JP2020031012A - Heat-absorbing sheet for battery pack and assembled battery - Google Patents

Abstract

To provide a heat-absorbing sheet for a battery pack capable of effectively suppressing the propagation of heat between a plurality of battery cells when a battery pack in which the battery cells are connected in series or in parallel is formed.SOLUTION: In a heat-absorbing sheet 10 used for a battery pack 100 in which a plurality of battery cells 30 are arranged via a heat absorbing sheet 10 and the plurality of battery cells 30 are connected in series or in parallel, and the heat-absorbing sheet includes endothermic materials 22 and 24 with two or more particle size distribution peaks.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat absorbing sheet for a battery pack and a battery pack preferably used for a battery pack serving as a power source of an electric motor for driving an electric vehicle or a hybrid vehicle, for example.

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

  These battery cells mainly use lithium-ion secondary batteries that have higher capacity and higher output than lead-acid batteries and nickel-metal hydride batteries, but due to internal short-circuiting and overcharging of the batteries, etc. When a thermal runaway occurs in one battery cell, heat may propagate to another adjacent battery cell, causing a thermal runaway of another battery cell.

  As a technique for suppressing the propagation of the thermal runaway as described above, for example, Patent Document 1 discloses a power storage device including one or more power storage elements, which is one of the one or more power storage elements. A first plate member and a second plate member arranged on the side of the first power storage element, including a first plate member and a second plate member arranged so that their surfaces face each other, the first plate member and the second plate member. A first heat storage element is formed between the two plate members by forming a low thermal conductive layer (for example, an air layer) that is a layer of a substance having a lower thermal conductivity than the first plate member and the second plate member. Radiant heat from the device, or radiant heat toward the first power storage element is blocked by the two plates, and the transfer of heat from one of the two plates to the other is suppressed by the low heat conductive layer. To provide effective insulation between the object and other objects Discloses that possible.

JP 2015-211013 A

  However, in Patent Literature 1, although it is described that the radiation heat from a certain power storage element or the radiation heat directed to a certain power storage element can be cut off and the heat transfer between two plate materials can be suppressed by the low heat conduction layer, the heat source becomes a heat source. When the amount of heat generated from each power storage element was large, the heat insulating effect was not always sufficient.

  The present invention has been made in view of such circumstances, and when configuring a battery pack in which a plurality of battery cells are connected in series or in parallel, the propagation of heat between the battery cells is effectively suppressed. It is an object of the present invention to provide a heat-absorbing sheet for a battery pack and a battery pack which can be used.

  In order to achieve the above object, the gist of the heat absorbing sheet for an assembled battery according to one embodiment of the present invention is a group in which a plurality of battery cells are arranged via a heat absorbing sheet, and the plurality of battery cells are connected in series or in parallel. A heat-absorbing sheet for use in a battery, wherein the peak of the particle size distribution contains two or more heat-absorbing materials.

  In a preferred embodiment of the heat absorbing sheet for an assembled battery, the heat absorbing material includes a first heat absorbing material having a large average particle diameter and a second heat absorbing material having a small average particle diameter. The mixing ratio of the second heat absorbing material is from 90:10 to 10:90 by mass.

  In a preferred embodiment of the heat absorbing sheet for an assembled battery, the content of the first heat absorbing material is smaller than the content of the second heat absorbing material.

  In a preferred embodiment of the heat absorbing sheet for a battery pack, the content of the first heat absorbing material is larger than the content of the second heat absorbing material.

  In a preferred embodiment of the heat absorbing sheet for an assembled battery, the first heat absorbing material has an average particle diameter of 5 μm or more and 100 μm or less, and the second heat absorbing material has an average particle diameter of 0.1 μm or more and less than 5 μm. is there.

  In a preferred embodiment of the heat absorbing sheet for an assembled battery, the heat absorbing material is an inorganic hydrate and / or a dehydrating agent.

  In a preferred embodiment of the heat-absorbing sheet for an assembled battery, the heat-absorbing material essentially contains the inorganic hydrate, and the inorganic hydrate is an inorganic hydrate having a thermal decomposition initiation temperature of 200 ° C or higher. .

  In a preferred embodiment of the heat-absorbing sheet for an assembled battery, the inorganic hydrate includes 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 heat absorbing sheet for an assembled battery, the inorganic hydrate is aluminum hydroxide.

  In a preferred embodiment of the heat absorbing sheet for an assembled battery, the heat absorbing material essentially contains the dehydrating agent, and the dehydrating agent includes silica gel, activated alumina, activated carbon, zeolite, ion exchange resin, sulfate hydrate, and sulfurous acid. It is at least one of the group consisting of salt hydrate, phosphate hydrate, nitrate hydrate, acetate hydrate and metal hydrate.

  In a preferred embodiment of the heat-absorbing sheet for an assembled battery, the first heat-absorbing material has a higher moisture-releasing temperature than the second heat-absorbing material.

  In a preferred embodiment of the heat-absorbing sheet for an assembled battery, a first heat-absorbing layer containing the first heat-absorbing material as a main component, and the second heat-absorbing material formed on both surfaces of the first heat-absorbing layer. A second heat absorbing layer as a component.

  In a preferred embodiment of the heat-absorbing sheet for a battery pack, the thickness of the first heat-absorbing layer is larger than the thickness of the second heat-absorbing layer.

  The gist of the heat absorbing sheet for a battery pack according to one embodiment of the present invention is a heat absorbing sheet used for a battery pack in which a plurality of battery cells are arranged via a heat absorbing sheet and the plurality of battery cells are connected in series or in parallel. Further, it is characterized by containing two or more heat absorbing materials having different average particle diameters.

  The gist of the battery pack according to one embodiment of the present invention is characterized in that a plurality of battery cells are arranged via the above-described heat absorbing sheet for a battery pack, and the plurality of battery cells are connected in series or in parallel. And

  ADVANTAGE OF THE INVENTION According to the heat-absorbing sheet for assembled batteries which concerns on this invention, the propagation of heat between each battery cell can be effectively suppressed, when constructing the assembled battery in which several battery cells were connected in series or parallel.

FIG. 1 is a cross-sectional view schematically showing a configuration of a heat absorbing sheet for an assembled battery according to one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically illustrating a configuration of a heat absorbing sheet for an assembled battery according to another embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing a configuration of a heat absorbing sheet for an assembled battery according to still another embodiment of the present invention. FIG. 4 is a cross-sectional view schematically showing a configuration of an assembled battery to which the heat absorbing sheet for an assembled battery according to one embodiment of the present invention is applied. FIG. 5 shows the heat absorbing sheet for an assembled battery of Example 1 and Comparative Examples 1 to 3, when heated by a heater from one surface side of the heat absorbing sheet for an assembled battery, the other surface side of the heat absorbing sheet for an assembled battery. 5 is a graph showing a relationship between a temperature change and an elapsed time at the time of FIG.

  The present inventors provide a heat-absorbing sheet for an assembled battery that can effectively suppress the propagation of heat between battery cells even when the amount of heat generated from each power storage element serving as a heat source is large. In order to do so, we have been working diligently.

  As a result, it has been found that the above problem can be solved by interposing a heat absorbing sheet containing two or more heat absorbing materials having two or more peaks in the particle size distribution between the battery cells arranged in the assembled battery.

  In other words, by containing a predetermined heat absorbing material as a substance that can be dehydrated when the temperature of the battery cell becomes abnormally high, when the temperature of the battery cell rises abnormally, the substance absorbs heat while absorbing moisture. Release. Due to this heat absorbing action, the calorific value of the battery cell can be effectively reduced.

  In addition, 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. Also found.

  Further, by containing two or more endothermic materials having peaks in the particle size distribution, in other words, containing two or more types of endothermic materials having different average particle sizes, as described later, two or more types of endothermic materials having different average particle sizes are used. It has also been found that the individual endothermic actions in the wood work effectively and produce a synergistic effect.

  That is, since the heat absorbing material having a small average particle diameter effectively absorbs heat in response to a rapid temperature rise in the early stage of the elapsed time, the rising gradient of the temperature in the early stage of the elapsed time is suppressed. In addition, since the heat absorbing material having a large average particle diameter continues to absorb heat for a relatively long time, the heat absorbing retention time after the temperature rise in the initial stage of the elapsed time is maintained long. Due to these synergistic effects, the elapsed time after the heat absorbing material releases moisture until the heat absorbing sheet reaches a stage (temperature equilibrium state) in which the heat absorbing sheet exerts a function as a normal heat insulating material can be lengthened.

  In addition, the present inventors have found that, when a heat absorbing material having two or more peaks in the particle size distribution is used, in addition to the above-described effects, the peak temperature of the battery cell surface adjacent to the battery cell serving as a heat source can be suppressed to be low. Also found.

  As described above, as a result, when a thermal runaway occurs in a certain battery cell, the propagation of heat to another adjacent battery cell can be effectively suppressed, so that the thermal runaway of another battery cell is prevented from being caused. Can be suppressed.

Hereinafter, an embodiment (this embodiment) of the present invention will be described in detail with reference to the drawings.
In the following, “to” means not less than the lower limit value and not more than the upper limit value.

(First embodiment)
First, the heat absorbing sheet for a battery pack according to the first embodiment of the present invention will be described. The first embodiment is a case where the heat absorbing sheet is a single layer.

<Basic configuration of heat absorbing sheet for assembled battery>
FIG. 1 is a cross-sectional view schematically illustrating a configuration example of the heat absorbing sheet 10 for a battery pack according to the first embodiment. The heat-absorbing sheet 10 for a battery pack according to the present embodiment includes, for example, heat-absorbing materials 22 and 24 having a thermal decomposition start temperature within a temperature range of 200 ° C. or more, which is the temperature range of the battery cell 30 at the time of abnormality. The heat absorbing sheet 10 for a battery pack contains heat absorbing materials 22 and 24 having two or more peaks in the particle size distribution, in other words, two or more heat absorbing materials 22 and 24 having different average particle diameters. More specifically, the heat-absorbing sheet 10 for an assembled battery includes a first heat-absorbing material 22 having a large average particle diameter and a second heat-absorbing material 24 having a small average particle diameter.

Then, when thermal runaway as an abnormal time occurs in the battery cell 30 and the temperature of the battery cell 30 rises abnormally, the second heat absorbing material 24 having a small average particle diameter causes a rapid temperature rise in the initial stage of the elapsed time. In order to effectively absorb the heat in response to the above, the rising gradient of the temperature in the initial stage of the elapsed time is kept small.
Here, since the second heat absorbing material 24 has a smaller average particle diameter than the first heat absorbing material 22, when compared with the same volume, the second heat absorbing material 24 has a larger surface area, and thus has a heat receiving area. Is greater. Therefore, the amount of heat absorbed by the second heat absorbing material 24 per unit time is larger than the amount of heat absorbed by the first heat absorbing material 22 per unit time. For this reason, it is considered that the rising gradient of the temperature in the initial stage of the elapsed time can be suppressed smaller than that of the heat absorbing sheet 10 containing only the first heat absorbing material 22 having a large average particle diameter.

In addition, since the first heat absorbing material 22 having a large average particle diameter continues to absorb heat for a relatively long time, the heat absorbing retention time after the temperature rise in the initial stage of the elapsed time is maintained long.
Here, since the first heat absorbing material 22 has a larger average particle diameter than the second heat absorbing material 24, the temperature of the heat absorbing material near the center thereof is the water release temperature, that is, the dehydration temperature (when the heat absorbing material is inorganic water). If it is a Japanese product, it takes some time to reach the reaction temperature). For this reason, it is considered that the heat absorption holding time after the temperature rise in the initial stage of the elapsed time can be maintained longer than the heat absorbing sheet 10 containing only the second heat absorbing material 24 having a small average particle diameter.

  Due to these synergistic effects, the heat-absorbing sheet after the heat-absorbing material has released moisture (if the heat-absorbing material is an inorganic hydrate, after the inorganic hydrate has released water of crystallization), has a normal heat insulating property. It is possible to lengthen the elapsed time until the stage of exhibiting the function as a material (temperature equilibrium state).

  By the way, the first heat absorbing material 22 having a large average particle diameter requires a certain time until the temperature of the heat absorbing material near the center reaches the dehydration temperature, and the first heat absorbing material 22 may not be fully dehydrated to the vicinity of the center. For this reason, when only the first heat absorbing material 22 having a large average particle size is used as the heat absorbing sheet 10 for a battery pack, there is a possibility that all the moisture of the first heat absorbing material 22 may not be used up. The peak temperature of the surface of the battery cell 30 (temperature at which the battery enters an equilibrium state) tends to increase. On the other hand, in the heat-absorbing sheet 10 for an assembled battery according to the present embodiment, the first heat-absorbing material 22 having a large average particle diameter and the second heat-absorbing material 24 having a small average particle diameter are used in combination. Since the number of heat absorbing materials that may not be completely reduced is relatively reduced, the peak temperature on the surface of the battery cell 30 can be kept low.

  As a specific usage pattern of the heat absorbing sheet 10 for an assembled battery, as shown in FIG. 4, a plurality of battery cells 30 are arranged via the heat absorbing sheet 10 for an assembled battery, and the plurality of battery cells 30 are connected in series. Alternatively, the battery pack 40 is stored in the battery case 40 in a state of being connected in parallel (the connected state is not shown), and the assembled battery 100 is configured. The battery cell 30 is preferably, for example, a lithium ion secondary battery, but is not particularly limited thereto, and may be applied to other secondary batteries.

<Details of heat absorbing sheet for assembled battery>
Next, the average particle size and the mixing ratio of the heat absorbing materials 22 and 24 constituting the heat absorbing sheet 10 for a battery pack will be described.

  The average particle size of the first heat absorbing material 22 is preferably 5 μm or more and 100 μm or less, more preferably 7 μm or more and 30 μm or less, and still more preferably 10 μm or more and 20 μm or less. By setting the average particle size of the first heat absorbing material 22 within the above range, heat is absorbed over a relatively long time, and the effect of maintaining a long heat absorbing holding time after the rise in temperature in the initial stage of the elapsed time is sufficiently achieved. Can be demonstrated.

  The average particle size of the second heat absorbing material 24 is preferably 0.1 μm or more and less than 5 μm, more preferably 0.5 μm or more and 3 μm or less, and further preferably 0.7 μm or more and 2 μm or less. By setting the average particle size of the second heat absorbing material 24 in the above range, heat is absorbed in response to a rapid temperature rise in the initial stage of the elapsed time, and the effect of suppressing the rising gradient of the temperature with respect to the elapsed time is sufficiently reduced. Can be demonstrated.

  The mixing ratio of the first heat absorbing material 22 having a large average particle diameter to the second heat absorbing material 24 having a small average particle diameter can be arbitrarily set within a range of 90:10 to 10:90 by mass. . A preferable mixing ratio is 70:30 to 30:70, and a more preferable mixing ratio is 65:35 to 35:65. By setting the preferable or more preferable mixing ratio as described above, the first heat absorbing material 22 acts, the effect of maintaining a long heat absorption holding time after the temperature rise in the initial stage of the elapsed time, and the second heat absorbing material A good balance can be achieved with the effect of 24 acting on the effect of suppressing the rising gradient of the temperature in the initial stage of the elapsed time.

Further, the content of the second heat absorbing material 24 is made larger than the content of the first heat absorbing material 22, that is, the content of the first heat absorbing material 22 is made smaller than the content of the second heat absorbing material 24. Therefore, the effect of the second heat absorbing material 24 can be exerted preferentially.
On the other hand, by making the content of the first heat absorbing material 22 larger than the content of the second heat absorbing material 24, the effect of the first heat absorbing material 22 can be exerted preferentially.
Therefore, the mixing ratio of the first heat absorbing material 22 having a large average particle diameter and the second heat absorbing material 24 having a small average particle diameter is appropriately set according to the effect of the endothermic reaction required for the heat absorbing sheet 10 for a battery pack. can do.

  Next, the materials of the heat absorbing materials 22 and 24 that constitute the heat absorbing sheet 10 for a battery pack will be described. The heat absorbing materials 22 and 24 are, for example, an inorganic hydrate and / or a dehydrating agent. That is, only the inorganic hydrate or only the dehydrating agent may be used as the heat absorbing materials 22 and 24, or these may be used in combination.

When the heat absorbing materials 22 and 24 essentially contain an inorganic hydrate, the inorganic hydrate may have, for example, a thermal decomposition start temperature of 200 ° C. or higher. Examples of the inorganic hydrate 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 ), zirconium hydroxide (Zr (OH) ₂ ), gallium hydroxide (Ga (OH) ₃ ), and the like.
These inorganic hydrates may be used alone or in combination of two or more. That is, the same material may be used for the first heat absorbing material 22 and the second heat absorbing material 24, and the same material may be used for the first heat absorbing material 22 and the second heat absorbing material 24. Is also good.

  The thermal decomposition onset temperature of aluminum hydroxide is about 200 ° C., the thermal decomposition onset temperature of magnesium hydroxide is about 330 ° C., the thermal decomposition onset temperature of calcium hydroxide is about 580 ° C., and zinc hydroxide is Is about 200 ° C., the thermal decomposition onset temperature of iron hydroxide is about 350 ° C., the thermal decomposition onset temperature of manganese hydroxide is about 300 ° C., and the thermal decomposition onset temperature of zirconium hydroxide is Is about 300 ° C., and the thermal decomposition onset temperature of gallium hydroxide is about 300 ° C. That is, the moisture release temperature differs depending on the type of the inorganic hydrate.

  If two or more kinds of heat absorbing materials 22 and 24 having different thermal decomposition initiation temperatures, that is, two or more kinds of heat absorbing materials 22 and 24 having different moisture release temperatures are used in combination, the battery cell 30 whose temperature has risen can be increased in a wide temperature range. This is preferable because cooling can be performed, and the propagation of heat between the battery cells 30 during thermal runaway can be effectively suppressed.

  When two or more kinds of heat absorbing materials 22 and 24 having different moisture releasing temperatures are used in combination, the moisture releasing temperature of the first heat absorbing material 22 can be set higher than the moisture releasing temperature of the second heat absorbing material 24. As a result, it takes a longer time for the first heat absorbing material 22 to reach the moisture release temperature. It is considered that the endothermic holding time after the temperature rise in the initial stage of the elapsed time can be maintained longer.

By the way, when aluminum hydroxide is used as the heat absorbing materials 22 and 24, about 35% of the water of crystallization is contained in the aluminum hydroxide, and as shown in the following formula, the water of crystallization is released by thermal decomposition. In addition, it can exhibit a quenching function (endothermic reaction).
2Al (OH) ₃ → Al ₂ O ₃ + 3H ₂ O
With this function, the high-temperature heat generated in the battery cells 30 can be absorbed, and the calorific value of the battery cells 30 can be reduced.

  An inorganic hydrate having a thermal decomposition temperature of 200 ° C. or higher, such as aluminum hydroxide, has a temperature range that greatly overlaps with the temperature rise on the surface of the battery cell 30 when the thermal runaway of the battery cell 30 occurs. Therefore, the dehydration reaction (endothermic reaction) occurs due to thermal decomposition in association with the temperature rise of the battery cell 30 at the time of an abnormality, so that the propagation of heat between the battery cells 30 can be effectively suppressed.

  In particular, in the case of aluminum hydroxide, since the thermal decomposition onset temperature is low (the thermal decomposition onset temperature: about 200 ° C.) among the above-mentioned inorganic hydrates, the initial stage of battery cell abnormality (relatively low) From the above temperature), the battery cell 30 can be cooled, which is preferable.

Subsequently, when the heat absorbing materials 22 and 24 contain a dehydrating agent as an essential component, the dehydrating agent may be, for example, a moisture adsorbent such as silica gel, activated alumina, activated carbon, zeolite, or an ion exchange resin, or sulfuric acid. Salt hydrate, sulfite hydrate, phosphate hydrate, nitrate hydrate, acetate hydrate, metal hydrate and the like.
These dehydrating agents may be used alone or in combination of two or more. That is, the same material may be used for the first heat absorbing material 22 and the second heat absorbing material 24, and the same material may be used for the first heat absorbing material 22 and the second heat absorbing material 24. Is also good.

Here, as the sulfate hydrate, for example, ammonium aluminum sulfate dodecahydrate, sodium aluminum sulfate dodecahydrate, aluminum sulfate 27 hydrate, aluminum sulfate 18 hydrate, aluminum sulfate 16 hydrate, aluminum sulfate Decahydrate, aluminum sulfate hexahydrate, potassium aluminum sulfate dodecahydrate, iron sulfate heptahydrate, iron sulfate nonahydrate, potassium iron sulfate dodecahydrate, magnesium sulfate heptahydrate, sulfuric acid Examples include sodium 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 and sodium sulfite heptahydrate.
Examples of the phosphate hydrate include aluminum phosphate dihydrate, cobalt phosphate octahydrate, magnesium phosphate octahydrate, magnesium ammonium phosphate hexahydrate, and magnesium hydrogen phosphate trihydrate. , Magnesium hydrogen phosphate heptahydrate, zinc phosphate tetrahydrate, zinc dihydrogen phosphate dihydrate and the like.

Examples of the nitrate hydrate include aluminum nitrate nonahydrate, zinc nitrate hexahydrate, calcium nitrate tetrahydrate, cobalt nitrate hexahydrate, bismuth nitrate pentahydrate, and zirconium nitrate pentahydrate , Cerium nitrate hexahydrate, iron nitrate hexahydrate, iron nitrate nonahydrate, 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, borax (sodium tetraborate pentahydrate, sodium tetraborate decahydrate), Borates such as disodium octaborate tetrahydrate and zinc borate 3.5 hydrate are exemplified.

  Among the dehydrating agents, it is particularly preferable to use zeolite from the viewpoint of releasing more water and having a wide dehydration temperature range. The type of zeolite is not particularly limited, 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 having a three-dimensional network structure. Since the zeolite that adsorbs moisture is stably present, moisture or the like is usually adsorbed in the gaps of the three-dimensional network structure under normal temperature conditions. However, when heat of a certain temperature or more is applied, the moisture adsorbed on the zeolite is desorbed from the zeolite. However, since the zeolite that does not adsorb moisture is unstable, the dehydrated zeolite has a high adsorptive effect, and thus adsorbs moisture again after the temperature is lowered.

  Next, other materials forming the heat absorbing sheet 10 for a battery pack will be described. The heat absorbing sheet 10 for an assembled battery may include inorganic fibers and pulp fibers for the purpose of improving strength during molding.

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

  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 cross section. Above all, fibers having a modified cross section having a hollow cross section, a flat cross section, or a polygonal cross section can be suitably used because their heat insulating properties are slightly improved.

  A preferable lower limit of the average fiber length of the inorganic fibers is 0.1 mm, and a more preferable lower limit is 0.5 mm. On the other hand, a preferred upper limit of the average fiber length of the inorganic fibers is 50 mm, and a more preferred upper limit is 10 mm. When the average fiber length of the inorganic fibers is less than 0.1 mm, entanglement between the inorganic fibers is unlikely to occur, and the mechanical strength of the obtained heat absorbing sheet 10 may be reduced. On the other hand, if it exceeds 50 mm, the reinforcing effect can be obtained, but the inorganic fibers cannot be tightly entangled with each other, or the inorganic fibers are curled only by a single inorganic fiber. There is a risk of lowering.

  A preferred lower limit of the average fiber diameter of the inorganic fibers is 1 μm, a more preferred lower limit is 2 μm, and a still more preferred lower limit is 3 μm. On the other hand, a preferred upper limit of the average fiber diameter of the inorganic fibers is 10 μm, and a more preferred upper limit is 7 μm. If the average fiber diameter of the inorganic fibers is less than 1 μm, the mechanical strength of the inorganic fibers themselves may be reduced. From the viewpoint of the effect on human health, 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 fibers is larger than 10 μm, solid heat transfer using the inorganic fibers as a medium may increase to cause a decrease in heat insulating properties, and the formability of the heat absorbing sheet 10 may deteriorate. There is.

  These inorganic fibers and pulp fibers can be used as needed in the range of 10 to 70% by mass based on the total weight of the materials constituting the heat absorbing sheet 10.

As a material constituting the heat absorbing sheet 10, an organic binder may be used as necessary. This organic binder is useful for the purpose of improving the strength at the time of molding, and for example, a polymer flocculant or an acrylic emulsion can be suitably used.
As the compounding amount of the organic binder, it can be used as needed within a range of 0.5 to 5.0% by mass based on the total weight of the materials constituting the heat absorbing sheet 10.

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

(Second embodiment)
Subsequently, a heat absorbing sheet for a battery pack according to a second embodiment of the present invention will be described. The second embodiment is a case where the heat absorbing sheet is a multilayer (laminated body).

FIG. 2 is a cross-sectional view schematically illustrating a configuration example of the heat absorbing sheet 10 for an assembled battery according to the second embodiment. In the heat-absorbing sheet 10 for an assembled battery according to the present embodiment, the first heat-absorbing layer 12 mainly composed of the first heat-absorbing material 22 is disposed in the center of the heat-absorbing sheet 10 in the thickness direction (vertical direction in the drawing), The first heat absorbing layer 12 is composed of three layers in which a second heat absorbing layer 14 mainly composed of a second heat absorbing material 24 is disposed on both surfaces. The thickness t ₁ of the first heat absorbing layer 12 is set to be larger than the thickness t ₂ of the second heat absorbing layer.

  According to the present embodiment, the second heat absorbing layer 14 mainly composed of the second heat absorbing material 24 having a small average particle diameter is disposed on both surfaces of the first heat absorbing layer 12 at the center in the thickness direction. Therefore, since the second heat absorbing layer 14 is in contact with the surface of the battery cell 30, the second heat absorbing material 24 having a larger heat absorption amount per unit time corresponds to the rapid temperature rise in the initial stage of the elapsed time, Absorb heat preferentially (aggressively). Further, since the first heat absorbing layer 12 mainly composed of the first heat absorbing material 22 having a large average particle diameter is disposed at the center in the thickness direction, the heat absorption holding after the temperature rise in the initial stage of the elapsed time. The time can be kept longer.

  That is, in the present embodiment, the role of the first endothermic layer 12 acts preferentially in the initial stage of the endothermic reaction, and the role of the second endothermic layer 14 acts preferentially in the late stage of the endothermic reaction. Therefore, the operation and effect of the present embodiment can be more effectively exhibited than in the first embodiment (when the heat absorbing sheet 10 is a single layer).

Further, as shown in FIG. 2, when the thickness t ₁ of the first heat absorbing layer 12 is larger than the thickness t _{2 of} the second heat absorbing layer 14, the action exerted by the first heat absorbing layer 12. Can be sufficiently exhibited, so that the heat-absorbing sheet 10 reaches a stage (temperature equilibrium state) where the heat-absorbing sheet 10 functions as a normal heat insulating material after the heat-absorbing material releases moisture as described above. This is preferable because the elapsed time can be maximized.

  By the way, FIG. 2 shows an example in which the first heat absorbing layer 12 is formed only of the first heat absorbing material 22 and the second heat absorbing layer 14 is formed of only the second heat absorbing material 24. As shown in FIG. 3, the first heat absorbing material 22 and the second heat absorbing material 24 can be mixed in any of the first heat absorbing layer 12 and the second heat absorbing layer 14 composed of three layers. In this case, the first heat absorbing layer 22 at the center in the thickness direction contains the first heat absorbing material 22 as a main component, and the second heat absorbing layer 14 contains the second heat absorbing material 24 as a main component. It may be a form. In addition, the main component means a material having the largest content among the materials forming the first heat absorbing layer 12 or the second heat absorbing layer 14.

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

  The heat absorbing sheet 10 according to the present embodiment is manufactured by molding a material composed of the first heat absorbing material 22 and the second heat absorbing material 24 by a dry molding method or a wet molding method. Hereinafter, a manufacturing method when the heat absorbing sheet 10 is obtained by each forming method will be described.

[When manufacturing by dry molding method]
First, in the dry molding method, the first heat absorbing material 22 and the second heat absorbing material 24, and if necessary, inorganic fibers, pulp fibers, or an organic binder are charged at a predetermined ratio into a mixer such as a V-type mixer. I do. After sufficiently mixing the materials charged in the mixer, the mixture is charged into a predetermined mold and pressed to obtain the heat absorbing sheet 10. At the time of pressing, heating may be performed if necessary.

  The pressing pressure is preferably in the range of 0.98 to 9.80 MPa. If the pressing pressure is less than 0.98 MPa, the resulting heat absorbing 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, workability may be reduced due to excessive compression, and solid heat transfer may be increased due to an increase in bulk density, and heat insulation may be reduced.

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

Next, the slurry containing the aggregate is put into a predetermined mold to obtain a wet endothermic sheet 10. By drying the obtained heat absorbing sheet 10, the target heat absorbing sheet 10 is obtained.

  As described above, the heat-absorbing sheet 10 can be obtained by either a dry molding method or a wet molding method, but it is preferable to use a wet molding method in view of easiness of integral molding and mechanical strength.

  Further, as shown in FIGS. 2 and 3, a first heat absorbing layer 12 mainly composed of a first heat absorbing material 22 as an intermediate layer, and a second heat absorbing material 24 mainly formed on both surfaces thereof. The heat-absorbing sheet 10 composed of three layers having the second heat-absorbing layer 14 and the first heat-absorbing layer 12 and the second heat-absorbing layer 14 is manufactured based on the above-described manufacturing method. It can be obtained by a pressure press in a wet state, a method of bonding these members using an adhesive after drying, and the like.

  Hereinafter, examples of the heat absorbing 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 having an average particle diameter of 1 μm and an average particle diameter of 17 μm was prepared as an inorganic hydrate used for the heat absorbing material. Then, these aluminum hydroxide powders were mixed at a mass ratio of 50:50 to 80% by mass, and 10% by mass of rock wool, 9% by mass of pulp fibers, and 1% of a polymer flocculant were used as inorganic fibers. % By mass and sufficiently stirred and mixed to prepare a slurry. The slurry was formed into a sheet to obtain a heat absorbing sheet for a battery pack having a thickness of 2 mm. The temperature at which thermal decomposition of the aluminum hydroxide used was about 200 ° C.

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

<Comparative Example 2>
Aluminum hydroxide (Al (OH) ₃ ) powder having an average particle diameter of 17 μm, which is the same as that used in Example 1, was prepared as the inorganic hydrate used for the heat absorbing material. Then, after making this aluminum hydroxide powder 80% by mass, 10% by mass of rock wool, 9% by mass of pulp fiber, and 1% by mass of polymer coagulant were added as inorganic fibers, and the mixture was sufficiently stirred and mixed to obtain slurry. Was prepared. The slurry was formed into a sheet to obtain a heat absorbing sheet for a battery pack having a thickness of 2 mm.

<Comparative Example 3>
As the inorganic hydrate used for the heat absorbing material, aluminum hydroxide (Al (OH) ₃ ) powder having an average particle diameter of 1 μm, which was the same as that used in Example 1, was prepared. Then, after making this aluminum hydroxide powder 80% by mass, 10% by mass of rock wool, 9% by mass of pulp fiber, and 1% by mass of polymer coagulant were added as inorganic fibers, and the mixture was sufficiently stirred and mixed to obtain slurry. Was prepared. The slurry was formed into a sheet to obtain a heat absorbing sheet for a battery pack having a thickness of 2 mm.

  A heater was arranged so as to be adjacent to one surface of the heat absorbing sheet for a battery pack obtained in Example 1 and Comparative Examples 1 to 3, and a metal plate simulating a battery cell adjacent to the other surface was arranged. . Heating was performed so that the heater temperature reached 700 ° C. in about 30 seconds, and the temperature change of the adjacent battery cell (metal plate) surface with respect to the elapsed time was measured.

  FIG. 5 is a graph plotting the temperature change of the adjacent battery cell surface with respect to the elapsed time in Example 1, Comparative Examples 1 to 3.

  Since the heat absorbing sheet for an assembled battery made of the alkali earth silicate (AES) fiber shown in Comparative Example 1 has only a function as a heat insulating material, the temperature of the adjacent cell surface continues to rise monotonically with the rise of the heater temperature. Was. After that, when the temperature of the adjacent cell surface reached about 250 ° C., the temperature became almost equilibrium.

  On the other hand, in the case of the heat absorbing sheet for an assembled battery containing the inorganic hydrate (Example 1, Comparative Example 2, and Comparative Example 3), the surface of the adjacent cell is affected while the heat absorbing action by the inorganic hydrate is working. Was once maintained at about 100 ° C. After that, that is, after releasing the water of crystallization, the temperature almost reached an equilibrium state when the temperature reached a predetermined temperature after a steep temperature rise to function as a normal heat insulating material.

  Comparative Example 2 is composed of only the first heat absorbing material 22 having a large average particle diameter (average particle diameter: 17 μm) as the heat absorbing material in the heat absorbing sheet 10. Here, when compared with the same volume, the first heat absorbing material 22 has a smaller average particle size (average particle size: 1 μm) and a smaller surface area than the second heat absorbing material 24, and therefore has a smaller heat receiving area. The amount of heat absorbed per contact is smaller than that of the second heat absorbing material 24. Therefore, as shown by the curve A in FIG. 5, the heat absorbing sheet 10 composed of only the second heat absorbing material 24 having a small average particle diameter (average particle diameter: 1 μm) (curve B in FIG. 5: Comparative Example 3) In comparison with the above, the rising gradient of the temperature in the initial stage of the elapsed time (the initial stage of the endothermic reaction) is larger (that is, the gradient of the temperature of the adjacent cell surface with respect to the elapsed time is steeper). Further, the peak temperature of the adjacent cell surface was lower than about 250 ° C. in Comparative Example 1, but rose to about 230 ° C.

Further, since the average particle diameter is large, it takes some time until the temperature of the inorganic hydrate (endothermic material) near the center reaches the reaction temperature. Therefore, the heat absorption retention time T _A maintained at a constant temperature of about 100 ° C. (see FIG. 5) is the same as the heat absorption sheet 10 composed of only the second heat absorbing material 24 having a small average particle diameter (average particle diameter: 1 μm). (curve in FIG. 5 B: Comparative example 3) was longer than the endothermic retention time in the case of using the T _B.

  On the other hand, Comparative Example 3 is composed of only the first heat absorbing material 22 having a small average particle diameter (average particle diameter: 1 μm) as the heat absorbing material in the heat absorbing sheet 10. Here, when compared with the same volume, the second heat absorbing material 24 has a larger average particle size (average particle size: 17 μm), and has a larger surface area than the first heat absorbing material 22, and therefore has a larger heat receiving area. The amount of heat absorbed per contact is smaller than that of the first heat absorbing material 22. Therefore, as shown by the curve B in FIG. 5, the heat absorbing sheet 10 composed only of the first heat absorbing material 22 having a large average particle diameter (average particle diameter: 17 μm) (curve A in FIG. 5: Comparative Example 2) Since the rising gradient of the temperature in the initial stage of the elapsed time (the initial stage of the endothermic reaction) is smaller than that of the above, it can be understood that it effectively acts on the heat that rapidly rises.

  In addition, since the average particle diameter is small, the inorganic hydrate (endothermic material) near the center also reaches the reaction temperature (for example, about 200 ° C.) in a relatively short time, and the entire second endothermic material 24 is in a short time. Works effectively. Therefore, it is considered that the effective total heat absorption of the second heat absorbing material 24 is larger than the effective total heat absorbing amount of the first heat absorbing material 22, and the peak temperature in the temperature saturated state is only the first heat absorbing material 22. From the endothermic sheet 10 (Comparative Example 2) composed of only about 210 ° C., which is lower than the peak temperature (about 230 ° C.).

Subsequently, 80% by mass of aluminum hydroxide (Al (OH) ₃ ) powder having an average particle diameter of 1 μm and an average particle diameter of 17 μm was mixed at a mixing ratio of 50:50 by mass, and 80% by mass was mixed. The heat-absorbing sheet 10 (curve C in FIG. 5) has a small average particle diameter (average particle diameter: 1 μm). diameter large (average particle size: 17 .mu.m) by the action of the first heat absorbing member 22 has the heat absorbing retention time T _C, until the equivalent endothermic holding time T _a in Comparative example 2 was able to maintain long.
As a result, the elapsed time after the inorganic hydrate releases water of crystallization until the heat absorbing sheet 10 reaches the stage where the heat absorbing sheet 10 exhibits the function as a heat insulating material (the stage where the temperature is in an equilibrium state) can be lengthened. Was. That is, it was confirmed by the experiment that the heat absorbing sheet 10 can maintain the function of the heat absorbing material for a longer time.

  Further, in Example 1, the peak temperature of the adjacent cell surface rose only up to about 210 ° C. This is the same as the result of the heat absorbing sheet 10 (Example 3) composed only of the second heat absorbing material 24 having a small average particle diameter, and two or more heat absorbing materials having different average particle diameters, that is, a particle size distribution. It was confirmed that the peak temperature could be maintained at a low temperature even when a heat absorbing material having two or more peaks was used.

  From the above, it has been experimentally shown that the heat absorbing sheet of Example 1 can effectively suppress the propagation of heat between the battery cells when the battery cell is abnormal.

DESCRIPTION OF SYMBOLS 10 Endothermic sheet for battery assembly 12 1st endothermic layer 14 2nd endothermic layer 22 1st endothermic material (endothermic material)
24 Second heat absorbing material (heat absorbing material)
Reference Signs List 30 battery cell 40 battery case 100 assembled battery t ₁ thickness of first heat absorbing layer t ₂ thickness of second heat absorbing layer

Claims (15)

A plurality of battery cells are disposed via a heat absorbing sheet, the plurality of battery cells is a heat absorbing sheet used for a battery pack connected in series or in parallel,
An endothermic sheet for an assembled battery, wherein a peak of a particle size distribution contains two or more endothermic materials. The heat absorbing material has a first heat absorbing material having a large average particle diameter and a second heat absorbing material having a small average particle diameter,
The heat absorbing sheet for an assembled battery according to claim 1, wherein a mixing ratio of the first heat absorbing material and the second heat absorbing material is 90:10 to 10:90 by mass ratio.   The heat absorbing sheet for an assembled battery according to claim 2, wherein the content of the first heat absorbing material is smaller than the content of the second heat absorbing material.   The heat absorbing sheet for an assembled battery according to claim 2, wherein the content of the first heat absorbing material is larger than the content of the second heat absorbing material.   The average particle diameter of the first heat absorbing material is 5 μm or more and 100 μm or less, and the average particle diameter of the second heat absorbing material is 0.1 μm or more and less than 5 μm. 4. The heat absorbing sheet for an assembled battery according to item 1.   The heat absorbing sheet for an assembled battery according to any one of claims 1 to 5, wherein the heat absorbing material is an inorganic hydrate and / or a dehydrating agent. The endothermic material contains the inorganic hydrate as essential,
The heat absorbing sheet for an assembled battery according to claim 6, wherein the inorganic hydrate is an inorganic hydrate having a thermal decomposition onset temperature of 200 ° C or higher.   The inorganic hydrate is at least one selected from the group consisting of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide and gallium hydroxide, Item 8. The heat absorbing sheet for an assembled battery according to Item 7.   The heat absorbing sheet for an assembled battery according to claim 8, wherein the inorganic hydrate is aluminum hydroxide. The heat absorbing material contains the dehydrating agent as essential,
The dehydrating agent comprises silica gel, activated alumina, activated carbon, 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 6, which is at least one of a group.   The heat absorbing sheet for an assembled battery according to any one of claims 2 to 5, wherein a moisture releasing temperature of the first heat absorbing material is higher than a moisture releasing temperature of the second heat absorbing material. A first heat absorbing layer containing the first heat absorbing material as a main component,
The heat absorption for an assembled battery according to any one of claims 2 to 5, further comprising: a second heat absorption layer formed on both surfaces of the first heat absorption layer and having the second heat absorption material as a main component. Sheet.   The heat absorbing sheet for an assembled battery according to claim 12, wherein the thickness of the first heat absorbing layer is larger than the thickness of the second heat absorbing layer. A plurality of battery cells are disposed via a heat absorbing sheet, the plurality of battery cells is a heat absorbing sheet used for a battery pack connected in series or in parallel,
A heat-absorbing sheet for an assembled battery, comprising two or more heat-absorbing materials having different average particle diameters.   A set wherein the plurality of battery cells are disposed via the heat-absorbing sheet for a battery pack according to any one of claims 1 to 14, and the plurality of battery cells are connected in series or in parallel. battery.

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