Abstract:
A circuit breaker which automatically interrupts the flow of current from a battery upon the development of a predetermined overcurrent. A weld connection around a periphery of an aperture determines a current path which has the lowest current carrying capacity in the battery. Therefore, the diameter of the aperture determines the amount of current which will break the weld thereby disconnecting the battery from a circuit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to controlling the flow of current from a battery and, more particularly, to controlling the flow of current from a rechargeable battery by way of an automatic circuit breaker which interrupts the flow of current from the battery upon the development of a predetermined overcurrent, with a device resistance of less than or equal to 0.2 milliohms. 
     2. Related Art 
     Batteries in the related art include circuit breakers for stopping the flow of current from the battery upon a predetermined condition. In particular, U.S. Pat. No. 4,188,460 to Kang et al. discloses an internal battery fuse in which excessive built-up heat resulting from a short circuit is concentrated in a portion which then heat fuses and interrupts the circuit. The heat fusible portion is formed as a thinned strip making up a portion of the current collector and is surrounded by a heat shield. When current exceeds a predetermined threshold, the thinned strip provides a greater electrical resistance than the rest of the current collector, and thus heats up. Because the shield retains the heat around the thinned strip, the thinned strip fuses to break the electrical connection within the current collector thus terminating current flow from the battery. Alternatively, the thinned strip may be a separate element which is welded between two portions of the current collector. However, Kang includes the disadvantage that the circuit is broken at a point within the cell itself. That is, the heat fusible portion is located adjacent the electrode stack which produces gasses that may be ignited by any arcing in the fusible portion. Further, because Kang requires a heat shield as well as either a thinned portion of an elongate strip current collector or a thinned strip welded to different portions of the current collector, his battery fuse is complex. 
     U.S. Pat. No. 4,690,879 to Huhndorff et al. and U.S. Pat. No. 5,057,382 to Tucholski also disclose complex mechanisms for interrupting the flow of current from a battery. In each of these batteries, the current flow is terminated upon the bulging of the cell due to excessive pressure therein. When pressure builds up within either battery, the ends bulge. In Huhndorff, the current is terminated due to a break in a weld connection between a cover terminal and a metal container upon the battery&#39;s bulging. In Tuchoski, the current is interrupted by the relative sliding movement between a secondary conductive cover and a container contact member upon the battery&#39;s bulging. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to overcome the disadvantages of the prior art. 
     A further object of the present invention is to provide a simple to manufacture mechanism which automatically interrupts the flow of current from a battery upon the development of a predetermined overcurrent. In the present invention, because a weld connection around the periphery of an aperture determines the current path, the diameter of the aperture determines the amount of current that will break the weld thereby opening the circuit. Thus, merely selecting a different aperture diameter allows variation in the amount of current allowed through the connection before it automatically opens. 
     A further object of the present invention is to provide a mechanism which automatically interrupts the flow of current from a battery with reduced risk of igniting gasses produced in an electrode stack of an electrochemical cell. The present invention includes an epoxy covering the weld connection which is broken to interrupt the flow of current such that the epoxy contains any arcing that occurs during interruption of current. Further, the weld connection which is broken to interrupt the flow of current is located on the outside of the battery enclosure so that even if any arcing does occur, it occurs away from gasses produced in the electrode stack, thereby reducing the risk of ignition. 
     The present invention automatically interrupts the current flow in a battery upon a predetermined overcurrent. In the battery of the present invention, a bussing structure within the battery enclosure is connected to a terminal assembly on the outside of the battery enclosure by an electric feed through. The electric feed through is connected to the terminal assembly by a weld connection formed around the periphery of an aperture formed in the terminal assembly. When a predetermined overcurrent develops, the weld connection is broken. The weld connection is circular and, thus its length is determined by the diameter of the aperture in the terminal plate around which the weld connection is made. The amount of overcurrent which breaks the connection is controlled by controlling the length of the weld which defines the length of conductor between the current bussing structure within the battery enclosure and the terminal plate on the outside of the battery enclosure. Further, the amount of overcurrent is controlled by the thickness and resistivity of the material chosen for the terminal assembly. Thus, the amount of overcurrent which breaks the connection is easily controlled by selecting an appropriate diameter for an aperture in, as well as thickness and resistivity of, a portion of the terminal assembly. Further, because the weld connection which breaks to interrupt current flow is formed between a terminal assembly and an electric feed through, on the outside of the battery enclosure, there is reduced risk of igniting battery gasses upon interruption of current. 
     In a lithium-ion cell, for example, the terminal assembly is made of copper and nickel, whereas the electric feed through is made of molybdenum. However, any suitable material may be used for the terminal assembly and electric feed through, depending on the type of battery in which the automatic circuit breaker is employed. In one embodiment of a lithium-ion cell, the thickness and resistivity of the terminal assembly, as well as the aperture diameter are selected so that the device has a resistance of less than or equal to 0.2 milliohms. Further, although the connection between the terminal assembly and the electric feed through is described as a weld connection, any suitable connection along the periphery of the aperture in the terminal assembly may be used. Moreover, although the present invention is particularly useful on rechargeable batteries used in electric vehicles, it may be used with any type of battery. 
    
    
     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 a top view of battery enclosure portion having a terminal assembly and electric feed through attached thereto according to the present invention; 
     FIG. 2 is an enlarged side view of a battery enclosure portion having a terminal assembly, an electric feed through and a bussing structure attached thereto according to the present invention; 
     FIG. 2A is an exploded view of that shown in FIG. 2; 
     FIG. 3 is a side view of a terminal assembly according to the present invention; 
     FIG. 4 is a top view of a terminal assembly having an electric feed through attached thereto according to the present invention; 
     FIG. 5 a  is a top view, whereas FIG. 5 b  is a side view, of a contact disk according to the present invention; 
     FIG. 6 is a top view of a current plate according to the present invention; 
     FIG. 7 a  is a top view, whereas FIG. 7 b  is a cross sectional side view taken along line I—I in FIG. 7 a , of an electric feed through according to the present invention; and 
     FIG. 8 is a side view of a battery enclosure portion having an electric feed through attached thereto, according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the automatic circuit breaker may be used in any size and type of battery, particularly rechargeable batteries for electric vehicles, and may be used on either the positive or negative side, it will be described as employed on the positive side of an electrode stack in a rechargeable lithium-ion battery. 
     FIG. 1 shows a top view of a battery enclosure portion  30 , whereas FIG. 2 shows a side view thereof. FIG. 2A is an exploded view of FIG.  2 . 
     The battery enclosure portion  30  includes a central aperture  36  for connection to a hollow core which extends through the battery. The outer periphery of the battery enclosure portion  30  is then connected to the periphery of the battery case (not shown) which holds an electrode stack therein. When a hollow core is not used in the battery, the battery enclosure portion  30  does not need to include aperture  36 . The details of the electrode stack and battery case have been omitted for clarity, and only the bussing structure  34  is shown. The bussing structure  34  may be connected to the electrode stack in any manner, but is preferably connected as described in copending application, filed on Jun. 11, 1999, the specification of which is hereby incorporated by reference. As best shown in FIG. 2A, the bussing structure  34  includes insulating disks  34   a , an insulating washer  34   b , and a positive bussing washer  34   d . The current collection tabs  34   c , extending from the electrode stack, are connected to the positive bussing washer  34   d.    
     In the battery, current flows in a path from the electrode stack to bussing structure  34 , then to electric feed through  20 , through weld connection  11  and finally to terminal assembly  2 . See FIGS. 1-4,  7   a  and  7   b . Specifically, the circuit breaker is formed in the weld connection  11  between the terminal assembly  2  and electric feed through  20 , because the weld connection  11  has the smallest current carrying capacity in the current path. An epoxy  9  (see FIG. 2) covers the weld connection  11  to contain any arcing that may occur when the weld connection  11  is broken to interrupt the flow of current. 
     Further, as shown in FIG. 2, the weld connection  11  is formed on the outside of the battery case portion  30 , i.e., the side opposite to that on which the bussing structure  34  and hence electrode stack are located. Thus, because the circuit breaker is located away from the electrode stack, there is reduced risk of igniting battery gasses upon interruption of current. That is, because the weld connection  11  which is broken to interrupt the flow of current is located on the outside of the battery enclosure  30 , even if any arcing did occur during the interruption of current, such arcing would occur away from gasses produced in the electrode stack, thereby reducing the risk of ignition. Details of the terminal assembly  2  and electric feed through  20 , the parts between which the weld connection  11  is made to form the circuit breaker, will now be described. 
     The terminal assembly  2  is shown in detail in FIG. 3, wherein portions thereof are shown in FIGS. 5 a ,  5   b  and  6 . A top view of the terminal assembly  2  as it is connected to the electric feed through  20  is shown in FIG.  4 . 
     The terminal assembly  2  is disposed adjacent the battery case portion  30 , on a side thereof which is opposite that on which bussing structure  34  is disposed. An external insulator  32  separates the battery case portion  30  and the terminal assembly  2 . The external insulator is made of a top external insulator  32   a  and a bottom external insulator  32   b . Although shown as being made of two pieces,  34   a ,  34   b , the external insulator  32  may be made as a single unit. The terminal assembly  2  includes a current plate  4 . Current plate  4  includes a hole  7  for connection to stud  12 . Although hole  7  is shown for connection to the stud, the stud and current plate  4  may be connected in any other suitable manner. The stud  12  includes a threaded portion  14  thereon for connection of the terminal assembly, and hence the battery, to a desired load during use. The current plate  4  further includes holes  6  to facilitate connection of the terminal assembly  2  to the electric feed through  20 . Each hole  6  allows access to an aperture  10  of a contact disk  8  which is connected to the current plate  4  on a side opposite to that on which the stud  12  is connected. That is, each hole  6  has a larger diameter than that of the aperture  10  of a respective contact disk  8 . The connection between the current plate  4  and contact disks  8  can be made by laser welding, for example, along a diameter larger than that of each hole  6 . The laser weld connection thus forms an electrical connection between the current plate  4  and contact disk  8 . In a lithium-ion battery, for example, the current plate  4  and stud  12  are preferably made of copper, whereas the contact disks  8  are preferably made of nickel. 
     An electric feed through  20  is shown in detail in FIGS. 7 a  and  7   b . The connection of the electric feed through  20  to the bussing structure  34  is shown in FIG. 2, whereas its connection to the terminal assembly  2  is shown in FIGS. 2 and 4. Further, in FIG. 8, the electric feed through  20  is shown connected to the battery enclosure portion  30  without the terminal assembly  2  and bussing structure  34 , for clarity. 
     Each electric feed through  20  includes a conductive post  22  which is surrounded by an insulating spacer  24  with a space  26  therebetween. The insulating spacer  24  prevents electrical contact between the conductive post  22  and the battery enclosure portion  30 . The bussing structure  34 , and in particular the insulating disks  34   a , may be supported against the spacer  24 , whereas external insulator  32 , and in particular top external insulator  32   a , may be supported by the other side of spacer  24 . The conductive post  22  of each electric feed through is connected on one end to the bussing structure  34  of the battery, as shown in FIG.  2 . Particularly, the conductive posts  22  are electrically connected to positive bus washer  34   d , and tabs  34   c . An end surface of the post  22  is connected to the bussing structure to form an electrical connection therewith. Further, the other end of each post  22  is welded to a respective contact disk  8  of the terminal assembly  2  to connect the bussing structure  34  on the inside of the battery with the terminal assembly  2  on the outside of the battery. In a lithium-ion battery, for example, the post  22  is preferably made of molybdenum. However, the post  22  may be made of any other suitable material depending on the type of battery in which the circuit breaker is employed. 
     Each post  22  is connected to a respective contact disk  8  by a weld connection  11  made around the periphery of aperture  10 . Because the hole  6  in the current plate  4  has a larger diameter than the aperture  10 , the weld connection  11  can easily be made from the outside of the battery. An epoxy  9  fills aperture  10  and hole  6  to cover weld connection  11 . Thus, when weld connection  11  is broken to interrupt current flow from the battery, epoxy  9  contains arcing. The post  22  has a larger diameter than that of the aperture  10 , so the weld connection  11  is formed on an end surface of the post  22  and forms an electrical connection between the post  22  and contact disk  8 . 
     Further, the relative diameters of the holes  6 , posts  22 , and apertures  10  are sized such that: the diameter of each weld connection between the current plate  4  and a contact disk  8  is larger than that of weld connection  11  between each contact disk  8  and a respective post  22 ; the diameter of each post is larger than that of each aperture  10 , so that the electrical connection between each post  22  and the bussing structure  34  is larger than that of weld connection  11  between each post  22  and a respective contact disk  8 . Thus, the weld connection  11  is the smallest diameter connection among the connections between the bussing structure  34 , the electric feed through  20  and the terminal assembly  2 . Therefore, because the weld connection  11  has the smallest diameter, it is the shortest length of conductor and hence has the least current carrying capacity; it will be the first to fail upon the development of overcurrent, and thus acts as a circuit breaker. 
     Additionally, because the weld connection is made in a portion of the contact disk  8  around the periphery of aperture  10 , the length of the weld connection is controlled by the size of the aperture  10 . Therefore, varying the size of the aperture  10  controls the amount of overcurrent which will cause the weld connection  11  to fail and interrupt current flow. That is, if the aperture  10  is made larger, the length of the weld connection  11  is longer thereby reducing impedance and, therefore, causing the circuit breaker to open at a larger overcurrent than when a smaller aperture  10  is used. Similarly, when the aperture  10  is made smaller, the length of the weld connection  11  is reduced thereby increasing impedance and, therefore, causing the circuit breaker to open at a smaller overcurrent than when a larger aperture  10  is used. 
     Thus, from the above it is seen that merely controlling the size of the aperture  10  controls the amount of overcurrent at which the circuit breaker will open to interrupt current flow. That is, selecting a different diameter for aperture  10  allows easy variation in the amount of current allowed through the weld connection  11  before it fails and current is automatically interrupted. 
     Further, the amount of overcurrent can be controlled by varying the thickness and resistivity of the materials chosen for the terminal assembly  2 . That is, by increasing the thickness of the contact disk  8 , the weld connection  11  is made thicker thereby reducing impedance such that an increased amount of current is allowed before failure of the weld connection  11 , i.e., before the circuit breaker opens. Similarly, by decreasing the thickness of the contact disk  8 , the weld connection  11  is made thinner thereby increasing impedance such that a decreased amount of current is allowed before failure of the weld connection  11 . Further, by increasing the resistivity of the material used for the contact disk  8 , impedance is again increased, thereby decreasing the current allowed before failure of weld connection  11 . Similarly, by decreasing the resistivity of the material used for the contact disk  8 , impedance is again decreased, thereby increasing the current allowed before failure of weld connection  11 . 
     Although preferred embodiments have been described above, it is contemplated that numerous modifications may be made to the automatic circuit breaker of the present invention without departing from the spirit and scope of the invention as defined in the following claims.