Abstract:
A low-profile battery pack having an electrolyte barrier is provided. The pack includes a plurality of rechargeable cells, being arranged in end to end pairs of two cells. A cleavage void formed by the convex geometry of the cells accommodates at least one insulator and a first circuit board. Tabs couple the cells to the first circuit board. A flexible substrate couples the first circuit board to a second circuit board. The assembly is then placed in a housing having a first compartment and a second compartment, such that the cells are placed in the first compartment and the second circuit board is placed in the second compartment. Between the first and second compartments exists an electrolyte barrier. The flexible substrate passes through an opening in the electrolyte barrier. Adhesive placed in the opening, about the flexible substrate, ensures a seal that keeps electrolyte that may appear in the first chamber from passing to the second chamber. The overall battery pack is both compact in size and robust in performance.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     This invention relates generally to rechargeable battery packs, and more specifically to a low-profile battery pack assembly having electrical and mechanical components arranged so as to reduce overall battery pack size and increase reliability.  
         [0003]     2. Background Art  
         [0004]     Some people think that a rechargeable battery pack is simply a rechargeable electrochemical cell wrapped in plastic. In reality, rechargeable battery packs are complex systems incorporating numerous components, including cells, protection circuitry, charging circuitry, and mechanical components. These components work in harmony to deliver safe, reliable power to portable electronic devices.  
         [0005]     Both the size and cost of electronic devices are rapidly decreasing. In today&#39;s modern devices, like cellular telephones, radios and laptop computers, the size of the device has become so small that a large portion of the volume of the host device is occupied by the battery pack. In other words, battery packs sometimes take up more room that any other component in the device. Additionally, the cost of the battery pack can rival the cost of the host device.  
         [0006]     Due to this reduction in the overall size of electronic devices, there is pressure on battery designers to reduce the overall dimensions of battery packs. One prior art solution used to reduce the overall size of the battery pack is removing some of the electronic circuitry from the battery pack and incorporating it into the host device. When this is done, electronic circuitry may be taken out of the battery pack and added to the host device&#39;s circuitry.  
         [0007]     This solution presents two problems: First, host devices must be designed to accommodate a particular battery pack. Since each battery pack requires a specific circuit design, adding the battery circuitry to the host device means that only one battery pack may be used with that particular device. Consequently, the device is unable to take advantage of new battery designs or technologies because the host device&#39;s internal circuitry is tailored only to one battery pack.  
         [0008]     The second issue is reliability. If the circuitry is removed from the battery pack, certain external conditions may compromise reliability of the battery pack. For example, protection circuitry is often included within the battery pack to protect the battery from an inadvertent shorting of the terminals. If this circuitry is removed, battery reliability may be compromised if the terminals are accidentally shorted while the battery is not coupled to the host device.  
         [0009]     There is thus a need for an improved, low-profile battery pack that ensures robust reliability. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  illustrates a plurality of cylindrical cells arranged in pairs of two, end to end, in accordance with the invention.  
         [0011]      FIG. 2  illustrates a cleavage space formed when two cylindrical cells are arranged adjacent to each other, in accordance with the invention.  
         [0012]      FIG. 3  illustrates an insulator in accordance with the invention.  
         [0013]      FIG. 4  illustrates a plurality of cell pairs, having insulators disposed within the cleavage space, in accordance with the invention.  
         [0014]      FIG. 5  illustrates an exploded view of a cell assembly in accordance with the invention.  
         [0015]      FIG. 6  illustrates a cell assembly having insulators, tabs and a first circuit board in accordance with the invention.  
         [0016]      FIG. 7  illustrates a cell assembly having a flexible substrate and second circuit board in accordance with the invention.  
         [0017]      FIG. 8  illustrates a cell assembly in an open housing in accordance with the invention.  
         [0018]      FIG. 9  illustrates a sectional view of a battery pack in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” 
         [0020]     One preferred embodiment of this invention is a low-profile battery pack capable of bringing multiple cell connections from a plurality of rechargeable, electrochemical cells to an external connector on the outside of the battery pack, while providing an electrolyte barrier between the cells and the external connector. When electrochemical cells malfunction, they occasionally release liquid electrolyte. The electrolyte barrier ensures that any liquid electrolyte that is released within the pack is isolated from the main circuit board and external connector.  
         [0021]     The battery pack includes an interconnect printed circuit board (PCB) that is placed within the “cleavage space” between pairs cylindrical cells. The interconnect PCB provides an interface mechanism for each cell connection. It also provides a place for electrical components to be mounted, like thermistors for sensing the temperature of the cells in operation. The interconnect PCB is connected to a second PCB by way of a flexible substrate or circuit. The flexible substrate passes through a water-tight, or liquid impenetrable, barrier in the housing. The assembly offers a very compact, low-profile battery pack that is easy to manufacture. The assembly eliminates the need for hand soldering manufacturing operations, thereby decreasing the possibilities for defects on the manufacturing floor.  
         [0022]     Turning now to  FIG. 1 , illustrated therein is a plurality of cylindrical, rechargeable, electrochemical cells  100  for use in a battery pack. While the exemplary embodiment of  FIG. 1  illustrates 6 cells, the invention may be employed with any number of cells, provided there are at least two. The cells  100  in  FIG. 1  are arranged in three pairs  101 , 102 , 103  of two cells. The three pairs  101 , 102 , 103  are arranged end to end.  
         [0023]     Turning now to  FIG. 2 , illustrated therein is one pair  200  of the three pairs of two cells from  FIG. 1 , viewed in cross section. Since the cells  201 , 202  are cylindrical in shape, the cross section of each cell is, of course, a circle. When the two cells  201 , 202  are placed adjacent to each other, as shown in  FIG. 2 , they intersect at a line  203 , shown here as a dot (indicating a line that runs into the page). The intersection is a line  203  because the exterior casing of each cell  201 , 202  is a convex curvature. The intersection of these convex curvatures is represented by line  203 , which runs the length of the cells.  
         [0024]     Due to this adjacent arrangement, a “cleavage space”  204  is formed between the intersection line  203  and a plane  205  running across the top of each cell  201 , 202  so as to be tangent to the convex curvature of each cell  201 , 202 . Note that the plane  205  is imaginary, but is useful as a reference in discussing the cleavage space  204 . The cleavage space  205 , also known as a cleavage void, is essentially a triangular shaped space, where the triangle has two concave sides. This invention takes advantage of this otherwise unused cleavage space  204  by filling it with components.  
         [0025]     Referring now to  FIG. 3 , illustrated therein is an insulator  300  in accordance with the invention. This insulator  300 , affectionately known as a “runner”, is a plastic member that has a geometric cross-section that fits within the cleavage space  204  of  FIG. 2 . The cross sectional shape is generally triangular, with two of the sides  301 , 302  having concave curvatures to mate between a pair of cylindrical cells. By way of example, if 18-650 cells are used, the concave curvatures of the sides  301 , 302  would have 9 mm radii, neglecting tolerances, to accommodate the outer, convex curves of the cell. The insulator  300  may be made from any of a number of plastics, including styrene, polystyrene, ABS, polycarbonates and the like. A preferred plastic is Noryl GTX 830. There are several manufacturing options available for construction of the insulator. One preferred method is injection molding.  
         [0026]     Turning to  FIG. 4 , three insulators  400 , 401 , 402  are disposed within the cleavage space of each pair  403 , 404 , 405  of a set of three pairs of cylindrical cells. When each insulator  400 , 401 , 402  is seated within the cleavage space or wedge area of the pairs  403 , 404 , 405  of cells, the concave curvatures of the insulators  400 , 401 , 402  mechanically mate with the convex curvatures of the cells.  
         [0027]     Turning now to  FIG. 5 , illustrated therein is an exploded view of a partial battery pack assembly in accordance with the invention. As with  FIG. 4 , three pairs of cells  403 , 404 , 405  are aligned end to end. The cells of  FIG. 5  are shown in an exploded view so that the interconnection tabs  500 , 501 , 502  can be seen. The cells will be placed in an end to end configuration, for placement into a housing, after the tabs  500 , 501 , 502  have been attached. The tabs  500 , 501 , 502  serve as electrical connections to transmit energy from the cells to an external connector on the battery pack.  
         [0028]     A first circuit board  503  is illustrated in  FIG. 5 . The first circuit board  503  includes at least one aperture  504  through which the tabs (e.g.  501 ) may pass for coupling the cells to the first circuit board. For multiple tab connections, multiple apertures  505 , 507  may be employed. An aperture may not be required for a tab (e.g.  500 ) that couples to the end of the first circuit board  503 .  
         [0029]     For ease and automation of assembly, a tab connection plate  505  or plates  505 , 508  may be included on the first circuit board  503 . The tab connection plate  505  is a small piece of metal that may be attached to the first circuit board  503  by an automated process, like reflow soldering for example. When a tab connection plate  505  is used, the tab  501  may be coupled to the board by welding, rather than hand soldering. Welding increases the reliability of the electrical connection by eliminating the need for hand soldering.  
         [0030]     Electrical components  506  may also be coupled to the first circuit board  503 . For example, some applications require that the temperature of the cells be communicated to the host device. As such, a thermistor may be coupled to the first circuit board  503 . Note that for the six-cell, exemplary embodiment, when the first circuit board  503  has a length greater than the length of two pairs of cells  403 , 404 , the temperature of any particular pair of cells may be measured simply by placing the thermistor above that pair of cells. Additionally, multiple temperatures within the battery pack may be measured by using multiple thermistors.  
         [0031]     Turning now to  FIG. 6 , illustrated therein is the first circuit board  503  disposed atop the insulators  400 , 401 , 402  such that the first circuit board  503  and insulators  400 , 401 , 402  all fit within the cleavage space between the pairs of cells  403 , 404 , 405  that are coupled end to end. Tabs  501 , 502  pass through the apertures  504 , 507  and couple to tab connection plates  505 , 508 . Tab  500  is able to wrap around the first circuit board  503  and also couples to a tab connection plate  600 .  
         [0032]     Turning now to  FIG. 7 , a flexible substrate  701  is coupled to the assembly  600  of  FIG. 6 . The flexible substrate  701  is a pliable member made from an insulating material, like Kapton™ for example, disposed about conductive metal traces. The flexible substrate  701  has a first end  702  and a second, distal end  703 . The first end  702  is connected to the first circuit board  503 . The flexible substrate  701  provides an electrical connection from the assembly  700  to the outside world.  
         [0033]     The distal end  703  of the flexible substrate  701  is coupled to a second circuit board  704 . The second circuit board  704  includes components like the external connector  705  and additional electronic circuitry  706 , like charging circuitry, fuel gauging circuitry and safety circuitry. The cell assembly  700 , flexible substrate  701  and second circuit board  704 , once coupled together, are ready to be inserted into the housing of the battery pack.  
         [0034]     Turning now to  FIG. 8 , illustrated therein is the assembly of  FIG. 7  seated in a housing, shown here having a top  801  and a bottom  800 . The housing has a first chamber  802  and a second chamber  803 . (These chambers, or compartments, will be more clearly shown in  FIG. 9 .) The cell assembly  700  is disposed in the first chamber  802 , while the second circuit board  704  is disposed in the second chamber  803 . The flexible substrate  701  serves as an electrical conduit between the first and second chambers  802 , 803 .  
         [0035]     Turning now to  FIG. 9 , illustrated therein is a cross section of the battery pack of  FIG. 8 . In this cross section, cell pair  404  can be seen, as can insulator  401  and the first circuit board  503 . The upper housing  801  has been coupled to the bottom housing  800 . Note that the upper housing  801  essentially becomes the plane that is tangent to cell pair  404 , and that both the first circuit board  503  and insulator  401  fit within the cleavage space  902  formed by the top housing  801  and the intersection  903  of cell pair  404 .  
         [0036]     In this sectional view, the first chamber  802  and second chamber  803 , first mentioned in the discussion of  FIG. 8 , can more clearly be seen. The first chamber  802  may be referred to as the “cell chamber”, and the second chamber  803  is sometimes referred to as the “sealing chamber”. The term “sealing” is used because a water-tight or liquid resistant barrier  900  is positioned between the first chamber  802  and second chamber  803 . The water-tight seal  900  is formed by a plastic wall through which the flexible substrate passes. When the upper housing  801  and lower housing  800  are coupled together, a layer of adhesive  901  is applied to the opening  902  through which the flexible substrate  701  passes. The adhesive is applied about the flexible substrate  701 . This adhesive, in conjunction with the barrier walls, provide a chamber  803  that is sealed in the sense that electrolyte leaked in the first chamber  802  can not pass to the second chamber  803 .  
         [0037]     While the preferred embodiments of the invention have been illustrated and described, it is clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions, and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the following claims.