Electric storage device

There is provided an electric storage device having a novel fastening structure of a plastic member which can reduce cost with a simple configuration. An electric storage device according to this invention includes an electrode assembly, a case housing the electrode assembly, a plastic member arranged at an outer surface of the case, the plastic member having a joining surface facing the outer surface of the case, and an external terminal supported by the plastic member and electrically connected to the electrode assembly. The plastic member is a synthetic resin containing an inorganic fiber and is bonded to the outer surface of the case with the inorganic fiber exposed at the joining surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Applications Nos. 2010-293138 and 2010-293140, the disclosures of which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to an electric storage device including an external terminal.

BACKGROUND ART

In recent years, rechargeable and dischargeable electric storage devices such as battery cells (e.g., a lithium ion battery cell and a nickel-metal hydride battery cell) and capacitors (e.g., an electric double layer capacitor) have been adopted as the power sources of vehicles (e.g., an automobile and a motorcycle) and various devices (e.g., a portable terminal and a laptop computer). For example, a battery cell includes an electrode assembly and a case composed of a case body which houses the electrode assembly and a cover plate which covers an opening of the case body. An external terminal is arranged at an outer surface of the cover plate, a current collector is connected to the electrode assembly, the current collector is arranged inside the case, and the external terminal and the current collector are directly or indirectly connected to each other. With this configuration, the external terminal and the electrode assembly are electrically connected.

There are two main methods for connecting an external terminal and a current collector. One is to directly connect an external terminal and a current collector, and the other is to indirectly connect an external terminal and a current collector via an auxiliary terminal and a connecting conductor.

The former method uses an external terminal which is composed of a body, a caulking part projecting from a lower surface of the body, and a male thread part projecting from an upper surface of the body. The external terminal is arranged at an outer surface of a cover plate via a sealing member, the caulking part of the external terminal is inserted into a through-hole of a current collector inside a case, and an end portion of the caulking part projecting downward from the through-hole is caulked from below. With this configuration, the external terminal and the current collector are directly connected to each other (Patent Document 1: JP-A-2001-357833).

The latter method uses an auxiliary terminal composed of a body, a first caulking part projecting from a lower surface of the body, and a second caulking part projecting from an upper surface of the body, an external terminal composed of a head and a male thread part projecting from an upper surface of the head, and a connecting conductor including through-holes into which the second caulking part of the auxiliary terminal and the male thread part of the external terminal are to be inserted. The auxiliary terminal is arranged at an outer surface of a cover plate via a sealing member, the first caulking part of the auxiliary terminal is inserted into a through-hole of a current collector inside a case, and an end portion of the first caulking part projecting downward from the through-hole is caulked from below. The external terminal is arranged at the outer surface of the cover plate via the sealing member, the second caulking part of the auxiliary terminal and the male thread part of the external terminal are inserted into the through-holes of the connecting conductor, and an end portion of the second caulking part projecting upward from the through-hole is caulked from above. With this configuration, the external terminal and the current collector are indirectly connected via the auxiliary terminal and the connecting conductor (Patent Document 2: Japanese Patent Laid-Open No. 2003-346774).

In either of the methods, a crimp contact of a lead wire of an external device fits on the male thread part of the external terminal, and the male thread part is fixed with a nut. With this configuration, the crimp contact of the lead wire is electrically connected to an electrode assembly, which causes the external device to be electrically connected to a battery cell.

According to the latter method, since the external terminal and the auxiliary terminal are separated from each other, rotational torque applied to the external terminal when the nut is tightened is not transmitted to the auxiliary terminal. For this reason, a situation does not occur in which rotation of the auxiliary terminal causes the auxiliary terminal and a connection part of the current collector fixed by caulking to come loose to impair the connection therebetween. The latter method is superior in this respect to the former method.

However, even in the latter method, rotational torque applied to the external terminal when the nut is tightened is directly transmitted to the sealing member. Accordingly, sealing with the sealing member may be impaired. In order to solve the problem, a structure including a terminal retainer provided separately from a sealing member and an external terminal arranged at an outer surface of a cover plate via the terminal retainer has been proposed (Patent Document 3: Japanese Patent Laid-Open No. 2010-97764).

Not only the sealing member disclosed in Patent Document 1 (“the upper gasket plate 6” in Patent Document 1) and the sealing member disclosed in Patent Document 2 (“the insulating sealer 7” in Patent Document 2) but also the terminal retainer disclosed in Patent Document 3 (“the retainer 10” in Patent Document 3) receives torque from the external terminal as it stops rotation of the external terminal when a nut is tightened. Accordingly, the sealing members and the terminal retainer (which are each made of plastic and are collectively called “plastic members”) each need to be securely fixed to the outer surface of the cover plate to overcome rotational torque from the external terminal.

In this respect, Patent Document 3 discloses the process of forming the terminal retainer by finishing a part where the terminal retainer is fastened of a metal surface at the outer surface of the cover plate so as to have microscopic asperities, arranging a mold to surround the part, pouring molten resin into the mold, and solidifying the resin and the process of directly injection molding the terminal retainer at the outer surface of the cover plate (cf., paragraph [0036]).

However, these methods involve complicated work processes and high cost.

The same applies to capacitors (e.g., an electric double layer capacitor).

SUMMARY OF THE INVENTION

The present invention has an object to provide a novel fastening structure of a plastic member which can reduce cost with a simple configuration.

An electric storage device according to the present invention includes:

an electrode assembly;

a case housing the electrode assembly;

a plastic member arranged at an outer surface of the case and having a joining surface facing the outer surface of the case; and

an external terminal supported by the plastic member and electrically connected to the electrode assembly,

wherein the plastic member is a synthetic resin containing an inorganic fiber and is bonded to the outer surface of the case at least with the inorganic fiber exposed at the joining surface.

In another embodiment of the electric storage device according to the present invention, the plastic member may comprise a resin material obtained by uniformly mixing a synthetic resin material with glass fiber as a filler.

In this case, polyphenylene sulfide (PPS) resin or polytetrafluoroethylene-perfiuoroalkylvinylether copolymer (PFA) resin may be used as the synthetic resin material.

As a first embodiment, the electric storage device may further include:

a sealing member arranged at the outer surface of the case, the sealing member having a joining surface facing the outer surface of the case; and

an auxiliary terminal supported by the sealing member, the auxiliary terminal extending from inside to outside the case, being electrically connected to the electrode assembly, and being electrically connected to the external terminal.

As a second embodiment of the electric storage device, the plastic member may be a sealing member, and

the device may further include an auxiliary terminal supported by the sealing member together with the external terminal, the auxiliary terminal extending from inside to outside the case, being electrically connected to the electrode assembly, and being electrically connected to the external terminal.

As a third embodiment of the electric storage device, the plastic member may be a sealing member, and the external terminal may extend from inside to outside the case and be electrically connected to the electrode assembly.

Note that if a sealing member is provided separately from the plastic member (in the case of the electric storage device according to the first embodiment), the electric storage device may further include: a current collector connected to the electrode assembly and connected to the auxiliary terminal; and a connecting conductor connecting together the auxiliary terminal and the external terminal. Furthermore, the plastic member may preferably comprise a material having hardness higher than hardness of the sealing member.

In still another embodiment of the electric storage device of the present invention, the case may include a non-circular recess which can receive at least a part of the joining surface of the plastic member in a predetermined region of the outer surface of the case.

In yet another embodiment of the electric storage device of the present invention, the case may include a non-circular recess which can receive at least a part of the joining surface of the sealing member in a predetermined region of the outer surface of the case.

In this case, the plastic member and the sealing member may be arranged close to each other, and the area of the recess for the sealing member may be larger than the area of the recess for the plastic member.

In another embodiment of the electric storage device of the present invention,

the plastic member may include a surrounding circumferential outer wall part and a recess inside the outer wall part,

the external terminal may include a head to be inserted into the recess of the plastic member and a shaft projecting from one surface of the head, and

the outer wall part of the plastic member may be formed to be high enough for the recess of the plastic member to entirely or substantially entirely receive the head of the external terminal.

In still another embodiment of the electric storage device of the present invention, the external terminal may include a head and a shaft projecting from one surface of the head, and the shaft may include a male thread part.

In yet another embodiment of the electric storage device of the present invention, the plastic member may be bonded to the outer surface of the case with an adhesive. In this case, the adhesive may preferably be an epoxy resin adhesive.

In another embodiment of the electric storage device of the present invention, the case may include a case body including an opening and a cover plate which covers the opening of the case body to seal the case, and

the plastic member may be arranged at an outer surface of the cover plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A battery cell which is an embodiment of an electric storage device according to the present invention will be described below with reference to the drawings. A battery cell according to the present embodiment is a non-aqueous electrolyte secondary battery cell and, more particularly, a lithium ion secondary battery cell. As shown inFIGS. 1 to 4, the battery cell according to the present embodiment includes a case1which is composed of a case body2and a cover plate3which covers an opening of the case body2to seal the case1. The cover plate3includes terminal structures9which are electrically connected to an electrode assembly4housed in the case1.

The case body2and cover plate3of the case1are metal members made of an aluminum alloy, steel, or the like. The case body2is a rectangular box flattened in the width direction so as to house the wound electrode assembly4that has been formed into an elliptic cylinder. The cover plate3is a rectangular plate material corresponding to the opening of the case body2. The cover plate3fits in the opening of the case body2and is fixed to the case body2by laser welding or the like so as to seal the opening.

In the electrode assembly4, a band-shaped positive electrode sheet5and a band-shaped negative electrode sheet6which are displaced to each other in different lateral directions with a band-shaped separator7sandwiched therebetween are wound about a lateral rotation axis into a cylinder in the shape of a vertically long ellipse. The electrode assembly4is entirely covered with an insulating cover (not shown) comprising an insulating sheet and is housed in the case1while being insulated from the case1. The positive electrode sheet5includes aluminum foil carrying a positive electrode active material at the surface. The negative electrode sheet6includes copper foil carrying a negative electrode active material at the surface. The positive electrode sheet5and the negative electrode sheet6each have a non-overlapped portion not coated with the active material at an edge in the lateral direction in which the sheet is displaced. With this arrangement, at the lateral ends of the electrode assembly4, the aluminum foil and copper foil are exposed, and thus these metal foils of the positive electrode and negative electrode project from the overlapped portion in a wound configuration.

Metal foils projecting at the lateral ends of the electrode assembly4are electrically connected to respective current collectors8. The current collectors8are vertically long conductive metal members. More specifically, the current collector8for the positive electrode comprises aluminum or an aluminum alloy, and the current collector8for the negative electrode comprises copper or a copper alloy. An upper part of each current collector8is horizontally bent to constitute a connection part8a. A part extending downward from the connection part8ais divided into a front part and a rear part, which project downward. The two front and rear parts are sandwiched between holding plates (not shown) together with the corresponding end of the electrode assembly4and are connected and fixed by ultrasonic welding or the like.

The terminal structures9include the terminal structure9for the positive electrode and the terminal structure9for the negative electrode. As shown in more detail inFIGS. 5 to 7, each terminal structure9includes a plastic plate10, an outer gasket11, a rivet12, a terminal retainer13, a terminal bolt14, and a connecting plate15. The plastic plate10and outer gasket11are arranged inside and outside the case1with through-holes3aformed in the right and left ends of the cover plate3interposed therebetween. The rivet12is inserted into the through-hole3avia the plastic plate10and outer gasket11and is electrically connected to the connection part8aof the current collector8. The terminal retainer13is arranged close to the outer gasket11. The terminal bolt14is arranged at an outer surface of the cover plate3via the terminal retainer13. The connecting plate15electrically connects the terminal bolt14and the rivet12. With this configuration, the electrode assembly4inside the case1and the terminal bolt14are electrically connected to each other.

Note that the plastic plate10, the outer gasket11and the terminal retainer13are made of plastic, and therefore each represent a plastic member. Also, the plastic plate10, outer gasket11, and terminal retainer13have an insulating function and therefore each represent an insulating member. In particular, the outer gasket11(and the plastic plate10in some instances) has a sealing function and thus also represents a sealing member. The rivet12represents an auxiliary terminal. The terminal bolt14represents an external terminal. The connecting plate15represents a connecting conductor.

The plastic plate10is a synthetic resin with at least insulating properties. More specifically, for example, polyphenylene sulfide (PPS) resin is used as the material for the plastic plate10. However, the material is not limited to this, and any appropriate material can be selected. The plastic plate10has a rectangular shape. A lower surface of the plastic plate10includes a recess10awhich can receive the connection part8aof the current collector8. The plastic plate10includes a through-hole10bwhich coincides in position with a through-hole8bformed in the connection part8awhile the recess10areceives the connection part8aof the current collector8.

The outer gasket11is a synthetic resin with insulating properties and sealing properties. More specifically, for example, polyphenylene sulfide (PPS) resin is used as the material for the plastic plate10. However, the material is not limited to this, and any appropriate material can be selected.

The outer gasket11is slightly larger than a body12aof the rivet12and has a rectangular shape. The outer gasket11includes a surrounding circumferential outer wall part11aat the outer periphery, which is formed by recessing an upper surface except for the outer periphery. The outer gasket11includes a recess11bwhich can receive the body12aof the rivet12inside the outer wall part11a. The outer gasket11includes a through-hole11cinto which a first caulking part12bof the rivet12can be inserted while the recess11breceives the body12aof the rivet12. A lower surface of the outer gasket11includes an annular projection11dwhich extends through the through-hole3aof the cover plate3and is inserted into the through-hole10bof the plastic plate10.

Note that the plastic plate10is arranged on a lower surface (an inner surface) of the cover plate3and is thus arranged inside the case1. The outer gasket11is arranged at an upper surface (the outer surface) of the cover plate3and is thus arranged at an outer surface of the case1. A region of the upper surface of the cover plate3where the outer gasket11is arranged includes a non-circular recess (first recess)3bwhich can receive a lower part (bridge part) of the outer gasket11. When the lower part (a joining surface to the cover plate3) of the outer gasket11is inserted into the first recess3b, the outer gasket11is restrained from rotating about its axis. Note that, in the present embodiment, the first recess3bis formed to be rectangular so as to correspond to the shape of the rectangular lower part of the outer gasket11. The first recess3bis formed by coining or the like.

The rivet12is a conductive metal member. More specifically, the rivet12for the positive electrode comprises aluminum or an aluminum alloy while the rivet12for the negative electrode comprises copper or a copper alloy. The first caulking part12bprojects downward from a lower surface of the body12aof the rivet12. A second caulking part12cprojects upward from an upper surface of the body12aof the rivet12. Note that, in the present embodiment, the first caulking part12bis hollow (tubular) while the second caulking part12cis solid (columnar). More specifically, the first caulking part12bhas a circular tubular shape while the second caulking part12chas a circular columnar shape. However, the shape is not limited to this, and any appropriate shape can be selected.

The dimensional relationship among the through-hole3aof the cover plate3, the through-hole8bof the connection part8aof the current collector8, the through-hole10bof the plastic plate10, the through-hole11c and annular projection11dof the outer gasket11, and the first caulking part12bof the rivet12will be described. As shown in detail inFIG. 5, the inner diameter of the through-hole3aof the cover plate3and the inner diameter of the through-hole10bof the plastic plate10are the same or substantially the same. The inner diameter of the through-hole3aof the cover plate3and the inner diameter of the through-hole10bof the plastic plate10are the same or substantially the same as the outer diameter of the annular projection11dof the outer gasket11. The length of the annular projection11dof the outer gasket11is the same or substantially the same as the sum of the thicknesses of the cover plate3and plastic plate10. The inner diameter of the annular projection11dof the outer gasket11and the inner diameter of the through-hole8bof the connection part8aof the current collector8are the same or substantially the same. The inner diameter of the annular projection11dof the outer gasket11and the inner diameter of the through-hole8bof the connection part8aof the current collector8are the same or substantially the same as the outer diameter of the first caulking part12bof the rivet12. The length of the first caulking part12bof the rivet12is the same or substantially the same as the sum of the thicknesses of the cover plate3, the connection part8aof the current collector8, the plastic plate10, and the outer gasket11.

Accordingly, the body12aof the rivet12is inserted into the recess11bof the outer gasket11, the first caulking part12bof the rivet12extends through the through-hole11cat a bottom surface of the recess11band is inserted into the through-hole8bof the connection part8aof the current collector8, and an end portion of the first caulking part12bprojecting downward from the through-hole8bof the connection part8ais caulked from below. With this configuration, the rivet12is attached to the cover plate3while the rivet12is electrically connected to the connection part8aof the current collector8and is insulated from the cover plate3.

The terminal retainer13is a synthetic resin with insulating properties, like the plastic plate10and outer gasket11. Note that a reinforced resin material obtained by uniformly mixing polyphenylene sulfide resin with glass fiber as a filler, for example, is used as the material for the terminal retainer13in order to make the hardness higher than those of the plastic plate10and outer gasket11. Alternatively, polytetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) resin is used instead of polyphenylene sulfide resin. An inorganic fiber other than glass fiber may be used. However, the material is not limited to this, and any appropriate material can be selected. However, the terminal retainer13may not have insulating properties. When aluminum or an aluminum alloy is used as a material for the case1, the terminal retainer13of the positive electrode may be non-isolated so that the potential of the positive electrode may be identical with the potential of the case1. This suppresses corrosion of the case1. When iron or stainless steel is used as a material for the case1, the terminal retainer13of the negative electrode may be non-isolated so that the potential of the negative electrode may be identical with the potential of the case1. In order for the positive electrode or negative electrode and the case1to have an identical potential, the terminal retainer13may comprise a material containing a conductive material (e.g., carbon) as well as a filler mixed therein so that the terminal retainer13becomes semi-conductive, for example.

The terminal retainer13is slightly larger than a head14aof the terminal bolt14and has a rectangular shape. The terminal retainer13includes a surrounding circumferential outer wall part13aat the outer periphery, which is formed by recessing an upper surface except for the outer periphery. The terminal retainer13includes a recess13bwhich can receive the head14aof the terminal bolt14inside the outer wall part13a. The terminal retainer13includes a non-circular fitting projection13cin the recess13b. The fitting projection13cfits in a non-circular fitting recess (fitting groove)14cformed in the head14aof the terminal bolt14while the recess13breceives the head14aof the terminal bolt14. Accordingly, when the fitting projection13cin the recess13b(i.e., the fitting projection13cat a lower position than an upper end surface of the outer wall part11ain the recess13b) fits in the fitting recess14cof the head14aof the terminal bolt14, the terminal retainer13receives the terminal bolt14while the terminal bolt14is restrained from rotating about its axis. Note that, in the present embodiment, the fitting recess14cof the terminal bolt14is formed by cutting out a part extending from one side to the opposite side and has a rectangular shape. The fitting projection13cof the terminal retainer13is formed to be rectangular so as to correspond to the rectangular fitting recess14c.

A lower surface of the terminal retainer13includes a non-circular projection13d. In the present embodiment, the projection13dis a rectangular projecting surface (raised surface). A region of the upper surface of the cover plate3where the terminal retainer13is arranged includes a non-circular recess (second recess)3cwhich can receive the projection13dof the terminal retainer13. When the projection13dof the terminal retainer13is inserted into the second recess3c, the terminal retainer13is restrained from rotating about its axis, like the outer gasket11. Note that, in the present embodiment, the second recess3cis formed to be rectangular so as to correspond to the rectangular projection13d. The second recess3cis formed by coining or the like.

When the terminal retainer13is to be arranged on the upper surface of the cover plate3, the lower surface (including a surface of the projection13d) of the terminal retainer13is treated by appropriate means so that the glass fiber is exposed at the lower surface of the terminal retainer13. A preferred example of the appropriate means is to mechanically cut off the lower surface of the terminal retainer13. For example, the glass fiber is exposed by cutting the lower surface of the terminal retainer13with a file or the like. The projection13dat the lower surface of the terminal retainer13fits in the second recess3cat the upper surface of the cover plate3, and the terminal retainer13is fixed to the upper surface of the cover plate3. A method for fixing the terminal retainer13to the cover plate3is not particularly limited. For example, appropriate adhesive means (e.g., an adhesive film, a liquid adhesive, or a solid adhesive) may be supplied to at least one of the upper surface (in particular, the second recess3c) of the cover plate3and the lower surface of the terminal retainer13, and the terminal retainer13may be fixed to the cover plate3via the adhesive means. Although a common adhesive can be used as the adhesive, an epoxy resin adhesive may preferably be used. An epoxy resin has poor adhesion to the synthetic resin used for the terminal retainer13but has good adhesion to an inorganic fiber. Accordingly, the glass fiber exposed at the lower surface of the terminal retainer13allows the terminal retainer13to be firmly bonded to the cover plate3.

The terminal bolt14is intended to electrically connect the battery cell to an external device. The terminal bolt14is a conductive metal member with high strength made of iron, steel such as stainless steel and chromium molybdenum steel, or the like. As described above, the terminal bolt14includes the head14asized to be inserted into the recess13bof the terminal retainer13and a shaft14bprojecting from an upper surface of the head14aand having a male thread at an outer peripheral surface. A lower surface of the head14aincludes a non-circular fitting recess (fitting groove)14c, as described above. Accordingly, when the fitting projection13cin the recess13bfits in the fitting recess19c, the terminal bolt14is insulated from the cover plate3and is supported on the terminal retainer13while the shaft14bis restrained from rotating about its axis.

The connecting plate15is a rectangular conductive metal member comprising a copper alloy or the like. A surface of the connecting plate15is plated with nickel for preventing rust, improving slipperiness, and other purposes. The connecting plate15includes a first through-hole15aat one end and a second through-hole15bat the other end. The second caulking part12cof the rivet12is inserted into the first through-hole15a. The shaft14bof the terminal bolt14is inserted into the second through-hole15b. An end portion of the second caulking part12cof the rivet12which projects upward from the first through-hole15aof the connecting plate15is caulked from above. With the caulking, the rivet12and connecting plate15are integrated.

Note that, in the terminal bolt14, the shaft14bis simply inserted into the second through-hole15bof the connecting plate15. However, for example, when a crimp contact of a lead wire of an external device (not shown) fits on the shaft14bof the terminal bolt14, and the shaft14bof the terminal bolt14is fixed with a nut, the terminal bolt14is slightly lifted, and the upper surface of the head14acomes into pressure contact with a lower surface of the connecting plate15. This causes the crimp contact of the lead wire together with the connecting plate15to be held between the head14aof the terminal bolt14and the nut. With this configuration, the crimp contact, terminal bolt14, and connecting plate15are electrically connected to one another with reliability. Accordingly, the crimp contact of the lead wire is electrically connected to the electrode assembly4via the terminal bolt14, connecting plate15, rivet12and current collector8which are insulated from the cover plate3by the terminal retainer13, outer gasket11, and plastic plate10. This causes the external device to be electrically connected to the battery cell.

Additionally, the fitting recess14cof the head14aof the terminal bolt14fitting on the fitting projection13cin the recess13bof the terminal retainer13fixed on the upper surface of the cover plate3reliably stops the terminal bolt14from rotating together with the nut when the nut is fixed to the shaft14bof the terminal bolt14. Even if there is some clearance between the fitting recess14cof the head14aof the terminal bolt14and the fitting projection13cin the recess13bof the terminal retainer13, the terminal bolt14only rotates icily by a certain degree and poses no special problem.

At this time, since the terminal retainer13stops the terminal bolt14from rotating, the terminal retainer13receives rotational torque from the terminal bolt14. However, the lower surface of the terminal retainer13with the glass fiber exposed is in intimate contact with the upper surface of the cover plate3, and therefore the terminal retainer13is fixed with increased frictional resistance against the cover plate3. Accordingly, the terminal retainer13is reliably stopped from rotating together with the terminal bolt14due to rotational torque from the terminal bolt14. The second recess3cof the upper surface of the cover plate3and the projection13dat the lower surface of the terminal retainer13fitting in with each other make the rotation-stopping effect more remarkable. As described above, since adhesive means (e.g., an adhesive) is supplied to one of the upper surface (in particular, the second recess3c) of the cover plate3and the lower surface of the terminal retainer13, and the terminal retainer13is fixed to the cover plate3by the adhesive means, stopping of rotation is further ensured.

Note that if the perimeter of the shaft14b(male thread part) of the terminal bolt14is smaller, i.e., the shaft14bof the terminal bolt14has a smaller diameter, and a synthetic resin such as polyphenylene sulfide resin (PPS) is used alone as the material for the terminal retainer13, the terminal retainer13may not withstand rotational torque from the terminal bolt14. However, mixing of a synthetic resin with an inorganic fiber such as glass fiber enhances the strength of the terminal retainer13. The mixing also contributes to cost reduction.

Since the terminal retainer13is provided separate from the outer gasket11at the cover plate3, rotational torque is not transmitted to the outer gasket11, which seals up a gap around the rivet12. Accordingly, unintentional force is not applied to the outer gasket11. Sealing with the outer gasket11(more specifically, sealing between the lower surface of the outer gasket11and the upper surface of the cover plate3(an upper surface of the first recess3b), sealing between an outer peripheral surface of the annular projection11dof the outer gasket11and an inner peripheral surface of the through-hole3aof the cover plate3and an inner peripheral surface of the through-hole10bof the plastic plate10, and sealing between an inner peripheral surface of the annular projection11dof the outer gasket11and an outer peripheral surface of the first caulking part12bof the rivet12) is not impaired.

Rotational torque applied to the shaft14bof the terminal bolt14is not transmitted to the rivet12, which is provided separate from the terminal bolt14. Accordingly, a situation does not occur in which rotation of the rivet12causes the rivet12and the connection part8aof the current collector8fixed by caulking to come loose to impair the connection therebetween. Additionally, unintentional force is not applied to the plastic plate10and outer gasket11. Further, sealing with the plastic plate10and outer gasket11(more specifically, sealing between an upper surface of the plastic plate10and the lower surface of the cover plate3, sealing between the lower surface of the outer gasket11and the upper surface of the cover plate3(the upper surface of the first recess3b), sealing between the outer peripheral surface of the annular projection lid of the outer gasket11and the inner peripheral surface of the through-hole3aof the cover plate3and the inner peripheral surface of the through-hole10bof the plastic plate10, and sealing between the inner peripheral surface of the annular projection11dof the outer gasket11and the outer peripheral surface of the first caulking part12bof the rivet12) is not impaired.

The separate provision of the outer gasket11and the terminal retainer13allows appropriate selection of a material with suitable hardness for a sealing member as the material for the outer gasket11and appropriate selection of a material with sufficient hardness to withstand rotational torque from the terminal bolt14as the material for the terminal retainer13. More specifically, since the outer gasket11has a greater sealing effect when the outer gasket11deforms elastically to come into intimate contact with surfaces of the conductive members (the cover plate3, current collector8, and rivet12), the outer gasket11is required to have a certain degree of flexibility. If the terminal retainer13is highly flexible, rotational torque from the terminal bolt14makes the fitting projection13clikely to be worn and chipped. As the wear progresses, the rotation-stopping function of the terminal bolt14is impaired. For this reason, the terminal retainer13is required to have rigidity enough to withstand rotational torque from the terminal bolt14.

In the rivet12according to the present embodiment, the dimension in an axial direction of the body12ais set to be larger than that of a conventional one so as to prevent or reduce plastic deformation across the rivet12caused by caulking by the first caulking part12band second caulking part12c. As a result, the position in height of the connecting plate15from the upper surface of the cover plate3is necessarily higher than that in a conventional terminal structure. The fitting projection13cof the terminal retainer13according to the present embodiment is a part which directly receives rotational torque from the terminal bolt14when the terminal retainer13stops the terminal bolt14from rotating.

Accordingly, the fitting projection13cof the terminal retainer13needs to have a sufficient thickness in a direction of height so as to have strength enough to withstand rotational torque. As a result, the position in height of the head14aof the terminal bolt14is high, and the position in height of the connecting plate15from the upper surface of the cover plate3is also necessarily higher than that in a conventional terminal structure. For this reason, in the present embodiment, the outer wall part11aof the outer gasket11is high, and the creepage distance from the upper surface of the cover plate3to the upper end surface of the outer wall part11ais long (the ratio of the creepage distance to the width dimension of the cover plate3is preferably 0.15 to 0.3). The outer wall part13aof the terminal retainer13is high, and the creepage distance from the upper surface of the cover plate3to an upper end surface of the outer wall part13ais long (the ratio of the creepage distance to the width dimension of the cover plate3is preferably 0.15 to 0.3).

More specifically, the outer wall part11aof the outer gasket11is formed so as to entirely or substantially entirely cover the body12aof the rivet12and such that the upper end surface of the outer wall part11ais in contact with or is slightly spaced from the lower surface of the connecting plate15. The outer wall part13aof the terminal retainer13is formed so as to entirely or substantially entirely cover the head14aof the terminal bolt14and such that the upper end surface of the outer wall part13ais in contact with or is slightly spaced from the lower surface of the connecting plate15.

With the above-described configuration, even if the battery cell is exposed to droplets of water generated by condensation or the like or a conductive atmosphere (static electricity or dust), the outer wall part11aof the outer gasket11and the outer wall part13aof the terminal retainer13serve as covers (or barriers). This conveniently prevents a short between the cover plate3and the rivet12and a short between the cover plate3and the terminal bolt14.

Note that an electric storage device according to the present invention is not limited to the above-described embodiment and that various changes may be made without departing from the spirit and scope of the present invention.

For example, the above embodiment has illustrated an example in which a resin material obtained by uniformly mixing a synthetic resin material with glass fiber as a filler is used as the material for the terminal retainer13. However, this resin material can also be used for the outer gasket11. The resin material can also be used as the sealing member of the battery cell disclosed in Patent Document 1 (a battery cell with a structure in which an external terminal and a current collector are directly connected) or the battery cell disclosed in Patent Document 2 (a battery cell with a structure in which an external terminal and a current collector are indirectly connected to each other via an auxiliary terminal and a connecting conductor). However, a resin material obtained by uniformly mixing a synthetic resin material (base material) with glass fiber as a filler has higher hardness than the material containing only the base material without the glass fiber, and thus has less flexibility to produce less sealing effect. Accordingly, a material with low hardness is preferably preselected as the base material in expectation of an increase in hardness caused by inclusion of glass fiber. Note that the auxiliary terminal and external terminal are integrated in the battery cell disclosed in Patent Document 1. Accordingly, the number of parts and the number of fabrication steps can be reduced.

The above embodiment has also illustrated an example in which the entire lower surface of the outer gasket11fits in the first recess3bin the upper surface of the cover plate3. Alternatively, a projection may be formed at the lower surface of the outer gasket11, the first recess of the cover plate3may be sized to receive the projection, and the projection of the outer gasket11may fit in the first recess, as with the case of the terminal retainer13.

The above embodiment has also illustrated an example in which the projection13dis formed in the lower surface of the terminal retainer13, the second recess3csized to receive the projection13dis formed in the upper surface of the cover plate3, and the projection13dof the terminal retainer13fits in the second recess3cof the cover plate3. Alternatively, the projection13dmay not be formed, the second recess of the cover plate3may be sized to receive the entire lower surface of the terminal retainer13, and the entire lower surface of the terminal retainer13may fit in the second recess, as with the case of the outer gasket11.

Alternatively, the first recess3bmay not be formed in the cover plate3, so that the outer gasket11may be arranged at a flat part of the upper surface of the cover plate3. The second recess3cmay not be formed in the cover plate3, so that the terminal retainer13may be arranged at a flat part of the upper surface of the cover plate3.

It is preferred, however, that the cover plate3have the first recess3band second recess3cbecause they can increase the moment of area of the cover plate3, which results in enhancement of the mechanical strength of the cover plate3. In this case, reducing the size of one of the first recess3band the second recess3cincreases the distance between the first recess3band the second recess3c. This prevents the first recess3band second recess3cfrom affecting each other. The above embodiment has illustrated an example in which the first recess3bfor the outer gasket11is larger than the second recess3cfor the terminal retainer13. This configuration is adopted on the ground that the flatness and mechanical strength of the cover plate3increase with an increase in the area of the first recess3b, which results in an increase in sealing effect and durability.

For either the outer gasket11or the terminal retainer13, the number of projections is not limited to one, and a plurality of projections may be formed. The outer gasket11and terminal retainer13need not be rectangular. For example, the outer gasket11and terminal retainer13may be circular, hexagonal, or octagonal.

The above embodiment has illustrated an example in which the current collector8for the positive electrode and the rivet12for the positive electrode comprises aluminum or an aluminum alloy while the current collector8for the negative electrode and the rivet12for the negative electrode comprises copper or a copper alloy. However, any materials may be used as long as the materials are conductive metal materials appropriate to the type of a battery cell. The above embodiment has also illustrated the materials for the terminal bolt14and connecting plate15. However, any materials may be used as long as the materials are conductive metal materials whose properties such as strength and conductivity are appropriate.

The above embodiment has illustrated an example in which the shaft (male thread part)14bprojects from the upper surface of the head14aof the terminal bolt14. However, a shaft in an appropriate form such as a circular or polygonal tube may project instead of the male thread part, and a threaded hole may be formed in an upper end surface of the shaft.

The electrode assembly is not limited to one of the winding type in the form of an elliptic cylinder as described in the above embodiment. The electrode assembly may have any other shape and may be one of the stacked type.

The above embodiment has illustrated an example in which the case1comprises an aluminum alloy, steel, or the like. However, any material may be used for the case1(the case body2and cover plate3). Accordingly, a material other than metal, such as an insulating material, can be used. The shape and structure of the case1(the case body2and cover plate3) are not limited to those described in the above embodiment, and any shape and structure may be adopted.

The above embodiment has illustrated an example in which the terminal structures9are arranged at the cover plate3. However, the terminal structures9may be arranged at the case body2.

The above embodiment has been described in the context of a lithium ion secondary battery cell. However, the type and size (capacity) of a battery cell may be arbitrarily selected.

The present invention is not limited to lithium ion secondary battery cells and can also be applied to various secondary battery cells, primary battery cells, and capacitors such as an electric double layer capacitor