Patent Description:
The present invention relates to an electrode having excellent weldability between an electrode lead and an electrode tab and a method of manufacturing the same. More particularly, the present invention relates to an electrode including an insulating layer on an electrode tab capable of reducing a welding defect rate between the electrode tab and an electrode lead and simplifying a process and a method of manufacturing the same.

A lithium secondary battery, which is capable of being charged and discharged, has attracted attention as a power source for devices that require high output and large capacity, including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (Plug-In HEV), which have been proposed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.

In such a device, a medium- or large-sized battery module including a plurality of battery cells electrically connected to each other is used in order to provide high output and large capacity.

It is preferable for the medium- or large-sized battery module to be manufactured so as to have as small a size and weight as possible, and therefore a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small ratio of weight to capacity, is mainly used as a battery cell (unit cell) of the medium- or large-sized battery module. In recent years, a pouch-shaped battery configured to have a structure in which a stacked type or stack/folded type electrode is mounted in a pouch-shaped battery case made of an aluminum laminate sheet has attracted considerable attention for reasons of low manufacturing cost, light weight, and easy deformation thereof, and the usage of the pouch-shaped battery has gradually increased.

One of the principal research projects for secondary batteries is to improve the safety of the secondary batteries. In general, a lithium secondary battery may explode due to high temperature and high pressure in the secondary battery which may be caused by an abnormal state of the secondary battery, such as short circuit in the secondary battery, overcharge of the secondary battery with higher than allowed current or voltage, exposure of the secondary battery to high temperature, or external impact applied to the secondary battery, such as dropping of the secondary battery. As one of such cases, there is a possibility of short circuit occurring in the secondary battery when the secondary battery is dropped or external force is applied to the secondary battery.

A general structure of a conventional pouch-shaped secondary battery including a stacked type electrode is shown in <FIG>.

Referring to <FIG>, the conventional pouch-shaped secondary battery includes an electrode <NUM>, electrode tabs <NUM> and <NUM> extending from the electrode <NUM>, electrode leads <NUM> and <NUM> welded to electrode tabs <NUM> and <NUM>, respectively, and a battery case configured to receive the electrode <NUM>.

In the electrode <NUM>, a positive electrode and a negative electrode may be sequentially stacked in the state in which a separator is interposed therebetween. The electrode <NUM> may be a jelly-roll type (wound type) electrode, configured to have a structure in which a long sheet type positive electrode and a long sheet type negative electrode are wound in the state in which a separator is interposed therebetween, a stacked type electrode, configured to have a structure in which a plurality of positive electrodes having a predetermined size and a plurality of negative electrodes cut to a predetermined size are sequentially stacked in the state in which separators are interposed therebetween, or a stacked and folded type electrode, configured to have a structure in which bi-cells or full cells, in each of which a predetermined number of positive electrodes and a predetermined number of negative electrodes stacked in the state in which separators are interposed therebetween, are wound.

The electrode tabs <NUM> and <NUM> extend from electrode plates of the electrode <NUM>. The electrode leads <NUM> and <NUM> are connected to a plurality of electrode tabs <NUM> and <NUM> extending from the electrode plates, and a portion of each of the electrode leads may be exposed outwards from the battery case.

A portion of each of the electrode leads <NUM> and <NUM> is electrically connected to a corresponding one of the electrode tabs <NUM> and <NUM>. At this time, joining therebetween is performed by welding to form a junction w. Joining may be performed by resistance welding, ultrasonic welding, laser welding, or riveting. In addition, protective films <NUM> and <NUM> may be interposed between the electrode leads and the battery case in order to improve sealability with the battery case and to secure electrical insulation.

When the battery drops or physical external force is applied to the upper end of the battery, whereby the electrode tab comes into contact with the upper end of the electrode, short circuit occurs in the battery. In many cases, short circuit occurs due to contact between the electrode tab and a negative electrode current collector or between the electrode tab and a negative electrode active material.

A front sectional structure and a side sectional structure of an electrode tab-electrode lead coupling portion having a conventional insulating layer are shown in <FIG>.

Referring to <FIG>, an insulating layer <NUM> may be provided at a portion of an electrode tab <NUM> that is joined to an electrode lead <NUM> in order to prevent short circuit. In this method, however, the force of joining between the electrode tab and the electrode lead is low and an electrode defect rate is increased due to the insulating layer, which is non-uniformly formed, a joining process is complicated, and it is not possible to completely prevent short circuit in the battery due to defects of the insulating layer. Consequently, there is a need for improvement.

Patent Document <NUM> relates to a positive electrode including an insulating layer formed on a positive electrode tab, wherein a portion of a positive electrode tab protruding from a positive electrode current collector is coated with an insulating material, thereby preventing internal short circuit when a cell is deformed or when an electrode is stacked as the result of the edge of the electrode is sharpened when the electrode is cut during manufacture of a battery or preventing physical short circuit between a positive electrode and a negative electrode due to contraction of a separator in a hightemperature atmosphere.

Patent Document <NUM> relates to a secondary battery including a sealing member disposed at a coupling portion between an electrode tab and an electrode lead, wherein the secondary battery includes an electrode having a stacked structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and an electrode lead electrically connected to electrode tabs of the electrode, the electrode lead extending outwards from a battery case, the electrode tab and the electrode lead are electrically connected to each other by ultrasonic welding to form a coupling portion therebetween, and the outer surface of the coupling portion is wrapped by a thermally fused sealing member. The force of sealing at the connection portion between the electrode tab and the electrode lead is increased using the sealing member, whereby it is possible to prevent short circuit.

Patent Document <NUM> and Patent Document <NUM> provide the construction of the insulating layer configured to prevent short circuit, but do not disclose the construction capable of simplifying the process of forming the insulating layer on the electrode tab by coating and reducing a rate of welding defect between the electrode tab and the electrode lead.

<CIT>, <CIT>, and <CIT> disclose an electrode tab and the insulation layer.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an electrode having excellent weldability between an electrode tab coated with an insulating layer and an electrode lead, thereby reducing a defect rate, and a method of manufacturing the same.

It is another object of the present invention to provide an electrode capable of forming an insulating layer through simple coating while expecting a sufficient insulation effect and a method of manufacturing the same.

In order to accomplish the above objects, an electrode according to the present invention is defined in the appended set of claims, the electrode includes an electrode current collector (<NUM>) coated with an electrode active material (<NUM>), an electrode tab (<NUM>) protruding from the electrode current collector (<NUM>), and an insulating layer (<NUM>) formed on the electrode tab (<NUM>) by coating, wherein the other surface of the electrode tab (<NUM>) having the insulating layer (<NUM>) formed thereon by coating is welded to an electrode lead (<NUM>).

In the electrode according to the present invention, the electrode tab (<NUM>) may be a non-coated portion including no electrode active material (<NUM>) layer.

In the electrode according to the present invention, the insulating layer (<NUM>) may be formed, by coating, on a portion or the entirety of the total length of the electrode tab (<NUM>) in a protruding direction of the electrode tab (<NUM>).

In the electrode according to the present invention, the insulating layer (<NUM>) may be formed by coating so as to have a width equal to the width of the electrode tab perpendicular to the protruding direction of the electrode tab (<NUM>).

In the electrode according to the present invention, the electrode tab (<NUM>) may include a portion of the electrode active material (<NUM>) layer.

In the electrode according to the present invention, the insulating layer (<NUM>) may include a portion or the entirety of the electrode active material (<NUM>), and may be formed, by coating, on a portion or the entirety of the total length of the electrode tab (<NUM>) in the protruding direction of the electrode tab (<NUM>).

In the electrode according to the present invention, the insulating layer (<NUM>) may be formed by coating so as to have a width equal to the width of the electrode tab (<NUM>) perpendicular to the protruding direction of the electrode tab (<NUM>).

In addition, the present invention provides a secondary battery including the electrode as defined in the appended set of claims.

Also, in the present invention, the secondary battery may be a cylindrical, prismatic, or pouch-shaped secondary battery.

The present invention provides an electrode manufacturing method as defined in the appended set of claims, the method includes a first step of forming, by coating, an insulating layer on a first side surface of an electrode tab formed at an electrode current collector so as to protrude therefrom and a second step of welding other side surface of the electrode tab opposite the first side surface on which the insulating layer is formed by coating and an electrode lead to each other.

Also, in the electrode manufacturing method according to the present invention, in the first step, the insulating layer may be formed, by coating, on the entirety of the first side surface of the electrode tab.

In addition, the electrode manufacturing method according to the present invention may further include a step of forming, by coating, the insulating layer on a pair of second side surfaces and a third side surface of the electrode tab in the first step.

In the present invention, one or more constructions that do not conflict with each other may be selected and combined from among the above constructions.

An electrode according to the present invention and a method of manufacturing the same have an advantage in that the other surface of an electrode tab having an insulating layer formed thereon by coating is welded to an electrode lead, whereby no insulating layer is included in the surface of the electrode tab that is welded, and therefore weldability with the electrode lead is improved, thus reducing a welding defect rate.

In addition, the electrode according to the present invention and the method of manufacturing the same have a merit in that, since the insulating layer is formed, by coating, on the surface the electrode lead of opposite the surface of the electrode tab to which the electrode lead is welded, a coating process and a welding process are simplified.

In addition, the electrode according to the present invention and the method of manufacturing the same have an advantage in that a process of manufacturing the electrode including the insulating layer formed on one surface thereof can be greatly simplified, whereby it is possible to reduce manufacturing cost.

A battery according to the present invention will be described with reference to the accompanying drawings.

<FIG> is a perspective view of an electrode having an electrode tab according to a first preferred embodiment of the present invention protruding therefrom, and <FIG> is a front view and a side sectional view of an electrode tab-electrode lead coupling portion including an insulating layer according to a first preferred embodiment of the present invention.

When describing the electrode according to the first embodiment of the present invention with reference to <FIG> and <FIG>, an electrode <NUM> including an electrode current collector <NUM> and an electrode active material <NUM>, an electrode tab <NUM> formed at one end of the electrode current collector <NUM> so as to protrude therefrom, an insulating layer <NUM> included in the electrode tab <NUM>, and an electrode lead <NUM> coupled to the electrode tab <NUM> by welding are provided.

When first describing the electrode <NUM> in detail, the electrode <NUM> may be a positive electrode or a negative electrode.

The positive electrode may be formed by applying a positive electrode active material, as the electrode active material <NUM>, to one surface or opposite surfaces of a positive electrode current collector, as the electrode current collector <NUM>.

Here, the positive electrode current collector is manufactured so as to have a thickness of <NUM> to <NUM>.

In addition, the positive electrode current collector is not particularly restricted as long as the positive electrode current collector exhibits high conductivity while the positive electrode current collector does not induce any chemical change in a battery to which the positive electrode current collector is applied. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, or sintered carbon. Alternatively, the positive electrode current collector may be made of aluminum or stainless steel, the surface of which is treated with carbon, nickel, titanium, or silver.

The current collector may have a micro-scale uneven pattern formed on the surface thereof so as to increase adhesive force of the positive electrode active material. The current collector may be configured in any of various forms, such as a film, a sheet, a foil, a net, a porous body, a foam body, and a non-woven fabric body.

In addition, the positive electrode active material may be a lithium-containing transition metal oxide or any one selected from among equivalents thereto. More specifically, the positive electrode active material may include a manganese-based spinel active material, a lithium metal oxide, or a mixture thereof. The lithium metal oxide may be selected from the group consisting of a lithium-manganese-based oxide, a lithium-nickel-manganese-based oxide, a lithium-manganese-cobalt-based oxide, and a lithium-nickel-manganese-cobalt-based oxide. More specifically, the lithium metal oxide may be LiCoO<NUM>, LiNiO<NUM>, LiMnO<NUM>, LiMn<NUM>O<NUM>, Li(NiaCobMnc)O<NUM> (where <NUM><a<<NUM>, <NUM><b<<NUM>, <NUM><c<<NUM>, a+b+c=<NUM>), LiNi<NUM>-YCoYO<NUM>, LiCo<NUM>-YMnYO<NUM>, LiNi<NUM>-YMnYO<NUM> (where <NUM>≤Y<<NUM>), Li(NiaCobMnc)O<NUM> (<NUM> < a < <NUM>, <NUM> < b < <NUM>, <NUM> < c < <NUM>, a+b+c=<NUM>), LiMn<NUM>-zNizO<NUM>, or LiMn<NUM>-zCozO<NUM> (where <NUM> < Z < <NUM>).

Also, a negative electrode current collector may be manufactured so as to have a thickness of <NUM> to <NUM>. The negative electrode current collector is not particularly restricted as long as the negative electrode current collector exhibits conductivity while the negative electrode current collector does not induce any chemical change in a battery to which the negative electrode current collector is applied. For example, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, or sintered carbon. Alternatively, the negative electrode current collector may be made of copper or stainless steel, the surface of which is treated with carbon, nickel, titanium, or silver, or an aluminum-cadmium alloy. In addition, the negative electrode current collector may have a micro-scale uneven pattern formed on the surface thereof so as to increase binding force of a negative electrode active material, in the same manner as the positive electrode current collector. The negative electrode current collector may be configured in any of various forms, such as a film, a sheet, a foil, a net, a porous body, a foam body, and a non-woven fabric body.

As the material for the negative electrode, for example, there may be used carbon, such as a nongraphitizing carbon or a graphite-based carbon; a metal composite oxide, such as LixFe<NUM>O<NUM> (<NUM>≤x≤<NUM>) , LixWO<NUM> (<NUM>≤x≤<NUM>), SnxMe<NUM>-xMe'yOz (Me: Mn, Fe, Pb, Ge; Me' : Al, B, P, Si, Group <NUM>, <NUM>, and <NUM> elements of the periodic table, halogen; <NUM><x≤<NUM>; <NUM>≤y≤<NUM>; <NUM>≤z≤<NUM>) ; lithium metal; a lithium alloy; a silicon-based alloy; a tin-based alloy; a metal oxide, such as SnO, SnO<NUM>, PbO, PbO<NUM>, Pb<NUM>O<NUM>, Pb<NUM>O<NUM>, Sb<NUM>O<NUM>, Sb<NUM>O<NUM>, Sb<NUM>O<NUM>, GeO, GeO<NUM>, Bi<NUM>O<NUM>, Bi<NUM>O<NUM>, or Bi<NUM>O<NUM>; a conductive polymer, such as polyacetylene; or a Li-Co-Ni-based material.

Next, the electrode tab <NUM> will be described. The electrode tab <NUM> may be formed at the electrode current collector <NUM> so as to protrude and extend therefrom.

Also, in the present invention, the electrode tab <NUM> may be formed by notching a continuous electrode sheet configured such that one surface or opposite surfaces of the electrode current collector <NUM> are coated with the electrode active material <NUM> at unit electrode intervals using a press die.

Consequently, the electrode tab <NUM> extends from one side of the electrode current collector <NUM>, and includes a pair of first side surfaces <NUM> opposite each other, corresponding to width direction (X-axis direction) surfaces, a pair of second side surfaces <NUM> opposite each other, corresponding to thickness direction (Y-axis direction) surfaces, and a third side surface <NUM> opposite the electrode current collector <NUM>.

Here, the electrode tab <NUM> is a non-coated portion, to which the electrode active material <NUM> is not applied, and includes an insulating layer <NUM> formed by coating one of the pair of first side surfaces <NUM> with an insulating material. The other of the first side surfaces <NUM>, on which no insulating layer <NUM> is formed, is coupled to the electrode lead <NUM>.

Meanwhile, the insulating layer <NUM> may be formed by coating the first side surface <NUM> of the electrode tab <NUM> with an insulating material in a protruding direction (Z-axis direction) from the electrode current collector <NUM>, and may be formed on a portion or the entirety of the length (Z-axis direction) of the first side surface <NUM>. Since there are no strict limitations on a coated region when the first side surface <NUM> of the electrode tab <NUM> is coated with an insulating material, insulating material coating may be simply and easily performed.

In addition, it is preferable for the insulating layer <NUM> to be formed by coating so as to have a width equal to the width (X-axis direction) of the electrode tab <NUM> perpendicular to the protruding direction of the electrode tab <NUM>. Since the electrode active material <NUM> is formed on the electrode current collector <NUM>, from which the electrode tab <NUM> protrudes and extends, the entire width of the first side surface <NUM> of the electrode tab <NUM> extending from the electrode current collector <NUM> is coated with an insulating material, which is advantageous to preventing short circuit caused by the electrode active material <NUM>.

Here, a dipping method, a dip coating method, a spray coating method, a spin coating method, a roll coating method, a die coating method, a roll coat method, a gravure printing method, or a bar coat method may be used as an insulating material coating method. However, the present invention is not limited thereto.

The insulating material may be polyethylene, polypropylene, polyether imide, polyacetal, polysulfone, polyether ether ketone, polyester, polyamide, an ethylene vinyl acetate copolymer, polystyrene, polytetrafluoroethylene, polysiloxane, polyimide, an arbitrary copolymer thereof, or an arbitrary mixture thereof. Thereamong, polyimide, which exhibits excellent electrical insulation and heat resistance, is particularly preferable. However, the insulating material is not limited to the above examples as long as the insulating material does not affect electrochemical reaction of a battery while exhibiting electrical insulation.

Depending on circumstances, an inorganic material may be further added to the polymer resin within a range within which the effect of the present invention is not damaged. SiO<NUM>, TiO<NUM>, Al<NUM>O<NUM>, ZrO<NUM>, SnO<NUM>, CeO<NUM>, MgO, CaO, ZnO, Y<NUM>O<NUM>, Pb(Zr,Ti)O<NUM> (PZT), Pb<NUM>-xLaxZr<NUM>-yTiyO<NUM> (PLZT), PB (Mg<NUM>Nb<NUM>/<NUM>) O<NUM>-PbTiO<NUM> (PMN-PT), BaTiO<NUM>, hafnia (HfO<NUM>), SrTiO<NUM>, and a mixture of two or more thereof may be mentioned as examples of the inorganic material.

In the present invention, the material for the electrode lead <NUM> is not particularly restricted as long as the electrode lead is made of a material capable of electrically connecting electrode tabs <NUM> to each other. Preferably, the electrode lead is a metal plate. A nickel plate, a copper plate plated with nickel, an aluminum plate, a copper plate, and an SUS plate may be mentioned as examples of the metal plate. However, the present invention is not limited thereto.

In the present invention, the electrode tab <NUM> and the electrode lead <NUM> may be joined to each other by welding. The electrode tab and the electrode lead are electrically connected to each other by ultrasonic welding. Coupling by ultrasonic welding is performed according to the principle by which high-frequency vibration generated by an ultrasonic wave of about <NUM> is applied, and vibration energy is converted into thermal energy due to friction at the interface between the electrode tab and the electrode lead as the result of operation of a horn and an anvil, whereby welding is rapidly performed.

A method of manufacturing the electrode according to the first embodiment of the present invention having the construction described above may include a step of coating a first side surface of an electrode tab <NUM> formed at an electrode current collector <NUM> so as to protrude therefrom with an insulating material to form an insulating layer <NUM> and a step of welding the other surface of the electrode tab <NUM> opposite the first side surface on which the insulating layer <NUM> is formed and an electrode lead <NUM> to each other.

In the coating step to form the insulating layer, the insulating layer may be formed on a portion or the entirety of the first side surface of the electrode tab <NUM> by coating.

<FIG> is a front view and a side sectional view of an electrode tab-electrode lead coupling portion including an insulating layer according to a second preferred embodiment of the present invention.

The second embodiment of the present invention is identical to the first embodiment of the present invention described with reference to <FIG> and <FIG> except that a portion of an electrode active material <NUM> is included in one surface of an electrode tab <NUM>, and therefore only the electrode active material <NUM> included in the electrode tab <NUM> will be described hereinafter.

Referring to <FIG>, an electrode active material may be formed on one surface of the electrode tab <NUM> in a protruding direction from one end of an electrode current collector <NUM> of the electrode according to the second embodiment of the present invention. The electrode active material formed on the electrode tab <NUM> may be formed as the result of an electrode active material <NUM> formed on the electrode current collector <NUM> extending to the electrode tab <NUM>.

The insulating layer <NUM> may be formed in a protruding direction (Z-axis direction) of the electrode tab <NUM>, including the entirety or a portion of the electrode active material formed on the electrode tab <NUM>, by coating. In addition, it is preferable for the insulating layer <NUM> to be formed by coating so as to have a width (X-axis direction) equal to the width of the electrode tab <NUM>. This is advantageous in preventing short circuit caused as the result of the electrode active material contacting another member. In addition, this is advantageous to delaying the progress of short circuit when a separator is contracted at high temperature.

A method of manufacturing the electrode according to the second embodiment of the present invention is identical to the method of manufacturing the electrode according to the first embodiment of the present invention described above except that the electrode active material is formed on the electrode tab <NUM>, and therefore a detailed description thereof will be omitted.

<FIG> is a front view and a side sectional view of an electrode tab-electrode lead coupling portion including an insulating layer according to a third preferred embodiment of the present invention.

The third embodiment of the present invention is identical to the first embodiment of the present invention described with reference to <FIG> and <FIG> except that an insulating layer <NUM> is further formed on a second side surface and a third side surface of an electrode tab <NUM> by coating, and therefore only the insulating layer <NUM> formed on the second side surface and the third side surface of the electrode tab <NUM> by coating will be described hereinafter.

In the third embodiment of the present invention, the insulating layer <NUM> may be formed on a pair of second side surfaces and a third side surface of the electrode tab <NUM> by coating, in addition to one first side surface of the electrode tab. The insulating layer <NUM> may be formed on a portion or the entirety of each of the four side surfaces. The insulating layer <NUM> may be formed by coating in a protruding direction (Z-axis direction) of the electrode tab <NUM>, and it is preferable for the insulating layer <NUM> to be formed by coating so as to have a width (X-axis direction) equal to the width of the electrode tab <NUM>.

Among five side surfaces of the electrode tab <NUM> extending and protruding from an electrode current collector <NUM>, the insulating layer is formed on the other four side surfaces, excluding the surface that is welded to an electrode lead <NUM>, which is advantageous in preventing short circuit due to corrosion of the electrode tab <NUM>.

A method of manufacturing the electrode according to the third embodiment of the present invention is identical to the method of manufacturing the electrode according to the first embodiment of the present invention described above except that the insulating layer is formed on a pair of second side surfaces and a third side surface of the electrode tab <NUM> by coating, in addition to the first side surface of the electrode tab, and therefore a detailed description thereof will be omitted.

The present invention may provide a secondary battery including the electrode described above. In general, for a lithium secondary battery, a negative electrode is manufactured so as to be larger than a positive electrode in consideration of a problem in that lithium ions are deposited on the negative electrode during charging and discharging. As a result, there is a high possibility of a positive electrode tab being brought into contact with a negative electrode (current collector or active material) of a power generating element first when external impact due to dropping is applied. In the case in which the positive electrode is smaller than the negative electrode, therefore, it is preferable to form an insulating layer on the positive electrode tab by coating. In the case in which the positive electrode and the negative electrode are the same size, on the other hand, the insulating layer may be formed on both the positive electrode tab and a negative electrode tab by coating.

Hereinafter, the present invention will be described in more detail with reference to the examples; however, the category of the present invention is not limited thereby.

LiNi<NUM>Mn<NUM>Co<NUM>O<NUM> was used as a positive electrode active material, carbon black was used as a conductive agent, and polyvinylidene fluoride (PVdF) was used as a binder. A mixture of the positive electrode active material, the conductive agent, and the binder mixed in a weight ratio of <NUM>:<NUM>:<NUM> was added to NMP, as a solvent, to manufacture a positive electrode active material slurry.

The positive electrode active material slurry was applied to an aluminum current collector having a thickness of <NUM> at a loading amount of <NUM> mAh/cm<NUM> at each surface thereof, dried, and pressed to obtain a positive electrode.

The positive electrode was punched to a size of <NUM> x <NUM> such that no electrode layer reached a portion of an electrode tab, a non-coated region of a front surface of the electrode tab was painted with a PVdF solution (NMP solution, containing <NUM>% of solid content) with a brush and dried at <NUM>, and a rear surface of the electrode tab and an electrode lead were welded to each other (<NUM>, <NUM> sec ultrasonic welding).

Example <NUM> is identical to Example <NUM> except that a positive electrode was punched to a size of <NUM> x <NUM> such that an electrode layer reached a portion of an electrode tab, and a non-coated region of a front surface of the electrode tab and a region that an active material reached were painted with a PVdF solution with a brush.

Example <NUM> is identical to Example <NUM> except that a non-coated region of a front surface of an electrode tab and a side surface of the electrode tab were painted with a PVdF solution with a brush.

Comparative Example <NUM> is identical to Example <NUM> except that a rear surface of an electrode tab was not welded, a front surface of the electrode tab was painted with a PVdF solution with a brush and was dried, and the front surface of the electrode tab was welded.

Comparative Example <NUM> is identical to Example <NUM> except that a rear surface of an electrode tab was not welded, <NUM>/<NUM> or more of the area of the electrode tab was painted with a PVdF solution with a brush and was dried, and the front surface of the electrode tab was welded.

Welding was performed <NUM> times on each of Examples <NUM> to <NUM> and Comparative Examples <NUM> and <NUM>, and the number of welding failures is shown in the following table.

In the present invention, failure of welding between an electrode tab and an electrode lead may be checked using the following method.

Claim 1:
An electrode (<NUM>) comprising:
an electrode current collector (<NUM>) coated with an electrode active material (<NUM>);
an electrode tab (<NUM>) protruding from the electrode current collector (<NUM>);
an insulating layer (<NUM>); and
an electrode lead (<NUM>),
wherein the electrode tab (<NUM>) includes:
- a pair of first side surfaces (<NUM>) opposite each other, corresponding to width direction (X-axis direction) surfaces,
- a pair of second side surfaces (<NUM>) opposite each other, corresponding to thickness direction (Y-axis direction) surfaces, and
- a third side surface (<NUM>) opposite the electrode current collector (<NUM>),
characterized in that
the insulating layer (<NUM>) is coated on one surface of the pair of first side surface (<NUM>), and
the electrode lead (<NUM>) is welded on the other surface of the pair of first side surface (<NUM>), said other surface being free of insulating layer coated thereon.