Patent Publication Number: US-2016240902-A1

Title: Electricity storage device

Description:
TECHNICAL FIELD 
     The present invention relates to a power storage device that houses a power storage module and, more particularly, to a power storage device provided with a cooling function of the power storage module. 
     BACKGROUND ART 
     A power storage device is mounted in an electric car, a hybrid car, and the like as a power source. The power storage device houses a plurality of power storage modules each having a plurality of secondary battery cells such as lithium-ion secondary battery cells. 
     The power storage device generates heat upon charging or discharging. The power storage device houses a number of secondary battery cells, so that a temperature difference may occur among the secondary battery cells. The temperature difference among secondary battery cells may affect cell performance and damage the battery cell and, thus, it is necessary to adopt a cooling structure capable of preventing the temperature difference from occurring as much as possible. 
     There is known a power storage device provided with a cooling structure described below. 
     A storage case has a cooling air introducing port and a cooling air lead-out port at one side and at a side opposite to the one side, respectively and houses, inside thereof, a plurality of power storage modules. Further, a cooling air control plate having a plurality of slits is provided between the cooling air introducing port of the storage case and a most upstream side power storage module. 
     In the above cooling structure, a vortex flow occurs in the cooling air at a periphery of the plurality of slits of the cooling air control plate, making density of the cooling air irregular, with the result that strength, speed, and the like of the air flow change with time. Thus, from a big perspective, even cooling is achieved with elapse of time (see, for example, PTL 1). 
     CITATION LIST 
     Patent Literature 
     PTL 1: Publication of Patent No. 2010-262758 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the above PTL 1, the cooling air that has passed through the cooling air control plate cools an outer peripheral surface of the power storage modules and is discharged through the cooling air lead-out port. In this process, the cooling air does not directly cool the secondary battery cells in each of the power storage modules. 
     Thus, in a configuration where a plurality of stages of the secondary battery cells are arranged in each of the power storage modules, a large temperature difference may occur between an inside secondary battery cell and an outside secondary battery cell. 
     Solution to Problem 
     According to a first aspect of the present invention, a a power storage device includes: a power storage module having a storage module case and a plurality of power storage elements arranged, in the storage module case, in a plurality of stages each including a plurality of the power storage elements, the storage module case having a refrigerant introducing port formed at one of a pair of side portions arranged in a longitudinal direction of the power storage elements and a refrigerant lead-out port at the other one of the pair of side portions; a storage case housing the power storage module and having an inlet communicating with the refrigerant introducing port and an outlet communicating with the refrigerant lead-out port; and a refrigerant control mechanism disposed at an outside of at least one of the pair of side portions of the storage module case in which the refrigerant introducing port is formed and the other one of the pair of side portions in which the refrigerant lead-out port is formed, wherein (i) when being disposed outside the refrigerant introducing port, the refrigerant control mechanism has circulation openings whose number is larger than the number of the refrigerant introducing ports, and an area of each circulation openings is smaller than the area of the refrigerant introducing port, and (ii) when being disposed outside the refrigerant lead-out port, the refrigerant control mechanism has circulation openings whose number is larger than the number of the refrigerant lead-out ports, and an area of each circulation openings is smaller than the area of the refrigerant lead-out port. 
     According to a second aspect of the present invention, in the power storage device according to the first aspect, the number of stages of the power storage elements arranged in the storage module case is preferably smaller than the number of power storage devices arranged in each stage. 
     According to a third aspect of the present invention, in the power storage device according to the second aspect, the refrigerant control mechanism may be a plate-like member disposed between the storage module case and storage case. 
     According to a fourth aspect of the present invention, in the power storage device according to the second aspect, the refrigerant control mechanism may be a plate-like member disposed outside the storage case. 
     According to a fifth aspect of the present invention, in the power storage device according to the third aspect or fourth aspect, the circulation openings of the refrigerant circulation control mechanism preferably satisfy one of the following conditions (i) and (ii): 
     (i) when the refrigerant control mechanism is disposed outside the refrigerant introducing port, the number of the circulation openings is larger than the number of the inlets, and an area of each circulation opening is smaller than the area of the inlet; 
     (ii) when the refrigerant control mechanism is disposed outside the refrigerant lead-out port, the number of the circulation openings is larger than the number of the outlets, and an area of each circulation opening is smaller than the area of the outlet. 
     According to a sixth aspect of the present invention, in the power storage device according to the second aspect, the refrigerant circulation control mechanism may be formed in the storage case. 
     According to a seventh aspect of the present invention, in the power storage device according to the first aspect, the power storage element may be a cylindrical secondary battery cell. 
     According to an eighth aspect of the present invention, in the power storage device according to the seventh aspect, at least one circulation opening is preferably disposed so as to correspond to each of the plurality of power storage elements arranged in one stage. 
     According to a ninth aspect of the present invention, in the Power storage device according to the seventh aspect, each circulation opening may be disposed over the plurality of power storage elements arranged in one stage. 
     According to a tenth aspect of the present invention, in the power storage device according to the first aspect, the plurality of power storage modules are provided inside the storage case, and the refrigerant circulation control mechanism is provided for each of the plurality of power storage modules and, in this configuration, at least one of a shape, an area, and an arrangement of the circulation openings of at least one refrigerant circulation control mechanism may be different from those of the circulation openings of another refrigerant circulation control mechanism. 
     According to an eleventh aspect of the present invention, in the power storage device according to the tenth aspect, the storage case has an inlet or an outlet of refrigerant and, in this configuration, a total area of the circulation openings of the refrigerant circulation control mechanism housed at a location close to the inlet side or outlet side is preferably smaller than a total area of the circulation openings of the refrigerant circulation control mechanism housed at a location distant from the inlet side or outlet side. 
     Advantageous Effects of Invention 
     According to the present invention, refrigerant is introduced inside the power storage module through the refrigerant introducing port, passes through a gap between the secondary battery cells arranged in a plurality of stages in the power storage module, and is led outside the power storage module through the refrigerant lead-out port. The refrigerant circulation control mechanism having the circulation openings is disposed outside the refrigerant introducing port or refrigerant lead-out port. The refrigerant is substantially equally distributed by the refrigerant circulation control mechanism, so that the power storage elements arranged in a plurality of stages in the power storage module can be equally cooled. This can reduce a temperature difference among the power storage elements. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating an outer appearance of an embodiment of a power storage device according to the present invention. 
         FIG. 2  is an exploded perspective view of the power storage device illustrated in  FIG. 1 . 
         FIG. 3  is an exploded perspective view illustrating a part of the power storage device illustrated in  FIG. 2  as viewed from a rear surface side thereof. 
         FIG. 4  is an exploded perspective view of the power storage device illustrated in  FIG. 2  in a state where power storage modules are removed from the power storage device. 
         FIG. 5  is an exploded perspective view illustrating the power storage module illustrated in  FIG. 2  and an attachment (refrigerant circulation control mechanism). 
         FIG. 6  is an exemplary perspective view illustrating an outer appearance of the power storage module illustrated in  FIG. 5 . 
         FIG. 7( a )  is an exploded perspective view for explaining a structure of the power storage module illustrated in  FIG. 5 , and  FIG. 7( b )  is an exemplary perspective view illustrating an outer appearance of the power storage module. 
         FIG. 8  is an exploded perspective view illustrating the power storage module illustrated in  FIG. 5 . 
         FIG. 9  is an exemplary cross-sectional view illustrating an embodiment of the power storage device according to the present invention. 
         FIGS. 10( a ) and 10( b )  are views each illustrating a modification of the attachment. 
         FIG. 11  is an exploded perspective view illustrating a main part of a second embodiment of a power storage device according to the present invention. 
         FIG. 12  is an exploded perspective view illustrating a main part of a third embodiment of a power storage device according to the present invention. 
         FIG. 13  is an exemplary cross-sectional view illustrating a fourth embodiment of a power storage device according to the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     [Entire Configuration of Power Storage Device] 
     An embodiment of a power storage device according to the present invention will be described below with reference to the drawings. 
     A power storage device according to the present embodiment is applied to an in-vehicle power supply in a motor drive system for an electric vehicle, for example, an electric car. The electric car conceptually includes a hybrid car provided with an internal combustion engine and an electric motor as a drive source for the vehicle and a pure electric car provided with only an electric motor as a drive source. 
     First, an entire configuration of the power storage device will be described using  FIGS. 1 to 4 . 
       FIG. 1  is a perspective view illustrating an outer appearance of an embodiment of the power storage device according to the present invention,  FIG. 2  is an exploded perspective view of the power storage device illustrated in  FIG. 1 ,  FIG. 3  is an exploded perspective view illustrating a part of the power storage device illustrated in  FIG. 2  as viewed from a rear surface side thereof, and  FIG. 4  is an exploded perspective view of the power storage device illustrated in  FIG. 2  in a state where power storage modules are removed from the power storage device. 
     A power storage device  1  is, for example, a lithium-ion battery device and houses, in a storage case  2 , a plurality of power storage modules  40  each having a plurality of secondary battery cells  101  (see  FIG. 8 : power storage elements) such as lithium-ion secondary battery cells. 
     The storage case  2  has a shape obtained by a small rectangular parallelepiped is connected to a left side of a large rectangular parallelepiped. 
     Hereinafter, a front-rear direction, a left-right direction, and an up-down direction are indicated by arrows illustrated in  FIGS. 1 and 2 . 
     The storage case  2  is constituted by a main case  11 , a side cover  12 , an under cover  13 , and a top cover  14 . The main case  11  has a side wall  31  (see  FIG. 3 ) at a rear side thereof and has a frame shape in which upper, lower, and front sides thereof are opened. The main case  11 , side cover  12 , under cover  13 , and top cover  14  are each formed by pressing a metal thin plate. 
     The side cover  12  is disposed opposite to the side wall  31  of the main case  11  so as to close a front opening of the main case  11 . The side wall  31  constitutes a rear wall, and the side cover  12  constitutes a front wall. The under cover  13  closes a lower opening of the main case  11 , and the top cover  14  closes an upper opening of the main case  11 . The side cover  12 , under cover  13 , and top cover  14  are each fixed to the main case  11  by a fastening member such as a bolt, thereby forming a space for housing electronic components. 
     There are formed, inside the storage case  2  formed by the main case  11 , side cover  12 , under cover  13 , and top cover  14 , a power storage module housing area  2 A that houses the power storage modules  40  and a control unit housing area  2 B that houses a control unit  4 . 
     In the power storage module housing area  2 A, a plurality of (in the present embodiment, three) power storage modules  40 A to  40 C are arranged. The power storage modules  40 A to  40 C each have a rectangular parallelepiped block shape. In the present embodiment, the power storage modules  40 A to  40 C are adjacently arranged in parallel in such a way that a longitudinal side of each module extends in the up-down direction in the main case  11 . The power storage modules  40 A,  40 B, and  40 C are arranged in this order in a direction separating away from the control unit housing area  2 B, i.e., from the left to the right in  FIG. 2 . 
     The power storage modules  40 A to  40 C each have, at its front side, a refrigerant introducing port  116 . Further, the power storage modules  40 A to  40 C each have, at its rear side, a refrigerant lead-out port  118  (see  FIG. 3 ). 
     The side cover  12  has inlet (inflow port)  22  formed so as to be opposed to the refrigerant introducing port  116  of each power storage module  40 . Further, the side wall  31  of the main case  11  has an outlet (outflow port)  32  formed so as to be opposed refrigerant lead-out port  118  of each of the power storage modules  40 A to  40 C. 
     Although not illustrated in  FIGS. 2 and 4 , as described later, a refrigerant control mechanism that controls circulation of refrigerant such as air, i.e., an attachment  150  (see  FIG. 5 ) is provided between the side cover  12  and each of the power storage modules  40 A to  40 C. 
       FIG. 5  is an exploded perspective view illustrating the power storage module illustrated in  FIG. 2  and attachment, and  FIG. 6  is an exemplary perspective view illustrating an outer appearance of the power storage module illustrated in  FIG. 5 .  FIG. 7( a )  is an exploded perspective view for explaining a structure of the power storage module illustrated in  FIG. 5 , and  FIG. 7( b )  is an exemplary perspective view illustrating an outer appearance of the power storage module. 
     As illustrated in the exemplary view of  FIG. 6 , the power storage modules  40 A to  40 C have, at their both end portions in a longitudinal (up-down) direction thereof, positive terminals  41 A to  41 C and negative terminals  42 A to  42 C. 
     The power storage modules  40 A and  40 B or the power storage modules  40 B and  40  can be electrically connected or disconnected by an SD (service disconnect) switch  53 . The SD switch  53  is a safety device provided for securing safety at maintenance inspection of the power storage device  1 . The SD switch  53  is constituted of an electric circuit in which a switch and a fuse are electrically connected in series and is operated by a serviceman at maintenance inspection. 
     The six external terminals from the positive terminal  41 A of the power storage module  40 A to the negative terminal  42 C of the power storage module  40 C are connected to one another by a harness such that the power storage modules  40 A to  40 C are connected in series, as well as, to a not illustrated external terminal of the control unit  4 . The power storage modules  40 A to  40 C each have two voltage detection substrates  201  and  202  (see  FIG. 2 ) disposed along longitudinal direction (up-down direction) sides, respectively, and a temperature detection sensor  45  (see  FIG. 2 ). The voltage detection substrates  201  and  202  are connected to a controller (not illustrated) of the control unit  4  by not illustrated voltage detection lines, and the temperature detection sensor  45  is connected to the controller by a not illustrated sensor line. 
     The power storage modules  40 A to  40 C have the same structure, so hereinafter a single power storage module (referred to as “power storage module  40 ”) will be described as a representative of the power storage modules  40 A to  40 C. 
     As illustrated in  FIG. 7( a ) , the power storage module  40  holds a plurality of secondary battery cells  101  in a storage module case, i.e., a holding case  111 . In the present embodiment, as described later, the secondary battery cells  101  are arranged in three stages in the front-rear direction. As illustrated in  FIG. 7( b ) , the holding case  111  has a hexahedron shape. The holding case  111  has upper and lower surfaces  112  and  113  which are separated from and opposed to each other in the up-down direction and a pair of vertical wall surfaces  114  which are separated from and opposed to each other in the left-right direction and each connect short sides of the upper and lower surfaces  112  and  113 . Further, the holding case  111  is formed of, for example, a resin and has a front end surface  115   a  and a rear end surface  115   b  (see  FIG. 9 ) which are separated from and opposed to each other in the front-rear direction and each connect long sides of the upper surface  112 , the lower surface  113 , and the pair of vertical wall surfaces  114 . 
     The above-mentioned refrigerant introducing port  116  is formed in the front end surface  115   a  of the holding case  111 . Further, the above-mentioned refrigerant lead-out port  118  is formed in the rear end surface  115   b  of the holding case  111 .  FIG. 7( b )  is an exemplary view for illustrating a positional relationship between the refrigerant introducing port  116  and refrigerant lead-out port  118 . Refrigerant such as air flows in the holding case  111  through the refrigerant introducing port  116 , circulates inside the holding case  111  in the front-rear direction, and flows out through the rear side refrigerant lead-out port  118 . 
     In a state where the power storage module  40  is housed in the storage case  2 , the front end surface  115   a  of the holding case  111  is disposed opposite to the side cover  12  and, thus, the refrigerant introducing port  116  of the front end surface  115   a  is opposed to the inlet  22  of the side cover  12 . Further, the rear end surface  115   b  of the holding case  111  of the power storage module  40  is disposed opposite to the side wall  31  and, thus, the refrigerant lead-out port  118  of the rear end surface  115   b  is opposed to the outlet  32  of the side wall  31 . 
     As illustrated in  FIG. 9 , in the storage case  2 , an attachment  150  to be described later is interposed between the side cover  12  and front end surface  115   a  of the holding case  111 . The side wall  31  of the main case  11  and rear end surface  115   b  of the holding case  111  are fixed closely to each other through a not illustrated insertion member. The refrigerant introducing port  116  of the front end surface  115   a  of the holding case  111  communicates with the inlet  22  of the side cover  12 , and the refrigerant lead-out port  118  of the rear end surface  115   b  of the holding case  111  directly communicates with the outlet  32  of the side wall  31  of the main case  11 . In this state, the side cover  12  and front end surface  115   a  of the holding case  111  are in tight contact with each other through the attachment  150 , and the side wall  31  of the main case  11  and rear end surface  115   b  are in tight contact with each other, whereby leakage of gas from the storage case  2  can be prevented. 
     Refrigerant such as air taken in through a not illustrated duct passes through the inlet  22  of the storage case  2  and refrigerant introducing port  116  to be introduced in the power storage module  40 . Then, the refrigerant passes through the refrigerant lead-out port  118  to be discharged outside the power storage module  40  through the outlet  32  of the storage case  2 . That is, the refrigerant directly contacts and cools the plurality of secondary battery cells  101  arranged inside the power storage module  40 . 
     A space formed at an upper portion between an upper portion of an area between the front end surface  115   a  of the holding case  111  and inlet  22  of the side cover  12  and a space formed at an upper portion of an area between the rear end surface  115   b  of the holding case  111  and outlet  32  of the side wall  31  of the main case  11  are used as a wiring passage, and wirings connecting the power storage modules  40 A to  40 C and control unit  4  are routed along the wiring passage. The wirings routed along the wiring passage include a harness for connecting the negative terminal  42 C of the power storage module  40 C and control unit  4 , a voltage detection line for transmitting a voltage detection signal from each of the power storage modules  40 A to  40 C to the control unit  4 , a sensor line for transmitting a detection signal from the temperature detection sensor  45  to the control unit  4 , and the like. 
     [Power Storage Module] 
     In the present embodiment, the power storage modules  40 A and  40 B each have 14 secondary battery cells  101 , and the power storage module  40 C has 12 secondary battery cells. 
     The 14 secondary battery cells  101  are arranged inside each of the power storage modules  40 A and  40 B. A positive electrode and a negative electrode of each secondary battery cell  101  are connected to opposite polarities (a negative electrode and a positive electrode), respectively, of the adjacent secondary battery cell  101  by a conductive member  191  (see  FIG. 7( a ) ), and all 14 secondary battery cells  101  are connected in series. Similarly, although not illustrated, in the power storage module  40 C, all 12 secondary battery cells  101  are connected in series. External lead-out terminals are connected respectively to the first secondary battery cell  101  and last secondary battery cell  101  of each of the power storage modules  40 A to  40 C and, respectively, to the positive terminal ( 41 A to  41 C) and negative terminal ( 42 A to  42 C) illustrated in  FIGS. 5 and 6 . 
     The secondary battery cell  101  is a cylindrical lithium-ion secondary battery and has a configuration in which components such as a battery element and a safety valve are housed inside a battery case into which an electrolyte is injected. The safety valve on the positive side is a cleavage valve that cleaves when a pressure inside the battery case becomes a predetermined pressure due to abnormality such as overcharge. The safety valve functions as a fuse mechanism that blocks electrical connection between a battery lid and a positive side battery element by cleavage and functions as a decompression mechanism that emits gas generated inside the battery case, i.e., mist carbon dioxide gas (jetted matters) including electrolytic solution, to outside the battery case. 
     The negative side of the battery case is also provided with a cleavage groove, which cleaves when the pressure inside the battery case becomes a predetermined pressure due to abnormality such as overcharge. This allows the gas generated inside the battery case to be emitted also from the negative terminal side. A nominal output voltage of the secondary battery cell  101  is 3.0 V to 4.2 V and an average nominal output voltage is 3.6 V. 
       FIG. 8  is an exploded perspective view illustrating the power storage module illustrated in  FIG. 5 . 
     The plurality of secondary battery cells  101  placed in the up-down direction are disposed in the holding case  111  such that central axes thereof extend in the left-right directions of the holding case  111 . 
     More specifically, a plurality of the secondary battery cells  101  are arranged in a plurality of stages (in the present embodiment, five cells, four cells, and five cells are arranged in three stages, respectively). That is, the power storage modules  40 A to  40 C each have a configuration in which a secondary battery cell arrays  103  each constituted by the plurality of secondary battery cells  101  are layered in a plurality of stages in the holding case  111 .  FIG. 8  illustrates the configuration of the power storage module  40 A or  40 B. In the power storage module  40 C, four cells are arranged in three stages, or five cells, four cells, and three cells are arranged in three stages, respectively. 
     In the holding case  111 , a front-side secondary battery cell array  103 F, a rear-side secondary battery cell array  103 R, and an intermediate secondary battery cell array  103 M are held. In the present embodiment, the front-side secondary battery cell array  103 F and rear-side secondary battery cell array  103 R are arranged in the same way; on the other hand, the intermediate secondary battery cell array  103 M is displaced from the front-side secondary battery cell array  103 F and rear-side secondary battery cell array  103 R in the longitudinal (up-down) direction of the holding case  111  by a half piece of the secondary battery cell  101 . That is, the front-side secondary battery cell array  103 F, rear-side secondary battery cell array  103 R, and intermediate secondary battery cell array  103 M have the same arrangement pitch, and they are displaced from one another by a half pitch. By holding the front-side, intermediate, and rear-side arrays in a displaced manner in a column direction as described above, the secondary battery cell arrays of the adjacent stages can be brought close to each other, whereby a dimension in a direction perpendicular to the column direction can be reduced. Therefore, a length, i.e., a height of each of the power storage modules  40 A to  40 C can be reduced. 
     The holding case  111  is constituted by four members, a rear holding frame member  121 , an intermediate holding frame member  131 , an intermediate holding frame member  132 , and a front holding frame member  141 . The intermediate holding frame member  131  has an intermediate holding frame  131 R at a side thereof opposite to the rear holding frame member  121  and has an intermediate holding frame  131 F at a side thereof opposite to the intermediate holding frame member  132 . The intermediate holding frame member  132  has an intermediate holding frame  132 R at a side thereof opposite to the intermediate holding frame member  131  and has an intermediate holding frame  132 F at a side thereof opposite to the front holding frame member  141 . 
     The rear holding frame member  121 , the intermediate holding frames  131 R and  131 E of the intermediate holding frame member  131 , the intermediate holding frames  132 R and  132 F of the intermediate holding frame member  132 , and front holding frame  141  each have semicircular concave portions  137  to be fitted to the cylindrical parts of the respective secondary battery cells  101 . 
     The secondary battery cells  101  of the secondary battery cell array  103 R are sandwiched and held between the rear holding frame member  121  and intermediate holding frame  131 R of the intermediate holding frame member  131 . The secondary battery cells  101  of the secondary battery cell array  103 M are sandwiched and held between the intermediate holding frame  131 F of the intermediate holding frame member  131  and intermediate holding frame  132 R of the intermediate holding frame member  132 . The secondary battery cells  101  of the secondary battery cell array  103 E are sandwiched and held between the intermediate holding frame  132 F of the intermediate holding frame member  132  and front holding frame member  141 . The positive and negative electrodes of each of the secondary battery cells  101  held between the holding frame members are exposed outside from the concave portions  137 , respectively. 
     The refrigerant introducing port  116  and refrigerant lead-out port  118  formed in the front and rear end surfaces  115   a  and  115   b  of the holding case  111  are each formed into a rectangular shape elongated in the up-down direction. That is, a straight line obtained by projecting upper sides of the refrigerant introducing port  116  and refrigerant lead-out port  118  onto the secondary battery cell arrays  103 F,  103 M, and  103 R is projected onto peripheral surfaces of the uppermost secondary battery cells  101 . Further, a straight line obtained by projecting lower sides of the refrigerant introducing port  116  and refrigerant lead-out port  118  onto the secondary battery cell arrays  103 F,  103 M, and  103 R is projected onto peripheral surfaces of the lowermost secondary battery cells  101 . 
     The secondary battery cells  101  constituting each of the secondary battery cell arrays  103 F,  103 M, and  103 R are arranged with a gap provided between adjacent secondary battery cells  101  in each cell arrays. Further, the secondary battery cells  101  are held by the holding frame members with a gap provided between the adjacent cell arrays. That is, each secondary battery cell  101  arranged in the holding case  111  is held spaced from the adjacent secondary battery cell  101  of the same cell array and spaced from the secondary battery cell  101  of the adjacent stage. As a result, a cooling structure is achieved, in which refrigerant such as air introduced through the refrigerant introducing port  116  passes through among the secondary battery cells  101  while contacting and cooling the individual secondary battery cells  101  and is discharged outside through the refrigerant lead-out port  118 . 
     The attachment  150  illustrated in  FIG. 5  is disposed in front of each of the power storage modules  40 A to  40 C. 
     The attachment  150  is a plate-like member made of a metal, a resin, or a rubber. As illustrated in  FIG. 9 , the attachment  150  has a plurality of circulation openings  151  which are formed so as to correspond to the refrigerant introducing port  116 . More in detail, the attachment  150  has a plurality of refrigerant introducing ports  116  arranged in the up-down direction of the refrigerant introducing port  116  and each having an area smaller than the refrigerant introducing port  116 . 
     [Attachment] 
     The above-described attachment, i.e., the refrigerant circulation control mechanism will be described more in detail. 
       FIG. 9  is an exemplary cross-sectional view illustrating an embodiment of the power storage device according to the present embodiment. 
     The power storage module  40  is housed in the storage case  2  of the power storage device  1 , and the secondary battery cell arrays  103  each constituted by the plurality of secondary battery cells  101  are housed in a plurality of stages in the holding case  111  of the power storage module  40 . Each secondary battery cell  101  is disposed spaced from the adjacent secondary battery cell  101  of the same stage and spaced from the secondary battery cell  101  of the secondary battery cell array  103  of the adjacent stage. 
     The inlet  22  is formed in the side cover  12  of the storage case  2 , and the outlet  32  is formed in the side wall  31  of the storage case  2 . The refrigerant introducing port  116  having an area substantially the same as that of the inlet  22  is formed in the front end surface  115   a  of the holding case  111  so as to correspond to the inlet  22 . The refrigerant lead-out port  118  having an area substantially the same as that of the outlet  32  is formed in the rear end surface  115   b  of the holding case  111  so as to correspond to the outlet  32 . 
     The attachment  150  is interposed between the side cover  12  and front end surface  115   a  of the holding case  111  of the power storage module  40 . The attachment  150  has, within an area corresponding to the inlet  22  and refrigerant introducing port  116 , a plurality of circulation openings  151  which are arranged at substantially equal intervals. Each circulation openings  151  communicates with the inlet  22  and refrigerant introducing port  116 . Each circulation opening  151  has an area smaller than those of the inlet  22  and refrigerant introducing port  116 . 
     Five circulation openings  151  are formed so as to correspond to five secondary battery cells  101  arranged in the secondary battery cell  103 F. That is, one circulation opening  151  is provided for one secondary battery cell  101 . For fixing, the attachment  150  may be fitted to the holding case  111 , or may be bonded to one or both of the holding case  111  and side cover  12 . 
     The circulation opening  151  of the attachment  150  has a function of controlling a refrigerant circulation state (flow rate, direction, flow velocity, etc.) of the refrigerant. Refrigerant such as air that has passed through the inlet  22  flows in the holding case  111  through the refrigerant introducing port  116  with the circulation state thereof controlled. The refrigerant that has passed through the inlet  22  is substantially equally distributed by the circulation openings  151  of the attachment  150 , and the distributed refrigerant cools each secondary battery cell  101  such that the secondary battery cells  101  have an equal temperature. As described above, the refrigerant passes through the gap between the secondary battery cells  101  arranged in the holding case  111  and is led to the refrigerant lead-out port  118 . Thus, a satisfactory refrigerant flow can be achieved to thereby obtain high cooling efficiency. 
     In the above cooling structure, when the number of stages of the secondary battery cell arrays  103  is made smaller than the number of the secondary battery cells  101  constituting each secondary battery cell array  103 , a refrigerant flow path from the refrigerant introducing port  116  to refrigerant lead-out port  118  becomes short, which can advantageously increase cooling effect. 
     Although the attachment  150  is provided at the refrigerant introducing port  116  side in the above embodiment, the attachment  150  may be provided at the refrigerant lead-out port  118  side. Further, the attachment  150  may be provided at both the refrigerant introducing port  116  side and refrigerant lead-out port  118  side. 
     Further, although not illustrated, a seal member may be provided between the attachment  150  and each case member. Assuming that, for example, the attachment  150  is provided at the refrigerant introducing port  116  side, the seal member may be provided in one or both of spaces between the attachment  150  and side cover  12  and between the attachment  150  and the front end surface  115   a  of the holding case  111 . 
     Although the refrigerant introducing port  116  and refrigerant lead-out port  118  have the same shape and area in the above embodiment, one or both of the shape and area thereof may be different. Further, although the refrigerant introducing port  116  and refrigerant lead-out port  118  are each formed as a single opening, one or both of them may be formed as a plurality of openings. 
     [Modifications of Attachment] 
       FIGS. 10( a ) and 10( b )  are views each illustrating a modification of the attachment. 
     An attachment  150 A illustrated in  FIG. 10( a )  has circulation openings  151 A each having a rectangular shape elongated in the up-down direction. In this modification, each circulation opening  151 A is disposed over all the five secondary battery cells  101  constituting the secondary battery cell array  103 F. 
     An attachment  150 B illustrated in  FIG. 10( b )  has a number of elliptical circulation openings  1515 . In the illustrated example, a laterally (left-right direction) arranged group constituted by two circulation openings  151 B and a laterally (left-right direction) arranged group constituted by a single circulation opening  151 B are alternately arranged in the up-down direction. However, laterally arranged group may be constituted by the same number of circulation openings  151 B. 
     The shape, arrangement, and area of the circulation openings  151 A and  151 B of the attachment  150 A and  150 B illustrated in  FIGS. 10( a ) and 10( b )  are illustrative. The circulation opening  151  may have a circular shape, a hexagonal shape, or an octagonal shape. Further, different shapes maybe combined. The arrangement, pitch, or area of the circulation openings  151  may be appropriately determined. 
     In short, it is only necessary for the circulation openings  151  to satisfy one of the following conditions (i) and (ii): 
     (i) when the attachment  150  is disposed at the refrigerant introducing port  116  side, the number of the circulation openings  151  is larger than the number of the refrigerant introducing ports  116 , and the area of each circulation opening  151  is smaller than the area of the refrigerant introducing port  116 ; 
     (ii) when the attachment  150  is disposed at the refrigerant lead-out port  118  side, the number of the circulation openings  151  is larger than the number of the refrigerant lead-out ports  118 , and the area of each circulation opening  151  is smaller than the area of the refrigerant lead-out port  118 . 
     As described above, according to the power storage device of the present embodiment, the following effects can be obtained. 
     (1) The attachment  150  having a plurality of circulation openings  151  each having an area smaller than the area of the refrigerant introducing port  116  or refrigerant lead-out port  118  is provided outside the refrigerant introducing port  116  or refrigerant lead-out port  118  of the power storage module  40 . 
     Refrigerant such as air is substantially equally distributed by the circulation openings  151  of the attachment  150  and cools individual secondary battery cells  101  constituting each of the secondary battery cell arrays  103  arranged in a plurality of stages such that the secondary battery cells  101  have an equal temperature. This reduces a temperature difference among the secondary battery cells  101 , allowing easy maintenance of battery performance. 
     (2) The attachment  150  is provided outside the refrigerant introducing port  116  or refrigerant lead-out port  118  of the power storage module  40 . When the attachment  150  is provided inside the power storage module  40  or when the attachment  150  is formed integrally with the power storage module  40 , a change in the structure of the power storage module  40  in association with a difference in the internal structure of the power storage module  40 , the number of the secondary battery cells  101  to be housed, and an installation location of the power storage module  40  may involve a need to change the attachment  150  correspondingly. The attachment  150  can be externally attached to the power storage module  40  so that it is possible to make the attachment  150  commonly usable among the different structures, whereby reduction in production cost and development cost and improvement in services such as maintenance can expected. 
     (3) The attachment  150  is provided outside the refrigerant introducing port  116  or refrigerant lead-out port  118  of the power storage module  40 , so that the attachment  150  can easily be fitted to the holding case  111 , or can easily be bonded to one or both of the holding case  111  and side cover  12 . That is, the attachment  150  can be mounted by a simple assembly work, whereby assembling workability can be improved. 
     Second Embodiment 
       FIG. 11  is an exploded perspective view illustrating a main part of a second embodiment of a power storage device according to the present invention. 
     A power storage device  1  of the second embodiment has a feature in that the attachment  150  of the first embodiment is omitted, and that an opening  150 C functioning as a refrigerant circulation control mechanism is formed in the side wall  31  of the storage case  2 . 
     Three refrigerant circulation control mechanisms  150 C are formed in the side wall  31  of the storage case  2  so as to correspond to the refrigerant lead-out ports  118  of the respective power storage modules  40 A to  40 C. 
     Each refrigerant circulation control mechanism  150 C is constituted by a plurality of circulation openings  151 C each having an area smaller than that of the refrigerant lead-out port  118 . 
     According to the power storage device  1  of the second embodiment, the refrigerant circulation control mechanisms  150 C are formed in the side wall  31  of the storage case  2 , so that the same effect as that described in (1) of the first embodiment can be obtained. Further, the refrigerant circulation control mechanisms  150 C are formed integrally with the storage case  2 , so that assembling workability can be improved more than in the first embodiment. 
     In the second embodiment, the inlet  22  of the side cover  12  may be replaced by the refrigerant circulation control mechanisms  150 C. In the configuration where the refrigerant circulation control mechanisms  150 C are formed in the side cover  12 , the refrigerant circulation control mechanisms  1500  may be formed also in the side wall  31  of the main case  11 . 
     Further, as in the first embodiment, the shape and area of the circulation openings  151 C formed in each refrigerant circulation control mechanism  150 C can appropriately be chanced. 
     Third Embodiment 
       FIG. 12  is an exploded perspective view illustrating a main part of a third embodiment of a power storage device according to the present invention. In the drawing, a correspondence relation between the power storage modules  40 A to  40 C and attachments  150 D to  150 F fixed to the power storage modules  40 A to  40 C, respectively. Attachments  150 D to  150 F are provided so as to correspond respectively to the refrigerant introducing ports  116  and/or the refrigerant lead-out ports  118  of the power storage modules  40 A to  40 C. Circulation openings  151 D are formed in each of the attachments  150 D to  150 F. Among the attachments  150 D to  150 F, the attachment  150 D has the largest number of the circulation openings  151 D, the attachment  150 E has the second largest number of the circulation openings  151 D, and the attachment  150 F has the smallest number of the circulation openings  151 D. In other words, the total area of the circulation openings  151 D formed in the attachments  150 D to  150 F becomes smaller in the order of attachment  150 D, attachment  150 E, and attachment  150 F. That is, a flow rate of the refrigerant passing through the circulation openings  151 D of the attachments  150 D to  150 F becomes smaller in the order of attachment  150 D, attachment  150 E, and attachment  150 F. 
     When the refrigerant flows to the power storage modules  40 A to  40 C in an illustrated X-direction, the flow rate of the refrigerant flowing around the attachments  150 D to  150 F is larger toward the upstream side. Thus, the flow rate of the refrigerant that has flowed through the attachments  150 D to  150 F is averaged. That is, the flow rates of the refrigerants flowing inside the respective power storage modules  40 A to  40 C are substantially the same, whereby cooling performance is equalized among the power storage modules  40 A to  40 C. 
     According to the third embodiment, the attachments  150 D to  150 F each having the circulation openings  151 D are disposed so as to correspond to the power storage modules  40 A to  40 C, so that the same effects as the effects (1) to (3) of the first embodiment can be obtained. In addition, the following effect can be obtained. 
     (4) The total area of the circulation openings  151 D is made different among the attachments  150 D to  150 F attached to the respective power storage modules  40 A to  40 C. Thus, it is possible to control the flow amount of the refrigerant flowing in the power storage modules  40 A to  40 C through the attachments  150 D to  150 F depending on a temperature around the power storage modules  40 A to  40 C, a duct position, or the like, thereby allowing a temperature difference among the secondary battery cells  101  in the power storage modules  40 A to  40 C to be reduced. That is, the temperature difference between the secondary battery cells  101  of different power storage modules  40  can be reduced. 
     As in the first and second embodiments, the shape and area of the circulation openings  151 D can appropriately be changed. Further, the shape of the circulation openings  151 D may be different among the attachments  150 D to  150 F in each of which the circulation openings  151 D are formed. 
     Fourth Embodiment 
       FIG. 13  is an exemplary cross-sectional view illustrating a fourth embodiment of a power storage device according to the present invention. 
     The fourth embodiment has a feature in that the attachment  150  is disposed outside the side cover  12  of the storage case  2 . 
     The power storage module  40  is housed in the storage case  2  of the power storage device  1 , and the secondary battery cell arrays  103  each constituted by the plurality of secondary battery cells  101  are housed in a plurality of stages in the holding case  111  of the power storage module  40 . Each secondary battery cell  101  is disposed spaced from the adjacent secondary battery cell  101  of the same stage and spaced from the secondary battery cell  101  of the secondary battery cell array  103  of the adjacent stage. 
     The inlet  22  is formed in the side cover  12  of the storage case  2 , and the outlet  32  is formed in the side wall  31  of the storage case  2 . The refrigerant introducing port  116  having an area substantially the same as that of the inlet  22  is formed in the front end surface  115   a  of the holding case  111  so as to correspond to the inlet  22 . The refrigerant lead-out port  118  having substantially the same area as that of the outlet  32  is formed in the rear end surface  115   b  of the holding case  111  so as to correspond to the outlet  32 . 
     The attachment  150  is attached to an outside of the side cover  12  of the storage case  2 . The attachment  150  has a plurality of circulation openings  151 . The circulation openings  151  are formed within an area corresponding to the inlet  22  and refrigerant introducing port  116  and each communicate with the inlet  22  and refrigerant introducing port  116 . Each circulation opening  151  has an area smaller than those of the inlet  22  and refrigerant introducing port  116 . The attachment  150  maybe fitted to or bonded to the side cover  12  for fixing. 
     The Refrigerant that has taken in through a not illustrated duct passes through the circulation openings  151  of the attachment  150 , inlet  22 , and refrigerant introducing port  116  and flows inside the power storage module  40 . When passing through the circulation openings  151  of the attachment  150 , the refrigerant is substantially equally distributed with the circulation state (flow rate, direction, flow velocity, etc.) thereof controlled and equally cools secondary battery cells  101  arranged in the power storage module  40 . Then, the refrigerant passes through the gap between the secondary battery cells  101  arranged in the holding case  111  and is led to the refrigerant lead-out port  118 . Thus, high cooling efficiency can be obtained. 
     Also in the fourth embodiment, presence of the attachment  150  (at the outside of the power storage case  2 ) allows the same effects as those described in (1) and (2) of the first embodiment to be obtained. Further, the attachment  150  can easily be fitted to or bonded to the storage case  2 , whereby assembling workability can be improved. 
     In the above cooling structure, when the number of stages of the secondary battery cell arrays  103  is made smaller than the number of the secondary battery cells  101  constituting each secondary battery cell array  103 , a refrigerant flow path from the refrigerant introducing port  116  to refrigerant lead-out port  118  becomes short, which can advantageously increase cooling effect. 
     Although the attachment  150  is provided at the refrigerant introducing port  116  side in the above embodiment, the attachment  150  may be provided at the refrigerant lead-out port  118  side. Further, the attachment  150  may be provided at both the refrigerant introducing port  116  side and refrigerant lead-out port  118  side. 
     Although the refrigerant introducing port  116  and refrigerant lead-out port  118  have the same shape and area in the above embodiment, one or both of the shape and area thereof may be different. Further, although the refrigerant introducing port  116  and refrigerant lead-out port  118  are each formed as a single opening, one or both of them may be formed as a plurality of openings. 
     Further, although not illustrated, a seal member may be provided between the attachment  150  and side cover  12 . 
     The present invention is applicable not only to a power storage device provided with the lithium-ion secondary battery, but also to a power storage device provided with a secondary battery using a water-soluble electrolyte, such as a nickel hydride battery, a nickel-cadmium battery, or a lead storage battery. Further, the present invention is applicable to a power storage device provided with a power storage element such as a lithium-ion capacitor or an electrolytic double-layer capacitor. 
     In the above respective embodiments, although air is exemplified as the refrigerant, the refrigerant to be used may be gas other than the air. Further, the refrigerant need not be gas, but may be liquid. 
     The power storage device of the present invention may be variously modified within the spirit of the invention. That is, the power storage device of the present invention may be configured as follows: the plurality of secondary battery cells are arranged in a plurality of stages in the storage module case; the refrigerant introducing port and refrigerant lead-out port opposed to each other in a longitudinal direction of the secondary battery cells in the storage module case are provided; the refrigerant control mechanism is provided at the outside of at least one of the refrigerant introducing port and refrigerant lead-out port; and the plurality of circulation openings each of which has an area smaller than those of the refrigerant introducing port and refrigerant lead-out port and whose number is larger than those of the refrigerant introducing port and refrigerant lead-out port are formed in the refrigerant control mechanism. 
     REFERENCE SIGNS LIST 
     
         
           1  power storage device 
           2  storage case 
           22  inlet (inflow port) 
           32  outlet (outflow port) 
           40 ,  40 A,  40 B,  40 C power storage module 
           101  secondary battery cell (power storage element) 
           111  holding case (storage module case) 
           116  refrigerant introducing port 
           118  refrigerant lead-out 
           150 ,  150 A to  150 F attachment (refrigerant circulation control mechanism) 
           151 ,  151 A to  151 D circulation opening