POWER STORAGE DEVICE

A power storage device includes: a power storage module including a plurality of power storage cells; and a restriction unit disposed between the power storage cells. The restriction unit includes: a first flat plate and a second flat plate; and a corrugated plate disposed between the first flat plate and the second flat plate. The corrugated plate has a plurality of first curved portions and a plurality of second curved portions. Each of the first curved portions has a shape curved to protrude toward one side in the stacking direction. Each of the second curved portions has a shape curved to protrude toward the other side in the stacking direction. The first curved portions and the second curved portions are alternately arranged in a direction intersecting with the stacking direction and the intersecting direction.

This nonprovisional application is based on Japanese Patent Application No. 2021-060113 filed on Mar. 31, 2021 with the Japan Patent Office, the entire contents of which are hereby incorporated by reference.

BACKGROUND

Field

The present disclosure relates to a power storage device.

Description of the Background Art

Conventionally, a battery cell in which an electrode assembly is accommodated in a laminate film has been known. For example, a battery cell disclosed in Japanese Patent Laying-Open No. 2019-139844 includes an electrode assembly, a laminate case accommodating the electrode assembly, and a terminal.

The electrode assembly includes a plurality of electrode sheets and a separator. Each electrode sheet includes a current collecting foil and an electrode active material layer formed on the current collecting foil. The current collecting foil is provided with an extending portion in which no electrode active material is formed. The extending portion is connected to the terminal inside the laminate case. The terminal is formed to protrude outward from the laminate case.

SUMMARY

A power storage device includes a power storage module in which power storage cells are stacked, and an accommodation case that accommodates the power storage module.

In this case, upon charging and discharging of the power storage device, the power storage module deforms so as to expand in the stacking direction. As a result, a load is applied from the power storage module to the accommodation case, so that the accommodation case may deform.

Further, when the power storage device is mounted on a vehicle and the like, the power storage device may undergo vibrations, for example, due to traveling of the vehicle. When the power storage device vibrates, the power storage module in the accommodation case may vibrate to thereby cause resonance of the power storage module.

On the other hand, upon charging and discharging of the power storage device, the temperature inside the power storage module becomes high. In particular, among a plurality of stacked power storage cells, each power storage cell disposed at a position away from the accommodation case has low heat dissipation performance. As a result, among the power storage cells, each power storage cell located away from the accommodation case tends to rise in temperature.

The present disclosure has been made in view of the above-described problems, and an object of the present disclosure is to provide a power storage device that is capable of reducing a load applied from a power storage module to an accommodation case during charging and discharging to thereby suppress vibration of the power storage device, and in which the heat dissipation performance of the power storage module is improved.

A power storage device includes: a power storage module including a plurality of power storage cells stacked in a stacking direction; an accommodation case that accommodates the power storage module; and a restriction unit disposed between the power storage cells. The restriction unit includes: a first flat plate and a second flat plate spaced apart from each other in the stacking direction, and a corrugated plate disposed between the first flat plate and the second flat plate. The corrugated plate has a plurality of first curved portions and a plurality of second curved portions. Each of the first curved portions has a shape curved to protrude toward one aide in the stacking direction and extending in an intersecting direction intersecting with the stacking direction. Each of the second curved portions has a shape curved to protrude toward the other side in the stacking direction and extending in the intersecting direction. The first curved portions and the second curved portions are alternately arranged in a direction intersecting with the stacking direction and the intersecting direction.

Each of the power storage cells includes an electrode assembly and a current collector plate connected to the electrode assembly. The power storage device further includes a filling portion provided inside the accommodation case so as to extend from an inner wall of the accommodation case to reach the current collector plate. The restriction unit is formed to reach the filling portion. The first flat plate and the corrugated plate are in contact with each other at a top of each of the first curved portions. The second flat plate and the corrugated plate are in contact with each other at a top of each of the second curved portions.

The restriction unit includes: an accommodation body that accommodates the first flat plate, the second flat plate, and the corrugated plate; and a dilatancy material accommodated in the accommodation body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present disclosure will be hereinafter described with reference to the accompanying drawings. In the accompanying drawings referred to below, the same or corresponding members are denoted by the same reference characters.

FIG. 1is a perspective view schematically showing a configuration of a battery pack including a power storage device according to an embodiment of the present disclosure.FIG. 2is a cross-sectional view taken along a line II-II inFIG. 1. A battery pack1is mounted, for example, on an electrically powered vehicle such as an electric vehicle.

As shown inFIGS. 1 and 2, battery pack1includes a power storage device10and a cooling device20. Cooling device20serves to cool power storage device10. Cooling device20is disposed in contact with a side portion of power storage device10. As shown inFIG. 1, cooling device20is configured such that a cooling medium (water or the like) C flows therethrough.FIG. 1shows a partially cutaway state of cooling device20.

As shown inFIG. 1, power storage device10includes a pair of external terminals11and12. One external terminal11is a positive electrode terminal and the other external terminal12is a negative electrode terminal. As shown inFIG. 2, power storage device10includes a power storage module100, a case200, an insulating sheet300, filling portions400and401, and a restriction unit500.

FIG. 3is an exploded perspective view schematically showing the configuration of the power storage module. As shown inFIGS. 2 and 3, power storage module100includes at least one power storage cell101. In the present embodiment, power storage module100includes a plurality of power storage cells101A,101B, and101C. Power storage cells101A,101B, and101C are stacked in a stacking direction H (in one direction). Note that power storage cell101B is located in the central area of power storage module100in stacking direction H.FIGS. 2 and 3each show three power storage cells101, but the number of power storage cells101is not particularly limited. Examples of power storage cell101may be a lithium ion battery.

Power storage cell101is what is called a laminate-type cell. As shown inFIG. 2, each power storage cell101includes a plurality of electrode assemblies110, a pair of current collector plates120, a laminate film130, an adhesive member140, and an electrolytic solution (not shown).

Each of electrode assemblies110includes a plurality of positive electrode sheets, a plurality of separators, and a plurality of negative electrode sheets that are stacked in stacking direction H A separator is disposed between the positive electrode sheet and the negative electrode sheet.

Each positive electrode sheet includes an aluminum foil and a positive electrode composite layer formed on each of the front and rear surfaces of the aluminum foil. The aluminum foil has an uncoated portion on which no positive electrode composite layer is formed.

Each negative electrode sheet includes a copper foil and a negative electrode composite layer formed on each of the front and rear surfaces of the copper foil. The copper foil has an uncoated portion on which no negative electrode composite layer is formed.

One current collector plate120is disposed adjacent to electrode assembly110in a width direction W. The other current collector plate120is disposed on the side opposite to one current collector plate120with respect to electrode assembly110. The uncoated portion of each positive electrode sheet is connected to one current collector plate120while the uncoated portion of each negative electrode sheet is connected to the other current collector plate120.

Laminate film130covers the plurality of electrode assemblies110and a part of current collector plate120. Laminate film130is filled with an electrolytic solution (not shown).

As shown inFIGS. 2 and 3, the outer peripheral edge portion of laminate film130is formed in a rectangular shape. Laminate film130is longer in a longitudinal direction L and shorter in width direction W. Longitudinal direction L and width direction W intersect with (are orthogonal to) stacking direction H. Longitudinal direction L and width direction W intersect with (are orthogonal to) each other. Note that longitudinal direction L and width direction W extend in the horizontal direction. Current collector plate120has a protrusion122protruding from laminate film130. Each protrusion122protrudes outward from the long side of laminate film130. Protrusions122are connected by a bus bar15such that power storage cells101are electrically connected in series.

As shown inFIG. 3, a bus bar13having external terminal11is connected to protrusion122of power storage cell101C disposed at one end in stacking direction H. A bus bar14having external terminal12is connected to protrusion122of power storage cell101A disposed at the other end in stacking direction H.

Adhesive member140serves to allow laminate film130to adhere to current collector plate120. Adhesive member140is made of an insulating material (resins or the like). Adhesive member140is shaped to protrude from laminate film130. In other words, adhesive member140covers a part of protrusion122.

Case200accommodates power storage module100. Case200is made of metal (aluminum or the like). As shown inFIG. 1, case200includes a case body210and closing plates220and221.

Case body210opens at least in longitudinal direction L. In the present embodiment, case body210is formed in a rectangular tubular shape having a central axis extending in a direction orthogonal to stacking direction H of each power storage cell101. Case body210is provided with an inlet port h (seeFIG. 2). Case body210includes atop plate30, a bottom plate31, and side walls32and33. Side walls32and33are spaced apart from each other in width direction W.

Closing plates220and221are welded to case body210so as to close the opening of case body210. Closing plates220and221each are formed in a flat plate shape.

Cooling device20is provided on each side of case body210to be in contact with each of side walls32and33of case body210. In other words, cooling device20is provided in contact with case200in the direction orthogonal to the stacking direction of power storage cells101.

Insulating sheet300covers the inner surface of case body210and the inner surface of closing plate220. As shown inFIG. 2, insulating sheet300may cover the upper surface and the lower surface of case body210.

Filling portions400and401each are made of an insulating material. Filling portions400and401each are preferably made of a material having thermal conductivity and elasticity. Filling portions400and401each are formed by injecting the above-mentioned material (an insulating material in the present embodiment) into case200through inlet port h of case200.

Filling portion400is formed to extend from side wall32to reach power storage module100. Filling portion401is formed to extend from side wall33to reach power storage module100. Filling portions400and401each cover the tip end of each protrusion122. Filling portions400and401each cover the entire area of each protrusion122together with each adhesive member140. Filling portions400and401each may cover the ends of each adhesive member140and each laminate film130.

Filling portions400and401each preferably cover the entire areas of bus bars102,13, and14. Filling portion400is preferably in contact with insulating sheet300provided on the inner surface of case body210and insulating sheet300provided on the inner surface of closing plate220.

Restriction unit500is disposed inside case200. Restriction unit500is disposed between power storage cells101. In the example shown inFIG. 2, restriction unit500is disposed between power storage cells101B and101C. Restriction unit500may also be disposed between power storage cells101A and101B.

Restriction unit500restricts the relative displacement of power storage module100with respect to case200in stacking direction H of power storage cells101. Restriction unit500exhibits a first elastic modulus when each power storage cell101is displaced relative to case200at a first speed, and exhibits a second elastic modulus greater than the first elastic modulus when each power storage cell101is to be displaced relative to case200at a second speed.

The first speed is a relative speed at which each power storage cell101of power storage module100is displaced relative to case200when each power storage cell101expands. The second speed is a relative speed at which each power storage cell101is displaced relative to case200, and is higher than the first speed. The second speed is a relative speed at which each power storage cell101is displaced relative to case200, for example, when power storage device10or battery pack1vibrates.

FIG. 4is an exploded perspective view showing restriction unit500. Restriction unit500includes a flat plate510, a flat plate520, and a corrugated plate530.

Flat plates510and520are spaced apart from each other in stacking direction H, and corrugated plate530is disposed between flat plates510and520. Flat plates510,520and corrugated plate530each are formed to be longer in longitudinal direction L than in width direction W.

Corrugated plate530is provided with a curved portion532and a curved portion534.

Curved portion532is formed to protrude toward one side (upward) in stacking direction H. Curved portion532is formed to extend in longitudinal direction L. Curved portion534is formed to protrude toward the other side (downward) in stacking direction H. Curved portion534is formed to extend in longitudinal direction L.

A plurality of curved portions532and a plurality of curved portions534are provided. Curved portions532and curved portions534are alternately arranged in width direction W.

In this case, in corrugated plate530, the moment of inertia of area in a plane extending in stacking direction H and width direction W is defined as a moment of inertia of area I1. Then, a flat plate having the same thickness as that of corrugated plate530and not having curved portions532and534is defined as a comparative flat plate, and the moment of inertia of area of the comparative flat plate is defined as a moment of inertia of area I2.

Moment of inertia of area I1is larger than moment of inertia of area I2. Thus, for example, during deformation caused by applying a load to one end in longitudinal direction L in the state where the other end in longitudinal direction L is fixed, corrugated plate530is less likely to deform than the comparative flat plate. Accordingly, restriction unit500exhibits high rigidity when it vibrates as described above.

Flat plate510is disposed on the upper surface of corrugated plate530and is in contact with curved portion532. Flat plate520is disposed on the lower surface of corrugated plate530and is in contact with curved portion534.

In this case, air exists in the gap between flat plate510and corrugated plate530, and also, air exists in the gap between flat plate520and corrugated plate530.

Flat plates510,520and corrugated plate530each are made of a metal material. Flat plates510,520and corrugated plate530each have a thermal conductivity of 10 W/mK or more.

Referring back toFIG. 2, flat plate510is disposed on the lower surface of power storage cell101B, and flat plate520is disposed on the upper surface of power storage cell101C.

Then, in width direction W, restriction unit500has one end penetrating into filling portion400and the other end penetrating into filling portion401.

As a result of charging and discharging in power storage device10configured as described above, power storage module100deforms to expand in stacking direction H.

In this case, flat plates510and520are displaced to come close to each other in stacking direction H. Then, corrugated plate530deforms such that the expansion of curved portions532and534become smaller. As curved portions532and534deform, corrugated plate530deforms to extend in width direction W.

In this case, as corrugated plate530deforms, the points of contact between flat plate510and curved portion532and between flat plate520and curved portion534move while flat plates510and520are in contact with curved portions532and534, respectively. Flat plates510and520each having a flat plate shape reduce the frictional resistance at these points of contact between flat plate510and curved portion532and between flat plate520and curved portion534. Thereby, restriction unit500can favorably deform.

Filling portions400and401each are made of an elastically deformable material. Thus, as corrugated plate530deforms, filling portions400and401also deform.

In this way, even when power storage module100deforms to expand in stacking direction H due to charging and discharging, restriction unit500deforms to contract in stacking direction H. Since restriction unit500deforms to contract, the load applied from power storage module100to case200can be reduced, so that deformation of case200can be suppressed.

When battery pack1is mounted on a vehicle, power storage device10may undergo vibrations due to traveling of the vehicle.

For example, four corners of bottom plate31of power storage device10are fixed to a front panel or the like. Case200is formed to be longer in longitudinal direction L. Thus, when power storage device10vibrates, power storage device10is more likely to vibrate in the state where both ends in longitudinal direction L act as fixed ends and a central portion in longitudinal direction L acts as an antinode.

At this time, due to large moment of inertia of area I1, corrugated plate530and restriction unit500are less likely to deform as described above. Thereby, deformation and vibration of each of case200, power storage module100, and power storage device10can be suppressed.

Upon charging and discharging of power storage device10, the temperature of power storage module100rises. Power storage cells101A and101C are located at respective ends of power storage module100in stacking direction H. Thus, the heat of power storage cells101A and101C is more likely to be dissipated directly to case200.

On the other hand, power storage cell101B is located in the central area of power storage module100in stacking direction H. Thus, the heat of power storage cell101B is less likely to be dissipated directly to case200.

Power storage cell101B is in contact with flat plate510of restriction unit500. The heat of power storage cell101B is transferred to flat plate510. In width direction W, both ends of flat plate510reach respective filling portions400and401. Thus, the heat transferred to flat plate510is dissipated to cooling device20through filling portions400and401and side walls32and33. Note that the heat of power storage cell101C is also similarly dissipated to cooling device20through flat plate520, filling portions400and401and side walls32and33.

In this case, flat plate510and corrugated plate530are in contact with each other at an upper end portion (a top) of each curved portion532, and the area of contact therebetween is small. Similarly, flat plate520and corrugated plate530are in contact with each other at a lower end portion (a top) of each curved portion534, and the area of contact therebetween is small.

Thus, the heat transferred to flat plate510is suppressed from being transferred to flat plate520through corrugated plate530, and also, the heat transferred to flat plate520is suppressed from being transferred to flat plate510through corrugated plate530. Thereby, for example, even when the temperature of power storage cell101B becomes high, transfer of heat from power storage cell101B to power storage cell101C can be suppressed.

Even if heat is transferred from flat plate510to corrugated plate530when the temperature of power storage cell101B becomes high, the heat of corrugated plate530is mainly transferred to filling portions400and401since the ends of corrugated plate530reach respective filling portions400and401. Thereby, transfer of heat to flat plate520is suppressed.

Further, air exists between corrugated plate530and each of flat plates510,520. Due to low thermal conductivity of air, heat transfer between flat plates510and520is suppressed.

FIG. 5is a cross-sectional view showing a restriction unit500A according to the first modification of restriction unit500. Restriction unit500A includes a flat plate510, a flat plate520, a corrugated plate530, and a low rigidity material531. Low rigidity material531is filled between flat plate510and corrugated plate530and also filled between flat plate520and corrugated plate530. Low rigidity material531is an elastically deformable material such as resin. Note that low rigidity material531is lower in thermal conductivity than flat plates510,520, and corrugated plate530. Thereby, heat transfer between flat plates510and520can be suppressed.

FIG. 6is a cross-sectional view showing a restriction unit500B according to the second modification of restriction unit500. Restriction unit500B includes a flat plate510, a flat plate520, a corrugated plate530, a dilatancy material535, and an accommodation bag536.

Flat plates510and520, corrugated plate530, and dilatancy material535are accommodated in accommodation bag536. The thermal conductivity of dilatancy material535is preferably greater than 0 W/mK and equal to or less than 1 W/mK, for example.

Thus, when power storage module100deforms to expand in stacking direction H due to charging and discharging, dilatancy material535deforms as power storage module100deforms.

Accordingly, also in restriction unit500B, application of a high load to case200can be suppressed even when power storage module100deforms due to charging and discharging.

When power storage device10undergoes vibrations, the vibration speed of power storage device10is higher than the speed at which power storage module100deforms during charging and discharging. Thus, the rigidity of dilatancy material535is high, and dilatancy material535is less likely to deform. Thereby, restriction unit500B is less likely to deform, so that the vibration of power storage device10can be suppressed.

FIG. 7is a cross-sectional view showing a restriction unit500C according to the third modification of restriction unit500.

Restriction unit500C includes a flat plate510, a flat plate520, and a corrugated plate530C. In width direction W, both ends of corrugated plate530C are connected to case200. Thereby, the heat transferred to corrugated plate530C is readily dissipated to case200, and thus, the heat dissipation efficiency of restriction unit500C is improved. Note that corrugated plate530C is provided with a through hole into which bus bar102is inserted.

Restriction units500,500B, and500C each may be disposed between power storage cells101. In the description of the example in the present disclosure, an electrolytic solution is accommodated in each power storage cell, but the technique of the present disclosure can also be applicable to an example in which a solid-state battery is employed as each power storage cell.