Abstract:
A traction battery assembly may include an array of battery cells having opposing end faces, opposing side faces, and a bottom face. The assembly may also include a pair of end plates and a pair of side plates arranged to form a four-sided enclosure around the end and side faces and configured to compress and retain the cells without being mechanically attached thereto or covering the bottom face. The side plates may partially cover an upper portion of the array. The side plates may have a lower horizontal edge, an upper horizontal edge, and at least one diagonal reinforcement rib configured to extend from a location where the vertical edge and lower horizontal edge meet upward to the upper horizontal edge.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to thermal management systems for high voltage batteries utilized in vehicles. 
       BACKGROUND 
       [0002]    Vehicles such as battery-electric vehicles (BEVs), plug-in hybrid-electric vehicles (PHEVs), mild hybrid-electric vehicles (MHEVs), or full hybrid-electric vehicles (FHEVs) contain a traction battery, such as a high voltage (HV) battery, to act as a propulsion source for the vehicle. The HV battery may include components and systems to assist in managing vehicle performance and operations. The HV battery may include one or more arrays of battery cells interconnected electrically between battery cell terminals and interconnector busbars. The HV battery and surrounding environment may include a thermal management system to assist in managing temperature of the HV battery components, systems, and individual battery cells. 
       SUMMARY 
       [0003]    A traction battery assembly includes an array of battery cells having opposing end faces, opposing side faces, and a bottom face. The assembly also includes a pair of end plates and a pair of side plates arranged to form a four-sided enclosure around the end and side faces and is configured to compress and retain the cells without being mechanically attached thereto or covering the bottom face. The side plates partially cover an upper portion of the array. The end plates and side plates may each have a pair of vertical edge portions and may be mechanically fastened to one another at the respective edge portions. The side plates may define a plane and at least one of the mechanical fasteners may be oriented substantially perpendicular with the plane. The side plates may have a lower horizontal edge, an upper horizontal edge, and at least one diagonal reinforcement rib configured to extend from a location where the vertical edge and lower horizontal edge meet upward to the upper horizontal edge. A midplate may be centrally located within the array, mechanically fastened to the side plates, and configured to receive a bending moment force generated by the side plates. A plurality of spacers may be located between adjacent battery cells and include a tab extending from an upper portion of the spacer configured to locate and mate with a busbar module extending between the opposing end faces of the array. Each of the end plates may define a vertically oriented lift aperture at an upper portion of the end plates configured to be gripped by an installation tool. 
         [0004]    A vehicle includes an array of battery cells having opposing end faces, opposing side faces, a bottom face, and an upper face. The vehicle also includes a pair of end plates corresponding to the end faces and a pair of side plates corresponding to the side faces. The plates are configured to compress and retain the array therebetween without being mechanically fastened to the array. The vehicle also includes a plurality of spacers each located between adjacent battery cells, including a tab extending above the upper face, being configured to locate and mate with a busbar module, and defining a lower ridge portion configured to contact and support the adjacent cells at a portion of the cells above the bottom face. Each of the spacers may further define an upper ridge portion configured to contact the adjacent cells at a portion of the cells below the upper face such that the lower ridge portion and upper ridge portion vertically retain the cells. The side plates may define an upper portion configured to cover a portion of the upper face of the cells and a vertically oriented receiving aperture at either ends of the upper portion configured to receive a mechanical fastener and develop a load between the side plates and the cells generated by the compression thereof. A pair of dielectric rails may be located between the upper portion of the side plates and upper face of the array and may have a thickness such that a force is generated between the bottom face and a surface therebelow. The thickness of the dielectric rails may be greater at a mid-span of the dielectric rails than at opposing ends of the dielectric rails. The surface may be an upper portion of a thermal plate in thermal communication with the array. A midplate may be centrally located within the array, mechanically fastened to the side plates, configured to receive a force generated by a bending moment of the side plates, and define a vertical lift aperture at an upper portion of the midplate configured to be gripped by a tool. 
         [0005]    A traction battery assembly includes an array of battery cells having opposing end faces, opposing side faces, an upper face, and a bottom face defining a footprint. The assembly also includes a thermal plate in thermal communication with the cells and configured to direct thermal fluid flow therein. The assembly also includes a four-sided support structure located outside the footprint, including opposing end plates and side plates configured to compress and retain the cells therebetween without being mechanically fastened thereto. The side plates include an upper portion covering and extending along a portion of the upper face such that the upper portion and thermal plate generate vertical forces against the upper face and bottom face, respectively. A plurality of spacers may be located between adjacent cells and define upper and lower ridges configured to contact and retain the cells therebetween without contacting the upper or lower face. The end plates and side plates may define attachment apertures oriented substantially parallel with a length of the cells at the four corners of the structure outside the footprint and configured to receive fasteners to mechanically attach the plates to one another. The end plates and side plates may define attachment apertures oriented substantially parallel with a height of the cells at the four corners of the structure outside the footprint and may be configured to receive fasteners to mechanically attach the plates to one another. The side plates may at least partially contact the respective opposing side faces of the array. A midplate may be centrally located within the array and attached to a substantially central portion of either side plate and configured to deflect compressional forces applied to the array. The side plates may define at least one diagonal reinforcement rib extending from a lower horizontal edge of the side plates to a location on the upper portion of the side plates which is substantially equidistant from the end plate and midplate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic illustration of a battery electric vehicle. 
           [0007]      FIG. 2  is a perspective view of a portion of a thermal management system for the traction battery of the vehicle in  FIG. 1 . 
           [0008]      FIG. 3  is a perspective view of a portion of a traction battery assembly. 
           [0009]      FIG. 4A  is a perspective view of a portion of another traction battery assembly including a battery assembly having an exo-support structure and a battery cell array. 
           [0010]      FIG. 4B  is a perspective view of a battery cell array from the battery assembly of  FIG. 4A . 
           [0011]      FIG. 5  is a perspective view of an end plate from the battery assembly of  FIG. 4A . 
           [0012]      FIG. 6  is a perspective view of a side plate from the battery assembly of  FIG. 4A . 
           [0013]      FIG. 7  is a perspective view of a midplate from the battery assembly of  FIG. 4A . 
           [0014]      FIG. 8  is a perspective view of a spacer from the battery assembly of  FIG. 4A . 
           [0015]      FIG. 9  is a perspective view of a battery cell from the battery assembly of  FIG. 4A . 
           [0016]      FIG. 10  is a side view of the spacer from  FIG. 8  and two battery cells. 
           [0017]      FIG. 11  is a perspective view of a dielectric rail from the battery assembly of  FIG. 4A . 
           [0018]      FIG. 12  is a perspective view of a portion of another traction battery assembly including multiple battery assemblies having exo-support structures and battery cell arrays. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0020]      FIG. 1  depicts a schematic of a typical plug-in hybrid-electric vehicle (PHEV). A typical plug-in hybrid-electric vehicle  12  may comprise one or more electric machines  14  mechanically connected to a hybrid transmission  16 . The electric machines  14  may be capable of operating as a motor or a generator. In addition, the hybrid transmission  16  is mechanically connected to an engine  18 . The hybrid transmission  16  is also mechanically connected to a drive shaft  20  that is mechanically connected to the wheels  22 . The electric machines  14  can provide propulsion and deceleration capability when the engine  18  is turned on or off. The electric machines  14  also act as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system. The electric machines  14  may also provide reduced pollutant emissions since the hybrid-electric vehicle  12  may be operated in electric mode or hybrid mode under certain conditions to reduce overall fuel consumption of the vehicle  12 . 
         [0021]    A traction battery or battery pack  24  stores and provides energy that can be used by the electric machines  14 . The traction battery  24  typically provides a high voltage DC output from one or more battery cell arrays, sometimes referred to as battery cell stacks, within the traction battery  24 . The battery cell arrays may include one or more battery cells. The traction battery  24  is electrically connected to one or more power electronics modules  26  through one or more contactors (not shown). The one or more contactors isolate the traction battery  24  from other components when opened and connect the traction battery  24  to other components when closed. The power electronics module  26  is also electrically connected to the electric machines  14  and provides the ability to bi-directionally transfer electrical energy between the traction battery  24  and the electric machines  14 . For example, a typical traction battery  24  may provide a DC voltage while the electric machines  14  may require a three-phase AC voltage to function. The power electronics module  26  may convert the DC voltage to a three-phase AC voltage as required by the electric machines  14 . In a regenerative mode, the power electronics module  26  may convert the three-phase AC voltage from the electric machines  14  acting as generators to the DC voltage required by the traction battery  24 . The description herein is equally applicable to a pure electric vehicle. For a pure electric vehicle, the hybrid transmission  16  may be a gear box connected to an electric machine  14  and the engine  18  may not be present. 
         [0022]    In addition to providing energy for propulsion, the traction battery  24  may provide energy for other vehicle electrical systems. A typical system may include a DC/DC converter module  28  that converts the high voltage DC output of the traction battery  24  to a low voltage DC supply that is compatible with other vehicle loads. Other high-voltage loads, such as compressors and electric heaters, may be connected directly to the high-voltage without the use of a DC/DC converter module  28 . In a typical vehicle, the low-voltage systems are electrically connected to an auxiliary battery  30  (e.g., 12V battery). 
         [0023]    A battery electrical control module (BECM)  33  may be in communication with the traction battery  24 . The BECM  33  may act as a controller for the traction battery  24  and may also include an electronic monitoring system that manages temperature and charge state of each of the battery cells. The traction battery  24  may have a temperature sensor  31  such as a thermistor or other temperature gauge. The temperature sensor  31  may be in communication with the BECM  33  to provide temperature data regarding the traction battery  24 . The temperature sensor  31  may also be located on or near the battery cells within the traction battery  24 . It is also contemplated that more than one temperature sensor  31  may be used to monitor temperature of the battery cells. 
         [0024]    The vehicle  12  may be, for example, an electric vehicle such as a PHEV, a FHEV, a MHEV, or a BEV in which the traction battery  24  may be recharged by an external power source  36 . The external power source  36  may be a connection to an electrical outlet. The external power source  36  may be electrically connected to electric vehicle supply equipment (EVSE)  38 . The EVSE  38  may provide circuitry and controls to regulate and manage the transfer of electrical energy between the power source  36  and the vehicle  12 . The external power source  36  may provide DC or AC electric power to the EVSE  38 . The EVSE  38  may have a charge connector  40  for plugging into a charge port  34  of the vehicle  12 . The charge port  34  may be any type of port configured to transfer power from the EVSE  38  to the vehicle  12 . The charge port  34  may be electrically connected to a charger or on-board power conversion module  32 . The power conversion module  32  may condition the power supplied from the EVSE  38  to provide the proper voltage and current levels to the traction battery  24 . The power conversion module  32  may interface with the EVSE  38  to coordinate the delivery of power to the vehicle  12 . The EVSE connector  40  may have pins that mate with corresponding recesses of the charge port  34 . 
         [0025]    The various components discussed may have one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a serial bus (e.g., Controller Area Network (CAN)) or via discrete conductors. 
         [0026]    The battery cells, such as a prismatic cell, may include electrochemical cells that convert stored chemical energy to electrical energy. Prismatic cells may include a housing, a positive electrode (cathode) and a negative electrode (anode). An electrolyte may allow ions to move between the anode and cathode during discharge, and then return during recharge. Terminals may allow current to flow out of the cell for use by the vehicle. When positioned in an array with multiple battery cells, the terminals of each battery cell may be aligned with opposing terminals (positive and negative) adjacent to one another and a busbar may assist in facilitating a series connection between the multiple battery cells. The battery cells may also be arranged in parallel such that similar terminals (positive and positive or negative and negative) are adjacent to one another. For example, two battery cells may be arranged with positive terminals adjacent to one another, and the next two cells may be arranged with negative terminals adjacent to one another. In this example, the busbar may contact terminals of all four cells. 
         [0027]    The traction battery  24  may be heated and/or cooled using a liquid thermal management system, an air thermal management system, or other method as known in the art. In one example of a liquid thermal management system and now referring to  FIG. 2 , the traction battery  24  may include a battery cell array  88  shown supported by a thermal plate  90  to be heated and/or cooled by a thermal management system. The battery cell array  88  may include a plurality of battery cells  92  positioned adjacent to one another and structural components. The DC/DC converter module  28  and/or the BECM  33  may also require cooling and/or heating under certain operating conditions. A thermal plate  91  may support the DC/DC converter module  28  and BECM  33  and assist in thermal management thereof. For example, the DC/DC converter module  28  may generate heat during voltage conversion which may need to be dissipated. Alternatively, thermal plates  90  and  91  may be in fluid communication with one another to share a common fluid inlet port and common outlet port. 
         [0028]    In one example, the battery cell array  88  may be mounted to the thermal plate  90  such that only one surface, of each of the battery cells  92 , such as a bottom surface, is in contact with the thermal plate  90 . The thermal plate  90  and individual battery cells  92  may transfer heat between one another to assist in managing the thermal conditioning of the battery cells  92  within the battery cell array  88  during vehicle operations. Uniform thermal fluid distribution and high heat transfer capability are two thermal plate  90  considerations for providing effective thermal management of the battery cells  92  within the battery cell arrays  88  and other surrounding components. Since heat transfers between thermal plate  90  and thermal fluid via conduction and convection, the surface area in a thermal fluid flow field is important for effective heat transfer, both for removing heat and for heating the battery cells  92  at cold temperatures. For example, charging and discharging the battery cells generates heat which may negatively impact performance and life of the battery cell array  88  if not removed. Alternatively, the thermal plate  90  may also provide heat to the battery cell array  88  when subjected to cold temperatures. 
         [0029]    The thermal plate  90  may include one or more channels  93  and/or a cavity to distribute thermal fluid through the thermal plate  90 . For example, the thermal plate  90  may include an inlet port  94  and an outlet port  96  that may be in communication with the channels  93  for providing and circulating the thermal fluid. Positioning of the inlet port  94  and outlet port  96  relative to the battery cell arrays  88  may vary. For example and as shown in  FIG. 2 , the inlet port  94  and outlet port  96  may be centrally positioned relative to the battery cell arrays  88 . The inlet port  94  and outlet port  96  may also be positioned to the side of the battery cell arrays  88 . Alternatively, the thermal plate  90  may define a cavity (not shown) in communication with the inlet port  94  and outlet port  96  for providing and circulating the thermal fluid. The thermal plate  91  may include an inlet port  95  and an outlet port  97  to deliver and remove thermal fluid. Optionally, a sheet of thermal interface material (not shown) may be applied to the thermal plate  90  and/or  91  below the battery cell array  88  and/or the DC/DC converter module  28  and BECM  33 , respectively. The sheet of thermal interface material may enhance heat transfer between the battery cell array  88  and the thermal plate  90  by filling, for example, voids and/or air gaps between the battery cells  92  and the thermal plate  90 . The thermal interface material may also provide electrical insulation between the battery cell array  88  and the thermal plate  90 . A battery tray  98  may support the thermal plate  90 , the thermal plate  91 , the battery cell array  88 , and other components. The battery tray  98  may include one or more recesses to receive thermal plates. 
         [0030]    Different battery pack configurations may be available to address individual vehicle variables including packaging constraints and power requirements. The battery cell array  88  may be contained within a cover or housing (not shown) to protect and enclose the battery cell array  88  and other surrounding components, such as the DC/DC converter module  28  and the BECM  33 . The battery cell array  88  may be positioned at several different locations including below a front seat, below a rear seat, or behind the rear seat of the vehicle, for example. However, it is contemplated the battery cell array  88  may be positioned at any suitable location in the vehicle  12 . 
         [0031]      FIG. 3  shows an example of a portion of a traction battery including a battery assembly  99  having two lateral end plates  100  and two longitudinal side rail assemblies  102 . A battery cell array  104  is located between the lateral end plates  100  and longitudinal side rail assemblies  102 . The lateral end plates  100  each include four apertures (not visible in this view) to receive four fasteners (not shown) oriented substantially parallel with a longitudinal axis of the battery cell array  104 . The longitudinal side rail assemblies  102  each include four apertures  106  which are in registration with the four apertures of the lateral end plates  100  to receive the four fasteners such that the lateral end plates  100  and longitudinal side rail assemblies  102  may mate. The lateral end plates  100  each include a lift boss  108  which includes an axis  109  substantially parallel with the longitudinal axis of the battery cell array  104 . The lift boss  108  provides a location for tooling in an assembly and/or installation setting to grasp the battery assembly. In this example, the location and orientation of the lift boss  108  requires the tooling to grasp in a direction parallel with the axis  109  of the lift bosses  108  and approximately halfway down a height of the battery assembly  99 . The longitudinal side rail assemblies  102  each include three columns  110  spaced apart from the battery cell array  104 . The side rail assemblies  102  include a lower portion which extends below and contacts the battery cell array  104  and which is configured to assist in supporting the battery cell array  104 . This battery assembly  99  is intended for use with an air cooled thermal management system. As such, the space between columns  110  and the battery cell array  104  provides a path for air flow. The structure of the lateral end plates  100  and the side rail assemblies  102  require additional packaging space on the vehicle and additional assembly space due to the tooling approach line which may not be desirable in a thermal management system for a traction battery. Additionally, the side rail assemblies  102  extend below the battery cell array  104  to support and cover a bottom portion of the battery cell array  104 , which may not be desirable in a liquid cooled thermal management system since battery cell to thermal plate contact is a factor which assists in providing efficient heat transfer between the two. 
         [0032]      FIGS. 4A through 7  show a portion of a traction battery assembly. A battery assembly  140  may include an exo-support structure  142  configured to retain and support a battery cell array  144  including a plurality of battery cells  146  without mechanically fastening thereto. The exo-support structure  142  may form a four-sided enclosure for the battery cell array  144  and may be used for multiple battery cell array  144  embodiments as described further below. The battery cell array  144  may have a bottom face  145 , opposing end faces  147 , opposing side faces  148 , and an upper face  149 . The exo-support structure  142  may include end plates  150  and side plates  152  which optionally do not cover or contact the bottom face  145 . 
         [0033]    The end plates  150  may define one or more locating apertures  154 , one or more vertically oriented lift apertures  156 , and one or more attachment apertures  158  and  159  to assist in assembling and installing the battery assembly  140 . For example, the locating apertures  154  may correspond to respective locating features and/or attachment points on a mounting surface for the battery assembly  140 . The lift apertures  156  may be located at an upper portion of the end plates  150  and may be configured to be gripped by a tool during, for example, assembly, installation, and/or shipping. As such, the tool may lower from above the battery assembly  140  and does not need to approach the end plates  150  from the side. This approach path may reduce an amount of assembly and/or installation space required for tooling. Further, package space of the battery assembly  140  may be reduced since the side plates  152  are close to the side faces  148  of the battery cell array  144 . An axis of the attachment apertures  158  may be oriented substantially parallel with a length of the battery cells  146  and located at or proximate to the four corners of the exo-support structure  142 . These attachment apertures  158  may be configured to receive fasteners  160  to assist in mechanically attaching the end plates  150  and side plates  152  at vertical edges of both. The axis of the attachment apertures  158  may also be substantially perpendicular with a plane defined by the side plates  152 . The attachment apertures  158  may also be outside a footprint defined by the battery cell array  144 . An axis of the attachment apertures  159  may be oriented substantially parallel with a height of the battery cells  146  and located at or proximate to the four corners of the exo-support structure  142 . 
         [0034]    The end plates  150  may correspond to the end faces  147  and be configured to receive a clamping compression load directed toward and transferred to the end faces  147  of the battery cell array  144  and other loads. These loads may twist and bend the battery cell array  144  during, for example, installation of the battery assembly  140 . 
         [0035]    A plurality of spaced apart cutouts  164  may at least be partially defined by diagonal ribs  166  of the side plates  152 . The cutouts  164  may have different shapes including the example shown in  FIGS. 4 and 6 . The side plates  152  may also define a lower horizontal edge  170  and an upper horizontal edge  172 . The side plates  152  may partially contact the side faces  148  of the battery cell array  144  or may not directly contact the side faces  148 . The diagonal ribs  166  may extend in approximately forty five degree angles from the lower horizontal edge  170  and upper horizontal edge  172  and may provide additional rigidity to the exo-support structure  142 . It is contemplated that the diagonal ribs  166  may also extend at angles other than forty five degrees. In one example, one or more of the diagonal ribs  166  may extend from a location in which the vertical edge of the respective end plate  150  is proximate to or meets the lower horizontal edge  170  of the respective side plate  152 . 
         [0036]    A midplate  180  may be centrally located within the battery cell array  144  and mechanically fastened to the side plates  152 . The midplate  180  may provide additional structural rigidity to the exo-support structure  142 . For example, it may be desirable to include a midplate  180  when a length of the battery cell array  144  is such that the structural integrity of the battery assembly  140  may be compromised when certain forces are applied. As mentioned above, assembly and/or installation processes may include an application of forces to the battery assembly  140 . The midplate  180  may be configured to receive and/or deflect a force generated by a bending load on the side plates  152  and/or the compression forces applied to the battery cell array  144 . The midplate  180  may define a vertical lift aperture  182  at an upper portion of the midplate  180  which may be configured to be gripped by a tool. The midplate  180  may also be configured to connect to a support structure above the battery cell array  144 , such as a cover for the battery assembly  140 . The midplate  180  may also define attachment apertures  184  which may be configured to receive fasteners to assist in mechanically fastening the midplate  180  and side plates  152 . To further assist in providing rigidity to the battery assembly  140 , the diagonal ribs  166  may extend from the lower horizontal edge  170  of the side plates  152  to a location on the upper horizontal edge  172  of the side plates  152  which is substantially equidistant from the end plates  150  and the midplate  180 . 
         [0037]    Now additionally referring to  FIGS. 8 through 10 , a plurality of spacers  190  may be located between adjacent battery cells  146 . The spacers  190  may be made of a material such as polypropylene and assist in providing electrical creepage and clearance distances between adjacent battery cells  146  and/or between the battery cells  146  and the end plates  150 . The spacers  190  may each include a tab  192  extending from an upper portion of the spacers  190 . The tabs  192  may be configured to assist in locating components to attach to or mate with the battery assembly  140 , such as a busbar module (not shown). The spacers  190  may also define one or more upper ridges  194  and one or more lower ridges  196  which may assist in orienting and retaining the battery cells  146  within the exo-support structure  142 . The upper ridges  194  may contact and assist in supporting the battery cells  146  and may be located at an upper edge of the battery cells  146 . The lower ridges  196  may contact and assist in supporting the battery cells  146  without interfering with a mating contact between the bottom face  145  defined by the battery cell array  144  or a lower edge of the battery cells  146  and a surface therebelow, such as a thermal plate (not shown). 
         [0038]      FIG. 11  shows an example of a dielectric rail  202 . The battery assembly  140  may include one or more dielectric rails  202  located between an upper portion  204  of the side plates  152  and the upper face  149  of the battery cell array  144 . The dielectric rails  202  may be composed of a resilient, insulating material such as a rubber, and have a thickness such that a force is generated between the bottom face  145  of the battery cell array  144  and a surface therebelow. One example of the surface is a thermal plate (not shown). The thickness of the dielectric rails  202  may be constant along the length of the dielectric rails  202  which may be in contact with the battery cell array  144 . Alternatively, the thickness of the dielectric rails  202  may increase at the mid-span of the dielectric rails  202  such that there is a greater interference contact to the battery cells  146  at the mid-span. Such an increase in thickness at the mid-span of the dielectric rail  202  may be tuned to compensate for a possible max bending deflection that may occur at the mid-span of the dielectric rail  202 . Any increase in thickness of the dielectric rails  202  may be gradual or may include discrete steps. The interference thickness may be achieved by a series of down standing bumps or nubs that tend to have a minimum interference contact to the battery cells  146  near the end plates  150 , and a maximum interference contact to the battery cells  146  at the mid-span of the dielectric rails  202 . The dielectric rails  202  may also assist in electrically isolating the battery cells  146  from the side plates  152 . The upper portion  204  of the side plates  152  may cover and extend along a portion of the upper face  149  of the battery cell array  144  such that the upper portion  204  and a surface below the battery cell array  144 , such as a thermal plate, may exert vertical forces thereto. 
         [0039]    While  FIG. 9  shows one example of the battery cell  146 , the exo-support structure  142  may also be used for other types of battery cells having different performance requirements and dimensional characteristics. For example, with PHEVs and BEVs, the desired geometry and package space provided for the respective battery cell array may dictate having multiple configurations of battery cells within multiple battery cell arrays. In these examples, the battery cells may be fourteen PHEV battery cells in the battery cell array. For FHEVs, the battery cells may be thirty FHEV battery cells in the battery cell array. It may also be beneficial to have different types of battery cell arrays within a vehicle. For example,  FIG. 12  shows a portion of a traction battery assembly including a group of battery assemblies  250  having four battery cell arrays  252 , four battery cell arrays  254 , and two battery cell arrays  256 . As shown, the end plates  258  and side plates  259  of each of the exo-support structures retaining the respective battery cell arrays may be modified to accommodate the particular battery cell array. The battery cell arrays  252  and  254  may not need additional structural support so a midplate is not included. However, the battery cell arrays  256  are slightly longer than the battery cell arrays  252  and  254  and as such, may include midplates  260 . 
         [0040]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.