JP7748969B2 - Cushioning material for battery cells and batteries - Google Patents

Description

This disclosure relates to a cushioning material for battery cells and a battery.

Lithium-ion batteries used in hybrid vehicles, electric vehicles, and other vehicles have multiple laminated battery cells (hereinafter simply referred to as battery cells) stacked and connected in series to form a battery pack, thereby increasing battery capacity. Battery cells repeatedly expand and contract during charging and discharging. Therefore, if the battery pack is subjected to vibration or impact due to this expansion and contraction, the battery cells may become misaligned, leading to problems such as internal short circuits. Therefore, to prevent misalignment of the battery cell stack, it is preferable to place a battery cell cushioning material between the battery cells, which deforms in response to the expansion and contraction of the battery cells.

Examples of cushioning materials for battery cells include polyurethane foam, polyethylene foam, and rubber sponge (see, for example, paragraph 0035 of Patent Document 1).

Furthermore, a cushioning material for battery cells has been proposed that is "a battery cushioning material made of a foam obtained by foaming a foamable resin sheet containing one or more elastomer components selected from rubber-based resins and polyolefin-based resins and a foaming agent, wherein the peel adhesion strength of each of one surface and the other surface of the battery cushioning material is 1.0 to 5.0 N/25 mm" (for example, Patent Document 2).

Patent Document 1: JP 2016-122633 A Patent Document 2: JP 2020-50841 A

The battery cell cushioning material described in Patent Document 2 has a low ability to restore its shape, so an adhesive is applied to the surface of the battery cell cushioning material to allow it to deform in accordance with the expansion and contraction of the battery cells.
However, the adhesive strength of the battery cell cushioning material described in Patent Document 2 was insufficient to allow the battery cell cushioning material to deform sufficiently in response to the expansion and contraction of the battery cells, and therefore the performance of the battery cell cushioning material described in Patent Document 2 was insufficient as a battery cell cushioning material.

In recent years, there has been a demand for further improvements in the performance of battery cell cushioning materials, specifically, materials that exhibit minimal changes in hardness due to temperature changes and that maintain a high degree of shape restoration even when temperature changes occur.
The inventors conducted preliminary studies by fabricating a model stacked battery by stacking a laminate cell (abbreviated as battery cell) and various existing polyurethane-based cushioning materials without adhesive, and conducting "impact tests" at temperatures ranging from low to high.
As a result, existing polyurethane-based cushioning materials made from conventional soft or semi-rigid polyurethane foams have low density and are slippery, resulting in weak battery cell fixing strength even when compressed at high compression rates. Furthermore, assembly workability is poor. On the other hand, existing polyurethane-based cushioning materials made from high-density polyurethane foams have high hardness. Therefore, existing polyurethane-based cushioning materials can fix batteries at low compression rates, resulting in good assembly workability. However, when existing polyurethane-based cushioning materials are compressed at high temperatures of 60°C for long periods of time, the sides of the cushioning material crack or become distorted, making it impossible to restore, resulting in problems with battery cell misalignment during impact tests. Furthermore, when existing polyurethane-based cushioning materials are exposed to low temperatures of -35°C, the cushioning material becomes so hard that it is no longer possible to compress or restore, resulting in frequent problems with battery cell misalignment during impact tests.

Therefore, the object of the present disclosure is to provide a battery cell cushioning material that is "compressible from low to high temperatures" and has "excellent recovery properties from low to high temperatures," which addresses the challenges of battery cell cushioning materials, and can fix battery cells without using an adhesive.
A battery cell cushioning material having the above characteristics, expressed in terms of physical properties, has a low hysteresis loss value that changes little from low to high temperatures, a low compression set, and high elongation.
Hysteresis loss indicates the speed at which the battery cell cushioning material restores its shape. A low hysteresis loss value indicates that the battery cell cushioning material restores its shape quickly. A small change in hysteresis loss value due to temperature changes indicates that the battery cell cushioning material changes little in its speed of restoring its shape and that its hardness performance changes little. The correlation between hysteresis loss and hardness changes will be discussed later. Furthermore, a small compression set ensures that the battery cell cushioning material retains its shape over the long term, and a high elongation indicates that the battery cell cushioning material is less likely to crack when compressed.
The statement that "hardness changes little with temperature changes, and high shape recovery is maintained even when temperature changes occur" is the same as saying that "it can be compressed from low to high temperatures" and "it has excellent recovery properties from low to high temperatures," and that battery cells can be fixed without using adhesive.

The above-mentioned problems can be solved by the following means: <1> a polyoxyalkylene polyol A having a hydroxyl group equivalent of 1500 to 9000 and a functionality of 2 to 3;
Polyol B having a hydroxyl group equivalent weight of 31 to 100 and a functionality of 2 to 3;
Diphenylmethane diisocyanate-based isocyanates,
A foaming agent;
a catalyst;
The battery cell cushioning material is made of a foam having an apparent density of 200 to 800 kg/m3, which is obtained from a composition in which the weighted average hydroxyl value of the polyoxyalkylene polyol A and the polyol B is 60 to 120 mgKOH/ ^g and the molecular weight between crosslinks is 3,500 to 16,000.
<2> The battery cell cushioning material according to <1>, wherein the polyoxyalkylene polyol A has a hydroxyl equivalent of 2,000 to 9,000, and the polyol B has a hydroxyl equivalent of 31 to 81.
<3> The battery cell cushioning material according to <1> or <2>, wherein the blending amount of the polyoxyalkylene polyol A relative to the mass of the entire composition is 50 mass % or more and 90 mass % or less.
<4> The battery cell cushioning material according to any one of <1> to <3>, wherein the blending amount of the polyol B relative to the mass of the entire composition is 1 mass % or more and 20 mass % or less.
<5> The battery cell cushioning material according to any one of <1> to <4>, wherein a blending amount of the diphenylmethane diisocyanate-based isocyanate relative to the mass of the entire composition is 1 mass % or more and 20 mass % or less.
<6> The battery cell cushioning material according to any one of <1> to <5>, wherein the compression set is 15% or less and the hysteresis loss measured under temperature conditions of −35° C. to 60° C. is 30% or less.
<7> The battery cell cushioning material according to any one of <1> to <6>, which has a self-skin layer.
<8> The battery cell cushioning material according to any one of <1> to <7>, wherein the composition includes a prepolymer that is a reaction product of the polyoxyalkylene polyol A and the isocyanate.
<9> The compression set is 15% or less,
The hysteresis loss measured under temperature conditions of -35°C to 60°C is 30% or less,
A cushioning material for battery cells having an elongation rate of 60% or more.
<10> A plurality of stacked battery cells;
the battery cell cushioning material according to any one of <1> to <9> interposed between the stacked battery cells;
A battery having a battery pack comprising:

This disclosure provides a polyurethane-based cushioning material that can be compressed at low to high temperatures, has excellent recovery properties at low to high temperatures, and can secure battery cells without the use of adhesives.

FIG. 1 is a schematic cross-sectional view showing an example of a battery according to the present disclosure. FIG. 10 is a schematic side view for explaining an impact test evaluation of a battery pack model. 1 is a graph schematically showing an example of a compression-deflection curve.

Hereinafter, exemplary embodiments according to the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the invention.
In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.
In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

Each component may contain multiple types of the corresponding substance.
When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

<Cushioning material for battery cells>
A battery cell cushioning material according to one embodiment of the present disclosure (hereinafter also referred to as "the cushioning material of the present disclosure" or simply "the cushioning material") comprises a foam having an apparent density of 200 to 800 kg/m3, which is obtained from a composition comprising: a polyoxyalkylene polyol A having a hydroxyl equivalent of 1500 to 9000 and a functionality of 2 to 3; a polyol B having a hydroxyl equivalent of 31 to 100 and a functionality of 2 to 3; a diphenylmethane diisocyanate-based isocyanate; a blowing agent; and a catalyst, wherein the polyoxyalkylene polyol A and the polyol B have a weighted average hydroxyl value of 60 to 120 mgKOH/ ^g and a molecular weight between crosslinks of 3500 to 16000.

The cushioning material of the present disclosure exhibits little change in hardness due to temperature changes, and maintains a high shape restoration force even when temperature changes occur.
By applying the cushioning material of the present disclosure to a battery cell stack, it is possible to maintain compliance with expansion and contraction of the battery cells even when temperature changes occur.
The cushioning material disclosed herein is non-slip, does not shift even when the battery cell stack is subjected to strong vibrations or impacts, and can withstand long-term use.
The cushioning material disclosed herein is thin and has a low compressibility, allowing for the effective use of small spaces to secure battery cells.

The details of the cushioning material disclosed herein are described below.

(composition)
The composition includes polyoxyalkylene polyol A, polyol B, a diphenylmethane diisocyanate-based isocyanate, a blowing agent, and a catalyst.

-Polyoxyalkylene polyol A-
The polyoxyalkylene polyol A is a polyoxyalkylene polyol having a hydroxyl equivalent of 1,500 to 9,000 and having 2 to 3 functional groups.

By setting the hydroxyl group equivalent weight and number of functional groups of the polyoxyalkylene polyol A within the above ranges and combining it with the low-molecular-weight polyol B described below, a cushioning material can be obtained that exhibits little change in hardness due to temperature changes and maintains a high degree of shape restoration even when temperature changes occur.
By setting the hydroxyl group equivalent of the polyoxyalkylene polyol A to 1500 to 9000, it is possible to obtain a cushioning material that has high elongation, little change in hardness due to temperature change, and maintains a high shape recovery force even when temperature changes occur, which is preferable.

Polyoxyalkylene polyol A is obtained by addition polymerization of an alkylene oxide such as ethylene oxide, propylene oxide, or butylene oxide to a difunctional compound (propylene glycol, ethylene glycol, etc.) or a trifunctional compound (glycerin, trimethylolpropane, etc.) as an initiator. Examples include polyols obtained by addition polymerization of propylene oxide (hereinafter also referred to as "PO") to an initiator (straight PO polyols), polyols obtained by adding PO and then adding ethylene oxide (hereinafter also referred to as "EO") (EO chip polyols), and polyols obtained by randomly adding PO and EO.

For the purpose of improving strength, adjusting foaming characteristics, or forming open cells, the polyoxyalkylene polyol A may contain other polyols.
Other polyols include polymer polyols (materials containing polymer particles obtained by copolymerizing acrylonitrile and styrene in polyol), polypropylene diols having a molecular weight of about 500 to 800, adipic acid-based polyester polyols, caprolactone-based polyols, polytetramethylene glycol, and polybutadiene polyols.
Examples of polymer polyols include Sannix KC (registered trademark) manufactured by Sanyo Chemical Industries, Ltd. and Actcoal POP (registered trademark) manufactured by Mitsui Chemicals, Inc.
Furthermore, as the polyoxyalkylene polyol A, a polyol obtained by blending a tetrafunctional polyol with a difunctional polyol in order to adjust the number of functional groups to 2 to 3, or a polyol obtained by blending two or more polyols in order to adjust the hydroxyl group equivalent of the polyol to 1500 to 9000, may be used.

The number of functional groups of the polyoxyalkylene polyol referred to here means the number of functional groups of the initiator.
When two or more types of polyoxyalkylene polyols A are blended, the number of functional groups and the molecular weight are determined as a weighted average.
The weighted average is calculated taking into consideration the content ratio of polyoxyalkylene polyol A based on the number of moles.

Here, the hydroxyl group equivalent of polyoxyalkylene polyol A is a value calculated from the following formula.
Formula: Hydroxyl equivalent of polyoxyalkylene polyol A=(56.1×1000)/(hydroxyl value of polyoxyalkylene polyol A) or Formula: Molecular weight of polyoxyalkylene polyol A/Number of functional groups of polyoxyalkylene polyol A The hydroxyl value is measured in accordance with JIS K1557-1:2007.
The molecular weight of polyoxyalkylene polyol A is the molecular weight determined from the measured value of the hydroxyl value of polyoxyalkylene polyol A according to JIS K1557-1:2007 and the number of functional groups of polyoxyalkylene polyol A.

From the viewpoint of further minimizing changes in hardness due to temperature changes and maintaining high shape recovery even when temperature changes occur, the amount of polyoxyalkylene polyol A relative to the mass of the entire composition is preferably 50% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 85% by mass or less, and even more preferably 70% by mass or more and 80% by mass or less.

-Polyol B-
The polyol B has a hydroxyl equivalent weight of 31 to 100 and a functionality of 2 to 3.

Polyol B acts as a chain extender or cross-linking agent.
By setting the hydroxyl group equivalent weight and the number of functional groups of the polyol B within the above ranges, it is possible to obtain a cushioning material that exhibits little change in hardness due to temperature changes, thus exhibiting low hysteresis loss, and that maintains a high degree of shape restoration even when temperature changes occur.

The hydroxyl equivalent of polyol B must be 31 to 100. By satisfying this requirement, the cushioning material will have good shape recovery, particularly at low temperatures, and the hysteresis loss of the cushioning material at low temperatures will be reduced. The mechanism behind this is presumed to be as follows.
The hard segments derived from polyol B aggregate and are finely dispersed in the soft segments formed by the reaction of polyoxyalkylene polyol A and isocyanate, resulting in good low-temperature properties. When polyol B has a hydroxyl group equivalent of more than 100, the hard segments derived from polyol B tend to dissolve easily in the soft segments, which deteriorates the flexibility of the soft segments at low temperatures and increases the hysteresis loss of the cushioning material at low temperatures.

The hydroxyl equivalent weight of polyol B is preferably 31 to 81, and most preferably 31 to 65, from the viewpoint of further minimizing changes in hardness due to temperature changes and maintaining high shape restoration even when temperature changes occur.

Examples of polyol B having two functional groups include ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 2-methylpropanediol, 3-methylpentanediol, 2-ethyl-1,3-hexanediol, ethylene glycol, propylene glycol, and compounds obtained by adding at least one of ethylene oxide (EO) and propylene oxide (PO) to these compounds. In particular, low-molecular-weight diols such as ethylene glycol (hydroxyl equivalent: 31) and 1,4-butanediol (hydroxyl equivalent: 45) are preferred because they have high cohesive strength after reaction with isocyanate, resulting in low hysteresis loss and little change in hysteresis loss even at low temperatures. Also preferred are 2-methylpropanediol and 3-methylpentanediol, which have alkyl groups in their side chains, due to their good low-temperature properties.
Examples of polyol B having three functional groups include glycerin (hereinafter also referred to as "G"), trimethylolpropane (hereinafter also referred to as "TMP"), and a compound in which at least one of EO and PO is added to a trihydric alcohol such as G or TMP. Particularly preferred polyol B having three functional groups is TMP or a compound in which 3 moles of ethylene oxide are added to TMP.
As the polyol B, alkanolamines such as triethanolamine, diethanolamine, and monoethanolamine can also be used.
The amount of polyol B to be blended must be such that the weighted average hydroxyl value calculated from the hydroxyl values of polyoxyalkylene polyol A and polyol B is 60 to 120.

Here, the hydroxyl group equivalent of polyol B is a value calculated from the following formula.
Formula: Hydroxyl equivalent of polyol B=(56.1×1000)/(hydroxyl value of polyol B) or Formula: Molecular weight of polyol B/Number of functional groups of polyol B The hydroxyl value is measured in accordance with JIS K1557-1:2007.
The molecular weight of polyol B is the molecular weight determined from the measured value of the hydroxyl value of polyol B according to JIS K1557-1:2007 and the number of functional groups of polyol B.

From the viewpoint of further minimizing changes in hardness due to temperature changes and maintaining high shape recovery even when temperature changes occur, the amount of polyol B relative to the mass of the entire composition is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 15% by mass or less, and even more preferably 3% by mass or more and 10% by mass or less.

The polyol B may be used singly or in combination of two or more kinds. When two or more kinds are used in combination, the number of functional groups and the molecular weight are calculated as a weighted average.
The weighted average is calculated taking into consideration the content ratio of polyol B based on the number of moles.
As the polyol B, it is preferable to use a mixture of a polyol B having two functional groups and a polyol B having three functional groups, from the viewpoint that an appropriate crosslinked structure is introduced into the cushioning material, and the compression set of the cushioning material is reduced, thereby further improving the shape recovery force of the cushioning material.
In order to adjust the number of functional groups to 2 to 3, it is also possible to blend a polyol having a functionality of 3 or more with a polyol having a functionality of 2.

-Diphenylmethane diisocyanate-based isocyanates-
Examples of diphenylmethane diisocyanate-based isocyanates (hereinafter also referred to as "MDI-based isocyanates") include 4,4'-diphenylmethane diisocyanate (hereinafter also referred to simply as "MDI"), 2,4'-MDI, carbodiimide-modified MDI, and polymeric MDI.

In addition to MDI-based isocyanates, aromatic isocyanates such as toluene diisocyanate and naphthalene diisocyanate; aliphatic and alicyclic isocyanates such as hexamethylene diisocyanate, isophorone diisocyanate (IPDI), hydrogenated diphenylmethane diisocyanate (hydrogenated MDI), xylylene diisocyanate, cyclohexane diisocyanate, norbornene diisocyanate (NBDI), xylylene diphenylmethane diisocyanate, and hydrogenated xylylene diphenylmethane diisocyanate (hydrogenated XDI); etc. may also be added.

From the viewpoint of further minimizing changes in hardness due to temperature changes and maintaining high shape recovery even when temperature changes occur, the amount of diphenylmethane diisocyanate-based isocyanate relative to the mass of the entire composition is preferably 1% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 30% by mass or less, and even more preferably 10% by mass or more and 25% by mass or less.

- Prepolymer -
It is highly preferable to use a prepolymer which is a reaction product of a part or all of the polyoxyalkylene polyol A with an MDI-based isocyanate, or a reaction product of another polyol with an MDI-based isocyanate, because the highly crystalline MDI-based isocyanate can be handled as a liquid.
In the present specification, the prepolymer functions as a type of diphenylmethane diisocyanate-based isocyanate.

When the composition contains the prepolymer, the amount of MDI-based isocyanate relative to the total composition is preferably 15 to 35 parts by weight, more preferably 20 to 32 parts by weight because this tends to reduce hysteresis loss even when temperature changes occur, and most preferably 25 to 30 parts by weight because this minimizes hysteresis loss and also tends to reduce changes in hysteresis loss. When the prepolymer is used, the amount of MDI-based isocyanate refers to the sum of the amount of MDI-based isocyanate used in synthesizing the prepolymer and the amount of MDI-based isocyanate contained in the composition.

- Foaming agent -
The foaming agent is preferably a foaming agent containing water.
Examples of the blowing agent to be used in combination with water include low-boiling organic compounds such as methylene chloride, hydrochlorofluorocarbons (e.g., HCFC-123), hydrofluorocarbons (e.g., HFC-245fa), butane, and pentane (cyclopentane, isopentane, normal pentane); and organic acids such as formic acid.
In addition to the water-containing blowing agent, other gases such as air, nitrogen gas, and carbon dioxide may be mixed into the composition to obtain a urethane foam. The preferred method for mixing the gases is a mechanical froth method using an Oaks mixer or the like, as this facilitates control of the expansion ratio. Using water and the gases as other blowing agents in combination is preferred, as it facilitates control of the expansion ratio.
The amount of the foaming agent other than water may be determined depending on the desired expansion ratio.
As the blowing agent, it is preferable to use water alone or in combination with the above-mentioned gas as another blowing agent, because this facilitates foaming, has high self-heating properties, and is therefore good in productivity.
When water is used alone as the blowing agent, and when water is used in combination with the above-mentioned gas as another blowing agent, the amount of water blended is preferably 0.01 to 0.3 parts by mass per 100 parts by mass of polyoxyalkylene polyol A. From the viewpoint of obtaining a cushioning material with less slippery properties due to finer bubbles in the foam, and from the viewpoint of obtaining a cushioning material with low hysteresis loss at low temperatures, when water is used alone as the blowing agent, and when water is used in combination with the above-mentioned gas as another blowing agent, the amount of water blended is most preferably 0.01 to 0.2 parts by mass per 100 parts by mass of polyoxyalkylene polyol A.

-catalyst-
Examples of the catalyst include organometallic compound catalysts and amine catalysts.

Examples of organometallic compound catalysts include tin-, titanium-, bismuth-, copper-, and nickel-based organometallic catalysts, such as organotin compounds such as stannous octoate and dibutyltin dilaurate.
The amine catalyst is preferably a tertiary amine, and examples thereof include monoamines, diamines, triamines, cyclic amines, alcohol amines, and ether amines, such as triethylenediamine, triethylamine, n-methylmorpholine, n-ethylformoline, and N,N,N',N'-tetramethylbutanediamine.
When water is used as a blowing agent in combination with the above-mentioned gases as other blowing agents, a temperature-sensitive catalyst may be used as the catalyst to prevent the initiation of curing during mechanical agitation of the gases.
The catalyst may be used alone or in combination of two or more kinds.

-Other additives-
Other additives include well-known additives such as silicone or non-silicone foam stabilizers; flame retardants; antioxidants; colorants; ultraviolet absorbers; and inorganic fillers such as calcium carbonate, alumina, and boron nitride.

- Weighted average hydroxyl value of polyol -
The weighted average hydroxyl value (abbreviated as average OHv) of the polyoxyalkylene polyol A and the polyol B is 60 to 120 mgKOH/g.
By setting the average OHv within the above range, the foam can have appropriate hardness and strength, and a cushioning material can be obtained that shows little increase in hardness due to temperature changes, particularly at low temperatures, and maintains a high degree of shape restoration even when temperature changes occur.
If the average OHv is less than 60 mgKOH/g, the resulting foam is soft and has low strength, making it unsuitable for practical use.If the average OHv is more than 120 mgKOH/g, the hysteresis loss at low temperatures increases, making the conformability of the cushioning material poor at low temperatures and increasing the hardness of the cushioning material at low temperatures, making it unsuitable for practical use.

From the viewpoint of suppressing an increase in hardness at low temperatures and obtaining a cushioning material that is excellent in both strength and elongation, it is most preferable that the average OHv is 70 mgKOH/g to 110 mgKOH/g.
Here, the average OHv is the weighted average of the hydroxyl values of polyoxyalkylene polyol A and polyol B.
The weighted average is calculated taking into consideration the mass-based content ratio of polyoxyalkylene polyol A and polyol B.

-Molecular weight between crosslinking points-
In the present disclosure, it is necessary to use polyoxyalkylene polyol A and polyol B, and to obtain a composition in which the molecular weight between crosslink points (abbreviated as Mc) is adjusted to 3,500 to 16,000 while satisfying the weighted average hydroxyl value.
When Mc is 3,500 to 16,000, it is possible to obtain a cushioning material that has a low compression set, a high elongation percentage, and a low hysteresis loss at low temperatures.
If Mc is less than 3,500, the cushioning material has good compression set, but its elongation decreases, so that when the cushioning material is compressed, its sides expand and stretch, making the sides more susceptible to cracking. Furthermore, if Mc exceeds 16,000, the cushioning material is exposed to high temperatures, resulting in increased heat fusion and compression set, and poor shape recovery. A molecular weight between crosslinks of 4,000 to 15,000 is preferred because it improves the elongation, compression set, and hysteresis loss at low temperatures of the cushioning material, and a molecular weight of 4,400 to 13,000 is most preferred because it minimizes changes in the physical properties of the cushioning material even when subjected to temperature changes.

Here, the molecular weight between crosslinks is a value calculated from the following formula.
Formula: Molecular weight between crosslinks = [100 parts of total composition - (2.44 × content of water per 100 parts of total composition) - content of catalyst per 100 parts of total composition - content of foam stabilizer per 100 parts of total composition] ÷ total amount of branch points of each polyol/polyisocyanate Here, the total amount of branch points of each polyol/polyisocyanate is calculated by the following formula.

The symbols in the above formula have the following meanings.
X: content of polyol per 100 parts of the total composition; Y: molecular weight of polyol; Z: number of hydroxy groups contained in one molecule of polyol; P: content of polyisocyanate per 100 parts of the total composition; Q: molecular weight of polyisocyanate; R: number of NCO groups contained in one molecule of polyisocyanate; x: number of types of polyol contained in the composition; y: number of types of polyisocyanate contained in the composition. Here, polyol refers to all polyols contained in the composition. Polyisocyanate refers to all polyisocyanates contained in the composition.

Specifically, the method for calculating the branch point will be explained using an example of a composition containing three types of polyols and two types of polyisocyanates.
For this composition, the above formula expands to:
{(X ₁ /Y ₁ )×(Z ₁ -2)}+{(X ₂ /Y ₂ )×(Z ₂ -2)}+{(X ₃ /Y ₃ )×(Z ₃ -2)}+{(P ₁ /Q ₁ )×(R ₁ -2)}+{(P ₂ /Q ₂ )×(R ₂ -2)}
For X, Y, and Z, and P, Q, and R with the same subscript, the molecular weight between crosslink points is calculated using a value calculated from the same type of polyol or isocyanate.
Here, _X1 is the content of the first polyol per 100 parts of the total composition, _Y1 is the molecular weight of the first polyol, and _Z1 is the number of hydroxy groups contained in one molecule of the first polyol. _X2 is the content of the second polyol per 100 parts of the total composition, _Y2 is the molecular weight of the second polyol, and _Z2 is the number of hydroxy groups contained in one molecule of the second polyol. _X3 is the content of the third polyol per 100 parts of the total composition, _Y3 is the molecular weight of the third polyol, and _Z3 is the number of hydroxy groups contained in one molecule of the third polyol.
Furthermore, _P1 is the content of the first polyisocyanate per 100 parts of the total composition, _Q1 is the molecular weight of the first polyisocyanate, and _R1 is the number of NCO groups contained in one molecule of the first polyisocyanate. _P2 is the content of the second polyisocyanate per 100 parts of the total composition, _Q2 is the molecular weight of the second polyisocyanate, and _R2 is the number of NCO groups contained in one molecule of the second polyisocyanate.
In the above formula for calculating the molecular weight between crosslink points, the isocyanate index is set to 100.

(Foam)
The foam constituting the cushioning material of the present disclosure will be described in detail below.
The foam is formed by foaming the above-mentioned composition.

-Apparent density-
The apparent density of the foam must be 200 to 800 kg/m ³ .
By setting the apparent density of the foam within the above range, it is possible to obtain a cushioning material with a more appropriate hardness, and the compression rate can be reduced to fix the battery cells, which has the advantage of making effective use of space, and the excellent shape recovery ability makes it a cushioning material that is reliable over the long term.

From the viewpoint of providing a cushioning material with excellent shape recovery, the apparent density of the foam is more preferably 200 to 650 kg/m ³ .

The apparent density is measured according to the following procedure.
First, a sample to be measured (approximate dimensions: length 100 mm x width 100 mm x thickness measurement value) is prepared in an environment of 23±3°C. Next, the mass of the sample is measured with a precision balance to an accuracy of 1/100 g. Next, using a digital gauge, the thickness dimension of the sample is measured at nine points with an accuracy of 1/100 mm using a probe with a diameter of Φ10 mm and a load of approximately 0.6 N, and the average value is calculated. The length and width dimensions of the sample are measured at three points each using digital calipers, and the average is calculated. The volume of the sample is calculated from the obtained dimensions. The apparent density is then calculated using the formula: apparent density = mass/volume.

(Characteristics of cushioning material)
The characteristics of the cushioning material of the present disclosure will be described below.

- Self-skin layer -
The cushioning material preferably has a self-skin layer on at least one side.
The cushioning material has a self-skin layer, which increases friction with the battery cell without the need for applying an adhesive to the surface of the cushioning material. This improves the cushioning material's ability to conform to battery cell expansion and contraction. This reduces the likelihood of misalignment of the cell stack, further reducing the occurrence of defects such as internal short circuits. Even when the battery cell is repeatedly compressed and restored multiple times, the cell stack is also less likely to misalign, further reducing the occurrence of defects such as internal short circuits. The fact that the cell stack is less likely to misalign is evident from the fact that the cushioning material is less likely to come loose in the dynamic friction test described below.

The self-skin layer is a smooth, dense layer that exists on the surface of the foam that makes up the cushioning material. As the name "self-skin" suggests, it is not formed by laminating another material on top of the foam or mechanically forming it after the cushioning material is formed, but is formed integrally with an internal layer that contains more cells than the surface layer.
For example, when a cushioning material is manufactured using a continuous web as described below, the self-skin layer is formed on the surface of the foam constituting the cushioning material at a portion that comes into contact with the continuous web. Also, when a cushioning material is manufactured using a continuous web as described below and a release paper or release film is placed between the continuous web and the foam, the self-skin layer is formed on the surface of the foam constituting the cushioning material at a portion that comes into contact with the release paper or release film.

The surface of the self-skin layer is preferably matte or mirror-like, which has a high coefficient of friction and is less slippery.
Here, the term "matt-like" means that the surface of the skin layer has minute irregularities (surface roughness Ra=0.2 to 0.5 or less).
Here, the term "mirror-like" means that the surface of the skin layer is smooth and mirror-like (surface roughness Ra is less than 0.2).

-Compression set-
The cushioning material preferably has a compression set of 15% or less.
By setting the compression set of the cushioning material within the above range, it is possible to ensure shape recovery over a long period of time, and the cushioning material for battery cells is likely to maintain a high degree of shape recovery even when temperature changes occur.

A compression set of 10% or less is preferred, and 5% or less is most preferred as this allows long-term resilience to be maintained.

Compression set is measured using the method shown in the examples below.

- Hysteresis loss -
The cushioning material preferably has a hysteresis loss of 30% or less when measured under temperature conditions of -35°C to 60°C.
By setting the hysteresis loss of the cushioning material measured under temperature conditions of -35°C to 60°C within the above range, the cushioning material's shape recovery speed is faster, the cushioning material's shape recovery is good from low to high temperatures, and the cushioning material's hardness change is small. From this relationship, cushioning materials with large hardness change also have large hysteresis loss values, and there is a correlation between hardness change and hysteresis loss change. Therefore, in all of the examples and comparative examples described below, the hysteresis loss value was evaluated.

The hysteresis loss of the cushioning material is measured as follows.
The hysteresis loss is a value obtained by a compression deflection test. The hysteresis loss is calculated from a compression-deflection measurement curve using a constant load compression method in accordance with JIS K6400-2 (2012).
Specifically, a test piece measuring 15 mm long x 15 mm wide (thickness is the thickness of the cushioning material) is cut out from the cushioning material to be measured as a measurement sample. The thickness of the measurement sample is measured with a digital gauge using a probe with a diameter of 10 mm and a load of approximately 0.6 N, with an accuracy of 1/100 mm. Next, the sample is compressed and deflected at room temperature (23±2°C; the room temperature in the following measurements is 23±2°C) at a compression rate of 0.5 mm/min to a maximum load of 675 N using a compression tester. The compression tester is then returned to the initial thickness at the same speed, and the measurement history is graphed (see Figure 3).

Fig. 3 is a graph showing a schematic example of a compression-deflection curve. The hysteresis loss is expressed as a percentage (%) of the area 0ABCD of the region surrounded by origin 0-curve A-point B-curve C-point D relative to the area 0ABE0 of the region surrounded by origin 0-curve A-point B-point E-origin 0 in the graph shown in Fig. 3, and is calculated by the following formula:
(Formula) Hysteresis loss Af = ((area ABCD / area ABE) × 100)
In FIG. 3, the horizontal axis DR (%) represents the deflection rate (%), and the vertical axis L (N) represents the load.

Subsequently, the hysteresis loss is measured under conditions of −35° C. and 60° C. in the same manner as above, except that the temperature during measurement is changed.
If the measured values of hysteresis loss under room temperature, -35°C, and 60°C conditions are 30% or less, it is considered that "the hysteresis loss measured under temperature conditions of -35°C to 60°C is 30% or less."

From the viewpoint of suppressing an increase in hardness at low temperatures and obtaining a cushioning material that is excellent in both strength and elongation, the hysteresis loss measured under temperature conditions of −35° C. to 60° C. is preferably 28% or less, more preferably 26% or less, and even more preferably 24% or less.
The lower limit of the hysteresis loss measured under temperature conditions of −35° C. to 60° C. is not particularly limited, but may be 5% or more, 10% or more, or 15% or more.

It is preferable that the cushioning material have a compression set of 15% or less and a hysteresis loss of 30% or less when measured under temperature conditions of -35°C to 60°C. This indicates that the cushioning material has a fast recovery rate and maintains a moderate hardness. This indicates that it is an excellent cushioning material that maintains its fixing force for battery cells over a wide temperature range and prevents battery cells from shifting even when subjected to vibration or impact.

-Thickness-
The thickness of the cushioning material is not particularly limited, but from the viewpoint of deforming in response to the expansion and contraction of the battery cells and suppressing misalignment of the battery cell stack, it is preferably 1.5 mm or more and 10 mm or less, and more preferably 2 mm or more and 6 mm or less.

(Another embodiment of the cushioning material)
According to one embodiment, the present disclosure provides a cushioning material having a compression set of 15% or less, a hysteresis loss measured under temperature conditions of −35° C. to 60° C. of 30% or less, and an elongation of 60% or more.

By setting the compression set, hysteresis loss, and elongation of the cushioning material within the above ranges, the hysteresis loss value is low and changes little from low to high temperatures, resulting in a cushioning material with low compression set and high elongation. This results in a cushioning material with little change in hardness due to temperature changes and which maintains a high degree of shape recovery even when temperature changes occur.

The preferred ranges of the compression set and the hysteresis loss measured under temperature conditions of −35° C. to 60° C. are the same as the ranges described above in “—Compression set—” and “—Hysteresis loss—.”
From the viewpoint of suppressing an increase in hardness at low temperatures and obtaining a cushioning material that is excellent in both strength and elongation, the elongation is preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 100% or more.
The upper limit of the elongation percentage is not particularly limited, but may be 200% or less.

Compression set, hysteresis loss measured under temperature conditions of -35°C to 60°C, and elongation are measured using the methods shown in the examples below.

The cushioning material of the other embodiment described above is preferably made of a foam obtained by foaming the composition used in the cushioning material of the present disclosure described above, for example.
The method for manufacturing the cushioning material of the another embodiment may be, for example, the method described later in (Method for manufacturing cushioning material).

(Method for manufacturing cushioning material)
There are no particular limitations on the method for producing the cushioning material of the present disclosure. For example, the following method can be used as the method for producing the cushioning material of the present disclosure.
A method for manufacturing a cushioning material, comprising: a coating step in which a urethane raw material liquid (composition) is continuously applied onto a first continuous web (strip) to form a coating film; and a heating step in which the coating film on the first continuous web is heated and hardened to form a foam.

Alternatively, the method may include a second continuous web supplying step after the coating step and before the heating step, in which a second continuous web (strip) is supplied to the coating film on the first continuous web (strip) and the coating film is sandwiched between the two continuous webs. In this case, the heating step may be a step in which the coating film is heated and cured while sandwiched between the two continuous webs to form a foam.

In addition to the methods mentioned above, well-known methods such as the general slabstock method or molding method can be used to manufacture cushioning material.

<Battery>
The battery of the present disclosure has a battery pack including a plurality of stacked battery cells and the cushioning material of the present disclosure interposed between the plurality of stacked battery cells.
Hereinafter, one embodiment of the battery of the present disclosure will be described with reference to FIG. 1, but the present disclosure is not limited thereto.

The battery 100 has a housing 10 and a battery pack 11 arranged inside the housing 10.

The housing 10 may be a metal can made from aluminum alloy, iron, stainless steel, etc., or a plastic container.

The battery pack 11 is formed by alternately stacking battery cells 13 and cushioning material 14.

The battery cell 13 includes, for example, a positive electrode current collector coated with a positive electrode active material, a negative electrode current collector coated with a negative electrode active material, and an electrolyte. The positive electrode current collector, negative electrode current collector, and electrolyte are laminated with a thin aluminum plate.

The type of battery cell 13 is not particularly limited, but examples thereof include secondary batteries such as lithium ion secondary batteries.
The shape of the battery cell 13 is not particularly limited, but it is preferably sheet-shaped.

The battery cell 13 has a positive electrode electrically connected to a positive electrode current collector (not shown), and a negative electrode electrically connected to a negative electrode current collector.
The battery cells 13 are connected in series. For example, the positive electrode of one battery cell 13 and the negative electrode of the other battery cell 13 are electrically connected to each other, thereby connecting the battery cells 13 in series.

The cushion material of the present disclosure is applied as the cushion material 14 .
1, by interposing the cushioning material 14 of the present disclosure between multiple battery cells 13, the adhesion of the cushioning material to the battery cells can be improved. This improves the ability of the cushioning material to conform to the expansion and compression of the battery cells 13, and further reduces the likelihood of the stack of battery cells shifting even when exposed to vibration or impact, thereby suppressing the occurrence of defects such as internal short circuits.

The number of battery cells and cushioning materials stacked can be changed as desired depending on the purpose.
The battery may have any known structure.

The following examples are provided, but the present disclosure is not limited to these examples. In the following description, all "parts" and "%" are by mass unless otherwise specified.

Examples and Comparative Examples
(Preparation of cushioning material)
--Examples 1 to 23, 28, and 29 and Comparative Examples 1 to 16--
Polyoxyalkylene polyol A, polyol B, a blowing agent, a foam stabilizer, and a catalyst, which are urethane raw materials, having the compositions shown in Tables 1 and 2, were stirred to form Liquid A, and isocyanate was formed into Liquid B. Liquids A and B were charged into a tank, and then transported to a mixing head by a metering pump and mechanically stirred.
The content of each component shown in the table is in parts by mass.
The stirred urethane raw material solution was applied to a release-treated polyester film (Film A) using a die coater so that the thickness after curing would be 2.0 to 3.0 mm. Another release film (Film B) was then placed on top of the coating film so that the release-treated surface was in contact with the coating film of the urethane raw material solution. Next, the film was heated in an oven at 100°C for 5 minutes, and then heated at 120°C for 7 minutes to heat-cure the coating film of the urethane raw material solution while sandwiched between two release films. Films A and B on both sides were then peeled off to obtain a cushioning material consisting of a foam with a thickness of 2.0 to 3.0 mm. The resulting cushioning material was post-cured at 120°C for 3 hours, and various physical properties were measured.

--Examples 24 to 27, 30 and Comparative Example 17--
The urethane raw materials polyol A, polyol B, foam stabilizer, and catalyst, having the compositions shown in Tables 1 and 2, were stirred to form Liquid A, and isocyanate was formed into Liquid B. Liquids A and B were placed in a tank and continuously fed to a disk-shaped mixer known as an Oaks mixer using a metering pump. Nitrogen was then fed in the amount shown in Table 2 (expressed as volume (ml) per 100 parts by mass of polyoxyalkylene polyol A). Polyol A, polyol B, and isocyanate were mixed while reacting and then discharged onto a release film. When water and nitrogen gas were used in combination as the blowing agent, water was mixed into Liquid A and the same procedure was carried out. The resulting mixture was then applied to a release-treated polyester film (Film A) using a die coater to a thickness of 2.0 to 3.0 mm after curing. Another release film (Film B) was then placed over the coating film so that the release-treated surface was in contact with the coating film of the urethane raw material liquid. Next, the coated film of the urethane raw material liquid was heated in an oven at 100°C for 5 minutes, and then heated and cured at 120°C for 7 minutes while sandwiched between two release films. Films A and B on both sides were then peeled off to obtain a cushioning material made of a foam with a thickness of 2.0 to 3.0 mm. The resulting cushioning material was after-cured at 120°C for 3 hours, and its physical properties were measured.

--Example 31--
A cushioning material was obtained in the same manner as in Example 2, except that the urethane raw material liquid was applied to a release-treated polyester film (Film A) using a die coater so that the thickness after curing would be 20 mm, and that a foam with a thickness of 20 mm was obtained and then sliced to a thickness of 3 mm to prepare a sample without self-skin.
Example 32
A cushioning material was obtained in the same manner as in Example 2, except that a film having a mirror-like surface (Ra less than 0.05) was used as the release film.

<Evaluation>
(Urethane Reactivity Evaluation)
The reactivity during the urethane reaction was evaluated as follows.
The urethane raw material liquid was applied onto a release film, and another release film was placed over the urethane raw material liquid, followed by heat curing for 5 minutes at 100° C. and 7 minutes at 120° C. Thereafter, the ease of peeling the release film was checked to evaluate the reactivity.
If the film could be easily peeled off, the reactivity was judged to be good, and if the film could not be easily peeled off, the reactivity was judged to be poor.

(Evaluation of cushioning materials)
The cushioning materials obtained in each example were subjected to various evaluations.
The evaluation methods for each are shown below.

- Measurement of tensile strength -
- Compliant with JIS K6400-5 (2012) - Pull speed: 500 mm/min
- Tensile test specimen size: Dumbbell No. 2 The specimen is pulled at a constant rate at the above speed, and the maximum stress until breakage is divided by the cross-sectional area of the specimen.

-Measurement of elongation rate-
- Compliant with JIS K6400-5 (2012) - Pull speed: 500 mm/min
- Tensile test specimen size: No. 2 dumbbell. The specimen is pulled at a constant rate at the above speed, and the elongation at break is measured.

- Measurement of C hardness -
- Measuring equipment: Asker rubber hardness tester type C - Tests conducted in accordance with JIS K 7312 standards.
Temperature conditions: Measurements were taken at -35°C, 25°C, and 60°C. The sample was left at each temperature for 24 hours before measurement.
- Test piece size: 30 x 30 mm square, stacked to a thickness of 10 mm or more

- C hardness change rate -
The rate of change in C hardness was calculated using the C hardness values measured under conditions of -35°C, 25°C, and 60°C according to the following formula.
C hardness change rate (-35°C,%) = C hardness at -35°C ÷ C hardness at 25°C × 100
C hardness change rate (60°C,%) = C hardness at 60°C ÷ C hardness at 25°C × 100

- Measurement of compression set -
Compression set was measured in accordance with JIS K 6400-4 Method A (2004). Specifically, a sample measuring 15 mm x 15 mm was cut out from the measurement object, and the thickness of the obtained sample was measured. Next, the sample was sandwiched between two stainless steel plates via a spacer having a thickness equivalent to 35% of the sample thickness, and fixed in a compressed state. In this state, it was kept in an oven at 65°C for 22 hours. Next, it was removed from the oven and removed from the stainless steel plates. Thereafter, the thickness of the sample was measured after leaving it at room temperature of 23°C for 30 minutes. Then, the compression set was calculated based on the following formula.
Formula: Compression set (%) = (t0-t)/t0×100
t0: thickness of sample before compression t: thickness of sample after compression

- Compression crack evaluation -
After the compression set test, the surface and cross section of the test piece were observed to visually check for cracks or material damage.

-Evaluation of the presence or absence of own skin-
The surface of the cushioning material obtained in each example was visually inspected to evaluate the presence or absence of self-skin.
In the case of a material without a self-skin, the foamed cell layer is exposed, so that it can be visually confirmed.

-Evaluation of dynamic friction coefficient-
The coefficient of dynamic friction on the surface of the cushioning material obtained in each example was measured under the following measurement conditions.
Measuring device: TL201Tt (manufactured by Trinity Lab Co., Ltd.)
Measurement conditions: Test speed 5 mm/sec
Measurement terminal: A PET film (Diafoil T100) manufactured by Mitsubishi Chemical Corporation is attached to the sample contact surface of the contact terminal. Measurement distance: After starting measurement, the dynamic friction coefficient is calculated from the value between 10 mm and 30 mm.

-comprehensive evaluation-
Based on the above evaluation results of the cushioning materials, the cushioning materials were comprehensively evaluated. The evaluation criteria are as follows:
A (○): Can be used as a cushioning material for battery packs in terms of reactivity and performance B (△): Has problems in terms of either reactivity or performance C (×): Has defects in terms of reactivity and performance that make it unsuitable for use as a cushioning material for battery packs

- Measurement of apparent density and hysteresis loss -
The apparent density and hysteresis loss were measured according to the methods already described.

- Calculation of hydroxyl group equivalent -
When polyoxyalkylene polyol A contains a plurality of polyols, the hydroxyl group equivalent of polyoxyalkylene polyol A was calculated by dividing the molecular weight of polyoxyalkylene polyol A (i.e., the weighted average of the molecular weights of the polyols contained in polyoxyalkylene polyol A) by the number of functional groups of polyoxyalkylene polyol A (i.e., the weighted average of the number of functional groups of the polyols contained in polyoxyalkylene polyol A).
When polyol B contains a plurality of polyols, the hydroxyl group equivalent of polyol B was calculated by dividing the molecular weight of polyol B (i.e., the weighted average of the molecular weights of the polyols contained in polyol B) by the number of functional groups of polyol B (i.e., the weighted average of the numbers of functional groups of the polyols contained in polyol B).

Hereinafter, the method for calculating the hydroxyl equivalent of polyoxyalkylene polyol A will be specifically described using Example 1 as an example.
Here, in the explanation of the method for calculating the hydroxyl group equivalent, the unit of the content of each component shown in the table is "g." Therefore, the number of moles of "Polyol A3" and "Polyol A4" contained as polyoxyalkylene polyol A is as follows.
Polyol A3 (molecular weight 6000, number of functional groups 3): 0.01333 mol
Polyol A4 (molecular weight 3000, number of functional groups 3): 0.00667 mol
First, the molecular weights of "Polyol A3" and "Polyol A4" were weighted-averaged in consideration of the molar content ratio. The calculation formula was as shown in the following formula (1).
Formula (1): {(6000×0.01333)+(3000×0.00667)}÷0.02000=5000
Next, taking into consideration the molar content ratio, the weighted average of the numbers of functional groups of "Polyol A3" and "Polyol A4" was calculated using the following formula (2).
Formula (2): {(3×0.01333)+(3×0.00667)}÷0.02000=3
The hydroxyl equivalent of polyoxyalkylene polyol A was calculated by dividing the weighted average of the calculated molecular weights by the weighted average of the number of functional groups, using the following formula (3).
Formula (3): 5000÷3=1667

The hydroxyl group equivalent of polyol B was calculated in the same manner.

(Impact test evaluation of a battery pack model)
The procedure for evaluating the impact test of the battery pack model will be explained with reference to FIG.
Three aluminum bodies 21 measuring 250 mm long, 150 mm wide, and 35 mm thick were prepared, and a Mitsubishi Chemical PET film 22 (Diafoil T100, 100 μm thick) was attached to the surface of each aluminum body 21 to form a battery cell model. Two pieces of cushioning material 23, each measuring 240 mm long, 140 mm wide, and 3 mm thick, were also prepared. As shown in FIG. 2 , the cushioning material 23 was sandwiched between the aluminum bodies 21 to form a structure that allowed it to be compressed and fixed (in this test, a compression ratio adjustment jig 24 was used to compress and fix the cushioning material 23). Next, as shown in FIG. 2 , a shock absorber 25 (made of aluminum) measuring 35 mm long, 35 mm wide, and 150 mm thick was installed below the central aluminum body 21 of the three aluminum bodies 21. This stack was then used as a battery pack model 200. The total mass of the battery pack model 200 was 12 kg.

Subsequently, the obtained battery pack model 200 was subjected to an impact test evaluation.
The battery pack model 200 was compressed by 50% by the cushioning material 23 under temperature conditions of -60°C, 25°C, and -35°C, and then left to stand for 24 hours. Thereafter, the compression rate was released to 15% at room temperature, and 10 minutes after release, the battery pack model 200 was dropped from a height of 10 cm onto the floor with the impact absorber 25 facing downwards. The displacement of the laminated structure of the battery pack model 200 was visually confirmed and evaluated according to the following evaluation criteria.
A (◯): No displacement of the aluminum body 21 occurred. B (△): There was slight displacement of the aluminum body 21, but it was still usable for practical use. C (×): There was severe displacement of the aluminum body 21, and it was not usable for practical use.

The dynamic friction coefficient measurement results showed that the cushioning material obtained in Example 2 (cushioning material with a matte surface) had a value of 0.997, while the cushioning material obtained in Example 32 (cushioning material with a mirror-like surface) had a higher value of 3.781. The mirror-like surface of the cushioning material is smoother, resulting in a higher dynamic friction coefficient. On the other hand, the cushioning material obtained in Example 31 (cushioning material with no native skin layer on the surface) had a dynamic friction coefficient of 0.449, a lower value than the cushion with a native skin layer. This indicates that the cushioning material with a native skin layer has better adhesion to the battery cell and is more effective in preventing battery cell misalignment.

According to the measurement results of the C hardness at each temperature, the cushioning material of this example has a smaller rate of change in C hardness than the cushioning material of the comparative example, and therefore it is understood that the hardness changes less with temperature changes.
According to the results of the hysteresis loss measurements, the cushioning material of this example has a lower hysteresis loss, especially at low temperatures, compared to the cushioning material of the comparative example, and therefore maintains a high shape restoration force even when temperature changes occur.
From the above results, it can be seen that the cushioning material of this example has little change in hardness due to temperature changes, and maintains a high shape restoration force even when temperature changes occur.
It is also clear that the battery provided with the cushioning material of this example is less likely to experience misalignment of the stack of battery cells even in an environment where temperature changes occur.

Details on the abbreviations in the table are as follows.

-Polyoxyalkylene polyol A-
Polyol A1: Polyoxyalkylene polyol "Molecular weight 15,000, number of functional groups 3, hydroxyl value 11.6"
Polyol A2: Polyoxyalkylene polyol "molecular weight 10,000, number of functional groups 3, hydroxyl value 16.7"
Polyol A3: Polyoxyalkylene polyol "molecular weight 6000, number of functional groups 3, hydroxyl value 24.0"
Polyol A4: Polyoxyalkylene polyol "molecular weight 3000, number of functional groups 3, hydroxyl value 56.1, 15% EO added"
Polyol A5: Polyoxyalkylene polyol "Molecular weight 4500, number of functional groups 3, hydroxyl value 37.4"
Polyol A6: Polyoxyalkylene polyol "molecular weight 2000, number of functional groups 3, hydroxyl value 84.2"
Polyol A7: Polyoxyalkylene polyol "molecular weight 3000, number of functional groups 3, hydroxyl value 56.1"
Polyol A8: Polyoxyalkylene polyol "molecular weight 800, number of functional groups 2, hydroxyl value 140.3"
Polyol A9: Polyoxyalkylene polyol "Molecular weight 2000, number of functional groups 2, hydroxyl value 56.1"
Polyol A10: Polyoxyalkylene polyol "Molecular weight 3000, number of functional groups 2, hydroxyl value 37.4"
Polyol A11: Polyoxyalkylene polyol "Molecular weight 4000, number of functional groups 2, hydroxyl value 28.1"
Polyol A12: Polyoxyalkylene polyol "Molecular weight 12,000, number of functional groups 2, hydroxyl value 9.6"
Polyol A13: Polyoxyalkylene polyol "molecular weight 18,000, number of functional groups 2, hydroxyl value 6.3"
Polyol A14: Polyoxyalkylene polyol "molecular weight 20,000, number of functional groups 2, hydroxyl value 5.6"

-Polyol B-
Polyol B1: 1,4-butanediol Polyol B2: Ethylene oxide adduct of trimethylolpropane (molecular weight 182.9, functionality 3, hydroxyl value 920)
Polyol B3: Ethylene glycol Polyol B4: Polyoxyalkylene polyol "Molecular weight 400, number of functional groups 3, hydroxyl value 420"
Polyol B5: Polyoxyalkylene polyol "Molecular weight 500, number of functional groups 3, hydroxyl value 337"

- MDI-based isocyanate -
P-MDI: Monomeric MDI "Millionate MT, manufactured by Tosoh Corporation"

-catalyst-
33Lv: Amine catalyst "DABCO 33-LV, manufactured by Air Products Japan Co., Ltd."
U-600: Bismuth catalyst "Neostan U-600, manufactured by Nitto Kasei Co., Ltd."

-Terminated isocyanate prepolymer-
Prepolymer A: A modified MDI-based isocyanate obtained by reacting 47 parts of monomeric MDI with 53 parts of Polyol A4.
Prepolymer B: A modified MDI-based isocyanate obtained by reacting 53.5 parts of monomeric MDI with 46.5 parts of Polyol A8.
When a prepolymer is used, it is added as the liquid B of the isocyanate.
-Foam stabilizer-
・SH190: "SH190, manufactured by Toray Dow Corning Co., Ltd."
・SZ1959: "SZ1959, manufactured by Toray Dow Corning Co., Ltd."

"Average hydroxyl value" in the table means "weighted average hydroxyl value of the hydroxyl values of polyoxyalkylene polyol A and polyol B."
A blank column in the table regarding the content of a chemical component, compound, etc. means that the chemical component, compound, etc. is not intentionally included.
Furthermore, blank spaces in the table related to evaluation results mean that the evaluation was not performed.

The disclosure of Japanese Patent Application No. 2020-201113, filed on December 3, 2020, is incorporated herein by reference in its entirety.
All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims (10)

a polyoxyalkylene polyol A having a hydroxyl group equivalent of 1,500 to 9,000 and a functionality of 2 to 3;
Polyol B having a hydroxyl group equivalent weight of 31 to 100 and a functionality of 2 to 3;
Diphenylmethane diisocyanate-based isocyanates,
A foaming agent;
a catalyst;
The battery cell cushioning material is made of a foam having an apparent density of 200 to 800 kg/m3, which is obtained from a composition in which the weighted average hydroxyl value of the polyoxyalkylene polyol A and the polyol B is 60 to 120 mgKOH/ ^g and the molecular weight between crosslinks is 3,500 to 16,000. The battery cell cushioning material according to claim 1, wherein the polyoxyalkylene polyol A has a hydroxyl equivalent of 2,000 to 9,000, and the polyol B has a hydroxyl equivalent of 31 to 81. The battery cell cushioning material according to claim 1 or 2, wherein the amount of polyoxyalkylene polyol A relative to the total mass of the composition is 50% by mass or more and 90% by mass or less. The battery cell cushioning material according to any one of claims 1 to 3, wherein the blending amount of polyol B relative to the total mass of the composition is 1% by mass or more and 20% by mass or less. The battery cell cushioning material according to any one of claims 1 to 4, wherein the amount of the diphenylmethane diisocyanate-based isocyanate relative to the total mass of the composition is 1% by mass or more and 20% by mass or less. A battery cell cushioning material according to any one of claims 1 to 5, having a compression set of 15% or less and a hysteresis loss measured under temperature conditions of -35°C to 60°C of 30% or less. The battery cell cushioning material according to any one of claims 1 to 6, which has a self-skin layer. The battery cell cushioning material according to any one of claims 1 to 7, wherein the composition includes a prepolymer that is a reaction product of the polyoxyalkylene polyol A and the isocyanate. The compression set is 15% or less,
The hysteresis loss measured under temperature conditions of -35°C to 60°C is 30% or less,
The battery cell cushioning material according to any one of claims 1 to 8, which has an elongation rate of 60% or more. A plurality of stacked battery cells;
the battery cell cushioning material according to any one of claims 1 to 9, which is interposed between the stacked battery cells;
A battery having a battery pack comprising: