Patent Publication Number: US-2022238951-A1

Title: Load applicator and power storage apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-010990 filed on Jan. 27, 2021, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     This disclosure relates to a load applicator and a power storage apparatus. 
     2. Description of Related Art 
     As described in Japanese Unexamined Patent Application Publication No. 2014-175078 (JP 2014-175078 A) or Japanese Unexamined Patent Application Publication No. 2003-036830 (JP 2003-036830 A), a power storage module is configured such that a plurality of power storage cells is connected in series or in parallel to each other in an integrated manner. A power storage apparatus includes a power storage module and a load applicator configured to apply a restraint load to the power storage module. The load applicator is configured to apply an appropriate restraint load for a long period, so that it is possible to achieve performance stable for a long period in the power storage apparatus. 
     SUMMARY 
     When the load applicator is used for a long period, there is such a possibility that the load applicator cannot apply a necessary and sufficient load to the power storage module due to deterioration by aging, or the like, for example. For example, in a case where the power storage cells constituting the power storage module contract in one direction, a load to be applied from the load applicator to the power storage module in the one direction may become insufficient. 
     As measures to such a case, it is conceivable that the load applicator is configured in advance to apply an excess load to prepare for an amount to become insufficient. However, this can separately cause such a concern that an excessive load may be applied at an initial stage of use or this can separately cause such a necessity that the power storage module should have a strong structure sufficient to tolerate a large load. 
     An object of this disclosure is to provide a load applicator having a configuration that can apply an appropriate load to a target object for a long period as compared to the related art, and a power storage apparatus including such a load applicator. 
     A load applicator of this disclosure is a load applicator for applying a restrain load to a power storage module including a plurality of power storage cells. The load applicator includes an elastic mechanism, a first member, a second member, and a switching device. The first member is placed between the elastic mechanism and the power storage module in one direction. The first member is configured to move along the one direction along with contraction of the power storage cells. The second member is provided on a side in the one direction, the side being opposite to a side where the first member is placed, across the elastic mechanism. The elastic mechanism contracts so as to correspond to a distance between the first member and the second member in the one direction. The elastic mechanism applies a restraint load to the power storage module via the first member in accordance with a contraction amount of the elastic mechanism. The elastic mechanism has a first form in which a first restraint load is applied to the power storage module when the power storage module expands by a first dimension, and a second form in which a second restraint load larger than the first restraint load is applied to the power storage module when the power storage module expands by the first dimension. The switching device is configured to perform an operation to switch from the first form to the second form in a case where a restraint load smaller than the first restraint load is applied to the power storage module when the power storage module expands by the first dimension. 
     In the load applicator, the one direction may be a direction where the power storage cells are stacked. 
     In the load applicator, an elastic modulus of the elastic mechanism in a case where the second form is formed may be larger than an elastic modulus of the elastic mechanism in a case where the first form is formed. 
     In the load applicator, the elastic mechanism forming the first form may include a predetermined number of elastic bodies configured to apply a restraint load to the power storage module. The elastic mechanism forming the second form may include elastic bodies the number of which is greater than the predetermined number, the elastic bodies being configured to apply a restraint load to the power storage module. 
     In the load applicator, the first member may include a first part and a second part having a thickness thicker than a thickness of the first part in the one direction. In a state where the elastic mechanism forms the first form, the elastic mechanism may apply a restraint load to the power storage module via the first part of the first member. In a state where the elastic mechanism forms the second form, the elastic mechanism may apply a restraint load to the power storage module via the second part of the first member. 
     A power storage apparatus according to this disclosure includes a power storage module and the load applicator described above. The power storage module includes a plurality of power storage cells. In a state where respective SOC values of the power storage cells constituting the power storage module are set to values out of a predetermined range, the switching device performs switching from the first form to the second form. 
     With the above configuration, it is possible to achieve a load applicator having a configuration that can apply an appropriate load to a target object for a long period as compared to the related art, and a power storage apparatus including such a load applicator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG. 1  is a plan view illustrating a load applicator and a power storage apparatus according to Embodiment 1 and illustrates a state where an elastic mechanism of the load applicator forms a first form; 
         FIG. 2  is a plan view illustrating the load applicator and the power storage apparatus according to Embodiment 1 and illustrates a state where the elastic mechanism of the load applicator forms a second form; 
         FIG. 3  is a plan view illustrating the load applicator and the power storage apparatus according to Embodiment 1 and illustrates a state where a switching device of the load applicator performs a switching operation to switch the elastic mechanism from the first form to the second form;  FIG. 4  is a plan view illustrating the load applicator and the power storage apparatus according to Embodiment 1 and illustrates a state where a restraint load to be applied to a power storage module by the load applicator becomes smaller than that in the case illustrated in  FIG. 1 ; 
         FIG. 5  is a plan view illustrating the load applicator and the power storage apparatus according to Embodiment 1 and illustrates a state where the restraint load to be applied to the power storage module by the load applicator becomes larger than that in the case illustrated in  FIG. 4  due to completion of the operation to switch from the first form to the second form; 
         FIG. 6  is a plan view illustrating the load applicator and the power storage apparatus according to a modification of Embodiment 1; 
         FIG. 7  is a plan view illustrating a load applicator and a power storage apparatus according to Embodiment 2 and illustrates a state where the elastic mechanism of the load applicator forms a first form; 
         FIG. 8  is a plan view illustrating the load applicator and the power storage apparatus according to Embodiment 2 and illustrates a state where the elastic mechanism of the load applicator forms a second form; and 
         FIG. 9  is a plan view illustrating the load applicator and the power storage apparatus according to Embodiment 2 and illustrates a state where the switching device of the load applicator performs an operation to switch the elastic mechanism from the first form to the second form. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The following describes embodiments of the present disclosure. In a case where a number, an amount, and the like are mentioned in the embodiments described below, the scope of this disclosure is not necessarily limited to the number, the amount, and the like, unless otherwise specified. Each constituent is not necessarily essential for this disclosure unless otherwise specified. The same reference numeral is assigned to the same component and its equivalent component, and a redundant description may not be repeated. 
     The absolute values of the dimensions (e.g., L 0 , L 1 , D 1  illustrated in  FIG. 1 ) of constituents illustrated in the drawings and relative ratios therebetween may not be necessarily illustrated faithfully as their actual values, and the dimensions may be exaggerated for convenience of the description. 
     Embodiment 1 
     Power Storage Apparatus  100   
       FIG. 1  is a plan view illustrating a load applicator  60  and a power storage apparatus  100  according to Embodiment 1. The power storage apparatus  100  includes a power storage module  50 , the load applicator  60 , an end plate  70 , and restraining tools  91 ,  92 . The power storage module  50  includes a plurality of power storage cells  5 . An insulating member (not illustrated) is placed between two power storage cells  5  adjacent to each other, so that the two power storage cells  5  adjacent to each other are electrically insulated from each other. 
     The load applicator  60  applies a restraint load to the power storage module  50  in collaboration with the end plate  70  and the restraining tools  91 ,  92 . More specifically, the load applicator  60  includes an elastic mechanism  30 , a receiving member  10  (a first member), an end plate  20  (a second member), and a switching device  40 . 
     The receiving member  10  is placed between the elastic mechanism  30  and the power storage module  50  in one direction  80  and moves along the one direction  80  along with contraction of one or more power storage cells  5 . The end plate  20  is provided on a side, in the one direction  80 , that is opposite to a side where the receiving member  10  is placed, across the elastic mechanism  30 . Here, the one direction  80  is a direction where the power storage cells  5  are stacked. The one direction  80  may not be a direction parallel to the direction where the power storage cells  5  are stacked. The one direction  80  may be a direction intersecting with the direction where the power storage cells  5  are stacked. 
     The receiving member  10  includes a main body portion  11  and an expansion portion  12  projecting from the main body portion  11  toward the end plate  20  side. An inclined surface  13  is formed on the expansion portion  12 , and the inclined surface  13  is provided to face a position where a restriction member  36  (particularly, an inclined portion  36   t ) (described later) is placed. 
     The load applicator  60  including the end plate  20  is placed on a first side from the power storage module  50  in the one direction  80 . The end plate  70  is placed on a second side from the power storage module  50  in the one direction  80 . The end plates  20 ,  70  have a plate shape and made of metal, for example. First end parts of the restraining tools  91 ,  92  are fixed to the end plate  20 , and second end parts of the restraining tools  91 ,  92  are fixed to the end plate  70 . The end plate  20  is connected to the end plate  70  via the restraining tools  91 ,  92 . 
     The elastic mechanism  30  includes elastic bodies  31 ,  32 ,  33  and the restriction member  36 . The elastic bodies  31 ,  32 ,  33  and the restriction member  36  are provided between the receiving member  10  and the end plate  20  in the one direction  80 . The elastic bodies  31 ,  32 ,  33  may be made of elastically deformable resin, for example, and may be made of springs having various shapes such as a plate shape, a dish shape, and a helical shape. The restriction member  36  is placed adjacent to the elastic body  32 , and the inclined portion  36   t  is provided in a distal end of the restriction member  36 . The elastic mechanism  30  has a first form S 1  illustrated in  FIG. 1  and a second form S 2  illustrated in  FIG. 2 . 
     First Form S 1  and Second Form S 2   
     In a state where the elastic mechanism  30  forms the first form S 1  ( FIG. 1 ), the elastic bodies  31 ,  33  of the elastic mechanism  30  contract so as to correspond to a distance D 1  between the receiving member  10  and the end plate  20  in the one direction  80 . In the state where the elastic mechanism  30  forms the first form S 1 , the elastic mechanism  30  (the elastic bodies  31 ,  33 ) applies a restraint load (arrows  71 ,  73 ) to the power storage module  50  via the receiving member  10  in accordance with the contraction amount (stroke amount) of the elastic mechanism  30 , more specifically, respective contraction amounts of the elastic bodies  31 ,  33 . 
     In the state where the elastic mechanism  30  forms the first form S 1  ( FIG. 1 ), the inclined portion  36   t  of the restriction member  36  is locked engagingly by a distal end of the elastic body  32 , and the elastic body  32  is maintained by the restriction member  36  to be shorter than its own natural length (the length in an unloaded condition). The elastic body  32  forms a compressed state (a state where the elastic body  32  has an internal stress (an arrow  72 ) in the one direction  80 ). The distal end of the elastic body  32  is distanced from the expansion portion  12  of the receiving member  10 , so that the internal stress (the arrow  72 ) does not act on the receiving member  10 . 
     In a state where the elastic mechanism  30  forms the second form S 2  ( FIG. 2 ), the elastic body  32  is released from the engagingly locked state with the restriction member  36 , and the elastic bodies  31 ,  32 ,  33  all make contact with the receiving member  10  and the end plate  20 . The elastic bodies  31 ,  32 ,  33  of the elastic mechanism  30  contract so as to correspond to a distance D 2  between the receiving member  10  and the end plate  20  in the one direction  80 . 
     That is, the elastic modulus of the elastic mechanism  30  in a case where the second form S 2  is formed is larger than the elastic modulus of the elastic mechanism  30  in a case where the first form S 1  is formed. In the state where the elastic mechanism  30  forms the second form S 2 , the elastic mechanism  30  (the elastic bodies  31 ,  32 ,  33 ) applies a restraint load (the arrows  71 ,  72 ,  73 ) to the power storage module  50  via the receiving member  10  in accordance with the contraction amount of the elastic mechanism  30 , more specifically, respective contraction amounts of the elastic bodies  31 ,  32 ,  33 . 
       FIG. 1  illustrates the state where the elastic mechanism  30  forms the first form S 1 .  FIG. 2  illustrates the state where the elastic mechanism  30  forms the second form S 2 . The switching device  40  is configured to perform switching from the first form S 1  to the second form S 2 . Herein, the switching device  40  includes a controlling portion, a charging circuit, and so on (not illustrated), and the switching device  40  is connected to the power storage module  50 . Charging and discharging of the power storage cells  5  constituting the power storage module  50  can be performed by the switching device  40 , and the state of charge (SOC) can be set to any value by the switching device  40 . 
     Assume a case where, in a state where the SOC is set to a predetermined value, the power storage module  50  has a predetermined reference length L 0  in the one direction  80 . In the first form S 1  ( FIG. 1 ), in a case where the power storage module  50  expands by a first dimension L 1  from the reference length L 0 , a first restraint load (the arrows  71 ,  73 ) is applied to the power storage module  50  by the elastic mechanism  30  of the load applicator  60 . 
     In the second form S 2  ( FIG. 2 ), in a case where the power storage module  50  expands by the first dimension L 1  from the reference length L 0 , a second restraint load (the arrows  71 ,  72 ,  73 ) is applied to the power storage module  50  by the elastic mechanism  30  of the load applicator  60 . The second restraint load (the arrows  71 ,  72 ,  73 ) is a value larger than the first restraint load (the arrows  71 ,  73 ). 
       FIG. 3  illustrates a state where the switching device  40  of the load applicator  60  performs a switching operation to switch the elastic mechanism  30  from the first form S 1  to the second form S 2 . For example, in a state where the switching device  40  sets respective SOC values of the power storage cells  5  constituting the power storage module  50  to values out of a predetermined range, the switching device  40  performs switching from the first form S 1  to the second form S 2 . 
     In the configuration illustrated in  FIG. 3 , the SOC is to a value larger than a normal usage range, so that the power storage module  50  expands by a second dimension L 2  from the reference length L 0 . The second dimension L 2  is a value larger than the first dimension L 1 . Due to the expansion of the power storage module  50 , the receiving member  10  moves in the one direction  80  more largely than in the cases illustrated in  FIGS. 1, 2 . 
     When the inclined surface  13  of the expansion portion  12  makes contact with the inclined portion  36   t  of the restriction member  36 , the engagingly locked state of the restriction member  36  (the inclined portion  36   t ) with the elastic body  32  is released, so that the elastic body  32  extends. Hereby, the switching from the first form S 1  to the second form S 2  by the switching device  40  is completed. The restriction member  36  should keep connected to the end plate  20  so that foreign matter or abnormal noise does not occur. 
     Operations and Effects 
     As described at the beginning, when the power storage apparatus  100  or the load applicator  60  is used for a long period, there is such a possibility that the load applicator  60  cannot apply a necessary and sufficient load to the power storage module  50  due to deterioration by aging, or the like, for example. For example, the lengths of the elastic bodies  31 ,  33  may become shorter than their initial states under the influence of creep deformation. Alternatively, the elastic moduli (Young&#39;s moduli) of the elastic bodies  31 ,  33  may become smaller than their initial states under the influence of creep deformation. 
     In  FIG. 4 , for convenience of the description, the phenomenon as described above is expressed as the receiving member  10  becoming thin. As illustrated in  FIG. 4 , in a case where the phenomenon occurs, when the power storage module  50  expands by the first dimension L 1  from the reference length L 0 , a restraint load smaller than the first restraint load (corresponding to the arrows  71 ,  73  in  FIG. 1 ) is applied to the power storage module  50 . In such a case, the switching device  40  is configured to perform an operation to switch from the first form S 1  to the second form S 2  by performing the operation described with reference to  FIG. 3 . 
       FIG. 5  illustrates a state where the restraint load to be applied to the power storage module  50  by the load applicator  60  becomes larger than that in the case illustrated in  FIG. 4  due to completion of the operation to switch from the first form S 1  to the second form S 2 . This state is a state different from the first form S 1  and the second form S 2  to be provided at the time of starting the use of the load applicator  60 . Since this state is formed, even in a case where the power storage cells  5  constituting the power storage module  50  contract in the one direction  80 , it is possible to effectively restrain insufficiency in the load to be applied from the load applicator  60  to the power storage module  50  in the one direction  80 , just by an increase in the load by the elastic body  32 . 
     Accordingly, with the above configuration, it is possible to achieve the load applicator  60  having a configuration that can apply an appropriate load to a target object for a long period as compared to the related art, and the power storage apparatus  100  including such a load applicator  60 . For example, in a case where the power storage apparatus  100  (e.g., a fully solid battery) having a high capacity is formed, an elastic body such as resin can be employed or effectively utilized as a material having a higher expansion coefficient. Even in such a case, by employing the technical idea described in the present embodiment, it is possible to take measures to creep deformation of the elastic body, thereby making it possible to achieve a longer operating life of the power storage apparatus  100  as a product. 
     In a case where the power storage apparatus  100  is used to be provided in a vehicle, the power storage apparatus  100  can be placed at a position where its maintenance is hard to be performed in general. Even in such a case, only by performing an SOC control by the switching device  40 , e.g., without a maintenance operator physically accessing the load applicator  60 , it is possible to perform the operation to switch from the first form S 1  to the second form S 2 . 
     The degree of creep of the elastic body can be predicted to some extent based on physical properties of the elastic body or the specification related to the load applicator  60 . The switching operation is performed by the switching device  40  at a timing when the restrain load may decrease on design, and at this time, the switching operation is performed under a cell chargeable environment. 
     For example, a predetermined threshold may be set based on values of resistance values obtainable during charging and discharging, the integrated number of times of charging and discharging, an integrated time of charging and discharging, an operating temperature, an integrated capacity for charging and discharging, a travel distance, or the like. The arrival of the threshold may be notified (a state where an operator can recognize the arrival of the threshold may be formed), or the switching operation may be automatically performed by the switching device  40  based on the arrival of the threshold. 
     In the load applicator  60 , the number of elastic bodies acting on the receiving member  10  increases along with changing from the first form S 1  to the second form S 2 . That is, the elastic mechanism  30  forming the first form S 1  includes a predetermined number of elastic bodies  31 ,  33  (herein, two elastic bodies  31 ,  33 ) configured to apply a restraint load to the power storage module  50 . The elastic mechanism  30  forming the second form S 2  includes three elastic bodies  31 ,  32 ,  33  the number of which is greater than the predetermined number (two), the elastic bodies being configured to apply a restraint load to the power storage module  50 . Since the load applicator  60  has this configuration, it is possible to perform the operation to switch from the first form S 1  to the second form S 2  by an easy operation illustrated in  FIG. 3 . 
     Modification of Embodiment 1 
       FIG. 6  is a plan view illustrating the load applicator  60  and the power storage apparatus  100  according to a modification of Embodiment 1. In Embodiment 1 described above, by performing the operation to switch from the first form S 1  to the second form S 2 , one elastic body  32  is added to two elastic bodies  31 ,  33  used to apply a restraint load to the receiving member  10 . 
     As illustrated in  FIG. 6 , the load applicator  60  may be configured such that, by performing the operation to switch from the first form S 1  to the second form S 2 , two elastic bodies  31 ,  33  are added to one elastic body  32  used to apply a restraint load to the receiving member  10 . The number of elastic bodies and the elastic modulus of the whole elastic mechanism  30  should be designed in consideration of a restraint load to be applied to the power storage module  50 . 
     Embodiment 2 
     With reference to  FIGS. 7 to 9 , the following describes a load applicator  61  and a power storage apparatus  101  according to Embodiment 2.  FIG. 7  is a plan view illustrating the load applicator  61  and the power storage apparatus  101  and illustrates a state where the elastic mechanism  30  of the load applicator  61  forms the first form S 1 .  FIG. 8  illustrates a state where the elastic mechanism  30  of the load applicator  61  forms the second form S 2 . 
     In the load applicator  61 , the elastic mechanism  30  includes the receiving member  10 , an elastic body  37 , and a pedestal  38 . The elastic body  37  is placed on the end plate  20  via the pedestal  38 . The elastic body  37  is provided between the receiving member  10  (a movable block  14  (described later)) and the pedestal  38  in the one direction  80 . The receiving member  10  includes the main body portion  11 , the movable block  14 , and a feed mechanism  16 . An inclined surface  15  is formed on the main body portion  11 , and the movable block  14  moves on the inclined surface  15 . 
     The receiving member  10  includes a first part P 1  ( FIG. 7 ) and a second part P 2  ( FIG. 8 ). The second part P 2  has a thickness thicker than that of the first part P 1  in the one direction  80 , and the inclined surface  15  is formed due to the presence of the first part 
     P 1  and the second part P 2 . In the load applicator  61 , the elastic mechanism  30  has the first form S 1  illustrated in  FIG. 7  and the second form S 2  illustrated in  FIG. 8 . 
     In a state where the elastic mechanism  30  forms the first form S 1  ( FIG. 7 ), the elastic body  37  of the elastic mechanism  30  contracts so as to correspond to the distance D 1  between the receiving member  10  (the movable block  14 ) and the end plate  20  in the one direction  80 . In the state where the elastic mechanism  30  forms the first form S 1 , the elastic mechanism  30  applies a restraint load (an arrow  74 ) to the power storage module  50  via the first part P 1  of the main body portion  11  of the receiving member  10 . In the state where the elastic mechanism  30  forms the first form S 1 , the elastic mechanism  30  (the elastic body  37 ) applies a restraint load (the arrow  74 ) to the power storage module  50  via the receiving member  10  in accordance with the contraction amount of the elastic mechanism  30 , more specifically, the contraction amount of the elastic body  37 . 
     In a state where the elastic mechanism  30  forms the second form S 2  ( FIG. 8 ), the elastic body  37  of the elastic mechanism  30  contracts so as to correspond to the distance D 2  between the receiving member  10  (the movable block  14 ) and the end plate  20  in the one direction  80 . In the state where the elastic mechanism  30  forms the second form S 2 , the elastic mechanism  30  applies a restraint load (an arrow  75 ) to the power storage module  50  via the second part P 2  of the main body portion  11  of the receiving member  10 . In the state where the elastic mechanism  30  forms the second form S 2 , the elastic mechanism  30  (the elastic body  37 ) applies a restraint load (the arrow  75 ) to the power storage module  50  via the receiving member  10  in accordance with the contraction amount of the elastic mechanism  30 , more specifically, the contraction amount of the elastic body  37 . 
     The second part P 2  has a thickness thicker than that of the first part P 1  in the one direction  80 . Accordingly, as the whole receiving member  10 , a thickness W 2  of the receiving member  10  at the time when the second form S 2  is formed is larger than a thickness W 1  of the receiving member  10  at the time when the first form S 1  is formed. 
     Assume a case where, in a state where the SOC is set to a predetermined value, the power storage module  50  has the predetermined reference length L 0  in the one direction  80 . In the first form S 1  ( FIG. 7 ), in a case where the power storage module  50  expands by the first dimension L 1  from the reference length L 0 , a first restraint load (the arrow  74 ) is applied to the power storage module  50  by the elastic mechanism  30  of the load applicator  61 . 
     In the second form S 2  ( FIG. 8 ), in a case where the power storage module  50  expands by the first dimension L 1  from the reference length L 0 , a second restraint load (the arrow  75 ) is applied to the power storage module  50  by the elastic mechanism  30  of the load applicator  61 . The second restraint load (the arrow  75 ) is a value larger than the first restraint load (the arrow  74 ). 
       FIG. 9  illustrates a state where the switching device  40  of the load applicator  61  performs a switching operation to switch the elastic mechanism  30  from the first form S 1  to the second form S 2 . For example, in a state where the switching device  40  sets respective SOC values of the power storage cells  5  constituting the power storage module  50  to values out of a predetermined range, the switching device  40  performs switching from the first form S 1  to the second form S 2 . 
     In the configuration illustrated in  FIG. 9 , the SOC is set to a value smaller than the normal usage range, so that the power storage module  50  expands by the second dimension L 2  from the reference length L 0 . The second dimension L 2  is a value smaller than the first dimension L 1 . Due to the expansion of the power storage module  50 , the receiving member  10  moves in the one direction  80  by an amount smaller than that in the cases illustrated in  FIGS. 7, 8 . 
     While such a state illustrated in  FIG. 9  is being formed, or when the state illustrated in  FIG. 9  has been formed, the feed mechanism  16  operates such that the position of the movable block  14  is changed from the first part P 1  to the second part P 2 . The feed mechanism  16  may be adjusted such that a load is always applied to the feed mechanism  16  by an elastic body such as a spring, and when a frictional force between the movable block  14  and the inclined surface  15  decreases, the feed mechanism  16  is pushed from the first part P 1  side toward the second part P 2  side. Hereby, the switching from the first form S 1  to the second form S 2  by the switching device  40  is completed. 
     As described at the beginning, when the power storage apparatus  101  or the load applicator  61  is used for a long period, there is such a possibility that the load applicator  61  cannot apply a necessary and sufficient load to the power storage module  50  due to deterioration by aging, or the like, for example. For example, the length of the elastic body  37  may become shorter than its initial state under the influence of creep deformation. Alternatively, the elastic modulus (Young&#39;s modulus) of the elastic body  37  may become smaller than its initial state under the influence of creep deformation. 
     In a case where such a phenomenon occurs, when the power storage module  50  expands by the first dimension L 1  from the reference length L 0 , a restraint load smaller than the first restraint load (corresponding to the arrow  74  in  FIG. 7 ) is applied to the power storage module  50 . In such a case, the switching device  40  is configured to perform an operation to switch from the first form S 1  to the second form S 2  by performing the operation described with reference to  FIG. 9 . 
     When the operation to switch from the first form S 1  to the second form S 2  is completed, the restraint load to be applied to the power storage module  50  by the load applicator  61  increases. This state is a state different from the first form S 1  and the second form S 2  to be provided at the time of starting the use of the load applicator  61 . Since this state is formed, even in a case where the power storage cells  5  constituting the power storage module  50  contract in the one direction  80 , it is possible to effectively restrain insufficiency in the load to be applied from the load applicator  61  to the power storage module  50  in the one direction  80 , just by an increase in the load by the elastic body  37 . 
     The embodiments have been described above, but the embodiments described herein are just examples in all respects and are not limitative. The scope of this disclosure is shown by Claims and is intended to include all modifications made within the meaning and scope equivalent to Claims.