Battery and related method

A battery is provided with a plurality of unit cells stacked in a stack direction, a plurality of conductive members each having an electric conductivity, and a plurality of insulation members each having an insulation property. The plurality of conductive members and the plurality of insulation members are alternately disposed in the stack direction with the plurality of unit cells having respective output terminals being sandwiched such that the plurality of unit cells are electrically connected in the stack direction.

BACKGROUND OF THE INVENTION

This invention relates to a battery and a related method and, more particularly, a battery, which has a high energy density and is small in size and lightweight in structure to be available as an electric power source to supply large energy, and its related method.

In recent years, with an increasing concern for environmental consciousness, there have been significant movements in shift of power sources of automotive vehicles from engines utilizing fossil fuel to motors utilizing electric energy. For this reason, there have been rapid developments in technologies of batteries playing roles as the power sources of the motors.

The automotive vehicles are expected to be installed with the batteries, which are small in size, lightweight in structure with a capability of charging and discharging large electric power at frequent cycles, and excellent vibration-proof property and heat radiation characteristic.

Japanese Patent Application Laid-Open Publication No. 2000-195480 (see paragraph numbers 0014 to 0029 and FIGS. 1, 2 and 4) discloses a battery. In particular, the battery has a structure that includes a plurality of flat-shaped unit cells, electrically connected in series, parallel and series and parallel, which are disposed in a thickness direction of the unit cells at given intervals, and pressurizing members located between the unit cells of a stack to pressurize the unit cells on both sides of the stack whereupon the plurality of unit cells are fastened by an outer sheath member. With such a structure, attempts have been made to cause the unit cells to have favorable heat radiating characteristics to provide a battery with improved cyclic characteristic and rate characteristic.

SUMMARY OF THE INVENTION

Upon studies conducted by the present inventors, since such a battery is comprised of flat-shaped cells as unit cells, the battery has a larger energy density than that of a battery formed of cells other than the flat-shaped cells and can be formed in miniaturization provided the cells with identical electric power capacity. For this reason, the battery formed of the flat-shaped cells is suited as a battery for installation on an automotive vehicle in view of a miniaturized structure with high energy density.

However, according to further extensive analysis conducted by the present inventors, since the battery includes a battery developed for use in an electric power storage system, it is considered that there exists a room required for conducting further study on such structure for the purpose of applying the battery to the automotive vehicle that requires a production efficiency, a small size with lightweight, anti-vibration capability and high reliability.

In particular, a need arises for realizing a battery with a structure that satisfies various requirements: such as a structure enabled to provide a high production efficiency and wherein unit cells are comprised of small number of component parts as less as possible to provide a miniaturization in lightweight to provide the maximum volumetric efficiency, a structure wherein the battery is able to prevent the occurrence of deterioration in capacity and drop in battery life as a result of gas generated inside the battery even in the presence of charging and discharging at frequently repeated cycles, a structure that has anti-vibration capability to be stably operative even in the exposure to vibrations at all times, and a structure enabled to efficiently radiate heat even in the unit cells being arranged in high density.

The present invention has been completed with the above studies conducted by the present inventors, and has an object to provide a battery with a structure that has a high energy density and small in size with lightweight in structure to be optimum as a power source to supply large energy.

Further, according to the studies conducted by the present inventors, it is considered that since a plurality of unit cells are assembled in series connection to form the battery and, during assembling process, with an increase in the number of unit cells to be connected in series, the series connected unit cells have an increased terminal voltage, attentions are required on handling and thus there exists a room for improving workability.

Therefore, the present invention has an another object to provide a method of manufacturing a battery wherein no high voltage is output in a manufacturing process of the battery.

To achieve the above object, in one aspect of the present invention, a battery comprises: a plurality of unit cells stacked in a stack direction; a plurality of conductive members each having an electric conductivity; and a plurality of insulation members each having an electric insulation property, the plurality of conductive members and the plurality of insulation members being alternately disposed in the stack direction with the plurality of unit cells having respective output terminals being sandwiched, whereby the plurality of unit cells are electrically connected in the stack direction.

In the meanwhile, in another aspect of the present invention, a method of manufacturing a battery, comprises: stacking a plurality of unit cells in a stack direction such that the plurality of conductive members and the plurality of insulation members are alternately disposed in the stack direction with the plurality of unit cells having respective output terminals being sandwiched while the plurality of conductive members have temporary insulation members; temporarily fastening the plurality of conductive members; removing the temporary insulation members from the plurality of conductive members; and fully tightening the plurality of unit cells by applying a compression force between the output terminals of the plurality of unit cells to remove the temporary insulation members from the conductive members.

Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, batteries and related methods of various embodiments according to the present invention are described with suitable reference to the accompanying drawings. Incidentally, throughout several views, x-, y- and z-axes form a three-axis rectangular coordinate system.

First Embodiment

Now, a battery and its related method of a first embodiment according to the present invention is described in detail with reference toFIGS. 1 to 7.

First, description is made of a schematic structure of the battery of the presently filed embodiment.

FIG. 1is a perspective view of the battery BA of the presently filed embodiment;.FIG. 2is a perspective view of a unit cell forming such a battery; andFIG. 3is a cross section taken on line A-A ofFIG. 1.

As shown inFIGS. 1 to 3, the battery BA of the presently filed embodiment has a schematic structure that is comprised of a stack of a plurality of flat-shaped cells1(hereinafter merely referred to as unit cells), heat sinks2a,2bstacked on the unit cells1, high friction sheets3interposed between the unit cells1and between the unit cells1and the heat sinks2a,2b, and a holding mechanism4by which the plural stacked unit cells1are pressurized on both sides in a stack direction (along z-direction) to be integrally held in place.

The unit cells1are connected in series in the stack direction. That is, two electrode tabs10,12extending from the respective unit cells1are connected in series to preclude short-circuiting by permitting electrically conductive washers50and insulation washers51to be alternately disposed.

Hereinafter, the battery BA and component elements thereof are described in detail further with reference to other drawings when needed.

The unit cell1, formed in a flat shape in the presently filed embodiment, internally includes an electric power generating element comprised of a positive electrode plate, a negative electrode plate and a separator, all of which are stacked in such order. The unit cell1forms a secondary battery, such as a lithium ion secondary battery, employing a gel polymer electrolyte.

With the unit cell1, a laminate film with a three-layer structure is used as an outer sheath and formed in three layers that include an aluminum foil interposed between resin films each made of polyamide resin. Of two laminate films, one sheet is formed in a flat shape by pressing and laminated onto another sheet of laminate film, remaining in a sheet form, at respective rims by thermal welding. The electric power generating element is hermetically sealed inside the laminated laminate films. When performing such pressing, although the laminate films are introduced into a die, the outermost layer of the laminate films is formed of a resin film with a small skin friction coefficient and, hence, no laminate film suffers from adverse affect arising from friction between the laminate film and the die. Incidentally, with the battery BA, the unit cells1are stacked in the same direction as the stack direction of the capsulated electric power generating element.

The unit cell1has the positive electrode tab10and the negative electrode tab12as tabs forming output terminals extending in a direction perpendicular to the stack direction. The positive electrode tab10and the negative electrode tab12are extracted outside an outer sheath. Formed in the positive electrode tab10and the negative electrode tab12, respectively, are holes11,13, to which insulator pins52, each having a surface subjected to insulation treatment, are inserted.

As will be understood by referring toFIG. 3, the unit cells1are alternately stacked such that the electrode tabs have positive and negative polarities alternately arranged in the stack direction, i.e., the positive electrode tab10and the negative electrode tab12are alternately stacked. The electrically conductive washers50and the insulation washes51are alternately set through the insulator pins52such that the positive electrode tabs10and the negative electrode tabs12are sandwiched. In particular, the insulation washer51is interposed between the positive electrode tab10and the negative electrode tab12layered thereon, and the electrically conductive washer50is interposed between the negative electrode tab12and the positive electrode tab10layered thereon. When focusing the washer on the same tier, with the presently filed embodiment, the insulation washer51is placed on the positive electrode tab10and the electrically conductive washer50is placed on the negative electrode tab12. Incidentally, although the electrically conductive washer50and the insulation washer51are located on the positive electrode tab10and the negative electrode tab12of the unit cell1remaining in the uppermost layer, respectively, in dependence on a sequence in which the electrode tabs are arranged, it doesn't matter if these component parts are dispensed with depending on circumstances.

The electrically conductive washer50may be formed of electrically conductive metal, such as copper or aluminum, to allow the positive electrode tab10and the negative electrode tab12, which remain in contact with one above the other, to be electrically connected. On the other hand, the insulation washer51is formed of insulation metal, such as ceramic, to allow the positive electrode tab10and the negative electrode tab12, which remain in contact with one above the other, to be insulated. The electrically conductive washer50and the insulation washer51serve as spacers by which direct contact is avoided between the positive electrode tab10and the negative electrode tab12of the unit cells1.

Thus, with the positive electrode tab10and the negative electrode tab12alternately arranged in the stack direction, the battery BA internally has a circuitry by which the unit cells1are electrically connected to allow electric current to flow from an upper layer to a lower layer of a stacked structure. Incidentally, when desired to allow electric current to flow from the lower layer to the upper layer of the stacked structure, it may be suffice for the electrically conductive washer50and the insulation washer51to be reversely arranged.

The insulator pins52are subjected to insulation treatment involving a heat contracting tube covered on a surface of a metallic bar, resin applied onto the metal surface, coating or shielding conducted on the metal surface. Nuts53a,53bare tightened on top and bottom ends of the insulator pins52. This allows the electrode tabs10,12of the unit cells1to be firmly interposed between the electrically conductive washers50and the insulation washers51, thereby enabling the electrode tabs10,12to electrically conduct or to be electrically insulated from one another in a reliable manner.

Here, the electrically conductive washer50and the insulation washer51may preferably have surface roughness of a value as small as possible. If surface roughness is large, surfaces of the electrically conductive washer50and the insulation washer51are caused to fatigue when tightening the electrically conductive washer50and the insulation washer51through the nuts53a,53bon both sides of the washers and deterioration occurs in tightening force to cause an increase in electrical resistance between the electrode tabs10,12and the electrically conductive washer50, resulting in deterioration in reliability of electrical connection between the electrode tabs10,12.

Incidentally, with the circuit structure formed inside the battery wherein electric current flows from the upper layer toward the lower layer, electric power terminals (not shown) may be placed between the nuts53aand the electrically conductive washers50and between the nuts53band the insulation washer51bto enable electric current to be extracted, while enabling a controller (not shown) to detect a voltage of the battery BA. Also, when combining a plurality of unit cells1shown inFIG. 1, it is, of course, to employ such electric power terminals.

FIG. 4Ais a perspective view of an outer layer heat sink2a, andFIG. 4Bis a perspective view of an inner layer heat sink2b.

As shown inFIGS. 4A and 4B, the heat sinks forming part of the presently filed embodiment include the outer layer heat sinks2aand the inner layer heat sinks2b, and the outer layer heat sinks2aare placed on the outermost layers of the stack structure while the inner layer heat sinks2bare arranged with the unit cells1in a middle of the stack structure of the battery BA.

Any of the heat sinks2a,2bis formed with a plurality of ventilation passages20to permit coolant, such as air, to pass therethrough. These ventilation passages20are formed in two sheets of plate materials, whose surfaces are formed with pluralities of recesses, respectively, which are laminated so as to allow the respective recesses to be mutually aligned for thereby forming the respective heat sinks2a,2b. This is based on a consideration on a difficulty encountered in hollowing the ventilation passages through the heat sinks2a,2bthat are extremely thin. Of course, the respective heat sinks2a,2bmay be formed of unitary plate materials, respectively, which are formed by extrusion molding if desired. The outer layer heat sink2ais formed with cutouts21to allow the electrode tabs10,12of the stacked unit cell1to be exposed to the outside and have four corners formed with holes22, respectively, between two of which the cutout21is intervened. The holes22are formed for the purpose of mounting pressurizing units40, respectively, to apply necessary surface pressures to the stacked unit cells1between the outer layer heat sinks2a.

No holes22, like those of the outer layer heat sinks2a, are present in the inner heat sinks2b. The inner heat sinks2bare held in pressured surface contact with the unit cells1by means of the pressurizing units40when the unit cells1are stacked in the battery BA. The inner layer heat sink2bis suitably disposed between the unit cells1in such away that when four sheets of unit cells1are stacked, one sheet of inner layer heat sink2bis set on such a stack, as shown inFIG. 3. This enables heat, built up in the unit cells1, to be radiated from the stack structure.

The high friction sheet3of the presently filed embodiment is interposed between the unit cells1or between the unit cell1and the heat sink2a,2bas shown inFIG. 3. The high friction sheet3is made of silicone rubber that is formed in a sheet configuration. Silicone rubber exhibits higher frictional resistance than that occurring when the unit cells1are mutually and directly laminated. Accordingly, intervening the high friction sheets3between the unit cells1or between the unit cells1and the heat sinks2a,2bminimizes transverse displacement of these component parts.

In the meanwhile, although the high friction sheet3exhibits a high frictional force in terms of transverse displacement, almost no adhesion is exhibited in terms of the stack direction of the unit cells1. Accordingly, the high friction sheet3has non-adhesiveness with respect to the unit cell1and the heat sink2. Stated another way, the high friction sheet3is not of the type to cause the unit cells1per se, or the unit ells1and the heat sinks2a,2bto be eternally joined and has a property to allow these component elements to be separated from one another.

As shown inFIG. 1, the holding mechanism4of the presently filed embodiment is comprised of the outer layer heat sinks (holding plate)2ato be stacked on the outermost layers of the battery BA, the pressurizing units40to be disposed between the outer layer heat sinks2a, and the nuts41by which the pressurizing units40are mounted to the outer layer heat sinks2a.

As previously noted, the outer layer heat sinks2aare stacked on the outermost layers of the battery BA to serve as cooling members for cooling the unit cells1. In the meanwhile, the outer layer heat sinks2aalso serves as parts of the holding mechanism4for applying the surface pressures to the unit cells1and the inner layer heat sinks2b, respectively, which are stacked in the middle of the stack structure in the stack direction, while holding these component elements in fixed place. As the parts of the holding mechanism4, the outer layer heat sinks2aexert forces in a direction to cause the associated component elements to get closer to one another by means of the pressurizing units40.

The pressurizing units40are inserted through the holes22formed in the outer layer heat sinks2aand tightened by the nuts41. The pressurizing units40have detailed structures, which are shown inFIGS. 5A to 6C.

FIG. 5Ais a view illustrating an overall structure of the pressurizing unit40;FIG. 5Bis a view illustrating a structure of a spring retainer of the pressurizing unit40;FIG. 6Ais a cross sectional view taken on line B-B ofFIG. 1and showing an initial state of the pressurizing unit40;FIG. 6Bis a cross sectional view taken on line B-B ofFIG. 1and showing a state where the pressurizing unit40is disposed between the outer layer heat sinks2a; andFIG. 6Cis a plan view of an inserter47of the spring retainer43of the pressurizing unit40.

As shown inFIGS. 5A to 6C, the pressurizing unit40is comprised of a tension coil spring (elastic body)42, and the spring retainers43that retain both ends of the tension coil spring42.

With the tension coil spring42disposed between the outer layer heat sinks2ain a tensioned state, the tension coil spring42exhibits a tensile force to create an elastic force in a direction to cause the outer layer heat sinks2ato get closer to one another.

The spring retainer43includes a body portion44, a screw portion45formed with a thread ridge with a pitch P2greater than a pitch P1of the tension coil spring42, an abutment portion46extending toward a center of the tension coil spring42, and an inserter47extending from the body portion44and inserted through the outer layer heat sink2a.

The body portion44is brought into abutting engagement with a distal end of the tension coil spring42to specify a position of the end of the same. Also, with the pressurizing unit40assembled to the battery, the body portion44is brought into abutting engagement with the outer layer heat sink2ato play a role to restrict the tension coil spring42from increasing in length.

The screw portion45is screwed into the distal end of the tension coil spring42and internally engages an inside of the tension coil spring42that is consequently fastened. The screw portion45has an outer peripheral surface formed with a thread ridge with the pitch P2as shown inFIG. 5B. The pitch P2of the screw portion45is greater than the pitch P1of the tension coil spring42. Consequently, the screw portion45can be screwed in a direction, as shown by an arrow inFIG. 5B, and screwing the screw portion45causes the abutment portion46to advance toward the center of the tension coil spring42.

When screwing the screw portions45from both ends of the tension coil spring42, the abutment portions46, advanced from the both sides, are brought into abutment with the associated distal end of the tension coil spring42as shown inFIG. 5A. Under such a situation, the tension coil spring42is caused to extend from a natural length, thereby affording an initial tensile force under an initial status of the pressurizing unit40.

The inserter47has a distal end formed with a thread ridge47ato which the nut41is fastened. The inserter47has a head formed with a fit drive slit48as shown inFIG. 6C. Fitting a tip of a minus driver to the slit48enables the spring retainer43to lock the rotation thereof.

Locating the pressurizing unit40between the outer layer heat sinks2aprovides a condition as shown inFIG. 6A.

As shown inFIG. 6A, the inserters47are inserted through the holes22of the outer layer hat sinks2a. Under such a condition, as shown inFIGS. 6B and 6C, the rotation of one of the spring retainers43is locked while the inserter47of the other spring retainer43is tightened by the nut41in the X-direction and fastened. Then, the spring retainer43is pulled toward the nut41. Likewise, driving the nut41allows the inserter43of the other remaining spring retainer43to be fastened. Then, the spring retainers43are pulled away relative to one another with the tension coil spring42being retained, and the tension coil spring42is retained under circumstances where the tension coil spring42is expanded between the outer layer heat sinks2a.

In such a way, since the tension coil spring42is expanded in compliance with a distance between the outer layer heat sinks2a, it becomes possible to obtain a resilient force acting in a direction to cause the tension coil spring42to contract regardless of fastening torques applied by the nuts41. Such a resilient force affords a pressurizing force to be applied to the unit cells1through the outer layer heat sinks2a.

Next, description is made of an assembling procedure for the battery BA of the presently filed embodiment with the structure set forth above.

FIG. 7is an exploded perspective view illustrating an essential part of the battery BA.

As shown inFIG. 7, first, the outer layer heat sink2ais set on the lowermost layer and the plural unit cells1are stacked thereon. Here, for the plural unit cells1, the electrode tabs10,12are set through the insulator pins52such that the positive electrode tab10and the negative electrode tab12are alternately arranged in the stack direction. The electrically conductive washer50and insulation washer51are also sequentially set through the insulator pins52each times the electrode tabs10,12of the unit cells1are set through the insulator pins52.

Here, the electrically conductive washers5o and the insulation washers51are set through the insulator pins52in alternative arrangement in the stack direction. For the positive electrode tab10and the negative electrode tab12of the same unit cell1, the electrically conductive washer50is set on the negative electrode tab12on one hand and, on the other hand, the insulation washer51is set on the positive electrode tab12. That is, different kinds of washers are set on the positive electrode tab10and the negative electrode tab12, respectively, of the same unit cell1.

Then, other unit cells1are stacked in a plurality of stages, i.e., four sheets of unit cells1are stacked, and another inner layer heat sink2bis set on top of the stacked unit cells1.

Subsequently, after repeatedly setting the unit cells1and the inner layer heat sinks2ba given number of times, lastly, the outer layer heat sink2ais set on the top of the stack structure.

Thereafter, the pressurizing units40are set between the outer layer heat sinks2aand the nuts41are fastened until the tension coil springs42of the pressurizing units40are expanded between the outer layer heat sinks2a, thereby assembling the battery BA as shown inFIG. 1.

Incidentally, the high friction sheets3are applied onto the respective surfaces of the unit cells1, the outer layer heat sinks2aand the inner layer heat sinks2bduring the stacking thereof.

As set forth above, with the battery BA of the presently filed embodiment, the electrically conductive washers50and the insulation washers51are alternately set through the insulator pins52in the stack direction between the positive electrode tabs10and the negative electrode tabs12of the stacked unit cells1. Accordingly, a circuitry, wherein the unit cells1stacked in a vertical direction are sequentially connected, can be easily realized through alternate arrangement of the electrically conductive washers50and the insulation washers51.

Incidentally, while the presently filed embodiment has been exemplarily shown in conjunction with a single piece of the battery BA in which the unit cells1are vertically stacked, of course, no limitation is intended by the presently filed embodiment and a plurality of batteries, each composed of a plurality of sets of unit cells1, may be juxtaposed in electrical connection to form a battery module with a further increased power output. In such case, it may be suffice for the batteries to be electrically connected to one another through bus bars mounted to both the batteries. The bus bars may be mounted to the insulator pins52and fastened by the nuts53a,53b.

Second Embodiment

Next, a battery and its related method of a second embodiment according to the present invention are described in detail with reference toFIG. 8.

FIG. 8is an exploded perspective view of the battery of the presently filed embodiment.

The presently filed embodiment differs from the first embodiment set forth above in that the first embodiment takes the form a structure wherein the insulator pins52are directly inserted to the electrode tabs10,12of the unit cells1and the electrically conductive washers50and the insulation washers51are alternately set through the insulator pins52, whereas the second embodiment takes the form of a structure wherein no insulator pins52are directly inserted to the electrode tabs10,12and the insulator pins52are inserted to bus bars (output terminals and parallel connected members) extending from the electrode tabs10,12, respectively, and the electrically conductive washer50and the insulation washer51are alternately set through the insulator pin52, and is identical in other structure. Hereinafter, such different points are focused in description and the same component parts as those of the first embodiment bear like reference numerals to omit or simplify description.

As shown inFIG. 8, for one set of two unit cells1, the mutual positive electrode tabs10and the mutual negative electrode tabs12are connected through the bus bars6, respectively, to allow the unit cells1of one set to be electrically connected in parallel. The bus bars6are welded onto and joined to the positive electrode tabs10and the negative electrode tabs12. That is, with such a structure, output terminals of the two unit cells1are constituted by the bus bars6.

Hereinafter, the bus bar6that is joined to the positive electrode tabs10is referred to as a bus bar6a, and the bus bar6that is joined to the negative electrode tabs12is referred to as a bus bar6b. The bus bars6a,6bare formed with holes60, respectively, to which the insulator pins52can be inserted. When structuring the battery, the one set of unit cells1is stacked while inserting the insulator pins52to the holes60. Here, when stacking the unit cells1, the insulator pins52are inserted to the holes60, respectively, such that the bus bars6a,6bare alternately stacked in the stack direction. Thus, with the bus bars6a,6bbeing inserted to the insulator pins52, respectively, each set of the unit cells1can be positioned.

The electrically conductive washers50and the insulation washers51are also set through the insulator pins52, respectively. The electrically conductive washers50and the insulation washers51are alternately set through each insulator pin52in the stack direction between the bus bars6a,6bone by one. As shown inFIG. 8, the insulation washer51is set through the insulator pin52in such a way that the insulation washer51is set on the bus bar6aat the lowermost layer, as viewed in the drawing figure, and the electrically conductive washer50is set through the insulator pin52such that it is set on the bus bar6babove the bus bar6a.

Incidentally, while the illustrations of the heat sinks2a,2band the high friction sheets3are omitted fromFIG. 8for the purpose of illustrating a way in which the unit cells1are stacked, it is, of course, to be appreciated that when forming the battery, the outer layer heat sinks2aare set on both surfaces of the outermost layers of the stack structure and the heat sink2bis set for each stack of the unit cells1set in plural stages like in the first embodiment. Then, the pressurizing units40are disposed between the outer layer heat sinks2ato apply the surface pressures to the unit cells1to hold the same in fixed place. Also, the high friction sheets3are applied to the respective surfaces of the unit cells1, the outer layer heat sinks2aand the inner heat sinks2bduring stacking procedure.

As set forth above, with the battery of the presently filed embodiment, the bus bars6a,6bare alternately set through the insulator pins52in the stack direction and the electrically conductive washers50and the insulation washers51are alternately set through the insulator pins52in the stack direction. Accordingly, the unit cells1are connected in parallel in a direction perpendicular to the stack direction and connected in series in the stack direction.

Incidentally, the presently filed embodiment has been described with reference to an exemplary structure wherein two unit cells1are connected in parallel through the bus bars6, no limitation is intended by the presently filed embodiment and more than three unit cells1may be connected in parallel if desired.

Third Embodiment

Now, a battery and its related method of a third embodiment according to the present invention are described in detail with reference toFIGS. 9 to 13.

FIG. 9is a plan view illustrating a frame7of a battery of the presently filed embodiment;FIG. 10is a perspective view illustrating a condition where the unit cells1are set on the frame7;FIG. 11is a perspective view illustrating the battery during assembling procedure;FIG. 12is a perspective view of the battery BA1after assembling; andFIG. 13is a schematic view illustrating a circuit structure of the battery BA1. Incidentally, inFIG. 11, the electrode tabs of the unit cells1are omitted for the electrically conductive washers50and the insulation washers51to be easily viewed.

The presently filed embodiment mainly differs from the first embodiment set forth above in that the first embodiment takes the form of a structure wherein the unit cells1are set through the electrically conductive washers50and the insulation washers51as they are, whereas the presently filed embodiment takes the form of a structure wherein the unit cells1are stacked under a condition where the fuel cells1are set on the frames7, and is identical in other structure. Hereinafter, such different point is focused on description and the same component parts as those of the first embodiment bear like reference numerals to omit or simplify description.

That is, the battery of the presently filed embodiment is similar to that of the first embodiment in that the outer layer heat sinks2aare set on the outermost layers of the stack structure but differs in structure in that the frames7and the inner layer heat sinks2b, shown inFIGS. 9 and 10, are incorporated in the stack structure wherein the inner layer heat sinks2bare set each for a plurality of stacked frames7. Also, in the presently filed embodiment, in order to form a series circuit in the battery BA1, the bus bars8are mounted to the stack structure. First, description is made of the frame7.

As shown inFIGS. 9 and 10, the frame7of the presently filed embodiment has one side in which the electrically conductive washers50are embedded and the other side in which the insulation washers51are embedded. The electrically conductive washers50are formed in a thickness slightly greater than that (thickness in the stack direction of the battery) of the frame7but less than that (thickness in the stack direction of the battery) of the unit cell1. The insulation washers51are also formed in a thickness greater than that of the frame7but less than that of the unit cell1like the electrically conductive washers50.

The frame7is formed with plural positioning sections70on which the associated unit cells1are set in given positions, respectively. The positioning sections70are formed of cutouts, respectively, each with a size less than an outer shape of each unit cell1. Each of the positioning sections70is opened in an area to the extent in that when setting the unit cell1on the positioning section70, a peripheral edge of the unit cell1can be retained while permitting the unit cell1to be brought into contact with the other unit cell1, set on upper or lower layers, at an area except the peripheral edge. The unit cells1are set on the frame7in such a way to allow the electrode tabs10,12to be brought into contact with the electrically conductive washers50and the insulation washers51. With the positioning being finished, the bores (holes) of the electrically conductive washers50and the insulation washers51are brought into alignment with the holes11of the positive electrode tabs10of the unit cells1and holes13of the negative electrode tabs12of the unit cells1, respectively.

Formed in the frame7are holes71that allow the pressurizing units40to be inserted during stacking work. The pressurizing units40are set between the outer layer heat sinks2aat areas outside the unit cells1in the first embodiment and, in the presently filed embodiment, set between the outer layer heat sinks2ain a way to extend through the frames7, the inner layer heat sinks2band the outer layer heat sinks2a.

On the frame7, adjacent unit cells1are set such that the positive electrode tab10and the negative electrode tab12are oriented in an opposite direction. As shown inFIG. 10, the unit cells1are arranged such that the positive electrode tabs10and the negative electrode tabs12are alternately arranged in order at a front side as shown inFIG. 10.

A plurality of frames7, on each of which a plurality of unit ells1are set, are stacked by setting the pressurizing units40and the insulator pins52as shown inFIG. 11. Incidentally, the pressurizing units40and the insulator pins52are fastened to the outer layer heat sinks2aby nuts, which are not shown, to stand upright. Further, with the battery BA1being completely assembled, the pressurizing units40are fixedly secured between the outer layer heat sinks2a, as shown inFIG. 12, to apply a force in a direction to cause the outer layer heat sinks2ato get closer to apply a certain surface pressure to each unit cell1.

When stacking the frames7, the electrode tabs10,12of the unit cells1are alternately arranged in the stack direction. Upon focusing on one side of the frame7in immediately lower layer, where the electrode tabs are arranged in an order with the positive electrode tab10, the negative electrode tab12, the positive electrode tab10and the negative electrode tab12, an upper layer immediately above the lower layer has the electrode tabs arranged in another order with the negative electrode tab12, the positive electrode tab10, the negative electrode tab12and the positive electrode tab10at the same side. Further, when stacking the frames7, since the electrically conductive washers50and the insulation washers51are embedded in the frames7, as set forth above, the frames7are stacked such that the electrically conductive washers50and the insulation washers51are alternately positioned in the stack direction.

Sequentially setting the plural unit cells1on the frame7in an array to allow the respective frames7to be stacked one above the other, as set forth above, results in a completed assembly of the battery BA1where the unit cells1, set in the stack direction, are connected in series. With the presently filed embodiment, as shown inFIGS. 11 and 12, the battery BA1has four arrays of units, each including a stack of the unit cells1and these units, i.e., battery units80a,80b,80c,80dthat are connected in series.

More particularly, in order for the battery units80aand80cto be connected in series from an upper layer toward a lower layer and for the battery units80band80dto be connected in series from the lower layer toward the upper layer, both a placement direction for the electrode tabs10,12of the respective unit cells1and a placement direction for the electrically conductive washers50and the insulation washers51are determined, and the battery units80a,80b,80c,80dare connected in series. In order for the battery units80a,80b,80c,80dto be connected in series, the bus bars8are employed. The battery units80a,80bare connected through the bus bar8in the lowermost layer, the battery units80b,80care connected through the bus bar8in the uppermost layer, and the battery units80c,80dare connected through the bus bar8in the lowermost layer, as shown inFIGS. 11 and 12.

Thus, with the plural battery units80ato80dconnected through the bus bars8, the unit cells1of the battery BA1as a whole are connected in series. This allows electrode terminals81,82to be connected to the negative electrode tab12of the uppermost layer of the battery unit80aand the positive electrode tab10of the uppermost layer of the battery unit80d, respectively, providing a high voltage. The resulting schematic circuit structure formed inside the battery is shown inFIG. 13.

As set forth above, with the third embodiment, the unit cells1are set on the frames7in an array and such frames7are stacked one above the other. Here, the electrically conductive washers50are embedded in one side of the frame7whose other side is embedded with the insulation washers51, whereupon the frames7are stacked by reversing the orientation of the frames7such that the washers50,51are alternately arranged in the stack direction. Accordingly, this results in a circuit structure where the unit cells1are connected in series in the stack direction like in the embodiments1,2.

Incidentally, the presently filed embodiment has been described in conjunction with an exemplary structure where the battery has four arrays of unit cells1on the frame7, no limitation is intended to such application and an alternative may have two or three, or more than five arrays of unit cells on the same frame7depending on circumstances.

Further, a voltage detection terminal83as that shown inFIG. 11may be set through the insulator pin52. Locating the voltage detection terminals83between the electrically conductive washers50and the insulation washers51, respectively, enables a voltage of each unit cell1to be detected. This enables a characteristic of each unit cell1to be grasped even after the battery is installed on a vehicle.

The battery, discussed above in conjunction with the embodiments 1 to 3, has a number of advantages as will be described below.

Such a battery takes a structure where the electrically conductive washers50and the insulation washers51are alternately arranged in a direction to allow the unit cells1to be stacked in electrical connection along the stack direction and no need arises for carrying out welding or soldering for electrical connection, enabling reduction in the number of man-hour while making it possible to easily and reliably form a circuitry to interconnect the unit cells in the battery. Especially, with the structure of the third embodiment, since the electrically conductive washers50and the insulation washers51are incorporated in the frames7, respectively, merely stacking the frames7, on each of which the unit cells1are set in array, provides a capability of realizing a circuitry in which the unit cells1are simply and reliably connected.

Further, the electrically conductive washers50and the insulation washers51are available to be set through the insulator pins52, providing an ease of mounting the electrically conductive washers50and the insulation washers51during assembly.

Furthermore, with the structures of the embodiments1and3, although the electrode tabs10,12of the unit cells1are set through the insulator pins52, the provision of the holes11,13, each with a diameter substantially equal to an outer diameter of each insulator pin52, allows the positioning of these component elements to be simply and reliably performed.

Moreover, with the structure of the second embodiment, inserting the insulator pins52through the bus bars6enables the unit cells1, connected in parallel, to be directly connected, thereby enabling the positioning of these component elements to be simply and reliably performed.

Additionally, since the surface pressures are applied to the unit cells1by the pressurizing units40, even if the unit cells1are subjected to frequent charging and discharging cycles, it becomes possible to preclude a capacity and operating life of the battery from being adversely affected by gases that would be created inside the unit cells1.

Besides, with such a battery, the unit cells1are stacked with no clearance so as to allow the requisite number of the inner layer heat sinks2bto be intervened depending upon a demanded amount of heat to be radiated whereby no appropriate surface pressure needs to be applied to the respective unit cells1, providing a capability of realizing a minimized battery, with high energy density, suited for installation on an automobile. Additionally, the battery has a rigid structure in the absence of clearance, resulting in an increased rigidity and excellent anti-vibration property.

Incidentally, with the structures of the embodiments 1 to 3, electrical connection is established among the entire unit cells in the stack direction through the use of electrically conductive washers, it doesn't matter if the unit cells are partly welded.

Fourth Embodiment

Next, a battery and its related method of a fourth embodiment according to the present invention are described in detail with reference toFIGS. 14 to 27.

FIG. 14is a perspective view of the battery BA2of the presently filed embodiment;FIG. 15Ais a perspective view illustrating one unit cell of such a battery;FIG. 15Bis a perspective view illustrating the other unit cell of the battery;FIG. 16is a cross sectional view taken on line C-C ofFIG. 14; andFIG. 17is a cross sectional view taken on line D-D ofFIG. 14.

The presently filed embodiment mainly differs from the first embodiment described above in that a unit cell1′ has a different structure, and is identical in other structure. Hereinafter, such a different point is focused in description and the same component parts as those of the first embodiment bear like reference numerals to omit or simplify description.

That is, the battery of the presently filed embodiment is comprised of a plurality of stacks of unit cells1′, the heat sinks2a,2bstacked with the unit cells1′, the high friction sheets3disposed between the unit cells1′ and between the unit cell1′ and the heat sink2, and the holding mechanism4by which the plurality of stacks of unit cells1′ are pressurized at both surfaces in the stack direction to be integrally supported.

The unit cells1′ are connected in series in the stack direction. The unit cell1′ has two electrode tabs, one of which is fitted to the tab of the other unit cell1′ to be electrically and mechanically connected. Also, the other tabs are connected to one another so as to avoid short-circuiting by alternately arranging the electrically conductive washers and the insulation washers between the tabs.

Hereinafter, various component parts of the battery BA2are described in detail also with reference to other drawings depending on needs.

With the presently filed embodiment, as shown inFIGS. 15A and 15B, the unit30cell1′ includes two kinds of a unit cell1aand a unit cell1b.

Both the unit cells1a,1bare cells formed in flat shapes and any of the unit cells includes a plurality of electric power generating elements, each including a positive electrode plate, a negative electrode plate and a separator, any of which is not shown, which are stacked in this order. For the battery BA2, the unit cells1a,1bare stacked in the same direction as that in which the internal electric power generating elements are stacked. The internal electric power generating elements form a lithium ion battery employing gel-polymer electrolyte.

The unit cells1a,1bemploy outer sheaths, respectively, each of which is comprised of a laminate film formed in a three-layer structure. The laminate film is formed in three layers in which an aluminum foil is sandwiched between resin films made of polyamide resin. Of the two laminate films, one sheet of laminate film is formed in a flat configuration, by press forming, that is laminated to the other sheet, remaining in a sheet shape, and thermally welded thereto at a peripheral edge.

Hermetically sealed inside the laminated laminate films are the electric power generating elements whose positive electrode tab and negative electrode tab, both serving as electrodes, are extracted outside the laminate films. The unit cells1a,1bhave two electrode tabs, such as positive electrode tabs10′,14and negative electrode tabs12,16, which extend in a direction perpendicular to the stack direction, respectively.

The unit cell1ahas the positive electrode tab10′ and the negative electrode tab12one of which i.e., the positive electrode tab10′ is formed with two holes11′. The negative electrode tab12is formed with one hole13.

The unit cell1bhas the positive electrode tab14having two projections15engageable with the holes11′ of the positive electrode tab10′ of the unit cell1a. The positive electrode tab16is formed with one hole17similar to that of the negative electrode tab12of the unit cell1a.

When stacking the unit cells1a,1b, the holes11′ of the unit cell1aare fitted to the associated projections15of the unit cell1b. With the positive electrode tab10′ fitted to the negative electrode tab14of the unit cell1b, the projections15of the negative electrode tab14protrude from the positive electrode tab10′ as shown inFIG. 16. This allows the unit cells1a,1bto be mutually positioned while electrically connected in series.

In the meanwhile, the negative electrode tab12of the unit cell1aand the positive electrode tab16of the unit cell1bare positioned and fixedly secured by permitting the electrically conductive washer50or the insulation washer51to be sandwiched between the other tabs12,16to allow the locating pin52to extend through the washers as shown inFIG. 17.

The electrically conductive washer50forms a part of component parts by which the battery is manufactured and is formed of an electrically conductive member, with a temporary insulator, which is made of electrically conductive metal such as copper or aluminum to allow the electrode tabs16,12, set on top and bottom surfaces of the washer50, to be electrically connected. The insulation washer51is formed of insulating metal such as ceramic to electrically insulate the tabs12,16, set on top and bottom surfaces of the washer51, from one another. The electrically conductive washer50and the insulation washer51serve as spacers to avoid direct contact between the electrode tabs12,16of the adjacent unit cells1′.

For the battery BA2, the insulation washer51is interposed between the positive electrode tab16of one unit cell1band the negative electrode tab12, placed above the positive electrode tab16, of the other unit cell1a. This is based on consideration in that for a tier where the unit cell1ais set on the unit cell1b, the negative electrode tab14of the unit cell1band the positive electrode tab10′ of the unit cell1aare fitted to one another to be mechanically and electrically connected, as shown inFIG. 16, and if the positive electrode tab16and the negative electrode tab12, placed thereon, are electrically connected, causing short-circuiting. In the meanwhile, the electrically conductive washer50is interposed between the negative electrode tab12of the unit cell1aand the positive electrode tab16of the unit cell1bplaced thereon.

As set forth above, with the structure of the presently filed embodiment, the electrically conductive washers50and the insulation washers51are alternately arranged such that for the tier where the unit cells1a,1bare mechanically and electrically connected at the electrode tabs10′,14, the electrode tabs12,16on opposite side are electrically insulated from one another by the insulation washer51, whereas in contrast, for the tier where no electrode tabs10′,14are electrically connected, the electrode tabs12,16are electrically connected by the electrically conductive washer50, thereby permitting the unit cells1aand the unit cells1bto be connected in series in the stack direction.

The locating pin52is subjected to insulation treatment by coating a surface of a metallic bar with resin or by covering the surface of the metallic bar with resin. Tightening nuts53a,53bonto the locating pin52at top and bottom ends thereof causes the electrode tabs12,16of the unit cell1′ to be firmly sandwiched between the electrically conductive washer50and the insulation washer51. Consequently, the electrode tabs12,16are electrically connected to one another or insulated from one another in a reliable manner.

Incidentally, the nuts53a,53bmay be utilized to fasten electrode terminals (not shown) for extracting electric power from the battery like in the first embodiment.

<Heat Sink, High Friction Sheet and Holding Mechanism>

The heat sink2a,2b, the high friction sheet3and the holding mechanism4fundamentally have the same structure as that of the first embodiment.

In particular, the heat sinks include two kinds of outer layer heat sinks2aand inner layer heat sinks2bthat are stacked with the unit cells1′ in a middle of the battery, and any of the heat sinks is formed with a ventilation passages20available for coolant, such as air, to flow through.

The outer layer heat sinks2aare formed with cutouts21, respectively, to allow the electrode tabs10′12,14,16of the stacked unit cells1′ to be exposed and have four corners formed with holes22, respectively, between two of which the cutout21is intervened. The inner layer heat sink2bis disposed between the unit cells1′ in such a way that when four sheets of unit cells1′ are stacked, one sheet of inner layer heat sink2bis placed on top of the four sheets as shown inFIGS. 16 and 17.

The high friction sheet3is made of silicone rubber that is formed in a sheet configuration to be interposed between the unit cells1′ or between the unit cell1′ and the heat sink2, thereby precluding transverse displacements of these component elements.

The holding mechanism4includes the outer layer heat sink2ato be stacked on the outermost layer, the pressurizing units40to be disposed between the outer layer heat sinks2a, and the nuts41by which the pressurizing units40are mounted to the outer layer heat sinks2a, and elastic forces exerted by the tension coil springs (resilient bodies)42of the pressurizing units40act on the unit cells1′ through the outer layer heat sinks2ato form a pressurizing force.

Now, description is made of assembling procedure for the battery BA2of the presently filed embodiment with the structure mentioned above.

FIG. 18is a flowchart illustrating a basic sequence of assembling the battery BA2of the presently filed embodiment;FIG. 19is an exploded perspective view illustrating a basic sequence of assembling the battery BA2; andFIG. 20is an exploded view illustrating a basic sequence of assembling the battery BA2consecutive to a condition shown inFIG. 19. Incidentally, the sequence of steps S1to S6ofFIG. 18will be suitably understood with reference toFIG. 19, and the sequence of steps S7to S17will be suitably understood with reference toFIG. 20. First, as shown inFIGS. 18 and 19, the high friction sheet3is set on the outer layer heat sink2a(step S1).

Next, the unit cell1bis set on the high friction sheet3placed on the outer layer heat sink2a(step S2) and the locating pin52is inserted to the electrode tab16, whereupon the locating pin52is temporarily fastened by the nut53bthrough the electrically conductive washer50, disposed outside the electrode tab16, and more particularly, through an electrically conductive washer100with an insulation film to set the locating pin (step S3). Incidentally, the locating pin52has both ends formed with thread ridges to screw the nuts53a,53b.

Subsequently, the insulation washer51is set through the locating pin52(step S4), and the unit cell1ais set on the unit cell1b(step S5).

Consecutively, the projections15of the negative electrode tab14of the unit cell1bare fitted to the holes11of the positive electrode tab10of the unit cell1a(step S6). This allows the unit cells1a,1bto be united.

Next, the high friction sheet3is set on the unit cell1a(step S7).

Subsequently, further as shown inFIG. 20, the electrically conductive washer100with the insulation film is set on the electrode tab12of the unit cell1athrough the locating pin52(step S8).

Here, repeating steps S2to S8except step S3allows a given number of sets of double unit cells1a,1bto be stacked (step S9).

Consecutively, after the given number of unit cells1a,1bhave been finally stacked, the inner layer heat sink2bis set on the high friction sheet3(step S10).

Subsequently, the high friction sheet3is also set on the inner layer heat sink2b(step S11).

Here again, repeating steps S2to S8except step S3allows (step S2to S11except step S3when setting the inner layer heat sinks2bin multiple layers) allows the given number of unit cells1a,1b, with the double sheet in one set, to be stacked (step S12).

Thus, after repeatedly, stacking the given number of unit cells1a,1band the inner layer heat sinks2b, an upper outer layer heat sink2ais set on the high friction sheet3of the uppermost unit cell1a(step S13).

The nut53ais temporarily fastened to a top of the locating pin52(step S14). Here, by the term “temporarily fastened” is meant the extent in which the nut is screwed not to cause the electrode tabs12and16of the plural unit cells1a,1b, stacked on assembly, to remove from the locating pin52.

Now, the electrically connecting relationship between the unit cells1a,1bis studied.

FIG. 21is a typical view illustrating a stacked condition where the insulation washers51and the electrically conductive washers100each with the insulation film are located. Also, in the drawing figure, the heat sinks are omitted.

As shown inFIG. 21, a stack body has areas in which the insulation washers51and the electrically conductive washers100with the insulation films101are located to cause all the electrode tabs12,16to remain in completely insulated conditions with all the unit cells1a,1bbeing assembled. That is, the insulation washer51provides insulation between the tabs12and16of the one set of the unit cells1a,1bin double sheets that are connected on the electrode tabs10′,14, and the electrically conductive washer100with the insulation film101results in insulation between the electrode tabs12and16related to the other set of unit cells.

Further, description is made of a structure to be taken by the electrically conductive washer with the insulation film.

FIG. 22Ais a plan view illustrating one example of the electrically conductive washer with the insulation film, andFIG. 22Bis a cross sectional view taken on line F-F ofFIG. 22A.

As shown inFIGS. 22A and 22B, the electrically conductive washer100A with the insulation film has a structure in which an annular insulation film101, similar to the electrically conductive washer50, is adhered onto the electrically conductive washer50made of copper or aluminum. Here, examples of the insulation film101may include resin films, such as a polyethylene film and vinyl film, or paper sheets.

FIG. 22Cis a plan view illustrating another example of an electrically conductive washer with an insulation film, andFIG. 22Dis a cross sectional view taken on line G-G ofFIG. 22C.

As shown inFIGS. 22C and 22D, the electrically conductive washer100B with the insulation film takes the form of a structure wherein the annular insulation film101, shown inFIGS. 22A and 22B, additionally has a pickup tag102that protrudes in a radial direction of the annulus outward from the electrically conductive washer50. The provision of such a pickup tag102allows the pickup tag102to be pulled out when desired to remove the insulation film101depending on needs for thereby enabling the same to be simply removed.

FIG. 22Eis a plan view of another example of an electrically conductive washer with an insulation film, andFIG. 22Fis a cross sectional view taken on line H-H ofFIG. 22E.

As shown inFIGS. 22E and 22F, the electrically conductive washer100C with the insulation film takes the form of a structure wherein the insulation film101formed with the pickup tag, shown inFIGS. 22C and 22D, is additionally formed with a slit103at a position in opposition to the pickup tag102. The provision of such a slit103allows the insulation film101to be torn at an area near the slit103, when removing the insulation film101depending on needs, for thereby providing a further ease of removal. When forming such a slit103, a need arises to pay attention not to cause the area near the slit103to be electrically conductive, that is, not to cause an exposure rate of the electrically conductive washer50to increase. Also, the slit103may be replaced with perforation, resulting in similar effects.

Of course, the pickup tag, slit and perforations set forth above may be mutually combined in various forms. The insulation film may be formed with the slit or perforation with no formation of the pickup tag, or may be formed with the perforation together with the slit. Or, additionally, slits and perforations may be located at plural positions.

By the way, after the component elements, such as the unit cells1a,1b, are stacked in assembly up to step S14and the nut53ais temporarily fastened to the top of the locating pin52, the pressurizing units40are set between the outer layer heat sinks2aand the nuts41are fastened until the coil springs42of the pressurizing units40extend by a given length for thereby fastening the pressurizing units40(step S15).

Subsequently, all the insulation films101are removed from above the electrically conductive washers50(step S16). At this stage, since the locating pin52is merely fastened, the insulation films101can be easily removed.

Finally, the nuts53a,53bon both sides of the locating pin52are fully fastened and tightened by a given torque to fasten the electrode tabs12,16in finish (step S17). This allows the electrically conductive washers50to be fully brought into contact with the electrode tabs12and16, by which the electrically conductive washers50is sandwiched, to connect all the unit cells1a,1bin series, providing an assembly of the battery BA2shown inFIG. 14.

With the structure of the presently filed embodiment set forth above, since the battery is assembled under a condition where the insulation films are placed on the electrically conductive washers through which the plurality of unit cells are connected in series, a total voltage of the unit cells connected in series during assembly just lies in a value (a total value of approximately 8 volts if the voltage of one unit cell is about 4 volts) equal to voltages of two unit cells at the highest, resulting in a capability of reliably and simply performing assembling work.

<Modified Form of Electrically Conductive Washer>

Hereinafter, a further modified form of the electrically conductive washer of the presently filed embodiment is described.

FIG. 23Ais a plan view illustrating one example of an electrically conductive washer with a temporary insulator;FIG. 23Bis a cross sectional view taken on line I-I ofFIG. 23Aillustrating a condition prior to the fastening of the locating pin; andFIG. 23Cis a cross sectional view taken on line I-I ofFIG. 23Aillustrating a condition subsequent to the fastening of the locating pin.

As shown inFIGS. 23A to 23C, the electrically conductive washer120with the temporary insulator has an insulating ring121as a temporary insulator that has an inner diameter I slightly smaller than an outer diameter O of the electrically conductive washer50and a thickness h2slightly less than a thickness h1, along a direction between the electrode tabs, of the electrically conductive washer50. The insulating ring121protrudes from the electrically conductive washer50, under a condition prior to the fastening of the locating pin, as shown inFIG. 23B, and the electrode tabs12and16are held in an insulated condition. In the meantime, after the locating pin is fastened, the insulating ring121is retracted toward the electrically conductive washer due to a compression force caused by fastening, as shown inFIG. 23C, and the electrode tabs12and16are held in an electrically conductive condition.

Incidentally, the inner diameter I of the insulating ring is determined to have a size affording a frictional force to the extent not to cause the insulating ring to readily drop off from the electrically conductive washer during a state prior to the locating pin being fastened and to allow the insulating ring to slide on the electrically conductive washer due to a fastening force applied to the locating pin. Moreover, the thickness h2of the insulating ring121is suffice to have a thickness less than the electrically conductive washer50not to cause the insulating ring to project from the electrically conductive washer50when the locating pin is fastened. Also, raw materials for the insulating ring121may include plastic or ceramic with insulation property.

FIG. 24Ais a plan view illustrating another example of an electrically conductive washer with a temporary insulator;FIG. 24Bis a cross sectional view taken on line J-J ofFIG. 24Aillustrating a condition prior to the fastening of the locating pin; andFIG. 24Cis a cross sectional view taken on line J-J ofFIG. 24Aillustrating a condition subsequent to the fastening of the locating pin. As shown inFIGS. 24A to 24C, the electrically conductive washer130with the temporary insulator is comprised of an annular electrically conductive washer131with an outer annular shoulder formed with a taper132, and an annular insulating ring135, having a tapered support133held in contact with the taper131to be supported, that has an inner diameter less than the outer diameter of the electrically conductive washer131and protrude from the electrically conductive washer131. Here, the insulating ring135may be preferably made of relatively fragile material such as ceramic or hard plastic.

The insulating ring135protrudes from the electrically conductive washer131, as shown inFIG. 24B, under a condition where the locating pin is fastened, the electrode tabs12and16are held in an insulated condition. In the meanwhile, as shown inFIG. 24C, when the locating pin is fastened, a compression force caused by the fastening results in a force to cause the tapers132,133to expand the insulating ring135outward, which is consequently ruptured. Accordingly, fastening the locating pin automatically causes the insulating rind135to remove from the electrically conductive washer131, causing the electrode tabs12and16to be held in an electrically conductive condition. Incidentally, the insulating ring135may be altered such that instead of causing the insulating ring135to be ruptured, the insulating ring135expands in diameter along the tapers when the locating pin is fastened to allow the insulating ring135to slip toward the electrically conductive washer131due to a force resulting from the fastening for thereby removing the insulating property.

FIG. 25Ais a plan view illustrating still another example of an electrically conductive washer with a temporary insulator;FIG. 25Bis a cross sectional view taken on line K-K ofFIG. 25Aillustrating a condition prior to the fastening of the locating pin; andFIG. 25Cis a cross sectional view taken on line K-K ofFIG. 25Aillustrating a condition subsequent to the fastening of the locating pin.

As shown inFIGS. 25A to 25C, the electrically conductive washer140with the temporary insulation means is comprised of an electrically conductive washer141formed with an annular concave recess142, and an insulating ring145, made of elastic material, and disposed in the concave recess142. The insulating ring145is formed to have a thickness h3greater than a depth h4of the concave recess142under a normal condition and a volume less than that of the concave recess142.

The insulating ring145made of such material projects from the electrically conductive washer141, as shown inFIG. 25B, under a condition prior to the fastening of the locating pin and, hence, the electrode tabs12and16are held in an insulated condition. In the meanwhile, as shown inFIG. 25C, when the locating pin is fastened, a compression force resulting from the fastening collapses the insulating ring141to cause the electrically conductive washer141to provide electrical conductance between the electrode tabs12and16.

FIG. 26is a schematic cross sectional view illustrating a further example of an electrically conductive washer with a temporary insulator and showing a state prior to the fastening of the locating pin, andFIG. 27shows a state of the electrically conductive washer with the temporary insulator, shown inFIG. 26, subsequent to the fastening of the locating pin.

As shown inFIGS. 26 and 27, the electrically conductive washer302with the temporary insulator takes the form of a structure wherein an elastic sheet301is placed to overlap an electrically conductive washer300. The electrically conductive washer300has a surface, on which the elastic sheet301is placed, formed with an electrically conductive protrusion305. In the meanwhile, the elastic sheet301forms a temporary insulator that is made of material, with an insulating property and an elasticity, including a member of rubber system such as synthetic rubber or silicone rubber.

The electrically conductive washer302with the temporary insulator remains in an insulated condition with the protrusion305being inoperative to smash through the elastic sheet301under a condition prior to the fastening of the locating pin52as shown inFIG. 26. On the other hand, under a condition where the nuts53are fastened to the locating pin52up and down, the elastic sheet301is compressed, as shown inFIG. 27, to cause the protrusion305formed on the electrically conductive washer300to smash through the insulation sheet, thereby allowing the electrically conductive washer300to be brought into contact with the electrode tab16.

Accordingly, during assembly of the battery, the stacked unit cells are electrically insulated and no series connection is provided among all the unit cells, and all the unit cells are brought into series connection at a timing in which the nuts53fasten the locating pin52up and down in a final stage.

Incidentally, with such a structure, it is possible to realize a structure wherein suitable selection of an elasticity of the elastic sheet300allows the elastic sheet to restore in an original position again to conceal the protrusion upon release of the fastening force subsequent to the phase of fastening the locating pin52up and down through the nuts53, an area near the protrusion is insulated to shut off connection between the plural unit cells that are stacked.

Further, with the electrically conductive washers120,130,140,302with the temporary insulators, since fastening the locating pin52automatically causes the electrode tabs12and16to be brought into an electrically conductive state and, among the assembling sequence of the battery set forth above, the assembling sequence needs no step (step S16) of removing the insulating film.

<Other Form of Manufacturing Procedure>

Finally, other form of assembling procedure for the battery of the presently filed embodiment is described.

FIG. 28is a typical view illustrating a condition of other example where an insulation washer and an electrically conductive washer with an insulation film are set.

Although in the manufacturing process of the battery set forth above mainly with reference toFIG. 18, all the electrically conductive washers are used which include the insulation films, it may be possible to locate one electrically conductive washer for a plurality of unit cells connected in series.

That is, as shown inFIG. 28, it may be possible to provide a structure that employs one electrically conductive washer100with the insulation film for a given number of unit cells, i.e., eight pieces of unit cells in the drawing figure. The reason why one electrically conductive washer100with the insulation film is used for the plural unit cells resides in that for one unit cell with a voltage of 4 volts, the presence of the unit cells connected in series with the number of pieces less than ten pieces provides an output voltage that has a value less than 40 volts to ensure a reliability on work and, as shown, the presence of one piece of electrically conductive washer100with the insulation film being interposed for eight pieces of unit cells results in a capability of realizing the reliability on such work.

In such a way, interposing one electrically conductive washer100with the insulation film to allow the unit cells, connected in series, to typically have a voltage less than 40 volts ensures the reliability on work and reduces the number of insulation films, thereby enabling reduction in a number of man-hour per se in removing the insulation films that would otherwise occur due to the use of the electrically conductive washer100with the insulation film.

The battery discussed above with reference to the fourth embodiment has a number of advantages described below.

With the battery of the presently filed embodiment, sine the electrically conductive washers100,120,130,140or302with the temporary insulators are used, it becomes possible to minimize the generation of useless voltage resulting from the unit cells being connected during fabrication for performing assembling work in a certain and reliable manner.

Further, since the electrically conductive washers100with the temporary insulators are enabled to permit easy removal of the temporary insulator means, it is suffice for assembling work to be conducted with no increase in the number of man-hour with minimal efforts. Also, since the electrically conductive washers120,130,140,302with the temporary insulators are effective to automatically remove insulated conditions, no increase results in the number of man-hour on assembling work.

Furthermore, if the number of unit cells connected in series provides an output voltage of a value approximately less than 40 volts, the use of the electrically conductive washers with the insulation films in less number of pieces than the number of unit cells to be connected in series enables reduction in the number of man-hour on removing the insulation films.

Moreover, since the high friction sheet3is disposed between the unit cells1′ and between the unit cell1′ and the heat sink2, no displacement occurs between the unit cells even in the presence of vibrations applied to the respective unit cells1′ and the heat sinks2that are stacked. Accordingly, even when applied to automobiles, it becomes possible to prevent the respective unit cells1′ and the heat sinks2from displacement or drop off resulting from vibrations.

Besides, no displacement or drop off occurs in the unit cells1′ as a result of vibrations, it is possible to avoid damages to the electrode tabs of the battery formed on the unit cells1′ connected in series or parallel.

Additionally, since no displacement occurs in the unit cells1′ due to the high friction sheets being interposed, no need arises in increasing a pressurizing force through which the stack of the unit cells1′ is pressurized from top and bottom thereof by the holding mechanism4for precluding displacement. Consequently, the unit cell1′ is not required to have an outer layer with an increased strength for withstanding a strong pressurizing force and the unit cell1′ can be formed in lightweight, resulting in reduction in light of the battery as a whole.

Further, the use of the high friction sheets3allows the unit cells1′ and the high friction sheets3to be alternately stacked when stacking the unit cells1′, enabling the battery to be easily manufactured.

Furthermore, since the high friction sheets3have non-adhesiveness with respect to the unit cells1′, the presence of failure in one of the unit cells1′ enables an arbitrary one of the unit cells1′ to be taken out for replacement.

Moreover, since the electrode tabs12,16of the unit cells1′ have bores13,17to allow the locating pin52to be inserted, inserting the locating pin52through the bores enables the unit cells1′ to be simply and reliably positioned with respect to one another.

Also, the projections15formed on the electrode tab14fit the holes of the other electrode tab10, enabling the unit cells1′ to be simply and reliably positioned with respect to one another. Additionally, since fitting the projections15to the holes enables the unit cells1′ to be electrically connected to one another in a simple and reliable manner, no mistake occurs in a direction in which the unit cells1′ are overlapped during stacking work, making it possible to provide simplified assembling.

Additionally, since the holding mechanism4has both the pressurizing function and the cooling function, it becomes possible for heat, built up in the unit cells1′, to be radiated while applying the unit cells1′ with appropriate surface pressures.

Besides, the use of the pressurizing unit40mounted between the outer layer heat sinks2aenables the outer layer heat sinks2ato come close to one another to pressurize the unit cells1′ and the pressurizing mechanism can be incorporated in the inside of the battery, enabling miniaturization of the battery.

Further, since the unit cells1′ are stacked in the same direction as that in which the electric power generating elements are stacked, it becomes possible to obtain electric current in a stable manner.

Furthermore, since the unit cells1′ take the form of a flat type battery, the battery is able to have a reduced thickness.

Incidentally, while with the presently filed embodiment, the positive electrode tabs10of the unit cell1ahas the holes11and the negative electrode tabs14of the unit cell1bhas the projections15, the presently filed embodiment is not limited to such a structure. The electrode tab in which the holes and projections are formed may have a reversed polarity. In addition, the electrode may be formed with concave portions in place of the holes11which the projections15fit.

Also, while with the presently filed embodiment, the electrode tabs extending from one sides of the unit cells1′ are connected through the fittings of the projections15and the holes11, whereas the other sides of the unit cells1′ are connected through the insulation washers51and the electrically conductive washers50, the presently filed embodiment is not limited to such a structure. Depending on circumstances, the both sides of the unit cells1′ may be connected through the fittings of the associated component parts or through insulation/electrically conductive washers. Or, ultrasonic welding may be employed to join the electrode tabs.

Further, while with the presently filed embodiment, there has been shown only one battery that is stacked in a vertical direction, the presently filed embodiment is not limited to such particular configuration and a plurality of batteries each formed of a stack of plural unit cells may be juxtaposed in electrical connection to provide a battery module with further increased power output. In such cases, bus bars may be mounted between the one of the batteries and the other one of the batteries to provide electrical connection. The bus bars may be mounted to and fixed to the locating pin52between the nut53and the electrically conductive washer50.

Furthermore, although the presently filed embodiment has been described with reference to an exemplary structure wherein the electrode tabs on one side fit one another through concave and convex configurations, the electrode tabs on both sides may be stacked one above the other using the electrically conductive washers50and the insulation washers51to form separate stacks of unit cells that are connected in series. In such cases, the electrically conductive washers with temporary insulators may be employed not to cause the number of each of the separate stacks of unit cells connected in series to provide an output voltage exceeding a value of 40 volts.

Incidentally, with the presently filed embodiments set forth above, although the high friction sheets3are used as displacement preventive means, no limitation is intended by the presently filed embodiment. The displacement preventive means may be formed of sticky liquid applied to the unit cells or the heat sinks. Here, by the term “sticky liquid” is meant the material such as urethane family resin and rubber liquid. The employment of sticky liquid as the displacement preventive means allows sticky liquid to be merely applied onto surfaces of outer sheaths of the unit cells, enabling the battery to be simply manufactured.

Besides, the displacement preventive means may be formed by roughly machining the outer sheath surfaces of the unit cells in a coarse surface roughness. A method of increasing the surface roughness of the outer sheath surfaces of the unit cells includes a sandblasting method and laser peening method. Of course, grinding may be possibly employed using a sand paper. The use of a structure to allow the outer sheath surface of the unit cell to have coarse surface roughness allows the unit cells to be merely stacked in a sequence for thereby preventing these unit cells from displacement.

Further, while the high friction sheets3are formed of only silicone rubber, no limitation is intended by the presently filed embodiment. Examples of such material may include a base substrate, made of PET (polyethylene terephthalate), on which silicone rubber is located. Thus, the provision of the base substrate improves a rigidity of the high friction sheet, resulting in improved workability when setting these component elements on the heat sinks and the unit cell surfaces.

For such a base substrate being employed, the base substrate may be coated with adhesive to be adhered onto the unit cell or the heat sink. In such cases, a bare side of the high friction sheet3is adhered to the unit cell or the heat sink2, but no adhesion occurs on the silicone rubber side. This enables the unit cells, stacked one above the other, or the unit cells and the heat sinks to be separated from one another.

The entire content of a Patent Application No. TOKUGAN 2003-351739 with a filing date of Oct. 10, 2003 in Japan and that of a Patent Application No. TOKUGAN 2003-351733 with a filing date of Oct. 10, 2003 in Japan are hereby incorporated by reference.