Patent Publication Number: US-2022231382-A1

Title: Battery pack with enhanced structure for preventing short circuit and shock

Description:
TECHNICAL FIELD 
     The present application claims priority to Korean Patent Application No. 10-2019-0125483 filed on Oct. 10, 2019 in the Republic of Korea, the disclosures of which are incorporated herein by reference. 
     The present disclosure relates to a battery pack, and more particularly, to a battery pack having a short circuit preventing structure capable of settling anxiety of a short circuit caused by an external impact applied while battery cells are being electrically connected or used. 
     BACKGROUND ART 
     A secondary battery has high applicability to various product groups and has an electrical characteristic of high energy density. The secondary battery is applied not only to portable electronic devices but also to an electric vehicle, a hybrid electric vehicle, an energy storage system, and the like driven by an electric drive source. 
     The secondary battery is attracting attention as a new energy source for eco-friendliness and energy efficiency enhancement in that no by-product is generated due to energy use, in addition to a primary advantage of greatly reducing the use of fossil fuels. 
     A battery pack applied to an electric vehicle or the like has a structure in which a plurality of battery modules respectively including a plurality of battery cells are connected to obtain high output. In addition, each battery cell includes a positive electrode current collector, a negative electrode current collector, a separator, an active material, an electrolyte, and the like an electrode assembly, and may be repeatedly charged and discharged by an electrochemical reaction between the components. 
     Recently, as the need for a large-capacity structure increases along with utilization as an energy storage source, the demand for a battery pack having a multi-module structure in which a plurality of battery modules having a plurality of secondary batteries connected in series and/or in parallel are aggregated is increasing. The battery pack is designed to accommodate as many battery modules as possible in a limited space by closely arranging the plurality of battery modules in a front and rear direction in order to increase the energy density. Here, each battery module refers to an assembly including cylindrical cells and a cell housing for accommodating the cylindrical cells. As the battery modules are electrically connected in series with each other by a metal plate, the battery pack has high output. 
     Referring to  FIG. 1 , for example, one metal plate  1  is in contact with positive electrode terminals of the cylindrical cells of one battery module, and another metal plate  2  is in contact with negative electrode terminals of cylindrical cells of another battery module. These two metal plates are disposed to be partially overlapped on a side surface of a module stack, and the corresponding overlapped portions are welded to connect the battery modules in series. 
     However, in the conventional battery pack, since unit battery modules are continuously densely arranged, metal plates that should not be in contact with each other when an external impact is applied may contact each other to cause a short circuit. 
     In addition, the metal plates are exposed at outer sides of the side surfaces of the unit battery modules, and a gap therebetween is also narrow, so there is a risk of short circuit caused by an accidental contact of any metal pieces before/after welding due to the mistake of a worker. 
     Accordingly, there is a need to improve the structure of the battery pack, at which a short circuit may easily occur due to an external impact or a contact between metal plates before/after a welding work. 
     DISCLOSURE 
     Technical Problem 
     The present disclosure is designed to solve the problems of the related art, and therefore the present disclosure is directed to providing a battery pack having a reinforced short circuit prevention structure that may eliminate the possibility of contact between metal plates when an external impact is applied and also significantly reduce the risk of short circuit before/after a welding work. 
     Technical Solution 
     In one aspect of the present disclosure, there is provided a battery pack, comprising: a plurality of cell assemblies respectively including battery cells having electrode terminals formed at upper and lower portions thereof and a cell housing for accommodating the battery cells so that the electrode terminals are exposed to the outside, the plurality of cell assemblies being arranged in a front and rear direction; a first metal plate mounted at a top portion of the cell housing and integrally contacting the upper electrode terminals of the battery cells; and a second metal plate mounted at a bottom portion of the cell housing and integrally contacting the lower electrode terminals of the battery cells, wherein the cell housing includes a side portion that has a slit forming a gap into which a part of the first metal plate and a part of the second metal plate are bent and inserted in an upper and lower direction and a perforated hole formed in a direction intersecting the slit, and the bent part of the first metal plate mounted to any one cell housing is overlapped with the bent part of the second metal plate mounted to another the cell housing adjacent thereto inside the perforated hole. 
     The side portion of the cell housing may include an outer sidewall and an inner sidewall that form a double wall structure, and the slit may be formed in a height direction between the outer sidewall and the inner sidewall. 
     The perforated hole may be formed in the outer sidewall. 
     The side portion of the cell housing may further include a short circuit prevention block configured to connect the outer sidewall and the inner sidewall inside the slit and divide an inner space of the slit. 
     The first metal plate may include a first terminal contact portion configured to cover the top portion of the cell housing; and first bent portions bent and extending from both ends of the first terminal contact portion and disposed to be inserted into the slit, and the second metal plate may include a second terminal contact portion configured to cover the bottom portion of the cell housing; and second bent portions bent and extending from both ends of the second terminal contact portion and disposed to be inserted into the slit. 
     The cell housing may include a bottom cover configured to accommodate a part of the battery cells; and a top cover assembled with the bottom cover in an upper and lower direction and configured to accommodate the remaining part of the battery cells. 
     A part of the perforated hole may be formed in the bottom cover and the remaining part of the perforated hole may be formed in the top cover. 
     The cell housing may include a coupling protrusion formed at a front surface thereof to protrude outward; and a guide groove formed at a rear surface thereof to be recessed inward. 
     The battery pack may comprise a first cell module and a second cell module respectively provided as one assembly in which the cell assemblies are assembled successively in a front and rear direction, and the second cell module may be stacked on the first cell module. 
     The battery pack may further comprise a heat dissipation plate assembled as an interlayer between the first cell module and the second cell module, and the heat dissipation plate may include a middle plate interposed between the first cell module and the second cell module; and vertical plates extending in an upper and lower direction at both ends of the middle plate to surround a front side and a rear side of the first cell module and the second cell module. 
     A heat transfer pad may be further interposed at a contact interface between an upper surface of the first cell module and a lower surface of the middle plate and between a lower surface of the second cell module and an upper surface of the middle plate. 
     In another aspect of the present disclosure, there is also provided an electric vehicle, comprising the battery pack described above. 
     Advantageous Effects 
     According to an embodiment of the present disclosure, it is possible to provide a battery pack having a reinforced short circuit prevention structure that may eliminate the possibility of contact between metal plates when an external impact is applied and also significantly reduce the risk of short circuit before/after a welding work. 
     In particular, since the cell housing of the battery pack according to the present disclosure is configured so that the end of the metal plate is inserted into the slit provided at the side surface, it is possible to minimize the exposure of the metal plate to the outside and secure fixability at the same time. 
     In addition, since the short circuit prevention block inside the slit acts as a physical barrier between adjacent metal plates, the risk of short circuit may be significantly reduced when an external impact is applied. 
     The effect of the present disclosure is not limited to the above, and effects not mentioned herein may be clearly understood by those skilled in the art from the specification and the accompanying drawings. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a reference view schematically showing an electrical connection structure by metal plates in a conventional battery pack. 
         FIG. 2  is a perspective view schematically showing a configuration of a battery pack according to an embodiment of the present disclosure. 
         FIG. 3  is a side view of  FIG. 2 . 
         FIG. 4  is an exploded perspective view showing a first cell module, a heat dissipation plate and a second cell module of  FIG. 3 . 
         FIG. 5  is an exploded perspective view showing a part of a unit cell assembly according to an embodiment of the present disclosure. 
         FIGS. 6 and 7  are diagrams for illustrating an assembling process of the cell assembly and the metal plate according to an embodiment of the present disclosure. 
         FIG. 8  is a plan view showing the cell assemblies of  FIG. 6 . 
         FIG. 9  is a sectioned perspective view corresponding to a portion A of  FIG. 7  and showing a structure of an inner side of an outer sidewall at the side portion of the cell housing. 
         FIG. 10  is a diagram corresponding to  FIG. 3  and showing a connection structure of the metal plates of the battery pack according to an embodiment of the present disclosure. 
         FIG. 11  is a schematic view for illustrating a welding process between the metal plates according to an embodiment of the present disclosure. 
     
    
    
     BEST MODE 
     Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. 
     Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the disclosure, so it should be understood that other equivalents and modifications could be made thereto without departing from the scope of the disclosure. 
       FIG. 2  is a perspective view schematically showing a configuration of a battery pack according to an embodiment of the present disclosure,  FIG. 3  is a side view of  FIG. 2 , and  FIG. 4  is an exploded perspective view showing a first cell module, a heat dissipation plate and a second cell module of  FIG. 3 . 
     Referring to the drawings, a battery pack according to an embodiment of the present disclosure includes a first cell module  100  that is an aggregate of a plurality of battery cells  11 , a second cell module  200  disposed on the first cell module  100 , a heat dissipation plate  300  assembled between the first cell module  100  and the second cell module  200 , and various devices for controlling charging and discharging of the battery cells  11 , for example a BMS  400 , a relay  500 , a voltage sensing means  600 , a current sensor, a fuse, or the like. 
     A main feature of the present disclosure is an assembly structure of cell assemblies  10 , which are components of the first and second cell modules  200 , and a short circuit prevention structure to eliminate the risk of short circuits between metal plates when an external impact is applied, and thus these main features will be explained in detail. Meanwhile, since the electronic components such as the BMS  400 , the current sensor and the fuse are well known in the art, and thus their general operations and assembly structures will be easily understood by those skilled in the art. 
     Seeing main components forming the first and second cell modules  100  and  200 , the first and second cell modules  100 ,  200  may include a plurality of cell assemblies  10  and first and second metal plates  20 ,  30 . 
     The first and second cell modules  100 ,  200  may be regarded as components in which the cell assemblies  10  are assembled successively in a front and rear direction and electrically connected by the first and second metal plates  20 ,  30 . 
     In the battery pack of this embodiment, the first cell module  100  and the second cell module  200  are arranged in a two-layer structure to increase capacity and energy density, but it is also possible to change the design of the battery pack to a single-layer structure including only the first cell module  100  or to a three- or four-layer structure including a third cell module and/or a fourth cell module further. 
     The heat dissipation plate  300  may include a middle plate  310  and vertical plates  320 ,  330 . Specifically, referring to  FIGS. 3 to 4 , the middle plate  310  may be disposed as an interlayer between the first cell module  100  and the second cell module  200 , and the vertical plates  320 ,  330  may extend in an upper and lower direction at both ends of the middle plate  310  to cover front and rear sides of the first cell module  100  and the second cell module  200 . 
     In addition, a heat transfer pad  900  may be further interposed at a contact interface between an upper surface of the first cell module  100  and a lower surface of the middle plate  310  and between a lower surface of the second cell module  200  and an upper surface of the middle plate  310 . 
     On the lower surface of the first cell module  100  and the upper surface of the second cell module  200 , upper and lower pads  700 ,  800  respectively having excellent heat transfer rates and a cooling medium (not shown) in contact with the upper and lower pads  700 ,  800  to absorb heat may be disposed. 
     According to this configuration, the heat of the battery cells  11  generated during charging and discharging of the battery pack may be dissipated to the outside through the lower portion of the first cell module  100  and the upper portion of the second cell module  200 . In particular, since the middle plate  310  and the heat dissipation plate  300  act as a heat transfer path between the first cell module  100  and the second cell module  200 , the heat at the upper portion of the first cell module  100  and the lower portion of the second cell module  200  may be smoothly dissipated. In addition, the middle plate  310  and the heat dissipation plate  300  may act as a firewall when the first cell module  100  ignites or explode due to some reason, thereby preventing chain fire or chain explosion to the second cell module  200 . 
     The cell assembly  10  includes battery cells  11  and a cell housing  12  for accommodating the battery cells  11 , as shown in  FIGS. 5 and 6 . 
     The battery cell  11  may be a cylindrical battery cell  11  having electrode terminals respectively formed at upper and lower portions thereof. The cylindrical battery cell  11  generally includes a jelly-roll type electrode assembly, a cylindrical metal battery can having an inner space to accommodate the electrode assembly and an open top, and a cap assembly formed to shield the top portion of the battery can. Here, the cap assembly forms a positive electrode terminal  11   a,  and the bottom surface of the battery can forms a negative electrode terminal. In addition, a side of the battery can may be covered with an insulating film. 
     In this embodiment, the cylindrical battery cell  11  is used as the battery cell  11 , but the battery cell  11  does not necessarily have a cylindrical shape. For example, the battery cell  11  may be preferably a secondary battery of a metal can type with high mechanical stiffness, which has a polygonal shape. 
     The cell housing  12  may include a bottom cover  12   a  for accommodating a part of the battery cells  11 , and a top cover  12   b  assembled on an upper portion of the bottom cover  12   a  to accommodate the remaining part of the battery cells  11 . 
     Each of the bottom cover  12   a  and the top cover  12   b  may include sockets into which the cylindrical battery cells  11  are inserted one by one, and the sockets may support the cylindrical battery cells  11  to stand upright. In addition, circular holes H 1  may be provided in the lower surface of the bottom cover  12   a  and the upper surface of the top cover  12   b  at locations corresponding to the sockets in the upper and lower direction. 
     After the cylindrical battery cells  11  are inserted into the bottom cover  12   a,  if the top cover  12   b  is assembled with the bottom cover  12   a  and the upper portion of the cylindrical battery cells  11  is covered, the cylindrical battery cells  11  may be constrained in the cell housing  12  not to move, and only the positive electrode terminals  11   a  and the negative electrode terminals of the cylindrical battery cells  11  may be exposed out of the cell housing  12  through the holes H 1  of the bottom cover  12   a  and the hole H 1  of the top cover  12   b.    
     For convenient assembly of the bottom cover  12   a  and the top cover  12   b,  for example, locking protrusions C 1  may be provided along the circumferential direction of the front surface and the rear surface of the top cover  12   b,  and locking holes C 2  capable of being locked with the locking protrusions C 1  may be provided at the front surface and the rear surface of the bottom cover  12   a.    
     In addition, the cell housing  12  may further include a coupling protrusion  15  formed to protrude outward from the front surface thereof, and a guide groove  16  formed at the rear surface to be recessed inward. 
     For example, as shown in  FIGS. 7 and 8 , the cell housing  12  may include two coupling protrusions  15  at the front surface thereof and include two guide grooves  16  corresponding to the coupling protrusion  15  at the rear surface thereof. 
     The coupling protrusion  15  and the guide groove  16  of the cell housing  12  may be used as a means for successively assembling several cell housings  12  in a front and rear direction. That is, two cell housings  12  may be assembled by inserting the coupling protrusion  15  of one cell housing  12  into the guide groove  16  of the other cell housing  12  in the upper and lower direction. In this case, since assembling is performed based on the coupling protrusion  15  and the guide groove  16 , there is no positional error between the cell housings  12 . Also, since the coupling protrusion  15  and the guide groove  16  are engaged with each other, the cell housings  12  may not be easily separated. 
     The shapes of the coupling protrusion  15  and the guide groove  16  are not limited to this embodiment, and for example, the coupling protrusion  15  and the guide groove  16  may have a cross section of a “T” shape or the like. 
     Referring to  FIGS. 6 and 7  again, the battery pack of the present disclosure includes a metal plate as an electrical connection means for the cylindrical battery cells  11 . The metal plate includes a first metal plate  20  mounted at a top portion of the cell housing  12  and is integrally in contact with the positive electrode terminals  11  a of the cylindrical battery cells  11 , and a second metal plate  30  mounted at a bottom portion of the cell housing  12  and is integrally in contact with the lower electrode terminals of the cylindrical battery cells  11 . 
     The cylindrical battery cells  11  are accommodated in each cell housing  12  such that the same polarity is oriented in the same direction. That is, the cylindrical battery cells  11  are disposed to stand upright so that the positive electrode terminals  11   a  face the top portion of the cell housing  12  and the negative electrode terminals face the bottom portion of the cell housing  12 . 
     The first metal plate  20  integrally contacts the positive electrode terminals  11   a  of the cylindrical battery cells  11 , and the second metal plate  30  integrally contacts the negative electrode terminals  11   a  of the cylindrical battery cells  11 . Therefore, the first metal plate  20  gives the same function as the positive electrode terminal of one cell assembly  10 , and the second metal plate  30  gives the same function as the negative electrode terminal of the one cell assembly  10 . Of course, if the cylindrical battery cells  11  are disposed to stand up so that the negative electrode terminals face the top portion of the cell housing  12  and the positive electrode terminals face the bottom portion of the cell housing  12 , the first metal plate  20  may function as the negative electrode terminal and the second metal plate  30  may function as the positive electrode terminal. 
     One cell assembly  10  according to this embodiment is configured such that the cylindrical battery cells  11  are connected in parallel by the first and second metal plates  20 ,  30 , thereby providing very high electrical capacity. If it is required to increase or decrease the electrical capacity per cell assembly  10 , it is possible to add or reduce the number of cylindrical battery cells  11  included in the cell assembly  10 . 
     In addition, the total output of the battery pack may be increased as desired by connecting a plurality of cell assemblies  10  in series as needed. That is, the output may be increased by connecting the cell assemblies  10  in series such that the positive electrode terminal of one cell assembly  10  is connected to the negative electrode terminal of another cell assembly  10 . 
     In the present disclosure, in order to connect the cell assemblies  10  in series with each other in a space-efficient way, both ends of the first and second metal plates  30  are bent and placed on both side portions  17  of the cell housing  12 , the cell assemblies  10  are successively assembled in the front and rear direction, and then the first and second metal plates  30  of the cell assemblies  10  are connected. 
     Specifically, referring to  FIGS. 6, 7 and 9  again, the first metal plate  20  includes a first terminal contact portion  21  having an approximately wide plate-like shape and provided to cover the top portion of the cell housing  12 , and first bent portions  22  bent and extending downward from both ends of the first terminal contact portion  21 , and the second metal plate  30  has a shape similar to the first metal plate  20  and includes a second terminal contact portion  31  provided to cover the bottom portion of the cell housing  12  and second bent portions  32  bent and extending upward from both ends of the second terminal contact portion  31 . 
     In addition, the first bent portion  22  and the second bent portion  32  are arranged side by side on the side portion  17  of the cell housing  12 , respectively, and may be used as a means to connect the cell assemblies  10  in series. For example, the first bent portion  22  of any one cell assembly  10  may extend obliquely downward perpendicular to the first terminal contact portion  21  beyond the range of width (W) of the cell housing  12 . If two cell assemblies  10  are assembled, one first bent portion  22  comes into contact with the other second bent portion  32 , and the corresponding contact portions are welded to connect the two cell assemblies  10  in series. In this way, all cell assemblies  10  may be connected in series. 
     Meanwhile, in the present disclosure, in order to eliminate the risk of short circuit between the metal plates, the first bent portion  22  and the second bent portion  32  are structured to be hidden by the side portion  17  of the cell housing  12 . 
     To this end, the cell housing  12  may further include a side portion  17  having a slit  17   c  forming a gap in which the first bent portion  22  of the first metal plate  20  and the second bent portion  32  of the second metal plate  30  may be inserted in the upper and lower direction, respectively, and a perforated hole  17   d  formed in a direction intersecting the slit  17   c.    
     The side portion  17  of the cell housing  12  may include an outer sidewall  17   a  and an inner sidewall  17   b  that form a double wall structure, and the slit  17   c  may be formed in a height direction between the outer sidewall  17   a  and the inner sidewall  17   b.  In other words, the outer sidewall  17   a  and the inner sidewall  17   b  are spaced apart from each other so that the slit  17   c  is provided (in ±Y-axis direction), and the first bent portion  22  and the second bent portion  32  may be inserted into the slit  17   c  (in ±Z-axis direction). At this time, if the first bent portion  22  of the first metal plate  20  and the second bent portion  32  of the second metal plate  30  inserted into the side portion  17  of the same cell housing  12  come into contact with each other, they are short-circuited. Thus, the first bent portion  22  of the first metal plate  20  and the second bent portion  32  of the second metal plate  30  may be provided to extend obliquely in the upper and lower direction oppositely so as not to contact each other inside the slit  17   c.    
     In addition, the perforated hole  17   d  communicating with the slit  17   c  may be formed in the outer sidewall  17   a.  More specifically, the bottom cover  12   a  and the top cover  12   b  are provided to be partially cut, and the bottom cover  12   a  and the top cover  12   b  having the partially cut area are coupled up and down to provide the perforated hole  17   d.  The perforated hole  17   d  may be used as a place for welding the metal plates, as will be described later. 
     The side portion  17  of the cell housing  12  may further include a short circuit prevention block  17   e  configured to connect the outer sidewall  17   a  and the inner sidewall  17   b  inside the slit  17   c  and divide the inner space of the slit  17   c.    
     Although the outer sidewall  17   a  is spaced apart from the inner sidewall  17   b  by a predetermined distance, the outer sidewall  17   a  is connected to the inner sidewall  17   b  via the short circuit prevention block  17   e,  and thus may be formed as one body together with the inner sidewall  17   b.    
     The short circuit prevention block  17   e  may be provided to approximately divide the inner space of the slit  17   c  into left and right areas. The first bent portion  22  of the first metal plate  20  may be disposed in the divided left space of the short circuit prevention block  17   e,  and the second bent portion  32  of the second metal plate  30  may be disposed in the right space of the short circuit prevention block  17   e.    
     As shown in  FIG. 9 , the short circuit prevention block  17   e  functions as a barrier to physically isolate the first bent portion  22  of the first metal plate  20  and the second bent portion  32  of the second metal plate  30  in the inner space of the slit  17   c.  In other words, since the first bent portion  22  of the first metal plate  20  and the second bent portion  32  of the second metal plate  30  mounted to the same cell housing  12  are arranged to miss each other with the short circuit prevention block  17   e  being interposed therebetween, it is possible to fundamentally block the first bent portion  22  of the first metal plate  20  and the second bent portion  32  of the second metal plate  30  from contacting each other. 
     Therefore, in the assembly process in which the first bent portion  22  of the first metal plate  20  and the second bent portion  32  of the second metal plate  30  are inserted at the upper portion and the lower portion of the side portion  17  of the cell housing  12 , the first bent portion  22  of the first metal plate  20  and the second bent portion  32  of the second metal plate  30  are guided to miss each other into two parts based on the short circuit prevention block  17   e,  respectively, so as to be mounted without contacting each other, thereby greatly lowering the risk of short circuit. In addition, even if a shock is applied from the outside (in the X-axis, Y-axis, Z-axis directions) after assembly, the first bent portion  22  of the first metal plate  20  and the second bent portion  32  of the second metal plate  30 , which are mounted to the same cell housing  12 , has little chance of contacting each other and thus causing a short circuit. 
     Meanwhile, the first metal plate  20  mounted on any one cell housing  12  may be disposed to overlap with the second metal plate  30  mounted to another the cell housing  12  adjacent thereto, inside the perforated hole  17   d.    
     Referring to  FIGS. 10 and 11 , the first bent portion  22  of the first metal plate  20  mounted to the {circle around (a)} cell housing  12  may be disposed over the slit  17   c  of the {circle around (a)} cell housing  12  and the slit  17   c  of the {circle around (b)} cell housing  12  to overlap with the second bent portion  32  of the second metal plate  30  mounted to the {circle around (b)} cell housing  12 . In addition, the overlapped area may be exposed to the outside through the perforated hole  17   d  of the {circle around (b)} cell housing  12 . 
     The first metal plate  20  of the {circle around (a)} cell housing  12  and the second metal plate  30  of the {circle around (b)} cell housing  12  may be connected to each other by laser welding through the perforated hole  17   d  of the {circle around (b)} cell housing  12 . 
     According to the configuration of the present disclosure, the welding work is easy because parts of the metal plates to be welded are fixedly located within the slit  17   c  of the cell housing  12 . In addition, since the metal plates are hidden inside the outer sidewall  17   a  of the cell housing  12 , a short circuit is substantially not generated even if a worker accidentally brings a welding jig or metal tool into contact with the side portion  17  of the cell housing  12  before/after performing the welding work. 
     The first cell module  100  and the second cell module  200  may be configured by connecting the cell assemblies  10  in series in the above pattern. In addition, the first cell module  100  and the second cell module  200  may be electrically connected to each other by a module connecting bus bar  40  provided in a metal plate shape. For example, the module connecting bus bar may connect the second metal plate  30  of a cell assembly  10  located last in the first cell module  100  and the second metal plate  30  of a cell assembly  10  located last in the second cell module  200 . For reference, in this embodiment, the battery cells  11  of the second cell module  200  are placed to stand upright such that the positive electrode terminals face downward and the negative electrode terminals face upward, as opposed to the first cell module  100 . Therefore, all of the first metal plates  20  of the second cell module  200  have negative polarity and all of the second metal plates  30  have positive polarity. It is desirable to secure insulation by further attaching an insulation pad on a path where the module connecting bus bar is disposed. 
     As described above, according to the configuration of the present disclosure, it is possible to provide a battery pack having a reinforced short circuit prevention structure that may eliminate the possibility of contact between metal plates when an external impact is applied and also significantly reduce the risk of short circuit before/after a welding work. 
     Meanwhile, the battery pack according to the present disclosure as described above may be applied to a large-capacity energy storage system or a vehicle such as an electric vehicle or a hybrid electric vehicle. 
     The present disclosure has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the scope of the disclosure will become apparent to those skilled in the art from this detailed description. 
     Meanwhile, even though the terms expressing directions such as “upper”, “lower”, “left” and “right” are used in the specification, they are just for convenience of description and can be expressed differently depending on the location of a viewer or a subject, as apparent to those skilled in the art.