KR101156954B1 - Electrode Assembly with Excellent Weldability between Electrode Lead and Electrode Tabs and Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention provides a stack / folding electrode assembly manufactured by winding a plurality of bicells using a long sheet of separator, and welding electrode tabs thereof to electrode leads, wherein the bicell positioned at the outermost part of the electrode assembly is provided. The material of its interlayer electrode plate and the corresponding electrode lead is different, and the thickness of the interlayer electrode plate provides an electrode assembly composed of relatively thicker than the corresponding electrode plate on other bicells.

Therefore, the electrode assembly according to the present invention minimizes the breakage of the electrode tab during the welding of the electrode lead and the electrode tab, thereby reducing the defective rate of the battery and improving the processability.

Description

Electrode Assembly with Excellent Weldability of Electrode Lead and Electrode Tab and Secondary Battery Containing the Same {Electrode Assembly with Excellent Weldability between Electrode Lead and Electrode Tabs and Secondary Battery Comprising the Same}

1 is a schematic diagram of the general structure of the anode / separator / cathode / separator / anode bicell;

2 is a schematic view of the structure of the anode / separator / cathode / separator / anode bicell which is the outermost bicell in the electrode assembly according to an embodiment of the present invention;

3 is a schematic diagram of an upper end portion of a secondary battery incorporating a stack / foldable electrode assembly according to an exemplary embodiment of the present invention;

4 is an X-ray photograph of a cross-sectional shape of an upper end portion of a secondary battery including a stack / foldable electrode assembly according to an exemplary embodiment of the present invention.

The present invention relates to an electrode assembly having an excellent weldability between an electrode lead and an electrode tab, and a secondary battery including the same. More specifically, the electrode tab is wound after winding a plurality of bicells using a separator sheet having a long length. A stack / foldable electrode assembly manufactured by welding the electrodes to an electrode lead, wherein the bicell located at the outermost part of the electrode assembly has different materials of its interlayer electrode plate and corresponding electrode lead, and the thickness of the interlayer electrode plate is different. An electrode assembly is relatively thicker than the corresponding electrode plate on the cells.

As technology development and demand for mobile devices are increasing, the demand for batteries as energy sources is rapidly increasing, and accordingly, a lot of researches on batteries capable of meeting various demands have been conducted.

Representatively, there is a high demand for rectangular secondary batteries and pouch secondary batteries, which can be applied to products such as mobile phones with a thin thickness in terms of shape of batteries, and lithium ion batteries with high energy density, discharge voltage, and output stability in terms of materials. There is a high demand for lithium secondary batteries such as lithium ion polymer batteries.

In addition, the electrode assembly of the positive electrode / separator / negative electrode structure constituting the secondary battery is largely divided into jelly-roll type (winding type) and stack type (lamination type) according to its structure. The jelly-roll type electrode assembly is coated with an electrode active material or the like on a metal foil used as a current collector, dried and pressed, cut into bands of a desired width and length, and the membrane is separated using a separator to form a spiral. It is manufactured by winding. The jelly-roll type electrode assembly is suitable for cylindrical batteries, but has disadvantages such as peeling problems of electrode active materials and low space utilization when applied to rectangular or pouch type batteries. On the other hand, the stacked electrode assembly has a structure in which a plurality of anode and cathode unit cells are sequentially stacked, and it is easy to obtain a rectangular shape, but when the manufacturing process is complicated and an impact is applied, the electrode is pushed out and a short circuit occurs. There is a disadvantage that is caused.

In order to solve this problem, the electrode assembly of the advanced structure of the jelly-roll type and the stacked form, a full cell or anode (cathode) / separator / cathode of a certain unit size of the anode / separator / cathode structure A stack-foldable electrode assembly was developed in which a bicell of (anode) / membrane / anode (cathode) structure was folded using a continuous separation film of a long length, which was disclosed by the applicant of Korean patent application. No. 2001-82058, 2001-82059, 2001-82060, and the like.

On the other hand, a stack-foldable electrode assembly is manufactured by bonding its electrode tabs to one electrode lead by ultrasonic welding or the like in a state where a plurality of pole plates or bicells (or full cells) are overlapped. However, in this process, when the material of the electrode tab and the electrode lead of the bi-cell (or full cell) is different and the number of stacked bi-cells is more than 9 bi-cells, the crystal lattice of the metal mainly in the mutual bonding of these metals Due to the difference in physical properties such as the material of the electrode tab and the electrode lead, overfusion occurs in the process of applying a stronger force or applying a high ultrasonic vibration than the case of the same material.

Therefore, the electrode tabs located at the outermost part of the stack-folding electrode assembly directly contacted with strong force from the outside and the welding tip may be damaged during the welding process, adversely affecting the processability of the battery manufacturing, and may also cause an increase in the defective rate. There is a problem.

In particular, the problem of breakage of the tabs and leads due to over-fusion caused by the welding process of the electrode tabs and the electrode leads (particularly the negative electrode tabs and the Ni leads) may be related to process variables such as welding pressure and high frequency frequency during ultrasonic welding. It is difficult to adjust and improve. Due to these process limitations, there is a need for a technology that can improve the stability of the process side through a more fundamental improvement in the material side, and dramatically improve the problem of defect rate generation such as breakage of the electrode tab and electrode lead. It is emerging.

In this regard, in the present invention, the bi-cell located at the outermost part of the electrode assembly is a bicell located at the outermost part of the electrode assembly by using that the thickness of its interlayer electrode plate is relatively thicker than the corresponding electrode plate on other bi-cells. In order to solve the above problems by increasing the thickness of the electrode tab of the interlayer electrode plate. Among some prior arts, a technique for thickening an electrode plate positioned at the outermost part in a manufacturing process of a stacked electrode assembly is known.

Japanese Patent Application Laid-Open No. 2002-110170 discloses a battery in which the thickness of the outermost electrode current collector includes an electrode assembly thicker than at least one of the thickness of the innermost electrode current collector.

Further, Japanese Patent Application Laid-Open No. 2001-068155 has the same polarity as that of such an electrode without forming an electrode mixture layer on at least one outermost electrode of the electrode group of the stacked electrode assembly in which the outer surface is covered with an outer package including a metal foil. The polymer electrolyte battery which connected the electrode lead of this, and connected the metal foil contained in the said exterior body to the electrode terminal which has a polarity opposite to the electrode terminal of the said outermost layer is disclosed.

Further, Japanese Patent Application Laid-Open No. 2004-139775 allows the outermost current collector to be formed thicker than the current collectors of other electrodes included therein in the stacked electrode assembly, and the outermost current collector has a heat dissipation member formed therein. Disclosed is a battery including a stacked electrode assembly.

On the other hand, Japanese Patent Application Laid-Open No. 2004-174691 discloses a bipolar battery in which the current collector of the outermost electrode includes a stacked electrode assembly thicker than the current collector therein.

However, since the prior arts are techniques applied to a stacked electrode assembly, a technique of only thickening the outermost current collector to secure safety during internal short circuit, and thus, stack-foldable electrodes using a bicell as a unit cell. When the material of the electrode tab and the electrode lead is different in the assembly, it does not provide a solution to serious problems caused by the breakdown of the electrode tab of the bi-cell located in the outermost of the electrode assembly during the welding process.

Therefore, there is a high need for a technique capable of fundamentally solving such problems.

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

After various experiments and in-depth studies, the inventors of the present application have a bicell-based stack / foldable electrode assembly, wherein when the material of the electrode layer corresponding to the middle layer plate of the outermost bicell and the electrode lead is different, When the thickness of the interlayer electrode plate is made relatively thicker than the corresponding electrode plate on other bicells, the defective rate of the battery caused by breakage of the electrode tabs located at the outermost part of the electrode assembly during the welding process is reduced, and the processability of the battery manufacturing is reduced. It confirmed that there exists an advantage of being improved, etc., and came to complete this invention.

Accordingly, the electrode assembly according to the present invention is a stack / folding electrode assembly manufactured by winding a plurality of bicells using a long sheet separator and then welding electrode tabs thereof to an electrode lead, the outermost part of the electrode assembly. The bicell located at is different in the material of its interlayer electrode plate and corresponding electrode lead, and the thickness of the interlayer electrode plate is composed of relatively thicker than the corresponding electrode plate on other bicells.

Since the electrode assembly of the present invention is basically based on the structure of the stack-foldable electrode assembly, it can be manufactured with higher productivity than the stacked structure, and its interlayer electrode plate and the corresponding electrode in the outermost bicell When the material of the lead is different, the thickness of the interlayer electrode plate is relatively thicker than that of the corresponding electrode plate on the other bicells. Therefore, when a plurality of electrode tabs and electrode leads are connected, a strong force is applied to the electrode tabs or high ultrasonic vibration is applied. Even if the welding tip is in direct contact, damage of the electrode tab protruding from the relatively thick interlayer electrode plate is minimized and breakage due to over-fusion is prevented, thereby improving processability of the battery manufacturing and reducing the defective rate. .

As described in the related arts of the stacked electrode assembly described above, a case in which the thickness of the outermost electrode plate is thickened in the outermost bicell may be considered, but in this case, the outer electrode is positioned on both sides of the intermediate layer in the outermost bicell. Since the thickness of the same electrode pole plate must be different, there is a problem that the manufacturing efficiency is greatly reduced. In consideration of this, a method of thickening all of the same electrode electrode plates on both sides of the outermost bicell with respect to the intermediate layer may be considered, but in this case, the thickness of the outermost bicell becomes too thick to reduce the battery capacity. This happens.

As a result, the electrode assembly of the present invention is thicker than the outermost layer (the middle layer of the outermost layer bicell) in the overall stacked structure, there is a difference from the configuration of the prior art described above.

In the present invention, the bi-cell is a structure in which the same electrode is located on both sides, that is, a cell having a positive electrode-positive electrode or a negative electrode structure, for example, the bi-cell is a positive electrode / separator / cathode / separator / anode cell and A cathode / separator / anode / separator / anode cell, etc. are mentioned. In consideration of the battery assembly process, operating performance, etc., the preferred number of bicells in one stack-foldable electrode assembly may be 3 to 30 pieces.

In one preferred example, the outermost bicell may be of a structure in which the interlayer electrode plate is a cathode.

In general, the electrode leads connected to the negative electrode are often different from the material of the negative electrode in view of electrical conductivity and mechanical strength. For example, copper is used as the negative electrode plate and nickel is used as the negative electrode lead. This is used. Therefore, when the interlayer electrode plate of the outermost bicell is a negative electrode, the material of the electrode tab and the electrode lead protruding from the interlayer electrode plate is different, so that the materials of the electrode tab and the electrode lead are more different than those of the same electrode tab. A stronger force or high ultrasonic vibration is applied to the joint. Therefore, in this case, the outermost bicell is preferably a case where the intermediate layer electrode plate is a cathode so as to prevent a problem of breakage of the electrode tab.

As described above, the negative electrode is made of a copper material, and the corresponding negative electrode lead is preferably made of a nickel material, and copper is a material of the negative electrode because of its advantages such as excellent electrical conductivity, excellent workability, and appropriate strength. Nickel may be suitably used, and nickel has almost the same characteristics as copper, but may be preferably used as a material of the negative electrode lead because it has better mechanical strength than copper.

On the other hand, in the electrode made of the same material as the electrode plate and electrode lead, the electrode plate and the electrode lead is preferably made of aluminum, aluminum has good electrical conductivity and corrosion resistance, due to the advantages of excellent malleability and ductility and excellent workability Can be used simultaneously as the material of the electrode lead. Therefore, the electrode made of the same material as the electrode plate and the electrode lead may be an anode.

Bicells positioned at the outermost part of the electrode assembly of the bicells are not preferably coated with an active material on the outer pole plate. Thus, the electrode assembly not coated with the active material on the outer pole plate has an internal short circuit. When a problem that threatens the safety of the battery such as application of an external shock or needle penetration is inevitable, the short-circuit current is concentrated in the bicell located at the outermost part of the thick layer of the middle layer, even though the amount of heat generation increases, Since there is no layer to facilitate heat dissipation, the possibility of ignition and explosion is reduced, and the safety of the battery can be improved.

In one preferred example, the thickness of the bilayer electrode plate of the outermost bicell may be 20 to 500% thicker than the bilayer electrode plate of the other bicells.

If the thickness of the middle layer electrode plate of the outermost bicell is too thick, the battery capacity per unit volume can be reduced by increasing the total thickness and volume of the electrode assembly, and if the thickness of the intermediate layer electrode plate is too thin, the electrode connected to the electrode plate Since the thickness of the tab is also thin, it is not preferable because it is difficult to expect the effect of preventing damage to the desired electrode tab and improving processability when connecting the electrode tab and the electrode lead.

As a specific example of the thickness ratio of the middle layer electrode plate of the outermost bicell and the middle layer electrode plates of the other bicells, the thickness of the corresponding electrode plate of the other bicells is 8 to 10 μm, The thickness of an intermediate | middle layer electrode plate can use preferably 10-50 micrometers in the range larger than the said range.

The welding may be preferably performed by applying ultrasonic waves to the contact portion of the welding base material to generate fine vibrations, thereby ultrasonically welding the contact portions by melting with heat energy by friction.

Coupling by the ultrasonic welding proceeds on the principle that welding is rapidly performed as vibration energy is converted into thermal energy by friction at the interface between the electrode tab and the electrode lead by using high frequency vibration generated by ultrasonic waves of about 20 KHz.

The present invention also provides a secondary battery comprising the electrode assembly, preferably a lithium secondary battery. The lithium secondary battery has a structure in which a lithium salt-containing non-aqueous electrolyte is impregnated into the electrode assembly.

Other components of the lithium secondary battery according to the present invention will be described below.

The positive electrode for a lithium secondary battery is prepared by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder in the form of a slurry on a positive electrode current collector, followed by drying and compressing the filler, and optionally adding a filler to the mixture. It can also be added.

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 , Cu ₂ V ₂ O ₇ and the like; 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 (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein 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 alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The conductive material is typically added in an amount of 1 to 50% by weight based on the total weight of the mixture including the positive electrode 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 whiskeys 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 the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode 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 for a lithium secondary battery is manufactured by coating, drying, and compressing a negative electrode material on a negative electrode current collector, and if necessary, components of the positive electrode (binder, conductive material, filler, etc.) as described above may be further included.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me ': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 <x≤1;1≤y≤3; 1≤ metal composite oxides such as z ≦ 8); Lithium metal; Lithium alloys; 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; Li-Co-Ni-based materials and the like can be used.

The nonaqueous electrolyte for lithium secondary batteries consists of a nonaqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, and 1,2-dimethoxy ethane. , Tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate , Phosphoric acid triester, trimethoxy methane, dioxolon derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyroionate Aprotic organic solvents, such as ethyl propionate, 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.

As the inorganic solid electrolyte, for example, 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 and the like 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 good material to be dissolved 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., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

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.

1 is a vertical cross-sectional view of a conventional anode / separator / cathode / separator / anode bicell is shown schematically, Figure 2 is a cathode / separator / cathode / separator / anode bicell according to an embodiment of the present invention A vertical cross section is schematically shown.

Referring to FIG. 1, in the bicell 40, a negative electrode 10 having active materials coated on both surfaces is disposed between two positive electrodes 20 having active materials coated on both surfaces thereof, with a boundary between the separators 30. When the anode / separator / cathode / separator / anode bicell of this general type is disposed at the outermost side of the stack / foldable electrode assembly, the thickness of the cathode tab protruding from the cathode is thin as a general thickness, and thus, When the electrode leads are coupled, they are likely to be damaged in the process of applying a strong force or strong ultrasonic vibration. In other words. Since the cathode, which is the intermediate layer of the outermost bicell, is ultrasonically welded in direct contact with a welding tip (not shown), there is a high possibility of breakage compared to the cathodes of the inner bicell.

On the other hand, referring to FIG. 2, when the bicell of FIG. 2 is disposed at the outermost part of the stack / foldable electrode assembly, the cathode 100, which is an intermediate layer of the bicell, is not only the anode 200 but also the cathode of FIG. 1. Since the electrode tab protruding from the cathode 100 may be thicker than that of the general electrode tab since it is relatively thick as compared with 10), a strong force or strong ultrasonic vibration may be applied to the electrode tab when the electrode tab and the electrode lead are combined. Even if applied, the likelihood of breakage or damage is significantly reduced.

In addition, the active material is not applied to the outermost electrode plate (anode: 210). Therefore, in case of a problem that threatens the safety of the battery such as internal short circuit and needle penetrating, even if the short circuit current is concentrated and the heat generation amount increases, the active material layer does not exist in the outermost electrode plate 210, thereby facilitating heat dissipation. The safety of the battery can be improved by reducing the possibility of fire and explosion.

3 schematically shows an upper end of an electrode assembly of a secondary battery in which a stack / foldable electrode assembly is incorporated;

Referring to FIG. 3, in the outermost bicell of the stack / foldable electrode assembly 500, the intermediate layer electrode plate 100 is a cathode, and is formed thicker than other cathodes inside. Since the negative electrode tab 110 protruding from the negative electrode 100 is also relatively thicker than other negative electrode tabs in the inside, during ultrasonic welding with the electrode lead 400, the negative electrode tab 110 is in direct contact with the welding tip at the welding region 600. Even if a strong ultrasonic vibration is applied in the state, the damage or damage thereof is minimized, which may contribute to the reduction of the defective rate of the battery and the improvement of fairness.

Hereinafter, the present invention will be further described with reference to Examples, but the scope of the present invention is not limited thereto.

Example 1

1-1. Manufacture of anode

LiCoO ₂ was used as a positive electrode active material, and 95% by weight of LiCoO ₂ , 2.5% by weight of Super-P (conductive material) and 2.5% by weight of PVdF (binder) were added to N-methyl-2-pyrrolidone (NMP) as a solvent. After preparing the positive electrode mixture slurry, the positive electrode sheet was prepared by coating, drying and pressing on a long sheet aluminum foil.

1-2. Preparation of Cathode

As the negative electrode active material, artificial graphite was used, 95% by weight of artificial graphite, 1% by weight of Super-P (conductive material), and 4% by weight of PVdF (binder) were added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode sheet was prepared by coating, drying and pressing on an elongated sheet copper foil.

1-3. Bicell  Produce

1-1 and 1-2 of the positive and negative electrodes and a porous separator (Cell Guard ^TM) for use in a cathode / separator / anode / separator / cathode bi-cell ( 'A-type bi-cell ") and a negative electrode / separator / cathode / separator / A plurality of cathode bicells ('C-type bicells') were manufactured, and the thicknesses of the cathodes on both sides of the intermediate layer cathode and the C-type bicell in the general A-type bicell were 9 μm. In addition, two outermost anode / separator / cathode / separation membrane / anode bicell ('outermost A-type bicell') were also manufactured, and the thickness of the cathode, which is an intermediate layer, was 30 in the outermost A-type bicell. [Mu] m.

1-4. Manufacture of batteries

By placing the A-type bicells and the C-type bicells in a proper arrangement on a long sheet-type porous separator (CellGuard ^TM ), and finally, the two outermost A-type bicells are placed side by side and wound up. In addition, a stack / foldable electrode assembly having a relatively thicker thickness of the cathode of the intermediate layer positioned at the outermost part of the electrode assembly than the corresponding cathode on other bicells was prepared. Then, the negative electrode tabs and the positive electrode tabs were ultrasonically welded to the electrode leads made of nickel and aluminum, respectively, and embedded in a rectangular battery case, and the stack / foldable electrode assembly was impregnated by impregnating a carbonate electrolyte of 1M LiPF ₆ . A built-in rectangular battery (see FIG. 4, which is an X-ray photograph of an upper cross-sectional shape of a secondary battery) was manufactured.

Comparative Example 1

A battery was manufactured in the same manner as in Example 1, except that general A-type bicells were also used at the outermost side of the stack / foldable electrode assembly.

[Experimental Example 1]

Ten batteries each of Example 1 and Comparative Example 1 were subjected to 10 charge / discharge processes, and then disassembled and observed inside.

As a result, the cells of Example 1 had no abnormality in the ultrasonic welding portions of the electrode tabs and the electrode leads in all 10 cells, but the cells of Comparative Example 1 had damaged or broken electrode tabs at the connection portions of the electrode tabs and the electrode leads. Four cells were found.

Therefore, in the battery of Example 1 according to the present invention, since the thickness of the interlayer electrode plate is relatively thicker than that of the corresponding electrode plate on other bicells in the bicell located at the outermost part of the electrode assembly, welding of the electrode lead and the electrode tab is performed. It can be seen that the failure rate of the battery is reduced because the breakage of the electrode tab is minimized in the process.

Those skilled 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.

As described above, in the stack / foldable electrode assembly according to the present invention, the material of the intermediate layer electrode plate of the outermost bicell and the electrode lead corresponding thereto is different, and the thickness of the intermediate layer electrode plate is different on the bicells. Since it is made of a relatively thicker than the corresponding electrode plate, the breakage of the electrode tab is minimized during the welding process of the electrode lead and the electrode tab, thereby reducing the defective rate of the battery and improving the processability.

Claims (10)

A stack / foldable electrode assembly fabricated by winding a plurality of bicells using a long length separator sheet and then welding their electrode tabs to an electrode lead, wherein the bicell located at the outermost part of the electrode assembly has its intermediate layer. The material of the electrode plate and the corresponding electrode lead is different, the thickness of the intermediate layer electrode plate is an electrode assembly, characterized in that relatively thicker than the corresponding electrode plate on the other bi-cells. The electrode assembly according to claim 1, wherein the outermost bicell has a structure in which the intermediate layer electrode plate is a cathode. The electrode assembly of claim 2, wherein the cathode of the bicell is made of a copper material, and the cathode lead corresponding thereto is made of a nickel material. The electrode assembly of claim 1, wherein the electrode plate and the electrode lead are made of aluminum. The electrode assembly of claim 1, wherein the bicells positioned at the outermost part of the electrode assembly are not coated with an active material on an outer electrode plate. The electrode assembly according to claim 1, wherein a thickness of the middle layer electrode plate of the outermost bicell is about 20 to 500% thicker than that of the corresponding electrode plates of other bicells. The thickness of the corresponding electrode plate of the other bi-cells is 8 to 10㎛, the thickness of the middle layer of the outermost bi-cell plate is 10 in a range larger than the thickness range of the corresponding electrode plate of the other bi-cells. Electrode assembly, characterized in that from 50 ㎛. The electrode assembly of claim 1, wherein the welding is ultrasonic welding. A secondary battery comprising the electrode assembly according to any one of claims 1 to 8. The secondary battery of claim 9, wherein the battery is a lithium secondary battery.

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