Abstract:
There is disclosed a battery system comprising a battery pack. Within the battery pack is a plurality of cells, which are electrically connected by physical contact between electrical terminals of adjacent cells. A resistive heater is attached to at least some of the electrical terminals in the battery pack to thereby warm the cells to a more optimum operating temperature in response to a sensed temperature.

Description:
PRIORITY CLAIM 
       [0001]    The present application claims priority to the following Chinese Patent Applications, which are hereby incorporated by reference: 
         [0002]    1) Chinese Patent Application No. 200810217018.1 (docket no. 081483), filed Oct. 10, 2008; 
         [0003]    2) Chinese Patent Application No. 200820116496.9 (docket no. 080394), filed Jun. 30, 2008; 
         [0004]    3) Chinese Patent Application No. 200810145734.3 (docket no. 080932), filed Aug. 14, 2008; 
         [0005]    4) Chinese Patent Application No. 200810135478.X (docket no. 080933), filed Aug. 7, 2008; 
         [0006]    5) Chinese Patent Application No. 200810135477.5 (docket no. 080934), filed Aug. 7, 2008; 
         [0007]    6) Chinese Patent Application No. 200810142082.8 (docket no. 081178), filed Aug. 27, 2008; 
         [0008]    7) Chinese Patent Application No. 200810142090.2 (docket no. 081180), filed Aug. 27, 2008; 
         [0009]    8) Chinese Patent Application No. 200820146848.5 (docket no. 081181), filed Aug. 27, 2008; 
         [0010]    9) Chinese Patent Application No. 200820146851.7 (docket no. 081183), filed Aug. 27, 2008; 
         [0011]    10) Chinese Patent Application No. 200820146849.X (docket no. 081184), filed Aug. 27, 2008; 
         [0012]    11) Chinese Patent Application No. 200810142084.7 (docket no. 081185), filed Aug. 27, 2008; 
         [0013]    12) Chinese Patent Application No. 200810142085.1 (docket no. 081186), filed Aug. 27, 2008; 
         [0014]    13) Chinese Patent Application No. 200810142089.X (docket no. 081187), filed Aug. 27, 2008; 
         [0015]    14) Chinese Patent Application No. 200810142086.6 (docket no. 081188), filed Aug. 27, 2008; 
         [0016]    15) Chinese Patent Application No. 200810142087.0 (docket no. 081189), filed Aug. 27, 2008; 
         [0017]    16) Chinese Patent Application No. 200810142088.5 (docket no. 081190), filed Aug. 27, 2008; 
         [0018]    17) Chinese Patent Application No. 200810142080.9 (docket no. 081192), filed Aug. 27, 2008; 
         [0019]    18) Chinese Patent Application No. 200810142083.2 (docket no. 081191), filed Aug. 27, 2008, and 
         [0020]    19) Chinese Patent Application No. 200720196395.2 (docket no. 071593), filed Dec. 25, 2007. 
       BACKGROUND 
       [0021]    1. Technical Field 
         [0022]    The present application is directed to battery cells and systems and, more particularly, to lithium ion battery cells and systems that may be used in a vehicle, such as an electric and/or hybrid vehicle, having an electric drive motor. 
         [0023]    2. Related Art 
         [0024]    Re-chargeable batteries, such as lithium ion polymer batteries, have a wide range of applications. These include, for example, laptop batteries, cell phone batteries, as well as power for other personal electronic devices. Such devices require low weight batteries having a moderate power output. However, lithium ion polymer batteries are also capable of providing power to devices needing substantially more power output than the personal electronic devices noted above. For example, high output lithium ion polymer batteries may be used to power industrial equipment, high power communications facilities, mobile vehicles, etc. The use of high output lithium ion polymer battery systems may be particularly significant in the area of mobile vehicle propulsion. 
         [0025]    The public has become increasingly sensitive to cost and environmental issues associated with the use of fossil-based fuels. One concern is the emissions from vehicles burning fossil-based fuels and the corresponding pollution. 
         [0026]    Alternatives to such vehicles include electric vehicles that are solely driven by electric motors, and hybrid electric vehicles that employ both electric motors and fossil-based fuel engines. These alternatives are likely to play an increasingly important role as substitutes for current vehicles. 
         [0027]    Although consumers are attracted to the environmental benefits of pure electric and hybrid vehicles, they want vehicles which use electric motors to have the same general characteristics as their fossil-fuel counterparts. Battery performance and safety issues must be overcome to achieve these goals. To this end, lithium ion batteries are preferable to other more conventional battery types. Lithium ion batteries are useful for this purpose in that they have a high energy density which reduces the amount of space needed for the battery in the vehicle. Further, they may be constructed so that they weigh less than the more conventional battery types. 
         [0028]    Battery systems for use with electric motors employed in pure electric and hybrid vehicles are currently deficient in many respects. Individual battery cells of the battery system are frequently heavy, bulky, and unreliable. Further, current battery cells are neither constructed nor used to effectively provide the high power output needed to accelerate the vehicle at an acceptable acceleration level. Still further, individual battery cells use electrochemistry, cell core constructions, electrical interconnections, and shell constructions that are often unreliable, unsafe, and generally not suitable for use in electrical powered vehicles. 
         [0029]    To overcome the power deficiencies associated with individual battery cells, attempts have been made to interconnect multiple individual battery cells with one another so that their combined power output provides the necessary driving power. The interconnections between the individual battery cells, again, are often unreliable. Further, little has been accomplished to ensure the safety of such multi-cell battery systems. Short-circuits as well as explosions have not been adequately addressed. High power output battery systems must be constructed to address issues such as performance, longevity, reliability, and safety if they are to find a place in the large number of applications available to such systems. 
       SUMMARY 
       [0030]    There is disclosed a battery system comprising a battery pack. Within the battery pack is a plurality of cells, which are electrically connected by physical contact between electrical terminals of adjacent cells. A resistive heater is attached to at least some of the electrical terminals in the battery pack to thereby warm the cells to a more optimum operating temperature in response to a sensed temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views. 
           [0032]      FIG. 1  is a cross-sectional view through an exemplary multilayer battery sheet that may be used to form a coiled battery core. 
           [0033]      FIG. 2A  is a perspective view of a flattened coiled core used in a battery cell. 
           [0034]      FIGS. 2B-2D  show an alternative embodiment of a core where the sheets forming the core are not coiled. 
           [0035]      FIG. 3  is an exploded view of the anode end of a battery cell  300  having the coiled core of  FIG. 2A . 
           [0036]      FIG. 4  is a schematic view through a cross-section of battery cell  300 . 
           [0037]      FIGS. 5 and 6  illustrate one manner of forming the regions of the anode sheet and/or cathode sheet which are proximate the exposed substrates. 
           [0038]      FIG. 7  is a cross-sectional view of one example of a coiled core. 
           [0039]      FIG. 8  shows one embodiment of a frangible bent connector. 
           [0040]      FIG. 9  illustrates a further embodiment of a frangible bent connector. 
           [0041]      FIG. 10  shows how the bent connector of  FIG. 8  may be used to interconnect adjacent battery cells. 
           [0042]      FIG. 11  shows another structure for interconnecting adjacent battery cells. 
           [0043]      FIGS. 12 and 13  show a connection structure that may be utilized to bring the core of a battery cell to an optimal operating temperature. 
           [0044]      FIG. 14A  shows one manner of connecting a multiple core battery cell to the bent connector of  FIG. 8 . 
           [0045]      FIG. 14B  shows one manner of connecting a single core structure of a battery cell to the bent connector of  FIG. 8 . 
           [0046]      FIG. 15  is a plan view of a gasket used at each end of the protective shell of the battery cell. 
           [0047]      FIGS. 16 and 17  show one manner of sealing the end of the protective shell that surrounds the periphery of the coiled core. 
           [0048]      FIGS. 18-20  show one embodiment of a blow out assembly that may be used on the end cover assembly of a battery cell. 
           [0049]      FIGS. 21 and 22  show alternative pressure relief structures that may be used to supplement and/or replace the blow out assembly shown in  FIG. 18 . 
           [0050]      FIG. 23  is a block diagram of a battery pack in which multiple battery cells are interconnected with one another and grouped within a single housing. 
           [0051]      FIGS. 24 through 26  illustrate one embodiment of a housing that may be used to form a battery pack. 
           [0052]      FIG. 27  shows a connector that may be used to mechanically and electrically interconnect adjacent battery packs. 
           [0053]      FIG. 28  shows how the connector of  FIG. 27  may be used. 
           [0054]      FIG. 29  shows a battery system that supplies electrical power to and receives electrical power from a motor/generator of a vehicle capable of being driven by electric power. 
           [0055]      FIGS. 30 through 34  illustrate advantages associated with providing connections to the anode and cathode of a coiled core at opposite ends of the core. 
           [0056]      FIGS. 35-41  illustrate further battery cell interconnection structures. 
           [0057]      FIG. 41A  illustrates a frangible connection structure having a thermally activated severing clamp. 
           [0058]      FIGS. 42 through 46  illustrate battery cell interconnection structures where the terminals of the battery cells are interconnected with one another by a bridge connector. 
           [0059]      FIGS. 47 and 48  illustrate battery cell interconnection structures having gravity assisted overcurrent protection substructures. 
           [0060]      FIGS. 49 through 51  illustrate battery cell interconnection structures having a thermal expansion structure that separates the battery cell terminals as a result of overcurrent conditions. 
           [0061]      FIGS. 52 and 53  illustrate battery cell interconnection structures having overcurrent protection substructures based on chemical interaction between a chemical released by the substructure and one or more portions of the terminals/terminals of the battery cell interconnection. 
           [0062]      FIGS. 54-60  illustrate battery cell interconnection structures having overcurrent protection substructures based on electrical connections/disconnections provided by the presence/absence of a liquid conductor. 
           [0063]      FIGS. 61 through 64  illustrate various embodiments of a protection cover for the end cover assembly of the battery cell. 
           [0064]      FIGS. 65 through 67  illustrate a further embodiment of a blow out vent. 
           [0065]      FIG. 68  shows a further embodiment of a connector that may be used to mechanically and electrically interconnect adjacent battery packs. 
           [0066]      FIG. 69  shows how the connectors of  FIG. 27 and 68  may be used when the battery packs are configured in a side-to-side arrangement. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0067]    Lithium-ion polymer batteries are a type of rechargeable battery in which a lithium ion moves between an anode and cathode. The lithium ion moves from the anode to the cathode during discharge and from the cathode to the anode when charging. 
         [0068]      FIG. 1  is a cross-sectional view through an exemplary multilayer battery sheet  100  that may be wound to form a coiled battery core. The battery sheet  100  of  FIG. 1  includes three functional components: an anode sheet  105 , a cathode sheet  110 , and a separator sheet  115 . The anode sheet  105  may include active anode layers  106  disposed on opposite sides of an anode substrate  107 . The anode substrate  107  may be formed from one or more layers of a metal foil, such as copper. The active anode layers  106  may be formed from graphite or other carbon-based material. In one example, active layers  106  of the anode sheet  105  may be produced using  100  grams of natural graphite with 3 grams of polyvinylidene fluoride (PVDF) binder material and  3  grams of acetylene black conductive agent to 100 grams of NI-methylpyrrolidone (NMP). The components may be mixed in a vacuum mixer into a uniform slurry. The slurry may be applied as a coating of about 12 microns thick to each side of substrate  107 , such as a copper foil, to form a structure having a combined layer thickness of about 100-110 μm. The coated foil may then be dried at a temperature of about 90° C. to form the anode  115 . 
         [0069]    The cathode sheet  110  may include active cathode layers  112  disposed on opposite sides of a cathode substrate  114 . The cathode substrate  114  may be formed from one or more layers of a metal foil, such as aluminum. The active cathode layers  112  may be formed from materials such as a layered oxide (e.g., lithium cobalt oxide), a material based on a polyanion (e.g., lithium iron phosphate), or a spinel (e.g., lithium manganese oxide), although materials such as TiS 2  (titanium disulfide) may also be used. 
         [0070]    In one example, the active layers  1   12  of the cathode sheet  110  may be formed by combining at least one lithium metal compound with at least one mixed metal crystal, wherein the mixed metal crystal includes a mixture of metal elements and metal oxides. The lithium compound may be a metal intercalation compound that has the general formula LiM a N b XO c , wherein M is a first-row transition metal such as Fe, Mn, Ni, V, Co and Ti; N is a metal selected from the group Fe, Mn, Ni, V, Co, Ti, Mg, Ca, Cu, Nb, Zr and rare-earth metals; X is selected from elements P, Si, S, V and Ge; and a, b and c have values that render the metal intercalation compound charge-neutral. The metal compound may have the general formula M c Nd, wherein M is a metal selected from IA,  11 A, IIIA, IVA, VA, IIIB, IVB and VB groups in the periodic table; N is selected from O, N, H, S, SO4, PO4, OH, Cl, F, and C; and 0&lt;c5.4 and 0&lt;d56. In other instances, the metal compound may include one or more members selected from the group consisting of MgO, SrO, Al 2 O 3 , SnO 2 , Sb 2 O 3 , Y 2 O 3 , TiO 2  and V200. The metal compound and the lithium compound may be heated or sintered at about 600-900° C. in an inert gas or reducing gas atmosphere for about 2 hours to form the material for the cathode sheet  110 . 
         [0071]    In a further example, the metal compound may be formed as a mixed crystal compound with the general formula LiaA 1—y B y (X04)b/McNd, wherein: A is a first-row transition metal including Fe, Mn, Ni, V, Co and Ti; B is a metal selected from the group Fe, Mn, Ni, V, Co, Ti, Mg, Ca, Cu, Nb, Zr and rare-earth metals; X is selected from elements P, Si, S, V and Ge; M is metal selected from groups IA, IIA, IIIA, IVA, VA, IIIB, IVB and VB of the periodic table; N is selected from O, N, H, S, SO4, PO4, OH, Cl, F and C; and wherein 0&lt;a51, 05y50.5, 0&lt;b51, 0&lt;c5.4 and 0&lt;d56. Particle sizes may be less than about 10 um, with 3-5 um being preferable. 
         [0072]    The active cathode material may include a first crystalline compound and a second crystalline compound. The first crystalline compound may be distributed within the second crystalline compound to form a composite compound. The first crystalline compound may be prepared by heating a combination of at least one lithium source, at least one iron source, and at least one phosphate source while the second crystalline compound may be prepared by heating at least two metal compounds. The second crystalline compound may also include one or more members selected from groups IA, IIA, IIIA, IVA, VA, IIIB, IVB and VB of the periodic table. 
         [0073]    During formation of the active cathode material, a large number of crystal defects may be introduced within the intermediary or composite crystals such that the electronic states and formation of the metal oxides are altered or changed. The metal compound with its mixed crystalline structure, therefore, may include a large number of oxygen vacancies and missing oxygen atoms. The oxygen vacancies may facilitate carrier conduction thereby enhancing the conductivity of the mixed crystal. To this end, the metal compound may have a smaller crystal lattice than the lithium compound so that it is received or distributed within the lithium compound. Alternatively, the metal compound may be received or distributed between two or more large crystal lattices. Still further, the metal compound may reside within grain boundaries of the lithium compound. Lastly, the metal compound may be dispersed about the exterior grain surfaces of the lithium compound. In each instance, lithium ion migration serves as a bridge either within a crystal lattice or in between two or more crystal lattices. The lithium ions may be fully released for enhanced electrical properties including electrical conductance, capacitance and recyclability. 
         [0074]    Preferably, the metal compound may be distributed within a lithium iron phosphate compound to form a composite compound for use in the cathode sheet  110 . The metal compound may be distributed within the lithium iron phosphate compound to form a mixed crystal. In one instance, the lithium iron phosphate compound and the metal compound may have molar ratios of about 1 to 0.001-0.1. The cathode material may be doped with carbon additives scattered between grain boundaries or coated on the grain surfaces. The doped carbon additive may provide the final cathode material product with 1-15% of carbon by weight. The carbon additive may include one or more members selected from the group consisting of carbon black, acetylene black, graphite and carbohydrate compound. 
         [0075]    The composite compound may include a lithium source, iron source, phosphate source and second crystalline compound having a Li:Fe:P:crystalline compound molar ratios of about 1:1:1:0.001-0.1. In other instances, various Li:Fe:P:crystalline compound molar ratios may be adopted. The lithium source may include one or more members selected from the group consisting of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide and lithium dihydrogen phosphate. The iron source may include one or more members selected from the group consisting of ferrous oxalate, ferrous acetate, ferrous chloride, ferrous sulfate, iron phosphate, ferrous oxide, ferric oxide, iron oxide and ferric phosphate. The phosphate source may include one or more members selected from the group consisting of ammonium, ammonium phosphate, ammonium dihydrogen phosphate, iron phosphate, ferric phosphate and lithium hydrogen phosphate. 
         [0076]    A method of preparing a mixed crystal lithium iron phosphate cathode material includes evenly mixing at least one LiFePO4 compound with a mixture compound and heating the resulting mixture to 600-900° C. in an inert gas or reducing gas atmosphere for between about 2-48 hours. The mixture compound may include two or more metal oxides wherein the metal can be selected from groups IA, IIA, IIIA, IVA, VA, IIIB, IVB and VB of the periodic table. The mixture compound provides a mixed crystalline structure, wherein a method of preparing the mixture compound with the corresponding mixed crystalline structure includes mixing metal oxides from groups IA, IIA, IIIA, IVA, VA, IIIB, IVB and VB, and heating the mixture to 600-1200° C. for between 2-48 hours. 
         [0077]    One method of preparing a mixed crystal cathode material includes evenly mixing lithium, iron and phosphate sources and heating them to 600-900° C. in an inert gas or reducing gas atmosphere for at least about 2 hours. The resulting mixture can then be combined with the mixed metal compound having a combination of two or more metal oxides selected from groups IA, IIA, IIIA, IVA, VA, IIIB, IVB and VB of the periodic table. In one embodiment, the lithium source, iron source, phosphate source and mixed metal compound are capable of providing Li:Fe:P:mixed metal compound molar ratios of 1:1:1:0.0010.1. In other embodiments, different Li:Fe:P:mixed metal compound molar ratios may be adopted. Furthermore, at least one carbon source can be added to the resulting mixture, the carbon source including one or more of the following without limitation: carbon black, acetylene black, graphite and carbohydrate compound. The amount of carbon source added to the resulting mixture should be able to provide the final product with 1-15% of carbon by weight. 
         [0078]    The lithium sources used to form the cathode material may include one or more of the following compounds without limitation: lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide and lithium dihydrogen phosphate. Iron sources include one or more of the following compounds without limitation: ferrous oxalate, ferrous acetate, ferrous chloride, ferrous sulfate, iron phosphate, ferrous oxide, ferric oxide, iron oxide and ferric phosphate. When using a trivalent iron compound as a source of iron, the ball milling process may include the addition of a carbon source to reduce the trivalent iron to a divalent iron. Phosphorous sources may include one or more of the following compounds without limitation: ammonium, ammonium phosphate, ammonium dihydrogen phosphate, iron phosphate, ferric phosphate and lithium hydrogen phosphate. 
         [0079]    During the grinding in a ball mill, one or more solvents may be introduced including ethanol, DI water and acetone. In other, embodiments, other mixing media and solvents may be utilized. In addition, the mixture can be dried between 40-80° C. or stirred until dry. 
         [0080]    The types of inert gases that may be utilized include helium, neon, argon, krypton, xenon, radon and nitrogen. Additionally, reducing gases including hydrogen and carbon monoxide can also be incorporated. Other suitable gases may also be adopted. 
         [0081]    The cathode sheet  110  may be formed using a cathode slurry that includes one of the foregoing active cathode materials. The cathode slurry may be formed by mixing a thickener, the active cathode material, and a solvent. First, the thickener and the solvent are mixed to provide a colloidal solution. The resulting colloidal solution, residual solvent, and the active material are mixed in a double planetary mixer. A portion of the solvent as well as a binder are then provided to the planetary mixer for further mixing. 
         [0082]    The colloidal solution, the active cathode material, and solvent may be mixed in the double planetary mixer in accordance with a specified mixing sequence. To this end, the colloidal solution, the active material, and the solvent may be mixed for about 3-5 minutes at a rotation frequency of about 2-20 Hz that decreases to a lower rotation frequency of about 0-2 Hz. Next, the colloidal solution, the active material, and the solvent may be mixed for about 30-50 minutes at a rotation frequency between about 35-60 Hz that decreases to a lower rotation frequency between about 35-60 Hz. At this point, the double planetary mixer may generate a vacuum lasting about 3-5 minutes so that the mixing takes place at a pressure of about 0.0005 MPa to about 0.05 MPa. The residual solvent and the adhesives are then added to the double planetary mixer and mixed for about 5-10 minutes at a rotation frequency of about 35-60 Hz that decreases to a lower rotation frequency between about 35-60 Hz. Again, the double planetary mixer may generate a vacuum lasting about 3-5 minutes so that the mixing takes place at a pressure of about 0.0005 MPa to about 0.05 MPa. The mixing then takes place between about 20-35 minutes at a rotation frequency that decreases from about 10-25 Hz to about 0 Hz. 
         [0083]    The proportion by weight of the active material of cathode, the thickener, the adhesives and the solvent may be about 100: (0.05-10): (0.01-10): (50-150). The proportion by weight of the solvent mixed with the thickener may be about 60-90%. When mixed with the colloidal solution and active material, the proportion by weight of the solvent may be about 0.1-30%, and may be about 8-20% when with binder is added. 
         [0084]    The cathode sheet  110  may be formed by coating a conductive substrate, such as an aluminum foil, with the slurry. The slurry may be applied onto the conductive substrate using a rolling operation, although other application methods may be employed. The conductive substrate and slurry are then dried to form the cathode sheet  110 . The cathode sheet  110  preferably has a thickness between 100 and 110 μm, although other thicknesses may also be used. 
         [0085]    The separator sheet  115  may be a micro-porous polypropylene and/or polyethylene electrolytic membrane. Such membranes are available from US Celgard of Charlotte, N.C. 
         [0086]    With reference again to  FIG. 1 , the anode sheet  105  includes a region in which the substrate  107  of the anode sheet  105  does not include active anode layers  106 . Rather, the copper substrate  107  is exposed to facilitate electrical connection with the anode sheet  105 . The exposed region of substrate  107  extends substantially along the entire length of the anode sheet  105  so that the first edge of the anode sheet  105  defines a conductive region  107  when the battery sheet  100  is wound to form a coiled core  200  (see  FIG. 2 ). The exposed region of substrate  107  may be formed by limiting the area to which the active anode layers  106  are applied to the substrate  107 . Additionally, or alternatively, the exposed region of substrate  107  may be formed after the application of the active anode layers  106  by selectively removing the active anode layers  106  from the substrate  107  along a predetermined width of the anode sheet  105 . This removal may be accomplished using a mechanical removal technique and/or chemical removal technique. 
         [0087]    The cathode sheet  110  includes a region in which the substrate  114  of the cathode sheet  110  does not include active cathode layers  112 . Rather, the aluminum substrate  112  is exposed to facilitate electrical connection with the cathode sheet  110 . The exposed region of substrate  112  extends substantially along the entire length of the cathode sheet  110  so that an edge of the cathode sheet  110  defines a conductive region  114  when the battery sheet  100  is wound to form the coiled core  200  of  FIG. 2A . The exposed region of substrate  114  may be formed by limiting the area to which the active cathode layers  112  are applied to the substrate  114 . Additionally, or alternatively, the exposed region of substrate  114  may be formed after the application of the active cathode layers  112  by selectively removing the active cathode layers  112  from the substrate  114  along a predetermined width of the cathode sheet  110 . This removal may be accomplished using a mechanical removal technique and/or chemical removal technique. 
         [0088]    As shown in  FIG. 2A , the anode sheet  105 , cathode sheet  110 , and separator sheet  115  may be wrapped to form the coiled core  200 . The exposed substrate  114  forms a multilayer current collector structure for the cathode of the coiled core  200  while the exposed substrate  107  forms a multilayer current collector structure for the anode of the coiled core  200 . The current collector for the cathode and current collector for the anode are disposed at opposite ends of the length of the core  200  and provide low resistance contacts that may carry a substantial amount of current. Forming the current collectors at opposite sides of the coiled core  200  also simplifies the manufacturing process. 
         [0089]    The current collectors may be formed in a number of different manners. For example, the current collectors may be formed solely from the exposed substrate layers. Additionally, or in the alternative, the current collectors may be formed by attaching a conductive ribbon of material along a length of each of the anode and cathode sheets, respectively, prior to or after winding. 
         [0090]    The exterior layer of the coiled core  200  may be an insulator. In one example, the separator sheet  115  is longer than the anode sheet  105  and cathode sheet  110 . As such, the anode sheet  105  and cathode sheet  110  are terminated in the wrapping operation before the end of the separator sheet  115  is reached. The excess length of the separator  105  is then wrapped about the core  200  a predetermined number of times (e.g., two or more) to form the exterior insulating layer  115 . This construction simplifies the manufacturing of the core  200  and, further, increases the homogeneity of the core structure. 
         [0091]    Once the coiled core  200  has been formed, the exposed layers of the anode substrate  107  and cathode substrate  114  are compressed to change their shape so that the outside cross-sectional area of each end portion of the coiled core  200  is less than the interior cross-sectional area of the core  200 . To this end, the exposed layers of the anode substrate  107  of the coiled core  200  may be welded to one another, secured to one another with a mechanical fastener, and/or secured to one another using an adhesive, etc. Preferably, the exposed layers of the anode substrate  107  are secured with one another by compressing them together, welding them together along the entire length or portions of the length of the exposed substrate  107  to form a single anode current collector structure. The layers of the cathode substrate  114  may be formed in a similar manner as the layers of the anode substrate  107 . 
         [0092]    An alternative structure for the core  200  is shown in  FIGS. 2B through 2D . In this embodiment, multiple anode sheets, cathode sheets, and separator sheets are layered adjacent one another. However, unlike the previously described core structure, the sheets forming the core are not wound to form a coil. Rather, the core  200  is comprised of a plurality of planar sheets, such as shown in the arrangement of  FIG. 2B . Preferably, the end sheets of the core  200  are insulator sheets and, more preferably, one or more separator sheets  115 . A top plan view of this embodiment of the core  200  is shown in  FIG. 2C  while a side plan view is shown in  FIG. 2D . As illustrated, the insulator/separator sheets preferably extend beyond the lateral edges of the stacked cathode and anode sheets and may be wrapped around the side edges to isolate the cathode and anode sheets from one another. Alternative methods for sealing the stacked cathode and anode sheets to prevent undesired contact between them and to prevent environmental exposure may also be used. Although the current collectors  114  and  107  of  FIGS. 2B through 2D  are formed from the substrate layers of the anode and cathode sheet material, they may also be formed as ribbons that are connected to the individual stacked substrate layers. 
         [0093]      FIG. 3  shows an exploded view of the anode end of a battery cell  300  having the coiled core  200  (not shown but implied in  FIG. 3 ). In  FIG. 3 , battery cell  300  includes a protective shell  305  that receives the coiled core  200 . Current collector  310  electrically engages a first end  320  of a connection structure  325  through an end cover assembly  335 . A second end  330  of the connection structure  325  extends through a corresponding cover plate/end cap  335  to provide an exterior contact for the anode of the battery cell  300 . 
         [0094]    As shown in  FIG. 3 , the protective shell  305  is rectangular in shape and is dimensioned so that the core  200  fits snugly within its interior. Although the shell  305  (and, as such, core  200 ) may have various dimensions, protective shell  305  may have a width W and a height H, where W is greater than about 50 mm and H is greater than about 100 mm. Preferably, the ratio between the width and height of the shell  305  corresponds to the following equation: 
         [0000]      0.18 &lt;W/H&lt; 0.5 
         [0095]    This relationship is also suitable to generally define the dimensions of the core  200 , and is particularly well-suited when the battery cell  300  is a high capacity, high power output battery. 
         [0096]    When the W/H ratio is larger than 0.5, the width of the battery cell  300  is very large, and the total surface area of the shell  305  may not be capable of withstanding the pressure generated within its interior thereby causing it to fail and/or distort. This may create a safety/security risk. When the W/H ratio is smaller than 0.18, the height of the battery cell  300  is very small, so that the battery cell  300  is very thin. The available volume available to the core  200  within the protective shell  305  is quite small and does not favor the accommodation of a high capacity, high current core. 
         [0097]      FIG. 4  is a schematic view through a cross-section of battery cell  300 . In this example, the connection structure  325  includes an angled connector  405  that extends through cover plate/end cap  335 . Here, the angled connector  405  is substantially Z-shaped. Current collector  310  may be formed in the manner described above. For simplicity, the current collector  310  of  FIG. 4  only illustrates a single anode current collector strip. A flexible connection piece  410  electrically connects the angled connector  405  to the current collector  310 . The flexible connection piece  410  may include multiple metal foil layers, such as copper, that have been annealed and welded to both the angled connector  405  and the current collector  310 . A similar technique may be used to connect the cathode collector to a corresponding angled connector of a connection structure. However, the flexible connection piece between the angled connector and the cathode current collector may be formed from multiple aluminum foil layers that have been annealed and welded to both the angled connector and cathode current collector. The use of this type of interconnection structure facilitates the ease with which a battery using coiled core  200  may be manufactured. Further, the interconnection structure may be used to provide a low resistance, high current path through the battery. Still further, this structure may be used to dissipate heat thereby promoting battery safety. 
         [0098]      FIGS. 5 and 6  show one manner of forming the regions of the anode sheet  105  and/or cathode sheet  110  which are proximate the exposed substrates  107  and/or  114 , respectively. Only the region proximate the exposed substrate  107  is described, although the corresponding region proximate the exposed substrate  114  may have the same basic structure. 
         [0099]    In  FIGS. 5 and 6 , the anode sheet  105  has a total width  505 . The active layers  106  of the anode sheet  105  are applied along a width  510  of the sheet leaving an uncoated region having a width  515 . Alternatively, the uncoated region may be formed by removing a portion of the active component of the anode sheet  105 . The coating of the active component is gradually thinned at the edge of the sheet along a width  520 . In the region to the left of region  520 , layers  106  are formed to their full thickness. Thinning begins at a coating thickness transition region  525 . An insulating plaster or coating is applied along region  530 . The width of the plaster (coated with insulating coatings) fully covers the thinning coating area on the conductive substrate and terminates in an area that exposes the conductive substrate. The plaster/coating should be electron or/and ion insulating, and capable of maintaining its integrity at high temperatures. One such coating is polyphenylene sulfide (PPS). Using this configuration reduces the possibility that a short circuit will occur between the anode and cathode. Further, thinning the coating in the described manner reduces wrinkling that may otherwise result from roller pressing a coating having a thick edge. 
         [0100]      FIG. 7  is a cross-sectional view of one example of a coiled core  200 . In a coiled core, variable thicknesses and/or forces on the core  200  at opposed regions A and B may be problematic. To limit such problems, the anode sheet  105  and cathode sheet  110  terminate at opposed arcuate regions C and D instead of terminating at opposed planar regions A and B. As shown in  FIG. 7 , the anode sheet  105  terminates at  705  of region C while the cathode sheet  110  terminates at  710  of region D. The separator sheet  115  extends beyond the termination points  705  and  710  so that it wraps around to form the outer portion of the core  200 . The separator sheet  115  terminates at  715  along an arced side of the core  200 . The direction in which the sheets are wound to form the core  200  is designated by arrow  720 . In this structure, the cathode sheet  110  may be longer than the anode sheet  105 . 
         [0101]    In accordance with the construction of the core  200  shown in  FIG. 7 , regions A and B are substantially flat and do not have significant thickness variations. As a result, there is a reduction in wrinkles that would otherwise form through swelling of the core  200  during electrolyte soakage as well as during charging and discharging of the battery cell. Such wrinkles occur when the forces on the core  200  at regions A and B are substantially non-uniform. By reducing this wrinkling, the lifespan of the core may be increased. Similarly, hidden safety issues caused by the non-uniform charging or discharging of the core  200  are addressed (e.g., situations in which a wrinkled area of the core  200  produces lithium dendrites that cause a short inside the battery resulting in an explosion). 
         [0102]      FIG. 8  illustrates one embodiment of a bent connector  800  that may be used in the connection structure  325  of  FIG. 4 . Bent connector  800  is formed from a conductive material that is suitable for establishing an electrical connection as well as a mechanical bond with the material used to form connector  410  of  FIG. 4  and preferably has a width that is at least  25 % of the width W of the protective shell  305 . The bent connector  800  of  FIG. 8  is generally Z-shaped and includes a first arm  805  and second arm  810  that extend in opposite directions from a transverse portion  815 . The second arm  810 , as will be described below, extends from an interior to an exterior portion of the battery cell where it engages transverse portion  815 . Transverse portion  815  is positioned exterior to the battery cell where it electrically connects the second arm  810  with the first arm  805 . First arm  805  effectively forms an electrical terminal of the battery that may be used to access the anode (or cathode) of the coiled core  200 . 
         [0103]    Bent connector  800  may include a weakening structure, such as groove  820 , which causes the bent connector  800  to break its electrical connection with the core  200  under certain extraordinary forces, such as those that occur when the vehicle is involved in an accident. In  FIG. 8 , a single groove  820  extends substantially along a width of the transverse member  820 . Additionally, or alternatively, groove  820  may extend along a length of the first arm  805  exterior to the battery cell  300  and/or along a portion of the second arm  810  exterior to the battery cell  300 . Multiple weakening structures may also be used. 
         [0104]    Depending on the electrical resistance characteristics of the material forming the bent connector  800 , the groove  820  may increase the resistance in an undesirable manner. In such instances, groove  820  may be filled with a conductive material that is mechanically ductile. A number of materials are suitable for this purpose including, without limitation, tin, conductive rubber, and other conductive ductile materials. The resistance of the area having the groove  820  is thus decreased while the overall safety characteristic that the groove is meant to enhance remains. 
         [0105]      FIG. 9  illustrates a further embodiment of a bent connector  900  that may be used in the connection structure  325  of  FIG. 4 . Bent connector  900  is formed from a conductive material that is suitable for establishing an electrical connection as well as a mechanical bond with the material used to form connector  410  of  FIG. 4 . The bent connector  900  of  FIG. 9  is generally L-shaped and includes an arm  910  that extends from an interior to an exterior portion of the battery cell where it engages transverse portion  915 . Transverse portion  915  is positioned exterior to the battery cell. Transverse portion  915  effectively forms an electrical terminal of the battery that may be used to access the anode (or cathode) of the coiled core  200 . 
         [0106]    Bent connector  900  may include a weakening structure, such as groove  920 , which causes the bent connector  900  to break its electrical connection in the region of the weakening structure. More particularly, the bent connector  900  breaks its electrical connection with the core  200  when subject to certain extraordinary forces, such as those that occur when the vehicle is involved in an accident/collision. In  FIG. 9 , a single groove  920  extends substantially along a width of the transverse member  915 . Additionally, or alternatively, groove  820  may extend along a length of the arm  910  at a portion of the arm  910  that is exterior to the battery cell. Multiple weakening structures may also be used. 
         [0107]    Depending on the electrical resistance characteristics of the material forming the bent connector  900 , the groove  920  may increase the resistance in an undesirable manner. In such instances, groove  920  may be filled with a conductive material that is mechanically ductile. A number of materials are suitable for this purpose including, without limitation, tin, conductive rubber, and other conductive ductile materials. The resistance of the area having the groove  920  is thus decreased while the overall safety characteristic that the groove is meant to enhance remains. 
         [0108]    The dimensions of the grooves  820  and  920  of the bent connectors  800  and  900  are dependent on the material used to form the connectors  800  and  900 . If the bent connector is formed from copper, the depth of the corresponding groove may be approximately 50%-90% of the thickness of the transverse portion. The width of the groove along the transverse portion may be between about 100%-500% of the depth of the groove. If the bent connector is formed from aluminum, the depth of the corresponding groove may be approximately 30%-80% of the thickness of the transverse portion. The width of the groove along the transverse portion may be between about 100%-300% of the depth of the groove. 
         [0109]      FIG. 10  shows how the bent connector of  FIG. 8  may be used to interconnect adjacent battery cells. As shown, a battery cell  300   a  is positioned adjacent battery cell  300   b  for connection with one another. Battery cell  300   a  includes an end cover structure  335   a.  A bent cathode connector  800   a  extends from an interior portion of the battery cell  300   a  where it is in electrical communication with the cathode collector of the corresponding coiled core (not shown). The transverse portion  815 a of the bent connector  800   a  extends in a direction toward the adjacent battery cell  300   b.  Similarly, battery cell  300   b  includes an end cover structure  335   b.  A bent anode connector  800   b  extends from an interior portion of the battery cell  300   b  where it is in electrical communication with the anode collector of the corresponding coiled core (not shown). The transverse portion  815   b  of the bent connector  800   b  extends in a direction toward the adjacent battery cell  300   a.    
         [0110]    The faces of the upstanding arms of connectors  800   a  and  800   b  are joined with one another at junction  1005 . Junction  1005  may be formed by welding the faces together, bonding the faces with one another using an adhesive such as a conductive rubber, mechanically interconnecting the faces with one another using a fastener, or similar joining structure and/or method. By interconnecting the bent connectors  800   a  and  800   b  at the faces of the upstanding arms, a low resistance connection capable of carrying a high current is established between the cathode of the battery cell  300   a  and the anode of the battery cell  300   b.  A similar structure may be used at an opposite end of each battery cell  300   a  and  300   b  to provide a low resistance connection capable of the carrying a high current between the anode of battery cell  300   a  and the cathode of the battery cell  300   b  with further adjacent cells to thereby connect all cells  300  with one another. In this manner, adjacent cells of a battery pack are electrically connected in series with one another. However, this interconnection architecture may also be used to electrically connect adjacent battery cells in parallel with one another. 
         [0111]    Both bent connector  800   a  and  800   b  include corresponding weakening grooves  820   a  and  820   b.  When either or both battery cells  300   a  and/or  300   b  are jarred from their respective positions as a result of an accidental impact with the vehicle, the material in the region of the grooves  820   a  and/or  820   b  will fail and cause the battery cells  300   a  and  300   b  to electrically disconnect from one another. The safety of the batteries used in the vehicle is enhanced in this manner. 
         [0112]      FIG. 11  shows another structure for interconnecting adjacent battery cells  300   a  and  300   b.  The interconnection is substantially the same as shown in  FIG. 10 . However, bent connectors  800   a  and  800   b  are joined to one another using a fusing member  1105  disposed between the faces of the upstanding arms. The fusing member  1105  may be a tin/lead solder composition or similar material that melts and/or vaporizes under excessively high electrical currents/temperatures that may occur during a failure of battery cell  300   a,  battery cell  300   b,  and/or the battery system that includes battery cells  300   a  and  300   b.  To this end, the thickness, width, length, and composition of the fusing member  1105  is selected to result in electrical disconnection between the bent connectors  800   a  and  800   b  when the electrical current and/or temperature between them exceeds a predetermined critical value. The safety of the battery cells  300   a  and  300   b  when overcurrent and/or temperature conditions are present is improved using this interconnection architecture. 
         [0113]      FIGS. 35 and 36  show another structure for interconnecting adjacent battery cells  300   a  and  300   b.  As shown, the connection structure includes a first bent connector  800   a  and a second bent connector  800   b.  Each bent connector  800   a,    800   b  includes a first arm  810   a,    810   b,  a transverse portion  815   a,    815   b,  and a further arm  805   a,    805   b.  In the embodiment shown in  FIGS. 35 and 36 , arms  805   a  and  805   b  are shorter than the corresponding arms of the connectors shown, for example, in  FIGS. 8 ,  10 , and  11 . Bent connectors  800   a  and  800   b  may be joined to one another using a fusing member  1105  disposed between the faces of the arms  805   a  and  805   b.  The fusing member  1105  may be a tin/lead solder composition or similar material that melts and/or vaporizes under excessively high electrical currents/temperatures that may occur during a failure of battery cell  300   a,  battery cell  300   b,  and/or the battery system that includes battery cells  300   a  and  300   b.  To this end, the thickness, width, length, and composition of the fusing member  1105  is selected to result in electrical disconnection between the bent connectors  800   a  and  800   b  when the electrical current and/or temperature between them exceeds a predetermined critical value. The safety of the battery cells  300   a  and  300   b  when overcurrent and/or temperature conditions are present is improved using this interconnection architecture. 
         [0114]    The connectors  800   a,    800   b  may also be adapted so that they break away from one another when the interconnection structure is subject to excessive forces that may occur during, for example, a vehicle impact. To this end, each transverse portion  815   a,    815   b  includes a narrowed section  3505   a  and  3505   b.  As shown, narrowed sections  3505   a  and  3505   a  define open regions  3520 . Open regions  3520  weaken the interconnection structure to facilitate disconnection of the connectors  800   a  and  800   b  under excessive forces. Each arm  805   a  and  805   b  may have a width that is substantially the same or otherwise corresponds to the width of the narrowed sections  3505   a  and  3505   b.    
         [0115]      FIG. 37  shows another structure for interconnecting adjacent battery cells  300   a  and  300   b.  This interconnection structure is similar to the interconnection structure shown in  FIGS. 36 and 37 . However, the arms  805   a  and  805   b  extend in a direction toward battery cells  300   a  and  300   b.    
         [0116]      FIG. 38  shows another structure for interconnecting adjacent battery cells  300   a  and  300   b.  In this interconnection structure, a first bent connector  3800   a  extends from battery cell  300   a  while a second bent connector  3800   b  extends from battery cell  300   b.  Each connector  3800   a,    3800   b  includes a first arm  3805   a,    3805   b  that extends from the respective battery cell  300   a,    300   b  and into engagement with a respective second arm  3810   a,    3810   b.  Arms  3810   a  and  3810   b  extend toward one another and overlap at a connection region  3815 . Arms  3810   a  and  3810   b  may be adapted to disconnect from one another under excessive forces, such as those that occur in a vehicle collision. To this end, one or both of arms  3810   a  and  3810   b  may include a weakening structure. In  FIG. 38 , the weakening structure comprises narrowed sections  3820   a  and  3820   b  formed in the overlapping portions of arms  3810   a  and  3810   b.  The narrowed sections  3820   a  and  3820   b  may be constructed as arcuate regions similar to the connection structures shown in  FIGS. 35-37 . 
         [0117]      FIG. 39  shows another structure for interconnecting adjacent battery cells  300   a  and  300   b.  In this interconnection structure, a first bent connector  3900   a  extends from battery cell  300   a  while a second bent connector  3900   b  extends from battery cell  300   b.  Each connector  3900   a,    3900   b  includes a first arm  3905   a,    3905   b  that extends from the respective battery cell  300   a,    300   b  and into engagement with a respective second arm  3910   a,    3910   b.  Arms  3910   a  and  3910   b  extend toward one another and are engaged in an end-to-end manner at a connection region  3915 . Connection region  3915  may include a generally V-shaped region that interconnects the arms  3810   a  and  3810   b  using a material that melts and/or vaporizes under temperatures that occur when the current flow between batteries  300   a  and  300   b  becomes excessively large. The material in connection region  3915 , for example, may be tin solder or another material capable of mechanically and electrically interconnecting arms while melting and/or vaporizing at the desired overcurrent temperature. Each connection arm  3900   a,    3900   b  may include a weakening structure such as the one at  920  on the connector  900  shown in  FIG. 9 . 
         [0118]      FIGS. 40 and 41  illustrate further interconnection structures that include mechanically weakened regions that break the electrical connection between batteries  300   a  and  300   b  at a predetermined location under excessive forces that occur, for example, during a vehicle accident/collision. In  FIG. 40 , connector  4005 a is connected to battery cell  300   a  while connector  4005   b  is connected to battery cell  300   b.  Transverse arms  4000   a  and  4000   b  terminate at respective arcuate portions  4010   a  and  4010   b  that join with one another at connection region  4015 . The arcuate regions  4010   a  and  4010   b  are sufficiently strong to facilitate mechanical and electrical interconnection between the connectors  4005   a  and  4005   b  under normal operating conditions. However, the thinning of these material regions produces a weakened connection structure at which the connection between the transverse members  4000   a  and  4000   b  is severed when subject to forces that occur during a vehicle accident/collision. 
         [0119]    In  FIG. 41 , connector  4105   a  is connected to battery cell  300   a  while connector  4100   b  is connected to battery cell  300   b.  Transverse arms  4100   a  and  4100   b  overlap one another at region  4110  where the connectors  4105   a  and  4105   b  are mechanically and electrically joined with one another. Each transverse arm  4100   a,    4100   b  includes a respective arcuate region  4115   a,    4115   b  at which the material forming the transverse arm is thinned. The transverse arms  4100   a  and  4100   b  are aligned so that arcuate regions  4115   a  and  4115   b  overlie one another in connection region  4110 . The resulting structure is sufficiently strong to facilitate mechanical and electrical interconnection between the connectors  4105   a  and  4105   b  under normal operating conditions. However, the thinning of the material regions at the joined arcuate regions  4115   a  and  4115   b  produces a weakened connection structure at which the connection between the transverse members  4100   a  and  4100   b  is severed when subject to forces that occur during a vehicle accident/collision. 
         [0120]      FIG. 41A  is a cross-sectional view through terminals  4100   a  and  4100   b  taken along section line  41 A- 41 A of  FIG. 41 . In  FIG. 41A , however, a multilayer clamp  4120  is disposed to engage arcuate regions  4115   a  and  4115   b.  Clamp  4120  includes a first layer  4125  and second layer  4130  having different thermal expansion characteristics. To this end, first layer  4125  may be an insulating material and have a higher coefficient of thermal expansion than second layer  4130 . During an overcurrent condition, the temperature of the terminals  4100   a  and  4100   b  increases. As the temperature increases, the first layer  4125  expands at a rate greater than the second layer  4130 . Since the expansion of the first layer  4125  is constrained by the second layer  4130 , the first layer  4125  is driven against the thinned material sections at the arcuate regions  4115   a  and  4115   b.  Ultimately, if the temperature exceeds a predetermined threshold value consistent with an overcurrent condition, the first layer  4125  exerts enough force against the arcuate regions  4115   a  and  4115   b  to sever the connection between the terminals  4100   a  and  4100   b.    
         [0121]      FIGS. 42 through 46  show various manners in which terminals  4200   a  and  4200   b  of adjacent battery cells  300   a  and  300   b  may be interconnected with one another. In each instance, the terminals  4200   a,    4200   b  are interconnected with one another using an electrically conductive bridge connector  4205 . The bridge connector  4205  may take on a variety of shapes including, but not limited to, a U-shape, an inverted U-shape, a Z-shape, an S-shape, or any other shape having one or more bending angles between about 0° and 180°. The bridge connector  4205  may be formed as a single layered metal structure, multiple layer structure, or as a multiple layer metal foil. Forming the bridge connector  4205  as a multiple layer metal foil allows the bridge connector  4205  to additionally function as a mechanical buffer that absorbs vibrational energy between the terminals  4200   a  and  4200   b  thereby increasing the integrity of the overall terminal connection structure. 
         [0122]    The bridge connector  4205  may be formed from a single metal material, multiple metal sheets having different thermal expansion coefficients, and/or from a memory alloy. Examples of materials having different expansion coefficients that may be used in a multiple metal sheet structure include a Fe—Ni sheet combination, a Fe—Cu sheet combination, and/or a memory alloy/common metal combination. Memory alloys that may be used in the bridge connector  4205  include Cu-based alloys and/or Fe-based alloys. These include, without limitation, Cu—Zn—Al, Cu—Al—Ni, and/or Fe—Mn. The common metal may be, for example, Cu, Al, and/or Ni. 
         [0123]    The bridge connector  4205  connects to face portions of the terminals  4200   a  and  4200   b.  The effective welding surface between the bridge connector  4205  and a respective terminal may be about 0.5˜4 times the cross-sectional surface of the terminal. Solder having a lower melting point than the metal of the connector and the terminal may be disposed at the junction between each end of bridge connector  4205  and the respective terminal. The connection between each terminal and the bridge connector  4205  may be formed through cold pressure welding, ultrasonic welding, solder welding, flash welding, friction welding, resistance welding, or the like. Preferably the connection is formed using solder welding where the melting point of the alloy used in the solder has a melting temperature between about 150° C. and 250° C. Materials that may be used include Sn, Au-20% Sn, lead-5% Sn, Ag—Sn and so on. 
         [0124]      FIG. 42  shows a bridge connector  4205  having an inverted U-shape. In this embodiment, terminals  4200   a  and  4200   b  may have the general characteristics of the terminals  800   a  and  800   b  shown in  FIG. 10 . Bridge connector  4205  may include first and second arms  4210  and  4215  that are interconnected with one another by a transverse member  4220 . First arm  4210  is connected to member  4225  of terminal  4200   a  while second arm  4215  is connected to member  4230  of terminal  4200   b.  Bridge connector  4205  may be formed as a multilayered soft metal piece, such as from a multilayered copper foil. When the battery cells  300   a  and/or  300   b  are subject to external forces, the transverse member  4220  may absorb the generated impact stresses and protect the terminals from excessive wear and harm. 
         [0125]    The bridge connector  4205  may be formed from a memory alloy or bimetal piece. When the temperature of the interconnection structure elevates suddenly due, for example, to an overcurrent or other abnormal condition, the memory alloy or the bimetal piece may shrink in the direction shown by arrows  4235  to withdraw itself from contact with each of the terminals as the solder between the bridge/terminal junctions melts. As a result, the electrical and mechanical connection between the terminals  4200   a  and  4200   b  is broken to prevent the explosion of the battery cells and/or other such dangerous consequences. 
         [0126]    Memory alloys that may be used to construct bridge connector  4205  include Cu based metal alloys and/or Fe based metal alloys, such as Cu—Zn, Cu—Zn—Al, Cu—Al—Ni, or Fe—Mn—Si alloys. In connection with the structure shown in  FIG. 42 , it is assumed that a Cu—Al—Ni alloy is employed. In such instances, the bridge connector  4205  may be initially formed so that the angle between each arm  4210  and  4215  with respect to transverse member  4220  is less than 90°. While in this shape, the bridge connector  4205  may be subject to a high-temperature treatment between about 300-1000° C. for several minutes to impart a memory effect. The bridge connector  4205  is then connected to terminals  4200   a  and  4200   b  in its normal assembled position. In this position, the angle between each arm  4210  and  4215  is at an angle of about 90° with respect to the transverse member  4220 . The memory alloy will attempt to recover its original shape when the temperature of the bridge connector  4205  is elevated to a temperature commensurate with an overcurrent and/or other abnormal battery cell operating condition. 
         [0127]      FIG. 43  shows a bridge connector  4205  having an S-shape. In this embodiment, terminals  4200   a  and  4200   b  may have the general characteristics of the terminals  800   a  and  800   b  shown in  FIG. 10 . Bridge connector  4205  may include first and second arms  4305  and  4310  that extend in opposite directions and that are interconnected with one another by a transverse member  4315 . First arm  4305  is connected to member  4225  of terminal  4200   a  while second arm  4310  is connected to member  4230  of terminal  4200   b.  As above, the bridge connector  4205  may be formed as a multilayer metal foil, bimetal piece, and/or memory alloy. When formed from a memory alloy, bridge connector  4205  may have an original shape that corresponds to the shape required to disconnect it from contact with terminals  4200   a  and  4200   b  under elevated temperatures that occur during overcurrent and/or other abnormal battery cell operating conditions. 
         [0128]      FIG. 44  shows a bridge connector  4205  having an inverted U-shape. In this embodiment, terminals  4200   a  and  4200   b  may have the general characteristics of the terminals  800   a  and  800   b  shown in  FIG. 10 . Bridge connector  4205  may include first and second arms  4405  and  4410  that are interconnected with one another by a transverse member  4415 . First arm  4405  is connected to an exterior surface of member  4225  of terminal  4200   a  while second arm  4410  is connected to an exterior surface of member  4230  of terminal  4200   b.  As above, the bridge connector  4205  may be formed as a multilayer metal foil, bimetal piece, and/or memory alloy. When formed from a memory alloy, bridge connector  4205  may have an original shape that corresponds to the shape required to disconnect it from contact with terminals  4200   a  and  4200   b  under elevated temperatures that occur during overcurrent and/or other abnormal battery cell operating conditions. In FIG.  44 , the original shape may be set so that the bridge connector  4205  expands in the directions shown by arrows  4420  under such elevated temperatures. 
         [0129]      FIG. 45  shows a bridge connector  4205  having a multilayer structure. In this embodiment, the bridge connector  4205  includes a first layer  4505  that is disposed interior to arms  4225  and  4230  and a second layer  4510  that is interior to and coextensive with the first layer  4505 . Each layer  4505 ,  4510  has an inverted U-shape. Layer  4510  may be formed from a common metal while layer  4505  may be formed from a memory alloy. The common metal layer  4510  and memory alloy  4505  may be bonded with one another so that changes in the shape of the memory alloy  4505  result in corresponding changes in the shape of the common metal layer  4510 . As such, the bridge connector  4205  changes shape under elevated temperatures that occur during overcurrent and/or other abnormal battery cell operating conditions. This shape change causes the bridge connector  4205  to disconnect terminals  4200   a  and  4200   b  from one another. 
         [0130]      FIG. 46  shows a bridge connector  4205  having a multilayer structure. In this embodiment, the bridge connector  4205  includes a first layer  4605  that is disposed exterior to arms  4225  and  4230  and a second layer  4610  that is exterior to and coextensive with the first layer  4605 . Each layer  4505 ,  4510  has an inverted U-shape. Layers  4610  and  4605  are formed from metals having different thermal expansion coefficients and may be mechanically bonded to one another so that changes in the shape of one layer will result in a corresponding change in the other layer. The difference in thermal expansion coefficients causes the bridge connector  4205  to change shape under elevated temperatures that occur during overcurrent and/or other abnormal battery cell operating conditions thereby disconnecting terminals  4200   a  and  4200   b  from one another. To further ensure that the terminals  4225  and  4230  are electrically isolated from one another when the bridge connector  4205  changes shape, an insulating layer  4615  may be disposed at an end portion of each arm  4225  and  4230  proximate the bridge connector  4205 . 
         [0131]    Battery cell interconnections such as those shown in  FIG. 39  may include gravity enhanced overtemperature protection structures. An example of one such structure is shown in  FIGS. 47 and 48 , where  FIG. 47  is a top view of the structure and  FIG. 48  is a side view of the structure. These figures show the orientation of the terminals when the battery cells are turned on their sides in the manner shown in  FIGS. 28A and 69  below. 
         [0132]    In the embodiment shown in  FIGS. 47 and 48 , terminal  3900   a  is electrically connected to battery cell  300   a  while terminal  3900   b  is electrically connected to battery cell  300   b.  A conductive block  4705  is secured to the end portions of each terminal  3900   a  and  3900   b  using a bonding material  4710 . The conductive block  4705  extends along the entire width  4805  of connectors  3900   a  and  3900   b  as well as along the entire thickness  4715 . The bonding material  4710  may be Sn-based solder, Bi-based solder, or Zn-based solder, but is preferably Sn-based. In one example, the solder may have a thickness of between about 0.3 mm and 1 mm and, preferably between about 0.5 mm and 0.8 mm. The melting point of the solder material may be between about 1000 Celsius and 4500 Celsius. If the melting point is too low, the interconnection structure may not be stable under ordinary operating conditions. If it is too high, the melting point may not be achieved during abnormal overtemperature conditions. Sn-based solder is preferred since it has a melting point of about 231.90 Celsius. 
         [0133]    The conductive block  4705  may be formed from a high density metal having a melting point that is at least about 50° Celsius above the melting point of the bonding material  4710 . In this manner, the conductive block  4705  may be securely fastened with terminals  3900   a  and  3900   b  using a suitable brazing technique. Such techniques may include induction brazing, iron soldering, resistance braze welding, or similar fastening technique. 
         [0134]    As shown in  FIG. 48 , the conductive block  4705  may have a trapezoidal shape in which the base portion  4810  is disposed at the lower portion of the connection structure. The conductive block  4705  is subject to the force of gravity in the direction shown by arrow  4815 . When the connection structure is subject to overtemperature conditions such as those that occur during overcurrent or other abnormal operation of the battery system, the bonding material  4710  begins to melt. As the bonding material melts, the conductive block  4705  moves downward in direction  4815  under the influence of gravity. Ultimately, the conductive block  4705  dislodges from engagement with the terminals  3900   a  and  3900   b  thereby severing the electrical and mechanical interconnection between them. 
         [0135]    Battery cell interconnections may also include overtemperature protection structures using electrical insulators that are dimensioned to expand the connection between the terminals when the temperature of the interconnection becomes excessive.  FIGS. 49 through 51  illustrate three embodiments of such interconnections. In  FIG. 49 , the terminals  4900   a  and  4900   b  are joined to one another by a bonding material  4710 . The bonding material  4710  may be Sn-based solder, Bi-based solder, or Zn-based solder, but is preferably Sn-based. In one example, the solder may have a thickness of between about 0.3 mm and 1 mm. The melting point of the solder material may be between about 1000 Celsius and 450° Celsius, with a preference of about 232° Celsius. An expansion member  4905  is disposed in the joint between the terminals  4900   a  and  4900   b.  As shown, the expansion member  4905  may have a circular cross-section, but other cross-sectional shapes may be used. Further, the expansion member  4905  may be formed from an electrically insulating material having a large thermal expansion coefficient. Still further, the material forming the expansion member  4905  may have a melting point that substantially exceeds the melting point of the bonding material  4710 . 
         [0136]    When the interconnection structure is subject to an overtemperature condition, the bonding material  4710  begins to melt. Additionally, the expansion member  4905  expands to drive arms  4910   a  and  4910   b  apart. The characteristics of the bonding material  4710 , expansion member  4905 , and spacing between arms  4910   a,    4910   b  are such that the expansion of the expansion member  4905  drives the arms  4910   a  and  4910   b  apart a sufficient distance to overcome the surface tension of the melted bonding material  4710 . The bonding material  4710  flows from the joint between the terminals and effectively severs the electrical connection between the battery cells. 
         [0137]    The interconnection shown in  FIG. 50  is similar to the one shown in  FIG. 49 . The principal difference between them is the shape of the terminals  5000   a  and  5000   b.  More particularly, the terminals  5000   a  and  5000   b  include inwardly extending arms  5005   a  and  5005   b  as opposed to the outwardly extending arms  4910   a  and  4910   b  of terminals  4900   a  and  4900   b.    
         [0138]    The interconnection structure shown in  FIG. 51  is similar to the ones shown in both  FIG. 49  and  FIG. 50 . The principal difference between them is the shape of the terminals. More particularly, the interconnection shown in  FIG. 51  includes a terminal  4900   a  having an outwardly extending arm  4910   a  that is electrically connected with an inwardly extending arm  5005   b  of a terminal  5000   b.  An electrically insulating member  5105  may be disposed between an end portion of arm  4910   a  of terminal  4900   a  and transverse portion  5110  of terminal  5000 . The electrically insulating member  5105  helps to ensure that terminals  4900   a  and  5000 b are electrically disconnected from one another when the bonding material  4710  melts and flows from the joint between arms  4910   a  and  5005   b.    
         [0139]    As described above, interconnection structures may include a bonding material between the terminals that melts under the excessively high temperatures that occur due to overcurrent conditions between the battery cells  300   a  and  300   b.  Additionally, or in the alternative, the interconnection structures may be provided with substructures that release chemicals which interact with the joint between the terminals so that the terminals are mechanically and electrically separated from one another under such excessively high temperature conditions.  FIGS. 52 and 53  show examples of these substructures as applied to the interconnection structures shown in  FIGS. 40 and 41 , respectively. 
         [0140]    In  FIG. 52 , connector  4005   a  is connected to battery cell  300   a  while connector  4005   b  is connected to battery cell  300   b.  Transverse arms  4000   a  and  4000   b  terminate at respective arcuate portions  4010   a  and  4010   b  that join with one another at connection region  4015 . Connection region  4015  may include a bonding material such as solder. The arcuate regions  4010   a  and  4010   b  are sufficiently strong to facilitate mechanical and electrical interconnection between the connectors  4005   a  and  4005   b  under normal operating conditions. However, the thinning of these material regions produces a weakened connection structure at which the connection between the transverse members  4000   a  and  4000   b  is severed when subject to forces that occur during a vehicle accident/collision. 
         [0141]    One embodiment of a substructure which releases chemicals that interact with the connection region  4015  is shown generally at  5205 . In this embodiment, the substructure  5205  includes an outer casing  5210  that contains a chemically reactive material  5215 . The casing  5210  has a generally circular cross-section and is adapted to fit within the arcuate regions  4010   a  and  4010   b.  Other cross-sectional shapes may be used depending on the particular structure of the terminals that are employed. The casing material should meet several requirements. For example, the casing material should be capable of being bonded with the materials of the arms  4005   a  and  4005   b.  Additionally, the casing material should be non-reactive with the chemically reactive material  5215 . Further, the temperature at which the casing material begins to melt should be close to the temperature generated during an overcurrent condition. The casing material may be a synthetic resin, rubber, ceramic, or the like. Preferably, the casing is formed from a plastic and/or rubber compound having a melting temperature between 100° C. and 350° C., depending on the overtemperature requirements. Such materials may include PP, PE, ABS, PPO, PPS, PTFE, and PEEK. 
         [0142]    The chemically reactive material  5215  is preferably a liquid at the overcurrent temperature. It may or may not be a solid at normal operating temperatures. For example, it may be an acidic or basic chemical solution that is reactive with the material at connection region  4015 . Preferably, the chemical is a basic chemical including, for example, NaOH. 
         [0143]    Under normal conditions, the temperature of the arms  4000   a  and  4000   b  are below the melting point of any material at interconnection region  4015  as well as below the melting point of the casing  5210  of the chemically reactive element  5205 . As the temperature increases due to, for example, an overcurrent condition, the casing  5210  begins to melt. As the casing  5210  melts, the chemically reactive material  5215  is released and engages the materials of arms  4000   a  and  4000   b  as well as any material in interconnection region  4015 . The released chemical reacts with the material at interconnection region  4015 , arm  4000   a,  and/or arm  4000   b.  The reaction is destructive and results in electrical disconnection of the arms  4000   a  and  4000   b  from one another. 
         [0144]    In  FIG. 53 , connector  4105   a  is connected to battery cell  300   a  while connector  4100   b  is connected to battery cell  300   b.  Transverse arms  4100   a  and  4100   b  overlap one another at region  4110  where the connectors  4105   a  and  4105   b  are mechanically and electrically joined with one another. Each transverse arm  4100   a,    4100   b  includes a respective arcuate region  4115   a,    4115   b  at which the material forming the transverse arm is thinned. The transverse arms  4100   a  and  4100   b  are aligned so that arcuate regions  4115   a  and  4115   b  overlie one another in connection region  4110 . The resulting structure is sufficiently strong to facilitate mechanical and electrical interconnection between the connectors  4105   a  and  4105   b  under normal operating conditions. However, the thinning of the material regions at the joined arcuate regions  4115   a  and  4115   b  produces a weakened connection structure at which the connection between the transverse members  4100   a  and  4100   b  is severed when subject to forces that occur during a vehicle accident/collision. 
         [0145]    As in  FIG. 52 , the interconnection structure of  FIG. 53  includes a substructure  5205  which may release chemicals that interact with the connection region  4110  under overtemperature/overcurrent conditions. The substructure  5205  includes outer casing  5210  that contains the chemically reactive material  5215 . The casing  5210  may have a generally circular cross-section and be adapted to fit within the arcuate regions  4115   a  and  4115   b.  Operation of the substructure  5205  with respect to the region  4110  is substantially similar to the operation described in connection with  FIG. 52 . 
         [0146]    The interconnection structures shown in  FIGS. 52 and 53  are based on a horizontal alignment of the arms of the terminals connecting batteries  300   a  and  300   b.  It will be recognized, however, that a substructure of the type generally shown at  5205  may be used in other interconnection structure orientations. In such alternate orientations, the substructure  5205  is constructed and aligned with the terminals so that the reactive material  5215  is released to sever the electrical connection between the terminals. Still further, the substructure  5205  may be positioned on a single one of the terminals to sever the electrical connection between the terminals. 
         [0147]    Overcurrent protection may also be based on the removal of a conductive liquid between the terminals of battery cells  300   a  and  300   b.  More particularly, the conductive liquid is present between the terminals of the battery cells  300   a  and  300   b  under normal operating conditions so that the terminals are electrically interconnected with one another to conduct current. The conductive liquid is drained from between the terminals of the battery cells  300   a  and  300   b  when the temperature of the terminals is elevated due, for example, to an overcurrent condition or other system fault. 
         [0148]      FIG. 54  shows one embodiment of an overcurrent protection substructure based on this principle. In this embodiment, terminal  5400   a  is connected to battery cell  300   a  and terminal  5400   b  is connected to battery cell  300   b.  Terminals  5400   a  and  5400   b  are mechanically isolated from one another at a separation region  5403 . Electrical connection between terminals  5400   a  and  5400   b  is established using interconnection substructure  5405 . The interconnection substructure  5405  includes a casing  5410  that holds a liquid conductor  5415  therein. The liquid conductor  5415  establishes an electrical connection between terminal  5400   a  and  5400   b  in region  5403 . Metals, metal alloys, and conductive solutions may be used as the liquid conductor  5415 . Preferably, the liquid conductor  5415  is mercury or an Na—K alloy. The casing  5405  has a generally circular cross-section, but other cross-sectional shapes may be used depending on the particular structure of the terminals that are employed. The casing material may be non-reactive with the liquid conductor  5415 . Further, the temperature at which the casing material begins to melt should be close to the temperature generated during an overcurrent condition. The casing material may be a synthetic resin, rubber, ceramic, or the like. Preferably, the casing is formed from a plastic and/or rubber compound having a melting temperature between 100° C. and 350° C., depending on the overtemperature requirements. Such materials may include PP, PE, ABS, PPO, PPS, PTFE, and PEEK. 
         [0149]    Under normal conditions, the temperature of the arms  5400   a  and  5400   b  are below the melting point of the casing  5410 , and the liquid conductor  5415  is retained in region  5403  to facilitate current flow between terminals  5400   a  and  5400   b.  As the temperature increases due to, for example, an overcurrent condition, the casing  5410  begins to melt. As the casing  5410  melts, the liquid conductor  5415  is released from the casing  5410  and open circuits region  5403 . Further current flow between batteries  300   a  and  300   b  through terminals  5400   a  and  5400   b  ceases. 
         [0150]      FIGS. 55 through 57B  show a further embodiment of an interconnection structure in which overcurrent protection is based on the removal of a conductive liquid between the terminals of battery cells  300   a  and  300   b.  In this embodiment, the overcurrent protection substructure, shown generally at  5500 , is constructed to operate with terminals that extend horizontally from each battery cell. As shown, terminal  5400   a  is connected to and extends horizontally from battery cell  300   a.  Terminal  5400   b  is connected to and extends horizontally from battery cell  300   b.  Each terminal  5400   a  and  5400   b  extends from the respective battery into a conduction chamber  5505  of the overcurrent protection substructure  5500 . A collection chamber  5510  is disposed below the conduction chamber  5505 . The conduction chamber  5505  and collection chamber  5510  are made from an insulating material such as plastic, rubber, ceramic, or the like. During normal battery system operation, the conduction chamber  5505  and collection chamber  5510  are sealed in a manner to prevent leakage from one chamber to the other. 
         [0151]    The protection substructure  5500  may be assembled in a number of different manners.  FIG. 56  shows one such manner. In  FIG. 56 , the substructure  5500  is formed from two portions  5600   a  and  5600   b.  Portion  5600   a  is connected to and sealed with terminal  5400   a.  Portion  5600   b  is connected to and sealed with terminal  5400   b.  Each portion  5600   a  and  5600   b  includes half of the conduction chamber  5505  and half of the collection chamber  5510 . The portions  5600   a  and  5600   b  may be joined with one another using a hot melt connection, rubber connection, adhesive connection, welded joint, or the like. The portions  5600   a  and  5600   b  may be sealed with the corresponding terminals  5400   a  and  5400   b  using injection molding, hot melting, adhesive bonding, penetration agents sealing, or the like. The method used to join the portions to one another and to the terminals should be sufficient to prevent leakage of any liquid from either the conduction chamber  5505  or the collection chamber  5510 . 
         [0152]      FIGS. 57A and 57B  are cross-sectional views through the protection substructure  5500  during normal operation of the battery system. During normal operation, a liquid conductor  5415  of the type described above is contained within the conduction chamber  5505  and establishes an electrical connection between terminal  5400   a  and terminal  5400   b.  The liquid conductor  5415  may be injected into the conduction chamber  5505  through an opening  5515  disposed at an upper portion of the conduction chamber  5505 . Once the conduction chamber  5505  has been filled with the desired amount of liquid conductor  5415 , the opening  5515  may be closed with a plug or other type of seal. 
         [0153]    The conduction chamber  5505  is sealed from the collection chamber  5510  to prevent leakage of the liquid conductor  5415  from the conduction chamber  5505  to the collection chamber  5510 .  FIG. 57B  shows one manner of sealing the conduction chamber  5505  from the collection chamber  5510 . In this example, the conduction chamber  5505  terminates at a lower chamber wall  5705  that separates the conduction chamber  5505  from the collection chamber  5510 . The lower chamber wall  5705  includes a flow opening  5715  that is normally sealed by a separation member  5720 . Separation member  5720  may be made from a plastic and/or rubber material having a melting temperature between about 100° C. and 350° C., depending on the desired temperature at which the overcurrent protection is to be activated. Suitable materials include, for example, PP, PE, ABS, PPO, PPS, PTFE, and/or PEEK. 
         [0154]    During an overcurrent/battery failure condition, the temperature of the liquid conductor  5415  will increase. As the temperature reaches the melting point of the separation member  5720 , the separation member  5720  will become ineffective in sealing the conduction chamber  5505  from the collection chamber  5510 . The liquid conductor  5415  will flow from the conduction chamber  5505  to the collection chamber  5510  through the flow opening  5715 . The flow may occur under the force of gravity and/or under the force generated by an elevated pressure in the conduction chamber  5505  (e.g., the force resulting from the overcurrent temperature of the liquid conductor  5415 ). As the liquid conductor  5415  exits the conduction chamber  5505 , it will create an open circuit condition between terminals  5400   a  and  5400   b.  In order to ensure that all of the liquid conductor  5415  drains from the conduction chamber  5505 , the volume of the collection chamber  5510  should be at least equal to or greater than the volume of the conduction chamber  5505 . [ 00133 ]The protection substructure  5500  is easily manufactured and readily repaired/recycled. By collecting the liquid conductor  5415  in the collection chamber  5510 , it may be reused in a repaired or new protection substructure  5500 . This is particularly beneficial if the liquid conductor  5415  is not environmentally friendly. Additionally, the protection substructure  5500  may be easily repaired by directing the liquid conductor  5415  back into the conduction chamber  5505  and replacing the sealing member  5720 . 
         [0155]      FIGS. 58 through 60  show a still further embodiment of an interconnection structure in which overcurrent protection is based on the removal of a conductive liquid between the terminals of battery cells  300   a  and  300   b.  In this embodiment, the overcurrent protection substructure, shown generally at  5800 , is constructed to operate with terminals that extend vertically from the respective battery cell. As shown, terminal  5800   a  is connected to and extends vertically from battery cell  300   a.  Terminal  5800   b  is connected to and extends vertically from battery cell  300   b.  Each terminal  5800   a  and  5800   b  extends from the respective battery into a conduction chamber  5805  of the overcurrent protection substructure  5800 . A collection chamber  5810  is disposed below the conduction chamber  5805 . The conduction chamber  5805  and collection chamber  5810  are made from an insulating material such as plastic, rubber, ceramic, or the like. During normal battery system operation, the conduction chamber  5805  and collection chamber  5810  are sealed in a manner to prevent leakage from one chamber to the other. 
         [0156]    The protection substructure  5800  may be assembled in a number of different manners.  FIG. 59  shows one such manner. In  FIG. 59 , the substructure  5800  is formed from two portions  5900   a  and  5900   b.  Portion  5900   a  is connected to and sealed with terminal  5900   a.  Portion  5900   b  is connected to and sealed with terminal  5800   b.  Each portion  5900   a  and  5900   b  includes half of the conduction chamber  5805  and half of the collection chamber  5810 . The portions  5900   a  and  5900   b  may be joined with one another using a hot melt connection, rubber connection, adhesive connection, welded joint, or the like. Further, the portions  5900   a  and  5900   b  may be sealed with the corresponding terminals  5800   a  and  5800   b  using injection molding, hot melting, adhesive bonding, penetration agent sealing, or the like. The methods used to join the portions to one another and to the terminals should be sufficient to prevent leakage of any liquid from either the conduction chamber  5805  or the collection chamber  5810 . 
         [0157]      FIG. 60  is a cross-sectional view through the protection substructure  5800 . During normal operation, a liquid conductor  5415  of the type described above is contained within the conduction chamber  5805  and establishes an electrical connection between terminal  5800   a  and terminal  5800   b.  The liquid conductor  5415  may be injected into the conduction chamber  5805  through an opening  5815  disposed at an upper portion of the conduction chamber  5805 . Once the conduction chamber  5805  has been filled with the desired amount of liquid conductor  5415 , the opening  5815  may be closed with a plug or other type of seal. 
         [0158]    The conduction chamber  5805  is sealed from the collection chamber  5810  to prevent leakage of the liquid conductor  5415  from the conduction chamber  5805  to the collection chamber  5810 . In  FIG. 60 , the conduction chamber  5805  terminates at a lower chamber wall  6005  that separates the conduction chamber  5805  from the collection chamber  5810 . The lower chamber wall  6005  includes a flow opening  6015  that is normally sealed by a separation member  6020 . Separation member  6020  may be made from a plastic and/or rubber material having a melting temperature between about 100° C. and 350° C., depending on the desired temperature at which the overcurrent protection is to be activated. Suitable materials include, for example, PP, PE, ABS, PPO, PPS, PTFE, and/or PEEK. 
         [0159]    During an overcurrent/battery failure condition, the temperature of the liquid conductor  5415  will increase. As the temperature reaches the melting point of the separation member  6020 , the separation member  6020  will become ineffective in sealing the conduction chamber  5805  from the collection chamber  5810 . The liquid conductor  5415  will flow from the conduction chamber  5805  to the collection chamber  5810  through the flow opening  6015 . The flow may occur under the force of gravity and/or under the force generated by an elevated pressure in the conduction chamber  5805  (e.g., the force resulting from the overcurrent temperature of the liquid conductor  5415 ). As the liquid conductor  5415  exits the conduction chamber  5805 , it will create an open circuit condition between terminals  5800   a  and  5800   b.  In order to ensure that all of the liquid conductor  5415  drains from the conduction chamber  5805 , the volume of the collection chamber  5810  should be at least equal to or greater than the volume of the conduction chamber  5805 .  FIGS. 12 and 13  show a connection structure  1200  that may be utilized to bring the core of battery cell  300  to an optimal operating temperature when the ambient temperature falls below a predetermined threshold. Connection structure  1200  includes a heating element  1205 , such as a ceramic heater, that is secured to bent connector  800 . A layer of a thermally conductive material  1210  is disposed between the bent connector  800  and the heating element  1205 . Heating element  1205  may have an L-shaped cross-section and be dimensioned to conform with a surface of bent connector  800  opposite the surface used to establish electrical contact with an adjacent battery cell. Layer  1210  may be formed from a material, such as a thermally conductive rubber, which serves as a conductive heating element, an electrical insulator, and/or as an adhesive between the heating element  1205  and the bent connector  800 . Additionally, or in the alternative, bent connector  800  and heating element  1205  may be secured with one another using a mechanical fastener that is formed from an electrical insulator, such as PA66. 
         [0160]      FIG. 13  shows a system that may be used to raise the temperature of the core of battery cell  300  when temperature conditions indicate that the core is at or may fall below a predetermined temperature threshold. As shown, the system includes a temperature sensor  1305  that is disposed to monitor a temperature associated with the need for core heating. The temperature sensor  1305  may be disposed to monitor the ambient temperature of the vehicle, the ambient temperature of the battery system environment, the temperature of the battery cell  300 , and/or other desired temperature. The temperature information is provided to a control system  1310 . The control system  1310  uses the temperature sensor information to determine when the temperature detected by the sensor  1305  falls below a predetermined threshold. When this occurs, the control system  1310  directs electrical power to the heating element  1205 . The electrical power may be provided by a generator connected to a gas powered engine of the vehicle and/or by a battery power system. Heating element  1205  responds to the electrical power by generating heat which is transferred through the layer  1210  to the bent connector  800 . Bent connector  800 , in turn, acts as a thermally conductive element that transfers heat to the interior of battery cell  300  thereby raising the temperature of the coiled core  200 . 
         [0161]      FIG. 14A  shows one manner of connecting a multiple core structure  1450  of a battery cell  300  to the bent connector  800 . In this embodiment, the multiple core structure  1450  includes three separate cores that are each constructed in the manner of core  200 . For the sake of simplicity, only a single end of the battery cell  300  is shown, although the same basic structure may be used for connecting the opposite end of the multiple core structure  1450  with a corresponding end connector  800 . 
         [0162]    In  FIG. 14A , multiple core structure  1450  is disposed within the rectangular protective shell  305 . An end cover assembly  335  engages with and seals an opening at the end of shell  305 . A gasket  1405  formed from an electrically insulating material is disposed within the shell  305  and positioned between the end of multiple core structure  1450  and the end cover assembly  335 . Bent connector  800  extends into the interior of the battery shell  305  through the end cover assembly  335  so that it is offset from a centerline running longitudinally through the shell  305 . 
         [0163]    A plan view of the gasket  1405  is shown in  FIG. 15 . The gasket  1405  includes three openings  1505 , 1510 , and  1515 . Each opening is defined by a respective set of contoured elements disposed on each side of the opening. Opening  1505  is defined by contoured elements  1520  and  1525 , opening  1510  by contoured elements  1525  and  1530 , and opening  1515  by contoured elements  1530  and  1535 . Each contoured element includes a rounded surface at a side proximate the coiled core  200  and a respective planar surface opposite the rounded surface. Contoured elements  1525  and  1530  are spaced from one another so that opening  1510  is larger than openings  1515  and  1520 . As a result, the planar surface of contoured element  1525  is positioned to facilitate protection of the core  200  in the event that the bent connector  800  is driven toward the core  200  under extraordinary forces, such as those that may occur during a vehicle collision. 
         [0164]    With reference again to  FIG. 14A , current collector strips  1415  extend from the anode (or cathode) of each core  200  of the multiple core structure  1450 . Each current collector strip  1415  may be formed from one or more foil layers, such as the foil layers forming the substrate layers of the anode (or cathode) of each core  200 . Although each current collector strip  1415  is shown as a single foil layer, each current collector strip  1415  may also be formed from multiple foil layers that are grouped with one another as they extend from the anode (or cathode) of each core  200  of the multiple core structure  1450 . In  FIG. 14A , there are three current collector strips  1415   a,    1415   b,  and  1415   c  that extend from the anode (or cathode) of a respective core  200  of the multiple core structure  1450 . These current collector strips extend through respective openings  1505 ,  1510 , and  1515  and into a cavity  1420  of the gasket  1405 . Within cavity  1420 , each current collector strip  1415   a,    1415   b,  and  1415   c  is electrically and mechanically bonded to a respective flexible connector foil  1425   a,    1425   b,  and  1425   c.  Various connection processes may be used to join the structures including, without limitation, ultrasonic welding, resistance welding, laser welding, and/or another binding process. 
         [0165]    As shown in FIG. of  14 A, the connector foils  1425   a,    1425   b,  and  1425   c  are coiled within the cavity  1420  to join at a common side of the bent connector  800 . Connector foils  1425   b  and  1425   c  are coiled within a first side of the cavity  1420  while connector foil  1425   a  is coiled within a second side of the cavity  1420 . The first side of the cavity  1420  is larger than the second side of the cavity  1420  due to the offset of the connector  800  with respect to the longitudinal centerline of the shell  305 . Consequently, connector foils  1425   b  and  1425   c  have more room in which to coil around to fasten with the connector  800  than connector foil  1425   a.  The angles at which the connector foils  1425   b  and  1425   c  are bent, therefore, are relatively gradual. Gradual bending angles are more desirable than drastic bending angles and are less likely to result in breakage of the corresponding connector foil. However, connector foil  1425   a  is disposed in a smaller portion of cavity  1420 . As such, connector foil  1425   a  may require a more drastic bend angle in order to coil around for connection to the connector  800 . Drastic bending angles are subject to substantial mechanical and thermal fatigue and may result in breakage of the connector foil  1425   a.    
         [0166]    In order to render the bending configuration of the connector foil  1425   a  more reliable, a coil guide member  1430  is bonded to the connector foil  1425   a.  Coil guide member  1430  includes a bonding portion  1435  and a rounded portion  1440 . The bonding portion  1435  is secured with the connector foil  1425   a  exterior to its connection with the other connector foils  1425   b  and  1425   c.  Rounded portion  1440  has a shape and diameter that directs connector foil  1425   a  to bend at a gradual angle as it approaches the bent connector  800  thereby increasing the reliability of the connector foil  1425   a.  Further, coil guide member  1430  may be dimensioned to drive the collector  1415   a  and connector foil  1425   a  toward a side wall of the gasket  1405 . In this manner, the collector  1415   a  and connector foil  1425   a  do not experience as much movement as might otherwise occur when the battery cell  300  is vibrated. Similarly, the lengths of connector foils  1425   b  and  1425   c  may be selected so that the corresponding bending configuration limits vibration of these components within the chamber  1420 . The reliability and safety of the battery cell  300  is increased with such structures. 
         [0167]    The use of the coil guide member  1430  may be extended to assemblies having more than three connector foils as well as assemblies having less than three connector foils. In each instance, the coil guide member  1430  is preferably secured to a connector foil that bends on the side at which it is connected to bent connector  800  as opposed to a connector foil that coils below and around bent connector  800  for connection. Further, additional coil guide members may be secured with connector foils  1425   b  and  1425   c  to prevent unnecessary bending of these connector foils as well. 
         [0168]      FIG. 14B  shows one manner of connecting a core of a battery cell  300  to the bent connector  800 . In this embodiment, only a single core  200  is utilized. Accordingly, only a single current collector  1415  extends from the core  200  for electrical connection with the bent connector  800 . To reduce the degree of the angles that need to be formed in connecting foil  1425  to reach bent connector  800 , the current collector  1415  is disposed through the opening  1515  that is furthest from the bent connector  800 . In all other respects, the end cover  300  of  FIG. 14B  is the same as the one shown in  FIG. 14A . 
         [0169]    The gasket  1405  may include tabs  1410  that engage corresponding recesses in the protective shell  305 . Tabs  1410  may be used to secure the gasket  1405  in the shell  305 . Additionally, or in the alternative, gasket  1405  may be secured within the protective shell  305  through welding, one or more mechanical fasteners, an adhesive, or other connection mechanism. 
         [0170]    Gasket  1405  assists in protecting the core  200  in several different ways. For example, the portion of the gasket  1405  proximate the core  200  helps maintain the core  200  in proper longitudinal alignment within the interior of the protective shell  305 . The offset contoured member  1525  assist in preventing the connector  800  and the connections at its side face from contacting the core  200  during an accident or mechanical failure. The narrowing of the openings provided by contoured members  1520 ,  1525 ,  1530 , and  1535  help guide current collectors  1415   a,    1415   b,  and  1415   c  into the chamber  1420  during the manufacturing of battery cell  300 . Still further, gasket  1405  helps to stiffen the protective shell  305  to provide increased protection to the coiled core  200 . 
         [0171]      FIGS. 16 and 17  show one manner of sealing the end of protective shell  305  with the end cover assembly  325 .  FIG. 16  is a cross-sectional view through a transverse section of the end cover assembly  325  while  FIG. 17  is a cross-sectional view through a longitudinal section of the and cover assembly  325 . 
         [0172]    End cover assembly  325  includes a cover plate/end cap  1605 , a scabbard  1610 , connector  800 , and a sealing material  1615 . To manufacture the end cover assembly  325 , the cover plate  1605  and scabbard  1610  are welded to one another to form an integral structure. Without limitation, the welding operation may include laser welding, argon arc welding, and other welding processes. The cover plate  1605  and scabbard  1610  may be formed from stainless steel. Once the cover plate  1605  and scabbard  1610  have been welded to one another, they may be placed over the connector  800  which extends from an interior portion of the battery cell to an exterior portion. End cover assembly  325  includes a cover plate  1605 , a scabbard  1610 , connector  800 , and a sealing material  1615 . To manufacture the end cover assembly  325 , the cover plate  1605  and scabbard  1610  are welded to one another to form an integral structure. Without limitation, the welding operation may include laser welding, argon arc welding, and other welding processes. The manufacturing operations that take place after the cover plate  1605  and scabbard  1610  have been welded to one another are not heat intensive. Consequently, the likelihood that other components of the battery cell will suffer damage as a result of the manufacturing of the end cover assembly  325  is reduced. 
         [0173]    The cover plate  1605  and scabbard  1610  may be formed from stainless steel. Before further processing, the surfaces of the cover plate  1605 , scabbard  1610 , and connector  800  that will be contacted by the sealing material  1615  may be abraded to increase adhesion between these structures and the sealing material  1615 . 
         [0174]    With reference to both  FIGS. 16 and 17 , the connector  800  includes upper channels  1620  disposed on opposed faces of the connector  800  and lower channels  1625  disposed on opposed faces of the connector  800 . The upper and lower channels  1620  and  1625  extend substantially along the length of connector  800 . Channels  1620  are positioned so that they are generally juxtaposed to inwardly extending lips  1630  of the scabbard  1610 . 
         [0175]    Connector  800  also includes a plurality of via holes  1635  that extend completely through the width of the connector. As shown in  FIG. 16 , the via holes  1635  are positioned adjacent a further set of inwardly extending lips  1640  of the scabbard  1610 . As shown in  FIG. 17 , the via holes  1635  may be disposed at various positions along the length of the connector  800  and between the channels  1620  and  1625 . 
         [0176]    Once the cover plate  1605  and scabbard  1610  have been welded to one another, the connector  800  is directed to its desired position within an interior channel of the scabbard  1610  and the sealing material  1615  is injected into the interstitial regions between the connector  800 , scabbard  1610 , and cover plate  1605 . The sealing material is injected under high pressure to fill channels  1620 ,  1625 , via holes  1635 , as well as the regions around inwardly extending lips  1630  and  1640 . 
         [0177]    The sealing material  1615  may be a plastic (e.g., PFA, PES, PPS, modified PP, etc.), a rubber compound, a resin (e.g., an epoxy resin, phenol aldehyde modified epoxy resin, etc.), an agglutination rubber (e.g., a double component epoxy, hot melt rubber, etc.). The sealing material  1615  should be an electrical insulator and be capable of sustaining exposure to the electrolyte and hydrochloric acid. Further, the sealing material  1615  should be capable of bonding with the various metals used to form the connector  800 , scabbard  1610 , and cover plate  1605  (e.g., copper, aluminum, stainless steel, and other metals). 
         [0178]    The sealing material  1615  extends beyond the upper portion of the scabbard  1610 . More particularly, the sealing material  1615  fills the interior region between the scabbard  1610  and connector  800  and wraps around the outside of the scabbard  1610  to form a protective flange  1645 . The protective flange  1645  further enhances the integrity of the seal. Further, the protective flange  1645  may absorb some of the vibrational and impact forces that would otherwise be imparted to the connector  800 . 
         [0179]    As shown in  FIG. 61 , the end cover assembly  325  may include a further protection cover  6105  that generally conforms to the outermost portions of other members of the end cover assembly  325 . In the illustrated embodiment, protection cover  6105  includes a first portion  6115  that extends along and conforms with an outer surface of the cover plate  1605 . Cover plate  1605  may include a cover plate flange  6120  that engages a corresponding flange  6125  of the first portion  6115 . The protection cover  6105  also includes a second portion  6110  that extends at an angle of, for example, about  900  from the first portion  6115 . The second portion  6110  extends about and conforms with an outer surface of the scabbard  1610  and protective flange  1645 , and terminates in an opening  6130  through which terminal  800  protrudes. Preferably, the second portion  6110  seals with the terminal  800  at the opening  6130 . Still further, the second portion  6110  includes an interior flange  6140  that engages the protective flange  1645 . The region of the second portion  6110  beneath the interior flange  6140  may be dimensioned so that the protective flange  1645  applies a force against the protection cover  6105  to assist in securing the protection cover  6105  against the cover plate  1605 . 
         [0180]    The protection cover  6105  may be formed from an electrical insulator. For example, the protection cover  6105  may be formed from a plastic (e.g., PFA, PES, modified PP, or the like), rubber (e.g., EPDM, styrene-butadiene rubber, or the like), resin (epoxy resin, phenolic aldehyde modified epoxy resin, or the like). Such materials are insulators, fire resistant, and are not readily degraded by the electrolyte of the battery cell. By forming the protection cover  6105  using insulating materials, short-circuits resulting from physical distortion of the connector  800  (e.g., during a vehicle collision/accident) with respect to the cover plate  1605  are reduced and/or eliminated. Similarly, the protection cover  6105  may extend about the edge portions of the cover plate  1605  to avoid undesired electrical contact between the battery cell and other battery system structures. 
         [0181]    Protection cover  6105  may be formed as an integral structure or multipiece structure.  FIGS. 62 and 63  illustrate multipiece protection cover structures while  FIG. 64  illustrates an integral protection cover structure. 
         [0182]    In  FIG. 62 , the protection cover  6105  is formed from two individual protection cover halves  6200   a  and  6200   b.  Each half  6200   a  and  6200   b  includes a respective first portion  6115   a,    6115   b  that is dimensioned to extend along and conform with an outer surface of the cover plate  1605 . Each half  6200   a  and  6200   b  also includes a respective flange  6125   a,    6125   b  that engages the corresponding cover plate flange  6120 . Second portions  6110   a,    6110   b  extend at an angle, for example, of about  900  from the first portions  6115   a,    6115   b.  The second portions  6110   a,    6110   b  are dimensioned to extend about and conform with an outer surface of the scabbard  1610  and protective flange  1645 . Openings  6130   a,    6130   b  are disposed through each half  6200   a,    6200   b  and are dimensioned to allow terminal  800  to protrude therethrough. Second portions  6110   a,    6110   b  include interior flanges  6140   a,    6140   b  that engage the protective flange  1645 . Protective flange  1645  may apply a force against the interior flanges  6140   a,    6140   b  to assist in securing the protection cover  6105  against the cover plate  1605 . 
         [0183]    The protection cover halves  6200   a,    6200   b  are joined with one another using mating structures. In  FIG. 62 , half  6200   a  includes a rectangular extension  6205   a  that is dimensioned to engage rectangular opening  6205   b  of half  6200   b.  In applying the protection cover  6105  to the end cover assembly  325 , halves  6200   a  and  6200   b  may be directed laterally toward one another so that the interior flanges  6140   a  and  6140   b  engage an underside of the protective flange  1645 . Concurrently, the mating structures  6205   a  and  6205   b  are directed toward one another until they are substantially or fully engaged. Depending on the dimensions and characteristics of the protection cover  6105 , a bonding agent may be applied to an exterior surface of each of the mating structures  6205   a  and  6205   b  prior to assembly to increase the overall integrity of the protection cover  6105 . Other bonding techniques may also be used. 
         [0184]    The mating structures may take on a variety of different shapes. In  FIG. 63 , half  6200   a  includes an oval extension  6305   a  that is dimensioned to engage a corresponding oval opening  6305   b  of half  6200   b.  Other mating structure shapes (e.g., triangular, trapezoidal, or the like) may also be used. 
         [0185]    In  FIG. 64 , the protection cover  6105  is formed as a singular, integrated structure. When formed in this manner, the protection cover material is preferably highly elastic so that the protection cover may be applied to the end cover assembly  325  over terminal  800 . 
         [0186]    The protection cover  6105  may include visual indicia indicative of the characteristics of the battery cell/terminal. In the protection covers shown in FIGS.  62 - 64 , a visual indicator  6215  of the pole type is provided to identify the corresponding terminal as a cathode terminal or anode terminal. The exemplary indicator  6215  identifies the corresponding terminal  800  as a cathode terminal. 
         [0187]    With reference to  FIG. 17 , the end cover assembly  325  includes a blow out vent  1800 . The blow out vent  1800  is adapted to prevent a catastrophic rupture of the battery cell  300  in the event that the interior pressure of the battery cell  300  reaches an unsafe level. If this pressure is not relieved, the battery cell  300  may explode. In each of  FIGS. 62 through 64 , the protection cover  6105  includes an exhaust vent  6210  that overlies the blow out vent  1800  so that the protection cover does not prevent the release of gases and/or other materials from the blow out vent  1800 . 
         [0188]      FIG. 18  shows one embodiment of a blow out assembly  1800  that may be used on the end cover assembly  325 . Blow out assembly  1800  includes a vent cover  1805 , a rupture pin  1810 , and a vent base  1815 . As shown, the blow out assembly  1800  is secured over an exhaust vent  1820  of the cover plate  1605 . 
         [0189]    The vent cover  1805  may be in the form of a truncated trapezoidal cone with an exposed bottom surface. A plurality of exhaust openings  1825  are disposed through the sides of the vent cover  1805 . The cumulative area of the exhaust openings  1825  should be greater than the area of opening  1820 . The rupture pin  1810  extends through an opening at the top of the vent cover  1805  where it is secured using, for example, spot laser welding. 
         [0190]    The vent base  1815 , as shown in both  FIGS. 18 and 19 , includes an annular ring  1830  and a flange  1835 . A deformable membrane  1840  is attached to the annular ring  1830  by welding it over the interior opening of the ring. The width of the annular ring  1830  has a diameter that is preferably less than about 70% of the width of its interior opening. Further, the width of lip  1845  of the annular ring  1830  preferably does not exceed 70%-80% of the width of the exhaust vent  1820 . 
         [0191]    The deformable membrane  1840  is preferably formed from the same material as the cover plate  1605  (e.g. aluminum, stainless steel, etc.) and has a thickness between about 0.01 mm-0.1 mm, with a preferable thickness between 0.01 mm and 0.05 mm. The thickness of the deformable membrane  1840 , however, may be adjusted based on the overpressure level at which the vent assembly  1800  is to fail. The deformable membrane  1840  may be brazed to properly seal over the opening of the annular ring  1830  and may be formed from a metal foil, such as aluminum foil, copper foil, etc. 
         [0192]    Valve base  1815  is welded to the cover plate  1605  using a high energy beam such as a laser or electronic beam. The vent cover  1805  includes a boss  1850  that is secured with vent base  1815 . Boss  1850  includes a plurality of openings  1855  that are distributed about its circumference to facilitate a high energy beam welding of the vent cover  1805  to the vent base  1815 . 
         [0193]    As the pressure within the battery cell  300  approaches a critical level, the deformable membrane  1840  distorts in the direction of the rupture pin  1810 . Upon reaching the critical pressure, the deformable membrane  1840  is pierced by the rupture pin  1810  to release the pressure and preventing explosion of the battery cell  300 . The pressure at which rupture of the deformable membrane  1840  occurs can be adjusted by adjusting the distance between the deformable membrane  1840  and the rupture pin  1810 . Further, the shape of the rupture pin  1810  may be used to cause different rupture modes under different critical pressures. Still further, during assembly of the battery cell, when the air within the battery cell  300  is exhausted during manufacturing, there is a reverse distortion of the deformable membrane  1840  that increases the distance between the membrane and the rupture pin  1810 . This characteristic facilitates rapid manufacture of normal batteries and safe removal of abnormal batteries from the production line. 
         [0194]      FIGS. 21 and 22  show alternative pressure relief structures  2100  and  2200 . Each structure may be disposed sealed with a corresponding exhaust opening of the cover plate  325 . Relief structure  2100  is formed from a deformable membrane  2105  having a weakening groove  2110 . Similarly, relief structure  2200  is formed from a deformable membrane  2205  having a weakening groove  2210 . The principal differences between structures  2100  and  2200  are in the shape formed by the edges of each membrane and the shape of the weakening groove disposed in each membrane. The dimensions of the deformable membranes  2105  and  2205  of each pressure relief structure  2100  and  2200  as well as the depth and extent of each weakening groove  2110  and  2210  are dependent on the particular pressure at which the respective structure is to fail to prevent explosion of the battery cell. A still further alternative pressure relief structure includes filling the exhaust vent with a polymer sealing material, where the polymer seal is adapted to fail above a predetermined pressure. 
         [0195]      FIGS. 65-67  illustrate a further embodiment of a blow out vent  1800 .  FIG. 65  shows the blow out vent  1800  in an assembled state on the cover plate  1605 .  FIG. 66  is an exploded view of the blow out vent  1800  while  FIG. 67  is a cross-sectional view of the vent. 
         [0196]    In this embodiment, blow out vent  1800  includes a membrane  6605  that is disposed over a trough  6610  that, in turn, surrounds an exhaust opening  1820  of cover plate  1605 . The trough  6610  includes an interior edge  6625  defining opening  1820  and an outer edge  6620  defining the periphery of the trough  6610 . The radial difference between edges  6620  and  6625  may be about 10% to 15% of the radius of exhaust opening  1820 . 
         [0197]    Membrane  6605  is dimensioned to fit snugly within the outer edge  6620  of the trough  6610 . A variety of materials may be used to form the membrane  6605  including, for example, aluminum, aluminum alloy, steel, or any other material that satisfies the material failure requirements for the vent  1800 . Further, the material may be selected so that it is one which may be easily welded. The thickness of the material may be between about 0.01 mm and 0.1 mm. Although the illustrated membrane  6605  is circular, other shapes (e.g., rectangular, elliptical, square, or the like) may also be used. 
         [0198]    A safety mask  6615  is disposed over membrane  6605 . The safety mask  6615  includes a rim  6630  that fits snugly with outer edge  6620  of trough  6610 , where it is welded to the outer edge  6620  at one or more joints  6705 . Welding techniques that may be used include, for example, laser welding and/or electron beam welding. 
         [0199]    A crown portion  6635  extends from rim  6630  in a direction away from membrane  6605 . The crown portion  6635  may have a radius that is generally equal to the radius of the opening  1820 . A plurality of oval-shaped openings  6640  are disposed in the sidewalls of the crown portion  6635 . The total area of the oval-shaped openings  6640  may be approximately equal to or greater than the area of opening  1820 . The wall thickness of the safety mask  6615  may be between about 0.1 mm-0.5 mm. 
         [0200]    The foregoing blow out vent structure may be used to achieve numerous advantages. For example, assembly of the structure is both simple and economical. When the membrane  6605  and safety mask  6615  are assembled over the opening  1820 , the assembly may be easily secured with the cover plate  1605  by welding the rim  6630  of the safety mask  6615  to the outer edge  6620  of the trough  6610 . Safety mask  6615  assists in protecting membrane  6605  from external forces thereby ensuring the integrity of the overall blow out vent  1800 . Still further, the safety mask  6615  may be used to reduce the expulsion of non-gaseous materials from the battery cell when the interior pressure of the battery cell exceeds safe levels. 
         [0201]      FIG. 23  is a block diagram of a battery pack  2300  in which multiple battery cells  300  are interconnected with one another in series and grouped within a single housing  2305 . The number of battery cells  300  in a single housing  2305  may range from 8 to 15, with 10 battery cells per pack being preferable. Terminal connectors  2810  are disposed at opposite ends of the battery pack  2300  and are used to provide a means for establishing an electrical and mechanical connection between multiple battery packs  2300 . Housing  2305  is preferably hermetically sealed and water-tight, but includes ducts  2310  to receive a flow of a thermal fluid therethrough. The ducts  2310  are disposed laterally on opposite sides of the battery pack  2300  so that the flow of thermal fluid runs proximate the connectors  800  to either heat or cool the battery cells  300  of the battery pack  2300 . The protective shells of adjacent battery cells may be proximate one another in that they are in direct contact with one another or disposed immediately adjacent one another at opposite faces of an insulator sheet. 
         [0202]      FIG. 24  is an exploded view of one embodiment of a housing  2305  that may be used to form battery pack  2300 . In this embodiment, housing  2305  includes a plurality of series connected battery cells  300 . The battery cells  300  are connected with one another in the manner shown in  FIG. 23 . A separator  2405  made from an insulating material is disposed between each battery cell  300  to electrically isolate the protective shells of the battery cells  300  from one another. Preferably, however, the separators  2405  are not employed. Rather, the protective shells are preferably in direct contact with one another so that they form a single thermal unit. Temperature control is thereby more easily maintained. 
         [0203]    Battery cells  300  are disposed between a bottom plate  2410  and a top plate  2415  to limit movement of the battery cells  300  along the y-axis. Baffle structures  2420  are disposed on each side of the group of battery cells  300  and oriented to traverse the length of the battery cells  300 . The baffle structures  2420  cooperate with one another to limit movement of the battery cells  300  along the x-axis. Side plates  2425  are disposed at opposite ends of the battery cells  300  and extend along the width of the battery cell group. The side plates  2425  limit motion of the battery cells  300  along the z-axis. 
         [0204]    Sealing elements  2450  may be located between each baffle structure  2420  and the top and bottom plates  2415 ,  2410  as well as between each side plate  2425  and the top and bottom plates  2415 ,  2410 . In this manner, the top and bottom plates  2415 ,  2410  form water-tight seals with the mating components. Such seals assist in preventing short circuits that would otherwise result when a battery cell  300  fails and allows liquid to escape. 
         [0205]    The baffle structures  2420  are made of an insulating plastic material having the desired mechanical strength, thermal degradation resistance, low temperature ductility, and resistance to battery and environmental chemicals in the vehicle. One embodiment of a baffle structure  2420  is shown in  FIG. 25 . Each baffle structure  2420  is comprised of a baffle plate  2430 , a baffle stiffener  2435 , and apertures  2440  disposed at the corners of the baffle structure  2420 . Apertures  2440  are adapted to accept corresponding tension rods that extend between the baffle structures  2420  to secure the battery cells  300  therebetween. The total thickness of each baffle structure  2420  may be between about 3 mm and 15 mm. The thickness of each baffle plate  2430  may be between about 3 mm and 5 mm. The thickness of each baffle stiffener  2435  may be between about 5 mm and 2 mm. The baffle stiffener  2435  evenly distributes horizontal and vertical forces throughout the baffle structure  2420  and increases the ability of the baffle structure  2420  to protect the battery cells  300 . Via holes may be pre-positioned to facilitate the use of mechanical fasteners, such as screws, at the four corners of the baffle structure  2420 . Such mechanical fastening is convenient for connecting the top and bottom plates  2415 ,  2410  to the baffle structure  2420 . There are L-shaped structures on the baffle structure  2420  that are positioned to mate with the top and bottom plates  2415 ,  2410 . The top plate  2415  is located between an upper L-shape structure and a lower L-shape structure of the baffle structure  2420 . An aperture is located between the top plate  2415  and the upper L-shaped structure of the baffle structure  2420 . The aperture is adapted to receive a pin which limits movement between the top plate  2415  and the baffle structure  2420  thereby inhibiting movement of the battery cells  300  along the x-axis and y-axis. 
         [0206]    The top and bottom plates  2415 ,  2410  are made from a plastic insulator material having the desired mechanical and chemical characteristics. As shown in  FIG. 26 , the top and bottom plates  2415 ,  2410  are each comprised of a flat plate  2605 , a stiffener  2610 , and apertures  2615 . The apertures  2615  are adapted to receive corresponding tension rods that extend between the top and bottom plates  2415 ,  2410 . The whole thickness of each of the top and bottom plates  2415 ,  2410  may be between about 3 mm and 15 mm. The thickness of each flat plate  2605  may be between about 3 mm and 5 mm. The thickness of each stiffener  2610  is between about 5 mm and 10 mm. The stiffener  2610  is adapted to distribute horizontal and vertical forces evenly over the respective top and bottom plate structures  2415 ,  2410 . Pre-embedded bolts on the top and bottom plates  2415 ,  2410  are used to connect the top and bottom plates  2415 ,  2410  with the baffle structures  2420  as well as with the side plates  2425 . A boss at the inner side of the top plate  2410  limits motion of the battery cells  300  along the y-axis. 
         [0207]    The side plates  2410  are made of plastic insulator material having the desired mechanical and chemical characteristics. As shown in  FIG. 26 , each side plate  2425  has an outline that matches the side openings formed when the top plate  2415  and bottom plate  2410  are connected with one another. 
         [0208]    The battery pack housing  2305  is advantageous for several reasons. For example, the battery pack housing  2305  limits movement of the battery cells  300  along every motion excess thereby improving the reliability of the battery pack  2300  and prolonging the battery service life. The movement of the battery cells  300  may be readily limited along each axis by designing the baffle structures  2420  and the top and bottom plates  2415  in a manner which decreases the volume occupied by the battery pack  2300 . By forming the housing  2305  from an insulating material, the risk of short-circuits is reduced because the battery cells  300  cannot electrically connect with each other through the housing  2305 . Further, by using a plastic material to form the components of the housing  2305  the weight of the battery pack  2300  is reduced. Still further, the likelihood that short-circuits will result from battery cell leakage is reduced since a sealing material is provided at the joints between the various components of the battery pack  2300  thereby preventing fluid leakage from the battery pack 
         [0209]      FIG. 27  shows a connector  2700  that is used to mechanically and electrically interconnect adjacent battery packs  2300 . Connector  2700  includes a first conductive arm  2705  and a second conductive arm  2710  that are connected by an arch-shaped, multilayer metal foil  2715 . The arch-shaped foil  2715  may have a thickness between about 0.01 mm and 5.0 mm and may be formed from copper foil to make it convenient for welding. Alternatively, conductive arms  2705  and  2710  as well as the arch-shaped foil  2715  may be formed from nickel, aluminum, or other metal. Preferably, conductive arms  2705 ,  2710  and arch-shaped foil  2715  are made from the same material to increase the overall conductivity of the connector  2700 . Formation of the arch-shaped foil  2715  may include hot pressing a plurality of thin metal sheets to one another while forging them into an arch-shaped structure. Each conductive arm  2705  and  2710  includes an L-shaped joint  2720  proximate the arch-shaped foil  2715  at which the arch-shaped foil  2715  is welded and/or hot pressed to the respective arm. The size of each conductive arm  2705 ,  2710  and arch-shaped foil  2715  is determined by the size of the electrode terminals of the battery packs that use connector  2700  as well as the current carrying capacity needed between the battery packs. The arch-shaped foil  2715  may be dimensioned so that it fails when subject to an impact force that exceeds a predetermined magnitude to thereby disconnect the battery pack from an adjacent battery pack. Still further, the arch-shaped foil  2715  may be dimensioned to function as a fuse to disconnect adjacent battery packs when the current between the adjacent battery packs exceeds a predetermined level. 
         [0210]      FIG. 68  shows a further connector  2700  that may be used to mechanically and electrically interconnect adjacent battery packs  2300 . In this embodiment, connector  2700  includes a first conductive arm  6805  and a second conductive arm  6810  that are connected by an arch-shaped metal member  6815 . The arch-shaped metal member  6815  may be formed as a metal mesh  6825  that extends between opposed arch-shaped support arms  6830 . The metal mesh  6825  may have a thickness between about 0.01 mm and 5.0 mm and may be formed from strands of a single type of metal or multiple metals to make it convenient for welding. Arms  6805 ,  6810  may be formed as metal sheets having openings  6820  through which fasteners extend to secure the connector  2700  to the respective battery packs. Conductive arms  6805  and  6810  as well as the arch-shaped metal member  6815  may be formed from copper, nickel, aluminum, or other metal. Preferably, conductive arms  6805 ,  6810  and arch-shaped metal member  6815  are made from the same material to increase the overall conductivity of the connector  2700 . The size of each conductive arm  6805 ,  6810  and arch-shaped metal member  6815  is determined by the size of the electrode terminals of the battery packs that use connector  2700  as well as the current carrying capacity needed between the battery packs. The arch-shaped metal member  6815  may be dimensioned so that it fails when subject to an impact force that exceeds a predetermined magnitude to thereby disconnect the battery pack from an adjacent battery pack. Further, the arch-shaped metal member  6815  may be adapted to function as a fuse to disconnect adjacent battery packs when the current between the adjacent battery packs exceeds a predetermined level. Still further, connector  2700  may be formed so that it is sufficiently elastic to mechanically buffer any motion between adjacent battery packs. 
         [0211]      FIG. 28  shows how connectors  2700  are used to interconnect multiple battery packs  2805   a  and  2805   b  that are arranged in a head-to-head configuration. However, the battery packs  2805   a  and  2805   b  may also be arranged in a side-to-side manner as shown in  FIG. 69  and still use connectors  2700 . As shown, battery packs  2805   a  and  2805   b  each have a pair of battery pack terminals disposed along a single side of the pack, one terminal at each end of the side. The battery pack terminals may be adapted to break when subject to the extraordinary forces that occur during a vehicle accident or the like. A connector  2700  is used at each end of the battery pack to establish a mechanical as well as electrical connection between the battery pack terminals. For simplicity, only terminals  2810   a  and  2810   b  are shown and discussed, although the same configuration is used between each terminal of a battery pack that is adjacent a terminal of another battery pack. The connector  2700  between the batteries packs  2805   a  and  2805   b  provides a mechanical buffer that absorbs impact forces when there is a relative displacement between the battery packs  2805   a  and  2805   b.  Still further, the connector  2700  may be adapted to sever the connection between adjacent battery packs when subject to the extraordinary forces that occur during a vehicle accident or the like. 
         [0212]    The connector  2700  is secured to the battery packs  2800   a  and  2800   b  by connecting the conductive arm  2710  to a connection plate  2830   a  of terminal  2810   a  and the conductive arm  2705  to a connection plate  2830   b  of the adjacent terminal  2810   b.  Each conductive arm  2705  and  2710  includes a groove  2725  adapted to receive a welding wire (see  FIG. 27 ). Further, each arm  2705 ,  2710  includes a plurality of apertures  2730  adapted to receive mechanical fasteners. To connect the adjacent terminals of the battery packs  2805   a  and  2805   b,  a welding wire is placed in each groove  2725 . Each arm  2705 ,  2710  is then welded (e.g., using brazing, laser welding, ultrasonic welding, etc.) to the corresponding terminal. Preferably, each arm is attached to the corresponding terminal using brazing. Brazing allows easy maintenance of the interconnection between the battery packs and, further, simplifies replacement of a battery pack in the battery system since the metal alloy forming the interconnection may be easily reheated to separate the battery pack from other battery packs in the battery system. Additionally, mechanical fasteners  2840 , such as screws, bolts, or the like, are inserted into apertures  2715  to engage corresponding apertures of the respective terminal and establish a more reliable connection between the conductive arm and corresponding terminal. Welding and securing the connector  2700  to the corresponding terminals of adjacent battery packs in this manner establishes a low resistance, high current capacity path between the adjacent battery packs. Although the adjacent battery packs may be connected so that they are electrically parallel with one another, the preferred arrangement is to have them connected serially. 
         [0213]      FIG. 29  shows a battery system  2900  that supplies electrical power to and receives electrical power from a motor/generator of a vehicle capable of being driven by electric power. Battery system  2900  includes multiple battery packs  2805 . The number of battery packs may be about five, and preferably ten. Each battery pack  2805  includes a plurality of cells  300 , preferably in a range between 8 and 15 packs, and, more preferably, ten packs. The cells  300  of each battery pack  2805  are electrically connected in series with one another. Further, the multiple battery packs  2805  are electrically connected in series with one another. 
         [0214]    Each battery pack  2805  is disposed in a respective battery pack housing  2305 . The vehicle is provided with a compartment containing the multiple battery packs and their housings. The compartment facilitates electrical connection to the motor/generator. The battery pack housing  2305  for each battery pack  2805  is substantially sealed from the ambient environment (e.g., water-tight) with the exception that openings are provided through each battery pack  2805  in a region proximate their respective terminals. The openings of adjacent battery pack housings  2305  are interconnected by duct work to facilitate circulation of a cooling fluid, such as air, throughout the battery system  2900 . 
         [0215]    The compartment containing battery system  2900  may be shaped and sized to fit partially under a rear passenger seat of the vehicle and partially in a trunk compartment of the vehicle. Alternatively, the compartment may be shaped and sized to fit under a floor of the vehicle. 
         [0216]    In  FIG. 29 , a thermal fluid, such as air, is driven through the battery system  2900  by a pump  2905 . The pump  2905  drives the thermal fluid through the system  2900  in the directions designated by the flow arrows  2910 . As illustrated by the flow arrows, the pump  2905  directs the thermal fluid through a thermal processing unit  2915  before it is provided to an entrance  2927  of a central duct  2930  for distribution to other portions of the system  2900 . The thermal processing unit  2915  may include a condenser  2920  to cool the thermal fluid and a heater  2925  to heat the thermal fluid. The condenser  2920  is activated when the temperature of the battery system  2900  exceeds a predetermined threshold. Likewise, the heater  2925  is activated when the temperature of the battery system  2900  falls below a predetermined threshold. 
         [0217]    As the thermal fluid circulates through the central duct  2930 , it either heats or cools the terminal portions of each battery pack  2805  proximate the central duct  2930 . Upon reaching an end portion  2940  of the duct work, the thermal fluid is directed toward the exterior ducts  2910 ,  2940  of the battery system  2900 . This allows the thermal fluid to either heat or cool the terminal portions of each battery pack  2805  proximate the exterior ducting of the battery system  2900 . The battery cells  300  within the battery system  2900  thus operate in a controlled environment in which the temperature is maintained at an optimal level. Some of the thermal fluid may be channeled from the ducts of the battery system  2900  to the passenger compartment of the vehicle. In this manner, the heat generated by the battery system  2900  is used to heat the interior passenger compartment of the vehicle. The amount of thermal fluid channeled from the ducts of the battery system  2900  may be controlled by an individual within the passenger compartment to regulate the compartment temperature. 
         [0218]      FIGS. 30 through 34  illustrate advantages associated with providing connections to the anode and cathode of a coiled core at opposite ends of the core. For comparison,  FIG. 30  shows a battery  3000  having a core  3005 , an anode connector  3010 , and a cathode connector  3115 . The anode connector  3010  and cathode connector  3015  are positioned at the same side of the core  3005 . The current distribution in the core  3005  during operation is indicated by shading. As shown, there is a substantial current density proximate the connectors  3010  and  3015 . Areas of high current density are associated with elevated temperatures in accordance with Ohm&#39;s law. Consequently, the areas proximate connectors  3010  and  3015  run hot during operation and degrade the performance of the battery. The longevity of the battery  3000  is also impacted. 
         [0219]      FIG. 31  shows a battery  3100  having a coiled core  3105 , an anode connector  3110 , and a cathode connector  3115 . The anode connector  3110  and cathode connector  3115  are disposed at opposite sides of the coiled core  3105 . The core  3105  has a length  3120  and a width  3125 . Anode connector  3110  has a width  3130  while cathode connector  3115  has a width  3135 . Although width  3130  and  3135  are shown as being less than the width  1025 , these widths may be extended so that they are substantially commensurate with the width  3125  of the core  3105 . 
         [0220]    The dimensions shown in  FIG. 31  may take on various proportions. For example, the ratio of length  3120  with respect to width  3125  may be between about 1.5 to 4.5, with a preference between about 2.5 and 3.5. The ratio of width  3130  with respect to width  3135  may be between about 0.8 and 1.2, with a preference between 0.9 and 1. The ratio of the width  3130  (as well as the width  3135 ) with respect to the width  3125  may be between about 0.3 and 0.6, with a preference between 0.4 and 0.5. 
         [0221]      FIG. 32  illustrates a situation in which the width  3130  and width  3135  are approximately the same. In this situation, the electric field  3200  forms an angle θ with respect to an edge of the core  3105 . The value of angle θ is determined by tan −1 ((W−a)/L), where W is the width  3125 , a is the width  3130 , and L is the length  3120 . When the angle θ is between about 0° and 20° the current density may be optimized. This occurs when 0&lt;(W−a)/L&lt;0.37. 
         [0222]      FIG. 33  illustrates the current density in the core  3105  during operation. As shown, the current density is not concentrated at one side of the core  3105  but, rather, is distributed at opposite sides proximate anode connector  3110  and cathode connector  3115 . The current density proximate the middle of the core  3105  is reduced compared with  FIG. 30 . Consequently, the central portion of the core  3105  is not subject to significant temperature elevations. Further, temperature variations are not concentrated at a single side of the core  3105 . 
         [0223]      FIG. 34  is a table comparing the performance of a battery constructed in accordance with  FIG. 30  (designated battery A) versus a battery constructed in accordance with  FIG. 31  (designated battery B). The columns of  FIG. 34  correspond to the following values:
       Column  3405  corresponds to the number of discharge/re-charge cycles for each battery;   Column  3410  corresponds to the battery capacity after the number of cycles shown in column  3405 ;   Column  3415  corresponds to the ratio of the current battery capacity to the original battery capacity after the number of cycles shown in column  3405 ;   Column  3420  corresponds to the maximum temperature proximate the anode connector that occurs during operation of the battery after it has been subject to the number of cycles shown in column  3405 ;   Column  3425  corresponds to the maximum temperature proximate the cathode connector that occurs during operation of the battery after it has been subject to the number of cycles shown in column  3405 ; and   Column  3430  corresponds to the maximum temperature proximate the center of the core that occurs during operation of the battery after it has been subject to the number of cycles shown in column  3405 .         
         [0230]    As shown, there are significant differences between the performance parameters of battery A and battery B. The performance differences become increasingly evident as the battery undergoes more charge/recharge cycles. Consequently, the performance of battery B is better than battery A over time and battery B has a greater longevity. 
         [0231]    While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.