Patent Description:
The document <CIT> discloses a secondary battery, and the document <CIT> discloses a rectangular secondary battery. Batteries such as alkaline secondary batteries and nonaqueous electrolyte secondary batteries are used for purposes such as driving power sources for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV), and stationary rechargeable battery systems for reducing output fluctuations in solar or wind power generation, for example, and for peak-shifting grid power to be stored at night and used in the daytime.

A foreign object may be mixed into such a battery while being assembled. In particular, a metal foreign object mixed into a battery may cause an internal short circuit. The internal short circuit has the following mechanism.

First, adhering to a positive electrode material, a metal foreign object is, as metal ions, dissolved into an electrolyte by a high potential of the positive electrode. After reaching a negative electrode, the metal ions precipitate as a metal. The metal precipitates to grow toward the positive electrode, break through a separator, and come into contact with the positive electrode, thereby causing an internal short circuit.

Secondary batteries are usually assembled in a cleanroom to reduce foreign objects such as metal foreign objects mixed into the batteries. In addition, the metal foreign objects attached to an electrode body during the assembly are removed by air blowing, suction, magnetic force adsorption, or wiping with a polishing tape, for example.

Patent Document <NUM> suggests a sealed battery obtained by inserting an electrode body into a bag-shaped porous body, and inserting, into a sealed container, the porous body with the electrode body inserted thereinto.

Patent Document <NUM> fails to specifically describe any method or advantage of interposing the porous body between the electrode body and the lid of the sealed container. The specific method is unknown. In addition, the used porous body is a bag, which consumes the active material and the battery capacity.

In view of the foregoing background, it is an objective of the present invention to provide a battery capable of effectively reducing foreign objects mixed into an electrode body, without reducing the battery capacity.

The battery of the present invention includes an electrode body obtained by stacking a positive electrode plate and a negative electrode plate with a separator interposed therebetween, an exterior body having an opening and housing the electrode body, a sealing plate sealing the opening, and an external terminal attached to the sealing plate. A tab is provided at at least one of the positive electrode plate or the negative electrode plate, and is electrically connected to the external terminal via a current collector between the electrode body and the sealing plate. The current collector includes a first current collector and a second current collector. The first current collector and the second current collector are welded to each other at a welding point covered with a covering member.

The first current collector has a recess. The first current collector and the second current collector are stacked and welded at the recess. The covering member covers the recess.

The recess includes a thinner part. The first current collector is welded to the second current collector by full penetration welding at the thinner part.

The covering member enters a dent formed by the recess.

A battery of the present invention include an electrode body obtained by stacking a positive electrode plate and a negative electrode plate with a separator interposed therebetween, an exterior body having an opening and housing the electrode body, a sealing plate sealing the opening, and positive and negative external terminals attached to the sealing plate. A positive electrode tab provided at the positive electrode plate is electrically connected to the positive electrode external terminal via a positive electrode current collector between the electrode body and the sealing plate. A negative electrode tab provided at the negative electrode plate is electrically connected to the negative electrode external terminal via a negative electrode current collector between the electrode body and the sealing plate. The positive electrode current collector includes a first positive electrode current collector and a second positive electrode current collector. The first positive electrode current collector and the second positive electrode current collector are welded to each other at a welding point covered with a first covering member. The negative electrode current collector includes a first negative electrode current collector and a second negative electrode current collector. The first negative electrode current collector and the second negative electrode current collector are welded to each other at a welding point covered with a second covering member.

The first positive electrode current collector has a first recess. The first positive electrode current collector and the second positive electrode current collector are stacked and welded at the first recess. The first covering member covers the first recess.

The first recess includes a first thinner part. The first positive electrode current collector is welded to the second positive electrode current collector by full penetration welding at the first thinner part.

The first covering member enters a dent formed by the first recess.

The first negative electrode current collector has a second recess. The first negative electrode current collector and the second negative electrode current collector are stacked and welded at the second recess. The second covering member covers the second recess.

The second recess includes a second thinner part. The first negative electrode current collector is welded to the second negative electrode current collector by full penetration welding at the second thinner part.

The second covering member enters a dent formed by the second recess.

In the battery of the present invention, the tab provided at at least one of the positive and negative electrode plates is electrically connected to the external terminal via the current collector between the electrode body and the sealing plate. The current collector includes the first and second current collectors. The first and second current collectors are welded to each other at the welding point covered with the covering member. This configuration effectively reduces the dust generated by the welding between the first and second current collectors and entering the inside of the electrode body.

The following description of an advantageous embodiment is a mere example in nature, and is not at all intended to limit the scope, applications or use of the present invention. In the drawings below, constituent features substantially sharing the same function are denoted with the same reference sign for the sake of simplicity.

A configuration of a rectangular secondary battery <NUM> as a secondary battery of a first embodiment will be described below. Note that the present invention is not limited to the following embodiment.

As shown in <FIG> and <FIG>, the rectangular secondary battery <NUM> includes a battery case <NUM> including a rectangular exterior body <NUM> and a sealing plate <NUM>. The rectangular exterior body <NUM> is in the shape of a bottomed rectangular tube with an opening. The sealing plate <NUM> seals the opening of the rectangular exterior body <NUM>. Each of the rectangular exterior body <NUM> and the sealing plate <NUM> is made of metal, particularly, aluminum or an aluminum alloy in one preferred embodiment. The rectangular exterior body <NUM> houses an electrode body <NUM> obtained by stacking a positive electrode plate and a negative electrode plate with a separator interposed therebetween, together with an electrolyte. As will be described later, in this embodiment, the electrode body <NUM> includes first and second electrode body elements which have the same configuration.

As shown in <FIG>, the electrode body <NUM> includes, at the end at the sealing plate <NUM>, a positive electrode tab group 40A of positive electrode tabs (or tabs) <NUM> and a negative electrode tab group 50A of negative electrode tabs (tabs) <NUM>. The positive electrode tab group 40A is electrically connected to a positive electrode terminal <NUM> via a first positive electrode current collector (or positive electrode current collector) 6a and a second positive electrode current collector 6b. The negative electrode tab group 50A is electrically connected to a negative electrode terminal <NUM> via a first negative electrode current collector (or negative electrode current collector) 8a and a second negative electrode current collector 8b. The first and second positive electrode current collectors 6a and 6b and the first and second negative electrode current collectors 8a and 8b are attached to the side of the sealing plate <NUM> inside the battery, and connected to the positive and negative electrode tab groups 40A and 50A on the surface of the sealing plate <NUM> facing the inside of the battery.

The first and second positive electrode current collectors 6a and 6b and the positive electrode terminal <NUM> are made of metal, particularly, aluminum or an aluminum alloy in one preferred embodiment. Interposed between the positive electrode terminal <NUM> and the sealing plate <NUM> is an external insulation member <NUM> of a resin. Interposed between the first and second positive electrode current collectors 6a and 6b and the sealing plate <NUM> is an internal insulation member <NUM> of a resin.

The first and second negative electrode current collectors 8a and 8b and the negative electrode terminal <NUM> are made of metal, particularly, copper or a copper alloy in one preferred embodiment. The negative electrode terminal <NUM> has a part made of aluminum or an aluminum alloy, and a part made of copper or a copper alloy in one preferred embodiment. In this case, the part made of copper or a copper alloy is connected to the second negative electrode current collector 8b, and the part made of aluminum or an aluminum alloy projects outward beyond the sealing plate <NUM> in one preferred embodiment. Interposed between the negative electrode terminal <NUM> and the sealing plate <NUM> is an external insulation member <NUM> of a resin. Interposed between the first and second negative electrode current collectors 8a and 8b and the sealing plate <NUM> is an internal insulation member <NUM> of a resin.

Interposed between the electrode body <NUM> and the rectangular exterior body <NUM> is an electrode body holder <NUM> that is a resin sheet. A resin insulation sheet is folded and molded into a bag or a box as the electrode body holder <NUM> in one preferred embodiment. This electrode body holder <NUM> reliably keeps the electrode body <NUM> and the rectangular exterior body <NUM> electrically insulated from each other.

The sealing plate <NUM> has an electrolyte inlet <NUM> which is sealed by a sealing member (not shown) after injecting the electrolyte. The sealing plate <NUM> has a gas discharge valve <NUM> which is broken once the pressure inside the battery case <NUM> reaches a predetermined value or more to discharge the gas inside the battery case <NUM> outside the battery case <NUM>.

Now, the details of a production method and components of the rectangular secondary battery <NUM> will be described.

First, a method of producing a positive electrode plate will be described.

A slurry for a positive electrode active material mixture layer is prepared by kneading a positive electrode active material, a conductive agent, and a binder, for example. Examples of the positive electrode active material include lithium composite oxides such as lithium nickel cobalt manganese composite oxides. In addition, examples of the binder include fluorine resins such as polyvinylidene fluoride (PVdF). Examples of the conductive agent include carbon materials such as carbon black.

Alumina powder, graphite as a conductive agent, polyvinylidene fluoride (PVdF) as a binder, N-methyl-<NUM>-pyrrolidone (NMP) as a dispersion medium are kneaded into a slurry for a positive electrode protective layer.

The slurries for the positive electrode active material mixture layer and the positive electrode protective layer prepared as described above are applied to both sides of an aluminum foil as a positive electrode core with a thickness of <NUM> by a die coater. The slurry for the positive electrode protective layer is applied to at least one transverse end of an area applied with the slurry of the positive electrode active material mixture layer.

The positive electrode core applied with the slurries for the positive electrode active material mixture layer and the positive electrode protective layer is dried to remove NMP inside the slurry. Accordingly, the positive electrode active material mixture layer and the protective layer are formed. After that, the positive electrode active material mixture layer passes between a pair of press rollers so as to be compressed into a positive electrode original plate. This positive electrode original plate is cut into a predetermined size as a positive electrode plate <NUM> shown in <FIG>. The positive electrode plate <NUM> has a rectangular shape with an upper side from which the positive electrode tabs <NUM> project. The positive electrode plate <NUM> includes a narrow positive electrode protective layer 4c along the upper side, and a positive electrode active material mixture layer 4b from the bottom of the positive electrode protective layer 4c to the lower side of the positive electrode plate <NUM>. As described above, the positive electrode tabs <NUM> may be formed from the positive electrode core, or another member may be connected to the positive electrode plate to serve as the positive electrode tabs.

Next, a method of producing a negative electrode plate will be described.

A slurry for a negative electrode active material mixture layer is prepared by kneading a negative electrode active material, a conductive agent, a binder, and a thickener, for example. Examples of the negative electrode active material include carbon materials such as graphite. Examples of the binder include styrene butadiene rubber (SBR). Examples of the thickener include carboxymethyl cellulose (CMC).

The slurry for the negative electrode active material mixture layer prepared as described above is applied to both sides of a copper foil as a negative electrode core with a thickness of <NUM> by a die coater.

The negative electrode core applied with the slurry for the negative electrode active material mixture layer is dried to remove water inside the slurry. Accordingly, the negative electrode active material mixture layer is formed. After that, the negative electrode active material mixture layer passes between a pair of press rollers so as to be compressed into a negative electrode original plate. This negative electrode original plate is cut into a predetermined size as a negative electrode plate <NUM> shown in <FIG>. The negative electrode plate <NUM> has a rectangular shape with an upper side from which the negative electrode tabs <NUM> project. Accordingly, the negative electrode active material mixture layer 5b is formed on the entire surface of the negative electrode core except the negative electrode tabs <NUM>. As described above, the negative electrode tabs <NUM> may be formed from the negative electrode core, or another member may be connected to the negative electrode plate to serve as the negative electrode tabs.

The positive and negative electrode plates <NUM> and <NUM> prepared as described above are stacked one on the other with a separator interposed therebetween to obtain the multilayer electrode body <NUM>. The numbers of the positive and negative electrode plates <NUM> and <NUM> included in the electrode body <NUM> are not particularly limited but may be tens or more in one preferred embodiment. As shown in <FIG>, the electrode body <NUM> includes, at one end, the positive electrode tab group 40A of the positive electrode tabs <NUM> and the negative electrode tab group 50A of the negative electrode tabs <NUM>.

The positive electrode tab group 40A described above is connected to the first positive electrode current collector 6a shown in <FIG> by welding. The first positive electrode current collector 6a has a current collector through-hole 6e to face the electrolyte inlet <NUM> of the sealing plate <NUM>. The negative electrode tab group 50A described above is connected to the first negative electrode current collector 8a shown in <FIG> by welding. <FIG> shows that the positive electrode tab group 40A is connected to the first positive electrode current collector 6a, and the negative electrode tab group 50A is connected to the first negative electrode current collector 8a.

In this embodiment, as shown in <FIG>, the electrode body <NUM> includes first and second electrode body elements 3a and 3b. Note that the first and second electrode body elements 3a and 3b are prepared by the same method as the electrode body <NUM> described above.

A first positive electrode tab group 40A1 of the first electrode body element 3a and a second positive electrode tab group 40A2 of the second electrode body element 3b are connected to the first positive electrode current collector (or positive electrode current collector) 6a. A first negative electrode tab group 50A1 of the first electrode body element 3a and a second negative electrode tab group 50A2 of the second electrode body element 3b are connected to the first negative electrode current collector (or negative electrode current collector) 8a. The first and second positive electrode tab groups 40A1 and 40A2 are welded and connected to the first positive electrode current collector 6a to form welding joints 60a and 60b. The two welding joints 60a and 60b on the positive electrode side are spaced apart from each other in the direction perpendicular to the upper side of the electrode body <NUM>, that is, in the direction perpendicular to the length of the sealing body <NUM>. The current collector through-hole 6e is interposed between the two welding joints 60a and 60b of the positive electrode.

The first and second negative electrode tab groups 50A1 and 50A2 are welded and connected to the first negative electrode current collector 8a to form welding joints 61a and 61b. The two welding joints 61a and 61b on the negative electrode side are also spaced apart from each other in the direction perpendicular to the upper side of the electrode body <NUM>, that is, in the direction perpendicular to the length of the sealing body <NUM>.

The first positive electrode current collector 6a has a thinner part 6c. At this thinner part 6c, the first positive electrode current collector 6a is connected to the second positive electrode current collector 6b.

The first negative electrode current collector 8a has a recess 8d with a thinner part 8c. At this thinner part 8c, the first negative electrode current collector 8a is connected to the second negative electrode current collector 8b.

The welding connection between the positive electrode tab group 40A and the first positive electrode current collector 6a and between the negative electrode tab group 50A and the first negative electrode current collector 8a are made by ultrasonic welding, resistance welding, or laser welding, for example. In this embodiment, the welding connection is made by ultrasonic welding.

The connection between the first and second positive electrode current collectors 6a and 6b and between the first and second negative electrode current collectors 8a and 8b are made by ultrasonic welding, resistance welding, or laser welding, for example. In this embodiment, the welding connection is made by laser welding.

<FIG> shows the surface of the sealing plate <NUM> facing the inside of the battery and attached with the components. The attachment of the components to the sealing plate <NUM> will be described with reference to <FIG> and <FIG>.

The external insulation member <NUM> surrounds a positive electrode terminal insertion hole of the sealing plate <NUM>. The internal insulation member <NUM> and a cup-shaped conductive member <NUM> are arranged on the inner surface of the battery around the positive electrode terminal insertion hole of the sealing plate <NUM>. The positive electrode terminal <NUM> is then inserted from the outside of the battery through the through-hole of the external insulation member <NUM>, the positive electrode terminal insertion hole of the sealing plate <NUM>, the through-hole of the internal insulation member <NUM>, and a terminal connection hole of the conductive member <NUM>. The tip of the positive electrode terminal <NUM> is crimped onto the conductive member <NUM>. As a result, the positive electrode terminal <NUM> and the conductive member <NUM> are fixed to the sealing plate <NUM>. The crimped part of the positive electrode terminal <NUM> and the conductive member <NUM> are welded and connected in one preferred embodiment.

The conductive member <NUM> has an opening inside the battery. A disk-shaped deformable plate <NUM> closes the opening of the conductive member <NUM>, and has a peripheral edge welded and connected to the conductive member <NUM>. Accordingly, the opening is sealed. Each of the conductive member <NUM> and the deformable plate <NUM> is made of metal, particularly, aluminum or an aluminum alloy in one preferred embodiment. The second positive electrode current collector 6b is then placed on the side of the deformable plate <NUM> closer to the inside of the battery. The two are welded and connected.

Next, the external insulation member <NUM> is placed on the outer surface of the battery around a negative electrode terminal insertion hole of the sealing plate <NUM>. Next, the internal insulation member <NUM> and the second negative electrode current collector 8b are arranged on the inner surface of the battery around the negative electrode terminal insertion hole of the sealing plate <NUM>. The negative electrode terminal <NUM> is then inserted from the outside of the battery through the through-hole of the external insulation member <NUM>, the negative electrode terminal insertion hole of the sealing plate <NUM>, the through-hole of the internal insulation member <NUM>, and the terminal connection hole of the second negative electrode current collector 8b. The tip of the negative electrode terminal <NUM> is crimped onto the second negative electrode current collector 8b. As a result, the negative electrode terminal <NUM> and the second negative electrode current collector 8b are fixed to the sealing plate <NUM>. The crimped part of the negative electrode terminal <NUM> and the second negative electrode current collector 8b are welded and connected in one preferred embodiment.

The internal insulation member <NUM> on the positive electrode side has a liquid injection opening 11a to face the electrolyte inlet <NUM> of the sealing plate <NUM>. The internal insulation member <NUM> has, at the edge of the liquid injection opening 11a, a tube 11b projecting in a cylindrical shape toward the inside of the battery. The internal insulation member <NUM> further includes an opening cover 11c projecting from two points on the edge of the tube 11b toward the inside of the battery to connect the two points like a bridge. The tube 11b and the opening cover 11c are inserted into the current collector through-hole 6e of the first positive electrode current collector 6a.

<FIG> shows the surface of the sealing plate <NUM> facing the inside of the electrode body after attaching the first positive electrode current collector 6a to the second positive electrode current collector 6b, and the first negative electrode current collector 8a to the second negative electrode current collector 8b.

The first positive electrode current collector 6a connected to the first and second positive electrode tab groups 40A1 and 40A2 is placed on the internal insulation member <NUM> so as to partially overlap the second positive electrode current collector 6b. By irradiating the thinner part 6c with a laser, the first and second positive electrode current collectors 6a and 6b are welded and connected to form a positive electrode current collector welding joint. The first negative electrode current collector 8a connected to the first and second negative electrode tab groups 50A1 and 50A2 is placed on the internal insulation member <NUM> so as to partially overlap the second negative electrode current collector 8b. By irradiating the thinner part 8c with a laser, the first and second negative electrode current collectors 8a and 8b are welded and connected to form a negative electrode current collector welding joint. The joint between the first and second negative electrode current collectors 8a and 8b will be described later in detail.

As shown in <FIG>, the welding joint 60a between the first positive electrode current collector 6a and the first positive electrode tab group 40A1, and the welding joint 60b between the first positive electrode current collector 6a and the second positive electrode tab group 40A2 are covered with a first covering member <NUM>. Accordingly, the first covering member <NUM> catches the foreign objects existing at the welding joints 60a and 60b, particularly the metal powder generated in a welding process not to cause the foreign objects to enter the inside of the electrode body <NUM>. This largely reduces the internal short circuits caused by the foreign objects. The first covering member <NUM> is bonded to the welding joints 60a and 60b. In the area between the two welding joints 60a and 60b, the first covering member <NUM> is spaced apart from and covers the area.

Next, the welding joint 61a between the first negative electrode current collector 8a and the first negative electrode tab group 50A1, and the welding joint 61b between the first negative electrode current collector 8a and the second negative electrode tab group 50A2 are covered with a second covering member <NUM>. The second covering member <NUM> also covers the surface of the first negative electrode current collector 8a between the two welding joints 61a and 61b. Accordingly, the second covering member <NUM> catches the foreign objects existing at the welding joints 61a and 61b, particularly the metal powder generated in a welding process not to cause the foreign objects to enter the inside of the electrode body <NUM>. This largely reduces the internal short circuits caused by the foreign objects. The second covering member <NUM> is attached to the covered part.

The second covering member <NUM> further covers the joint (i.e., the negative electrode current collector welding joint) between the first and second negative electrode current collectors 8a and 8b. That is, a part of the second negative electrode current collector 8b is covered with the second covering member <NUM>. Accordingly, the second covering member <NUM> catches the foreign objects (e.g., metal powder) generated by welding the first and second negative electrode current collectors 8a and 8b not to cause the foreign objects to enter the inside of the electrode body <NUM>.

A third covering member <NUM> is then placed and bonded to cover the joint (i.e., the positive electrode current collector welding joint) between the first and second positive electrode current collectors 6a and 6b. Accordingly, the third covering member <NUM> catches the foreign objects existing at the positive electrode current collector welding j oint, particularly the metal powder generated in the welding process between the first and second positive electrode current collectors 6a and 6b not to cause the foreign objects to enter the inside of the electrode body <NUM>. As shown in <FIG>, the second positive electrode current collector 6b and the third covering member <NUM> are then covered with a cover member <NUM>.

In this embodiment, the first to third covering members <NUM>, <NUM>, and <NUM> are adhesive sheets obtained by applying an adhesive to a plastic film. The plastic film is not particularly limited, but a polypropylene film is selected in one preferred embodiment. The first to third covering members <NUM>, <NUM>, and <NUM> are not limited to the adhesive sheets.

Next, the two positive electrode tab groups 40A1 and 40A2 and the two negative electrode tab groups 50A1 and 50A2 are curved so that the upper surfaces of the first and second electrode body elements 3a and 3b in <FIG> are in direct contact or indirect contact with each other with other members interposed therebetween. Accordingly, the two electrode body elements 3a and 3b are integrated into one electrode body <NUM>. The integrated electrode body <NUM> is placed in the electrode body holder <NUM> obtained by molding an insulating sheet into a box or a bag.

The electrode body <NUM> wrapped with the electrode body holder <NUM> is inserted into the rectangular exterior body <NUM>. The sealing plate <NUM> and the rectangular exterior body <NUM> are welded to seal the opening of the rectangular exterior body <NUM> with the sealing plate <NUM>. The electrolyte is then injected into the rectangular exterior body <NUM> through the electrolyte inlet <NUM> of the sealing plate <NUM>. After that, the electrolyte inlet <NUM> is sealed with a sealing member such as a blind rivet. As a result, the rectangular secondary battery <NUM> is complete.

The joint between the first and second negative electrode current collectors 8a and 8b will be further described. <FIG> shows that only the first and second negative electrode current collectors 8a and 8b are taken out and stacked for connection. <FIG> shows an enlarged cross-section of the joint. The first negative electrode current collector 8a has the recess 8d on a surface which is opposite to the surface overlapping the second negative electrode current collector 8b. The recess 8d has two thinner parts 8c. The first negative electrode current collector 8a has a dent 8f formed by the recess 8d.

In the state described above, the thinner parts 8c are irradiated with a laser to connect the first and second negative electrode current collectors 8a and 8b by full penetration welding as shown in <FIG>. The laser welding is performed at the thinner parts 8c, which facilitates the formation of a full penetration welding point <NUM>.

Next, the second covering member <NUM> is bonded to the first and second negative electrode current collector 8a and 8b to cover the joint between the first and second negative electrode current collectors 8a and 8b. As shown in <FIG>, the second covering member <NUM> closes the entire recess 8d (i.e., the dent 8f) and further enters the dent 8f. That is, a part 82a covering the dent 8f of the second covering member <NUM> has a shape recessed along the dent 8f.

The second covering member <NUM> has the recess 8c which is used to facilitate the alignment in the laser welding.

The above embodiment is an example of the present invention. The present invention is not limited to the example. The present invention may be a combination of a well-known art, a background technique, and a publicly-known technique with the example, and may also have a part of the example replaced. Moreover, the present invention includes modifications at which those skilled in the art easily arrive.

The electrode body may be wound after stacking the positive electrode plate, the negative electrode plate, and the separator. The electrode body element may also have a wound structure.

An example has been described above in the embodiment where the two electrode body elements are arranged in the exterior body, but the number of the electrode body elements may be one, three, or more.

An example has been described above in the embodiment where each of the positive and negative electrode current collectors includes two parts, but each of the positive electrode and negative electrode current collectors may include a single component.

The positive electrode plate, the negative electrode plate, the separator, the electrolyte, and other components may be made of known materials.

Claim 1:
A battery comprising:
an electrode body (<NUM>) obtained by stacking a positive electrode plate (<NUM>) and a negative electrode plate (<NUM>) with a separator interposed therebetween;
an exterior body (<NUM>) having an opening and housing the electrode body (<NUM>);
a sealing plate (<NUM>) sealing the opening; and
an external terminal (<NUM>,<NUM>) attached to the sealing plate (<NUM>),
a tab (<NUM>,<NUM>) being provided at at least one of the positive electrode plate (<NUM>) or the negative electrode plate (<NUM>) and being electrically connected to the external terminal (<NUM>,<NUM>) via a current collector (6a,6b,8a,8b) between the electrode body (<NUM>) and the sealing plate,
the current collector (6a,6b,8a,8b) including a first current collector (6a,8a) and a second current collector (6b,8b),
the first current collector (6a,8a) and the second current collector (6b,8b) being welded to each other at a welding point (<NUM>) covered with a covering member (<NUM>,<NUM>), characterized in that
the first current collector (6a,8a) has an overlapped portion to the second current collector (6b,8b),
a thinner part (6c,8c) is disposed in the overlapped portion of the first current collector (6a,8a),
any boundary of the thinner part (6c,8c) is disposed apart from any boundary of the first current collector (6a,8a), and
the welding point (<NUM>) is disposed at the thinner part (8c).