JP7092536B2 - Endothermic sheet for assembled battery and assembled battery - Google Patents

Description

The present invention relates to, for example, a heat absorbing sheet for an assembled battery that is suitably used for an assembled battery that is a power source for an electric motor that drives an electric vehicle or a hybrid vehicle.

In recent years, from the viewpoint of environmental protection, the development of electric vehicles or hybrid vehicles driven by electric motors has been actively promoted. This electric vehicle or hybrid vehicle is equipped with an assembled battery in which a plurality of battery cells are connected in series or in parallel to serve as a power source for a driving electric motor.

Lithium-ion secondary batteries, which have higher capacity and higher output than lead storage batteries and nickel-hydrogen batteries, are mainly used for these battery cells, but due to internal short circuits and overcharging of the batteries, etc. When a thermal runaway occurs in one battery cell (that is, in an abnormal situation), heat propagation to another adjacent battery cell may cause a thermal runaway of another battery cell.

As a technique for suppressing the propagation of thermal runaway as described above, Patent Document 1 describes a power storage device including one or more power storage elements, which is one of the one or more power storage elements. The first plate material and the second plate material arranged on the side of the power storage element, the first plate material and the second plate material arranged so that the surfaces face each other are provided, and the first plate material and the second plate material are provided. A low thermal conductive layer (for example, an air layer), which is a layer of a substance having a lower thermal conductivity than the first plate material and the second plate material, is formed between the first plate material and the first plate material. Since the radiant heat or the radiant heat toward the first storage element is blocked by the two plates, and the heat transfer from one of the two plates to the other is suppressed by the low thermal conductive layer, the storage element and the other It is disclosed that effective insulation between the object and the object can be realized.

Further, as another technique for suppressing the propagation of thermal runaway, Patent Document 2 describes a battery housing containing an electrolytic solution and a thermal runaway suppressing substance provided in the battery housing. A secondary battery including a thermal runaway inhibitor accommodating structure accommodating the thermal runaway inhibitor, and various materials such as aluminum hydroxide hydrate are disclosed as examples of the thermal runaway inhibitor.

JP-A-2015-210113 Japanese Unexamined Patent Publication No. 2009-301798

On the other hand, in the case of performing a charge / discharge cycle on a battery cell made into an assembled battery (that is, during normal use), in order to fully exhibit the charge / discharge performance of the battery cell, the temperature of the battery cell surface should be kept below a predetermined value (that is, during normal use). For example, it is necessary to maintain the temperature below 150 ° C.
However, in Patent Document 1, since a heat insulating layer is provided between a plurality of battery cells in order to suppress heat propagation during thermal runaway, it is possible to effectively cool the battery cells that generate heat during the charge / discharge cycle. It wasn't a thing.
Further, since the purpose of Patent Document 2 is only to promptly put the lithium ion secondary battery into a safe state when an abnormal situation occurs, as a solution to the problem, aluminum hydroxide hydrate is used. It is only assumed that a thermal runaway inhibitor that releases water to cool the surroundings under high temperature (for example, 200 ° C. or higher) conditions is contained in the battery. Therefore, it cannot be said that it is always sufficient to effectively cool the battery cell that generates heat during the charge / discharge cycle.

The present invention has been made by paying attention to such a situation, and suppresses heat propagation between each battery cell at the time of abnormality in constructing an assembled battery in which a plurality of battery cells are connected in series or in parallel. However, it is an object of the present invention to provide an endothermic sheet for an assembled battery capable of cooling each battery cell during normal use.

In order to achieve the above object, the gist of the heat absorbing sheet for an assembled battery according to one aspect of the present invention is a set in which a plurality of battery cells are arranged via the heat absorbing sheet and the plurality of battery cells are directly or in parallel connected. A heat absorbing sheet used for a battery, which contains two or more substances having different dehydration temperatures, and at least one of the substances can be dehydrated during normal use of the battery cell, and at least one of the substances. One is characterized in that it can be dehydrated in the event of an abnormality in the battery cell.

In a preferred embodiment of the heat-absorbing sheet for an assembled battery, the substance that can be dehydrated during normal use is a dehydrating agent that can be dehydrated at a temperature of 150 ° C. or lower, and the substance that can be dehydrated at the abnormal time starts thermal decomposition. It is an inorganic hydrate having a temperature of 200 ° C. or higher.
In a preferred embodiment of the heat absorbing sheet for an assembled battery, the dehydrating agent is silica gel, active alumina, activated charcoal, zeolite, ion exchange resin, sulfate hydrate, sulfite hydrate, phosphate hydrate, nitrate hydrate. , Acetate hydrate, metal hydrate, at least one of the group.
In a preferred embodiment of the endothermic sheet for assembled batteries, the dehydrating agent is zeolite.
In a preferred embodiment of the heat absorbing sheet for an assembled battery, the inorganic hydrate is aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide and gallium hydroxide. At least one of the group consisting of.
In a preferred embodiment of the endothermic sheet for assembled batteries, the inorganic hydrate is aluminum hydroxide.
In a preferred embodiment of the endothermic sheet for an endothermic battery, the more the endothermic sheet is from the center in the thickness direction to both ends, the larger the content of the substance that can be dehydrated during normal use is, and the more the endothermic sheet is in the thickness direction. The more from both ends to the center, the greater the content of the substance that can be dehydrated at the time of the abnormality.
In a preferred embodiment of the endothermic sheet for an assembled battery, it is formed on both sides of a first endothermic layer containing a substance that can be dehydrated at the time of abnormality as a main component and the first endothermic layer, and is dehydrated at the time of normal use. It has a second endothermic layer whose main component is a possible substance.

Further, the gist of the assembled battery according to one aspect of the present invention is characterized in that a plurality of battery cells are arranged via the above-mentioned endothermic sheet for assembled batteries, and the plurality of battery cells are connected in series or in parallel. And.

According to the endothermic sheet for an assembled battery according to the present invention, when constituting an assembled battery in which a plurality of battery cells are connected in series or in parallel, it is normally used while suppressing heat propagation between the battery cells in an abnormal situation. It is possible to provide an endothermic sheet for an assembled battery capable of cooling each battery cell at the time.

FIG. 1 is a cross-sectional view schematically showing a configuration example of an endothermic sheet for an assembled battery according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing another configuration example of the endothermic sheet for an assembled battery according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing a configuration example of an endothermic sheet for an assembled battery according to a second embodiment of the present invention. FIG. 4 is a cross-sectional view schematically showing another configuration example of the endothermic sheet for an assembled battery according to the second embodiment of the present invention. FIG. 5 is a cross-sectional view schematically showing a configuration example of an assembled battery to which the endothermic sheet for an assembled battery according to the first embodiment of the present invention is applied. FIG. 6 is a graph plotting the temperature change on the surface of the battery cell, which is a heat source, with respect to the elapsed time when the endothermic sheets of Example 1, Comparative Example 1 and Comparative Example 2 are heated by a heater (heater temperature: 150 ° C.). be. FIG. 7 plots the temperature change of the surface of the adjacent battery cell with respect to the elapsed time when the endothermic sheets of Example 1, Comparative Example 1, Comparative Example 2 and Reference Example 1 are heated by a heater (heater temperature: 700 ° C.). It is a graph.

The present inventors can cool each battery cell in normal use in which relatively low temperature heat is generated, while suppressing heat propagation between the battery cells in an abnormal state in which high temperature heat is generated. We have been diligently studying to provide heat-absorbing sheets for assembled batteries.

As a result, two or more substances having different dehydration temperatures are contained, and at least one of the substances can be dehydrated during normal use of the battery cell, and at least one of the substances is the battery cell. It has been found that the above-mentioned problems can be solved by interposing a heat-absorbing sheet that can be dehydrated in the event of an abnormality between the battery cells arranged in the assembled battery.

That is, by containing a substance that can be dehydrated during normal use when the temperature of the battery cell is relatively low, the substance releases water when the temperature of the battery cell rises at a relatively low temperature, so that during normal use The battery cell in the above can be effectively cooled.

Further, since the temperature range of the battery cell during normal use is generally from room temperature (about 20 ° C) to a maximum of about 150 ° C, dehydration is performed at a temperature of 150 ° C or lower as a substance that can be dehydrated during normal use. It has also been found that it is preferable to use a possible dehydrating agent.

On the other hand, by containing a substance that can be dehydrated when the temperature of the battery cell becomes high abnormally, when the temperature of the battery cell rises abnormally, the substance releases water, so that each battery cell at the time of abnormality is released. The heat transfer between them can be suppressed.

Further, since the temperature range of the battery cell at the time of abnormality is generally 200 ° C. or higher, it is preferable to use an inorganic hydrate having a thermal decomposition start temperature of 200 ° C. or higher as a substance that can be dehydrated at the time of abnormality. I also found.

In addition, in order to cool the battery cells during normal use, a space for releasing the generated heat to the outside is provided between the battery cells, and in order to suppress heat propagation between the battery cells in an abnormal situation. Since the space is not provided between the battery cells, it is not necessary to take an extremely large distance between the battery cells. Therefore, it is possible to reduce the thickness of the entire heat absorbing sheet (for example, 5 mm or less), and as a result, the volume energy of the assembled battery is ensured while ensuring the safety of the assembled battery and sufficient charge / discharge performance of the battery cell. It is also possible to improve the density.

Hereinafter, embodiments of the present invention (the present embodiment) will be described in detail with reference to the drawings. In the following, "to" means that the value is equal to or more than the lower limit value and is equal to or less than the upper limit value.

(First Embodiment)
First, the endothermic sheet for an assembled battery according to the first embodiment of the present invention will be described. The first embodiment is a case where the endothermic sheet is a single layer.
<Basic configuration of endothermic sheet for assembled batteries>
FIG. 1 is a cross-sectional view schematically showing a configuration example of the endothermic sheet 10 for an assembled battery according to the first embodiment. The endothermic sheet 10 for an assembled battery according to the present embodiment contains a dehydrating agent 22 that can be dehydrated at a temperature of 150 ° C. or lower, and an inorganic hydrate 24 having a thermal decomposition start temperature of 200 ° C. or higher.

The endothermic sheet for an assembled battery according to the present embodiment has a dehydrating agent 22 that can be dehydrated within a temperature range from normal temperature (about 20 ° C.) to a maximum of about 150 ° C., which is the temperature range of the battery cell 20 during normal use. .. Then, when the charge / discharge cycle during normal use as the battery cell 20 is performed, when the temperature of the battery cell 20 rises at a relatively low temperature, the dehydrating agent 22 releases water, so that the battery cell during normal use 20 can be effectively cooled.

Further, the endothermic sheet for an assembled battery according to the present embodiment has an inorganic hydrate 24 having a thermal decomposition start temperature within a temperature range of 200 ° C. or higher, which is the temperature range of the battery cell 20 at the time of abnormality. Then, when thermal runaway occurs as the battery cell 20 abnormally and the temperature of the battery cell 20 rises abnormally, an endothermic reaction occurs due to the decomposition of the inorganic hydrate 24, so that each battery cell 20 at the time of abnormality occurs. The heat transfer between them can be effectively suppressed.

As a specific usage pattern of the endothermic sheet 10 for assembled batteries, as shown in FIG. 5, a plurality of battery cells 20 are arranged via the endothermic sheet 10 for assembled batteries, and the plurality of battery cells 20 are directly connected to each other. Alternatively, the assembled battery 100 is configured by being stored in the battery case 30 in a state of being connected in parallel (the connected state is not shown). As the battery cell 20, for example, a lithium ion secondary battery is preferably used, but the battery cell 20 is not particularly limited to this, and can be applied to other secondary batteries.

<Details of endothermic sheet for assembled battery>
Next, each component of the endothermic sheet 10 for an assembled battery will be described in detail.

First, the dehydrating agent 22 constituting the endothermic sheet 10 for an assembled battery will be described. The dehydrating agent 22 can be dehydrated at a temperature of 150 ° C. or lower. Examples of the dehydrating agent 22 include water adsorbents such as silica gel, active alumina, activated charcoal, zeolite, and ion exchange resin, or sulfate hydrate, sulfite hydrate, phosphate hydrate, and nitrate hydrate. Substances, acetate hydrates, metal hydrates and the like can be mentioned. These dehydrating agents 22 may be used alone or in combination of two or more.

Here, examples of the sulfate hydrate include ammonium aluminum sulfate dodecahydrate, sodium aluminum sulfate dodecahydrate, aluminum sulfate 27 hydrate, aluminum sulfate 18 hydrate, aluminum sulfate hexahydrate, and sulfuric acid. Aluminum decahydrate, aluminum sulfate hexahydrate, potassium aluminum sulfate dodecahydrate, iron sulfate heptahydrate, iron sulfate 9 hydrate, potassium iron sulfate dodecahydrate, magnesium sulfate heptahydrate, Examples thereof include sodium sulfate decahydrate, nickel sulfate hexahydrate, zinc sulfate heptahydrate, beryllium sulfate tetrahydrate, zirconium sulfate tetrahydrate and the like.
Examples of the sulfite hydrate include zinc sulfite dihydrate, sodium sulfite heptahydrate and the like.
Examples of the phosphate hydrate include aluminum phosphate dihydrate, cobalt phosphate octahydrate, magnesium phosphate octahydrate, magnesium ammonium phosphate hexahydrate, and magnesium hydrogen phosphate trihydrate. Examples thereof include Japanese products, magnesium hydrogen phosphate heptahydrate, zinc phosphate tetrahydrate, zinc dihydrogen phosphate dihydrate and the like.
Examples of the nitrate hydrate include aluminum nitrate hexahydrate, zinc nitrate hexahydrate, calcium nitrate tetrahydrate, cobalt nitrate hexahydrate, bismuth nitrate pentahydrate, and zirconium nitrate pentahydrate. Examples thereof include cerium nitrate hexahydrate, iron nitrate hexahydrate, iron nitrate 9 hydrate, nickel nitrate hexahydrate, magnesium nitrate hexahydrate and the like.
Examples of the acetate hydrate include zinc acetate dihydrate, cobalt acetate tetrahydrate and the like.
Examples of the metal hydrate include chloride salts such as cobalt chloride hexahydrate and iron chloride tetrahydrate, and hosand (sodium tetraborate pentahydrate, sodium tetraborate decahydrate). , Disodium octaborate tetrahydrate, zinc borate 3.5 hydrate and other borates and the like.

For example, if zeolite having a large amount of water adsorbed on the high temperature side (75 ° C. to 150 ° C.) in the temperature range of 150 ° C. or lower and silica gel having a small amount of water adsorbed on the high temperature side are used in combination, the temperature rises. This is preferable because the battery cell 20 can be cooled in a wide temperature range.

Among the dehydrating agents 22, zeolite is particularly preferable from the viewpoint of being able to release more water and having a wide dehydration temperature range. The zeolite is not particularly limited in type, and examples thereof include β-type zeolite, Y-type zeolite, ferrierite, ZSM-5 type zeolite, mordenite, forgesite, zeolite A, and zeolite L.

Zeolites are aluminosilicates with a three-dimensional network structure. Since zeolite that adsorbs water is stably present, it usually adsorbs water or the like in the gaps of the three-dimensional network structure under normal temperature conditions. However, when heat above a certain temperature is applied, the water adsorbed on the zeolite is desorbed from the zeolite.
However, since zeolite that does not adsorb water is unstable, dehydrated zeolite has a high adsorption action, so that it adsorbs water again after the temperature drops.

For example, the dehydrating agent 22 that can be dehydrated at a temperature of 150 ° C. or lower, such as zeolite, has a temperature range that greatly overlaps with the rising temperature of the surface of the battery cell 20 when the charge / discharge cycle is performed. As the temperature of the cell 20 rises, the battery cell 20 can be effectively cooled by releasing water.

Further, particularly in the case of zeolite, after the battery cell 20 is cooled and the temperature of the dehydrating agent 22 in the endothermic sheet 10 for the assembled battery drops, the moisture around the endothermic sheet 10 for the assembled battery is adsorbed again. Therefore, it can be reused as many times as necessary for repeated charge / discharge cycles.

As for the blending amount of the dehydrating agent 22, the preferable upper limit is 90% by mass, and the more preferable upper limit is 65% by mass with respect to the total mass of the materials constituting the endothermic sheet 10 for assembled batteries.
On the other hand, the preferable lower limit of the blending amount of the dehydrating agent 22 is 10% by mass, and the more preferable lower limit is 35% by mass. If this blending amount is less than 10% by mass, a sufficient dehydration effect may not be obtained. Further, if this compounding amount exceeds 90% by mass, it may not be possible to maintain sufficient strength as the endothermic sheet 10.

Subsequently, the inorganic hydrate 24 constituting the endothermic sheet 10 for the assembled battery will be described. The inorganic hydrate 24 has a thermal decomposition start temperature of 200 ° C. or higher.
Examples of the inorganic hydrate 24 include aluminum hydroxide (Al (OH) ₃ ), magnesium hydroxide (Mg (OH) ₂ ), calcium hydroxide (Ca (OH) ₂ ), and zinc hydroxide (Zn (OH)). ) ₂ ), iron hydroxide (Fe (OH) ₂ ), manganese hydroxide (Mn (OH) ₂ ), zinc hydroxide (Zr (OH) ₂ ), gallium hydroxide (Ga (OH) ₃ ), etc. Be done.
These inorganic hydrates 24 may be used alone or in combination of two or more.

The thermal decomposition start temperature of aluminum hydroxide is about 200 ° C., the thermal decomposition start temperature of magnesium hydroxide is about 330 ° C., the thermal decomposition start temperature of calcium hydroxide is about 580 ° C., and zinc hydroxide The thermal decomposition start temperature of iron hydroxide is about 200 ° C, the thermal decomposition start temperature of iron hydroxide is about 350 ° C, the thermal decomposition start temperature of manganese hydroxide is about 300 ° C, and the thermal decomposition start temperature of zirconium hydroxide. Is about 300 ° C., and the thermal decomposition start temperature of gallium hydroxide is about 300 ° C.
By using two or more kinds of inorganic hydrates 24 having different thermal decomposition start temperatures in combination, the battery cell 20 whose temperature has risen can be cooled in a wide temperature range, and the heat between the battery cells during thermal runaway can be cooled. It is preferable because it can effectively suppress the propagation of.

For example, in the case of aluminum hydroxide, about 35% of water of crystallization is contained in aluminum hydroxide, and as shown in the following formula, the water of crystallization is released during thermal decomposition to provide a flame-extinguishing function (endothermic reaction). Can be demonstrated.
2Al (OH) ₃ → Al ₂ O ₃ + 3H ₂ O
With this function, the high-temperature heat generated in the battery cell 20 can be absorbed, and the calorific value of the battery cell 20 can be reduced.

For example, the inorganic hydrate 24 having a thermal decomposition temperature of 200 ° C. or higher, such as aluminum hydroxide, has a large overlap in temperature range with the temperature rise on the surface of the battery cell 20 when the battery cell 20 undergoes thermal runaway. Therefore, as the temperature of the battery cell 20 rises at the time of abnormality, a dehydration reaction (heat absorption reaction) occurs due to thermal decomposition, so that heat propagation between the battery cells can be effectively suppressed.

In particular, in the case of aluminum hydroxide, the thermal decomposition start temperature is lower (thermal decomposition start temperature: about 200 ° C.) in the inorganic hydrate 24, so that it is in the initial stage (relatively lower) when the battery cell is abnormal. The battery cell 20 can be cooled from the above temperature), which is preferable.

As for the blending amount of the inorganic hydrate 24, a preferable upper limit is 90% by mass, and a more preferable upper limit is 65% by mass with respect to the total mass of the materials constituting the endothermic sheet 10 for assembled batteries.
On the other hand, the preferable lower limit of the blending amount of the dehydrating agent 22 is 10% by mass, and the more preferable lower limit is 35% by mass. If this blending amount is less than 10% by mass, a sufficient dehydration effect may not be obtained. Further, if this compounding amount exceeds 90% by mass, it may not be possible to maintain sufficient strength as the endothermic sheet 10.

The endothermic sheet 10 for an assembled battery may contain inorganic fibers or pulp fibers for the purpose of improving the strength at the time of molding.

Examples of the inorganic fiber include silica-alumina fiber, alumina fiber, silica fiber, rock wool, alkaline earth silicate fiber, glass fiber, zirconia fiber and potassium titanate whisker fiber. These inorganic fibers are preferable in terms of heat resistance, strength, availability, and the like. The above-mentioned inorganic fibers may be used alone or in combination of two or more. Among the above-mentioned inorganic fibers, silica-alumina fiber, alumina fiber, silica fiber, rock wool, alkaline earth silicate fiber, and glass fiber are particularly preferable from the viewpoint of handleability.

The cross-sectional shape of the inorganic fiber is not particularly limited, and examples thereof include a circular cross section, a flat cross section, a hollow cross section, a polygonal cross section, and a core sheath cross section. Among them, the modified cross-section fiber having a hollow cross-section, a flat cross-section or a polygonal cross-section can be preferably used because the heat insulating property is slightly improved.

The preferable lower limit of the average fiber length of the inorganic fiber is 0.1 mm, and the more preferable lower limit is 0.5 mm. On the other hand, the preferable upper limit of the average fiber length of the inorganic fiber is 50 mm, and the more preferable upper limit is 10 mm. If the average fiber length of the inorganic fibers is less than 0.1 mm, the inorganic fibers are less likely to be entangled with each other, and the mechanical strength of the obtained endothermic sheet 10 may decrease. On the other hand, if it exceeds 50 mm, although the reinforcing effect can be obtained, the inorganic fibers cannot be closely entangled with each other, or the inorganic fibers are curled up by only a single inorganic fiber, which tends to generate continuous voids, so that the heat insulating property is improved. May cause deterioration.

The preferable lower limit of the average fiber diameter of the inorganic fiber is 1 μm, the more preferable lower limit is 2 μm, and the further preferable lower limit is 3 μm. On the other hand, the preferable upper limit of the average fiber diameter of the inorganic fiber is 10 μm, and the more preferable upper limit is 7 μm. If the average fiber diameter of the inorganic fiber is less than 1 μm, the mechanical strength of the inorganic fiber itself may decrease. Further, from the viewpoint of the influence on the health of the human body, the average fiber diameter of the inorganic fibers is preferably 3 μm or more. On the other hand, if the average fiber diameter of the inorganic fiber is larger than 10 μm, solid heat transfer using the inorganic fiber as a medium may increase and the heat insulating property may be deteriorated, and the moldability of the heat absorbing sheet 10 may be deteriorated. There is.

The inorganic fiber or pulp fiber can be used as needed in the range of 10 to 70% by mass with respect to the total weight of the materials constituting the endothermic sheet 10.

As a material constituting the endothermic sheet 10, an organic binder may be used as needed. This organic binder is useful for the purpose of improving the strength at the time of molding, and for example, a polymer flocculant, an acrylic emulsion, or the like can be preferably used.
As the blending amount of the organic binder, it can be used as needed in the range of 0.5 to 5.0% by mass with respect to the total weight of the materials constituting the endothermic sheet 10.

The thickness of the endothermic sheet 10 is not particularly limited, but is preferably in the range of 0.05 to 5 mm. If the thickness of the endothermic sheet 10 is less than 0.05 mm, sufficient mechanical strength cannot be imparted to the endothermic sheet 10. On the other hand, if the thickness of the endothermic sheet 10 exceeds 5 mm, the molding of the endothermic sheet 10 itself may become difficult.

As a specific combination of the dehydrating agent 22 and the inorganic hydrate 24 used in the heat absorbing sheet 10, the amount of water adsorbed is high even at a relatively high temperature (about 100 ° C. to 150 ° C.) in the dehydrating agent 22. The above zeolite and aluminum hydroxide (thermal decomposition start temperature: about 200 ° C.) having a lower thermal decomposition start temperature among the inorganic hydrates 24 are preferable.
This is because the battery cell 20 can be effectively cooled even in the boundary temperature range (about 150 ° C. to 200 ° C.) between the temperature range during normal use and the temperature range at the time of abnormality in the battery cell 20. preferable.

By the way, in FIG. 1, an example in which the dehydrating agent 22 and the inorganic hydrate 24 are uniformly dispersed is shown, but as shown in FIG. 2, the thickness direction of the heat absorbing sheet 10 (the vertical direction in the figure). ) The more from the center to both ends, the larger the content of the substance that can be dehydrated in normal use, that is, the dehydrating agent 22, and the more toward the center from both ends in the thickness direction of the heat absorbing sheet 10, the more dehydrated in an abnormal situation. It is preferable that the content of a possible substance, that is, the inorganic hydrate 24 is large.
The reason is that, as shown in FIG. 5, since both ends of the endothermic sheet 10 are close to the battery cell 20, it is necessary to efficiently cool the battery cell 20 during normal use of the battery cell 20. Therefore, it is preferable that more dehydrating agents 22 that can sufficiently exert their effects during normal use are present on both ends in the endothermic sheet 10.

On the other hand, as shown in FIG. 5, battery cells 20 are present on both ends of the endothermic sheet 10 in the thickness direction, and in the event of an abnormality in the battery cells 20, thermal runaway may occur from any of the battery cells 20. There is sex. Therefore, in order to effectively suppress the heat propagation between the battery cells 20 due to the thermal runaway generated from the battery cells 20, the inorganic hydrate 24 capable of exerting an effect at the time of abnormality is contained in the endothermic sheet 10. It is preferable that a large amount of the battery is present on the central side of the battery.

(Second embodiment)
Subsequently, the endothermic sheet for an assembled battery according to the second embodiment of the present invention will be described. The second embodiment is a case where the endothermic sheet is a multi-layer (laminated body).

FIG. 3 is a cross-sectional view schematically showing a configuration example of the endothermic sheet 10 for an assembled battery according to the second embodiment. The endothermic sheet 10 for an assembled battery according to the present embodiment is formed as an intermediate layer on both sides of a first endothermic layer 14 containing a substance that can be dehydrated in an abnormal state, that is, an inorganic hydrate 24 as a main component. It is composed of three layers having a substance that can be dehydrated during normal use, that is, a second endothermic layer 12 containing a dehydrating agent 22 as a main component.
The main component means the most abundant component, and the content is usually more than 50% by mass, preferably more than 70% by mass, and more preferably more than 90% by mass.

According to the present embodiment, as described above, the content of the dehydrating agent 22 is larger toward both ends from the center in the thickness direction of the endothermic sheet 10, and the endothermic sheet 10 is from both ends in the thickness direction to the center. It is preferable because it is possible to easily realize a structure in which the content of the inorganic hydrate 24 increases toward the distance.

Further, FIG. 3 shows an example in which the first endothermic layer 14 is composed of only the inorganic hydrate 24 and the second endothermic layer 12 is composed of only the dehydrating agent 22. For example, FIG. 4 shows an example. As shown, although both the first endothermic layer 14 and the second endothermic layer 12 contain the dehydrating agent 22 and the inorganic hydrate 24, the first endothermic layer 14 contains the inorganic hydrate 24. It may be contained as a main component, and the second heat absorbing layer 12 may contain the dehydrating agent 22 as the main component.

(Manufacturing method of endothermic sheet for assembled battery)
Subsequently, a method for manufacturing the endothermic sheet 10 for an assembled battery will be described in detail.

The endothermic sheet 10 according to the present embodiment is manufactured by molding a material composed of at least the dehydrating agent 22 and the inorganic hydrate 24 by a dry molding method or a wet molding method. Hereinafter, a manufacturing method when the endothermic sheet 10 is obtained by each molding method will be described.

[When manufacturing using drywall]
First, in the dry molding method, the dehydrating agent 22 and the above-mentioned inorganic hydrate 24, and if necessary, inorganic fibers, pulp fibers, or organic binders are charged into a mixer such as a V-type mixer at a predetermined ratio. After the materials charged in the mixer are sufficiently mixed, the mixture is charged into a predetermined mold and pressed to obtain an endothermic sheet 10. At the time of pressing, it may be heated if necessary.

The press pressure is preferably in the range of 0.98 to 9.80 MPa. If the press pressure is less than 0.98 MPa, the obtained endothermic sheet 10 may not be able to maintain its strength and may collapse. On the other hand, if the press pressure exceeds 9.80 MPa, the workability may be lowered due to excessive compression, and the bulk density may be increased, so that the solid heat transfer may be increased and the heat insulating property may be lowered.

[When manufacturing using the wet molding method]
Subsequently, in the wet molding method, the dehydrating agent 22 and the above-mentioned inorganic hydrate 24, and if necessary, inorganic fibers, pulp fibers, or an organic binder are mixed and stirred in water to sufficiently disperse them, and then the flocculant is applied. Add to obtain primary agglomerates. Next, if necessary, an emulsion of an organic elastic substance or the like is added to the water within a predetermined range, and then a polymer flocculant is added to obtain a slurry containing aggregates.

Next, the slurry containing the agglomerates is put into a predetermined mold to obtain a wet endothermic sheet 10. By drying the obtained endothermic sheet 10, the desired endothermic sheet 10 can be obtained.

As described above, the endothermic sheet 10 can be obtained by either a dry molding method or a wet molding method, but it is preferable to use the wet molding method from the viewpoint of ease of integral molding and mechanical strength.

As shown in FIG. 2, the content of the dehydrating agent 22 is larger toward both ends from the center in the endothermic sheet 10 in the thickness direction (upper and lower directions in the figure), and both ends in the endothermic sheet 10 in the thickness direction. The endothermic sheet 10 in which the content of the inorganic hydrate 24 increases toward the center is, for example, with the first endothermic layer 14 containing the inorganic hydrate 24 as a main component, as shown in FIG. It can be obtained by preparing each of the second endothermic layers 12 containing the dehydrating agent 22 as a main component and laminating the second endothermic layer 12 on both surfaces of the first endothermic layer 14.

Further, as shown in FIGS. 3 and 4, a first endothermic layer 14 having an inorganic hydrate 24 as a main component as an intermediate layer and a second endothermic layer 14 formed on both sides thereof and having a dehydrating agent 22 as a main component are formed. In the endothermic sheet 10 composed of three layers having the endothermic layer 12, after the first endothermic layer 14 and the second endothermic layer 12 are produced according to the above manufacturing methods, these layers are in a wet state. It can be obtained by a pressure press or a method of adhering these members with an adhesive after drying.

Hereinafter, examples of the endothermic sheet for an assembled battery according to the present embodiment will be described, but the present invention is not limited to these examples.

<Example 1>
Aluminum hydroxide (Al (OH) ₃ ) powder (average particle size: 1 μm) is 40% by mass, zeolite powder (average particle size: 7 μm) is 40% by mass, rock wool is 10% by mass as inorganic fiber, and pulp fiber is used. 9% by mass and 1% by mass of the polymer flocculant were added, and the mixture was sufficiently stirred and mixed to prepare a slurry. The above slurry was machined to obtain an endothermic sheet for assembled batteries having a thickness of 2 mm.
It was confirmed that the thermal decomposition start temperature of the aluminum hydroxide used was 200 ° C., and the zeolite was dehydratable at a temperature of 150 ° C. or lower.

<Comparative Example 1>
A sheet having a thickness of 2 m composed of alkaline earth silicate (AES) fiber was prepared and used as an endothermic sheet for an assembled battery.

<Comparative Example 2>
80% by mass of the same zeolite powder (average particle size: 7 μm) used in Example 1, 10% by mass of rock wool as inorganic fibers, 9% by mass of pulp fibers, and 1% by mass of polymer flocculants were added. , Sufficient stirring and mixing was performed to prepare the slurry. The above slurry was machined to obtain an endothermic sheet for assembled batteries having a thickness of 2 mm.

<Reference example 1>
80% by mass of the same aluminum hydroxide (Al (OH) ₃ ) powder (average particle size: 1 μm) used in Example 1, 10% by mass of rock wool as inorganic fibers, 9% by mass of pulp fibers, 1% by mass of the polymer flocculant was added, and the mixture was sufficiently stirred and mixed to prepare a slurry. The above slurry was machined to obtain an endothermic sheet for assembled batteries having a thickness of 2 mm.

A metal plate simulating a battery cell as a heat source is arranged so as to be in contact with one surface of the endothermic sheet for assembled batteries obtained in Example 1, Comparative Example 1 and Comparative Example 2, and further adjacent to the metal plate. The heater was arranged so as to. Further, a thermocouple was attached to the metal plate and heated so that the heater temperature became 150 ° C., and the temperature change on the surface of the battery cell (metal plate) serving as a heat source with respect to the elapsed time was measured.
FIG. 6 shows a graph plotting the temperature change on the surface of the battery cell as a heat source with respect to the elapsed time in Example 1, Comparative Example 1 and Comparative Example 2.

Further, a heater is arranged so as to be adjacent to one surface of the endothermic sheet for assembled batteries obtained in Example 1, Comparative Example 1, Comparative Example 2 and Reference Example 1, and a battery cell adjacent to the other surface is simulated. The metal plate was placed. Further, a thermocouple was arranged on the metal plate and heated so that the heater temperature became 700 ° C., and the temperature change on the surface of the adjacent battery cell (metal plate) with respect to the elapsed time was measured.
FIG. 7 shows a graph plotting the temperature change of the surface of the adjacent battery cell with respect to the elapsed time in Example 1, Comparative Example 1, Comparative Example 2 and Reference Example 1.

As shown in the results of FIG. 6, the endothermic sheet for the assembled battery of Example 1 in which zeolite and aluminum hydroxide are used in combination has the maximum endothermic surface of the cell surface as a heat source as in the endothermic sheet of Comparative Example 2 in which only zeolite is used. Although the temperature could not be kept low, the maximum temperature of the cell surface as a heat source could be kept lower than that of the endothermic sheet of Comparative Example 1 using AES.

Further, as shown in the results of FIG. 7, the endothermic sheet of Example 1 was able to significantly reduce the maximum temperature of the adjacent cell surface as compared with the endothermic sheets of Comparative Example 1 and Comparative Example 2. When the endothermic sheet of Example 1 and the endothermic sheet of Reference Example 1 using only aluminum hydroxide were compared, the maximum temperature of the adjacent cell surface was almost the same.

From the above, the endothermic sheet of Example 1 effectively cools the battery cells during normal use as a battery cell, and at the same time, effectively propagates heat between the battery cells during an abnormality as a battery cell. It was experimentally shown that it can be suppressed.

10 Endothermic sheet for batteries 12 Second heat absorbing layer 14 First heat absorbing layer 20 Battery cell 22 Dehydrating agent (moisture adsorbent)
24 Inorganic hydrate 30 Battery case 100 sets Battery

Claims (8)

A heat absorbing sheet used for an assembled battery in which a plurality of battery cells are arranged via a heat absorbing sheet and the plurality of battery cells are directly or in parallel connected.
It contains two or more substances with different dehydration temperatures, and at least one of the substances can be dehydrated during normal use of the battery cell, and at least one of the substances is at the time of abnormality of the battery cell. Can be dehydrated in
The more from the center in the thickness direction to both ends of the endothermic sheet, the greater the content of the substance that can be dehydrated during normal use, and the more
An endothermic sheet for an assembled battery in which the content of a substance that can be dehydrated in the event of an abnormality increases from both ends in the thickness direction toward the center of the endothermic sheet. A second endothermic layer whose main component is a substance that can be dehydrated at the time of abnormality and which is formed on both sides of the first endothermic layer and whose main component is a substance that can be dehydrated during normal use. The endothermic sheet for an assembled battery according to claim 1 , which has a layer. The substance that can be dehydrated during normal use is a dehydrating agent that can be dehydrated at a temperature of 150 ° C. or lower, and the substance that can be dehydrated during abnormal conditions is an inorganic hydrate having a thermal decomposition start temperature of 200 ° C. or higher. , The heat absorbing sheet for an assembled battery according to claim 1 or 2 . The dehydrating agent comprises silica gel, active alumina, activated charcoal, zeolite, ion exchange resin, sulfate hydrate, sulfite hydrate, phosphate hydrate, nitrate hydrate, acetate hydrate, and metal hydrate. The heat absorbing sheet for an assembled battery according to claim 3 , which is at least one of the groups. The endothermic sheet for an assembled battery according to claim 4 , wherein the dehydrating agent is zeolite. The inorganic hydrate is at least one of the group consisting of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide and gallium hydroxide. Item 5. The heat absorbing sheet for an assembled battery according to any one of Items 3 to 5 . The endothermic sheet for an assembled battery according to claim 6 , wherein the inorganic hydrate is aluminum hydroxide. An assembled battery in which the plurality of battery cells are arranged via the endothermic sheet for assembled batteries according to any one of claims 1 to 7 , and the plurality of battery cells are connected in series or in parallel.

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