POWER STORAGE DEVICE

A power storage device includes a power storage stack and a housing case. In the power storage stack, a plurality of unit cells and a plurality of spacers are alternately stacked in a first direction. A first support surface of each spacer among the plurality of spacers is angled corresponding to and is in contact with a first tapered surface of the unit cell that is adjacent to the spacer in the first direction. A second support surface of each spacer among the plurality of spacers is angled corresponding to and is in contact with a second tapered surface of the unit cell that is adjacent to the spacer in the first direction. The plurality of spacers are each formed of a thermoplastic resin.

This nonprovisional application is based on Japanese Patent Application No. 2020-096116 filed on Jun. 2, 2020 with the Japan Patent Office, the entire content of which is hereby incorporated by reference.

BACKGROUND

Field

The present disclosure relates to a power storage device to be mounted on a vehicle.

Description of the Background Art

Japanese Patent Laying-Open No. 2018-32519 discloses a configuration of a power storage device. The power storage device disclosed in Japanese Patent Laying-Open No. 2018-32519 is a cell module, which includes a cell stack and a housing case. The cell stack includes a stack of cells in which multiple rectangular cells are stacked in the direction of thickness of the stack of cells, and a pair of end plates. The end plates are disposed at the opposing ends of the cell stack in the stacking direction of the cells. One least one of the end plates has a stack-facing surface that is angled so that the dimension of the housing case in the stacking direction of the cells decreases toward the lower end. The accommodating space has case-facing surfaces that are angled so that the dimension of the accommodating space in the stacking direction of the cells decreases. Since the stack-facing surface and the case-facing surface, which are facing each other, are angled, a constraining load can be applied to the cell stack by pressing a cell stack in place into the accommodating space.

SUMMARY

As with the power storage device disclosed in Japanese Patent Laying-Open No. 2018-32519, a constraining load is applied to a power storage stack in a conventional power storage device. Heat is thus easily transferred among the unit cells included in the power storage stack. Due to this, if one of the unit cells is abnormally heated, heat is transferred from the abnormally-heated unit cell to other unit cells. If these other unit cells are heated, they may also be heated abnormally. In this manner, a chain of heat generation by unit cells can occur in a conventional power storage device.

The present disclosure is made in view of the above problem, and an object of the present disclosure is to provide a power storage device which can inhibit, when one of unit cells included in a power storage stack is abnormally heated, conduction of the heat from the unit cell to other unit cells.

A power storage device according to the present disclosure includes a power storage stack and a housing case. In the power storage stack, a plurality of unit cells and a plurality of spacers are alternately stacked in a first direction. The housing case accommodates the power storage stack. The power storage stack is constrained in the first direction within the housing case. Each unit cell among the plurality of unit cells has a first tapered surface and a second tapered surface. The first tapered surface and the second tapered surface are angled so that a spacing formed between the first tapered surface and the second tapered surface decreases toward one side of the second direction intersecting with the first direction, the first tapered surface and the second tapered surface forming opposing end surfaces of the unit cell in the first direction. Each spacer among the plurality of spacers has a first support surface and a second support surface. The first support surface and the second support surface form opposing end surfaces of the spacer in the first direction. The first support surface of each spacer among the plurality of spacers is angled corresponding to and is in contact with the first tapered surface of a unit cell adjacent to the spacer on one side of the first direction. The second support surface of each spacer among the plurality of spacers is angled corresponding to and is in contact with the second tapered surface of a unit cell adjacent to the spacer on the other side of the first direction. The plurality of spacers are each formed of a thermoplastic resin.

A friction force is generated between the tapered surface of the unit cell and the support surface of the spacer formed of the thermoplastic resin. This inhibits the unit cell from being displaced out of position in the second direction by a constraining force acting on the power storage stack. The power storage stack can, in turn, maintain the constraining force bearing state. Furthermore, if any one of the plurality of unit cells is abnormally heated, the support surface of the spacer, formed of the thermoplastic resin, adjacent to the unit cell is thermally distorted. This reduces a friction coefficient between the support surface of the spacer and the tapered surface of the unit cell. The constraining force is applied to the heated unit cell, which, in turn, slides on the support surface of the spacer and is displaced out of position in the second direction. The heated unit cell being displaced out of position reduces the constraining force. The reduction in the constraining force can inhibit the conduction of heat from the abnormally heated unit cell to other unit cells within the power storage stack.

In the power storage device according to one embodiment of the present disclosure, the power storage stack has a first end surface and a second end surface. The first end surface and the second end surface form opposing end surfaces of the power storage stack in the first direction. The first end surface of the power storage stack is formed of the first tapered surface of the unit cell that is disposed on one end of the power storage stack in the first direction. The second end surface of the power storage stack is formed of the second tapered surface of a unit cell that is disposed on the other end of the power storage stack in the first direction. The housing case has a first inner surface and a second inner surface. The first inner surface and the second inner surface are facing each other in the first direction. The first inner surface includes a first angled portion. The first angled portion is angled corresponding to the first tapered surface. The second inner surface includes a second angled portion. The second angled portion is angled corresponding to the second tapered surface. The power storage stack is held by the housing case, with the first end surface in contact with the first angled portion and the second end surface in contact with the second angled portion.

This allows the power storage stack to be held within the housing case, without having to provide another member, such as an end plate, between the inner surface of the housing case and the opposing end surfaces of the power storage stack in the first direction.

The power storage device according to one embodiment of the present disclosure further includes a cooler. The cooler is disposed between the bottom of the housing case and the power storage stack. The cooler cools the plurality of unit cells. On the one side of the second direction, the bottom is facing the power storage stack. The plurality of spacers are each positioned in the second direction by being in contact with the cooler.

The plurality of spacers being positioned in the second direction as such stabilizes the position of the entirety of the power storage stack in the second direction, which, in turn, improves the reliability of the power storage device.

In the power storage device according to one embodiment of the present disclosure, the housing case has a bottom. On one side of the second direction, the bottom is facing the power storage stack. The plurality of spacers are each positioned in the second direction by being in contact with the bottom.

The plurality of spacers being positioned in the second direction as such stabilizes the position of the entirety of the power storage stack in the second direction, which, in turn, improves the reliability of the power storage device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a power storage device according to a respective embodiment will be described, with reference to the accompanying drawings. In the following description of embodiments, the same reference sign is given to the same or corresponding part in the figures, and description thereof will not be repeated.

FIG. 1is a schematic view illustrating a vehicle which includes a power storage device according to Embodiment 1. Referring toFIG. 1, a vehicle1is described which includes a power storage device100according to Embodiment 1.

The vehicle1includes a vehicle body2, a driving gear3, front wheels5, rear wheels6, and power storage device100. An engine compartment, a boarding space, and a luggage room are formed within the vehicle body2. The engine compartment is formed on the front side of the vehicle1. The boarding space is formed on the rear side of the engine compartment. The luggage room is formed behind the boarding space.

The driving gear3is accommodated within the engine compartment. The driving gear3includes a rotating electric machine7and a power control unit (PCU)8. The PCU8includes an inverter and a converter. The PCU8is electrically connected to the power storage device100and the rotating electric machine7.

The PCU8boosts the voltage of a direct-current (DC) power supplied from the power storage device100, further converts the DC power into an alternating-current (AC) power and supplies the AC power to the rotating electric machine7.

Using the AC power supplied from the PCU8, the rotating electric machine7generates a driving force for rotating the front wheels5. Note that the vehicle1is an electric-powered vehicle, such as electric vehicles and hybrid vehicles.

Next, the power storage device100is now described.FIG. 2is a schematic plan view of the power storage device according to Embodiment 1.FIG. 3is a schematic cross-sectional view of the power storage device ofFIG. 2, as viewed in the direction of the arrow of line As shown inFIGS. 2 and 3, the power storage device100according to Embodiment 1 includes a power storage stack110, a housing case140, and a cooler190.

As shown inFIGS. 2 and 3, in the power storage stack110, multiple unit cells120and multiple spacers130are alternately stacked along a first direction DR1. The housing case140accommodates the power storage stack110. The housing case140includes a lower case150and an upper case160.

Within the housing case140, the power storage stack110is constrained in the first direction DR1. In other words, the power storage stack110is bearing a constraining load in the first direction DR1. The power storage stack110being constrained in the first direction DR1regulates the positions of the unit cells120and the positions of the spacers130, thereby improving the reliability of the power storage stack110. Details of the constraining load will be described below.

The first direction DR1is, specifically, the horizontal direction. While the power storage device100according to the present embodiment is described with reference to the first direction DR1being the front-rear direction of the vehicle1, the first direction DR1may be the width direction of the vehicle1.

As shown inFIG. 3, the power storage stack110has a first end surface111and a second end surface112. The first end surface111and the second end surface112form the opposing ends of the power storage stack110in the first direction DR1.

In the present embodiment, for example, a single cell can be employed as each one of the unit cells120. Examples of the single cell include a secondary battery such as a nickel-hydrogen battery or a lithium-ion battery. The single cell has, for example, a rectangular shape. The secondary battery may be one using liquid electrolyte or one using a solid electrolyte. Note that the unit cell120may be a chargeable/dischargeable unit capacitor.

The unit cells120are electrically connected to one another in series within the housing case140. The structure for electrically connecting the unit cells120to one another is not shown inFIGS. 2, 3, and the subsequent figures.

The unit cells120are each, what is called, a rectangular battery as noted above, and they have a rectangular prism shape whose opposing end surfaces in the first direction DR1are angled. The unit cells120each have a first tapered surface121and a second tapered surface122. The first tapered surface121and the second tapered surface122form the opposing end surfaces of the unit cell120in the first direction DR1. The first tapered surface121and the second tapered surface122are angled so that the spacing formed between the two decreases toward one side of the second direction DR2intersecting with the first direction DR1.

In the present embodiment, the second direction DR2is, specifically, orthogonal to the first direction DR1. The second direction DR2is, specifically, the vertical direction. The one side of the second direction DR2is, specifically, the downward direction, and the other one side of the second direction DR2is, specifically, the upward direction.

The first tapered surface121has a rectangular profile as viewed in a direction orthogonal to the first tapered surface121. The second tapered surface122has a rectangular profile as viewed in a direction orthogonal to the second tapered surface122. The unit cells120each have an upper surface and a lower surface intersecting with the second direction. The upper surface and the lower surface of the unit cell120each have a rectangular profile.

The first end surface111of the power storage stack110is formed of the first tapered surface121of the unit cell120that is disposed on one end of the power storage stack110in the first direction DR1. The second end surface112of the power storage stack110is formed of the second tapered surface122of the unit cell120that is disposed on the other end of the power storage stack110in the first direction DR1.

As shown inFIG. 3, the spacers130each have a first support surface131and a second support surface132. The first support surface131and the second support surface132form the opposing end surfaces of a spacer130in the first direction DR1.

The first support surface131of each of the spacers130is angled corresponding to and is in contact with the first tapered surface121of a unit cell120that is adjacent to the spacer130on one side of the first direction DR1. The second support surface132of each of the spacers130is angled corresponding to and is in contact with the second tapered surface122of a unit cell120that is adjacent to the spacer130on the other side of the first direction DR1. Note that, for ease of discussion,FIGS. 2 and 3schematically illustrate the members adjacent to each other in the first direction DR1, with a space in between.

In the present embodiment, the spacers130are not coupled to each other, and are spaced apart from each other. The spacers130may be coupled to one another within the housing case140. In this case, preferably, the spacers130can each be displaceable in the first direction DR1when a unit cell120is displaced out of position in the second direction DR2, as described below.

The spacers130are each formed of a thermoplastic resin so that when a unit cell120adjacent to the spacer130is abnormally heated, a portion of the first support surface131that is in contact with the first tapered surface121of the unit cell120and a portion of the second support surface132that is in contact with the second tapered surface122of the unit cell120can be thermally distorted. Functional effects of the spacer130when thermal distorted will be described below.

The housing case140accommodates the power storage stack110. The housing case140may accommodate multiple power storage stacks110. The housing case140is formed of a metallic material, such as aluminum.

The lower case150(the housing case140) has a first inner surface151, a second inner surface152, and a bottom153. The first inner surface151and the second inner surface152are facing each other in the first direction DR1.

The first inner surface151includes a first angled portion151a.The first angled portion151ais angled corresponding to the first tapered surface121of a unit cell120that is disposed on the one end of the power storage stack110in the first direction DR1. The first angled portion151amay form a portion of the first inner surface151, or may form the entirety of the first inner surface151.

The second inner surface152includes a second angled portion152a.The second angled portion152ais angled corresponding to the second tapered surface122of a unit cell120that is disposed on the other end of the power storage stack110in the first direction DR1. The second angled portion152amay form a portion of the second inner surface152, or form the entirety of the second inner surface152.

The power storage stack110is held by the housing case140, with the first end surface111in contact with the first angled portion151aand the second end surface112in contact the second angled portion152a.

On the one (lower) side of the second direction DR2of the power storage stack110, the bottom153of the housing case140is facing the power storage stack110. In the present embodiment, the power storage stack110and the bottom153are spaced apart from each other.

The lower case150has an opening154on the side opposite the bottom153. The upper case160closes off the opening154.

The cooler190is disposed between the bottom153and the power storage stack110. The cooler190cools the unit cells120. The spacers130are in contact with the cooler190, thereby being positioned in the second direction DR2.

The cooler190may be formed of, for example, coolant piping through which a liquid refrigerant or a gas refrigerant flows.

The power storage device100according to Embodiment 1 is now described with reference to one example method of formation of the power storage stack110within the housing case140.

FIG. 4is a cross-sectional view of a housing case in which multiple unit cells and multiple spacers disposed, except for one unit cell, according to Embodiment 1.FIG. 4illustrates the same cross-sectional view asFIG. 3, but without the upper case160, for convenience. As the final one unit cell120is accommodated within the housing case140ofFIG. 4, a constraining force acts on the power storage stack110in the first direction DR1, thereby forming the power storage stack110according to the present embodiment as shown inFIG. 3.

As shown inFIG. 4, initially, the unit cells120and the spacers130are disposed within the housing case140, except for one unit cell120.

As shown inFIG. 4, since one unit cell120is not yet positioned, two of the spacers130are adjacent to each other in the first direction DR1with no unit cell120in between. In the following, a description will be given with reference to disposing the final unit cell120between the two adjacent spacers130. However, the final unit cell120may be disposed in a position that is in contact with the housing case140in the first direction DR1. Stated differently, the final unit cell120may be one that forms the first end surface111or the second end surface112of the power storage stack110.

FIG. 5is a cross-sectional view of the housing case ofFIG. 4, with the final one unit cell being pressed in place into the housing case in order to form the power storage stack, according to Embodiment1.FIG. 5illustrates the same cross-sectional view asFIG. 3.

As shown inFIG. 5, the final unit cell120is being disposed between the adjacent two spacers130within the housing case140. The final unit cell120is being disposed into the housing case140from the other (upper) side of the second direction DR2. This causes the first tapered surface121of the final unit cell120to abut the first support surface131of one of the two adjacent spacers130. The second tapered surface122of the final unit cell120abuts the second support surface132of the other one of the adjacent two spacers130.

At this time, the final unit cell120is projecting toward the other (upper) side of the second direction DR2, as compared to the other unit cells120. The unit cells120and the spacers130illustrated inFIG. 5are bearing an extremely small load in the first direction DR1, while the unit cells120and the spacers130according to Embodiment 1 are bearing the constraining load when all the unit cells120are disposed in the housing case140. The unit cell120and the spacers130in an unloaded condition will be described below.

Then, as the final unit cell120projecting as mentioned above is pressed into the housing case140toward the one (lower) side of the second direction DR2, a force Fp to press that unit cell120toward the one (lower) side of the second direction DR2is converted into a pressing force Fq1and a pressing force Fq2, due to a wedging effect of the unit cell120having the first tapered surface121and the second tapered surface122. The pressing force Fq1is a force of the unit cell120, being pressed in place, to press against the first support surface131of the spacer130that is in contact with the first tapered surface121of the unit cell120being pressed in place. The pressing force Fq2is a force of the unit cell120, being pressed in position, to press against the second support surface132of the spacer130that is in contact with the second tapered surface122of the unit cell120being pressed in place.

Due to a component Fr1of the pressing force Fq1in the first direction DR1, the spacers130and other unit cells120that are on the first tapered surface121side of the unit cell120being pressed in position bear the reaction force from the first inner surface151(the first angled portion151a) of the housing case140, and are compressed in the first direction DR1. Due to the component Fr2of the pressing force Fq2in the first direction DR1, the spacers130and other unit cell120that are on the second tapered surface122side of the unit cell120being pressed in position bear the reaction force from the second inner surface152(the second angled portion152a) of the housing case140, and are compressed in the first direction DR1. The unit cell120being pressed in position is also compressed in the first direction DR1by the reaction force from the spacer130, generated by the component Fr1and the component Fr2in the first direction DR1.

As described above, the projecting unit cell120squeezes in between the spacers130while the unit cells120and the spacers130are being compressed in the first direction DR1in the housing case140. This forms the power storage stack110according to Embodiment1in the housing case140, while the power storage stack110is bearing the constraining load in the first direction DR1.

While the above description has been given with reference to forming the power storage stack110by pressing the final unit cell120in position between two spacers130, it should be noted that, even if the power storage stack110is formed by pressing in place a unit cell120that is to form the first end surface111or the second end surface112of the power storage stack110, the power storage stack110according to Embodiment1can be formed within the housing case140while bearing a constraining load in the first direction DR1, as with the above.

Specifically, as the unit cell120that is to form the first end surface111of the power storage stack110is pressed in place into the housing case140, the first tapered surface121of the unit cell120being pressed is brought into contact with the first inner surface151(the first angled portion151a). Consequently, due to a wedging effect similar to the above, the power storage stack110can be formed which is bearing the constraining load in the first direction DR1. When the unit cell120that is to form the second end surface112of the power storage stack110is pressed in place into the housing case140, the second tapered surface122of the unit cell120being pressed is brought into contact with the second inner surface152(the second angled portion152a). Consequently, due to a wedging effect similar to the above, the power storage stack110can be formed which is bearing the constraining load in the first direction DR1.

While the power storage stack110is compressed in the first direction DR1and bearing a constraining load Ft1in the first direction DR1, the position of the power storage stack110is regulated within the housing case140.

FIG. 6is a schematic cross-sectional view illustrating a force acting on the unit cells in the power storage device according to Embodiment1.FIG. 7is a schematic cross-sectional view illustrating the power storage stack according to Embodiment1in an unloaded condition.FIGS. 6 and 7illustrate the power storage device100and the power storage stack110, respectively, in the same cross-sectional view asFIG. 3. Moreover, for ease of discussion,FIGS. 6 and 7schematically illustrate the members adjacent to each other in the first direction DR1, with a space in between.

Ds1>Du is satisfied, where Du is the length, in the first direction DR1, of the power storage stack110in the power storage device100according to Embodiment1, as viewed from the other (upper) side of the second direction DR2as shown inFIG. 6, and Ds1is the length, in the first direction DR1, of the power storage stack110in an unloaded condition, as viewed from the other (upper) side of the second direction DR2as shown inFIG. 7. Due to this, the constraining load Ft1that is applied to the power storage stack110in the first direction DR1can be represented as: Ft1≈K·(Ds1−Du), where K is a spring constant of the power storage stack110in the first direction DR1.

In the following, for ease of illustration, the spring constant K of the power storage stack110is regarded as a constant value.

In the present embodiment, while the power storage stack110can be formed by pressing the final one unit cell120in place into the housing case140as noted above, the constraining load Ft1can also be controlled by adjusting the force Fp to press the unit cell120in place into the housing case140, as shown inFIG. 5.

Specifically, as shown inFIGS. 5 and 6, the magnitude, in the first direction DR1, of the component Fr1(Fr2) of the pressing force Fq1(Fq2) to press against the spacer130adjacent to the unit cell120with the force Fp to press the unit cell120in place can be as is the magnitude of the constraining load Ft1. Note that, in order to adjust the magnitude of the constraining load Ft1to be small, the final unit cell120to be pressed may be located on the other (upper) side of the second direction DR2relative to an end of an adjacent spacer130on the one (lower) side of the second direction DR2. In other words, the final unit cell120to be pressed may be spaced apart from the cooler190. In this case, a heat transfer agent may be previously injected between the final unit cell120to be pressed in place and the cooler190. Accordingly, in the power storage device100according to Embodiment 1, the heat transfer agent may be located between the cooler190and at least one of the unit cells120.

Next, forces acting on the unit cell120according to Embodiment 1 will be described. As shown inFIG. 6, in each unit cell120, a reaction force in a direction along the first direction DR1is generated by the constraining load Ft1. For example, the constraining load Ft1from the spacer130adjacent to a unit cell120on the first tapered surface121side generates the reaction force Fl in the first tapered surface121. Since the first tapered surface121and the first support surface131of the spacer130in contact with the first tapered surface121are positioned non-parallel to the second direction DR2, the reaction force F1is resolved into a force component F2in a direction orthogonal to the first tapered surface121(the first support surface131) and a force component F3in a direction along the first tapered surface121(the first support surface131). Then, since the spacer130is formed of a thermoplastic resin, the force component F3causes in the first tapered surface121a friction force F4in a direction opposite the direction of the force component F3. The magnitude of the friction force F4is equal to the magnitude of the force component F3. A similar friction force is also generated on the second tapered surface122of the unit cell120. As such, the positions of the unit cells120are regulated by these friction forces while the power storage stack110is bearing the constraining load Ft1. Accordingly, in the power storage device100according to Embodiment1, the unit cells120are maintained bearing the constraining load Ft1and the positions of the unit cells120are maintained regulated, without requiring the unit cells120to be fixedly coupled by a member, such as a restraining band.

Note that, due to the force component F2, a normal reaction that is equal in magnitude to the force component F2is applied to the unit cell120from the first support surface131of the spacer130. Due to this, the maximum static friction force between the first tapered surface121and the first support surface131is μ·F2, where μ. is a coefficient of static friction between the first tapered surface121of the unit cell120and the first support surface131of the spacer130. The power storage device100according to Embodiment1is configured to satisfy F4<μ·F2.

Next, the power storage device100according to Embodiment1will be described in the case where one of the unit cells120is abnormally heated. As shown inFIG. 6, when a unit cell120is abnormally heated, the first support surface131of the spacer130that is in contact with the first tapered surface121of that unit cell120is heated. This thermally distorts the first support surface131of the spacer130formed of a thermoplastic resin, resulting in a reduction of the coefficient of static friction p. between the first tapered surface121of the unit cell120and the first support surface131of the spacer130. The reduction of the coefficient of static friction p. reduces the maximum static friction force (μ·F2) between the first tapered surface121and the first support surface131.

As the maximum static friction force (μ·F2) decreases small enough to satisfy μ·F2<F3, the friction force F4is in turn equal to the maximum static friction force (μ·F2), and the force component F3is in turn greater than the friction force F4which is now the maximum static friction force. This causes the unit cell120to move along the direction of the force component F3. In other words, the unit cell120slides along the first support surface131, with the first tapered surface121in contact with the first support surface131. Similarly, in a spacer130that is in contact with the second tapered surface122of the abnormally-heated unit cell120, the second support surface132is thermally distorted, and the maximum static friction force is thereby reduced, causing, as with the first tapered surface121, the unit cell120to slide along the second support surface132, with the second tapered surface122in contact with the second support surface132.

As described above, in the case where one of the unit cells120in the power storage stack110is abnormally heated, the unit cell120is displaced to the other (upper) side of the second direction DR2.

FIG. 8is a schematic cross-sectional view illustrating the power storage device in which an abnormally-heated unit cell is displaced out of position, according to Embodiment 1.FIG. 9is a cross-sectional view schematically illustrating the power storage stack in an unloaded condition in the first direction, while an abnormally-heated unit cell is kept displaced out of position in the second direction, according to Embodiment 1.FIGS. 8 and 9illustrate the power storage device100and the power storage stack110in the same cross-sectional view asFIG. 3. For ease of discussion,FIGS. 8 and 9schematically illustrate the members adjacent to each other in the first direction DR1, with a space in between.

As shown inFIG. 8, the first tapered surface121and the second tapered surface122of each unit cell120are angled so that a spacing formed between the two decreases toward the one (lower) side of the second direction DR2. Consequently, as an abnormally-heated unit cell120is displaced to the other (upper) side of the second direction DR2, Ds2<Ds1is satisfied, where Ds2is the length of the power storage stack110in the first direction DR1as viewed from the other (upper) side of the second direction DR2when the power storage stack110is in an unloaded condition in the first direction DR1while the abnormally-heated unit cell120is maintained projected in the second direction DR2, as shown inFIG. 9, and Ds1is the length of the power storage stack110in the first direction DR1as viewed from the other (upper) side when the power storage stack110is in an unloaded condition in the first direction DR1and no unit cell120is abnormally heated, as shown inFIG. 7.

Then, as shown inFIGS. 8 and 9, the constraining load Ft2that is applied to the power storage stack110in the first direction DR1while an abnormally-heated unit cell120is displaced out of position can be represented as Ft2≈K·(Ds2−Du). Here, since Ds2is less than Ds1as noted above, K·(Ds2−Du)<K·(Ds1−Du), that is, Ft2<Ftl is satisfied. As such, the constraining load applied to the power storage stack110in the first direction DR1is reduced by the unit cell120being displaced out of position, as described above. The reduction in the constraining load reduces the thermal conductivity within the power storage stack110in the first direction DR1. Accordingly, conduction of heat from a heated unit cell120to other unit cells120can be inhibited.

As noted above, in the power storage device100according to Embodiment 1, the first support surface131of each of the spacers130is angled corresponding to and is in contact with the first tapered surface121of a unit cell120that is adjacent to the spacer130on the one side of the first direction DR1. The second support surface132of each of the spacers130is angled corresponding to and is in contact with the second tapered surface122of a unit cell120that is adjacent to the spacer130on the other side of the first direction DR1. The spacers130are each formed of a thermoplastic resin.

This causes a friction force between the tapered surface of the unit cell120and at least one of the first support surface131and the second support surface132of the spacer130formed of a thermoplastic resin. This inhibits the unit cell120from being displaced out of position in the second direction DR2by a constraining force acting on the power storage stack110in the first direction DR1. The power storage stack110can, in turn, maintain the constraining force bearing state. Furthermore, if any one of the unit cells120is abnormally heated, at least one of the first support surface131and the second support surface of the spacer130, formed of a thermoplastic resin, adjacent to the unit cell120is thermally distorted. This reduces the friction coefficient between the first support surface131(the second support surface132) of the spacer130and the first tapered surface121(the second tapered surface122) of the unit cell120. Due to this, the constraining force is applied to the heated unit cell120, which, in turn, slides on the first support surface131(the second support surface132) of the spacer130and is displaced out of position in the second direction DR2. The heated unit cell120being displaced out of position reduces the constraining force. The reduction in the constraining force can inhibit the conduction of heat from the abnormally-heated unit cell120to other unit cells120within the power storage stack110.

Moreover, in the power storage device100according to Embodiment 1, the first angled portion151ais angled corresponding to the first tapered surface121. The second inner surface152includes the second angled portion152a.The second angled portion152ais angled corresponding to the second tapered surface122. The power storage stack110is held by the housing case140, with the first end surface111in contact with the first angled portion151aand the second end surface112in contact with the second angled portion152a.This allows the power storage stack110to be held within the housing case140, without having to provide another member, such as an end plate, between the first end surface111and the first inner surface151and between the second end surface112and the second inner surface152.

Moreover, in the power storage device100according to Embodiment1, the spacers130are in contact with the cooler190, thereby being positioned in the second direction DR2. This stabilizes the position of the entirety of the power storage stack110in the second direction DR2, which, in turn, improves the reliability of the power storage device100.

In the following, a power storage device according to Embodiment 2 is described. The power storage device according to Embodiment 2 is primarily different from Embodiment 1 in terms of a method of positioning of spacers in a second direction. Thus, description of the same configuration as Embodiment 1 will be omitted.

FIG. 10is a schematic cross-sectional view of the power storage device according to Embodiment2.FIG. 10illustrates the same cross-sectional view asFIG. 3.

FIG. 10also schematically illustrates the members adjacent to each other in a first direction DR1, with a space in between.

As shown inFIG. 10, in a power storage device200according to Embodiment2, no cooler is disposed between a power storage stack110and a bottom153. Due to this, in the power storage device200according to Embodiment 2, spacers230are in contact with the bottom153, thereby being positioned in a second direction DR2. Due to this, since the spacers130are positioned in the second direction DR2also in the present embodiment, the position of the entirety of the power storage stack110is stabilized in the second direction DR2, which, in turn, improves the reliability of the power storage device100.