Electrical energy storage device and manufacturing method thereof

Disclosed is an electrical energy storage device provided with a metallic casing to receive a bare cell and first and second terminals located outside of the metallic casing corresponding to each electrode of the bare cell, including a plate-like member provided on at least one of the first and second terminals, an inner terminal contacting the plate-like member to form the boundary between the inner terminal and the plate-like member, and a laser welded portion formed along the boundary between the inner terminal and the plate-like member to connect the plate-like member with the inner terminal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from Korean Patent Application Nos. 10-2011-0022012, 10-2011-0022013, and 10-2011-0022015, filed on Mar. 11, 2011, the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND

Exemplary embodiments relate to an electrical energy storage device and manufacturing method thereof, and more particularly, to an electrical energy storage device with improved connection structure between an outer terminal and an inner terminal and manufacturing method thereof.

2. Description of the Related Art

Generally, an ultracapacitor, also known as a supercapacitor, is an energy storage device having characteristics in between those of an electrolytic condenser and a secondary battery. Since an ultracapacitor has high efficiency and a semipermanent life span, the ultracapacitor is considered as a next-generation energy storage device that is useable in parallel with or in replace of a secondary battery.

An ultracapacitor can also be used to replace a storage battery in applications that are not easy to maintain and that require a long service life. Since an ultracapcitor has quick charging/discharging characteristics, the ultracapacitor is very suitable as a main or auxiliary power supply of electric vehicles, road indicator lamps, or uninterrupted power supplies (UPSs) that requires high capacity, as well as an auxiliary power supply of mobile communication information equipment such as mobile phones, laptop computers, or personal digital assistants (PDAs), and thus has been widely being used as the same.

As shown inFIG. 1, an ultracapacitor mainly has a cylindrical shape for minimization.

Referring toFIG. 1, a cylindrical ultracapacitor includes an internal housing10that accommodates a bare cell composed of a cathode, an anode, a separator, and an electrolyte, a metallic casing40that receives the internal housing10, inner terminals20and30located at the upper and lower portions of the metallic casing40to connect to the anode and the cathode of the bare cell, respectively, and an outer anode terminal51and an outer cathode terminal45located at the top and bottom of the metallic casing40, respectively.

In the cylindrical ultracapacitor, the inner anode terminal20is electrically isolated from the metallic casing40by an insulating member60and electrically connected to the outer anode terminal51located in the middle of a plate-like member50, and the inner cathode terminal30is electrically connected to the metallic casing40.

Conventionally, the connections between the inner anode terminal20and the plate-like member50, and between the inner cathode terminal30and the metallic casing40are made using a bolt70. However, a connection between an inner terminal and an outer terminal using the bolt70has disadvantages of a complicated assembly process and low connection stability.

Particularly, since the outer anode terminal51is formed with an electrolyte injection hole at the center thereof and has components such as a safety valve and the like, it is not easy to apply a bolt to the outer anode terminal51.

To solve this problem, suggestion has been made to weld, using a hot compress, the surface of the plate-like member50provided with the outer anode terminal51and the corresponding surface of the inner anode terminal20. However, this involves a complicated welding process, and since the connected part between the outer anode terminal51and the inner anode terminal20is weak against the external vibration, the outer anode terminal51and the inner anode terminal20may easily separate from each other, which will deteriorate the contact resistance characteristics.

On the other hand, since the inner cathode terminal30directly contacts the metallic casing40, it is very important to minimize the contact resistance between the inner cathode terminal30and the metallic casing40and stabilize the contact state therebetween to improve the electrical characteristics of the ultracapacitor.

Meanwhile, a side reaction may occur at the interference between the electrolyte and the electrode of the ultracapacitor at room temperature under abnormal conditions such as overcharge, overdischarge, overvoltage, and the like, and as a result, gas is generated. When gas accumulates in the ultracapacitor, the internal pressure of the metallic casing40increases and finally swells the metallic casing40. In some cases, when gas abruptly discharges through a weak area of the metallic casing40, the metallic casing40may explode.

In particular, the metallic casing40swells more severely at the side and the bottom of the metallic casing40near the inner cathode terminal30than in the vicinity of the inner anode terminal20.

Since the metallic casing40has a curled portion41formed on the top thereof near the inner anode terminal20, it is easy to reinforce the pressure resistance performance of the side of the metallic casing40near the inner anode terminal20by controlling an amount of curling, however since a curled portion is not formed in the vicinity of the outer cathode terminal45, it is not easy to reinforce the pressure resistance performance of the side of the metallic casing40near the outer cathode terminal45.

SUMMARY OF THE INVENTION

The present invention is designed to solve the above problems, and therefore it is an object of the present invention to provide an electrical energy storage device with improved connection strength and resistance characteristics by precision welding between an outer terminal and an inner terminal, and manufacturing method thereof.

It is another object of the present invention to provide an electrical energy storage device with improved resistance characteristics by increasing the contact area and contact stability between a metallic casing and an inner terminal, and manufacturing method thereof.

It is still another object of the present invention to provide an electrical energy storage device with improved pressure resistance performance by optimizing a thickness distribution of a metallic casing.

To achieve the object of the present invention, provided is an electrical energy storage device provided with a metallic casing to receive a bare cell and first and second terminals located outside of the metallic casing corresponding to each electrode of the bare cell, including a plate-like member provided on at least one of the first and second terminals, an inner terminal contacting the plate-like member to form the boundary between the inner terminal and the plate-like member, and a laser welded portion formed along the boundary between the inner terminal and the plate-like member to connect the plate-like member with the inner terminal.

Preferably, the laser welded portion is made up of a plurality of welding points repeatedly formed along the boundary between the plate-like member and the inner terminal, and a distance between the centers of adjacent welding points is within the diameter of the welding points.

A beading groove may be formed along the outer periphery of the inner terminal, and the metallic casing may have a bead portion closely contacting the beading groove.

A rounded corner may be formed between the bottom and the side of the metallic casing to control the internal pressure, and a slope portion may be formed on the inner terminal corresponding to the corner of the metallic casing.

The inner terminal may be provided corresponding to each of the first terminal and the second terminal, and any one of the inner terminals corresponding to the first terminal and the second terminal may closely contact the bead portion with an insulating member interposed therebetween and the other may directly contact the bead portion.

The metallic casing may have a thickness gradient over the side thereof such that the thickness of a portion near the second terminal is larger than the thickness of a portion near the first terminal.

Preferably, the side of the metallic casing has a thickness of a portion corresponding to the height of the inner terminal corresponding to at least the second terminal larger than the thickness of the other portion.

Preferably, a ratio of the thickness of the portion near the second terminal to the thickness of the portion near the first terminal is 120 to 150%.

A protrusion for concentricity may be formed at the center of at least one terminal of the metallic casing.

The protrusion for concentricity may be integrally formed with the body of the metallic casing.

According to another aspect of the present invention, provided is a method for manufacturing an electrical energy storage device provided with a metallic casing to receive a bare cell and first and second terminals located outside of the metallic casing corresponding to each electrode of the bare cell, including (a) preparing a subject for welding by contacting an inner terminal with a plate-like member provided on at least one of the first terminal and the second terminal, (b) aligning the subject with a beam radiating unit of a laser welding machine to radiate a laser beam on the boundary between the plate-like member and the inner terminal, and (c) performing laser welding on the boundary along the outer periphery of the subject while moving any one of the subject and the beam radiating unit relative to the other.

Preferably, step (c) includes repeatedly forming a plurality of laser welding points along the outer periphery of the subject while rotating the subject relative to the beam radiating unit at a predetermined rate.

Preferably, a distance between the centers of adjacent welding points is within the diameter of the welding points.

A beading groove may be formed along the outer periphery of the inner terminal.

The method may further comprise placing the inner terminal in the metallic casing, and beading a portion of the metallic casing corresponding to the inner terminal to form a bead portion that closely contacts the beading groove of the inner terminal

A slope portion may be formed along the periphery edge of the inner terminal.

The inner terminal may be put in the metallic casing such that the slope portion faces the corner between the bottom and the side of the metallic casing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described in detail with reference to the accompanying drawings. Prior to description, it should be understood that terms and words used in the specification and the appended claims should not be construed as having common and dictionary meanings, but should be interpreted as having meanings and concepts corresponding to technical ideas of the present invention in view of the principle that the inventor can properly define the concepts of the terms and words in order to describe his/her own invention as best as possible. Accordingly, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention.

FIG. 2is a perspective view illustrating an electrical energy storage device according to a preferred embodiment of the present invention.FIG. 3is a partial cross-sectional view ofFIG. 2.

Referring toFIGS. 2 and 3, an electrical energy storage device according to a preferred embodiment of the present invention includes a metallic casing130that receives a bare cell (not shown), a first terminal or outer anode terminal141located outside of the metallic casing130corresponding to an anode of the bare cell, a second terminal or outer cathode terminal132located outside of the metallic casing130corresponding to a cathode of the bare cell, and an inner anode terminal110and an inner cathode terminal120respectively connected to the anode and the cathode of the bare cell in the metallic casing130.

The bare cell includes a cathode, an anode, a separator, and an electrolyte, and provides an electrochemical energy storage function.

The inner anode terminal110and the inner cathode terminal120are respectively connected to the anode and the cathode of the bare cell. Each of the inner anode terminal110and the inner cathode terminal120has a circular plate shape with a circular outer periphery corresponding to the inner periphery of the metallic casing130.

The inner anode terminal110is electrically isolated from the metallic casing130by an insulating member150and at the same time, contacts the plate-like member140and connects to the outer anode terminal141located in the middle of a plate-like member140, and the inner cathode terminal120contacts the metallic casing130and connects to the outer cathode terminal132located in the middle of the bottom of the metallic casing130.

The metallic casing130has a cylindrical body with an inner space in which the bare cell housed in an internal housing100after winding is received. Preferably, the metallic casing130has a cylindrical shape of aluminum. Although not shown, the metallic casing130preferably has a rounded corner between the bottom142and the side131thereof to improve the resistance to the internal pressure.

A protrusion133for concentricity is formed inside the center of the bottom142of the metallic casing130integrally extending from the side131of the metallic casing130, and the outer cathode terminal132protrudes downwards outside of the center of the bottom142of the metallic casing130.

A curled portion160is formed on the top of the metallic casing130near the inner anode terminal110to maximize the connection and sealing performances. The pressure resistance performance of the side131of the metallic casing130near the inner anode terminal110is easily controlled by adjusting the curling amount of the curl160.

Additionally, bead portions135and136may be formed on the side131of the metallic casing130to fix the inner cathode terminal120and the inner anode terminal110to the metallic casing130, respectively.

In the present invention, the connection between the plate-like member140provided with the outer anode terminal141and the inner anode terminal110is made by laser welding.

FIG. 4illustrates a terminal connection structure of the electrical energy storage device according a preferred embodiment of the present invention.

Referring toFIG. 4, the plate-like member140provided with the outer anode terminal141contacts with the inner anode terminal110of a plate shape, and a laser welded portion170is formed in the circular shape on the boundary along the outer periphery between the plate-like member140and the inner anode terminal110. Here, the boundary is where laser welding is to be performed, and includes a microgap between the plate-like member140and the inner anode terminal110, and circular periphery edges of the plate-like member140and the inner anode terminal110adjacent to the microgap.

The laser welded portion170is made up of a plurality of laser welding points formed repeatedly along the boundary between the plate-like member140and the inner anode terminal110. Preferably, a plurality of the laser welding points overlap with each other to form a substantially continuous weld line. For this purpose, a distance D between the centers of adjacent welding points should be within the diameter of the welding points.

FIG. 5is a schematic plane view illustrating a terminal welding process according to a preferred embodiment of the present invention.

Referring toFIG. 5, the terminal welding process according to a preferred embodiment of the present invention includes preparing a subject for welding, aligning the subject with a laser welding machine, and performing laser welding along the outer periphery of the subject.

In the preparing step, the plate-like member140provided with the outer anode terminal141is stacked on top of the inner anode terminal110.

In the aligning step, the side of the subject is aligned with a beam radiation unit200of the laser welding machine to radiate a laser beam on the circular boundary formed along the outer periphery as a result of the contact between the plate-like member140and the inner anode terminal110.

In the laser welding step, the plate-like member140and the inner anode terminal110are welded with each other by performing laser welding along the outer periphery of the subject while rotating the subject relative to the beam radiation unit200at a predetermined rate. In this instance, laser welding is repeatedly performed to overlap a plurality of welding points at a predetermined pitch along the outer periphery of the subject.

FIG. 6is a photographic image illustrating a laser welded result between the plate-like member140provided with the outer anode terminal141and the inner anode terminal110according to the present invention. As shown inFIG. 6, the laser welded portion170is formed as a substantially continuous weld line by the overlap of a plurality of the laser welding points formed along the boundary between the plate-like member140and the inner anode terminal110.

According to the present invention, the electrical energy storage device can provide high connection strength by the laser welded portion170between the outer terminal and the inner terminal, and improvements in the resistance characteristics as a consequence of the close connection between the outer terminal and the inner terminal.

Referring toFIG. 3again, the bead portion135is formed at a portion of the metallic casing130corresponding to at least the inner cathode terminal120and extends in the circular shape along the inner periphery of the metallic casing130. The bead portion135closely contacts the outer periphery of the inner cathode terminal120.

As shown inFIG. 7, a circular beading groove121is formed along the outer periphery of the inner cathode terminal120. The beading groove121is used to receive the bead portion135of the metallic casing130. The beading groove121can effectively increase the lateral surface area of the inner cathode terminal120.

Preferably, a slope portion122is formed along the periphery edge of the inner cathode terminal120and corresponds to the rounded corner of the metallic casing130for controlling the internal pressure. The slope portion122prevents an increase in the contact resistance caused by the offset of the inner cathode terminal120due to the interference between the inner cathode terminal120and the rounded corner of the metallic casing130for controlling the internal pressure.

Preferably, like the inner cathode terminal120, the inner anode terminal110has a beading groove formed along the outer periphery thereof to improve the connection with the metallic casing130, and the metallic casing130has the bead portion136corresponding to the beading groove of the inner anode terminal110. Preferably, the bead portion136of the metallic casing130contacts the beading groove of the inner anode terminal110with the insulating member150interposed therebetween.

The above-described electrical energy storage device may be manufactured by a process including electrode plate fabrication, electrode plate assembly, and housing assembly.

In the electrode plate fabrication and the electrode plate assembly, an electrode plate is fabricated by preparing an electrode active material, followed by mixing, coating, rolling, and slitting in a sequential manner, and winding the electrode plate together with a separator to make a bare cell.

In the housing assembly, the bare cell is dried under vacuum and then received in the metallic casing130, followed by welding between the plate-like member140and the inner anode terminal110, processing of the metallic casing130including beading and curling, and electrolyte injection into the metallic casing130and electrolyte impregnation.

In the beading of the metallic casing130, the beading groove121is formed along the outer periphery of the inner cathode terminal120and the slope portion122is formed along the periphery edge of the inner cathode terminal120. Next, the inner cathode terminal120is placed in the metallic casing130such that the slope portion122faces the corner between the bottom and the side of the metallic casing130. Next, the bead portion135is formed by applying the pressure to the side of the metallic casing130corresponding to the inner cathode terminal120while moving a beading jig of a beading machine along the outer periphery of the metallic casing130. Accordingly, the bead portion135formed on the side of the metallic casing130corresponding to the inner cathode terminal120is engaged with and closely contacts the beading groove121of the inner cathode terminal120.

In this instance, the bead portion136formed on the side of the metallic casing130corresponding to the inner anode terminal110is engaged with and closely contacts the inner anode terminal110with the insulating member150interposed therebetween.

On the other hand, the bead portion135of the metallic casing130closely contacts the beading groove121of the inner cathode terminal120without a gap therebetween, thereby stably achieving a wider contact area than the conventional art, resulting in improved resistance characteristics (SeeFIG. 10).

FIG. 8is a partial cross-sectional view illustrating an electrical energy storage device according to another embodiment of the present invention.

Referring toFIG. 8, the side131of the metallic casing130has a thickness gradient such that the thickness of the side131of the metallic casing130in the vicinity of the inner cathode terminal120is larger than that of the vicinity of the inner anode terminal110. That is, the side131of the metallic casing130has a thickness of a portion B near the inner cathode terminal120larger than that of a portion A near the inner anode terminal110.

Preferably, the thickness gradient is set such that the thickness of the portion corresponding to at least the height h of the inner cathode terminal120from the bottom142of the metallic casing130is larger than that of the portion A near the inner anode terminal110. This structure compensates for a thickness loss that may occur to the side131of the metallic casing130corresponding to the inner cathode terminal120when beading is performed on the side131of the metallic casing130to establish a close connection between the metallic casing130and the inner cathode terminal120, thereby preventing deterioration in the pressure resistance characteristics.

In the present invention, a relatively thick portion on the side131of the metallic casing130is not limited to a portion corresponding to the height h of the inner cathode terminal120, and may extend to a predetermined distance in the direction facing away from the inner cathode terminal120. Also, the thickness gradient over the side131of the metallic casing130may be sharp or gradual.

Preferably, the thickness gradient is set such that a ratio of the thickness of the portion B near the inner cathode terminal120to the thickness of the portion A near the inner anode terminal110is 120 to 150%. When the ratio is less than the minimum, the effect of reinforcing the vicinity of the inner cathode terminal120is insufficient, and when the ratio exceeds the maximum, it is not easy to assemble the internal components such as the bare cell and the like and perform a beading process and thus the contact state between the terminals110and120and the metallic casing130becomes unstable, resulting in increased resistance.

As shown inFIG. 9, the protrusion133for concentricity is formed at the center of the bottom142of the metallic casing130. Since the protrusion133for concentricity is located inside the center of the inner cathode terminal120, the protrusion133for concentricity enables the inner cathode terminal120to be correctly arranged inside the center of the metallic casing130. When the protrusion133for concentricity is formed integrally with the side131and the bottom142of the metallic casing130, the metallic casing130is reinforced and consequently has improvement in a shape deformation prevention performance.

FIG. 10is an actual X-ray image of the electrical energy storage device according to the present invention.

Referring toFIG. 10, it is found that the side131of the metallic casing130has a thickness gradient such that the side131of the metallic casing130has a thickness of a portion near the inner cathode terminal120larger than that of the other portion. As seen inFIG. 10, the metallic casing130has the bead portion135on the side131thereof to establish a close connection with the inner cathode terminal120. Accordingly, it is found that the thickness of the portion near the inner cathode terminal120is reinforced and as a result, a thickness loss occurring due to beading can be compensated.

As described above, the electrical energy storage device according to the present invention can effectively reinforce the side131of the metallic casing130near the inner cathode terminal120that is weaker against the internal pressure than in the vicinity of the inner anode terminal110due to the thickness gradient of the side131of the metallic casing130, thereby improving the pressure resistance characteristics.

Accordingly, the present invention can improve the electrical characteristics and stability of the electrical energy storage device, for example, an ultracapacitor, and simplify the manufacturing process and reduce the manufacturing costs.

According to the foregoing, the connection between the outer terminal and the inner terminal can be improved by the laser welded portion and a close contact is made therebetween, resulting in improved contact resistance characteristics. Also, it is possible to precisely control the size or pitch of the welding points, which makes it easy to control the tensile strength of the welded portion.

Also, the bead portion of the metallic casing is engaged with and closely contacts the beading groove of the inner terminal, thereby achieving a wide contact area and a stable contact, resulting in simple assembly of the metallic casing and the inner terminal and the improved resistance characteristics. Furthermore, the slope portion of the inner terminal can prevent the offset of the inner terminal when contacting the metallic casing, thereby stably maintaining the contact resistance.

Moreover, the side of the metallic casing near the terminal that is relatively weak against the internal pressure is reinforced and consequently resistant against the shape deformation, and the pressure resistance performance can be easily controlled by adjusting the thickness gradient of the side of the metallic casing.

Also, the protrusion for concentricity formed on the metallic casing enables the inner terminal to be correctly arranged inside of the center of the metallic casing, and reinforces the metallic casing, thereby improving the shape deformation prevention performance.

Although the present invention has been described hereinabove, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.