Abstract:
A lithium battery includes a lithium cell package disposed within an enclosure having means to route gases vented from the package in a controlled fashion. A plurality of enclosures may be stacked, defining a vent conduit for collecting and routing gases vented from any of the plurality of enclosures. Means for interfacing a gas conveyance means to the vent conduit are provided. In a further aspect, the enclosure may include features to control the location in the cell package at which vented gases are released.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to a battery pack with venting provisions for routing of gases that may be produced internal to the battery pack. 
       BACKGROUND OF THE INVENTION 
       [0002]    Automobile manufacturers are interested in Plug-in Hybrid Electric Vehicles (PHEV) using lithium batteries. A requirement for lithium batteries is that the active material must be isolated from oxygen. This requirement may be met by a metalized barrier surrounding the active lithium cell, such as by encasing the cell in a hard metal case or by providing a metalized film package to surround the cell. Examples of cell packaging are found in U.S. Patent Publication 2006/0234119 and U.S. Patent Publication 2010/0143782, both of which are incorporated by reference. 
         [0003]    Under certain conditions, cells may generate gases, resulting in a pressurized condition within the cell package. When the pressure exceeds the strength of the package, the package may rupture or explode, releasing the gas to the exterior of the cell. Gases generated in lithium cells may be noxious or harmful. This limits flexibility in positioning lithium cells in a vehicle to locations that will not expose people to any vented gases from the battery, in particular to locations outside of the passenger compartment of the vehicle. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    In a lithium battery embodying principles of the invention, a cell package is disposed within an enclosure having means to route gases vented from the package to the exterior of the enclosure in a controlled fashion. In this way, the battery may be mounted, for example, in proximity with the passenger compartment of the vehicle without concern of exposing passengers to noxious gases discharged from a ruptured cell package. 
         [0005]    In another aspect of the invention, the location in the cell package where venting will occur in the event of pressure within the cell exceeding the burst strength of the cell package is controlled by the enclosure within which the cell package is disposed. As a result, for example, venting may be controlled to occur near the top of the cell package so as to allow the relief of gas pressure while retaining liquids within the cell package. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0006]      FIG. 1  depicts an exploded view of a cell module embodying principles of the present invention; 
           [0007]      FIG. 2  depicts an assembled cell module embodying principles of the present invention; 
           [0008]      FIG. 3  depicts a plurality of cell modules partially arranged in a battery embodying principles of the present invention; 
           [0009]      FIG. 4  depicts a battery pack embodying principles of the present invention; 
           [0010]      FIG. 5  depicts an alternative cell enclosure embodying principles of the present invention, configured to control where cell venting will occur; and 
           [0011]      FIG. 6  depicts regions on a battery cell defined by the enclosure of  FIG. 5 , embodying principles of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring to  FIG. 1 , a cell module  10  comprises a cell package  12 . As used herein, the term “cell package” includes an electrochemical cell  14  and packaging material, such as for example metalized film  16 , surrounding the electrochemical cell  14  to isolate the electrochemical cell  14  from contact with air and to allow handling of the packaged cell. The electrochemical cell  14  may be, for example, a lithium cell as is known in the art. Metalized film  16  is disposed around the electrochemical cell  14 , and is sealed in a region surrounding the electrochemical cell  14 . The seal may be achieved, for example, by a fold in the film  16 , a heat seal joining a front layer of the metalized film  16  to a rear layer of the metalized film  16 , by combinations of folds and heat seals, or by other means as known in the art. The cell package  12  also includes terminals  18  to provide electrical communication from the electrochemical cell  14  to the exterior of the cell package  12 . 
         [0013]    As depicted in  FIG. 1 , the cell module  10  further comprises a first enclosure portion  20 , and a second enclosure portion  22 . In the depiction, the first enclosure portion  20  defines a first vent opening  24 , and the second enclosure portion  22  defines a second vent opening  26 . As depicted, the first enclosure portion  20  includes a first sealing surface  28 , and the second enclosure portion  22  includes a second sealing surface  30 . While  FIG. 1  depicts the first sealing surface  28  and the second sealing surface  30  as planar surfaces, either of the sealing surfaces  28 ,  30  may define a recess into which a sealing means such as a gasket or a sealant material may be disposed. Alternately, the sealing surfaces  28 ,  30  may cooperate when abutted to one another to define a recess into which a sealing means such as a gasket or a sealant material may be disposed. The enclosure portions  20  and  22  may be structurally identical to each other, which may allow manufacturing efficiency. 
         [0014]      FIG. 2  depicts an assembled cell module  10 . In the cell module  10  in  FIG. 2 , the first enclosure portion  20  and the second enclosure portion  22  have been brought together such that the first sealing surface  28  sealingly abuts the second sealing surface  30 . The cell module  10  is sealed along the entire periphery defined by the sealing surfaces  28 ,  30  so that the only fluid communication between the interior of the cell module  10  and the exterior of the cell module  10  is by way of the first vent opening  24  and the second vent opening  26 . The terminals  18  extend through the interface defined by the first sealing surface  28  and the second sealing surface  30  so as to provide electrical communication between the electrochemical cell package  12  and the exterior of the cell module  10 . Sealing is additionally provided to prevent fluid communication between the interior of the cell module  10  and the exterior of the cell module  10  at the interface between the terminals  18  and the sealing surfaces  28 ,  30 . Alternate means for providing electrical communication between the electrochemical cell package  12  and the exterior of the cell module  10  while preventing fluid communication between the interior of the cell module  10  and the exterior of the cell module  10  may be provided without departing from the intended scope of the present invention. 
         [0015]    Referring to  FIG. 3 , a plurality of cell modules  10  is shown partially assembled into a multiple cell battery  32 . The cell vent openings  24 ,  26  of adjacent cells are aligned to define a vent conduit  34  extending through the entire length of the multiple cell battery  32 . The battery  32  may include a sealing means  36  to prevent gas vented from a cell package from escaping from the vent conduit  34  at an interface between cell modules  10 . Such a sealing means  36  may include a face seal peripherally surrounding vent openings  24 ,  26 . Other sealing means as are known in the art may alternatively be employed without departing from the intended scope of the present invention. 
         [0016]      FIG. 4  depicts a battery pack  32  along with an interface means  38  to fluidly connect the vent conduit  34  with a gas conveyance means  40  such as a tube to route vent gases from the vent conduit  34  away from the battery pack  32 . The gas conveyance means  40  is preferably fluidly coupled to the atmosphere at a location where vent gases can be safely discharged. For example, this invention enables a battery pack  32  to be mounted inside the passenger compartment of a vehicle without exposing the vehicle occupants to noxious gases in the event of a cell venting episode by routing vent gases through the gas conveyance means  40  to the exterior of the vehicle. Although depicted as a separate piece in  FIG. 5 , the interface means  38  may alternatively be a feature defined in a cell module  10  or a feature defined in an endplate disposed at an end of a stack of cell modules  10 , without departing from the intended scope of the present invention. 
         [0017]    A further aspect of the invention is illustrated in  FIGS. 5 and 6 . As depicted in  FIG. 5 , a cell module  110  comprises a first enclosure portion  120  and a second enclosure portion  122 . In the depiction, the first enclosure portion  120  defines a first vent opening  124 , and the second enclosure portion  122  defines a second vent opening  126 . As depicted, the first enclosure portion  120  includes a first sealing surface  128 , and the second enclosure portion  122  includes a second sealing surface  130 . The first enclosure portion  120  further includes a first interior wall  132 , and the second enclosure portion  122  includes a second interior wall  134 . While  FIG. 5  depicts the first sealing surface  128  and the second sealing surface  130  as planar surfaces, either of the sealing surfaces  128 ,  130  may define a recess into which a sealing means such as a gasket or a sealant material may be disposed. Alternately, the sealing surfaces  128 ,  130  may cooperate when abutted to one another to define a recess into which a sealing means such as a gasket or a sealant material may be disposed. The enclosure portions  120  and  122  may be structurally identical to each other, which may allow manufacturing efficiency. 
         [0018]    The functions of the first interior wall  132  and the second interior wall  134  will now be described. Referring to  FIG. 6 , the electrochemical cell  14  is disposed between front and back layers of the metalized film  16 , and the front and back layers of the metalized film  16  are sealed to each other in a region surrounding the electrochemical cell  14  as previously described. When assembled into a cell module  110 , the first interior wall  132  and the second interior wall  134  in proximity to the cell package  12  cooperate to impart localized pressure on the metalized film  16  to define a reinforcement region  42  outside of the extent of electrochemical cell  14 . The reinforcement region  42  represents a region in which pressure generated by gases which may be produced by electrochemical cell  14  is impeded from applying stress to the seal between the layers of the metalized film  16 . The reinforcement region  42  does not impede the application of pres sure-generated stress to the entire seal region between the layers of the metalized film  16 , but rather the first internal wall  132  and the second internal wall  134  are disposed such that an unreinforced region  44  is defined in a predetermined location of the cell package  12 . In the event of the electrochemical cell  14  producing gas, the pressure between the layers of metalized film  16  may increase until the strength of the seal in the unreinforced region  44  is exceeded, at which time the layers of the metalized film  16  will separate in the unreinforced region  44 , resulting in the release of vent gas at a controlled location in the cell package  12 . 
         [0019]    While this invention has been described in terms of the embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.