Abstract:
A modular battery pack assembly and method of making the same. Prismatic battery cells are placed along a stacking axis within a structural frame that is made of a polymeric material that includes foldable components made up of a top section disposed adjacent an edge of the stacked cells, and numerous side sections cooperatively coupled to the top sections to define an enclosure about the cells. In one form, apertures, protrusions and other features may be formed in or on the enclosure surface that faces or otherwise engages the cells, while in another form, built-in hinges permit selective latching between adjacent enclosure sections. A bottom section, which may be made of the same or similar material, may be secured to the remainder of the enclosure that is formed by the top and side sections such that the stacked cells are completely enclosed in a portable, modular assembly. In assembling the battery pack, top-down construction is employed so that the edge of the cell stack that defines the battery electrical terminals is first seated into the top section of the frame along a generally downward vertical axis.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to packaging structure for battery cells within a battery pack, and more particularly to coupling a low part-count rigid frame made of a polymeric material for containing and supporting the battery cells. 
         [0002]    Lithium-ion and related batteries, collectively known as a rechargeable energy storage system (RESS), are being used in automotive and related transportation applications as a way to supplement, in the case of hybrid electric vehicles (HEVs), or supplant, in the case of purely electric vehicles (EVs), conventional internal combustion engines (ICEs). The ability to passively store energy from stationary and portable sources, as well as from recaptured kinetic energy provided by the vehicle and its components, makes such batteries ideal to serve as part of a propulsion system for cars, trucks, buses, motorcycles and related vehicular platforms. In one form suitable for automotive applications, individual battery cells (i.e., a single electrochemical unit) are shaped as generally thin rectangular members. The flow of electric current to and from the cells is such that when several such cells are combined into larger assemblies, the current or voltage can be increased to generate the desired power output. In the present context, larger module and pack assemblies are made up of one or more cells joined in series, parallel or both, and may include additional structure to ensure proper installation and operation of these calls. Although the term “battery pack” is used herein to discuss a substantially complete battery assembly for use in propulsive power applications, it will be understood by those skilled in the art that related terms—such as “battery unit” or the like—may also be used to describe such an assembly and that either term may be used interchangeably without a loss in such understanding. 
         [0003]    In one form, the individual cells that make up a battery pack are configured as rectangular (i.e., prismatic) cans that define a rigid outer housing known as a cell case. As with their similarly-shaped prismatic pouch cell counterparts, prismatic can-style cells can be placed in a facing arrangement (much like a deck of cards) along a stacking axis formed by the aligned parallel plate-like surfaces. Positive and negative terminals situated on one edge on the cell case exterior are laterally-spaced from one another relative to the stacking axis and act as electrical contacts for connection (via busbar, for example) to an outside load or circuit. Within the cell case, numerous individual alternating positive and negative electrodes are spaced apart from one another along the stacking direction and kept electrically isolated by non-conductive separators. Leads from each of the negative electrodes are gathered together inside the cell case to feed the negative terminal, while leads from each of the positive electrodes are likewise gathered together to feed the positive terminal. 
         [0004]    Traditional frames used to house battery cells are made from joined metal components. While capable of providing satisfactory support for the numerous cells, they tend to be heavy, while an assembly based on such frames involves a high part count, often requiring (in addition to the cells and the flex circuit) roughly 20 separate pieces. Moreover, they are prone to leakage due to the large gaps between mating components in the assembled module and additionally may provide a conductive path between the cells and ground, as well as between the positive and negative voltage terminals within each of the cells. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention solves the above problems by providing a rigid battery cell frame made from non-conductive plastic-based materials. In one aspect, an automotive battery pack assembly includes a plurality of prismatic battery cells arranged along a stacking axis, each of the cells defining laterally-spaced positive and negative cell terminals along an edge thereof. The assembly also includes a separate frame made up of foldable components that are made substantially from a polymeric material. The frame includes a top section disposed adjacent one edge of each of the cells, and numerous side sections cooperatively coupled to the top section to define an enclosure about the cells. The foldable sections of the frame are attached to a bottom section (which is preferably made from a polymeric material) disposed adjacent the terminal-bearing edge of each of the cells. In one form, apertures, protrusions and other features may be formed in or on the enclosure surface that faces or otherwise engages the cells, while in another form, built-in hinges permit selective latching between adjacent enclosure sections. While in a preferred configuration the bottom section is a separate, discrete piece that may be subsequently attached to the frame, in another form, it may also be integrally formed through the flexible hinges; both forms are deemed to be within the scope of the present invention. In the present context, the act of securing the various sections of the frame to one another, as well as securing the other attachable components (such as the bottom section) are sufficient to render the frame as an assembly. Other components made from other plastics, silicone or the like) may also be used; however, the predominant frame structure is made from polymeric materials with suitable structural (including fatigue) and electrical properties, such as polypropylene, polyphthalamide (PPA), nylon, polycarbonate/polybutylene terephthalate (PBT), thermoplastic olefin (TPO) or the like. With such construction, the proposed cage reduces gaps and leak paths where mating components are joined. 
         [0006]    Within the present context, the assembly and the batteries contained therein form a modular structure that is compatible with automotive usage. Such modular structure may form a significant part of a battery pack that is considered to be a substantially complete assembly or system of components necessary for propulsion of the vehicle for which the pack was designed. Under such understanding, the battery modules and individual battery cells are (as mentioned above) considered to be subcomponents that are subsequently assembled into the pack or other larger part of the overall system Likewise, an assembly of components for a battery pack used for vehicular applications may include—in addition to numerous battery cells—cooling plates, securing mechanisms and other equipment that, while not contributing to the production of electric power or formation of the assembled cells and frame, make up an important part of the overall battery system packaging and assembly. 
         [0007]    According to another aspect of the invention, an automotive battery pack assembly includes numerous prismatic can battery cells arranged along a stacking axis, each of the cells defining laterally-spaced positive and negative cell terminals along an edge thereof. A frame made substantially from a polymeric material includes a top section and various side sections. The top section forms a base to receive a corresponding edge of each of the cells that includes the projecting terminals, while the side sections are unitarily hinged to the top section such that prior to being folded into the shape of a cell-supporting enclosure, the shape of the top and side sections resemble an as-yet unfolded cardboard box. A bottom section may be secured to one or more of the side sections such that upon complete formation of the enclosure around the cells, the bottom is disposed adjacent the edge of the stacked cells that is opposite of the edge with the terminals. Such a bottom section may be either a separate section attachable to the unitary frame, or form part of the frame itself through a unitarily hinged connection. In the present context, a unitarily hinged connection or coupling is one where the hinge and the sections to which it is attached are formed of a one-piece construction (such as through molding of the same material); a more particular form of such hinge that is discussed within the present context is a living hinge, where the hinge is often necked or otherwise thinned relative to the more rigid sections to which it is attached. 
         [0008]    According to yet another aspect of the invention, a method of a placing prismatic battery cells into a module includes providing a unitary frame made substantially from a polymeric material to define at least a top section and numerous side sections hingedly coupled to the top section. The cells are placed in a facingly adjacent (i.e., stacked) orientation with one another on the top section such that an edge defined along each of the cells is seated on a corresponding surface of the top section. The construction of the frame is such that its hinges allow folding of the side sections around the stacked cells such that an open box-like enclosure is formed except for the bottom of the cell stack that is opposite the edges with the protruding electrical terminals. Once such hinging has been performed to substantially enclose the top and side edges of the stacked batteries, a bottom section of the frame is placed such that an enclosure is formed substantially around the facingly adjacent cells. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The following detailed description of the preferred embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
           [0010]      FIG. 1  shows a vehicle with a hybrid propulsion system in the form of a battery pack and an internal combustion engine; 
           [0011]      FIG. 2A  shows an exploded view of various individual battery cells placed within a frame to define a battery pack or module assembly according to an aspect of the present invention; 
           [0012]      FIG. 2B  shows partial internal details of one of the prismatic can battery cells of the assembly of  FIG. 2A ; 
           [0013]      FIGS. 3A through 3G  show a sequence used to produce the assembly of  FIG. 2A ; 
           [0014]      FIG. 4  shows a top view of the rigid polymeric frame of  FIGS. 3A and 3B  in its generally planar pre-assembled state to show the location of numerous living hinges; 
           [0015]      FIG. 5  shows a section view taken from  FIG. 3G  that highlights a snap-fit feature between the terminals of the battery cells and a complementary apertures formed into the rigid polymeric frame; and 
           [0016]      FIG. 6  shows a perspective view of a rigid polymeric frame according to another embodiment of the present invention with a different snap-fit closure for the sides of the frame. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Referring first to  FIG. 1 , a vehicle  1  includes a hybrid propulsion system in the form of an electric power source made up of a conventional ICE  5  and a battery pack  10 , both cooperative with an electric motor  15 . Such a vehicle is known as a hybrid electric vehicle (HEV). It will be appreciated by those skilled in the art that vehicle  1  may not require an ICE  5 , in such case, rather than being an HEV, it is an electric vehicle (EV); either form is within the scope of the present invention. Additional drivetrain components (none of which are shown) useful in providing propulsive power to one or more of the wheels and coupled to one or both of the battery pack  10  and ICE  5  are understood to include rotating shafts, axles, transmission, controllers or the like. While vehicle  1  is presently shown as a car, the applicability of the hybrid propulsion system to other such automotive forms (including trucks, buses, aircraft, watercraft, spacecraft and motorcycles) is deemed to be within the scope of the present invention. 
         [0018]    Referring next to  FIGS. 2A and 2B , an exploded view of an assembly  200  made from a stacked arrangement of numerous prismatic lithium-ion battery cells (also referred to herein as prismatic can cell, prismatic cell, or more simply cell)  100  is shown, as well as a notional structure of each cell  100 , for placement within the battery pack  10  of  FIG. 1 . As shown with particularity in  FIG. 2A , the assembly  200 —which is made from as few as four parts (in addition to the cells  100  and flex circuit (a portion of which is shown in  FIG. 6  as  260 ) that may include bus cables, bus bars and their associated connectors)—includes a lower plate or tray  210 , an optional set of cooling fins  220 , a rigid frame  230  and a vent cap  240  arranged together such that a cage-like housing is formed around the stack of cells  100  and the cooling fins  220 . Significantly, the lower plate  210 , the frame  230  and the vent cap  240  are made from a polymeric material such as those mentioned above. The vent cap  240  in particular is used to provide a means to contain and properly route gases in the event of venting from one or more of cells  100 . Threaded studs (or related terminals)  245  provide clamping interface for a main power connection; as such, they act as collars to facilitate the secure, accurate placement of electrode studs or terminals (not shown) to external electrical circuitry, such as the aforementioned flex circuit. 
         [0019]    Referring with particularity to  FIG. 2B , unlike pouch-style battery cell variants (not shown), which—although they have in common a generally flat, rectangular stackable shape in a manner generally similar to a prismatic cell—include numerous cells interspersed with cooling plates and other components, as well as thin peripheral edge and even thinner conductive foil tabs extending from the pouch edge, the prismatic cell  100  has the anode and cathode packaged within a welded rigid metal (for example, aluminum) rectangular canister, enclosure or similar self-supporting housing. While the cell  100  promotes scale-up and related design flexibility, increased care must be taken to promote more thorough sealing and thermal management approaches. Shown in a partial cutaway view, the notional construction of cell  100  that is usable with the present invention includes positive and negative terminals  110 ,  120  projecting out of its top edge, along with a safety vent  130 ; this safety vent  130  may be used in conjunction with the vent cap  240  to provide a secure venting path in the event of a need for one or more of the cells  100  to vent. Within the cell&#39;s  100  rigid outer case  140  are numerous positive and negative electrodes  150 ,  160  and non-conductive interspersed separators  170 . Leads (in the form of tabs  180 ,  190 ) from each of the electrodes  150 ,  160  are gathered together inside the cell case  140  to feed the respective terminals  110 ,  120 . As mentioned above, the cells  100  define a rigid, rectangular (i.e., prismatic) shape such that they are easily stacked in a facingly-adjacent relationship along a stacking axis A-A. The flex circuits (not shown) may be placed on top of the assembly  200  to form an electric circuit between the terminals  110 ,  120  of the stacked batteries  100  and a suitable load (such as electric motor  15  for propulsion, as well as other systems used to provide functionality to vehicle  10 ). 
         [0020]    Referring next to  FIGS. 3A through 3G  in conjunction with  FIG. 4 , steps associated with forming the assembly  200  are shown. In general, the cells  100  are stacked in a face-to-face relationship such that their edges substantially align to define a generally rectangular shape. In the present context, the face-to-face relationship may also include configurations where there is a slight gap G between adjacent cells  100  to permit the placement of the optional cooling fins  220 ; the corrugated (or other undulated) shape of such fins  220  helps to define a cooling path. 
         [0021]    Referring with particularity to  FIG. 3A , rigid frame  230  is initially presented as a generally planar sheet that resembles a corrugated cardboard box prior to folding and gluing where, instead of cardboard, the frame  230  is made up of a single piece of the polymeric material discussed above. As will be discussed in more detail below in conjunction with  FIG. 4 , the frame  230  can be elastically deformed in select locations such as hinges to form a box-like housing structure for the stacked cells  100 . The rigid frame  230  defines a top section  231  and hingedly-connected side sections  233  the latter of which in turn include both lateral portions  235  and end portions  237 . The placement of the stack of cells  100  is such that the terminals  110 ,  120  are oriented downward along a substantially vertical axis. 
         [0022]    As shown with particularity in  FIG. 4 , the frame  230  defines an inverted construction that differs from conventional box-like enclosures in that the placement of the stack of cells  100  starts along the top section  231  rather than the bottom section  210 . Moreover, frame  230  includes numerous living hinges  238  that act as generally flat flexible springs to permit pivoting movement between the central top section  231  and the lateral portions  235  and end portions  237  of side section  233 . Likewise, numerous fasteners in the form of latches  239  include a cooperative snap-fit between tabs  239 A and apertures  239 B each of which are formed on or in a respective part of the lateral portions  235  and end portions  237 . The resiliently-biased nature of the latches  239  that are integrally formed along the edge of the end portions  237  is such that the protruding distal end of the tabs  239 A may be temporarily compressed until it is moved into contact engagement with a corresponding aperture  239 B near the edge of the adjacent lateral portion  235 . As with the region that joins the top section  231  to the side section  233 , the region where the tabs and apertures are formed may also include living hinges  238  to facilitate the snap-fit connection. The combined effect of the latches  239  and hinges  238  have the effect of permitting semi-permanent assembly of the top section  231  and the various flaps defined by the side sections  233  into a unitary—and substantially rectangular-shaped—box-like cage or housing such as shown in  FIGS. 1 and 3D through 3G . Moreover, the construction of the assembly  200  of the present invention is better at controlling leakage than that of a conventional metal frame, as it seals around the cell terminals  110 ,  120  with no gaps between the top section  231  and the lateral portions  235 . Moreover, the cooperation between the end portions  237  have fewer leak paths, making the frame  230  easier to be sealed. An array of generally rectangular-shaped apertures  231 A are formed within the planar surface of the top section  231  to permit—among other things, access to the tops of the various battery cells  100 . Additional details of these apertures  231 A will be discussed in more detail in conjunction with  FIG. 5 . Similar apertures  235 A may be formed in the surface of one or both of the lateral portions  235 , and their function will be discussed in more detail below in conjunction with  FIG. 3D . 
         [0023]    As shown with particularity in  FIGS. 3B through 3D  in conjunction with  FIG. 4 , the aligned stack of cells  100  are first placed onto the top section  231  such the top edges (which contains the positive and negative terminals  110 ,  120 ) of each cell  100  rest upon the surface of the top section  231 . At least a portion of the array of apertures  231 A are sized and shaped to accept the corresponding-shaped terminals  110 ,  120  such that the latter are seated in the former. Periodically-spaced projections  235 P formed in the lateral portion  235  of side section  233  may help define channels or related seating along the height wise dimension of the formed frame  230 ; in addition to promoting a secure, repeated placement of the stacked cells  100  into the cage-like housing formed by the frame  230 , these projections  235 P help establish the axial gap G identified in  FIG. 3A  between adjacent cells  100 , as well as help establish seating or related registration (i.e., cell positioning or locating) between each of the cells  100  and their corresponding place within the frame  230 . Notwithstanding the fact that the cells  100  include projections in the form of terminals  110 ,  120  along their top edge, and that the cell-engaging surfaces of the frame  230  may include various seats, channels and projections as a way to better secure the cells  100 , both the frame  230  and the cells  100  define substantially rigid rectangular shapes with substantially planar complementary surfaces, as readily apparent from  FIGS. 3A through 3D . 
         [0024]    As assembled per  FIG. 3D , five of the six sides of the box-like structure to provide containment and support for the numerous individual battery cells  100  are in place. At this juncture, and referring with particularity to  FIG. 3E , the stacked prismatic can battery cells  100  that are spaced an amount sufficient along the stacking axis A-A with axial gaps G may receive corrugated cooling fins  220 . As mentioned above, in the event that fins  220  or other cooling structure is required, the projections  235 P that can be seen in  FIGS. 3A through 3D  help keep the spacing between adjacent cells  100  consistent and repeatable. Moreover, the apertures  235 A that are formed in the lateral portion  235  of side section  233  are generally aligned with the fins  220  so that heat may be directed outward (under either passive or forced convection) from the stacked cells  100  and frame  230  along flowpaths defined by the apertures  235 A and fins  220 . 
         [0025]    Referring next to  FIGS. 3F, 3G and 5 , the stacked cells  100  and frame  230  are then turned upside down so that the lower plate  210  can be attached from the top. Lower plate  210  may also include spring biased projections  243  formed on its surface to help provide a tight fit against the bottom edge of the various cells  100 . In one preferred configuration, the projections  243  are integrally-formed within the lower plate  210  to define a unitary structure; in one manner, they together may be made from a suitably-configured mold. Thus, the weight of the cells  100  is sufficient to slightly compress the projections  243  in order to promote a secure, substantially rattle-free placement of the cells  100  within frame  230 . Moreover, because the size and shape of both the cell  100  and the corresponding inner surfaces of the frame  230  is such that both define a generally rectangular profile so that the generally planar complementary contact surfaces between the outer lateral edges of the cell  100  and the adjacent inner sidewalls defined by the frame  230  further promote contact engagement to ensure a snug, secure fit of the former into the latter. Once the lower plate  210  is secured to the frame  230 , the assembly defines all six sides of the box-like structure to provide containment and support for the numerous individual battery cells  100 . In a preferred embodiment, the lower plate  210  is designed to be ultrasonically welded to the top frame, thereby further helping to keep leakage low in a manner similar to the continuously-formed hinges between the lateral portion  235  of side section  233  and top section  231 , as well as between the end portions  237  of side section  233  and the top section  231 . At this time, the assembly  200  may be returned to its proper orientation as shown with particularity in  FIG. 3G  so that the terminals  110 ,  120  of each of the cells  100  are upward-facing. 
         [0026]    Referring with particularity to  FIG. 5 , the apertures  231 A that are formed in the surface of the top section  231  may further define resiliently-biased connectors  231 C that by pressing against the sides of cell terminals  110 ,  120  can help to maintain the snug fit of the cells  100  in the box-like enclosure formed by frame  230 . The resilient bias of the connectors  231 C may also be made to resemble the snap-fit features of the latches  239  discussed above; either form of biasing of the connectors  231 C is deemed to be within the scope of the present invention. As mentioned above, with the containment construction enabled by the assembly  200  of the present invention, gaps and leak paths where mating components are joined are significantly reduced or eliminated. This is especially true in the areas adjacent the battery terminals  110 ,  120 , where the assembly  200  provides a sealed joint on its top section. 
         [0027]    Referring next to  FIG. 6 , variations on the snap-fit features of the latches  239  used to secure the sides of the frame of  FIGS. 3A through 3G and 4 —as well as a few additional components associated with assembly  200 —are shown. In essence, the snap-fit features form a different hinge arrangement in that rather than having the tabs  239 A inserted into apertures  239 B, a surface-mounted buckle arrangement is used. In this way, there are fewer leakage pathways formed near the seam where the lateral portions  235  and end portions  237  are joined. Additional assembly  200  components, such as the module cover  250  (which may also be made from a polymeric material) may be placed on top of the top section  231 . Such a cover provides additional environmental protection for the battery, as well as a mounting surface for a flex circuit connector  260  to receive a corresponding end of flex circuit  270 , as well as a cell balancing board  280 . Likewise, other electrical features (such as ring terminals  290  that extend from the flex circuit  260 ) are disposed around the threaded studs  245  that protrude from the top of the assembly  200 . 
         [0028]    It is noted that terms like “preferably”, “commonly,” and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention. Likewise, terms such as “substantially” are utilized to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. It is also utilized to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
         [0029]    For the purposes of describing and defining the present invention it is noted that the term “device” is utilized herein to represent a combination of components and individual components, regardless of whether the components are combined with other components. For example, a device according to the present invention may comprise a battery or related source of electric power that in turn may be used to provide motive power. A device may also refer to a vehicle incorporating the source of motive power or other equipment that may make up, or be used in conjunction with, the vehicle or source of motive power; the nature of the device will be clear from the context. Furthermore, variations on the terms “automobile”, “automotive”, “vehicular” or the like are meant to be construed generically unless the context dictates otherwise. As such, reference to an automobile will be understood to cover cars, trucks, buses, motorcycles and other similar modes of transportation unless more particularly recited in context Likewise, the invention may be used in conjunction with battery cells unrelated to automotive applications, where temperature-sensitive equipment may need added thermal protection; such additional configurations are understood as being within the scope of the present invention. 
         [0030]    Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.