Patent Publication Number: US-2021175536-A1

Title: Finishing tape and secondary battery comprising same

Description:
TECHNICAL FIELD 
     The present disclosure relates to a finishing tape which is capable of reducing flow of an electrode assembly in a casing and a secondary battery including the same. 
     BACKGROUND ART 
     In general, secondary batteries can be charged and discharged, unlike primary batteries, which are not rechargeable once discharged. Secondary batteries are widely used in various applications including advanced electronic devices such as cellular phones, notebook computers, camcorders, etc. 
     Specifically, lithium secondary batteries operating at 3.6 V are rapidly expanding their uses and applications in place of nickel-cadmium (Ni—Cd) batteries or nickel-hydride (Ni-MH) batteries, which have widely been used as power sources for electronic devices, because the operating voltage of these lithium secondary batteries is approximately three times higher than that of nickel-cadmium (Ni—Cd) batteries or nickel-hydride (Ni-MH) batteries and the lithium secondary batteries have excellent energy density per unit weight. Lithium secondary batteries 
     Lithium secondary batteries generally employ a lithium oxide positive active material, and a carbon negative active material. Such lithium secondary batteries may be classified as liquid electrolyte cells or polymer electrolyte cells based on the kind of electrolyte used. Lithium batteries using a liquid electrolyte are generally referred to as lithium-ion batteries, and lithium batteries using a polymer electrolyte are generally referred to as lithium-polymer batteries. Typically, lithium secondary batteries are manufactured in cylindrical, rectangular, or pouch-type shapes. 
     In the lithium secondary batteries, an electrode assembly is inserted into a casing together with the electrolyte or electrolytic solution. In this regard, in order to secure mechanical/electrical reliability of the battery, the electrode assembly needs to be fixedly positioned in the casing. 
     DESCRIPTION OF EMBODIMENTS 
     Technical Problem 
     The present disclosure provides a finishing tape which is capable of reducing flow or movement of an electrode assembly in a casing and a secondary battery including the same. 
     Solution to Problem 
     According to an embodiment of the present disclosure, provided is a finishing tape including a first layer formed of a resin and forming a substrate; and a second layer formed on at least one side of the first layer and including a microsphere structure. 
     Here, the microsphere structure may be configured to react with an electrolytic solution including a lithium salt to cause a volumetric expansion. 
     In addition, the electrolytic solution may include at least one of a non-aqueous organic electrolytic solution having a lithium salt, such as LiPF 6 , LiBF 4 , or LiClO 4 , and a high-purity organic solvent mixed therein, and a polymer electrolytic solution having a polymer electrolyte. 
     In addition, the microsphere structure of the second layer may include a shell formed of a thermoplastic resin and an encapsulating member encapsulated by the shell and including hydrocarbon. 
     According to an embodiment of the present disclosure, provided is a secondary battery including a casing having an internal space; an electrode assembly inserted into the casing with an electrolyte; a finishing tape covering the electrode assembly and undergoing a volumetric expansion when reacting with the electrolyte; and a cap plate coupled to an upper portion of the casing and sealing the casing. 
     Here, the electrolytic solution may include at least one of a non-aqueous organic electrolytic solution having a lithium salt, such as LiPF 6 , LiBF 4 , or LiClO 4 , and a high-purity organic solvent mixed therein, and a polymer electrolytic solution having a polymer electrolyte. 
     In addition, the finishing tape may include a first layer formed of a resin and forming a substrate; and a second layer formed on at least one side of the first layer and including a microsphere structure. 
     In addition, the microsphere structure of the second layer may include a shell formed of a thermoplastic resin and an encapsulating member encapsulated by the shell and including hydrocarbon. 
     In addition, the microsphere structure may have a diameter in a range of 5 μm to 50 μm. 
     Advantageous Effects of Disclosure 
     As described above, in the finishing tape according to the present disclosure and the secondary battery using the same, a layer having a microsphere structure is formed on at least one surface of the finishing tape, and, when the finishing tape reacts with an electrolytic solution, the finishing tape may expand due to a volumetric expansion of the microsphere structure and fix the electrode assembly, thereby suppressing an increasing of resistance due to movement of the electrode assembly in the casing. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a state in which a finishing tape according to an embodiment is wound. 
         FIG. 2  is a cross-sectional view illustrating the finishing tape according to an embodiment. 
         FIG. 3  is a perspective view illustrating a state in which a finishing tape is attached to an electrode assembly in a secondary battery according to an embodiment. 
         FIG. 4  is an exploded perspective view of the secondary battery according to an embodiment. 
         FIG. 5A  is a perspective view illustrating a diameter of a microsphere of the finishing tape according to an embodiment. 
         FIG. 5B  is a perspective view illustrating a radius of a microsphere of the finishing tape according to an embodiment. 
         FIGS. 6A and 6B  are optical microscopic images showing microspheres before and after foaming in the finishing tape according to an embodiment. 
         FIGS. 7A and 7B  are SEM photographs showing microspheres before and after foaming in the finishing tape according to an embodiment 
         FIGS. 8A to 8C  are photographs showing a process of the experiments in which the finishing tape according to an embodiment is allowed to react with an electrolyte. 
     
    
    
       
     
       
         
           
               
             
               
                   
               
               
                 [Explanation of Reference Numerals] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 100: Secondary battery 
               
               
                   
                   
                 110: Casing 
               
               
                   
                   
                 120: Electrode assembly 
               
               
                   
                   
                 130: Finishing tape 
               
               
                   
                   
                 131: First layer 
               
               
                   
                   
                 132: Second layer 
               
               
                   
                   
                 150: Cap assembly 
               
               
                   
                   
                 160: Insulation case 
               
               
                   
                   
               
            
           
         
       
     
     MODE OF DISCLOSURE 
     Hereinafter, examples of embodiments of the invention will be described in detail with reference to the accompanying drawings such that they can readily be made and used by those skilled in the art. 
       FIG. 1  illustrates a state in which a finishing tape according to an embodiment is wound.  FIG. 2  is a cross-sectional view illustrating the finishing tape according to an embodiment. 
     Referring to  FIGS. 1 and 2 , the finishing tape  130  according to an embodiment may be provided in a wound state, and may include a first layer  131  and a second layer  132 . 
     The first layer  131  may constitute a substrate layer and may define an outermost surface contacting the casing after being covered by the electrode assembly. The first layer  131  may be formed of a material selected from polyethylene (PE), polystyrene (PS) and oriented polystyrene (OPS). Since the first layer  131  is an electrically insulating material, it may prevent an electrical short from occurring between the electrode assembly and the casing. 
     The second layer  132  may be formed along one surface of the first layer  131 . The second layer  132  may be positioned to make contact with the electrode assembly when the finishing tape  130  is combined with the electrode assembly. Here, the second layer  132  may include an expandable material which causes a volumetric expansion when it reacts with an electrolyte or electrolytic solution present in the casing  110 . More specifically, the second layer  132  may be formed in a microsphere structure. 
     The microsphere structure may include an encapsulating member in a thermoplastic resin shell so as to be expandable when reacting with an electrolyte. For example, the encapsulating member included in the shell may include hydrocarbon. Even if the hydrocarbon having hydrophobicity does not react with water, it still has a capability of absorbing the electrolyte. The thus configured microsphere structure operates according to the mechanism in which the electrolyte reacts with the encapsulating member when it penetrates into the shell, and the encapsulating member is then expanded. Accordingly, since the volume of the second layer  132  including the microsphere structure is increased, the electrode assembly may be fixedly positioned by filling gaps between the casing and the electrode assembly, thereby suppressing flow or movement of the electrode assembly in the casing and preventing resistance due to the flow or movement of the electrode assembly from increasing. 
     In addition, the microsphere may have a diameter in a range of 5 μm to 50 μm. When the microsphere has a diameter of greater than or equal to 5 μm in the finishing tape applied to the electrode assembly, the fixing of the finishing tape to the electrode assembly and prevention of the volumetric expansion thereof may be advantageously achieved. When the microsphere has a diameter of less than or equal to 50 μm, it is advantageous to fill gaps between the casing and the electrode assembly, resulting after reacting with an electrolytic solution. 
     Hereinafter, a configuration of a secondary battery according to an embodiment will be described. 
       FIG. 3  is a perspective view illustrating a state in which a finishing tape is attached to an electrode assembly in a secondary battery according to an embodiment.  FIG. 4  is an exploded perspective view of the secondary battery according to an embodiment. 
     Referring to  FIGS. 3 and 4 , the secondary battery  100  according to an embodiment includes the casing  110 , the electrode assembly  120 , the finishing tape  130 , and a cap assembly  150 . In addition, an insulation case  160  may further be formed between the electrode assembly  120  and the cap assembly  150 . 
     The casing  110  is substantially hexahedral. The casing  110  has an internal space  110 , and has an opening at its top portion. The casing  110  may be made of aluminum (Al), iron (Fe), or alloys thereof. In addition, the inner surface of the casing  110  may be subjected to insulation treatment. The casing  110  may include a groove  111  formed along the periphery of its top portion to allow the insulation case  160  to be mounted in the groove  111  in a subsequent process. In addition, the electrode assembly  120  may be accommodated in the internal space  110   a  of the casing  110  with an electrolytic solution. 
     Here, the electrolytic solution may be an organic liquid containing a salt-injection allowing lithium ions to move between positive and negative electrode plates of the electrode assembly  120 , and may include a non-aqueous organic electrolytic solution having a lithium salt, such as LiPF 6 , LiBF 4 , or LiClO 4 , and a high-purity organic solvent mixed therein, or a polymer electrolytic solution having a polymer electrolyte. 
     The electrode assembly  120  is accommodated in the internal space  110   a  of the casing  110 . The electrode assembly  120  includes a positive electrode plate coated with a positive active material (e.g., lithium cobalt oxide (LiCoO 2 )), a negative electrode plate coated with a negative active material (e.g., graphite), and a separator positioned between the positive electrode plate and the negative electrode plate to prevent an electrical short-circuit and to allow the lithium ions to move between the positive and negative electrode plates. The electrode assembly  120  may be formed by winding a stacked structure of the positive electrode plate, the separator, and the negative electrode plate multiple times in a substantially jellyroll-like configuration. The positive electrode plate may be made of an aluminum (Al) foil, the negative electrode plate may be made of a copper (Cu) foil, and the separator may be made of polyethylene (PE) or polypropylene (PP) material. 
     In addition, an upwardly extending positive electrode lead  125  is connected to the positive electrode plate, and an upwardly extending negative electrode lead  124  is connected to the negative electrode plate. Here, the positive electrode lead  125  may be made of aluminum (Al), and the negative electrode lead  124  may be made of nickel (Ni). 
     In addition, the electrolytic solution may be injected into the casing  110  together with the electrode assembly  120 . During charging and discharging, the electrolytic solution serves as a medium for movement of the lithium ions generated by an electrochemical reaction taking place between the positive electrode plate and the negative electrode plate within the battery. 
     As described above, the finishing tape  130  may be coupled to the electrode assembly  120  while covering the outer circumferential surface of the electrode assembly  120 . The finishing tape  130  covers the outer circumferential surface of the electrode assembly  120  in a state in which the first layer thereof faces the casing  110  and the second layer  132  thereof faces the electrode assembly  120 . Accordingly, the finishing tape  130  may cover the electrode assembly  120  and thus may prevent the electrode assembly  120  from expanding in volume. 
     In addition, if the electrolyte in the casing  110  infiltrates the finishing tape  130 , the microsphere forming the second layer  132  of the finishing tape  130  may react with the electrolyte and expands. Accordingly, expansion of the second layer  132  may be caused, thereby fixing the position of the electrode assembly  120  in the casing  110  and suppressing movement of the electrode assembly  120 . The structure and operation of the microsphere in the second layer  132  will later be described. 
     The cap assembly  150  is coupled to a top portion of the casing  110 . The cap assembly  150  may include a cap plate  151 , an insulation plate  152 , a terminal plate  153 , an electrode terminal  154  and an insulation gasket  155 . 
     The cap plate  151  is coupled to the opening  110   a  of the can  110  and may be shaped of a plate having long sides and short sides. The cap plate  151  is welded at its peripheral portion in a state in which it is coupled to the opening  110   a  of the can  110  to thus seal the can  110 . The cap plate  151  includes a terminal hole  151   a  to be engaged with the electrode terminal  154  and an electrolyte injection hole  151   b  for electrolyte injection. Here, the electrode terminal  154  and the insulation gasket  155  are coupled to the terminal hole  151   a , thereby coupling the electrode terminal  154  and lower structures thereof to each other. In addition, once the electrolyte is injected, a plug is engaged with the electrolyte injection hole  151   b  to then be fixedly sealed with the cap plate  151 , thereby preventing leakage of the electrolyte. 
     The insulation plate  152  is positioned under the cap plate  151 . A terminal hole  152   a  corresponding to the terminal hole  151   a  of the cap plate  151  is formed in the insulation plate  152 , and the insulation gasket  155  is engaged with the terminal hole  152   a . In addition, the terminal hole  152   a  of the insulation plate  152  is passed through by a lower portion of the electrode terminal  154 . 
     The terminal plate  153  is positioned under the insulation plate  152 . A terminal hole  153   a  corresponding to the terminal hole  152   a  of the insulation plate  152  is formed in the terminal plate  153 , and the electrode terminal  154  is engaged with the terminal hole  153   a . In addition, the negative electrode lead  124  of the electrode assembly  120  may be coupled to the terminal plate  153 . Therefore, the electrode terminal  154  may be electrically connected to the negative electrode lead  124  of the electrode assembly  120 . 
     The electrode terminal  154  passes through the terminal holes  151   a  and  152   a  of the cap plate  151  and insulation plate  152  in the order in which the underlying structures are coupled thereto, as described above, and is then electrically connected to the negative electrode lead  124 . 
     The insulation gasket  155  is located between the electrode terminal  154  and the cap plate  151  to prevent the electrode terminal  154  and the cap plate  151  from electrically contacting each other. 
     The insulation case  160  positioned above the electrode assembly  120  may be coupled to the opening  110   a  of the can  110 . More specifically, the insulation case  160  may be coupled to a stepped portion  111  of the can  110 . Lead passage holes  160   a  and  160   b  are formed in the insulation case  160  to allow the negative electrode lead  124  and the positive electrode lead  125  to penetrate the insulation case  160 . 
     Hereinafter, the operation of a finishing tape in a secondary battery according to an embodiment will be described in more detail. 
       FIG. 5A  is a perspective view illustrating a diameter of a microsphere of the finishing tape according to an embodiment.  FIG. 5B  is a perspective view illustrating a radius of a microsphere of the finishing tape according to an embodiment.  FIGS. 6A and 6B  are optical microscopic images showing microspheres before and after foaming in the finishing tape according to an embodiment.  FIGS. 7A and 7B  are SEM photographs showing microspheres before and after foaming in the finishing tape according to an embodiment. 
     First, referring to  FIG. 5A , the microsphere forming the finishing tape  130  has a substantially spherical shape and has a predetermined diameter (d). 
     Next, referring to the cross-sectional view of  FIG. 5B , the microsphere includes an encapsulating member having a first radius (r1) and a shell surrounding the encapsulating member and having a second radium (r1+r2). 
     Here, the encapsulating member may include hydrocarbon, as described above. The hydrocarbon may be a material that does not react with water but reacts with an electrolyte and may be expandable when it reacts with the electrolyte, causing a volumetric expansion. Accordingly, the radius r1 of the hydrocarbon may increase. 
     In addition, the shell surrounding the encapsulating member is capable of withstanding the expansion of the encapsulating member and may have increasing radius (r1+r2) the expansion of the encapsulating member. The shell may be formed of a thermoplastic resin so as to be deformable. Examples of the material available as the thermoplastic resin may include polyethylene, nylon, polyacetal resin, polyvinyl chloride, polystyrene, ABS resin, and acryl resin, but embodiments of the disclosure are not limited to the above materials. 
     Next,  FIGS. 6A and 7A  are compared with  FIGS. 6B and 7B , and the comparison result confirms that the volume of the microsphere structure is increased by the infiltration of the electrolyte, causing a volumetric expansion of the finishing tape  130  including the microsphere, and thus the electrode assembly  120  may be fixedly positioned. 
     Hereinafter, the effects of the present disclosure will be described through the results of the experiment in which the finishing tape according to the embodiment is allowed to react with an electrolyte. 
       FIGS. 8A to 8C  are photographs showing an experiment process in which the finishing tape according to an embodiment is allowed to react with an electrolyte. 
       FIGS. 8A, 8B and 8C  are photographic images sequentially showing the finishing tape photographed before, during and after the experiment, respectively. 
     In the experiments, the electrolyte obtained by mixing 1.0 M LiPF 6  with EC/EMC/DEC/PC/DMC at a ratio of 2:2:2:2:2 and the finishing tape  130  including a first layer  131  formed of polyethylene and a second layer  132  having a microsphere, were used. In addition, the experiment was conducted such that the finishing tape was immersed in the electrolytic solution and, after one hour, changes in the color and thickness were observed. 
     The experimental results are summarized in Table 1 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Thickness of  
                 Thickness of  
               
               
                   
                 first layer 
                 second layer 
               
               
                   
                 (131) (μm) 
                 (132) (μm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Before experiment 
                 12 
                 51 
               
               
                 After experiment 
                 12 
                 81 
               
               
                 Thickness difference 
                 0 
                 30 
               
               
                   
               
            
           
         
       
     
     The experimental result showed the diameter of the microsphere structure was changed from 51 μm to 81 μm, confirming that there is a thickness difference of 30 μm before and after the experiment, by which the electrode assembly is fixedly positioned when the finishing tape  130  reacts with the electrolyte. 
     In addition, the photographs shown in  FIGS. 8A and 8C  were compared with each other. The comparison result visually confirmed that the color of the microsphere structure after the experiment, as shown in  FIG. 8C , became pale, compared with the color of the microsphere structure before the experiment, as shown in  FIG. 8A . This result is attributable to the volumetric expansion of the microsphere structure included in the second layer  132  of the finishing tape  130 . 
     As described above, in the finishing tape  130  according to the embodiment and the secondary battery  100  using the same, the layer  132  including the microsphere structure is formed on at least one side of the finishing tape  130  to allow the finishing tape  130  to be expandable due to a volumetric expansion of the microsphere structure by reacting with the electrolytic solution, thereby preventing resistance due to flow or movement of the electrode assembly in the casing from increasing by fixing the position of the electrode assembly. 
     Although the foregoing embodiments have been described to practice the finishing tape of the present invention and the secondary battery using the same, these embodiments are set forth for illustrative purposes and do not serve to limit the invention. Those skilled in the art will readily appreciate that many modifications and variations can be made, without departing from the spirit and scope of the invention as defined in the appended claims, and such modifications and variations are encompassed within the scope and spirit of the present invention. 
     INDUSTRIAL APPLICABILITY 
     In the finishing tape according to the embodiment and the secondary battery using the same, the finishing tape is allowed to be expandable due to a volumetric expansion of the microsphere structure when it reacts with an electrolytic solution by forming a layer including a microsphere structure on at least one side of the finishing tape, thereby preventing resistance due to flow or movement of an electrode assembly from increasing by fixing the position of the electrode assembly.