Patent Publication Number: US-2021167460-A1

Title: Secondary Battery and Battery Pack Including the Same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/KR2020/004752, filed on Apr. 8, 2020, published in Korean, which claims priority from Korean Patent Application No. 10-2019-0066143, filed on Jun. 4, 2019, all of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a secondary battery and a battery pack including the secondary battery, and more particularly, to a secondary battery having a structure in which, when an internal pressure of the secondary battery increases, a gas within the secondary battery is discharged in a desired direction, and a battery pack including the secondary battery. 
     BACKGROUND ART 
     Secondary batteries that are repetitively chargeable and dischargeable may be classified into cylindrical type secondary batteries, prismatic type secondary batteries, and pouch type secondary batteries according to their structures or manufacturing methods. Among them, the pouch type secondary battery has a structure in which an electrode assembly having a structure in which electrodes and separators are alternately disposed in a sheet-shaped pouch exterior is accommodated. In particular, the pouch type secondary battery has been widely used due to its relatively simple process and low manufacturing cost. 
     A pressure within the secondary battery may increase due to an abnormal operation of the secondary battery. Particularly, when the pressure within the secondary battery abnormally increases, there is a possibility of explosion of the secondary battery. In order to prevent the secondary battery from being exploded, when the pressure within the secondary battery exceeds a certain value, it is necessary to discharge a gas within the secondary battery to the outside. 
     However, since the gas within the secondary battery is in a high-temperature and high-pressure state, if the gas within the secondary battery is discharged to a wrong direction, structures around the secondary battery may be damaged. In order to prevent such a problem, it is necessary to design the secondary battery so that the gas within the secondary battery is discharged through a certain path. 
     DISCLOSURE OF THE INVENTION TECHNICAL PROBLEM 
     Therefore, an object to be achieved by the present invention is to prevent structures around a secondary battery from being damaged by discharging a gas within the secondary battery through a certain path when a pressure within the secondary battery abnormally increases. 
     Technical Solution 
     According to one aspect of the prevent invention for achieving the above object, a secondary battery includes: an electrode assembly having a structure in which electrodes and separators are alternately disposed; an exterior having an inner space in which the electrode assembly is accommodated; a waterproof part provided within the exterior to surround at least a portion of a circumference of the electrode assembly and configured to allow a gas to pass through the waterproof part, but prevent a liquid from passing through the waterproof part; and a vent part provided at a first portion of the exterior to provide a path through which gas within the exterior is discharged to an outside when an internal pressure of the exterior exceeds a predetermined value. 
     The exterior may include two sheets that face each other, each of the two sheets having a circumferential part, and a first portion of the circumferential part extends away from the first portion of the exterior at which the vent is provided. 
     The secondary battery may further include an electrode lead protruding outward from a second portion of the exterior different from the first portion of the exterior at which the vent is provided. 
     The waterproof part may surround an entire circumference of the electrode assembly. 
     The vent part may include a first vent member and a second vent member, which face each other, and a distance between the first vent member and the second vent member may decrease in an outward direction of the exterior. 
     One end of the first vent member and one end of the second vent member, which extend in the outward direction, may contact each other to block the path through which the gas within the exterior is discharged to the outside, and when the internal pressure of the exterior exceeds the predetermined value, the one end of the first vent member and the one end of the second vent member may be spaced apart from each other to provide the path through which the gas within the exterior is discharged to the outside. 
     The secondary battery may further include an elastic part provided between an inner surface of the circumferential part and the vent part to press the vent part by elastic force. 
     The elastic part may include: a first elastic member provided between the inner surface of the circumferential part and the first vent member to press the first vent member by the elastic force; and a second elastic member provided between the inner surface of the circumferential part and the second vent member to press the second vent member by the elastic force. 
     When the internal pressure of the exterior decreases below the predetermined value, the one end of the first vent member and the one end of the second vent member may contact each other to block the path through which the gas within the exterior is discharged to the outside. 
     A second portion of the circumferential part of the two sheets may be bonded to each other to provide a sealing part, and the first portion of the two sheets of the circumferential part may not be bonded to each other, or may be bonded to each other with a bonding force that is less than that of the sealing part on the second portion of the two sheets. 
     According to another aspect of the prevent invention for achieving the above object, a battery pack including the secondary battery is provided. 
     The exterior may include two sheets that face each other, each of the two sheets having a circumferential part, and a first portion of the circumferential part extends away from the first portion of the exterior at which the vent part may be provided. 
     Advantageous Effects 
     According to the present invention, when the pressure within the secondary battery abnormally increases, the gas within the secondary battery may be discharged through the certain path to prevent the structure around the secondary battery from being damaged. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a structure of a secondary battery according to an embodiment of the present invention. 
         FIG. 2  is a side cross-sectional view illustrating a normal state of an upper structure of a secondary battery according to a first embodiment of the present invention. 
         FIG. 3  is a side cross-sectional view illustrating a state of the upper structure of the secondary battery when an internal pressure of the secondary battery exceeds a certain value according to a first embodiment of the present invention. 
         FIG. 4  is a side cross-sectional view illustrating a state of an upper structure of a secondary battery according to a second embodiment of the present invention. 
         FIG. 5  is a side cross-sectional view illustrating a state of an upper structure of a secondary battery according to a third embodiment of the present invention. 
         FIG. 6  is an enlarged side cross-sectional view of a region A of  FIG. 5 . 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, a secondary battery and a structure of a battery pack according to the present invention will be described with reference to the drawings. 
     Secondary Battery 
       FIG. 1  is a perspective view illustrating a structure of a secondary battery according to an embodiment of the present invention, and  FIG. 2  is a side cross-sectional view illustrating a normal state of an upper structure of a secondary battery according to a first embodiment of the present invention.  FIG. 3  is a side cross-sectional view illustrating a state of the upper structure of the secondary battery when an internal pressure of the secondary battery exceeds a certain value according to a first embodiment of the present invention, and  FIG. 4  is a side cross-sectional view illustrating a state of an upper structure of a secondary battery according to a second embodiment of the present invention. 
     As illustrated in  FIGS. 1 and 3 , a secondary battery  10  according to the present invention may include an electrode assembly  100 . The electrode assembly  100  may have a structure in which electrodes and separators are alternately disposed. 
     Also, the secondary battery  10  may include an exterior  200  having an inner space in which the electrode assembly  100  is accommodated. The exterior  200  may have a pouch type exterior. That is, the secondary battery according to the present invention may be a pouch type secondary battery. 
     Continuously, referring to  FIGS. 1 to 3 , the exterior  200  of the secondary battery  10  according to the present invention may include a first exterior sheet  210   a  and a second exterior sheet  220   a . Also, the secondary battery  10  according to the present invention may include a circumferential part  200   a  at which the first exterior sheet  210   a  and the second exterior sheet  220   a  of the exterior  200  face each other. The circumferential part  200   a  may have a structure in which ends of the first exterior sheet  210   a  and the second exterior sheet  220   a  face each other. The circumference  200   a  may be disposed on at least one surface of outer surfaces of the exterior  200 .  FIG. 1  illustrates a state in which the circumferential part  200   a  is disposed on each of a top surface and a bottom surface of the exterior  200 . 
     In addition, the secondary battery  10  according to the present invention may further include an electrode lead  300  protruding from one surface of the exterior  200 . The electrode lead  300  is configured to be electrically connected to an electrode tab (not shown) of the electrode assembly  100  and may have a structure that protrudes outward from one surface of inner surfaces of the exterior  200 .  FIG. 1  illustrates a state in which two electrode leads  300  protrude in opposite directions. 
     As illustrated in  FIGS. 2 and 3 , the secondary battery  10  according to the present invention may include a vent part  400  that provides a path through which a gas within the exterior  200  is discharged to the outside when an internal pressure of the exterior  200  exceeds a certain value. 
     The vent part  400  may include a first vent member  410  and a second vent member  420 . Here, the first vent member  410  and the second vent member  420  may be disposed to symmetrically face each other. 
     The vent part  400  may be provided in an inner surface corresponding to an outer surface on which the circumferential part  200   a  is disposed, among the inner surfaces of the exterior  200 .  FIGS. 2 and 3  illustrate a state in which the vent part  400  is provided in the inner surface corresponding to the upper outer surface on which the circumferential part  200   a  is disposed among the inner surfaces of the exterior  200 . 
     Also, the first vent member  410  and the second vent member  420  may extend outward from the exterior  200 . Here, a distance between the first vent member  410  and the second vent member  420  may gradually decrease as closer to the outside of the exterior  200  from the inside of the exterior  200 . Also, as illustrated in  FIG. 2 , since one end of the first vent member  410  and one end of the second vent member  420 , which extend outward from the exterior  200 , contact each other, the path through which the gas within the exterior  200  passes through the vent part  400  and is discharged to the outside may be blocked in ordinary time. 
     Continuously, referring to  FIGS. 2 and 3 , the vent part  400  may be provided in the inner surface except for the inner surface, from which the electrode lead  300  protrudes, among the inner surfaces of the exterior  200 . 
     When the vent part is provided in the inner surface from which the electrode lead protrudes, the gas may contact the electrode lead while the gas within the secondary battery is discharged to the outside through the vent part. In this case, the electrode lead may be deformed or damaged by a temperature and pressure of the gas that is discharged to the outside through the vent part. Thus, according to the present invention, the vent part  400  may be provided in the inner surface except for the inner surface, through which the electrode lead  300  protrudes, among the inner surfaces of the exterior  200 . 
     The principle in which the gas within the secondary battery  10  is discharged to the outside through the vent part  400  according to the present invention is as follows. 
     When the internal pressure of the exterior  200  exceeds a certain value due to an abnormal operation of the secondary battery  10 , as illustrated in  FIG. 3 , the one end of the first vent member  410  and the one end of the second vent member  420 , which are in a state of contacting each other in the ordinary time, are spaced apart from each other by the internal pressure of the exterior  200 , and thus, the gas within the secondary battery  10  is discharged to the outside. 
     That is, when the internal pressure of the exterior  200  exceeds a fixed one value in a region adjacent to the vent part  400 , the secondary battery  10  may be manufactured so that the first vent part  410  and the second vent part  420  of the vent part  400  are spaced apart from each other. For example, when the internal pressure of the exterior  200  exceeds a specific value A in the region adjacent to the vent part  400 , the first vent member  410  and the second vent member  420  may be spaced apart from each other, and thus, the gas within the secondary battery  10  may be discharged to the outside. 
     When the gas within the exterior  200  is discharged, and thus, the internal pressure of the exterior  200  decreases again below the certain value, the one end of the first vent member  410  and the one end of the second vent member  420  may contact again each other to block again the path through which the gas within the exterior  200  is discharged to the outside. That is, the first vent member  410  and the second vent member  420  of the vent part  400  according to the present invention may be configured so that the contact and space therebetween is repeatedly performed according to the internal pressure of the exterior  200 . 
     According to the present invention, since the vent part  400  is provided in the secondary battery  10 , when the pressure inside the secondary battery increases abnormally, the gas within the secondary battery  10  may be discharged to the outside through the certain path provided by the opening vent part  400 . Thus, according to the present invention, it is possible to prevent unexpected damage of structures around the secondary battery, which may occur when the path through which the gas within the secondary battery is discharged is not constant. 
     Referring to  FIGS. 1 to 3 , in the secondary battery  10  according to the present invention, two sheets of exterior sheets may be bonded to each other on at least a portion of the circumferential surface  200   a . That is, according to the present invention, the first exterior sheet  210   a  and the second exterior sheet  220   a  may be bonded to each other to provide a sealing part on the circumferential part except for the circumferential part disposed on the outer surface corresponding to the inner surface, in which the vent part  400  is provided, on the circumferential part  200   a . Referring to  FIG. 1 , the first exterior sheet  210   a  and the second exterior sheet  220   a  may be bonded to each other to provide the sealing part at the circumferential part  200   a  disposed on the bottom surface of the exterior  200 . 
     On the other hand, in the secondary battery  10  according to the present invention, the two sheets of exterior sheets may not be bonded to each other or may be bonded to each other with bonding force less than that of the sealing part at the other portion of the circumferential part  200   a . Referring to  FIG. 1 , the first exterior sheet  210   a  and the second exterior sheet  220   a  may not be bonded to each other or may be bonded to each other with bonding force less than that of the sealing part at the circumferential part  200   a  disposed on the top surface of the exterior  200 . In this case, when the internal pressure of the exterior  200  exceeds the certain value, the gas within the exterior  200  may be quickly discharged to the outside through the vent part  400  before the other region of the exterior is broken. 
     The secondary battery  10  according to the present invention may further include a waterproof part  500  provided in the exterior  200  to surround at least a portion of a circumference of the electrode assembly  100 . The waterproof part  500  may be configured to allow the gas within the exterior  200  to pass therethrough and allow a liquid within the exterior  200  so as not to pass therethrough. The waterproof part  500  may have a waterproof property and may be fabric having a mesh structure. 
     As illustrated in  FIG. 2 , the waterproof part  500  may be provided to face the inner surface, in which the vent part  400  is provided, among the inner surfaces of the exterior  200 .  FIG. 2  illustrates a state in which the waterproof part  500  is provided to face the upper inner surface of the exterior  200  in which the vent part  400  is provided. 
     According to the present invention, since the waterproof part  500  is provided to face the inner surface, in which the vent part  400  is provided, among the inner surfaces of the exterior  200 , when the internal pressure of the exterior  200  exceeds a certain value, the gas within the secondary battery  10  may be discharged to the outside via the vent part  400  and the circumferential part  200   a  after passing through the waterproof part  500 , but the liquid (for example, an electrolyte) within the secondary battery  10  may not be discharged to the outside, or discharge of the liquid to the outside may be minimized. 
     A main effect on the internal pressure of the exterior  200  of the secondary battery  10  may be affected to the gas, not the liquid, within the secondary battery  10 . Particularly, when the electrolyte leaks to the outside, the secondary battery may not properly operate. Thus, according to the present invention, when the internal pressure of the exterior exceeds a certain value, only the gas affected by the main effect of the internal pressure of the exterior  200  may be discharged to the outside. As a result, even though the internal pressure of the exterior  200  increases abnormally, the operation of the secondary battery  10  may be stopped due to the discharge of the liquid within the secondary battery. 
       FIG. 4  is a side cross-sectional view illustrating a state of an upper structure of a secondary battery according to a second embodiment of the present invention. 
     As illustrated in  FIG. 3 , according to the first embodiment of the present invention, the waterproof part  500  may surround only a portion of the circumferential part of the electrode assembly  100  (particularly, a region facing the vent part in the electrode assembly). However, as illustrated in  FIG. 4 , according to the second embodiment of the present invention, a waterproof part  500  may surround an entire circumference of an electrode assembly  100 . According to a second embodiment of the present invention, since the waterproof part  500  surrounds the entire region of the electrode assembly  100 , it may be possible to fundamentally block discharge of a liquid within the waterproof part  500  to the outside. 
       FIG. 5  is a side cross-sectional view illustrating a state of an upper structure of a secondary battery according to a third embodiment of the present invention, and  FIG. 6  is an enlarged side cross-sectional view of a region A of  FIG. 5 . 
     A secondary battery  10  according to a third embodiment of the present invention may further include an elastic part  600  provided between an inner surface of a circumferential part  200   a  and a vent part  400 . The elastic part  600  is configured to press the vent part  400  by elastic force and may be made of a material having elasticity. 
     As illustrated in  FIGS. 5 and 6 , the elastic part  600  may include a first elastic member  610  and a second elastic member  620 . The first elastic member  610  may be provided between the inner surface of the circumferential part  200   a  and a first vent member  410 , and the second elastic member  620  may be provided between the inner surface of the circumferential part  200   a  and a second vent member  420 . The first elastic member  610  may press the first vent member  410  by the elastic force, and the second elastic member  620  may press the second vent member  420  by the elastic force. For example, each of the first elastic member  610  and the second elastic member  620  may be a spring. One end and the other end of the first elastic member  610  may be attached to an inner surface of a first exterior sheet  210   a  and the first vent member  410 , respectively. In addition, one end and the other end of the second elastic member  620  may be attached to an inner surface of a second exterior sheet  220   a  and the second vent member  420 . 
     According to the third embodiment of the present invention, when an internal pressure of the exterior  200  is less than a certain value, the first vent member  410  and the second vent member  420  may more stably contact each other by the elastic force of the elastic part  600 . More preferably, the first elastic member  610  and the second elastic member  620  may press an area on which the first vent member  410  and the second vent member  420  contact with each other (that is, an area on which the one end of the first vent member and the one end of the second vent member, which extend outward from the exterior, contact each other). 
     Battery Pack 
     A battery pack according to the present invention may include a plurality of secondary batteries. 
     As described above, a circumferential part on which two sheets of exterior sheets face each other may be disposed on at least a portion of outer surfaces of an exterior of the secondary battery according to the present invention. Here, the circumferential part may be disposed on an upper outer surface, which facing an upper side, among the outer surfaces of the exterior. 
     Also, a vent part of the secondary battery may be provided in an inner surface corresponding to the upper outer surface, on which the circumferential part is disposed, among the inner surfaces of the exterior. 
     Other contents of the structure of the secondary battery  10  are replaced with the contents described above with reference to  FIGS. 1 to 6  for the structure of the secondary battery. 
     While the embodiments of the present invention have been described with reference to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims. 
     DESCRIPTION OF THE SYMBOLS 
     
         
           10 : Secondary battery 
           100 : Electrode assembly 
           200 : Exterior 
           200   a : Circumferential part 
           210   a : First exterior sheet 
           220   a : Second exterior sheet 
           300 : Electrode lead 
           400 : Vent part 
           410 : First vent member 
           420 : Second vent member 
           500 : Waterproof part 
           600 : Elastic part 
           610 : First Elastic member 
           620 : Second Elastic member