Structured compressible layer and articles thereof

Abstract

Described herein is a structured compressible layer that comprises a polymer having a modulus of at least 3 MPa and at most 80 MPa and when measured at a temperature 25ºC. The structured compressible layer comprises a base with a plurality of projections therefrom. Each projection comprises a height, a minimum width at half height, and a maximum width at half height, with an aspect ratio less than 1.2. The projections on the structured compressible layer have a planar area coverage of at least 40% and at most 65%.

Description

PA104319W002STRUCTURED COMPRESSIBLE LAYER AND ARTICLES THEREOF TECHNICAL FIELD

[0001] A layer comprising polymeric projections that can be compressed is disclosed. Such layers may find use in providing compression to items such as a battery system, specifically a solid-state battery.SUMMARY

[0002] Cushioning between battery cells for solid state batteries is a challenging and evolving problem. Unlike the current generation of pouch and prismatic cells with liquid electrolytes, solid state batteries require much higher operating pressures, in some cases between 1-5 MPa. This is approximately an order of magnitude higher than what is needed for the current generation of liquid electrolyte batteries.Furthermore, the pressure requirements for solid state batteries are not just advantageous to optimize performance, but are critical to the basic operation of the cells. If the pressure drops too low, dendrites can form and degrade the cell’s performance. If pressure rises too high, the encasement of the cell can rupture and cause a short circuit. Structured materials have been identified for use as a compression material for battery cells. There is a need to identify structured materials that have improved pressure uniformity while also maximizing the strain operating window.

[0003] In one aspect, a structured compressible layer is disclosed. The structured compressible layer comprises a polymer having a modulus of at least 3 MPa and at most 80 MPa when measured at a temperature of 25°C, wherein the structured compressible layer has a first surface and an opposing second surface, wherein the first surface comprises a base with a plurality of projections therefrom. Each projection comprises (a) a height, (b) a minimum width at half height, (c) a maximum width at half height, and (d) an aspect ratio of less than 1.2, wherein the plurality of projections have an area coverage on the first surface of at least 40% and at most 65%.

[0004] In one embodiment, the plurality of projections is uniaxially compressible.

[0005] In another aspect, an article comprising the structured compressible layer is disclosed. In some embodiments, the article further comprises a pressure distribution layer.

[0006] In yet another aspect, a battery assembly comprising the structured compressible layer is disclosed, wherein the stmctured compressible layer is disposed on a battery cell. In some embodiments, a pressure distribution layer is used along with the structured compressible layer in the battery assembly. In some embodiments, the battery assembly is an all-solid-state battery.

[0007] The above summary is not intended to describe each embodiment. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present disclosure is explained in more detail on the basis of the drawings.

[0009] Fig. 1 is a cross-sectional view of a structured compressible layer according to one embodiment of the present disclosure.

[0010] Fig. 2 is an isometric view of a portion of a structured compressible layer according to one embodiment of the present disclosure.

[0011] Fig. 3 A is a top view of a structured compressible layer according to one embodiment of the present disclosure. Fig. 3B is an isometric view of a unit cell of a structured compressible layer according to one embodiment of the present disclosure.

[0012] Fig. 4 is a top view of a structured compressible layer according to one embodiment of the present disclosure.

[0013] Fig. 5 is a simplified cross-sectional view of a battery assembly comprising a structured compressible layer according to one embodiment of the present disclosure.

[0014] While the above-identified drawing figures set forth several embodiments of the disclosure, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale.DETAILED DESCRIPTION

[0015] The terms "a", "an", and "the" are used interchangeably with the term "at least one".

[0016] The phrase “and / or” is used to indicate one or both stated cases may occur, for example A and / or B includes, (A and B) and (A or B).

[0017] Recitation of ranges by endpoints includes the endpoints and all numbers subsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0018] Also herein, recitation of “at least one” includes all numbers of one and greater (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0019] The terms used to indicate the direction, such as “top” and “bottom”, are relative terms and may change based on a relative position of a viewer.

[0020] In the present disclosure, it has been found that a structured compressible layer such as those disclosed herein can be designed to provide pressure uniformity across the layer while maximizing the strain operating window. Such structured layers are comprised of a given amount of projections made with particular geometries and materials constraints.

[0021] Fig. 1 shows one exemplary embodiment of a stmctured compressible layer of the present disclosure. Stmctured compressible layer 10 comprises first surface 11 and opposing second surface 13. First surface 11 comprises base 12 with a plurality of projections 14 therefrom.

[0022] Each projection has a projection height (hi), and width (w). Unless otherwise mentioned or apparent, the measurements given for various features of the structured compressible layer (such asheight, width, etc.) are for the features in their uncompressed, virgin state (i.e., before use) at ambient conditions.

[0023] In some embodiments of the present disclosure, the plurality of projections has an average projection height (hi) of at least 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, or even 6 mm. In some embodiments, the plurality of projections has an average height of at most 15, 14, 13, 12, 11, 10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6, 5.5, 5, 4.5, or even 4 mm.

[0024] The structured compressible layer has a total height or thickness, T. In some embodiments of the present disclosure, the average thickness of the stmctured compressible layer (T) is at least 0.21, 0.25, 0.3, 0.4, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, or even 7 mm. In some embodiments, the average thickness is at most 15, 14, 13, 12, 11, 10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6, 5.5, 5, 4.5, or even 4 mm.

[0025] The difference between the total height (T) and height of the projections (hi) is the base height, h2. In some embodiments of the present disclosure, the average base height (h2) is at least 10, 25, 50, 75, 100, 150, 200, 250, 300, 350, 400, or even 500 micrometers. Generally, the base height should be thin so that the performance properties of the structured compressible layer are not sacrificed. In some embodiments of the present disclosure, the base height is at most 3, 2.5, 2, 1.5, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, or even 0.1 mm.

[0026] The structured compressible layer of the present disclosure is designed so that ideally, all of the projections compress uniaxially, meaning that the projections decrease in height in the z direction and expand in the x and / or y direction (see key in Fig. 2) with minimal bending or buckling when a force is applied. Thus, if an initial axis of the projection (shown by dashed line p in Fig. 1) is drawn perpendicular to base, that axis remains substantially perpendicular to the base throughout the compression of the projection. Due to imperfections in manufacturing, etc., the plurality of projections may compress substantially uniaxially, meaning that the initial perpendicular axis of the projection deviates from its initial angle (e.g., 90 °) by less than 20, 15, 10, 8, 6, 4, 3, 2, 1, or even 0.5 degrees.

[0027] The sidewalls of the projections of Fig. 1 are shown to be perpendicular to the base. However, the projections may have sidewalls extending to the top of the projection that are not perpendicular to the base. In some embodiments, the projections may have at least one sidewall that is sloped at angle 0 as shown by the dashed line in Fig. 1. In some embodiments, the angle 0 is at least 0.5, 1, 2, 3, 4, 5, 8, or even 10 degrees. In some embodiments, the angle 0 is at most 30, 25, 20, 15, 12, 10, or even 8 degrees. The sidewall of the projections may not be linear from the top of the projection to the base as shown in Fig. 1. In some embodiments, the sidewalls may be curvilinear, having for example, a curved (e.g., semiparabolic, exponential, etc.) profile.

[0028] The projections can have a variety of shapes. Exemplary shapes for the projections include: cylindrical shapes, polygonal prisms (e.g., triangular prisms, square prisms, hexagonal prisms, etc.), polygonal pyramids (e.g., triangular pyramid, square pyramid, pentagonal pyramid, etc.), conical shapes, a frustrum of a cone, or a fmstmm of a pyramid. The cross-section of the projection may not be the same size or have the same shape moving from the base to the top of the projection. In some embodiments, theprojections may comprise one cross-sectional shape near the base (e.g., having a polygonal cross-section) and a different cross-sectional shape near the top of the projection (e.g., a circular cross-section).

[0029] Shown in Fig. 2 is an isometric blow-up of structured compressible layer 20 with projection 24 extending from base 22. Projection 24 has an oval cross-section. Depicted in Fig. 2 is the minimum width (Wmin) of the projection and the maximum (wmax) width of the projection.

[0030] In some embodiments, the plurality of projections has an average maximum width (wmax) that is defined as the longest length within the cross-section of the projection parallel to the base at half height of the projection. In some embodiments of the present disclosure, the plurality of projections has an average maximum width (wmax) at half the height of the projection or half height (hi / 2) of at least 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, or even 4 mm. In some embodiments of the present disclosure, the plurality of projections has an average maximum width at half height of at most 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7.5, 7, 6.5, 6, 5.5, 5.2, 5, 4.8, 4.5, or even 4.2 mm.

[0031] In some embodiments, the plurality of projections has an average minimum width (wmin) that is defined as the longest length perpendicular to the line of the maximum width (wmax) within the crosssection of the projection parallel to the base at half height. In some embodiments of the present disclosure, the plurality of projections has an average minimum width (wmm) at half height (hi / 2) of at least 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, or even 3 mm. In some embodiments of the present disclosure, the plurality of projections has an average minimum width (wmm) at half height of at most 10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6, 5.5, 5.2, 5, 4.8, 4.5, 4.2, 4, 3.8, or even 3.5 mm.

[0032] The plurality of projections are discrete, meaning they are separate and distinct from adjacent projections. For example, the projections of the present disclosure are not ribs or fins that run the length of the sample. In the present disclosure, the maximum width (wmax) at half height (hi / 2) is less than 2 times the minimum width (wmin) at half height of the projection. In some embodiments, the maximum width at half height is less than 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, or even 1.1 times the minimum width at half height. In some embodiments, the maximum width at half height is the same as the minimum width at half height such as in the case of a circular cross-section. With projections having similar values of Wmax and wmm, the projection is free to bulge in both the x- and y- dimension as it is compressed. The allowance for bulging in two dimensions limits strain concentrations within the projection allowing for improved elasticity and less damage to the polymer at high compressive stresses. In contrast, in a comparative hypothetical projection that is continuous in the x-dimension, bulging is constrained to occur only in the y-dimension in response to compression. This constraint of bulging leads to concentrated, higher strains in the y-dimension within the projection, which can lead to damage or irreversible deformation.

[0033] In some embodiments, the plurality of projections has an average shape factor that is defined as the load bearing area divided by the bulge area. The load bearing area can be defined as the area of the projection at half height. The bulge area can be defined as the unconfined edges of the projection including any sidewall that is sloped at angle of less than 30 degrees relative to a line perpendicular to the base. In some embodiments, the shape factor is at least 0.12, 0.15, 0.20, 0.25, 0.30, or even at least 0.35.In some embodiments, the shape factor is at most 1.5, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.55, 0.5, 0.45, 0.40, 0.35, or even at most 0.30. In some embodiments, the shape factor is between 0.20 and 0.55, inclusive. If the shape factor is too low, the projection can have a tendency to buckle rather than compress uniaxially. If the shape factor is too high, the material can be degraded more quickly or undergo undesirable stiffening at high loads.

[0034] Compression of the projections is preferred over bending or buckling. Each projection has an aspect ratio defined as the projection height (hi) divided by the minimum width (wmin) at half height. The aspect ratio of the projections contributes to the potential buckling or bending behavior. High aspect ratio projections tend to undergo buckling or bending. However, in the present disclosure it is preferable to provide projections that undergo compression without bending. This uniaxial compression is generally favored to occur with aspect ratios below about 1.5. In the present disclosure, the plurality of projections has an average aspect ratio of at least 0.25. It is not necessary for every projection to have the same aspect ratio. In some embodiments, at least 80% (or even at least 85, 90, 95, or 100%) of the plurality of projections have an aspect ratio of at least 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, or even 0.7. In some embodiments, at least 80% (or even at least 85, 90, 95, or 100%) of the plurality of projections have an aspect ratio of at most 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, or even 0.8. With a fixed projection height, low aspect ratio projections have a larger area than high aspect ratio projections. If the low aspect ratio projections are closely spaced, then their relatively large area leads to rapid densification and high slopes upon unloading. If the low aspect ratio projections are spaced farther apart to accommodate their relatively high area, then the force distribution becomes poor. Therefore, the preferred aspect ratio is 0.25 to 1.10 or even 0.45 to 1.10.

[0035] The projections should be spaced a given distance apart to enable optimal compressive performance. In some embodiments, there is at most 20, 15, 12, 10, 9, 8, 7, 6.5, 6, 5.5, or even 5 mm between adjacent projections. Projections that are spaced far apart lead to poor uniformity of force distribution across the working surface, with areas adjacent to projections having high forces and areas not adjacent to projections having low forces. Therefore, it is desirable to have closer spacing of projections, which leads to smaller distances between force extremes. In some embodiments, the average distance between adjacent projections is no more than twice the width of the projections. However, if the projections are spaced too close together, then the projections can contact each other as they bulge before the target working pressure is achieved. This contact between projections can lead to undesirable stiffening of the layer. Therefore, in some embodiments, there is at least 0.7, 0.8, 1, 1.2, 1.4, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 12, 15, or even 20 mm between the adjacent projections as measured from the center of the projection to the center of the adjacent projection. In some embodiments, the average distance between adjacent projections when measured center to center of the projections is at least 15% (or at least 20, 25, 30, 40, or even 50% so long as the area coverage criteria is met) of the width of the projections.

[0036] The plurality of projections (34 and 44) may be arranged in a pattern in the compressible structured layer such as a square (FIG. 3A) or hexagonal (FIG. 4) pattern. The unit repeat, i.e., the areaconsuming the repeat pattern may have a triangular, quadrilateral (e.g., square, rhombus, rectangle, parallelogram), hexagonal, or other repeat pattern shape. Although not preferred, in some embodiments, the plurality of projections may be arranged in no discernable, or even a random pattern.

[0037] Ideally, the structured compressible layer, which comprises projections, has as close to a uniform pressure distribution across the surface. It has been surprisingly discovered that for the structured compressible layer, the projections should have a planar area coverage in a certain range, wherein if the planar area coverage is too small then the strain operating range is below optimal and if the planar area coverage is too large the strain operating range is also below optimal. To calculate the planar area coverage, the cross-sectional surface area at the half height of the uncompressed projection is divided by the total planar area of the sample. Shown in Fig. 3B, is a repeat unit 35 of the pattern of projections from Fig. 3 A, which can be used to calculate the planar area coverage of the projections on the structured compressible layer. The area of the surface of projection 34 at its half height, represented by shaded area 301 is divided by the area calculated from width 303 and length 302 of the sample. In some embodiments, the planar area coverage of the structured compressible layer should be at least 40, 45, or even 50%. In some embodiments, the planar area coverage of the structured compressible layer should be at most 65, 62, 60, or even 58%.

[0038] In addition to the structured compressible layer having a specific geometry, the structured compressible layer should be made from a particular polymeric material. The polymers of the present disclosure should be elastomeric, for example having a storage modulus of at least 3 MPa (megapascal) and at most 80 MPa when measured at 25°C. In some embodiments, the storage modulus is at least 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, or even 40 MPa. With moduli that are too low, the structures require severe deformations to develop enough strain to reach the target working pressures. The severe deformations damage the polymer or result in densification of the projections (e.g., loss of free volume to accommodate further deformation). In some embodiments, the storage modulus is at most 80, 75, 70, 65 ,60, 55, 50, 45, 40, 35, 30, 28, 25, 20, 18, 15, 12, 10, or even 9 MPa. Moduli that are too high can result in insufficient deformation to produce a desirable working cushioning distance and localized high-stress areas on the surface of the projections.

[0039] The polymer should also have high elasticity. This can similarly be stated that the polymer preferably should have low viscous character. The elasticity of the polymer can be characterized by the tan delta value of the material as measured in dynamic mechanical analysis testing. In some embodiments, the tan delta at 25 °C is no more than 0.10, 0.08, and even 0.06.

[0040] Preferably, the polymer of the stmctured compressible layer maintains similar properties over a wide temperature range. To avoid becoming stiff and brittle at low temperatures, the polymer should have a glass transition temperature no more than 0 °C, more preferably lower than -10 °C, and even more preferably lower than -15 °C. The glass transition temperature can be measured as the peak of the tan delta curve in a dynamic mechanical analysis test.

[0041] Exemplary polymers that can be used in the structured compressible layer include a polyurethane, a polyolefin elastomer, an ionic elastomer, a polyester, a silicone, a rubber, or combinations thereof.

[0042] In some embodiments, the polymer is a polyurethane derived from a polyol and a polyisocyanate (such as a diisocyanate). U.S. Pat. Publ. 2024 / 025423 (Rule, et al.) discloses a reaction product to make polyurethanes, particularly paragraphs

[0039] to

[0059] , which is herein incorporated by reference.

[0043] In some embodiments, the polymer is a polyurethane containing 5 weight percent (wt %) to 25 wt % units derived from hydroquinone bis (2 -hydroxyethyl) ether. Such polyurethanes are disclosed in U.S. Pat. Prov. No. 63 / 756465 (Rule, etal.), herein incorporated by reference.

[0044] In some embodiments, the polymer is a polyurethane urea derived from a reaction product of a polyurethane diol having a molecular weight greater than 10,000 grams per mole and a multifunctional isocyanate monomer in an amount of 5 wt % or greater, based on a total weight of the polyurethane diol and the multifunctional isocyanate monomer. Such polyurethanes are disclosed in U.S. Pat. Prov. No. 63 / 756457 (Rule, etal.), herein incorporated by reference.

[0045] Exemplary types of commercially available polyurethanes include those available under the trade designation EST ANE 58309 available from Lubrizol, Cleveland, OH; IROGRAN A95 K4977 available from Huntsman, The Woodlands, TX; and DESMOP AN 487 available from Covestro, Leverksun, Germany.

[0046] In some embodiments, the polymer is a polyolefin elastomer, such as a rubber made from ethylene, propylene and a diene comonomer (EPDM). Typical diene comonomers include ethylidene norbomene, dicyclopentadiene and vinyl norbomene.

[0047] In some embodiments, the polymer is an ionic polymer. Commercially available ionic polymer include those available under the trade designation “SURLYN” from Dow Chemical, Midland, MI; or “PRIMACOR” from SK Functional Polymer, Paris, France.

[0048] In some embodiments, the polymer is a polyester such as a thermoplastic polyester elastomer such as those available under the trade designation “HYTREL” by Celanese Corp., Irving, TX.

[0049] In some embodiments, the polymer is a silicone. Suitable silicone resins include moisture-cured silicones, condensation-cured silicones, and addition-cured silicones, such as hydroxyl-terminated silicones, silicone rubber, and fluoro-silicone. An example of two-part silicone resin commercially available is that sold under the trade designation “SILASTIC J” or “SYLGARD 184” from Dow Chemical Company.

[0050] In some embodiments, the polymer is a rubber, such as a natural rubber.

[0051] In some embodiments, the polymer is a thermoplastic elastomer derived from amides and ethers, such as poly-ether-block-amide (PEBA).

[0052] In some embodiments, a reinforcing layer may be added to stmctured layer 10 to aid, for example handling. The reinforcing layer may be a woven or nonwoven material. Such materials may include a paper, a polymeric scrim, etc. Generally, these reinforcing layers are thin and are positioned either directly on the non-structured side of the structured layer (i.e., opposing second surface 13) or are embedded into the polymer near the base of the projections.

[0053] In some applications, including battery applications, compression is required to operate within a specified working pressure range. Therefore, it is useful for the structured compressible layer to be able tobe compressed over a large distance (i.e., compress in the z direction) while staying within that working pressure range. The working compression distance can often be maximized by increasing the overall thickness of the structured compressible layer. However, it is also useful for the structured compressible layer to be as thin as possible to allow for compact constmctions that employ the structured compressible layer. Therefore, the objectives of maximizing the working compression distance and minimizing the overall thickness (T) of the structured compressible layer are often opposing each other. The balance of working compression distance and the overall thickness can be quantified with a concept of strain window. As used herein, strain window is the working cushioning distance divided by the thickness of the uncompressed compressible layer. The strain window can be measured in a compression test where the structured compressible layer is loaded to the highest pressure value (or maximum working pressure) of the target pressure range and then unloaded to at least the lowest pressure value (or minimum working pressure) of the target pressure range. The change in thickness (T) of the structured compressible layer between the highest pressure value and the lowest pressure value is then divided by original, unloaded thickness of the structured compressible layer to provide the strain window for that pressure range. In some embodiments,

[0054] The preferred strain window value can vary based on the designated range of working pressures. In some embodiments, maximum working pressures include 6.0, 5.5, 5.0, 4.5, 4.0, 3.5, or even 3.0 MPa. In some embodiments, minimum working pressures include 0.5, 1.0, or even 1.5 MPa. With a working pressure range of 0.5 MPa to 4.0 MPa, in some embodiments, the strain window during unload is preferably at least 16, 18, 20, 25, 30, 32, or even 35% with higher strain windows (ideally 100%) being preferred.

[0055] In some embodiments, opposing second surface 13 in Fig. 1 is substantially planar, meaning that in use, the structured compressible layer is in a planar or flat position and not in a rolled format.

[0056] In some embodiments, the structured compressible layer of the present disclosure is used in an article such as a battery, more specifically an all-solid-state battery. All-solid-state battery configurations are known in the art. Referring to FIG. 5, a simplified side-view of battery assembly 57 is provided, comprising battery cells 59 comprising a negative and a positive terminal. Battery cells 59 are positioned between structured compressible layers 50. The battery stack is positioned within pressing device 58, which may comprise two jig plates held on opposing sides of the stack and a mechanism to connect the two jig plates together. In some embodiments, the structured compressible layer is used around the perimeter of the batter stack, for example between the stack of battery cells and a housing. In some embodiments, the structured compressible layer is provided with a pressure distribution layer as described below.

[0057] The compression forces provided by the structured layers disclosed herein are produced by the individual projections of the pattern. When the structured layer is compressed, the local pressure directly adjacent to a compressed projection will therefore be higher than the average pressure over the entire array of projections. The local pressure directly adjacent to the spaces between compressed projections can be much lower than the average pressure over the entire array of projections. In some cases, theselocal variations in applied pressure are not desirable. For example, in some battery applications, these local variations in pressure can lead to damage within a battery cell.

[0058] Cushioning articles used in battery assemblies should maintain consistent levels of stress over long periods of time to enable long battery lifetimes. Therefore, the materials of such cushioning articles will preferably undergo minimal stress relaxation. One way to characterize the stress stability of these designs is to compare the unloading curves between two cycles, for example, between the first compression cycle and the third compression cycle, between the first and tenth compression cycles, between the first and one hundred compression cycles, between the first and ten thousand compression cycles, etc., using the test method above. Samples with good stress stability will show a minimal change in strain at a benchmark stress level - for example, 1 MPa. Samples with poor stress stability will show a more significant difference in strain between the first and third cycles at that stress level. Therefore, the difference in strain between the two cycles (e.g., first cycle and third cycle) at 1 MPa stress upon unloading - i.e., “AelMPa” can be used as a parameter to gauge performance in these cushions, with lower values being desirable. Values below 0.015 (e.g., 1.5% strain) are preferred, and values below 0.009 are more preferred.

[0059] As previously mentioned, it is important that the cushioning article provides a uniform cushion across the surface of the article. Surface pressure mapping can be used to visualize the distribution and magnitude of pressure between the structured surface contacting a planar surface (e.g., a battery cell). Ideally, the distribution and magnitude of pressure of the structured surface would be uniform across its surface as the projections deform with the applied stress. One way to quantify the uniform cushioning of the structured surface is monitor the pressure experienced by the article under a load. The pressure map of the surface can then be digitally analyzed and a statistical method called nonparametric inter-quartile range (NIQR) can be used to quantify the results. NIQR examines the difference in the data between the 75th quartile and the 25thquartile. In a material with a uniformly flat surface contacting a parallel counter face, i.e., uniform distribution of pressure across the surface, the NIQR is 1.0. In some embodiments, the structured article of the present disclosure has an NIQR of at most 5.0, 4.5, 4.0, 3.5, 3.0, 2.5, 2.0, or even 1.5.EXAMPLES

[0060] Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight (wt), and all reagents used in the examples were obtained, or are available, from general chemical suppliers such as, for example, Sigma-Aldrich Company, Saint Louis, Missouri, or may be synthesized by conventional methods.

[0061] These abbreviations are used in the following examples: °C = degree Celsius; cm = centimeter; g= gram; °F = degree Fahrenheit; kN = kilonewton; hr= hour; Hz = Hertz; in = inch; kg= kilograms; lb(s)= pound(s); Ibf = poundforce; min= minute; mm = millimeter; mL= milliliter; MN = number average molecular weight; Mw= weight average molecular weight; MPa = megapascal; mol = mol; N = Newton; RPM = revolutions per minute; and s= second.Table 1. Materials List

[0062] Preparatory Example 1 (Prep. Ex. 1)

[0063] 99.98 wt% Fomrez G24-56 and 0.02 wt% Bicat 8 was mixed and placed in one tank. This mixture was fed by a precision gear pump at a level of (82.25 wt%) into one of the inlet ports of a two inlet static mixer manifold. Rubinate 1234 (17.75 wt%) was fed in by another precision gear pump into the other static mixer manifold inlet. The reactive mixture was discharged into polypropylene trays where it was left to polymerize into polyurethane for 5 days.

[0064] The polyurethane was removed from the trays and cut into strips. The strips were fed via a roll feed extmder (Davis-Standard Corp., Pawcatuck, CT) and the flow rate was metered by a gear pump at the outlet of the roll feed extruder. The polyurethane was pumped into a twin screw extruder at a rate of 8.4 Ibs / hr (3.8 kg / hr). Additionally, PAPI 20 was fed at 1.5 Ibs / hr (0.66 kg / hr), and EMI 24 was fed at a rate of 0.1 Ibs / hr (0.045 kg / hr) at a temperature of about 300 °F (149°C). The molten mixture was coated between polypropylene liners at a thickness of 0.3 mm. The resulting material was stored in a nitrogen- purged metal pail to exclude ambient moisture.

[0065] Preparatory Example 2 (Prep. Ex. 2)

[0066] Tool 1 was custom machined with 2.00 mm straight holes (no draft angle) 4.4 mm apart in a 3.1 mm high aluminum sheet.

[0067] Tools 3, 4, and 5 were sourced through McMaster-Carr as 24 in x 24 in (61 cm x 61 cm) sheets of 3003 aluminum with staggered holes under part numbers 9232T346, 9232T348, and 9232T351, respectively.

[0068] Tool 6 was custom machined by boring out the holes in Tool 4 with a 7 / 32 in (0.55 cm) drill bit. This resulted in a hole diameter of 5.59 mm.

[0069] Comparative Example 2 (CE 2)

[0070] Material from Prep. Ex. 1 was cut into rectangular sheets with dimensions of approximately 115 mm by 260 mm. 2 sheets were laminated together using a hand roller, with a 1 wt% solution of OFX 5211 in water lightly sprayed on the top, bottom, and interface between the 2 layers. The sample sat for 10 min at room temperature following the lamination step. Prior to assembling the stack, the tool was wiped lightly with Release Agent to improve release. A stack consisting of the following layers was then assembled: bottom aluminum plate, Tool 1, the laminated sheets, nonwoven scrim, silicone rubber pad, top aluminum plate. The stack was processed for 3 min in a press (Model 50-2424-2TM from Wabash MPI, Wabash, IN) at 10 tons and 150°C, followed by quenching under load to a temperature of 60°C. Once the load was removed, the stack was removed from the press and the sample was removed from the tool.

[0071] Example 3 (Ex 3)

[0072] Material from Prep Ex 1 was cut into rectangular sheets with dimensions of approximately 115 mm by 230 mm. 3 sheets were laminated together using a hand roller, with a 1% solution of OFX 5211 in water lightly sprayed on the top, bottom, and interface between each layer. The sample sat for 10 min at room temperature following the lamination step. Prior to assembling the stack, the tool was coated with Release Agent. A stack consisting of the following layers was then assembled: bottom aluminum plate, Tool 3, the laminated sheets, nonwoven scrim, silicone rubber pad, top aluminum plate. The stack was processed for 3 min in a press at 10 tons and 150°C. The stack was removed while hot and allowed to cool for 2 min on an aluminum block. The sample was then removed from the tool.

[0073] Example 4 (Ex 4)

[0074] Material from Prep Ex 1 was cut into rectangular sheets with dimensions of approximately 115 mm by 305 mm. 3 sheets were laminated together using a hand roller, with a 1% solution of OFX 5211 in water lightly sprayed on the top, bottom, and interface between the 2 layers. A stack consisting of the following layers was assembled: bottom aluminum plate, Tool 4, the laminated sheets, silicone rubber pad, top aluminum plate. The stack was processed for 10 min in a press at 10 tons and 100°C. Once the load was removed, the stack was removed from the press and allowed to cool for 2 min on an aluminum block. The sample was then removed from the tool.

[0075] Comparative Example 5 (CE 5)

[0076] Material from Prep Ex 1 was cut into rectangular sheets with dimensions of approximately 130 mm by 130 mm. 3 sheets were laminated together using a hand roller, with a 1% solution of OFX 5211 inwater lightly sprayed on the top, bottom, and interface between each layer. The sample sat for 10 min at room temperature following the lamination step. Prior to assembling the stack, the tool was coated with Release Agent. A stack consisting of the following layers was then assembled: bottom aluminum plate, Tool 2, the laminated sheets, nonwoven scrim, silicone rubber pad, top aluminum plate. The stack was processed for 3 min in a press at 10 tons and 150°C. The stack was removed while hot and allowed to cool for 2 min on an aluminum block. The sample was then removed from the tool.

[0077] Example 6 (Ex 6)

[0078] Material from Prep Ex 1 was cut into rectangular sheets with dimensions of approximately 130 mm by 130 mm. 5 sheets were laminated together using a hand roller, with a 1% solution of OFX 5211 in water lightly sprayed on the top, bottom, and interface between each layer. The sample sat for 10 min at room temperature following the lamination step. Prior to assembling the stack, the tool was coated with Release Agent. A stack consisting of the following layers was then assembled: bottom aluminum plate, Tool 5, 0.33 mm shims placed at the comers of the tool, the laminated sheets placed in the center of the tool, a silicone rubber pad, top aluminum plate. The stack was processed for 10 min in a press at 10 tons and 100°C. The stack was quenched to 40°C while under 10 tons load. The sample was then removed from the tool.

[0079] Example 7 (Ex 7)

[0080] Material from Prep Ex 1 was cut into rectangular sheets with dimensions of approximately 40 mm by 40 mm. 5 sheets were laminated together using a hand roller, with a 1% solution of OFX 5211 in water lightly sprayed on the top, bottom, and interface between each layer. The sample sat for 10 min at room temperature following the lamination step. Prior to assembling the stack, the tool was coated with Release Agent. A stack consisting of the following layers was then assembled: bottom aluminum plate, Tool 6, 0.33 mm shims placed at the comers of the tool, the laminated sheets placed in the center of the tool, a silicone rubber pad, top aluminum plate. The stack was processed for 10 min in a press at 3 tons and 100°C. The stack was quenched to 40°C while under 3 tons load. The sample was then removed from the tool.

[0081] Comparative Example 8 (CE 8)

[0082] A shim was prepared by cutting 10 cm x 10 cm square opening in a sheet of aluminum measuring 23 cm x 20 cm x 0.2 mm. This was placed on Tool 4, which had been coated with Release Agent. 48 grams of DES 453 was mixed in a microcompounder (MC 40, Xplore Instalments, Sittard, The Netherlands) at 230 °C and 100 RPM for 3 min to form a molten resin. 24 g of the molten resin was then deposited onto Tool 4, and the shim was placed over the molten resin. This assembly was placed between polytetrafluoroethylene films and pressed in a hydraulic press with 30,000 Ibf (133 kN) for 5 min at 440 °F (226.67 °C). After cooling, the patterned polyurethane sample was removed.

[0083] Comparative Example 1 (CE 1)- XY foam

[0084] Silicone foam SSF-T100 supplied by Hubei Xiangyuan New Material Tech at a nominal thickness of 1.5 mm. The foam was stacked into 2 layers, nominally 3 mm, to allow for enough thickness in CFD testing.

[0085] Assuming good fidelity of the polymer to the features of the tool, shown in Table 2 below are the calculated values for the resulting projections derived from the tools and the average thickness of the base layer . As the holes in the tooling were straight, the width at half height of the projections was the same as the width of the hole in the tooling. The aspect ratio was calculated by hi / W at hi / 2. The % Projection Planar Area coverage is calculated as the area of the apex of the projection versus the total planar area of top surface of the sample in an uncompressed material.Table 2.

[0086] Dynamic Mechanical Analysis (DMA) Test Method

[0087] For Prep. Ex. 1, a piece of the material was sprayed with water then placed between two pieces of polyester liner and pressed for 3 minutes at 100 °C with 18,000 Ibf (80 kN). A 6.2 mm x 0.39 mm x 50 mm sample was cut from the resulting film and the liners removed for DMA testing.

[0088] For the DES 453, DMA was performed on a 6.2 mm x 1.23 mm x 50 mm sample that was cut from molded plaque obtained from Covestro.

[0089] The thickness of each film was measured. The films were mounted in the tensile grips of an RSA-G2 DMA (TA Instruments, New Castle, DE, USA) with an initial grip separation of 25 mm. The samples were then tested at an oscillation of 0.1% strain and 1 Hz throughout a temperature ramp from at least 0 °C to 100 °C at a rate of 3 °C per minute. The storage modulus (E’) at 25 °C and the tan delta at 25 °C were reported. The temperature of the tan delta peak is reported as the glass transition temperature (TG) in Table 3.Table 3

[0090] Compression force deflection (CFD) test method

[0091] CFD measurements were taken using circular disc specimens, 35 mm in diameter, punched out of each sample. Specimens were loaded between parallel platens in a load frame (Model 5581, Instron, Norwood, MA) with a 10 kN load cell. Specimens were first loaded to a preload of 725 Pa and held for15 sec, followed by three consecutive compression cycles from 0.725 kPa to 5000 kPa stress with a constant displacement of 1 mm / minute. The unload cycle in each case was also at 1 mm / min, returning to a strain of 0%. The 3rd unloading cycle was used for evaluation and calculation of various parameters.

[0092] Pressure uniformity test method

[0093] Surface pressure was mapped with a pressure mapping sensor (model 5027 available from Tekscan, Norwood, MA) with a sensing area of 28 x 28 mm and maximum pressure of 345 kPa. Test specimens were loaded between parallel platens on a load frame (model C43 from MTS Systems Corp., Eden Prairie, MN). 35 mm diameter specimens were punched from each sample. The pressure sensor was attached to the bottom platen and the specimen oriented with the structured surface facing down towards the sensor. Specimens were loaded at 1 mm / min up to a maximum stress of 5 MPa, followed by unloading to 2 MPa at the same rate. A 5 second load-controlled hold was added after 5 MPa and 2 MPa points during unload to facilitate pressure map data collection. Variation within the local stress measurements was quantified by taking the difference between the first (25%) and third (75%) quartiles of the data set normalized by the median local stress at an applied stress of 2 MPa to generate the NIQR. Shown in Table 4 is the calculated % planar area coverage of the projections at half height and projection half height to total height, the strain data and the NIQR.Table 4>na= not applicablenr = not reported

[0094] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document mentioned or incorporated by reference herein, this specification as written will prevail.

Claims

What is claimed is:

1. A structured compressible layer comprising a polymer having a storage modulus of at least 3 MPa and at most 80 MPa when measured at 25°C,wherein the structured compressible layer has a first surface and an opposing second surface, wherein the first surface comprises a base with a plurality of projections therefrom, wherein each projection comprises a height, a minimum width at half height, and a maximum width at half height having an aspect ratio (height / minimum width at half height) of less than 1.2, andwherein the projections have a planar area coverage on the first surface of at least 40% and at most 65%.

2. The structured compressible layer of claim 1, wherein the projection has a minimum width at half height of at least 0.5 mm.

3. The structured compressible layer of any one of the previous claims, wherein the projection has a minimum width at half height of at least 1 mm.

4. The structured compressible layer of any one of the previous claims, wherein the projection has a sidewall extending from the base to a top of the projection, wherein the sidewall is perpendicular to the base.

5. The structured compressible layer of any one of claims 1-3, wherein the projection has a sidewall extending from the base to the top of the projection, wherein the sidewall has an angle of at least 1 to at most 30 degrees from perpendicular to the base.

6. The structured compressible layer of any one of the previous claims, wherein the plurality of projections has a shape selected from the group consisting of cylindrical shapes, polygonal prisms, polygonal pyramids, conical shapes, frustrums of cones, frustrums of pyramids, and combinations thereof.

7. The structured compressible layer of any one of the previous claims, wherein the projections in the plurality of projections are less than 10 mm apart center to center.

8. The structured compressible layer of any one of the previous claims, wherein at least 80% of the plurality of projections have an aspect ratio of at least 0.4 and at most 1.10.

9. The structured compressible layer of any one of the previous claims, wherein the projection has an average height of at least 1 mm to at most 15 mm.

10. The structured compressible layer of any one of the previous claims, wherein the average minimum width at half height is at least 0.5 mm to at most 10 mm.

11. The structured compressible layer of any one of the previous claims, wherein the average maximum width at half height is at least 0.5 mm to at most 20 mm.

12. The structured compressible layer of any one of the previous claims, wherein the distance between nearest adjacent projections is at least 0.7 mm to at most 20 mm.

13. The structured compressible layer of any one of the previous claims, wherein the polymer has a modulus of at least 5 MPa and at most 50 MPa when measured at 25°C.

14. The structured compressible layer of any one of the previous claims, wherein the polymer has a modulus of at least 5 MPa and at most 25 MPa when measured at 25°C.

15. The structured compressible layer of any one of the previous claims, wherein the polymer comprises a polyurethane, a polyolefin elastomer, an ionic elastomer, a polyester, a silicone, a rubber, or combinations thereof.

16. The structured compressible layer of any one of the previous claims, wherein the polymer comprises a polyurethane containing 5 wt% to 25 wt% units derived from hydroquinone bis (2 -hydroxyethyl) ether.

17. The structured compressible layer of any one of claims 1 to 15, wherein the polymer comprises a polyurethane urea derived from a reaction product of a polyurethane diol having a molecular weight greater than 10,000 grams per mole and a multifunctional isocyanate monomer in an amount of 5 wt % or greater, based on a total weight of the polyurethane diol and the multifunctional isocyanate monomer.

18. The structured compressible layer of any one of the previous claims, wherein the second surface is substantially planar.

19. The structured compressible layer of any one of the previous claims, wherein when a force is applied to the first surface, the plurality of projections uniaxially compress.

20. The structured compressible layer of any one of the previous claims, wherein the structured compressible layer has an NIQR of less than 5.

21. The structured compressible layer of any one of the previous claims, wherein the strain operating window during uniaxial compression from 4 MPa to 0.5 MPa during unload is at least 20%.

22. An article comprising the structured compressible layer of any one of the previous claims.

23. A battery assembly comprising the article of any one of claims, wherein the article is disposed on a battery cell.

24. The battery assembly of claim 23, wherein the battery cell comprises an all-solid-state battery cell.

Images