Patent Publication Number: US-2023133220-A1

Title: Secondary battery

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0150530, filed on Nov. 4, 2021 in the Korean Intellectual Property Office, the entire content of which is herein incorporated by reference. 
     BACKGROUND 
     1. Field 
     Aspects of embodiments of the present disclosure relate to a secondary battery. 
     2. Description of the Related Art 
     Unlike a primary battery that cannot be charged, a secondary battery is a rechargeable and dischargeable battery. A low-capacity secondary battery comprised of one single cell packaged in the form of a pack may be used for various portable small-sized electronic devices, such as cellular phones or camcorders, and a high-capacity secondary battery in which several tens of cells are connected in a battery pack is widely used as a power source for motor drives, such as those in hybrid vehicles or electric vehicles. 
     The secondary battery may be configured by incorporating into a case an electrode assembly provided by interposing a separator between a positive electrode and a negative electrode, and an electrolyte, and installing a cap plate on the case. Here, a representative example of the electrode assembly may be a winding type or a stack type. In such an electrode assembly, an uncoated portion tab may protrude in a lateral or upward direction, and a current collecting member may be connected to the uncoated portion tab. 
     The above information disclosed in this Background section is provided for enhancement of understanding of the background of the invention and, therefore, it may contain information that does not constitute prior art. 
     SUMMARY 
     According to an aspect of embodiments of the present disclosure, a secondary battery is capable of efficiently discharging internal heat to the outside through a vent hole in a short time by preventing or substantially preventing a vent hole blocking phenomenon by an electrode assembly when an event, such as bottom penetration, occurs in the secondary battery. 
     According to one or more embodiments of the present disclosure, a secondary battery includes: an electrode assembly; a case accommodating the electrode assembly; a cap plate sealing the case; and an insulating member between the electrode assembly and the cap plate, wherein a relationship of M/E&gt;R1 is satisfied, where M is a melting point (° C.) of the insulating member, E is an energy density (Wh/kg) of the secondary battery, and R1 is 0.5 to 3.5. 
     R1 may be 1 to 3. 
     R1 may be 0.6 to 3.5. 
     A relational expression R1*T&gt;R2 may be satisfied, where T is a time (seconds) taken for heat to be propagated to another secondary battery adjacent to the secondary battery, and R2 is 10 to 170. 
     R2 may be 50 to 80. 
     R2 may be 46 to 170. 
     The insulating member may include polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenylene (PP), or polyether ether ketone (PEEK). 
     The insulating member may further include a member vent hole, and the cap plate may include a plate vent hole provided in a region corresponding to the member vent hole and a safety vent may be attached to the plate vent hole. 
     A relational expression (A1/A2)/E&lt;R3 may be satisfied, where A1 is a size of the insulating member (mm 2 ), A2 is a size of the member vent hole (mm 2 ), and R3 is 0.01 to 0.1 
     The size of the member vent hole may be the same as or smaller than that of the plate vent hole. 
     The insulating member may be in close contact with the cap plate and may be spaced apart from the electrode assembly. 
     The member vent hole may be blocked by the safety vent. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view illustrating a secondary battery according to an embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view of a secondary battery according to an embodiment of the present disclosure. 
         FIG.  3    is a perspective view illustrating a battery module to which the secondary battery of  FIG.  1    is applied, according to an embodiment of the present disclosure. 
         FIG.  4    is a perspective view illustrating a relationship between a cap plate and an insulating member in a secondary battery according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Herein, some embodiments of the present invention will be described in further detail with reference to the accompanying drawings. 
     Some examples of the present invention are provided to more completely explain the present invention to those skilled in the art; however, the following examples may be modified in various other forms. That is, the present invention may be embodied in many different forms and should not be construed as being limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete and will convey the aspects and features of the present invention to those skilled in the art. 
     In addition, in the accompanying drawings, sizes or thicknesses of various components may be exaggerated for brevity and clarity. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. In addition, it is to be understood that when an element A is referred to as being “connected to” an element B, the element A may be directly connected to the element B or one or more intervening elements C may be present therebetween such that the element A and the element B are indirectly connected to each other. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is to be further understood that the terms “comprise” and/or “comprising” when used in this specification, specify the presence of stated features, numbers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof. 
     It is to be understood that, although the terms “first,” “second,” etc. may be used herein to describe various members, elements, regions, layers, and/or sections, these members, elements, regions, layers, and/or sections should not be limited by these terms. These terms are used to distinguish one member, element, region, layer, and/or section from another. Thus, for example, a first member, a first element, a first region, a first layer, and/or a first section discussed below could be termed a second member, a second element, a second region, a second layer, and/or a second section without departing from the teachings of the present invention. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It is to be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the element or feature in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “on” or “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. 
     Here, the same reference numerals are given to parts having similar configurations and operations throughout the specification. In addition, when a part is said to be connected, coupled, or electrically coupled with another part, this includes not only the case in which it is directly connected, coupled, or electrically coupled, but also the case in which it is connected, coupled, or electrically coupled with one or more other elements interposed therebetween. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the inventive concept pertains. It is also to be understood that terms defined in commonly used dictionaries should be interpreted as having meanings consistent with the meanings in the context of the related art, and are expressly defined herein unless they are interpreted in an ideal or overly formal sense. 
       FIGS.  1  and  2    are a perspective view and a cross-sectional view of a secondary battery according to an embodiment.  FIG.  3    is a perspective view of a battery module in which the secondary battery of  FIG.  1    is alternately disposed with an insulating sheet. 
     In the embodiment shown in  FIGS.  1  and  2   , a secondary battery  100  according to an embodiment may include an electrode assembly  110 , a first terminal  120 , a second terminal  130 , a case, or can,  140 , a cap assembly  150 , and an insulating member  160 . 
     The electrode assembly  110  may be provided by winding or overlapping a laminate of a first electrode plate  111 , a separator  113 , and a second electrode plate  112 , which are in forms of a thin plate or film. In some examples, the electrode assembly  110  may have a winding axis in a horizontal direction (that is, a direction parallel or substantially parallel to a longitudinal direction of the cap assembly  150  and the insulating member  160 ) or may be wound in a vertical direction (that is, a direction perpendicular or substantially perpendicular to the cap assembly  150  and the insulating member  160 ). In some examples, the electrode assembly  110  may be of a winding type or a stack type. In some examples, the electrode assembly  110  may be stacked such that two or more electrode assemblies  110  have long sides adjacent to each other. 
     In some examples, the first electrode plate  111  of the electrode assembly  110  may function as a negative electrode, and the second electrode plate  112  may function as a positive electrode. However, the reverse is also possible. 
     In some examples, the first electrode plate  111  may be provided by coating a first electrode active material, such as graphite or carbon, on a first electrode current collector provided as a metal foil, such as copper, a copper alloy, nickel, or a nickel alloy, and may include a first electrode tab (or a first uncoated portion)  111   a  to which the first electrode active material is not applied. The first electrode tab  111   a  may be a passage for current flow between the first electrode plate  111  and the first terminal  120 . 
     In some examples, the first electrode tab  111   a  may be provided by being cut to protrude from a side in advance when the first electrode plate  111  is manufactured, and may be formed integrally with the first electrode plate  111 . 
     In some examples, a plurality of first electrode tabs  111   a  may be collected and welded (e.g., tack-welded), and a first current collector plate  121  of the first terminal  120  may be welded to the welded (e.g., tack-welded) first electrode tab  111   a  to then be coupled thereto. 
     In some examples, the second electrode plate  112  is provided by coating a second electrode active material, such as a transition metal oxide, on a second electrode current collector provided with a metal foil, such as aluminum or an aluminum alloy, and may include a second electrode tab (or a second uncoated portion)  112   a  to which the second electrode active material is not applied. The second electrode tab  112   a  may be a passage for current flow between the second electrode plate  112  and the second terminal  130 . 
     In some examples, the second electrode tab  112   a  may be provided by being cut to protrude from a side in advance when the second electrode plate  112  is manufactured, and may be formed integrally with the second electrode plate  112 . 
     In some examples, a plurality of second electrode tabs  112   a  may be collected and welded (e.g., tack-welded), and a second current collector plate  131  of the second terminal  130  may be welded to the welded (e.g., tack-welded) second electrode tab  112   a  to then be coupled thereto. 
     In some examples, the first electrode tab  111   a  may be located on a short side end of the electrode assembly  110 , and the second electrode tab  112   a  may be located on another short side end of the electrode assembly  110 . 
     In some examples, the separator  113 , which is positioned between the first electrode plate  111  and the second electrode plate  112 , may prevent or substantially prevent a short circuit and enable the movement of lithium ions, and may include polyethylene, polypropylene, or a composite film of polyethylene and polypropylene. In some examples, the separator  113  may be replaced with an inorganic solid electrolyte, such as a sulfide-based, oxide-based, or phosphate compound-based electrolyte that does not require a liquid or gel electrolyte. 
     In some examples, the first terminal  120  and the second terminal  130 , which are respectively electrically connected to the first electrode uncoated portion  111   a  of the first electrode plate  111  and the second electrode uncoated portion  112   a  of the second electrode plate  112 , may be positioned at opposite ends of the electrode assembly  110 . 
     In some examples, the electrode assembly  110  may be accommodated in the case  140  together with an electrolyte. In some examples, the electrolyte may include a lithium salt, such as LiPF 6  or LiBF 4 , in an organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), or dimethyl carbonate (DMC). In addition, the electrolyte may be in liquid or gel phase. In some examples, when an inorganic solid electrolyte is used, the electrolyte may be omitted. 
     The first terminal  120  may be provided as a metal and may be electrically connected to the first electrode plate  111 . In some examples, the first terminal  120  may include the first current collector plate  121 , a first terminal post  122 , and a first terminal plate  124 . In some examples, the first current collector plate  121  may be in contact with the first electrode uncoated portion  111   a  protruding from an end of the electrode assembly  110 . The first current collector plate  121  may be welded to the first electrode uncoated portion  111   a . In some examples, the first current collector plate  121  is provided in an approximately “ ” shape, and a terminal hole  121   a  may be provided at an upper portion thereof. In some examples, the first terminal post  122  may be inserted into the terminal hole  121   a  to be riveted and/or welded. In some examples, the first current collector plate  121  may be made of copper or a copper alloy. 
     In some examples, the first terminal post  122  may protrude and extend by a length (e.g., a predetermined length) upward through a cap plate  151  of the cap assembly  150  and may be electrically connected to the first current collector plate  121  under the cap plate  151 . In addition, in some examples, the first terminal post  122  may protrude and extend by a length (e.g., a predetermined length) upward from the cap plate  151 , and a flange  122   a  may be provided under the cap plate  151  to prevent or substantially prevent the first terminal post  122  from being dislodged from the cap plate  151 . In the first terminal post  122 , a region positioned below the flange  122   a  may be inserted into the first terminal hole  121   a  of the first current collector plate  121  and then riveted and/or welded. In some examples, the first terminal post  122  may be made of copper, a copper alloy, aluminum, or an aluminum alloy. 
     The first terminal plate  124  may have a hole  124   a , and the first terminal post  122  may be coupled to the hole  124   a , and then be riveted and/or welded. In some examples, an interface between the first terminal post  122  that is exposed upward and the first terminal plate  124  may be welded to each other. For example, by providing a laser beam to boundary regions of the first terminal post  122  that is exposed upward and the first terminal plate  124 , the boundary regions may be melted and then cooled and welded to each other. In some examples, the first terminal post  122  and the first terminal plate  124  may be electrically insulated from the cap plate  151 . 
     The second terminal  130  may also be made of a metal and may be electrically connected to the second electrode plate  112 . In some examples, the second terminal  130  may include the second current collector plate  131 , a second terminal post  132 , and a second terminal plate  134 . The second current collector plate  131  may be in contact with the second electrode uncoated portion  112   a  protruding from an end of the electrode assembly  110 . In some examples, the second current collector plate  131  may be provided in an approximately “ ” shape, and a terminal hole  131   a  may be provided at an upper portion thereof. In some examples, the second terminal post  132  is fitted and coupled to the terminal hole  131   a . The second current collector plate  131  may be made of, for example, but is not limited to, aluminum or an aluminum alloy. The second terminal post  132  may protrude and extend upward by a length (e.g., a predetermined length) through the cap plate  151 , to be described later, and may be electrically connected to the second current collector plate  131  under the cap plate  151 . The second terminal post  132  may protrude and extend by a length (e.g., a predetermined length) upward from the cap plate  151 , and a flange  132   a  may be provided under the cap plate  151  to prevent or substantially prevent the second terminal post  132  from being dislodged from the cap plate  151 . In the second terminal post  132 , a region positioned below the flange  132   a  may be inserted into a second terminal hole  131   a  of the second current collector plate  131  and then riveted and/or welded. 
     In some examples, the second terminal post  132  may be made of aluminum or an aluminum alloy. The second terminal plate  134  may have a hole  134   a . In addition, the second terminal plate  134  may be coupled to the second terminal post  132 . That is, the second terminal post  132  may be coupled to the hole  134  of the second terminal plate  134 . In addition, the second terminal post  132  and the second terminal plate  134  may be riveted and/or welded to each other. In some examples, boundary regions of the second terminal post  132  that is exposed upward and the second terminal plate  134  may be welded to each other. For example, by providing a laser beam to boundary regions of the second terminal post  132  that is exposed upward and the second terminal plate  134 , the boundary regions may be melted and then cooled and welded to each other. 
     In some examples, the second terminal post  132  and the second terminal plate  134  may be electrically insulated from the cap plate  151 . In some examples, the second terminal post  132  and the second terminal plate  134  may be electrically connected to the cap plate  151 . Here, the cap plate  151  of the cap assembly  150  may have a same polarity (e.g., a positive polarity) as the second terminal  130 . 
     In some examples, the case  140  may be shaped of a substantially hollow rectangular parallelepiped having an opening therein. Through the opening, the electrode assembly  110  may be inserted into the case  140 . In addition, the first current collector plate  121  of the first terminal  120  and the second current collector plate  131  of the second terminal  130  may also be located inside the case  140 . In some examples, the case  140  may include a rectangular bottom surface  141  and four side surfaces  142  that extend in or approximately in the vertical direction from four sides of the bottom surface  141 . 
     The cap assembly  150  may be coupled to the case  140 . In some examples, the cap assembly  150  may include the cap plate  151 , a seal gasket  152 , a plug  153 , a safety vent  154 , and an upper coupling member  155 . 
     The cap plate  151  may seal the opening of the case  140  and may be made of a same material as the case  140 . In some examples, the cap plate  151  may be coupled to the case  140  by laser welding. In some examples, the cap plate  151  may have a same polarity as the second terminal  130  as described above, and, thus, the cap plate  151  and the case  140  may have the same polarity. 
     The cap plate  151  may further include an electrolyte injection hole  151   a  and a plate vent hole  151   b , which pass through between upper and lower surfaces of the cap plate  151 . The cap plate  151  may further include a first terminal hole  156  and a second terminal hole  157  (see  FIG.  4   ), through which the first terminal post  122  and the second terminal post  132  pass. 
     The seal gasket  152  made of an insulating material is provided between the cap plate  151  and the first terminal post  122  of the first terminal  120  and between the cap plate  151  and the second terminal post  132  of the second terminal  130 , to seal between each of the first terminal post  122  and the second terminal post  132  and the cap plate  151 . The seal gasket  152  prevents or substantially prevents external moisture from penetrating into the secondary battery  100  and prevents or substantially prevents the electrolyte contained in the secondary battery  100  from leaking to the outside. 
     The plug  153  may seal the electrolyte injection hole  151   a  after the electrolyte is injected into the case  140  through the electrolyte injection hole  151   a  of the cap plate  151 . The safety vent  154  may be installed in the plate vent hole  151   b  of the cap plate  151  and may include a notch  154   x  to be opened at a certain pressure (e.g., a set pressure). 
     The upper coupling member  155  may be provided between each of the first terminal post  122  and the second terminal post  132  and the cap plate  151  on an upper portion of the cap plate  151 . Also, the upper coupling member  155  may be in close contact with the cap plate  151 . Further, the upper coupling member  155  may also be in close contact with the seal gasket  152 . The upper coupling member  155  may insulate the first terminal post  122  and the second terminal post  132  from the cap plate  151 . In some examples, the upper coupling member  155  that is interposed between the second terminal plate  134  and the cap plate  151  may electrically connect the second terminal plate  134  and the cap plate  151  to each other, and, thus, the cap plate  151  may have the same polarity as the second terminal  130 . 
     As shown in  FIG.  3   , a battery module  10  may include a plurality of secondary batteries  100  and an insulating sheet  200  interposed between the secondary batteries  100 . The insulating sheet  200  may be interposed between long sides of pairs of adjacent secondary batteries  100 . The battery module  10  may further include an end plate and a side plate surrounding the plurality of secondary batteries  100 . In some examples, the insulating sheet  200  may include an insulating material, such as mica, capable of blocking heat propagation between two adjacent secondary batteries  100 . 
       FIG.  4    is a perspective view illustrating a relationship between the cap plate  150  and the insulating member  160  in the secondary battery  100  according to an embodiment of the present disclosure. Here, reference is also made to  FIG.  2   . 
     The insulating member  160  may be provided in a size approximately corresponding to the size of the cap plate  151 . In some examples, the insulating member  160  may be an approximately rectangular flat plate. In some examples, the insulating member  160  may be in close contact with a lower surface of the cap plate  151  and may be spaced apart from the electrode assembly  110  by a distance (e.g., a predetermined distance). In some examples, the insulating member  160  may include an electrolyte injection hole  161   a  and a member vent hole  161   b  provided at positions corresponding to the electrolyte injection hole  151   a  and the plate vent hole  151   b  provided in the cap plate  151 . In some examples, electrolyte injection holes  161   a  are provided on both sides of the member vent hole  161   b , and, thus, the electrolyte may be easily injected regardless of the assembly direction of the insulating member  160  during a battery assembling process. In some examples, the insulating member  160  may further include a first terminal hole  162  and a second terminal hole  163  provided at positions corresponding to the first terminal hole  156  and the second terminal hole  157  of the cap plate  151 . 
     In this way, the insulating member  160  may prevent or substantially prevent an undesired short circuit between the first current collector plate  121  and the cap plate  151 , and may prevent or substantially prevent an undesired short circuit between the second current collector plate  131  and the cap plate  151 . In addition, the insulating member  160  may also prevent or substantially prevent an undesired short circuit between the electrode assembly  110  and the cap plate  151 . 
     In some examples, between a melting point M (° C.) of the insulating member  160  and an energy density E (Wh/kg) of the secondary battery  100 , a relationship of M/E&gt;R1 may be satisfied. In an embodiment, R1 is approximately 0.5 to approximately 3.5, and, in an embodiment, approximately 1 to approximately 3, and, in an embodiment, approximately 0.6 to approximately 3.5. 
     For example, when R1 is less than approximately 0.5, the melting point and/or tensile strength of the insulating member  160  is relatively low, compared to the energy density of the secondary battery  100 , and, thus, when an event occurs in the secondary battery  100  (for example, when the bottom of the secondary battery is penetrated by a nail), the insulating member  160  may be melted at a relatively low temperature. Accordingly, during an event of the secondary battery  100 , the insulating member  160  may be melted, and the plate vent hole  151   b  of the cap plate  151  may be directly blocked by the electrode assembly  110 . Thus, the internal heat of the secondary battery  100  may not be quickly discharged to the outside, such that the cap plate  151  may be blasted, or the case  140  may be damaged. In addition, heat may be quickly propagated from the secondary battery where the event has occurred to another secondary battery adjacent thereto, such that a chain of events may occur. 
     According to embodiments, when R1 is approximately 0.5 to approximately 3.5, a melting point and/or tensile strength of the insulating member  160  is relatively high, compared to the energy density of the secondary battery  100 , and, thus, when an event occurs in the secondary battery  100  (for example, when the bottom of the secondary battery is damaged by a nail), the insulating member  160  may not be melted. Accordingly, during an event of the secondary battery  100 , the insulating member  160  is not melted and maintains a certain shape (e.g., a predetermined shape), thereby quickly discharging the internal heat of the secondary battery  100  to the outside through the member vent hole  161   b  of the insulating member  160  and the plate vent hole  151   b  of the cap plate  151 , and, thus, the cap plate is not blasted, and the case  140  is not damaged. In addition, heat is not propagated from the secondary battery  100  where an event has occurred to another secondary battery adjacent thereto, thereby preventing or substantially preventing a chain of events from occurring. 
     In some examples, it may be difficult in practice to provide materials having R1 greater than approximately 3.5. In some examples, a material having R1 greater than 3.5 may be a ceramic or a metal, which not only increases the weight of the secondary battery but also causes additional problems inside the secondary battery (e.g., an internal short circuit) when the secondary battery is deformed. 
     In some examples, the insulating member  160  may include a resin having a relatively high tensile strength and/or melting point. In some examples, the insulating member  160  may include polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenylene (PP), or polyether ether ketone (PEEK). 
     The properties of these materials are summarized in Table 1 below. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Melting 
                 Heat Deflection 
               
               
                   
                 Resin 
                 Temperature (Tm, ° C.) 
                 Temperature (HDT, ° C.) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 PTFE 
                 327 
                 260 
               
               
                   
                 PPS 
                 285 
                 265 
               
               
                   
                 PP 
                 165 
                 120 
               
               
                   
                 PEEK 
                 340 
                 260 
               
               
                   
                   
               
            
           
         
       
     
     In some examples, a relational expression R1*T&gt;R2 between R1 and a time (T, sec) taken for heat to be propagated to another secondary battery adjacent to the secondary battery is satisfied, and, in an embodiment, R2 is approximately 10 to approximately 170, and, in an embodiment, approximately 50 to approximately 80, and, in an embodiment, approximately 46 to approximately 170. 
     When R2 is approximately 10 to approximately 170, a sufficiently long time is taken for heat to be propagated from the secondary battery where an event has occurred to another secondary battery adjacent thereto, thereby preventing or substantially preventing a chain of events from occurring. When R2 is smaller than approximately 10, a short time is taken for heat to be propagated from the secondary battery where an event has occurred to another secondary battery adjacent thereto, such that a chain of events may occur in a battery module. When R2 is greater than approximately 170, it may be difficult in practice to provide materials satisfying this condition. 
     In some examples, between a size of the insulating member A1 (mm 2 ), a size of the member vent hole A2 (mm 2 ), and the energy density of the secondary battery E (Wh/kg), a relational expression (A1/A2)/E&lt;R3 is satisfied, and, in an embodiment, R3 is approximately 0.01 to approximately 0.1 and, in an embodiment, approximately 0.01 to approximately 0.07. In some examples, a size of the member vent hole  161   b  may be the same as or smaller than that of the plate vent hole  151   b . In some examples, the member vent hole  161   b  may be blocked by the safety vent  154 . 
     When R3 is less than approximately 0.01, due to an increase in the size of the safety vent  154 , it may not be easy to provide the first and second terminal plates  124  and  134  and the electrolyte injection hole  151   a  on the cap plate  151 . In addition, when R3 is greater than approximately 0.1, during occurrence of an event, heat may not be easily discharged through the safety vent  154 , and, thus, there is a risk of rupture, thermal runaway, or ignition and explosion. For example, when R3 is less than approximately 0.07, during occurrence of an event, heat may be easily discharged through the safety vent  154 . In some examples, a rupture pressure of the notch  154   x  of the safety vent  154  may be approximately 10 kgf/cm 2 . 
     Meanwhile, hazard levels of a secondary battery may be categorized from 0 to 7, and the secondary battery  100  according to embodiments of the present disclosure may be managed at a hazard level of 5 or less. For reference, the state of the secondary battery for each hazard level may be summarized as shown in Table 2 below. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                 Hazard level 0 
                 No change (No effect, no loss of functionality) 
               
               
                 Hazard level 1 
                 Passive protection enabled (No defect, no leakage; no 
               
               
                   
                 venting, no fire or flame; no rupture; no explosion; no 
               
               
                   
                 exothermic reaction or thermal runaway. Cell reversibly 
               
               
                   
                 damaged →Repair of protection needed) 
               
               
                 Hazard level 2 
                 Defect/damage (No leakage; no venting, no fire or flame; 
               
               
                   
                 no rupture; no explosion; no exothermic reaction or 
               
               
                   
                 runaway. Cell irreversibly damaged →Repair needed 
               
               
                 Hazard level 3 
                 Leakage mass &lt; 50% (No venting, no fire or flame; no 
               
               
                   
                 rupture; no explosion. Weight loss &lt; 50% of electrolyte 
               
               
                   
                 (solvent + salt) weight) 
               
               
                 Hazard level 4 
                 Venting mass ≥ 50% (No fire or flame; no rupture; no 
               
               
                   
                 explosion. Weight loss ≥ 50% of electrolyte (solvent + 
               
               
                   
                 salt) weight) 
               
               
                 Hazard level 5 
                 Fire or flame (No rupture; no explosion (i.e. no flying 
               
               
                   
                 parts)) 
               
               
                 Hazard level 6 
                 Rupture (No explosion, but flying parts of active mass) 
               
               
                 Hazard level 7 
                 Explosion 
               
               
                   
               
            
           
         
       
     
     As described above, according to embodiments of the present disclosure, an insulating member having a high melting point and tensile strength is interposed between an electrode assembly and a cap plate, thereby preventing or substantially preventing a vent hole blocking phenomenon by the electrode assembly when an event (e.g., bottom penetration, etc.) occurs in a secondary battery. Accordingly, the internal heat of the secondary battery can be efficiently and quickly discharged to the outside through the insulating member and the vent hole of the cap plate in a short time when an event occurs in the secondary battery. 
     In addition, since the heat of the secondary battery is quickly discharged to the outside through the vent hole when an event occurs in the secondary battery, blast of the cap plate or rupture of the case, or can, may be prevented or substantially prevented. 
     In addition, by delaying a time taken for heat to be propagated to another secondary battery adjacent to the secondary battery, it is possible to suppress a chain of events from occurring in other adjacent secondary batteries. 
     While one or more embodiments have been described herein, the present disclosure is not limited thereto, and it will be understood by a person skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as set forth in the following claims.