Patent Publication Number: US-2011052960-A1

Title: Secondary battery module having cooling conduit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application No. 10-2009-0083151, filed in the Korean Intellectual Property Office on Sep. 3, 2009, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to secondary battery modules, and more particularly, to secondary battery modules including a sealed cooling conduit, through which a heat transfer medium flows between adjacent unit batteries. 
     2. Description of the Related Art 
     Secondary batteries are widely used as a power supply source to drive various portable electronic devices, such as mobile phones, lap tops, digital cameras, and Moving Picture Experts Group audio layer 3 (MP3) players. Recently, secondary batteries have expanded to being used as a power supply source for moving devices, such as a car. Moreover, demand for secondary batteries in apparatuses for storing renewable energy, such as sunlight power or wind power, as electric power is expected to increase. 
     A secondary battery used for a car or an apparatus to store electric power is generally required to have higher capacity and higher output than a secondary battery used for a portable electric device. Accordingly, a secondary battery system that has high capacity and high output may be formed by connecting a plurality of unit batteries in series or in parallel. A bundle of a plurality of unit batteries connected in series or in parallel is generally called a secondary battery module, and at least one secondary module may form a secondary battery pack or a secondary battery system. 
     In secondary battery modules, heat is generated inside each unit battery when unit batteries are charged or discharged. When the generated heat is not properly dissipated out of the unit batteries, performance of the unit batteries may deteriorate. Also, when there are temperature variations in a unit battery, the performance deterioration of the unit battery may become worse as the temperature variations increase. Accordingly, the heat generated in each unit battery in the secondary battery module should be appropriately dissipated out of the unit batteries. Consequently, various cooling structures of a secondary battery module to dissipate heat generated in the unit batteries out of the unit batteries are suggested. Such cooling structures should not cause any mechanical, thermal, or chemical problems to the unit batteries and the secondary battery module, even when the volume of the unit batteries changes. 
     SUMMARY 
     Provided are secondary battery modules including a sealed cooling conduit, through which a heat transfer medium flows between adjacent unit batteries. 
     According to an aspect of the present invention, a secondary battery module is provided. The secondary battery module includes: a plurality of cooling conduits disposed in parallel facing each other and sealed so that a heat transfer medium flows therein; a plurality of unit batteries disposed between the plurality of cooling conduits; a supply conduit to supply the heat transfer medium to the plurality of cooling conduits; an exhaust conduit to exhaust the heat transfer medium from the plurality of cooling conduits; and a spacer disposed inside each of the plurality of cooling conduits to maintain a space in each of the cooling conduits. 
     According to another aspect of the present invention, the spacer may serve as a compression spring having elasticity in a direction that in which cooling conduits are compressed by the unit batteries on each side of each of the cooling conduits. 
     According to another aspect of the present invention, the spacers may have a shape of a bent board, a shape of a board having an uneven surface or having protrusions, a shape of a board partially cut or having a hole, a mesh shape, a wire shape, a sphere shape, a tube shape, or a combination of shapes thereof. 
     According to another aspect of the present invention, the spacers may be formed separately from the cooling conduits and inserted into the cooling conduits. 
     According to another aspect of the present invention, the spacers may be formed with the cooling conduits as a single body. 
     According to another aspect of the present invention, a shape, an arrangement configuration, or an arrangement frequency of the spacers may differ according to a location of the spacers within the cooling conduits. 
     According to another aspect of the present invention, an occupation density or occupation surface area of the spacers may increase downstream of a moving path of the heat transfer medium in the cooling conduits. 
     According to another aspect of the present invention, an occupation density of the spacers at the edge of a moving path of the heat transfer medium in the cooling conduits may be higher than an occupation density of the spacers at the center of the moving path. 
     According to another aspect of the present invention, the cooling conduits may be divided into a plurality of sections according to location, and spacers disposed in one of the plurality of sections have a shape different from spacers disposed in each of the other sections. 
     According to another aspect of the present invention, the plurality of cooling conduits and the plurality of unit batteries may have flat board shapes having wide and flat surfaces in width and height directions, and narrow and long surfaces in a thickness direction. 
     According to another aspect of the present invention, the wide and flat surfaces of the cooling conduits and the unit batteries may contact each other. 
     According to another aspect of the present invention, insulation films may be disposed between each of the plurality of cooling conduits and the unit batteries. 
     According to another aspect of the present invention, a thickness of each of the plurality of cooling conduits a range from about 0.1 mm to about 20 mm. 
     According to another aspect of the present invention, the supply conduit and the exhaust conduit may be disposed on sides of the cooling conduits, and a plurality of parallel grooves may be formed on inner walls of the supply conduit and the exhaust conduit. 
     According to another aspect of the present invention, the plurality of cooling conduits are inserted into the plurality of grooves formed on the inner walls of the supply conduit and the exhaust conduit so as to connect the plurality of cooling conduits to the supply conduit and the exhaust conduit. 
     According to another aspect of the present invention, the cooling conduits may be connected to the supply conduit and the exhaust conduit via a brazing method. 
     According to another aspect of the present invention, the supply conduit and the exhaust conduit may have a pipe shape, the supply conduit may be disposed on one edge of the cooling conduit, and the exhaust conduit may be disposed on another edge of the cooling conduits, and a plurality of first subsidiary conduits connected to the supply conduit may be connected to one corner of the cooling conduits, and a plurality of second subsidiary conduits connected to the exhaust conduit may be connected to another corner of the cooling conduits, so as to supply and exhaust the heat transfer medium. 
     According to another aspect of the present invention, the secondary battery module may further include a separate heat exchanger connected to the supply conduit and the exhaust conduit. 
     According to another aspect of the present invention, the spacers may have a parallel lattice pattern. A width of the spacers may be larger than a width of the cooling conduits. 
     According to another aspect of the present invention, the secondary battery module may further include: two end plates respectively disposed on each end of the secondary battery module; and a restraining unit fixed between the two end plates to provide resistance in a direction such that a distance between the two end plates increases. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a perspective view illustrating a schematic structure of a secondary battery module including a cooling conduit, according to an embodiment of the present invention; 
         FIGS. 2A through 2C  are perspective views schematically illustrating a structure and an arrangement of the cooling conduit and a unit battery of the secondary battery module illustrated in  FIG. 1 ; 
         FIG. 2D  is a diagram illustrating an example of a structure where an insulation film is disposed between a cooling conduit and a unit battery; 
         FIG. 3  is a perspective view illustrating a secondary battery module including a cooling conduit, according to another embodiment of the present invention; 
         FIG. 4  is a cross-sectional view schematically illustrating a cooling conduit and a spacer disposed inside the cooling conduit; 
         FIGS. 5A through 5F  are cross-sectional views schematically illustrating various examples of a cooling conduit and a spacer disposed inside the cooling conduit; 
         FIGS. 6A through 6L  are cross-sectional views illustrating various shapes of a spacer that may be disposed in a cooling conduit; 
         FIGS. 7A through 7D  are plan views illustrating various shapes of a spacer; 
         FIGS. 8A through 8E  are cross-sectional views illustrating various shapes of a spacer integrated into a cooling conduit; 
         FIGS. 9A and 9B  are diagrams illustrating shape change of a cooling conduit according to volume change of a unit battery during charging and discharging; 
         FIGS. 10A through 10C  are plan views illustrating arrangements of a spacer; 
         FIGS. 11A and 11B  are perspective views showing how a spacer having various shapes is inserted into a cooling conduit; 
         FIG. 12  is a plan view illustrating a structure of a spacer; 
         FIGS. 13A and 13B  are diagrams of a combination relationship between the spacer of  FIG. 12  and a cooling conduit; and 
         FIGS. 14A through 14C  are plan views illustrating various modified examples of the spacer of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
       FIG. 1  is a perspective view illustrating a schematic structure of a secondary battery module  10  including a cooling conduit  12 , according to an embodiment of the present invention. The secondary battery module  10  may include a plurality of the cooling conduits  12  disposed in parallel and facing each other, a unit battery  11  disposed between the plurality of cooling conduits  12 , a supply conduit  13 , and an exhaust conduit  14 . The supply conduit  13  supplies a heat transfer medium into the plurality of cooling conduits  12 . The exhaust conduit  14  exhausts the heat transfer medium from the plurality of cooling conduit  12 . The cooling conduits  12  are disposed in the spaces between the unit batteries  11  and on outer sides of the unit batteries  11  at each end of the secondary battery module  10 . 
     Although not illustrated in  FIG. 1 , an end plate having a flat board shape and may be disposed on each end of the secondary battery module  10  parallel to the unit battery  11  and the cooling conduits  12 . In order to prevent a change in the overall length of the secondary battery module  10  due to an increase of volume of the unit battery  11  while charging the unit battery  11 , a restraining unit (not shown) may be disposed between the two end plates. Since the restraining unit is fixed between the two end plates, resistance may be provided in a direction such that a space between the end plates increases. 
     The unit battery  11  is a secondary battery that can be repeatedly charged and discharged, and may be square shaped or pouch shaped. As shown in  FIG. 1 , each of a plurality of the unit batteries  11  may have wide and flat surfaces in width and height directions and narrow and long surfaces in a thickness direction so as to be easily inserted into and disposed in the secondary battery module  10 . The plurality of unit batteries  11  may be arranged in such a way that the wide and flat surfaces are parallel and face each other. A plurality of predetermined spaces may be provided between the plurality of unit batteries  11  for the cooling conduits  12 . 
     As shown in  FIG. 1 , like the unit batteries  11 , the cooling conduits  12  may also have wide and flat surfaces in width and height directions and narrow and long surfaces in a thickness direction. In this case, the unit batteries  11  may be effectively cooled since areas of contact between the wide and flat surfaces of the cooling conduits  12  and the wide and flat surfaces of the unit batteries  11  are maximized. However, portions of surfaces of the cooling conduits  12  that do not contact the wide and flat surfaces of the unit batteries  11  may be shaped differently, and are not limited to the shown arrangements. 
     In  FIG. 1 , the cooling conduits  12  disposed between the plurality of unit batteries  11  are each connected to the supply conduit  13  and the exhaust conduit  14  and are parallel to each other. When the heat transfer medium flows in a direction A through the supply conduit  13 , the heat transfer medium is supplied to each cooling conduit  12  from the supply conduit  13 . After the heat transfer medium flows in a direction B within the cooling conduits  12 , the heat transfer medium is then exhausted in a direction C through the exhaust conduit  14  from each cooling conduit  12 . 
     Alternatively, although not illustrated, the plurality of cooling conduits  12  may be connected in series. In this case, the supply conduit  13  and the exhaust conduit  14  may be disposed at the cooling conduits  12  at each end of the secondary battery module  10 . The heat transfer medium is supplied to the cooling conduit  12  at one end of the secondary battery module  10  from the supply conduit  13  and then successively flows from the cooling conduit  12  at one end, through the intermediate cooling conduits  12 , and then to the cooling conduit  12  at another end of the secondary battery module  10 . The heat transfer medium is then exhausted from the cooling conduit  12  at the other end of the secondary battery module  10  to the exhaust conduit  14 . When the cooling conduits  12  are connected in series, the cooling conduits  12  may be configured to have zigzag shapes via a bending process, or the like. Alternatively, other conduits having another shape may be connected in parallel to sides of the cooling conduits  12 . 
     The cooling conduits  12  are sealed from external air such that the heat transfer medium only flows through the cooling conduits  12 . The entire conduit system including the supply conduit  13  and the exhaust conduit  14  respectively supplying and exhausting the heat transfer medium to and from the cooling conduits  12  in the secondary battery module  10  may be sealed from external air. 
     The entire thickness of each of the cooling conduits  12  may, for example, range from about 0.1 mm to about 20 mm. When the entire thickness of the cooling conduits  12  is above 20 mm, the volume that may be occupied by the unit batteries  11  in the secondary battery module  10  decreases, and thus the energy density of the secondary battery module  10  may decrease. On the other hand, when the entire thickness of the cooling conduits  12  is below 0.1 mm, the amount of the heat transfer medium that flows through the cooling conduits  12  may not be sufficient, since the resistance of line inside the cooling conduits  12  increases. In this case, the thickness of an external wall of the cooling conduits  12  may be decreased, but then mechanical stability of the cooling conduits  12  may deteriorate. 
     The cooling conduits  12  contact the unit batteries  11 , and thus there may be a thermal conduction path where the heat generated in the unit batteries  11  is transferred to the heat transfer medium inside the cooling conduits  12 . Accordingly, the cooling conduits  12  may be formed of a material having high thermal conductivity. When the cooling conduits  12  deform elastically due to the volume change of the unit batteries  11 , changes in the thermal conductivity may be reduced if the cooling conduits  12  are maintained in contact with the unit batteries  11 . Accordingly, the cooling conduits  12  may be formed of a material that can repeatedly elastically deform. 
     Metal is one example of a material that can satisfy the above conditions. For example, stainless steel, copper, aluminum, or silver, may be used to form the cooling conduits  12 . When a metal is used to form the cooling conduits  12 , the internal heat transfer medium may be easily sealed in the cooling conduits  12 , and the cooling conduits  12  may be easily processed using a metal board, or the like. The thickness of the metal material may be, for example, about 10 μm or greater. However, a non-metal may be used to form the cooling conduits  12 , as long as the non-metal has heat resistance and high thermal conductivity, and can be repeatedly deformed elastically. 
     As described above, the heat transfer medium flows inside the cooling conduits  12  in order to dissipate the heat generated in the unit batteries  11 . Since the cooling conduits  12  are sealed, the heat transfer medium only flows inside the cooling conduits  12 , does not contact external air, and does not leak out of the cooling conduits  12 . For sufficient heat dissipation, the heat transfer medium may have an average volumetric heat capacity value of 0.1 MJ/(m 3 ·K) or greater. For example, the average volumetric heat capacity value may be 1 MJ/(m 3 ·K) or greater. Examples of the heat transfer medium include liquid water, methanol, ethanol, propanol, butanol, silicon oil, ammonia, acetone, and mixtures thereof, but the heat transfer medium is not limited thereto. Such examples of the heat transfer medium are in a fluid state in environments in which heat dissipating is normally performed. Alternatively, the heat transfer medium may be a mixture in which various types of materials are mixed, a heterogeneous mixture in which various phases of materials are mixed, a suspension, or a colloid. 
       FIGS. 2A through 2C  are perspective views schematically illustrating a structure and an arrangement of the cooling conduits  12  and the unit batteries  11  of the secondary battery module  10  illustrated in  FIG. 1 . Referring to  FIG. 2A , the entire conduit system, including the cooling conduits  12 , the supply conduit  13 , and the exhaust conduit  14 , is illustrated. All of the cooling conduits  12 , the supply conduit  13 , and the exhaust conduit  14  have a board shape having flat and wide surfaces, and may be fixed to a bottom board  18 . A plurality of parallel grooves  14   a  are formed on an inner wall of the exhaust conduit  14 , and the cooling conduits  12  may be fixed to the exhaust conduit  14  by being inserted into the grooves  14   a,  perpendicularly. The heat transfer medium in the cooling conduits  12  may flow to the exhaust conduit  14  through the grooves  14   a.  Although not illustrated, grooves identical to the grooves  14   a  of the exhaust conduit  14  may be formed on an inner wall of the supply conduit  13 . Accordingly, the heat transfer medium may flow along a direction indicated by arrows, from the supply conduit  13  to the exhaust conduit  14  through the cooling conduits  12 . 
     As illustrated in  FIG. 2A , the cooling conduits  12  may have an empty rectangular box shape so that the heat transfer medium may flow inside the cooling conduits  12 . Specifically, the cooling conduits  12  may have a flat board shape having wide and flat surfaces in width and height directions and narrow and long surfaces in a thickness direction. Accordingly, the cooling conduits  12  may be formed by processing a metal board. For example, the cooling conduits  12  may be formed by bending a board such that corners of the board are adjacent to each other, or by combining edges of two boards facing each other. 
     The cooling conduits  12  prepared as described above may be fixed and connected after being inserted into the supply conduit  13  and the exhaust conduit  14 , as shown in  FIG. 2B . When all of the cooling conduits  12 , the supply conduit  13 , and the exhaust conduit  14  are formed of a metal, they may be connected to each other using a well known brazing method. According to the brazing method, two metal portions are connected to each other by applying heat in a temperature lower than solid temperature using a filler metal having a liquid temperature of  450  degrees Celsius or above. Accordingly, the cooling conduits  12 , the supply conduit  13 , and the exhaust conduit  14  may be completely sealed. The plurality of unit batteries  11  may then be inserted between the cooling conduits  12  as shown in  FIG. 2C , so as to complete the secondary battery module  10 . 
     Though the wide and flat surfaces of the cooling conduits  12  and the wide and flat surfaces of the unit batteries  11  may contact each other directly, insulation films  19  (shown in  FIG. 2D ) may be disposed between the cooling conduits  12  and the unit batteries  11  in order to prevent current leakage from the unit batteries  11  to the cooling conduits  12 .  FIG. 2D  illustrates an example of a structure where the insulation films  19  are disposed between the cooling conduits  12  and the unit batteries  11 . The insulation films  19  may not only function as an insulator but may also improve thermal conductivity. Thus, the insulation films  19  may be an oxide layer or a polymer layer. For example, the insulation films  19  may be formed of thermal grease, although the composition of the insulation films  19  is not limited thereto. In order to prevent the thermal conductivity from decreasing, the thickness of each of the insulation films  19  may be about 1 mm or less. 
     According to the secondary battery module  10  described above, since the area of contact of the unit batteries  11  and the heat transfer medium is large, the heat generated in all of the unit batteries  11  included in the second battery module  10  may be effectively dissipated out of the unit batteries  11 . In addition, since the cooling conduits  12  having the flat board shape restrain the unit batteries  11 , the cooling conduits  12  may accommodate the unit batteries  11 . 
       FIG. 3  is a perspective view illustrating a secondary battery module  10 ′ including the cooling conduits  12 , according to another embodiment of the present invention. For convenience, the unit batteries  11  are not illustrated in  FIG. 3 . Referring to  FIG. 3 , unlike  FIG. 1 , a supply conduit  15  and an exhaust conduit  16  have a pipe shape instead of a flat board shape. However, the cooling conduits  12  have a flat board shape, such as in  FIG. 1 . As shown in  FIG. 3 , the supply conduit  15  and the exhaust conduit  16  are each disposed on two upper edges of the cooling conduits  12 , respectively. In other words, the supply conduit  15  is disposed on one edge of the cooling conduits  12 , and the exhaust conduit  16  is disposed on another edge of the cooling conduits  12 . 
     However, the locations of the supply conduit  15  and the exhaust conduit  16  are not limited to the upper edges of the cooling conduits  12 . For example, the supply conduit  15  and the exhaust conduit  16  may each be disposed on two bottom edges of the cooling conduits  12 , respectively, or on both of top and bottom edges of the cooling conduits  12 , respectively. Alternatively, the supply conduit  15  and the exhaust conduit  16  may be disposed diagonally to the cooling conduits  12 , with one on the top edge and the other on the bottom edge. A plurality of first subsidiary conduits  15   a  connected to the supply conduit  15  may be connected to one corner of the cooling conduits  12 , and a plurality of second subsidiary conduits  16   a  connected to the exhaust conduit  16  may be connected to another corner of the cooling conduits  12 , in order to supply and exhaust the heat transfer medium. 
     A heat exchanger  30  may be separately connected to the supply conduit  15  and the exhaust conduit  16  in order to increase cooling efficiency. In this case, the heat transfer medium that absorbed heat from the unit batteries  11  while flowing through the cooling conduits  12  dissipates the absorbed heat to the heat exchanger  30 , and then is supplied back to the cooling conduits  12 . Although not illustrated in  FIG. 1 , the heat exchanger  30  may also be included in the secondary battery module  10  of  FIG. 1 . 
     As described above, the unit batteries  11  may repeatedly expand and contract while the unit batteries  11  are being repeatedly charged and discharged. Even when the unit batteries  11  expand or contract, the surfaces of the cooling conduits  12  may maintain contact with the surfaces of the unit batteries  11  without detaching therefrom. Accordingly, the cooling conduits  12  having the flat board shape have elasticity and hardness. However, since the cooling conduits  12  are thin, mechanical reliability of the cooling conduits  12  may be low. Consequently, a reinforcing material may be further added in order to maintain spaces in the cooling conduits  12 . 
       FIG. 4  is a cross-sectional view schematically illustrating one of the cooling conduits  12  and a spacer  17  disposed inside the shown cooling conduit  12 . As shown in  FIG. 4 , the spacer  17  may have a structure where a plurality of protrusions  21  is formed on a thin board  20 . The spacer  17  may maintain the space in the cooling conduit  12  from shrinking below a predetermined degree. Accordingly, a uniform space in the cooling conduit  12  is obtained so that the heat transfer medium may flow through the cooling conduit  12 . The spacer  17  may function as a compression spring so as to provide elastic stability to walls of the cooling conduit  12 . The spacer  17  may be formed of any material and may have any shape, so long as the spacer  17  is able to perform the functions described above. For example, a metal having excellent thermal conductivity, such as stainless steel, aluminum, or copper, may be used to form the spacer  17 , in order to quickly transfer heat from inner walls of the cooling conduit  12  to the heat transfer medium. However, other non-metallic materials having excellent thermal conductivity may also be employed.  FIG. 4  illustrates the spacer  17  contacting two inner walls of the cooling conduit  12 , but the spacer  17  may instead contact only one inner wall, or may not contact any inner wall at all. 
     In  FIG. 4 , the spacer  17  having the protrusions  21  formed on the thin board  20  is illustrated, but the spacer  17  may have any one of various shapes. For example, the spacer  17  may have a spherical shape or a shape similar to a sphere, such as a hemisphere or an oval. Alternatively, the spacer  17  may have a mesh shape, a wire shape or a shape similar to a wire, a plurality of tubes shape or a shape where a plurality of tubes are combined, a shape where at least a portion of a board is bent, a shape where a board has an uneven surface or has protrusions, a shape where at least a portion of a board is processed, for example, a portion is cut or a hole is formed, a shape where another material is adhered to a part of a board, or a shape formed of a combination of shapes thereof. The above shapes should be seen as merely examples, and the spacer  17  may have any shape including shapes not expressly discussed above. 
     Thus, the spacer  17  may be formed to have one of several shapes through various methods.  FIGS. 5A through 5F  are cross-sectional views schematically illustrating various examples of the cooling conduits  12  and spacers disposed inside the cooling conduits  12 . As shown in  FIGS. 5A through 5C , the spacers may have a spherical or hemispherical shape, and may be formed on one inner wall of the cooling conduits  12 . Alternatively, as shown in  FIGS. 5D through 5F , the spacers may have a shape where a plurality of boards contact both inner walls of the cooling conduits  12  at various angles. 
     The spacer  17  may be elastically stressed in a thickness direction of the cooling conduits  12 , i.e., in a direction in which the cooling conduits  12  are compressed by the unit batteries  11  on both sides of the cooling conduits  12 . Accordingly, the spacer  17  may be formed of a material having a wide intrinsic elastic deformation range, such as metal or rubber. The spacer  17  may have a spring shape, an uneven shape, a curved shape, a folded shape, a bent shape, a hollow shape, a curved surface or curved line shape, or a shape formed of a combination of shapes thereof, in order to have high elasticity. 
       FIGS. 6A through 6L  are cross-sectional views illustrating various shapes of a spacer, and  FIGS. 7A through 7D  are plan views illustrating various shapes of a spacer. As shown in  FIGS. 6A through 6L , spacers that may be elastically stressed may be prepared by adhering protrusions of various shapes to a thin board, or by bending a thin board into various shapes. Also, as shown in  FIGS. 7A through 7C , the spacers  17  may be prepared in such a way that the protrusions  21  formed on the thin board  20  are uniformly arranged in a 2 dimension (2D) arrangement in various directions. Alternatively, as shown in  FIG. 7D , a spacer  17 ′ having a mesh shape may be prepared. 
     The spacer  17  may be prepared separately from the cooling conduits  12  and then inserted into one of the cooling conduits  12 . Alternatively, the spacer  17  and one of the cooling conduits  12  may be prepared as a single body using the same material.  FIGS. 8A through 8E  are cross-sectional views illustrating various shapes of the spacer  17  integrated into one of the cooling conduits  12 . 
     When the spacer  17  is elastically stressed in one of the cooling conduits  12 , the spacer  17  may push the walls of the cooling conduits  12  when the unit batteries  11  are installed inside the second battery module  10 . Accordingly, the surfaces of the cooling conduits  12  maintain contact with the surfaces of the unit batteries  11 . In this case, heat conduction occurs uniformly and smoothly between the surfaces of the unit batteries  11  and the cooling conduits  12 . 
     The volume of the unit batteries  11  may change as the unit batteries  11  expand and contract when charging and discharging. Spaces between the unit batteries  11  may change, and a degree of the change may differ according to location. The spacer  17  may deform elastically according to the change of spaces between the unit batteries  11  as the unit batteries  11  are charged or discharged. Thus, the spacer  17  continuously compresses the walls of one of the cooling conduits  12 , so that the surfaces of the cooling conduits  12  and the unit batteries  11  uniformly contact each other. 
       FIGS. 9A and 9B  are diagrams illustrating a shape change of the cooling conduits  12  according to a volume change of the unit batteries  11  during charging and discharging. In  FIGS. 9A and 9B , the spacer  17  is simply illustrated as compression springs. Using the spacer  17 , the surfaces of one of the cooling conduits  12  and the unit batteries  11  uniformly contact each other even when the unit batteries  11  contract by being discharged as shown in  FIG. 9A , or expand by being charged as shown in  FIG. 9B . 
     The spacer  17  may have a uniform surface, or a surface state of the spacer  17  may change according to location. Generally, when heat is transferred by convection, more heat is transferred when the heat transfer medium has a higher flow rate, a turbulent flow, or a wider heat transferring area. Since the spacer  17  is located inside the cooling conduits  12 , the spacer  17  affects the flow of the heat transfer medium. Specifically, the overall shape and surface state of the spacer  17  may affect the flow rate and formation of turbulent flow of the heat transfer medium, and may change areas of surfaces where convection heat transmission occurs. Accordingly, the degree of the convection heat transmission between the surfaces of the cooling conduits  12  and the heat transfer medium, or between the spacer  17  and the heat transfer medium may change according to the overall shape and the surface state of the spacer  17 . Accordingly, it is possible to adjust flux density of heat transferred to the cooling conduits  12  at a predetermined location of the unit batteries  11 . 
     Another configuration example of the spacer  17  in view of details discussed above will now be described. Generally, when the heat transfer medium moves through the cooling conduits  12 , the temperature of the heat transfer medium increases as the heat transfer medium absorbs heat generated in the unit batteries  11 . Accordingly, a temperature difference between the surfaces of the cooling conduits  12  and the heat transfer medium decreases downstream of the moving path of the heat transfer medium, and thus the amount of heat transferred through the convection downstream also decreases. In order to prevent such a phenomenon, the flow rate may be higher downstream of the moving path than upstream of the moving path, higher turbulent flow may be formed, or the area of heat transmission may be increased. Such conditions may be achieved by changing the shape of the spacer  17  formed inside the cooling conduits  12 . In addition, if a temperature of one location is higher than a temperature of another location in the secondary battery module  10 , the spacer  17  near the warmer location may be adjusted so as to increase heat flux density of the warmer location. 
       FIGS. 10A through 10C  are plan views illustrating example arrangements of spacers.  FIG. 10A  illustrates the spacer  17  having a shape where a plurality of parallel linear protrusions  21  are formed on the thin board  20 .  FIG. 10B  illustrates the spacer  17  having a shape where a plurality of spherical protrusions  21  are formed on the thin board  20 .  FIG. 10C  illustrates the spacer  17 ′ having a mesh shape. 
     Referring to the surfaces of the spacers  17  and  17 ′ illustrated in  FIGS. 10A through 10C , occupation density or occupation surface area of the protrusions  21  or the mesh increases in the moving direction of the heat transfer medium indicated in an arrow. The occupation density of the spacers  17  and  17 ′ is higher at the top and bottom edges than at the center. According to such surfaces, the heat transfer medium has a lower flow rate and less turbulent flow upstream, whereas the heat transfer medium has a higher flow rate and more turbulent flow downstream. Similarly, the heat transfer medium has higher flow rate and more turbulent flow at the upper and bottom edges than at the center. Accordingly, excellent convection heat transmission by the heat transfer medium is maintained downstream. By changing the shape, the arrangement configuration, and the arrangement frequency of the spacer  17  according to locations in the cooling conduits  12 , the heat flux density may be adjusted according to the location. Consequently, temperatures in the secondary battery module  10  may be substantially uniformly maintained in all locations, without using a separate complex control device. 
       FIGS. 11A and 11B  are perspective views describing how the spacer  17  having various shapes is inserted into one of the cooling conduits  12 .  FIGS. 11A and 11B  are diagrams showing how the spacer  17  having the shape illustrated in  FIG. 10B  may be inserted into one of the cooling conduits  12 . In  FIG. 11A , one spacer  17  having different surfaces according to location is inserted into the cooling conduits  12 . However, a plurality of spacers  17  having different surfaces may also be inserted into the cooling conduits  12 . Referring to  FIG. 11B , a plurality of spacers  17   a,    17   b,  and  17   c  formed by bending boards several times are inserted into the cooling conduits  12 . The boards of each of the spacers  17   a,    17   b,  and  17   c,  may have different bending frequencies. As shown in  FIG. 11B , the spacer  17   c  having the lowest bending frequency may be disposed upstream of the moving direction of the heat transfer medium, and the spacer  17   a  having the highest bending frequency may be disposed downstream of the moving direction. In this manner, the cooling conduits  12  may be divided into a plurality of sections according to location, and spacers having different shapes may be disposed in each section. 
       FIG. 12  is a plan view illustrating a structure of a spacer  27 .  FIGS. 13A and 13B  illustrate a combination relationship between the spacer  27  of  FIG. 12  and the cooling conduits  12 . The spacer  27  has a shape of a parallel lattice pattern so that conduits for the heat transfer medium are formed in the cooling conduits  12 . As shown in  FIG. 13A , a width D of the spacer  27  may be larger than a width d of the cooling conduits  12 . Thus, both edges of the spacer  27  protrude to the sides of the cooling conduits  12 . In this case, as shown in  FIG. 13B , when sealing members  28  and  29  are each adhered to two sides of the cooling conduits  12  respectively, it is possible to connect the cooling conduits  12  to a supply conduit and an exhaust conduit through the sealing members  28  and  29 . Alternatively, the cooling conduits  12  illustrated in  FIG. 13A  may be inserted into grooves of the supply conduit  13  and the exhaust conduit  14  of  FIG. 2A . Alternatively, the sealing members  28  and  29  may be used as the first and second subsidiary conduits  15   a  and  16   a  of  FIG. 3 . 
     As described above with reference to  FIGS. 10A through 10C , the shape of the spacer  27  of  FIG. 12  may change according to the location in the cooling conduits  12 .  FIGS. 14A through 14C  are plan views illustrating various modified examples of the spacer  27  of  FIG. 12 . As shown in  FIGS. 14A through 14C , the interval and length of the lattice in the spacer  27  may differ according to the location in the cooling conduits  12 . 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.