Secondary battery

A secondary battery includes a reverse plate formed using a conductive material and provided in a case, and a fixing member formed using an elastically deformable material and joined to the reverse plate. When an internal pressure in the case is increased, the reverse plate deforms in response to the internal pressure, to thereby electrically connect a positive electrode terminal and a negative electrode terminal. With the increase in the internal pressure, the fixing member elastically deforms from a state where it is inserted into the through hole, exits the through hole and is fixed between the reverse plate and the case. The reverse plate in the deformed state is supported by the fixed fixing member.

This nonprovisional application is based on Japanese Patent Application No. 2016-201605 filed on Oct. 13, 2016, with the Japan Patent Office, the entire contents of which are hereby incorporated by reference.

BACKGROUND

Field

The present disclosure relates to a secondary battery.

Description of the Background Art

In a secondary battery such as a lithium-ion secondary battery or a nickel-metal hydride battery, an internal pressure in a case may be increased due to gas generation associated with overcharging or the like. In preparation for such an occasion, there has been proposed a short-circuiting mechanism that short-circuits a positive electrode terminal and a negative electrode terminal by utilizing the internal pressure increase. According to Japanese Patent Laying-Open No. 2011-54561, for example, a short-circuiting mechanism can operate to short-circuit a positive electrode terminal and a negative electrode terminal to thereby reduce the state of charge (SOC) of a secondary battery, thus suppressing heat generation, breakage and the like associated with overcharging.

SUMMARY

The short-circuiting mechanism disclosed in Japanese Patent Laying-Open No. 2011-54561, for example, includes a positive electrode short-circuit portion electrically connected to a positive electrode terminal (first electrode terminal), a negative electrode short-circuit portion electrically connected to a negative electrode terminal (second electrode terminal), and a reverse plate formed using a conductive material. The reverse plate is provided in a case. When the internal pressure is increased and a predetermined pressure is applied to the reverse plate, the reverse plate deforms (is reversed) and makes contact with both the positive electrode short-circuit portion and the negative electrode short-circuit portion. A positive electrode short-circuit plate and a negative electrode short-circuit plate are thereby brought into conduction through the reverse plate, causing the positive electrode terminal and the negative electrode terminal to be short-circuited (electrically connected).

After the reverse plate has deformed as described above, the internal pressure may be reduced. When the case is provided with an explosion-proof valve, for example, if the explosion-proof valve operates after the deformation of the reverse plate, the inside and outside of the case are communicated with each other, which may cause a reduction in the internal pressure to atmospheric pressure. The internal pressure may also be reduced due to a reduction in ambient temperature of the secondary battery.

With such a reduction in the internal pressure, force of pressing the reverse plate against the positive electrode short-circuit portion and the negative electrode short-circuit portion is reduced. Accordingly, a gap may be formed between the reverse plate and the positive electrode short-circuit portion or between the reverse plate and the negative electrode short-circuit portion, or the reverse plate may return to the original shape (state before the deformation). This causes the positive electrode short-circuit portion and the negative electrode short-circuit to fall out of conduction, resulting in failure to maintain the short-circuited state between the positive electrode terminal and the negative electrode terminal.

The present disclosure was made to solve the above-described problem, and has an object to provide a secondary battery capable of more reliably maintaining a state where a first electrode terminal and a second electrode terminal are electrically connected after deformation of a reverse plate.

A secondary battery according to one aspect of the present disclosure includes a battery element, a case, a first electrode terminal and a second electrode terminal, a reverse plate, and a fixing member. The battery element includes a first electrode and a second electrode. The case is formed with a through hole and has a housing space that houses the battery element. The first electrode terminal is provided in the case and electrically connected to the first electrode. The second electrode terminal is provided in the case and electrically connected to the second electrode. The reverse plate is formed of a conductive material and provided in the case. The fixing member is formed to include an elastically deformable material, and coupled to the reverse plate while being inserted into the through hole. A communication space is formed between the case and the reverse plate, the communication space being communicated with the housing space through the through hole. An increase in internal pressure in the housing space also causes an increase in internal pressure in the communication space. The reverse plate deforms in response to the increased internal pressure in the communication space, to thereby electrically connect the first electrode terminal and the second electrode terminal. The fixing member inserted into the through hole elastically deforms and exits the through hole with the increase in the internal pressure in the housing space, to be fixed in the communication space. The reverse plate in the deformed state is supported by the fixing member fixed in the communication space.

Preferably, the fixing member includes a projection projecting toward an outer circumference with respect to the through hole when the through hole is seen in plan view. The projection is disposed in the housing space before the increase in the internal pressure in the housing space.

Preferably, the fixing member includes a solid cylindrical shaft portion with one end coupled to the reverse plate. When the internal pressure in the housing space is increased, the shaft portion exits the through hole and is restored from a state where it is bent and inserted into the through hole, and is fixed in the communication space.

Preferably, the fixing member includes a hollow cylindrical shaft portion with one end coupled to the reverse plate. When the internal pressure in the housing space is increased, the shaft portion exits the through hole and is restored from a state where it is radially compressed and inserted into the through hole, and is fixed in the communication space.

According to the above structure, when the internal pressure in the housing space is increased, the fixing member exits the through hole and is fixed in the communication space, thereby supporting the reverse plate in the deformed state. Thus, the state where the first electrode terminal and the second electrode terminal are electrically connected through the reverse plate can be more reliably maintained.

Preferably, the secondary battery further includes a short-circuit portion electrically connected to one of the first electrode terminal and the second electrode terminal. The case includes a case body formed with an opening, and a lid member that closes the opening and forms the communication space between the reverse plate and the lid member. The short-circuit portion is provided opposite to the case body with the lid member interposed therebetween, and spaced from the lid member. The reverse plate deforms from the lid member side toward the short-circuit portion in response to the increased internal pressure in the housing space, to thereby make contact with the short-circuit portion. In a direction from the lid member toward the short-circuit portion, a length of the fixing member before the increase in the internal pressure in the housing space is equal to or greater than a distance between the lid member and the short-circuit portion.

According to the above structure, when the fixing member is fixed in the communication space, the fixing member contracts in a direction from the lid member toward the short-circuit portion. Thus, elastic force applied to the reverse plate from the fixing member trying to be restored can be increased. Therefore, the reverse plate in the deformed state can be more reliably supported.

Preferably, the case is further formed with a communication hole communicated with the communication space.

According to the above structure, the housing space and the communication space are communicated with each other by the communication hole in addition to the through hole. Accordingly, when the internal pressure in the housing space is increased, even if the through hole is closed by the fixing member, the internal pressure increase in the housing space is transmitted to the communication space through the communication hole, causing the internal pressure to be applied to the reverse plate. This internal pressure reinforces the force applied to the reverse plate. Therefore, the reverse plate in the deformed state can be more reliably supported.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts are designated by the same characters in the drawings and description thereof will not be repeated.

First Embodiment

<Overall Structure of Secondary Battery>

FIG. 1is a perspective sectional view of a secondary battery1according to a first embodiment. Secondary battery1is a lithium-ion secondary battery, for example. A plurality of secondary batteries1are connected in series to form a battery pack (not shown) having a desired voltage. This battery pack can be mounted on an electrically powered vehicle (not shown) such as a hybrid vehicle. However, the application of secondary battery1is not particularly limited. In the following description, a z direction in the drawings may be referred to as a “vertical direction,” a positive z direction may be referred to as “upward,” and a negative z direction may be referred to as “downward.”

Secondary battery1includes a case10and an electrode body20. Case10is formed in the shape of a flat rectangular parallelepiped, with a housing space S1(seeFIG. 3) that houses electrode body20and an electrolyte solution (not shown) formed in case10. Case10includes a case body11having the shape of a substantially rectangular parallelepiped and formed with an opening that opens in one direction, and a lid member12that closes the opening provided in case body11. Case body11and lid member12are formed of a metal material such as aluminum, and welded to each other.

Electrode body20includes a positive electrode sheet, a negative electrode sheet and a separator (none shown). The positive electrode sheet and the negative electrode sheet are wound (or stacked) with the separator interposed therebetween. Electrode body20has a positive electrode exposed portion (first electrode)25and a negative electrode exposed portion (second electrode)26provided on its one end and the other end, respectively. Electrode body20and the electrolyte solution correspond to a “battery element” according to the present disclosure.

Lid member12is provided with an explosion-proof valve30and an infusion plug40. Explosion-proof valve30operates to prevent explosion of case10when an internal pressure P1in case10(internal pressure in housing space S1) is increased and reaches a predetermined pressure. Infusion plug40is used to infuse the electrolyte solution into case10.

Secondary battery1includes a positive electrode terminal (first electrode terminal)50and a negative electrode terminal (second electrode terminal)60provided in lid member12. Positive electrode terminal50and negative electrode terminal60are spaced from each other in a long side direction (y direction) of case10. Positive electrode terminal50includes a bolt51, a positive electrode external terminal52, a rivet member53, an insulator55and a gasket56. Bolt51, positive electrode external terminal52and rivet member53are formed of a conductive material (for example, a metal material such as aluminum or copper).

Bolt51is provided to project upward from lid member12. Bolt51is configured such that it can be fastened to a bolt (not shown) on the negative electrode side of another secondary battery adjacent to secondary battery1. Rivet member53is spaced from bolt51, and is inserted into a through hole formed in lid member12. Positive electrode external terminal52is in the form of a thin plate extending between bolt51and rivet member53, and electrically connects bolt51and rivet member53. A collector electrode54is electrically connected to positive electrode exposed portion25of electrode body20.

Insulator55and gasket56are formed of an insulating material. Examples of such an insulating material include a resin material such as PFA (perfluoroalkoxy fluororesin) or a rubber material such as EPDM (ethylene-propylene-diene rubber). Insulator55is disposed between positive electrode external terminal52and lid member12, and electrically insulates positive electrode external terminal52from lid member12. Gasket56is disposed between lid member12and the upper end of collector electrode54, and electrically insulates lid member12from collector electrode54while sealing case10.

Secondary battery1includes collector electrode54that electrically connects positive electrode terminal50and positive electrode exposed portion25of electrode body20. Collector electrode54is also formed of a conductive material, similarly to rivet member53and positive electrode external terminal52.

Secondary battery1further includes, similarly on the negative electrode side, a bolt61, a negative electrode external terminal62, a rivet member63, a collector electrode64, an insulator65and a gasket66. Since the structure on the negative electrode side of secondary battery1is basically equivalent to the structure on the positive electrode side of secondary battery1, detailed description will not be repeated.

Secondary battery1further includes a short-circuiting mechanism100between positive electrode external terminal52and negative electrode external terminal62. Short-circuiting mechanism100is configured to short-circuit (electrically connect) positive electrode external terminal52and negative electrode external terminal62when an internal pressure P2in a communication space S2(described later) is increased due to gas generation associated with overcharging or the like of secondary battery1.

Short-circuiting mechanism100includes a positive electrode short-circuit plate150and a negative electrode short-circuit plate160each formed using a conductive material. Positive electrode short-circuit plate150and negative electrode short-circuit plate160are spaced from lid member12so as to face lid member12. More specifically, positive electrode short-circuit plate150and negative electrode short-circuit plate160are provided opposite to case body11(electrode body20) with lid member12interposed therebetween. Positive electrode short-circuit plate150is electrically connected to positive electrode external terminal52. Negative electrode short-circuit plate160is electrically connected to negative electrode external terminal62. Positive electrode short-circuit plate150may be formed integrally with or separately from positive electrode external terminal52. Negative electrode short-circuit plate160may be formed integrally with or separately from negative electrode external terminal62. At least one of positive electrode short-circuit plate150and negative electrode short-circuit plate160corresponds to a “short-circuit portion” according to the present disclosure.

In the first embodiment, secondary battery1is characterized by the structure of short-circuiting mechanism100. To facilitate understanding of this characteristic, the structure of a short-circuiting mechanism900included in a secondary battery according to a comparative example will be described first. The structure other than short-circuiting mechanism900of the secondary battery according to the comparative example is common to the corresponding structure of secondary battery1according to the first embodiment.

<Short-Circuiting Mechanism of Secondary Battery According to Comparative Example>

FIG. 2is a schematic diagram for illustrating the structure of short-circuiting mechanism900included in the secondary battery according to the comparative example.FIG. 2andFIG. 3which will be described later show the structure of a portion enclosed by a broken line circle inFIG. 1. As shown inFIG. 2, short-circuiting mechanism900includes a reverse plate110provided to cover a through hole13formed in lid member12.

Reverse plate110is in the form of a thin plate, which is circular when seen in plan view in the vertical direction, and is formed using a conductive material such as aluminum. Reverse plate110is welded to lid member12along its circumference. Reverse plate110has a shape projecting toward through hole13in a normal state. In this state, positive electrode short-circuit plate150and negative electrode short-circuit plate160are not electrically connected.

When secondary battery1is in an overcharged state, for example, gas is generated due to decomposition or the like of the electrolyte solution housed in case10, which may cause an increase in internal pressure P1in housing space S1. The increase in the internal pressure in the housing space also causes an increase in internal pressure P2in communication space S2formed between lid member12and reverse plate110. When a predetermined pressure is applied from the through hole13side to reverse plate110, reverse plate110deforms from lid member12toward positive electrode short-circuit plate150and negative electrode short-circuit plate160(deforms into a shape recessed toward through hole13), and makes contact with both positive electrode short-circuit plate150and negative electrode short-circuit plate160. Positive electrode short-circuit plate150and negative electrode short-circuit plate160are thereby brought into conduction through reverse plate110, causing positive electrode terminal50and negative electrode terminal60to be short-circuited (indicate a current I). As a result, the SOC of secondary battery1is reduced, thereby allowing protection of secondary battery1against heat generation, breakage or the like due to overcharging. In the following description, reverse plate110deforming to expand outward is also simply referred to as “reversed.”

Here, if internal pressure P1is further increased, explosion-proof valve30operates (for example, becomes cracked). The inside and outside of case10are thereby communicated with each other, causing a reduction in internal pressure P1in housing space S1to atmospheric pressure, which in turn causes a reduction in internal pressure P2in communication space S2to atmospheric pressure. As a result, a gap may be formed between reverse plate110and positive electrode short-circuit plate150, or between reverse plate110and negative electrode short-circuit plate160, or reverse plate110may return to the original shape (shape before the reversal). This causes positive electrode short-circuit plate150and negative electrode short-circuit plate160to fall out of conduction, resulting in failure to maintain the short-circuited state between positive electrode terminal50and negative electrode terminal60.

Thus, in the first embodiment, a fixing member120coupled below reverse plate110is adopted as a structure for supporting the state where reverse plate110after the reversal is in contact with positive electrode short-circuit plate150and negative electrode short-circuit plate160even when internal pressure P2in communication space S2is reduced after the reversal of reverse plate110. As will be described below in detail, when internal pressure P2is increased, fixing member120slips out of through hole13with the reversal of reverse plate110, and is fixed between reverse plate110and lid member12(communication space S2). The state where reverse plate110is in contact with positive electrode short-circuit plate150and negative electrode short-circuit plate160can thereby be retained.

<Short-Circuiting Mechanism of Secondary Battery According to First Embodiment>

FIG. 3is a schematic diagram for illustrating the structure of short-circuiting mechanism100included in secondary battery1according to the first embodiment.FIG. 4is an enlarged perspective view showing in more detail the structure of short-circuiting mechanism100.

Referring toFIGS. 3 and 4, short-circuiting mechanism100is different from short-circuiting mechanism900in the comparative example (seeFIG. 2) in that it further includes fixing member120formed using an elastically deformable material (for example, rubber), and that a communication hole130is formed in lid member12.

Reverse plate110is provided to cover communication hole130in addition to through hole13. That is, communication hole130causes communication between communication space S2and housing space S1.

Fixing member120includes, as its components, an outer flange portion121, a shaft portion122and an inner flange portion123.

Shaft portion122is coupled (joined, for example, bonded) to the lower surface of reverse plate110, and extends in the form of a solid cylinder between outer flange portion121and inner flange portion123. Shaft portion122is provided as being inserted into through hole13(as extending through through hole13) in the normal state.

Outer flange portion121is located above the upper surface of lid member12, that is, outside case10. When through hole13is seen in plan view in the vertical direction, outer flange portion121has the shape of a circle concentric with shaft portion122, and projects toward the outer circumference from through hole13. The upper surface of outer flange portion121is coupled to the lower surface of reverse plate110. The lower surface of outer flange portion121and the upper surface of lid member12abut each other in the normal state.

Inner flange portion123is located below the lower surface of lid member12, that is, inside case10, in the normal state. When through hole13is seen in plan view in the vertical direction, inner flange portion123has the shape of a circle concentric with shaft portion122, and projects toward the outer circumference from through hole13. Inner flange portion123corresponds to a “projection” according to the present disclosure.

Reverse plate110has a diameter of 18 mm, for example, and a thickness of 0.3 mm, for example. Through hole13has a tapered shape of decreasing diameter from a circular opening provided in the upper surface of lid member12toward the inside of case10(downward). Through hole13has a diameter of up to (namely, at the upper surface of lid member12) 2.0 mm, for example. Communication hole130has a diameter of 1.0 mm, for example. The lower surface (bottom surface) of inner flange portion123is a planar surface, and inner flange portion123has a tapered shape of decreasing diameter toward reverse plate110(upward). Inner flange portion123has a diameter of up to (namely, at the lower surface of inner flange portion123) 2.2 mm, for example. It should be noted that the specific numerical values described herein are merely exemplary in order to facilitate understanding.

When internal pressure P1in housing space S1is increased, fixing member120rises in response to internal pressure P1, thus pushing up and reversing reverse plate110. When reverse plate110is reversed, fixing member120is pulled upward. In so doing, inner flange portion123, which is formed using an elastically deformable material, can elastically deform and pass through (exit) through hole13. After passing through through hole13, inner flange portion123is restored and placed on the upper surface of lid member12. Fixing member120is thereby fixed in communication space S2between reverse plate110and lid member12. Then, the force of pressing reverse plate110against positive electrode short-circuit plate150and negative electrode short-circuit plate160continues to be applied from fixing member120to reverse plate110.

Therefore, even when explosion-proof valve30operates to reduce internal pressure P1and internal pressure P2due to a further increase in internal pressure P1, the reversed shape of reverse plate110can be supported and reverse plate110can be prevented from returning to the original shape. Thus, the state where positive electrode short-circuit plate150and negative electrode short-circuit plate160are in contact with reverse plate110can be retained, and the short-circuited state between positive electrode terminal50and negative electrode terminal60can thereby be more reliably maintained. As a result, secondary battery1is discharged and reduced in SOC, and therefore, the overcharged state of secondary battery1can be eliminated.

Shaft portion122has a length H (the length of fixing member120along a depth direction of through hole13, or the length of fixing member120in a direction from lid member12toward positive electrode short-circuit plate150and negative electrode short-circuit plate160) of 25 mm, for example. On the other hand, a distance (spacing) D5between positive electrode short-circuit plate150and lid member12and a distance (spacing) D6between negative electrode short-circuit plate160and lid member12are almost equal (D5≈D6), which are 25 mm, for example. In this manner, length H of shaft portion122is preferably equal to or greater than the longer one of distance D5between positive electrode short-circuit plate150and lid member12, and distance D6between negative electrode short-circuit plate160and lid member12. The sum (=25.3 mm) of the thickness of reverse plate110(=0.3 mm) and length H of shaft portion122(=25 mm) is thus greater than distances D5and D6(=25 mm).

With such a structure, when fixing member120is fixed in communication space S2, fixing member120contracts in the vertical direction. Thus, elastic force (restoring force) applied to reverse plate110from fixing member120trying to be restored can be increased. Accordingly, reverse plate110can more reliably retain the reversed shape.

Furthermore, since the diameter of inner flange portion123of fixing member120(2.2 mm at the lower surface) is greater than the diameter of through hole13(2.0 mm at the upper surface), through hole13may be closed by inner flange portion123when fixing member120is fixed in communication space S2. In the first embodiment, however, since communication hole130is formed in lid member12, internal pressure P2can be applied directly (without delay) to reverse plate110through communication hole130. Accordingly, the reversal of reverse plate110can be more reliably effected.

Even if communication hole130is not provided, when internal pressure P1in housing space S1is greater than internal pressure P2in communication space S2(P1>P2) with fixing member120being fixed in communication space S2, fixing member120continuously or intermittently floats from lid member12, to form a gap between inner flange portion123and lid member12. An increase in internal pressure P1in housing space S1can thereby be transmitted to communication space S2. Thus, communication hole130is not a required component.

As described above, in the first embodiment, when internal pressure P1in housing space S1is increased, internal pressure P1pushes fixing member120upward to apply a force to reverse plate110, thereby reversing reverse plate110. Furthermore, internal pressure P2in communication space S2is applied to reverse plate110through communication hole130, thereby reinforcing the force for reversing reverse plate110. When reverse plate110is reversed, fixing member120is pulled upward and fixed between reverse plate110and lid member12. Fixing member120is then stretched taut in the vertical direction, causing the force of pressing reverse plate110against positive electrode short-circuit plate150and negative electrode short-circuit plate160to be applied from fixing member120to reverse plate110. Accordingly, even when internal pressures P1and P2are reduced after the reversal of reverse plate110, the state where reverse plate110is in contact with positive electrode short-circuit plate150and negative electrode short-circuit plate160can be retained. Thus, positive electrode short-circuit plate150and negative electrode short-circuit plate160can be brought into conduction through reverse plate110, and the short-circuited state between positive electrode terminal50and negative electrode terminal60can be more reliably maintained.

Although not shown, when a plurality of secondary batteries1are connected in series and mounted as a battery pack on an electrically powered vehicle, if any one of secondary batteries1is short-circuited, electric power can be taken out of other normal secondary batteries1. Thus, the electrically powered vehicle can run using the electric power supplied from the other secondary batteries1. In addition, since fixing member120is retained as being inserted into through hole13in the normal state (before reverse plate110is reversed), fixing member120is prevented from colliding with the other components due to vibration during the running of the electrically powered vehicle. Accordingly, breakage of fixing member120is less likely to occur, thereby improving the reliability of short-circuiting mechanism100.

To verify the effect of short-circuiting mechanism100configured as described above, the present inventors performed the following verification tests. Five samples of the secondary battery according to the comparative example and five samples of secondary battery1according to the first embodiment were prepared. Each of the samples had a hole (for example, a hole of 0=5.0 mm; not shown) for adjusting internal pressure P1in housing space S1(and in turn P2) provided on a side surface of case10. First, compressed air was delivered through this hole into case10, to adjust internal pressure P1to 1.0 MPa (megapascal). That state was then maintained for 10 seconds, and it was determined whether or not positive electrode terminal50and negative electrode terminal60were short-circuited. Then, the air inside case10was released into the atmosphere to reduce internal pressure P1to atmospheric pressure (about 0.10 MPa), and it was again determined whether or not positive electrode terminal50and negative electrode terminal60were short-circuited.

In the comparative example, when internal pressure P1reached 1.0 MPa, reverse plate110was normally reversed to short-circuit positive electrode terminal50and negative electrode terminal60in all the secondary batteries. Internal pressures P1upon reversal of reverse plates110were measured, and their average value was 0.65 MPa. However, when internal pressure P1was subsequently reduced to atmospheric pressure, reverse plate110could not retain the reversed shape in any of the secondary batteries. In other words, there was no secondary battery that could maintain the short-circuited state between positive electrode terminal50and negative electrode terminal60.

In contrast, in the first embodiment, when internal pressure P1reached 1.0 MPa, reverse plate110was normally reversed in all of secondary batteries1. An average value of internal pressures P1upon reversal of reverse plates110was 0.70 MPa, which was slightly higher than that of the comparative example. When internal pressure P1was subsequently reduced to atmospheric pressure, reverse plate110retained the reversed shape and the short-circuited state between positive electrode terminal50and negative electrode terminal60was maintained in all of secondary batteries1.

Although the first embodiment has described an example where internal pressure P1is reduced due to the operation of explosion-proof valve30, internal pressure P1may be reduced due to a reduction in ambient temperature of secondary battery1(environmental temperature), for example. Thus, explosion-proof valve30is not a required component in secondary battery1according to the first embodiment.

[First Variation of First Embodiment]

The structure of the fixing member is not limited to that shown inFIG. 3 or 4. A first variation of the first embodiment and a second variation which will be described later will describe other structure examples of the fixing member.

FIG. 5is a perspective view showing a fixing member120A in the first variation of the first embodiment. An outer flange portion121A and a shaft portion122A of fixing member120A are equivalent to outer flange portion121and shaft portion122of fixing member120in the first embodiment, respectively.

An inner flange portion123A of a short-circuiting mechanism100A is different from inner flange portion123of short-circuiting mechanism100in that it is provided with notches124A at four locations, for example. These notches124A are each fan-shaped when fixing member120A is seen in plan view in the vertical direction, and are provided in a rotationally symmetric manner around a central axis Az of shaft portion122A.

When seen in plan view in the vertical direction, an angle θ1formed by a radius portion of the fan shape of inner flange portion123A (portion not provided with notch124A) and an angle θ2formed by a radius portion of the fan shape of notch124A are each 45°, for example. The number of notches124A provided and angles θ1, θ2can be changed as appropriate. Inner flange portion123A has a diameter ϕ of 2.2 mm, for example, as in the first embodiment.

FIG. 6is an enlarged perspective view showing in detail the structure of short-circuiting mechanism100A in the first variation of the first embodiment. Short-circuiting mechanism100A is different from short-circuiting mechanism100in the first embodiment (seeFIG. 4) in that communication hole130is not provided in lid member12.

In short-circuiting mechanism100A, since inner flange portion123A is provided with notches124A, the complete closure of through hole13by inner flange portion123B is prevented even when inner flange portion123A is elastically deforming and exiting through hole13(and after exiting through hole13) with an increase in internal pressure Pb. Therefore, even in the structure not provided with communication hole130, internal pressure P1is reliably applied to reverse plate110through notches124A. However, short-circuiting mechanism100A may also be provided with communication hole130.

Since the structure of short-circuiting mechanism100A is otherwise equivalent to the corresponding structure of short-circuiting mechanism100in the first embodiment, detailed description will not be repeated. In addition, since numerical values equivalent to those described in the first embodiment can be employed as the sizes of the respective components, detailed description will not be repeated.

In short-circuiting mechanism100A, too, similarly to short-circuiting mechanism100, even when explosion-proof valve30operates due to an increase in internal pressure P1, fixing member120A is stretched taut between lid member12and reverse plate110, so that the force of pressing reverse plate110against positive electrode short-circuit plate150and negative electrode short-circuit plate160continues to be applied from fixing member120A to reverse plate110. Thus, reverse plate110can retain the reversed shape. Accordingly, reverse plate110can be prevented from returning to the original shape, and the state where positive electrode short-circuit plate150and negative electrode short-circuit plate160are in contact with reverse plate110can be more reliably maintained. Thus, the short-circuited state between positive electrode terminal50and negative electrode terminal60can be more reliably maintained.

In the first variation of the first embodiment, too, verification tests similar to those in the first embodiment were performed. The results were that when internal pressure P1reached 1.0 MPa, reverse plate110was normally reversed in all the secondary batteries. An average value of internal pressures P1upon reversal of reverse plates110was 0.67 MPa, which was slightly lower than the value in the first embodiment (0.70 MPa). It was also confirmed that the short-circuited state between positive electrode terminal50and negative electrode terminal60was normally maintained even when internal pressure P1was reduced to atmospheric pressure.

[Second Variation of First Embodiment]

The first embodiment and the first variation have described structure examples where through hole13having a circular opening was provided. A second variation of the first embodiment will describe a structure where a through hole13B having a substantially rectangular opening is provided.

FIG. 7is a perspective view showing a fixing member120B and through hole13B in the second variation of the first embodiment.FIG. 8is an enlarged perspective view showing in more detail the structure of a short-circuiting mechanism100B in the second variation of the first embodiment.

Referring toFIGS. 7 and 8, a lid member12B is provided with through hole13B having a substantially rectangular opening. Through hole13B has a long side length Y1of 5.0 mm, for example, and a short side length X1of 2.5 mm, for example. Through hole13B has a depth of 1.0 mm, for example.

Inner flange portion123B of fixing member120B has the shape of a substantially rectangular parallelepiped, in conformity with the shape of through hole13B. Inner flange portion123B has a long side length Y2of 6.0 mm, for example, which is longer than long side length Y1of through hole13B. Accordingly, when internal pressure P1is increased with fixing member120B being inserted into through hole13B, inner flange portion123B elastically deforms in its long side direction and exits through hole13B, and has opposite end portions in the long side direction placed on the upper surface of lid member12B after restoration.

On the other hand, inner flange portion123B has a short side length X2of 2.0 mm, for example, which is shorter than short side length X1of through hole13B. Although fixing member120B is not provided with notches124A such as those of fixing member120A in the first variation (seeFIG. 5), when fixing member120B is inserted into through hole13B, communication space S2and housing space S1are communicated with each other in a short side direction of inner flange portion123B. Therefore, short-circuiting mechanism100B is not provided with communication hole130, similarly to short-circuiting mechanism100A in the first variation. Inner flange portion123B has a thickness of 0.60 mm, for example.

Since the structure of short-circuiting mechanism100B is otherwise equivalent to the corresponding structure of short-circuiting mechanism100in the first embodiment (seeFIG. 4), detailed description will not be repeated. In addition, since numerical values equivalent to those described in the first embodiment can be employed as the sizes of the respective components, detailed description will not be repeated.

In short-circuiting mechanism100B, too, similarly to short-circuiting mechanism100, even when explosion-proof valve30operates due to an increase in internal pressure P1, fixing member120B is stretched taut between lid member12B and reverse plate110, causing the force of pressing reverse plate110against positive electrode short-circuit plate150and negative electrode short-circuit plate160to be applied from fixing member120B to reverse plate110. Thus, reverse plate110can retain the reversed shape. Accordingly, reverse plate110can be prevented from returning to the original shape, and the state where positive electrode short-circuit plate150and negative electrode short-circuit plate160are in contact with reverse plate110can be more reliably maintained. Thus, the short-circuited state between positive electrode terminal50and negative electrode terminal60can be more reliably maintained.

In the second variation of the first embodiment, too, verification tests similar to those in the first embodiment were performed. The results were that when internal pressure P1reached 1.0 MPa, reverse plate110was normally reversed in all the secondary batteries. An average value of internal pressures P1upon reversal of reverse plates110was 0.71 MPa, which was higher than the values in the first embodiment and its first variation. It was also confirmed that the short-circuited state between positive electrode terminal50and negative electrode terminal60was normally maintained even when internal pressure P1was reduced to atmospheric pressure.

Second Embodiment

Although the first embodiment as well as the first and second variations have described structure examples where inner flange portions123,123A and123B are provided, the inner flange portion is not a required component. A second embodiment will describe a structure where the inner flange portion is not provided.

FIG. 9is a schematic diagram for illustrating the structure of a short-circuiting mechanism200included in a secondary battery according to the second embodiment.FIG. 10is an enlarged perspective view showing in more detail the structure of short-circuiting mechanism200.

Referring toFIGS. 9 and 10, short-circuiting mechanism200is different from short-circuiting mechanism100in the first embodiment (seeFIG. 3 or 4) in that it includes a fixing member220instead of fixing member120, and that a through hole23is formed instead of through hole13in a lid member22.

Through hole23has a shape extending in a straight line from a circular opening. That is, through hole23does not have such a tapered shape as that of through hole13in the first embodiment (seeFIG. 4). Through hole23has a diameter of 1.2 mm, for example.

Fixing member220includes, as its components, an outer flange portion221and a shaft portion222, but does not include an inner flange portion. Fixing member220is formed using an elastically deformable material such as rubber, similarly to fixing member120. Shaft portion222has a solid cylindrical shape with one end joined to reverse plate110. Shaft portion222has a diameter of 1.2 mm, for example, which is almost equal to that of through hole23.

When short-circuiting mechanism200is seen in plan view in the vertical direction, the center of shaft portion222is shifted (off-centered) from the center of through hole23at the upper surface of lid member22. The magnitude of this shift (distance between the two centers) is 0.3 mm, for example. Shaft portion222has a diameter almost equal to that of through hole23. In this manner, in the second embodiment, shaft portion222that has not elastically deformed is provided to make contact with, in other words, to interfere with, the upper surface of lid member22. Therefore, shaft portion222is inserted into through hole13in an elastically bent state. AlthoughFIGS. 9 and 10show solid shaft portion222, shaft portion222may have a hollow shape.

Since the structure of the secondary battery according to the second embodiment is otherwise equivalent to the corresponding structure of secondary battery1according to the first embodiment, detailed description will not be repeated. In addition, since numerical values equivalent to those described in the first embodiment can be employed as the sizes of the respective components, detailed description will not be repeated.

When reverse plate110is reversed and fixing member220is pulled upward and exits through hole13due to an increase in internal pressure P1, shaft portion222is restored from the elastically deformed state. Consequently, the other end of shaft portion222(end opposite to the one end joined to reverse plate110) is placed on the upper surface of lid member22. Accordingly, fixing member220is fixed in communication space S2between reverse plate110and lid member22, while being stretched taut in the vertical direction to support reverse plate110.

As described above, according to the second embodiment, fixing member220is inserted into through hole23in a bent state. Fixing member220exits through hole due to an increase in internal pressure P1, and is restored from the bent state, to be fixed between reverse plate110and lid member22. Then, fixing member220is stretched taut in the vertical direction, causing the force of pressing reverse plate110against positive electrode short-circuit plate150and negative electrode short-circuit plate160to be applied from fixing member220to reverse plate110. Accordingly, even when internal pressures P1and P2are reduced after the reversal of reverse plate110, reverse plate110can retain the reversed shape. Thus, positive electrode short-circuit plate150and negative electrode short-circuit plate160can be brought into conduction through reverse plate110, and the short-circuited state between positive electrode terminal50and negative electrode terminal60can be more reliably maintained.

In short-circuiting mechanism200, too, the length of shaft portion222is preferably equal to or greater than the longer one of the distance between positive electrode short-circuit plate150and lid member22, and the distance between negative electrode short-circuit plate160and lid member22.

In the second embodiment, too, verification tests similar to those in the first embodiment were performed. The results were that when internal pressure P1reached 1.0 MPa, reverse plate110was normally reversed in all the secondary batteries. An average value of internal pressures P1upon reversal of reverse plates110was 0.68 MPa. It was also confirmed that the short-circuited state between positive electrode terminal50and negative electrode terminal60was normally maintained even when internal pressure P1was reduced to atmospheric pressure.

[Variation of Second Embodiment]

Although the second embodiment has described a structure where shaft portion222is inserted into through hole23in a bent state, a variation of the second embodiment will describe a structure where a shaft portion222A is inserted into through hole13B in a radially compressed state.

FIG. 11is a perspective view showing an exemplary fixing member220A in a variation of the second embodiment.FIG. 12is a perspective view showing another exemplary fixing member220B in a variation of the second embodiment.

As shown inFIG. 11, shaft portion222A of fixing member220A has a hollow cylindrical shape (annular ring shape). Shaft portion222A has an outer diameter ϕ1of 4.0 mm, for example, and an inner diameter ϕ2of 3.0 mm, for example. As has been described in the second variation of the first embodiment, short side length X1of through hole13B is 2.5 mm, which is shorter than outer diameter ϕ1of shaft portion222A. Accordingly, shaft portion222A is provided to make contact with, and interfere with, lid member12B.

As shown inFIG. 12, shaft portion222B of fixing member220B may be formed to have a cross section inclined in the vertical direction. Communication space S2and housing space S1can thereby be communicated with each other more reliably when fixing member220B is fixed in communication space S2.

Since the structure of the secondary battery according to the variation of the second embodiment is otherwise equivalent to the corresponding structure of secondary battery1according to the first embodiment, detailed description will not be repeated. In addition, since numerical values equivalent to those described in the first embodiment can be employed as the sizes of the respective components, detailed description will not be repeated.

FIG. 13is an enlarged perspective view showing in detail the structure of a short-circuiting mechanism200A in the variation of the second embodiment. In the normal state, shaft portion222A is inserted into through hole13B while being elastically compressed in a radial direction of shaft portion222A (a short side direction of through hole13B or an x direction) so that the outer diameter of shaft portion222A is equal to short side length X2of through hole13B.

When reverse plate110is reversed and fixing member220A is pulled upward and exits through hole13B due to an increase in internal pressure P1, shaft portion222B is restored from the compressed state. Shaft portion222B is thereby placed on the upper surface of lid member12B without falling into through hole13B again. Thus, fixing member220B is fixed in communication space S2, while being stretched taut in the vertical direction to retain reverse plate110in the reversed state.

As described above, in short-circuiting mechanism200A, too, even when explosion-proof valve30operates to reduce internal pressures P1and P2due to an increase in internal pressure P1, fixing member220A (or220B) is stretched taut between lid member12B and reverse plate110, causing the force of pressing reverse plate110against positive electrode short-circuit plate150and negative electrode short-circuit plate160to be applied from fixing member120to reverse plate110. Reverse plate110can thereby retain the reversed shape. Accordingly, reverse plate110can be prevented from returning to the original shape, and the state where positive electrode short-circuit plate150and negative electrode short-circuit plate160are in contact with reverse plate110can be more reliably maintained. Thus, the short-circuited state between positive electrode terminal50and negative electrode terminal60can be more reliably maintained.

In the variation of the second embodiment, too, verification tests similar to those in the first embodiment were performed. The results were that when internal pressure P1reached 1.0 MPa, reverse plate110was normally reversed in all the secondary batteries. An average value of internal pressures P1upon reversal of reverse plates110was 0.67 MPa. It was also confirmed that the short-circuited state between positive electrode terminal50and negative electrode terminal60was normally maintained even when internal pressure P1was reduced to atmospheric pressure.

Although the first and second embodiments have described examples where the secondary battery is a lithium-ion secondary battery, the secondary battery may be another secondary battery (for example, a nickel-metal hydride battery). Although the case of the secondary battery has been described as having a prismatic shape by way of example, the shape of the case is not particularly limited, and may be a cylindrical shape, for example. In addition, although the short-circuiting mechanism has been described as being formed in the lid member by way of example, the short-circuiting mechanism may be formed in another portion (for example, a side surface) of the case.

Third Embodiment

Although the first and second embodiments have described structures where positive electrode short-circuit plate150and negative electrode short-circuit plate160are short-circuited through reverse plate110by way of example, the structure may be such that positive electrode terminal50and negative electrode terminal60are short-circuited through the reverse plate and the case.

FIG. 14is a sectional view of a secondary battery3according to a third embodiment. Since the structure of a short-circuiting mechanism300provided in secondary battery3is basically equivalent to the structure of short-circuiting mechanism100in the first embodiment (seeFIG. 1), detailed description will not be repeated.

As shown inFIG. 14, negative electrode terminal60is electrically connected to a connection plate (short-circuit portion)163, but is insulated from lid member12by insulator65. On the other hand, positive electrode terminal50is electrically connected to lid member12by a connection member57.

When a reverse plate310is reversed (not shown) with an increase in internal pressure P1in housing space S1, reverse plate310and connection plate163make contact with each other. Positive electrode terminal50and negative electrode terminal60are thereby short-circuited (electrically connected) through connection plate163, reverse plate310and lid member12. In so doing, a fixing member320is fixed between reverse plate310and lid member12(communication space S2), to thereby support reverse plate310after the reversal. Although short-circuiting mechanism300is provided on the negative electrode side in the example ofFIG. 14, short-circuiting mechanism300may be provided on the positive electrode side.

Fourth Embodiment

FIG. 15is a sectional view of a secondary battery4according to a fourth embodiment. A shown inFIG. 15, secondary battery4may have a structure including two short-circuiting mechanisms400A and400B. Since the structure of each of short-circuiting mechanisms400A and400B is basically equivalent to the structure of short-circuiting mechanism100in the first embodiment (seeFIG. 1), detailed description will not be repeated.

Positive electrode terminal50is electrically connected to a connection plate153, but is insulated from lid member12by insulator55. Similarly, negative electrode terminal60is electrically connected to connection plate163, but is insulated from lid member12by insulator65.

According to the structure shown inFIG. 15, both reverse plates410A and410B are reversed (not shown) with an increase in internal pressure P1. The reversal of reverse plate410A causes reverse plate410A to make contact with connection plate153. Positive electrode terminal50and lid member12are thereby electrically connected through reverse plate410A and connection plate153. Similarly, the reversal of reverse plate410B causes reverse plate410B to make contact with connection plate163. Negative electrode terminal60and lid member12are thereby electrically connected through reverse plate410B and connection plate163. As a result, positive electrode terminal50and negative electrode terminal60are short-circuited (electrically connected) through connection plate153, lid member12and connection plate163.

In so doing, a fixing member420A is fixed between reverse plate410A and lid member12(communication space S2), to thereby support reverse plate410A after the reversal. Similarly, a fixing member420B is fixed between reverse plate410B and lid member12(communication space S2), to thereby support reverse plate410B after the reversal.

[Variation of First to Fourth Embodiments]

The first to fourth embodiments have described structures where the reverse plate provided directly above the through hole covers the through hole by way of example. However, the reverse plate may be provided at a position different from the position directly above the through hole, so long as the space above the through hole is sealed by the reverse plate. In addition, of the outer flange portion, the shaft portion and the inner flange portion which are the components of the fixing member, the outer flange portion is not a required component.

FIG. 16is an enlarged sectional view schematically showing the structure of a short-circuiting mechanism100C in a variation of the first to fourth embodiments. As shown inFIG. 16, a reverse plate110C is provided at a position different from the position of a through hole13C in the vertical direction. A fixing member120C includes a shaft portion122C and an inner flange portion123C, but does not include an outer flange portion. Inner flange portion123C is located below the lower surface of lid member12, that is, in housing space S1, in the normal state (before an increase in internal pressure P1; see the upper figure). Shaft portion122C is coupled to the lower surface of reverse plate110, and extends between reverse plate110and inner flange portion123C in a direction along the surface of lid member12.

In such a structure, too, when reverse plate110C is reversed with an increase in internal pressure P1, positive electrode short-circuit plate150and negative electrode short-circuit plate160are short-circuited through reverse plate110C (see the lower figure). In so doing, fixing member120C elastically deforms from the state where it is inserted into through hole13C, exits through hole13C and is fixed between reverse plate110C and lid member12(communication space S2), thereby supporting reverse plate110after the reversal.

The first to fourth embodiments and the respective variations discussed above have described examples where the fixing member is entirely formed of an elastically deformable material. However, in order not to obstruct and inhibit the passing of the fixing member through the through hole, the fixing member may only partly be formed of an elastically deformable material, and the remaining part may be a rigid body formed of an elastically undeformable material. In other words, the fixing member may be formed to include an elastically deformable material.