Abstract:
A stand alone battery module including: (a) a mechanical configuration; (b) a thermal management configuration; (c) an electrical connection configuration; and (d) an electronics configuration. Such a module is fully interchangeable in a battery pack assembly, mechanically, from the thermal management point of view, and electrically. With the same hardware, the module can accommodate different cell sizes and, therefore, can easily have different capacities. The module structure is designed to accommodate the electronics monitoring, protection, and printed wiring assembly boards (PWAs), as well as to allow airflow through the module. A plurality of modules may easily be connected together to form a battery pack. The parts of the module are designed to facilitate their manufacture and assembly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a stand alone battery module of juxtaposed electrochemical cells. A plurality of modules are in turn assembled together to form a battery pack. Although the cells may be of any type, lithium-ion cells are particularly suitable when the module is used in a battery pack for an electric vehicle. 
     2. Related Art 
     U.S. Pat. No. 5,378,555 to Waters et al. discloses an electric vehicle battery pack wherein a plurality of batteries are set in a supporting tray, and are mechanically connected together by interlocking plugs. The interlocking plugs include passages for electric connection between the batteries by cables, as well as for cooling tubes, and for wiring systems for the pack&#39;s electronic controllers. However, the battery pack disclosed in Waters includes the disadvantages of having a large volume and complex mechanical, electrical, as well as thermal connections, between the batteries in the battery pack. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to overcome the disadvantages of the prior art. Another object of the present invention is to provide a battery module for retaining a plurality of electrochemical cells for convenient use as a battery. Another object is to provide a battery module having component parts which are easy to manufacture. A further object is to provide a battery module which is easy to assemble. A further object of the present invention is to provide a simply designed battery module which can accommodate different sized cells while eliminating rattle, maintaining a proper thermal operating temperature, and simple electrical connections. A further object is to provide a battery module having decreased volume and weight. 
     The stand alone battery module of the present invention includes a configuration which reduces the overall volume of the module as well as facilitates the connection of a plurality of modules to form a battery pack. Further, the configuration of the module reduces the overall weight of the module, thereby increasing the power to weight and energy to weight ratios of the module as well as that of any battery pack in which it is included. Moreover, the parts which make up the module are designed to facilitate their manufacture, as well as facilitate assembly of the module. 
     The stand alone battery module of the present invention includes: (a) a mechanical configuration; (b) a thermal management configuration; (c) an electrical connection configuration; and (d) an electronics configuration. Such a module is fully interchangeable in a battery pack assembly, mechanically, from the thermal management point of view, and electrically. With the same hardware, the module can accommodate different cell sizes and, therefore, can easily have different capacities because Saft cells are designed with the same diameter but different lengths for different capacities. The module structure is designed to accommodate the electronics monitoring, protection, and printed wiring assembly boards (PWAs), as well as to allow airflow through the module. A plurality of modules easily may be connected together to form a battery pack. The battery pack is especially useful as a power source for an electric vehicle. 
     a) Mechanical Configuration 
     In the battery module of the present invention, a cell assembly is formed of a plurality of cells which are held between a pair of cell holding boards which in turn are connected by tie rods, for example. The cells are aligned so that their longitudinal axes are parallel with one another, and are perpendicular to the holding boards. The cell assembly is contained within a shell. An end cap is then attached to each holding board with a space between the end cap and holding board. Within each end cap there are two ports. On one side of the module, the ports in one end cap are for air intake, whereas the ports in the opposite end cap are for exhaust. On the intake side, the space between the end cap and the holding board is an air manifold. Because the ports in the end caps are similar, either end cap may be the inlet or exhaust side of the module. 
     Each holding board includes a first side, a second side, and a thickness therebetween. On the first side are a plurality of cavities which extend into the holding board, but to an extent less than the thickness of the holding board, so as to form a cavity bottom. The peripheral shape of each cavity matches the peripheral shape of the cell to be held therein. Preferably the cells and cavities have a circular peripheral shape as such provides good reduction in volume of the module due to the ease in nesting of the cells with one another. A plurality of cavities are aligned along the length of the holding board to form a first line. A second line includes a plurality of cavities which are staggered with respect to the cavities of the first line. A third line includes a plurality of cavities which are staggered with respect to the cavities of the second line, but are aligned with respect to the cavities of the first line. The foregoing arrangement of circular cavities allows the cells to easily nest with one another thereby reducing the overall volume of the module. Because the second line is offset from both the first and third line, it forms in the module a protrusion on one side and a recess on the other side. The protrusion and recess assist in locking modules together to form a battery pack having an overall reduced volume, as well as increased stability. That is, when the protrusion on one module is aligned with the recess on an adjacent module, the modules nest together, and are stably held with respect to one another while producing an overall minimum volume for the battery pack. 
     Within the periphery of each cavity there is a first through hole which accommodates a terminal of the cell held by the cavity. Some of the cavities also include a second through hole which accommodates a fill tube of the cell. The second through hole is in the cavities which hold the negative end of the cell because that end of the cell includes the fill tube. The cavity bottom may include a recessed portion to accommodate a terminal plate of the cell. Each cavity also may include a plurality of wedges around the periphery thereof. Each wedge may be shaped as a triangular web extending between the side wall and the cavity bottom. The wedges assist in holding a cell within a cavity of the holding board. By applying pressure and/or heat at the right places during assembly of the cells between the cell holding boards, the wedges are formed so as to eliminate rattle of the cell within the cavity, and accommodate variations in cell height. 
     Each holding board also includes a plurality of holes through the thickness thereof, but which are not located within the periphery of any cavity. Some of the through holes accommodate airflow through the holding board. This type of through hole may be of various sizes depending on its location relative to the cavities on the holding board, and may be of a slot type configuration, for example. This type of through hole, in conjunction with the openings in the end caps, provides an easy to manufacture mechanism for controlling the module&#39;s thermal management. Of course any other suitable shape may be used for the airflow through holes. Other through holes accommodate tie rods, or other suitable means, which extend between the pair of holding boards to attach the holding boards together with the cells therebetween. 
     The second side of each holding board includes lugs for the attachment of an end cap. Because the lugs are formed as a part of the holding board, a reduced number of separate parts is necessary for assembly of the module, which is thereby facilitated. The lugs may have various configurations depending on how the end cap and the holding board are connected. In a first configuration, the lugs include threaded inserts therein which receive screws. The screws are inserted through an end cap, and into the threaded insert in the lug, to form the connection. In a second configuration, the lugs include blind holes therein, into which rivets are inserted. The rivets are inserted through an end cap, and into the hole in the lug. The rivets are then expanded within the hole in the lug to form the connection. In a third configuration, the lugs include two portions. A first portion extends from the second side of the holding board. A second portion, slightly smaller in periphery than the first portion, extends from the first portion. Because the second portion is smaller in periphery than the first, a shoulder, or stepped, portion is formed to about against an end cap. The second portion is inserted through an aperture in an end cap so as to extend therefrom. Then, the second portion is heated and deformed, as by a plastic riveting process, to form the connection. In the first and second configurations, the height of the lugs determines the height of the air manifold, whereas in the third configuration, the height of the first portion does so. Thus, the lugs also provide an easy manner in which to connect the end caps to the holding boards, especially in the third embodiment, while also easily maintaining an accurate manifold height. 
     The second side of each holding board also includes recesses shaped to accommodate electrical bus connectors which extend between pairs of the cells. The recesses do not extend through the entire thickness of the holding board, but are deep enough so that the bus connectors are below the second side of the holding board. In such a manner, the holding board itself provides electrical insulation between the connectors, each of which extend between a pair of cell terminals. The holding board itself also provides insulation between the connectors and the cell cases which are negatively charged. Because the cell holding board provides the necessary insulation, separate insulating materials are eliminated thereby reducing weight of the module. Further, the recesses are shaped so as to accommodate a complementarily shaped bus connector. Thus, the cell holding boards serve as a template, or map, for making the electrical connections between the cells in the module. Because the recesses only accommodate a complementarily shaped bus connector, assembly of the module is facilitated. 
     The cell assembly, comprised of a plurality of cells held between two holding boards, is inserted in a shell, and then the end caps are attached to the holding boards. The shell is dimensioned so that it is slightly shorter than the distance between the end caps after they have been attached to the holding boards. In such a manner, the shell does not receive any stress load applied to the end caps. That is, the shell is allowed to “float” between the end caps. Therefore, the shell may be made thin thus further reducing the weight of the module. Moreover, the thin shell has a simple overall shape which can easily be manufactured. Because the end caps take a force load, they may include stiffening ribs on a surface thereof. 
     In another embodiment, only one holding board is provided. With this arrangement the module does not stand alone, but is used as part of a battery pack. 
     b) Thermal Management Configuration 
     In the module, the cells are spaced from one another by a cell-to-cell distance measured between the outer periphery of one cell and the outer periphery of an adjacent cell. The cells adjacent the shell are spaced therefrom by a cell-to-shell distance. The temperature difference between the inner surface (at an inside diameter of a cell having a hollow core) and an outer surface (at an outside diameter of a cell having a hollow core) of each cell is ΔT. An end cap is attached to each holding board with a space between the end cap and holding board. Within each end cap there are two ports. On one side of the module, the ports in one end cap are for air intake, whereas the ports in the opposite end cap are for exhaust. On the intake side, the space between the end cap and the holding board is an air manifold. 
     1) First Embodiment of the Module Thermal Management Configuration: 
     A battery module arrangement wherein uniform air velocity within the module is attained. To attain uniform air velocity distribution at all gaps between cells as well as between cells and the shell inside wall, an air intake manifold is designed—both analytically and experimentally—with 2 ports of air intake on the intake end cap; each port having a set of openings with specially selected geometry and size on the side wall and the bottom. The air intake velocity distribution is controlled by the size and location of each intake port, the height of the air manifold created between the end cap inner surface and the top surface of the cell board, the size as well as geometry and location of each opening on the side wall and/or bottom of each air intake port. As a nonlimiting example, the manifold and intake ports are designed so that intake air entering at 5 m/s leaves on the exhaust side of the module at velocities ranging between 3.5 and 4.5 m/s measured at the exhaust point of cell-to-cell or cell-to-shell gaps. This has been verified experimentally for a selected manifold design. The air manifold, which is easily and accurately formed by the connection between the cell holding board and end cap, allows the control of the temperature within the cell by controlling the air flow rate. 
     2) Second Embodiment of the Module Thermal Management Configuration: 
     A battery module arrangement wherein uniform temperature distribution across each cell is attained. To attain uniform temperature distribution, the manifold height is minimized while still accommodating the cells, necessary hardware, and cell-to-cell connectors. The air intake ports do not need to include any specialized shape. The cell-to-cell and cell-to-shell distances were experimentally and analytically selected to maintain a uniform velocity of air through the cell assembly with a minimum pressure drop across the module and minimum air flow rate. 
     Because there is no specialized shape necessary for the air intake ports, there is no dedicated air intake and exhaust. That is, either side of the module may be the intake/exhaust, and air can flow through the module in either direction. With the above configuration, each cell within the module can be maintained at a predetermined ΔT depending on the intake air flow rate. 
     c) Module Electrical Connector Configuration 
     There are two types of electrical connector within the module. A first type of connector extends between cells of the module. A second type of connector extends between common potentials of the electrically connected group of cells in the module and the desired load application outside of the module. 
     The first type of connector is an electrically conductive bus connector. Each bus connector is a strip of material having a first end and a second end. There is a hole on each the first end and the second end to accommodate a cell terminal stud. The first type of connector may be either straight, or include a curved section. The shapes of the connectors are complementary to the shape of the recesses in the cell holding boards to ensure that the cells are properly connected. A flag terminal is attached between the first and second ends of the strip. The flag terminal provides a simple connection between the module cells and the module electronic control system. The connectors are treated for anticorrosion. Because of their configuration, the bus connectors are easily made. Moreover, because of the simple connection provided by the flag terminal on the bus connector, assembly of the module is facilitated. 
     The second type of connector, a power connector, includes an L-shaped electrically conductive block. In the end of a first leg of the L-shaped block there is a blind threaded hole. The first leg extends through a square hole in an end cap of the module to enable connection to the threaded hole from outside of the module. The second leg of the L-shaped block includes a through hole in a side face thereof. A wire is connected to the hole in the second leg, and to a tab connection. The tab connection is then connected to the common potential of all the cells within the module. 
     d) Module Electronics Configuration 
     The module includes an electronic control system which is connected to the cells within the module so as to monitor voltage and temperature of each cell. Also, the electronic control system is used for communication with other modules, as well as cell balancing during the charge cycle of the module. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the accompanying drawings, wherein: 
     FIG. 1 is an exploded perspective view of the module of the present invention; 
     FIG. 2 is a bottom plan view of an intake cell holding board according to the present invention; 
     FIG. 3 is a top view of the intake cell holding board of FIG. 2 having electrochemical cells and bussing connectors attached thereto; 
     FIG. 4 is a top view of the intake cell holding board of FIG. 2; 
     FIG. 5 is a cross sectional view of the intake cell holding board as taken along lines I—I of FIG. 4; 
     FIG. 6 is a bottom view of the intake cell holding board of FIG. 2; 
     FIG. 7 is a bottom view of an exhaust cell holding board according to the present invention; 
     FIG. 8 is a bottom plan view of an intake end cap according to the present invention; 
     FIG. 9 is a bottom view of the intake end cap as shown in FIG. 8; 
     FIGS. 10 a-c  are top, perspective, and side views of a long bus connector according to the present invention; 
     FIGS. 11 a-c  are top, perspective, and side views of a short bus connector according to the present invention; 
     FIGS. 12 a-f  show a power connector of the present invention, wherein FIG. 12 a  is a perspective view including a cable attached to one embodiment of the power connector, and FIGS. 12 b-c  are top and side views of the power connector as shown in FIG. 12 a , and FIGS. 12 d-f  show, respectively, plan, top and side views of a second embodiment of the power connector; 
     FIG. 13 shows a perspective view of an electrochemical cell; and 
     FIGS. 14 a-d  show side views of first to third embodiments of a lug for connecting a cell holding board to an end cap according to the present invention; 
     FIGS. 15 a-c  show views of a second embodiment of cell holding board, wherein FIG. 15 a  shows a top view, FIG. 15 b  shows a cross sectional view taken along the line II—II of FIG. 15 a , and FIG. 15 c  is a perspective view. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1, the module of the present invention includes a cell assembly  2  which is inserted in a shell  80  which, in turn, is closed by end caps  50 ,  50 ′. 
     The cell assembly  2  is formed of a plurality of cells  4  which are held between a pair of cell holding boards  20 ,  20 ′ which, in turn, are connected by tie rods  14  and nuts  16 . The cells  4  are cylindrical and are aligned so that their longitudinal axes are parallel with one another, and are perpendicular to the holding boards  20 ,  20 ′. The cells  4  are aligned in three staggered rows such that they nest to reduce the overall volume of the module. 
     The cell assembly  2  is contained within a shell  80 . End caps  50 ,  50 ′ are then attached to the holding boards  20 ,  20 ′ with a space between each end cap  50 ,  50 ′ and a respective holding board  20 ,  20 ′. The end caps  50 ,  50 ′ and holding boards  20 ,  20 ′ each include similar protrusions on one end and recesses on an opposite end. The protrusions of the end caps  50 ,  50 ′ and holding boards  20 .  20 ′ are received in a protrusion accommodation portion  86  of the shell  80  so as to from a protrusion on one end of the module. The recesses of the end caps  50 ,  50 ′ and holding boards  20 ,  20 ′ receive indentation  88  in the shell  80 . Thus, the module includes a recess at an end thereof opposite to that on which the protrusion is located. The protrusion of one module may thus easily be received in the recess of an adjacent module thereby interlocking the modules for a secure connection between the modules of a battery pack. Further, overall volume of the battery pack is reduced because adjacent modules interlock. 
     The shell  80  is dimensioned so that it is slightly shorter than the distance between the end caps  50 ,  50 ′ after they have been attached to the holding boards  20 ,  20 ′. With such an arrangement, the shell  80  does not receive any stress load applied to the end caps  50 ,  50 ′. That is, the shell  80  is allowed to “float” between the end caps  50 ,  50 ′. Therefore, the shell  80  may be made thin thus reducing the weight of the module. Because Saft cells are designed with the same diameter but different lengths for different capacities, the capacity of the module can easily be varied by merely varying the length of the shell  80  and that of the tie rods  14  which hold the cell holding boards  20 ,  20 ′ on either side of the cells  4 . 
     Additionally, the cell holding boards  20 ,  20 ′, and end caps  50 ,  50 ′ include similar recesses  46 , and  58 ′, respectively, along each longitudinal side. See FIGS. 4 and 9. The shell  80  includes corresponding indentations  85  which are received in the recesses  46 , of the cell boards  20 ,  20 ′, as well as in the recesses  58 ′ of the end caps  50 ,  50 ′. The foregoing arrangement reduces the weight of the cell boards  20 ,  20 ′ and end caps  50 ,  50 ′ while at the same time strengthening the shell  80 . 
     Each of the parts which make up the module will now be described in further detail. 
     Cell 
     A preferred embodiment of an electrochemical cell for use in the module is shown in FIG.  13 . Each electrochemical cell  4  includes a positive end  3  and a negative end  5 . The negative end  5  of the cell includes a safety vent  6 , a terminal plate  8 , a threaded stud  10 , and a fill tube  12 . The safety vent  6  allows the escape of excess pressure that builds up within the cell. The terminal plate  8 , serving as a current bus, is connected to the negative electrode (not shown) within the cell  4 , and to the threaded terminal stud  10 . The threaded stud  10  is then used to connect the cell to other cells within the module, or to a power connector  60  of the module. The fill tube  12  is used, during the manufacture of the cell, for inserting electrolyte within the cell casing. Further, the cell may have a hollow core  13  to assist in the thermal management of the module. The cell  4  may be of any desired type, for example, a rechargeable lithium-ion cell. Saft cells are designed with the same diameter but different lengths for different capacities. 
     Cell Holding Boards 
     The intake cell holding board  20  and exhaust cell holding board  20 ′ have a similar, complementary, structure and, therefore, only the intake cell holding board  20  is shown, and described in detail with reference to FIGS. 2-6. 
     The cell holding board  20  includes a first side  21  and a second side  23  opposite to the first side  21 , with a thickness therebetween. 
     The first side  21  of the holding board  20  includes a plurality of cavities  22  and  22 ′ therein. Each of the cavities  22 ,  22 ′ includes a bottom  24 , and a periphery. Each of the cavities  22  includes a through hole  28 , a through hole  30 , and a recess  26  within the periphery thereof to accommodate the structure on the negative end of an electrochemical cell  4 . The through hole  28  accommodates threaded terminal stud  10 , the through hole  30  accommodates fill tube  12 , and recess  26  accommodates terminal plate  8 . Only the cavities  22 ′ need to include respective through holes  28  to accommodate respective threaded terminal studs  10  on the positive sides of the cells. Additionally, both types of cavity  22 , and  22 ′ may include webs  32  formed between the bottom  24  and a side wall around the periphery of the cavity  22 ,  22 ′. 
     The webs  32  accommodate variations in cell height as well as prevent rattling of the cells within the cavities  22 ,  22 ′ of the holding boards. That is, after all the cells of a module have been placed between the holding boards  20 ,  20 ′, in respective cavities, force and possibly heat are applied to the holding boards to push them together. When the holding boards are pushed together with the cells  4  therebetween, the webs  32  of a particular cavity deform to the particular cell placed within that cavity. For example, if a cell  4  in one cavity is slightly taller than a cell in a second cavity, the webs of the one cavity will deform more than those in the second cavity thereby maintaining a uniform spacing between the cell holding boards  20 ,  20 ′ even though the cells are of a different height. Further, the webs  32  prevent rattle of the cells within the cavities, when a cell has a slightly smaller diameter than that of a the cavity in which it is placed, by providing a variable effective diameter for the cavity. Although only one of each type of cavity  22 ,  22 ′ is shown as including webs  32 , all the cavities in the holding board preferably include webs  32 . Further, although in one cavity three webs are shown, each cavity can have any suitable number of webs. 
     The second side of the holding board  20  includes recesses  42  and  44  for accommodating the bus connectors  70  and  76 , respectively. The recesses  42 ,  44  extend from the through hole  28  of one cavity to the through hole  28  of an adjacent cavity and are positioned depending on how the cells  4  of the module are to be connected, i.e., in series, parallel, or a combination thereof. Because the recesses determine how the cells are connected, the holding boards serve as a template, or map, which facilitates assembly of the module. Additionally, the recesses  42 ,  44  extend below the second side  23  of the holding board to an extent greater than, or equal to, the thickness of the bus connectors  70 ,  76 . By such an arrangement, the cell holding board  20 , itself, provides insulation between the bus connectors  70 ,  76  of the module. Therefore, no additional insulation is needed, and the module weight is reduced. Moreover, the thickness of the cell holding board is such that the portion between the recesses  42 ,  44  and the cavities provides sufficient insulation between the bus connectors  70 ,  76  and the electrochemical cells  4  whose outside containers are negatively charged in a lithium-ion cell, for example. Again, because the cell holding board  20  itself provides sufficient insulation, no additional insulation is necessary, thus the weight of the module is reduced and manufacture is simplified. 
     Additionally, the second side of the cell holding board  20  includes lugs  40  for connecting the holding board  20  to an end cap  50 . Because the lugs  40  are formed with the holding board  20 , the number of separate parts is reduced thereby simplifying assembly of the module. Although four lugs  40  are shown, any suitable number may be used. Each of the lugs  40  includes a structure which facilitates attachment of the end cap  50  to the holding board  20  while also accurately maintaining a space therebetween for use as an air manifold in thermal management of the module. 
     In a first embodiment, as shown in FIGS. 14 c-d , the lugs  40  extend from the cell holding board  20 , and contain holes  41  in the ends thereof. The holes  41  are sized to receive rivets  49 ′ therein. After the rivets  49 ′ are inserted into the holes  41 , the ends of the rivets  49 ′ are expanded in the holes  41  to securely attach the end cap  50  to the cell holding board  20 . The rivets  49 ′ may be those typically known as “pop rivets”. In a second embodiment, the holes  41  are screw threaded so as to receive screws  49  therein. The screws  49  are inserted through apertures  51  in the end cap  50  and into the holes  41  to securely attach the end cap to the cell holding board  20 . In the first and second embodiments, the end cap  50  rests on the lugs  40 , so that the height of the lugs easily and accurately determines the height of the air manifold between the end cap  50  and the cell holding board  20 . 
     In a third embodiment, as shown in FIGS. 14 a-b , lugs  40 ′ have a special shape. A first portion  43  of the lug extends from the cell holding board  20 . A second portion  47  extends from the first portion  43 . The second portion  47  has a smaller periphery than that of the first portion  43  so as to form a stepped portion  45  at the junction of the first portion  43  and second portion  45 . The lugs  40 ′ of the third embodiment are arranged so that the second portion  47  fits through the apertures  51  in the end cap  50  which then rests on the stepped portion  45 . Thus, in the third embodiment of the lugs, the height of the stepped portion  45  above the second side  23  of the holding board  20  easily and accurately determines the height of an air manifold between the holding board  20  and the end cap  50 . To secure the end cap  50  to the holding board  20 , the second portion  47  is deformed, as by heat stake riveting for example, to form a head  47 ′ which is larger than aperture  51 . The head  47 ′ then prevents the end cap  50  from coming off of the lug  40 ′ on the cell holding board  20 . The third embodiment is preferred for its ease and speed in assembling the module. 
     Further, the cell holding board  20  includes through holes  34 ,  34 ′,  34 ″ which are not within the periphery of any cavity  22 ,  22 ′. The through holes  34 ,  34 ′,  34 ″ accommodate fluid flow through the cell holding board  20 . The through holes  34 ,  34 ′,  34 ″ are spaced and sized so that when taken together with the cell-to-cell spacing, cell-to-shell spacing, and air manifold height, a desired thermal management configuration for the module is achieved. The through holes  34 ,  34 ′,  34 ″ are shown as circular and oblong, however, any suitable shape may be used. 
     Moreover, the cell holding board  20  includes through holes  48  which receive tie rods  14  when the cell assembly  2  is formed. That is, tie rods  14  extend through a through hole  48  in the intake cell holding board  20  as well as a through hole  48  in exhaust cell holding board  20 ′ to thereby hold the cell holding boards together with the electrochemical cells  4  therebetween. 
     In addition to the special surface characteristics of the cell holding board  20 , it has an overall shape which assists in the manufacture and assembly of the module. The cell holding board  20  includes a protrusion  36  on one end, and a recess  38  on an opposite end, thereof. The protrusion  36  accommodates a portion of one cavity which is offset on the one end of the cell holding board  20 . The recess  38  is formed on the opposite end of the cell holding board  20  as is protrusion  36 , and is aligned therewith to facilitate nesting of modules when more than one is used, as in a battery pack. That is, a first line of cavities extends along an edge of the cell holding board which includes recess  46 , and includes four cavities as shown in FIGS. 2 and 6, for example. Although each line is shown as having four cavities, any suitable umber may be used. A third line of cavities extends along an opposite edge of the cell holding board, and a second line of cavities is formed between said first line and said second line. The second line is offset from the first and third lines which are aligned with each other. As shown in FIGS. 2 and 6, the second line is offset to the left thereby producing protrusion  36  and recess  38 . The cavities of the second line are offset, and in a nesting arrangement, with respect to both the first line and third line so as to achieve a compact arrangement of cells  4  and, thereby, a compact module having minimum volume. The cavities in each of the first through third lines may be either  22  or  22 ′. In the embodiment shown, cavities  22  and  22 ′ alternate in each of the lines—such an arrangement being useful in connecting the cells  4  of the module in series. 
     The main differences between the cell holding boards will now be described. First, the cavities on cell holding board  20 ′ have an opposite configuration from corresponding cavities on cell holding board  20 . That is, a cavity  22  on cell holding board  20 ′ would correspond to a cavity  22 ′ on cell holding board  20  to hold a cell  4  therebetween, in the cell assembly  2 . Similarly, a cavity  22 ′ on cell holding board  20 ′ would correspond to a cavity  22  on cell holding board  20  to hold a cell  4  therebetween. Thus, when the positive end of a cell  4  is held by a cavity  22 ′ on one holding board,  20 ′ for example, the corresponding cavity on the other cell holding board  20  would be a cavity  22  for holding the negative end of the cell  4 . In such a manner, the cells  4  are held so as to be perpendicular to both the holding boards  20 ,  20 ′, and are held in such a manner that they can be easily connected to one another. Thus, the cavities serve as a template, or map, of how the cells are inserted within the cell assembly thereby facilitating assembly of the module. 
     Also, the recesses  42 ,  44  of the holding board  20 ′ would not be in the same positions as those shown for holding board  20 , but would be in positions complementary thereto, depending upon how the cells in the module are connected. In a preferred embodiment, the recesses  42 ,  44  of the holding board  20 ′ are positioned as shown in FIG.  7 . 
     In the cell assembly  2 , the cells  4  are held within cavities  22 ,  22 ′ in the holding boards so that threaded terminal studs  10  of the cells  4  extend through holes  28  and through recesses  42 ,  44 . An appropriate bus connector  70 ,  76 —that is, one having a complementary shape to the recess in which it is placed—is then placed in each of the recesses  42 ,  44 , so that the terminal studs  10  are received in its holes  72 ,  78 . A nut  18  is then threaded onto the each of the terminal studs  10  to lock the bus connector  70 ,  76  in place thereby completing an electrical connection between the cells  4 . Because the recesses  42 ,  44  have a shape that is complementary to that of the respective bus connectors  70 ,  76 , the cell holding board serves as a template for placement of the connectors, which facilitates assembly of the module. Further, because one type of bus connector  70 ,  76  can only fit in one type of complementarily shaped recess  42 ,  44 , respectively, proper connection of the cells  4  is ensured. 
     A second embodiment of cell holding board is shown in FIGS. 15A-C. Elements of the second embodiment of the cell holding  120  board which are similar to like elements of the first embodiment are labeled with similar reference numerals, i.e., with one hundred added thereto. Similarly to the cell holding boards of the first embodiment, the cell holding board  120  includes cavities  122  and  122 ′ therein. The cavities  122  include a cavity bottom  124  and a recess in the cavity bottom  124 . Further, the cavities  122  include through holes  130  for the cell fill tube and vent. Both types of cavities  122  and  122 ′ include a through hole for accommodating the cell terminal stud and, although not shown, may contain webs to assist in holding the cells in place. Additionally, the cell holding board includes very small through holes  134 ′″, small through holes  134 , and larger through holes  134 ′. The function and purpose of these holes is the same as in the first embodiment. The cell holding board  120  also includes through holes  148  for accommodating tie rods and the like to hold cell holding boards together. 
     Different from the first embodiment, the cell holding board  120 , is designed to be used without a shell and, therefore, an electronic system accommodating portion  182  is formed therein. Further different from the first embodiment, the rows of cavities are not staggered with respect to one another but, instead, are aligned side-by-side. This arrangement of the rows of cavities allows the module to have less volume than that of the first embodiment. A module having this type of cell holding board is not typically a stand alone module because there is no shell. However, a shell could be used with this embodiment of cell holding board, as in the first embodiment. 
     In another embodiment, only one cell holding board is used. In this embodiment, the module does not stand alone, but is used as a part of a battery pack. Either of the above-described first and second embodiments of cell holding board may be used in this manner. 
     Bus Connectors 
     The bus connectors  70 ,  76  form a part of the electrical connector configuration within the module. At least two types of bus connectors, a short bus connector  70  and a long bus connector  76 , are used to connect the ends of adjacent cells  4  together. That is, for example, when the cells are connected in series, one connector would extend between the positive end of one cell and the negative end of an adjacent cell  4 . Alternatively, the connectors may be used to connect the cells of the module in parallel. Moreover, depending on the desired module voltage and current output, a combination of series and parallel connections may be made within the module by bus connectors  70 ,  76 . 
     The short bus connector  70  includes holes  72  at each end thereof. Each of the holes  72  accommodates a threaded stud  10  of an electrochemical cell  4 . A flag connector  74  may be attached to the bus connector  70  between the holes  72 . The flag connector  74  facilitates connection of the bus connector  70 , and thus the cells  4 , to the electronic control system of the module. Short bus connectors  70  have a complementary shape to, and are thus accommodated within, recesses  42  in the cell holding boards  20 ,  20 ′. 
     The long bus connector  76  includes holes  78  at the ends thereof. Each of the holes  78  accommodates a threaded stud  10  of an electrochemical cell  4 . A flag connector  74  may also be attached to the long bus connector  76  between holes  78 . The long bus connector includes a bend intermediate its ends to facilitate connection between electrochemical cells in different lines within the module. Long bus connectors  76  have a complementary shape to, and are thus accommodated within, recesses  44  in the cell holding boards  20 ,  20 ′. 
     The bus connectors  74 ,  76  are attached to the cell assembly  2  in the following manner. A threaded terminal stud  10  of an electrochemical cell  4  extends through one hole  28  in a cell holding board  20  and is adjacent a recess,  42  for example, on the second side of the cell holding board  20 . A second threaded terminal stud  10  of a second electrochemical cell  4  extends through an adjacent hole  28  in the cell holding board  20 , and extends so as to be adjacent the opposite end of the recess  42 . Short bus connector  70  is placed in the appropriate recess  42  so that the terminal studs  10  of the adjacent cells  4  extend through the holes  72  of the bus connector  70 . A nut  18  is then threaded onto each of the terminal studs  10  so as to form an electrical connection between the two cells  4 . The long bus connector  76  is used in a similar manner. Many such connections are made on both the intake cell holding board  20  and the exhaust cell holding board  20 ′ which serve as templates, or maps, for the placement of the connectors  70 ,  76 . Moreover, the two types of bus connectors  70 ,  76  are easy to manufacture, and are the only two types necessary to connect all the cells  4  within a module. Therefore, the assembly of the module is facilitated by a reduction in the number of different parts required. 
     Power Connectors 
     Power connectors  60  form a second part of the electrical connector configuration within the module. A power connector  60  is connected to a common potential within the module. That is, one power connector  60  is connected to the positive potential of the cell assembly  2  whereas another power connector  60  is connected to the negative potential of the cell assembly  2 . Each power connector  60  is then used to connect the module to a desired application, i.e., to other modules thereby forming a battery pack, or to a load. The power connector  60  may have any suitable shape, however, an L-shaped connector is preferred. 
     Each L-shaped power connector  60  includes a first leg  61 , and a second leg  65  which is perpendicular to the first leg. The first leg  61  is inserted within one of the holes  53  in the end cap  50  of the module. The first leg  61  includes a blind hole  62  therein. The blind hole  62  includes threads  63  to facilitate connection of the power connector  60 , and thus the module, to a desired application. At least a portion of the second leg  65  includes a through hole  64 . The through hole  64  extends in a direction perpendicular to that in which the blind hole  62  extends. A cable  68 , having a tab  69  connected at a first end thereof, facilitates connection of the L-shaped power connector to a common potential within the module. The tab  69  includes a hole  69 ′ therein sized to accommodate a threaded stud  10  of an electrochemical cell  4 . The tab may then be secured to the threaded stud  10  using a nut  18 , for example. A second end of the cable  68  is attached within the through hole  64 . The connector  60  thus provides a simple structure, taking up little room in the module and adding little weight thereto, for connection between the cells in the module and a desired application outside the module. 
     The shape of the power connector  60  facilitates manufacture and assembly of the module. That is, the first leg  61  of power connector has a shape which is complementary to that of the holes  53  in the end cap  50  of the module to thereby easily prevent rotation of the power connector with respect to the end cap. For example, both the first leg  61  and the holes  53  may be rectangular so that when a bolt is screwed into the blind hole  62 , the connector  60  does not rotate. Of course any other suitable shape which prevents rotation, for example a star shape, is possible. Further, when the first leg  61  is inserted within a hole  53  in the end cap, the second leg  65  prevents the power connector from falling through the hole  53 . That is, the second leg  65  acts as a stop which abuts the first side  52  of the end cap  50 . Moreover, the edges of the connector  60  may be beveled as at  66  to facilitate insertion within a hole  53 , and to reduce stress risers. 
     A second embodiment of power connector is shown in FIGS. 12 d-f . This version of the power connector is used to connect one module to another module, and is particularly useful with the second embodiment of cell holding board. The power connector  160  includes a hole  169 ′ to accommodate a threaded stud of an electrochemical cell, and a nut  167  that is attached to a neighboring module. The nut  167  is press fit to the body of the power connector  160 . Further, the power connector  160  includes a flag terminal  174  so that connections for measuring voltage, and other module parameters, may conveniently be made. 
     Module End Caps 
     There are two cell end caps in the module—an intake end cap  50 , and an exhaust end cap  50 ′. The end caps are similar and, therefore, only the intake end cap  50  is shown and described in detail. See FIGS. 1,  8 , and  9 . 
     End cap  50  includes a first side  52 , which faces the interior of the module, and a second side  54  which faces the exterior of the module. Apertures  51  extend from the first side  52  to the second side  54  for forming a connection between the end cap  50  and cell holding board  20 . Although four apertures  51  are shown, any suitable number can be used. The end cap  50  further includes holes  53  therein for accommodating power connectors  60  which are connected to the common potentials within the cell. The holes  53  have a shape which is complementary to that of the power connectors  60  so as to prevent rotation of the power connectors  60  when a desired load is being attached. Each hole  53  includes a rim  53 ′ on the first side of the end cap  50 , and another rim  53 ″ on the second side  54  of the end cap  50 . The rim  53 ′ does not extend entirely around the hole  53  but allows an open space for second leg  65  thereby ensuring that the power connector  60  is positioned correctly within the hole  53 . That is, the power connector  60  can only be inserted within the hole  53  in one manner, i.e., so that one leg  65  of the connector extends within the opening formed in the rim  53 ′. Correct positioning of the power connector  60  ensures that the cable  68  attached thereto extends in the proper direction for connection to the cells within the module. The main difference between end caps  50 ,  50 ′ is that only one need include holes  53 , and rims  53 ′  53 ″ for the power connectors  60 . 
     Because the shell  80  is shorter than the distance between the end caps  50 ,  50 ′ when they are attached to the cell assembly, the end caps  50 ,  50 ′ receive all axial force which acts on the module. Therefore, the end caps  50 ,  50 ′ include stiffening ribs  55  to prevent deformation. By including stiffening ribs  55 , the remaining portion of the end cap can be made thin, thereby reducing overall weight of the module, yet still ensuring that the end caps can withstand axial forces. 
     Further, the end cap  50  includes a protrusion  56  on one end thereof, and a recess  58  on an opposite end thereof. The protrusion  56  and recess  58  are of a shape complementary to that of protrusion  36  and recess  38  of the cell holding board  20 , as well as to that of protrusion accommodating portion  86  and indent  88  of the shell  80 . Moreover, the end cap  50  includes a recess  57  around the periphery thereof to accommodate the shell  80 . Because the end of the shell is received in recess  57 , inward deformation thereof is prevented thereby strengthening the module. The recess  57  is made wider on one end of the end cap  50  in order to accommodate the electronic system accommodating portions  82  within the shell  80 . By having the above configuration, the end cap  50  is easily aligned with, and mated to, the cell assembly  2  and shell  80 . 
     Additionally, the end cap  50  includes ports  59  for the intake or exhaust of heat exchanging fluid from the module. Each port  59  includes a beveled portion  59 ′ where it meets the first side  52  of the end cap  50 , and includes a rim  59 ″ extending from the second side  54  of the end cap. The beveled portion  59 ′ assists in fluid flow to or from the interior of the module, whereas rim  59 ″ may be used to connect the module to a fluid circulation system. On one side of the module, the ports  59  in one end cap  50  are for air intake, whereas the ports  59  in the opposite end cap  50 ′ are for exhaust. On the intake side, the space between the end cap  50  and the holding board  20  is an air manifold. Because the ports  59  in the end caps  50 ,  50 ′ are similar, either end cap  50 ,  50 ′ may be the inlet or exhaust side of the module, i.e., the air flow can easily be reversed. 
     Shell 
     As shown in FIG. 1, shell  80  includes an overall shape which is complementary to that of the cell assembly  2 , holding boards  20 ,  20 ′, and end caps  50 ,  50 ′, to facilitate assembly of the module. That is, one end of the shell includes a protrusion accommodating portion  86 , whereas the opposite end of the shell  80  includes an indentation  88 . The protrusion accommodating portion  86  encloses the protrusions  36  of the cell holding boards  20 ,  20 ′, as well as receives the protrusions  56  on the end caps  50 ,  50 ′. The indentation  88  is shaped so as to fit within the recesses  38  of the cell holding boards  20 ,  20 ′, as well as mate with the recesses  58  in the periphery of the end caps  50 ,  50 ′. Additionally, the shell  88  includes indentations  85  in the longitudinal sides thereof to mate with indentations  46  in the cell holding boards  20 ,  20 ′ and with similar indentations  58 ′ in the end caps  50 ,  50 ′. The indentations  85  in the sides of the shell assist in giving the shell rigidity in order to facilitate handling thereof during assembly and handling of the module. That is, the shell is thin and, therefore, may be easily flexed during handling thereof, however, the indentations  85  provide a stiffening effect. 
     Further, the shell  80  includes an electronic control system accommodating portion  82 . Although the electronic control system accommodating portion  82  is shown as being adjacent to the protrusion accommodating portion  86 , it may be located at any suitable spot within the module. The accommodating portion  82  includes a sliding cover  84  for allowing easy access to the electronic control system within the accommodating portion  82 . The electronic control system (not shown) forms the electronics configuration of the module, and may be of any suitable type for monitoring voltage and temperature of the cells. Further it is preferable that the electronic control system includes circuitry for communicating with other modules as well as for cell balancing during the charge cycle of the module. The electronic control system is connected to the cells through the use of the flag connectors  74 . For example, the preferred electronic control system is that described in copending U.S. application Ser. No. 09/350,375, filed on Jul. 9, 1999, which is hereby incorporated by reference. 
     Thermal Management Configuration 
     In the module, the cells  4  are spaced from one another by a cell-to-cell distance measured between the outer periphery of one cell and the outer periphery of an adjacent cell. The cell-to-cell distance is exemplified by the distance DC between adjacent cavities in the cell holding board  20 . See FIG.  6 . The cells  4  which are adjacent the shell  80  are spaced therefrom by a cell-to-shell distance. The cell-to-shell distance is exemplified by the distance DS between a cavity in cell holding board  20  and the nearest edge of the holding board  20 . Again, see FIG.  6 . The temperature difference between the inner surface (at an inside diameter of a cell  4  having a hollow core  13 ) and an outer surface (at an outside diameter) of each cell is ΔT. An end cap is attached to each holding board with a space between the end cap and holding board. Within each end cap there are two openings  59 . On one side of the module, the openings in one end cap  50  are for air intake, whereas the openings  59  in the opposite end cap  59 ′ are for exhaust. On the intake side, the space between the end cap  50  and the holding board  20  is an air manifold. 
     1) First embodiment of the module thermal management configuration: 
     The battery module is arranged so that uniform air velocity within the module is attained. To attain uniform air velocity distribution at all gaps between cells  4  as well as between cells  4  and the inside wall of the shell  80 , an air intake manifold is designed, both analytically and experimentally, with two ports  59  of air intake on the intake end cap  50 ; each port  59  having a set of openings with specially selected geometry and size on the side wall and the bottom. The air intake velocity distribution is controlled by the size and location of each intake port  59 , the height of the air manifold created between the end cap  50  inner surface  52  and the top surface  23  of the cell board  20 , the size as well as geometry and location of each opening on the side wall and/or bottom of each air intake port  59 . The through holes  34 ,  34 ′ and  34 ″ in the cell holding boards  20 ,  20 ′, are sized as well as shaped and located so as to maintain the air intake velocity distribution created by the intake ports  59  and manifold. As a non-limiting example, the above configuration is designed so that intake air entering at 5 m/s leaves on the exhaust side of the module at velocities ranging between 3.5 and 4.5 m/s measured at the exhaust point of the cell-to-cell or cell-to-shell gaps. This has been verified experimentally for the shown module design. The air manifold allows the control of the temperature within the cell by controlling the air flow rate. 
     2) Second embodiment of the module thermal management configuration: 
     The battery module is arranged so that uniform temperature distribution across each cell  4  is attained. To attain uniform temperature distribution, the manifold height is minimized while accommodating the cells  4 , hardware and cell-to-cell bus connectors  70 ,  76 . The air intake openings  59  do not need to include any specialized shape. The cell-to-cell and cell-to-shell distances, as shown, were experimentally and analytically selected to maintain a uniform velocity of air through the cell assembly  2  with a minimum pressure drop across the module, and with a minimum air flow rate. 
     Because there is no specialized shape necessary for the air intake openings  59 , there is no dedicated air intake and exhaust end of the module. That is, either side of the module may be the intake/exhaust, and fluid can flow through the module in either direction. With the above configuration, each cell  4  within the module can be maintained at a predetermined ΔT depending on the intake air flow rate. 
     Although preferred embodiments of the present invention have been described above, it is contemplated that numerous modifications may be made to the module of the present invention without departing from the spirit and scope of the invention as defined in the following claims.