Composite thermal management sheet, method of manufacture, assembly for a battery using the same, and battery including the same

Abstract

A composite thermal management sheet for battery packs includes a polysiloxane foam layer and a reactive filler composition disposed within the polysiloxane foam layer. The reactive filler composition includes a first filler that decomposes to produce water upon initial heating, and a second filler that is different from the first filler. The second filler forms a thermal insulation layer with the decomposition products of the first filler, or absorbs water, or both.

Description

Technical Field

[0001] This invention provides a composite thermal management sheet for use in battery packs, particularly for delaying or preventing heat dissipation in lithium-ion battery packs. Further, this invention relates to a method for manufacturing the composite thermal management sheet and battery modules and battery packs incorporating the composite thermal management sheet. Prior Technology

[0002] The demand for electrochemical energy storage devices, such as lithium-ion batteries, is increasing due to applications such as electric vehicles and grid energy storage systems, as well as the growth of other multi-cell battery applications, such as e-bikes, uninterruptible power supply (UPS) systems, and alternatives to lead-acid batteries. This increased use necessitates thermal management methods. For large-scale applications, such as grid energy storage and electric vehicles, multiple electrochemical battery cells are often connected in series and parallel arrays, which can lead to heat dissipation. Once a battery cell is in a heat-dissipating mode, the heat generated by that cell can cause heat dissipation propagation reactions in adjacent cells, potentially creating a cascade effect that could ignite the entire battery pack.

[0003] While attempts to reduce heat dissipation from battery packs have been considered, most remain flawed. For example, improving the electrolyte by adding flame-retardant additives or using inherently non-flammable electrolytes has been considered, but these methods negatively impact the electrochemical performance of the battery pack. Other methods for thermal management or preventing cascaded heat dissipation include adding insulation between battery cells or cell clusters to reduce heat transfer during thermal events. However, these methods limit the achievable upper limit of energy density.

[0004] With the increasing demand for batteries with improved thermal management and lower risk of heat dissipation, there is a need for methods and components for battery packs that can prevent or delay the propagation of heat, energy, or both to surrounding battery cells. Summary of the Invention

[0005] In one embodiment, the composite thermal management sheet for a battery pack includes a polysiloxane foam layer and a reactive filler composition disposed within the polysiloxane foam layer. The reactive filler composition includes a first filler that decomposes to produce water upon initial heating and a second filler that is different from the first filler. The second filler and the decomposition products of the first filler form a thermal insulation layer, or absorb water, or both.

[0006] The battery pack components include the aforementioned composite thermal management sheet placed on the surface of an electrochemical battery cell.

[0007] This sample also reveals a battery pack containing the aforementioned components.

[0008] The foregoing description and other features are illustrated by the following figures, implementation methods, examples, and claims. Simple Explanation of the Diagram

[0009] The following is a brief description of the drawings, which are intended to illustrate, and not limit, the exemplary embodiments disclosed in this invention.

[0010] [Figure 1] Figure 1 is a cross-sectional schematic diagram of one state of the composite thermal management sheet; [Figure 2] is a schematic diagram of one state of the composite thermal management sheet, which is located between two battery cells; [Figure 3] is a schematic diagram of one state of the composite thermal management sheet, which is located between two electrochemical cell units; [Figure 4] is a schematic diagram illustrating one state of the composite thermal management sheet, which is located in the battery cell array; [Figure 5] is a schematic diagram illustrating a state of a battery pack assembly including composite thermal management sheets; [Figure 6] is a schematic diagram of the apparatus used for hot plate testing; [Figure 7] is a diagram of the deformable partition located between the hot plate and the top layer of the device used in hot plate testing; [Figure 8] is a photograph of a borosilicate insulation layer formed from a reactive filler composition containing borax and zinc borate; [Figure 9] is a graph showing the temperature (°C) versus time (min) of the heat dissipation simulation test results of Comparative Example 1 and Examples 1 to 6; [Figure 10] Figure 10A is a schematic diagram of the unfolded view of the first device used for puncture testing; Figure 10B is a schematic diagram of the non-unfolded view shown in Figure 10A; [Figure 11] is a graph showing the relationship between temperature (°C) and time (min) for the puncture test results of Comparative Example 3 and Example 7; [Figure 12] is a graph showing the relationship between volts (V) and time (min) for puncture test results of Comparative Examples 2 and 3 and Example 7 at different thicknesses; [Figure 13] is a graph showing the relationship between heat release rate (HRR) (watts / gram (W / g)) and temperature (°C) in Comparative Example 3; [Figure 14] is a graph showing the relationship between HRR (W / g) and temperature (°C) in Example 7; [Figure 15] is a graph showing the relationship between HRR (W / g) and temperature (°C) in Example 8; [Figure 16] Figure 16A is a schematic diagram of the unfolded view of the second device used for puncture testing; Figure 16B is a schematic diagram of the non-unfolded view shown in Figure 16A; [Figure 17] is a graph showing the relationship between temperature (°C) and time (seconds) for the puncture test results of Comparative Example 3; [Figure 18] is a graph showing the relationship between temperature (°C) and time (seconds) for the puncture test results of Example 7; [Figure 19] is a photograph of Example 7 after the puncture test; and [Figure 20] is a graph showing the relationship between temperature (°C) and time (seconds) for the puncture test results of Example 8. Implementation

[0011] Thermal management of battery packs, such as preventing heat dissipation, is a challenge, especially for packs containing multiple electrochemical cells. This is because adjacent cells to a cell experiencing heat dissipation can absorb enough energy to rise above their designed operating temperature, triggering adjacent cells to also enter a heat-dissipating state. This propagation of the heat-dissipating event can lead to a cascading chain reaction of heat dissipation, as the cell ignites adjacent cells. Achieving effective thermal management in extremely thin sheets is particularly difficult, for example, sheets with a total thickness of 30 mm or less, or 20 mm or less, or 15 mm or less, or 10 mm or less, or 8 mm or less, or 6 mm or less. The demand for thin sheets is increasing to reduce product size and weight and save material.

[0012] The inventors of this invention have discovered that a composite thermal management sheet comprising a polysiloxane foam and a reactive filler composition can be used to prevent or reduce the intensity of such cascade heat dissipation events. The reactive filler composition is formulated such that, upon exposure to a heat source, it first generates and absorbs moisture, which can mitigate heat transfer to adjacent battery cells. In one state, water can be trapped or desorbed to provide for water recycling. In another state, under continuous heating, the elastic polysiloxane layer and the reactive filler composition can form an insulating layer, which can further mitigate heat transfer to adjacent battery cells.

[0013] An unexpected discovery revealed that the use of reactive filler compositions is particularly helpful in manufacturing very thin composite thermal management sheets, i.e., 30 mm or less, or 20 mm or less, or 15 mm or less, or 10 mm or less, or 8 mm or less, or 6 mm or less, and composite thermal management sheets with good thermal insulation properties. These composite thermal management sheets can possess additional advantageous properties, such as good puncture resistance. They can maintain good thermal insulation even after multiple heating and cooling cycles. They can further provide pressure management for electrochemical cell units and battery packs. The thermal insulation layer provided by these composite thermal management sheets can be used in various locations within the battery pack to prevent heat loss. These composite thermal management sheets can further improve the flammability of the battery pack.

[0014] As previously described, the composite thermal management sheet comprises an elastic porous layer and at least two fillers with specific properties. As shown in Figure 1, the composite thermal management sheet 10 includes an elastic polysiloxane foam layer 12 having a first outer surface 14 and a corresponding second outer surface 16. Although depicted as flat, one or both or all of the outer surfaces may be contoured to better fit with a surface of the electrochemical cell.

[0015] The elastic polysiloxane foam layer 12 further includes a plurality of open pores, i.e., pores 18. The pores are defined by the inner surface 20 of the pores in the elastic polysiloxane foam material. The pores can be interconnected or dispersed. Combinations of interconnected or dispersed pores may exist. The pores may be completely contained within the sheet, or at least a portion of the pores may be open to the surface of the sheet, allowing them to interact with the surrounding environment. In one embodiment, at least a portion of the pores are interconnected and at least a portion of the pores are open, allowing air, water, water vapor, etc., from the first outer surface 14 to pass through to the opposing second outer surface 16; this is referred to herein as an "open-cell foam." In another embodiment, the foam material may be a "closed-cell foam," wherein the pores are interconnected or not, and are substantially not open to the surface of the sheet, or are completely closed, so that the sheet does not allow large amounts of air, water, water vapor, or similar substances to pass through from one outer surface to another. In another case, the foam material is basically a closed-cell foam material, or a completely closed-cell foam material.

[0016] Referring further to Figure 1, the filler composition comprises two or more different fillers 22, 24 distributed within the elastic polysiloxane foam layer 12. The fillers may be substantially uniformly distributed or gradient distributed, for example, increasing from the first outer surface 14 towards the second outer surface 16. As used herein, the term "disposed within" may refer to the reactive filler composition being distributed within the matrix of the polysiloxane foam layer, as shown in Figure 1. Furthermore, as used herein, the term "disposed within" may refer to the reactive filler composition being located within the pores 18 of the polysiloxane foam layer, for example, coated on the inner surface 20 of the elastic foam material, or located in the pores in particulate form. A portion of the pores in the polysiloxane foam layer may contain the reactive filler composition, or substantially all, or all, of the pores may contain the reactive filler composition. Each pore containing the reactive filler composition may be partially filled, substantially completely filled, or completely filled.

[0017] A polysiloxane foam material that is inert to the typical operating conditions of battery packs (such as lithium-ion batteries) is selected as a carrier for the reactive filler composition and to provide a silicon source for the formation of the thermal insulation layer, as described in more detail below. Various polysiloxane foam materials are known and usable in the art. In one embodiment, the polysiloxane foam material comprises poly(dialkylsiloxane), for example: poly(dimethylsiloxane).

[0018] This reactive filler composition comprises at least two fillers with specific properties. As will be understood from the following discussion, the term "reactive" in relation to the filler composition includes both chemical reactions, such as breaking existing chemical bonds or forming new ones, and physical processes, such as breaking or forming hydrogen bonds. First, the types and quantities of at least two fillers in the reactive filler composition are selected to generate water upon heating. As used in this specification, "generating water" can refer to the release of water, such as from hydrates, or the formation of water, such as through a chemical reaction process. Furthermore, the generated water can be in the form of liquid or water vapor. As used in this specification, the term "water" accordingly includes liquid water, water vapor, or a combination thereof. As used in this specification, the term "heat" refers to heat above the normal operating temperature of the battery, including heat generated by or in contact with a flame. This temperature can be 100°C or higher, or 200°C or higher, or 300°C or higher, or 500°C or higher. Without being bound by theory, it is believed that water generated from the reactive filler composition can provide insulating properties by absorbing heat, redistributing heat, or by evaporation.

[0019] Further, at least two types and quantities of fillers can be selected to form an insulating layer in its original position upon heating, water absorption, or both. As used in this specification, the term "thermal barrier layer" refers to a layer that is physically, chemically, or both different from the composite thermal management sheet, providing conduction or convection of heat, flame, or both. "Insulating layer" includes carbon layers or water-swellable polymers usable in the art. The inventors have discovered that if the insulating layer is not formed in its original position, hot air and water vapor can be rapidly transferred to adjacent battery cells via the elastic porous layer, including transport through the battery cell walls. Without being bound by theory, it is believed that with the insulating layer formed in its original position, hot air and water generated on the side of the failed battery cell of the composite thermal management sheet are confined to the surface of the failed battery cell, or within the composite thermal management sheet, or both. This can protect adjacent battery cells by generating pressure in the insulation layer, or by preventing convective heat transfer, conductive heat transfer, or both from entering adjacent battery cells.

[0020] At least two fillers are preferably in particulate form to facilitate their integration into the polysiloxane foam during manufacturing. As described above, the particulate reactive filler composition may be located within the polysiloxane matrix of the polysiloxane foam layer, within the pores of the polysiloxane foam layer, or both. Some pores in the polysiloxane foam layer may contain the particulate active filler composition, or substantially all, or all pores may contain the particulate active filler composition. Each pore containing the particulate active filler composition may be individually partially filled, substantially completely filled, or completely filled. In one state, where the reactive filler particles are relatively large compared to the pore diameter, or the pores are substantially or completely filled by multiple smaller particles, particle movement within the pores may be restricted. In this configuration, the particulate reactive filler composition may be located in the pores during the fabrication of the layer (e.g., by incorporating the particulate reactive filler composition into the components used to form the polysiloxane foam layer), or the particulate reactive filler composition may be impregnated in the pores by a suitable liquid carrier, vacuum, or other known methods after the polysiloxane foam layer has been fabricated.

[0021] Combinations of different reactive filler compositions can be used, including different types, forms, or locations. For example, particulate reactive filler compositions in the pores of a polysiloxane foam layer can be used in combination with particulate reactive filler compositions distributed in the polysiloxane foam layer.

[0022] The reactive particles can be of any shape, irregular or regular, such as approximately spherical, round, or disc-shaped. An important characteristic is that the maximum size of most, substantially all, or all of the particles is smaller than the thickness of the layer or pores in which they reside, to provide a smooth surface for that layer. The specific diameter used therefore depends on the location of the particles. Bimodal, trimodal, or even higher multimodal particle distributions can be used. For example, a bimodal particle distribution can be observed when the filler particles are in the matrix and pores of the polysiloxane foam layer.

[0023] At least two fillers that are different from each other are aluminum trihydrate, ammonium nitrate, borax, sodium silicate hydrate, magnesium hydroxide, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, zinc borate, superabsorbent polymer, or at least two of water glass.

[0024] Fillers that produce water upon heating include various hydrated mineral fillers, such as: aluminum trihydrate (also known as aluminum hydroxide or ATH), borax (sodium tetraborate pentahydrate), sodium silicate hydrate, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, superabsorbent polymers, and water glass. The aforementioned fillers can also be used in combination. It should be understood that hydrated mineral fillers and water glass can be represented by different chemical formulas, and the foregoing includes various chemical formulas. Unused portions of hydrated mineral fillers known to be used as phase change materials release water at lower temperatures (e.g., below 100°C or below 200°C) to prevent phase change at normal operating temperatures.

[0025] Fillers that can participate in the formation of the insulation layer, absorb water, or both, include various mineral fillers containing sodium, silicon, and boron. A single filler can both generate water and participate in the formation of the insulation layer. Exemplary fillers of this type may include ATH, ammonium nitrate, borax, hydrated sodium silicate, magnesium hydroxide, pentahydrate basic magnesium carbonate, octahydrate magnesium phosphate, zinc borate, superabsorbent polymers, water glass, or combinations thereof.

[0026] In the first state, the reactive filler composition comprises ATH and zinc borate. This combination generates water upon heating. The water causes the polysiloxane foam to expand, thus providing a counter-pressure. Unbound from theoretical constraints, the generated water can absorb heat to prevent heat loss. Further heat can be absorbed by the conversion of liquid water into water vapor. The heat capacity of ATH and zinc borate further promotes heat absorption. Upon exposure to a heat source, a porous insulating layer can be formed.

[0027] In the second state, the selected first and second fillers both generate water and, upon heating, form a borosilicate glass insulation layer in its original location. In this state, the first and second fillers may comprise a combination of borax and hydrated sodium silicate. Borax and hydrated sodium silicate generate water and provide sodium and boron to form borosilicate glass. The decomposition of the elastic silica layer provides silica to form borosilicate glass. Alternatively, in this state, a combination of ATH, zinc borate, and hydrated sodium silicate may be used. Without being theoretically constrained, it is believed that upon exposure to a heat source, the composite thermal management sheet absorbs heat due to the heat capacity of the polysiloxane and borax, the heat from the water and any vapor generated from the borax, and the endothermic formation of the borosilicate glass. The insulation layer can form and expand upon exposure to a heat source.

[0028] Advantageously, a combination of borax and zinc borate can be used in the reactive filler composition. Unexpectedly, it was found that when borax and zinc borate are used, the borosilicate glass insulating layer expands and deforms to form a resilient yet rigid layer. This deformation acts as a positive force on adjacent expanding battery cells, reducing or preventing damage caused by heat loss from the expanding cells. Without being constrained by theory, it is believed that the positive force generated by the expansion pressure and the shape of the carbon layer can further impede convective and conductive heat transfer.

[0029] In these isotropic samples, the composition and concentration of the reactive filler can be selected to provide phased water release, thereby providing continuous heat reduction. For example, it has been found that in hot-plate tests on filler compositions containing a combination of borax and zinc borate, heat from the hot plate diffuses into the elastic foam, initially generating water vapor from borax at 140°C, and subsequently from zinc borate at 340°C. Similarly, without theoretical constraints, it is believed that the initial release of water from borax initiates and sustains the formation of the insulation layer, affecting the final thickness of the borosilicate glass insulation layer, and thus influencing the applied pressure. This process also absorbs heat due to the heat capacity of polysiloxane, zinc borate, and borax, the generation of water from zinc borate and borax, the heat of any vapors, and the endothermic formation of the borosilicate glass. Furthermore, deformation of the composite layer provides resistance to heat transfer.

[0030] In another embodiment of phased water release, a reactive filler composition comprising borax and aluminum trihydrate can first generate water vapor from borax at 140°C, and then generate water vapor from the decomposition of ATH at 220°C.

[0031] Another reactive filler composition that can provide staged water release may include borax, ATH, and zinc borate. This combination can provide a three-stage water generation system that generates water from borax at 140°C, from ATH at 220°C, and from zinc borate at 340°C.

[0032] In the third state, a reactive packing composition for absorbing water is further formulated, allowing water to be retained or released (recycled). In this state, water absorption provides an additional mechanism to delay, reduce, or prevent convective heat transfer. Water absorption can further promote the expansion of the composite heat-conducting layer to provide additional pressure relief. In this state, the reactive packing composition comprises a packing that generates water upon heating and a packing that absorbs the generated water. Water can be permanently absorbed (i.e., retained) or releasably absorbed (desorbed), allowing for water recycling.

[0033] In this state, the filler material that generates water may include borax, ATH, magnesium hydroxide pentahydrate (MDH), or a combination thereof.

[0034] Fillers capable of absorbing generated water include superabsorbent polymers (SAPs). Under certain conditions, SAPs absorb and retain moisture, with the retained moisture only released upon SAP decomposition. Under other conditions, without SAP decomposition, SAPs can absorb and release water. Superabsorbent polymers are known in the art, for example: hydrolysates grafted with acrylonitrile homopolymers or copolymers, such as hydrolyzed starch-polyacrylonitrile; starch grafted with acrylic acid, acrylamide, polyvinyl alcohol (PVA), or combinations thereof, such as starch-g-poly(2-propeneamide-co-2-propenoic acid, sodium salt). Hydrolyzed starch-polyacrylonitrile-ethylene-maleic anhydride copolymer; crosslinked carboxymethyl cellulose; acrylate homopolymers and copolymers thereof, such as poly(sodium acrylate) and poly(acrylate-co-acrylamide), especially poly(sodium acrylate-co-acrylamide); hydrolyzed acrylonitrile homopolymers; 2-acrylate homopolymers and copolymers thereof, such as poly(2-acrylate, sodium salt) and poly(2-acrylamide-co-2-acrylate, sodium salt) or poly(2-acrylamide-co-2-acrylate, potassium salt); crosslinked modified polyacrylamide; polyvinyl alcohol copolymers, crosslinked polyethylene oxide, etc. Combinations of two or more different SAPs can be used.

[0035] SAP is preferably an electrolyte, such as a salt of poly(acrylate), such as sodium poly(acrylate). The expansion ratio of SAP can be from 15:1 to 1000:1, with a higher expansion ratio preferred. When absorbing moisture, SAP traps the moisture and expands. This expansion acts as a positive force against the expansion of adjacent battery cells, reducing or preventing damage caused by the expansion of the battery cells that allow heat to dissipate.

[0036] SAP can be selectively hydrated in water (by spraying, soaking, or other methods). For example, SAP can be hydrated before being incorporated into the polysiloxane foam, or the composite thermal management layer containing SAP can be soaked in room temperature water for 24 hours.

[0037] Without being bound by theory, it is believed that in this state, as previously described, water initially emerges from the filler as the temperature increases (various temperatures can be selected). The water is absorbed by the SAP. In this state, the water absorbed by the SAP is retained and not released. In another state, the water absorbed by the SAP absorbs heat and is then released, leaving the system containing the electrochemical cell unit, or absorbed by other dehydrated SAPs at different locations within the composite thermal management sheet. Ultimately, the borosilicate glass can form a continuous and flexible insulating layer.

[0038] Another filler material that can be used to absorb water is water glass. As is known in the art, water glass is soluble in water and contains sodium oxide (Na₂O) and silicon dioxide (SiO₂). Under certain conditions, water glass can absorb water to trap it, or absorb water and release it.

[0039] In another formulation, the reactive filler composition can be formulated to generate water glass in its original location without decomposing the elastic polysiloxane layer. In this formulation, the filler may contain borax and sodium silicate hydrate. Other components may be present, such as aluminum trihydrate, magnesium hydroxide, basic magnesium carbonate pentahydrate, or ammonium nitrate, or combinations thereof. Without being bound by theory, it is believed that depending on the combination of water-generating fillers used, heat will diffuse into the polysiloxane foam layer, generating water at different temperatures. Residual ions from the decomposition of the water-generating filler can form Lewis acids or Lewis bases, which react with sodium silicate hydrate to form water glass. The water can be released for recycling. Alternatively, when the water evaporates due to heating, the water glass solution can solidify to provide a glassy solid that can serve as a heat transfer layer inside or outside the polysiloxane foam.

[0040] Composite thermal management sheets can be manufactured from polysiloxane foaming compositions using methods known in the art. Reactive filler compositions can be incorporated into the polysiloxane foaming composition prior to foaming and curing. For example, suitable polysiloxane foams can be generated by reactive foaming and curing of polysiloxane foaming compositions containing terminally unsaturated polysiloxanes, such as vinyl groups and terminally hydride groups. The viscosity of the polysiloxanes used to form the polysiloxane foam at 25°C can be from 100 to 1,000,000 poise. Polysiloxanes used to form polysiloxane foams can have chain-like substituents, such as hydrides, methyl, ethyl, propyl, vinyl, phenyl, and trifluoropropyl. Besides terminal hydrides and vinyl groups, they can also have hydroxyl, alkoxy, acetoxy, allyl, oxime, aminooxy, isopropoxy, epoxy, thiosulfate, or other known reactive terminal groups. The desired foam can also be produced from various polysiloxane-based polymers with different functional groups or reactive groups. Polysiloxane foams can also be produced using various polysiloxanes with different molecular weights (e.g., bimodal or trimodal molecular weight distributions), provided that the combined viscosity allows for easy incorporation into reactive filler compositions and ease of manufacturing.

[0041] Polysiloxane foaming compositions may further include catalysts, such as catalysts containing noble metals, preferably platinum-containing catalysts. The catalyst can be deposited on an inert support, such as silicone, alumina, or carbon black. Various platinum catalyst inhibitors may also be present to control the kinetics of the foaming and curing reactions, thereby controlling the porosity and density of the polysiloxane foam. Examples of such inhibitors include polymethylvinylsiloxane cyclic compounds and alkynyl alcohols. These inhibitors should not interfere with foaming and curing in a way that damages the foam material. Chemical foaming agents may be present.

[0042] In the production of polysiloxane foam, the reactive component of the polysiloxane foam molding composition can be formulated into two parts: one part ("Part A") contains a polysiloxane with terminal unsaturation and a reactive filler composition, and if Part A is used, it also contains a catalyst, an inhibitor, and a chemical blowing agent; and the other part ("Part B") contains a polysiloxane with hydride groups. These parts can be metered, mixed, and cast, for example, poured into a mold or fed into a continuous coating line. Foaming and curing then occur in the mold or on the continuous coating line. In another production method, the reactive component of the polysiloxane foam molding composition can be introduced into an extruder together with the reactive filler composition and chemical blowing agents, physical blowing agents, or other additives (if used). A catalyst can then be metered into the extruder to initiate the foaming and curing reaction. Using physical foaming agents such as liquid carbon dioxide or supercritical carbon dioxide in combination with chemical foaming agents such as water can produce foamed materials with lower density.

[0043] Alternatively, the composite thermal management sheet can be immersed in water for a period of time, such as 24 hours, to immerse the composite thermal management sheet in water. The high heat capacity of liquid water helps to significantly delay the transfer of heat from one surface of the composite thermal management sheet to the other surface.

[0044] As previously mentioned, the content of each filler in the reactive filler composition is adjusted to provide the required degree of water generation and insulation layer formation. Based on the total weight of Part A of the polysiloxane foam molding composition, Part A may contain 10 to 80% by weight, 20 to 70% by weight, or 30 to 60% by weight of the reactive filler composition, with the remainder of Part A consisting of other components of Part A.

[0045] When the reactive filler composition contains ATH and zinc borate, each of them is based on the total weight of part A. Part A may contain 5 to 40% by weight, or 10 to 40% by weight, or 20 to 40% by weight of ATH and 5 to 40% by weight, or 10 to 40% by weight, or 20 to 40% by weight of zinc borate. The remaining part of the composition of part A consists of other components of part A.

[0046] When the reactive filler composition contains borax and sodium silicate hydrate, each is based on the total weight of part A. Part A may contain 5 to 50% by weight, or 10 to 40% by weight, or 20 to 40% by weight of borax and 5 to 30% by weight, or 10 to 30% by weight of sodium silicate hydrate. The remaining part of the composition of part A consists of other components of part A.

[0047] When the reactive filler composition includes ATH, sodium silicate hydrate, and zinc borate, each component is based on the total weight of part A. Part A may contain 5 to 30% by weight, or 10 to 20% by weight of ATH, 5 to 30% by weight, or 10 to 30% by weight of sodium silicate hydrate, and 5 to 40% by weight, or 10 to 30% by weight, or 10 to 30% by weight of 20 to 30% by weight of zinc borate. The remaining components of part A are other components of part A.

[0048] When the reactive filler composition includes borax and zinc borate, the content of borax, based on the total weight of part A, may be 5 to 45% by weight, or 10 to 40% by weight, preferably 15 to 35% by weight and more preferably 20 to 30% by weight, and the content of zinc borate may be 5 to 40% by weight, or 10 to 40% by weight, preferably 15 to 35% by weight and more preferably 20 to 30% by weight, and the remainder of the composition of part A is other components of part A.

[0049] When SAP is present in a reactive filler composition, each portion is based on the total weight of part A, which may contain SAP in a content of 1 to 60% by weight, or 5 to 35% by weight, or 10 to 35% by weight, and the remainder of part A is one or more different fillers and other components of part A.

[0050] Composite thermal management sheets may contain other additives known in the art, such as processing aids, antioxidants, anti-ozone agents, ultraviolet (UV) or heat stabilizers, dyes, pigments, flame retardants (e.g., organophosphorus compounds), flame retardant synergists (e.g., antimony oxide), or combinations thereof. A thermally insulating filler may be present to increase thermal insulation, heat absorption, or heat deformation properties. Exemplary thermally insulating fillers include ceramics such as silica, talc, calcium carbonate, clay, mica, vermiculite, etc., or combinations thereof. In another embodiment, a thermally conductive filler may be present to increase thermal conductivity, such as boron nitride, aluminum nitride, etc., or combinations thereof. A reinforcing particulate filler may be present. Exemplary reinforced particulate materials include lignin, carbon black, talc, mica, silica, quartz, metal oxides, glass microspheres (e.g., cenospheres, glass microspheres such as borosilicate microspheres, or combinations thereof), polyhedral oligomeric silsesquioxanes, substituted polyhedral oligomeric silsesquioxanes, or combinations thereof. These additives may be added simultaneously with the reinforcing filler composition.

[0051] Polysiloxane foam molding compositions can be foamed and cured in the presence of reinforcing fibers to provide fiber reinforcement. The reinforcing fibers may comprise polyester, oxidized polyacrylonitrile, carbon, silicon dioxide, polyarylamine, polycarbonate, polyolefin, rayon, nylon, glass fiber (e.g., E-glass fiber, S-glass fiber, D-glass fiber, L-glass fiber, quartz fiber, or combinations thereof), high-density polyolefin, ceramic, acrylic, fluoropolymer, polyurethane, polyamide, polyimide, or combinations thereof. The reinforcing fibers may be in any form, such as woven or non-woven felt or tape. The thickness of the felt or tape may be, for example, 0.005 to 10 mm, or 0.05 to 8 mm, or 0.25 to 6 mm, or 0.5 to 10 mm, or 0.25 to 10 mm, or 0.5 to 10 mm, or 1 mm to 6 mm. Combinations of reinforcing granular materials and reinforcing fibers may be used.

[0052] The thickness of the composite thermal management sheet can be 0.5 to 30 mm, or 0.5 to 20 mm, or 0.5 to 15 mm, or 0.5 to 10 mm, or 0.5 to 8 mm, or 1 to 6 mm, or 1 to 5 mm, or 1 to 4.5 mm, or 1 to 4 mm, or 1 to 3.5 mm, or 1 to 3 mm, or 1 to 2.5 mm. Compared to flame-retardant sheets of competing technologies, the composite thermal management sheet disclosed in this invention can provide equal or better thermal resistance while having a thinner thickness. In some configurations, for example, at the location where the insulation layer is formed, the thickness of the composite thermal management layer is preferably 1.5 to 30 mm, or 1.5 to 20 mm, or 1.5 to 15 mm, or 1.5 to 10 mm, or 1.5 to 8 mm, or 1.5 to 6 mm, or 1.5 to 5 mm, or 1.5 to 4.5 mm, or 1.5 to 4 mm, or 1.5 to 3.5 mm, or 1.5 to 3 mm, or 1.5 to 2.5 mm. Thicker composite thermal management sheets can provide greater pressure for generation, deformation, and borosilicate glass formation, thereby improving thermal delay. In this configuration, the thickness of the composite thermal management layer is preferably 1.5 to 30 mm, or 1.5 to 20 mm, or 1.5 to 15 mm, or 1.5 to 10 mm, or 1.5 to 8 mm, or 1.5 to 6 mm, or 2 to 30 mm, or 2 to 20 mm, or 2 to 15 mm, or 2 to 10 mm, or 2 to 8 mm, or 2 to 6 mm, or 3 to 0 mm, or 3 to 8 mm, or 3 to 6 mm.

[0053] In one sample, the density of the composite thermal management sheet is 5 to 65 pounds per cubic foot (1,041 kg / m³), or 5 to 55 pounds per cubic foot (881 kg / m³), or 10 to 25 pounds per cubic foot (400 kg / m³). In another sample, the density of the foam is 5 to 30 pounds per cubic foot (80 to 481 kg / m³). Based on the total volume of the foam, the void volume content of the composite thermal management sheet can be 5% to 99%, preferably greater than or equal to 30%.

[0054] The composite thermal management sheet is elastic and maintains its elastic behavior over multiple cycles of compression flexure throughout the battery pack's lifespan. These properties are reflected in the compressive flexural stress and compression set of the foam. Foam with good resistance to compression set provides cushioning and maintains its original shape or thickness under load for extended periods. In a single sample, the composite thermal management sheet, measured according to ASTM D3574-17 at 25% flexure, exhibits compressive flexural stresses of 0.2 to 125 psi (1 to 862 kPa), or 0.25 to 20 psi (1.7 to 138 kPa), or 0.5 to 10 psi (3.4 to 68.905 kPa) per square inch. Composite thermal management sheets, measured at 70°C according to ASTM D 3574-95 Test D, have a compressibility of 0 to 15%, or 0 to 10%, or 0 to 5%; or a density of 5 to 65 lb / ft³ (80 to 1041 kg / m³), or 6 to 20 lb / ft³ (96 to 320 kg / m³), or 8 to 15 lb / ft³ (128 to 240 kg / m³).

[0055] In a single-layer composite thermal management sheet, the composite thermal management sheet is used as a single layer. Multiple single-layer composite thermal management sheets can be stacked; however, the composite thermal management sheet is used as a single layer. Other layers can be used in conjunction with the composite thermal management sheet, such as flame-retardant layers, non-porous elastic insulating layers, adhesive layers, or combinations thereof. However, one advantage of composite thermal management sheets is that a single-layer composite thermal management sheet can be effective without the presence of other layers, even with thicknesses as low as 1 to 30 mm, or 1 to 20 mm, or 1 to 15 mm, or 1 to 10 mm, or 1 to 8 mm, or 1 to 6 mm.

[0056] If a flame-retardant layer is used, it may contain flame-retardant inorganic materials, such as: gibbsite, aluminum hydroxide, magnesium hydroxide, intumescent materials, or combinations thereof. The intumescent material may contain an acid source, a foaming agent, and a carbon source. The components may exist in different layers or as a mixture, preferably a tightly packed mixture. For example, the intumescent material may contain an acid source, a foaming agent, and a carbon source. For example, when the temperature reaches a value such as 200 to 280°C, the acidic substance (e.g., an acidic form of polyphosphoric acid) can react with the carbon source (e.g., neopentyl tertrol) to form char. As the temperature increases, for example, to 280 to 350°C, the foaming agent decomposes to produce gaseous products, causing the char to expand.

[0057] The acid source may include, for example, organic or inorganic phosphorus compounds, organic or inorganic sulfates (e.g., ammonium sulfate), or combinations thereof. The organic or inorganic phosphorus compound may include: organic phosphates or organic phosphonates (e.g., tris(2,3-dibromopropyl) phosphate, tris(2-chloroethyl) phosphate, tris(2,3-dichloropropyl) phosphate, tris(1-chloro-3-bromoisopropyl) phosphate, bis(1-chloro-3-bromoisopropyl)-1-chloro-3-bromoisopropyl phosphonate, polyaminotriazine phosphate, melamine phosphate, triphenyl phosphate, or formamidinyl phosphate); organic phosphites (e.g., trimethyl phosphite or triphenyl phosphite); phosphazenes (e.g., hexaphenoxycyclotriphosphazene); phosphorus-containing inorganic compounds (e.g., phosphoric acid, phosphorous acid, phosphites, urea phosphate, ammonium phosphate (e.g., ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, or ammonium polyphosphate)); or combinations thereof.

[0058] The blowing agent may contain an agent that decomposes (e.g., decomposes into smaller compounds, such as amines or carbon dioxide) at temperatures greater than or equal to 120°C, for example, at 120 to 200°C or at 130 to 200°C. The blowing agent may contain dicyandiamide, azodimethylamine, melamine, guanidine, glycine, urea (e.g., urea-formaldehyde resin or methoxylated formamidinyl urea phosphate), halogenated organic materials (e.g., chlorinated paraffin), or combinations thereof.

[0059] The expanded material may contain a carbon source. A polysiloxane foam layer can be used as a carbon source. The carbon source may contain dextrin, phenolic resin, neopentyl tertrol (e.g., its dimer or trimer), clay, polymers (e.g., polyamide 6, amino-poly(imidazoline-amide), or polyurethane), or combinations thereof. Amino-poly(imidazoline-amide) may contain repeating amide bonds and imidazoline groups.

[0060] The expandable material may optionally further comprise an adhesive. The adhesive may comprise epoxy resin, polysulfide, polysiloxane, polysiloxane, or a combination thereof. Based on the total weight of the expandable material, the adhesive may be present in the expandable material in an amount of less than or equal to 50% by weight, or 5 to 50% by weight, or 35 to 45% by weight. Based on the total weight of the expandable material, the adhesive may be present in the expandable material in an amount of 5 to 95% by weight, or 40 to 60% by weight.

[0061] The intumescent material may selectively include synergistic compounds to further enhance its flame retardancy. Synergistic compounds may include boron compounds (e.g., zinc borate, boron phosphate, or boron oxide), silica compounds, aluminosilicates, metal oxides (e.g., magnesium oxide, iron oxide, or aluminum oxide hydrates (boehmite)), metal salts (e.g., alkali metal salts or alkaline earth metal salts of organic sulfonic acids, or alkaline earth metal carbonates), or combinations thereof. A preferred synergistic combination includes a phosphorus-containing compound and at least one of the aforementioned compounds.

[0062] The flame-retardant layer may further comprise a charring agent, preferably lignin, gibbsite, clay nanocomposite materials, expandable graphite, neopentyl terephthalol, cellulose, nano-silica, ammonium polyphosphate, lignosulfonate, melamine, cyanuric acid, zinc borate, calcium magnesium carbonate, magnesite, or combinations thereof. Not limited by theory, similar to intumescent materials, it is believed that the charring agent can utilize two energy absorption mechanisms to reduce flame spread, including the formation of char followed by its expansion.

[0063] The flame-retardant layer may further comprise a polymeric adhesive, such as polysiloxane, polyurethane, ethylene-vinyl acetate, ethylene-methacrylate, ethylene-butyl acrylate, or combinations thereof. The thickness of the flame-retardant layer may be 0.1 to 2 mm, 0.5 to 1.5 mm, or 0.8 to 1.1 mm.

[0064] If a non-porous elastic barrier layer is used, the non-porous elastic barrier layer comprises an elastomer having a water permeability coefficient of less than 20 g-mm / m² / day, or less than 10 g-mm / m² / day, or less than 5 g-mm / m² / day, each measured at 25°C and 1 atm; or a tensile stress of 0.5 to 15 MPa at 100% tension, measured according to ASTM 412 at 21°C; or a combination thereof. The thickness of the non-porous elastic barrier layer can be 0.25 to 1 mm or 0.4 to 0.8 mm.

[0065] The non-porous elastic barrier layer may contain a hydrophobic elastic material to prevent water or water vapor penetration. For example, the elastic barrier layer may contain a thermoplastic elastomer (TPE), provided that it has good hydrophobicity (no water or water vapor penetration). Types of TPEs include styrene-based block copolymers (TPS or TPE-s), polyolefin elastomers (TPO or TPE-o), thermoplastic dynamically crosslinked elastomers (TPV or TPE-v), thermoplastic polyurethane elastomers, thermoplastic copolyesters (TPC or TPE-E), thermoplastic polyamide elastomers (TPA or TPE-A), and others.

[0066] Specific examples of usable elastic materials include acrylic rubber, butyl rubber, halogenated butyl rubber, copolyester, epichlorohydrin rubber, ethylene-acrylic rubber, ethylene-butylacrylic rubber, ethylene-diene rubber (EPR) such as ethylene-propylene rubber, ethylene-propylene-diene monomer rubber (EPDM), ethylene-vinyl acetate, fluororubber, perfluorinated rubber, polyamide, polybutadiene, polychloroprene, polyolefin rubber, polyisoprene, polysulfide rubber, natural rubber, nitrile rubber, low-density polyethylene, polypropylene, thermoplastic polyurethane elastomer (TPU), polysiloxane rubber, fluorinated polysiloxane rubber, styrene-butadiene, styrene-isoprene, vinyl rubber, or combinations thereof. In one state, the non-porous elastic insulating layer comprises ethylene-propylene-diene monomer rubber, polychloroprene, or combinations thereof.

[0067] Adhesive layers can be used to bond composite thermal management sheets to another composite thermal management sheet, another type of layer, or a component of a battery cell array or battery pack. Various known adhesives are available for composite thermal management sheets. Adhesives can be selectively used to make the battery pack easy to use and stable in operation. The adhesive layers can be the same or different, and have the same or different thicknesses. Suitable adhesives include phenolic resins, epoxy adhesives, polyester adhesives, polyvinyl fluoride adhesives, acrylic or methacrylic adhesives, or polysiloxane adhesives, preferably acrylic or polysiloxane adhesives. In one embodiment, the adhesive is a polysiloxane adhesive. Solvent casting, hot melt, and two-component adhesives can be used. The thickness of each adhesive layer can be 0.00025 to 0.010 inches (0.006 to 0.25 mm) or 0.0005 to 0.003 inches (0.01 to 0.08 mm).

[0068] When the composite thermal management sheet includes an adhesive layer, the composite thermal management sheet may further include a release layer. A "release layer" refers to any single or composite layer containing a release coating, optionally supported by one or more additional layers containing release liner. The thickness of each release layer may be 5 to 150 micrometers (μm), 10 to 125 μm, 20 to 100 μm, 40 to 85 μm, or 50 to 75 μm.

[0069] A composite thermal management sheet is disposed on an electrochemical battery cell to provide a battery cell assembly for a battery pack. The battery cell can be a lithium-ion battery cell, particularly a prismatic battery cell, a pouch cell, or a cylindrical battery cell. Figure 2 illustrates one configuration of the composite thermal management sheet in the battery cell assembly 1002. Figure 3 illustrates another configuration of the composite thermal management sheet in the battery cell assembly 1003. Figures 2 and 3 illustrate that the composite thermal management sheet 10 can be located between the first battery cell 103 and the second battery cell 104. Figure 2 illustrates that the dimensions of the composite thermal management sheet 10 can be approximately the same as the height and width of the battery cells 103 and 104. Figure 3 illustrates that the composite thermal management sheet 10 can be smaller than each of the battery cells 103 and 104. Also as shown in Figure 3, the composite thermal management sheet 10 may extend beyond the edges of the electrochemical battery cells 103 and 104. The composite thermal management sheet extending beyond the edges of the electrochemical battery cells can surround and cover at least another portion or all of the surface of the battery cell.

[0070] Figure 4 illustrates that a multi-cell assembly 1004 may include two or more battery cells 103 and 104, with composite thermal management sheets 10 located between the respective battery cells 103 and 104. These batteries may be lithium-ion battery cells, particularly pouch cell cells. Figure 4 also illustrates that a battery pack assembly 1004 may include two or more battery cells (e.g., 103 and 104), with composite thermal management sheets 10 located between the respective batteries 103 and 104 and other battery cells. In one embodiment, when manufacturing the battery pack assembly 1004, two to ten composite thermal management sheets may be disposed on the battery or in the battery array. For example, two to ten composite thermal management sheets may be disposed internally, for example facing the electrodes, or externally, facing outwards from the battery pack. Two to ten flame-retardant composite thermal management sheets may be disposed on or adhered to the pouch cell, or both. Depending on the number of battery cells and the number of battery cell arrays, one or more composite thermal management sheets may be present. Figure 4 further illustrates that the composite thermal management sheet 10a is disposed on the outside of the battery pack component 1004, facing outwards from the battery pack.

[0071] In one embodiment, at least a portion of the exposed outer edge of the composite thermal management sheet may comprise a material 88 that carries heat away from the body of the composite thermal management sheet. Exemplary materials applied to the exposed edge of the composite thermal management sheet include ceramics, such as boron nitride or aluminum nitride, metals, such as aluminum, high-heat-capacity waxes, phase change materials, etc., or combinations thereof.

[0072] For use with battery cells in a battery pack. A battery pack includes a housing that at least partially surrounds one or more electrochemical battery cells or arrays of battery cells. The housing can be of any type, such as a polymer or pouch cell. Composite thermal management sheets can be disposed or directly disposed on any configuration of battery cells or arrays of battery cells in the battery pack. Composite thermal management sheets can be disposed between individual battery cells or arrays of battery cells in the battery pack. Composite thermal management sheets can be disposed above, in the middle, below, adjacent to, or in combination thereof on the sides of battery cells or arrays of battery cells in the battery pack, on a portion thereof, or on a designated group of battery cells or arrays of battery cells in the battery pack. Composite thermal management sheets can be placed or adhered to multiple pouch cells, pressure management pads, cooling plates, or other internal components of the battery pack. Assembly pressure of the battery pack can hold the stacked components in place.

[0073] For example, as shown in Figure 5, the battery pack 2001 may include multiple battery cells in multiple battery cell arrays 700 within the housing 800. A composite thermal management sheet 10 may be placed between two battery cell arrays 700. Further, as shown in Figure 12, the composite thermal management sheet 10 may be disposed along the multiple battery cells of the battery cell arrays, between one side of the housing 800 and one side of the battery arrays 700. Also as shown in Figure 12, the thermally insulating composite thermal management sheet 10 may be disposed between one end of the housing 800 and one end of one or more battery cell arrays 700.

[0074] If more than one composite thermal management sheet or other layer is used, the sheet and layer can be assembled using methods known in the art. The sheet and layer can be assembled onto the surface of a battery cell or other components of a battery pack (e.g., battery case walls). In one state, the sheet and layer are assembled individually and then placed or adhered to components of a battery cell, battery pack, or both. Each sheet or layer can be manufactured individually and then stacked (placed or adhered, e.g., using one or more adhesive layers) in the desired order. Alternatively, one or more individual layers can be manufactured on another individual layer, e.g., by coating, casting, or laminating using heat and pressure. For example, in one state, a flame-retardant layer and an adhesive layer can be directly cast onto the composite thermal management sheet. Direct coating or casting can reduce thickness and improve flame retardancy by removing the adhesive layer.

[0075] The disclosure of this invention will be illustrated by the following embodiments. These embodiments are for illustrative purposes only and are not intended to limit the apparatus manufactured according to the disclosure of this invention in terms of the materials, conditions, or process parameters described therein. [Example]

[0076] The materials listed in Table 1 are used in the examples. Table 1 Element describe Company Name Manufacturer Vinyl-PDMS Vinyl-terminated polydimethylsiloxane; viscosity at 25°C: 100,000 mm² / s; specific gravity at 25°C: 0.973; flash point: >300°C (closed cup); freezing point: -45°C; surface tension: 21.1 mN / m; vapor pressure at 200°C: 1.33 Pascals. FLD V100000 Elkem Silicones Polysiloxane Polysilicon oxyhydride; viscosity at 25°C: 25 mm² / s; specific gravity at 25°C: 1.0; active ingredient (%): 100; flash point (closed cup): 110°C; diluent: aliphatic or aromatic hydrocarbons; ester, ketone, and SiH content: 44.5%. WR-68 Elkem Silicones catalyst Karstead's platinum catalyst, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum (0) in polysiloxane. 10% Pt 0 PT56710C Umicore Precious Metals Chemistry, LLC Inhibitors MVT inhibitors; methyl vinyl cyclic inhibitors ((Me-4-Vi-CYC)). FLD 50842 Elkem Silicones ATH Aluminum trihydrate; particle size from 1 to 5 micrometers (µm) Micral 855 JM Huber Borax 1 Sodium tetraborate pentahydrate; CAS # [12179-04-3] Na₂B₄O₇·5H₂O Borax MiniScience Inc. Borax 2 Sodium borate; also known as borax pentahydrate or "5 molar borax". ETiBOR-48 ETİMINE USA Inc. SAP Superabsorbent polymer, sodium polyacrylate; average particle size distribution: 0 to 45 µm; absorption capacity (g / g deionized water): >320; humidity (%): <10 X-S025R Zappa Stewart Sodium silicate Hydrate, Na₂SO₄H₂O, weight ratio of SiO₂ / Na₂O: 3.22, 19.2% Na₂O, 61.8% SiO₂, 18.5% H₂O; density: 0.70 g / cm³; characteristics: white fine powder; CAS# 1344-09-8 Sodium silicate, low alkalinity MiniScience Inc. Zinc borate 2ZnO*3B2O3*3.5H2O (Zinc borate hydrate (2335), dodecaborium, zinc tetradioctyl ether, heptahydrate); Humidity (%): <1.2; SG: 2.77; Solubility (water): <0.28% at 25°C; MW: 434.7 g / mol; Thermal stability: stable to 290°C; pH value at 20°C: 6.8 to 7.5 (aqueous solution); Particle size: 7 μm; Refractive index: 1.58; Water of crystallization, H2O: 14.50%, Boron oxide: 48.05%, Zinc oxide: 37.45%, Anhydrous equivalent: 85.50%, CAS: 138265-88-0 Firebrake ZB US Borax Corporation Sample preparation

[0077] The samples of Examples 1 to 6 were prepared using a two-part formulation having parts A and B as shown in Table 2, and using benzyl alcohol as a foaming agent. The filler was included in part A. Parts A and B were then mixed and cast between two release layers. After foaming and curing the casting mixture, the casting amount was adjusted to achieve the desired thickness. Foaming and curing were performed at 70°C for 10 minutes. The composite thermal management sheets of Examples 1 to 6 were cured at 94°C for 12 hours and cut to appropriate sizes. The composite thermal management sheets were then tested as described below. thermal test

[0078] The thermal properties of each sample were determined in a heat dissipation simulation experiment. Figure 6 illustrates the apparatus 5000 used for the thermal test. A composite thermal management sheet 10 was directly disposed on a hot plate 960 and the temperature was set to 550°C. The pyrogel surface of Comparative Example 1 was placed on the hot plate. A 12.7 mm mica panel battery cell analogue 970 was placed on the upper surface of the composite thermal management sheet 10. A thermocouple sensor 980 was inserted into a through hole in the mica panel battery cell analogue 970 to dispose the thermocouple sensor 980 on the upper surface of the composite thermal management sheet 10. Comparative Example 1

[0079] A comparative example comprising an unfilled polyurethane foam layer and a pyrogel insulation layer was tested. The two layers were bonded together using a multipurpose polysiloxane adhesive. Examples 1 to 6

[0080] Examples 1 to 6 were prepared using the components shown in Table 2. The amounts are expressed in parts by weight for each component, with 100 parts by weight comprising the vinyl-terminated polysiloxane and reactive filler composition. Part B contains only hydride polysiloxane. Parts A and B are mixed in a weight ratio of A:B = 20:1 (20 parts of part A to 1 part of part B).

[0081] Table 2 also shows the thickness of each cured sample before the test, regardless of whether the insulation layer was formed in its original position or whether the insulation layer was deformed during the test.

[0082] Table 2 Element Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Part A Vinyl-PDMS 50 50 50 50 50 50 catalyst 0.0085 0.0085 0.0085 0.0085 0.0085 0.0085 Inhibitors 0.0795 0.0795 0.0795 0.0595 0.098 0.098 benzyl alcohol 0.31 0.31 0.31 0.15 0.31 0.31 Borax 1 25 25 30 Zinc borate 25 25 30 20 ATH 20 30 10 SAP 20 Sodium silicate 20 20 nature Thickness, millimeters 5 1 3.2 3.2 2.79 2.5 Insulation layer yes yes yes yes yes yes Deformation yes yes no no no no

[0083] As shown in Figure 7, a reactive filler containing a combination of borax and zinc borate (Examples 1 and 2) provides an insulating layer 11 with a deformable (bent) surface. Despite a downward force applied to the sheet by a battery cell analog 970 on the test equipment, a bent surface is still formed. This force is similar to that that might be applied by a battery pack pad. Because deformation of the sheet occurs even under a downward force applied by the battery cell analog 970, the formed insulating layer lifts the battery cell analog 970, effectively pushing back the expanding battery cell and delaying convective heat transfer by creating cavitation. It also reduces the surface area at the contact points, thus delaying conductive heat transfer as well.

[0084] Figure 8 shows another view of the insulation layer formed from the reactive filler composition comprising borax and zinc borate of Examples 1 and 2. The insulation layer is continuous and elastic. This insulation layer is significantly different from the discontinuous and inelastic (fragile) insulation layers formed from prior art compositions, such as those resembling charcoal.

[0085] Figure 9 shows the temperature rise of each sample over time as sensed by a thermocouple sensor. Advantageously, all samples exhibit thermal resistance properties. The reactive filler compositions containing a combination of borax and zinc borate (Examples 1 and 2) provide better thermal performance than Examples 3 to 6.

[0086] Examples 1 and 2 have the same composition, but the thicker sheet in Example 1 provides better thermal protection to the opposing surfaces compared to the thinner sheet in Example 2. After 10 minutes, the temperature measured in Example 1 was lower than that measured in Comparative Examples 1 and 2 through 6. For electric vehicle battery pack applications, the time required to reach 150°C is crucial for determining technical feasibility, and ideally, the longer the better, for example, at least 10 minutes. Although the exposure was extended to 20 minutes, the opposing surfaces of the composite thermal management sheet in Example 1 only reached 140°C, failing to reach 150°C.

[0087] Unrestricted by theory, the superior results of Example 1 are believed to be due to the synergistic operation of different mechanisms. First, heat is believed to be absorbed due to the heat capacity of borax and zinc borate. Water in the borax is released, further absorbing heat. The generation of water vapor can provide more heat convection away from the heat source through the elastic porous layer. However, increased exposure to the heat source leads to the formation of an insulating layer that prevents the heat convection of water vapor and hot gases, thereby providing better heat resistance at high temperatures. The formation of the insulating layer can further reduce or prevent heat conduction. In the case of the deformed insulating layer formation shown in Examples 1 and 2, additional heat conduction can be reduced. Puncture test

[0088] A puncture test is performed. Figures 10A and 10B are schematic unfolded and non-unfolded views, respectively, of the first device 7000 used for the puncture test, including aluminum end plates 910 and 920 (with dimensions of 185 mm × 90 mm × 15.2 mm), polytetrafluoroethylene insulating films 930 and 940 (with dimensions of 185 mm × 90 mm × 1 mm), pouch battery cells 201 and 202, and test sample 950 (e.g., composite thermal management sheet). Features of battery cells 201 and 202 are provided in Table 3. Battery cell 201 is punctured by an 8 mm needle inserted at an indentation speed of 10 mm / s to initiate dissipation. Battery cells 201 and 202 are electrically insulating. Multiple thermocouples measure temperature profiles. Position V1 is between the punctured (e.g., failed) battery cell 201 and test sample 950, and position V2 is between test sample 950 and adjacent battery cell 202. It also measures voltage.

[0089] Table 3 Battery cell information Hi Power Polymer Lithium-ion (Nickel Manganese Cobalt (NMC) Flexible Pack) capacity 80 ampere-hours (Ah) 296 watt-hours (Wh) Voltage 3.7 volts (V) (standard); 4.2 V (charging) Energy density 250.8 Wh / kilogram Dimensions (height x width x length) 337 mm x 146 mm x 12 mm weight 1.18 kg Comparative Example 2

[0090] Test 1 includes a comparative example without a foaming layer. Comparative Example 3

[0091] Test 1: A comparative example containing an unfilled polyurethane foam layer. Examples 7 and 8

[0092] Examples 7 and 8 were prepared using the ingredients shown in Table 4. Part A and Part B were mixed at a weight ratio of A:B = 20:1 (20 parts Part A to 1 part Part B).

[0093] Table 4 Element Example 7 Example 8 Part A Vinyl-PDMS 0.498 lbs (225.9 g) 0.498 lbs (225.9 g) catalyst 0.0384 g 0.0384 g Inhibitors 0.3592 g 0.3592 g benzyl alcohol 0.003 lbs (1.4 g) 0.003 lbs (1.4 g) Zinc borate 0.299 lbs (135.5 g) 0.249 lbs (112.9 g) ATH 0.199 lbs (90.4 g) Borax 2 0.249 lbs (112.9 g) Part B Sodium silicate 0.4 lbs (181.4 g) 0.4 lbs (181.4 g) Vinyl-PDMS 0.6 lbs (272.2 g) 0.6 lbs (272.2 g)

[0094] Tables 5 and 6, and Figures 11 and 12 provide the puncture test results for Comparative Examples 2 and 7. Figure 11 is a graph showing the relationship between temperature (°C) and time (minutes), illustrating the puncture test results for Comparative Examples 3 and 7. As shown in Figure 11, Example 7 was able to prevent heat dissipation during the test. Figure 12 is a graph showing the relationship between voltage (V) and time (minutes), illustrating the puncture test results for Comparative Examples 2 and 3 and Example 7 at different thicknesses. The results in Figure 12 include an 18-second delay for Comparative Example 12, a 31-second delay for Comparative Example 2, a 102-second delay for Example 7 at a thickness of 2 mm, and no heat dissipation for Example 7 at a thickness of 3 mm.

[0095] Table 5 sample Thickness (mm) Maximum temperature (°C) Based on a delay of volts (seconds) The result of heat dissipation in the film Comparative Example 2 - Punctured battery cell: 1024.1 Adjacent battery cell: 1014 18 Battery unit punctured: Fire started at 11:31:56 Adjacent battery unit: Fire started at 11:32:14 Adjacent battery cells without foam material caught fire after 18 seconds. Example 7 3.126 Punctured battery cell: 708.8 Adjacent battery cell: 737.9 Infinite Battery unit punctured: Fire started at 15:23:08 Adjacent battery cells: No fire ignited

[0096] Table 6 Quality loss (%) Short-circuit delay (seconds) Example 7 10.3 Infinite Comparative Example 3 91.4 twenty one UL94 500 W (125 mm) Vertical Burning Test

[0097] According to the conditions in Section 6.2 of UL 94, 20 different material types were conditioned at 70±2°C for 168±2 hours. All samples were arranged and tested according to Section 9.5 of UL 94. Table 7 provides the classification requirements for vertically burning materials, and Table 8 provides the test results.

[0098] Table 7 standard 94.55VA 94.5VB The afterburn time of each individual sample rod plus the afterburn time after the fifth combustion application. ≤60 seconds ≤60 seconds Cotton indicator ignited by burning particles or droplets of any sample rod no no Any case of burn-through (hole) in sheet-like specimens no yes

[0099] Table 8 Sample number Afterburn time and afterglow time (seconds) Has the cotton indicator been ignited? Burn through Example 7 1.5 mm 1 5 no no 2 9 no no 3 18 no no 4 52 no no 5 14 no no result 94-5VA Example 7 3 mm 1 DNI † no no 2 DNI no no 3 DNI no no 4 DNI no no 5 DNI no no result 94-5VA Example 8 1.5 mm Group 1 1 95 no no 2 114 no no 3 101 no no 4 97 no no 5 104 no no result fail Example 8 1.5 mm Group 2 1 88 no no 2 75 no no 3 49 no no 4 112 no no 5 53 no no result fail Example 8 3 mm Group 1 1 189 no no 2 94 no no 3 DNI no no 4 15 no no 5 47 no no result fail Example 8 3 mm Group 2 1 DNI no no 2 5 no no 3 DNI no no 4 52 no no 5 DNI no no result 95-5VA †Not ignited (DNI)

[0100] Figure 13 and Table 9 provide the microcalorimetric test results for Comparative Example 3, Figure 14 and Table 10 provide the microcalorimetric test results for Example 7, and Figure 15 and Table 11 provide the microcalorimetric test results for Example 8. Figures 13, 14, and 15 have different X and Y axis scales.

[0101] Table 9 Comparative Example 3 Heat release (HRC) (joules / gram Kelvin (J / gK)) Peak heat release rate (HRR) (watts per gram (W / g)) Total heat release (HR) (kJ / g) Sample 1 338 275 17.5 Sample 2 330 263 17.1 Sample 3 303 213 13.2 Sample 4 305 239 14.8 average 319 ± 15 248 ± 24 15.7 ± 1.8

[0102] Table 10 Example 7 Heat release (J / gK) Peak heat release rate (W / g) Total heat release (kJ / g) Sample 1 63.7 27.4 7.3 Sample 2 66.5 28.2 7.7 Sample 3 66.1 28.4 7.8 average 65.4 ± 1.4 28.0 ± 0.4 7.6 ± 0.2

[0103] Table 11 Example 8 Heat release (J / gK) Peak heat release rate (W / g) Total heat release (kJ / g) Sample 1 83.4 36.9 7.8 Sample 2 75.2 30.1 6.2 Sample 3 90.6 42.6 8.8 average 83.1 ± 6.3 36.5 ± 5 7.6 ± 1

[0104] Figures 16A and 16B are schematic unfolded and non-unfolded views, respectively, of the second device 8000 used for the puncture test. It includes aluminum end plates 911 and 921, PTFE insulating films 931 and 941, 12 Ah soft-pack battery cells 203, 204, and 205, and test samples 951 and 952 (e.g., composite thermal management sheets). Battery cell 204 is punctured by a needle to initiate heat dissipation. Battery cells 203, 204, and 205 are electrically insulated. As shown in Figure 16A, multiple thermocouples measure temperature curves at positions V3, V4, V5, TC1, TC2, and TC8.

[0105] Table 10 and Figure 17 provide the results of the puncture test for Comparative Example 3; Table 11 and Figures 18 and 19 provide the results of the puncture test for Example 7; and Table 12 and Figure 20 provide the results of the puncture test for Example 8. Figures 17, 18, and 20 show the relationship between temperature (°C) and time (seconds). Figure 19 is a photograph of Example 7 after the puncture test; as shown, it still retains its elasticity.

[0106] Table 10 Comparative Example 3 Original mass (grams (g)) Final mass (g) Does it prevent short circuits? Short-circuit delay (seconds) Sample 1 7.3 1 to 1.5 grams (cannot be measured precisely) no 58 Sample 2 7.6 1 to 1.5 grams (cannot be measured precisely) no 52

[0107] Table 11 Example 7 Original mass (g) Final mass (g) Does it prevent short circuits? Short-circuit delay (seconds) Sample 1 34.8 30.2 yes unlimited Sample 2 34.4 29.9 yes unlimited

[0108] Table 12 Example 8 Original mass (g) Final mass (g) Does it prevent short circuits? Short-circuit delay (seconds) Sample 1 24.2 21.7 yes unlimited Sample 2 25.8 23.6 yes unlimited

[0109] The following are non-limiting embodiments disclosed in this invention.

[0110] Sample 1: A composite thermal management sheet for a battery pack, the composite thermal management sheet comprising: a polysiloxane foam layer; a reactive filler composition disposed within the polysiloxane foam layer, wherein the reactive filler composition comprises a first filler that decomposes to produce water upon initial heating; and a second filler, which is different from the first filler, wherein the second filler and the decomposition products of the first filler form a thermal insulation layer, or absorb water, or both.

[0111] Sample 2: The composite thermal management sheet as described in Sample 1, wherein the thermal insulation layer comprises a borosilicate glass layer, preferably a borosilicate glass layer with a curved surface.

[0112] Sample 3: A composite thermal management sheet as described in Sample 2, wherein the borosilicate glass contains silicon obtained from the decomposition of a polysiloxane foam layer.

[0113] Sample 4: The composite thermal management sheet as described in any of the aforementioned samples, wherein the first filler and the second filler are at least two of aluminum trihydrate, ammonium nitrate, borax, sodium silicate hydrate, magnesium hydroxide, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, zinc borate, superabsorbent polymer, or water glass.

[0114] Sample 5: The composite thermal management sheet as described in Sample 4, wherein the first filler comprises aluminum trihydrate, sodium silicate hydrate, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, superabsorbent polymer, water glass, or a combination thereof.

[0115] Sample 6: A composite thermal management sheet as described in Sample 4 or 5, wherein the second filler comprises ammonium nitrate, borax, sodium silicate hydrate, magnesium hydroxide, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, zinc borate, superabsorbent polymer, or a combination thereof.

[0116] Sample 7: The composite thermal management sheet as described in Sample 4, wherein the reactive filler composition comprises aluminum trihydrate and zinc borate.

[0117] Sample 8: The composite thermal management sheet as described in Sample 4, wherein the reactive filler composition comprises borax and sodium silicate hydrate.

[0118] Sample 9: The composite thermal management sheet as described in Sample 4, wherein the reactive filler composition comprises aluminum trihydrate, zinc borate and sodium silicate hydrate.

[0119] Sample 10: A composite thermal management sheet as described in Sample 4, wherein the reactive filler composition comprises borax and zinc borate.

[0120] Sample 11: The composite thermal management sheet as described in Sample 4, wherein the reactive filler composition comprises borax, zinc borate and aluminum trihydrate.

[0121] Sample 12: A composite thermal management sheet as described in any of Samples 4 to 11, wherein the reactive filler composition further comprises a superabsorbent polymer, water glass, or both.

[0122] Sample 13: The composite thermal management sheet as described in Sample 12, wherein the reactive filler composition comprises aluminum trihydrate, sodium silicate hydrate, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, or a combination thereof; and a superabsorbent polymer, preferably poly(sodium acrylate).

[0123] Sample 14: A composite thermal management sheet as described in any of the preceding samples, the composite thermal management sheet having a thickness of 1 to 30 mm, or 1 to 20 mm, or 1 to 15 mm, or 1 to 10 mm, or 1 to 8 mm, or 1.5 to 8 mm, or 1.5 to 6 mm, or 2.5 to 6 mm.

[0124] Sample 15: A composite thermal management sheet as described in any of the preceding samples, wherein the density of the composite thermal management sheet is 5 to 65 pounds per cubic foot (80 to 1041 kg / m³), or 6 to 20 pounds per cubic foot (96 to 320 kg / m³), or 8 to 15 pounds per cubic foot (128 to 240 kg / m³); the compressive flexural stress at 25% flexure, measured according to ASTM D3574-17, is 0.2 to 125 pounds per square inch (1 to 862 kPa), or 0.25 to 20 pounds per square inch (1.7 to 138 kPa), or 0.5 to 10 pounds per square inch (3.4 to 68.905 kPa); and the compression ratio, measured according to ASTM D 3574-95 Test D at 70°C, is 0 to 15%, or 0 to 10%, or 0 to 5%; or a combination thereof.

[0125] Sample 16: A component of a battery pack comprising a composite thermal management sheet as described in any of the preceding samples, the composite thermal management sheet being disposed on the surface of an electrochemical battery cell, preferably a lithium-ion electrochemical battery cell.

[0126] Sample 17: A battery pack assembly as described in Sample 16, wherein the electrochemical battery cell comprises a square battery cell, a pouch battery cell, or a cylindrical battery cell.

[0127] State 18: A battery pack assembly as described in either State 16 or 17, wherein the battery pack assembly comprises at least two electrochemical cell units.

[0128] Specimen 19: A battery pack comprising components of a battery pack as described in any one of Specimens 16 to 18, and a housing that at least partially surrounds the components of the battery pack.

[0129] The composition, method, and article may alternatively include, or consist of or be primarily composed of, any suitable materials, steps, or ingredients disclosed herein. The composition, method, and article may be additionally or alternatively formulated to avoid or substantially eliminate any materials (types), steps, or ingredients that are otherwise unnecessary for achieving the function or purpose of the composition, method, and article.

[0130] The term "one" does not indicate a limitation on quantity, but rather signifies that at least one referenced item exists. Unless otherwise expressly stated in the text, the term "or" means "and / or". References to "one state" and "another state" in this specification indicate that a specific element (e.g., feature, structure, step, or characteristic) described in connection with that state is included in at least one state described herein, and may or may not be present in other states. Furthermore, it should be understood that the elements described may be combined in any suitable manner across various states.

[0131] When an element, such as a layer, film, region, or matrix, is indicated as being "on" another element, it may be directly on that other element, or there may be intermediate elements present. Conversely, when an element is indicated as being "directly" on another element, there are no intermediate elements present.

[0132] Unless otherwise stated herein, all test standards are the most recent standards in effect as of the filing date of this invention, or, if priority is claimed, the most recent standards in effect as of the filing date of the earliest priority claim of the invention.

[0133] The endpoints of all ranges involving the same composition or properties are included, can be combined independently, and include all intermediate points and ranges. For example, the range "up to 25% by weight, or 5 to 20% by weight" includes the endpoint and all intermediate values ​​within the range of "5 to 25% by weight," such as 10 to 23% by weight. The terms "first," "second," etc., and "primary," "secondary," etc., as used herein, do not indicate any order, quantity, or importance, but are used to distinguish one element from another. The term "the aforementioned combination" is open-ended and indicates that the list includes all individual elements, combinations of two or more elements in the list, and combinations of at least one element in the list with unnamed similar elements. Similarly, the term "combination" includes blends, mixtures, alloys, and reactants.

[0134] Unless otherwise defined, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0135] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if any terminology used in this invention contradicts or conflicts with any terminology used in any of the incorporated references, the terminology used in this invention shall prevail over the conflicting terminology used in the incorporated references.

[0136] In the drawings, for clarity and ease of explanation, the width and thickness of layers and regions may be exaggerated. Identical component symbols in the drawings represent the same component.

[0137] This document describes exemplary embodiments with reference to cross-sectional schematic diagrams of ideal implementations. Therefore, variations in the shapes of the figures are to be expected due to factors such as manufacturing techniques and / or tolerances. Thus, the embodiments described herein should not be construed as limiting the specific shape of the areas shown in the figures, but rather encompass shape deviations, for example, due to manufacturing processes. For instance, areas illustrated or described as flat may generally have rough and / or non-linear characteristics. Furthermore, sharp corners in the figures may be rounded. Therefore, the areas shown in the figures are schematic in nature, and their shapes are not intended to illustrate the precise shape of a region, nor are they intended to limit the scope of the invention.

[0138] Although a particular form has been described, alternatives, modifications, alterations, improvements, and substantially equivalent forms that the applicant or others skilled in the art would conceive of but are not currently foreseen or may not be foreseen. Therefore, the scope of the accompanying patent application, filed at the time of filing and subject to modification, is intended to cover all such alternatives, modifications, alterations, improvements, and substantially equivalent forms.

[0139] This invention claims priority to U.S. Patent Application No. 63 / 158,675, filed March 9, 2021. The entire contents of that application are incorporated herein by reference.

[0140] 10: Composite thermal management sheet 10a: Composite thermal management sheet 11: Insulation layer 12: Elastic polysiloxane foam layer 14: First outer surface 16: Relative to the second outer surface 18: Porosity 20: Inner surface of elastic foam material 22: Packing 24: Packing 88: Material that removes heat from the main body of the composite thermal management sheet 103: Battery Unit 104: Battery cell 201: Soft-pack battery cell 202: Soft-pack battery cell 203: Soft-pack battery cell 204: Soft-pack battery cell 205: Soft-pack battery cell 700: Battery cell array 800: Casing 910: End plate 911: End plate 920: End plate 921: End plate 930: Insulating film 940: Insulating film 941: Insulating film 950: Sample 951: Sample 960: Hot Plate 970: Battery cell analogues 980: Thermocouple Sensor 1002: Components of a Battery Cell 1003: Components of a Battery Cell 1004: Components of Multi-cell Battery 2001: Battery Pack 5000: Apparatus for thermal testing 7000: The primary device used for puncture testing 8000: Second device used for puncture testing V1: Position V2: Position V3: Location V4: Position V5: Location TC1: Position TC2: Position TC8: Position

Claims

1. A composite thermal management sheet for a battery pack, characterized in that it comprises: a polysiloxane foam layer; and a reactive filler composition disposed within the polysiloxane foam layer, wherein, The reactive packing composition includes: a first packing that decomposes to produce water upon initial heating; and a second packing that differs from the first packing, wherein the second packing forms a heat-insulating layer with the decomposition products of the first packing, or absorbs water, or both.

2. The composite thermal management sheet as described in claim 1, wherein, The insulation layer contains a borosilicate glass layer.

3. The composite thermal management sheet as described in claim 2, wherein, The borosilicate glass layer contains silicon obtained from the decomposition of the polysiloxane foam layer.

4. The composite thermal management sheet as described in claim 1, wherein, The first and second packing materials are at least two of the following: aluminum trihydrate, ammonium nitrate, borax, sodium silicate hydrate, magnesium hydroxide, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, zinc borate, superabsorbent polymer, or water glass.

5. The composite thermal management sheet as described in claim 4, wherein, The first filler comprises aluminum trihydrate, sodium silicate hydrate, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, superabsorbent polymer, water glass, or a combination thereof.

6. The composite thermal management sheet as described in claim 4, wherein, The second filler comprises ammonium nitrate, borax, sodium silicate hydrate, magnesium hydroxide, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, zinc borate, superabsorbent polymer, or a combination thereof.

7. The composite thermal management sheet as described in claim 4, wherein, The reactive filler composition includes aluminum trihydrate and zinc borate.

8. The composite thermal management sheet as described in claim 4, wherein, The reactive filler composition includes borax and sodium silicate hydrate.

9. The composite thermal management sheet as described in claim 4, wherein, The reactive filler composition includes aluminum trihydrate, zinc borate, and sodium silicate hydrate.

10. The composite thermal management sheet as described in claim 4, wherein, The reactive filler composition includes borax and zinc borate.

11. The composite thermal management sheet as described in claim 4, wherein, The reactive filler composition includes borax, zinc borate, and aluminum trihydrate.

12. The composite thermal management sheet as described in claim 4, wherein, The reactive filler composition includes superabsorbent polymers, water glass, or both.

13. The composite thermal management sheet as described in claim 12, wherein, The reactive filler composition includes aluminum trihydrate, sodium silicate hydrate, basic magnesium carbonate pentahydrate, magnesium phosphate octahydrate, or combinations thereof; and a superabsorbent polymer.

14. The composite thermal management sheet as described in claim 1, wherein, The thickness of the composite thermal management sheet ranges from 1 to 30 millimeters.

15. The composite thermal management sheet as described in claim 1, wherein, The composite thermal management sheet has a density of 80 to 1041 kg per cubic foot.

16. The composite thermal management sheet as described in claim 1, wherein, This composite thermal management sheet has the following characteristics: compressive flexural stress of 1 to 862 kPa when measured at 25% flex according to ASTM D3574-17.

17. The composite thermal management sheet as described in claim 1, wherein, This composite thermal management sheet has the following characteristics: a compressibility of 0 to 15% as measured at 70°C according to ASTM D 3574-95 Test D.

18. A component of a battery pack, characterized in that it comprises: a composite thermal management sheet as described in claim 1, the composite thermal management sheet being disposed on the surface of an electrochemical battery cell.

19. The battery pack assembly as described in claim 18, wherein, The electrochemical battery unit includes square battery units, pouch battery units, or cylindrical battery units.

20. A component of the battery pack as described in claim 18, wherein, The battery pack comprises at least two electrochemical cell units.

21. A battery pack, characterized in that it comprises: a battery pack assembly as described in any one of claims 18 to 20; and a housing that at least partially surrounds the battery pack assembly.

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