrode assembly, characterized in that all porosity from the outermost unit cell to the k-th unit cell. delete delete The method according to claim 1, wherein among the unit cells located in the inner portion, the porosity of the unit cell located at the center is the highest, and the porosity of the unit cell is sequentially decreased according to the distance from the unit cell located at the center. electrode assembly with The electrode assembly according to claim 1, wherein the porosity is controlled by the rolling rate when rolling after coating the electrode assembly on the electrode plate. A secondary battery, characterized in that the electrode assembly according to any one of claims 1 to 4, 6 to 8, and 11 is embedded in the battery case together with the non-aqueous electrolyte. A battery module comprising the secondary battery according to claim 13 as a unit cell. A battery pack comprising the battery module according to claim 14 . A device comprising the battery pack according to claim 15 . 17. The method of claim 16, wherein the device is a computer, a mobile phone, a power tool, an electric vehicle (EV), a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric two-wheeled vehicle, an electric golf cart, or power storage. A device, characterized in that for a system.

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