Energy storage device

An energy storage device includes an electrode unit in which a cathode having a cathode lead, an anode having an anode lead, and a separator located between the cathode and the anode to separate the cathode and the anode from each other are rolled together; a housing receiving the electrode unit; an electrolyte filled in the housing; an inner terminal arranged in the housing to face the electrode unit; and an outer terminal connected to the inner terminal. A groove is formed in a side of the inner terminal, and a side protrusion is formed on an inner wall of the housing at a location corresponding to the groove.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an energy storage device, and more particularly to an energy storage device that maximizes the utilization of the inside of a housing by the improvement of an inner structure thereof and also ensures the reliability by keeping an inner pressure below a certain level.

2. Description of the Related Art

Generally, representative examples of a device storing an electric energy are batteries and capacitors. Among them, a capacitor is an energy storage device, which is called a ultra capacitor or a super capacitor and has features in between an electrolytic condenser and a secondary battery.

Such an energy storage device makes side reactions at an interface between an electrolyte and an electrode when being misused with an overvoltage or the like or used for a long time at high temperature, and gas is generated as a byproduct accordingly.

Considering the generation of gas, a conventional energy storage device is designed to have some space between an electrode unit and an inner side of the housing of the energy storage device.

However, in a case where the energy storage device is used for a transportation means such as a vehicle, the electrode unit in the housing may be shaken right and left due to an external force such as vibration, and accordingly the electrode unit or a lead wire connected thereto may be broken, which results in the deterioration of life or reliability of the energy storage device.

In addition, in a case where the inner pressure of the housing keeps increasing due to the generation of gas, the housing may swell out, or gas may be leaked at a weak region of the housing, which may cause explosion.

In order to prevent such explosion caused by the generation of gas, a notch structure is formed in a partial region of the housing of the conventional energy storage device, so that the notch is fractured at a pressure over a certain level to allow the relief of pressure.

However, in this case, the housing is kept in an opened state after the notch of the housing is fractured, which may seriously deteriorate the performance of the energy storage device due to the leakage of electrolyte or the introduction of impurities.

SUMMARY OF THE INVENTION

The present invention is designed to solve the problems of the prior art, and therefore it is an object of the present invention to provide an energy storage device capable of preventing an electrode unit from being broken due to an external force such as vibration by improving an inner structure of the energy storage device. Also, another object of the present invention is to improve the reliability of the energy storage device by preventing the excessive increase of an inner pressure of the housing and intercepting the introduction of impurities into the housing from the outside.

In order to accomplish the above object, the present invention provides an energy storage device, which includes an electrode unit in which a cathode having a cathode lead, an anode having an anode lead, and a separator located between the cathode and the anode to separate the cathode and the anode from each other are rolled together; a housing receiving the electrode unit; an electrolyte filled in the housing; an inner terminal arranged in the housing to face the electrode unit; an outer terminal connected to the inner terminal; and a pressure relief unit for relieving an inner pressure of the housing, wherein a groove is formed in a side of the inner terminal, and a side protrusion is formed on an inner wall of the housing at a location corresponding to the groove, wherein openings are respectively formed in the inner terminal and the outer terminal for the communication with the outside, and wherein the pressure relief unit is installed in the openings and selectively opens the openings in association with the change of the inner pressure of the housing when the inner pressure is increased over an allowable level.

Preferably, the electrode unit is coupled with the inner terminal by laser welding.

Preferably, the side protrusion is formed by partially denting the side of the housing, and the side protrusion is formed to be fit with the groove of the inner terminal.

Preferably, the outer terminal is fixed by bending an upper portion of the housing.

Preferably, the energy storage device according to the present invention further includes a sealing member provided to the outer terminal at a location where the upper portion of the housing is bent and fixed.

Preferably, the energy storage device according to the present invention further includes an insulation film between the housing and both of the inner and outer terminals.

Preferably, the housing has a cylindrical shape, and the inner terminal and the outer terminal are respectively constituted by a cathode terminal or an anode terminal at upper and lower portions of the housing.

Preferably, the pressure relief unit is installed in the opening of the outer terminal.

Preferably, the energy storage device according to the present invention further includes a coupling member installed through the openings of the inner and outer terminals to couple the inner and outer terminals with each other, the coupling member having a hollow therein, wherein the pressure relief unit is mounted to a head of the coupling member so that the hollow of the coupling member is selectively opened or closed.

Preferably, the energy storage device according to the present invention further includes a fixing member for fixing the pressure relief unit to the openings.

Preferably, the energy storage device according to the present invention further includes a sealing means interposed between the pressure relief unit and the fixing member.

Preferably, the fixing member and the coupling member may be coupled to the openings by screwing, inserting, or inserting and laser-welding.

Preferably, the opening of the inner terminal may have a different diameter from the opening of the outer terminal, and the opening of the inner terminal may have a relatively smaller diameter than the opening of the outer terminal.

In another aspect of the present invention, there is also provided an energy storage device, which includes an electrode unit in which a cathode having a cathode lead, an anode having an anode lead, and a separator located between the cathode and the anode to separate the cathode and the anode from each other are rolled together; a housing receiving the electrode unit; an electrolyte filled in the housing; an inner terminal arranged in the housing to face the electrode unit; an outer terminal connected to the inner terminal; and a pressure relief unit for relieving an inner pressure of the housing, wherein openings are respectively formed in the inner and outer terminals for the communication with the outside, and the pressure relief unit is installed in the openings and selectively opens the openings in association with the change of the inner pressure of the housing when the inner pressure is increased over an allowable level.

According to the present invention, it is possible to prevent an electrode unit from being broken due to vibration or the like by improving an inner structure of an energy storage device. Also, it is possible to design the housing into a slimmer shape and increase the capacity of the energy storage device by eliminating any need to ensure a separate space between the inside of the housing and the electrode unit. In addition, it is possible to prevent the excessive increase of an inner pressure of the housing and also the introduction of external impurities into the housing. Moreover, an opening of an electrode terminal may be used as an electrolyte injection hole, which allows simplifying the assembling process of the energy storage device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a perspective view showing an appearance of an energy storage device according to the present invention,FIG. 2is a perspective view showing exploded and assembled states of electrodes, a separator, and leads, which are rolled and arranged in the energy storage device according to the present invention, andFIG. 3is a sectional view showing an inner configuration of the energy storage device according to the present invention.

Referring toFIGS. 1 to 3, an energy storage device according to the present invention includes an electrode unit15in which a cathode10having a cathode lead6, an anode20having an anode lead16, and a separator30located between the cathode10and the anode20to electrically separate the cathode10and the anode20from each other are rolled together; a housing40receiving the electrode unit15; an electrolyte filled in the housing40; inner cathode and anode terminals51,52arranged in the housing40to face the electrode unit15; and outer cathode and anode terminals61,62connected to the inner cathode and anode terminals51,52, respectively. Also, a groove53is formed in a side of the inner cathode terminal51, and a side protrusion45is formed on an inner wall of the housing40at a location corresponding to the groove53and fitted into the groove53.

The energy storage device according to the present invention includes the housing40made of metal material, and the cathode10and the anode20, which are mounted in the housing40.

As shown inFIG. 2, the cathode10has a metallic current collector, and an active material layer made of porous active carbon. The cathode lead6is connected to one side of the cathode10.

The current collector is generally constituted with a metallic foil, and the active material layer is formed by widely applying active carbon on both surfaces of the metallic current collector.

The active material layer allows storing positive or negative electric energy, and the current collector serves as a passage of charges emitted from or supplied to the active material layer.

Between the cathode10and the anode20, which are laminated subsequently, the separator30is arranged to limit electronic conduction between the cathode10and the anode20, and an electrolyte is filled in the housing40.

Here, the porous active material layer contains micro pores similar to a spherical shape, and thus has a great surface area. Also, the porous active material layer gives a function of active material identically to the cathode10and the anode20, and the surface of each porous active material layer contacts the electrolyte.

If a voltage is applied to the cathode10and the anode20, cations and anions contained in the electrolyte are moved to the cathode10and the anode20, respectively, and then penetrate into the micro pores of the porous active material layer.

Here, the electrode, in other words the cathode10or the anode20, and the lead may be produced separately and then connected with each other. However, it is also possible that, in a state where the current collector and the lead are integrally formed with a metallic foil, the active material layer is applied to the current collector so that the electrode and the lead are integrally formed.

In a state where the cathode10, the anode20, and the separator30, which are laminated as above, are rolled into a cylindrical shape, the cathode and anode leads6,16connected to the cathode10and the anode20may be evenly bent, thereby forming the electrode unit15.

At this time, in order to facilitate the easy bending of the cathode and anode leads6,16, the cathode and anode leads6,16may be cut at regular intervals in a length direction thereof.

In addition, in order to prevent short-circuit, upper and lower portions of the separator30are preferably protruded outwards over 2 mm from the cathode10and the anode20, respectively, and the cathode lead6and the anode lead16are preferably protruded outwards over 2 mm from the separator30, respectively.

The housing40may have a cylindrical shape and be constituted with metallic or synthetic resin material, preferably aluminum or its alloy.

The housing40is used for receiving the cathode10, the anode20, the separator30for electrically separating the cathode10and the anode20from each other, and the cathode and anode leads6,16.

The inner cathode and anode terminals51,52are arranged between the electrode unit15and the outer cathode and anode terminals61,62in order to electrically connect the cathode and anode leads6,16of the electrode unit15with the outer cathode and anode terminals61,62. Here, the inner cathode and anode terminals51,52may be fixed to the electrode unit15by laser welding in order to reduce electric resistance with the electrode unit15and ensure secure connection.

Since the inner cathode and anode terminals51,52are coupled with the electrode unit15by means of the laser welding, the inner cathode and anode terminals51,52and the electrode unit15are locally integrated in the laser welding region, thereby minimizing micro discontinuous surfaces and further reducing the resistance against electric flow.

FIG. 4is an enlarged sectional view showing the A portion ofFIG. 3.

As shown inFIG. 4, in the energy storage device according to the present invention, the groove53is formed in the side of the inner cathode terminal51, and the side protrusion45is formed on the inner wall of the housing at a location corresponding to the groove53of the inner cathode terminal51, in order that the electrode unit15and the inner cathode unit51are fixed to the housing40.

The side protrusion45is preferably formed by denting the sidewall of the housing40by means of beading at a location corresponding to the groove53formed in the side of the inner cathode terminal51so that the protruded portion of the sidewall of the housing40by denting is in agreement with the groove53in the side of the inner cathode terminal51. The side protrusion45allows the electrode unit15coupled with the inner cathode terminal51to be directly fixed to the housing40, thereby minimizing the shaking of the electrode unit15by an external vibration applied to the energy storage device.

Also, the outer cathode terminal61is structurally combined with the upper portion of the inner cathode terminal51. The structural combination between the outer cathode terminal61and the inner cathode terminal50will be described in detail later.

In addition, an insulation film55is provided between the housing40and both of the inner and outer cathode terminals51,61for the electric insulation between the housing40and the inner and outer cathode terminals51,61.

Further, an end portion46of the housing40is protruded over the uppermost portion of the outer cathode terminal61by a predetermined length, and the end portion46of the housing40is bent toward the outer cathode terminal61to fix the housing40to the outer cathode terminal61. Here, a sealing member56may be provided to the outer cathode terminal61at a location where the end portion46of the housing40is bent and fixed, so as to keep the airtightness of the energy storage device.

FIG. 5is an enlarged sectional view showing the B portion ofFIG. 3.

As shown inFIG. 5, in the energy storage device according to the present invention, openings73,74are formed in the inner cathode terminal51and the outer cathode terminal61, respectively, for the communication with the outside, and a pressure relief unit70is installed in the opening74of the outer cathode terminal61so as to relieve an increased inner pressure of the housing40.

The pressure relief unit70has an elastic member (not shown) so that the elastic member is operated to relieve the inner pressure of the housing40if a pressure applied from the opening73of the inner cathode terminal51is over a predetermined level. If the inner pressure of the housing40is relieved below a predetermined level, the pressure relief unit70returns to its original position by means of the elastic force of the elastic member to close the housing40.

As mentioned above, the pressure relief unit70plays a role of keeping the inner pressure of the housing below a predetermined level though a pressure over a predetermined level is applied to the housing40, and also the pressure relief unit70plays a role of preventing impurities from flowing into the housing40.

A coupling member71is coupled to the opening73of the inner cathode terminal51and the opening74of the outer cathode terminal61. The coupling member71is installed in the opening73of the inner cathode terminal51and the opening74of the outer cathode terminal61and fixes the inner and outer cathode terminals51,61to each other. The coupling member71also has a hollow therein. In this connection, the inner cathode terminal51and the outer cathode terminal61are structurally secured, and also the openings73,74may be used as an electrolyte injection hole, which allows simplifying the assembling process of the energy storage device.

Here, the opening73of the inner cathode terminal51preferably has a relatively smaller diameter than the opening74of the outer cathode terminal61. In this case, a step is formed between the openings73,74due to the difference in diameters, and thus the coupling member71may be secured in a more stable way.

In addition, the coupling member71may have the same thickness at a region located at the opening73of the inner cathode terminal51and a region located at the opening74of the outer cathode terminal61so that the step formed due to the difference in diameters of the openings73,74is also formed in the coupling member71. This step may be used as a support when the pressure relief unit70is installed.

Here, the coupling member71may be constituted as a bolt on which a thread is formed, and a thread corresponding thereto may be formed in the opening73of the inner cathode terminal51and the opening74of the outer cathode terminal61so that the coupling member71is fixed to the inner and outer cathode terminals51,61by means of bolt coupling.

As described above, in a state where the coupling member71is fixed to the opening73of the inner cathode terminal51and the opening74of the outer cathode terminal61, the pressure relief unit70is placed and installed in the coupling member71. Also, in a state where the coupling member71is installed, a fixing member72is coupled to the opening74of the outer cathode terminal61in order to fix the pressure relief unit70.

Here, the fixing member72may be constituted as a bolt on which a thread is formed, and a thread corresponding thereto may be formed in the opening74of the outer cathode terminal61so that the fixing member72fixes the pressure relief unit70by means of bolt coupling. In addition, a sealing means (not shown) such as an O-ring may be further interposed between the pressure relief unit70and the fixing member72in order to prevent the electrolyte from leaking out. Also, the fixing member72may be inserted into the opening74of the outer cathode terminal61, or for the better coupling, the pressure relief unit70may be fixed thereto by means of laser welding after the fixing member72is inserted into the opening74of the outer cathode terminal61.

Meanwhile, though it is illustrated in this embodiment that the pressure relief unit70is installed to the opening73of the inner cathode terminal51and the opening74of the outer cathode terminal61, the present invention is not limited thereto, and it is obvious that the pressure relief unit70may also be installed on the inner anode terminal52and the outer anode terminal62. In this case, when the inner pressure of the housing40is increased, the increased pressure may be relieved at both upper and lower portions of the housing40, which may solve any problem caused by the directivity of pressure.

As described above, the energy storage device according to the present invention allows the inner pressure of the housing40to be automatically relieved when the inner pressure exceeds a predetermined level, and thus there is no need to form a separate space between the electrode unit15and the inner side of the housing40where the electrode unit15is located, which was required conventionally in consideration of the generation of gas due to side reactions between the electrode unit and the electrolyte.

In a conventional energy storage device, a space should be formed between the electrode unit and the inner side of the housing in consideration of the generation of gas caused by side reactions.

However, in the present invention, since there is no need to form a separate space between the electrode unit15and the inner side of the housing40, it is possible that the housing40is designed to have the substantially same diameter as the electrode unit15.

Thus, the housing40of the energy storage device according to the present invention may be designed into a slimmer shape in comparison to conventional housings.

In addition, since the side protrusion45is fit with the groove53of the inner cathode terminal51, the electrode unit15may be directly fixed to the housing40, and thus it is possible to minimize the shaking of the electrode unit15due to external vibrations applied to the energy storage device.

Thus, it is possible to prevent the electrode unit15from being deformed or broken due to external vibrations.

Hereinafter, the present invention will be described in more detail based on examples of the present invention and comparative examples, for better understanding of the present invention.

EXAMPLES AND COMPARATIVE EXAMPLES

The table 1 shows measurement results of leakage currents of energy storage devices (according to the example) in which the side protrusion45is formed and fitted into the groove53formed in the side of the inner cathode terminal51according to the present invention, and energy storage devices (according to the comparative example) in which no side protrusion is formed, after charging for 12 hours.

As understood from the experiment results, the energy storage devices according to the example and the comparative examples exhibited the same leakage current when vibration was not applied thereto. However, when vibration was applied, the energy storage devices according to the example and the comparative examples exhibited different leakage currents.

In other words, it could be found that the energy storage device according to the example in which the side protrusion45is formed and fit into the groove53in the side of the inner cathode terminal51exhibited a reduced leakage current by half in comparison to the energy storage device of the comparative example.