Battery assembly

A battery assembly of the invention includes a secondary battery formed by stacking a plurality of unit battery cells having a cathode and an anode, collector electrodes provided on respective end surfaces of the secondary battery positioned in the stacking direction of the unit battery cells; and terminal portions formed at the collector electrodes, protruded outward from a side surface of the secondary battery, to which conductive members are connected for charging and discharging. A coolant is supplied to the terminal portions to cool the terminal portions.

This is a 371 national phase application of PCT/JP2007/062474 filed 14 Jun. 2007, claiming priority to Japanese Patent Application No. 2006-196980 filed 19 Jul. 2006, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a battery assembly formed by stacking a plurality of secondary batteries.

BACKGROUND OF THE INVENTION

Conventionally, a battery assembly formed by stacking a plurality of battery cells has been proposed as a storage battery. A battery cell includes a plate-shaped electrolyte, having a cathode active material formed on a main surface and an anode active material formed on the other main surface. The battery cells as such are arranged in series and a collector plate is placed between each of the battery cells, whereby a battery assembly is formed. In the battery assembly formed in this manner, electrode reaction takes place between the cathode active material and the anode active material in each battery cell, to discharge power.

Japanese Patent Laying-Open Nos. 2005-071784, 2004-031281 and 2002-056904 propose various types of battery assemblies and cooling structures therefor, for cooling heat generated by the electrode reaction. For instance, Japanese Patent Laying-Open No. 2005-071784 proposes a battery assembly and its cooling structure, in which a cooling tab is attached to each collector plate arranged between battery cells, and by blowing cooling air to the tab, each collector plate is cooled and hence the battery assembly is cooled.

In the battery assembly mentioned above, however, a separate cooling tab is attached to each cooling plate and, therefore, the number of components increases, resulting in higher cost.

SUMMARY OF THE INVENTION

The present invention was made in view of the problem described above, and its object is to provide a battery assembly whose inside can be cooled at a low cost, without increasing the number of components.

The present invention provides a battery assembly, including: a secondary battery formed by stacking a plurality of unit battery cells having a cathode and an anode; a collector electrode provided on each end surface of the secondary battery positioned in the stacking direction of the unit battery cells; and a terminal portion formed at the collector electrode, protruded outward from a side surface of the secondary battery, to which a conductive member is connected for charging and discharging; wherein a coolant is supplied to the terminal portion to cool the terminal portion, and a vent hole is formed in the terminal portion T1, allowing flow of the coolant.

Preferably, it further includes a guide wall formed around the vent hole, guiding the coolant to the vent hole. Preferably, it further includes a connecting portion formed at the terminal portion, to which the conductive member is connected, and the vent hole is formed around the connecting portion.

According to another aspect, the present invention provides a battery assembly, including: a secondary battery formed by stacking a plurality of unit battery cells having a cathode and an anode; a collector electrode provided on each end surface of the secondary battery positioned in the stacking direction of the unit battery cells; and a terminal portion formed at the collector electrode, protruded outward from a side surface of the secondary battery, to which a conductive member is connected for charging and discharging; wherein a coolant is supplied to the terminal portion to cool the terminal portion, the secondary battery includes first and second secondary batteries stacked to have the cathodes opposed to each other or the anodes opposed to each other; the collector electrode has a first collector electrode provided between the first secondary battery and the second secondary battery for electrically connecting the first secondary battery and the second secondary battery, and a second collector electrode of a polarity different from that of the first collector electrode, formed on a surface of the first secondary battery positioned opposite to the surface on which the first collector electrode is formed; and the terminal portion has a first terminal portion provided on the first collector electrode and a second terminal portion provided on the second collector electrode.

According to a further aspect, the present invention provides a battery assembly, comprising: a secondary battery formed by stacking a plurality of unit battery cells having a cathode and an anode; a collector electrode provided on each end surface of the secondary battery positioned in the stacking direction of the unit battery cells; and a terminal portion formed at the collector electrode, protruded outward from a side surface of the secondary battery, to which a conductive member is connected for charging and discharging; wherein a coolant is supplied to the terminal portion to cool the terminal portion; further including a collector foil provided between the unit battery cells; wherein the collector electrode is formed to be thicker than the collector foil.

In the battery assembly in accordance with the present invention, the terminal portion, which is an essential component of the battery assembly, is also used as the cooling plate and, therefore, the battery assembly can well be cooled without increasing the number of components and cost.

DETAILED DESCRIPTION

Referring toFIGS. 1 to 6, a battery assembly100in accordance with Embodiment 1 of the present invention will be described.

FIG. 1is a plan view of a cooling apparatus200arranged around a battery pack120containing the battery assembly, for cooling a terminal portion of the battery assembly, andFIG. 2is a perspective view of battery assembly100in accordance with Embodiment 1.

Cooling apparatus200of battery assembly100includes a housing51housing battery pack120therein, and a fan53for supplying outer air through an air intake duct52provided on housing51.

Battery pack120is formed to have a substantially rectangular parallelepiped shape, and includes a casing101containing battery assembly100therein, and battery assembly100. Battery pack120has a plurality of terminal portions T1and T2protruding outward from casing101, on one side surface of battery pack120. Fan53blows air (coolant) to terminal portions T1and T2, so that terminal portions T1and T2are cooled and, consequently, battery assembly100is cooled.

As shown inFIG. 2, battery assembly100is formed by stacking a plurality of bipolar secondary batteries4, a plurality of negative collector electrodes21and a plurality of positive collector electrodes23.

Terminal portions T1and T2are formed at negative collector electrode21and positive collector electrode23, and wires (conductive members) U1and U2for discharging and supplying power shown inFIG. 2are connected. Terminal portions T1and T2are essential components for battery assembly100to function as a storage battery, and by utilizing terminal portions T1and T2as cooling plates, it becomes possible to cool battery assembly100without increasing the number of components of battery assembly100.

Terminal portion (first terminal portion) T1is integrally molded with negative collector electrode21, and terminal portion (second terminal portion) T2is integrally molded with positive collector electrode23. When terminal portions T1and T2are formed integral with collector electrodes21and23, respectively, efficiency of heat transfer can be improved than, for example, when terminal portions T1and T2are formed separate from negative collector electrode21and positive collector electrode23and connected by using solder, and therefore, inside of battery assembly100can better be cooled.

Terminal portion T1has a connection hole (connection portion) a1to which wire U1is connected, and terminal portion T2has a connection hole b1to which wire U2is connected.

Wires U1and U2are used for discharging electric power from battery assembly100to the outside or for charging battery assembly100, and connect battery assembly100, for example, to a PCU (Power Control Unit). In Embodiment 1, lead wires or the like are used as wires U1and U2. These are not limiting, and any conductive member such as a conductive pin, may be used.

Terminal portions T1and T2are formed alternately, shifted in the direction of main surface of negative collector electrode21and positive collector electrode23.

Therefore, it is possible to form connection hole a1at a position of terminal portion T1away from terminal portion T2and to form connection hole b1at a position of terminal portion T2away from terminal portion T1. This facilitates connection of wires U1and U2to connection holes a1and b1.

Terminal portions T1are arranged to be overlapped in the stacking direction, and connection holes a1formed in each of the terminal portions T1are also aligned in the stacking direction. Therefore, by putting wire U1through each of the connection holes a1aligned in the stacking direction, all negative collector electrodes21can easily be connected.

Similarly, terminal portions T2are arranged to be overlapped in the stacking direction, and connection holes b1are also aligned in the stacking direction. Therefore, by putting wire U2through each of the connection holes b1aligned in the stacking direction, all positive collector electrodes23can easily be connected.

At that portion of negative collector electrode21which is adjacent to terminal portion T1, a cut-out portion40is formed, and in the stacking direction of cut-out portions40, terminal portion T2of positive collector electrode23is positioned. Further, at that portion of positive collector electrode23which is adjacent to terminal portion T2, a cut-out portion41is formed, and in the stacking direction of cut-out portions41, terminal portion T1of negative collector electrode21is positioned. Therefore, even when terminal portions T1and T2are bent or curved in the stacking direction, contact between terminal portions T1and T2can be prevented.

Terminal portions T1and T2are formed on one side surface of battery assembly100and, therefore, it is possible to arrange other member or members near other circumferential surfaces of battery assembly100. Therefore, dead space can be reduced.

In the example shown inFIG. 2, negative collector electrode21and positive collector electrode23are formed to have a substantially rectangular shape having sides21ato21dand23ato23d, and provided with terminal portions T1and T2protruded outward from sides21dand23d.

Terminal portions T1and T2are formed to extend from end portions of sides21dand23dto the central portions of sides21dand23d, and terminal portions T1and T2are arranged not be overlapped in the stacking direction of bipolar secondary batteries4.

The shape of terminal portions T1and T2is not limited to the above. By way of example,FIG. 3is a perspective view showing a first modification of battery assembly100, and as shown inFIG. 3, terminal portions T1and T2may extend from one end to the other end of sides21dand23d, and terminal portions T1and T2may partially overlap in the stacking direction of bipolar secondary batteries4.

By forming terminal portions T1and T2in this manner, surface areas of terminal portions T1and T2can be increased, whereby cooling effect can be improved.

FIG. 4is a perspective view showing a second modification of battery assembly100and, as shown inFIG. 4, terminal portions T1and T2may be formed to extend over opposite ends of negative collector electrode21and positive collector electrode23.

By forming terminal portions T1and T2in this manner, it becomes possible to ensure larger surface area of terminal portions T1and T2and, therefore, cooling effect can further be improved.

When terminals T1and T2are formed over opposite ends of sides, terminal portions T1and T2are formed on different side surfaces of battery assembly100, to facilitate routing of wires U1and U2.

Further, surface areas of terminal portions T1and T2positioned at the central portion in the thickness direction of battery assembly100may be made larger than the surface areas of terminal portions T1and T2positioned at opposite ends in the thickness direction of battery assembly100. This improves heat radiation near the central portion in the thickness direction of battery assembly100, to prevent heat build-up in battery assembly100.

FIG. 5is a cross-sectional view showing in detail the structure in battery assembly100. As shown inFIG. 5, bipolar secondary battery4is formed by successively stacking a plurality of electrode sheets (unit battery cells)25and collector foils29provided between each of the electrode sheets25. The direction of stacking respective electrode sheets25is the same as the direction of stacking bipolar secondary batteries4, and both correspond to the thickness direction of battery assembly100.

Electrode sheet25includes an electrolyte layer27formed as a plate, an anode active material layer26formed on one main surface (first main surface)27aof electrolyte layer27, and a cathode active material layer28formed on the other main surface (second main surface)27bof electrolyte layer27. Electrode sheets25are stacked in series one after another with collector foil29inserted therebetween.

A plurality of bipolar secondary batteries4are stacked with the plate-shaped negative collector electrode21or the plate-shaped positive collector electrode23interposed. Negative collector electrode21and positive collector electrode23are arranged between bipolar secondary batteries4stacked such that cathode active materials (cathodes)28oppose to each other or anode active materials (anodes)26oppose to each other, to connect bipolar secondary batteries4with each other, and also provided at opposite ends of battery assembly100in the stacking direction of bipolar secondary batteries.

On a main surface of negative collector electrode21provided on one end of battery assembly100, anode active material layer26of bipolar secondary battery4adjacent in the stacking direction is formed, and on a main surface of positive collector electrode23provided on the other end, cathode active material layer28of bipolar secondary battery4adjacent in the stacking direction is formed.

Referring toFIG. 2, by way of example, among the plurality of bipolar secondary batteries4, negative collector electrode (first collector electrode)21is provided between bipolar secondary battery (first secondary battery)4A and bipolar secondary battery (second secondary battery)4B. On that surface of bipolar secondary battery4A which is positioned opposite to the surface of bipolar secondary battery4A having negative collector electrode21formed thereon, a positive collector electrode (second collector electrode)23is provided.

Bipolar secondary batteries4adjacent to each other with positive collector electrode23interposed are arranged such that cathode active material layers (cathodes)28oppose to each other as shown inFIG. 5, and on the front and rear surfaces of positive collector electrode23, cathode active material layers28of adjacent bipolar secondary batteries are connected. Further, bipolar secondary batteries4adjacent to each other with negative collector electrode21interposed are arranged such that anode active material layers26oppose to each other, and on the front and rear surfaces of negative collector electrode21, anode active material layers26of adjacent bipolar secondary batteries are connected. Specifically, bipolar secondary electrodes4are connected in parallel with each other.

Bipolar secondary batteries4positioned on opposite sides of positive collector electrode23or negative collector electrode21in the stacking direction share the positive collector electrode23or negative collector electrode21. Therefore, as compared with a conventional battery assembly formed by stacking a plurality of bipolar secondary batteries one after another with an insulating film interposed, the insulating film becomes unnecessary, and as the neighboring secondary batteries share the collector electrode, battery assembly100itself can be made compact.

Referring toFIG. 5, electrolyte layer27forming the electrode sheet25is formed of a material having ion conductivity. Electrolyte layer27may be solid electrolyte, or gel electrolyte. By interposing electrolyte layer27, ion conduction between cathode active material layer28and anode active material layer26becomes smooth, and output of bipolar secondary battery4can be improved. By a collector foil29formed on each electrode sheet25, cathode active material layer28formed by sputtering on one main surface29bof collector foil29and anode active material layer26formed on the other main surface29, a bipolar electrode30is formed.

Here, thickness of positive collector electrode23and negative collector electrode21provided on end surfaces at the ends in the stacking direction of electrode sheets25of bipolar secondary batteries4is made thicker than collector foil29formed in each bipolar secondary battery4.

Therefore, when terminal portions T1and T2formed at positive collector electrode23and negative collector electrode21function as heat radiating plates, higher effect of heat radiation can be attained than when part of collector foil29is protruded from bipolar battery4and used as a heat radiating plate.

Casing101shown inFIG. 1has an opening54to which terminal portions T1and T2are inserted. Around opening54, a seal member55is provided to keep air-tightness of casing101. It is noted that when a part of collector foil29is to be used as a heat radiating plate, a large number of openings must be formed in casing101and, therefore, it is very difficult to ensure air-tightness of casing101.

Next, each of the components forming bipolar secondary battery4will be described in detail. Collector foil29is formed, by way of example, of aluminum. Here, even if the active material layer provided on the surface of collector foil29contains solid polymer electrolyte, it is possible to ensure sufficient mechanical strength of collector foil29. Collector foil29may be formed by providing aluminum coating on metal other than aluminum, such as copper, titanium, nickel, stainless steel (SUS) or an alloy of these.

Cathode active material layer28includes a cathode active material layer and a solid polymer electrolyte. Cathode active material layer28may contain a supporting electrolyte (lithium salt) for improving ion conductivity, a conduction assistant for improving electron conductivity, NMP (N-methyl-2-pyrolidone) as a solvent for adjusting slurry viscosity, AIBN (azobisisobutyronitrile) as a polymerization initiator or the like.

As the cathode active material, composite oxide of lithium and transition metal generally used in a lithium ion secondary battery may be used. Examples of the cathode active material may include Li/Co based composite oxide such as LiCoO2, Li/Ni based composite oxide such as LiNiO2, Li/Mn based composite oxide such as spinel LiMn2O4, and Li/Fe based composite material such as LiFeO2. Other examples are sulfated compound or phosphate compound of lithium and transition metal such as LiFePO4; sulfide or oxide of transition metal such as V2O5, MnO2, TiS2, MoS2and MoO3; PbO2, AgO, NiOOH and the like.

The solid polymer electrolyte is not specifically limited and it may be any ion-conducting polymer. For example, polyethylene oxide (PEO), polypropylene oxide (PPO) or copolymer of these may be available. Such a polyalkylene oxide based polymer easily dissolves lithium salt such as LiBF4, LiPF6, LiN(SO2CF3)2, or LiN(SO2C2F5)2. The solid polymer electrolyte is included in at least one of cathode active material layer28and anode active material layer26. More preferably, the solid polymer electrolyte is included both in cathode active material layer28and anode active material layer26.

As the supporting electrolyte, Li(C2F5SO2)2N, LiBF4, LiPF6, LiN(SO2C2F5)2or a mixture of these may be used. As the electron conduction assistant, acethylene black, carbon black, graphite or the like may be used.

Anode active material layer26includes an anode active material layer and a solid polymer electrolyte. Anode active material layer may contain a supporting electrolyte (lithium salt) for improving ion conductivity, a conduction assistant for improving electron conductivity, NMP (N-methyl-2-pyrolidone) as a solvent for adjusting slurry viscosity, AIBN (azobisisobutyronitrile) as a polymerization initiator or the like.

As the anode active material layer, a material generally used in a lithium ion secondary battery may be used. If a solid electrolyte is used, however, it is preferred to use a composite oxide of carbon or lithium and metal oxide or metal, as the anode active material layer. More preferably, the anode active material layer is formed of a composite oxide of carbon or lithium and transition metal. Further preferably, the transition metal is titanium. Specifically, it is more preferred that the anode active material layer is of a composite oxide of titanium and lithium or a titanium oxide.

As the solid electrolyte forming electrolyte layer27, by way of example, a solid polymer electrolyte such as polyethylene oxide (PEO), polypropylene oxide (PPO) or copolymer of these may be used. The solid electrolyte contains supporting electrolyte (lithium salt) for ensuring ion conductivity. As the supporting salt, LiBF4, LiPF6, LiN(SO2CF3)2, LiN(O2C2F5)2or a mixture of these may be used.

Specific examples of materials for cathode active material layer28, anode active material layer26and electrolyte layer27are listed in Tables 1 to 3. Table 1 shows specific examples when electrolyte layer27is of an organic solid electrolyte, Table 2 shows specific examples when electrolyte layer27is of an inorganic solid electrolyte, and Table 3 shows specific examples when electrolyte layer27is of a gel electrolyte.

It most cases, the electrolyte used in a secondary battery is liquid. By way of example, in a lead storage battery, dilute sulfuric acid is used as the electrolytic solution. Positive collector electrode23and negative collector electrode21have some degree of strength. In Embodiment 1, each of the plurality of bipolar secondary batteries4is sandwiched between positive collector electrode23and negative collector electrode21. When positive collector electrode23and negative collector electrode21are sandwiched between bipolar secondary batteries4, a space between positive collector electrode23and bipolar secondary battery4or a space between negative collector electrode21and bipolar secondary battery4can be eliminated. Thus, strength of battery assembly100can be ensured.

FIG. 6is a schematic cross-sectional view showing a vehicle mounting battery assembly100in accordance with Embodiment 1.

Referring toFIG. 6, a vehicle1is, for example, an electric vehicle using a rechargeable electric power supply as a power source, or a hybrid vehicle using an internal combustion engine such as a gasoline engine or a diesel engine and a rechargeable electric power supply as the power sources. Battery assembly100shown inFIG. 1is mounted as a power source in such a vehicle.

In a passenger space (vehicle interior)50of vehicle1, a front seat12and a rear seat6are arranged. In the passenger space50, battery pack120including battery assembly100shown inFIG. 1is arranged below front seat12. Battery pack120is surrounded by a cover5arranged below front seat12and a floor300. It is easier to make a space for housing battery pack120below front seat12, than at other portions of vehicle1. In most cases, a vehicle body consists of a portion that collapses and a portion that does not collapse but protects an occupant or occupants at the time of a crash. Specifically, by arranging battery pack120below front seat12, it becomes possible to protect battery assembly100against any shock, if the vehicle body is hard hit.

Referring toFIGS. 7 to 13, a cooling apparatus for a battery assembly in accordance with Embodiment 2 of the present invention will be described. The same components as in the battery assembly100and its cooling apparatus200in accordance with Embodiment 1 above are denoted by the same reference characters, and description thereof will not be repeated.

FIG. 7is a plan view of negative collector electrode21provided at battery assembly100in accordance with Embodiment 2. As shown inFIG. 7, openings60to63are formed around connection hole a1of terminal portion T1.

Around the openings60to63, guide walls60ato63aare formed for guiding cooling air shown inFIG. 1to openings60to63.

Guide walls60ato63aare formed by cutting and folding parts of terminal portion T1, when openings60to63are formed. Therefore, guide walls60ato63acan be formed without increasing the number of components.

When air flows from the direction R shown inFIG. 7, the air is guided by guide walls60ato63ato openings60to63.

Therefore, the air supplied by fan53shown inFIG. 1to terminal portions T1and T2passes through openings60to63, and flows threading through front and rear surfaces of terminal portions T1and T2. Therefore, flow path of the air passing through terminal portions T1and T2becomes longer, and the distance over which heat exchange takes place between the air and the surfaces of terminal portions T1and T2increases. Thus, terminal portions T1and T2can be cooled well.

Heat generation is highest at the connection hole a1that is in contact with wire U1. By arranging openings60to63and guide walls60ato63aaround connection hole a1, heat generated at connection hole a1can effectively be radiated. This reduces temperature increase of terminal portion T1. Partial degradation of electrode sheet25shown inFIG. 5, caused when only a part of the sheet positioned close to terminal portion T1has its temperature increased and electrode reaction at that portion is activated, can be prevented.

Further, guide walls60ato63aguide air and are cooled by heat exchange with the air, contributing to cooling of battery assembly100.

In the present embodiment, fan53is adopted as the air supplying mechanism. An air inlet that takes in air as the vehicle moves may be adopted.

FIG. 8is a plan view showing an example, different from that ofFIG. 7, of the arrangement of guide walls60ato63a, andFIG. 9is a cross-sectional view taken along the line IX-IX ofFIG. 8.

As shown inFIGS. 8 and 9, guide walls60ato63ainclude guide walls60aand62athat guide the air from the rear surface side to the front surface side of terminal portion T1and guide walls61aand63aguiding the air from the front surface side to the rear surface side, arranged alternately.

By arranging guide walls60ato63ain this manner, longer air flow path can be provided, and terminal portion T1can be cooled satisfactorily.

FIG. 10is a plan view showing a first modification of terminal portion T1, andFIG. 11is a cross-sectional view taken along the line XI-XI ofFIG. 10.

As shown inFIGS. 10 and 11, of the guide walls60ato63a, guide walls60aand63aformed on the upstream side of air passage may be inclined such that the air is guided from the rear surface side to the front surface side of terminal portion T1, and guide walls61aand62aformed on the downstream side may be inclined such that the air is guided from the front surface side to the rear surface side of terminal portion T1.

By inclining each of the guide walls60ato63ain this manner, longer air flow path can be provided, and air flow resistance is made smaller, so that fresh air can successively be supplied to housing51.

FIG. 12is a cross-sectional view showing a second modification of terminal portion T1, and as shown inFIG. 12, at opening edges of openings60to63, guide walls60a1to63a2may be formed at upstream and downstream portions in the direction of air flow.

FIG. 13is a perspective view showing a third modification of terminal portion T1. As shown inFIG. 13, rolled members70may be formed on opposite sides of connection hole a1, by rolling parts of terminal portion T1. Rolled members70are formed on opposite sides of connection hole a1, by rolling portions70aextending outward than connection hole a1. Rolled members80are arranged such that opposite end portions are arranged along the flow direction of supplied air.

Rolled member70is rolled to form spaces inside and, therefore, when air is fed from one end surface, the air escapes from the other end surface. By the air flowing through rolled member70, rolled member70is cooled, and battery assembly100can be cooled. As the rolled member70has large surface, the effect of cooling battery assembly100can be improved.

Alternatively, the surface area of terminal portion T1may be increased by curving terminal portion T1in a wavy shape, or by forming protrusions/recesses at terminal portion T1, to improve the effect of heat radiation at terminal portion T1.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a battery assembly formed by stacking a plurality of battery cells, and it is particularly suitable to a battery assembly formed by stacking a plurality of bipolar secondary batteries.