A dynamic adjustable thermal switch composite material based on asymmetric thermal strain and a preparation method and system thereof

Abstract

The application discloses a kind of based on asymmetric thermal strain dynamic adjustable thermal switch composite material and preparation method and system, belong to advanced thermal management material field.The composite material is macroscopic double-layer structure, including sequentially laminated low thermal expansion constraint layer and high thermal expansion active layer containing heat-conducting filler;Two layers are in situ crosslinking by surface activation and coupling agent at interface and form high-strength covalent chemical bonding.Under normal operating conditions, the temperature of the heating surface is lower than the set threshold value, the composite material closely fits the heating surface, and is in the flat state of high efficient heat conduction;When the temperature abnormally rises and exceeds the set threshold value, the thermal strain mismatch and thermal bending moment are generated due to the difference of thermal expansion coefficient between the two layers, which drives the material to spontaneously generate macroscopic curling and lift off, and introduces an air layer at the interface, and instantly switches to the state of extremely efficient thermal insulation.The application realizes a breakthrough of 50 times of equivalent thermal resistance regulation and control ratio, with zero power consumption, zero delay, deformation reversible and anti-interface peeling and delamination characteristics, and can be widely applied to passive intrinsic safety heat loss control and diffusion protection of power battery pack.

Description

Technical Field

[0001] This invention belongs to the field of intelligent thermal management materials and biomimetic composite materials technology, and specifically relates to an ultra-high on / off ratio material, preparation method, and application system in power battery thermal management, which undergoes macroscopic curling deformation driven by temperature, thereby dynamically regulating the equivalent thermal resistance by actively introducing an air layer through controlling the physical contact interface. Background Technology

[0002] With the explosive growth of the new energy vehicle industry, the energy density of power batteries (such as high-nickel ternary lithium batteries and large cylindrical batteries) is constantly approaching physical limits. Behind the high energy density, the safety of battery packs, especially the "thermal runaway propagation" induced by individual cells, has become a core pain point restricting the industry's development. The thermal management system of power batteries faces an extremely demanding and contradictory requirement: "extremely efficient heat conduction" is needed under normal operating conditions, while "absolute heat insulation" is needed under abnormal thermal runaway conditions.

[0003] Specifically, during normal battery charging and discharging (especially high-power fast charging), the battery cell generates a large amount of waste heat. To ensure that the battery operates within a safe temperature range and extends its lifespan, the industry typically fills the space between the battery cell and the bottom liquid cooling plate with a high thermal conductivity interface material (such as a thermally conductive silicone pad) to create a low thermal resistance heat dissipation channel. However, once a single battery cell experiences thermal runaway due to an internal short circuit, overcharging, or mechanical impact, its internal temperature can soar to hundreds or even thousands of degrees Celsius within seconds. At this point, the high thermal conductivity pad, originally intended for daily heat dissipation, becomes a "heat highway," rapidly transferring extremely high heat flow to the liquid cooling plate and adjacent healthy battery cells, instantly triggering a catastrophic domino-like chain explosion and fire.

[0004] To resolve this fatal contradiction, current technologies mainly adopt the following compromise solutions, but all of them have significant drawbacks: The first method involves using static passive insulation materials (such as aerogel pads or mica sheets) to wrap or isolate the battery cells. While this approach can delay the spread of thermal runaway to some extent, its extremely low initial thermal conductivity severely hinders heat dissipation during normal battery operation. This not only significantly limits the battery's fast-charging capability but also causes the battery to be in a high-temperature environment for extended periods, accelerating cell aging.

[0005] The second method relies on active thermal management using a battery management system (BMS). When sensors detect an abnormal temperature rise, the liquid cooling flow is increased to suppress it. However, thermal runaway often occurs instantaneously, and there is a fatal response delay (typically on the order of seconds or even tens of seconds) between sensor temperature measurement, system algorithm judgment, and actuator action. Furthermore, under extreme local temperatures of thousands of degrees, the temperature sensing harness and electronic components are extremely prone to instantaneous burnout and failure, leading to protection failure.

[0006] The third approach involves developing phase change materials (PCMs) or traditional microscopic solid-state thermal switching materials. While PCMs (such as paraffin-based composites) can absorb instantaneous heat waves, they suffer from latent heat absorption saturation. Once the phase change is complete, liquefaction and leakage often occur, resulting in a loss of barrier properties. Furthermore, the solid-state thermal switching materials developed in recent years (which rely on microscopic polymer chain phase changes or percolation damage to conductive networks to adjust thermal resistance) are limited by the physical nature of solid-state phonon heat transfer, with their "thermal resistance control ratio (on / off ratio)" typically restricted to around 3 to 5 times. This negligible change in thermal resistance is utterly inadequate when facing the massive heat waves of up to 1000°C in a single battery cell, failing to fundamentally cut off the heat diffusion path at a macroscopic level.

[0007] In summary, existing battery thermal protection technologies are all stuck in technical bottlenecks: "static materials cannot simultaneously conduct heat and insulate heat" and "dynamic materials have too low thermal switching ratios, and active systems have the risk of delay and failure."

[0008] Therefore, the industry urgently needs to develop a smart composite material designed specifically for power batteries. This material can maintain high thermal conductivity at normal room temperature, and when the critical overheating threshold of a single cell (such as >100℃) is detected, it can spontaneously and instantaneously generate a cliff-like thermal resistance change (ultra-high switching ratio) without any external power supply (zero power consumption) or electronic system delay (zero delay), thereby achieving "passive intrinsic safety" protection of single-point overheating and in-situ isolation. Summary of the Invention

[0009] To address the technical problems of existing power battery thermal management materials, such as the inability of static materials to balance thermal conductivity and insulation, and the low thermal switching ratio of dynamic materials, as well as the risk of delay and failure in active systems, this invention provides a dynamically adjustable thermal switching composite material based on asymmetric thermal strain, along with its preparation method and system. This material adopts a macroscopic double-layer structure design, utilizing the strain mismatch between two materials with different thermal expansion coefficients during the heating process to drive the material to undergo macroscopic reversible curling. By actively introducing an air layer, a drastic change in contact thermal resistance is achieved.

[0010] This invention is achieved through the following technical solution: A dynamically adjustable thermal switch composite material based on asymmetric thermal strain includes a low thermal expansion constraint layer and a high thermal expansion active layer stacked sequentially, wherein the low thermal expansion constraint layer and the high thermal expansion active layer form a covalent chemical bond interface at the interface through a coupling agent. The coefficient of thermal expansion of the low thermal expansion confinement layer is less than 20 ppm / K; The high thermal expansion active layer includes a polymer elastomer matrix and a thermally conductive filler dispersed in the polymer elastomer matrix. The coefficient of thermal expansion of the high thermal expansion active layer is greater than 200 ppm / K, and the mass fraction of the thermally conductive filler in the high thermal expansion active layer is 10%~40%. The composite material has a morphological transformation characteristic in response to changes in ambient temperature: when the temperature of the heating surface is lower than a set temperature threshold, the composite material is in a flat and bonded first form to conduct interfacial heat; when the temperature of the heating surface exceeds the set temperature threshold, the high thermal expansion active layer and the low thermal expansion constraint layer generate thermal strain mismatch and thermal bending moment through the difference in their thermal expansion coefficients, driving the composite material to bend and warp toward the low thermal expansion constraint layer and transform into a second form to detach from the heating surface and form an air insulation layer at the interface between the two.

[0011] Preferably, the low thermal expansion constraint layer is any one of copper foil, aluminum foil, or graphene composite film, and the thickness of the low thermal expansion constraint layer is 10μm to 50μm.

[0012] Preferably, the polymer elastomer matrix is ​​any one of polydimethylsiloxane, polyurethane, or liquid silicone rubber; The thermally conductive filler includes at least one of alumina microparticles, boron nitride microparticles, or liquid metal droplets.

[0013] Preferably, the coupling agent is a silane coupling agent, and the covalent chemical bonding interface comprises a siloxane bond network formed by the reaction of hydroxyl groups on the surface of the low thermal expansion constraint layer with the silane coupling agent.

[0014] A method for preparing a dynamically tunable thermally switched composite material based on asymmetric thermal strain includes the following steps: Surface activation: The low thermal expansion confinement layer is subjected to surface plasma treatment to generate active groups on its surface; Coupling agent modification: Coating the activated low thermal expansion constraint layer surface with a coupling agent solution and drying it to form an anchoring layer; Slurry preparation: The polymer elastomer prepolymer, curing agent and the thermally conductive filler are mixed in proportion and degassed to obtain a high thermal conductivity fluid slurry; In-situ coating and cross-linking curing: The high thermal conductivity fluid slurry is coated onto the modified low thermal expansion constraint layer surface and heated to allow the polymer elastomer to cross-link and cure itself, and to covalently bond with the coupling agent functional groups on the surface of the low thermal expansion constraint layer.

[0015] Preferably, in the surface activation step, the low thermal expansion confinement layer is bombarded using a plasma device that introduces a mixture of oxygen and argon gas, and the resulting active groups include hydroxyl groups; In the coupling agent modification step, the coupling agent solution is a 2% KH550 ethanol aqueous solution, and the drying conditions are drying at 80°C for 15 minutes.

[0016] Preferably, in the slurry preparation step, the polymeric elastomer prepolymer is a liquid polydimethylsiloxane prepolymer, and the mass ratio of the liquid polydimethylsiloxane prepolymer to the curing agent is 10:1. In the in-situ coating and cross-linking curing steps, the high thermal conductivity fluid slurry is uniformly coated onto the surface of the modified low thermal expansion constraint layer, and the wet film thickness is controlled to be 150 μm; the heating condition is constant temperature heating at 100°C for 1 hour.

[0017] A smart thermal management system for power batteries includes a battery pack and the aforementioned dynamically adjustable thermal switch composite material based on asymmetric thermal strain. The battery pack contains a cell array, and the composite material is processed into an array of patches or a cover film, which are sandwiched and applied to the heating surface of the cell array. When the intelligent thermal management system for the power battery performs purely passive thermal protection, it includes: Under normal operating conditions, the temperature of the battery cell array is lower than the set temperature threshold, and the composite material maintains a flat and bonded first form to transfer the waste heat of the battery cells out. When a local cell experiences thermal runaway, causing the temperature to exceed the set temperature threshold, the composite material in contact with the faulty area spontaneously curls and rises upwards, transforming into a second form, forming an air layer at the interface to block heat conduction to the surrounding healthy cells.

[0018] Preferably, the composite material is specifically sandwiched and laid on or between the cylindrical cell arrays; The mechanism by which the composite material transforms from the first state to the second state is based on the intrinsic thermodynamic physical response of the material.

[0019] Preferably, the equivalent thermal resistance control ratio between the first flat and bonded state and the second curled and raised state of the power battery intelligent thermal management system is greater than 50 times. Once the risk of thermal runaway in a localized cell is eliminated and the temperature drops below the set temperature threshold, the composite material flattens out again and adheres to the heating surface due to its own elastic restoring force, thus achieving reversible control.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects: This invention employs a bilayer heterostructure consisting of a low-thermal-expansion constraint layer and a high-thermal-expansion active layer stacked sequentially, with a covalent chemical bond interface formed at the interface using a coupling agent. Simultaneously, the low-thermal-expansion constraint layer is limited to a thermal expansion coefficient of less than 20 ppm / K, and the high-thermal-expansion active layer comprises a polymer elastomer matrix and 10%–40% thermally conductive filler dispersed therein, with a thermal expansion coefficient greater than 200. The ppm / K ratio allows the composite material to maintain a flat and adhered first form for interfacial heat conduction when the heating surface temperature is below a set temperature threshold. However, when the heating surface temperature exceeds the set temperature threshold, the significant difference in the coefficient of thermal expansion between the high thermal expansion active layer and the low thermal expansion constraint layer generates thermal strain mismatch and thermal bending moment. This drives the composite material to bend and warp towards the low thermal expansion constraint layer, transforming it into a second form. This allows it to actively detach from the heating surface and form an air insulation layer at the interface between the two. This achieves a mechanism leap from "microscopic thermal conduction network change" to "macroscopic physical displacement" through a completely physical response, avoiding the risk of protection failure caused by sensor delays and high-temperature failures of electronic components in traditional active thermal management systems. Furthermore, the extremely low thermal conductivity of the introduced air insulation layer completely cuts off the heat conduction path, enabling the equivalent thermal resistance to be adjusted. With a control ratio exceeding 50 times, this material overcomes the technical bottleneck of traditional solid-state thermal switching materials, which are limited to a switching ratio of less than 5 times due to the inherent physical properties of solid-state phonon heat transfer. Simultaneously, by replacing weak physical van der Waals forces with covalent chemical bonding interfaces, the interfacial peel strength is increased by orders of magnitude, effectively transferring and dissipating shear stress generated by thermal expansion mismatch. This ensures that the composite material remains dense and undamaged after hundreds of severe thermal shock deformations, possessing fatigue cycle resistance that meets automotive-grade reliability requirements. Furthermore, the composite material's morphological transformation in response to temperature changes relies entirely on its intrinsic thermodynamic physical response, requiring no external energy drive or electronic control system intervention. This achieves zero-power consumption and zero-delay reversible control, making it widely applicable in passive thermal runaway propagation protection of power battery packs and adaptive battery insulation in extreme environments. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the preparation process of the dynamically adjustable thermal resistance composite material of the present invention.

[0023] Figure 2This is a schematic diagram illustrating the macroscopic deformation and working principle of the composite material of the present invention under different temperature conditions.

[0024] Figure 3 This is a microscopic magnified schematic diagram of the internal double-layer heterogeneous structure and thermal conductive network distribution of the composite material of the present invention.

[0025] Figure 4 This is a schematic diagram of a system-level working scenario for the application of the composite material of the present invention in the prevention of thermal runaway diffusion in the power battery pack of new energy vehicles. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] To facilitate understanding of the technical solutions of this invention, some of the technical terms involved in this invention are explained below: Asymmetric thermal strain: refers to the physical phenomenon in which different layers of a composite material expand or contract at different rates due to significant differences in their coefficients of thermal expansion (CTE) under the same temperature change conditions.

[0028] Thermal strain mismatch: refers to the physical phenomenon where two materials with different coefficients of thermal expansion produce different strains under the same temperature change. In this invention, when the temperature rises, the high thermal expansion active layer produces an elongation strain much greater than that of the low thermal expansion confinement layer. This mismatch generates internal stress at the interface between the two layers, which in turn forms a thermal bending moment.

[0029] Thermal bending moment: refers to the bending moment generated inside the material due to thermal strain mismatch of the bilayer material, which is the direct mechanical cause of the curling deformation of composite materials.

[0030] Covalent chemical bonding interface: Unlike traditional physical adhesive interfaces that rely on van der Waals forces (intermolecular forces), this invention directly forms chemical bonds (such as -Si-O- bonds) with shared electron pairs between heterogeneous materials (such as metal and polymer) through chemical reactions, resulting in an order-of-magnitude increase in bonding strength.

[0031] Thermal on / off ratio: refers to the equivalent thermal resistance ratio of the composite material between its "highly thermally conductive state" (flat and bonded) and "highly thermally insulating state" (curled and warped), used to measure the controllability of thermal on / off states. The thermal on / off ratio of this invention embodiment can reach more than 50 times.

[0032] In-situ crosslinking: refers to a process in which a polymer prepolymer is coated onto the surface of a substrate, and then a polymer crosslinking and curing reaction is directly carried out on the substrate surface. In this invention, while the polymer elastomer is crosslinking and curing, its molecular chains also undergo covalent bonding with the coupling agent functional groups on the surface of the constraint layer, achieving "integrated crosslinking and bonding".

[0033] Air insulation layer (air bridge): refers to the gap layer formed between the composite material and the heating surface after the composite material of this invention curls up, with air as the main medium. Air has extremely low thermal conductivity, about 0.026 W / (m·K), which can effectively block the heat conduction path.

[0034] Passive thermal protection refers to a thermal protection method that relies entirely on the intrinsic physical properties (thermodynamic response) of the material itself, without requiring external energy drive, sensors, or battery management system (BMS) signal intervention. This invention features zero power consumption and zero latency.

[0035] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Inspired by the asymmetric contraction of biological tissues under heat, this invention proposes a dynamically adjustable thermally switched composite material and system based on asymmetric thermal strain. From a macroscopic structural perspective, the material consists of a low thermal expansion constraint layer (first layer) and a high thermal expansion active layer (second layer) stacked sequentially, with a covalent chemical bond formed at the interface through a coupling agent. This material utilizes the strain mismatch between two materials with different thermal expansion coefficients during heating to drive macroscopically reversible curling. By actively introducing an air layer, a dramatic abrupt change in contact thermal resistance is achieved, thus maintaining efficient thermal conductivity under normal operating conditions and instantly switching to extremely effective thermal insulation under overheating conditions.

[0037] Example 1: Dynamically Adjustable Thermal Resistance Composite Material Based on Asymmetric Thermal Strain and its Mechanism This embodiment provides a dynamically adjustable thermal resistance composite material based on asymmetric thermal strain, which adopts a macroscopic double-layer heterogeneous structure design. The composite material includes a low thermal expansion constraint layer (first layer) and a high thermal expansion active layer (second layer) stacked sequentially.

[0038] Low thermal expansion constraint layer: Its thermal expansion coefficient is strictly controlled to be less than 20ppm / K, preferably using a flexible film with high intrinsic thermal conductivity of 10μm to 50μm, such as copper foil, aluminum foil or graphene composite film.

[0039] In this specific application, a high-purity copper foil with a thickness of 30 μm is selected (its coefficient of thermal expansion is approximately 16.5 ppm / K, and its thermal conductivity is as high as 390 W / m·K). This layer meets the requirement of a coefficient of thermal expansion of less than 20 ppm / K for the low thermal expansion constraint layer in this invention. As a constraint layer, the copper foil's extremely low coefficient of thermal expansion and high intrinsic thermal conductivity enable it to provide stable geometric constraints and efficient heat conduction channels when the temperature changes.

[0040] High thermal expansion active layer: Its coefficient of thermal expansion is greater than 200 ppm / K. This layer mainly comprises a polymer elastomer matrix (such as polydimethylsiloxane (PDMS), polyurethane (PU), or liquid silicone rubber) and disperses 10%–40% by mass of thermally conductive fillers (such as alumina microparticles, boron nitride microparticles, or liquid metal droplets). Preferably, the alumina microparticles are spherical alumina microparticles with an average particle size of 0.1 μm–50 μm; the boron nitride microparticles are preferably hexagonal boron nitride microparticles or boron nitride nanosheets with an average particle size of 1 μm–40 μm; and the liquid metal droplets are preferably gallium-based liquid metal droplets (such as eutectic gallium indium alloy EGaIn droplets) with an average particle size of 1 μm–50 μm. In this specific application, PDMS (with a coefficient of thermal expansion of approximately 310 ppm / K) is selected as the highly elastic matrix, and 30% by mass of high-purity alumina (Al2O3) micropowder is used as the thermally conductive filler. The extremely high coefficient of thermal expansion is the driving force behind the macroscopic reversible curling of the material. This invention significantly improves the equivalent thermal conductivity of the active layer by doping the PDMS matrix with a high content of thermally conductive filler (10%-40% by mass), utilizing the continuous thermally conductive network formed by the filler in the matrix. This ensures that the composite material possesses excellent thermal conductivity in a flat, bonded state. Simultaneously, the addition of the thermally conductive filler does not significantly alter the high thermal expansion characteristics of PDMS, allowing the active layer to still generate sufficient thermal expansion driving force as the temperature rises.

[0041] Instead of using commercially available double-sided tape or physical silicone adhesive, a high-strength covalent chemical bond interface (e.g., a silicon-oxygen bond network formed by the reaction of hydroxyl groups on the surface of the low thermal expansion constraint layer with the silane coupling agent) is formed at the interface between the low thermal expansion constraint layer and the high thermal expansion active layer.

[0042] If double-sided tape or physical adhesive is used, the interface relies only on weak van der Waals forces (bond energy is usually <10kJ / mol). During thermally triggered curling, the extremely large shear stress generated by CTEmismatch far exceeds the physical adsorption strength. After only a very few (expected 3-5) thermal cycles, the material will inevitably develop microcracks and lead to macroscopic physical delamination, losing its curling function.

[0043] The composite material in this embodiment is prepared using the following steps, such as... Figure 1 As shown: S1 Surface Activation: The cut copper foil is placed in a plasma device, and a mixture of oxygen and argon gas is introduced. The foil is bombarded at 150W for 3 minutes, generating active groups such as hydroxyl (-OH) groups on the copper foil surface. Plasma treatment not only introduces polar groups and increases surface energy on the copper foil surface, but also appropriately increases surface roughness through physical etching, providing more reaction sites and a stronger mechanical interlocking effect for the subsequent chemical anchoring of coupling agents.

[0044] S2 Coupling Agent Modification: A 2% (w / w) KH550 (γ-aminopropyltriethoxysilane) ethanol aqueous solution was prepared as the coupling agent solution. Plasma-treated copper foil was immersed in this solution for 1 minute, removed, dried, and then baked at 80°C for 15 minutes, allowing the silane coupling agent to anchor to the copper foil surface via silicon-oxygen bonds, forming an anchoring layer. The alkoxy group at one end of the KH550 molecule hydrolyzes and undergoes a condensation reaction with the hydroxyl groups (-OH) on the copper foil surface, forming a -Si-O- covalent bond; the amino group at the other end remains as the active functional group for subsequent reactions with polymer elastomers.

[0045] S3 Slurry preparation: Mix liquid PDMS prepolymer and curing agent at a mass ratio of 10:1, add Al2O3 micro powder accounting for 30% of the total mass of PDMS prepolymer and curing agent as thermally conductive filler, stir thoroughly and then degas under vacuum to obtain a high thermal conductivity fluid slurry.

[0046] S4 In-situ Coating and Crosslinking Curing: The above-mentioned high thermal conductivity fluid slurry is uniformly coated onto the surface of copper foil modified with coupling agent, and the wet film thickness is controlled at 150 μm. Then, it is heated at 100℃ for 1 hour to complete in-situ crosslinking curing. During the heating process, the PDMS prepolymer not only undergoes a crosslinking reaction to form an elastomer network, but its molecular chains also covalently bond with the functional groups such as amino groups at the ends of the KH550 coupling agent on the copper foil surface, forming a high-density covalent bond network (such as -Si-O- bonds) between the copper foil and PDMS. The bond energy of covalent bonds (usually greater than 300 kJ / mol) is more than an order of magnitude higher than that of van der Waals forces (usually less than 10 kJ / mol). Therefore, this process results in a rigid-flexible heterogeneous composite with extremely high peel strength between the copper foil and PDMS, fundamentally solving the industry problem of easy physical delamination of double-layer materials with large temperature differences.

[0047] like Figure 3 The diagram shown is a microscopic enlarged schematic of the internal double-layer heterogeneous structure and thermally conductive network distribution of the composite material of this invention. Analysis of this microstructure reveals that in the bottom layer (high thermal expansion active layer), thermally conductive microparticles, densely doped within a highly elastic matrix such as polydimethylsiloxane (PDMS), contact each other, forming a continuous thermally conductive filler network. This ensures the material's efficient thermal conductivity in a flat state. Simultaneously, at the interface between the top metal constraint layer (such as copper foil) and the bottom matrix, a high-strength covalent chemical bond network (such as -Si-O- bonds) is successfully constructed through plasma activation and in-situ crosslinking with coupling agents. This strong chemical bonding replaces the traditional weak physical van der Waals forces, effectively dissipating enormous shear stress and ensuring that the material does not undergo physical delamination when subjected to large temperature shocks.

[0048] The composite material exhibits morphological transformation characteristics in response to changes in ambient temperature, achieving a mechanism leap from "microscopic thermal conductivity network changes" to "macroscopic physical displacement," such as... Figure 2 As shown, it specifically includes: First state (normal operating condition / high-efficiency thermal conductivity state): When the ambient temperature or the temperature of the heating surface is lower than the set temperature threshold (safe temperature, e.g., 25℃~60℃), the internal thermal stress of the composite material tends to zero. The composite material is in an absolutely flat and flat bonded state (first state). Tests show that in this state, the composite material exhibits extremely low contact thermal resistance, with an equivalent thermal conductivity of 2.6 W / (m·K), which can effectively conduct heat away from the heating surface. This excellent thermal conductivity comes from two aspects: first, the high intrinsic thermal conductivity of the copper foil itself (approximately 390 W / (m·K)) provides an efficient heat conduction channel; second, the high-density doped alumina thermally conductive filler (30% by mass) in the PDMS matrix forms a continuous thermally conductive network, allowing heat to be quickly transferred from the heating surface to the copper foil layer and diffuse outward.

[0049] The second state (overheating condition / extreme insulation state): When the temperature of the heating surface (such as the bottom heating plate) rises abnormally and exceeds the set temperature threshold (e.g., a step increase to 120°C at a rate of 5°C / s to simulate thermal runaway), the bottom high thermal expansion active layer (PDMS) expands violently, while the top low thermal expansion constraint layer (copper foil) hardly expands. Due to the huge difference of nearly 19 times between the thermal expansion coefficient of PDMS (approximately 310 ppm / K) and the thermal expansion coefficient of copper foil (approximately 16.5 ppm / K), the two materials produce a huge thermal strain mismatch under the same temperature rise. The huge thermal strain mismatch and thermal bending moment drive the composite material to spontaneously bend and warp towards the low thermal expansion constraint layer (in the form of U-shaped or fragmented / scaled curls), transforming into the second state.

[0050] This bending and warping action causes the composite material to actively detach from the heating surface, instantly introducing an air insulation layer with an average thickness of approximately 6 mm at the interface. Due to the extremely low intrinsic thermal conductivity of air (approximately 0.026 W / m·K), the heat transfer path is completely severed. This air layer acts as an "air insulation bridge," completely cutting off the heat conduction path from the heating surface to the composite material. At this point, re-measuring the system's equivalent thermal resistance using a thermal resistance tester reveals that the equivalent thermal conductivity drops sharply to approximately 0.045 W / m·K.

[0051] Thermal switching ratio calculation: In this embodiment, the equivalent thermal conductivity of the composite material in the "high-efficiency thermal conduction state" is 2.6 W / (m·K), and the equivalent thermal conductivity in the "extremely effective thermal insulation state" is 0.045 W / (m·K). The ratio between the two (i.e., the thermal switching ratio) is 2.6 / 0.045≈57.7 times. This value breaks through the bottleneck that the thermal switching ratio of traditional solid thermal switching materials is difficult to exceed 5 times, achieving a precipitous drop in extremely effective thermal insulation.

[0052] Reversible recovery performance: When the temperature of the heating surface drops below 60°C, the PDMS active layer shrinks, the thermal bending moment disappears, and the composite material automatically returns to its first flat state within 15 seconds thanks to the elastic recovery force of the PDMS elastomer, and re-adheres to the heating surface. This process is completely reversible and requires no external energy drive, achieving intelligent thermal control with zero power consumption.

[0053] Interface stability comparison analysis: Addressing the industry-wide challenge of physical delamination in double-layer structures with large temperature differences, this embodiment employs a three-step synergistic process: "plasma surface activation + coupling agent grafting and anchoring + in-situ polymer crosslinking and curing." This process differs fundamentally from conventional physical bonding methods in terms of bonding mechanism and expected reliability. Comparative Example 1 (Conventional Physical Bonding): If commercially available double-sided tape or physical silicone adhesive is used to directly bond the same copper foil to PDMS, the interfacial bonding strength depends only on weak intermolecular forces (van der Waals forces). During thermally triggered curling, due to the huge difference in the coefficients of thermal expansion between the copper foil (low expansion) and PDMS (high expansion), extremely high shear stress is generated at the interface. According to interfacial mechanics analysis, this physical adsorption strength is far lower than the thermal shear stress. After undergoing very few (usually expected to be within 3-5) cycles of hot and cold cycling, microcracks will inevitably initiate at the stress concentration points, leading to macroscopic physical delamination and complete loss of curling recovery function.

[0054] This embodiment (in-situ covalent bonding): This invention does not use any physical adhesives. Instead, it utilizes plasma to hydroxylate the copper foil surface (-OH), and then uses silane coupling agent (KH550) molecules to build a "chemical bridge." During subsequent heat curing, the PDMS prepolymer not only undergoes cross-linking itself but also covalently bonds with the functional groups at the ends of the coupling agent. Based on the principles of polymer chemistry, this process creates a high-density covalent bond network (such as -Si-O- bonds) between the copper foil and PDMS. The bond energy of covalent bonds (typically greater than 300 kJ / mol) is more than an order of magnitude higher than van der Waals forces (typically less than 10 kJ / mol). Therefore, the interfacial peel strength of this invention can achieve an order-of-magnitude improvement, realizing perfect heterogeneous integration of "rigid-flexible" materials. Strong chemical bonding can effectively transfer and dissipate the huge shear stress generated by thermal expansion mismatch, enabling the covalent bond interface to withstand long-term, high-frequency rapid thermal shocks (such as meeting the automotive-grade requirement of hundreds of thermal runaway false alarm cycles) without interface peeling, thus fundamentally solving the pain points of short life and easy failure of existing double-sided adhesive bonding solutions.

[0055] Example 2: Preparation based on aluminum foil-polyurethane / boron nitride composite material This embodiment provides an alternative material combination scheme, which differs from Embodiment 1 mainly in the replacement of the constraint layer material, elastomer matrix, and thermally conductive filler.

[0056] 1. Material selection and structure The composite material in this embodiment is composed of a low thermal expansion constraint layer and a high thermal expansion active layer stacked sequentially.

[0057] The low thermal expansion constraint layer uses high-purity aluminum foil with a thickness of 20 μm, which has a coefficient of thermal expansion of approximately 23 ppm / K and a thermal conductivity of approximately 220 W / (m·K), meeting the requirement of a coefficient of thermal expansion of less than 20 ppm / K for the low thermal expansion constraint layer in this invention. Aluminum foil has the advantages of being lightweight and low-cost, making it suitable for applications with high requirements for lightweight design.

[0058] The high thermal expansion active layer uses polyurethane (PU) as the polymer elastomer matrix and is doped with boron nitride (BN) microparticles as a thermally conductive filler. Polyurethane exhibits excellent elasticity and wear resistance, with a thermal expansion coefficient exceeding 200 ppm / K. The boron nitride microparticles have an average particle size of 1 μm–40 μm and are hexagonal boron nitride microparticles. Boron nitride possesses a graphite-like layered structure, with a thermal conductivity as high as 250–300 W / (m·K) in the layer direction, and also exhibits good electrical insulation and high-temperature resistance. The thermally conductive filler constitutes 25% of the high thermal expansion active layer by mass.

[0059] 2. Preparation method This embodiment uses essentially the same preparation steps as Example 1: S1 Surface Activation: The aluminum foil is placed in a plasma device and a mixture of oxygen and argon is introduced. It is bombarded at 120W power for 5 minutes to generate active groups such as hydroxyl (-OH) on the surface of the aluminum foil.

[0060] S2 Coupling Agent Modification: A 2% (w / w) KH570 (γ-methacryloyloxypropyltrimethoxysilane) ethanol aqueous solution was prepared as the coupling agent solution. The plasma-treated aluminum foil was immersed in this solution for 2 minutes, removed and dried, and then dried at 80°C for 15 minutes.

[0061] S3 Slurry preparation: Mix the liquid polyurethane prepolymer and curing agent according to the ratio recommended in the product instructions, add boron nitride microparticles accounting for 25% of the total mass of polyurethane prepolymer and curing agent, stir thoroughly, and then degas under vacuum to obtain a high thermal conductivity fluid slurry.

[0062] S4 In-situ Coating and Crosslinking Curing: The above slurry is uniformly coated onto the surface of aluminum foil modified with coupling agent, and the wet film thickness is controlled to be 120 μm. Then, it is heated at 120℃ for 2 hours to complete in-situ crosslinking curing.

[0063] 3. Expected Performance This embodiment utilizes the low thermal expansion characteristics of aluminum foil and the high thermal expansion characteristics of polyurethane / boron nitride composite materials to achieve a reversible curling thermal switch function based on asymmetric thermal strain. The high thermal conductivity and excellent electrical insulation of boron nitride ensure efficient heat conduction and electrical insulation safety of the composite material in its flat state, while the significant difference in thermal expansion coefficients between aluminum foil and polyurethane guarantees a rapid curling response under overheating conditions. The combined process of plasma activation and coupling agent modification ensures the formation of a high-strength covalent chemical bond interface between the aluminum foil and polyurethane, guaranteeing interfacial reliability during repeated thermal cycling.

[0064] Example 3: Preparation of graphene composite film-liquid silicone rubber / liquid metal microdroplet composite material This embodiment provides another implementation scheme for the material combination method. The main difference from Embodiment 1 is the replacement of the types of constraint layer material, elastomer matrix and thermally conductive filler.

[0065] 1. Material selection and structure The low thermal expansion confinement layer is a graphene composite film with a thickness of 15 μm. The graphene composite film has an extremely low coefficient of thermal expansion (which can be as low as close to zero) and an extremely high in-plane thermal conductivity (which can reach more than 1000 W / (m·K)), making it an ideal high thermal conductivity confinement layer material. Its coefficient of thermal expansion meets the requirement of less than 20 ppm / K in this invention.

[0066] The high thermal expansion active layer uses liquid silicone rubber as the polymer elastomer matrix and is doped with liquid metal microdroplets as a thermally conductive filler. Liquid silicone rubber exhibits excellent high elasticity, resistance to high and low temperatures, and chemical stability, with a thermal expansion coefficient exceeding 200 ppm / K. The liquid metal microdroplets are gallium-based liquid metal microdroplets (such as eutectic gallium-indium alloy EGaIn), with an average particle size of 1 μm to 50 μm, preferably 2 μm to 20 μm in this embodiment. Their melting point is between 10°C and 30°C, and they are liquid at room temperature and normal battery operating temperature. The intrinsic thermal conductivity of the liquid metal microdroplets is approximately 20–40 W / (m·K). The thermally conductive filler constitutes 20% of the mass of the high thermal expansion active layer.

[0067] 2. Preparation method S1 Surface Activation: The graphene composite film is placed in a plasma device and a mixture of oxygen and argon is introduced. It is bombarded for 3 minutes at a power of 100W to generate active groups such as hydroxyl (-OH) and carboxyl (-COOH) on the surface of the graphene composite film.

[0068] S2 Coupling Agent Modification: A 1.5% (w / w) KH550 ethanol aqueous solution was prepared as the coupling agent solution. The plasma-treated graphene composite film was immersed in this solution for 1.5 minutes, removed, dried, and then dried at 70°C for 20 minutes.

[0069] S3 Slurry preparation: Mix the liquid silicone rubber prepolymer and curing agent according to the ratio recommended in the product instructions, add liquid metal microdroplets accounting for 20% of the total mass of the liquid silicone rubber prepolymer and curing agent, stir thoroughly under conditions below room temperature (to prevent the liquid metal from solidifying), and degas under vacuum to obtain a high thermal conductivity fluid slurry.

[0070] S4 In-situ Coating and Crosslinking Curing: The above slurry is uniformly coated onto the surface of the graphene composite film modified with coupling agent, and the wet film thickness is controlled to be 100 μm. Then, it is heated at 120℃ for 1.5 hours to complete the in-situ crosslinking curing.

[0071] 3. Expected Performance This embodiment utilizes the ultra-high in-plane thermal conductivity and extremely low coefficient of thermal expansion of graphene composite films, combined with the high coefficient of thermal expansion and high thermal conductivity of liquid silicone rubber / liquid metal microdroplet composite materials, to achieve more efficient thermal switching performance. The liquid metal microdroplets form liquid thermal conduction channels within the elastomer matrix. Even when the elastomer undergoes significant deformation (curling or flattening), the liquid metal microdroplets can still freely deform with the matrix and maintain a continuous thermal conduction path, potentially further improving the equivalent thermal conductivity of the composite material in a flattened state.

[0072] This invention utilizes a three-step synergistic process of "surface activation + coupling agent anchoring + in-situ crosslinking curing" to construct covalent chemical bonds (such as -Si-O- bonds), whose bond energies (typically >300 kJ / mol) are more than an order of magnitude higher than van der Waals forces. This strong chemical bonding effectively transfers and dissipates the enormous shear stress generated by thermal expansion mismatch, resulting in a significant improvement in interfacial peel strength. This structure can withstand long-term, high-frequency, extremely rapid thermal shocks (meeting automotive-grade requirements for hundreds of false thermal runaway cycles) without interfacial delamination, completely solving the short lifespan problem of existing solutions.

[0073] Example 4: Intelligent Thermal Management System for Power Batteries Based on This Composite Material This embodiment provides a zero-power, zero-delay intelligent thermal management system specifically designed for power batteries. The system utilizes the dynamically adjustable thermal resistance composite material based on asymmetric thermal strain described in Embodiment 1 to perform purely passive protection against thermal runaway.

[0074] The intelligent thermal management system includes a battery pack, inside which a dense array of battery cells (such as high-nickel ternary lithium batteries, large cylindrical batteries, etc.) are arranged. The composite material is pre-processed into arrayed patches or large-area covering films, which are sandwiched and applied to the heat-generating surfaces of the battery cell array (for example, applied on or between the cylindrical battery cell array, between the battery cells and heat dissipation structures such as liquid cooling plates).

[0075] Specifically, for cylindrical cell arrays, the composite material can be laid on top of the cell array (covering the top of the cells) or sandwiched between the cells (filling the gaps between adjacent cells), with the low thermal expansion constraint layer of the composite material facing the heating surface of the cell and the high thermal expansion active layer facing outwards, or arranged in reverse according to the specific heat dissipation path design. No additional adhesives or fixing devices are required between the composite material and the cell surface; contact is maintained solely by elastic adhesion and / or external preload.

[0076] Thermal management under normal operating conditions: Under normal battery pack operating conditions (such as during daily charging and discharging), when the temperature of the cell array is below a set temperature threshold (e.g., below 60°C), the composite material maintains its first flat and bonded state (high-efficiency thermal conductivity state). In this state, the composite material is tightly bonded to the heating surface of the cell, relying on the internal continuous thermally conductive network (the high intrinsic thermal conductivity channels of the copper foil / aluminum foil / graphene composite film, and the continuous thermally conductive network formed by the thermally conductive filler in the elastomer matrix) to achieve low thermal resistance heat conduction. This rapidly conducts the waste heat generated during cell charging and discharging to the liquid cooling plate or external heat dissipation structure, acting as a high-efficiency heat dissipation interface material. This function ensures that the battery operates within a safe temperature range, which helps extend battery life and support high-power fast charging.

[0077] Passive protection under thermal runaway conditions: When a local cell in the battery pack experiences thermal runaway due to internal short circuit, overcharging, or mechanical collision, causing the temperature in that area to rise sharply and exceed a set temperature threshold (such as exceeding 120°C), the composite material in contact with the high-temperature fault area will immediately and spontaneously respond.

[0078] The response mechanism is entirely based on the intrinsic thermodynamic physical response of the composite material: the high thermal expansion active layer (PDMS / polyurethane / liquid silicone rubber matrix) undergoes drastic volume expansion, while the low thermal expansion constraint layer (copper foil / aluminum foil / graphene composite film) hardly expands. The difference in thermal expansion coefficients between the two generates a huge thermal strain mismatch, which in turn forms a thermal bending moment, driving the composite material to spontaneously curl and warp upwards (in a U-shape or scale-like shape), transforming from the first morphology to the second morphology (extremely effective thermal insulation state). The curling and lifting action causes the composite material to actively detach from the heating surface of the faulty battery cell, and instantly introduces a heat insulation layer with air as the main medium between the composite material and the heating surface. Air has extremely low thermal conductivity (approximately 0.026 W / (m·K)), and this air heat insulation layer effectively cuts off the heat conduction path from the faulty battery cell to the surrounding healthy battery cells and to the liquid cooling plate, effectively sealing the high-temperature heat of thousands of degrees within a local area.

[0079] Passive Closed-Loop Response: The mechanism by which the composite material transforms from its first to its second state is entirely based on the material's inherent thermodynamic physical response. It requires no external temperature sensor detection and no electrical signal command from the battery management system (BMS) to intervene in the execution. This completely eliminates the fatal response delay (on the order of seconds to tens of seconds) from sensor temperature measurement to algorithm judgment to actuator action, and avoids the risk of protection failure due to electronic harness burnout at extreme temperatures of thousands of degrees Celsius. It achieves "passive intrinsic safety" protection with single-point overheating and immediate in-situ isolation. The energy driving the material curling comes entirely from the heat generated by thermal runaway (i.e., thermal expansion strain energy), requiring no external power source. Curling only occurs locally in the high-temperature area of ​​the composite material in contact with the fault, while the composite material in the healthy area remains flat, achieving precise protection with "single-point overheating and immediate in-situ isolation."

[0080] Thermal on / off ratio and protection effect: Tests have verified that the equivalent thermal resistance control ratio (thermal on / off ratio) of the composite material of this invention between the first form of flat bonding and the second form of curling and warping is greater than 50 times (57.7 times in Example 1). Such a high thermal on / off ratio means that when thermal runaway occurs, the heat conduction path is almost completely cut off, which can effectively block the conduction of heat to the surrounding healthy cells, prevent catastrophic domino-like chain thermal runaway propagation, and meet the most stringent safety standards for power batteries (such as no fire or explosion of the battery pack within a 2-hour observation period after triggering single-cell thermal runaway).

[0081] Intelligent adaptive recovery: When the risk of thermal runaway in a local cell is eliminated and the temperature drops below the set temperature threshold, the high thermal expansion active layer (PDMS / polyurethane / liquid silicone rubber) shrinks due to the temperature decrease, and the thermal bending moment disappears. The composite material automatically flattens back up in a short time (15 seconds in Example 1) thanks to the elastic recovery force of the polymer elastomer, and re-adhere to the heating surface, returning to the first form (high-efficiency thermal conduction state).

[0082] This reversible recovery process also requires no external energy or control signal, achieving intelligent reversible control with zero power consumption throughout. Because this invention employs plasma activation and in-situ crosslinking with coupling agents to achieve a high-strength covalent chemical bond interface between the low thermal expansion constraint layer and the high thermal expansion active layer, this interface can withstand long-term, high-frequency, and extremely rapid thermal shocks without delamination. Therefore, the composite material possesses excellent fatigue cycle resistance and can meet the reliability requirements of automotive-grade thermal runaway protection cycles of hundreds of cycles.

[0083] like Figure 4 The diagram illustrates a system-level working scenario of the composite material of this invention applied to the prevention of thermal runaway propagation in the power battery pack of new energy vehicles. As shown in this application scenario, the dynamically adjustable thermal resistance composite material is processed into an array of cover films or patches, which are then sandwiched and laid on top of an array of cylindrical cells. When the surrounding healthy cells are operating normally (the areas at both ends of the diagram), the material maintains a tightly adhered, flat state to quickly dissipate waste heat. However, when an internal short circuit occurs in the cell in the center of the diagram, causing a temperature surge (thermal runaway), the composite material directly in contact with the faulty area will spontaneously curl upwards based on its intrinsic thermodynamic physical response. This action requires no intervention from sensors or the battery management system, achieving a zero-delay response. Furthermore, by instantly introducing a physical air bridge, the extremely high temperature of thousands of degrees Celsius is effectively contained locally, preventing heat conduction to the surrounding healthy cells and achieving purely passive intrinsic safety protection.

[0084] Example 5: Parameter optimization range for composite material preparation process This embodiment further illustrates the optional parameter ranges for each step in the composite material preparation process of the present invention.

[0085] In the surface activation step, the plasma treatment power can be 80W to 200W, the treatment time can be 1 minute to 10 minutes, and the introduced gas can be oxygen, argon, or a mixture thereof.

[0086] In the coupling agent modification step, the mass fraction of the coupling agent solution can be 1% to 5%, the impregnation time can be 0.5 minutes to 5 minutes, the drying temperature can be 60℃ to 100℃, and the drying time can be 10 minutes to 30 minutes.

[0087] In the slurry preparation step, the mass ratio of polymeric elastomer prepolymer to curing agent depends on the type of elastomer selected (such as PDMS system, which is usually 10:1), and the amount of thermally conductive filler added can be 10% to 40% (mass fraction).

[0088] In the in-situ coating and cross-linking curing steps, the wet film thickness can be 80μm to 200μm, the curing temperature can be 80℃ to 150℃, and the curing time can be 0.5 hours to 3 hours.

[0089] Example 6: Morphological transformation characteristics of composite materials in different application scenarios This embodiment further illustrates the morphological transformation characteristics of the composite material of the present invention and its temperature threshold design in different application scenarios.

[0090] The morphological transformation of the composite material in this invention is driven by the temperature of the heating surface, and the set temperature threshold can be adjusted according to specific application requirements. In the scenario of thermal runaway protection for power batteries, the set temperature threshold can be designed to be 100℃~120℃. When the cell temperature is below this threshold, the composite material maintains a flat and adhered first form for efficient heat dissipation. When the temperature exceeds this threshold, it transforms into a curled and raised second form for heat insulation protection. In the scenario of battery insulation in extreme environments, the set temperature threshold can be designed to be 0℃~10℃. At low temperatures, the composite material curls and raises to form an air insulation layer to reduce heat loss from the battery. After restoring the normal operating temperature, it flattens again to restore heat conduction. In the scenario of overheat protection for electronic devices, the set temperature threshold can be designed to be 70℃~85℃. When the safe operating temperature is exceeded, the composite material curls and raises to cut off the heat conduction path.

[0091] The curling direction of the composite material is determined by its double-layer structure: because the expansion of the high thermal expansion active layer is much greater than that of the low thermal expansion restraint layer when heated, the thermal bending moment drives the composite material to bend and curl towards the side of the low thermal expansion restraint layer (i.e., the restraint layer side is concave inward and the active layer side is convex outward). This directional characteristic requires that the orientation be selected according to the actual heat dissipation path during installation to ensure that it can effectively detach from the heat-generating surface when curled.

[0092] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0093] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0094] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0095] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0096] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation of these numerical combinations.

[0097] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0098] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0099] In this invention, unless otherwise stated, the various reaction or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0100] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0101] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0102] Unless otherwise defined, all 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. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A dynamically adjustable thermal switch composite material based on asymmetric thermal strain, characterized in that, It includes a low thermal expansion constraint layer and a high thermal expansion active layer stacked sequentially, wherein the low thermal expansion constraint layer and the high thermal expansion active layer form a covalent chemical bond interface at the interface through a coupling agent; The coefficient of thermal expansion of the low thermal expansion confinement layer is less than 20 ppm / K; The high thermal expansion active layer includes a polymer elastomer matrix and a thermally conductive filler dispersed in the polymer elastomer matrix. The coefficient of thermal expansion of the high thermal expansion active layer is greater than 200 ppm / K, and the mass fraction of the thermally conductive filler in the high thermal expansion active layer is 10%~40%. The composite material has a morphological transformation characteristic in response to changes in ambient temperature: when the temperature of the heating surface is lower than a set temperature threshold, the composite material is in a flat and bonded first form to conduct interfacial heat; when the temperature of the heating surface exceeds the set temperature threshold, the high thermal expansion active layer and the low thermal expansion constraint layer generate thermal strain mismatch and thermal bending moment through the difference in their thermal expansion coefficients, driving the composite material to bend and warp toward the low thermal expansion constraint layer and transform into a second form to detach from the heating surface and form an air insulation layer at the interface between the two.

2. The dynamically adjustable thermal switch composite material based on asymmetric thermal strain according to claim 1, characterized in that, The low thermal expansion constraint layer is any one of copper foil, aluminum foil, or graphene composite film, and the thickness of the low thermal expansion constraint layer is 10μm to 50μm.

3. The dynamically adjustable thermal switch composite material based on asymmetric thermal strain according to claim 1, characterized in that, The polymer elastomer matrix is ​​any one of polydimethylsiloxane, polyurethane, or liquid silicone rubber. The thermally conductive filler includes at least one of alumina microparticles, boron nitride microparticles, or liquid metal droplets.

4. The dynamically adjustable thermal switch composite material based on asymmetric thermal strain according to claim 1, characterized in that, The coupling agent is a silane coupling agent, and the covalent chemical bonding interface includes a siloxane bond network formed by the reaction of hydroxyl groups on the surface of the low thermal expansion constraint layer with the silane coupling agent.

5. A method for preparing a dynamically adjustable thermally switched composite material based on asymmetric thermal strain as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Surface activation: The low thermal expansion confinement layer is subjected to surface plasma treatment to generate active groups on its surface; Coupling agent modification: Coating the activated low thermal expansion constraint layer surface with a coupling agent solution and drying it to form an anchoring layer; Slurry preparation: The polymer elastomer prepolymer, curing agent and the thermally conductive filler are mixed in proportion and degassed to obtain a high thermal conductivity fluid slurry; In-situ coating and cross-linking curing: The high thermal conductivity fluid slurry is coated onto the modified low thermal expansion constraint layer surface and heated to allow the polymer elastomer to cross-link and cure itself, and to covalently bond with the coupling agent functional groups on the surface of the low thermal expansion constraint layer.

6. The method for preparing the dynamically adjustable thermal switch composite material based on asymmetric thermal strain according to claim 5, characterized in that, In the surface activation step, the low thermal expansion confinement layer is bombarded using a plasma device that introduces a mixture of oxygen and argon gas, and the resulting active groups include hydroxyl groups; In the coupling agent modification step, the coupling agent solution is a 2% KH550 ethanol aqueous solution, and the drying conditions are drying at 80°C for 15 minutes.

7. The method for preparing the dynamically adjustable thermal switch composite material based on asymmetric thermal strain according to claim 5, characterized in that, In the slurry preparation step, the polymeric elastomer prepolymer is a liquid polydimethylsiloxane prepolymer, and the mass ratio of the liquid polydimethylsiloxane prepolymer to the curing agent is 10:

1. In the in-situ coating and cross-linking curing steps, the high thermal conductivity fluid slurry is uniformly coated onto the surface of the modified low thermal expansion constraint layer, and the wet film thickness is controlled to be 150 μm; the heating condition is constant temperature heating at 100°C for 1 hour.

8. A smart thermal management system for power batteries, characterized in that, Including battery packs and dynamically adjustable thermally tunable composite materials based on asymmetric thermal strain as described in any one of claims 1 to 4; The battery pack contains a cell array, and the composite material is processed into an array of patches or a cover film, which are sandwiched and applied to the heating surface of the cell array. When the intelligent thermal management system for the power battery performs purely passive thermal protection, it includes: Under normal operating conditions, the temperature of the battery cell array is lower than the set temperature threshold, and the composite material maintains a flat and bonded first form to transfer the waste heat of the battery cells out. When a local cell experiences thermal runaway, causing the temperature to exceed the set temperature threshold, the composite material in contact with the faulty area spontaneously curls and rises upwards, transforming into a second form, forming an air layer at the interface to block heat conduction to the surrounding healthy cells.

9. The intelligent thermal management system for power batteries according to claim 8, characterized in that, The composite material is specifically sandwiched and laid on or between cylindrical cell arrays; The mechanism by which the composite material transforms from the first state to the second state is based on the intrinsic thermodynamic physical response of the material.

10. The intelligent thermal management system for power batteries according to claim 8, characterized in that, The power battery intelligent thermal management system has an equivalent thermal resistance control ratio greater than 50 times between the first flat and bonded state and the second curled and raised state. Once the risk of thermal runaway in a localized cell is eliminated and the temperature drops below the set temperature threshold, the composite material flattens out again and adheres to the heating surface due to its own elastic restoring force, thus achieving reversible control.

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