Patent Publication Number: US-10763488-B2

Title: Overcharge protection assembly for a battery module

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 14/794,530, entitled “OVERCHARGE PROTECTION ASSEMBLY FOR A BATTERY MODULE,” filed Jul. 8, 2015, which claims priority from and the benefit of U.S. Provisional Application Ser. No. 62/033,001, entitled “AN OVERCHARGE PROTECTION DEVICE,” filed Aug. 4, 2014, which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present disclosure relates generally to the field of batteries and battery modules. More specifically, the present disclosure relates to features of a battery cell that may protect a battery module from thermal runaway during an overcharge event. 
     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. 
     A vehicle that uses one or more battery systems for providing all or a portion of the motive power for the vehicle can be referred to as an xEV, where the term “xEV” is defined herein to include all of the following vehicles, or any variations or combinations thereof, that use electric power for all or a portion of their vehicular motive force. For example, xEVs include electric vehicles (EVs) that utilize electric power for all motive force. As will be appreciated by those skilled in the art, hybrid electric vehicles (HEVs), also considered xEVs, combine an internal combustion engine propulsion system and a battery-powered electric propulsion system, such as 48 Volt (V) or 130V systems. The term HEV may include any variation of a hybrid electric vehicle. For example, full hybrid systems (FHEVs) may provide motive and other electrical power to the vehicle using one or more electric motors, using only an internal combustion engine, or using both. In contrast, mild hybrid systems (MHEVs) disable the internal combustion engine when the vehicle is idling and utilize a battery system to continue powering the air conditioning unit, radio, or other electronics, as well as to restart the engine when propulsion is desired. The mild hybrid system may also apply some level of power assist, during acceleration for example, to supplement the internal combustion engine. Mild hybrids are typically 96V to 130V and recover braking energy through a belt or crank integrated starter generator. Further, a micro-hybrid electric vehicle (mHEV) also uses a “Stop-Start” system similar to the mild hybrids, but the micro-hybrid systems of a mHEV may or may not supply power assist to the internal combustion engine and operates at a voltage below 60V. For the purposes of the present discussion, it should be noted that mHEVs typically do not technically use electric power provided directly to the crankshaft or transmission for any portion of the motive force of the vehicle, but an mHEV may still be considered an xEV since it does use electric power to supplement a vehicle&#39;s power needs when the vehicle is idling with internal combustion engine disabled and recovers braking energy through an integrated starter generator. In addition, a plug-in electric vehicle (PEV) is any vehicle that can be charged from an external source of electricity, such as wall sockets, and the energy stored in the rechargeable battery packs drives, or contributes to drive, the wheels. PEVs are a subcategory of EVs that include all-electric or battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicle conversions of hybrid electric vehicles and conventional internal combustion engine vehicles. 
     xEVs as described above may provide a number of advantages as compared to more traditional gas-powered vehicles using only internal combustion engines and traditional electrical systems, which are typically 12V systems powered by a lead acid battery. For example, xEVs may produce fewer undesirable emission products and may exhibit greater fuel efficiency as compared to traditional internal combustion vehicles and, in some cases, such xEVs may eliminate the use of gasoline entirely, as is the case of certain types of EVs or PEVs. 
     As technology continues to evolve, there is a need to provide improved power sources, particularly battery modules, for such vehicles. For example, battery modules may undergo overcharge testing to determine boundaries and/or limits of the battery module and its individual battery cells. Additionally, in certain instances, for example due to changing environmental conditions or other operating conditions, battery cells may be subject to overcharging. Overcharge tests and overcharging may lead to thermal runaway (e.g., an internal short circuit) caused by overheating in the battery cells. Thermal runaway may render the battery cell and an associated battery module permanently inoperable. Therefore, devices that may prevent or block thermal runaway are desired. 
     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. 
     The present disclosure relates to a lithium-ion battery module that has a housing and a lithium-ion plurality of battery cells disposed in the housing. Each of the plurality of lithium-ion battery cells includes a first terminal with a first polarity, a second terminal with a second polarity opposite the first polarity, an overcharge protection assembly, and a casing electrically coupled to the first terminal such that the casing has the first polarity, where the casing has an electrically conductive material. The lithium-ion battery module includes a vent of the overcharge protection assembly electrically coupled to the casing and a conductive component of the overcharge protection assembly electrically coupled to the second terminal, and the vent is configured to contact the conductive component to cause a short circuit and to vent a gas from the casing into the housing when a pressure in the casing reaches a threshold value. 
     The present disclosure also relates to a battery module that includes a plurality of battery cells disposed in a housing. Each of the plurality of battery cells has a casing that includes an electrically conductive material, a first terminal electrically coupled to the casing, a second terminal, a vent, a conductive spring electrically coupled to the second terminal, and an insulative component disposed between the conductive spring and the casing. The vent is configured to vent a gas from the casing into the housing and to urge the insulative component from between the conductive spring and the casing such that the conductive spring electrically contacts the casing when a pressure in the casing exceeds a threshold value. 
     The present disclosure also relates to a lithium ion battery cell that includes a first terminal with a first polarity, a second terminal of with a second polarity opposite the first polarity, a casing coupled to the first terminal and having an electrically conductive material such that the casing has the first polarity, and an overcharge protection assembly having a vent, a first conductive component, an intermediate conductive component, and an insulating component. The first conductive component is electrically coupled to the second terminal, the intermediate conductive component is electrically coupled to the casing, the insulating component is positioned between the first conductive component and the casing such that a gap is formed between the first conductive component and the casing, and the vent is configured to vent a gas from the casing and to urge the intermediate conductive component to span the gap and to contact the first conductive component when a pressure in the casing reaches a threshold value such that a short circuit occurs. 
    
    
     
       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 perspective view of a vehicle having a battery system configured in accordance with present embodiments to provide power for various components of the vehicle; 
         FIG. 2  is a cutaway schematic view of an embodiment of the vehicle and the battery system of  FIG. 1 ; 
         FIG. 3  is an elevational view of a lithium-ion battery cell that includes an overcharge protection assembly, in accordance with an aspect of the present disclosure; 
         FIG. 4  is an expanded cross-sectional view of a portion of the battery cell of  FIG. 3  depicting a configuration in which a vent disk of the overcharge protection assembly is in a first position, in accordance with an aspect of the present disclosure; 
         FIG. 5  is the cross-sectional view of  FIG. 4 , depicting a configuration in which the vent disk of the overcharge protection assembly is in a second position, in accordance with an aspect of the present disclosure; 
         FIG. 6  is a perspective view of the vent disk of  FIGS. 4 and 5 , in accordance with an aspect of the present disclosure; 
         FIG. 7  is a cross sectional elevation view of the vent disk of  FIGS. 4-6 , in accordance with an aspect of the present disclosure; 
         FIG. 8  is an elevational view of the vent disk of  FIGS. 4-7  in the second position when a recessed surface of the vent disk is inverted, in accordance with an aspect of the present disclosure; 
         FIG. 9  is an elevational view of the vent disk of  FIGS. 4-8  in the second position and depicting an example of the manner in which the recessed surface is configured to remain substantially rigid, in accordance with an aspect of the present disclosure; 
         FIG. 10  is a cross-sectional perspective view of an embodiment of a conductive component of the overcharge protection assembly that includes a plurality of openings, in accordance with an aspect of the present disclosure; 
         FIG. 11  is an overhead perspective view of the battery cell of  FIG. 3  when the vent disk of  FIGS. 4-9  is in the second position and the conductive component is removed, in accordance with an aspect of the present disclosure; 
         FIG. 12  is a perspective view of the battery cell of  FIG. 11  with the conductive component attached to the negative terminal of the battery cell, in accordance with an aspect of the present disclosure; 
         FIG. 13  is a cross-sectional view of another embodiment of the overcharge protection assembly that includes an intermediate conductive component and the vent disk is in the first position, in accordance with an aspect of the present disclosure; 
         FIG. 14  is a cross-sectional side view of the overcharge protection assembly of  FIG. 13  when the vent disk is in the second position, in accordance with an aspect of the present disclosure; 
         FIG. 15  is a perspective view of another embodiment of the overcharge protection assembly that includes a vent flap in a first position, in accordance with an aspect of the present disclosure; 
         FIG. 16  is a perspective view of the overcharge protection assembly of  FIG. 15  with the vent flap in a second position, in accordance with an aspect of the present disclosure; and 
         FIG. 17  is a graphical representation of results from an overcharge test performed on a battery cell utilizing an overcharge protection assembly, in accordance with an aspect of the present disclosure. 
     
    
    
     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. 
     The battery systems described herein may be used to provide power to various types of electric vehicles (xEVs) and other high voltage energy storage/expending applications (e.g., electrical grid power storage systems). Such battery systems may include one or more battery modules, each battery module having a number of battery cells (e.g., Lithium-ion (Li-ion) electrochemical cells) arranged to provide particular voltages and/or currents useful to power, for example, one or more components of an xEV. As another example, battery modules in accordance with present embodiments may be incorporated with or provide power to stationary power systems (e.g., non-automotive systems). 
     During the design and manufacturing process of a battery module, various tests may be performed upon the battery module and its individual battery cells to determine optimal performance parameters. For example, overcharge tests may provide excess electrical current to an individual battery cell of a battery module using a power supply with a voltage that exceeds a voltage of the individual battery cell. Overcharge testing may provide data related to temperature, heat output, and/or voltage of the overcharged battery cell, which may enable designers or manufacturers to modify various components of the battery cell to enhance performance (e.g., minimize damage to an overcharged battery cell). Therefore, such tests may be desirable for providing information that may enable manufacturers to optimize a battery module. In addition to overcharge testing, battery cells may be overcharged as a result of environmental conditions or abnormal operating parameters. 
     In certain cases, overcharging a battery cell may lead to thermal runaway (e.g., an internal short circuit) or another event causing permanent damage to the battery cell. For instance, charging a battery cell may generate dendrites as a result of intercalation of positive ions in the anode. Thermal runaway may result due to an excess buildup of dendrites on a separator of a battery cell (e.g., the dendrites may penetrate the separator enabling mixing of the positive electrode and the negative electrode) when the battery cell is overcharged (e.g., from an overcharge test or under abnormal operating conditions). Thermal runaway may be undesirable because it generates excessive heat, which may cause permanent damage to the battery cell and/or render the battery cell permanently inoperable. 
     Various features may be included in the battery cell that prevent or block thermal runaway when the battery cell is overcharged. Some battery cells may include a mechanism that completely breaks (e.g., disrupts a flow of electrical current) an electrical connection to at least one terminal of the battery cell when a pressure in the battery cell reaches a certain level. Such a mechanism thereby disrupts current flow to at least one terminal of the battery cell, which may ultimately lead to decreased current capacity of the battery cell. However, it is now recognized that it may be desirable to maintain the electrical connection to one or both terminals of the battery cell while preventing thermal runaway during overcharge. In accordance with aspects of the present disclosure, when a pressure in the battery cell exceeds a threshold level, an external short circuit may be triggered by electrically coupling the positive terminal and the negative terminal of the battery cell via a casing of the battery cell, for example. Accordingly, thermal runaway may be prevented and an electrical current capacity of the battery cell terminals is not reduced because the electrical pathway (e.g., connection) from an external load to the terminals remains intact. 
     Certain embodiments of the present disclosure relate to an overcharge protection assembly for battery modules having battery cells with polarized cans (e.g., casings). As used herein a “polarized can” may be defined as a battery cell casing which is electrically coupled to the positive terminal or the negative terminal (e.g., the positive terminal or the negative terminal contacts the battery cell casing). Conversely, other embodiments of the present disclosure relate to an overcharge protection assembly for battery cells with a neutral can. As used herein, a “neutral can” may be defined as a battery cell casing that is not electrically coupled to either the positive terminal or the negative terminal of the individual battery cell. 
     To help illustrate,  FIG. 1  is a perspective view of an embodiment of a vehicle  10 , which may utilize a regenerative braking system. Although the following discussion is presented in relation to vehicles with regenerative braking systems, the techniques described herein are adaptable to other vehicles that capture/store electrical energy with a battery, which may include electric-powered and gas-powered vehicles. 
     As discussed above, it would be desirable for a battery system  12  to be largely compatible with traditional vehicle designs. Accordingly, the battery system  12  may be placed in a location in the vehicle  10  that would have housed a traditional battery system. For example, as illustrated, the vehicle  10  may include the battery system  12  positioned similarly to a lead-acid battery of a typical combustion-engine vehicle (e.g., under the hood of the vehicle  10 ). Furthermore, as will be described in more detail below, the battery system  12  may be positioned to facilitate managing temperature of the battery system  12 . For example, in some embodiments, positioning a battery system  12  under the hood of the vehicle  10  may enable an air duct to channel airflow over the battery system  12  and cool the battery system  12 . 
     A more detailed view of the battery system  12  is described in  FIG. 2 . As depicted, the battery system  12  includes an energy storage component  13  coupled to an ignition system  14 , an alternator  15 , a vehicle console  16 , and optionally to an electric motor  17 . Generally, the energy storage component  13  may capture/store electrical energy generated in the vehicle  10  and output electrical energy to power electrical devices in the vehicle  10 . 
     In other words, the battery system  12  may supply power to components of the vehicle&#39;s electrical system, which may include radiator cooling fans, climate control systems, electric power steering systems, active suspension systems, auto park systems, electric oil pumps, electric super/turbochargers, electric water pumps, heated windscreen/defrosters, window lift motors, vanity lights, tire pressure monitoring systems, sunroof motor controls, power seats, alarm systems, infotainment systems, navigation features, lane departure warning systems, electric parking brakes, external lights, or any combination thereof. Illustratively, in the depicted embodiment, the energy storage component  13  supplies power to the vehicle console  16  and the ignition system  14 , which may be used to start (e.g., crank) an internal combustion engine  18 . 
     Additionally, the energy storage component  13  may capture electrical energy generated by the alternator  15  and/or the electric motor  17 . In some embodiments, the alternator  15  may generate electrical energy while the internal combustion engine  18  is running. More specifically, the alternator  15  may convert the mechanical energy produced by the rotation of the internal combustion engine  18  into electrical energy. Additionally or alternatively, when the vehicle  10  includes an electric motor  17 , the electric motor  17  may generate electrical energy by converting mechanical energy produced by the movement of the vehicle  10  (e.g., rotation of the wheels) into electrical energy. Thus, in some embodiments, the energy storage component  13  may capture electrical energy generated by the alternator  15  and/or the electric motor  17  during regenerative braking. As such, the alternator  15  and/or the electric motor  17  are generally referred to herein as a regenerative braking system. 
     To facilitate capturing and supplying electric energy, the energy storage component  13  may be electrically coupled to the vehicle&#39;s electric system via a bus  19 . For example, the bus  19  may enable the energy storage component  13  to receive electrical energy generated by the alternator  15  and/or the electric motor  17 . Additionally, the bus  19  may enable the energy storage component  13  to output electrical energy to the ignition system  14  and/or the vehicle console  16 . Accordingly, when a 12 volt battery system  12  is used, the bus  19  may carry electrical power typically between 8-18 volts. 
     Additionally, as depicted, the energy storage component  13  may include multiple battery modules. For example, in the depicted embodiment, the energy storage component  13  includes a lithium ion (e.g., a first) battery module  20  and a lead-acid (e.g., a second) battery module  22 , which each includes one or more battery cells. In other embodiments, the energy storage component  13  may include any number of battery modules. Additionally, although the lithium ion battery module  20  and lead-acid battery module  22  are depicted adjacent to one another, they may be positioned in different areas around the vehicle. For example, the lead-acid battery module  22  may be positioned in or about the interior of the vehicle  10  while the lithium ion battery module  20  may be positioned under the hood of the vehicle  10 . 
     In some embodiments, the energy storage component  13  may include multiple battery modules to utilize multiple different battery chemistries. For example, when the lithium ion battery module  20  is used, performance of the battery system  12  may be improved since the lithium ion battery chemistry generally has a higher coulombic efficiency and/or a higher power charge acceptance rate (e.g., higher maximum charge current or charge voltage) than the lead-acid battery chemistry. As such, the capture, storage, and/or distribution efficiency of the battery system  12  may be improved. 
     To facilitate controlling the capturing and storing of electrical energy, the battery system  12  may additionally include a control module  24 . More specifically, the control module  24  may control operations of components in the battery system  12 , such as relays (e.g., switches) within energy storage component  13 , the alternator  15 , and/or the electric motor  17 . For example, the control module  24  may regulate an amount of electrical energy captured/supplied by each battery module  20  or  22  (e.g., to de-rate and re-rate the battery system  12 ), perform load balancing between the battery modules  20  and  22 , determine a state of charge of each battery module  20  or  22 , determine temperature of each battery module  20  or  22 , control voltage output by the alternator  15  and/or the electric motor  17 , and the like. 
     Accordingly, the control module  24  may include one or more processors  26  and one or more memory components  28 . More specifically, the one or more processors  26  may include one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more general purpose processors, or any combination thereof. Additionally, the one or more memory components  28  may include volatile memory, such as random access memory (RAM), and/or non-volatile memory, such as read-only memory (ROM), optical drives, hard disc drives, or solid-state drives. In some embodiments, the control module  24  may include portions of a vehicle control unit (VCU) and/or a separate battery control module. 
     As discussed above, before a battery module may be used to supply power to an xEV, various tests may be conducted upon the battery module and its individual battery cells to optimize operating parameters of the battery module. One such test may be an overcharge test that determines how much electrical current a battery cell may receive, or how long a battery cell may receive an electrical current, before damage occurs to the battery cell. However, in certain instances, overcharge tests may result in thermal runaway (e.g., an internal short circuit within the battery cell), which may cause permanent damage to the battery cell because of excess heat generated from the overcharge. It is now recognized that it may be desirable to prevent thermal runaway (e.g., an internal short circuit) by triggering an external short circuit (e.g., electrically coupling the positive terminal and the negative terminal of the battery cell) before thermal runaway occurs. In certain embodiments, the external short circuit may be triggered by establishing an electrical connection between an insulated terminal of the battery cell and the cell casing (e.g., can) such that the insulated terminal is electrically coupled to a non-insulated terminal (e.g., the terminal directly contacting the casing) via the casing. 
       FIG. 3  is an illustration of a prismatic, lithium-ion battery cell  50  that includes an overcharge protection assembly  51 . The battery cell  50  may be used in the lithium-ion battery module  20  that supplies power to an xEV  10 . It should be noted that while the current discussion focuses on an overcharge protection assembly in a lithium-ion battery cell, embodiments of the overcharge protection assembly may be employed in any suitable battery cell that may be subject to overcharge. 
     As shown in the illustrated embodiment of  FIG. 3 , the battery cell  50  includes a positive (e.g., first) terminal  52  and a negative (e.g., second) terminal  54 . The positive terminal  52  has a first polarity (e.g., positive polarity) and the negative terminal  54  has a second polarity (e.g., negative polarity), where the second polarity (e.g., negative polarity) is opposite to the first polarity (e.g., positive polarity) of the positive terminal  52 . Additionally, the battery cell  50  includes a casing  56 . The casing  56  may house various chemicals and other components that enable the battery cell  50  to supply electrical power to a load (e.g., an xEV). In certain embodiments, the casing  56  may include an electrically conductive material. When the casing includes an electrically conductive material, the battery cell casing may or may not be polarized (e.g., when polarized, the casing  56  is electrically coupled to the positive terminal  52  or the negative terminal  54 , thereby having the first or second polarity). In the illustrated embodiment of  FIG. 3 , the casing  56  is positively polarized in that the positive terminal  52  is electrically coupled to the casing  56  and the casing  56  has the first polarity (e.g., positive polarity). For example, the positive terminal  52  extends through the casing  56  such that the positive terminal  52  contacts the casing  56  and establishes an electrical connection with the casing  56 . Moreover, the negative terminal  54  is electrically insulated from the casing  56 . For example, in certain embodiments, an insulative gasket  58  is disposed about the negative terminal  54  to prevent contact between the negative terminal  54  and the casing  56 . 
     Although the following discussion focuses on a battery casing that is positively polarized, it should be understood that in other embodiments, the casing  56  may be negatively polarized. A negatively polarized casing may include electrically coupling (e.g., via contact) the negative terminal  54  to the casing  56  and disposing the insulative gasket  58  over the positive terminal  52 . In still further embodiments, the casing  56  may be neutral (e.g., not polarized), such that neither the positive terminal  52  nor the negative terminal  54  are electrically coupled to the casing  56 , and the insulative gasket  58  is disposed over both the positive terminal  52  and the negative terminal  54 . 
     In the embodiments of the battery cell  50  where the casing  56  is polarized (e.g., either positively or negatively), the battery cell may include the overcharge protection assembly  51 . The overcharge protection assembly  51  may include a conductive component  60  disposed over the terminal insulated from the casing  56  (e.g., the terminal  52 ,  54  opposite of polarity). In other words, when the casing  56  is positively polarized, the conductive component  60  may be disposed over the negative terminal  54 , and when the casing  56  is negatively polarized, the conductive component  60  may be disposed over the positive terminal  52 . 
     As shown in the illustrated embodiment of  FIG. 3 , the conductive component  60  may be Z-shaped such that the conductive component includes a recess  62 . The recess  62  may enable the conductive component  60  to electrically couple two components that lie on different planes. In the illustrated embodiment of  FIG. 3 , the recess  62  is formed between a coupling portion  64  of the conductive component  60  (e.g., the portion of the conductive component  60  that couples to the negative terminal  54 ) and a flange portion  66  of the conductive component  60 . Accordingly, the coupling portion  64  may be positioned on a first plane and the flange portion  66  may be positioned on a second plane (e.g., parallel to the first plane). It should be noted that in other embodiments, the conductive component  60  may include any suitable shape that couples the conductive component  60  to the negative terminal  54  and also positions the conductive component  60  a suitable distance away from the casing  56 . 
     The flange portion  66  of the conductive component  60  may be electrically insulated from the casing  56  to prevent a short circuit from occurring during normal operation of the battery cell (e.g., when the pressure in the casing  56  is below the threshold value). In certain embodiments, the flange portion  66  of the conductive component  60  may include a shape configured to contact the casing  56  (e.g., the Z shape), but an insulative component  68  may be disposed between the casing  56  and the flange portion  66  to block formation of an electrical connection between the casing  56  (e.g., when the casing  56  includes an electrically conductive material) and the conductive component  60 . In other embodiments, the conductive component  60  may include a shape configured to form a gap  70  between the flange portion  66  and the casing  56  (e.g., the shape of the conductive component  60  prevents contact with the casing  56 ). In such embodiments, the insulative component  68  may not be included because the gap  70  may be sufficient to prevent contact between the flange portion  66  and the casing  56 . However, it should be recognized that in certain embodiments, the insulative component  68  may be included when the conductive component  60  forms the gap  70 . Accordingly, the insulative component  68  may be configured to fit within the gap  70  and further prevent contact between the flange portion  66  and the casing  56 . 
     When the positive terminal  52  and the negative terminal  54  of the individual battery cell  50  come into electrical contact with one another, a short circuit may occur. A short circuit may be a low resistance connection between the positive terminal  52  and the negative terminal  54  of same the battery cell  50 . Low resistance may lead to a high current flow between the terminals  52 ,  54 , which may cause the cell  50  to discharge (e.g., a flow of current to the casing  56  and/or a conductive component positioned adjacent to the casing  56 ). In the event of an overcharge of the battery cell  50 , an external short circuit between the positive terminal  52  and the negative terminal  54  may be desirable to avoid an internal short circuit (e.g., thermal runaway) that may permanently damage the battery cell  50 . For example, discharge resulting from the external short circuit may prevent additional current from being absorbed by the internal components of the battery cell  50 , and thus, avoid thermal runaway. Therefore, during overcharge, it may be desirable for the negative terminal  54  (e.g., the negative terminal of a positively polarized casing) to contact the casing  56  and generate an external short circuit (e.g., external electrical connection between the positive terminal  52  and the negative terminal  54 ) before thermal runaway occurs. 
       FIGS. 4 and 5  illustrate an embodiment of the overcharge protection assembly  51  that may trigger an external short circuit and prevent thermal runaway during overcharge of the battery cell  50 . In accordance with present embodiments, the external short circuit may be triggered via contact between the casing  56  and the insulated negative terminal  54  (e.g., for a positively polarized can). However, an electrical connection between the positive and/or negative terminal  52 ,  54  and an external load (e.g., another battery) is not disrupted (e.g., by breaking a connection between the terminal and the external load). 
       FIG. 4  illustrates a cross-sectional view of an embodiment of the battery cell  50  that includes the overcharge protection assembly  51 . In certain embodiments, the overcharge protection assembly  51  may include a vent disk  80 . The vent disk  80  may be recessed in the casing  56  of the battery cell  50 . In other embodiments, the casing  56  may include a cover  81  (e.g., a lid) and the vent disk  80  may be positioned within the cover  81  of the casing  56 . Additionally, in certain embodiments, the vent disk  80  may be configured to move in a direction  82  (e.g., by inverting, collapsing, or tearing) when a pressure within the battery cell  50  reaches a threshold value. For example, to produce electrical power in the battery cell  50 , one or more chemical reactions may take place. In some cases, such reactions form a gas as a byproduct, and thus, the pressure within the casing  56  increases as more gas is produced. When a battery is overcharged, a temperature within the casing  56  may increase to an extent which may cause thermal runaway, which in turn, may further increase the pressure in the casing  56 . In certain embodiments, the vent disk  80  may enable the gas to escape (e.g., flow out of) from the casing  56  and into a housing of the battery module  20  when the pressure reaches the threshold value. For example, the vent disk  80  may be in a first position as shown in  FIG. 4  when a pressure in the casing  56  is below the threshold value. Conversely, when the pressure in the casing  56  is at or above the threshold value, the vent disk  80  may transition (e.g., invert, collapse, tear) into a second position (e.g., as shown in  FIG. 5 ). In certain embodiments, the transition from the first position to the second position may be permanent (e.g., the vent disk  80  may not return to the first position when the pressure in the casing  56  returns to a value below the threshold value). In other embodiments, the vent disk  80  may be configured to return to the first position when the pressure in the casing  56  returns to a value below the threshold value. 
     As shown in the illustrated embodiment of  FIG. 4 , the an opening  84  is formed in both the insulative component  68  and the casing  56  enabling the vent disk  80  to move outwardly (e.g., away from the source of the gas and/or internal components of the battery cell  50 ) and to contact the conductive component  60  when the vent disk  80  transitions to the second position (e.g., position in  FIG. 5 ). In certain embodiments, at least a portion of the vent disk  80  is configured to contact the conductive component  60  upon reaching the second position to establish an electrical connection between the negative terminal  54  and the casing  56 , thereby creating a short circuit (e.g., when the battery cell includes a positively polarized can). As can be seen in the illustrated embodiment of  FIG. 4 , when the vent disk  80  is in the first position, the vent disk  80  may be disposed within the opening  84  of the insulative component  68  and the casing  56 . 
     In certain embodiments, the vent disk  80  includes an outer ring  86 , which may be coupled (e.g., electrically) to the casing  56  around an edge of the opening  84 . Accordingly, the outer ring  86  may include a diameter that is greater than a diameter of the opening  84  so that the vent disk  80  covers the opening  84 . Coupling the outer ring  86  to the casing  56  enables the vent disk  80  to remain coupled to the casing  56  when the vent disk  80  is in both the first position and the second position. In certain embodiments, the outer ring  86  may be physically coupled (e.g., laser welded or ultrasonic welded) to the casing  56  to form an electrical connection between the vent disk  80  and the casing  56 . In other embodiments, the outer ring  86  may be electrically coupled (and physically coupled) to the casing  56  using any suitable technique that secures the vent disk  80  to the casing  56 . 
     When in the first position, the vent disk  80  may include a recessed surface  88  whereby the vent disk  80  extends into the casing  56  (or the cover  81 ) through the opening  84 . The vent disk  80  may also include a convex portion  89  (e.g., convex with respect to an interior of the battery cell  50 ). The convex portion  89  may have a top portion  90  that may be substantially flush with a bottom surface  91  of the casing  56  (e.g., the cover  81  of the casing  56 ) when the vent disk  80  is in the first position. In other embodiments, the convex portion  89  may be in any suitable position when the vent disk  80  is in the first position. However, when the vent disk  80  is in the first position (e.g., when the pressure in the casing is below the threshold value) the convex portion  89 , and thus the vent disk  80 , does not contact the conductive component  60 . 
     The recessed surface  88  and the convex portion  89  may be connected to one another via an inner ring  92 . In certain embodiments, the inner ring  92  may include a thickness that is less than a combined thickness of the recessed surface  88  and the convex portion  89 . The smaller thickness of the inner ring  92  may enable a first portion of the inner ring  92  to tear such that a part of the convex portion  89  may separate from the recessed surface  88  and create an opening for trapped gas to escape from the casing  56 . However, an electrical pathway between the casing  56  and the convex portion  89  may be retained via a second portion of the inner ring  92  that maintains contact between the recessed surface  88  and the convex portion  89 . For example, the inner ring  92  may include a circumference that is substantially equal to a circumference of the convex portion  89 . However, the first portion of the circumference of the inner ring  92  may be coined (e.g., perforated) such that it ruptures (e.g., breaks) at a lower pressure than the second portion of the inner ring  92 , which may not be coined (e.g., perforated). In other words, coining located on the inner ring  92  may define a boundary between the first and second portions of the inner ring  92 . Coining the first portion of the inner ring  92  may enable a portion of the convex portion  89  to tear from the recessed surface  88  and contact the conductive component  60 , while the second portion of the inner ring  92  maintains contact (e.g., an electrical connection) between the convex portion  89  and the casing  56  (e.g., via the outer ring  86 ). Therefore, an electrical connection may be established between the conductive component  60  and the casing  56 . The coining of the inner ring  92  is described in more detail below with reference to  FIG. 6 . In other embodiments, the inner ring  92  may be the same thickness as the recessed surface  88  and convex portion  89 . 
     When the vent disk  80  is in the first position the vent disk  80  may cover the opening  84  such that no gas may escape from the casing  56 . The gas may then accumulate within the casing and cause the pressure within the casing  56  to increase. As pressure builds in the casing  56 , the vent disk  80  may move in the direction  82  (e.g., by bulging or rupturing). In certain embodiments, the vent disk  80  may move in the direction  82  as a result of inversion of the recessed surface  88  (e.g., the recessed surface  88  moves in the direction  82  from a position below the outer ring  86  to a position above the outer ring  86 ). Once inverted, the vent disk  80  may reach the second position, as illustrated in  FIG. 5 . In certain embodiments, when the recessed surface  88  inverts from the pressure buildup within the casing  56 , a portion of the inner ring  92  may break (e.g., rupture or tear) as a result of tension created from the inversion. For example, the inner ring  92  may form a weak connection between the recessed surface  88  and the convex portion  89  such that a relatively small force may break the first portion of the inner ring  92  (e.g., due to the smaller thickness of the inner ring  92  or coining). Additionally, as the recessed surface  88  inverts, the inner ring  92  may be compressed and then subsequently stretched as a result of the convex portion  89  and the recessed surface  88  simultaneously moving in the direction  82 . Such movement may further weaken the inner ring  92  such that the first portion of the inner ring  92  is more susceptible to breaking. Accordingly, breaking the first portion of the inner ring  92  may form a gap  94 , through which gas  96  may escape from the casing  56 . 
     It is now recognized that forming the gap  94  may be desirable so that gas  96 , and thus pressure, may be released from the battery cell casing  56 . For example, the battery cell  50  may incur permanent damage when the pressure in the casing  56  reaches a certain level. In certain embodiments, the threshold level of the vent disk  80  may be a pre-determined pressure value that is less than a pressure that may cause permanent damage to the battery cell  50  and/or thermal runaway. The vent disk  80  of embodiments of the present disclosure may be utilized both to cause an external short circuit to prevent thermal runaway as well as to release an undesirable buildup of pressure within the casing  56 . 
     In other embodiments, the recessed surface  88  may not be configured to invert, but to remain substantially rigid. For example, the first portion of the inner ring  92  may break as a result of pressure building and applying a force to the convex portion  89  of the vent disk. Accordingly, once the pressure in the casing  56  reaches the threshold value, the pressure applies a force upon the convex portion  89  that causes the convex portion  89  to break away from the recessed surface  88 . The inner ring  92  may have a thickness that enables the convex portion  89  to break away from the recessed surface  88  at the threshold pressure. The substantially rigid recessed surface  88  is discussed in detail below with reference to  FIG. 9 . 
     When the vent disk  80  moves in the direction  82  from the pressure buildup within the casing  56 , the convex portion  89  that breaks away from the recessed surface  88  may be configured to contact the conductive component  60 . The contact between the convex portion  89  and conductive component  60  may create an electrical connection between the negative terminal  54  and the casing  56 . Accordingly, a short circuit may result from the established electrical connection, which in certain embodiments, may lead to a discharge of the cell  50  (e.g., flow of electrical current to the casing  56  and/or another conductive component proximate to the casing  56 ). Therefore, in certain situations (e.g., when conducting an overcharge test), the vent disk  80  may trigger an external short circuit when the pressure in the casing  56  reaches the threshold pressure such that thermal runaway may be prevented. 
       FIG. 6  illustrates a perspective view of the vent disk  80 , in accordance with aspects of the present disclosure. As shown in the illustrated embodiment of  FIG. 6 , the vent disk  80  includes a connection ring  100  that couples the outer ring  86  to the recessed surface  88 . In accordance with certain embodiments, a portion of the connection ring  100  may also be configured to break such that the recessed surface  88  separates from the outer ring  86  when the pressure in the casing  56  reaches the threshold value and the vent disk  80  transitions from the first position to the second position. 
     As shown in the illustrated embodiment of  FIG. 6 , the inner ring  92  includes coining  101  (e.g., perforations) that may separate a first portion  102  of the inner ring  92  (e.g., the portion that includes the coining  101 ) from a second portion  103  of the inner ring  92  (e.g., the portion that does not include the coining  101 ). Accordingly, when the pressure in the casing  56  reaches the threshold value, the first portion  102  of the inner ring  92  may tear, such that the convex portion  89  no longer contacts the recessed surface  88 . However, the second portion  103  of the inner ring  92  may maintain contact between the convex portion  89  and the recessed surface  88 . Therefore, when the first portion  102  tears, a segment of the convex portion  89  may contact the conductive component  60 , thereby establishing an electrical connection between the conductive component  60  and the casing  56 , and therefore, the positive and negative terminals  52 ,  54 . 
     In certain embodiments, each component of the vent disk  80  may include the same material. For example, the components of the vent disk  80  may be a flexible metal (e.g., aluminum) that is configured to collapse, break, or tear when a desired force is applied to the vent disk  80  (e.g., to the convex portion  89 ). Further, the convex portion  89  and the outer ring  86  may include a conductive metal (e.g., aluminum), whereas the connection ring  100 , the recessed surface  88 , and/or the inner ring  92  may include another suitable material. For example, in embodiments where the recessed surface  88  is configured to remain substantially rigid, the recessed surface  88  may include a hard plastic, a metal, or any other rigid material configured to withstand the threshold pressure. Additionally, the inner ring  92  and/or the connection ring  100  may include a relatively weak material configured to break (e.g., rupture or tear) at lower pressures (e.g., the threshold pressure) than the other materials. In such embodiments when the connection ring  100 , the recessed surface  88 , and/or the inner ring  92  include a non-conductive component, a conductive lead may be configured to electrically couple the outer ring  86  to the convex portion  89 . For example, the conductive lead may be a conductive strip of metal disposed over the connection ring  100 , the recessed surface  88 , and/or the inner ring  92 . Accordingly, when the convex portion  89  contacts the conductive component  60  (see  FIG. 5 ), an electrical connection is established between the casing  56  and the negative terminal  54 . 
       FIG. 7  illustrates a cross section of the vent disk  80 . The illustrated embodiment of  FIG. 7  shows the convex portion  89  as including a height  110  that is substantially the same as a height  112  between the inner ring  92  and the outer ring  86 . In other embodiments, the convex portion  89  may include any suitable height such that when the convex portion  89  breaks away from the recessed surface  88 , at least a portion of the convex portion  89  contacts the conductive component  60  by an amount sufficient to create a short circuit. Additionally, the illustrated embodiment of  FIG. 7  shows the convex portion  89  as including a hollow convex surface  114 . Accordingly, as gas builds within the casing  56 , the resulting pressure may apply a force upon the surface  114 . In certain embodiments, the convex portion  89  may include an angle of curvature chosen to increase a surface area of the surface  114 . Increasing or maximizing the surface area may enable the surface  114  to experience a greater overall force from the pressure in the casing  56 . The surface  114  may have any suitable surface area that enables the vent disk to transition from the first position to the second position at the threshold pressure value. 
       FIG. 8  illustrates a side view of the vent disk  80  in the second position when the recessed surface  88  is configured to invert (e.g., the recessed surface  88  is not rigid and not able to withstand the threshold pressure). As shown in the illustrated embodiment, the gap  94  forms between the recessed surface  88  and the convex portion  89  because of a rupture of a portion of the inner ring  92 . Despite the formation of the gap  94 , the convex portion  89  remains electrically coupled to the outer ring  86 , and in turn, the casing  56 . Accordingly, when the convex portion  89  contacts the conductive component  60 , an electrical pathway may be formed between the casing  56  and the negative terminal  54 , and thus, between the negative terminal  54  and the positive terminal  52  (e.g., the positive terminal is electrically coupled to the casing  56  causing the casing  56  to be positively polarized). 
     While the illustrated embodiment of  FIG. 8  shows the inner ring  92  as rupturing at a specific point, the inner ring  92  may break at any point along a circumference of the inner ring  92  depending on coining and/or other features of the inner ring  92 . However, at least a portion of the inner ring  92  remains intact (e.g., couples the recessed surface  88  to the convex portion  89 ). Additionally, it should be noted that in other embodiments, the connection ring  100  may rupture causing a portion of the recessed surface  88  to separate from the outer ring  86 . In such embodiments, the gap  94  may form between the recessed surface  88  and the outer ring  86  and/or the recessed surface  88  and convex portion  89  (e.g., either or both of the connection ring  100  and the inner ring  92  may tear). In view of the foregoing, it should be appreciated that the convex portion  89  is configured to contact the conductive component  60  when the pressure in the casing  56  reaches the threshold value, and an electrical connection remains present between the convex portion  89  and the outer ring  86  when the vent disk  80  is in the second position (e.g., the convex portion  89  contacting the conductive component  60 ). 
       FIG. 9  illustrates a side view of the vent disk  80  in the second position when the recessed surface  88  is configured to remain substantially rigid (e.g., to not collapse at the threshold pressure). In the illustrated embodiment of  FIG. 9 , the inner ring  92  is configured to rupture when the pressure in the casing  56  reaches the threshold value. However, the recessed surface  88  withstands the pressure, thereby causing the convex portion  89  to separate from the recessed surface  88  and to form the gap  94  between the convex portion  89  and the recessed surface  88 . Accordingly, gas  96  may flow out of the casing  56  via the gap  94 , thereby relieving the pressure buildup within the cell  50 . 
     In certain embodiments, the conductive component  60  may create an obstruction for gas  96  flowing out of the gap  94 , which may be undesirable because the obstruction may slow a flow of the gas  96  exiting the battery cell  50 .  FIG. 10  illustrates an embodiment of the conductive component  60  that includes a plurality of openings  116 . The openings  116  may enable the gas  96  to flow through the gap  94  of the vent disk  80  and into the housing of the battery module  20  with minimal obstruction. Additionally, the openings  116  may decrease an amount of heat transferred to the conductive component  60 . Decreasing an amount of heat transferred to the conductive component  60  may mitigate damage to the conductive component  60  and/or the negative terminal  54  due to contact between the conductive component  60  and the gas  96  (e.g., battery cell effluent). 
     Further, the openings  116  enable gas  96  to flow into the housing of the battery module  20  while still providing a sufficient surface area for the convex portion  89  of the vent disk  80  to contact the conductive component  60  and to establish the electrical connection between the negative terminal  54  and the casing  56 . Therefore, the openings  116  may be a sufficient size to enable gas  96  to pass through the conductive component  60 , but not so large as to eliminate a contact area for the convex portion  89  of the vent disk  80 . While the illustrated embodiment of  FIG. 10  shows the openings  116  as circular holes, in other embodiments the openings  116  may be square, oval, rectangular, or any other suitable shape. 
       FIG. 11  illustrates a perspective view of the vent disk  80  in the second position when the conductive component  60  is removed. As shown in  FIG. 11 , the battery cell casing  56  is positively polarized as the positive terminal  52  is directly coupled to the casing  56 . In other embodiments, the battery cell casing  56  may be negatively polarized such that the negative terminal  54  is directly coupled to the casing  56  and the positive terminal  52  is insulated from the casing  56  via the insulative gasket  58 . Additionally,  FIG. 11  shows the insulative component  68  disposed over a surface  118  of the casing  56 . As described above, the insulative component  68  may block the conductive component  60  from contacting the casing  56  when the battery cell  50  is operating under normal conditions (e.g., below the threshold pressure value when the vent disk  80  has not deployed). 
     Additionally, the positive terminal  52  and the negative terminal  54  each have an opening  120 . In certain embodiments, the opening  120  may include threading  122  configured to receive a screw or bolt. The opening  120  may enable the battery cell  50  to be coupled to other battery cells. Additionally, the opening may enable other components (e.g., the conductive component  60 ) to be coupled to one of the terminals  52 ,  54 . 
       FIG. 12  illustrates a perspective view of the battery cell  50  of  FIG. 11  with the conductive component  60  attached to the negative terminal  54 . In the illustrated embodiment of  FIG. 12 , the conductive component  60  is coupled to the negative terminal  54  via a screw  124 . Therefore, in certain embodiments, the conductive component  60  may include an opening that enables the screw  124  or a bolt to pass through the conductive component  60  and into the opening  120  of the negative terminal  54 . Accordingly, the screw  124  may secure the conductive component  60  to the negative terminal  54  via the threading  122  within the opening  120  of the negative terminal  54 . In other embodiments, the conductive component  60  may be coupled to the negative terminal  54  via another type of fastener, a weld, or another suitable technique that secures and electrically couples the conductive component  60  to the negative terminal  54 . In such embodiments, the battery cell  50  may not include the screw  124  and the conductive component  60  may not include the opening to receive the screw  124 . 
     Additionally, the illustrated embodiment of  FIG. 12  shows the Z-shape of the conductive component  60 . The conductive component  60  may include the recess  62  that enables the conductive component  60  to couple two components positioned in different planes. For example, the conductive component  60  is coupled to the negative terminal  54  and positioned a sufficient distance from the vent disk  80  to ensure contact when the vent disk  80  transitions to the second position. 
     In some cases, the vent disk  80  may be too short to contact the conductive component  60  and establish an electrical connection between the conductive component  60  and the casing  56 . An intermediate conductive component may be utilized when the vent disk  80  itself cannot make sufficient contact with the conductive component  60  and avoid issues related to the electrolyte vapor encountering an external short that could damage components of present embodiments. For example, the intermediate conductive component may block gas from contacting the external short circuit because the gap  94  in the vent disk  80  and a contact area of the external short circuit are on opposite sides of the intermediate conductive component.  FIGS. 13 and 14  illustrate an embodiment of the cell  50  that includes the vent disk  80 , the conductive component  60 , as well as an intermediate conductive component  130 . In the illustrated embodiment of  FIG. 13 , the casing  56  is positively polarized (e.g., the positive terminal  52  is directly or indirectly physically and electrically coupled to the casing  56 ). However, it should be noted that the casing  56  may also be negatively polarized (e.g., the negative terminal  54  may be directly or indirectly physically and electrically coupled to the casing  56  and the positive terminal may be electrically insulated from the casing  56 ). When the casing  56  is negatively polarized, the conductive component  60  would be disposed over the positive terminal  52  rather than the negative terminal  54 . 
     Additionally, the embodiment of  FIG. 13  shows the intermediate conductive component  130  disposed between the vent disk  80  and the conductive component  60  and over the opening  84 . In certain embodiments, the intermediate conductive component  130  may be disk-shaped and fully cover the opening  84 . In other embodiments, the intermediate conductive component  130  may be a rectangular shape that covers a portion of, or all of, the opening  84 . In still further embodiments, the intermediate conductive component  130  may be any suitable shape that contacts the conductive component  60  when the vent disk  80  moves from the first position to the second position, but not before. In other words, the intermediate conductive component  130  may not contact the conductive component  60  when the vent disk  80  is in the first position, but may be urged into contact with the conductive component  60  when the vent disk  80  is in the second position (e.g., when the disk  80  transitions to the second position). Further, the intermediate conductive component  130  may be disposed within grooves  132  of the insulative component  68 . In other embodiments, the intermediate conductive component  130  may not contact the insulative component  68  at all. The intermediate conductive component  130  may include a thickness that is less than a thickness of the insulative component  68  so that the intermediate conductive component  130  is driven into contact with the conductive component  60  by the vent disk  80  (e.g., the intermediate conductive component  130  is not constantly in contact with the conductive component  60 ). 
     In certain embodiments, the intermediate conductive component  130  may be any flexible metal (e.g., aluminum, nickel plated copper, steel, or another metal) that may establish an electrical connection when in contact with the conductive component  60 . In other embodiments, the intermediate conductive component  130  may include aluminum. 
     In certain embodiments, the intermediate conductive component  130  may be disposed directly on the casing  56  and a first edge  134  of the intermediate conductive component  130  may be electrically coupled to the casing  56  (e.g., via a laser weld, another weld, or any other suitable technique that electrically couples the intermediate conductive component  130  to the casing  56 ). A second edge  136  of the intermediate conductive component  130  may remain unfixed to the casing  56  such that the second edge  136  of the intermediate conductive component  130  may move in the direction  82  when the vent disk  80  moves in the direction  82 . In other embodiments, the intermediate conductive component  130  may be disposed in any other suitable location so long as it is configured to make sufficient contact with the conductive component  60  when the vent disk  80  is in the second position. 
       FIG. 14  illustrates a cross-sectional side view of the battery cell  50  having the intermediate conductive component  130  when the vent disk  80  is in the second position. As shown in the illustrated embodiment of  FIG. 14 , when the vent disk  80  transitions to the second position, the vent disk  80  not only creates the gap  94  enabling gas  96  to escape from the casing  56 , but the vent disk  80  contacts and urges the intermediate conductive component  130  in the direction  82 . The intermediate conductive component  130  may contact the conductive component  60  to establish an electrical pathway between the casing  56  and the negative terminal  54 . For example, electrical current may flow from the negative terminal  54 , to the conductive component  60 , to the intermediate conductive component  130 , to the convex portion  89  of the vent disk  80 , to the outer ring  86  of the vent disk  80 , and to the casing  56 . Accordingly, an electrical connection is established between the positive terminal  52  and the negative terminal  54 , thereby creating an external short circuit when the pressure in the casing  56  reaches the threshold value. The external short circuit may be triggered via an electrical connection between the casing  56  and the insulated negative terminal  54 . However, an electrical connection between the positive and/or negative terminal  52 ,  54  and an external load (e.g., another battery) is not disrupted (e.g., by breaking a connection between the terminal and the external load). 
     In some cases, the battery cell  50  may not include the vent disk  80 . Rather, in certain embodiments, the battery cell  50  may include a vent flap  150  as shown in  FIGS. 15 and 16 . Accordingly, the embodiments of the overcharge protection assembly  51  discussed above with respect to  FIGS. 3-14  may not be suitable for creating an external short when the pressure in the casing reaches the threshold value. Therefore, another configuration of the overcharge protection assembly  51  may be utilized when the battery cell  50  includes the vent flap  150  rather than the vent disk  80 . 
       FIG. 15  is a perspective view of the battery cell  50  having the vent flap  150 . As shown in the illustrated embodiment of  FIG. 15 , the battery cell  50  also includes the overcharge protection assembly  51 , which includes a conductive spring  152  and a second insulative component  154 . While the battery cell casing  56  of  FIG. 15  is positively polarized, the present embodiment may also be utilized for a negatively polarized battery cell casing. The conductive spring  152  may be coupled to the terminal opposite of polarity (e.g., the negative terminal  54  for a positively polarized casing or the positive terminal  52  for a negatively polarized casing). As shown in the illustrated embodiment of  FIG. 15 , the conductive spring  152  is coupled to the negative terminal  54 . In certain embodiments, the conductive spring  152  may be coupled to the negative terminal  54  via a fastener (e.g., screw or bolt). In other embodiments, the conductive spring  152  may be welded (e.g., laser welded) to the negative terminal  54 . In still further embodiments, the conductive spring  152  may be secured to the negative terminal  54  using any other suitable device for establishing an electrical connection between the negative terminal  54  and the conductive spring  152 . 
     Additionally, the conductive spring  152  may include a conductive metal (e.g., aluminum or copper) shaped to bias the conductive spring  152  toward the casing  56 . For example, when the conductive spring  152  is coupled to the negative terminal  54 , a recessed portion  156  of the conductive spring  152  may contact the casing  56 . Such contact may be sufficient to establish an electrical connection between the negative terminal  54  and the casing  56 , and thus, between the negative terminal  54  and the positive terminal  52 . 
     To avoid establishing such an electrical connection during normal operation of the battery cell  50  (e.g., when the pressure in the casing  56  is below the threshold value), the second insulative component  154  may be disposed between the recessed portion  156  of the conductive spring  152  and the casing  56 . The second insulative component  154  may include any material (e.g., plastic, ceramic, or another non-conductive material) configured to prevent electrical current from flowing through the second insulative component  154 . Therefore, during normal operation of the battery cell  50 , the second insulative component  154  may block formation of the electrical connection between the negative terminal  54  (e.g., via the conductive spring  152 ) and the casing  56 . 
       FIG. 16  illustrates a perspective view of the battery cell  50  including the vent flap  150  when a pressure in the casing  56  reaches the threshold value. When the pressure in the casing  56  reaches the threshold value, the vent flap  150  may be configured to open as shown in  FIG. 16 . Therefore, during normal operation when pressure is below the threshold, the vent flap  150  may be biased toward a closed position (e.g., the position shown in  FIG. 15 ). When the pressure in the casing  56  reaches the threshold value, the pressure force may be sufficient to overcome a biasing force of the vent flap  150  and urge the vent flap  150  to the open position (e.g., the position shown in  FIG. 16 ). In certain embodiments, the vent flap  150  may include a dual-door configuration such that the vent flap  150  opens down a crease  157  (e.g., shown in  FIG. 15 ) in a center of the vent flap  150  (e.g., as if the vent flap  150  is connected to the casing  56  via two hinges, one for each door). In other embodiments, the vent flap  150  may be configured to open as if connected to the casing  56  via a hinge. In still further embodiments, the vent flap  150  may be configured to open in any suitable manner that may move the second insulative component  154  from between the conductive spring  152  and the casing  56 . 
     Accordingly, when the pressure in the casing  56  reaches the threshold value, the vent flap  150  may move to the open position and move the second insulative component  154  such that it no longer is positioned between the conductive spring  152  and the casing  56 . When the second insulative component  154  is moved by the vent flap  150 , the conductive spring  152  may contact the casing  56  and establish an electrical connection between the negative terminal  54  and the casing  56 , and thus, between the negative terminal  54  and the positive terminal  52  (e.g., for a positively polarized casing). As discussed above, the electrical connection may cause a short circuit, which may lead to a discharge of electrical current from the cell  50 . Such an external short circuit may avoid thermal runaway within the battery cell  50  when the battery cell  50  is overcharged (e.g., during an overcharge test). The external short circuit may be triggered via contact between the casing  56  and the insulated negative terminal  54 . However, an electrical connection between the positive and/or negative terminal  52 ,  54  and an external load (e.g., another battery) is not disrupted (e.g., by breaking a connection between the terminal and the external load). 
       FIG. 17  illustrates a graphical representation  170  of data from an overcharge test performed on a battery cell utilizing an overcharge protection assembly of the present disclosure. The graph  170  includes a first curve  172  representing voltage  174  as a function of state of charge (SOC)  176  for a battery cell that includes the overcharge protection assembly. The first curve  172  shows how voltage  174  generally increases as SOC  176  increases for the battery cell including the overcharge protection assembly. However, as SOC  176  continues to increase, the pressure in the casing  56  of the battery cell also increases. As shown in the illustrated embodiment of  FIG. 17 , when the pressure reaches the threshold value, the overcharge protection assembly triggers an external short circuit by creating an electrical connection between the positive terminal  52  and the negative terminal  54  via the casing  56 . This is depicted at point  178  where the short circuit occurs and the voltage  174  of the battery cell decreases significantly. Accordingly, the battery cell  50  discharges, thereby preventing thermal runaway. 
     Conversely, a second curve  180  shows an effect on a battery cell that does not include an overcharge protection assembly of the present disclosure. Accordingly, the voltage  174  continues to increase beyond the point  178  as the SOC  176  increases. Eventually, thermal runaway occurs. Additionally, the graph  170  illustrates a third curve  184  representing a temperature  186  as a function of SOC  176  for a battery cell that includes the overcharge protection assembly. As shown, the temperature  186  also increases as SOC  176  increases. Additionally, at the point  178  (e.g., when the external short circuit is triggered), the temperature  186  continues to increase. However, the temperature  186  does not incur a significant spike. Rather, the temperature  186  increases to a maximum point  187 , and eventually decreases. Accordingly, thermal runaway does not occur. 
     Conversely, a fourth curve  188  illustrates the temperature  186  of a battery cell that does not include the overcharge protection assembly. As shown, the temperature  186  incurs a large increase where the voltage  174  spikes as a result of thermal runaway. Accordingly, the excessive temperature experienced by the battery cell may create permanent damage to the battery cell. Therefore, it is now recognized that the overcharge protection assembly of the present disclosure may prevent thermal runaway and may prevent permanent damage to the battery cell. 
     One or more of the disclosed embodiments, alone or in combination, may provide one or more technical effects useful in the manufacture of battery modules, and portions of battery modules. The disclosed embodiments relate to battery cells that include an overcharge protection assembly. The overcharge protection assembly may include a vent that opens (e.g., transitions from a first position to a second position) when a pressure in a casing of the battery cell reaches a threshold value. Accordingly, the opening of the vent may enable electrical contact between an insulated terminal and the battery cell casing, which may create an external circuit by electrically coupling the positive terminal and the negative terminal of the battery cell. Such an external short circuit may discharge the battery cell, but the external short circuit may prevent thermal runaway and/or permanent damage to the battery cell. Moreover, such an external short circuit may be triggered without disrupting electrical current from an external load to the positive and/or negative terminal. Therefore, a current capacity of the battery cell may not decrease. 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.