Abstract:
Provided is a battery pack formed by coupling a cover case and a bare cell. The battery pack includes: a bare cell including a cap plate having a surface in which at least one screw receiving groove is formed; a cover case disposed at a side of the cap plate, and having a surface in which at least one mounting groove is formed and a hole penetrating a center of the mounting groove; and at least one tapping screw including a head part and a body part that are mounted in the mounting groove of the cover case, wherein the body part penetrates the hole and is coupled to the screw receiving groove of the cap plate; wherein the cap plate includes a protruding unit formed in the second surface of the cap plate in correspondence to the screw receiving groove of the cap plate.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2009-0110914, filed on. Nov. 17, 2009, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    One or more embodiments of the present invention relate to a battery pack, and more particularly, to a battery pack formed by coupling a cover case and a bare cell. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, portable electric/electronic devices are being made compact and light, for example compact and light cellular phones, notebook computers, camcorders, etc., are being actively developed and produced. Accordingly, portable electric/electronic devices include battery packs so as to be operated even in places where additional power sources are not available. Recently, battery packs have employed economical secondary batteries which are capable of charging and discharging. Representative secondary batteries include a nickel (Ni)-cadmium (Cd) battery, a Ni—MH battery, a lithium (Li) battery, a Li-ion secondary battery, etc. In particular, operation voltage of the lithium ion secondary battery is about three times higher than that of the Ni—Cd battery or the Ni—MH battery, which are usually used as a power source for portable electronic devices. Also, the Li-ion secondary battery is widely used in view of high energy density per unit weight. Secondary batteries generally use lithium-based oxides as positive electrode active materials and carbon-based materials as negative electrode active materials. In general, a secondary battery may be a liquid electrolyte battery or a polymer electrolyte battery according to the type of electrolyte in the secondary battery. In this instance, a Li battery using a liquid electrolyte is referred to as a Li-ion battery, and a Li battery using a polymer electrolyte is referred to as a lithium polymer battery. A secondary battery is formed of a bare cell formed by sealing a can accommodating an electrode assembly and an electrolyte, and a protection circuit substrate electrically connected to the bare cell. The bare cell charges/discharges electricity via a chemical reaction. The protection circuit substrate controls charging/discharging of the bare cell and prevents overcharging/overdischarging of the bare cell to protect the bare cell. When the bare cell and the protection circuit are connected to form the secondary battery, electrical resistance therebetween should be reduced in order to improve charging/discharging efficiency. In more detail, if the electrical resistance between the bare cell and the protection circuit module is high, the charging/discharging efficiency of the bare cell is reduced. 
         [0006]    Meanwhile, the secondary battery may be put through a reliability test for determining whether the secondary battery is stable enough to withstand impact caused when mounting the secondary battery in an electronic product, after being formed in a pack by integrally connecting the bare cell and the protection circuit substrate. If there is an external impact, the electrical resistance between the bare cell and the protection circuit substrate could conceivable be increased. The electrical resistance increases as contact resistance increases in a part where the bare cell and the protection circuit substrate are connected. 
       SUMMARY OF THE INVENTION 
       [0007]    One or more embodiments of the present invention include a battery pack formed by coupling a cover case and a bare cell. 
         [0008]    Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
         [0009]    According to one or more embodiments of the present invention, the battery pack including: a bare cell including a cap plate having a surface in which at least one screw receiving groove is formed; a cover case disposed at a side of the cap plate, and including a surface in which at least one mounting groove is formed and has a hole penetrating a center of the mounting groove; and at least one tapping screw including a head part and a body part that are mounted in the mounting groove of the cover case, wherein the body part penetrates the hole and is coupled to the screw receiving groove of the cap plate; wherein the cap plate comprises a protruding unit formed in the second surface of the cap plate in correspondence to the screw receiving groove of the cap plate. 
         [0010]    The battery pack further may include a protection circuit substrate that is disposed between the cap plate and the cover case and comprises a tap in which a coupling hole is formed in correspondence to the screw receiving groove, wherein the body part of the tapping screw penetrates the coupling hole of the tap, and the tap is electrically connected to the bare cell through the connection between the tapping screw and the screw receiving groove. 
         [0011]    The coupling hole of the tap may be formed to be greater than an inside diameter of the body part of the tapping screw and less than an outside diameter of the outside diameter of the body part of the tapping screw. 
         [0012]    A connection part between the protruding unit of the cap plate and the second surface of the cap plate may be a curved surface. 
         [0013]    A connection part between the protruding unit of the cap plate and the second surface of the cap plate may be an inclined surface. 
         [0014]    When the tapping screw fixes the cover case to the cap plate, the screw receiving groove of the cap plate may have such a depth so as to have a space between a lower end surface of the body part of the tapping screw and a bottom surface of the screw receiving groove of the cap plate. 
         [0015]    An inner diameter of the screw receiving groove of the cap plate may be greater than an inside diameter of the body part and less than an outside diameter of the body part, thus when the screw receiving groove is coupled to the tapping screw, the shape of an inner circumferential surface of the screw receiving groove is deformed to be tightly adhered to the body part of the first tapping screw, and at least a part of scraps generated due to the shape-change is accommodated in the space. 
         [0016]    An inner circumferential surface of the screw receiving groove includes a projection, so that an inscribed circle is greater than the inside diameter of the body part of the tapping screw and is less than the outside diameter of the body part of the tapping screw, when the screw receiving groove is coupled to the tapping screw, the projection of the screw receiving groove is cut and deformed to be tightly adhered to the body part of the tapping screw, and at least a part of the scraps generated due to the shape-change is accommodated in the space. 
         [0017]    When the tapping screw fixes the cover case to the cap plate, a length of the body part of the tapping screw and a thickness of the cap plate may each have a predetermined value, so that a lower end surface of the body part reaches or does not reach an upper surface of the cap plate. 
         [0018]    The thickness of the cap plate may be in the range of from about 0.8 mm to about 1 mm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0020]      FIG. 1A  is an exploded perspective view illustrating a battery pack according to an embodiment of the present invention; 
           [0021]      FIG. 1B  is a perspective view illustrating an assembled state of the battery pack of  FIG. 1A  according to an embodiment of the present invention; 
           [0022]      FIG. 1C  is a partial cross-sectional view taken along a line I-I of  FIG. 1B  according to an embodiment of the present invention; 
           [0023]      FIG. 1D  is an enlarged cross-sectional view illustrating a peripheral portion of a screw bolt of  FIG. 1C  according to an embodiment of the present invention; 
           [0024]      FIG. 2  is a cross-sectional view illustrating the peripheral portion of a screw bolt of  FIG. 1D , according to another embodiment of the present invention; 
           [0025]      FIG. 3A  is a cross-sectional view illustrating the peripheral portion of a screw bolt of  FIG. 1D , according to another embodiment of the present invention; 
           [0026]      FIG. 3B  is a cross-sectional view illustrating the peripheral portion of a screw bolt of  FIG. 1D , according to another embodiment of the present invention; 
           [0027]      FIG. 4  is a perspective view of the peripheral portion of a screw bolt of  FIG. 1D  including a projection, according to another embodiment of the present invention; and 
           [0028]      FIGS. 5A and 5B  are plane views of a screw receiving groove according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. 
         [0030]      FIG. 1A  is an exploded perspective view illustrating a battery pack  100  according to an embodiment of the present invention.  FIG. 1B  is a perspective view illustrating an assembled state of the battery pack  100  of  FIG. 1A  according to an embodiment of the present invention.  FIG. 1C  is a partial cross-sectional view taken along a line I-I of  FIG. 1B  according to an embodiment of the present invention.  FIG. 1D  is an enlarged cross-sectional view illustrating a peripheral portion of a screw bolt of  FIG. 1C  according to an embodiment of the present invention. As illustrated in  FIGS. 1A through 1D , the battery pack  100  includes a bare cell  110 , a protection circuit substrate  120 , a cover case  150 , and tapping screws  141  and  142 . 
         [0031]    The bare cell  110  includes an electrode assembly (not shown) and a sealing assembly  111  accommodating the electrode assembly. The electrode assembly may be formed by winding a positive electrode plate (not shown), a negative electrode plate (not shown), and a separator (not shown). The sealing assembly  111  may include a cap plate  111   a  and a metal type can  111   b  and may be formed of a conductive material, for example, aluminum. The metal type can  111   b  has an open end, and the cap plate  111   a  covers the open end of the metal type can  111   b . An electrode terminal  114  that is insulated by an insulator  114   a  may be formed in either the metal type can  111   b  or the cap plate  111   a . Referring to  FIGS. 1A and 1C , the electrode terminal  114  insulated by the insulator  114   a  is inserted into the cap plate  111   a . The positive electrode plate of the bare cell  110  may be electrically connected to the sealing assembly  111 , and the negative electrode plate of the bare cell  110  may be electrically connected to the electrode terminal  114 . The electrode terminal  114 , which is connected to the negative electrode plate of the bare cell  110 , and the sealing assembly  111 , which is connected to the positive electrode plate of the bare cell  110 , may have different polarities. In the current embodiment, the electrode terminal  114  is electrically connected to the negative electrode plate of the electrode assembly of the bare cell  110  to be a negative electrode P−, and the sealing assembly  111  is electrically connected to the positive electrode plate of the electrode assembly of the bare cell  110  to be a positive electrode P+, but the present invention is not limited thereto. In other words, the bare cell  110  may be a rectangular battery in which the electrode assembly is sealed in the sealing assembly  111  formed of a metal material, in which the positive electrode plate or the negative electrode plate of the electrode assembly is electrically connected to the sealing assembly  111 , and the other plate is connected to the electrode terminal  114 . 
         [0032]    Here, one surface of the cap plate  111   a  of the bare cell  110  may include at least one selected from the group consisting of screw receiving grooves  112  and  113 . Referring to  FIG. 1A  or  1 C, the cap plate  111   a  includes the first screw receiving groove  112  and the second screw receiving groove  113 . The first screw receiving groove  112  may be coupled with the first tapping screw  141 , and the second screw receiving groove  113  may be coupled with the second tapping screw  142 . Also, a screw thread may be formed in each of inner circumferential surfaces of the first and second screw receiving grooves  112  and  113  in order for the first and second tapping screws  141  and  142  to be coupled therewith. The cap plate  111   a  may form a protruding part P corresponding to the screw receiving grooves  112  and  113 . Various shapes of the protruding part P will be described later with reference to drawings. 
         [0033]    The protection circuit substrate  120  may include an insulating substrate  121 , a printed circuit pattern (not shown), a conductive pad  123 , a protection circuit unit  124 , a charging/discharging terminal  125 , and first and second taps  131  and  132 . The conductive pad  123 , the protection circuit unit  124 , and the charging/discharging terminal  125  may be soldered to the printed circuit pattern formed on the insulating substrate  121 . The protection circuit substrate  120  may be electrically connected to the bare cell  110 . That is, a negative electrode of the protection circuit substrate  120  may be electrically connected to the electrode terminal  114 , which is the negative electrode P− of the bare cell  110 , by a lead tap  120   a , and a positive electrode of the protection circuit substrate  120  may be electrically connected to the sealing assembly  110 , which is the positive electrode P+ of the bare cell  110 , by the first tap  131 . A Positive Temperature Coefficient (PTC) device  120   a   1  is electrically connected between the negative electrode of the protection circuit substrate  120  and the electrode terminal  114  and may block the electrical connection between the negative electrode of the protection circuit substrate  120  and the electrode terminal  114  when the temperature thereof is excessively high or a current excessively flows therethrough. The protection circuit unit  124  may selectively comprise a passive device such as a resistor, a capacitor, or the like, an active device such as a field-effect transistor, a safety device such as the PTC device  120   a   1 , and integrated circuits. The protection circuit unit  124  charges or discharges the bare cell  110  when the bare cell  110  is to be charged/discharged, and blocks a charging/discharging path in the bare cell  110  when the bare cell  110  is overheated or is in an overcurrent state, thereby preventing the bare cell  110  from lifetime degradation, overheating, exploding, and the like. 
         [0034]    The first and second taps  131  and  132  are respectively formed on different ends of the protection circuit substrate  120  to electrically connect the protection circuit substrate  120  and the bare cell  110 . First and second coupling holes  131   a  and  132   a  may be formed in the first and second taps  131  and  132  corresponding to the screw receiving grooves  112  and  113 , respectively. Referring to  FIG. 1C , the first tap  131  and the second tap  132  are in contact with the cap plate  111   a  of the bare cell  110 . The first and second coupling holes  131   a  and  132   a  respectively corresponding to the first and second screw receiving grooves  112  and  113  of the cap plate  111   a  are formed in the first tap  131  and the second tap  132 . The first tap  131  and the second tap  132  support the protection circuit substrate  120  to be disposed on a surface of the bare cell  110 , and electrically connect the positive electrode of the protection circuit module  120  and the positive electrode of the bare cell  110 . The first tap  131  and the second tap  132  may comprise first sections  131   b  and  132   b , second sections  131   c  and  132   c , and third sections  131   d  and  132   d . Since the first tap  131  and the second tap  132  may be curved in the same manner, descriptions of one tap may be applied to the other tap. For example, the first section  131   b  of the first tap  131  is soldered to the protection circuit substrate  120 . The second section  131   c  of the first tap  131  is curved in a first direction with respect to the first section  131   b . The third section  132   d  of the first tap  131 , in which the first coupling hole  131   a  is formed, is curved in a second direction with respect to the second section  131   c , that is, in an opposite direction to the direction with respect to the first section  131   b  that the second section  131   c  is curved. The second and third section  131   c  and  131   d  of the first tap  131  are curved so that the protection circuit substrate  120  and a surface of the bare cell  110  may be disposed parallel to each other. The first screw receiving groove  112  formed in the cap plate  111   a  and the first coupling hole  131   a  of the first tap  131  are formed corresponding to each other, in such a way that the first tapping screw  141  may be coupled perpendicularly to the bare cell  110 . Meanwhile, the second tapping screw  142  passing through the second coupling hole  132   a  formed in the third section  132   d  of the second tap  132  may be coupled perpendicularly to the second screw receiving groove  113 . The first tap  131  and the second tap  132  are formed of nickel or an alloy including nickel, and thus the coupling and conductivity between the first tap  131  and the second tap  132  and the protection circuit substrate  120  via soldering are enhanced. The first tap  131  and the second tap  132  are disposed to face the protection circuit substrate  120 , and thus the conductivity and coupling between the first tap  131  and the second tap  132  and the bare cell  110  are enhanced, thereby reducing contact resistance between the first and second taps  131  and  132  and the bare cell  110 . 
         [0035]    The cover case  150  includes at least one selected from the group consisting of first and second holes  151   a  and  152   a . Mounting grooves  151   b  and  152   b  are formed outside of the first and second holes  151   a  and  152   a . For example, the mounting grooves  151   b  and  152   b  are formed to have inner diameters greater than those of the first and second holes  151   a  and  152   a  so as to support head parts  141   b  and  142   b  of the first and second tapping screws  141  and  142 . Hereinafter, the mounting grooves  151   b  and  152   b  will be referred to as a first mounting groove  151   b  and a second mounting groove  152   b , respectively. The first tapping screw  141  may be coupled to the first screw receiving groove  112  formed in the bare cell  110  after passing through the first hole  151   a  formed in the cover case  150  and the first coupling hole  131   a  formed in the first tap  131 . The head part  141   b  of the first tapping screw  141  may be tightly adhered to the first mounting groove  151   b  of the cover case  150 . The second tapping screw  142  may be coupled in a similar manner. Therefore, the first tapping screw  141  and the second tapping screw  142  couple the cover case  150  to the bare cell  110 . The cover case  150  is a plastic case made by molding a resin material such as polycarbonate, and protects the protection circuit substrate  120  from an external impact and prevents a short circuit in the protection circuit substrate  120 . 
         [0036]    Referring to  FIG. 1C , a rib  161  is formed inside the cover case  150 , and a rib  161  supports an upper surface of the protection circuit substrate  120  to tightly adhere the protection circuit substrate  120  to the bare cell  110 , which prevents the protection circuit substrate  120  from moving, and the contact resistance between the first and second taps  131  and  132  soldered to the protection circuit substrate  120  and the bare cell  110  from increasing. When the cover case  150  is coupled with the first and second tapping screws  141  and  142 , the first and second taps  131  and  132  are more tightly adhered to the bare cell  110  to prevent an increase in the contact resistance between the first tap  131  and the bare cell  110 . 
         [0037]    Referring to  FIG. 1D , chamfer parts  151   c  and  152   b  are corner parts where the first and second mounting grooves  151   b  and  152   b  of the cover case  150  and the first and second holes  151   a  and  152   a  of the cover case  150  contact each other. Chamfer parts  141   c  and  142   c  of the first and second tapping screws  141  and  142  are slidingly inserted into the chamfer parts  151   c  and  152   c  of the cover case  150 , such that a center axis of the first and second holes  151   a  and  152   a  of the cover case  150  and a center axis of the first and second tapping screws  141  and  142  are aligned, thereby reducing assembly error between the cover case  150  and the first and second tapping screws  141  and  142 . The cover case  150  is tightened onto the bare cell  110  via the first and second tapping screws  141  and  142  and is integrally formed with the bare cell  110 . The cover case  150  tightly adheres the protection circuit substrate  120  to the cap plate  111   a  so as to prevent the protection circuit substrate  120  from moving. In addition, the first tap  131  is soldered to the protection circuit substrate  120  and is thus electrically connected to the bare cell  110 . Since the first tap  131  is tightly adhered to the cap plate  111   a  by the pressure of the cover case  150 , it prevents an increase in the contact resistance between the first tap  131  and the cap plate  111   a . Meanwhile, when the first tapping screw  141  is coupled to the first screw receiving groove  112  of the bare cell  110 , a space G ( FIG. 2 ) having a greater diameter than that of the first screw receiving groove  112  is formed in an upper end part of the first screw receiving groove  112  to prevent a burr from being generated, thereby preventing an increase in the contact resistance due to external impact. 
         [0038]    The first and second tapping screws  141  and  142  include body parts  141   a  and  142   a  and head parts  141   b  and  142   b . The body parts  141   a  and  142   a  of the first and second tapping screws  141  and  142  include a screw thread that is screw-coupled to the screw receiving groove  112  and  113  of the bare cell  110 . The head parts  141   b  and  142   b  of the first and second tapping screws  141  and  142  are formed in an upper part of the body parts  141   a  and  142   a , and have a diameter greater than that of the body parts  141   a  and  142   a . In  FIG. 1A , grooves marked with + are formed in the head parts  141   b  and  142   b  of the first and second tapping screws  141  and  142  to facilitate rotation. The shape of the grooves is not limited thereto. In the present invention, one of ordinary skill in the art may envision the groove having various shapes. In addition to the + mark, the grooves may be marked with ′− or *. A screw driver is inserted into the grooves so that the first and second tapping screws  141  and  142  may be screw-coupled to the bare cell  110 . The first and second tapping screws  141  and  142  are coupled to the first and second screw receiving grooves  112  and  113   b  formed on different sides of the bare cell  110 , so that the protection circuit substrate  120  may not be twisted and so that the coupling between the first and second taps  131  and  132  and the protection circuit substrate  120  by soldering is enhanced, thereby preventing an increase in contact resistance. 
         [0039]    A method of coupling the protection circuit substrate  120  and the cover case  150  with the cap plate  111   a  of the bare cell  110  using the first and second tapping screws  141  and  142  will now be described with reference to  FIG. 1D . Since operation of the first tapping screw  141  is similar to that of the second tapping screw  142 , only the first tapping screw  141  will be described below. The first tapping screw  141  may be coupled to the first screw receiving groove  112  formed in the cap plate  111   a  of the bare cell  110  after passing through the first hole  151   a  formed in a center of the cover case  150  and the first coupling hole  131   a  formed in the first tap  131 . The cap plate  111   a  includes the protruding part P so as to be coupled with the first tapping screw  141 . If the cap plate  111   a  is formed as a straight flat plate not including the protruding part P, the first and second tapping screws  141  and  142  may be coupled to the cap plate  111   a  by an amount corresponding to a thickness of the cap plate  111   a . Therefore, when the coupling between the first and second tapping screws  141  and  142  and the cap plate  111   a  is low, and thus If the first and second tapping screws  141  and  142  is penetrated, electrolyte may leak. However, referring to  FIG. 1D , a part of the cap plate  111   a  corresponding to where the first tapping screw  141  and the cap plate  111   a  are coupled to each other is formed to be thick, that is, the protruding part P is formed in the thick part, thereby increasing stability. Also, when the first tapping screw  141  fixes the cover case  150  and the protection circuit substrate  120  to the cap plate  111   a , the screw receiving groove  112  of the cap plate  111   a  may have a sufficient depth so as to form a space V between a lower end surface of the body part  141   a  of the first tapping screw  141  and a bottom surface of the screw receiving groove  112  of the cap plate  111   a . In this instance, when the first tapping screw  141  fixes the cover case  150  and the protection circuit substrate  120  to the cap plate  111   a , a length of the body part  141   a  of the first tapping screw  141  and a thickness of the cap plate  111   a  may each be a predetermined value, so that the lower end surface of the body part  141   a  reaches or does not reach an upper surface of the cap plate  111   a . That is, referring to  FIG. 1D , the lower end surface of the first tapping screw  141  is coupled not to exceed the thickness of the cap plate  111   a , thereby forming the space V in the lower end part of the body part  141   a  of the first tapping screw  141 . In order to form this structure, the thickness of the cap plate  111   a , the length of the body part  141   a  of the first tapping screw  141 , or step heights of the first and second holes  151   a  and  152   a  of the first and second mounting grooves  151   b  and  152   b  of the cover case  150  may be controlled. For example, the thickness of the cap plate  111   a  may be in a range of from about 0.8 mm to about 1 mm. 
         [0040]    A screw groove may be formed in an inner circumferential surface of the screw receiving groove  112  to be coupled with the first tapping screw  141 . Alternatively, the screw groove is not formed, and the inner circumferential surface is formed to be smaller than an outside diameter of the first tapping screw  141 , so that the screw thread of the first tapping screw  141  is coupled to the inner circumferential surface of the screw receiving groove  112  by cutting an outer surface of the screw groove. For example, the inner diameter of the screw receiving groove  112  of the cap plate  111   a  is greater than an inner diameter of the body part  141   a  and less than an outside diameter of the body part  141   a . Therefore, when the screw receiving groove  112  is coupled to the first tapping screw  141 , the inner circumferential surface of the screw receiving groove  112  is deformed to be tightly adhered to the body part  141   a  of the first tapping screw  141 . At this time, if the inner circumferential surface of the screw receiving groove  112  is cut and deformed by the screw thread of the body part  141   a  of the first tapping screw  141 , scraps are generated. These scraps may be accommodated in the space V, formed between the screw  141  and the protruding part P of the cap plate  111   a . The cap plate  111   a  may include a light alloy, such as aluminum, so as to be easily deformed by the screw thread of the first tapping screw  141 . 
         [0041]    Also, the cap plate  111   a  may include not only the space V but also the groove G in the upper part of the screw receiving groove  112  in order to accommodate the scraps. Referring to  FIG. 2 , an inner diameter  1  of the screw receiving groove  112  of a cap plate  111   a   1  is greater than a inside diameter d 1  of the body part  141   a  and less than an outside diameter d 2  of the body part  141   a  of the first tapping screw  141 . Thus, when the screw receiving groove  112  is coupled to the first tapping screw  141 , the inner circumferential surface of the screw receiving groove  112  is deformed, thereby generating scraps. The groove G has an inner diameter greater than the inner circumferential surface of the screw receiving groove  112  and is formed in the upper part of the screw receiving groove  112  of the cap plate  111   a   1 , and thus may accommodate scraps generated when the first tapping screw  141  is coupled with the cap plate  111   a   1 . 
         [0042]    Referring to  FIG. 3A , a connection part between the protruding part P of the cap plate  111   a   2  and a lower plane of a cap plate  111   a   2  may be an inclined surface F. However, the shape of the connection part is not limited thereto, and the connection part may be a curved surface R as illustrated in a cap plate  111   a   3  of  FIG. 3B . As such, the connection part between the protruding part P and the cap plate  111   a   2  or  111   a   3  may be the inclined surface F or the curved surface R, so that stress is not concentrated in the connection part therebetween, thereby increasing stability. For example, the flat inclined surface F and the curved surface R effectively withstands pressure due to an electrolyte included inside the sealing assembly  110 , thereby preventing the electrolyte from leaking. Also, even when the first tapping screw  141  is coupled in a wrong direction, the first tapping screw  141  does not penetrate the cap plates  111   a   2  and  111   a   3 , thereby preventing the electrolyte from leaking. 
         [0043]    Referring to  FIG. 4 , the first tapping screw  141  passes through the first coupling hole  131   a  of the first tap  131  and is coupled to the screw receiving groove  112  of the cap plate  111   a . In this instance, an inner diameter of the first coupling hole  131   a  may be greater than the is inside diameter d 1  of the body part  141   a  of the first tapping screw  141  and less than the outside diameter d 2 . When the screw receiving groove  112  is coupled with the first tapping screw  141 , the inner diameter of the coupling hole  131   a  is deformed, for example, enlarged. Thus, the coupling hole  131   a  is tightly adhered to the first tapping screw  141 , thereby reducing electrical resistance (therebetween). The screw receiving groove  112  of the cap plate  111   a  may include a projection S. The projection S may be formed to have an inscribed circle r that is greater than the inside diameter d 1  of the body part  141   a  of the first tapping screw  141  and less than the outside diameter d 2  of the body part  141   a  of the first tapping screw  141 . When the screw receiving groove  112  is coupled to the first tapping screw  141 , the projection S of the screw receiving groove  112  is cut and deformed by the screw thread of the first tapping screw  141  to be tightly adhered to the body part  141   a  of the first tapping screw  141 . Scraps generated by the deformation of the projection S may be moved to the space V through a gap between the projections S and accommodated in the space V. The arrangement and the shape of the projection S are not limited thereto, and one of ordinary skill in the art would understand that various other configurations are possible.  FIGS. 5A and 5B  are plane views of the screw receiving groove  112  according to an embodiment of the present invention. Two projections S may be formed as illustrated in  FIG. 5A , or a plurality of projections S may be formed as illustrated in  FIG. 5B . In this instance, a distance r of ends of the projection S may be formed to be greater than the inside diameter d 1  of the body part  141   a  of the first tapping screw  141  and to be less than the outside diameter d 2  of the body part  141   a  of the first tapping screw  141  to deform the projection S when the first tapping screw  141  is coupled to the screw receiving groove  112 , thus the first tapping screw  141  is coupled to the screw receiving groove  112  and they may be further tightly adhered to each other. 
         [0044]    It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other to similar features or aspects in other embodiments.