Patent Publication Number: US-2016226052-A1

Title: Secondary battery

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2015-0015592, filed on Jan. 30, 2015, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     The described technology generally relates to secondary batteries. 
     2. Description of the Related Technology 
     Unlike primary batteries, secondary batteries are rechargeable. They are used as energy sources for mobile devices, electric vehicles, hybrid vehicles, and electric bicycles, or as uninterruptible power supplies. According to the types of devices that operate based on such batteries, the secondary batteries may be used in the form of one battery or a pack including a plurality of batteries electrically connected to one another to form one unit. 
     SUMMARY OF CERTAIN INVENTIVE ASPECTS 
     One inventive aspect relates to secondary batteries that are used to provide power of set devices and are advantageous to make the entire device together with the set devices compact. 
     Another aspect is a secondary battery that includes: at least two or more battery cells; a protective circuit module placed at a rear position of the battery cells and configured to control a charging/discharging operation; a connection tab configured to form a current path between the at least two or more battery cells and the protective circuit module; and an external terminal configured to form a current path between the protective circuit module and an external device, wherein the connection tab and the external terminal may extend in parallel to each other along a longitudinal direction of the secondary battery and may be placed at different levels in a first direction different from the longitudinal direction. 
     The protective circuit module may be placed in an upright position in the first direction so that front and rear surfaces thereof form a main surface. 
     The connection tab and the external terminal may be placed in front of the protective circuit module. 
     A height H 1  of the battery cells in the first direction may be less than a height H 2  of the protective circuit module in the first direction satisfies (H 1 &lt;H 2 ). 
     A length L 1  of battery cells in the longitudinal direction may be greater than a length L 2  of the protective circuit module in the longitudinal direction (L 1 &gt;L 2 ). 
     The at least two or more battery cells may be arranged in a curved direction along a circular arc shape. 
     The secondary battery may further include a cell holder into which the battery cells are inserted so as to connect the plurality of battery cells and to define an assembling position of the battery cells. 
     The cell holder may include a composite material. 
     The battery cells may be arranged in a first row and a second row at a rear position of the first row. 
     The battery cells in the first row and the battery cells in the second row may be arranged in the same curved direction. 
     The secondary battery may further include connection members configured to electrically connect the battery cells to one another. 
     The connection members may include: a first connection member configured to electrically connect the battery cells to each other in the same first row or in the same second row; and a second connection member configured to electrically connect the battery cells in the first row to the battery cells in the second row. 
     The second connection member may connect the battery cells in the first row to the battery cells in the second row. 
     The secondary battery may further include a case including a cell accommodation portion in which the battery cells are accommodated, and a circuit accommodation portion in which the protective circuit module is accommodated, and terminal holes for exposing the external terminal may be formed in the circuit accommodation portion that protrudes upward from the cell accommodation portion. 
     The case may include first and second cases assembled in the first direction so that the first and second cases face each other, and a step height caused by a difference in heights of the cell accommodation portion and the circuit accommodation portion may be formed in the first case in an upward position, and the cell accommodation portion and the circuit accommodation portion may be formed in the second case in a downward position and may have same height. 
     The terminal holes may include first and second terminal holes for exposing first and second external terminals having opposite polarities, respectively, and an inversed insertion prevention portion for preventing inversed insertion caused by polarity confusion may be formed in a vicinity of the first and second terminal holes. 
     The inversed insertion prevention portion may include protrusions formed asymmetrically in the vicinity of the first and second terminal holes. 
     Another aspect is a secondary battery comprising: a plurality of battery cells; a protective circuit module placed at a first side of the battery cells and configured to control a charging/discharging operation; a connection tab electrically connecting the battery cells and the protective circuit module; and an external terminal in electrical connection with the protective circuit module, wherein the connection tab and the external terminal extend in substantially parallel to each other along a longitudinal direction of the secondary battery and are placed at different levels in a first direction different from the longitudinal direction. 
     In the above battery, the protective circuit module is placed in an upright position in the first direction so that front and rear surfaces thereof form a main surface. In the above battery, the connection tab and the external terminal are placed in a first surface of the protective circuit module, wherein the first surface faces the batteries. In the above battery, the height H 1  of the battery cells defined in the first direction is less than the height H 2  of the protective circuit module defined in the first direction satisfies (H 1 &lt;H 2 ). In the above battery, the length L 1  of the battery cells defined in the longitudinal direction is greater than the length L 2  of the protective circuit module defined in the longitudinal direction (L 1 &gt;L 2 ). In the above battery, the battery cells are arranged in a curved direction. The above battery further comprises a cell holder into which the battery cells are inserted so as to connect the battery cells and to define an assembling position of the battery cells. 
     In the above battery, the cell holder is formed of a composite material. In the above battery, the battery cells are arranged in a first row and a second row adjacent to each other. In the above battery, the battery cells in the first row and the battery cells in the second row are arranged in the same curved direction. The above battery further comprises a plurality of connection members configured to electrically connect the battery cells to one another. In the above battery, the connection members comprise: a first connection member configured to electrically connect the battery cells to each other in the same first row or in the same second row; and a second connection member configured to electrically connect the battery cells in the first row to the battery cells in the second row. In the above battery, the second connection member connects the battery cells in the first row to the battery cells in the second row. 
     The above battery further comprises a case comprising a cell accommodation portion in which the battery cells are accommodated, and a circuit accommodation portion in which the protective circuit module is accommodated, and wherein at least one terminal hole configured to expose the external terminal is formed in the circuit accommodation portion that protrudes upwardly from the cell accommodation portion. In the above battery, the case comprises first and second cases assembled in the first direction so that the first and second cases face each other, wherein a step height caused by a difference in heights of the cell accommodation portion and the circuit accommodation portion is formed in the first case in an upward position, and wherein the cell accommodation portion and the circuit accommodation portion are formed in the second case in a downward position and have substantially the same height. 
     In the above battery, the terminal holes comprise first and second terminal holes respectively configured to expose first and second external terminals having opposite polarities, respectively, and wherein an inversed insertion prevention portion configured to prevent inversed insertion caused by polarity confusion is formed in a vicinity of the first and second terminal holes. In the above battery, the inversed insertion prevention portion comprises a plurality of protrusions formed asymmetrically adjacent to the first and second terminal holes. 
     Another aspect is a secondary battery comprising: a first cell holder configured to accommodate a first group of battery cells, wherein the first cell holder is curved to have a first curvature; and a second cell holder adjacent to the first cell holder and configured to accommodate a second group of battery cells electrically connected to the first group of battery cells, wherein the second cell holder is curved to have a second curvature substantially the same as the first curvature, and wherein the first and second cell holders are arranged to accommodate the first and second groups of battery cells to be substantially aligned in a longitudinal direction thereof. 
     The above battery further comprises: a protective circuit module placed at a side of the first or second group of battery cells and configured to control a charging/discharging operation; a connection tab electrically connecting the battery cells and the protective circuit module; and an external terminal in electrical connection with the protective circuit module, wherein the connection tab and the external terminal are placed on the same side of the protective circuit module. In the above battery, each of the first and second groups of battery cells are arranged in a curved direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings. 
         FIG. 1  is a perspective view of a secondary battery according to an exemplary embodiment. 
         FIG. 2  is an exploded perspective view of the secondary battery illustrated in  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the secondary battery illustrated in  FIG. 2  in an electrical connection state. 
         FIG. 4  is a perspective view of a protective circuit module of the secondary battery of  FIG. 2 . 
         FIG. 5  is a view of a case of the secondary battery of  FIG. 1 . 
         FIG. 6  is a view showing terminal holes formed in the case of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS 
     Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present exemplary embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the exemplary embodiments are merely described below, by referring to the figures, to explain aspects of the present description. In this disclosure, the term “substantially” includes the meanings of completely, almost completely or to any significant degree under some applications and in accordance with those skilled in the art. Moreover, “formed on” can also mean “formed over.” The term “connected” includes an electrical connection. 
       FIG. 1  is a perspective view of a secondary battery according to an exemplary embodiment.  FIG. 2  is an exploded perspective view of the secondary battery illustrated in  FIG. 1 .  FIG. 3  is an exploded perspective view of the secondary battery illustrated in  FIG. 2  in an electrical connection state.  FIG. 4  is a perspective view of a protective circuit module of the secondary battery of  FIG. 2 . 
     Referring to  FIG. 2 , the secondary battery includes a plurality of battery cells  10 , a protective circuit module  130  that is placed at a rear position of the battery cells  10  and controls a charging/discharging operation of the battery cells  10 , a connection tab  131  that intermediates electrical connection between the battery cells  10  and the protective circuit module  130 , and an external terminal  132  that intermediates electrical connection between the protective circuit module  130  and an external device (not shown). For example, the connection tab  131  forms a path of a charging/discharging current between the battery cells  10  and the protective circuit module  130 , and the external terminal  132  forms a path of a charging/discharging current between the protective circuit module  130  and the external device (not shown). The connection tab  131  and the external terminal  132  extend in substantially parallel to each other along a longitudinal direction of the secondary battery (e.g., forward/backward direction) and are placed at different levels in a substantially vertical direction (which corresponds to a first direction, hereinafter, the same as above). 
     The battery cells  10  may be electrically connected to each other, and may provide necessary electrical outputs. For example, the battery cells  10  may be connected to each other in series or in parallel or may be connected to each other in a serial/parallel mixed manner. In some embodiments, the secondary battery includes six battery cells  10 . These six battery cells  10  may be connected to each other in series and may provide necessary outputs with high voltages. 
     For example, the battery cells  10  may be arranged in two rows along the longitudinal direction. For example, the battery cells  10  are arranged along a first row R 1  and a second row R 2  at a rear position of the first row R 1 , substantially parallel to the first row R 1 . For example, the longitudinal direction throughout the specification is a direction in which the battery cells  10  and the protective circuit module  130  are arranged. As will be described later, a charging/discharging operation of the battery cells  10  may be performed according to control of the protective circuit module  130  placed at a rear position of the battery cells  10 . 
     The battery cells  10  and the protective circuit module  130  may be accommodated in first and second cases  110  and  120  that face and are coupled to each other in a substantially vertical direction. An insulating plate  180  may be placed on the first case  110  in an upward position. In this case, the insulating plate  180  may provide a contact surface with a set device (not shown) having a secondary battery used to provide driving power and may perform a function of insulation and protection from the set device. 
     As illustrated in  FIG. 3 ; the battery cells  10  may be electrically connected to each other via connection members  151 ,  152 , and  153 . The connection members  151 ,  152 , and  153  may include first and second connection members  151  and  152  having different shapes. For example, the first connection member  151  may electrically connect the battery cells  10  to each other in the same first row R 1  or in the same second row R 2 . The first connection member  151  may have a plate shape and can extend in a predetermined position in the forward/backward direction. 
     The first connection member  151  may be placed at at least two or more locations, for example, at three locations. The second connection member  152  may electrically connect the battery cells  10  in the first row R 1  to the battery cells  10  in the second row R 2 . For example, the second connection member  152  connects electrodes of the battery cells  10  in the first row R 1  to electrodes of the battery cells  10  in the second row R 2 . The battery cells  10  placed in the respective first and second rows R 1  and R 2  to be electrically connected may include a first pair of electrodes placed close to each other and a second pair of electrodes placed away from each other compared to the first pair of electrodes. In this case, the second connection member  152  may electrically connect the second pair of electrodes placed away from each other. The second connection member  152  may include a conductive member with a wire shape extended along the forward/backward direction. As will be described later, adjacent electrodes of the battery cells  10  in the first row R 1  and the battery cells  10  in the second row R 2  may be electrically connected to each other using the third connection member  153 . 
     The first and second connection members  151  and  152  can have different shapes in terms of a connection length between the battery cells  10  and the protective circuit module  130 . That is, the connection length may be shortened by placing the battery cells  10  to be connected to the protection circuit module  130  at a rear position where the battery cells  10  are placed to face the protection circuit module  130 . Accordingly, in order to position the battery cells  10  of both ends with the highest and lowest potentials among the electrically connected battery cells  10  at the same rear portion, it may be necessary to have not only the first connection member  151  but also the second connection member  152  which connects the battery cells  10  placed in the different first and second rows R 1  and R 2 . 
     The third connection member  153  can connect pairs of adjacent electrodes of the battery cells  10  in the first row R 1  and the battery cells  10  in the second row R 2  to each other. For example, the third connection member  153  may be provided as needed. The battery cells  10  in the first row R 1  and the battery cells  10  in the second row R 2  may contact each other so that the pairs of adjacent electrodes thereof may be connected to each other. In this case, the third connection member  153  may be omitted. 
     The protective circuit module  130  controls the charging/discharging operation of each of the battery cells  10 . For example, the protective circuit module  130  collects status information, such as a voltage, a current, or a temperature of each of the battery cells  10  and controls the charging/discharging operation of each battery cell  10 . For example, the protective circuit module  130  may detect an unusual situation, such as over-charging or over-discharging, and may perform a safety operation corresponding to the unusual situation. 
     Referring to  FIG. 4 , the protective circuit module  130  may extend in the vertical direction that is different from the forward/backward direction. The protective circuit module  130  may be placed in an upright position in the vertical direction. That is, the protective circuit module  130  may not be placed in a flat lying position along the forward/backward direction. The arrangement of the protective circuit module  130  may reduce the length of the secondary battery in the forward/backward direction and may contribute to making the entire device compact. 
     The protective circuit module  130  may include a circuit board and electric devices mounted on a circuit board. In this case, the circuit board may be placed in the upright position in the vertical direction so as to have a front surface and a rear surface as a main surface. Here, the main surface can be a surface having the largest area when the circuit board is viewed in the form of a plate. The protective circuit module  130  may be placed in the upright position in the vertical direction and may have the front and rear surfaces as the main surface. 
     Since the protective circuit module  130  is placed in the upright position in the vertical direction, the protective circuit module  130  has a relatively large dimension in the vertical direction. Contrary to this, the battery cells  10  are placed along the forward/backward direction, and the battery cells  10  in the first row R 1  and the battery cells  10  in the second row R 2  are arranged along the forward/backward direction, the battery cells  10  have a relatively large dimension in the forward/backward direction. Thus, the height H 1  of the battery cells  10  (or the arrangement of battery cells) in the vertical direction is less than the height H 2  of the protective circuit module  130  in the vertical direction (H 1 &lt;H 2 ). Also, the length L 1  of the battery cells (or the arrangement of battery cells) in the longitudinal direction is greater than the length L 2  of the protective circuit module  130  in the forward/backward direction (L 1 &gt;L 2 ). 
     The protective circuit module  130  is placed on an electrical path between the battery cells  10  and the external device (not shown), i.e., between a charging device and a load. That is, the protective circuit module  130  intermediates electrical connection between the battery cells  10  and the external device. In some embodiments, the connection tab  131  is interposed between the protective circuit module  130  and the battery cells  10 . On the other hand, the external terminal  132  is interposed between the protective circuit module  130  and the external device. In this case, the connection tab  131  and the external terminal  132  extend to be substantially parallel to each other. For example, the connection tab  131  and the external terminal  132  extend to be substantially parallel to each other along the forward/backward direction. Furthermore, each of the connection tab  131  and the external terminal  132  may have a locally slightly-bent shape. However, overall, the connection tab  131  and the external terminal  132  may extend to be substantially parallel to each other along the forward/backward direction. 
     The secondary battery may be mounted on a set device (not shown), such as a cleaning device, and may provide driving power. In this case, the secondary battery may be implemented in a compact shape in a state in which it is coupled to the set device. The secondary battery is used while being coupled to the set device, and a design of the entire device coupled to the set device may affect consumers&#39; preference. For this reason, the connection tab  131  and the external terminal  132  may be placed together on the same side of the protective circuit module  130 , e.g., in front of the protective circuit module  130 . For example, when the connection tab  131  and the external terminal  132  are placed on opposite sides of the protective circuit module  130 , i.e., in front and rear of the protective circuit module  130  that are different from each other, the battery cells  10  connected to the connection tab  131  are placed in front of the protective circuit module  130 , and the set device connected to the external terminal  132  is placed in rear of the protective circuit module  130  so that the configuration of the entire device extends long in the forward/backward direction and is not advantageous to making the entire device compact. 
     In an exemplary embodiment, all of the connection tab  131  and the external terminal  132  are placed in front of the protective circuit module  130  so that all of the battery cells connected to the connection tab  131  and the set device (not shown) connected to the external terminal  132  may be placed in front of the protective circuit module  130 . Thus, the length of the entire device in the forward/backward direction may be reduced, and the configuration of the entire device may be advantageous to making the secondary battery compact. 
     All of the connection tab  131  and the external device  132  form connection with the protective circuit module  130  and are placed in front of the protective circuit module  130 . Thus, the connection tab  131  and the external terminal  132  may be placed at different levels in the vertical direction so as to prevent confusion of the electrical path. Also, the external terminal  132  is placed in the upward position in which the battery cells  10  are excluded, and forms connection with the set device (not shown) in the position. That is, the external terminal  132  forms connection with the set device in the upward position of the protective circuit module  130 , whereas the connection tab  131  forms connection with the battery cells  10  in a downward position of the protective circuit module  130 . Thus, a dead space may be removed from a vertical position of the protective circuit module  130 , and the secondary battery may form compact coupling to the set device (not shown). 
     The battery cells  10  may be arranged to be rounded. For example, the battery cells  10  may not extend in a straight line shape along a left/right direction but are arranged in a rounded, circular arc shape. In this embodiment, the battery cells  10  are arranged in a curved shape. The arrangement of the battery cells  10  in the curved shape may be expressed as an exterior of the secondary battery, may implement an ergonomically rounded shape, and may provide a more aesthetic design. 
     The battery cells  10  in the first row R 1  may be arranged in the curved shape, and the battery cells  10  in the second row R 2  may be arranged in the curved shape. The battery cells  10  in the first row R 1  and the battery cells  10  in the second row R 2  may be arranged in substantially the same curved shape. 
     The arrangement of the battery cells  10  in the curved shape may contribute to matching with the set device (not shown). For example, the secondary battery may be mounted on the set device, such as the cleaning device, and may supply driving power to the set device. The secondary battery in the curved shape that closely contacts a round shape of a periphery of a motor (not shown) of the cleaning device may be advantageous to making the entire device together with the set device compact, which provides a stable supporting base for the secondary battery through closely-contacting matching with the set device. 
     As illustrated in  FIG. 3 , the battery cells  10  may be electrically connected to each other using the connection members  151 ,  152 , and  153  and may also be structurally connected to each other using a cell holder  20  into which the battery cells  10  are inserted. The cell holder  20  may implement the arrangement of the battery cells  10  in the first row R 1  in a predetermined curved shape and may implement the arrangement of the battery cells  10  in the second row R 2  in the same curved shape. For example, the cell holder  20  may include a first cell holder  21  into which the battery cells  10  in the first row R 1  are inserted, and a second cell holder  22  into which the battery cells  10  in the second row R 2  are inserted. 
     The cell holder  20  may connect the battery cells  10  structurally, may define an assembling position of the battery cells  10 , and may promote heat-dissipation of the battery cells  10 . The cell holder  20  may be formed of a material having an electrical insulation property and high thermally high conductivity. For example, the cell holder  20  may be formed of a composite material including a matrix resin that accommodates glass fiber or carbon fiber having excellent thermal conductivity. 
     The cell holder  20  may include an opening  20 ′ (see  FIG. 3 ) having the shape of a cylinder that surrounds an outer circumference of each of the battery cells  10 , may form thermal contact with the battery cells  10  inserted into the opening  20 ′, and may dissipate heat transferred from the battery cells  10  to the environment quickly. For example, the battery cells  10  in the first row R 1  are assembled to the cell holder  20 . Even when thermal accumulation occurs in part of the battery cells  10  due to a position effect or a difference in a manufacturing process, thermal concentration may be prevented and driving heat may be quickly propagated using the cell holder  20 . 
       FIG. 5  is a view for describing a structure of cases  110  and  120  of the secondary battery of  FIG. 1 .  FIG. 6  is a view for describing a structure of terminal holes  110   a  and  110   b  formed in the cases  110  and  120  of  FIG. 5 . 
     The battery cells  10  and the protective circuit module  130  are accommodated in the cases  110  and  120 . The cases  110  and  120  may include first and second cases  110  and  120  assembled to face each other in a state in which the battery cells  10  and the protective circuit module  130  are interposed between the first and second cases  110  and  120 . In some embodiments, the cases  110  and  120  include a cell accommodation portion C 1  in which the battery cells  10  are accommodated, and a circuit accommodation portion C 2  in which the protective circuit module  130  is accommodated. As described above, the battery cells  10  are placed in the first and second rows R 1  and R 2  along the forward/backward direction, and the protective circuit module  130  is placed in the upright position in the vertical direction. Thus, the cell accommodation portion C 1  and the circuit accommodation portion C 2  may be formed to have different heights along the vertical direction. The height of the circuit accommodation portion C 2  may be greater than the height of the cell accommodation portion C 1 . 
     The first and second cases  110  and  120  can be assembled to face in the vertical direction. In this case, the height of the cell accommodation portion C 1  and the height of the circuit accommodation portion C 2  in the first case  110  placed in the upward direction may be set to be different from each other, and the height of the cell accommodation portion C 1  and the height of the circuit accommodation portion C 2  in the second case  120  placed in the downward direction may be set to be substantially the same. For example, a step height caused by a difference between the heights of the cell accommodation portion C 1  and the circuit accommodation portion C 2  is formed in the first case  110 , wherein the cell accommodation portion C 1  and the circuit accommodation portion C 2  in the second case  120  may be formed at substantially the same level in a flat shape. 
     As the height of the cell accommodation portion C 1  and the height of the circuit accommodation portion C 2  are set to be different from each other, the circuit accommodation portion C 2  has a step height that protrudes upward from the cell accommodation portion C 1 . As illustrated in  FIG. 6 , terminal holes  110   a  and  110   b  for exposing the external terminal  132  are formed in the circuit accommodation portion C 2  that protrudes upward from the cell accommodation portion C 1 . The external terminal  132  exposed from the secondary battery through the terminal holes  110   a  and  110   b  is connected to the external device and forms a path of a charging/discharging current. 
     The terminal holes  110   a  and  110   b  can be formed as a pair to correspond to external terminals  132   a  and  132   b  having opposite-polarity electrodes, i.e., positive and negative electrodes. In this case, an inversed insertion prevention portion  140  for preventing inversed insertion of polarity confusion may be formed in the vicinity of the terminal holes  110   a  and  110   b.  The inversed insertion prevention portion  140  is formed in the vicinity of the terminal holes  110   a  and  110   b,  and protrusions may be asymmetrically formed in the vicinity of a positive electrode terminal hole  110   a  (first terminal hole) and the vicinity of a negative electrode terminal hole  110   b  (second terminal hole). For example, the secondary battery may be connected to a set device (not shown) and may provide driving power of the set device. In this case, in order to prevent inversed insertion into the set device, i.e., polarity confusion between the set device and the secondary battery, protrusions having an asymmetric shape are provided in the vicinity of the terminal holes  110   a  and  110   b  of the secondary battery, i.e., in the vicinity of the positive electrode and negative electrode terminal holes  110   a  and  110   b  so that inversed insertion caused by confusion of polarities may be fundamentally prevented. For example, when the secondary battery and the set device (not shown) are properly connected to each other, they may be smoothly connected to each other without disturbance of the inversed insertion prevention portion  140 . However, when inversed insertion caused by confusion of polarities occurs, connection between the secondary battery and the set device is not allowed by disturbance of the inversed insertion prevention portion  140 . Each of the terminal holes  110   a  and  110   b  can include a plurality of holes. 
     According to at least one of the disclosed embodiments, a secondary battery may be used to provide power of a set device. In this case, the secondary battery may provide a structure advantageous to making the entire device together with the set device compact. In an exemplary embodiment, battery cells and a protective circuit module for controlling a charging/discharging operation of the battery cells are placed in different directions, and a connection tab and an external terminal that intermediate electrical connection between the battery cells and the set device are placed on the same side of the protective circuit module so that the entire device may be made compact. 
     In addition, a plurality of battery cells can be arranged in a curved shape so that a more aesthetic exterior can be realized and the entire device may be made compact through matching with the set device. 
     It should be understood that exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each exemplary embodiment should typically be considered as available for other similar features or aspects in other exemplary embodiments. 
     While the inventive technology has been described with reference to the figures, 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 as defined by the following claims.