Patent Publication Number: US-2023163380-A1

Title: Battery pack

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 17/041,426, filed on Sep. 24, 2020, which is a U.S. National Phase Patent Application of International Application Number PCT/KR2019/004403, filed on Apr. 12, 2019, which claims priority to Korean Patent Application Number 10-2018-0055656, filed on May 15, 2018, the entire contents of all of which are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a battery pack. 
     BACKGROUND 
     In general, secondary batteries refer to batteries that can be repeatedly charged and recharged unlike non-rechargeable primary batteries. Secondary batteries are used as energy sources of devices such as mobile devices, electric vehicles, hybrid vehicles, electric bicycles, or uninterruptible power supplies. Secondary batteries are individually used or secondary battery modules (battery packs) each including a plurality of secondary batteries connected as one unit are used according to the types of external devices using secondary batteries. 
     Unlike small mobile devices such as cellular phones each operable for a certain period of time using a single battery, devices such as electric vehicles or hybrid vehicles having long operation times and consuming large amounts of electricity may prefer battery modules (battery packs) each including a plurality of batteries to handle problems relating to power and capacity, and the output voltages or currents of battery modules may be increased by adjusting the number of batteries included in each battery module. 
     SUMMARY 
     An embodiment of the present disclosure includes a battery pack improved in heat dissipation efficiency by using a liquid cooling medium contained to face different surfaces of the battery pack. 
     An embodiment of the present disclosure includes a battery pack configured to realize high heat dissipation efficiency with relatively low costs through a simple high-efficiency heat dissipation structure. 
     A battery pack of the present disclosure includes: battery cells each including a terminal surface on which an electrode terminal is formed, a top surface which is opposite the terminal surface, and a lateral surface which is between the terminal surface and the top surface; a first tank facing the terminal surfaces of the battery cells; a second tank extending from the first tank and facing the lateral surfaces of the battery cells; and a third tank extending from the second tank and facing the top surfaces of the battery cells, wherein a cavity is formed in the first to third tanks to extend across the first to third tanks, and the cavity is filled with a first cooling medium and is fluidically isolated from outside of the battery pack, wherein a cooling tube is accommodated in the third tank to extend across the cavity, and the cooling tube accommodates flow of a second cooling medium different from the first cooling medium. 
     According to the present disclosure, battery cell cooling efficiency may be improved by using cooling media which are contained in first to third tanks to face different surfaces of battery cells, and realizing a fluid cooling system with a cooling medium having a relatively high heat capacity. 
     According to the present disclosure, since a cooling medium contained in the first and second tanks relatively close to electrode terminals are allowed to naturally convect at a relatively low flow speed or dissipate heat in a static state in which the flow speed of the cooling medium is substantially zero, it may be unnecessary to provide a duct structure for introducing or discharging the cooling medium or a fluid pump for forcing the cooling medium to circulate. Therefore, heat dissipation efficiency may be improved using the cooling medium having a relatively high heat capacity while decreasing the possibility of a short circuit at the electrode terminals caused by leakage or accumulation of the cooling medium, and high heat dissipation efficiency may be realized with low costs owing to simplification in structure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view illustrating a battery pack according to a preferred embodiment of the present disclosure. 
         FIG.  2    is an exploded perspective view illustrating the battery pack illustrated in  FIG.  1   . 
         FIG.  3    is a perspective view illustrating a battery cell illustrated in  FIG.  1   . 
         FIG.  4    is a cross-sectional view taken along line IV-IV of  FIG.  1   . 
         FIG.  5    is an enlarged view illustrating a portion of  FIG.  4   . 
         FIG.  6    is a perspective view illustrating a battery pack according to another embodiment of the present disclosure. 
         FIG.  7    is a cross-sectional view taken along line VII-VII of  FIG.  6   . 
         FIGS.  8  to  11    are views illustrating flow guides according to various embodiments of the present disclosure. 
         FIG.  12    is a view illustrating flow modification portions according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A battery pack of the present disclosure includes: battery cells each including a terminal surface on which an electrode terminal is formed, a top surface which is opposite the terminal surface, and a lateral surface which is between the terminal surface and the top surface; a first tank facing the terminal surfaces of the battery cells; a second tank extending from the first tank and facing the lateral surfaces of the battery cells; and a third tank extending from the second tank and facing the top surfaces of the battery cells, wherein a cavity is formed in the first to third tanks to extend across the first to third tanks, and the cavity is filled with a first cooling medium and is fluidically isolated from outside of the battery pack, wherein a cooling tube is accommodated in the third tank to extend across the cavity, and the cooling tube accommodates flow of a second cooling medium different from the first cooling medium. 
     For example, the cavity may extend continuously from the first tank to the third tank across the second tank. 
     For example, the cavity in the first tank may face the terminal surfaces of the battery cells, the cavity in the second tank may face the lateral surfaces of the battery cells, and the cavity in the third tank may face the top surfaces of the battery cells. 
     For example, the battery cells may be disposed such that the terminal surfaces of the battery cells may be on a lower side and the top surfaces of the battery cells are on an upper side in a vertical direction corresponding to a direction of gravity. 
     For example, the first tank may be a high-temperature region, and the third tank may be a low-temperature region, wherein the first cooling medium may expand as being heated in the cavity of the first tank disposed on the lower side and may receive upward pressure, and the first cooling medium may contract as being cooled in the cavity of the third tank disposed on the upper side and may receive downward pressure, such that the first cooling medium may naturally convect between the first tank and the third tank. 
     For example, the first to third tanks may continuously surround the terminal surfaces, the lateral surfaces, and the top surfaces of the battery cells around cross-sectional surfaces of the battery cells, and the cooling tube may extend in an arrangement direction of the battery cells, the arrangement direction crossing the cross-sectional surfaces of the battery cells. 
     For example, the cooling tube may extend across the battery cells in the arrangement direction of the battery cells to cross the first to third tanks extending around the cross-sectional surfaces of the battery cells. 
     For example, the first to third tanks may each include an inner wall which faces the battery cells and an outer wall which is opposite the battery cells, and a width of the cavity between the inner wall and the outer wall may be greater than a total width of the inner wall and the outer wall. 
     For example, flow guides may be formed in the cavity to guide a flow direction of the first cooling medium. 
     For example, the flow guides may be formed in the cavity of the second tank. 
     For example, the flow guides may extend in a vertical direction in which the terminal surfaces of the battery cells face the top surfaces of the battery cells. 
     For example, the flow guides may obliquely extend to follow an arrangement direction of the battery cells and a vertical direction in which the terminal surfaces of the battery cells face the top surfaces of the battery cells. 
     For example, the flow guides may include ribs configured to guide the flow direction of the first cooling medium. 
     For example, the battery cells may include a plurality of battery cells, and flow paths filled with the first cooling medium and the ribs may be alternately arranged in the second tank in an arrangement direction of the plurality of battery cells. 
     For example, the flow guides may include reinforcement blocks configured to guide the flow direction of the first cooling medium, limit volume of the first cooling medium, and reinforce rigidity of the second tank in which the flow guides are formed. 
     For example, the battery cells may include a plurality of battery cells, and flow paths filled with the first cooling medium and the reinforcement blocks may be alternately arranged in the second tank in an arrangement direction of the plurality of battery cells. 
     For example, in a direction perpendicular to an extension direction of the reinforcement blocks, a width of the reinforcement blocks may be equal to or greater than a width of flow paths filled with the first cooling medium. 
     For example, flow modification portions may be formed in the cavity to change a flow type of the first cooling medium flowing in the cavity. 
     For example, the flow modification portions may include a plurality of flow modification portions isolated from each other and formed in a uniform pattern. 
     For example, the first cooling medium accommodated in the cavity and the second cooling medium accommodated in the cooling tube may have different heat capacities. 
     For example, the heat capacity of the first cooling medium may be greater than the heat capacity of the second cooling medium. 
     For example, the first cooling medium may naturally convect in the cavity, and the second cooling medium may forcedly convect in the cooling tube. 
     For example, a flow rate of the second cooling medium may be greater than a flow rate of the first cooling medium. 
     Hereinafter, a battery pack will now be described according to preferred embodiments of the present disclosure with reference to the accompanying drawings. 
       FIG.  1    is a perspective view illustrating a battery pack according to a preferred embodiment of the present disclosure.  FIG.  2    is an exploded perspective view illustrating the battery pack shown in  FIG.  1   .  FIG.  3    is a perspective view illustrating a battery cell illustrated in  FIG.  1   .  FIG.  4    is a cross-sectional view taken along line IV-IV of  FIG.  1   .  FIG.  5    is an enlarged view illustrating a portion of  FIG.  4   . 
     Referring to the drawings, the battery pack may include: a plurality of battery cells  10 ; and first, second, and third tanks T 1 , T 2 , and T 3  which surround the battery cells  10 . The first, second, and third tanks T 1 , T 2 , and T 3  may be arranged around the battery cells  10  and may dissipate heat from the battery cells  10  at different positions around the battery cells  10 , and for dissipating heating from the battery cells  10 , the first, second, and third tanks T 1 , T 2 , and T 3  may accommodate cooling media having high heat capacities. As described later, the first, second, and third tanks T 1 , T 2 , and T 3  may dissipate heat from the battery cells  10  by a liquid cooling method using first and second cooling media F 1  and F 2  which have relatively high heat capacities instead of using gases such air. 
     The first, second, and third tanks T 1 , T 2 , and T 3  may be formed in one piece to have a continuous structure. For example, the first, second, and third tanks T 1 , T 2 , and T 3  may be formed as one part through, for example, one process such as a high-pressure die casting process instead of forming the first, second, and third tanks T 1 , T 2 , and T 3  as individual parts and then combining the first, second, and third tanks T 1 , T 2 , and T 3  with each other. 
     In particular, each pair of the first and second tanks T 1  and T 2  may share one cavity C (refer to  FIG.  4   ) that is continuously formed, and to prevent leakage of the first cooling medium F 1  (refer to  FIG.  4   ) filled in the cavity C (refer to  FIG.  4   ), each pair of the first and second tanks T 1  and T 2  may be formed as one part to maintain the fluid tightness of the cavity C (refer to  FIG.  4   ). Since the first and second tanks T 1  and T 2  are positioned relatively close to electrode terminals  15  at which charge-discharge current is concentrated, it is needed to tightly seal the first cooling medium F (refer to  FIG.  4   ) to prevent a short circuit caused by leakage of the first cooling medium F 1  (refer to  FIG.  4   ), and thus at least the first and second tanks T 1  and T 2  may be continuously connected to each other in a seamless form without any joints therebetween. 
     The first and second tanks T 1  and T 2  may be connected to each other with first bent portions B 1  as boundaries therebetween, and may extend in different directions from the first bent portions B 1  to face different surfaces of the battery cells  10 . Similarly, the second and third tanks T 2  and T 3  may be connected to each other with second bent portions B 2  as boundaries therebetween, and may extend in different directions from the second bent portions B 2  to face different surfaces of the battery cells  10 . 
     Referring to  FIG.  3   , each of the battery cells  10  may include: a terminal surface  10 U on which electrode terminals  15  are formed; a bottom surface  10 L which is opposite the terminal surface  10 U; main surfaces  10 M which extend between the terminal surface  10 U and the bottom surface  10 L and having a relatively large area; and lateral surfaces  10 S which extend between the terminal surface  10 U and the bottom surface  10 L and having a relatively small area. 
     Each of the battery cells  10  may be formed in a substantially rectangular parallelepiped shape including a terminal surface  10 U, a bottom surface  10 L, a pair of main surfaces  10 M, and a pair of lateral surfaces  10 S. The battery cells  10  may be arranged in one direction, and in this case, the main surfaces  10 M of neighboring battery cells  10  may face each other. 
     The first, second, and third tanks T 1 , T 2 , and T 3  may surround the terminal surfaces  10 U, the bottom surfaces  10 L, and the lateral surfaces  10 S between the terminal surfaces  10 U and the bottom surfaces  10 L, that is, may surround four different surfaces  10 U,  10 S, and  10 L except the main surfaces  10 M which face each other in the arrangement direction of the battery cells  10 . 
     The first, second, and third tanks T 1 , T 2 , and T 3  may be formed in one piece, and since the first, second, and third tanks T 1 , T 2 , and T 3  surrounding the four different surfaces  10 U,  10 S, and  10 L of the battery cells  10  are formed in one piece, structures for joining individual members may not be required, thereby guaranteeing simplicity in structure. 
     The assembly of the battery pack will be described below with reference to  FIG.  2   . That is, the first, second, and third tanks T 1 , T 2 , and T 3  formed in one piece to surround the four different surfaces  10 U,  10 S,  10 L except the main surfaces  10 M which face each other in the arrangement direction of the battery cells  10  may first be prepared; the battery cells  10  may be assembled by sliding the battery cells  10  in one direction (corresponding to the arrangement direction) into the first, second, and third tanks T 1 , T 2 , and T 3  that are open in the direction (corresponding to the arrangement direction); and a pair of end plates (not shown) may be placed on one open end and the other open end of the first, second, and third tanks T 1 , T 2 , and T 3  in the direction (corresponding to the arrangement direction) as finishing member for the open ends of the first, second, and third tanks T 1 , T 2 , and T 3 . 
     Referring to  FIGS.  4  and  5   , the first tanks T 1  may be arranged to face the terminal surfaces  10 U of the battery cells  10 . Since charge-discharge current is concentrated on the terminal surfaces  10 U of the battery cells  10 , and the electrode terminals  15  connected to electrode assemblies (not shown) provided inside the battery cells  10  are formed on the terminal surfaces  10 U, the generation of heat may be concentrated on the terminal surfaces  10 U of the battery cells  10 , and thus it may be required to dissipate heat mainly from the terminal surfaces  10 U of the battery cells  10 . The first tanks T 1  may be arranged to face the terminal surfaces  10 U of the battery cells  10  and dissipate heat from the terminal surfaces  10 U of the battery cells  10  at a close distance. 
     A pair of electrode terminals  15  facing each other may be formed on the terminal surface  10 U of each of the battery cells  10 , and the first tanks T 1  may be arranged outside the pair of electrode terminals  15 . For example, the first tanks T 1  may not entirely cover the terminal surface  10 U of each of the battery cells  10 , but may cover a portion of the terminal surface  10 U, that is, only outer regions of the terminal surface  10 U. Since the first tanks T 1  selectively cover the outer regions of the terminal surface  10 U as described above, the pair of electrode terminals  15  may be exposed from the first tanks T 1  in an inner region of the terminal surface  10 U, and bus bars (not shown) may be coupled to the exposed electrode terminals  15  to electrically connect the electrode terminals  15  with electrode terminals  15  of adjacent battery cells  10 . 
     The first tanks T 1  may extend from inner positions PI relatively adjacent to the electrode terminals  15  to outer positions PO relatively distant from the electrode terminals  15 , and the cavities of the first tanks T 1  may have a uniform width W 1  (refer to  FIG.  5   ) from the inner positions PI to the outer positions PO. In this case, the width W 1  of the cavities C of the first tanks T 1  may be measured in a direction perpendicular to the terminal surface  10 U of each of the battery cells  10  which face the first tanks T 1 . 
     Since the first tanks T 1  are arranged to face the terminal surfaces  10 U requiring dissipation of a relatively large amount of heat and have relatively small lengths limited within the outer regions of the battery cells  10  so as not to cover the electrode terminals  15 , it is preferable that the first cooling medium F 1  be contained in the cavities C in a sufficient amount for coping with heat dissipation requirements, and the cavities C of the first tanks T 1  may have a uniform width W 1  from the inner positions PI close to the electrode terminals  15  to the outer positions PO distant from the electrode terminals  15 . When the cavities C of the first tanks T 1  have a nonuniform width W 1 , heat may be poorly dissipated in a region in which the width W 1  is relatively small because of an insufficient amount of the first cooling medium F 1 . 
     The first tanks T 1  are responsible for dissipation of heat from the terminal surfaces  10 U of the battery cells  10  at positions close to the terminal surfaces  10 U of the battery cells  10 . As described later, the first, second, and third tanks T 1 , T 2 , and T 3  are thermally connected to each other and cooperate with each other for dissipating heat from the battery cells  10 , and heat of the terminal surfaces  10 U may be transferred to the second and third tanks T 2  and T 3  through the first tanks T 1  closest to the terminal surfaces  10 U and may then be finally dissipated to the outside of the battery pack through the third tank T 3 . 
     The second tanks T 2  may be arranged to face the lateral surfaces  10 S of the battery cells  10 . The second tanks T 2  may extend through the first bent portions B 1  from the first tanks T 1  facing the terminal surfaces  10 U of the battery cells  10  to face the lateral surfaces  10 S of the battery cells  10 . The second tanks T 2  may be arranged to face the lateral surfaces  10 S of the battery cells  10  and may dissipate heat from the lateral surfaces  10 S of the battery cells  10  at a close distance from the lateral surfaces  10 S of the battery cells  10 . 
     Each of the second tanks T 2  may share one cavity C with one first tank T 1 , and the cavities C may extend across the first and second tanks T 1  and T 2  to fluidically connect the first and second tanks T 1  and T 2  to each other. For example, the cavities C may extend through the first bent portions B 1  forming boundary regions between the first and second tanks T 1  and T 2  to fluidically connect the first and second tanks T 1  and T 2  to each other and thus to allow a fluid to flow between the first and second tanks T 1  and T 2 . In the present specification, the expression “the cavities C extend across the first and second tanks T 1  and T 2 ,” or “the cavities C extend through the first and second tanks T 1  and T 2 ” may mean that the cavities C fluidically connect the first and second tanks T 1  and T 2  through the boundaries between the first and second tanks T 1  and T 2 . 
     The first cooling medium F 1  filled in the cavities C may allow direct heat transfer between the first and second tanks T 1  and T 2  while moving in the cavities C by natural convection. For example, since the first and second tanks T 1  and T 2  are fluidically connected to each other, natural convection in the first tanks T 1  and natural convection in the second tanks T 2  may affect each other, and this may mean that: natural convection in the first tanks T 1  and natural convection in the second tank T 2  may come into direct contact with each other or mix with each other to result in heat exchange; or heat transfer may occur between the first and second tanks T 1  and T 2  by natural convection of the first cooling medium F 1  filled in the cavities C extending through the first and second tanks T 1  and T 2 . 
     Since the first tanks T 1  face the terminal surfaces  10 U on which heat is concentrated, the first tanks T 1  may absorb heat from the terminal surfaces  10 U at a close distance from the terminal surfaces  10 U, and the first cooling medium F 1  which has absorbed heat from the terminal surfaces  10 U may transfer the heat to the second tanks T 2  by natural convection. The first and second tanks T 1  and T 2  may be connected to each other through the first bent portions B 1  and may extend in difference directions from the first bent portions B 1  to respectively face the terminal surfaces  10 U and the lateral surfaces  10 S of the battery cells  10 . In this case, the cavities C of the first and second tanks T 1  and T 2  may penetrate the first bent portions B 1  to fluidically connect the first and second tanks T 1  and T 2  to each other. 
     Natural convection may occur due to thermal imbalance between the first and second tanks T 1  and T 2 , and for example, natural convection in the first tank T 1  and natural convection in the second tank T 2  may occur in opposite directions like clockwise and counterclockwise circulations and may meet and mix with each other at the first bent portions B 1 . For example, in the cavities C extending through the first and second tanks T 1  and T 2 , one flow may be formed by natural convection, or circulations may be formed in opposite directions by natural convection and may meet and mix with each other at the first bent portions B 1 . 
     The cavities C extending through the first and second tanks T 1  and T 2  are filled with the first cooling medium F 1 , and thermal imbalance may occur in the cavities C according to the distances from the electrode terminals  15  at which heat is intensively generated such that the first cooling medium F 1  may directly transfer heat by natural convection. For example, heat may transfer between the first and second tanks T 1  and T 2  by natural convection in the cavities C extending through the first and second tanks T 1  and T 2 . That is, heat may transfer from the first tanks T 1  to the second tanks T 2 , and thus heat may transfer from the terminal surfaces  10 U through the first and second tanks T 1  and T 2  to the third tank T 3  which is thermally connected to the second tanks T 2  such that the heat may be finally dissipated to the outside of the battery pack through the third tank T 3 . 
     The second tanks T 2  may extend from upper positions PU close to the first tanks T 1  to lower positions PL close to the third tank T 3 . In this case, the cavities C of the second tanks T 2  may have a width W 2  (refer to  FIG.  5   ) that gradually decreases from the upper positions PU to the lower positions PL. Here, the width W 2  of the cavities C of the second tanks T 2  may be measured in a direction perpendicular to the lateral surfaces  10 S of the battery cells  10  facing the second tanks T 2 . 
     The second tanks T 2  may be arranged to face the lateral surfaces  10 S of the battery cells  10 , and may have inner walls SI facing the battery cells  10  and outer walls SO which are opposite the battery cells  10 , wherein the width between the inner walls SI and the outer walls SO of the second tanks T 2  may be uniform from the upper positions PU to the lower positions PL. Here, the width of the second tanks T 2  may be measured in a direction perpendicular to the lateral surfaces  10 S of the battery cells  10  facing the second tanks T 2 . 
     The second tanks T 2  may have a uniform width from the upper positions PU to the lower positions PL, and the cavities C formed in the second tanks T 2  may have a width W 2  which gradually decreases in a direction from the upper positions PU to the lower positions PL. This structure may be formed by adjusting a first thickness A 1  (refer to  FIG.  5   ) between the inner walls SI and the cavities C of the second tanks T 2  to be uniformly thin to bring the cavities C of the second tanks T 2  as close as possible to the battery cells  10  (more specifically, the lateral surfaces  10 S of the battery cells  10 ), and adjusting a second thickness A 2  (refer to  FIG.  5   ) between the outer walls SO and the cavities C of the second tanks T 2  to gradually increase from the upper positions PU to the lower positions PL for varying the width W 2  of the cavities C in a direction from the upper positions PU to the lower positions PL. 
     For example, the cavity C of each of the second tanks T 2  may have a right-angled triangular cross-section, and as the hypotenuse of the right-angled triangular cross-section obliquely extends in a direction from a vertex located at the upper position PU to a vertex located at the lower positions PL, the width W 2  of the cavity C may gradually decrease. The first cooling medium F 1  may be filled in the cavities C, and since the width W 2  of the cavities C are designed to be different at the upper positions PU and the lower positions PL, the volume of the first cooling medium F 1  filled in the cavies C may be differentially changed. That is, the volume of the first cooling medium F 1  may change from a maximum value to a minimum value in a direction from the upper positions PU to the lower positions PL, and in the manner, the volume of the first cooling medium F 1  may be differentially designed according to the amounts of heat to be dissipated at different positions. 
     Heat may be relatively intensively generated in the electrode terminals  15  of the battery cells  10  in which charge-discharge currents is concentrated. By considering this, heat may be differentially dissipated from the upper positions PU close to the electrode terminals  15  by adjusting the width W 2  of the cavities C of the second tanks T 2  to be relatively great at the upper positions PU. That is, the upper positions PU at which the need for heat dissipation is relatively great may face a relatively great width W 2  of the cavities C and may thus face the maximum volume of the first cooling medium F 1 . In addition, the lower positions PL at which the need for heat dissipation is relatively low may face a relatively small width W 2  of the cavities C and may thus face the minimum volume of the first cooling medium F 1 . 
     The cavities C may extend through the first and second tanks T 1  and T 2  and may have different shapes in the first and second tanks T 1  and T 2 . That is, the cavities C of the first tanks T 1  may have a uniform width W 1  from the inner positions PI relatively close to the electrode terminals  15  to the outer positions PO relatively distant from the electrode terminals  15 . The cavities of the first tanks T 1  facing the terminal surfaces  10 U may have a uniform width W 1  such that the first cooling medium F 1  may be provided in a sufficient amount for the terminal surfaces  10 U having a relatively high heat dissipation demand. When the cavities C of the first tanks T 1  have a nonuniform width W 1 , since the first tanks T 1  have a relatively small length covering outer regions of the terminal surfaces  10 U, the amount of the first cooling medium F 1  may be insufficient at some positions to result in poor heat dissipation. Thus, the cavities C of the first tanks T 1  may be formed to have a uniform width W 1 . 
     The width W 2  of the cavities C of the second tanks T 2  may be relatively great at the upper positions PU at which the heat dissipation demand is concentrated and may be relatively small at the lower positions PL at which the heat dissipation demand is relatively low, and thus, the volume of the first cooling medium F 1  may be differentially designed according to the width W 2  of the cavities C which varies from the upper positions to the lower positions PL for efficient distribution of the first cooling medium F 1  in accordance with the heat dissipation demand. 
     The cavities C extending through the first and second tanks T 1  and T 2  are fluidically isolated, and the first cooling medium F 1  is filled in the cavities C. The expression “the cavities C are fluidically isolated” may mean that each of the cavities C is not provided with a structure such as a duct for allowing the introduction and discharge of a fluid. That is, the cavities C may be fluidically isolated, and the first cooling medium F 1  may be statically filled in the cavities C without any flow of the first cooling medium F 1  into or out of the cavities C. The cavities C extending through the first and second tanks T 1  and T 2  may be fluidically isolated from the surrounding environment without fluidical connection with the surrounding environment, that is, without any flow of a fluid into or out of the cavities C. 
     The expression “the cavities C of the first and second tanks T 1  and T 2  are fluidically isolated” does not mean that the first and second tanks T 1  and T 2  are thermally insulated from the surrounding environment, and as described later, the first and second tanks T 1  and T 2  are thermally connected to the third tank T 3  such that the first and second tanks T 1  and T 2  may exchange heat with the third tank T 3  through heat conduction blocks CB. For example, the first and second tanks T 1  and T 2  are not fluidically connected to the third tank T 3 , and thus direct convection for heat transfer does not occur therebetween. However, since the first and second tanks T 1  and T 2  are thermally connected to the third tank T 3  through the heat conduction blocks CB, heat transfer may occur therebetween by conduction. As described later, since the heat conduction blocks CB are provided between the first cooling medium F 1  of the first and second tanks T 1  and T 2  and the second cooling medium F 2  of the third tank T 3 , heat transfer may occur between the first and second cooling media F 1  and F 2 , and heat transferred from the first cooling medium F 1  may be dissipated to the outside of the battery pack through the second cooling medium F 2  by convection forced by a fluid pump (not shown). 
     Natural convection may occur in the cavities C due to thermal imbalance, and the first cooling medium F 1  may naturally convect at a low flow speed or may absorb heat in a stationary state in which the flow speed of the first cooling medium F 1  is almost zero. As described above, in the cavities C, the first cooling medium F 1  naturally convects at a low flow speed or absorbs heat in a stationary state in which the flow speed of the first cooling medium F 1  is almost zero, and thus it is preferable that a fluid having a high heat capacity be used as the first cooling medium F 1 . As described later, the first cooling medium F 1  of the first and second tanks T 1  and T 2  may be a fluid having a heat capacity greater than the heat capacity of the second cooling medium F 2  of the third tank T 3 . This will be described in more detail later. 
     The first cooling medium F 1  does not flow into or out of the cavities C and is not forced to convect by a fluid pump, but is simply contained in the cavities C in a static state. That is, it is not needed to provide the first and second tanks T 1  and T 2  with a duct structure for allowing the first cooling medium F 1  to flow into or out of the cavities C, or a device such as a fluid pump for forcing the first cooling medium F 1  to convect, and thus a simple fluid cooling structure may be provided using the first cooling medium F 1 . 
     Since the first and second tanks T 1  and T 2  in which the first cooling medium F 1  is stored are arranged at positions closer to the electrode terminals  15  than the third tank T 3  is to the electrode terminals  15 , when the first and second tanks T 1  and T 2  adjacent to the electrode terminals  15  are provided with a structure such as a duct structure or a fluid pump, the possibility of leakage of the first cooling medium F 1  stored in the first and second tanks T 1  and T 2  may increase. When the first cooling medium F 1  leaks toward the electrode terminals  15  at which charge-discharge current is concentrated, the possibility of accidents such as an electrical short circuit may increase. Thus, in the present disclosure, fluid cooling is implemented using the first cooling medium F 1  having a relatively high heat capacity to efficiently dissipate heat from the electrode terminals  15  having a relatively high heat dissipation demand, but the first and second tanks T 1  and T 2  storing the first cooling medium F 1  are not provided with a duct for introduction or discharge of the first cooling medium F 1  or a fluid pump for forcing the first cooling medium F 1  to convent so as to prevent leakage of the first cooling medium F 1  to the electrode terminals  15 , such that the first cooling medium F 1  may dissipate heat from the electrode terminals  15  while the first cooling medium F 1  naturally convects or absorbs heat at a low flow speed. 
     The first cooling medium F 1  may be a fluid which has a high heat capacity and is electrically insulative. The first cooling medium F 1  is filled in the cavities C of the first and second tanks T 1  and T 2  which are close to the electrode terminals  15 . In this case, in the process of injecting the first cooling medium F 1  into the cavities C of the first and second tanks T 1  and T 2 , the first cooling medium F 1  may leak toward the electrode terminals  15 , and when the first cooling medium F 1  leaking toward the electrode terminals  15  accumulates on the terminal surfaces  10 U, an electrical short circuit may occur between the electrode terminals  15  and other conductive members. Thus, it is preferable that the first cooling medium F 1  be electrically insulative. For example, the first cooling medium F 1  may be a fluid which is more electrically insulative than the second cooling medium F 2  of the third tank T 3  which is relatively distant from the electrode terminals  15 , and for example, the first cooling medium F 1  may be a fluid having electrical conductivity lower than that of the second cooling medium F 2 . 
     The third tank T 3  may be arranged to face the bottom surfaces  10 L of the battery cells  10 . The third tank T 3  may extend through the second bent portions B 2  from the second tanks T 2  facing the lateral surfaces  10 S of the battery cells  10  to face the bottom surfaces  10 L of the battery cells  10 . The third tank T 3  may be arranged to face the bottom surfaces  10 L of the battery cells  10  and may dissipate heat from the bottom surfaces  10 L of the battery cells  10  at a close distance from the bottom surfaces  10 L of the battery cells  10 . 
     A flow path D for receiving the flow of the second cooling medium F 2  different from the first cooling medium F 1  may be formed in the third tank T 3 . The flow path D of the third tank T 3  is isolated from the cavities C extending through the first and second tanks T 1  and T 2  without fluidical connection with the cavities C. That is, the flow path D of the third tank T 3  may contain a fluid different from a fluid contained in the cavities C of the first and second tanks T 1  and T 2 , that is, the second cooling medium F 2  different from the first cooling medium F 1  of the first and second tanks T 1  and T 2 , and the first and second cooling media F 1  and F 2  may be isolated from each other without being mixed with each other for dissipating heat from different regions of the battery pack. For example, the cavities C extending through the first and second tanks T 1  and T 2  may be fluidically isolated from the outside of the cavities C without fluidical connection with the third tank T 3 . 
     The cavities C extending through the first and second tanks T 1  and T 2  is not fluidically connected to the flow path D of the third tank T 3 , but the first and second tanks T 1  and T 2  are thermally connected to the third tank T 3  such that heat may transfer between the first cooling medium F 1  of the first and second tanks T 1  and T 2  and the second cooling medium F 2  of the third tank T 3  through the heat conduction blocks CB. For example, the heat conduction blocks CB may be formed between the cavities C extending through the first and second tanks T 1  and T 2  and the flow path D of the third tank T 3  as metal blocks having no fluid-containing space. For example, the heat conduction blocks CB may include solid portions of the second tanks T 2  in which the cavities C are not formed, and solid portions of the third tank T 3  in which the flow path D is not formed. 
     The heat conduction blocks CB may include the second bent portions B 2  which connect the second and third tanks T 2  and T 3  to each other. The second bent portions B 2  may connect the second and third tanks T 2  and T 3  to each other such that the second tanks T 2  facing the lateral surfaces  10 S of the battery cells  10  may be connected to the third tank T 3  facing the bottom surfaces  10 L of the battery cells  10  through the second bent portions B 2 , and the second and third tanks T 2  and T 3  may extend from the second bent portions B 2  in different directions to respectively face the lateral surfaces  10 S and the bottom surfaces  10 L of the battery cells  10 . 
     Heat transfer between the second and third tanks T 2  and T 3  occurs through the heat conduction blocks CB and is thus different from heat transfer between the first and second tanks T 1  and T 2  which occurs by natural convection. That is, since the second and third tanks T 2  and T 3  are not fluidically connected to each other, convection heat transfer does not occur between the second and third tanks T 2  and T 3 , but heat transfer occurs between the second and third tanks T 2  and T 3  through the heat conduction blocks CB which thermally connect the second and third tanks T 2  and T 3  to each other. That is, the first cooling medium F 1  of the second tank T 2  and the second cooling medium F 2  of the third tank T 3  do not come into direct contact with each other or mix with each other, but heat transfer may occur between the first cooling medium F 1  and the second cooling medium F 2  by conduction through the heat conduction blocks CB. 
     The third tank T 3  may include the flow path D through which the second cooling medium F 2  flows, and the second cooling medium F 2  may be forced to flow at a certain flow speed by a fluid pump (not shown) such that heat transferred from the second tanks T 2  or the bottom surfaces  10 L of the battery cells  10  may be dissipated to the outside of the battery pack. 
     It is preferable that the second cooling medium F 2  be a fluid having a relatively high heat capacity for cooling efficiency. That is, it is preferable that both the first cooling medium F 1  of the first and second tanks T 1  and T 2  and the second cooling medium F 2  of the third tank T 3  be fluids having relatively high heat capacities. Since the first cooling medium F 1  transfers heat while naturally convecting at a low flow speed in the cavities C of the first and second tanks T 1  and T 2  or absorbing heat in the cavities C of the first and second tanks T 1  and T 2  in a stationary state in which the flow speed of the first cooling medium F 1  is almost zero, it is preferable that the first cooling medium F 1  be a fluid having a relatively high heat capacity, and since the second cooling medium F 2  is forced to flow at a controlled flow speed by the fluid pump, the flow speed of the second cooling medium F 2  may be adjusted according to the heat dissipation demand such that the second cooling medium F 2  may be a fluid having a heat capacity lower than that of the first cooling medium F 1 . For example, the average flow speed of the first cooling medium F 1  may be less than the average flow speed of the second cooling medium F 2 , and the first cooling medium F 1  may be a fluid having a heat capacity greater than that of the second cooling medium F 2  to compensate for a cooling efficiency decrease caused by the flow speed difference. 
     Since the third tank T 3  is arranged at a position more distant from the electrode terminals  15  than the first and second tanks T 1  and T 2  are from the electrode terminals  15 , the possibility of leakage of the second cooling medium F 2  to the electrode terminals  15  is relatively low. Therefore, the second cooling medium F 2  may be a fluid less electrically insulative than the first cooling medium F 1 . That is, the second cooling medium F 2  may be a fluid having relatively low heat capacity and electrical insulative characteristics compared to the first cooling medium F 1 . For example, the second cooling medium F 2  may be a fluid such as water which is inexpensive compared to the first cooling medium F 1 . 
     The second cooling medium F 2  may flow in the flow path D of the third tank T 3 , and the third tank T 3  may include an inlet/outlet  10  for introducing the second cooling medium F 2  having a low temperature or discharging the second cooling medium F 2  having a high temperature. The second cooling medium F 2  may circulate along a closed loop path including the flow path D of the third tank T 3  or an open loop path including the flow path D of the third tank T 3 , and in the closed loop path along which the second cooling medium F 2  circulates, a cooling unit (not shown) may be provided to cool the second cooling medium F 2 . 
     The first, second, and third tanks T 1 , T 2 , and T 3  may be formed of a metallic material which has high thermal conductivity and high formability for forming spaces for storing fluids such as the cavities C or the flow path D in the first, second, and third tanks T 1 , T 2 , and T 3 . The first, second, and third tanks T 1 , T 2 , and T 3  may surround four different surfaces  10 U,  10 S, and  10 L of each of the battery cells  10 , and may be formed of a metallic material having high heat conductivity for efficient heat transfer from the battery cells  10  to the first and second cooling media F 1  and F 2 . For example, the first, second, and third tanks T 1 , T 2 , and T 3  may be formed of an aluminum material. 
     The first, second, and third tanks T 1 , T 2 , and T 3  may be formed in one piece, and the second tanks T 2  connected through the second bent portions B 2  to the third tanks T 3  facing the bottom surfaces  10 L of the battery cells  10  may be provided as a pair facing each other and may face the lateral surfaces  10 S of the battery cells  10 . In addition, the first tanks T 1  connected the through the first bent portions B 1  to the second tanks T 2  facing the lateral surfaces  10 S of the battery cells  10  may be provided as a pair and may face the terminal surfaces  10 U of the battery cells  10 . 
       FIG.  6    is a perspective view illustrating a battery pack according to another embodiment of the present disclosure.  FIG.  7    is a cross-sectional view taken along line VII-VII of  FIG.  6   .  FIGS.  8  to  11    are views illustrating flow guides according to various embodiments of the present disclosure.  FIG.  12    is a view illustrating flow modification portions according to another embodiment of the present disclosure. 
     Referring to  FIGS.  6  and  7   , the battery pack may include: battery cells  10  each including a terminal surface  10 U on which an electrode terminal  15  is formed, a top surface  10 L′ opposite the terminal surface  10 U, lateral surfaces  10 S between the terminal surface  10 U and the top surface  10 L′; a first tank T 1  facing the terminal surfaces  10 U of the battery cells  10 ; a second tank T 2  extending from the first tank T 1  and facing the lateral surfaces  10 S; and a third tank T 3  extending from the second tank T 2  and facing the top surfaces  10 L′, wherein a cavity C may extend continuously in the first, second, and third tanks T 1 , T 2 , and T 3  and may be fluidically isolated from the outside of the battery pack with a first cooling medium F 1  being filled therein, and cooling tubes CP may be accommodated in the third tank T 3  across the cavity C to allow a second cooling medium F 2  different from the first cooling medium F 1  to flow therein. 
     In detail, referring to  FIGS.  6  and  7   , the battery pack may include the battery cells  10  and the first, second, and third tanks T 1 , T 2 , and T 3  surrounding the battery cells  10 . For example, the battery cells  10  illustrated in  FIGS.  6  and  7    may be turned upside down compared with the battery cells  10  illustrated in  FIG.  4   . That is, although the terminal surfaces  10 U of the battery cells  10  illustrated in  FIG.  4    are at an upper position in a vertical direction Z 1  corresponding to the direction of gravity, the terminal surfaces  10 U of the battery cells  10  illustrated in  FIGS.  6  and  7    may be at a lower position in the vertical direction Z 1 . In detail, the battery cells  10  illustrated in  FIGS.  6  and  7    may include the terminal surfaces  10 U at lower sides and the top surfaces  10 L′ at upper sides opposite the terminal surfaces  10 U. As described later, because the terminal surfaces  10 U in which a relatively large amount of heat accumulates are provided on the lower sides of the battery cells  10  in the vertical direction Z 1  corresponding to the direction of gravity, the first tank T 1  facing the terminal surfaces  10 U is a relatively high-temperature region, and the third tank T 3  accommodating the cooling tubes CP is a relatively low-temperature region. Thus, when heated in the lower high-temperature region, the first cooling medium F 1  may expand and reduce in specific weight to receive upward force due to buoyancy, and when cooled in the upper low-temperature region, the first cooling medium F 1  may contract and reduce in specific gravity to receive downward force. Therefore, the first cooling medium F 1  may naturally convect between the first tank T 1  corresponding to the high-temperature region and the third tank T 3  corresponding to the low-temperature region, and thus heat transfer may occur between the first tank T 1  and the third tank T 3  owing to the natural convection of the first cooling medium F 1 . 
     In an embodiment of the present disclosure, the first, second, and third tanks T 1 , T 2 , and T 3  may be continuously connected to each other while sharing the cavity C. That is, in an embodiment of the present disclosure, the first, second, and third tanks T 1 , T 2 , and T 3  may respectively face the terminal surfaces  10 U of the battery cells  10 , the lateral surfaces  10 S of the battery cells  10 , and the top surfaces  10 L′ of the battery cells  10  while surrounding the battery cells  10 . In the present specification, the expression “the first, second, and third tanks T 1 , T 2 , and T 3  share the cavity C” may mean that the first, second, and third tanks T 1 , T 2 , and T 3  are fluidically connected to each other through the cavity C, and may also mean that the first, second, and third tanks T 1 , T 2 , and T 3  accommodate a fluid flowing through the first, second, and third tanks T 1 , T 2 , and T 3 . 
     The first, second, and third tanks T 1 , T 2 , and T 3  may be disposed around the battery cells  10  and may dissipate heat from the battery cells  10  at different positions around the battery cells  10 . For example, the first, second, and third tanks T 1 , T 2 , and T 3  may accommodate the first cooling medium F 1  having a high heat capacity to dissipate heat from the battery cells  10 . In an embodiment of the present disclosure, the first, second, and third tanks T 1 , T 2 , and T 3  may dissipate heat from the battery cells  10  by a liquid-cooling method using the first cooling medium F 1  which is a liquid having a high heat capacity instead of using a gas such as air. 
     The first, second, and third tanks T 1 , T 2 , and T 3  may be formed in one piece to have a continuous structure. For example, the first, second, and third tanks T 1 , T 2 , and T 3  may be formed as one part through one process such as a high-pressure die casting process instead of forming the first, second, and third tanks T 1 , T 2 , and T 3  as individual parts and then combining the first, second, and third tanks T 1 , T 2 , and T 3  with each other. 
     In the embodiment shown in  FIGS.  6  and  7   , the first, second, and third tanks T 1 , T 2 , and T 3  may share one cavity C that is continuously formed, and to prevent leakage of the first cooling medium F 1  filled in the cavity C, the first, second, and third tanks T 1 , T 2 , and T 3  may be formed as one part to maintain the fluid tightness of the cavity C. Unlike in the embodiment shown in  FIG.  4    in which the first and second tanks T 1  and T 2  share one cavity C, in the embodiment shown in  FIGS.  6  and  7   , the first, second, and third tanks T 1 , T 2 , and T 3  continuously surrounding the battery cells  10  may share one cavity C. In an embodiment of the present disclosure, the expression “the first, second, and third tanks T 1 , T 2 , and T 3  share one cavity C” may mean that a fluid is allowed to flow between the first, second, and third tanks T 1 , T 2 , and T 3  across the first, second, and third tanks T 1 , T 2 , and T 3 . For example, natural convection of the first cooling medium F 1  may be possible from the first tank T 1  facing the terminal surfaces  10 U of the battery cells  10  to the third tank T 3  facing the top surfaces  10 L′ of the battery cells  10  via the second tank T 2  facing the lateral surfaces  10 S of the battery cells  10 . That is, natural convection of the first cooling medium F 1  is possible across the first, second, and third tanks T 1 , T 2 , and T 3 . 
     In an embodiment of the present disclosure, the first, second, and third tanks T 1 , T 2 , and T 3  may accommodate natural convection occurring therebetween, and thus owing to natural convection including transfer of a substance, that is, natural convection including transfer of the first cooling medium F 1 , heat may be dissipated outward from the battery cells  10 . For example, in an embodiment of the present disclosure, convection may occur across the first, second, and third tanks T 1 , T 2 , and T 3 , for example, in the vertical direction Z 1  corresponding to the direction of gravity. For example, natural convection may occur due to a temperature difference between the first tank T 1  facing the terminal surfaces  10 U accumulating a relatively large amount of heat and the third tank T 3  accommodating the cooling tubes CP. The first cooling medium F 1  contained in the first tank T 1  (specifically, a portion of the first cooling medium F 1  that is close to the terminal surfaces  10 U) may decrease in specific weight due to high-temperature expansion and may thus receive upward pressure due to buoyancy such that the first cooling medium F 1  may rise from the first tank T 1  to the third tank T 3  via the second tank T 2 . Then, the first cooling medium F 1  having a relatively high temperature and rising from the first tank T 1  to the third tank T 3  accommodating the cooling tubes CP may exchange heat with the second cooling medium F 2  flowing in the cooling tubes CP and may thus contract into a low-temperature and high-specific-gravity state, thereby receiving downward pressure and flowing down back to the first tank T 1 . For example, the first cooling medium F 1  cooled in the third tank T 3  may flow down in the second tank T 2  at a position relatively distant from the lateral surfaces  10 S (for example, in a horizontal direction Z 3 ), and may make a U-turn in an end portion of the first tank T 1  while expanding by receiving heat from the terminal surfaces  10 U at a position close to the lateral surfaces  10 S (for example, in the horizontal direction Z 3 ) such that the first cooling medium F 1  may flow upward to the third tank T 3  through the second tank T 2  due to a specific gravity difference caused by expansion. That is, in an embodiment of the present disclosure, the first, second, and third tanks T 1 , T 2 , and T 3  may accommodate natural convection occurring across the first, second, and third tanks T 1 , T 2 , and T 3 . Thus, heat transfer may occur between the first, second, and third tanks T 1 , T 2 , and T 3  by natural convection, and heat may be dissipated through the cooling tubes CP accommodated in the third tank T 3 . In the embodiment illustrated in  FIGS.  6  and  7   , the first, second, and third tanks T 1 , T 2 , and T 3  may be continuously connected to each other (share the cavity CC continuously formed therein) unlike the example illustrated in  FIG.  4    in which the first and second tanks T 1  and T 2  share the continuous cavity C, and the heat conduction blocks CB are disposed between the second and third tanks T 2  and T 3  to prevent the formation of a fluidical connection between the second and third tanks T 2  and T 3 . As described above, because the first, second, and third tanks T 1 , T 2 , and T 3  share the cavity C, natural convection may be possible between the first tank T 1  provided in the relatively high-temperature region and the third tank T 3  provided in the relatively low-temperature region. In an embodiment of the present disclosure, the first cooling medium F 1  may be contained in the first, second, and third tanks T 1 , T 2 , and T 3 , and may be a liquid having a relatively high heat capacity. That is, the first, second, and third tanks T 1 , T 2 , and T 3  may contain a substantially homogeneous cooling medium (the first cooling medium F 1 ) unlike the embodiment illustrated in  FIG.  4    in which the first, second, and third tanks T 1 , T 2 , and T 3  contain the first and second cooling media F 1  and F 2  having different characteristics (for example, different thermal characteristics such as different heat capacities) with the heat conduction blocks CB being between the first, second, and third tanks T 1 , T 2 , and T 3 . In an embodiment of the present disclosure, however, the third tank T 3  may accommodate the first cooling medium F 1  together with the cooling tubes CP in which the second cooling medium F 2  having thermal characteristics (for example, heat capacity) different from those of the first cooling medium F 1  are contained. In an embodiment of the present disclosure, for example, the first, second, and third tanks T 1 , T 2 , and T 3  may contain the first cooling medium F 1  capable of natural convection across the first, second, and third tanks T 1 , T 2 , and T 3 , and unlike the first and second tanks T 1  and T 2 , the third tank T 3  may also accommodate the cooling tubes CP in which the second cooling medium F 2  different from the first cooling medium F 1  is contained. In an embodiment of the present disclosure, the cavity C, which the first, second, and third tanks T 1 , T 2 , and T 3  share, may be fluidically isolated without any fluidical connection to the outside of the battery pack and any fluidical entrance/exit connected to the outside of the battery pack. However, the cooling tubes CP accommodated in the third tank T 3  may include a fluidical connection to the outside of the battery pack. For example, the cooling tubes CB extending across the third tank T 3  may be connected to each other in a closed-loop form through a heat exchanger (not shown) provided outside the battery pack. 
     In an embodiment of the present disclosure, the cooling tubes CP may include a plurality of cooling tubes CP connected in parallel to each other and a plurality of cooling tubes CP extending parallel to each other to increase a heat transfer area inside the third tank T 3 . In an embodiment of the present disclosure, for example, the cooling tubes CP may extend parallel to each other in an arrangement direction Z 2  of the battery cells  10 . In an embodiment of the present disclosure, for example, the cooling tubes CP may extend in the arrangement direction Z 2  of the battery cells  10  such that the second cooling medium F 2  may flow inside the cooling tubes CP in a direction crossing the direction in which the first cooling medium F 1  naturally convects around cross-sectional surfaces of the battery cells  10 . The cooling tubes CP may extend across the battery cells  10  in the arrangement direction Z 2  of the battery cells  10 , that is, the cooling tubes CP may extend in a direction (arrangement direction Z 2  of the battery cells  10 ) crossing the first cooling medium F 1  flowing around the cross-sectional surfaces of the battery cells  10 , to exchange heat with the natural convection of the first cooling medium F 1  flowing along the cross-sectional surfaces of the battery cells  10 . In an embodiment of the present disclosure, the term “natural convection” or “the natural convection of the first cooling medium F 1 ” may refer to the flow of the first cooling medium F 1  occurring to remove a thermal imbalance condition between the high-temperature region (for example, the first tank T 1 ) and the low-temperature region (for example, the third tank T 3 ) having different temperatures. For example, unlike forced convection driven by an additional fluid machine such as a fluid pump configured to impart a pressure difference, the term “natural convection” or “the natural convection of the first cooling medium F 1 ” may refer to the flow of the first cooling medium F 1  occurring due to a specific gravity difference caused by a temperature difference between the high-temperature region (for example, the first tank T 1 ) and the low-temperature region (for example, the third tank T 3 ). That is, in an embodiment of the present disclosure, the flow of the first cooling medium F 1  occurring in the cavity C of the first, second, and third tanks T 1 , T 2 , and T 3  may not rely on the operation of a fluid machine, and unlike the flow of the first cooling medium F 1 , the flow of the second cooling medium F 2  occurring in the cooling tubes CP extending in a direction (the arrangement direction Z 2  of the battery cells  10 ) crossing the flow of the first cooling medium F 1  occurring around the cross-sectional surfaces of the battery cells  10  may be driven by a fluid machine such as a fluid pump configured to impart a pressure difference for forced convection. For example, the second cooling medium F 2  may be circulated in a closed-loop circulation path, which includes the cooling tubes CP and a separate heat exchanger (not shown) connected to the cooling tubes CP from the outside of the battery pack. 
     The first cooling medium F 1  flowing in the cavity of the first, second, and third tanks T 1 , T 2 , and T 3  may be fluidically isolated from the outside of the battery pack, and for example, a fluidical connection such as a fluid entrance/exit (for example, an inlet and an outlet) may not be provided for the first cooling medium F 1 . Unlike the first cooling medium F 1 , the second cooling medium F 2  may be connected to the outside of the battery pack through the cooling tubes CP. For example, the cooling tubes CP extending parallel to each other in the arrangement direction Z 2  of the battery cells  10  from an end to another end of the battery pack may have a branching position (not shown) and a joining position (not shown), and the cooling tubes CP provided inside the battery pack may be fluidically connected to an external flow path through an inlet and an outlet that are connected to manifolds (not shown) or header pipes (not shown) connected to the cooling tubes CP at the branching position (not shown) and the joining position (not shown). 
     In an embodiment of the present disclosure, the first cooling medium F 1  may naturally convect in the cavity C of the first, second, and third tanks T 1 , T 2 , and T 3  between the first tank T 1  and the third tank T 3  which respectively form the relatively high-temperature region and the relatively low-temperature region around the cross-sectional surfaces (Z 1 -Z 3  plane) of the battery cells  10 . In the present specification, the expression “the first cooling medium F 1  naturally convects around the cross-sectional surfaces (Z 1 -Z 3  plane) of the battery cells  10 ” does not limit the flow direction of the first cooling medium F 1 . For example, the first cooling medium F 1  may naturally convect around the cross-sectional surfaces (Z 1 -Z 3  plane) of the battery cells  10  and may also naturally convect across neighboring battery cells  10  in the arrangement direction Z 2  of the battery cells  10 . In an embodiment of the present disclosure, the natural convection of the first cooling medium F 1  occurring in the cavity C of the first, second, and third tanks T 1 , T 2 , and T 3  is caused by thermal imbalance between different positions. Thus, for example, the natural convection of the first cooling medium F 1  may occur across neighboring battery cells  10  in the arrangement direction Z 2  of the battery cells  10 , and a natural convectional flow of the first cooling medium F 1  occurring around the cross-sectional surfaces (Z 1 -Z 3  plane) of the battery cells  10  may mix with or continue together with another natural convectional flow of the first cooling medium F 1  occurring in the arrangement direction Z 2  of the battery cells  10 . For example, a natural convectional flow (driving force of flow) of the first cooling medium F 1  occurring around the cross-sectional surfaces (Z 1 -Z 3  plane) of the battery cells  10  may combine with another natural convectional flow (driving force of flow) of the first cooling medium F 1  occurring in the arrangement direction Z 2  of the battery cells  10  to form a diagonal flow occurring around the cross-sectional surfaces of the battery cells  10  and following the arrangement direction Z 2  of the battery cells  10 . In an embodiment of the present disclosure, thermal imbalance may occur in the arrangement direction Z 2  of the battery cells  10  because accumulation of heat occurs more at a center position at which battery cells  10  are adjacent to each other in the arrangement direction Z 2  of the battery cells  10  than at an edge position adjacent to the outside of the battery pack in the arrangement direction Z 2  of the battery cells  10 . This thermal imbalance acts as a driving force causing a natural convection between a relatively low-temperature region (for example, the edge position) and a relatively high-temperature region (for example, the center position). In an embodiment of the present disclosure, the flow of the first cooling medium F 1  inside the second tank T 2  facing the lateral surfaces  10 S of the battery cells  10  may not occur along a shortest path in the vertical direction Z 1  corresponding to the direction of gravity but may occur along an approximately diagonal path sloped with respect to the arrangement direction Z 2  of the battery cells  10 . That is, the flow of the first cooling medium F 1  inside the second tank T 2  connecting the first tank T 1  and the third tank T 3  to each other may occur from the first tank T 1  to the third tank T 3  along an oblique or diagonal path sloped with respect to the arrangement direction Z 2  of the battery cells  10  rather than along a shortest path between the first tank T 1  and the third tank T 3 . Thus, because the first cooling medium F 1  flows along a path longer than the shortest path, heat exchange between the first cooling medium F 1  and the battery cells  10  may be facilitated, and local heat accumulation may be more effectively prevented in the battery pack. In other words, according to an embodiment of the present disclosure, the first cooling medium F 1  flowing in the second tank T 2  removes thermal imbalance around the cross-sectional surfaces (Z 1 -Z 3  plane) of the battery cells  10  and thermal imbalance in the arrangement direction Z 2  of the battery cells  10 , thereby preventing local accumulation of heat in the battery pack. 
     Referring to  FIGS.  8  to  11   , in an embodiment of the present disclosure, flow guides FG may be formed in the second tank T 2  to control the flow of the second cooling medium F 2  in the second tank T 2 . For example, the flow guides FG may be formed in a direction following the vertical direction Z 1  from the first tank T 1  to the third tank T 3 . For example, the flow guides FG may include flow guides FG 1  and FG 2  formed in the vertical direction Z 1  from the first tank T 1  to the third tank T 3 , or the flow guides FG may include diagonal flow guides FG 3  and F 4  formed in a direction following the vertical direction Z 1  and the arrangement direction Z 2  of the battery cells  10 . For example, the flow guides FG may include: ribs FG 1  and FG 2  formed in the vertical direction Z 1  as shown in  FIGS.  8  to  9 B , or diagonal ribs FG 3  and F 4  formed in a direction following the vertical direction Z 1  and the arrangement direction Z 2  of the battery cells  10  as shown in  FIGS.  10 A and  10 B . As described above, the flow guides FG may be formed in the vertical direction Z 1  or in an oblique direction following the vertical direction Z 1  and the arrangement direction Z 2  of the battery cells  10 . For example, the flow guides FG may include: ribs FG 1  and F 3  each continuously formed across the second tank T 2  as shown in  FIGS.  8 ,  9 A, and  9 B ; or ribs FG 2  and F 4  formed in the form of segments which are apart from each other with gaps g 1  and g 2  therebetween as shown in  FIGS.  9 B and  10 B . 
     In the various embodiments of the present disclosure shown in  FIGS.  8  to  10 B , the second tank T 2  may include flow paths P and ribs FG 1  to FG 4  (flow guides FG) that are alternately arranged in the arrangement direction Z 2  of the battery cells  10 . 
     Referring to  FIG.  7   , in an embodiment of the present disclosure, the first, second, and third tanks T 1 , T 2 , and T 3  may include inner walls SI facing the battery cells  10  and outer walls SO opposite the battery cells  10 , and the cavity C may be formed between the inner walls SI and the outer walls SO and may correspond to the width between the inner walls SI and the outer walls SO. For example, each of the first, second, and third tanks T 1 , T 2 , and T 3  may include: an inner wall SI and an outer wall SO; and the cavity C formed between the inner wall SI and the outer wall SO. The inner wall SI and the outer wall SO may have a uniform width along the battery cells  10 , and the cavity C may be formed between the inner wall SI and the outer wall SO. In an embodiment of the present disclosure, the width WC of the cavity C may be greater than the widths WI and WO of the inner walls SI and the outer walls SO. For example, the width WC of the cavity C may be greater than the width WI of the inner walls SI and the width WO of the outer walls SO. In various embodiments of the present disclosure, the width WC of the cavity C may be greater than the sum (WI+WO) of the width WI of the inner walls SI and the width WO of the outer walls SO. 
     Referring to  FIG.  7   , the diameter D of the cooling tubes CP accommodated in the third tank T 3  may be ⅓ to ½ of the width WC of the cavity C formed between the inner wall SI and the outer wall SO of the third tank T 3  (⅓≤D/WC≤½). In other words, when the diameter D of the cooling tubes CP accommodated in the third tank T 3  is excluded from the width WC of the cavity C formed between the inner wall SI and the outer wall SO of the third tank T 3 , the width WA of a flow space in which the first cooling medium F 1  may flow inside the third tank T 3  may be ½ to ⅔ of the width WC of the cavity (½≤WA/WC≤⅔). For example, in an embodiment of the present disclosure, the width WA of a flow space formed above the cooling tubes CP in the vertical direction Z 1 , the diameter D of the cooling tubes CP, and the width WA of a flow space formed below the cooling tubes CP may have a ratio of 1:1:1. In this case, the width WA of the flow space, in which the first cooling medium F 1  may flow, may be maximized while minimizing the diameter D of the cooling tubes CP. In another embodiment, the width WA of a flow space formed above and below the cooling tubes CP in the vertical direction Z 1  and the diameter D of the cooling tubes CP may have a ratio of 1:1. In this case, the width WA of the flow space in which the first cooling medium F 1  may flow may be minimized, and the diameter D of the cooling tubes CP may be maximized. In these embodiments, when the diameter D of the cooling tubes CP is smaller than the minimum described above, the heat capacity of the second cooling medium F 2  flowing through the cooling tubes CP may be limited and may act as a limiting factor during heat transfer between the first and second cooling media F 1  and F 2 , decreasing the heat dissipation performance of the battery cells  10 . 
     Conversely, when the diameter D of the cooling tubes CP is greater than the maximum described above, the width WC of the flow space, which is calculated by subtracting the diameter D of the cooling tubes CP from the width WC of the cavity C formed between the inner wall SI and the outer wall SO of the third tank T 3 , is relatively limited. Thus, the heat capacity of the first cooling medium F 1  flowing through the flow space may be limited and may thus act as a limiting factor during heat transfer between the first and second cooling media F 1  and F 2 , decreasing the heat dissipation performance of the battery cells  10 . 
     Referring to  FIG.  11   , in addition to guiding the flow direction of the first cooling medium F 1 , the flow guides FG may include reinforcement blocks F 5  to limit the volume of the first cooling medium F 1  and reinforce the rigidity of the second tank T 2  in which the flow guides FG are formed. That is, the flow guides FG (reinforcement blocks FG 5 ) may guide the flow direction of the first cooling medium F 1  like the ribs FG 1  to FG 4  shown in  FIGS.  8  to  10 B , and in addition to this, the flow guides FG (reinforcement blocks FG 5 ) may limit the volume of the first cooling medium F 1  and reinforce the rigidity of the second tank T 2  in which the flow guides FG are formed. 
     According to the embodiment shown in  FIG.  11   , the second tank T 2  may include flow paths P and the reinforce blocks FG 5  (corresponding to flow guides FG), which are alternately formed. For example, in an embodiment of the present disclosure, the flow paths P and the reinforcement blocks FG 5  may be alternately arranged in the arrangement direction Z 2  of the battery cells  10 . The flow guides FG may control the flow direction of the first cooling medium F 1  in the second tank T 2 , and the flow guides FG or the reinforcement blocks FG 5  may have a relatively large width W 21  in a direction (the arrangement direction Z 2  of the battery cells  10 ) perpendicular to the extension direction (the vertical direction Z 1 ) of the flow guides FG or the reinforcement blocks FG 5 . For example, the width W 21  of the reinforcement blocks FG 5  may be equal to or greater than the width W 11  of the flow paths P which are arranged between the reinforcement blocks FG 5  and filled with the first cooling medium F 1 . Thus, for example, the amount of the first cooling medium F 1  filled in the second tank T 2  may be controlled, and the rigidity of the second tank T 2  may be reinforced. 
     For example, as shown in  FIG.  7   , the width WC of the cavity C (in the vertical direction Z 1 ) is greater than the width WI of the inner wall SI and the width WO of the outer wall SO of the second tank T 2 , and thus the rigidity of the second tank T 2  may not be sufficient because the inner wall SI and the outer wall SO of the second tank T 2  are not sufficiently thick compared with an increase in the amount or weight of the first cooling medium F 1  filled in the second tank T 2  (specifically, the cavity C of the second tank T 2 ). Thus, the second tank T 2  may be physically damaged due to the weight of the first cooling medium F 1  filled in the second tank T 2  or shocks applied to the second tank T 2 . 
     In the embodiment of the present disclosure shown in  FIG.  11   , the fraction or weight of the first cooling medium F 1  in the second tank T 2  may be reduced because the width W 11  of the flow paths P (in the arrangement direction Z 2  of the battery cells  10 ) in which the first cooling medium F 1  is filled may be limited by the reinforcement blocks FG 5 , and the width W 21  of the reinforcement blocks FG 5  reinforcing the rigidity of the second tank T 2  may increase. Thus, the second tank T 2  may not be physically damaged due to insufficient rigidity of the second tank T 2 . 
     For reference, in an embodiment of the present disclosure, the flow guides FG formed in the second tank T 2  may partition the cavity C shared with the first tank T 1  and the third tank T 3 . For example, in an embodiment of the present disclosure, the cavity C shared by the first, second, and third tanks T 1 , T 2 , and T 3  is a space in which the first cooling medium F 1  may be filled. For example, the cavity C may refer to the flow paths P in which the first cooling medium F 1  may be filled except for the flow guides FG. The cavity C may be partitioned by the flow guides FG. 
     Referring to  FIG.  12   , in an embodiment of the present disclosure, flow modification portions FD may be formed in the cavity C. The flow modification portions FD may be structures for increasing heat exchange efficiency between the battery cells  10  and the first cooling medium F 1  flowing in the cavity C by modifying the flow type of the first cooling medium F 1  flowing in the cavity C, for example, by modifying laminar flow, turbulent flow, or eddy flow of the first cooling medium F 1  in the cavity C. To this end, the flow modification portions FD may have structures capable of changing the type of flow by modifying, depending on the type of flow, the spatial gradient or distribution of pressure, velocity, or the like related to the energy of flow, such as the distribution of pressure and/or the distribution of flow velocity. 
     In an embodiment of the present disclosure, the first cooling medium F 1  may naturally convect in the cavity C shared by the first, second, and third tanks T 1 , T 2 , and T 3 . Unlike forced convection occurring according to a pressure difference imparted by a fluid machine such as a fluid pump, the natural convection of the first cooling medium F 1  may occur at a relatively low flow rate without a pressure difference imparted by a fluid machine and may have a laminar or near-laminar flow form. In an embodiment of the present disclosure, the flow modification portions FD may be formed in the cavity C of the second tank T 2  in the form of isolated islands. Inside the cavity C, the flow modification portions FD may change laminar flow of the first cooling medium F 1  to a flow form similar to turbulent flow or eddy flow, and thus the efficiency of heat exchange between the first cooling medium F 1  and the battery cells  10  may be increased. For example, in the laminar flow of the first cooling medium F 1 , a boundary layer having a relatively low flow rate (or a flow rate substantially equal to or close to zero) may accumulate on the inner walls SI adjacent to the battery cells  10  due to friction between the first cooling medium F 1  and the inner walls SI, and the accumulation of the boundary layer may cause thermal resistance between the inner walls SI and the first cooling medium F 1 . In addition, layers of the laminar flow of the first cooling medium F 1  may hardly mix with each other in a direction perpendicular to the inner walls SI, and thus the laminar or near-laminar flow of the first cooling medium F 1  does not guarantee sufficient heat exchange with the battery cells  10 . 
     In an embodiment of the present disclosure, the flow modification portions FD may be formed in the cavity C in which the first cooling medium F 1  flows, to change the flow of the first cooling medium F 1  from laminar or near-laminar flow to turbulent flow, eddy flow, near-turbulent flow, or near-eddy flow. For example, the flow modification portions FD may include a plurality of flow modification portions FD that are provided inside the cavity C of the second tank T 2  as islands isolated from each other and arranged in a uniform pattern. The flow modification portions FD may cause a turbulent flow or eddy flow (or flow similar thereto) in at least a portion of the first cooling medium F 1  by applying flow resistance to laminar flow or near-laminar flow of the first cooling medium F 1 , or applying a pressure distribution resistant to laminar flow or near-laminar flow of the first cooling medium F 1 . In an embodiment of the present disclosure, laminar or near-laminar flow of the first cooling medium F 1  may include a boundary layer having a relatively low flow rate (or a flow rate substantially equal to or close to zero) on the inner walls SI adjacent to the battery cells  10  due to friction between the first cooling medium F 1  and the inner walls SI, and layers of the laminar or near-laminar flow of the first cooling medium F 1  may hardly mix with each other in a direction perpendicular to the inner walls SI. Thus, the flow modification portions FD may change the laminar or near-laminar flow of the first cooling medium F 1  to turbulent flow, eddy flow, or flow similar thereto at positions close to the flow modification portions FD to cause the first cooling medium F 1  to collide with the inner walls SI adjacent to the battery cells  10  or cause layers of the laminar or near-laminar flow of the first cooling medium F 1  to mix with each other in a direction perpendicular to the inner walls SI, thereby facilitating heat transfer from the inner walls SI adjacent to the battery cells  10 . 
     In the accompanying drawings of the present specification, the flow guides FG and/or the flow modification portions FD are formed in the cavity C of the second tank T 2 . In various embodiments of the present disclosure, however, the flow guides FG and/or the flow modification portions FD may be formed at any positions in the cavity C of the first, second, and third tanks T 1 , T 2 , and T 3 . For example, the flow guides FG and/or the flow modification portions FD may be formed in the cavity C of at least one, two or more, or all of the first, second, and third tanks T 1 , T 2 , and T 3 . 
     In an embodiment of the present disclosure, the first cooling medium F 1  accommodated in the cavity C shared by the first, second, and third tanks T 1 , T 2 , and T 3  may have heat capacity different from the heat capacity of the second cooling medium F 2  contained in the cooling tubes CP extending across the cavity C of the third tank T 3 . For example, the heat capacity of the first cooling medium F 1  may be greater than the heat capacity of the second cooling medium F 2 . For example, the first cooling medium F 1  may naturally convect in the cavity C, and the second cooling medium F 2  may forcedly convect in the cooling tubes CP. The second cooling medium F 2  flowing in the cooling tubes CP at a relatively high flow rate may facilitate heat transfer more than the first cooling medium F 1  flowing in the cavity C at a relatively low flow rate. For example, the flow rate of forced convection (the flow rate of the second cooling medium F 2 ) in the cooling tubes CP, which is relatively ease to control, may be adjusted to precisely control heat transfer occurring by the second cooling medium F 2  having a relatively low heat capacity. For example, manufacturing costs may be reduced by using the second cooling medium F 2  having a relatively low heat capacity, and the flow rate of controllable forced convection of the second cooling medium F 2  may be increased or decreased for balance between heat transfer by the second cooling medium F 2  and heat transfer by the first cooling medium F 1  flowing in the cavity C. 
     While embodiments of the present disclosure have been described with reference to the accompanying drawings, the embodiments are for illustrative purposes only, and it will be understood by those of ordinary skill in the art that various modifications and equivalent other embodiments may be made therefrom. Therefore, the scope and spirit of the present disclosure should be defined by the following claims. 
     The present disclosure may be applied to battery packs which are rechargeable energy sources, and to various devices using battery packs as power sources.