Patent Publication Number: US-2022231266-A1

Title: Secondary battery

Description:
TECHNICAL FIELD 
     Embodiments of the present invention relate to a secondary battery. 
     BACKGROUND ART 
     Unlike a primary battery that cannot be charged, a secondary battery can be charged and discharged. Low-capacity secondary batteries are mainly used for portable small electronic devices such as smartphones, laptops, digital cameras, and camcorders, and large-capacity secondary batteries are widely being used for motor driving and power storage in hybrid and electric vehicles. 
     Such a secondary battery includes an electrode assembly, a terminal drawn out from the electrode assembly, and a case for accommodating the electrode assembly and an electrolyte. The electrode assembly, including a positive electrode plate, a negative electrode plate, and a separator, may be stacked on each other or rolled together (in a jelly-roll type). In addition, the case may be classified into cylindrical, prismatic, and pouch types according to case appearance. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not constitute prior art. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
     An embodiment of the present invention provides a secondary battery capable of improving the flatness of an electrode assembly and reducing internal resistance when the electrode assembly is rolled. 
     Solution to the Problem 
     A secondary battery according to an embodiment of the present invention comprises: an electrode assembly rolled including a positive electrode plate, a negative electrode plate, and a separator, wherein the positive electrode plate has positive electrode uncoated portions provided at a rolled central portion thereof and a rolled end portion thereof, and the negative electrode plate has negative electrode uncoated portions provided at a rolled central portion thereof and a rolled end portion thereof; a first positive electrode foil tab and a second positive electrode foil tab respectively connected to the positive electrode uncoated portions; a first negative electrode foil tab and a second negative electrode foil tab respectively connected to the negative electrode uncoated portions; a positive electrode current collection tab connected together to the first positive electrode foil tab and the second positive electrode foil tab; a negative electrode current collection tab connected together to the first negative electrode foil tab and the second negative electrode foil tab; and a pouch-type case for accommodating the electrode assembly. 
     In addition, the first positive electrode foil tab and the second positive electrode foil tab may have a thickness smaller than a region of the positive electrode plate to which the positive electrode active material is applied, and the first negative electrode foil tab and the second negative electrode foil tab may have a thickness smaller than a region of the negative electrode plate to which the negative electrode active material is applied. 
     In addition, the first positive electrode foil tab and the second positive electrode foil tab may have a thickness of 25 to 35 [μm], and the region of the positive electrode plate to which the positive electrode active material is applied may have a thickness of 90 to 110 [μm]. 
     In addition, the positive electrode current collection tab may have a thickness of 80 to 100 [μm] 
     In addition, the first negative electrode foil tab and the second negative electrode foil tab may have a thickness of 25 to 35 [μm], and the region of the negative electrode plate to which the negative electrode active material is applied may have a thickness of 100 to 130 [μm]. 
     In addition, the negative electrode current collection tab may have a thickness of 80 to 100 [μm]. 
     Effect of the Invention 
     In the secondary battery according to an embodiment of the present invention, the positive electrode foil tab and the negative electrode foil tab have a very small thickness compared to the positive electrode plate and the negative electrode plate as a whole, and thus the positive electrode foil tab and the negative electrode foil tab may not protrude more outwardly than the region of the positive electrode plate to which the positive electrode active material is applied and the region of the negative electrode plate to which the negative electrode active material is applied, when coupled to the positive electrode uncoated portion and the negative electrode uncoated portion, thereby improving the flatness when the electrode assembly is rolled, and increasing the energy density and reducing the internal resistance. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a secondary battery according to an embodiment of the present invention. 
         FIG. 2A  is a plan view of a positive electrode plate of a secondary battery according to an embodiment of the present invention. 
         FIG. 2B  is a cross-sectional view taken along line X-X of  FIG. 2A . 
         FIGS. 3A to 3E  are views sequentially illustrating a process of connecting a positive electrode current collection tab to positive electrode foil tabs of a secondary battery according to an embodiment of the present invention. 
     
    
    
     MODE FOR IMPLEMENTING THE INVENTION 
     Hereinafter, example embodiments of the present invention will be described in detail. 
     Embodiments of the present invention are provided to more completely explain the present invention to one skilled in the art, and the following example embodiments may be modified in various other forms and the present invention should not be construed as being limited to the 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 are 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 will be understood that when an element A is referred to as being “connected to” an element B, the element A can be directly connected to the element B or an intervening element 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 only and is not intended to be limiting of the invention. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms that the terms “comprise or 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 will 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 only 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 will 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 exemplary term “below” can encompass both an orientation of above and below. 
     
       
     
       FIG. 1  is a perspective view of a secondary battery  100  according to an embodiment of the present invention. 
     In addition,  FIG. 2A  is a plan view of a positive electrode plate  111  of a secondary battery  100  according to an embodiment of the present invention, and  FIG. 2B  is a cross-sectional view taken along line X-X of  FIG. 2A . 
     
       
     
     Referring to  FIG. 1 , the secondary battery  100  includes an electrode assembly  110 , positive electrode foil tabs  121  and  122 , negative electrode foil tabs  131  and  132 , a positive electrode current collection tab  140 , a negative electrode current collection tab  150 , and a pouch-type case  160 . 
     
       
     
     The electrode assembly  110  includes a positive electrode plate  111 , a negative electrode plate  112 , and a separator  113 . 
     The positive electrode plate  111  includes a positive electrode current collector which is made of, for example, aluminum foil, and a positive electrode active material  111 A which is made of, for example, a transition metal oxide, and is applied to the positive electrode current collector. Here, as shown in  FIGS. 2A and 2B , the positive electrode plate  111  includes positive electrode uncoated portions  111 B, which are regions to which the positive electrode active material  111 A is not applied, at both left and right ends thereof. Here, the positive electrode current collector itself may have a thickness of about 10 to 12 [μm], and the region to which the positive electrode active material  111 A is applied may have a thickness of about 100 [μm], for example, about 90 to 110 [μm]. 
     The negative electrode plate  112  includes a negative electrode current collector which is made of, for example, copper or nickel foil, and a negative electrode active material which is made of, for example, graphite or carbon, and is applied to the negative electrode current collector. Here, the negative electrode plate  112  also includes negative electrode uncoated portions, which are regions to which the negative electrode active material is not applied, at both left and right ends thereof. Here, the negative electrode current collector itself may have a thickness of about 8 to 10 [μm], and the region to which the negative electrode active material is applied may have a thickness of about 100 to 130 [μm]. 
     The separator  113  is made of, for example, polyethylene, polypropylene or a composite film of polyethylene and polypropylene. In addition, the separator  113 , which is interposed between the positive electrode plate  111  and the negative electrode plate  112 , prevents a short circuit between the positive electrode plate  111  and the negative electrode plate  112  while allowing the movement of, for example, lithium ions. 
     The electrode assembly  110  is rolled in a so-called jelly-roll configuration on the basis of one end thereof. Hereinafter, the one end is referred to as a “rolled central portion” and the other end is referred to as a “rolled end portion”. 
     
       
     
     The positive electrode foil tabs  121  and  122 , as shown in  FIG. 2A , are respectively electrically connected to the two negative electrode uncoated portions  111 B of the positive electrode plate  111  to then be exposed beyond the top ends thereof. 
     In addition, the positive electrode foil tabs  121  and  122  may be made of the same material as the positive electrode current collector. For example, if the positive electrode current collector is made of aluminum, the positive electrode foil tabs  121  and  122  may also be made of aluminum. 
     In addition, the positive electrode foil tabs  121  and  122  may have a very small thickness compared to the positive electrode plate  111  as a whole. For example, the positive electrode foil tabs  121  and  122  may have a thickness of about ⅓ of an area of the positive electrode plate  111  coated with the positive electrode active material  111 A. More specifically, the positive electrode foil tabs  121  and  122  may have a thickness of about 25 to 35 [μm]. 
     Hereinafter, in the positive electrode plate  111 , the positive electrode foil tab  121  connected to the negative electrode uncoated portion  111 B on a side of the rolled central portion is referred to as a “first positive electrode foil tab  121 ”, and the positive electrode foil tab  122  connected to the negative electrode uncoated portion  111 B on a side of the rolled end portion is referred to as a “second positive electrode foil tab  122 ”. 
     The first positive electrode foil tab  121  and the second positive electrode foil tab  122  are arranged so as to be substantially parallel to each other when the electrode assembly  110  is rolled. 
     
       
     
     The negative electrode foil tabs  131  and  132  are respectively electrically connected to the two uncoated portions of the negative electrode plate  112  to then be exposed beyond the top ends thereof. 
     In addition, the negative electrode foil tabs  131  and  132  may be made of the same material as the negative electrode current collector. For example, if the negative electrode current collector is made of copper, the negative electrode foil tabs  131  and  132  may also be made of copper. 
     In addition, the negative electrode foil tabs  131  and  132  may have a very thickness compared to the negative electrode plate  112  as a whole. For example, the negative electrode foil tabs  131  and  132  may have a thickness of about ¼ of the area of the negative electrode plate  112  coated with the negative electrode active material. More specifically, the negative electrode foil tabs  131  and  132  may have a thickness of about 25 to 35 [μm]. 
     Hereinafter, in the negative electrode plate  112 , the negative electrode foil tab  131  connected to the negative electrode uncoated portion on a side of the rolled central portion is referred to as a “first negative electrode foil tab  131 ”, and the negative electrode foil tab  132  connected to the negative electrode uncoated portion on a side of the rolled end portion is referred to as a “second negative electrode foil tab  132 ”. 
     The first negative electrode foil tab  131  and the second negative electrode foil tab  132  are arranged so to be aligned substantially parallel to each other when the electrode assembly  110  is rolled. 
     
       
     
     The positive electrode current collection tab  140  is connected together to the first positive electrode foil tab  121  and the second positive electrode foil tab  122 . 
     
       
     
     In this regard,  FIGS. 3A to 3E  are views sequentially illustrating a process of connecting a positive electrode current collection tab  140  to positive electrode foil tabs  121  and  122  of a secondary battery  100  according to an embodiment of the present invention, which are viewed from a side surface when the electrode assembly  110  is rolled. 
     
       
     
     First, when the electrode assembly  110  is rolled as shown in  FIG. 3A , the first positive electrode foil tab  121  is bent toward the second positive electrode foil tab  122  to overlap each other as shown in  FIG. 3B . Of course, when necessary, the second positive electrode foil tabs  122  may also be bent toward the first positive electrode foil tabs  121  to overlap each other, and the first positive electrode foil tabs  121  and the second positive electrode foil tabs  122  may be bent together to overlap each other. 
     Thereafter, as shown in  FIG. 3C , the ends of the first positive electrode foil tab  121  and the second positive electrode foil tab  122  are cut to an appropriate length to then be aligned. 
     Next, as shown in  FIG. 3D , the positive electrode current collection tab  140  is welded together to the first positive electrode foil tab  121  and the second positive electrode foil tab  122 . 
     Lastly, as shown in  FIG. 3E , an insulating tape (T) is attached and finished. 
     
       
     
     Meanwhile, the positive electrode current collection tab  140  may have a thickness of about 80 to 100 [μm]. 
     
       
     
     The negative electrode current collection tab  150  is also connected together to the first negative electrode foil tab  131  and the second negative electrode foil tab  132 . 
     In  FIGS. 3A to 3E , the first negative electrode foil tab  131 , the second negative electrode foil tab  132 , and the negative electrode current collection tab  150  are hidden behind the first positive electrode foil tab  121 , the second positive electrode foil tab  122  and the positive electrode current collection tab  140  and are not seen, but the same process as described above can be performed thereon. 
     That is, while the electrode assembly  110  is rolled, the first negative electrode foil tab ( 131 ) and the second negative electrode foil tab ( 132 ) are overlapped with each other, the ends of the first negative electrode foil tab  131  and the second negative electrode foil tab  132  are then cut to an appropriate length and aligned, the negative electrode current collection tab  150  is then welded together to the first negative electrode foil tab  131  and the second negative electrode foil tab  132 , followed by finishing by attaching the insulation tape (T). 
     Here, the negative electrode current collection tab  150  may have a thickness of about 80 to 100 [μm]. 
     
       
     
     The case  160  includes a lower case  161  that has a concave space to accommodate the electrode assembly  110  and an electrolyte, and an upper case  162  that is coupled to the lower case  161  and seals same. 
     Here, the electrolyte may include, for example, an organic solvent such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and a lithium salt such as LiPF 6  or LibF 4 . 
     
       
     
     According to the above-described secondary battery  100 , the positive electrode foil tabs  121  and  122  and the negative electrode foil tabs  131  and  132  have a very small thickness compared to the positive electrode plate  111  and the negative electrode plate  112  as a whole, and thus the positive electrode foil tabs  121  and  122  and the negative electrode foil tabs  131  and  132  may not protrude more outwardly than the region of the positive electrode plate  111  to which the positive electrode active material  111 A is applied and the region of the negative electrode plate  112  to which the negative electrode active material is applied, when coupled to the positive electrode uncoated portion  111 B and the negative electrode uncoated portion, thereby improving the flatness when the electrode assembly  110  is rolled. 
     
       
     
     Additionally, according to the secondary battery  100 , the energy density can be increased and the internal resistance of a cell can be reduced. 
     
       
     
     In this regard, Table 1 shows DCIR (Direct Current Internal Resistance) measurements when a current is applied to a secondary battery for 1 second, and Table 2 shows DCIR measurements when a current is applied to a secondary battery for 30 seconds. 
     As used herein, the term “Conventional secondary battery” refers to a secondary battery including an electrode assembly in which a positive electrode plate and a negative electrode plate have a positive electrode uncoated portion and a negative electrode uncoated portion each provided at one end, and a positive electrode material tab and a negative electrode material tab of about 80 [μm] are respectively connected to the positive electrode uncoated portion and the negative electrode uncoated. 
     
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Secondary battery 
                 Internal 
               
               
                   
                   
                 Conventional 
                 according to an 
                 resistance 
               
               
                   
                   
                 secondary 
                 embodiment of the 
                 reduction 
               
               
                 Temp. 
                 DOD 
                 battery 
                 present invention 
                 rate 
               
               
                   
               
             
            
               
                 35° C. 
                 30% 
                 42 mΩ 
                 23 mΩ 
                 46% 
               
               
                   
                 80% 
                 43 mΩ 
                 23 mΩ 
                 47% 
               
               
                   
                 90% 
                 44 mΩ 
                 24 mΩ 
                 47% 
               
               
                 25° C. 
                 30% 
                 49 mΩ 
                 28 mΩ 
                 42% 
               
               
                   
                 80% 
                 51 mΩ 
                 31 mΩ 
                 40% 
               
               
                   
                 90% 
                 53 mΩ 
                 32 mΩ 
                 40% 
               
               
                 10° C. 
                 30% 
                 82 mΩ 
                 52 mΩ 
                 36% 
               
               
                   
                 70% 
                 96 mΩ 
                 59 mΩ 
                 39% 
               
               
                   
                 80% 
                 105 mΩ  
                 62 mΩ 
                 41% 
               
               
                 Avg. 
                   
                   
                   
                 42% 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 Secondary battery 
                 Internal 
               
               
                   
                   
                 Conventional 
                 according to an 
                 resistance 
               
               
                   
                   
                 secondary 
                 embodiment of the 
                 reduction 
               
               
                 Temp. 
                 DOD 
                 battery 
                 present invention 
                 rate 
               
               
                   
               
             
            
               
                 35° C. 
                 30% 
                 58 mΩ 
                 34 mΩ 
                 41% 
               
               
                   
                 80% 
                 59 mΩ 
                 32 mΩ 
                 46% 
               
               
                   
                 90% 
                 64 mΩ 
                 35 mΩ 
                 46% 
               
               
                 25° C. 
                 30% 
                 65 mΩ 
                 42 mΩ 
                 36% 
               
               
                   
                 80% 
                 69 mΩ 
                 43 mΩ 
                 37% 
               
               
                   
                 90% 
                 80 mΩ 
                 53 mΩ 
                 34% 
               
               
                 10° C. 
                 30% 
                 105 mΩ  
                 75 mΩ 
                 28% 
               
               
                   
                 70% 
                 129 mΩ  
                 94 mΩ 
                 27% 
               
               
                   
                 80% 
                 152 mΩ  
                 115 mΩ  
                 24% 
               
               
                 Avg. 
                   
                   
                   
                 36% 
               
               
                   
               
            
           
         
       
     
     Referring to Tables 1 and 2, it can be confirmed that the internal resistance of the secondary battery  100  according to the embodiment of the present invention is reduced by about 36 to 42 [%] compared to the conventional secondary battery. 
     
       
     
     While the foregoing embodiment has been described to practice the secondary battery  100  according to the present invention, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.