Patent Publication Number: US-11658369-B2

Title: Overcharge protection systems having dual spiral disk features for prismatic lithium ion battery cells

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 16/312,879, filed on Dec. 21, 2018, which is a submission under 35 U.S.C. § 371 for U.S. National Stage Patent Application of International Application No. PCT/US2017/044957 entitled “OVERCHARGE PROTECTION SYSTEMS HAVING DUAL SPIRAL DISK FEATURES FOR PRISMATIC LITHIUM-ION BATTERY CELLS,” filed on Aug. 1, 2017, which claims priority to and the benefit of U.S. Provisional Application Ser. No. 62/369,718, entitled “OVERCHARGE PROTECTION DEVICES FOR PRISMATIC CELLS,” filed Aug. 1, 2016, and which claims priority from and the benefit of U.S. Provisional Application Ser. No. 62/369,720, entitled “OVERCHARGE PROTECTION DEVICES FOR CELLS WITH NEUTRAL CANS,” filed Aug. 1, 2016, all which are hereby incorporated by reference in their entireties for all purposes. 
    
    
     BACKGROUND 
     The present disclosure relates generally to the field of batteries and battery modules. More specifically, the present disclosure relates to overcharge protection systems for prismatic lithium-ion battery cells. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Battery systems can provide viable alternatives or supplements to systems that operate based on fossil fuel combustion. Certain automotive vehicles (e.g., full electric vehicles, hybrid electric vehicles, micro-hybrid electric vehicles, or other types of “xEVs”) incorporate battery systems to provide all or a portion of their vehicular motive force. Homes, offices, buildings, and similar locations, for instance, often include backup power sources, such as gas-powered electrical generators, that may be used in the event of a central power failure (e.g., due to inclement weather). Similarly, certain settings, such as temporary offices, temporary housing, or other settings located remotely from a power grid, may not necessarily be tied to an electrical grid and may instead rely on energy supplied by a relatively portable source, such as an engine-driven electrical generator. Stationary battery systems can be an attractive alternative for such settings, not only because they can be discharged with relatively low emissions compared to combustion processes, but also because other sources of energy, such as wind and solar, may be coupled to such stationary battery systems to enable energy capture for later use 
     A lithium ion battery module generally includes a number of lithium ion battery cells that are electrically connected together in a suitable manner to store and provide charge, for example, within a stationary or automotive battery system. When a battery module is receiving power, the battery cells of the module are charged for later use. However, during this process, a battery cell can become overcharged, leading to unstable conditions in and around the battery cell, potentially including thermal runaway, rupture, ignition, and/or explosion of the battery cell. As such, it is desirable to reduce the risk of overcharging lithium ion battery cells in order to reduce the risk of damage to the battery module or the stationary/automotive power system resulting from these unstable battery cell conditions. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     In an embodiment, a prismatic lithium ion battery cell includes a packaging having a cover sealed to a can. A power assembly is disposed within the packaging, and a first terminal pad and a second terminal pad are respectively disposed above the cover and electrically coupled to the power assembly. The cover includes: a first spiral disk feature disposed below the first terminal pad; a second spiral disk feature disposed below the second terminal pad; a first reversal disk disposed below the first spiral disk feature; and a second reversal disk disposed below the second spiral disk feature. The first and second reversal disks are configured to deflect upwards to displace the first and second spiral disk features to contact the first and second terminal pads, respectively, in response to a pressure within the packaging being greater than a predefined pressure threshold and form an external short-circuit between the first and second terminal pads via the first and second spiral disk features. Subsequently, a portion of the power assembly fails in response to the external short-circuit and interrupts current flow between the first and second terminal pads. 
     In another embodiment, a prismatic lithium-ion battery cell, includes a packaging having a cover sealed to a can. A power assembly is disposed within the packaging and includes: a coil stack with at least one coil; a first current collector coupled to a first electrode of the at least one coil; a second current collector coupled to a second electrode of the at least one coil; a first terminal post coupled to the first current collector that extends through the cover; and a second terminal post coupled to a second current collector that extends through the cover, wherein the second terminal post is electrically connected to the cover. The cell also includes a first terminal pad coupled to the first terminal post and a second terminal pad coupled to the second terminal post. The cover includes: a first spiral disk feature disposed below the first terminal pad; a second spiral disk feature disposed below the second terminal pad; a first reversal disk disposed below the first spiral disk feature; and a second reversal disk disposed below the second spiral disk feature. The first and second reversal disks are configured to deflect upwards to displace the first and second spiral disk features to contact the first and second terminal pads, respectively, in response to a pressure within the packaging being greater than a predefined pressure threshold and form an external short-circuit between the first and second terminal pads via the first and second spiral disk features. Subsequently, a portion of the power assembly fails in response to the external short-circuit and interrupts current flow between the first and second terminal pads. 
     In another embodiment, a prismatic lithium-ion battery cell includes a packaging that having a cover sealed to a can. A power assembly is disposed within the packaging and includes a positive side and a negative side. A first terminal pad is disposed above the cover of the packaging and electrically coupled to the negative side of the power assembly, and a second terminal pad disposed above the cover of the packaging and electrically coupled to the positive side of the power assembly. The cover includes: a first spiral disk feature disposed below the first terminal pad; a second spiral disk feature disposed below the second terminal pad; a first reversal disk sealed to the cover below the first spiral disk feature; and a second reversal disk sealed to the cover below the second spiral disk feature. In response to a pressure within the packaging being greater than a first predefined pressure threshold, the first and second reversal disks are configured to deflect upwards to displace the first and second spiral disk features to contact the first and second terminal pads, respectively, and form an external short-circuit between the positive and negative sides of the power assembly via the first and second spiral disk features. The cover also includes a vent disk sealed to the cover and configured to activate to release effluent from an interior of the packaging at a second predefined pressure threshold, wherein the first predefined pressure threshold is substantially less than the second predefined pressure threshold. 
    
    
     
       DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG.  1    is a schematic view of a stationary energy storage system that includes a stationary drawer housing and a battery module, in accordance with embodiments of the present approach; 
         FIG.  2    is an exploded perspective view of the battery module of the stationary storage system illustrated in  FIG.  1   , in accordance with embodiments of the present approach; 
         FIG.  3    is a perspective view of the stationary energy storage drawer of the stationary storage system illustrated in  FIG.  1   , in accordance with embodiments of the present approach; 
         FIG.  4    is a perspective view of a prismatic lithium ion battery cell that includes an overcharge protection system, in accordance with embodiments of the present technique; 
         FIG.  5    is an exploded view of the prismatic lithium ion battery cell of  FIG.  4   , in accordance with embodiments of the present technique; 
         FIGS.  6 A and  6 B  are perspective and cross-sectional views, respectively, of an example cover for the prismatic lithium ion battery cell illustrated in  FIG.  5   , in accordance with embodiments of the present technique; 
         FIG.  7    is a perspective view of another example cover for the prismatic lithium ion battery cell illustrated in  FIG.  5   , wherein the cover includes dual integrated spiral disk features, in accordance with embodiments of the present technique; 
         FIG.  8 A  is a perspective view of an example current collector for the prismatic lithium ion battery cell illustrated in  FIG.  5    that lacks a fuse, in accordance with embodiments of the present technique; 
         FIG.  8 B  is a perspective view of another example current collector for the prismatic lithium ion battery cell illustrated in  FIG.  5    that includes a fuse, in accordance with embodiments of the present technique; 
         FIG.  9    is a cross-sectional view of an assembled current diverge device (CDD) of an overcharge protection system of a prismatic lithium ion battery cell, in accordance with embodiments of the present technique; 
         FIG.  10    is a flow diagram of a process by which an overcharge protection system of a prismatic lithium ion battery cell having a CDD with a single integrated spiral disk feature interrupts current flow between the terminal pads of the cell in response to an overcharge event, in accordance with embodiments of the present technique; 
         FIG.  11    is a flow diagram of a process by which an overcharge protection system of a prismatic lithium ion battery cell having a CDD with dual integrated spiral disk features interrupts current flow between the terminal pads of the cell in response to an overcharge event, in accordance with embodiments of the present technique; 
         FIG.  12 A  is a cross-sectional view of another embodiment of an assembled CDD of an overcharge protection system of a prismatic lithium ion battery cell before activation, in accordance with embodiments of the present technique; 
         FIG.  12 B  is a cross-sectional view of the CDD of  FIG.  12 A  after activation, in accordance with embodiments of the present technique; 
         FIG.  13    is a flow diagram of a process by which the overcharge protection system illustrated in  FIGS.  12 A and  12 B  interrupts current flow between the terminal pads of the cell in response to an overcharge event, in accordance with embodiments of the present technique; 
         FIG.  14 A  is a cross-sectional view of another embodiment of an assembled CDD of an overcharge protection system of a prismatic lithium ion battery cell before activation, in accordance with embodiments of the present technique; 
         FIG.  14 B  is a cross-sectional view of the CDD of  FIG.  14 A  after activation, in accordance with embodiments of the present technique; and 
         FIG.  15    is a cross-sectional view of a spiral disk feature having a relatively thicker central portion and relatively thinner leg portions, in accordance with embodiments of the present technique 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     As set forth above, when a lithium ion battery cell becomes overcharged, the resulting unstable conditions in and around the battery cell (e.g., thermal runaway, cell rupture, cell ignition, and/or cell explosion) may result in substantial damage to surrounding systems. When the battery cell is part of a larger battery module, or an even larger stationary energy storage system, the resulting damage may include damage to the battery cell, the battery module, as well as other portions of the stationary energy storage system. Additionally, larger battery cells (e.g., 100 amp hour (Ah) or greater) offer increased capacity to stationary energy storage systems. However, these larger battery cells can potentially release a greater amount of energy as a result of an overcharge event, increasing the risk of substantial damage to the battery module and/or the stationary energy storage system that includes the cell. With this in mind, present embodiments are directed toward overcharge protection systems for prismatic lithium-ion battery cells that are designed to suitably interrupt current within the battery cell to interrupt and limit or mitigate damage from an overcharge event. While the present technique is primarily discussed in relation to stationary energy storage systems, it should be appreciated that the disclosed approach is also applicable to automotive (e.g., vehicular) energy storage systems, as well as other suitable types of energy storage systems 
     More specifically, in response to an overcharge event, the disclosed embodiments of the overcharge protection system are designed and arranged to first externally short-circuit the battery cell. The resulting current from the short-circuit is sufficiently high to damage (e.g., melt) one or more internal components of the battery cell. This damage electrically disconnects at least one of the terminals (e.g., the positive terminal, the negative terminal, or both) from the corresponding electrode (e.g., cathode or anode) in the interior of the battery cell, interrupting internal current flow between the terminals of the battery cell. Accordingly, by interrupting this current flow in response to an overcharge event, embodiments of the disclosed overcharge protection system prevent a battery cell from proceeding to thermal runaway, limiting damage within a battery module and/or an energy storage system (e.g., a stationary energy storage system or vehicular energy storage system) that includes the battery cell. 
     As discussed below, the presently disclosed overcharge protection systems include at least one current diverge device (CDD) that externally short-circuits a prismatic lithium ion battery cell in response to an increase in pressure within the cell&#39;s interior. When a battery cell is overcharged, a portion of the electrolytes within the battery cell may thermally expand, volatize, and/or decompose, generally increasing pressure in the interior of the battery cell. Other potential sources of gassing during overcharging include decomposition of the active materials and reactions between the active materials and the electrolyte and/or electrolyte additives. With this in mind, certain lithium ion battery cells include a vent feature that eventually opens to relieve this pressure, once the pressure surpasses a particular threshold, typically around approximately 6 bar or more. In contrast, in certain embodiments, the presently disclosed overcharge protection system includes a low-pressure current diverge device designed and arranged to interrupt current in battery cells in response to substantially lower pressures (e.g., around approximately 3-4 bar) within the interior of the battery cell. As such, certain embodiments of the present approach are able to respond more quickly (e.g., at a relatively low pressure, at a relatively lower state of charge (SOC) of the battery cell) to interrupt current in the battery cell in response to an overcharge condition before other protection features (e.g., a vent feature), reducing the aforementioned risks of damage to the battery module and/or the stationary energy storage system. Additionally, despite being able to interrupt current in a battery cell in response to a low activation pressure, the disclosed CDDs are designed and arranged to carry a sufficient amount of current during short-circuiting to ensure that the flow of current is permanently interrupted between the terminals of the battery cell in response to an overcharging event, as discussed below. 
     The presently disclosed CDD designs include three embodiments, which are discussed in detail below. In all of these CDD designs, a cover of the battery cell includes at least one reversal disk that deforms when a pressure within a packaging of battery cell reaches a predefined threshold. The deformation of the at least one reversal disk displaces at least one conductive element (e.g., a spiral disk feature, a conductive member) to contact at least one terminal pad of the battery cell, forming a short-circuit between the terminals that eventually leads to an interruption in current flow within the cell. More specifically, the disclosed embodiments include a battery cell having a single reversal disk and an unbiased or non-conductive packaging (as generally illustrated and discussed with regard to  FIGS.  4 ,  5 ,  12 ,  13 , and  14   ), in which a single conductive element contacts both terminal pads to form the short-circuit. The disclosed embodiments also include a battery cell having a single reversal disk and a biased packaging (generally illustrated and discussed with regard to  FIGS.  9  and  10   ), in which a single conductive element contacts a single terminal pad to form the short-circuit via the cover of the battery cell. Additionally, the disclosed embodiments include a battery cell having dual reversal disks and an unbiased packaging (generally illustrated and discussed with regard to  FIGS.  9  and  11   ), in which two conductive elements contact different respective terminal pads to form the short-circuit via the cover of the battery cell. Those skilled in the art will appreciate that various aspects of these disclosed embodiments can be combined or interchanged to provide CDD-protected battery cells having suitable packaging (e.g., materials, bias) for different battery module designs, in accordance with the present disclosure. 
     With the foregoing in mind,  FIG.  1    is a schematic view of an embodiment of a battery system  10  in which a battery module  12  (e.g., lithium ion battery module  12 ) is configured to be used in a stationary energy storage system  16 . More specifically, the battery module  12  may be used as all or a part of a stationary energy storage drawer  20 . The stationary energy storage drawer  20  may be removably coupled to a stationary drawer housing  22  of the stationary energy storage system  16 . Each stationary energy storage drawer  20  may include one or more battery modules  12 , and the stationary energy storage system  16  may include one or more of the stationary energy storage drawers  20 . 
     By way of example, the battery module  12  may have a plurality of lithium ion battery cells, such as between 10 and 20. The general configuration of the battery module  12  will be described in further detail below. One or more of the battery modules  12  may be incorporated into the stationary energy storage drawer  20 , several of which may connect with the larger stationary energy storage system  16  to provide a desired energy storage, energy conditioning, and/or energy output capability for a facility  24 . 
     As shown, the facility  24  may include a building or similar setting normally connected to an electrical power grid  26  or other main source of energy to provide power for everyday power consumption. However, in other embodiments the facility  24  may be a facility that is not connected to the electrical power grid  26  and therefore completely relies on other means to provide electrical energy (e.g., the stationary storage system  16 ). Further, the facility  24  may be a home or other setting. The stationary energy storage system  16  may be incorporated into or otherwise connected to an electrical grid of the facility  24  to provide power as needed. As non-limiting examples, the stationary energy storage system  16  may provide power to the facility  24  as a backup to the electrical power grid  26  (e.g., due to power outage), for power conditioning, for supplementing power or offsetting power consumption from the electrical power grid  26 , and so forth. 
       FIG.  2    is an exploded perspective view of an embodiment of the battery module  12  of stationary storage system  16  illustrated in  FIG.  1   . As illustrated, certain embodiments of the battery module  12  include a plurality of prismatic lithium ion battery cells  30  (also referred to herein as “cells” for simplicity), which may be arranged in various configurations (e.g., orientations, orders of stacking). However, the cells  30  will generally be provided in an amount and configuration so as to have a sufficient energy density, voltage, current, capacity, and so forth, for a particular stationary application. As discussed in greater detail below, in different embodiments, the cells  30  may have a polymeric casing, or a metallic casing, or a combination, enclosing the electrochemically active components of the battery cells  30 . 
     The battery module  12  of  FIG.  2    includes a stack or lineup of the battery cells  30 , with a bus bar carrier  32  being positioned over the terminals  34 ,  36  so as to enable electrical interconnection of the terminals  34 ,  36  using the bus bar assembly  38 . The bus bar assembly  38  generally electrically connects the battery cells  30  as an electrical assembly. In certain embodiments, the bus bar assembly  38  may be integrated onto the bus bar carrier  32 , in some instances along with other suitable features (e.g., voltage sense connectors). 
     For the illustrated embodiment, a traceboard  40  is positioned over the bus bar assembly  38  such that the bus bar assembly  38  is positioned between the traceboard  40  and the bus bar carrier  32 . A battery management system (BMS)  42  is integrated onto the traceboard  40  to connect the BMS  42  to any sense features (e.g., temperature and/or voltage sense features) and to enable control of the cells  30  and the overall operation of the battery module  12 . In some embodiments, the BMS  42  may also monitor and control operations of the stationary energy storage drawer  20 . 
     The housing  44  of the illustrated embodiment completely encloses the cells  30  as well as some or all of the features described above with respect to  FIG.  2   . As illustrated, the module housing  44  takes the shape of its constituent battery cells  30 ; in this instance a prismatic form. However, the housing  44  may be formed to have any appropriate shape for a particular application. A cover  46  is provided above the BMS  42 , traceboard  40 , and bus bar assembly  38  and attaches to an upper portion of the battery module housing  44 . The cover  46  is configured to substantially enclose the BMS  42 , traceboard  40 , and bus bar assembly  38  to prevent inadvertent contact with electrical and control components. Accordingly, the cover  46  may be formed from an electrically insulative material, which may be the same or different than the material forming the housing  44 . In certain embodiments, the outer perimeter of the traceboard  40  may correspond to an inner perimeter of the cover  46 . 
     Integrating battery modules  12  into the stationary energy storage drawer  20  may have a number of advantages and enable various configurations of the stationary energy storage drawer  20 . For example,  FIG.  3    depicts an embodiment of the stationary energy storage drawer  20  having two of the battery modules  12  (e.g., first and second battery modules  12 ) positioned side-by-side within a stationary drawer housing  52 . Specifically, in  FIG.  3   , each of the battery modules  12  is secured within the stationary energy storage drawer  20  in an orientation in which respective terminals  34 ,  36  of the battery cells  30  are axially oriented crosswise relative to the base  50  of the stationary drawer housing  22 . The stationary energy storage drawers  20  of the present disclosure may include various types of battery modules  12  (e.g., having the same or different capacities, voltages, sizes, shapes) to enable a flexible solution for various stationary energy storage applications. 
       FIG.  4    is a perspective view of an embodiment of a prismatic lithium ion battery cell  60 , in accordance with embodiments of the present approach. As used herein, “prismatic” refers to the generally box-like (e.g., polygonal) shape of the substantially rigid packaging  62  of the battery cell  60 . As such, it should be appreciated that the disclosed prismatic cells  60  are distinct from pouch battery cells, which have a substantially flexible laminate packaging. Further, it should be appreciated that the disclosed prismatic cells  60  are also distinct from cylindrical battery cells, which have a substantially rigid cylindrical packaging. Those skilled in the art will appreciate that these different cell shapes and packaging materials present different limitations and modes of failure, and issues or solutions that are effective for one type of battery cell may not be applicable to others. 
     The packaging  62  of the illustrated prismatic lithium ion battery cell  60  may be generally described as having a first and a second substantially flat side portion,  64  and  66 , disposed opposite one another. Additionally, the packaging  62  includes a first and a second end portion  68  and  70 , disposed opposite one another. In certain embodiments, the end portions  68  and  70  may be substantially flat, rounded, or substantially flat will slight rounded corners  72 , as illustrated. 
       FIG.  5    is a perspective exploded view of the embodiment of the prismatic lithium ion battery cell  60  illustrated in  FIG.  4   . The packaging  62  of the illustrated battery cell  60  includes a can  80  that is coupled to (e.g., hermetically sealed to, welded to) a cover  84 . In certain embodiments, the can  80  and cover  84  may both be made of metal (e.g., aluminum), while in other embodiments, one or both of the can  80  and cover  84  may be made of an electrically insulating material (e.g., polymer, polypropylene plastic). Once sealed together (e.g., via welding), the can  80  and cover  84  form a substantially rigid packaging that resists (e.g., blocks, prevents) expansion as pressure within the cell  60  increases (e.g., due to thermal expansion, due to an overcharging event) and as pressure is externally applied to the cell  60 . 
     Within the can  80 , the illustrated prismatic lithium ion battery cell  60  includes a stack  85  having two electrode (e.g., cathode/anode) coils  86  and  88 . Each of the coils  86  and  88  include a cathode layer and an anode layer, along with suitable separating layers, that are wound together to form the charge storage elements of the cell  60 . In other embodiments, a cell  60  may include only one coil, or include a stack  85  having three, four, five, or more coils, in accordance with the present disclosure. Current collectors  92 A and  92 B, which are discussed in greater detail below with respect to  FIGS.  8 A and  8 B , are welded to the appropriate electrode (e.g., cathode or anode) at the ends of the coils  86  and  88  of the coil stack  85 . Additionally, terminal posts  94 A and  94 B are welded to the current collectors  92 A and  92 B, respectively, to yield an assembled power assembly  95  of the cell  60 . The assembled power assembly  95  may be generally described herein as having a first or negative side (e.g., corresponding to the current collector  92 A) and a second or positive side (e.g., corresponding to the current collector  92 B) that are respectively coupled to the terminal pads  112 A and  112 B. Additionally, an insulation pouch  96  wraps a sufficient amount of the power assembly  95  to electrically isolate the power assembly  95  from the can  80  of the battery cell  60 . 
     The cover  84  is disposed above the power assembly  95 , having the terminal posts  94 A and  94 B extending through (and hermetically sealed within) corresponding openings  98 A and  98 B defined in the cover  84 . The illustrated cover  84  includes an opening  100  about which a vent disk  101  is sealed (e.g., welded) to a bottom side  103  of the cover  84 , wherein the top side  105  faces away from the power assembly  95 . Additionally, the illustrated cover  84  includes an opening  102 , and a reversal disk  104  is sealed (e.g., welded) about the opening  102  on the bottom side  103  of the cover  84 , while a conductive element (e.g., spiral disk feature  106 , or another suitable conductive member) is welded to a top side  105  of the cover  84 . The cover  84  further includes a fill hole  108  for adding electrolyte to the cell  60  after assembly. 
     In certain embodiments, the reversal disk  104  may be made of a suitable metallic or polymeric material and have suitable dimensions (e.g., thickness, diameter) to deflect (e.g., invert) when the pressure within the packaging  62  of the cell  60  reaches or exceeds a particular threshold value. In certain embodiments, the vent disk  101  is sized, designed, and configured to activate at a threshold pressure greater than the threshold pressure of the reversal disk  104  at least 50% greater (e.g., between 50% and 80% greater) to ensure that the reversal disk  104  externally short-circuits the cell  60  before effluent is released from the interior of the cell  60  by the vent disk  101 . 
     Further, by using the disclosed conductive element (e.g., spiral disk feature  106 , as discussed for embodiments below with respect to  FIGS.  5 ,  6 ,  7 ,  9  and  14   , or another suitable conductive member  180 , as discussed for embodiments below with respect to  FIGS.  12  and  13   ) the presently disclosed reversal disk  104  can be substantially thinner and activate in response to substantially lower pressures (e.g., less than 6 bar, about 3-4 bar) than the activation pressures of designs in which the external short-circuit must traverse a thicker reversal disk  104  (e.g., at activation pressures greater than about 6 bar). That is, in the present designs, the reversal disk  104  is not required to be part of the short-circuit path or required to carry a substantial amount of current. Rather, in the present designs, the reversal disk  104  displaces the conductive element (e.g., a spiral disk feature  106  or a conductive member  180 ) with a substantially greater current capacity to form the external short-circuit with one or both of the terminal pads. For example, for the embodiment illustrated in  FIG.  5   , the conductive element (i.e., spiral disk feature  106 ) contacts both terminal pads  112 A and  112 B once the reversal disk  104  is deployed to form a short-circuit pathway. It may be appreciated that since, in certain embodiments, the reversal disk  104  may be in electrical contact with the conductive element (e.g., spiral disk feature  106  or conductive member  180 ), a small portion of the short-circuit current may traverse or electrify the reversal disk  104 , the cover  84 , and the packaging  62  of the battery cell  60  for such embodiments. However, the conductive element may be substantially (e.g., 2×-10×, 5×-10×) thicker, or have portions that are substantially thicker, than the reversal disk  104 . As such, it is presently recognized that the conductive element (e.g., spiral disk feature  106  or conductive member  180 ) demonstrates substantially lower electrical resistance than the reversal disk  104 . Accordingly, for such embodiments, a substantial portion of the short-circuit current traverses the lower resistance spiral disk feature  106  or conductive member  180  instead of the reversal disk  104 . In other embodiments discussed below, the reversal disk  104  may be electrically insulated from the conductive element (e.g., conductive member  180 ) via an electrically insulating layer (e.g., via insulating layer  182  illustrated in  FIGS.  12 A and  12 B ) such that the short-circuit current is substantially blocked or prevented from reaching the reversal disk  104 , the cover  84 , or any other portion of the packaging  62  of the battery cell  60 . It may be appreciated that this generally reduces the risk of electrical damage to components that may be in contact with the packaging  62  of the battery cell  60  within the battery module  12  during the short-circuit event. As such, the disclosed CDD design enables improved current carrying capability, greater sensitivity (e.g., lower pressure threshold), and more short-circuit pathway options than other CDD designs. 
     In the illustrated embodiment, a polymeric terminal insulator  110  is disposed over the cover and provides selective electrical isolation between certain metallic features of the cell  60 . For example, the terminal insulator  110  generally defines openings to allow certain components (e.g., terminal posts  94 A and  94 B, spiral disk feature  106 ) to pass through (e.g., extend through, deflect through) the terminal insulator  110 , as desired. Additionally, the terminal insulator  110  electrically isolates portions of the cover  84  from one or both terminal pads  112 A and  112 B in certain embodiments. 
     The terminal pads  112 A and  112 B of the illustrated cell  60  are coupled to the terminal posts  94 A and  94 B, respectively, and are disposed above the terminal insulator  110  and the cover  84  of the battery cell  60 . The illustrated cell  60  also includes electrically insulating terminal covers  114 A and  114 B respectively disposed over portions of the terminal pads  112 A and  112 B, which help to avoid accidental contact with or between the terminal pads  112 A and  112 B. Additionally, the illustrated cell  60  includes a fill hole seal disk  116  that seals the fill hole  108  of the cover  84  after the interior of the cell  60  is filled with electrolyte, as previously mentioned. 
       FIG.  6 A  is a perspective of another embodiment of a cover  84  of a prismatic lithium ion battery cell  60 , in accordance with the present approach.  FIG.  6 B  is a cross-sectional view of the embodiment of the cover  84  of  FIG.  6 A , taken along line  6 B. The illustrated cover  84  includes and/or defines certain features described above, including openings  98 A and  98 B that correspond to terminal posts  94 A and  94 B, respectively, opening  100  corresponding to the vent disk  101 , and the fill hole  108 . However, instead of the opening  102  illustrated in the cover  84  of  FIG.  5   , the cover  84  of  FIGS.  6 A and  6 B  includes an integrated spiral disk feature  120  formed in relief. For example, a metallic cover  84  as illustrated may be fabricated using a stamping and/or pressing operation that simultaneously forms the features of the illustrated cover  84 , including the integrated spiral disk feature  120  formed in relief. As such, the illustrated integrated spiral disk feature design reduces manufacturing time and costs, and provides a more reliable (e.g., thicker, more controlled, more regular) connection between the spiral member  120  and the cover  84  for the external short-circuit to traverse compared to other designs. 
       FIG.  7    is a perspective view of another embodiment of the cover  84  for the prismatic lithium ion battery cell  60  illustrated in  FIG.  5   . Again, the illustrated cover  84  includes and/or defines features described above, including openings  98 A and  98 B that correspond to terminal posts  94 A and  94 B, respectively, opening  100  corresponding to the vent disk  101 , and the fill hole  108 . However, the cover  84  of  FIGS.  6 A and  6 B  includes dual integrated spiral disk features  120 A and  120 B formed in relief. For embodiments of the CDD that include the illustrated cover  84  with the dual integrated spiral disk features  120 A and  120 B, a respective reversal disk  104  is sealed (e.g., welded) to the bottom side  103  of the cover  84  below each disk. The operation of the cover  84  with dual integrated spiral disk features  120 A and  120 B is discussed below with respect to  FIG.  11   . 
       FIGS.  8 A and  8 B  are perspective views of different embodiments of the current collector  92 A for the prismatic lithium ion battery cell  60  illustrated in  FIG.  5   . Both illustrated current collectors  92 A include extensions  130  that are welded to the corresponding electrodes of the coils (e.g., coils  86 ,  88 ), and also include the platform  132  onto which the terminal post  94 A is welded, as mentioned above. However, the embodiment of the current collector  92 A illustrated in  FIG.  8 B  includes one or more fuses  134 , while the embodiment of the current collector  92 A illustrated in  FIG.  8 A  lacks any such fuse feature. 
     Therefore, it may be noted that, in certain embodiments, at least one of the current collectors (e.g., current collector  92 A, current collector  92 B, or both) that electrically couples an electrode (e.g., cathode or anode) to its corresponding terminal pad may include such a fuse  134  that preferentially melts and fails before other portions of the power assembly  95  of the cell  60  in response to an external short-circuit. In contrast, for embodiments that include current collector  92 A of  FIG.  8 A  that lacks such fuse features, when the cell  60  is externally short-circuited, an unexpected (e.g., unplanned, random) portion of the power assembly  95  melts and fails, interrupting continuity between an electrode (e.g., cathode or anode) and the corresponding terminal of a battery cell. By disconnecting at least one electrode from the corresponding terminal in response to an induced external short-circuit, present embodiments enable an automatic cut-off of current within the cell  60  in response to an overcharge event, which protects the cell  60  from thermal runaway and limits damage within a battery module  12  and/or a stationary energy storage system  16  that includes the cell  60 . 
       FIG.  9    is a cross-sectional view of an embodiment of an assembled current diverge device (CDD)  140  of an overcharge protection system for the prismatic lithium ion battery cell  60 . More specifically, for the embodiment of the CDD  140  illustrated in  FIG.  9    and discussed below, the opposite terminal (not illustrated) is electrically coupled to the cover  84  of the packaging  62  of the battery cell  60 . In certain embodiments, either the positive side or the negative side of the power assembly  95  is electrically coupled to the cover  84 , while the opposite (e.g., positive or negative) side of the power assembly  95  is electrically coupled to the illustrated terminal  112 A disposed above the reversal disk  104  and spiral disk feature  106 . It should be appreciated that the design illustrated in  FIG.  9    is also representative of one terminal region for an embodiment of a CDD  140  that includes a reversal disk  104  and a spiral disk  106  disposed below both terminal pads  112 , as discussed below with respect to  FIG.  11   . 
     In addition to the components described above, the illustrated embodiment of  FIG.  9    includes a gasket  142  positioned between the terminal post  92 A and the cover  84 . For embodiments in which the cover  84  is metallic, the gasket  142  electrically isolates the terminal post  94 A from the cover  84 .  FIG.  10    is a flow diagram of a process  150  by which an embodiment of the overcharge protection system of the prismatic lithium ion battery cell  60  having a CDD with a single integrated spiral disk feature  120  and a packaging  62  with positive polarity interrupts current flow between the terminal pads  112 A and  112 B of the cell  60  in response to an overcharge event. As such,  FIG.  10    is discussed below in the context of the CDD  140  illustrated in  FIG.  9   . For this example, the CDD  140  of the overcharge protection system includes a single reversal disk  104  and a single integrated spiral disk feature  120  disposed under a portion of the terminal pad  112 A that is not electrically coupled to the cover  84  or packaging  62  of the cell  60 . As mentioned, the other terminal pad  112 B (not shown) is electrically coupled to the cover  84  and packaging  62 , resulting in a biased (e.g., positively biased) cover  84  and packaging  62 . 
     For this example embodiment, the illustrated process  150  begins with the pressure in the cell  60  increasing in response to aforementioned electrochemical processes (e.g., thermal expansion, electrolyte decomposition) that occur within the interior of the cell  60  as a result of an overcharge event (block  152 ). When the pressure in the cell  60  reaches a pressure threshold, based on the dimensions of the reversal disk  104 , the reversal disk  104  deflects upwards (e.g., outwards from the interior of the cell  60 , as indicated by the arrow  156  in  FIG.  9   ) (block  154 ). This deflection provides sufficient force to displace (e.g., deflect, bend, twist, and/or otherwise deform) the spiral disk feature  120  upwards (e.g., in the direction of arrow  156 ) towards a the terminal pad  112 A disposed above the integrated spiral disk feature  120  (block  158 ). 
     For the illustrated example, since the cover  84  is physically and electrically coupled with the spiral disk feature  120 , the physical contact between the spiral disk  120  and the terminal pad  112 B forms a short circuit between the positive and negative sides of the power assembly  95  of the cell  60 . In other words, since the cover  84  of the packaging  62  is biased (e.g., positively biased), the physical contact between the integrated spiral disk feature  120  and the terminal pad  112 A set forth in block  158  forms a short-circuit, as indicated by the arrows  159  (see  FIG.  9   ) between positive and negative sides of the power assembly  95 , wherein the short-circuit current passes through the cover  84  of the cell (block  160 ). The power assembly  95  of the cell  60  resistively heats in response to the external short-circuit (block  162 ) until a portion (e.g., the fuse  134  illustrated in  FIG.  8 B , or a random/unplanned portion) of the power assembly  95  fails in response to the resistive heating, interrupting the internal electrical pathway and electrical current between the terminal pads  112 A and  112 B. The cell  60  subsequently cools in response to the interruption in the internal electrical pathway between the terminal pads  112 A and  112 B as the overcharge event is mitigated/interrupted. 
       FIG.  11    illustrates a process  170  whereby an embodiment of the disclosed overcharge protection system responds to an overcharge event within a battery cell having a neutral, unbiased packaging  62  (e.g., the cover  84  is electrically insulated from the terminal pads  112 A and  112 B and terminal posts  94 A and  94 B). For such an embodiment, the CDD of the overcharge protection system includes two reversal disks and two corresponding integrated spiral disk features disposed under a portion of the terminal pads  112 A and  112 B, respectively. As such, the process  170  corresponds to an embodiment of the CDD having the cover  84  of  FIG.  7   , which includes the dual integrated spiral disk features  120 A and  120 B. 
     Like the process  150  illustrated in  FIG.  10   , the process  170  illustrated in  FIG.  11    begins with the pressure in the cell  60  increasing in response to the overcharge event (block  152 ). When the pressure in the cell  60  reaches a pressure threshold, based on the dimensions of the reversal disks  104 , the reversal disks  104  both deflect upwards (e.g., as illustrated by the arrow  156  in  FIG.  9   ) (block  171 ). This deflection provides sufficient force to displace (e.g., deflect, bend, twist, deform) the integrated spiral disk features  120 A and  120 B upwards (e.g., as illustrated by the arrow  156  in  FIG.  9   ) towards the terminal pads  112 A and  112 B, respectively (block  172 ). In this example, the physical contact between the integrated spiral disk feature  120 A and the terminal pad  112 A, in addition to the physical and electrical contact between the integrated spiral disk feature  120 B and the terminal pad  112 B, forms a short-circuit between the terminal pads  112 A and  112 B, wherein the short-circuit current again passes through the cover  84  of the cell (block  174 ). Similar to the process  150  of  FIG.  10   , as illustrated in  FIG.  11   , the power assembly  95  of the cell  60  resistively heats in response to the external short-circuit (block  162 ) until a portion of the power assembly  95  fails (block  164 ), and the cell  60  subsequently cools in response to the interruption in the internal electrical pathway and current between the terminal pads  112 A and  112 B as the overcharge event is mitigated/interrupted. 
       FIG.  12 A  is a cross-sectional schematic view of another embodiment of an assembled CDD  140  of an overcharge protection system of a prismatic lithium ion battery cell  60  before activation.  FIG.  12 B  is a cross-sectional view of the CDD of  FIG.  12 A  after activation. The illustrated embodiment includes certain similar components to the ones discussed above, including terminal pads  112 A and  112 B, terminal insulator  110 , cover  84 , and reversal disk  104 . The illustrated reversal disk  104  is disposed in a central region between and below the terminal pads  112 A and  112 B. The illustrated embodiment further includes a conductive element (e.g., conductive member  180 ), which is illustrated as a flat metallic disk that is disposed above the reversal disk  104 . In other embodiments, the conductive member  180  may be implemented as all or a portion of a spiral disk feature that is coupled or integrated into the cover  62  of the battery cell  60 . The illustrated design also includes an electrically insulating layer  182  disposed between the conductive member  180  and the reversal disk  104 . For example, in certain embodiments, the insulating layer  182  can include an adhesive to enable the conductive member  180  to attach to the reversal disk  104 . In other embodiments, the insulating layer  182  may additionally or alternatively include snap features to secure the conductive member  180  to the surface of the reversal disk  104 . 
       FIG.  14 A  is a cross-sectional schematic view of yet another embodiment of an assembled CDD  140  of an overcharge protection system of a prismatic lithium ion battery cell  60  before activation.  FIG.  14 B  is a cross-sectional view of the CDD  140  of  FIG.  14 A  after activation. Like the design illustrated in  FIGS.  12 A and  12 B , for the design illustrated in  FIGS.  14 A and  14 B , the cover  62 , and/or the remainder of the packaging  84 , may be made of a conductive (e.g., metallic) or non-conductive (e.g., polymeric) material. For embodiments having a conductive cover  62  and/or packaging  84 , the cover  62  and packaging  84  may be electrically isolated from both terminal pads  112 A and  112 B such that the packaging  84  of the battery cell  60  is unbiased until the activation of the CDD, as illustrated in  FIGS.  12 B and  14 B . For the embodiment illustrated in  FIGS.  14 A and  14 B , the conductive element is implemented as a spiral disk feature  106  that is disposed above the reversal disk  104 . The embodiment illustrated in  FIGS.  14 A and  14 B  lacks the electrically insulating layer  182  disposed between the conductive element (e.g., the conductive member  180  or the spiral disk feature  106 ) and the reversal disk  104 , as illustrated in  FIGS.  12 A and  12 B . As such, the reversal disk  104 , as well as the cover  62 , is in electrical contact with the spiral disk feature  106  for the embodiment illustrated in  FIGS.  14 A and  14 B . 
     Additionally,  FIG.  15    illustrates a cross-sectional view of a conductive element (i.e., a spiral disk feature  106 ) of a cover  84  of a battery cell  60  that can be used for embodiments of the CDD in which the conductive element contacts both terminal pads  112 A and  112 B, such as those illustrated in  FIGS.  5  and  14   . As illustrated in  FIG.  15   , the spiral disk feature  106  includes a central portion  200  having a first thickness  201 , which facilitates the passage of current between the terminal pads  112 A and  112 B. In certain embodiments, the central portion  200  of the spiral disk feature  106  may be used and/or referred to as a conductive member  180  (e.g., conductive member  180  in  FIGS.  12 A and  12 B ). The relatively thicker central portion  200  is coupled to the cover  84  via a plurality of legs  202  having a second thickness  203 , which enables deflection of the central portion  200  by the reversal disk  104 . As illustrated, the first thickness  201  may be substantially greater than the second thickness  203 , in certain embodiments. In other words, since the legs  202  of the spiral disk feature  106  are not required to carry the short-circuit current for the illustrated embodiment (as illustrated in  FIG.  14 B ), the legs  202  can be substantially (e.g., 2×-5×) thinner than the central portion  200  of the spiral disk feature  106 , which reduces the force required to displace the spiral disk feature  106  to contact the terminal pads  112 A and  112 B. 
       FIG.  13    illustrates an example of a process  190  whereby the CDD  140  illustrated in  FIGS.  12  and  14    respond to an overcharge event within the cell  60 . For this example, the cover  84  and remainder of packaging  62  of the cell  60  may be conductive (e.g., metallic) and neutral, or may be non-conductive (e.g., polymeric, plastic). Like the processes  150  and  170  discussed above, the process  190  illustrated in  FIG.  13    begins with the pressure in the cell  60  increasing in response to the overcharge event (block  152 ). When the pressure in the cell  60  reaches a pressure threshold, based on the dimensions of the reversal disk  104 , the reversal disk  104  deflects upwards, as indicated by the arrows  192  illustrated in  FIGS.  12 B and  14 B , respectively (block  154 ). This deflection provides sufficient force to displace (e.g., move, translate, deflect) the conductive element (e.g., conductive member  180  or spiral disk feature  106 ) upwards (e.g., along the arrow  192  of  FIGS.  12 B and  14 B ) towards the terminal pads  112 A and  112 B (block  194 ). The physical contact between the conductive element (e.g., conductive member  180  or spiral disk feature  106 ) and both terminal pads  112 A and  112 B forms a short-circuit between the terminal pads, wherein a substantial portion (e.g., a majority, most) of the current passes through the conductive element (e.g., conductive member  180  or spiral disk feature  106 ), as indicated by the arrows  195  in  FIGS.  12 B and  14 B , respectively (block  196 ). For the embodiment illustrated in  FIG.  12 B , since the reversal disk  104  is electrically insulated from the conductive member  180 , the short-circuit current does not traverse or electrify the cover  84  or packaging  62  of the cell  60 . For the embodiment illustrated in  FIG.  14 B , since the reversal disk  104  is in electrical contact with the spiral disk feature  106 , and since the legs  202  of the spiral disk feature  106  are coupled to the cover  84 , a small portion of the short-circuit current can traverse or electrify the cover  84  or packaging  62  of the cell  60 . However, as mentioned above, at least the portion of the conductive element (e.g., conductive member  180  or the central portion  200  of the spiral disk feature  106 ) is substantially (e.g., 2×-10×) thicker and, therefore, less resistive than the reversal disk  104 . As such, a substantial portion of the short-circuit current traverses the lower resistance conductive element (e.g., conductive member  180 , the central portion  200  of the spiral disk feature  106 ), as opposed to the reversal disk  104 , the cover  84 , or the packaging  62 . Similar to the processes  150  and  170  discussed above, as illustrated in  FIG.  13   , the power assembly  95  of the cell  60  resistively heats in response to the external short-circuit (block  162 ) until a portion of the power assembly  95  fails (block  164 ), and the cell  60  subsequently cools in response to the interruption in the internal electrical pathway and current between the terminal pads  112 A and  112 B as the overcharge event is mitigated/interrupted. 
     One or more of the disclosed embodiments, alone or on combination, may provide one or more technical effects including the manufacture of battery modules having a current diverge device (CDD) that externally short-circuits a prismatic lithium ion battery cell in response to an increase in pressure within the cell&#39;s interior. Certain embodiments of lithium ion battery cells of the present approach are able to respond more quickly (e.g., at a relatively low pressure, at a relatively lower state of charge (SOC) of the battery cell) to interrupt current in the battery cell in response to an overcharge condition, reducing the risk of damage to the battery module and/or the stationary energy storage system. Additionally, despite being able to interrupt current in a battery cell in response to a low activation pressure, the disclosed CDDs are designed and arranged to carry a sufficient amount of current during short-circuiting to ensure that the flow of current is permanently interrupted between the terminals of the battery cell in response to an overcharging event. The technical effects and technical problems in the specification are exemplary and are not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems. 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.