Patent Publication Number: US-2019198882-A1

Title: Secondary battery

Description:
TECHNICAL FIELD 
     Embodiments of the present invention relate to a secondary battery having a high-output characteristic and a reduced defective rate. 
     BACKGROUND ART 
     Unlike primary batteries, secondary batteries can be repeatedly charged and discharged. In general, a low capacity secondary battery may be used as a power source for various small portable electronic devices, such as cellular phones, laptop computers or camcorders and a high capacity secondary battery may be used as power sources for electric automobiles or the like. The secondary battery includes an electrode assembly performing, for example, charge/discharge operations, a case accommodating the electrode assembly, and a cap assembly coupled to the case to prevent electrode assembly from being dislodged. 
     Meanwhile, gradually increasing application fields of the secondary batteries have led to increasing demands for high-capacity/high-output secondary batteries. Hence, there are increasing demands for suppressing various types of defects, such as a voltage drop or an open circuit voltage (OCV) deviating from an appropriate reference value, which may be caused when the secondary battery is fully charged. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     Technical Problems to be Solved 
     Embodiments of the present invention provide a secondary battery having a high-output characteristic and a reduced defective rate. 
     The above and other objects of the present invention will be described in or be apparent from the following description of the preferred embodiments. 
     Technical Solutions 
     In accordance with an aspect of the present invention, there is provided a secondary battery including a can, a cap assembly for sealing the can, and an electrode assembly contained in the can, the electrode assembly including a cathode plate, an anode plate, a separator disposed between the cathode plate and the anode plate, a cathode tab attached to the cathode plate and extending toward one of the can and the cap assembly, and an anode tab attached to the anode plate and extending toward the other of the can and the cap assembly, wherein the anode tab is made of nickel-plated copper. 
     In addition, the anode tab may be made of nickel entirely plated on an outer circumferential surface with respect to a longitudinal direction in which the anode tab extends. 
     In addition, the anode tab may be made of nickel plated to have a weight ratio of 1 wt % or less. 
     In addition, the anode tab may be made of nickel plated to a thickness of 1.5 μm or less. 
     In addition, the anode tab may have a surface further processed with heat treatment. 
     In addition, the anode tab may have a surface further processed with chromate (CrO 3 ) treatment. 
     In addition, the anode tab may have at least one edge further processed with chamfer treatment. 
     Here, the chamfer-treated edge of the anode tab may be planar. 
     In addition, the chamfer-treated edge of the anode tab may be curved. 
     Advantageous Effects 
     As described above, according to embodiments of the present invention, the secondary battery is made of nickel-plated copper, thereby demonstrating a high-output characteristic while reducing a defective rate, compared to a case where the anode tab is made of nickel only. 
     In addition, according to embodiments of the present invention, the secondary battery has an anode tab having at least one edge processed with chamfer treatment, thereby increasing welding quality in resistance welding. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cut-away view of a secondary battery according to an embodiment of the present invention. 
         FIG. 2  is a transverse sectional view of an anode tab of the secondary battery according to an embodiment of the present invention. 
         FIG. 3  is a graph illustrating experimental data for comparing dissolution potentials in cases where the anode tab is made of copper only and where the anode tab is made of nickel-plated copper. 
         FIG. 4  is a transverse sectional view of an anode tab of a secondary battery according to another embodiment of the present invention. 
         FIG. 5  is a transverse sectional view of an anode tab of a secondary battery according to still another embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, a preferred embodiment of the present invention will be described in detail. 
     Various embodiments of 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 of the disclosure are provided so that this disclosure will be thorough and complete and will convey inventive concepts of the disclosure to those skilled in the art. 
     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 and 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 disclosure. 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 “comprise or include” and/or “comprising or including,” 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 disclosure. 
     Spatially relative terms, such as “below,” “beneath,” “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 device 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 cut-away view of a secondary battery  100  according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the secondary battery  100  includes a can  110 , an electrode assembly  120 , a cap assembly  130 , and a gasket  140 . 
     The can  110  may include a bottom surface  111  having a substantially circular shape and sidewalls  112  upwardly extending a predetermined length from the bottom surface  111 . That is to say, as illustrated in  FIG. 1 , the can  110  may be formed to have a substantially cylindrical shape. Of course, the can  110  may be formed to have a prismatic shape, unlike in  FIG. 1 . Meanwhile, a top end of the can  110  may be opened so as to receive the electrode assembly  120 , an electrolyte solution, etc. therein in assembling the secondary battery  100 . 
     The can  110  may include, for example, steel, a steel alloy, aluminum, an aluminum alloy or equivalents thereof. These materials are provided only for illustration, but the present invention does not limit the material of the can  110  to those disclosed therein. 
     In addition, a beading part  112   a  recessed into the can  110  to support a lower portion of the cap assembly  130  and a crimping part  112   b  bent to cover an upper portion of the cap assembly  130  to prevent the cap assembly  130  from being dislodged, which will later be described, may be formed at upper sides of the sidewalls  112  of the can  110 . 
     The electrode assembly  120  may include a cathode plate  121 , a separator  122 , an anode plate  123 , a cathode tab  124  and an anode tab  125 . 
     The cathode plate  121  is formed by coating a cathode active material on a cathode current collector shaped of a metal foil. The cathode current collector may include, for example, aluminum, and the cathode active material may include, for example, a transition metal oxide, such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2) or lithium manganese oxide (LiMn2O4), which are provided only for illustration, but the present invention does not limit the material of the cathode plate  121  to those disclosed therein. 
     Here, a cathode non-coating portion  121   a  without a cathode active material coated thereon is formed at a portion of the cathode plate  121 . 
     The separator  122  is disposed between the cathode plate  121  and the anode plate  123  and prevents a short circuit from occurring due to a contact between the cathode plate  121  and the anode plate  123 . In addition, the separator  122  may serve as a passageway for movement of, for example, lithium ions. 
     The separator  122  may include, for example, polyethylene (PE), polypropylene (PP) or a composite film of PE and PP, which are provided only for illustration, but the present invention does not limit the material of the separator  122  to those disclosed therein. 
     The anode plate  123  is formed by coating an anode active material on an anode current collector shaped of a metal foil. The anode current collector may include, for example, copper (Cu) or nickel (Ni), and the anode active material may include, for example, carbon. These materials are provided only for illustration, but the present invention does not limit the material of the anode plate  123  to those disclosed therein. 
     Here, an anode non-coating portion  123   a  without an anode active material coated thereon is also formed at a portion of the anode plate  123 . 
     A stack including the cathode plate  121 , the separator  122  and the anode plate  123  is wound in a jelly roll configuration to be received in the can  110 , as stated above. 
     The cathode tab  124  made of a conductive material, such as aluminum, has one end attached to the cathode non-coating portion  121   a  and the other end generally extending toward the cap assembly  130 , as illustrated in  FIG. 1 , to then be coupled to the cap assembly  130 . In this case, the cap assembly  130  may function as a cathode. Of course, the cathode tab  124  may be coupled to be electrically connected to the can  110 , unlike in  FIG. 1 . However, the following description will be made by way of example with regard to a case where the cathode tab  124  is coupled to be electrically connected to the cap assembly  130 , as illustrated in  FIG. 1 . 
     The anode tab  125  made of a conductive material has one end attached to the anode non-coating portion  123   a  and the other end generally extending toward the bottom surface  111  of the can  110  by resistance welding, as illustrated in  FIG. 1 , to then be coupled to the can  110 . In this case, the can  110  may function as an anode. Of course, as stated above, if the cathode tab  124  is coupled to be electrically connected to the can  110 , the anode tab  125  is coupled to be electrically connected to the cap assembly  130 , unlike in  FIG. 1 . 
     Meanwhile, nickel (Ni) has been proposed as a material of the anode tab  125 . However, nickel has a specific resistance of approximately 69.3 nΩ·m, which is relatively high, making it disadvantageous in providing the secondary battery  100  having a high-output characteristic, and generating high temperature heat to cause unwanted deformation to the separator  122 . 
     In addition, copper (Cu) having a smaller specific resistance than nickel (Ni) has been proposed as an alternative material of the anode tab  125 . However, copper has a low dissolution potential so that it is easily dissolved, resulting in a minute short circuit and increasing a defective rate with respect to dV and OCV. Moreover, since copper is highly brittle, a relatively large amount of alien materials may be produced due to burrs during manufacture, causing a minute short circuit during operation of the secondary battery  100  and resulting in an increased possibility of further increasing the defective rate. 
     In light of the foregoing, the anode tab  125  of the present invention is made of nickel-plated copper. 
       FIG. 2  is a transverse sectional view of an anode tab  125  of the secondary battery  100  according to an embodiment of the present invention, that is, a cross-sectional view of the anode tab  125 , taken along a plane perpendicular to a longitudinal direction in which the anode tab  125  extends. 
     Referring to  FIG. 2 , the anode tab  125  is configured such that surfaces of copper are enclosed by nickel, as described above. That is to say, as illustrated in  FIG. 2 , four surfaces, i.e., top, bottom, right and left surfaces, of copper are all enclosed by nickel. Although it is preferable to plate all of the four surfaces with nickel, all of the four surfaces are not necessarily plated with nickel. When necessary, unlike in  FIG. 2 , some of the four surfaces may be entirely plated with nickel or may be partially plated with nickel. However, the following description will be made by way of example with regard to a case where all of the four surfaces are entirely plated with nickel, as illustrated in  FIG. 2 . 
     Here, nickel may be plated by electroplating, electroless plating or a combination thereof. 
     Accordingly, the anode tab  125  may have a reduced specific resistance, compared to a case where the anode tab  125  is made of nickel only, thereby providing the secondary battery  100  having an improved high-output characteristic. Here, nickel may be plated to have a weight ratio of approximately 1 wt % or less so as to obtain a high-output characteristic equivalent to a case where the anode tab  125  is made of pure copper. 
     In addition, since the surfaces of copper are not exposed, it is possible to prevent dissolution of copper, as confirmed from the graph illustrated in  FIG. 3 . 
       FIG. 3  is a graph illustrating experimental data for comparing dissolution potentials in cases where the anode tab  125  is made of copper only and where the anode tab  125  is made of copper plated with nickel to a thickness of approximately 1.5 μm. 
     Referring to  FIG. 3 , dissolution of copper starts in a range of generally used voltages when the anode tab  125  is made of copper only, but no dissolution is observed even in a slightly higher range than the generally used voltage range when the anode tab  125  is made of nickel-plated copper. 
     Table 1 shows data of defective rates measured when the anode tab  125  is made of copper (Cu) only and when the anode tab  125  is made of copper (Cu) plated with nickel (Ni) to thicknesses of approximately 0.5 μm, approximately 1 μm and approximately 1.5 μm, respectively. Here, tests were carried out a number of times in each case, and ratios of defective anode tabs relative to a total number of tested anode tabs were calculated. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Appr. 0.5 μm 
                 Appr. 1 μm 
                 Appr. 1.5 μm 
               
               
                   
                 Cu 
                 plated with Ni 
                 plated with Ni 
                 plated with Ni 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Total test 
                 8,483 
                 249 
                 420 
                 399 
               
               
                 pieces 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Defective 
                   
                 Defective 
                   
                 Defective 
                   
                 Defective 
               
               
                   
                 Defects 
                 rate 
                 Defects 
                 rate 
                 Defects 
                 rate 
                 Defects 
                 rate 
               
               
                   
               
               
                 OCV after 
                 37 
                 0.44% 
                 3 
                 1.20% 
                 1 
                 0.24% 
                 0 
                 0.00% 
               
               
                 high 
               
               
                 temperature 
               
               
                 exposure 
               
               
                 OCV3 
                 32 
                 0.38% 
                 1 
                 0.40% 
                 3 
                 0.71% 
                 0 
                 0.00% 
               
               
                 dV 
                 118 
                 1.39% 
                 1 
                 0.40% 
                 1 
                 0.24% 
                 1 
                 0.25% 
               
               
                 Sum 
                 187 
                 2.20% 
                 5 
                 2.01% 
                 5 
                 1.19% 
                 1 
                 0.25% 
               
               
                   
               
            
           
         
       
     
     As indicated from Table 1, when the anode tab  125  is made of copper only, the sum of defective rates ([Sum]=[OCV after high temperature exposure]+[OCV3]+[dV]) was 2.20%, which is relatively high. However, when the anode tab  125  is made of nickel-plated copper, sums of defective rates were reduced from 2.01% to 0.25% according to the thickness of nickel plated. This suggests that dissolution of copper can be prevented by employing nickel-plated copper as a material for forming the anode tab  125 , as stated above. 
     In addition, as confirmed from Table 1, as the thickness of nickel plated is increased, the defective rate was further reduced. However, since an appropriate rate of good products is attained when nickel is plated on the surface(s) of copper to a thickness of approximately 1.5 μm, it is preferably to plate nickel on the surface(s) of copper to a thickness of approximately 1.5 μm or less, thereby avoiding an excessive increase in the manufacturing cost due to unnecessarily thickly plated nickel. 
     Once the anode tab  125  is made of nickel-plated copper, the defective rate can be further reduced, compared to a case where the anode tab  125  is made of copper only. Thus, a lower limit of the weight ratio or thickness of nickel plated will not be specifically defined. 
     In order to obtain desired material characteristics, heat treatment for achieving, for example, increased hardness, may further be performed on surfaces of the anode tab  125 . In addition, in order to increase corrosion resistance, chromate (CrO 3 ) treatment may further be performed on surfaces of the anode tab  125 . 
     Referring back to  FIG. 1 , the cap assembly  130  installed on the beading part  112   a  of the can  110  may seal the can  110 . The cap assembly  130  may include a cap-up  131 , a safety device  132  and a safety vent  133 . 
     An upwardly convexly protruding terminal part  131   a  is formed at the center of the cap-up  131  to be electrically connected to an external circuit. In addition, an outlet  131   b  is formed to release internal gases generated in the can  110 . 
     The safety device  132  may be disposed under the cap-up  131 . The safety device  132 , which is a positive temperature coefficient (PTC) device having increased resistance as the temperature rises, may function to prevent current from flowing between the cathode tab  124  and the cap-up  131  of the electrode assembly  120  due to increased resistance when the secondary battery  100  is over-heated. 
     The safety vent  133  is disposed under the safety device  132  to then be electrically connected to the cathode tab  124  of the electrode assembly  120 . A notch  133   a  is formed in the safety vent  133 . When a pressure is applied to the safety vent  133  due to the gases generated in the can  110 , the safety vent  133  is ruptured along the notch  133   a . Here, the gases are released through gaps created by the rupturing of the safety vent  133 , thereby preventing the secondary battery  100  from exploding due to excessive pressure. 
     When necessary, the cap assembly  130  may further include an insulation sheet or an auxiliary plate between the cap-up  131  and the safety device  132  or between the safety device  132  and the safety vent  133 . 
     The gasket  140  made of an insulating material is installed between the can  110  and the cap assembly  130 . As described above, the can  110  may operate as an anode, and the cap assembly  130  may operate as a cathode. Here, based on the foregoing description, the gasket  140  may function to prevent a short circuit from occurring due to a contact between the can  110  and the cap assembly  130 . 
       FIG. 4  is a transverse sectional view of an anode tab  225  of a secondary battery according to another embodiment of the present invention, and  FIG. 5  is a transverse sectional view of an anode tab  325  of a secondary battery according to still another embodiment of the present invention. 
     As stated above, the anode tab  125  may be coupled to the bottom surface  111  of the can  110  by resistance welding. Here, since the anode tab  125  includes copper having low resistivity, welding strength of the anode tab  125  may be slightly lowered, compared to a case where the anode tab  125  includes only nickel. In this regard, the welding strength of the anode tab  125  may be increased by applying increased current. However, unwanted conduction may occur to edges of the anode tab  125 , specifically burrs of the edges generated in the course of shaping the anode tab  125 , thereby increasing the possibility of lowering welding quality. 
     To avoid this, the edges of the anode tabs  225  and  325  may be processed by chamfer treatment. 
     Here, the chamfer-treated edges of the anode tabs  225  and  325  may be planar, as illustrated in  FIG. 4 . 
     In addition, the chamfer-treated edges of the anode tabs  225  and  325  may be curved, as illustrated in  FIG. 5 . 
     In addition, the chamfer treatment may be performed on all of the edges of the anode tabs  225  and  325 . However, as illustrated in  FIGS. 4 and 5 , the chamfer treatment may be performed on the edges of the anode tabs  225  and  325 , which are parallel with longitudinal directions in which the anode tabs  225  and  325  extend, respectively. Alternatively, unlike in  FIGS. 4 and 5 , the chamfer treatment may be performed on some of the edges of the anode tabs  225  and  325 , respectively. 
     Meanwhile, the processing may be performed in such an order that chamfer treatment is first subjected to copper formed in a tab-like shape, edges of the tab-like copper are cut and nickel is then plated on the edges. Alternatively, the processing may be performed in such an order that nickel is first plated on the tab-like copper and chamfer treatment is then subjected to the nickel plated copper. 
     That is to say, the processing may be performed in different manners according to individual design conditions. 
     Although the foregoing embodiments have been described to practice the secondary battery of the present invention, 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.