Preparation method of thermal-mechanical coupling change-over switch material based on wormlike material

Abstract

The invention provides a preparation method of a thermal-mechanical coupling change-over switch material based on a wormlike material. The material comprises an elastomer matrix; a volume deformation material, wherein the volume deformation material is dispersed in the elastomer matrix; and the heat conduction filler is dispersed in the elastomer matrix. The basic principle does not depend on any specific chemical change, but utilizes physical volume deformation caused by heating of the material as driving force to actively regulate and control a heat conduction network topological structure in the composite material through the mechanical action of a micro scale, so that step type change of the heat conductivity at a specific temperature trigger point is realized.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to a method for preparing thermo-mechanical coupling switching materials based on worm-like materials. Background Technology

[0002] Currently, thermal control materials for battery thermal management systems are mainly divided into three categories: mechanical thermal control materials, fluid thermal control materials, and all-solid thermal control materials. Each type of technical solution has different implementation principles and typical representatives.

[0003] Mechanical thermal control materials alter thermal resistance by achieving contact or separation between the hot and cold ends through macroscopic mechanical movement. Specific implementation schemes include: 1) Shape memory alloy (SMA) driven scheme: Utilizing the phase change characteristics of SMA to drive the movement of the thermal interface. When paired with an immersion cooling system, at low temperatures, the SMA spring shortens, causing the heat-conducting plate to adhere to the battery (off state); at high temperatures, the SMA elongates, allowing the battery to directly contact the coolant (on state), achieving an on / off ratio of up to 174.7. 2) Phase change material (PCM) driven scheme: Utilizing the thermal expansion characteristics of PCM materials such as stearic acid to drive the opening and closing of fluid pathways. When the PCM melts, it expands and compresses the elastic channels, allowing the coolant to flow across the battery surface for heat dissipation; upon solidification, it contracts in volume, allowing the coolant to bypass the battery. 3) Bimetallic strip driven scheme: Utilizing the thermal bending characteristics of metal strips with different coefficients of thermal expansion, it drives the displacement of the heat-conducting medium to change the contact area.

[0004] Fluid-based thermal control materials achieve thermal resistance regulation by changing the position or state of the fluid, and are mainly divided into passive and active types: 1) Hydrogel composite material scheme: High water content hydrogel is combined with flame-retardant fibers. At room temperature, water imparts thermal conductivity to the material; at high temperatures, water vaporizes and absorbs heat, and the remaining fiber layer forms a thermal insulation barrier, with an on / off ratio of approximately 7. 2) Phase change fluid cavity scheme: A hydrated salt / paraffin / expanded graphite composite material is filled into a sealed cavity, and the thermal pathway is connected or disconnected through solid-liquid phase change. 3) Active pump-controlled fluid scheme: Two fluids with different thermal conductivities (such as air and liquid) are switched by a pump or valve, requiring external power system support.

[0005] All-solid thermal control materials rely on changes in the thermal properties of the solid material itself to regulate heat flow, requiring no moving parts or fluids: 1) Multilayer staggered structure scheme: A temperature gradient induces graphene sheets and thermally expanding microspheres to form a directional layered structure. At room temperature, the graphene sheets constitute a continuous thermally conductive pathway (thermal conductivity 1.33 W·m). - ¹·K - ¹), at high temperatures, the thermal expansion of the microspheres pushes the graphene sheet apart, switching to a thermal insulation state (thermal conductivity 0.11 W·m). - ¹·K -¹), On / off ratio greater than 10. 2) Phase change alloy scheme: Thermal conductivity can be reversibly adjusted by utilizing the amorphous-crystalline phase transition of alloys such as GeSbTe, but the on / off ratio is low (about 3.9). 3) Electric field / magnetic field responsive materials: Thermal conductivity can be changed by controlling the polarization state of ferroelectric materials (such as PVDF) or the arrangement order of liquid crystal polymers by external field, but external energy input is required and the response speed is slow.

[0006] Currently, fire extinguishing agents for preventing the spread of thermal runaway in lithium-ion batteries can be divided into four categories: gaseous, liquid, solid, and new intelligent types. Each category has significant differences in extinguishing mechanism, core performance, and application scenarios. Summary of the Invention

[0007] The inventors discovered that although existing thermal control materials show some potential in specific scenarios, they all suffer from the following key drawbacks, making it difficult to meet the comprehensive requirements of battery systems for thermal management materials: (1) Mechanical and fluid materials have high structural complexity Mechanical types rely on moving parts such as springs and levers, which pose a risk of vibration, and their thickness is usually greater than 8 cm, making them unsuitable for the millimeter-level gap requirements of battery modules.

[0008] Fluid-type systems require sealed pipes or cavities, which are prone to failure due to fluid leakage during long-term operation. Furthermore, external drive devices such as pumps and valves increase system costs and maintenance difficulty.

[0009] (2) The performance limitations of all-solid materials are prominent. Insufficient on / off ratio: Most all-solid materials have an on / off ratio below 10, such as GeSbTe alloy (3.9) and squid cyclodentin (3.9), which cannot achieve the high thermal conductivity (>1 W·m) required for battery systems. - ¹·K - ¹) to high insulation (<0.1 W·m) - ¹·K - ¹) significant switching.

[0010] The preparation process is complex: the multi-layered interlaced structure requires temperature gradient method and hydrophilicity difference to achieve directional arrangement, the process is complicated and difficult to scale up production.

[0011] Insufficient response speed and stability: the crystal phase transformation of phase change alloys takes tens of minutes, and electric field / magnetic field modulated materials are easily affected by external interference, neither of which can meet the requirements of second-level response to battery thermal runaway.

[0012] (3) Disconnected from the actual needs of the battery system Existing materials have poor matching between their switching temperature window and the characteristic temperature of battery thermal runaway, or they may act too early, affecting heat dissipation, or act too late, leading to heat propagation.

[0013] Mechanical and fluid materials cannot be directly integrated into existing battery pack designs due to size and structural limitations, requiring a complete overhaul of the system architecture, which is costly.

[0014] In summary, the inventors found that mechanical and fluid-type thermal control devices, due to their fluid components and moving parts, are complex and require precise manufacturing. Adding them to battery systems would incur significant design, production, manufacturing, and maintenance costs, making them unsuitable for current battery system designs. Furthermore, the switching performance of all-solid thermal control materials still needs optimization. The core difference between this invention and existing technologies lies in its creative use of a simple blending process to achieve a dual-component synergistic deformation mechanism of expandable graphite and thermally expandable microspheres. This mechanism achieves a high thermal switching ratio within a precise temperature window (140-160°C), seamlessly integrating and dynamically switching between the two opposing functions of "efficient heat dissipation" and "strong thermal insulation" on a single material, thus resolving the fundamental contradiction in battery thermal safety management.

[0015] This invention aims to solve the technical problem of contradictory heat transfer requirements in existing battery thermal management systems. Specifically, high thermal conductivity is needed under normal operating conditions to achieve uniform temperature and heat dissipation, while high thermal insulation is required under fault conditions to prevent the spread of thermal runaway. Existing thermal control materials cannot simultaneously meet the requirements of high thermal conductivity-high thermal insulation switching, rapid response, millimeter-level action, and ease of fabrication. This invention aims to provide a two-phase composite thermal switching material that achieves thermally triggered thermal conductivity-thermal insulation switching through a simple mechanical blending process. When applied to lithium-ion battery modules, it can improve battery cycle life and thermal safety.

[0016] According to embodiments of the present invention, the present invention provides a composite material capable of intelligently changing its thermal conductivity according to ambient temperature and a method for preparing the same. The core of the composite material, according to embodiments of the present invention, lies in: combining one or more expandable micromaterials (first functional components) capable of significant volume expansion at specific temperatures with one or more worm-like thermally conductive fillers (second functional components) whose ordered thermally conductive network can be effectively disrupted under expansion, in an elastomer matrix via mechanical blending or skeleton infusion. At room temperature, the thermally conductive fillers form effective thermally conductive pathways; when the temperature reaches or exceeds the trigger temperature of the expandable micromaterials, the micromechanical effects (pushing, separation, isolation) generated by their violent expansion will disrupt or block the original thermally conductive network, causing a step-like decrease in the overall thermal conductivity of the material, thereby achieving an intelligent switching from a "high thermal conductivity state" to a "high thermal insulation state".

[0017] The smart materials according to embodiments of the present invention exhibit multiple advantages: their trigger temperature can be precisely designed through material selection to match different application scenarios; their switching response is fast and significant, enabling immediate protection against thermal events; their normal high thermal conductivity helps with temperature equalization and heat dissipation, improving system energy efficiency and lifespan.

[0018] The smart materials according to embodiments of the present invention can be used in electronic devices or industrial fields that require intelligent thermal regulation, especially in the thermal management of electrochemical energy storage devices. As an intelligent thermal management interface layer, they can provide active thermal safety protection while improving system energy efficiency and cycle life.

[0019] In one aspect of the invention, a smart composite material with switchable thermal conductivity is proposed, characterized in that it comprises: Elastomer matrix; A volumetric deformable material (first functional component), wherein the volumetric deformable material is dispersed in the elastomer matrix; A thermally conductive filler (second functional component) is dispersed in the elastomer matrix. According to an embodiment of the invention, the volumetric deformation material is one or more micron-scale volumetric deformation materials capable of significant volume expansion at a specific trigger temperature, and the thermally conductive filler is one or more thermally conductive fillers capable of forming a thermally conductive network.

[0020] According to embodiments of the present invention, the above-mentioned smart composite material with switchable thermal conductivity may further include at least one of the following additional technical features: According to an embodiment of the present invention, the volumetric deformation material is selected from at least one of thermally expandable microspheres, thermally induced phase change materials, or other inorganic or organic materials that can expand in volume when heated.

[0021] According to an embodiment of the present invention, the volumetric deformation material undergoes volume expansion after reaching its trigger temperature, and the material may be selected from at least one of thermally expandable microspheres, thermally induced phase change materials, or other inorganic or organic materials that can expand volume when heated.

[0022] According to an embodiment of the present invention, the volumetric deformation material expands in volume by 3 to 50 times after being heated.

[0023] According to an embodiment of the present invention, the initial expansion temperature of the volumetric deformation material is 40 °C to 250 °C.

[0024] According to an embodiment of the present invention, the maximum expansion temperature of the volumetric deformation material is 120 °C to 290 °C.

[0025] According to an embodiment of the present invention, the thermally conductive filler is selected from worm-like thermally conductive materials; According to an embodiment of the present invention, the worm-like thermally conductive material is selected from expandable graphite, expanded vermiculite, or a combination thereof with graphene and boron nitride.

[0026] According to an embodiment of the present invention, the thermally conductive filler forms a three-dimensional interconnected thermally conductive pathway within the elastomer matrix to provide high thermal conductivity under normal conditions. The micromechanical action generated after the volume deformation of the first functional component can destroy or block the thermally conductive network, resulting in a significant reduction in thermal conductivity.

[0027] According to an embodiment of the present invention, the elastomer matrix is ​​selected from silicone rubber, silicone resin, or a composite thereof.

[0028] According to an embodiment of the present invention, the mass ratio of the sum of the mass of the volumetric deformation material and the thermally conductive material to the mass of the elastomer matrix is ​​1:3 to 1:1.

[0029] According to an embodiment of the present invention, the smart composite material further includes a component (third functional component) for enhancing mechanical properties or imparting other functions.

[0030] According to embodiments of the present invention, the enhancement of mechanical properties or the imparting of other functions are selected from reinforcing fibers or flame retardants.

[0031] According to an embodiment of the present invention, the reinforcing fiber is selected from mullite fiber, ceramic fiber or polymer fiber.

[0032] According to an embodiment of the present invention, the flame retardant is selected from ammonium polyphosphate, aluminum hydroxide, or magnesium hydroxide.

[0033] In another aspect of the invention, a method for preparing the aforementioned intelligent composite material with switchable thermal conductivity is proposed. According to an embodiment of the invention, the method includes: mechanically blending, skeletal casting, or using an ice-templating method with a volumetric deformable material, a thermally conductive filler, and optionally components for enhancing mechanical properties or imparting other functions with an elastomer matrix precursor to prepare a homogeneous mixture, followed by curing or molding to obtain the aforementioned intelligent composite material with switchable thermal conductivity. According to an embodiment of the invention, a three-dimensional interconnected thermally conductive pathway is formed within the matrix to provide high thermal conductivity under normal conditions. The material trigger temperature can be controlled by selecting a first functional component and a second functional component with different expansion temperatures, and rapid switching of thermal conductivity can be achieved near the trigger temperature.

[0034] According to embodiments of the present invention, the above method may further include at least one of the following additional technical features: In another aspect of the invention, the invention proposes the application of the aforementioned switchable thermal conductivity smart composite material or the switchable thermal conductivity smart composite material prepared according to the aforementioned method in devices requiring thermal management.

[0035] According to embodiments of the present invention, the above application may further include one of the following additional technical features: According to an embodiment of the present invention, the intelligent composite material with switchable thermal conductivity is prepared as a thermal management interface layer or component and disposed between the heating component and the protected component of the device, or between multiple heating components, for intelligently regulating heat flow according to temperature.

[0036] According to embodiments of the present invention, a general design paradigm for "thermo-mechanical coupling" thermal switching materials is provided. Its basic principle does not rely on any specific chemical change, but rather utilizes the physical volume deformation induced by heating of the material as the driving force. Through microscopic mechanical action, the topology of the heat conduction network within the composite material is actively controlled, thereby achieving a step change in thermal conductivity at a specific temperature trigger point.

[0037] In the composite material of this fundamental embodiment of the invention, a continuous or quasi-continuous thermally conductive network formed by a highly thermally conductive filler is pre-constructed. Simultaneously, one or more micromaterials with specific thermally triggered volumetric expansion characteristics are introduced into this network path. When the ambient temperature does not reach the trigger threshold, the thermally conductive network remains intact, and the material exhibits high thermal conductivity. Once the local temperature rises and reaches the preset trigger temperature, the expandable material rapidly undergoes significant volumetric expansion. The resulting expansion stress directly acts on the fragile connection points of the thermally conductive network, physically disrupting or blocking the original efficient heat flow path through mechanical means such as pushing, peeling, and breaking. Consequently, the macroscopic thermal conductivity of the material drops sharply, switching to a "shutdown state." The entire process is scalable, rapid, and has a high on / off ratio.

[0038] To achieve high initial thermal conductivity, the key to this invention lies in constructing a highly efficient thermally conductive network with a low penetration threshold within the elastomer matrix. This is achieved by introducing worm-like thermally conductive fillers with a high aspect ratio. These fillers easily overlap and contact each other within the matrix, forming three-dimensional interconnected thermal pathways even at low filler concentrations. Heat can be rapidly conducted along the fillers themselves and efficiently transferred across the network through contact points between fillers or minimal matrix barriers, resulting in a composite material exhibiting high thermal conductivity close to the intrinsic thermal conductivity of the fillers on a macroscopic scale. Suitable thermally conductive fillers include, but are not limited to, expanded graphite and boron nitride. The selection criteria include their intrinsic thermal conductivity, aspect ratio, cost, and interfacial compatibility with the matrix.

[0039] The triggering of the "off state" is an active process driven by thermal triggering and primarily by mechanical destruction. Expandable micromaterials act as the "switch" for this function. Their core characteristic is the rapid and significant volume expansion near a specific temperature point, with expansion ratios reaching several to tens of times. Typical examples include thermally expandable microspheres, thermo-induced phase change materials, or compounds that decompose to produce gas upon heating. These expandable materials are pre-dispersed uniformly within a pre-constructed thermally conductive network. When the temperature rises to the trigger temperature, the expandable material expands rapidly. The resulting expansion force pushes apart adjacent worm-like thermally conductive fillers, increasing their spacing or even completely separating them, thereby significantly increasing interfacial thermal resistance and cutting off the main path of phonon conduction. The simultaneous action of numerous expandable bodies causes the originally dense thermally conductive network to be "disintegrated" in a short time, forming a composite structure dominated by isolated thermally conductive fillers, numerous air bubbles, and expanded debris, resulting in a sharp drop in thermal conductivity.

[0040] Worm-like materials possess the dual functions of expansion and thermal conductivity. Taking expandable graphite as an example, some or all of it initially acts as a thermally conductive filler, constructing an initial thermally conductive network. When the temperature reaches its expansion temperature, it expands. This expansion process further disrupts the thermally conductive network. The worm-like remnants formed after the expansion of expandable graphite are themselves excellent lightweight, porous, and high-temperature stable flame-retardant materials, further enhancing safety.

[0041] To withstand the internal stresses generated during expansion and the potential high temperatures (such as battery thermal runaway), reinforcing fibers (such as mullite fibers and glass fibers) can be introduced to improve mechanical integrity. Adding ceramic precursors (such as silicon- or phosphorus-containing polymers or fillers) allows the material to undergo a ceramization reaction at higher temperatures, forming robust ceramic flame-retardant materials. The addition of flame retardants (such as ammonium polyphosphate and aluminum hydroxide) can inhibit the combustion of the elastomer matrix, improving the intrinsic safety of the material.

[0042] The trigger temperature is not a fixed value, but an engineerable parameter. By selecting different types of thermally expandable microspheres and expandable graphite, or other materials with similar functions, the trigger temperature can be adjusted to a range of 80°C to 300°C or even wider to meet the precise needs of different application scenarios, from overheat protection of electronic devices to thermal runaway protection of batteries.

[0043] The materials prepared by this design paradigm are particularly suitable for resolving the contradiction between "efficient heat dissipation under normal conditions" and "absolute heat insulation during thermal runaway" in high-energy-density battery systems. They have demonstrated excellent thermal propagation blocking capabilities in battery module testing. At the same time, they provide an innovative solution for other fields with overheating risks or requiring intelligent thermal flow control, such as other electrochemical energy storage systems, high-power electronic devices, and special protection scenarios.

[0044] According to embodiments of the present invention, a smart thermal management material based on a "thermo-mechanical coupling" design paradigm is provided, offering a revolutionary solution for next-generation high-safety, long-life lithium-ion battery systems. The core value of this material lies in its unique temperature-triggered, mechanically-responsive smart switching characteristics.

[0045] First, the composite material according to embodiments of the present invention achieves dynamic adaptive and intelligent management of heat flow. Its core mechanism lies in the synergistic effect between the internally pre-placed expandable micromaterials and the constructed thermally conductive network. Within the normal operating temperature range of the battery, the thermally conductive components within the material overlap to form an efficient three-dimensional thermal conductive pathway, maintaining high thermal conductivity and rapidly homogenizing heat between battery cells, preventing the formation of "hot spots." When a local anomaly occurs in the battery, and the temperature rises to a preset trigger temperature matching the thermal runaway initiation temperature, the expandable micromaterials in the system are activated, undergoing violent volume expansion. The micro-mechanical force generated by this expansion actively pushes, peels off, or even destroys the original continuous thermal conductive path, thereby causing a rapid, step-like drop in the macroscopic thermal conductivity of the material within a short time, automatically and quickly switching from a high thermal conductivity state to a highly effective thermal insulation state. This intelligent behavior of "normal conduction, fault shutdown" fundamentally solves the inherent contradiction between "normal heat dissipation" and "thermal runaway insulation" in battery modules.

[0046] Secondly, the application of composite materials according to embodiments of the present invention can significantly improve the overall performance and lifespan of the battery system. Its excellent thermal conductivity and temperature uniformity create a mild and consistent operating environment for the battery. Comparative tests show that battery modules using this smart material as the interlayer between cells exhibit a maximum internal temperature difference that is approximately 2.08°C lower than modules using traditional static insulation materials during 1C rate cycling, and also have a lower average operating temperature. This optimized thermal environment effectively slows down the battery degradation rate. Experimental data confirms that the capacity retention rate of its module after 500 cycles (89.2%) is significantly better than the control group (79.8% after 253 cycles), and it is expected to nearly double the cycle life of the battery module. Attached Figure Description

[0047] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 The image shown is a cross-sectional scanning electron microscope (SEM) image of the composite thermal switching material prepared in Example 1 of the present invention at room temperature, showing the uniform dispersion of expandable graphite sheets (sheet-like), thermally expandable microspheres (spherical), and mullite fibers (fibrous) in the matrix. Figure 2The images show a comparison of cross-sectional SEM images of the composite thermal switching material after heat treatment at different temperatures, visually demonstrating the morphological evolution process of the thermally expanding microspheres first expanding and rupturing, followed by the expansion of expandable graphite. Figure 3 The graph shows the thermal conductivity of the composite heat-switching material as a function of temperature, clearly demonstrating the rapid decrease in thermal conductivity of the material in the temperature range of approximately 140-160°C. Figure 4 Infrared thermal images and photographs of the composite heat-switching material during 30 seconds of burning in a butane torch flame (1100°C) demonstrate its slow backwall temperature rise and self-extinguishing characteristics. Figure 5 A schematic diagram of a test device for the thermal management performance of a 1*4 battery module; Figure 6 The cycle performance of a battery module consisting of four 1Ah soft-pack batteries, with heat-switching materials and pure heat-insulating materials used between the batteries; Figure 7 Temperature-time curves and temperature difference curves of a battery module (4 1Ah pouch cells) using composite thermal switching material as the interlayer are obtained under 1C rate cycling, and compared with a module using pure thermal insulation material. Figure 8 After the first battery thermal runaway was triggered, the temperature and voltage change curves of the four batteries in the battery module using composite thermal switching materials showed that thermal propagation was successfully blocked. Detailed Implementation

[0048] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0049] Example 1: Preparation and Properties of Composite Thermal Switching Materials Ingredients: Weigh by mass fraction: silicone rubber (31.5%), silicone resin (4.5%, mass ratio of the two is 7:1), ammonium polyphosphate (7.9%), aluminum hydroxide (7.9%), mullite fiber (7.9%), thermally expandable microspheres (initial expansion temperature 100°C, particle size 10μm, 15.7%), expandable graphite (initial expansion temperature 200°C, 80 mesh, 15.7%).

[0050] preparation: a. Place ammonium polyphosphate, aluminum hydroxide, thermally expandable microspheres, and expandable graphite into a ball mill jar and ball mill at 300 rpm for 12 hours.

[0051] b. Mix silicone rubber with platinum catalyst (mass ratio 15:1), mix silicone resin with its catalyst (mass ratio 25:1), then mix the two evenly and degas under vacuum.

[0052] c. Add the ball-milled filler to the matrix precursor and stir at 500 rpm for 20 minutes. Add mullite fibers and continue stirring at 500 rpm for 10 minutes.

[0053] d. After vacuum degassing the mixture, inject it into a mold, cure it in a hot press at 60°C for 10 minutes, and then transfer it to a 60°C oven for curing for 24 hours to obtain a sheet material with a thickness of 3 mm.

[0054] Performance testing: Thermal conductivity: Measured using a thermal conductivity meter, it is 0.75 W / (m·K) at room temperature (25°C); after being fully heated on a 200°C heating platform, the thermal conductivity drops to 0.13 W / (m·K), and the calculated on / off ratio is 5.77.

[0055] Temperature switching: By raising the temperature through a controlled step and measuring the thermal conductivity, it was determined that the thermal conductivity drops sharply in the range of 140-160°C.

[0056] Flame retardancy: Passes UL-94 vertical burning test, achieving V-0 rating; Limiting oxygen index (LOI) is 36.5%.

[0057] Insulation properties: The volume resistivity at room temperature is 2.05 × 10¹³ Ω·cm; after heat treatment at 200°C, the volume resistivity is 5.15 × 10¹² Ω·cm.

[0058] Thermal stability: Under nitrogen atmosphere, the char residue rate at 800°C is 68.6%.

[0059] The thermal management capability of two-phase composite thermal switching materials in actual battery modules was evaluated by testing the cycle life and operating temperature of the actual battery modules. A battery module with pure thermal insulation material between the cells was selected as a comparison. The test setup is shown below. Figure 5 Four 1Ah pouch lithium-ion batteries are packaged into a battery module without electrical connections, with each battery separated by a 3mm thick thermal switching material or pure thermal insulation material. Within a voltage range of 2.75-4.3V, battery #2 in both battery modules is cycled at a constant charge / discharge rate of 1C, with a 1s rest period between each charge and discharge cycle. Thermocouples are placed at the center and edge points of the battery module to monitor temperature fluctuations in real time during the cycling process, and the temperature difference is calculated by subtracting the two measurements.

[0060] Figure 6The battery module exhibits cycle performance under a 1C charge-discharge rate. The battery module using thermal switching materials has an initial discharge capacity of 844mAh and retains 89.2% of its capacity after 500 stable cycles at 25°C. In contrast, the battery module using pure thermal insulation materials has an initial discharge capacity of 921mAh, but its capacity retention drops to 79.8% after 253 stable cycles at 25°C. The cycle life of the battery using thermal switching materials is more than 1.97 times that of the thermal insulation materials, thus improving overall battery cycle life.

[0061] Figure 7 The graphs show the temperature and temperature difference at the center of the battery module during 1C charge / discharge cycles over time. The battery module using a two-phase composite heat-switching material exhibits an average temperature of 25.92°C and an average temperature difference of 0.38°C during the cycle. In contrast, the battery module using pure heat-insulating materials has an average temperature of 28.01°C and an average temperature difference of 2.46°C. Compared to pure heat-insulating materials, the battery module using heat-switching materials demonstrates superior heat dissipation during charge / discharge cycles, resulting in an average temperature 2.09°C lower and an average temperature difference 2.08°C lower, thus reducing overall operating temperature and improving battery cycle life.

[0062] In the thermal runaway experiment, a 1Ah pouch cell was used as the research object. Before the experiment, the state of charge was 100%, and there was no electrical connection between the cells. The thermal runaway was triggered by simulating thermal abuse, i.e., using a heating element to heat the cell and trigger thermal runaway. Once the first cell experienced thermal runaway, the heating element power was stopped. Four cells were used in a group, arranged in a 1×4 configuration. Thermocouples were attached to the center of the two large faces of the cells, and signal lines were connected to the tabs and then to a data acquisition instrument for recording. Two-phase composite thermal switching material was inserted between adjacent cells, and the clamp preload was set to 1 N·m. Cells were labeled #1, #2, #3, and #4 from closest to the heating element to furthest away from it.

[0063] During the experiment, a data acquisition device collected and recorded the temperature and voltage data of each battery. The thermal runaway experiment was conducted in an explosion-proof room with the ventilation system continuously running. After the first battery experienced thermal runaway, it first produced a large amount of white smoke, followed by a violently burning flame that ignited the signal wire. The burning process lasted for about 1 minute, during which the two-phase composite thermal switching material underwent significant expansion. The other three batteries did not experience thermal runaway. The overall structure of the debris remained relatively intact.

[0064] The battery temperature versus voltage curve in the thermal propagation experiment is as follows: Figure 8As shown. Around 1000 seconds into the heating process, battery #1 experienced thermal runaway, with its voltage dropping from 4.18V to 0V. The highest temperature reached was 738°C. After thermal runaway, the battery can be considered an extremely hot heat source, transferring heat primarily through conduction under the influence of the temperature gradient to battery #2. Battery #2 is adjacent to battery #1. Its front surface temperature continued to rise after battery #1's thermal runaway, reaching 149°C before decreasing, but not exceeding the critical thermal runaway temperature. The temperature fluctuation on the rear surface of battery #2 is likely due to thermocouple displacement caused by mechanical vibration resulting from the thermal runaway. The voltages of batteries #2, #3, and #4 did not decrease. Therefore, thermal runaway was successfully prevented in batteries #2, #3, and #4.

[0065] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0066] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A smart composite material with switchable thermal conductivity, characterized in that, Include: Elastomer matrix; A volumetric deformable material, wherein the volumetric deformable material is dispersed in the elastomer matrix; Thermally conductive filler, wherein the thermally conductive filler is dispersed in the elastomer matrix.

2. The intelligent composite material with switchable thermal conductivity according to claim 1, characterized in that, The volumetric deformation material is selected from at least one of thermally expandable microspheres, thermally induced phase change materials, or other inorganic or organic materials that can expand in volume when heated. Optionally, the volumetric deformation material expands in volume by 3 to 50 times after being heated; Optionally, the initial expansion temperature of the volumetric deformation material is between 40 °C and 250 °C; Optionally, the maximum expansion temperature of the volumetric deformation material is between 120 °C and 290 °C.

3. The intelligent composite material with switchable thermal conductivity according to claim 1, characterized in that, The thermally conductive filler is selected from worm-shaped thermally conductive materials; Optionally, the worm-like thermally conductive material is selected from expandable graphite, expanded vermiculite, or a combination thereof with graphene and boron nitride.

4. The intelligent composite material with switchable thermal conductivity according to claim 1, characterized in that, The elastomer matrix is ​​selected from silicone rubber, silicone resin, or a composite thereof.

5. The intelligent composite material with switchable thermal conductivity according to claim 1, characterized in that, The mass ratio of the sum of the volumestric deformation material and the thermally conductive material to the mass of the elastomer matrix is ​​1:3 to 1:

1.

6. The intelligent composite material with switchable thermal conductivity according to claim 1, characterized in that, The smart composite material further includes components for enhancing mechanical properties or imparting other functions.

7. The intelligent composite material with switchable thermal conductivity according to claim 6, characterized in that, The enhancement of mechanical properties or the imparting of other functions are selected from reinforcing fibers or flame retardants; Optionally, the reinforcing fiber is selected from mullite fiber, ceramic fiber or polymer fiber; Optionally, the flame retardant is selected from ammonium polyphosphate, aluminum hydroxide, or magnesium hydroxide.

8. A method for preparing the intelligent composite material with switchable thermal conductivity as described in any one of claims 1-7, characterized in that, include: A homogeneous mixture is prepared by mechanically blending, skeletonizing, or ice-templating an elastomer matrix with a volumetric deformable material, thermally conductive filler, and optional components for enhancing mechanical properties or imparting other functions. The mixture is then cured or molded to obtain the aforementioned smart composite material with switchable thermal conductivity.

9. The application of the intelligent composite material with switchable thermal conductivity according to any one of claims 1-7 or the intelligent composite material with switchable thermal conductivity prepared according to the method of claim 8 in a device requiring thermal management.

10. The application according to claim 9, characterized in that, The intelligent composite material with switchable thermal conductivity is prepared into a thermal management interface layer or component and disposed between the heating component and the protected component of the device, or between multiple heating components, for intelligent control of heat flow according to temperature.

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