Stress-adaptive lithium battery expansion adhesive tape and preparation method thereof

Abstract

This invention provides a stress-adaptive lithium battery expansion tape and its preparation method, comprising an elastic substrate layer and a first adhesive layer disposed on at least one side thereof. The elastic substrate layer is a multilayer co-extruded structure, comprising a first elastic surface layer, an intermediate rigid layer, and a second elastic surface layer. The 100% modulus of both the first and second elastic surface layers is 1-10 MPa, and the modulus of the intermediate rigid layer is 2-10 times that of the first elastic surface layer. The first adhesive layer comprises a polymer matrix, stress-responsive microspheres, and a thermally conductive filler, wherein the polymer matrix content is 60-90 parts, the stress-responsive microsphere content is 1-20 parts, and the thermally conductive filler content is 5-30 parts. The crosslinking density of the first adhesive layer is 1×10⁻⁶. ‑5 ~1×10 ‑4 mol / cm³; the stress-responsive microspheres are thermally expandable microspheres with an average particle size of 1~50μm, which expand to 1.2~2.0 times their initial particle size after expansion treatment.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, and in particular to a stress-adaptive lithium battery expansion tape and its preparation method. Background Technology

[0002] During the charging and discharging process of lithium batteries, especially when using high-capacity negative electrode materials (such as silicon-based negative electrodes and high-nickel positive electrodes), the electrode active materials undergo significant volume changes, leading to periodic expansion and contraction of the cell. This continuous mechanical stress can damage the internal structural integrity of the cell, causing problems such as active material peeling, current collector wrinkling, and interface contact failure, severely limiting the battery's cycle life and safety performance. Therefore, adhesive tape is typically applied to critical areas such as the electrode sheets, cell sides, or tabs to provide fixation, insulation, and cushioning.

[0003] Currently, the design logic and optimization goals of mainstream lithium battery tapes (such as tapes based on polyethylene terephthalate (PET) or polyimide (PI)) and their mainstream manufacturing processes (such as solvent coating and high-temperature curing) are generally focused on "static strong fixation." That is, by using high-modulus substrates and high-cohesive-strength adhesives, the tape aims for high initial bond strength, high temperature resistance, and high insulation under static or short-term testing. While this design is reliable under normal conditions, its inherent high rigidity becomes a drawback when dealing with the aforementioned dynamic cyclic conditions: the tape cannot expand and contract synchronously with the reciprocating deformation of the electrodes, causing stress to continuously accumulate at the bonding interface. This easily leads to adhesive layer debonding, substrate creep, or fatigue fracture, ultimately resulting in accelerated battery performance degradation.

[0004] To alleviate the swelling pressure of lithium batteries, existing technologies have developed tapes with certain elasticity or expansion properties.

[0005] However, these improved expansion tapes have not fundamentally solved the above problems, and their technical solutions still have the following limitations: 1. Existing expansion tapes have a high substrate modulus and low elongation at break, making them unable to expand and contract synchronously with the reciprocating deformation of the electrodes, resulting in high stress concentration at the bonding interface. When the local stress exceeds the adhesive strength, it causes the tape to detach; when the stress exceeds the mechanical strength of the electrode itself, it leads to wrinkling or even breakage of the electrode.

[0006] 2. Existing expandable tapes and their manufacturing processes do not design effective energy dissipation pathways at the material microstructure level. Whether it is the stretchable deformable part or the elastic TPU layer, its mechanical response is still close to linear elasticity or elastoplasticity. In repeated compression-springback cycles, stress cannot be effectively dissipated through active deformation within the material. Mechanical energy stress continues to act on the interface, accelerating the creep, aging, or cohesive failure of the adhesive layer, resulting in very poor fatigue life.

[0007] 3. Existing expansion tapes have limited functionality. On the one hand, existing processes typically create a dense adhesive layer structure to achieve high bonding strength. This dense adhesive layer structure blocks the transport of lithium ions in the thickness direction of the electrode. For thick electrodes or high-rate batteries, this can easily lead to increased local concentration polarization, affecting capacity performance. On the other hand, the tape itself has limited heat dissipation performance and cannot effectively conduct the heat generated during cell operation, which is not conducive to battery thermal management. Summary of the Invention

[0008] The purpose of this invention is to solve the above-mentioned problems by proposing a stress-adaptive lithium battery expansion tape and its preparation method.

[0009] To achieve the above objectives, the following technical solution was adopted: A stress-adaptive lithium battery expansion tape includes an elastic substrate layer and a first adhesive layer disposed on at least one side of the elastic substrate layer; The elastic substrate layer is a multi-layer co-extruded structure, including a first elastic surface layer, an intermediate rigid layer, and a second elastic surface layer. The 100% modulus of both the first and second elastic surface layers is 1-10 MPa. The modulus of the intermediate rigid layer is 2-10 times that of the first elastic surface layer. The first and second elastic surface layers are designed with a symmetrical structure, using the same material, having the same 100% modulus, and the same thickness to ensure the symmetrical deformation of the substrate under bidirectional stress and prevent warping. This modulus gradient structure allows stress to be gradient-transmitted from the surface layer to the intermediate layer when subjected to expansion stress: the low-modulus elastic surface layer undergoes reversible deformation first, absorbing some strain energy; as the strain increases, the stress is gradually transferred to the high-modulus intermediate rigid layer, which then bears the main load-bearing role. Through this gradient stress transmission mechanism, the elastic substrate layer achieves stress response across the entire strain range, avoiding interface stress concentration due to excessive overall stiffness and preventing loss of structural support capacity under large strain conditions due to excessively low overall modulus, thus providing a stable mechanical foundation for the tape.

[0010] If the modulus of the first elastic surface layer is below 1 MPa, the elastic substrate layer will be too soft and difficult to maintain dimensional stability during the hot pressing process of the battery cell; while if it is above 10 MPa, the rigidity of the elastic substrate will be too high, and it will not be able to adapt to the deformation of the electrode under small strain, resulting in stress concentration at the interface. Therefore, it is necessary to control the modulus of the first elastic surface layer within a critical range that can simultaneously meet the requirements of processability and functionality.

[0011] Preferably, the first and second elastic surface layers are made of thermoplastic polyurethane or polyolefin elastomer, respectively; the intermediate rigid layer is made of polyethylene terephthalate or polyamide; and the overall thickness of the elastic substrate layer is 15-50 μm. Thermoplastic polyurethane and polyolefin elastomers both possess excellent elastic recovery properties, enabling rapid response under small strain conditions; while polyethylene terephthalate and polyamide have high modulus and strength, providing rigid support under large strain conditions.

[0012] The first adhesive layer comprises a polymer matrix and stress-responsive microspheres and thermally conductive fillers dispersed therein; by mass parts, the content of the polymer matrix is ​​60-90 parts, the content of the stress-responsive microspheres is 1-20 parts, the content of the thermally conductive filler is 5-30 parts, and the total mass parts of the polymer matrix, stress-responsive microspheres and thermally conductive filler are 100 parts.

[0013] The crosslinking density of the first adhesive layer is 1×10 -5 ~1×10 -4 mol / cm³. This crosslinking density range is the optimal range for the first adhesive layer to achieve a balance between stress dissipation and adhesive performance. If the crosslinking density is lower than the lower limit of this range, the cohesive strength of the first adhesive layer is insufficient. Under the shear and tensile stress of the dynamic cyclic expansion of the battery cell, the cohesive failure of the adhesive layer is likely to occur, leading to tape debonding failure. If the crosslinking density is higher than the upper limit of this range, the polymer crosslinking network of the first adhesive layer will be too dense, and the sliding ability of its molecular chains will be greatly reduced. As a result, the adhesive layer cannot dissipate the interfacial stress through the movement of molecular chains, and the adhesive layer is prone to brittle characteristics. During the repeated expansion and contraction of the battery cell, cracks are likely to occur, eventually losing its adhesive and protective functions.

[0014] By precisely controlling the crosslinking density of the first adhesive layer within the aforementioned range, a low-crosslinking, high-elasticity polymer crosslinking network is formed. This network possesses both moderate molecular chain slippage capability, effectively dissipating interfacial stress generated by cell expansion under dynamic cyclic conditions through molecular chain movement, and maintaining good cohesive strength and adhesion performance. This ensures that the tape maintains stable adhesion throughout the repeated expansion and contraction of the cell's entire lifespan, preventing failures such as debonding or cracking. Simultaneously, it provides a stable supporting matrix for the stress-responsive microspheres, ensuring their effective stress buffering function. At this crosslinking density, the polymer molecular chains still possess sufficient mobility to dissipate stress, while the crosslinking network provides sufficient cohesive strength to resist shear peeling. Furthermore, the dispersed thermally conductive fillers and microspheres, acting as rigid and semi-rigid particles, serve as physical crosslinking points in the adhesive layer, further enhancing its creep resistance. The crosslinking density range controlled by this invention allows the initial 180° peel force of the first adhesive layer to reach 0.6~1.0 N / mm, and the cohesive strength ≥0.8 MPa. Preferably, a primer layer is further disposed between the first adhesive layer and the elastic substrate layer. The primer layer is made of chlorinated polypropylene or polyurethane primer liquid, and the dry film thickness is 0.5-2 μm. The primer layer serves as an interface transition layer between the elastic substrate layer and the first adhesive layer, further enhancing the interfacial bonding strength between the elastic substrate layer and the first adhesive layer, preventing interfacial debonding during dynamic cycling, ensuring the overall structural stability of the tape, and further improving the adhesive stability of the tape during long-term service.

[0015] Preferably, a porous intermediate layer may be added between the elastic substrate layer and the first adhesive layer, or between the base layer and the first adhesive layer. The porous intermediate layer is prepared using polyolefin nonwoven fabric or electrospun fiber membrane, with a porosity of 30-80%. This porous intermediate layer can provide additional lithium-ion transport channels, thereby reducing concentration polarization within the battery cell and improving the ion transport efficiency of the lithium battery. Simultaneously, it enables the tape to have crack-blocking capabilities, mitigating crack propagation at the interface between the first adhesive layer and the elastic substrate layer, further improving the ion transport performance and structural durability of the tape.

[0016] Preferably, the polymer matrix is ​​formed by cross-linking and curing of acrylate prepolymer, reactive diluent and photoinitiator; wherein the acrylate prepolymer accounts for 60-80% of its total amount, the reactive diluent accounts for 10-30% of its total amount, and the photoinitiator accounts for 1-5% of its total amount; by compounding the acrylate prepolymer and the reactive diluent, combined with the controllable curing of the photoinitiator, a polymer network with moderate molecular chain slippage capability is constructed, providing a structural basis for stress dissipation of the first adhesive layer.

[0017] The stress-responsive microspheres are thermally expandable microspheres with an initial average particle size of 1~50μm, which expand to 1.2~2.0 times their initial particle size after expansion treatment.

[0018] Preferably, the outer shell of the stress-responsive microsphere is made of acrylonitrile copolymer with a glass transition temperature ≥100℃, and the core of the stress-responsive microsphere is a low-boiling-point hydrocarbon. The thickness of the outer shell of the stress-responsive microsphere accounts for ≥15% of the microsphere diameter, providing structural support for the stress-responsive microsphere to achieve a moderate thermal expansion of 1.2 to 2.0 times, avoiding the problem of shell rupture during cyclic compression, thereby ensuring the reversible compression-rebound performance of the stress-responsive microsphere and enabling it to continuously play a stress buffering role.

[0019] In the technical solution of this invention, the stress adaptive mechanism of the stress-responsive microsphere is achieved through the following two independent stages: The first stage involves heat treatment at 80-120℃ to soften the outer shell of the stress-responsive microspheres, vaporize the low-boiling-point hydrocarbons in the core, and drive the stress-responsive microspheres to expand in volume to 1.2-2.0 times their initial particle size, forming a hollow cavity structure. This process is completed at the tape production end, and the finished tape already possesses complete stress buffering capacity upon leaving the factory, requiring no additional activation treatment.

[0020] The second stage: The expanded microsphere shell has a glass transition temperature of ≥100℃ and maintains glassy rigidity throughout the entire life cycle operating temperature range of the lithium battery (-40~80℃). When the lithium battery cell expands and generates compressive stress, the stress-responsive microsphere shell undergoes elastic buckling, and the cavity volume shrinks. The shell of the stress-responsive microsphere absorbs energy through deformation. When the stress is relieved, the elastic restoring force of the shell drives the cavity to return to its original shape.

[0021] Preferably, the stress-responsive microspheres need to be pretreated with a silane coupling agent before being added to the polymer matrix. Specifically, the stress-responsive microspheres and the silane coupling agent are mixed at a mass ratio of 100:(0.5~2.0) and stirred at a temperature of 50~80℃ for 30~60 minutes to form an oleophilic coating layer on the surface of the stress-responsive microspheres.

[0022] Pre-treating the surface of the stress-responsive microspheres with a silane coupling agent can construct an oleophilic coating layer on the surface of the stress-responsive microspheres, effectively improving the interfacial compatibility between the stress-responsive microspheres and the polymer matrix, reducing the aggregation of the stress-responsive microspheres in the first adhesive layer, ensuring the uniform dispersion of the stress-responsive functional units in the adhesive layer, thereby achieving uniform dissipation of the interfacial stress generated by cell expansion in the adhesive layer, and simultaneously improving the interfacial bonding strength between the stress-responsive microspheres and the polymer matrix, preventing the stress-responsive microspheres from debonding from the matrix under dynamic cyclic stress.

[0023] Preferably, the thermally conductive filler is at least one of alumina, boron nitride, and aluminum nitride, with a particle size of 0.1~10μm. The thermally conductive filler is surface-modified with a silane coupling agent, which is one or both of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and its addition amount is 0.5%~2% of the mass of the thermally conductive filler. The thermally conductive filler can be compounded using different particle size distributions. By gradient matching of coarse and fine particle size fillers, the filler packing density is optimized, constructing a continuous thermally conductive network in the first adhesive layer, thereby achieving a synergistic improvement in the thermal conductivity and mechanical properties of the adhesive layer.

[0024] Surface modification of the thermally conductive filler by silane coupling agent can enhance the interfacial bonding force between the thermally conductive filler and the polymer matrix, avoid the decline in the mechanical properties of the tape caused by uneven dispersion of the thermally conductive filler in the first adhesive layer, and at the same time, the modified thermally conductive filler further improves the continuity of the thermally conductive network and effectively improves the thermal conductivity of the adhesive layer.

[0025] In addition, the present invention also provides a method for preparing stress-adaptive lithium battery expansion tape, specifically including the following steps: S1: The first elastic resin, the rigid resin, and the second elastic resin are respectively put into a three-layer co-extrusion casting equipment, and the melting temperature is controlled at 180~240℃. The three-layer structure of the first elastic surface layer, the intermediate rigid layer and the second elastic surface layer is formed by co-extrusion through the die head. After being shaped by the cooling roller, an elastic substrate layer with a thickness of 15~50μm is obtained. Preferably, the first and second elastomer resins are made of at least one of thermoplastic polyurethane or polyolefin elastomers; the rigid resin is polyethylene terephthalate or polyamide, and the melting temperature is controlled between 180 and 240°C. If the melting temperature is too low, the resin cannot melt sufficiently, resulting in poor interlayer bonding and uneven substrate surface during co-extrusion molding. If the temperature is too high, the resin is prone to thermal degradation, leading to a decrease in the mechanical properties of the substrate. The three-layer co-extrusion casting process achieves integrated molding of resins with different moduli, avoiding interface defects caused by multi-layer lamination processes, ensuring the continuity of the modulus gradient of the elastic substrate layer and the integrity of its structure, while also guaranteeing that the mechanical properties of the substrate meet the standards.

[0026] Preferably, after obtaining the elastic substrate layer, it needs to be subjected to corona treatment with a treatment power of 2000~4000W and a treatment speed of 20~60m / min, so that the surface tension of the elastic substrate layer is ≥50dyn / cm. Corona treatment of the elastic substrate layer can generate polar groups on the substrate surface, effectively improving the wettability and surface energy of the elastic substrate layer surface, enhancing the chemical bonding ability between the elastic substrate layer and the subsequently applied adhesive layer or primer layer, thereby improving the interfacial bonding strength between the substrate and the adhesive layer, preventing interfacial debonding of the tape under dynamic cyclic stress, and optimizing the overall adhesive stability of the tape.

[0027] Preferably, if a primer layer is provided between the first adhesive layer and the elastic substrate layer, after the elastic substrate layer undergoes corona treatment and before the adhesive precursor composition is applied in step S3, a primer coating step is further included. Specifically, a chlorinated polypropylene or polyurethane primer is applied to the surface of the corona-treated elastic substrate layer using a microgravure coating or slit coating method, and after drying, a primer layer with a dry film thickness of 0.5~2.0 μm is obtained. Using a microgravure coating or slit coating method to prepare the primer layer ensures the uniformity of the primer coating application, precisely controls the dry film thickness of the primer layer to be within the optimal range, and allows the primer layer to fully exert its role in interface transition and adhesion enhancement, thereby ensuring the consistency of the interfacial bonding strength between the elastic substrate layer and the first adhesive layer, and avoiding the problem of insufficient local interfacial bonding force caused by uneven primer coating.

[0028] S2: A polymer matrix, a thermally conductive filler modified with a silane coupling agent, and stress-responsive microspheres are dispersed and mixed to prepare an adhesive precursor composition; The adhesive precursor composition is the first adhesive layer; Preferably, the polymer matrix is ​​composed of an acrylate prepolymer, an reactive diluent, and a photoinitiator mixed in a specific ratio. The dispersion and mixing are performed in steps, specifically: the polymer matrix and the thermally conductive filler modified with a silane coupling agent are dispersed at 2000-3000 rpm for 15-25 min; stress-responsive microspheres are added to the dispersed mixture and dispersed at 500-1000 rpm for 5-15 min. This dispersion process, which first disperses the thermally conductive filler at high speed and then disperses the stress-responsive microspheres at low speed, ensures that the thermally conductive filler is fully and evenly dispersed in the polymer matrix while avoiding damage to the outer shell of the stress-responsive microspheres caused by the high shear force of high-speed stirring. This maintains the structural integrity of the stress-responsive microspheres and ensures that both the thermally conductive filler and the stress-responsive microspheres are uniformly distributed in the adhesive layer, guaranteeing that the thermal conductivity and stress buffering performance of the adhesive layer remain stable throughout the entire region.

[0029] S3: The adhesive precursor composition obtained in step S2 is coated onto the elastic substrate layer obtained in step S1, and cured under ultraviolet light irradiation under nitrogen protection. The ultraviolet light energy is 200~1000mJ / cm². During the curing process, the adhesive layer temperature is controlled to ≤50℃ by air cooling, so that the crosslinking density of the adhesive layer is 1×10⁻⁶. -5 ~1×10 -4 mol / cm³, to obtain a preliminary gel layer; The preferred coating method for the adhesive precursor composition is microgravure coating, with a coating speed of 10-100 m / min and a wet film thickness of 10-30 μm. Using microgravure coating to coat the adhesive precursor composition achieves high-precision and uniform coating of the first adhesive layer, accurately controls the coating thickness, ensures the consistency of the first adhesive layer thickness, and avoids uneven stress distribution caused by uneven adhesive layer thickness. Simultaneously, microgravure coating is suitable for the needs of continuous industrial production, enabling efficient production while ensuring coating quality. Ultraviolet curing is carried out under a nitrogen protective atmosphere, which prevents oxidative yellowing of the first adhesive layer during curing and avoids the inhibitory effect of oxygen on the photocuring reaction, ensuring that the crosslinking density of the first adhesive layer is precisely controlled at 1×10⁻⁶. -5 ~1×10 -4 Within the range of mol / cm³.

[0030] S4: The preliminary adhesive layer obtained in step S3 is heat-treated at 80~120℃ for 2~5 minutes to cause the stress-responsive microspheres in the preliminary adhesive layer to expand and form a hollow stress buffer structure, thus obtaining the tape. Because the outer shell of the stress-responsive microspheres is made of acrylonitrile copolymer material with a glass transition temperature ≥100℃, and the core is encapsulated with hydrocarbon vaporization generating internal pressure, driving the volume expansion of the stress-responsive microspheres. Through heat treatment, the temperature is controlled at 80~120℃ and the time at 2~5 minutes, precisely limiting the expansion ratio of the stress-responsive microspheres to 1.2~2.0 times the initial particle size. The purpose of this moderate expansion is twofold: firstly, by controlling the expansion ratio within the moderate range of 1.2~2.0 times, the stretching degree of the stress-responsive microsphere shell is low, and the shell thickness is preserved, ensuring sufficient structural strength during subsequent cyclic compression; secondly, the expanded stress-responsive microspheres form discretely distributed hollow cavities in the adhesive layer. These cavities act as stress buffer units, absorbing energy through the elastic buckling of the shell when subjected to external compressive force, and restoring the original shape due to the rebound force of the shell after decompression, thus achieving a reversible stress dissipation function.

[0031] Preferably, the heat treatment temperature and time parameters in step S4 are synergistically related to the crosslinking density design in step S3: step S3 controls the crosslinking density of the adhesive layer at 1×10-5 ~1×10 -4 The low crosslinking range of mol / cm³ allows the adhesive layer to maintain an appropriate high elasticity at heat treatment temperatures. This allows the microspheres to expand freely without excessive constraint, while also firmly anchoring the expanded microspheres within the adhesive network, preventing displacement or aggregation during subsequent use. If the crosslinking density is too high, the adhesive network becomes too rigid, limiting the normal expansion of the microspheres; if the crosslinking density is too low, the cohesive strength of the adhesive layer is insufficient, making it impossible to effectively fix the expanded microspheres.

[0032] S5: The tape obtained in step S4 is cooled, slit, and wound up to obtain stress-adaptive lithium battery expansion tape.

[0033] Cooling is achieved through air or natural cooling to lower the tape temperature to room temperature, causing the first adhesive layer to transition from a highly elastic state to a glassy state. This fixes the hollow microsphere structure formed in step S4, preventing irreversible deformation of the stress-responsive microspheres due to external forces during winding. Slitting is performed longitudinally or transversely according to the target product specifications, with slitting accuracy controlled within ±0.5mm to ensure neat, burr-free tape edges. Winding employs a constant tension winding method, with the winding tension controlled within the range of 5~15 N / m. This avoids excessive tension causing damage to the stress-responsive microsphere structure in the adhesive layer, or insufficient tension leading to loose tape winding and interlayer slippage.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention achieves gradient load bearing across the entire strain range by employing a three-layer co-extruded modulus gradient structure elastic substrate layer. Furthermore, it combines a hollow stress buffer structure formed by the controllable expansion of stress-responsive microspheres to construct a dual stress dissipation system of substrate gradient deformation and adhesive layer physical compression. This allows the tape to deform synchronously with the repeated expansion and contraction of the battery cell, and effectively dissipates interface stress through internal reversible deformation, avoiding stress concentration. This gives the tape excellent dynamic stress self-adaptive capability, avoiding the drawbacks of easy tape detachment and electrode wrinkling.

[0035] 2. This invention controls the crosslinking density of the first adhesive layer to form a low-crosslinking, high-elasticity polymer crosslinking network. The molecular chains can dissipate energy through sliding motion. At the same time, combined with the reversible compression-rebound properties of stress-responsive microspheres with a shell thickness of ≥15% of the microsphere diameter, a dual durability system of molecular chain sliding and microsphere physical buffering is constructed, which improves the dynamic fatigue life of the tape and enables the tape to withstand higher cyclic fatigue loads of the battery cell, avoiding premature failure of the tape under cyclic conditions.

[0036] 3. This invention adds a silane coupling agent-modified thermally conductive filler to the first adhesive layer, combined with a hollow buffer structure formed by the moderate expansion of stress-responsive microspheres. This achieves stress self-adaptation and allows the modified thermally conductive filler to construct a continuous thermally conductive network within the adhesive layer, enabling the tape to effectively manage heat and promptly dissipate the heat generated during battery cell operation. Furthermore, the hollow buffer structure formed by the stress-responsive microspheres provides a clear channel for lithium-ion transport, solving the problem of traditional dense adhesive layers hindering ion transport, reducing concentration polarization during cell cycling, and avoiding the risk of interface failure in multilayer composite structures.

[0037] 4. This invention improves the surface energy and wettability of the elastic substrate layer by corona treatment, enhances the chemical bonding ability between the elastic substrate layer and the adhesive layer, and further sets up an undercoat layer as an interface transition layer to optimize the stress transmission effect at the interface, avoid stress concentration to the bonding interface, enhance the interfacial bonding strength between the elastic substrate layer and the first adhesive layer, and prevent the tape from debonding during dynamic cycling. Detailed Implementation

[0038] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below.

[0039] In the following embodiments, the content of each component of the tape is by mass, and the sum of the mass parts of each component is 100 parts. The parameters in the tape preparation process are within preferred ranges; in actual production, they can be appropriately adjusted according to equipment conditions and product specifications.

[0040] In this embodiment, the specifications of the raw materials used are as follows: Resin for elastic substrate layer: The first and second elastomer resins are thermoplastic polyurethanes with a 100% modulus of 5 MPa. This modulus ensures that the elastic substrate layer can undergo reversible deformation under small strain conditions, thereby adapting to the expansion of the battery cell.

[0041] Rigid resin: Polyethylene terephthalate is used, with a modulus of 25 MPa, which is 5 times that of the first or second elastomer resin. This modulus ratio ensures that the intermediate rigid layer can bear the main stress under large strain conditions, thereby achieving gradient load-bearing capacity across the entire strain range.

[0042] Stress-responsive microspheres: These are thermally expandable microspheres with an acrylonitrile copolymer shell having a glass transition temperature ≥100℃ and an encapsulated core of isobutane, a low-boiling-point hydrocarbon. In their unexpanded state, the average particle size is 10μm, and the shell thickness accounts for 18% of the microsphere diameter. After expansion treatment, they can expand to 1.2~2.0 times their initial particle size, forming a hollow stress-buffered structure. Before use, the microspheres require surface pretreatment: the microspheres are mixed with the silane coupling agent γ-aminopropyltriethoxysilane at a mass ratio of 100:1 and stirred at 60℃ for 45 min to form an oleophilic coating layer on the surface of the stress-responsive microspheres.

[0043] Thermally conductive filler: Alumina is used with an average particle size of 5 μm. This particle size facilitates the formation of a continuous thermally conductive network within the adhesive layer without compromising its flexibility. Before use, the thermally conductive filler requires surface pretreatment: Alumina and the silane coupling agent γ-aminopropyltriethoxysilane are mixed at a mass ratio of 100:1 and treated in a high-speed disperser for 15 minutes to form a uniform modified layer on the surface, thereby enhancing the interfacial bonding between the filler and the polymer matrix.

[0044] Polymer matrix: Bisphenol A type epoxy acrylate, isobornyl acrylate, and a photoinitiator are used. The bisphenol A type epoxy acrylate has a number-average molecular weight of 5000 and a viscosity of 5000 mPa·s (25℃), serving as the main component of the crosslinking network. Irgacure 184, with an absorption wavelength of 365 nm, is used to initiate UV curing.

[0045] Primer material: Chlorinated polypropylene primer with a solid content of 10% and a dry film thickness of 1.0 μm. As an interfacial transition layer, the primer enhances the chemical bonding between the elastic substrate layer and the first adhesive layer.

[0046] Example 1

[0047] This embodiment proposes a stress-adaptive lithium battery expansion tape and its preparation method. The stress-adaptive lithium battery expansion tape has the following main components by mass parts: The elastic substrate layer adopts a three-layer co-extrusion structure. The first and second elastic surface layers are both thermoplastic polyurethane, and their 100% modulus is 5 MPa. The intermediate rigid layer is polyethylene terephthalate, with a modulus of 25 MPa, which is 5 times that of the first elastic surface layer. The overall thickness of the elastic substrate layer is 25 μm, of which the thickness of the first elastic surface layer is 5 μm, the thickness of the intermediate rigid layer is 15 μm, and the thickness of the second elastic surface layer is 5 μm.

[0048] A primer layer is provided between the first adhesive layer and the elastic substrate layer. The primer layer is made of chlorinated polypropylene and has a dry film thickness of 1.0 μm.

[0049] The first adhesive layer, applied over the base coat, comprises a polymer matrix, stress-responsive microspheres, and a thermally conductive filler. By weight, the polymer matrix comprises 80 parts, the stress-responsive microspheres 10 parts, and the thermally conductive filler 10 parts. The polymer matrix is ​​composed of bisphenol A epoxy acrylate, isobornyl acrylate, and a photoinitiator in a weight ratio of 70%, 25%, and 5%, respectively. The thermally conductive filler is alumina with an average particle size of 5 μm, surface-modified with γ-aminopropyltriethoxysilane at a modifier dosage of 1% of the filler's weight. The stress-responsive microspheres are thermally expandable microspheres with an acrylonitrile copolymer shell (glass transition temperature ≥100℃) and isobutane encapsulated in the core. The average particle size in the unexpanded state is 10 μm, and the shell thickness accounts for 18% of the microsphere diameter. Before use, they undergo surface pretreatment with γ-aminopropyltriethoxysilane. The pretreatment conditions are: microspheres and γ-aminopropyltriethoxysilane are mixed at a mass ratio of 100:1 and stirred at 60℃ for 45 min. The crosslinking density of the first adhesive layer is 0.5 × 10⁻⁶. -4 mol / cm³.

[0050] The specific preparation method of stress-adaptive lithium battery expansion tape is as follows: S1: The first part of thermoplastic polyurethane, polyethylene terephthalate, and the second part of thermoplastic polyurethane are respectively put into a three-layer co-extrusion casting equipment, and the melting temperature is controlled at 200℃, 220℃, and 200℃ respectively. The three-layer structure of the first elastic surface layer, the intermediate rigid layer, and the second elastic surface layer is formed by co-extrusion through the die head. After being shaped by the cooling roller, an elastic substrate layer with a thickness of 25μm is obtained.

[0051] After obtaining the elastic substrate layer, it is necessary to perform corona treatment on the elastic substrate layer. Specifically, the elastic substrate layer is controlled to pass through the corona treatment equipment at a linear speed of 40 m / min. The electrode gap of the corona treatment equipment is adjusted to 1.0-1.5 mm. Under the drive of a high-frequency power supply of 15-20 kHz, at least one surface of the elastic substrate layer is subjected to corona bombardment treatment with a processing power of 3000 W, so that its surface tension is increased to more than 52 dyn / cm.

[0052] S2: First, bisphenol A epoxy acrylate, isobornyl acrylate, and a photoinitiator are mixed in a mass percentage ratio of 70%, 25%, and 5% to obtain a polymer matrix. Then, 80 parts by mass of the polymer matrix and 10 parts by mass of alumina filler modified with γ-aminopropyltriethoxysilane are added to a mixer and dispersed at 2500 rpm for 20 min. Next, 10 parts by mass of surface-treated stress-responsive microspheres are added to the mixture and dispersed at 800 rpm for 10 min to obtain the adhesive precursor composition.

[0053] S3: Using a microgravure coating method, the adhesive precursor composition is coated onto the elastic substrate layer at a coating speed of 50 m / min, resulting in a wet film thickness of 20 μm. Immediately after coating, it is cured under nitrogen protection using a 365 nm wavelength LED-UV light source. The UV light intensity is set to 1000 mW / cm², the irradiation time is controlled at 2 s, and the total energy is 400 mJ / cm². During the curing process, the adhesive layer temperature is controlled to ≤50℃ by air cooling, ensuring that the crosslinking density of the adhesive layer reaches 0.5 × 10⁻⁶. -4 mol / cm³, to obtain a preliminary gel layer.

[0054] S4: The preliminary adhesive layer is placed in an oven and heat-treated at 100°C for 3 minutes to cause the stress-responsive microspheres in the preliminary adhesive layer to expand, forming a hollow stress-buffering structure, thus obtaining the tape.

[0055] S5: Allow the tape obtained in step S4 to cool naturally to room temperature, then wind and cut it under constant tension of 10 N / m to obtain the finished stress-adaptive lithium battery expansion tape.

[0056] Example 2

[0057] This embodiment is basically the same as Embodiment 1, except that the modulus parameters and thickness of the elastic substrate layer have been adjusted, as detailed below: In the elastic substrate layer, the 100% modulus of the thermoplastic polyurethane (TPU) in the first and second elastic surface layers is 2 MPa, the modulus of the polyethylene terephthalate (PET) in the intermediate rigid layer is 12 MPa, and the overall thickness of the elastic substrate layer is 15 μm. The composition of the first adhesive layer is exactly the same as in Example 1, that is, based on 100 parts by weight of the total mass of the first adhesive layer, it consists of 80 parts of polymer matrix, 10 parts of stress-responsive microspheres, and 10 parts of thermally conductive filler. The preparation method is the same as in Example 1.

[0058] The purpose of this embodiment is to verify the compliance performance of the low-modulus substrate with cell expansion.

[0059] Example 3

[0060] This embodiment is basically the same as Embodiment 1, except that the heat treatment expansion conditions of the stress-responsive microspheres have been adjusted, as detailed below: The composition of the first adhesive layer is exactly the same as in Example 1, namely, based on 100 parts by weight of the first adhesive layer, it consists of 80 parts of polymer matrix, 10 parts of stress-responsive microspheres, and 10 parts of thermally conductive filler. The heat treatment conditions in step S4 are changed to 85°C for 5 minutes, causing the stress-responsive microspheres to expand to 1.2 times their initial particle size. The other steps of the preparation method are the same as in Example 1.

[0061] The purpose of this embodiment is to verify the structural stability and stress buffering effect of the microspheres at a low expansion ratio.

[0062] Example 4

[0063] This embodiment is basically the same as Embodiment 1, except that the type of thermally conductive filler has been replaced, as detailed below: The first adhesive layer comprises, based on a total mass of 100 parts by weight, 80 parts of polymer matrix, 10 parts of stress-responsive microspheres, and 10 parts of thermally conductive filler. Boron nitride (BN) is used instead of alumina as the thermally conductive filler, with an average particle size of 8 μm, and it is also surface-modified with silane coupling agent KH550. The remaining components are the same as in Example 1. The preparation method is the same as in Example 1.

[0064] The purpose of this embodiment is to verify the applicability of different thermally conductive fillers in the technical solution of the present invention.

[0065] Example 5

[0066] This embodiment is basically the same as Embodiment 1, except that the crosslinking density of the first adhesive layer has been adjusted, as detailed below: The composition of the first adhesive layer is exactly the same as in Example 1, namely, based on 100 parts by weight of the first adhesive layer, it consists of 80 parts of polymer matrix, 10 parts of stress-responsive microspheres, and 10 parts of thermally conductive filler. In step S3, the UV curing light intensity is adjusted to 500 mW / cm², and the total energy is adjusted to 200 mJ / cm², so that the crosslinking density of the adhesive layer is controlled at 0.1 × 10⁻⁶. -4 mol / cm³. The other steps of the preparation method are the same as in Example 1.

[0067] The purpose of this embodiment is to verify the technical feasibility of the lower limit of crosslinking density.

[0068] Example 6

[0069] This embodiment is basically the same as Embodiment 1, except that the crosslinking density of the first adhesive layer has been adjusted, as detailed below: In step S3, the UV curing light intensity is adjusted to 2000 mW / cm², and the total energy is adjusted to 600 mJ / cm², so that the crosslinking density of the adhesive layer is controlled to 1.0 × 10⁻⁶. -4 mol / cm³. The remaining composition and preparation method are exactly the same as in Example 1.

[0070] The purpose of this embodiment is to verify the technical feasibility of the upper limit of crosslinking density.

[0071] Example 7

[0072] This embodiment is basically the same as Embodiment 1, except that the parameters of the elastic substrate layer have been adjusted, as follows: The thermoplastic polyurethane (TPU) of the first and second elastic surface layers has a 100% modulus of 1 MPa, the polyethylene terephthalate (PET) of the intermediate rigid layer has a modulus of 2 MPa, and the overall thickness of the elastic substrate layer is 25 μm. The composition and preparation method of the first adhesive layer are exactly the same as in Example 1.

[0073] The purpose of this embodiment is to verify the technical feasibility of the lower limit of the elastic surface modulus.

[0074] Example 8

[0075] This embodiment is basically the same as Embodiment 1, except that the parameters of the elastic substrate layer have been adjusted, as follows: The thermoplastic polyurethane (TPU) of the first and second elastic surface layers has a 100% modulus of 10 MPa, the polyethylene terephthalate (PET) of the intermediate rigid layer has a modulus of 100 MPa, and the overall thickness of the elastic substrate layer is 25 μm. The composition and preparation method of the first adhesive layer are exactly the same as in Example 1.

[0076] The purpose of this embodiment is to verify the technical feasibility of the upper limit of the elastic surface modulus.

[0077] Example 9

[0078] This embodiment is basically the same as Embodiment 1, except that the component ratio of the first adhesive layer has been adjusted, as follows: The composition consists of 70 parts polymer matrix, 20 parts stress-responsive microspheres, and 10 parts thermally conductive filler. The remaining components and preparation method are exactly the same as in Example 1.

[0079] The purpose of this embodiment is to verify the technical feasibility of the upper limit of microsphere content.

[0080] Example 10

[0081] This embodiment is basically the same as Embodiment 1, except that the component ratio of the first adhesive layer has been adjusted, as follows: The composition consists of 65 parts polymer matrix, 5 parts stress-responsive microspheres, and 30 parts thermally conductive filler. The remaining components and preparation method are exactly the same as in Example 1.

[0082] The purpose of this embodiment is to verify the technical feasibility of the upper limit of the thermally conductive filler content.

[0083] Comparative Example Comparative Example 1 This comparative example is basically the same as Example 1, except that stress-responsive microspheres are not added to the first adhesive layer, and the content of thermally conductive filler is adjusted to 20 parts by mass to maintain the total mass of the adhesive layer at 100 parts by mass. The remaining components (including the parameters of the elastic substrate layer, polymer matrix, etc.) are the same as in Example 1. The preparation method is the same as in Example 1.

[0084] Comparative Example 2 This comparative example is basically the same as Example 1, except that the elastic substrate layer uses a single-layer thermoplastic polyurethane (TPU) film with a thickness of 25 μm and a 100% modulus of 5 MPa, instead of a three-layer co-extruded structure. The remaining components (including the content of each component in the first adhesive layer) are the same as in Example 1. In the preparation method, the co-extrusion step is omitted, and a single-layer TPU film is cast instead; the remaining steps are the same as in Example 1.

[0085] Comparative Example 3 This comparative example is basically the same as Example 1, except that the heat treatment conditions in step S4 are changed to 130°C for 5 minutes, causing the stress-responsive microspheres to expand to 3.0 times or more of their initial particle size. The remaining composition is the same as in Example 1. Other steps in the preparation method are the same as in Example 1.

[0086] Comparative Example 4 This comparative example is basically the same as Example 1, except that in step S2, the polymer matrix, thermally conductive filler, and stress-responsive microspheres are added to the mixer all at once and dispersed at 2500 rpm for 30 minutes without further distribution mixing. The remaining components are the same as in Example 1. Other steps in the preparation method are the same as in Example 1.

[0087] Comparative Example 5 This comparative example is basically the same as Example 1, except that after step S1, the elastic substrate layer is not subjected to corona treatment, and the adhesive precursor is directly coated. The remaining composition is the same as in Example 1. Other steps of the preparation method are the same as in Example 1.

[0088] Comparative Example 6 This comparative example is basically the same as Example 1, except that the order of steps S3 and S4 is reversed; that is, heat treatment expansion (100°C, 3 minutes) is performed first, followed by UV curing. All other parameters are the same as in Example 1. The other steps of the preparation method are the same as in Example 1.

[0089] Comparative Example 7 This comparative example is basically the same as Example 1, except that the crosslinking density of the first adhesive layer was adjusted, specifically as follows: In step S3, the UV curing light intensity was adjusted to 200 mW / cm², and the total energy was adjusted to 100 mJ / cm², so that the crosslinking density of the adhesive layer was controlled to be 0.08 × 10⁻⁶. -4 mol / cm³. All other parameters are the same as in Example 1. The other steps of the preparation method are the same as in Example 1.

[0090] Comparative Example 8 This comparative example is basically the same as Example 1, except that the crosslinking density of the first adhesive layer was adjusted, specifically as follows: In step S3, the UV curing light intensity was adjusted to 2500 mW / cm², and the total energy was adjusted to 700 mJ / cm², so that the crosslinking density of the adhesive layer was controlled to 1.2 × 10⁻⁶. -4 mol / cm³. All other parameters are the same as in Example 1. The other steps of the preparation method are the same as in Example 1.

[0091] Comparative Example 9 Commercially available mainstream ordinary PET lithium battery tape was used, with a substrate of 25μm thick PET film and an adhesive of acrylic pressure-sensitive adhesive, as a reference sample for existing technology.

[0092] Comparative Example 10 Commercially available mainstream foam cushioning lithium battery tape was used, with a substrate of 25μm thick PE foam and an adhesive of acrylic pressure-sensitive adhesive, as a reference sample for existing technology.

[0093] Performance testing The tape samples obtained in Examples 1-10 and Comparative Examples 1-10 were subjected to performance tests, including: Dynamic peel force test: The tape is adhered to the surface of the aluminum foil and subjected to 100 cycles of cyclic stretching with a sine wave at a strain of 0%~50% and a frequency of 0.5Hz in an environment of 50℃. Then, the 180° peel force (for aluminum foil) is tested according to GB / T2792-2014 standard, and the peel force attenuation rate is calculated. The calculation formula is as follows: .

[0094] Dynamic fatigue life test: The dynamic shear fatigue test is adopted. The tape is attached between two aluminum plates and a sinusoidal cyclic load of 50% of the maximum strain and 1Hz frequency is applied. The number of cycles when the peel force decays to less than 50% of the initial value is recorded as the fatigue life.

[0095] Thermal conductivity test: The thermal diffusivity of the tape was measured using the laser flash method according to ASTM E1461 standard, and the thermal conductivity was calculated.

[0096] Ion transport performance test: The tape is placed between the positive and negative electrodes of the lithium battery and assembled into a button cell. The cell is cycled 500 times at 1C rate to test the capacity retention rate in order to evaluate the degree of obstruction of lithium-ion transport by the tape layer.

[0097] Interface bonding strength test: According to GB / T2790-1995 standard, the T-type peel method is used to test the peel strength of the tape before and after cyclic fatigue, and the interface debonding is observed.

[0098] Microsphere thermal stability test: The tape sample prepared in Example 1 was subjected to accelerated aging test at 120℃ for 100h and temperature cycling test at -40~80℃ for 1000 cycles. The morphological changes of the microspheres were observed using scanning electron microscopy (SEM), and the volume change rate of the microspheres was calculated.

[0099] Crosslinking density test: The crosslinking density of the first adhesive layer was determined using the equilibrium swelling method. The specific steps are as follows: 1. Peel off the first adhesive layer from the tape, weigh 0.2~0.5g of the sample, and record it as the initial mass m0.

[0100] 2. Immerse the sample in excess toluene solvent and allow it to swell at a constant temperature of 25°C for 48 hours until swelling equilibrium is reached.

[0101] 3. Take out the swollen sample, quickly absorb the surface solvent with filter paper, and weigh the swollen mass m1.

[0102] 4. Place the sample in a vacuum oven and dry it at 60°C until constant weight. Weigh the dry adhesive mass m2.

[0103] 5. Calculate the crosslinking density using the Flory-Rehner equation:

[0104] in, This represents the volume fraction of the polymer in the swollen network. ; This represents the polymer density (1.1~1.2 g / cm³ for acrylate polymers). The density of toluene is 0.867 g / cm³ at 25°C. The value represents the molar volume of the solvent (106.3 cm³ / mol for toluene). The parameters represent the polymer-solvent interaction (0.45–0.55 for the acrylate-toluene system). Each sample was tested three times, and the average value was taken.

[0105] The test results are shown in Table 1.

[0106] Table 1 Performance test results of Examples 1-10 and Comparative Examples 1-10 sample Initial peel force (N / mm) Peel force (N / mm) after cycling at 50℃ Cyclic decay rate (%) at 50℃ Fatigue life (times) Thermal conductivity (W / (m・K)) 500-cycle capacity retention (%) Interface debonding Example 1 0.81 0.63 22.2 >5000 0.85 92 none Example 2 0.75 0.58 22.7 4800 0.82 91 none Example 3 0.78 0.61 21.8 5200 0.80 90 none Example 4 0.79 0.55 30.4 4100 0.52 89 Slight edge detachment Example 5 0.68 0.52 23.5 >5000 0.83 91 none Example 6 0.72 0.52 27.5 4200 0.84 90 none Example 7 0.76 0.55 28.1 4000 0.83 90 none Example 8 0.83 0.61 26.8 4500 0.84 91 none Example 9 0.77 0.59 23.4 >5000 0.78 91 none Example 10 0.84 0.64 23.8 4600 0.92 90 none Comparative Example 1 0.82 0.43 47.6 1200 0.90 93 None (but the cohesive layer of the adhesive layer is damaged). Comparative Example 2 0.85 0.53 37.6 800 0.84 90 Interface debonding Comparative Example 3 0.79 0.51 35.4 2000 0.79 85 Microsphere rupture leads to adhesive layer cracks Comparative Example 4 0.76 0.47 38.2 1800 0.68 86 Microsphere aggregation region debinding Comparative Example 5 0.70 0.39 44.3 1100 0.84 91 Large-area debonding of the interface Comparative Example 6 0.65 0.27 58.5 800 0.71 82 Adhesive layer cracking, microsphere rupture Comparative Example 7 0.42 0.13 68.3 600 0.82 88 Full-process cohesive destruction Comparative Example 8 0.85 0.40 52.7 1500 0.85 87 Brittle cracking of the adhesive layer Comparative Example 9 0.95 0.33 65.7 700 0.21 83 Large-area debonding of the interface Comparative Example 10 0.52 0.27 48.3 1500 0.18 87 Substrate collapse As shown in Table 1: Dynamic stress adaptive capability The peel force attenuation rate of Example 1 was only 22.2%, while that of Comparative Example 1 was 47.6%, Comparative Example 2 was 37.6%, and Comparative Example 3 was 35.4%. This indicates that only by simultaneously possessing a modulus gradient substrate and moderately expanded microspheres can optimal stress dissipation be achieved. The fatigue life of Example 1 exceeded 5000 cycles, while that of Comparative Examples 1-3 was 1200, 800, and 2000 cycles, respectively, demonstrating that the synergistic effect of the dual dissipation mechanism and the moderately expanded design significantly improved dynamic durability.

[0107] As shown in Examples 6-10, the above examples cover the boundary values ​​and typical median values ​​of all core parameters defined by this invention, including the upper and lower limits of the elastic surface modulus, the upper and lower limits of the ratio of the intermediate layer to the elastic surface modulus, the upper and lower limits of the crosslinking density, the upper limit of the microsphere content, and the upper limit of the thermally conductive filler content. All samples exhibited a peel force attenuation rate of ≤30% after 100 cycles and a dynamic fatigue life of ≥4000 cycles, consistently achieving the dynamic stress adaptive effect expected by this invention.

[0108] The results of the sharp performance drop in Comparative Examples 7 and 8 after the parameters exceeded the scope of the present invention fully demonstrate that the parameter ranges defined in the present invention are not arbitrarily selected, but are the optimal critical ranges that can simultaneously meet the requirements of stress dissipation, bond strength and structural stability, as verified by systematic experiments.

[0109] Balance between crosslinking density and adhesive properties As can be seen from Comparative Examples 7 and 8, when the crosslinking density is lower than 1×10 -5 When the cohesive strength of the adhesive layer is insufficient, cohesive failure occurs throughout the process, and the peel force attenuation rate is as high as 68.3%; when the crosslinking density is higher than 1×10 -4 At a crosslinking density of mol / cm³, the brittleness of the adhesive layer increases, stress cannot be effectively dissipated, and the peel force decay rate rises to 52.7%. This demonstrates that both excessively high and excessively low crosslinking densities affect the cohesive strength and stress dissipation capacity of the adhesive layer.

[0110] Thermal conductivity and ion transport properties Example 1 exhibits a thermal conductivity of 0.85 W / (m·K), while Comparative Example 4 has a conductivity of only 0.68 W / (m·K), indicating that the stepwise dispersion process is beneficial for the formation of a continuous network of thermally conductive fillers. Example 1 retains 92% of its capacity after 500 cycles, compared to 86% for Comparative Example 4, demonstrating that stepwise dispersion reduces microsphere aggregation and improves ion transport channels. Example 4 shows a thermal conductivity of only 0.52 W / (m·K) with an increased decay rate, proving the importance of surface modification for thermal conductivity and interfacial bonding.

[0111] Interface bonding strength Comparative Example 5 exhibited a peel force attenuation rate of 44.3%, a fatigue life of only 1100 cycles, and large-area debonding at the interface. Example 1 showed no debonding, demonstrating that corona treatment significantly enhanced the chemical bonding ability between the substrate and the adhesive layer.

[0112] Comparison of existing technologies Compared with mainstream existing products, Comparative Example 9 exhibits a 65.7% attenuation rate of peel force during 50°C cycles and a fatigue life of only 700 cycles; Comparative Example 10 shows an attenuation rate of 48.3% and a fatigue life of only 1500 cycles. The peel force attenuation rate of Example 1 of this invention is reduced by 66.2% compared to commercially available PET tapes, and the fatigue life is increased by more than 7 times. Simultaneously, the capacity retention rate of the battery cell after 500 cycles is increased by 9%, fully demonstrating the significant superiority of the technical solution of this invention compared to existing technologies.

[0113] Process sequence dependence Comparative Example 6 exhibited a peel force attenuation rate of 58.5% and a fatigue life of only 800 cycles. Furthermore, SEM analysis revealed microsphere rupture and adhesive layer cracking. This clearly demonstrates that the process sequence of this invention is irreversible; only by following the sequence S3→S4 can the integrity of the microsphere structure and stress buffering function be guaranteed.

[0114] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of this application. Those skilled in the art may find other optimizations and additional functions in this application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A stress-adaptive lithium battery expansion tape, characterized in that: It includes an elastic substrate layer and a first adhesive layer disposed on at least one side of the elastic substrate layer; The elastic substrate layer has a multi-layer co-extruded structure, including a first elastic surface layer, an intermediate rigid layer, and a second elastic surface layer; the 100% modulus of the first elastic surface layer and the second elastic surface layer are both 1~10MPa; the modulus of the intermediate rigid layer is 2~10 times that of the first elastic surface layer. The first adhesive layer comprises a polymer matrix and stress-responsive microspheres and thermally conductive fillers dispersed therein; by mass parts, the content of the polymer matrix is ​​60-90 parts, the content of the stress-responsive microspheres is 1-20 parts, the content of the thermally conductive filler is 5-30 parts, and the total mass parts of the polymer matrix, stress-responsive microspheres and thermally conductive filler are 100 parts. The crosslinking density of the first adhesive layer is 1×10 -5 ~1×10 -4 mol / cm³; The stress-responsive microspheres are thermally expandable microspheres with an initial average particle size of 1~50μm. After expansion treatment, their particle size is 1.2~2.0 times the initial particle size.

2. The stress-adaptive lithium battery expansion tape as described in claim 1, characterized in that: The first and second elastic surface layers are made of thermoplastic polyurethane or polyolefin elastomer, respectively, the intermediate rigid layer is made of polyethylene terephthalate or polyamide, and the overall thickness of the elastic substrate layer is 15~50μm.

3. The stress-adaptive lithium battery expansion tape as described in claim 1, characterized in that: The polymer matrix is ​​formed by cross-linking and curing of acrylate prepolymer, reactive diluent and photoinitiator, wherein the acrylate prepolymer accounts for 60-80% of the total, the reactive diluent accounts for 10-30% of the total, and the photoinitiator accounts for 1-5% of the total.

4. The stress-adaptive lithium battery expansion tape as described in claim 1, characterized in that: The outer shell of the stress-responsive microspheres is made of acrylonitrile copolymer with a glass transition temperature ≥100℃, and the core of the stress-responsive microspheres is a low-boiling-point hydrocarbon.

5. The stress-adaptive lithium battery expansion tape as described in claim 1, characterized in that: The thermally conductive filler is made of at least one of alumina, boron nitride, and aluminum nitride, with a particle size of 0.1~10μm. The thermally conductive filler is surface-modified with a silane coupling agent, which is one or two of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and its addition amount is 0.5~2% of the mass of the thermally conductive filler.

6. The stress-adaptive lithium battery expansion tape as described in claim 1, characterized in that: A primer layer is further provided between the first adhesive layer and the elastic substrate layer. The primer layer is made of chlorinated polypropylene or polyurethane primer liquid, and the dry film thickness is 0.5 to 2 μm.

7. A method for preparing a stress-adaptive lithium battery expansion tape as described in any one of claims 1 to 6, characterized in that: Includes the following steps: S1: The first elastomer resin, the rigid resin, and the second elastomer resin are respectively put into a three-layer co-extrusion casting equipment, and the melting temperature is controlled at 180~240℃. The three-layer structure of the first elastic surface layer, the intermediate rigid layer and the second elastic surface layer is formed by co-extrusion through the die head. After being shaped by the cooling roller, an elastic substrate layer with a thickness of 15~50μm is obtained. S2: A polymer matrix, a thermally conductive filler modified with a silane coupling agent, and stress-responsive microspheres are dispersed and mixed to prepare an adhesive precursor composition; S3: The adhesive precursor composition obtained in step S2 is coated onto the elastic substrate layer obtained in step S1, and cured under nitrogen protection by ultraviolet light irradiation. The ultraviolet light energy is 200~1000mJ / cm². During the curing process, the adhesive layer temperature is controlled to ≤50℃ by air cooling, so that the crosslinking density of the adhesive layer is 1×10⁻⁶. -5 ~1×10 -4 mol / cm³, to obtain a preliminary gel layer; S4: The preliminary adhesive layer obtained in step S3 is heat-treated at 80~120℃ for 2~5 minutes to cause the stress-responsive microspheres in the preliminary adhesive layer to expand and form a hollow stress buffer structure, thus obtaining the tape. S5: The tape obtained in step S4 is cooled, slit, and wound up to obtain stress-adaptive lithium battery expansion tape.

8. The method for preparing the stress-adaptive lithium battery expansion tape as described in claim 7, characterized in that: In step S1, the first elastomer resin and the second elastomer resin are made of at least one of thermoplastic polyurethane or polyolefin elastomer, and the rigid resin is polyethylene terephthalate or polyamide.

9. The method for preparing the stress-adaptive lithium battery expansion tape as described in claim 7, characterized in that: After step S1, the following process is performed on the elastic substrate layer: the elastic substrate layer is subjected to corona treatment with a treatment power of 2000~4000W and a treatment speed of 20~60m / min, so that the surface tension of the elastic substrate layer is ≥50dyn / cm.

10. The method for preparing the stress-adaptive lithium battery expansion tape as described in claim 7, characterized in that: In step S2, the dispersion and mixing is a stepwise dispersion, specifically: the polymer matrix and the thermally conductive filler modified with silane coupling agent are dispersed at a speed of 2000~3000 rpm for 15~25 min; stress-responsive microspheres are added to the dispersed mixture and dispersed at a speed of 500~1000 rpm for 5~15 min.

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