Power battery thermal runaway protection structure, power battery and manufacturing method

Abstract

The application relates to the technical field of power battery thermal safety protection, in particular to a power battery thermal runaway protection structure, a power battery and a manufacturing method. Firstly, a plurality of stress release cavities in a thermal stress release structure layer change in a gradient along a thermal runaway heat flow direction, equivalent compression stiffness gradient distribution of an elastic deformation area is formed, a stress migration path from a high stiffness area to a low stiffness area is established along the heat flow direction when thermal runaway occurs, and the problems of delamination, cracking and even structural failure caused by random concentration of interface thermal stress at the interlayer weak position are avoided. Meanwhile, a thermal response driving element is used to generate thermal induced deformation in response to temperature change, a displacement conversion mechanism is used to drive a separation moving piece to move to change a heat transfer path, the protection structure can autonomously complete heat path switching from a continuous heat conduction state to a discontinuous heat insulation state in a thermal runaway state, and the efficient heat dissipation demand under a normal working condition and the heat insulation blocking demand under the thermal runaway state are considered.

Description

Technical Field

[0001] This application relates to the field of power battery thermal safety protection technology, and in particular to a power battery thermal runaway protection structure, power battery and manufacturing method. Background Technology

[0002] With the development of new energy vehicles, energy storage systems, and power equipment, lithium-ion power batteries are widely used in power battery systems due to their high energy density and good cycle performance. However, when batteries are affected by factors such as mechanical damage, electrical abuse, thermal abuse, or internal defects, safety issues such as localized temperature rise, thermal runaway, and thermal diffusion may occur. When a single cell experiences thermal runaway, the large amount of heat it releases may propagate to adjacent cells or battery modules through structural connection areas, further inducing continuous thermal runaway and affecting the safety performance of the entire battery system.

[0003] Traditional power battery thermal safety protection technologies are usually designed around the heat transfer process. For example, heat insulation materials, fireproof materials, flame-retardant materials, or thermal barrier structures are placed between cells or between cells and the casing to reduce the speed at which heat spreads to adjacent areas; or elastic buffer materials are used to absorb the mechanical deformation caused by cell expansion, thereby improving the reliability of the battery structure.

[0004] When a power battery experiences thermal runaway, the heat release process inside the cell causes a rapid change in the temperature field. The generated heat is transferred to the surrounding area through the cell, interface materials, and protective structure. During thermal runaway, an unsteady temperature field is formed inside the protective structure. This temperature field changes along the heat transfer path from the cell module to the battery pack casing, further causing differences in the thermal expansion response between different materials.

[0005] In the process of thermal runaway of power batteries, in addition to the problem of rapid heat release and propagation, the different coefficients of thermal expansion of the cell materials, battery pack shell materials, and internal protective materials can lead to thermal expansion mismatch during rapid temperature rise, resulting in interfacial thermomechanical stress. This type of thermomechanical stress has obvious localized concentration characteristics, which may lead to deformation of the cell constraint area, failure of structural connections, damage to the protective layer, and even further reduce the effectiveness of the thermal isolation structure.

[0006] Traditional technologies such as foam, elastic adhesive layers, and ordinary buffer structures typically rely on the material's own elastic deformation capacity to passively absorb mechanical loads. Their structural stiffness distribution is usually relatively uniform, which can only reduce local stress peaks and is difficult to form spatially different deformation capabilities based on the location of thermomechanical stress generation and the direction of thermal runaway heat flow during thermal runaway.

[0007] On the other hand, current thermal insulation structures typically employ fixed insulation or barrier layers, whose heat transfer paths remain largely unchanged after the structural design is completed. Some schemes that use thermally responsive materials to drive the movement of the insulation structure primarily rely on temperature changes to trigger the insulation action, without further considering the sequential relationship between the redistribution of interfacial thermomechanical stress and the change in the thermal path.

[0008] For example, CN118057652A discloses a battery system with multiple thermal isolation zones. This system divides the battery cell stack into two or more distinct thermal regions and places different thermal regulation components at the separation points between these regions, providing different heat transfer characteristics to adjacent thermal regions. The thermal regulation components in this type of solution are determined by the structural arrangement, and their heat transfer areas and thermal regulation relationships typically do not change actively during operation. As another example, CN219498046U discloses a battery module and battery pack, in which expansion components and buffer components are stacked and sandwiched between adjacent cell groups. The expansion components expand when heated, increasing the distance between runaway and unrunaway cells to enhance thermal insulation. Furthermore, CN120767473A discloses a method and application for improving the safety of high-energy battery modules through thermal conductivity and stress uniformity control. This method involves filling the space between battery cells with a thermally conductive layer-stress layer composite material and using a pre-loaded force design to dynamically balance the stress generated by battery expansion and contraction during charging and discharging. This solution addresses the problem of balancing mechanical stress generated by the cyclic expansion and contraction of the battery cell. This stress originates from the volume change caused by electrochemical cycling, but does not address the transient interfacial thermomechanical stress regulation caused by the thermal expansion mismatch of multiple materials during rapid thermal runaway.

[0009] When the material and structural parameters of each region of the buffer structure are relatively uniform, the difference in compressive deformation capacity at different locations is small, and the distribution of interfacial thermomechanical stress is mainly affected by local structural constraints. Therefore, in the thermal runaway protection structure of a power battery, it is necessary to simultaneously consider the interfacial thermomechanical stress caused by thermal expansion mismatch and the state changes of the heat transfer path, and to establish a clear sequential relationship between the two under structural arrangement and material response conditions. Summary of the Invention

[0010] In view of the above-mentioned shortcomings and deficiencies of the prior art, this application provides a power battery thermal runaway protection structure, a power battery and a manufacturing method, the main purpose of which is to solve the problem of premature failure of the current power battery thermal runaway protection structure due to neglect of the controllable release of interface thermomechanical stress.

[0011] To achieve the above objectives, the main technical solutions adopted in this application include: In a first aspect, this application provides a power battery thermal runaway protection structure, disposed between the battery pack casing and the cell module, comprising: A thermal stress relief structure layer is disposed between the battery pack housing and the cell module. The thermal stress relief structure layer includes an elastic deformation region. The elastic deformation region is provided with multiple stress relief cavities and stress redistribution channels connecting adjacent stress relief cavities. The spatial density and / or aperture size of the multiple stress relief cavities vary in a gradient along the direction of thermal runaway heat flow, so that the elastic deformation region forms an equivalent compressive stiffness distribution along the direction of thermal runaway heat flow. A passive thermal path reconfiguration layer is disposed on the side of the thermal stress relief structure layer away from the battery cell module. The passive thermal path reconfiguration layer includes a thermal response driving element, a displacement conversion mechanism, and an isolation moving component. The thermal response driving element generates thermal deformation in response to temperature changes and drives the isolation moving component to move through the displacement conversion mechanism to change the heat transfer path. Wherein, a heat transfer path is formed between the thermal response driving element and the thermal stress relief structure layer, the heat transfer path having a preset thermal resistance and / or thermal capacity, and the structural parameters of the thermal stress relief structure layer, the material parameters of the thermal response driving element, and the thermal resistance and / or thermal capacity of the heat transfer path are configured such that the time when the thermal stress relief structure layer reaches the preset interface thermomechanical stress redistribution state is earlier than the time when the thermal response driving element generates thermal deformation to drive the isolation moving part to move.

[0012] Optionally, the equivalent compressive stiffness of the thermal stress relief structure layer varies in a gradient along the direction of thermal runaway heat flow.

[0013] Optionally, the equivalent compressive stiffness of the thermal stress relief structure layer along the direction of thermal runaway heat flow exhibits a monotonically decreasing distribution.

[0014] Optionally, the power battery thermal runaway protection structure further includes: a thermal diffusion path layer disposed between the thermal stress relief structure layer and the passive thermal path reconstruction layer; a high-temperature thermal blocking layer disposed on the side of the passive thermal path reconstruction layer away from the thermal stress relief structure layer; and an insulating protection layer disposed on the side of the protection structure close to the cell module for electrical insulation protection.

[0015] Optionally, a heat transfer path with a preset thermal resistance and / or thermal capacity is formed between the thermal response driving element and the thermal stress relief structure layer, so that the time when the thermal response driving element reaches the trigger state is later than the time when the thermal stress relief structure layer reaches the preset interface thermomechanical stress redistribution state.

[0016] Optionally, the temperature corresponding to the thermal stress relief structure layer reaching the preset interface thermomechanical stress redistribution state is T1, and the temperature corresponding to the thermal response driving element generating deformation sufficient to drive the isolating moving part to complete the thermal path switching is T2, and T1 <T2。

[0017] Optionally, the thermal response driving element is made of shape memory alloy, bimetallic composite material or thermal response metal material with a coefficient of thermal expansion greater than that of the adjacent layer material; the isolation moving part is a sliding structure, a rotating structure or a flipping structure, and adopts one or more of mica sheet, ceramic fiber sheet, high temperature resistant polyimide sheet or metal composite heat insulation sheet.

[0018] Optionally, the displacement conversion mechanism includes a wedge-shaped pusher, the wedge-shaped pusher having a guide slope that is angled to the expansion direction of the thermal response driving element; the expansion displacement x1 generated by the thermal response driving element acts on the guide slope, causing the wedge-shaped pusher to drive the isolation moving member to move along a direction perpendicular to the expansion direction; the wedge-shaped pusher has a preset wedge angle θ, and the moving displacement x2 of the isolation moving member and the expansion displacement x1 of the thermal response driving element satisfy a displacement conversion relationship determined by the wedge angle θ.

[0019] Optionally, the power battery thermal runaway protection structure further includes: the protection structure is divided into multiple thermal safety units, and a heat propagation blocking region is provided between adjacent thermal safety units, wherein the heat propagation blocking region includes a heat diffusion path layer disconnection region and / or a stress relief groove.

[0020] Secondly, this application provides a power battery, including a battery pack housing, a cell module disposed within the battery pack housing, and a power battery thermal runaway protection structure as described in the first aspect.

[0021] Thirdly, this application provides a method for manufacturing a thermal runaway protection structure for a power battery, wherein the thermal runaway protection structure is as described in the first aspect, and the method includes: S1: Surface activation treatment is performed on the inner wall of the battery pack casing; S2: A fixed connection layer is formed on the inner wall of the shell; S3: A thermal stress relief structure layer with a stress relief cavity array and stress migration channel is composited into a fixed connection layer. The stress relief cavities are arranged in a non-uniform gradient along the direction of thermal runaway heat flow. The spatial density, aperture or interconnection area of ​​the stress relief cavities vary gradient along the direction of heat flow. S4: Composite the thermal diffusion path layer onto the thermal stress relief structure layer; S5: A passive thermal path reconstruction layer is formed on the thermal diffusion path layer. The passive thermal path reconstruction layer is formed by coating or bonding thermal response driving material, setting wedge-shaped push blocks with a wedge angle of 15° to 45° and installing isolation moving parts. S6: Composite the high-temperature thermal blocking layer onto the passive thermal path reconstruction layer; S7: The insulating protective layer is laminated onto the high-temperature heat-blocking layer; S8: Perform hot-press curing treatment on the composite structure; S9: A thermal diffusion path layer disconnection region and stress relief groove are formed at the boundary of adjacent thermal safety units.

[0022] By employing the above technical solution, this application provides a thermal runaway protection structure for power batteries. Firstly, the spatial density and / or aperture size of multiple stress relief cavities in the thermal stress relief structure layer vary gradient along the direction of thermal runaway heat flow, thereby creating an equivalent compressive stiffness gradient distribution in the elastic deformation region. This establishes a stress migration path from the high stiffness region to the low stiffness region along the heat flow direction when thermal runaway occurs. This allows the interfacial thermomechanical stress caused by the difference in thermal expansion coefficients of each material layer to be controllably redistributed and concentrated in the low stiffness region through the stress redistribution channel connecting adjacent stress relief cavities along this gradient direction. This avoids the problem of delamination, cracking, or even structural failure caused by the random concentration of interfacial thermal stress at weak points between layers. Meanwhile, by placing the passive thermal path reconstruction layer on the side of the thermal stress relief structure layer away from the battery cell module, the thermal response driving element generates thermal deformation in response to temperature changes. This deformation, driven by a displacement conversion mechanism, moves the isolation moving component to change the heat transfer path. This allows the protective structure to autonomously switch from a continuous heat conduction state to a discontinuous heat insulation state under thermal runaway conditions, without the need for external energy input or electronic control signals. This balances the high-efficiency heat dissipation requirements under normal operating conditions with the heat insulation and blocking requirements under thermal runaway conditions. Furthermore, the thermal transfer path, the structural parameters of the thermal stress relief structure layer, and the material parameters of the thermal response driving element are configured such that the time for the thermal stress relief structure layer to reach the preset interface thermomechanical stress redistribution state is earlier than the time for the thermal response driving element to generate thermal deformation that drives the isolation moving component. This ensures that, in terms of timing, the thermal stress relief structure layer first completes the controllable redistribution of interface thermomechanical stress to ensure structural integrity, and then the passive thermal path reconstruction layer performs thermal path switching to block heat propagation. A sequential triggering and functionally dependent collaborative protection mechanism is formed between the two functional modules, prioritizing structural protection and then blocking the thermal path. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a power battery and a thermal runaway protection structure provided in an embodiment of this application; Figure 2 A schematic flowchart illustrating a method for manufacturing a thermal runaway protection structure for a power battery, as provided in an embodiment of this application. Figure 3 This is a schematic diagram of a power battery manufacturing process provided in an embodiment of this application. Detailed Implementation

[0024] To better understand the above technical solutions, exemplary embodiments of this application will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this application can be understood more clearly and thoroughly, and that the scope of this application can be fully conveyed to those skilled in the art.

[0025] Power batteries typically consist of multiple cells assembled into modules, which are then integrated into a battery pack casing, along with a battery management system and structural protection components. The protective structure is usually a multi-layered composite sheet material placed between the inner wall and / or bottom surface of the battery pack casing and the cell modules, serving as an inner protective layer to ensure heat dissipation under normal operating conditions and block heat propagation under abnormal conditions. Thermal runaway refers to a self-accelerating process in which the temperature inside a lithium-ion cell rises continuously due to irreversible exothermic side reactions, with the rate of temperature increase increasing exponentially. It is typically characterized by the cell surface temperature exceeding the safe operating range. As an example, a cell surface temperature exceeding the safe operating range, such as a continuous temperature rise rate ≥1℃ / s or a peak temperature exceeding 80℃, is considered a thermal runaway state. However, the specific criteria for thermal runaway are not limited; those skilled in the art can reasonably determine the safe operating temperature range and the corresponding critical conditions for thermal runaway based on the cell's material system, capacity, and structural design.

[0026] To address the problem of premature failure in current thermal runaway protection structures for power batteries due to neglecting the controllable release of interfacial thermomechanical stress, this application proposes a thermal runaway protection structure for power batteries, as follows: Figure 1 The diagram shows a schematic representation of a power battery and its protective structure, including a battery pack housing 1, a cell module 2, and a power battery thermal runaway protection structure disposed between the battery pack housing 1 and the cell module 2. In some embodiments, depending on the design of the power battery, Figure 1 The thermal runaway protection structure for power batteries can also be installed between two cell modules inside the battery pack casing.

[0027] Furthermore, the power battery thermal runaway protection structure includes a thermal stress relief structure layer 4, disposed between the battery pack shell 1 and the cell module 2. The thermal stress relief structure layer 4 includes an elastic deformation region, within which multiple stress relief cavities and stress redistribution channels connecting adjacent stress relief cavities are provided. The spatial density and / or aperture size of the multiple stress relief cavities vary gradient along the direction of thermal runaway heat flow, causing the elastic deformation region to form an equivalent compressive stiffness distribution along the direction of thermal runaway heat flow. The stress redistribution channels, also known as stress migration channels, aim to allow interfacial thermal stress to migrate along the path of least resistance.

[0028] The passive thermal path reconfiguration layer 6 is located on the side of the thermal stress relief structure layer away from the battery cell module. The passive thermal path reconfiguration layer includes a thermal response driving element, a displacement conversion mechanism, and an isolation moving part. The thermal response driving element generates thermal deformation in response to temperature changes, and drives the isolation moving part to move through the displacement conversion mechanism to change the heat transfer path.

[0029] Furthermore, a heat transfer path is formed between the thermal response driving element and the thermal stress relief structure layer. The heat transfer path has a preset thermal resistance and / or thermal capacity. The structural parameters of the thermal stress relief structure layer, the material parameters of the thermal response driving element, and the thermal resistance and / or thermal capacity of the heat transfer path are configured such that the time when the thermal stress relief structure layer reaches the preset interface thermomechanical stress redistribution state is earlier than the time when the thermal response driving element generates thermal deformation to drive the isolation moving part.

[0030] In this embodiment, as mentioned above, the physical chain leading to the failure of the protective structure due to thermal runaway is the interfacial thermal stress caused by the mismatch in thermal expansion and deformation of different materials, rather than the heat conduction itself, which is the focus of traditional solutions. The inventive concept in this embodiment is that if the interfacial thermal stress is not effectively released, even if the insulation material has excellent performance, its structural integrity may be compromised under the action of thermal stress, thus losing its insulation function. Therefore, it is necessary to achieve the controllable release of interfacial thermal stress before heat propagation occurs. Specifically, this embodiment sets up a thermal stress release structure layer in the protective structure, with multiple stress release cavities arranged in a gradient along the direction of thermal runaway heat flow to form an equivalent compressive stiffness distribution. Along the direction of heat flow, the local equivalent stiffness of the structure decreases monotonically, meaning that the stiffness is high and the constraint is strong on the side closer to the heat source, while the stiffness is low and the constraint is weak on the side farther from the heat source. As a result, the interfacial thermal stress will preferentially migrate along the path of least resistance and be concentrated and released to the low-stiffness region far away from the heat source through the stress migration channels connecting each stress release cavity. This transforms the originally randomly distributed and uncontrollable interfacial thermal stress into a controllable migration and concentrated release along a preset direction, avoiding the random concentration of stress at weak points between layers that could lead to delamination and cracking. This solves the problem of premature failure of the protective structure caused by interfacial thermal stress.

[0031] Furthermore, the aforementioned stress release provides a structural integrity prerequisite for subsequent thermal path reconfiguration. If the thermal path reconfiguration mechanism is triggered before thermal stress is released, the isolation moving part may become stuck or misaligned due to interface delamination or cracking, making reliable thermal path switching impossible. Therefore, in this embodiment, the passive thermal path reconfiguration layer is placed on the side of the thermal stress release structure layer away from the heat source, ensuring a sequential relationship: the thermal stress release structure layer completes stress release first, and then the passive thermal path reconfiguration layer performs thermal path switching. When the interface thermal stress is released and structural integrity is maintained, if the temperature continues to rise to the preset temperature, the thermal response driving element deforms, driving the isolation moving part to move and cutting off the originally continuous heat transfer path, switching the heat transfer path from a continuous heat conduction state to a discontinuous heat insulation state, thereby blocking the spread of heat to adjacent areas.

[0032] Therefore, this embodiment achieves a gradient distribution of equivalent compressive stiffness in the elastic deformation region by varying the spatial density and / or aperture size of multiple stress relief cavities in the thermal stress relief structure layer along the direction of thermal runaway heat flow. This establishes a stress migration path from the high stiffness region to the low stiffness region along the heat flow direction when thermal runaway occurs. This allows the interfacial thermomechanical stress caused by the difference in thermal expansion coefficients of each material layer to be controllably redistributed and concentrated in the low stiffness region through the stress redistribution channel connecting adjacent stress relief cavities along this gradient direction. This avoids the problem of delamination, cracking, or even structural failure caused by the random concentration of interfacial thermal stress at weak points between layers. Meanwhile, by placing the passive thermal path reconstruction layer on the side of the thermal stress relief structure layer away from the battery cell module, the thermal response driving element generates thermal deformation in response to temperature changes. This deformation, driven by a displacement conversion mechanism, moves the isolation moving component to change the heat transfer path. This allows the protective structure to autonomously switch from a continuous heat conduction state to a discontinuous heat insulation state under thermal runaway conditions, without the need for external energy input or electronic control signals. This balances the high-efficiency heat dissipation requirements under normal operating conditions with the heat insulation and blocking requirements under thermal runaway conditions. Furthermore, the thermal transfer path, the structural parameters of the thermal stress relief structure layer, and the material parameters of the thermal response driving element are configured such that the time for the thermal stress relief structure layer to reach the preset interface thermomechanical stress redistribution state is earlier than the time for the thermal response driving element to generate thermal deformation that drives the isolation moving component. This ensures that, in terms of timing, the thermal stress relief structure layer first completes the controllable redistribution of interface thermomechanical stress to ensure structural integrity, and then the passive thermal path reconstruction layer performs thermal path switching to block heat propagation. A sequential triggering and functionally dependent collaborative protection mechanism is formed between the two functional modules, prioritizing structural protection and then blocking the thermal path.

[0033] It should be noted that, in this embodiment, the direction of thermal runaway heat flow refers to the main direction of heat transfer from the side of the battery cell module where thermal runaway occurs to the outside of the protective structure and adjacent areas. The terms "side closer to the battery cell module" and "side farther from the battery cell module" used later in this text are based on this spatial relationship. Stress redistribution refers to the change in stress distribution within the structure through elastic deformation and deformation coordination in areas of existing localized stress concentration under the influence of thermal expansion mismatch and structural constraints. This makes localized deformation more likely to occur in areas with lower equivalent compressive stiffness, thereby reducing the degree of localized stress concentration in highly constrained areas. Stress redistribution channels are structures connecting adjacent stress relief cavities, used to transfer deformation between different areas, thus coordinating the deformation states between adjacent areas.

[0034] To describe the stiffness variation of the above structure along the direction of thermal runaway heat flow, the direction of thermal runaway heat flow is defined as the x-direction in spatial coordinates. The side closer to the battery cell module is x=0, and the side farther from the battery cell module 2 is x=L, where L is the effective compressive thickness of the thermal stress relief structure layer along the direction of thermal runaway heat flow, satisfying 0≤x≤L. Through structural parameter design, the equivalent compressive stiffness can be made to form a monotonically decreasing distribution along the direction of thermal runaway heat flow, i.e.: ; In a linear approximation of structural design characterization, it can be expressed as: ; In the above formula, K0 is the initial equivalent compressive stiffness at the x=0 position, K eff (x) represents the equivalent compressive stiffness, or the local equivalent stiffness of the structure, and β is the stiffness gradient coefficient. Equivalent compressive stiffness K eff This linear relationship characterizes the equivalent compressive deformation capacity of a thermal stress-relieving structural layer when subjected to compressive loads at corresponding spatial locations. Its specific value can be determined based on material parameters, cavity geometry parameters, cavity density, and structural boundary conditions. The aforementioned linear relationship is used to characterize structural design relationships and does not require the actual structure to strictly follow a linear function.

[0035] In one feasible implementation, the power battery thermal runaway protection structure further includes a fixing connection layer 3, a heat diffusion path layer 5, a high-temperature heat blocking layer 7, and an insulating protection layer 8. The fixing connection layer 3 is located on the side of the thermal stress relief structure layer near the battery pack housing, used to fix the protection structure to the battery pack housing, ensuring that the protection structure does not shift or detach under long-term service conditions such as vehicle vibration and impact. The fixing connection layer 3 can be formed by coating or bonding with a modified epoxy high-temperature resistant structural adhesive, and its thickness can be selected from 0.10 to 0.20 mm. The heat diffusion path layer 5 is located between the thermal stress relief structure layer and the passive thermal path reconstruction layer, used to rapidly diffuse the heat generated by the battery cell along the planar direction under normal operating conditions, ensuring uniform temperature distribution on the battery cell surface and preventing the formation of local hot spots. The heat diffusion path layer 5 is made of a high thermal conductivity material, such as one of artificial graphite film, graphene thermal conductive film, or high thermal conductivity carbon-based composite film, with a thermal conductivity greater than 1000 W / m² in this embodiment. The thickness is 0.08~0.15mm. The high-temperature thermal blocking layer 7 is disposed on the side of the passive thermal path reconstruction layer away from the thermal stress release structure layer. It serves as the main thermal barrier in the event of thermal runaway, limiting the propagation of heat towards the battery pack casing and its diffusion to adjacent cells or modules. The high-temperature thermal blocking layer 7 is made of a low thermal conductivity, high-temperature resistant material, such as one or more of an aerogel material layer, a mica material layer, a ceramic fiber composite layer, or a polyimide aerogel layer. In this embodiment, the thermal conductivity is selected to be less than 0.030 W / m³. The temperature resistance is greater than 800℃, and the thickness ranges from 0.8 to 1.2 mm. The insulating protective layer 8 is set on the side of the protective structure close to the cell module to provide electrical insulation protection and prevent high voltage breakdown or leakage between the cell module and the battery pack shell. It can be made of mica sheet with a thickness of 0.15 to 0.30 mm, and the overall structural thickness is about 2.0 to 3.0 mm.

[0036] In one feasible implementation, the power battery thermal runaway protection structure may further include thermal safety units 9 and heat propagation blocking regions 10. The interior of the battery pack housing 1 can be divided into multiple independent thermal safety units 9 according to the arrangement of the cell modules 2. Heat propagation blocking regions 10 are provided between adjacent thermal safety units 9 to confine thermal runaway within a cell of a thermal safety unit 9 when it occurs, preventing heat and high-temperature gases from propagating across regions and causing cascading thermal runaway in adjacent units. In one example, the heat propagation blocking region 10 includes a thermal diffusion path layer disconnection region and / or stress relief grooves located at the cell boundary. The thermal diffusion path layer disconnection region refers to the partial disconnection of the thermal diffusion path layer 5 at the cell boundary, making the thermal diffusion path layer 5 discontinuous between adjacent thermal safety units 9, thereby cutting off the in-plane heat conduction path. The stress relief grooves are groove-like structures opened on the protective structure at the cell boundary, used to absorb the deformation of the protective structure caused by thermal expansion during thermal runaway, preventing structural damage in the boundary area due to thermal stress accumulation. By setting up the aforementioned thermal safety unit 9 and heat propagation blocking region 10, localized isolation of thermal runaway is achieved, further enhancing the overall safety of the power battery pack.

[0037] Optionally, the thermal stress relief structure layer includes an elastic deformation region, and the stress relief cavity is a cavity structure opened inside the elastic deformation region. The spatial density, pore size or interconnection area of ​​multiple stress relief cavities varies in a gradient from the direction close to the heat source to the direction far away from the heat source, so as to form an equivalent compressive stiffness gradient.

[0038] In this embodiment, the thermal stress relief structure layer achieves directional migration and controllable release of interfacial thermal stress through the aforementioned gradient structure. Specifically, the elastic deformation region provides matrix support for the opening of the stress relief cavities, which, as porous structures, provide space for elastic deformation. The spatial density, aperture, or interconnected area of ​​multiple stress relief cavities varies gradient from the direction closer to the heat source to the direction farther from the heat source. This results in relatively high rigidity on the side closer to the heat source, providing stronger constraint on deformation, while relatively low rigidity on the side farther from the heat source, providing weaker constraint on deformation. This equivalent compressive stiffness gradient causes thermomechanical stress to preferentially migrate directionally along the direction of lower resistance, i.e., from the high-stiffness region to the low-stiffness region, and finally concentrate and release in the low-stiffness region far from the heat source, avoiding random stress concentration at the interface that could lead to delamination or cracking. At the same time, each stress relief cavity provides space for elastic deformation, ensuring that the thermal stress relief structure layer does not generate excessive internal reaction force due to the incompressibility of the material volume during compressive deformation, thus guaranteeing smooth stress release. Therefore, the thermal stress relief structure layer can effectively release the interfacial thermal stress caused by the difference in thermal expansion coefficients of each material layer in the early stage of thermal runaway, thus maintaining the integrity and reliability of the protective structure.

[0039] Optionally, the elastic deformation region is made of an elastic material, including one or more of closed-cell silicone foam, polyurethane foam, microporous rubber, or silicone rubber elastic composite materials.

[0040] In this embodiment, the elastic material exhibits excellent compression resilience and temperature resistance. Closed-cell silicone foam and polyurethane foam possess high porosity and low compression set, enabling them to maintain stable elastic recovery after repeated compressions, ensuring the structural stability of the thermal stress relief layer during long-term battery service. Microporous rubber and silicone rubber elastic composite materials combine excellent elasticity and high-temperature resistance, maintaining structural integrity even under high-temperature conditions caused by thermal runaway, preventing loss of stress relief function due to material softening or decomposition. These materials also possess good processing performance, allowing for the formation of stress relief cavity arrays through molding, microsphere foaming, or laser micropore processing to meet the design requirements of different battery pack structures.

[0041] Optionally, the spatial density of the stress relief cavity gradually decreases from the direction closer to the heat source to the direction farther from the heat source; and / or, the aperture of the stress relief cavity gradually increases from the direction closer to the heat source to the direction farther from the heat source; and / or, the interconnecting area of ​​the stress relief cavity gradually increases from the direction closer to the heat source to the direction farther from the heat source.

[0042] In this embodiment, the three gradient change methods described above can be implemented individually or in combination to achieve the technical effect of monotonically decreasing equivalent compressive stiffness along the heat flow direction. Specifically, the spatial density of the stress relief cavity gradually decreases, resulting in a larger number and denser arrangement of cavities near the heat source, with a higher proportion of solid material in the elastic deformation region, thus leading to a larger equivalent stiffness; while the number and sparser arrangement of cavities away from the heat source, with a lower proportion of solid material, result in a smaller equivalent stiffness, thereby forming a gradient network transitioning from high stiffness to low stiffness. The aperture of the stress relief cavity gradually increases, resulting in a smaller aperture and relatively dispersed stress concentration on the side near the heat source, with better material continuity; while the aperture is larger on the side away from the heat source, providing greater deformation space for stress release and reducing the equivalent stiffness. The interconnected area of ​​the stress relief cavity gradually increases, making the stress migration channel on the side away from the heat source more unobstructed, allowing stress to migrate and be released more smoothly along the interconnected path to the low stiffness region. As a feasible implementation method, the stress relief cavity can be one or more of the following: circular hole, elliptical hole, honeycomb hole, or polygonal hole.

[0043] As a specific application, the elastic deformation region uses closed-cell silicone foam with a thickness of 0.5–1.0 mm and a porosity of 40%–60%. The stress relief cavities form an array of microcavities within the elastic deformation region, with a cavity diameter of 0.15–0.35 mm and an area ratio of 30%–50%. The stress relief cavities exhibit a density gradient distribution along the direction from the area near the heat source to the area away from the heat source, with the cavity density near the heat source being higher than that away from the heat source. For example, the area near the heat source has high-density small pores, while the area away from the heat source has large pores and low density, forming a directional equivalent compressive stiffness distribution induced by thermal runaway.

[0044] Optionally, the passive thermal path reconfiguration layer further includes a wedge-shaped pusher disposed between the thermal response driving element and the isolation moving element. When the thermal response driving element reaches a preset temperature, it expands along a first direction. The wedge-shaped pusher converts the expansion displacement of the thermal response driving element into the displacement of the isolation moving element along a second direction.

[0045] In this embodiment, a wedge-shaped pusher is used to achieve directional conversion and displacement amplification of the expansion displacement, enabling the passive thermal path reconfiguration layer to autonomously switch thermal paths without external energy input. Specifically, the thermal response driving element expands in volume when it reaches a preset temperature, generating an expansion displacement along a first direction. This expansion displacement acts on the inclined surface of the wedge-shaped pusher. According to the principle of inclined plane mechanics, the wedge-shaped pusher decomposes the thrust along the first direction into a component force along a second direction, thereby driving the isolation moving component to move along the second direction. This directional conversion transforms the original expansion displacement along the thickness direction of the protective structure into a lateral pushing displacement along the in-plane direction of the protective structure, allowing the isolation moving component to laterally insert into the interface between the heat diffusion path layer and the high-temperature heat blocking layer from a position outside the continuous heat transfer area, thus physically cutting off the heat transfer path. The entire process does not rely on external sensors, power supplies, or electronic control signals.

[0046] Furthermore, the first direction and the second direction are set at an angle; wherein, the wedge angle of the wedge pusher ranges from 15° to 45°, and the displacement x2 of the isolation moving part and the expansion displacement x1 of the thermal response driving element satisfy x2=x1·tanθ, where θ is the wedge angle, which is the angle between the inclined surface of the wedge pusher and the first direction.

[0047] In this embodiment, the wedge angle is selected to be between 15° and 45°, which ensures both sufficient displacement amplification and sufficient driving force to ensure reliable execution of thermal path reconstruction. Specifically, when the thermal response driving element generates an expansion displacement x1, under the action of the inclined surface of the wedge-shaped pusher, the displacement x2 generated by the isolating moving part along the second direction satisfies a tangent relationship with x1. Taking θ as 30° as an example, tan30°≈0.58, that is, the displacement of the isolating moving part is approximately 0.58 times the expansion displacement of the thermal response driving element. By reasonably selecting the wedge angle and designing according to the expansion displacement of the thermal response driving element, the moving distance of the isolating moving part can be precisely controlled to ensure that it can be fully inserted into the heat transfer interface to form an effective thermal insulation gap.

[0048] Optionally, the insulating moving part is one of a sliding structure, a rotating structure, or a flipping structure, and the insulating moving part is made of one or more of mica sheets, ceramic fiber sheets, high-temperature resistant polyimide sheets, or metal composite heat insulation sheets.

[0049] In this embodiment, the isolating moving component can adopt various structural forms to adapt to the spatial layout and installation requirements of different battery packs. A sliding structure is suitable for scenarios with ample space where a straight-line translation is required to cut off the heat path; its movement trajectory is straight, resulting in smooth movement and accurate positioning. A rotating structure is suitable for scenarios with limited space where a rotational approach is needed to cut into the heat transfer interface; it occupies little space and moves quickly. A flipping structure is suitable for scenarios requiring a large displacement or where a flip-top mechanism is needed to cut off the heat path.

[0050] Optionally, the protective structure has a three-level response temperature window; wherein the normal operating temperature range is 25℃~80℃, the response temperature range of the thermal stress relief structure layer is 80℃~120℃, and the trigger temperature range of the thermal response driving element is 120℃~200℃.

[0051] In this embodiment, the aforementioned three-level response temperature windows correspond to three functional states of the protective structure in different temperature ranges. Within the normal operating temperature range of 25℃ to 80℃, the battery cell is in normal operating condition, the thermal response driving element maintains its initial shape, the isolation moving part does not move, and the thermal conduction path between the thermal diffusion path layer and the high-temperature thermal blocking layer remains continuous. The heat generated by the battery cell can be rapidly diffused along the in-plane direction through the thermal diffusion path layer to achieve normal heat dissipation. In this embodiment, the judgment threshold for thermal runaway is set at 80℃. When the temperature rises to 80℃ to 120℃, the thermal expansion mismatch effect in the initial stage of thermal runaway begins to appear, and the thermal stress release structure layer responds. It releases the interface thermal stress through the equivalent compressive stiffness gradient, maintaining the interface integrity and bonding reliability between the layers of the protective structure. The response process can be referred to the above description and will not be repeated here. When the temperature continues to rise to 120℃~200℃, in this embodiment, the preset temperature for triggering the deformation of the thermal response driving element mentioned above is also 120℃, indicating that thermal runaway has entered a more serious stage. The thermal response driving element is triggered, generating deformation to drive the isolation moving part to move, switching the continuous heat conduction state to a discontinuous heat insulation state, blocking the spread of heat to adjacent areas. The three response temperature windows are interconnected, and the temperature ranges of 80℃~120℃ and 120℃~200℃ are set to ensure that the response of the thermal stress release structure layer precedes the triggering of the passive thermal path reconstruction layer, satisfying the sequential relationship and avoiding unreliable execution due to structural damage if the thermal path reconstruction mechanism acts prematurely because the interface thermal stress has not been released.

[0052] To illustrate the overall response of the thermomechanical sequential response mechanism throughout the thermal runaway process, a specific implementation is described using three temperature windows: 25℃~80℃, 80℃~120℃, and 120℃~200℃. It should be noted that the temperature thresholds are exemplary settings, and those skilled in the art can make adaptive adjustments based on the cell's material system, capacity, and structural design. Within the normal operating temperature range of 25℃~80℃, the cell is in a normal charging / discharging or static state, and no irreversible exothermic side reactions occur inside the cell. At this time, the stress relief cavity inside the thermal stress relief structure layer maintains its initial uncompressed shape, the elastic deformation area is in a naturally relaxed state, and no significant interfacial thermal stress is generated; therefore, the equivalent compressive stiffness distribution is in a state of waiting to be activated. The thermal response driving element maintains its initial shape, without volume expansion or deformation, and the isolating moving part is located outside the continuous heat transfer area, not interfering with the interfacial contact between the heat diffusion path layer and the high-temperature thermal blocking layer. The Joule heat and operating heat generated by the battery cell during charging and discharging diffuse rapidly inward along the high thermal conductivity surface of the heat diffusion path layer, making the surface temperature of the cell tend to be uniform, and dissipating heat outward through the battery pack casing. During this stage, the overall protective structure exhibits a low thermal resistance thermal conductivity state, with the thermal path state G(t)=1, meeting the heat dissipation requirements of the power battery under normal operating conditions.

[0053] Furthermore, when the battery cell triggers thermal runaway due to factors such as overcharging, internal short circuit, or mechanical damage, the surface temperature of the battery cell continues to rise. When the temperature reaches 80°C, it reaches the exemplary judgment threshold for thermal runaway in this embodiment, marking the initial stage of thermal runaway. Within this temperature range, the heat released by thermal runaway causes the temperature of the materials of each functional layer of the protective structure to rise rapidly. Due to the significant differences in the coefficients of thermal expansion between the aluminum alloy shell, adhesive layer, heat diffusion path layer, and high-temperature heat blocking layer, and because each layer is constrained by bonding or pressing and cannot deform freely, thermal mismatch strain is generated at the interlayer interface and further accumulates into interfacial thermal stress. At this time, the thermal stress relief structure layer begins to respond, and the spatial density of its internal stress relief cavity gradually decreases and the pore size gradually increases along the direction closer to the heat source to the direction farther from the heat source, forming an equivalent compressive stiffness gradient. Because the side closer to the heat source (cell) has high stiffness and strong constraint, while the side farther from the heat source (shell) has low stiffness and weak constraint, interfacial thermal stress preferentially migrates along the direction of least resistance, i.e., through the stress migration channels connecting each stress relief cavity, from the high-constraint region to the low-constraint region, and finally concentrates and releases in the low-stiffness relief region far from the heat source, completing the state transition M(t):0→1. This process is usually completed within 0.1 to 10 seconds, effectively avoiding random concentration of interfacial thermal stress at weak points between layers. Within this temperature range, although the cell temperature has exceeded the normal operating range, the trigger temperature of the thermal response drive element is set to 120℃, so the thermal response drive element has not yet been triggered, the isolation moving part remains in the initial position, and the thermal conduction path between the thermal diffusion path layer and the high-temperature thermal blocking layer remains continuous.

[0054] When the interfacial thermal stress has been released (M(t)=1) and the cell temperature continues to rise to 120℃, it indicates that thermal runaway has entered a more serious stage. Stress release alone is insufficient to ensure safety, and the heat propagation path needs to be cut off immediately to prevent heat from spreading to adjacent cells or modules. At this time, the preset temperature of 120℃ for triggering the deformation of the thermal response drive element is reached. The thermal response drive element undergoes volume expansion, generating an expansion displacement x1 along the first direction. This expansion displacement acts on the inclined surface of the wedge-shaped pusher. According to the principle of inclined plane mechanics, the wedge-shaped pusher decomposes the thrust along the first direction into a component force along the second direction, causing the isolation moving part to generate a lateral displacement x2 along the second direction. The two satisfy x2=x1·tanθ, where θ is the wedge angle, which is the angle between the inclined surface of the wedge-shaped pusher and the first direction. The isolating moving component is laterally inserted into the interface between the heat diffusion path layer and the high-temperature thermal barrier layer from outside the continuous heat transfer region. This creates an air gap or a low thermal conductivity barrier layer between the two previously tightly contacted layers, causing a step change in the interface thermal resistance that tends towards infinity, physically severing the continuous heat conduction path. At this point, the heat transfer path switches from a continuous heat conduction state G(t)=1 to a discontinuous thermal insulation state G(t)=0, with zero heat flow, achieving active reconstruction of the heat propagation path. This process typically completes within 10–120 seconds. Within this temperature range, the high-temperature thermal barrier layer acts as the primary thermal insulation barrier, further limiting heat propagation towards the battery pack casing and adjacent thermal safety units. Simultaneously, the disconnected areas of the heat diffusion path layer and stress relief grooves at the boundary of adjacent thermal safety units further ensure that thermal runaway is confined within the originating unit, preventing cascading thermal runaway.

[0055] To more clearly illustrate the working principle and technical effects of this embodiment, the following will explain the thermo-mechanical coupling mechanism, thermomechanical stress gradient migration principle, and timing control mechanism involved in this embodiment from the perspectives of physics and mechanics.

[0056] (1) Multiphysics coupling problem in the thermal runaway process of power battery When a power battery experiences thermal runaway, internal electrochemical side reactions release a large amount of heat, causing the cell temperature to rise rapidly. The heat source can be represented as: Q_gen=Q_rxn+Q_ohm+Q_pol+Q_side; Where Q_gen is the total heat generated by thermal runaway, Q_rxn is the heat of chemical reaction, Q_ohm is the ohmic heat, Q_pol is the polarization heat, and Q_side is the heat of side reaction. In the early stages of thermal runaway, heat mainly accumulates rapidly in localized areas, and its heat transfer control equation can be expressed as: ; This equation is the classical heat conduction governing equation, also known as the unsteady-state heat conduction equation, where ρ is the material density. Let T be the specific heat capacity, t be the temperature field, t be the time field, and k be the thermal conductivity. Represents the gradient operator. Let be the spatial curvature of the temperature field. This equation describes the rate of change of heat stored per unit volume of material, which is equal to the sum of the thermal conductivity and diffusion capacity and the input from the internal heat source.

[0057] (2) Thermal expansion mismatch generates interfacial thermomechanical stress Power battery packs typically contain multiple materials, including an aluminum alloy casing, adhesive layer, foam buffer layer, graphite thermal conductive layer, mica thermal insulation layer, and aerogel layer. These different materials have different coefficients of thermal expansion: α1≠α2≠α3. When the temperature changes by ΔT=T-T0, the theoretical free expansion strain of each material is: ; Where ε_th is the thermal expansion strain, α is the thermal expansion coefficient of different materials, and ΔT is the temperature rise. Because different materials form a composite interface through bonding, compression, or mechanical constraints, the materials cannot deform freely, thus resulting in a thermal mismatch strain Δε: Δε=(α1-α2)·ΔT; This further generates interfacial thermomechanical stress: σ_th=[E / (1-ν)]·(α1-α2)·ΔT; Where σ_th is the interfacial thermal stress, E is the material's elastic modulus, and ν is Poisson's ratio, typically ranging from 0.3 to 0.4. If α1 is taken as the aluminum shell material, then the coefficient of thermal expansion ranges from 23 × 10⁻⁶. -6 / K, α2 is the protective layer material, and its coefficient of thermal expansion ranges from 1×10. -6 / K~7×10 -6 / K, ΔT is the temperature rise. As α1-α2 increases, the interfacial stress increases rapidly. Taking aluminum shell and mica as an example, for aluminum shell, α_Al = 23 × 10⁻⁶. -6 / K, mica α_m≈7×10 -6 / K, when the temperature rise ΔT = 200K, we have: Δε=(23-7)×10 -6 ×200=3.2×10 -3 ; Therefore, the failure of the protective structure during thermal runaway is not solely caused by high temperature, but rather by the following complete physical chain: thermal runaway → temperature rise → thermal expansion mismatch → interfacial thermal stress σ_th → stress concentration → interfacial damage → protective failure. In this physical chain, σ_th is the core driving variable, and its magnitude determines the extent of subsequent structural damage.

[0058] (3) Directional equivalent compressive stiffness distribution Traditional cushioning structures (foam, sponge, elastic adhesive layer) only provide passive deformation absorption with F=k·x, resulting in relatively uniform stiffness in all directions, random stress release direction, and inability to actively migrate high-stress areas. This approach is essentially scalar cushioning, only changing the stress amplitude without controlling the stress direction. In contrast, this embodiment constructs a directional equivalent compressive stiffness distribution through the density gradient, aperture gradient, and connectivity area gradient of the stress release cavity. The local equivalent stiffness K of the structure... eff (x) can be represented as: K eff (x) = E(x)·A(x) / L; Where E(x) is the gradient elastic modulus, A(x) is the effective load-bearing area, and L is the structural thickness. Along the direction of thermal runaway heat flow (x-direction), the stiffness distribution satisfies: K(x) = K0 + K·x; K(x) represents the equivalent compressive stiffness of the thermal stress relief structure layer at any position x along the direction of thermal runaway heat flow (x direction). K represents the rate of change of the equivalent stiffness K along the heat flow direction x, also known as the equivalent stiffness gradient. That is, along the heat flow direction, K1>K2>K3; corresponding to the high-constraint region, transition region, and low-stiffness release region, thus forming high-rigidity region, transition region, and low-rigidity region. Furthermore, the protective structure has a non-uniform stiffness field along the spatial direction, unlike ordinary isotropic buffer structures. More specifically, the distribution of K(x) can be expressed as: K(x)=K0·(1-β·x / L), 0<β<1; Where K0 is the initial stiffness near the heat source region, β is the stiffness gradient coefficient, and L is the thickness of the release layer along the heat flow direction. This distribution satisfies dK / dx < 0, meaning the stiffness monotonically decreases along the heat flow direction. This design allows thermomechanical stress to migrate from the high-constraint region to the low-constraint region, achieving directional release. This structure differs from ordinary buffer structures; its essence is vectorized stress management, which not only reduces the stress amplitude but, more importantly, controls the direction of stress release. Traditional scalar buffers transform random failure modes into designable, predictable, and controllable stress migration modes.

[0059] (4) Passive thermal path reconfiguration mechanism Traditional thermal insulation reduces heat flux Q = -kA·ΔT / L by lowering the thermal conductivity k, where A is the heat transfer cross-sectional area perpendicular to the heat flux direction. Its thermal path structure is fixed, maintaining the path of cell → thermally conductive layer → shell → environment regardless of normal operation or thermal runaway. Therefore, it cannot simultaneously address both normal heat dissipation and abnormal thermal insulation. In this embodiment, the thermal conductivity of the material is not changed; instead, the connection relationship of the heat transfer network is altered. Specifically, this can be understood as defining the thermal path state G(t): G(t) = 1 (continuous thermal conduction state), T <T1; G(t)=0 (discontinuous heat insulation state), T>T2; Herein, T1 is the temperature at which stress release is completed, T2 is the trigger temperature for thermal path reconstruction, and T1 is less than T2. Under normal conditions, the thermal resistance network is in series, the total thermal resistance Q is the sum of the thermal resistances R1-R3 of each layer, and the heat transfer equation is: Q=ΔT / (R1+R2+R3); Under thermal runaway conditions, the movable isolation member acts to cause a step change in the interfacial thermal resistance, where the interfacial thermal resistance R_interface→∞, so the heat flow Q_new≈0. At this time, the heat flow path is cut off by changing the connection relationship of the thermal resistance network. When the temperature is lower than the threshold, that is, T<Tc, the thermally responsive element maintains the initial state (continuous path of the heat conduction layer); when T≥Tc, the thermally responsive material undergoes volume expansion, shape change or phase change displacement, and the axial expansion is converted into a lateral displacement x2=x1·tanθ through a wedge mechanism, pushing the movable isolation member into the thermal path, and finally forming a state where the heat conduction layer is disconnected to form a heat insulation gap, realizing active reconstruction of the thermal path.

[0060] (5) Time sequence control principle of thermo-mechanical sequential response In this embodiment, a thermo-mechanical state variable M(t) and a heat transfer state variable C(t) are defined, where M(t)=0 (normal state), M(t)=1 (stress release completed), C(t)=1 (heat conduction path continuous), and C(t)=0 (heat conduction path disconnected). The two satisfy a time sequence coupling relationship: C(t)=f(M(t)), that is, the time sequence constraint condition t_s<t_r, where t_s is the completion time of thermo-mechanical stress release, and t_r is the trigger time of thermal path reconstruction.

[0061] Stage 1: Thermal runaway starts → thermal stress is generated → thermo-mechanical stress gradient migration network is activated → interfacial thermal stress is released (M: 0→1).

[0062] Stage 2: The temperature reaches the threshold → the thermally responsive element acts → the thermal path is reconstructed → heat propagation is blocked (C: 1→0).

[0063] It should be noted that the two form a sequential trigger mechanism that releases stress first to maintain structural integrity, and then reconstructs the thermal path to block heat propagation, that is, there is a functional dependency relationship between the two structures. Without the thermal stress release structural layer, interface cracking, interlayer separation, mechanism jamming, and thermal path reconstruction failure will occur. Therefore, the thermal stress release layer is a precondition guarantee structure for the reliable operation of the thermal path reconstruction mechanism.

[0064] Exemplarily, this embodiment further provides a manufacturing method for the above power battery thermal runaway protection structure, such as Figure 2 shown, including the following steps: S1: Perform surface activation treatment on the inner wall of the battery pack housing; S2: A fixed connection layer is formed on the inner wall of the shell; S3: A thermal stress relief structure layer with a stress relief cavity array and stress migration channel is composited into a fixed connection layer. The stress relief cavities are arranged in a non-uniform gradient along the direction of thermal runaway heat flow. The spatial density, aperture or interconnection area of ​​the stress relief cavities vary gradient along the direction of heat flow. S4: Composite the thermal diffusion path layer onto the thermal stress relief structure layer; S5: A passive thermal path reconstruction layer is formed on the thermal diffusion path layer. The passive thermal path reconstruction layer is formed by coating or bonding thermal response driving material, setting wedge-shaped push blocks with a wedge angle of 15° to 45° and installing isolation moving parts. S6: Composite the high-temperature thermal blocking layer onto the passive thermal path reconstruction layer; S7: The insulating protective layer is laminated onto the high-temperature heat-blocking layer; S8: Perform hot-press curing treatment on the composite structure; S9: A thermal diffusion path layer disconnection region and stress relief groove are formed at the boundary of adjacent thermal safety units.

[0065] It should be noted that the positions of the passive thermal path reconstruction layer and the high-temperature thermal blocking layer can be interchanged depending on the actual application scenario. In combination with any of the above embodiments, the technical solution proposed in this application has at least the following technical effects: This application addresses the interfacial thermomechanical stress failure problem caused by material thermal expansion mismatch in the protective structure during thermal runaway transients, rather than the heat conduction itself or the cyclic expansion stress of the battery cell, as addressed in traditional solutions. Unlike methods that achieve stress homogenization through material composites or passive insulation by increasing cell spacing, this embodiment constructs a directional equivalent compressive stiffness distribution induced by thermal runaway. This is achieved by setting a stress relief cavity density gradient, continuously connected stress migration channels, and a low-stiffness release region within the thermal stress relief structure layer, ensuring that the equivalent stiffness gradient is not zero and that there exists a gradual path of stiffness from high to low. K eff The design, with a value not equal to 0, allows for the controllable migration and concentrated release of interfacial thermal stress from the high-constraint region to the low-constraint region along the direction defined by the equivalent compressive stiffness distribution. This prevents stress from randomly concentrating at weak points in the interface, which could lead to delamination, cracking, or structural failure of the protective layer. This achieves vectorized management of the thermomechanical stress within the protective structure itself. Simultaneously, through the use of thermal response driving elements, wedge-shaped pushers with wedge angles of 15°–45°, and isolation moving parts in the passive thermal path reconfiguration layer, the heat transfer path switches from a continuous heat conduction state to a discontinuous insulation state during thermal runaway. This allows for autonomous thermal path reconfiguration based on temperature conditions without external energy input or electrical control signals, balancing the high-efficiency heat dissipation requirements under normal operating conditions with the insulation and blocking requirements under thermal runaway conditions.

[0066] Furthermore, this embodiment does not simply superimpose a traditional buffer structure with a traditional thermal insulation structure, but establishes a functional coupling relationship based on the evolutionary law that thermomechanical failure precedes heat propagation during thermal runaway. In the early stages of thermal runaway, the protective structure is first subjected to interfacial thermomechanical stress impact caused by thermal expansion mismatch; if the structural integrity cannot be maintained at this stage, the subsequent thermal path reconstruction structure will fail to execute reliably due to interfacial delamination, cracking, or mechanical jamming. Therefore, the gradient migration network of the thermal stress relief structure layer ensures the structural integrity prerequisite for the normal operation of the passive thermal path reconstruction layer; furthermore, by placing the passive thermal path reconstruction layer on the side of the thermal stress relief structure layer away from the heat source, and ensuring that the triggering temperature of the thermal response driving element is higher than the temperature at which the thermal stress relief structure layer completes the interfacial thermal stress release, the two stages are ensured to be triggered sequentially in time, first releasing stress to maintain structural integrity, and then reconstructing the thermal path to block heat propagation, thus satisfying the temporal constraints of a two-stage collaborative protection mechanism.

[0067] The technical solution of this embodiment is further illustrated below with reference to a comparative example. As a comparative example, the thermal stress relief structure layer 4 is replaced with a common foam buffer layer with a uniform pore structure, while the other structural parameters remain unchanged. In a uniform structure, each region has similar equivalent compressive stiffness, and the deformation capacity at different locations varies little. When thermal expansion mismatch occurs between the cell module and the battery pack casing due to temperature changes, the interfacial thermomechanical stress is difficult to redistribute through differentiated deformation in different regions. Therefore, high local stress concentration is likely to occur in highly constrained areas, which may further lead to interface delamination or structural deformation. When interface delamination or structural deformation occurs in the region associated with the isolating moving component, it may affect the operation of the isolating moving component. With the gradient structure of this embodiment, since different regions have different equivalent compressive stiffness, the compressive deformation caused by thermal expansion mismatch preferentially occurs in the region with lower equivalent compressive stiffness, thereby redistributing the interfacial thermomechanical stress within the structural constraint range, reducing the degree of local stress concentration in highly constrained areas, and reducing the impact of interface deformation on the operation of the isolating moving component.

[0068] also, Figure 3 A flowchart illustrating a method for manufacturing a power battery is also provided, with the numbers in the flowchart corresponding to each step of the method, as follows: ①: Battery pack housing pretreatment - Pretreatment of the inner wall of the battery pack housing.

[0069] ②: Formation of fixed connection layer - A fixed connection layer is formed on the inner wall of the shell.

[0070] ③: Thermal stress relief structure layer setting - The thermal stress relief structure layer with stress relief cavity array and stress migration channel is combined with the fixed connection layer.

[0071] ④: Gradient stress relief network formation—the stress relief cavities are arranged in a monotonically gradient along the direction of thermal runaway heat flow, forming an equivalent compressive stiffness gradient distribution.

[0072] ⑤: Setting up a heat diffusion path layer - Composite the heat diffusion path layer onto the heat stress relief structure layer.

[0073] ⑥: Formation of passive thermal path reconstruction layer - A passive thermal path reconstruction layer is formed on the thermal diffusion path layer.

[0074] ⑦: Assembly of thermal response drive mechanism — Assembly of thermal response drive components, wedge push blocks and isolation moving parts.

[0075] ⑧: Setting of high temperature heat blocking layer - The high temperature heat blocking layer is composited on the passive heat path reconstruction layer.

[0076] ⑨: Formation of insulating protective layer - The insulating protective layer is laminated onto the high-temperature heat-blocking layer.

[0077] ⑩: Multi-layer structure hot pressing curing - hot pressing curing treatment of composite structures.

[0078] The protective structure is integrated and assembled with the battery module.

[0079] Assembly complete.

[0080] Through the above description of the embodiments, those skilled in the art can clearly understand that this application can be implemented by means of software plus necessary general-purpose hardware platforms, or it can be implemented by hardware. By applying the solution of this embodiment, firstly, the spatial density and / or aperture size of multiple stress relief cavities in the thermal stress relief structure layer change in a gradient along the direction of thermal runaway heat flow, so that the elastic deformation region forms an equivalent compressive stiffness gradient distribution. Thus, when thermal runaway occurs, a stress migration path from the high stiffness region to the low stiffness region is established along the heat flow direction. This allows the interfacial thermomechanical stress caused by the difference in thermal expansion coefficients of each material layer to be controllably redistributed and concentratedly released to the low stiffness region through the stress redistribution channel connecting adjacent stress relief cavities along the gradient direction. This avoids the problem of delamination, cracking, or even structural failure caused by the random concentration of interfacial thermal stress at weak locations between layers. Meanwhile, by placing the passive thermal path reconstruction layer on the side of the thermal stress relief structure layer away from the battery cell module, the thermal response driving element generates thermal deformation in response to temperature changes. This deformation, driven by a displacement conversion mechanism, moves the isolation moving component to change the heat transfer path. This allows the protective structure to autonomously switch from a continuous heat conduction state to a discontinuous heat insulation state under thermal runaway conditions, without the need for external energy input or electronic control signals. This balances the high-efficiency heat dissipation requirements under normal operating conditions with the heat insulation and blocking requirements under thermal runaway conditions. Furthermore, the thermal transfer path, the structural parameters of the thermal stress relief structure layer, and the material parameters of the thermal response driving element are configured such that the time for the thermal stress relief structure layer to reach the preset interface thermomechanical stress redistribution state is earlier than the time for the thermal response driving element to generate thermal deformation that drives the isolation moving component. This ensures that, in terms of timing, the thermal stress relief structure layer first completes the controllable redistribution of interface thermomechanical stress to ensure structural integrity, and then the passive thermal path reconstruction layer performs thermal path switching to block heat propagation. A sequential triggering and functionally dependent collaborative protection mechanism is formed between the two functional modules, prioritizing structural protection and then blocking the thermal path.

[0081] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0082] In the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. 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. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0083] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A thermal runaway protection structure for a power battery, disposed between the battery pack casing and the cell module, characterized in that, include: A thermal stress relief structure layer is disposed between the battery pack housing and the cell module. The thermal stress relief structure layer includes an elastic deformation region. The elastic deformation region is provided with multiple stress relief cavities and stress redistribution channels connecting adjacent stress relief cavities. The spatial density and / or aperture size of the multiple stress relief cavities vary in a gradient along the direction of thermal runaway heat flow, so that the elastic deformation region forms an equivalent compressive stiffness distribution along the direction of thermal runaway heat flow. A passive thermal path reconfiguration layer is disposed on the side of the thermal stress relief structure layer away from the battery cell module. The passive thermal path reconfiguration layer includes a thermal response driving element, a displacement conversion mechanism, and an isolation moving component. The thermal response driving element generates thermal deformation in response to temperature changes and drives the isolation moving component to move through the displacement conversion mechanism to change the heat transfer path. Wherein, a heat transfer path is formed between the thermal response driving element and the thermal stress relief structure layer, the heat transfer path having a preset thermal resistance and / or thermal capacity, and the structural parameters of the thermal stress relief structure layer, the material parameters of the thermal response driving element, and the thermal resistance and / or thermal capacity of the heat transfer path are configured such that the time when the thermal stress relief structure layer reaches the preset interface thermomechanical stress redistribution state is earlier than the time when the thermal response driving element generates thermal deformation to drive the isolation moving part to move.

2. The power battery thermal runaway protection structure according to claim 1, characterized in that, The equivalent compressive stiffness of the thermal stress relief structure layer varies in a gradient along the direction of thermal runaway heat flow.

3. The power battery thermal runaway protection structure according to claim 2, characterized in that, The equivalent compressive stiffness of the thermal stress relief structure layer along the direction of thermal runaway heat flow exhibits a monotonically decreasing distribution.

4. The power battery thermal runaway protection structure according to claim 1, characterized in that, Also includes: A heat diffusion path layer is disposed between the heat stress relief structure layer and the passive heat path reconstruction layer; A high-temperature heat-blocking layer is disposed on the side of the passive heat path reconstruction layer away from the heat stress relief structure layer; An insulating protective layer is disposed on the side of the protective structure near the battery cell module for electrical insulation protection.

5. The power battery thermal runaway protection structure according to claim 1, characterized in that, A heat transfer path with a preset thermal resistance and / or thermal capacity is formed between the thermal response driving element and the thermal stress relief structure layer, so that the time when the thermal response driving element reaches the trigger state is later than the time when the thermal stress relief structure layer reaches the preset interface thermomechanical stress redistribution state.

6. The power battery thermal runaway protection structure according to claim 5, characterized in that, The temperature at which the thermal stress relief structure layer reaches the preset interface thermomechanical stress redistribution state is T1, and the temperature at which the thermal response driving element generates deformation sufficient to drive the isolating moving component to complete the thermal path switching is T2, and T1 <T2。 7. The power battery thermal runaway protection structure according to claim 1, characterized in that, The thermal response driving element is made of shape memory alloy, bimetallic composite material or thermal response metal material with a coefficient of thermal expansion greater than that of the adjacent layer material; the isolation moving part is a sliding structure, a rotating structure or a flipping structure, and adopts one or more of mica sheet, ceramic fiber sheet, high temperature resistant polyimide sheet or metal composite heat insulation sheet.

8. The power battery thermal runaway protection structure according to claim 1, characterized in that, The displacement conversion mechanism includes a wedge-shaped pusher block, which has a guide slope that is angled to the expansion direction of the thermal response driving element. The expansion displacement x1 generated by the thermal response driving element acts on the guide slope, causing the wedge-shaped pusher block to drive the isolation moving member to move perpendicular to the expansion direction. The wedge-shaped pusher block has a preset wedge angle θ, and the moving displacement x2 of the isolation moving member and the expansion displacement x1 of the thermal response driving element satisfy a displacement conversion relationship determined by the wedge angle θ.

9. The power battery thermal runaway protection structure according to claim 1, characterized in that, The power battery thermal runaway protection structure also includes: The protective structure is divided into multiple thermal safety units, and a heat propagation blocking region is set between adjacent thermal safety units. The heat propagation blocking region includes a heat diffusion path layer disconnection region and / or a stress relief groove.

10. A power battery, characterized in that, It includes a battery pack housing, a cell module disposed within the battery pack housing, and a power battery thermal runaway protection structure as described in any one of claims 1 to 9.

11. A method for manufacturing a thermal runaway protection structure for a power battery, characterized in that, The power battery thermal runaway protection structure is described in any one of claims 1 to 9, and the manufacturing method of the power battery thermal runaway protection structure includes: S1: Surface activation treatment is performed on the inner wall of the battery pack casing; S2: A fixed connection layer is formed on the inner wall of the shell; S3: A thermal stress relief structure layer with a stress relief cavity array and stress migration channel is composited into a fixed connection layer. The stress relief cavities are arranged in a non-uniform gradient along the direction of thermal runaway heat flow. The spatial density, aperture or interconnection area of ​​the stress relief cavities vary gradient along the direction of heat flow. S4: Composite the thermal diffusion path layer onto the thermal stress relief structure layer; S5: A passive thermal path reconstruction layer is formed on the thermal diffusion path layer. The passive thermal path reconstruction layer is formed by coating or bonding thermal response driving material, setting wedge-shaped push blocks with a wedge angle of 15° to 45° and installing isolation moving parts. S6: Composite the high-temperature thermal blocking layer onto the passive thermal path reconstruction layer; S7: The insulating protective layer is laminated onto the high-temperature heat-blocking layer; S8: Perform hot-press curing treatment on the composite structure; S9: A thermal diffusion path layer disconnection region and stress relief groove are formed at the boundary of adjacent thermal safety units.

Images