KR20180113693A - Battery Cell Comprising Electrode Tab of Improved Weld-ability - Google Patents

Abstract

The present invention relates to a battery cell including an electrode with improved weldability. According to the present invention, a surface of an electrode tab is ginned through a ginning process to ensure the reliability of welding strength when welding with parts in a battery cell. The ginning process is performed in a slitting process of manufacturing an electrode tap so that each entity can be uniformly ginned, thereby providing an electrode tap with high process efficiency without deviation of the welding strength.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a battery cell including an electrode tab having improved weldability,

The present invention relates to a battery cell including an electrode tab with improved weldability.

BACKGROUND ART [0002] In recent years, rechargeable secondary battery cells have been widely used as energy sources for wireless mobile devices. In addition, the battery cell may be an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (HEV), a hybrid electric vehicle (E-bikes), electric scooters (E-scooters), electric golf carts (electric golf carts), and the like. carts, or power storage systems.

The battery cell has a structure in which an electrode assembly in which a separator is interposed between an anode and a cathode is sealed in a case in which the electrolyte is impregnated. The electrode assembly includes a jelly-roll type in which a positive electrode coated with an electrode active material on both sides of a long sheet-like current collector foil and a jelly-roll type wound roundly with a separator interposed therebetween, and a plurality of electrode active materials coated on both sides of a current collector foil And stacked in a stacked structure in which an anode and a cathode are sequentially stacked with a separator interposed therebetween.

The battery cell may be classified according to the shape in which the electrode assembly is housed in the battery case. The battery cell may be classified into a cylindrical battery cell built in a cylindrical metal can, a rectangular battery cell built in a rectangular metal can, and a pouch- There is a pouch-shaped battery cell built into the case. Among them, a cylindrical battery cell has a relatively large capacity and is structurally stable.

Generally, in a cylindrical battery cell, a negative electrode tab extending from a negative electrode of an electrode assembly is welded to the lower end of a can while a jelly-roll type electrode assembly is mounted on a cylindrical metal can, and the battery is sealed A positive electrode tab extending from the anode of the electrode assembly is welded to the protruding terminal of the cap assembly coupled to the top of the cap assembly.

However, due to impact or dropping applied from the outside of the battery cell, the bonding force of the welded portion inside the battery is weakened, so that a part or the whole of the welded portion is detached or cut off. In this state, a large amount of current There is a risk of heat generation and explosion by the short circuit.

Therefore, there is a high need for a battery cell having a structure with improved welding strength.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

An object of the present invention is to provide a battery cell having a structure with improved welding strength.

According to an aspect of the present invention, there is provided a battery cell comprising:

A battery cell having a structure in which a jelly-roll in which a positive electrode tab and a negative electrode tab protrude outward is embedded in a metal can as a battery case together with an electrolyte,

The jelly-roll has a structure in which a positive electrode sheet and a negative electrode sheet are wound with a separator interposed therebetween;

Wherein the positive electrode tab has one end portion coupled to an unoccupied portion of a positive electrode current collector to which the positive electrode active material is not applied on the positive electrode sheet and the other end portion is coupled to the inside of the battery cell, The sheet is coupled to the non-coated portion of the negative electrode current collector to which the negative electrode active material is not applied, and the other end portion is coupled to the inside of the battery cell;

Wherein at least one of the positive electrode tab and the negative electrode tab is bonded to the inside of the non-coated portion or the battery cell in a state in which the surface of the tab is roughened by a chemical method or a mechanical method.

That is, in the battery cell of the present invention, since the surfaces of the positive electrode tab and the negative electrode tab are roughened by a chemical method or a mechanical method, the welding between the tab and the welded member, for example, And thus has a structural advantage of high welding strength.

In the present invention, one end portion of the positive electrode tab and the negative electrode tab may be respectively coupled to the non-coated portion of the current collector by ultrasonic welding.

In one specific example, the battery cell is a cylindrical battery cell having a cap assembly coupled to an open top end of a cylindrical metal can;

The other end portion of the positive electrode tab may be coupled to the lower end of the cap assembly by resistance welding. The other end portion of the negative electrode tab may be coupled to the lower end inner surface of the metal can by resistance welding.

In this structure, the welding surfaces of the tabs at the other end portions of the positive electrode tab and the negative electrode tab respectively coupled by the resistance welding may be roughened, and the other end portions of the positive electrode tab and the negative electrode tab, And further improved weld strength between the metal can.

In another specific example, the battery cell is a prismatic battery cell having a cap plate coupled to an open top end of a rectangular metal can including a protruding terminal;

The other end portion of the positive electrode tab may be connected by resistance welding to the lower surface of the cap plate electrically insulated from the protruding terminal. The other end portion of the negative electrode tab may be coupled to the lower end of the protruding terminal by resistance welding.

Similarly, the welding surfaces of the tabs may be roughened at the other end portions of the positive electrode tab and the negative electrode tab respectively coupled by the resistance welding, and the other end portions of the positive electrode tab and the negative electrode tab, Thereby providing a further improved weld strength between the lower end of the projecting portion and the projecting terminal.

That is, the roughened electrode tab according to the present invention can provide an improvement in the weld quality of all parts where welding with parts inside the case is performed.

In order to improve the welding strength described above, fine grooves having shapes corresponding to the shape of the roughened surface may be formed on the other side opposite to one surface of the roughened taps, and a portion of the electrolyte is introduced into the fine grooves . When the electrolytic solution impregnated into the electrode is depleted due to repetitive charging and discharging of the battery cell, the electrolytic solution may replace the electrolytic solution, thereby contributing to the improvement of the life characteristics of the secondary battery.

On the other hand, the surface of the roughened tab of the present invention may have minute unevenness of 1 micrometer to 1 millimeter in size.

When the size of the fine concavities and convexities is less than 1 micrometer, it is difficult to process for forming micro-irregularities, it is difficult to satisfy the desired improvement of the welding strength and it is not preferable. When the size is more than 1 millimeter, The strength becomes relatively weak, which is undesirable because it reduces the strength of the electrode tab.

The size of the fine irregularities can be determined by an average of the intervals formed by the minute irregularities and the depths of the valleys, which in other words can indicate the degree of surface roughness.

The fine irregularities may be formed by fine protrusions formed on the surface of the tab, or the fine irregularities may be formed by a plurality of fine grooves formed on the surface of the tab.

The fine unit means one selected from the width and the height of the projection and groove within at least 1 micrometer to 1000 micrometer.

Meanwhile, in the present invention, the surface of the electrode tab may be roughened by a chemical method or a mechanical method.

Specifically, the chemical method may be performed by etching, and the mechanical method may be performed by sandblasting or rolling.

The present invention also provides a secondary battery characterized by an electrode tab whose surface is roughened by the above method.

The secondary battery is not particularly limited in its kind, but specific examples thereof include a lithium ion (Li-ion) secondary battery having advantages such as high energy density, discharge voltage, and output stability, a lithium polymer secondary battery Battery, or a lithium secondary battery such as a lithium ion polymer secondary battery.

Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

The positive electrode is prepared, for example, 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 the resultant. Optionally, do.

The cathode current collector and / or the elongated current collector are generally made to have a thickness of 3 to 500 micrometers. The positive electrode current collector and the elongate current collector are not particularly limited as long as they have high conductivity without causing a chemical change in the battery, and examples thereof include stainless steel, aluminum, nickel, titanium, A surface treated with carbon, nickel, titanium, or silver on the surface of stainless steel may be used. The anode current collector and the elongate current collector may have various shapes such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, or the like by forming fine irregularities on the surface thereof to increase the adhesive force of the cathode active material.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; 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 , LiMnO ₂ and the like; 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 (where, M = Fe, Co, 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; 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 30% 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, 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 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 which 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 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing 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.

The negative electrode is manufactured by applying and drying a negative electrode active material on the negative electrode current collector and / or the extended current collector, and may optionally further include the components as described above.

The cathode current collector and / or the extension current collector are generally made to a thickness of 3 to 500 micrometers. The negative electrode current collector and / or the elongated current collector are not particularly limited as long as they have electrical conductivity without causing chemical changes in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, Surface treated with carbon, nickel, titanium, silver or the like on the surface of copper or stainless steel, and aluminum-cadmium alloy may be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane 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 membrane is generally 0.01 to 10 micrometers, and the thickness is generally 5 to 300 micrometers. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The electrolytic solution may be a non-aqueous electrolytic solution containing a lithium salt, and is composed of a non-aqueous electrolytic solution and a lithium salt. As the non-aqueous electrolyte, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like are used, but the present invention is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

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

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

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

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the nonaqueous electrolytic solution is preferably a solution prepared by dissolving or dispersing in a solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added have. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In one specific _{example, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing non-aqueous electrolyte.

The present invention also provides a battery pack including at least one secondary battery, a battery module including at least two secondary batteries, or a device including at least one secondary battery.

As described above, in the battery cell according to the present invention, since the surfaces of the positive electrode tab and the negative electrode tab are roughened by a chemical method or a mechanical method, the tab and the material to be welded thereto, So that the welding strength is high, which is a structural advantage.

1 is a vertical sectional view of a cylindrical rechargeable battery according to an embodiment of the present invention;
2 is a plan view of an electrode sheet constituting a jelly-roll type electrode assembly according to an embodiment of the present invention;
3 is a vertical cross-sectional view of a roughened electrode tab according to one embodiment of the present invention;
4 is a plan view of a roughened electrode tab according to another embodiment of the present invention;
5 is a plan view of a roughened electrode tab according to another embodiment of the present invention;
FIG. 6 is a schematic diagram illustrating a process of a slitting process according to an embodiment of the present invention; FIG.
7 is an exploded perspective view of a prismatic secondary battery according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited by the scope of the present invention.

FIG. 1 is a vertical sectional view of a cylindrical rechargeable battery according to the present invention. FIG. 2 is a plan view of an electrode sheet constituting a jelly-roll type electrode assembly according to an embodiment of the present invention. A vertical cross-sectional view of a roughened electrode tab according to one embodiment of the present invention is shown.

1 to 3, a cylindrical rechargeable battery 100 according to the present invention includes a cylindrical can 30, a jelly-roll type electrode assembly 30 accommodated in the can 30, a can 20, A cap assembly 40 coupled to an upper portion of the cap assembly 40 to form a positive electrode terminal 11 at an open upper end thereof, and a clamping portion 50 for sealing the battery. The electrode assembly 20 is housed in a battery case with a structure in which a positive electrode 21 and a negative electrode 22 are sandwiched between a separator 23 and a separator 23 therebetween.

The positive electrode 21 of the cylindrical battery 100 has an uncoated portion 23 of the positive electrode 21 to which the active material is not applied so that the positive electrode coating portion 27 coated with the active material is located on one side of the positive electrode tab 25 And one negative electrode tab 26 is attached to one end of the negative electrode 22, that is, the negative uncoated portion 24, which is the remaining portion except for the portion 28 coated with the negative active material, Respectively.

Since the electrode tabs 25 and 26 are attached to the electrode uncoated portions 23 and 24 as described above, it is possible to reduce the internal resistance as much as possible and generate less heat in an actual use environment, which is advantageous in high rate discharge .

The fine protrusions 270 or the fine grooves 280 are formed on the surface of the electrode tabs 25 and 26 where the welding is performed by a chemical or physical method. It is possible to improve the welding strength of all the welds performed in the welds 25,

4 is a schematic plan view of a roughened electrode tab according to another embodiment of the present invention. The positive electrode tab and the negative electrode tab have the same structure. For convenience of explanation, in the plan view of FIG. 4, .

Referring to FIG. 4, the positive electrode tab 300 includes a roughened portion 323, that is, a fine protrusion (270 in FIG. 3) or a fine groove (280 in FIG. 3) on one surface, (376) includes fine grooves (375).

The fine grooves 375 have a shape corresponding to the fine protrusions (270 in FIG. 3) or fine grooves (280 in FIG. 3) which are roughened regions 323 formed on one surface 375, It is possible to improve the electrolyte impregnability of the secondary battery, thereby contributing to improvement in the lifetime characteristics of the battery, and also to assure the reliability of the welding strength.

5 is a plan view of a roughened electrode tab according to another embodiment of the present invention. Similarly, only a positive electrode tab is illustrated in the plan view of FIG.

5, one surface 475 of the positive electrode tab 400 includes the roughened surface 423 and the other surface 424 of the opposite surface includes the fine grooves 423.

This structure is designed to further improve the electrolyte impregnation property. The structure has a roughened portion 423 including fine protrusions or fine grooves formed on the remaining surface (b) except the surface portion (a) of the positive electrode tab where welding is performed, Is an easy structure for fusing an electrolyte solution, which can further improve the electrolyte impregnability of the secondary battery, thereby contributing to improvement in the lifetime characteristics of the battery.

FIG. 6 schematically shows a slitting process according to an embodiment of the present invention.

Referring to FIG. 6, a roughing apparatus 501, a transferring member 502, a slitting apparatus 503, and a cutting apparatus 505 are shown as apparatuses constituting a slitting process.

More specifically, before the metal plate 508, which is moved through the transferring member 502, is cut by the slitting apparatus 503 and made into an electrode tab, the metal plate 508 are subjected to a roughening process. In this case, the roughening process is performed in a direction perpendicular to the moving direction of the metal plate 508, that is, in the width direction of the metal plate 508, and fine protrusions or fine grooves are included on the surface of the metal plate 508 through the roughening process Thereby forming a roughened portion 510 to be formed.

Thereafter, the metal plate 508 subjected to the roughening process is moved by the feeding member 502 to be fed into the slitting apparatus 503, and is fed by the slitting apparatus 503 to the metal plate 508 in the moving direction of the metal plate 508 The metal plate 508 is moved in the width direction of the electrode tab and is moved to the cutting device 505. The metal plate 508 is cut in the width direction of the metal plate by the cutting device 505, The electrode tab including the electrode tab 510 is completed.

Since the roughening process is performed on the electrode plate at a time prior to the slitting process, the electrode tabs are uniformly roughened, and the electrode tabs It is possible to increase the efficiency of the process.

The size of the electrode tab according to the manufacturing method described above can be freely set by adjusting the slitting apparatus 503 and the cutting apparatus 505. The roughing apparatus 501 is set according to the standard of the set electrode tab, The position and size of the cotton part 510 can be modified.

7 is an exploded perspective view of a prismatic secondary battery according to another embodiment of the present invention.

Referring to FIG. 7, the prismatic secondary battery 600 has a structure in which the electrode assembly 610 is housed in a sealed state. The positive electrode tab 602 is coupled to the lower surface of the cap plate 610, And the electrode terminal 603 is coupled to the protruding terminal 606 electrically insulated from the cap plate 610. The remaining structure is the same as that of the cylindrical secondary battery and the electrode tab of FIGS. A detailed description will be omitted.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

Claims (11)

A battery cell having a structure in which a jelly-roll in which a positive electrode tab and a negative electrode tab protrude outward is embedded in a metal can as a battery case together with an electrolyte,
The jelly-roll has a structure in which a cathode sheet and a cathode sheet are wound with a separator interposed therebetween;
Wherein the positive electrode tab has one end portion coupled to an unoccupied portion of a positive electrode current collector to which the positive electrode active material is not applied on the positive electrode sheet and the other end portion is coupled to the inside of the battery cell, The sheet is coupled to the non-coated portion of the negative electrode current collector to which the negative electrode active material is not applied, and the other end portion is coupled to the inside of the battery cell;
Wherein at least one of the positive electrode tab and the negative electrode tab is bonded to the inside of the non-molded portion or the battery cell in a state in which the surface of the tab is roughened by a chemical method or a mechanical method. The battery cell according to claim 1, wherein one end portion of each of the positive electrode tab and the negative electrode tab is coupled to an unoccupied portion of the current collector by ultrasonic welding. The method according to claim 1,
Wherein the battery cell is a cylindrical battery cell having a cap assembly coupled to an open upper end of a cylindrical metal can;
Wherein the other end portion of the positive electrode tab is coupled to the lower end of the cap assembly by resistance welding and the other end portion of the negative electrode tab is coupled to the lower end inner surface of the metal can by resistance welding. The battery cell according to claim 3, wherein the welding surfaces of the tabs are roughened at the other end portions of the positive electrode tab and the negative electrode tab, which are respectively connected by resistance welding. The method according to claim 1,
Wherein the battery cell is a prismatic battery cell having a cap plate coupled to an open upper end of a rectangular metal can including a protruding terminal;
The other end portion of the positive electrode tab is coupled by resistance welding to the lower surface portion of the cap plate electrically insulated from the protruding terminal and the other end portion of the negative electrode tab is coupled to the lower end of the protruding terminal by resistance welding. . The battery cell according to claim 5, wherein the welding surfaces of the tabs are roughened at the other end portions of the positive electrode tab and the negative electrode tab, which are respectively connected by resistance welding. The battery cell according to claim 1, wherein the surface of the roughened tab is formed with fine irregularities having a size of 1 micrometer to 1 millimeter. The battery cell according to claim 7, wherein the fine irregularities are formed by fine protrusions formed on a surface of the tab. 8. The battery cell of claim 7, wherein the fine irregularities are formed by a plurality of fine grooves formed on a surface of the tab. The battery cell according to claim 1, wherein the chemical method is performed by etching. The battery cell of claim 1, wherein the mechanical method is performed by sandblasting or rolling.

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