Abstract:
A battery includes an electrode group, a case, a sealing member, and a mesh portion. The electrode group includes a positive electrode, a negative electrode opposing the positive electrode, an electrolyte interposed between the positive electrode and the negative electrode. The case has an opening and contains the electrode group. The sealing member closes the opening of the case. The mesh portion is provided so as to face an exhaust hole formed in at least one of the case and the sealing member. The mesh is formed of a thermally conductive material to put off frame coming out of the exhaust hole, in case where the battery is so defective to ignite fire.

Description:
RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. JP2008-053000 filed on Mar. 4, 2008, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a battery including a case containing a positive electrode and a negative electrode that are disposed with a separator sandwiched therebetween, a battery pack having an enclosure containing the battery and a circuit, and a method of manufacturing a connection terminal for making up the battery pack. 
     2. Background Art 
     Recently, with the widespread of portable and cordless electronic equipment, batteries as driving power sources of the equipment have been increasingly used. Among them, compact and lightweight secondary batteries having large energy density such as nickel hydrogen storage batteries and lithium ion batteries have received attention. 
     However, cases have been reported that lithium ion batteries cause firing due to contamination of conductive foreign matters in a cell during manufacture or failure in a safety protection function of a pack circuit. In order to address such problems of firing, a configuration in which a fire-extinguishing agent is provided inside a battery, and a configuration in which a fire-extinguishing agent is provided inside a battery pack containing batteries have been proposed. 
     However, the configuration in which a fire-extinguishing agent is provided in a battery or a battery pack is disadvantageous to miniaturization of the battery or the battery pack. When the miniaturization of a battery or a battery pack is hindered, a miniaturization of equipment incorporating the battery or the battery pack may be hindered. 
     SUMMARY OF THE INVENTION 
     A battery of the present invention includes an electrode group, a case, a sealing member, and a mesh portion. The electrode group includes a positive electrode, a negative electrode opposing the positive electrode, an electrolyte interposed between the positive electrode and the negative electrode. The case has an opening and contains the electrode group. The sealing member closes the opening of the case. The mesh portion is provided so as to face an exhaust hole formed in at least one of the case and the sealing member. 
     Furthermore, a battery pack of the present invention includes a battery, a connection terminal, an enclosure, and a mesh portion. The battery includes an electrode group, a case and a sealing member. The electrode group includes a positive electrode, a negative electrode facing the positive electrode, an electrolyte interposed between the positive electrode and the negative electrode. The case has an opening and contains the electrode group. The sealing member closes the opening of the case. An exhaust hole is formed on at least one of the case and the sealing member. The connection terminal is electrically connected to the battery. The enclosure contains the battery and the connection terminal. The mesh portion is provided so as to face the exhaust hole. 
     Furthermore, in a method of manufacturing a connection terminal of the present invention, firstly, a plurality of staggered holes are formed on a metal plate except for a band-shaped portion. Then, the portion provided with the staggered holes is stretched in the direction away from the band-shaped portion, thereby forming a mesh portion from the portion provided with the staggered holes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a battery in accordance with a first embodiment of the present invention. 
         FIG. 2A  is a plan view of the battery shown in  FIG. 1 . 
         FIG. 2B  is a perspective view of the battery shown in  FIG. 2A . 
         FIG. 3A  is a plan view showing a state in which a connection terminal is connected to the battery shown in  FIG. 2A . 
         FIG. 3B  is a perspective view showing a state in which a connection terminal is connected to the battery shown in  FIG. 2B . 
         FIG. 4A  is an exploded perspective view showing a principal part of a battery in accordance with a second embodiment of the present invention. 
         FIG. 4B  is a perspective view showing a principal part of the battery shown in  FIG. 4A . 
         FIG. 5  is a perspective view of a battery in accordance with a third embodiment of the present invention. 
         FIG. 6A  is a plan view of a battery in accordance with a fourth embodiment of the present invention. 
         FIG. 6B  is a perspective view of the battery shown in  FIG. 6A . 
         FIG. 7A  is a perspective view of a battery in accordance with a fifth embodiment of the present invention. 
         FIG. 7B  is a perspective view of another battery in accordance with the fifth embodiment of the present invention. 
         FIG. 8A  is a configuration view of a battery pack in accordance with a sixth embodiment of the present invention. 
         FIGS. 8B to 9B  are configuration views of other battery packs in accordance with the sixth embodiment of the present invention. 
         FIGS. 10A and 10B  are configuration views showing a principal part of other battery packs in accordance with the sixth embodiment of the present invention. 
         FIG. 11  is a plan view showing a principal part of a battery pack in accordance with a seventh embodiment of the present invention. 
         FIG. 12  is a plan view showing a principal part of another battery pack in accordance with the seventh embodiment of the present invention. 
         FIG. 13  is a plan view showing a principal part of a battery pack in accordance with an eighth embodiment of the present invention. 
         FIGS. 14A and 14B  are views showing a method of manufacturing a connection terminal used in a battery pack in accordance with a ninth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention are described with reference to drawings. Note here that the present invention is not necessarily limited to the below-mentioned embodiments as long as it is based on the basic features described in the specification. 
     First Embodiment 
       FIG. 1  is a sectional view of a battery in accordance with a first embodiment of the present invention, and  FIG. 2  is a plan view and a perspective view thereof. A battery in this embodiment includes a lithium ion battery as a nonaqueous electrolyte secondary battery as a component. 
     Battery main body  1  made of a cylindrical lithium ion battery includes electrode group  7  in which positive electrode  3  and negative electrode  5  opposing positive electrode  3  are wound via separator  6 . Positive electrode  3  includes positive electrode lead  2  made of, for example, aluminum. At one end of negative electrode  5 , negative electrode lead  4  made of, for example, copper is provided. 
     Insulating plates  8   a  and  8   b  are mounted on the upper and lower parts of electrode group  7 . In this state, electrode group  7  is inserted into case  9 , another end of positive electrode lead  2  is welded to sealing member  10 , and another end of negative electrode lead  4  is welded to the inner bottom of case  9 . 
     Furthermore, a nonaqueous electrolyte (not shown) conducting lithium ion is filled in case  9  and an opening end portion of case  9  is caulked to sealing member  10  via gasket  11 . Positive electrode  3  has positive current collector  3   a  and positive electrode mixture layer  3   b  including a positive electrode active material. Negative electrode  5  has negative electrode current collector  5   a  and negative electrode active material layer  5   b  formed of columnar bodies. 
     Sealing member  10  has junction portion  10   a , safety valve  10   b , safety valve holder  10   c , current-limiting element  10   d , and positive terminal  10   e . An end of positive electrode lead  2  is welded to junction portion  10   a . When an internal pressure of case  9  is increased, safety valve  10   b  ruptures before case  9  is destroyed, thus reducing the internal pressure of case  9 . Safety valve holder  10   c  holds safety valve  10   b . Current-limiting element  10   d  is located between safety valve  10   b  and safety valve holder  10   c , and prevents a not less than a specified current from flowing. Junction portion  10   a , safety valve  10   b , safety valve holder  10   c , current-limiting element  10   d  and positive terminal  10   e  are electrically connected to each other at the edge portions. 
     Furthermore, each element of sealing member  10  except for safety valve  10   b  is provided with a vent hole. The vent hole formed in positive terminal  10   e  is exhaust hole  12  from which a gas is discharged when the internal pressure of case  9  is increased and safety valve  10   b  ruptures. Three to four exhaust holes  12  are formed in a circular arrangement at substantially equal intervals on the upper part of positive terminal  10   e . The thus configured sealing member  10  together with case  9  defines a contour of battery main body  1 . 
     Mesh portion  13  made of incombustible, thermally conductive and electrically conductive wires is provided on positive terminal  10   e  so as to face exhaust hole  12 . The wire of mesh portion  13  is formed of stainless steel (SUS), an elemental substance such as copper, nickel, aluminum, iron, gold, platinum, and silver, or plurality of layers of a plated substance or a clad. Mesh portion  13  is fixed to positive terminal  10   e  by using a conductive adhesive or by ultrasonic welding or resistance welding, and the like. 
     Mesh portion  13  is formed in a circular shape (or disk-like shape) as shown in  FIGS. 2A and 2B , and is disposed in such a manner that it overlaps with the entire surface of the upper end portion of battery main body  1  including positive terminal  10   e . However, mesh portion  13  may not cover entire exhaust hole  12 . Mesh portion  13  may be provided to face exhaust hole  12  so that a gas or a flame passes through mesh portion  13  when the gas or the flame is discharged from exhaust hole  12 . However, it is preferable that mesh portion  13  covers exhaust hole  12 . Thus, flames discharged from exhaust hole  12  are brought into contact with mesh portion  13  without fail. As a result, the flames can be extinguished reliably. 
     Furthermore, it is preferable that mesh portion  13  covers an opening of case  9  when exhaust hole  12  is formed in sealing member  10 . Thus, flames are brought into contact with mesh portion  13  without fail regardless of the direction in which the flames are discharged from exhaust hole  12 . Moreover, mesh portion  13  covers an opening of case  9  provided with sealing member  10  having exhaust hole  12 . Thus, mesh portion  13  can be extended without increasing the size of a battery, so that the heat capacity of mesh portion  13  is increased and the heat absorbing effect is strengthened. Consequently, the flames can be extinguished more reliably. 
     When the hole size of mesh portion  13  is too small, mesh portion  13  blocks flames and bounces the flames back. When the hole size is too large, the heat exchange efficiency drops and heat cannot be absorbed efficiently. Thus, flames cannot be extinguished. Therefore, the hole size is preferably, for example, not smaller than 0.1 mm×0.1 mm and not larger than 3.0 mm×3.0 mm. The preferable size is similarly applied to mesh portions in other embodiments. 
     An example of materials to be used for positive current collector  3   a  includes aluminum (Al), carbon, electrically conductive resin, and the like. Furthermore, any of these materials may be subjected to surface treatment with carbon and the like. 
     Positive electrode mixture layer  3   b  includes a lithium-containing composite oxide such as LiCoO 2 , LiNiO 2 , LiMnO 4 , or a mixed compound thereof or a composite compound thereof as the positive electrode active material. As the positive electrode active material, besides the above-mentioned materials, olivine-type lithium phosphate expressed by the general formula: LiMPO 4  (M represents V, Fe, Ni or Mn) and lithium fluorophosphate expressed by the general formula: Li 2 MPO 4 F (M represent V, Fe, Ni or Mn) can be used. Furthermore, a part of the constituent elements of these lithium-containing compounds may be substituted by a different kind of element. The surface of lithium-containing compounds may be treated with metallic oxide, lithium oxide, conductive agent, and the like. The surface of lithium-containing compounds may be subjected to hydrophobic treatment. 
     Positive electrode mixture layer  3   b  may further include a conductive agent and/or a binder. An example of the conductive agent may include graphites including natural graphites and artificial graphites; carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lampblack and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as aluminum powders; conductive whiskers of zinc oxide, potassium titanate, and the like; conductive metallic oxide such as titanium oxide; an organic conductive material such as phenylene derivatives, and the like. 
     For negative electrode current collector  5   a , a metal foil of SUS, nickel, copper, titanium, and the like, and a thin film of carbon and conductive resin, and the like, may be used. In addition, such material can be subjected to a surface treatment with carbon, nickel, titanium, and the like 
     A material of the columnar bodies constituting negative electrode active material layer  5   b  may include an active material such as silicon (Si) and tin (Sn) capable of reversibly absorbing and releasing lithium ions and having a theoretical capacity density of more than 833 mAh/cm 3 . Negative electrode active material layer  5   b  may be formed by using fine particles of a negative electrode active material, and a conductive agent and a binder similar to those for positive electrode mixture layer  3   b  in addition to the above-mentioned columnar bodies. In this case, as the negative electrode active material, in addition to the above-mentioned materials, carbon materials capable of reversibly absorbing and releasing lithium ions may be used. 
     As the nonaqueous electrolyte, an electrolyte solution obtained by dissolving a solute in an organic solvent, a polymer electrolyte layer containing such an electrolyte solution and immobilized by a polymer can be used. When the electrolyte solution is used, it is preferable that separator  6  such as a non-woven fabric and a microporous membrane is used between positive electrode  3  and negative electrode  5 , and separator  6  is impregnated with an electrolyte solution. An example of materials of separator  6  includes polyethylene, polypropylene, aramid resin, amide-imide, polyphenylene sulfide, polyimide, and the like. 
     Furthermore, the inside or on the surface of separator  6 , a heat resistant filler such as alumina, magnesia, silica, and titania may be included. Besides separator  6 , a heat resistant layer composed of such heat resistant filler and a binder similar to that used for positive electrode  3  or negative electrode  5  may be provided. 
     The material of the nonaqueous electrolyte is selected based on the oxidation-reduction potential of each active material. An example of a solute preferably used for the nonaqueous electrolyte may include salts generally used in a lithium battery, for example, LiPF 6 , LiBF 4 , LiClO 4 , LiAlCl 4 , LiSbF 6 , LiSCN, LiCF 3 SO 3 , LiNCF 3 CO 2 , LiAsF 6 , LiB 10 C 10 , lower aliphatic lithium carboxylate, LiF, LiCl, LiBr, LiI, chloroborane lithium, bis(1,2-benzenedioleate(2-)-O,O′)borate, lithium bis(2,3-naphthalenedioleate(2-)-O,O′)borate, lithium bis(2,2′-biphenyldioleate(2-)-O,O′)borate, lithium bis(5-fluoro-2-oleate-1-benzenesulfonate-O,O′)borate and other borates, (CF 3 SO 2 ) 2 NLi, LiN(CF 3 SO 2 )(C 4 F 9 SO 2 ), (C 2 F 5 SO 2 ) 2 NLi, lithium tetraphenyl borate, and the like. 
     Furthermore, as an example of an organic solvent in which the above-mentioned salts are dissolved, for example, ethylene carbonate (EC), propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate (EMC), dipropyl carbonate, methyl formate, methyl acetate, methyl propionate, ethyl propionate, dimethoxymethane, γ-butyrolactone, γ-valerolactone, 1,2-diethoxyethane, 1,2-dimethoxyethane, ethoxymethoxyethane, trimethoxy methane, tetrahydrofuran, tetrahydrofuran derivative such as 2-methyltetrahydrofuran, dimethyl sulfoxide, dioxolane derivative such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, formamide, acetamide, dimethylformamide, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphotriester, acetic acid ester, propionic acid ester, sulfolane, 3-methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, ethyl ether, diethyl ether, 1,3-propanesultone, anisole, and fluorobenzene, may be used singly or may be in a combination of one or more thereof. 
     In this way, it is possible to use a solvent that is generally used in a lithium battery. 
     Furthermore, an additive such as vinylene carbonate, cyclohexylbenzene, biphenyl, diphenyl ether, vinyl ethylene carbonate, divinyl ethylene carbonate, phenylethylene carbonate, diallyl carbonate, fluoroethylene carbonate, catechol carbonate, vinyl acetate, ethylene sulfite, propanesultone, trifluoropropylene carbonate, dibenzofuran, 2,4-difluoroanisole, o-terphenyl, and m-terphenyl may be included. 
     Note here that a nonaqueous electrolyte may be used as a solid electrolyte obtained by mixing the above-mentioned solute in one or more of polymer materials such as polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene. Furthermore, it may be used as a gel-state mixture with the above-mentioned organic solvent. 
     Furthermore, an inorganic material such as lithium nitride, lithium halide, lithium oxoate, Li 4 SiO 4 , Li 4 SiO 4 —LiI—LiOH, Li 3 PO 4 —Li 4 SiO 4 , Li 2 SiS 3 , Li 3 PO 4 —Li 2 S—SiS 2 , a phosphorus sulfide compound, and the like, may be used as a solid electrolyte. 
     When a gel-state nonaqueous electrolyte is used, a gel-state nonaqueous electrolyte instead of a separator may be disposed between positive electrode  3  and negative electrode  5 . Alternatively, the gel-state nonaqueous electrolyte may be disposed in the vicinity of separator  6 . 
       FIGS. 3A and 3B  are a plan view and a perspective view each showing a configuration in which connection terminals  14  and  15  are connected to a battery in accordance with this embodiment, respectively. Connection terminal  14  is electrically connected to positive terminal  10   e  via mesh portion  13 . Connection terminal  15  is electrically connected to a bottom of case  9  serving as a negative terminal. Since mesh portion  13  has electric conductivity, it does not prevent connection terminal  14  and positive terminal  10   e  from being electrically connected to each other. 
     With the above-mentioned configuration, in the battery in accordance with this embodiment, even if a flame is discharged from exhaust hole  12  for some cause, the flame is extinguished by the heat absorbing effect of mesh portion  13 . This is because when the flame discharged from exhaust hole  12  is brought into contact with mesh portion  13 , the heat of burning gas becomes lower than the combustion temperature by the heat absorbing effect of mesh portion  13 . Then, extinguished gas passes through mesh portion  13 . Consequently, it is possible to minimize the damage to the surrounding, for example, a flame spreading to the surrounding. Moreover, since a gas discharged from an exhaust hole passes through mesh portion  13 , it is possible to prevent battery main body  1  from being destroyed due to the increase in the internal pressure and to prevent the damage to the surrounding by the destruction. Furthermore, mesh portion  13  facing exhaust hole  12  can be formed without substantially changing the size of the battery. Therefore, it can be used as a battery of equipment whose containing volume is limited, in particular, mobile equipment. 
     Note here that in a battery in accordance with this embodiment, case  9  serves as a negative terminal, and sealing member  10  is provided with positive terminal  10   e . However, the present invention is not necessarily limited to this configuration. The present invention can be executed by a configuration in which case  9  serves as a positive terminal and sealing member  10  serves as a negative terminal. The same is true in the below-mentioned embodiments. 
     Note here that this battery can be electrically connected to connection terminal  14  via mesh portion  13 . Thus, this battery can be handled similarly to a conventional battery without including mesh portion  13  and can be used in a wide application of use. 
     Furthermore, in a battery in accordance with this embodiment, battery main body  1  is a lithium ion battery. However, the present invention is not necessarily limited to this. For example, other batteries such as a manganese dioxide—lithium primary battery, a carbon fluoride—lithium primary battery, a thionyl chloride battery, and a sodium sulfur battery, and electrochemical element such as an electric double layer capacitor can be used as battery main body  1 . 
     Second Embodiment 
       FIGS. 4A and 4B  show a principal part of a battery in accordance with a second embodiment of the present invention. In the first embodiment, mesh portion  13  is provided on positive terminal  10   e  of sealing member  10 . Meanwhile, mesh portion  13  is provided on connection terminal  14  in this embodiment. 
     Mesh portion  13  and connection terminal  14  are fixed to each other by using a conductive adhesive, or by ultrasonic welding or resistance welding. For example, positive terminal  10   e  of battery main body  1  which is a lithium ion battery shown in  FIGS. 1 to 3  is electrically connected to connection terminal  14 . At this time, battery main body  1  and connection terminal  14  are disposed in such a manner that mesh portion  13  faces exhaust hole  12 . 
     Although battery main body  1  and mesh portion  13  are not fixed directly to each other, a configuration in which mesh portion  13  is located to face exhaust hole  12  is included in the present invention. 
     In the battery in accordance with this embodiment, when connection terminal  14  is connected to positive terminal  10   e , it is necessary to adjust the position of mesh portion  13  with respect to exhaust hole  12 . However, battery main body  1  can be stored and handled separately from mesh portion  13  that needs to be carefully in order not to be deformed or destroyed, thus facilitating assembling operation as a whole. 
     Third Embodiment 
       FIG. 5  is a perspective view showing a battery in accordance with a third embodiment of the present invention. The battery in accordance with this embodiment includes, for example, mesh portion  16  that covers only exhaust hole  12  formed on positive terminal  10   e  of battery main body  1 . 
     With this configuration, a gas or a flame discharged from exhaust hole  12  passes through mesh portion  16  reliably. Consequently, the flame can be extinguished by the heat absorbing effect of mesh portion  16 . Furthermore, since a gas passes through mesh portion  16 , destruction of battery main body  1  can be prevented. 
     Furthermore, since mesh portion  16  does not protrude from the contour of battery main body  1 , the battery can be stored and handled easily. Moreover, connection terminal connected to positive terminal  10   e  need not to be subjected to processing or dimensional coordination, conventionally used connection terminals and the configurations of battery packs can be used. 
     Fourth Embodiment 
       FIG. 6A  and  FIG. 6B  are a plan view and a perspective view each showing a configuration of a battery in accordance with a fourth embodiment of the present invention, respectively. Mesh portion  17  of the battery in accordance with this embodiment is formed in a cylindrical shape. Mesh portion  17  covers an opening of battery main body  1  including positive terminal  10   e  of a sealing member (not shown) having an exhaust hole (not shown). 
     Since the exhaust hole is covered with mesh portion  17 , a gas or a flame discharged from an exhaust hole passes through mesh portion  17  without fail. Thus, the flame can be extinguished reliably. In particular, since mesh portion  17  is formed in a cylindrical shape, a surface area is increased and the thermal capacity is increased. Therefore, the heat absorbing effect becomes higher and the probability that flames can be extinguished reliably and rapidly increases. Furthermore, since the heat of flames expanding along mesh portion  17  is absorbed by mesh portion  17  extending to the side surface of case  9 , flames can be extinguished more reliably. 
     Fifth Embodiment 
       FIG. 7A  is a perspective view showing a configuration of a battery in accordance with a fifth embodiment of the present invention. Battery main body  18  of a battery in accordance with this embodiment includes exhaust holes not only on a sealing member at an opening located on the upper side of battery main body  18  but also on a bottom of case  9 A defining a contour of battery main body  18 . Since a safety valve is provided also on the bottom of case  9 A, contents of battery main body  18  do not flow out unless the internal pressure of battery main body  18  is increased to the specified value or more. 
     Since mesh portion  13  facing an exhaust hole (not shown) of a sealing member provided on an opening of battery main body  18  is the same as mesh portion  13  shown in  FIG. 2 , the description thereof is omitted. Mesh portion  19  is formed in a disk-like shape (circular shape) similar to mesh portion  13 . Since the size of mesh portion  19  is the same as that of the bottom surface of battery main body  18 , this battery can be stored and handled easily as in battery main body  18  alone. 
     It is preferable that the exhaust hole is formed on the bottom surface of case  9 A and mesh portion  19  covers the bottom of case  9 A in this way. Thus, even when the exhaust hole is formed on the bottom surface, it is possible to extinguish a discharged flame and to prevent the flame from spreading to the surrounding of battery main body  18 . 
       FIG. 7B  is a perspective view showing another configuration of a battery in accordance with the fifth embodiment of the present invention. This battery is different from the battery shown in  FIG. 7A  in that mesh portion  17  is used instead of mesh portion  13  and mesh portion  20  is used instead of mesh portion  19 . Since mesh portion  17  is the same as mesh portion  17  shown in  FIG. 6 , the description thereof is omitted herein. Mesh portion  20  is formed in a cylindrical shape similar to mesh portion  17 . Since mesh portion  20  is formed so as to oppose the side surface of case  9 A, heat capacity is increased and a larger excellent extinguishing effect can be expected. Furthermore, since the heat of flames expanding along mesh portion  20  is absorbed by mesh portion  20  extending to the side surface of case  9 A, flames can be extinguished more reliably. 
     Note here that  FIGS. 7A and 7B  show a configuration in which an exhaust hole (not shown) is formed in a sealing member of an opening of battery main body  18 . However, an exhaust hole may be formed only on the bottom of the case constituting battery main body  18  without forming an exhaust hole on a sealing member, and mesh portion  19  or mesh portion  20  may be applied. Furthermore, depending upon the inside configuration of battery main body  18 , an exhaust hole may be formed in a portion other than the bottom of the case and the portion in which the exhaust hole is formed may be covered with a mesh portion. 
     Sixth Embodiment 
       FIG. 8A  is a configuration view showing a battery pack in accordance with a sixth embodiment of the present invention. Battery pack  31  of this embodiment includes circuit  32 , battery  33 , connection terminals  35  and  36 , enclosure  70  containing them therein, and partition  37 . Connection terminals  35  and  36  connect circuit  32  to battery  33 . Partition  37  separates a portion for containing circuit  32  from a portion for containing battery  33 . 
     Battery pack  31  is incorporated and used in mobile equipment such as notebook-sized personal computer in a state in which battery pack  31  contains circuit  32  and battery  33 . Battery  33  has an exhaust hole (not shown) only on the upper part in the drawings. Connection terminal  35  is provided with circular shaped mesh portion  38  according to the exhaust hole of battery  33 . Mesh portion  38  is disposed to face the exhaust hole formed on battery  33 . That is to say, mesh portion  38  is the same as mesh portion  13  shown in  FIG. 4B . Therefore, it is preferable that mesh portion  38  covers the exhaust hole of battery  33 . 
       FIG. 8B  is a configuration view showing another battery pack in accordance with the sixth embodiment of the present invention. Battery pack  31 A is different from battery pack  31  shown in  FIG. 8A  in that battery  34  is used instead of battery  33  and mesh portion  39  is used on the lower part of battery  34 . 
     Battery  34  has an exhaust hole (not shown) also on the lower part in addition to the upper part. Connection terminal  36  is provided with circular shaped mesh portion  39  with respect to the exhaust hole on the lower part of battery  34 . Mesh portion  39  is also disposed so as to face the exhaust hole formed on battery  34 . 
     When the internal pressure of batteries  33  and  34  is increased to the specified value or higher, safety valves rupture and a gas or a flame is discharged from the exhaust holes for some causes, the flame or gas is extinguished by mesh portions  38  and  39 . Therefore, it is possible to prevent the flame from spreading to the surrounding of batteries  33  and  34 . Furthermore, since mesh portions  38  and  39  can be formed without substantially changing the size of batteries  33  and  34 , the size of the battery pack is not substantially changed. Therefore, it can be used as a battery of equipment whose containing volume is limited, in particular, mobile equipment. 
     It is preferable that enclosure  70  and partition  37  are made of flame retardant materials, for example, phenolic resin, glass epoxy resin, and UNILATE® so as to minimize the damage to circuit  32  and equipment to be used. 
       FIG. 9A  is a configuration view showing a further battery pack in accordance with the sixth embodiment of the present invention. In battery pack  31  B, mesh portion  40  is formed in a cylindrical shape. Mesh portion  40  covers an opening of a case constituting battery  33  and covers an exhaust hole. That is to say, mesh portion  40  is the same as mesh portion  17  shown in  FIG. 6A . That is to say, a part of mesh portion  40  covering an opening of the case of battery  33  is disposed so as to oppose the side surface of the case. With this configuration, since a flame discharged from an exhaust hole (not shown) of battery  33  passes through mesh portion  40  without fail, the flame can be extinguished by the heat absorbing effect of mesh portion  40  whose heat capacity is large. Moreover, without increasing the size of battery  33 , mesh portion  40  can be expanded. 
       FIG. 9B  is a configuration view showing a yet further battery pack in accordance with the sixth embodiment of the present invention. In battery pack  31  C, mesh portion  41  is also formed in a cylindrical shape on the lower side of battery  34  in addition to mesh portion  40 . Mesh portion  41  is disposed in such a manner that a part of mesh portion  41  opposes the lower side surface of battery  34  and covers an exhaust hole (not shown) formed on the bottom surface of battery  34 . Since a flame discharged from the exhaust hole formed on the bottom surface of battery  34  passes through mesh portion  41  without fail, the flame can be extinguished by the heat absorbing effect of mesh portion  41  whose heat capacity is large. 
       FIGS. 10A and 10B  are configuration views showing a principal part of other battery packs in accordance with the sixth embodiment of the present invention. In battery packs  31  to  31 C shown in  FIGS. 8A to 9B , connection terminal  35  is electrically connected to the battery via a mesh portion at the end portion thereof. On the other hand, connection terminals  42  shown in  FIGS. 10A and 10B  are electrically connected to the battery via a mesh portion at the middle portion other than the end portion. 
     Connection terminals  35  shown in  FIGS. 8A through 9B  are positioned and fixed at a position along the inner wall surface of enclosure  70 . Consequently, the tip portion of connection terminal  35  has a degree of freedom. On the other hand, connection terminal  42  has a shape in which the tip portion is further extended. With this shape, the tip portion of connection terminal  42  can be positioned and fixed on the inner wall surface of enclosure  70 . 
     With this configuration, the degree of freedom of the position of connection terminal  42  is controlled, so that displacement and tilt of mesh portions  38  and  40  provided on connection terminal  42  can be prevented. As a result, the displacement in positional relation between the exhaust hole of battery  33  and mesh portions  38  and  40  can be controlled, so that the extinguishing effect by mesh portions  38  and  40  can be sufficiently exhibited. 
     Seventh Embodiment 
       FIGS. 11 and 12  are plan views showing a principal part of a battery pack in accordance with a seventh embodiment of the present invention. A battery pack in this embodiment contains a plurality of batteries  51  in which a mesh portion is disposed so as to face an exhaust hole of each batteries  51 . Note here that an enclosure and the like are omitted in the drawings. 
       FIG. 11  shows a battery pack containing two batteries  51 , and  FIG. 12  shows a battery pack containing six batteries  51 . In both cases, band-shaped connection terminals  53  and  54  electrically connect circuit (not shown) to batteries  51 . Accordance to the shapes of connection terminals  53  and  54 , mesh portions  55  and  56  are attached to connection terminals  53  and  54 . 
     As shown in  FIG. 11 , when two batteries  51  are contained, connection terminal  53  is formed in a linear shape. Then, mesh portion  55  is disposed on the upper part of batteries  51  each having an exhaust hole (not shown) thereon in such a manner that mesh portion  55  faces each of the exhaust holes. 
     In order to extinguish a flame discharged from the exhaust holes, mesh portion  55  may be disposed only on the upper part of battery  51 . However, as shown in  FIG. 11 , mesh portion  55  has middle portion  55   a  that is a portion other than the upper part of batteries  51  according to the shape of connection terminal  53 . With such a configuration, the heat capacity of mesh portion  55  is increased and a flame extinguishing effect is improved. Furthermore, the strength of mesh portion  55  is improved and the displacement and tilt can be suppressed. Thus, the positional relation with respect to the exhaust holes can be kept appropriately and the extinguishing effect can be maintained. 
     As shown in  FIG. 12 , when six batteries  51  are contained, connection terminal  54  is formed in a parallelogram shape according to the arrangement of batteries  51 . Then, mesh portion  56  is disposed on the upper part of batteries  51  each having an exhaust hole (not shown) thereon in such a manner that mesh portion  56  faces each of the exhaust holes. 
     In order to extinguish a flame discharged from the exhaust holes, mesh portion  56  may be disposed only on the upper part of batteries  52 . However, mesh portion  56  has middle portion  56   a  that is other than the upper part of batteries  51  according to the shape of connection terminal  54 . With such a configuration, the heat capacity of mesh portion  56  is increased, and a flame extinguishing effect is improved. Furthermore, the strength of mesh portion  56  is improved and displacement and tilt can be suppressed. Thus, the positional relation with respect to the exhaust holes can be kept appropriately and the extinguishing effect can be maintained. 
     Eighth Embodiment 
       FIG. 13  is a plan view showing a principal part of a battery pack in accordance with an eighth embodiment of the present invention. A battery pack in accordance with this embodiment contains a plurality of batteries  57  in which mesh portion  59  is disposed so as to face an exhaust hole of each battery  57 . Note here that an enclosure and the like are omitted in the drawing. 
     Also in this battery pack, band-shaped connection terminal  58  electrically connects a circuit (not shown) to four batteries  57 . Mesh portion  59  is formed according to the shape of connection terminal  58  and attached to connection terminal  58 . 
     However, mesh portion  59  faces not all exhaust holes  57 a formed on the upper part of battery  57 . That is to say, mesh portion  59  is disposed so as to face exhaust holes facing the other batteries among exhaust holes  57 a of four batteries  57 . In other words, mesh portion  59  is disposed so as to face exhaust holes that may heat other batteries due to a discharged flame. Thus, even if one of the plurality of contained batteries  57  fires, a flame discharged from exhaust holes facing the other batteries  57  is brought into contact with mesh portion  59  without fail. As a result, heat is deprived off and the flame is extinguished. Consequently, flame spreading to the other batteries  57  that do not fire can be prevented. With this configuration, it is possible to prevent a flame from spreading from one battery to another by using the necessary minimum members. That is to say, fire spreading can be prevented while preventing the size of a battery pack from increasing. 
     Ninth Embodiment 
       FIGS. 14A and 14B  are views showing a method of manufacturing a connection terminal used in a battery pack in accordance with a ninth embodiment of the present invention. 
     As shown in  FIG. 14A , firstly, metal plate  61  made of nickel or copper is provided with staggered holes  63  except for a part of connection terminal  62  formed in a band shape. The shape of hole  63  is preferably rhombus. However, the shape is not necessarily limited to rhombus. 
     Thereafter, a portion provided with holes  63  is stretched in the direction away from connection terminal  62 , thereby expanding holes  63 . As a result, as shown in  FIG. 14B , it is possible to form mesh portion  64  formed along band-shaped connection terminal  62 . 
     Thus, in the method of manufacturing a connection terminal used in a battery pack in accordance with this embodiment, connection terminal  62  provided with mesh portion  64  is manufactured by the above-mentioned processes. Thus, since mesh portion  64  and connection terminal  62  are formed together, handling of a battery pack at the time of manufacturing becomes easy. Moreover, an operation for fixing and connecting between mesh portion  64  and connection terminal  62  is not necessary, and an optimum connection terminal according to the arrangement of a battery pack and a battery can be manufactured easily. Furthermore, heat conduction between mesh portion  64  and connection terminal  62  is large, so that the heat absorbing effect with respect to the heat of a flame can be also increased. 
     That is to say, it is preferable that mesh portion  64  is provided with connection terminal  62 . Thus, mesh portion  64  is held by connection terminal  62  fixed inside a battery pack. Therefore, the position of mesh portion  64  can be kept stably inside the battery pack, and the positional relation with respect to an exhaust hole of a battery can be kept appropriately. Moreover, since the heat of a flame discharged from the exhaust hole of the battery is absorbed by not only mesh portion  64  but also connection terminal  62 , the extinguishing function is improved. Consequently, a flame can be extinguished for a shorter time. 
     Furthermore, it is preferable that connection terminal  62  is formed in a band shape, and mesh portion  64  is provided along connection terminal  62 . Mesh portion  64  is formed along connection terminal  62  to expand an area, and thereby the heat absorbing effect of mesh portion  64  can be improved and the flame extinguishing function can be improved. Moreover, since mesh portion  64  is provided along connection terminal  62 , even when an area of mesh portion  64  is expanded, the position of mesh portion  64  can be kept stably inside the battery pack. 
     Note here that in the above description, a configuration in which a mesh portion is disposed between a battery and a connection terminal. The present invention is not necessarily limited to this configuration. The mesh portions may be disposed on the connection terminal connected to the battery. 
     Furthermore, a cylindrical battery is described as an example. However, the shape of a battery is not particularly limited. 
     Furthermore, a battery pack having circuit  32  is described in the sixth to eighth embodiments. However, circuit  32  is not essential. 
     As mentioned above, the present invention is useful for realizing a nonaqueous electrolyte secondary battery having an increased capacity and high reliability, which is expected to be demanded in the future.