Membrane material for packaging power battery and preparation method of membrane material

Abstract

The invention provides a membrane material for packaging a power battery and a preparation method of the membrane material, and belongs to the field of battery packaging materials. The layer structure of the film material sequentially comprises an outer high-temperature-resistant barrier layer, a gradient transition layer, a middle tear-resistant barrier layer and an inner bonding layer from outside to inside, wherein the outer high-temperature-resistant barrier layer consists of a polyether-ether-ketone base material, nano silicon dioxide, nano aluminum oxide and fluorinated carbon nanotubes; the gradient transition layer is composed of a gradient spinning fiber layer of nano aluminum oxide and polyimide; the middle anti-tearing barrier layer is a high-density polyethylene layer of which the surface is provided with a nano silicon dioxide / polyvinylidene fluoride composite coating, and phase change microcapsules are embedded into the high-density polyethylene layer; and the inner bonding layer is an irradiation crosslinking ethylene-vinyl acetate copolymer layer. By reasonably designing the layered structure of the membrane material for packaging the power battery, the high-temperature protection, the heat management, the mechanical strength and the interface stability of the membrane material for packaging the power battery are simultaneously improved.

Description

Technical Field

[0001] This application relates to the technical field of battery packaging materials, and particularly to a film material for power battery packaging and a preparation method thereof. Background Art

[0002] The battery is the "heart" of new energy vehicles, and its performance directly determines the vehicle's endurance, safety, and cost. As one of the core components of the battery, the packaging film material undertakes multiple functions such as cell protection, insulation sealing, thermal management, and lightweighting. According to statistics, power batteries account for more than 40% of the total vehicle cost, and packaging materials (such as aluminum-plastic films, diaphragms) account for 15-20% of the battery cost. With the development of new energy vehicles towards high energy density and long life, the technological iteration of packaging film materials has become the focus of the industry.

[0003] Existing packaging film materials are mostly aluminum-plastic composite films, which are composed of an aluminum foil layer (purity > 99.5%), a polypropylene (PP) or nylon (PA) layer through an adhesive composite, and have both metal barrier properties and plastic flexibility. However, aluminum-plastic films have poor oxygen permeability (prone to steam accumulation and mildew in humid environments), and the plastic layer (such as LDPE) has low tear resistance. At the same time, the PP / PA layer is prone to softening and deformation at high temperatures (> 120°C), resulting in packaging failure. Therefore, how to simultaneously improve the high-temperature protection, thermal management, mechanical strength, and interfacial stability of the film material for power battery packaging is a technical problem that urgently needs to be solved at present. Summary of the Invention

[0004] This application provides a film material for power battery packaging and a preparation method thereof to solve the following technical problems: how to simultaneously improve the high-temperature protection, thermal management, mechanical strength, and interfacial stability of the film material for power battery packaging.

[0005] In the first aspect, this application provides a film material for power battery packaging. The layer structure of the film material from the outside to the inside is successively: an outer high-temperature resistant barrier layer, a gradient transition layer, an intermediate tear-resistant barrier layer, and an inner adhesive layer; wherein,

[0006] The outer high-temperature resistant barrier layer is composed of a polyether ether ketone substrate, nano-silica, nano-aluminum oxide, and fluorinated carbon nanotubes;

[0007] The gradient transition layer is composed of a gradient spinning fiber layer of nano-aluminum oxide and polyimide;

[0008] The intermediate tear-resistant barrier layer is a high-density polyethylene layer with a nano-silica / polyvinylidene fluoride composite coating on the surface, and phase change microcapsules are embedded in the high-density polyethylene layer;

[0009] The inner adhesive layer is an irradiated cross-linked ethylene-vinyl acetate copolymer layer.

[0010] Optionally, the thickness of the outer high temperature resistant barrier layer is 50 to 80 μm;

[0011] The thickness of the gradient transition layer is 20 to 30 μm;

[0012] The thickness of the intermediate tear-resistant barrier layer is 80 to 120 μm;

[0013] The thickness of the inner adhesive layer is 30-50 μm.

[0014] Optionally, the mass of the nano-silicon dioxide is 5-8% of the mass of the outer high temperature resistant barrier layer;

[0015] The mass of the nano-alumina is 3-5% of the mass of the outer high temperature resistant barrier layer;

[0016] The mass of the fluorinated carbon nanotubes is 1-3% of the mass of the outer high temperature resistant barrier layer.

[0017] Optionally, the fluorinated carbon nanotubes are treated with CF4 plasma, and the surface fluorination rate of the fluorinated carbon nanotubes is 30-50%;

[0018] The particle size of the nano silicon dioxide is 30 to 50 nm;

[0019] The particle size of the nano-alumina is 40-60 nm.

[0020] Optionally, the gradient spun fiber layer is composed of an outer layer, a middle layer and an inner layer formed by layer-by-layer deposition by an electrospinning process; wherein,

[0021] The nano-alumina content of the outer layer is 4-6%, the thickness of the outer layer is 8-12 μm, and the pore size of the outer layer is 180-200 nm;

[0022] The nano-alumina content of the intermediate layer is 8-12%, the thickness of the intermediate layer is 7-10 μm, and the pore size of the intermediate layer is 80-100 nm;

[0023] The nano aluminum oxide content of the inner layer is 13-17%, the thickness of the inner layer is 5-8 μm, and the pore size of the inner layer is 40-60 nm.

[0024] Optionally, the thickness of the nano-silicon dioxide / polyvinylidene fluoride composite coating is 2 to 5 μm, and the mass ratio of the nano-silicon dioxide to the polyvinylidene fluoride is 1:(4 to 6);

[0025] The particle size of the phase-change microcapsule is 100-200nm, the core material is a paraffin / stearic acid compound, the shell material is nano silicon dioxide, and the thickness of the shell material is 20-40nm.

[0026] Optionally, the mass fraction of vinyl acetate in the molecular chain of the ethylene-vinyl acetate copolymer is 5-40%.

[0027] In a second aspect, the present application provides a method for preparing the film material according to any one of the embodiments in the first aspect, the method comprising the following steps:

[0028] S1. Through a twin-screw extruder, melt-blend the polyetheretherketone substrate, nano-silica, nano-alumina and fluorinated carbon nanotubes, and then perform hot pressing to obtain the outer high-temperature barrier layer;

[0029] S2. Dissolve nano-alumina and polyimide in a solvent according to a gradient ratio, and then sequentially deposit the outer layer, the intermediate layer and the inner layer through multi-nozzle electrospinning to obtain the gradient transition layer;

[0030] S3. Disperse the phase change microcapsules in the high-density polyethylene melt, and after cooling, coat the surface of the high-density polyethylene to form a nano-silica / polyvinylidene fluoride composite coating to obtain the intermediate tear-resistant barrier layer;

[0031] S4. Mix and extrude vinyl acetate, ethylene resin and additives, and then perform irradiation crosslinking through electron beam irradiation to form a three-dimensional crosslinked network, and perform hot pressing to obtain the inner bonding layer;

[0032] S5. Using a five-layer co-extrusion device, form a four-layer structure of the outer high-temperature barrier layer, the gradient transition layer, the intermediate tear-resistant barrier layer and the inner bonding layer at one time, and enhance the bonding between the layers through maleic anhydride grafted polypropylene to obtain a film material for power battery packaging.

[0033] Optionally, the temperature of the melt blending is 380-400 °C;

[0034] In the electrospinning process, the concentration of the spinning solution is 15-20 wt%, the diameter of the nozzle is 0.3-0.5 mm, the receiving distance is 15-20 cm, and the voltage is 20-25 kV;

[0035] The dose of the electron beam irradiation is 12-15 kGy;

[0036] The additives include 0.1-0.5 wt% antioxidant 1010 and 0.5-1.0 wt% calcium stearate;

[0037] The die head temperature of the five-layer co-extrusion device is 380-400 °C, and the bonding between the layers is enhanced through a maleic anhydride grafted polypropylene casting film. The grafting rate of the maleic anhydride grafted polypropylene is 1.0-1.5%, and the addition amount is 1-2% of the total thickness between the layers;

[0038] The carbon fluoride nanotubes are treated with CF4 plasma, the treatment power is 50-100 W, and the treatment time is 10-20 min.

[0039] Optionally, the preparation method of the phase change microcapsules includes:

[0040] Melting and mixing paraffin wax and stearic acid in a mass ratio of 1:1, and then adding them to an aqueous phase containing an emulsifier, and forming a core material emulsion through a high-shear emulsifier;

[0041] Dripping a sodium silicate solution as a silica precursor into the core material emulsion drop by drop, and carrying out an interfacial hydrolysis and condensation reaction under the catalysis of ammonia water to generate a uniform silica shell layer, obtaining a mixed solution;

[0042] Centrifuging, washing and drying the mixed solution in sequence to obtain the phase change microcapsules.

[0043] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0044] The present application provides a film material for power battery packaging. The layer structure of the film material from the outside to the inside is: an outer high-temperature resistant barrier layer, a gradient transition layer, an intermediate tear-resistant barrier layer and an inner bonding layer; wherein, the outer high-temperature resistant barrier layer is composed of a polyether ether ketone substrate, nano-silica, nano-aluminum oxide and carbon fluoride nanotubes; the gradient transition layer is composed of a gradient spinning fiber layer of nano-aluminum oxide and polyimide; the intermediate tear-resistant barrier layer is a high-density polyethylene layer with a nano-silica / polyvinylidene fluoride composite coating on the surface, and phase change microcapsules are embedded in the high-density polyethylene layer; the inner bonding layer is an irradiated cross-linked ethylene-vinyl acetate copolymer layer. By reasonably designing the layered structure of the film material for power battery packaging, the PEEK layer resists external heat sources and prevents heat from directly entering; the intermediate layer absorbs heat during phase change, and the phase change microcapsules absorb heat during thermal runaway to delay the temperature rise rate; the gradient layer has thermal expansion matching to avoid shear stress generated between layers due to temperature difference and improve the overall thermal stability. At the same time, the outer layer resists puncture + the intermediate layer resists tearing, and PEEK and HDPE form a "rigid-flexible" composite structure to improve the anti-external force impact ability. The gradient layer buffers vibration, and the porous fiber layer absorbs mechanical vibration energy to reduce the risk of inner layer debonding; it has a dual barrier network, the outer layer nano-filler barrier + the intermediate layer dense coating barrier, to reduce the oxygen permeability. Thereby improving the high-temperature protection, thermal management, mechanical strength and interface stability of the film material for power battery packaging at the same time. Description of the Drawings

[0045] The drawings here are incorporated into the specification and constitute a part of this specification, showing the embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0046] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0047] Figure 1 Schematic structural diagram of a film material for power battery packaging provided by an embodiment of the present application;

[0048] Figure 2 Schematic flow diagram of a preparation method of a film material for power battery packaging provided by an embodiment of the present application;

[0049] Reference numerals:

[0050] 1 - Outer high - temperature barrier layer, 2 - Gradient transition layer, 21 - Outer layer, 22 - Intermediate layer, 23 - Inner layer, 3 - Intermediate tear - resistant barrier layer, 4 - Inner bonding layer. Detailed implementation manners

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0052] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the present application can be obtained through market purchase or can be prepared by existing methods.

[0053] Figure 1 Schematic structural diagram of a film material for power battery packaging provided by an embodiment of the present application.

[0054] As Figure 1 shown, the present application provides a film material for power battery packaging. The layer structure of the film material from the outside to the inside is successively: an outer high - temperature barrier layer, a gradient transition layer, an intermediate tear - resistant barrier layer, and an inner bonding layer; wherein,

[0055] The outer high - temperature barrier layer is composed of a polyether ether ketone substrate, nano - silica, nano - alumina, and fluorinated carbon nanotubes;

[0056] The gradient transition layer is composed of a gradient spinning fiber layer of nano - alumina and polyimide;

[0057] The intermediate tear-resistant barrier layer is a high-density polyethylene layer with a nano-silica / polyvinylidene fluoride composite coating on its surface, and phase change microcapsules are embedded in the high-density polyethylene layer;

[0058] The inner adhesive layer is an irradiated cross-linked ethylene-vinyl acetate copolymer layer.

[0059] In some embodiments, the thickness of the outer high-temperature resistant barrier layer is 50-80 μm;

[0060] The thickness of the gradient transition layer is 20-30 μm;

[0061] The thickness of the intermediate tear-resistant barrier layer is 80-120 μm;

[0062] The thickness of the inner adhesive layer is 30-50 μm.

[0063] It should be noted that the functions of each layer are as follows:

[0064] Outer high-temperature resistant barrier layer (50-80 μm): The polyether ether ketone (PEEK) substrate has a temperature resistance > 250 °C, preventing the outer layer from melting or deforming during battery thermal runaway (such as local high temperature during a short circuit instant); meanwhile, nano-silica and alumina form a rigid network, and the puncture resistance strength ≥ 50 MPa (superior to traditional aluminum-plastic films); fluorinated carbon nanotubes construct a conductive path, and the surface resistance ≤ 10 6 Ω, avoiding short circuits caused by electrostatic accumulation; in addition, the nano-fillers are densely stacked, and the oxygen permeability is close to the level of metal aluminum foil.

[0065] Gradient transition layer (20-30 μm): The content gradient of nano-alumina changes, enabling the coefficient of thermal expansion to smoothly transition from 5×10 -6 / °C (matching PEEK) in the outer layer to 12×10 -6 / °C (matching HDPE) in the intermediate layer, avoiding thermal stress delamination; meanwhile, the electrospun fiber layer (outer layer pore diameter 200 nm → inner layer 50 nm) forms a gradient pore structure to absorb mechanical vibration energy during charge and discharge cycles; in addition, the dense inner layer (50 nm pore diameter) cooperates with the outer layer to block water and oxygen permeation.

[0066] Intermediate tear-resistant barrier layer (80-120 μm): The tear resistance strength of the high-density polyethylene (HDPE) matrix ≥ 40 MPa, supporting the battery packaging structure; the phase change microcapsules (phase change enthalpy 160-180 J / g) absorb heat at 80-100 °C, delaying the spread of thermal runaway; meanwhile, the nano-SiO2 / PVDF coating enhances the barrier performance, compensating for the inherent air permeability defect of HDPE; the elastic modulus of HDPE matches that of the inner layer EVA, adapting to the volume change of the battery during charge and discharge.

[0067] Inner adhesive layer (30 - 50 μm): The inner layer (adhesive layer) is in direct contact with the battery cell core and requires high bonding strength and resistance to electrolyte corrosion. After irradiation crosslinking, the peel strength is enhanced and it can withstand long-term immersion in electrolyte; at the same time, the flexibility of EVA can absorb the deformation stress of the battery and prevent interfacial debonding.

[0068] Thus, the present application rationally designs the layered structure of the film material for power battery packaging. The PEEK layer resists external heat sources and prevents heat from directly entering; the intermediate layer absorbs heat through phase change, and the phase change microcapsules absorb heat during thermal runaway to delay the temperature rise rate; the gradient layer has a thermal expansion match to avoid shear stress generated between layers due to temperature difference and improve the overall thermal stability. At the same time, the outer layer resists puncture + the intermediate layer resists tearing, and PEEK and HDPE form a "rigid-flexible" composite structure to improve the ability to resist external force impact. The gradient layer buffers vibration, and the porous fiber layer absorbs mechanical vibration energy to reduce the risk of inner layer debonding; it has a dual barrier network, with the outer layer of nano-fillers barrier + the intermediate layer of dense coating barrier to reduce the oxygen permeability.

[0069] In some embodiments, the mass of the nano-silica is 5 - 8% of the mass of the outer high-temperature resistant barrier layer;

[0070] The mass of the nano-aluminum oxide is 3 - 5% of the mass of the outer high-temperature resistant barrier layer;

[0071] The mass of the fluorinated carbon nanotube is 1 - 3% of the mass of the outer high-temperature resistant barrier layer.

[0072] In some embodiments, the fluorinated carbon nanotube is treated by CF4 plasma, and the surface fluorination rate of the fluorinated carbon nanotube is 30 - 50%;

[0073] The particle size of the nano-silica is 30 - 50 nm;

[0074] The particle size of the nano-aluminum oxide is 40 - 60 nm.

[0075] Nano-silica (rigid) and fluorinated carbon nanotubes (tough) form a "rigid-flexible combination" structure. While maintaining the impact strength, it improves the puncture resistance; aluminum oxide improves the wear resistance, and carbon nanotubes assist in heat conduction to avoid material softening caused by local overheating. At the same time, aluminum oxide (low expansion) and PEEK (medium expansion) cooperate, and the overall thermal expansion coefficient is stable at 6×10 -6 / ℃, reducing the risk of thermal cycle delamination; the conductive network of fluorinated carbon nanotubes combines with the dense barrier layer of silica / aluminum oxide to prevent static electricity and block water and oxygen. In addition, the graded particle sizes of silica and aluminum oxide reduce the voids between fillers and improve the melt fluidity; the -CF2 groups of fluorinated carbon nanotubes form interfacial hydrogen bonds with the ketone groups of PEEK to improve the bonding strength.

[0076] In some embodiments, the gradient spun fiber layer is composed of an outer layer, an intermediate layer, and an inner layer formed by layer-by-layer deposition through an electrospinning process; wherein,

[0077] the nano-aluminum oxide content in the outer layer is 4-6%, the thickness of the outer layer is 8-12 μm, and the pore size of the outer layer is 180-200 nm;

[0078] the nano-aluminum oxide content in the intermediate layer is 8-12%, the thickness of the intermediate layer is 7-10 μm, and the pore size of the intermediate layer is 80-100 nm;

[0079] the nano-aluminum oxide content in the inner layer is 13-17%, the thickness of the inner layer is 5-8 μm, and the pore size of the inner layer is 40-60 nm.

[0080] The combination of the outer flexible fibers (low aluminum oxide) and the inner rigid fibers (high aluminum oxide) enhances the tear resistance. Meanwhile, the large pore size of the outer layer supports rapid ion diffusion, and the dense structure of the inner layer inhibits dendrite growth. The gradient aluminum oxide content in the intermediate layer matches the thermal expansion coefficients of battery encapsulation materials (such as PEEK and HDPE), reducing the risk of thermal cycling delamination. In addition, the combination of the gas permeability of the outer layer (pore size 200 nm) and the barrier property of the inner layer (pore size 40 nm) reduces the oxygen transmission rate compared with the single-layer structure. Through the triple-gradient design of composition-pore size-thickness and precise control of the electrospinning process parameters, the gradient spun fiber layer realizes the synergistic optimization of mechanical, thermal, and electrochemical properties.

[0081] In some embodiments, the thickness of the nano-silica / polyvinylidene fluoride composite coating is 2-5 μm, and the mass ratio of the nano-silica to the polyvinylidene fluoride is 1:(4-6);

[0082] The particle size of the phase change microcapsules is 100-200 nm, the core material is a paraffin / stearic acid composite, and the shell material is nano-silica with a shell thickness of 20-40 nm.

[0083] With a coating thickness of 2-5 μm and a mass ratio of nano-SiO2 to PVDF of 1:(4-6), the high chemical stability of PVDF and the nano-enhancing effect of SiO2 can be combined to optimize the mechanical strength and functionality of the coating. The addition of SiO2 can increase the β-phase content of PVDF and enhance the piezoelectric performance. Nano-SiO2 fills the pores of the PVDF matrix, forming a tortuous path and prolonging the diffusion path of water and oxygen molecules. PVDF provides flexibility, and SiO2 enhances rigidity, making the coating have both scratch resistance and anti-deformation ability.

[0084] The microcapsules absorb heat at 80-100 °C and delay battery thermal runaway for ≥5 min. The nano-SiO2 shell layer (elastic modulus ~70 GPa) protects the core material and prevents the leakage of the core material during HDPE processing.

[0085] In some embodiments, the mass fraction of vinyl acetate in the molecular chain of the ethylene-vinyl acetate copolymer is 5-40%.

[0086] Figure 2 It is a schematic flow chart of a preparation method of a film material for power battery packaging provided by an embodiment of the present application.

[0087] As Figure 2 shown, the present application provides a preparation method of the film material described in any one of the above embodiments, and the method includes the following steps:

[0088] S1. Through a twin-screw extruder, melt-blend a polyether ether ketone substrate, nano-silica, nano-alumina, and fluorinated carbon nanotubes, and then perform hot pressing to obtain the outer high-temperature barrier layer;

[0089] S2. Dissolve nano-alumina and polyimide in a solvent according to a gradient ratio, and then sequentially deposit an outer layer, a middle layer, and an inner layer through multi-nozzle electrospinning to obtain the gradient transition layer;

[0090] S3. Disperse phase change microcapsules in a high-density polyethylene melt, and after cooling, coat the surface of the high-density polyethylene to form a nano-silica / polyvinylidene fluoride composite coating to obtain the middle tear-resistant barrier layer;

[0091] S4. Mix and extrude vinyl acetate, an ethylene resin, and an auxiliary agent, and then perform irradiation cross-linking through electron beam irradiation to form a three-dimensional cross-linked network, and perform hot pressing to obtain the inner bonding layer;

[0092] S5. Use a five-layer co-extrusion device to integrally form a four-layer structure of the outer high-temperature barrier layer, the gradient transition layer, the middle tear-resistant barrier layer, and the inner bonding layer, and enhance the bonding between each layer through maleic anhydride grafted polypropylene to obtain a film material for power battery packaging.

[0093] It should be noted that a five-layer co-extrusion device is used to produce a four-layer functional layer (outer PEEK layer, gradient layer, middle HDPE layer, inner adhesive layer), and a MAH-g-PP adhesive layer (a total of 5 layers) is injected between adjacent layers through an independent runner. The co-extrusion molding process using the five-layer co-extrusion device is as follows: Each extruder transports the melt to the co-extrusion die head according to the set parameters, and MAH-g-PP is injected into the interface between adjacent layers through an independent runner (such as between the PEEK layer and the gradient layer, and between the gradient layer and the HDPE layer); a MAH-g-PP film with a thickness of 2 - 5 μm is added between each layer, accounting for 1% - 2% of the total film thickness. Subsequently, the melt is layered and stacked in the die head, and the thickness of each layer is controlled through a precision runner (outer layer 50 - 80 μm, gradient layer 20 - 30 μm, middle layer 80 - 120 μm, inner layer 30 - 50 μm); the polar groups (-COOH) of MAH-g-PP form hydrogen bonds and physical entanglements with adjacent layers (such as the keto group of PEEK and the non-polar chains of HDPE), increasing the peel strength. Finally, the composite melt is rapidly cooled by a cooling roller (water temperature 10 - 15 °C), the cooling rate > 50 °C / s, the crystallinity is inhibited (HDPE crystallinity ≤ 60%), the flexibility is improved, and the winding tension ≤ 50 N to avoid interlayer slip or deformation.

[0094] In some embodiments, the temperature of the melt blending is 380 - 400 °C;

[0095] In the electrospinning process, the concentration of the spinning solution is 15 - 20 wt%, the nozzle diameter is 0.3 - 0.5 mm, the receiving distance is 15 - 20 cm, and the voltage is 20 - 25 kV;

[0096] The dose of the electron beam irradiation is 12 - 15 kGy;

[0097] The additives include 0.1 - 0.5 wt% of antioxidant 1010 and 0.5 - 1.0 wt% of calcium stearate;

[0098] The die head temperature of the five-layer co-extrusion device is 380 - 400 °C, and the bonding between layers is enhanced by a maleic anhydride grafted polypropylene casting film. The grafting rate of the maleic anhydride grafted polypropylene is 1.0 - 1.5%, and the addition amount is 1 - 2% of the total interlayer thickness;

[0099] The fluorinated carbon nanotubes are treated by CF4 plasma, the treatment power is 50 - 100 W, and the treatment time is 10 - 20 min.

[0100] In some embodiments, the preparation method of the phase change microcapsules includes:

[0101] Paraffin and stearic acid are melt-mixed in a mass ratio of 1:1, and then added to the water phase containing an emulsifier, and a core material emulsion is formed by a high-shear emulsifier;

[0102] The sodium silicate solution is added dropwise as a silica precursor to the core material emulsion, and an interfacial hydrolysis and condensation reaction is carried out under the catalysis of ammonia water to form a uniform silica shell layer, obtaining a mixed solution;

[0103] The mixed solution is centrifuged, washed and dried in sequence to obtain the phase change microcapsules.

[0104] In some embodiments, the emulsifier type is a composite emulsifier of Span-80 / Tween-80, the mass ratio of Span-80 to Tween-80 is 2:1, the HLB is 12-14, and the emulsifier concentration is 3 wt%.

[0105] In some embodiments, the rotation speed of the high-shear emulsifier is 15000 rpm and the emulsification time is 10 min.

[0106] In some embodiments, the pH value of the interfacial hydrolysis and condensation reaction is 9.0-9.5, the reaction temperature is 25-30 °C, and the reaction time is 2 h; the concentration of the sodium silicate solution is 10 wt%, and tetraethyl orthosilicate is added as an auxiliary precursor, and the mass ratio of tetraethyl orthosilicate to sodium silicate is 1:5.

[0107] In summary, the technical solution provided by this application has the following advantages:

[0108] (1) Multifunctional integrated design

[0109] Synergy of high-temperature protection and thermal management: The outer high-temperature resistant material combines with the intermediate layer phase change endothermic structure to effectively delay the spread of thermal runaway and improve the battery safety.

[0110] Optimization of mechanical properties: Through the "rigid-flexible combination" interlayer design, it takes into account puncture resistance, tear resistance and flexibility to adapt to mechanical stresses under complex working conditions.

[0111] Dual barrier network: The synergistic effect of nano-fillers and dense coatings significantly improves the barrier performance and effectively isolates the penetration of water and oxygen.

[0112] (2) Bionic gradient structure innovation

[0113] Smooth transition of thermal expansion coefficient: The gradient transition layer relieves the interlayer thermal stress through the gradient changes of composition and pore size, avoiding the risk of delamination.

[0114] Dynamic stress buffering: The gradient pore structure absorbs mechanical vibration energy and improves the durability of the material.

[0115] (3) Process efficiency and precise control

[0116] Integrated co-extrusion molding: The five-layer co-extrusion process realizes the efficient integration of multi-layer structures, ensuring the interlayer bonding strength and consistency.

[0117] Precise regulation of electrospinning: The multi-nozzle layer-by-layer deposition technology precisely constructs the gradient pore size and composition distribution, optimizing the functional adaptability.

[0118] Controlled encapsulation of microcapsules: The interfacial hydrolysis and condensation process realizes the efficient encapsulation of phase change materials, ensuring the stability of the thermal management function.

[0119] (4) Environmental protection and cost advantages

[0120] Adaptation of green processes: Processes such as water-based microcapsule preparation and solvent-free coating reduce environmental pollution and meet the requirements of sustainable development.

[0121] Improvement of material utilization rate: The design of nano-fillers and composite structures reduces the usage of high-cost substrates, achieving cost reduction and efficiency improvement.

[0122] (5) Interface stability and long-term sealing

[0123] Enhanced bonding through chemical bonding: Polar compatibilizers and radiation cross-linking technology strengthen the interlayer interface, ensuring no delamination during long-term use.

[0124] Optimization of corrosion resistance: The specially treated inner layer material can withstand the erosion of electrolytes, ensuring the battery cycle life.

[0125] (6) Lightweight and adaptability

[0126] Efficient design of thin layers: Through nano-reinforcement and structural optimization, lightweight is achieved while maintaining high performance, meeting the requirements of high-energy density batteries.

[0127] Wide temperature range adaptability: Material selection and modification ensure the stability of all working conditions from low temperature (-50°C) to high temperature (250°C).

[0128] This application breaks through the performance limitations of traditional encapsulation materials through material innovation, structural bionics, and process coordination, achieving a comprehensive improvement in the dimensions of high-temperature protection, thermal management, mechanical strength, and interface stability for power battery encapsulation films. At the same time, it has the advantages of lightweight, environmental protection, and industrialization potential, providing a core material solution for the next generation of high-safety and long-life power batteries.

[0129] The following will further elaborate on this application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0130] Example 1

[0131] This embodiment provides a film material for power battery packaging. The layer structure of the film material from the outside to the inside is successively: an outer high-temperature resistant barrier layer 1, a gradient transition layer 2, an intermediate tear-resistant barrier layer 3, and an inner adhesive layer 4; wherein,

[0132] The outer high-temperature resistant barrier layer 1 is composed of a polyether ether ketone (CAS No. 29658-26-2) substrate, nano-silica, nano-aluminum oxide, and fluorinated carbon nanotubes (the CAS No. of carbon nanotubes is 68647-86-9);

[0133] The gradient transition layer 2 is composed of a gradient spinning fiber layer of nano-aluminum oxide and polyimide (CAS No. 62929-02-6);

[0134] The intermediate tear-resistant barrier layer 3 is a high-density polyethylene layer (the CAS No. of high-density polyethylene (HDPE) is 9002-88-4) with a nano-silica / polyvinylidene fluoride (the CAS No. of polyvinylidene fluoride is 24937-79-9) composite coating on the surface, and phase change microcapsules are embedded in the high-density polyethylene layer;

[0135] The inner adhesive layer 4 is an irradiated cross-linked ethylene-vinyl acetate copolymer layer.

[0136] The thickness of the outer high-temperature resistant barrier layer 1 is 60 μm;

[0137] The thickness of the gradient transition layer 2 is 25 μm;

[0138] The thickness of the intermediate tear-resistant barrier layer 3 is 100 μm;

[0139] The thickness of the inner adhesive layer 4 is 40 μm.

[0140] The mass of the nano-silica is 6% of the mass of the outer high-temperature resistant barrier layer 1;

[0141] The mass of the nano-aluminum oxide is 4% of the mass of the outer high-temperature resistant barrier layer 1;

[0142] The mass of the fluorinated carbon nanotubes is 2% of the mass of the outer high-temperature resistant barrier layer 1.

[0143] The fluorinated carbon nanotubes are treated by CF4 plasma, and the surface fluorination rate of the fluorinated carbon nanotubes is 40%;

[0144] The particle size of the nano-silica is 30 - 50 nm;

[0145] The particle size of the nano-aluminum oxide is 40 - 60 nm.

[0146] The gradient spun fiber layer is composed of an outer layer 21, an intermediate layer 22, and an inner layer 23 formed by layer-by-layer deposition through the electrospinning process; among them,

[0147] The nano-aluminum oxide content in the outer layer 21 is 5%, the thickness of the outer layer 21 is 10 μm, and the pore size of the outer layer 21 is 180 - 200 nm;

[0148] The nano-aluminum oxide content in the intermediate layer 22 is 10%, the thickness of the intermediate layer 22 is 8 μm, and the pore size of the intermediate layer 22 is 80 - 100 nm;

[0149] The nano-aluminum oxide content in the inner layer 23 is 15%, the thickness of the inner layer 23 is 7 μm, and the pore size of the inner layer 23 is 40 - 60 nm.

[0150] The thickness of the nano-silica / polyvinylidene fluoride composite coating is 3 μm, and the mass ratio of the nano-silica to the polyvinylidene fluoride is 1:5;

[0151] The particle size of the phase change microcapsules is 100 - 150 nm, the core material is a paraffin / stearic acid composite, the shell material is nano-silica, and the thickness of the shell material is 30 nm.

[0152] The mass fraction of vinyl acetate in the molecular chain of the ethylene-vinyl acetate copolymer is 20%.

[0153] Based on the above film materials, this embodiment also provides a preparation method for the film materials described in the above embodiment, and the method includes the following steps:

[0154] S11. Through a twin-screw extruder, melt-blend the polyether ether ketone substrate, nano-silica, nano-aluminum oxide, and fluorinated carbon nanotubes, and then perform hot pressing to obtain the outer high-temperature barrier layer 1;

[0155] S21. Dissolve polyimide (PI) in the DMAC solvent, add 5% - 15% nano-aluminum oxide (increasing gradient) in stages to form spinning solutions with different concentrations, and then through a multi-channel electrospinning device, spray out the spinning solutions with different aluminum oxide contents in sequence to form a fiber layer with a gradient pore size distribution, and deposit the outer layer 21, the intermediate layer 22, and the inner layer 23 in sequence to obtain the gradient transition layer 2;

[0156] S31. Disperse the phase change microcapsules in the high-density polyethylene melt, and after cooling, coat the surface of the high-density polyethylene to form a nano-silica / polyvinylidene fluoride composite coating to obtain the intermediate tear-resistant barrier layer 3;

[0157] S41. Mix vinyl acetate, ethylene resin and additives and extrude them. Then, perform radiation crosslinking through electron beam irradiation to form a three-dimensional crosslinked network, and carry out hot pressing to obtain the inner adhesive layer 4.

[0158] S51. Using a five-layer co-extrusion device, form a four-layer structure of the outer high-temperature resistant barrier layer 1, the gradient transition layer 2, the intermediate tear-resistant barrier layer 3 and the inner adhesive layer 4 at one time, and enhance the bonding between each layer through maleic anhydride grafted polypropylene (commercial model: Exxelor PO 1020 Exxon) to obtain the film material for power battery packaging.

[0159] Among them, the temperature of the melt blending is 400 °C;

[0160] In the electrospinning process, the concentration of the spinning solution is 18 wt%, the nozzle diameter is 0.4 mm, the receiving distance is 16 cm, and the voltage is 22 kV;

[0161] The dose of the electron beam irradiation is 14 kGy;

[0162] The additives include 0.3 wt% antioxidant 1010 (pentaerythritol tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]) and 0.8 wt% calcium stearate;

[0163] The die head temperature of the five-layer co-extrusion device is 400 °C, and the bonding between layers is enhanced through a maleic anhydride grafted polypropylene casting film. The grafting rate of the maleic anhydride grafted polypropylene is 1.2%, and the addition amount is 1.5% of the total thickness between layers;

[0164] The fluorinated carbon nanotubes are treated by CF4 plasma, the treatment power is 70 W, and the treatment time is 15 min.

[0165] The preparation method of the phase change microcapsules includes: melting and mixing paraffin (CAS No. 8002-74-2) and stearic acid (CAS No. 57-11-4) in a mass ratio of 1:1, and then adding them into the aqueous phase containing an emulsifier, and forming a core material emulsion through a high-shear emulsifier; adding a sodium silicate solution as a silica precursor dropwise into the core material emulsion, and carrying out an interfacial hydrolysis and condensation reaction under the catalysis of ammonia water to generate a uniform silica shell layer, obtaining a mixed solution; centrifuging, washing and drying the mixed solution in sequence to obtain the phase change microcapsules. The type of the emulsifier is a composite emulsifier of Span-80 / Tween-80, the mass ratio of Span-80 to Tween-80 is 2:1, the HLB is 12-14, and the concentration of the emulsifier is 3 wt%. The rotation speed of the high-shear emulsifier is 15000 rpm, and the emulsification time is 10 min. The pH value of the interfacial hydrolysis and condensation reaction is 9.0-9.5, the reaction temperature is 30 °C, and the reaction time is 2 h; the concentration of the sodium silicate solution is 10 wt%, and tetraethyl orthosilicate is added as an auxiliary precursor, and the mass ratio of tetraethyl orthosilicate to sodium silicate is 1:5.

[0166] Example 2

[0167] This example provides a film material for power battery packaging. The layer structure of the film material from the outside to the inside is successively: an outer high-temperature resistant barrier layer 1, a gradient transition layer 2, an intermediate tear-resistant barrier layer 3, and an inner adhesive layer 4; among them,

[0168] The outer high-temperature resistant barrier layer 1 is composed of a polyether ether ketone (CAS No. 29658-26-2) substrate, nano-silica, nano-alumina, and fluorinated carbon nanotubes (the CAS No. of the carbon nanotubes is 68647-86-9);

[0169] The gradient transition layer 2 is composed of a gradient spinning fiber layer of nano-alumina and polyimide (CAS No. 62929-02-6);

[0170] The intermediate tear-resistant barrier layer 3 is a high-density polyethylene layer (the CAS No. of high-density polyethylene (HDPE) is 9002-88-4) with a nano-silica / polyvinylidene fluoride (the CAS No. of polyvinylidene fluoride is 24937-79-9) composite coating on the surface, and phase change microcapsules are embedded in the high-density polyethylene layer;

[0171] The inner adhesive layer 4 is an irradiated cross-linked ethylene-vinyl acetate copolymer layer.

[0172] The thickness of the outer high-temperature resistant barrier layer 1 is 80 μm;

[0173] The thickness of the gradient transition layer 2 is 30 μm;

[0174] The thickness of the intermediate tear-resistant barrier layer 3 is 120 μm;

[0175] The thickness of the inner adhesive layer 4 is 50 μm.

[0176] The mass of the nano silicon dioxide is 8% of the mass of the outer high temperature resistant barrier layer 1;

[0177] The mass of the nano-alumina is 5% of the mass of the outer high temperature resistant barrier layer 1;

[0178] The mass of the fluorinated carbon nanotubes is 3% of the mass of the outer high temperature resistant barrier layer 1 .

[0179] The fluorinated carbon nanotubes are treated with CF4 plasma, and the surface fluorination rate of the fluorinated carbon nanotubes is 50%;

[0180] The particle size of the nano silicon dioxide is 30 to 50 nm;

[0181] The particle size of the nano-alumina is 40-60 nm.

[0182] The gradient spun fiber layer is composed of an outer layer 21, a middle layer 22 and an inner layer 23 formed by layer-by-layer deposition through an electrospinning process; wherein,

[0183] The nano-alumina content of the outer layer 21 is 6%, the thickness of the outer layer 21 is 12 μm, and the pore size of the outer layer 21 is 180-200 nm;

[0184] The nano-alumina content of the intermediate layer 22 is 12%, the thickness of the intermediate layer 22 is 10 μm, and the pore size of the intermediate layer 22 is 80-100 nm;

[0185] The nano-alumina content of the inner layer 23 is 17%, the thickness of the inner layer 23 is 8 μm, and the pore size of the inner layer 23 is 60 nm.

[0186] The thickness of the nano-silicon dioxide / polyvinylidene fluoride composite coating is 5 μm, and the mass ratio of the nano-silicon dioxide to the polyvinylidene fluoride is 1:6;

[0187] The particle size of the phase-change microcapsule is 100-200 nm, the core material is a paraffin / stearic acid compound, the shell material is nano silicon dioxide, and the thickness of the shell material is 40 nm.

[0188] The mass fraction of vinyl acetate in the molecular chain of the ethylene-vinyl acetate copolymer is 40%.

[0189] Based on the above film material, this embodiment also provides a method for preparing the film material described in the above embodiment, and the method comprises the following steps:

[0190] S11. Through a twin-screw extruder, melt-blend the polyether ether ketone substrate, nano-silica, nano-alumina, and fluorinated carbon nanotubes, and then perform hot pressing to obtain the outer high-temperature barrier layer 1;

[0191] S21. Dissolve polyimide (PI) in the DMAC solvent, add 5%-15% nano-alumina in stages (increasing gradient), form spinning solutions with different concentrations, and then through a multi-channel electrospinning device, spray out the spinning solutions with different alumina contents in sequence to form a fiber layer with a gradient pore size distribution, and deposit the outer layer 21, the intermediate layer 22, and the inner layer 23 in sequence to obtain the gradient transition layer 2;

[0192] S31. Disperse the phase change microcapsules in the high-density polyethylene melt, and after cooling, coat the surface of the high-density polyethylene to form a nano-silica / polyvinylidene fluoride composite coating to obtain the intermediate tear-resistant barrier layer 3;

[0193] S41. Mix and extrude vinyl acetate, ethylene resin, and additives, and then perform irradiation cross-linking through electron beam irradiation to form a three-dimensional cross-linked network, and perform hot pressing to obtain the inner bonding layer 4;

[0194] S51. Using a five-layer co-extrusion device, form a four-layer structure of the outer high-temperature barrier layer 1, the gradient transition layer 2, the intermediate tear-resistant barrier layer 3, and the inner bonding layer 4 in one step, and enhance the bonding between each layer through maleic anhydride grafted polypropylene (commercial model: Exxelor PO1020 Exxon) to obtain the film material for power battery packaging.

[0195] Among them, the temperature of the melt-blending is 400 °C;

[0196] In the electrospinning process, the concentration of the spinning solution is 20 wt%, the nozzle diameter is 0.5 mm, the receiving distance is 20 cm, and the voltage is 25 kV;

[0197] The dose of the electron beam irradiation is 15 kGy;

[0198] The additives include 0.5 wt% antioxidant 1010 and 1.0 wt% calcium stearate;

[0199] The die head temperature of the five-layer co-extrusion device is 380 °C, and the bonding between layers is enhanced through a maleic anhydride grafted polypropylene casting film. The grafting rate of the maleic anhydride grafted polypropylene is 1.0%, and the addition amount is 1% of the total layer thickness;

[0200] The fluorinated carbon nanotubes are treated by CF4 plasma, the treatment power is 100 W, and the treatment time is 10 min.

[0201] The preparation method of the phase change microcapsules includes: melting and mixing paraffin (CAS No. 8002-74-2) and stearic acid (CAS No. 57-11-4) in a mass ratio of 1:1, then adding them into the aqueous phase containing an emulsifier, and forming a core material emulsion through a high-shear emulsifier; adding a sodium silicate solution as a silica precursor dropwise into the core material emulsion, and carrying out an interfacial hydrolysis and condensation reaction under the catalysis of ammonia water to generate a uniform silica shell layer, obtaining a mixed solution; centrifuging, washing, and drying the mixed solution in sequence to obtain the phase change microcapsules. The type of the emulsifier is a composite emulsifier of Span-80 / Tween-80, the mass ratio of Span-80 to Tween-80 is 2:1, the HLB is 12-14, and the concentration of the emulsifier is 3 wt%. The rotation speed of the high-shear emulsifier is 15000 rpm, and the emulsification time is 10 min. The pH value of the interfacial hydrolysis and condensation reaction is 9.0-9.5, the reaction temperature is 30 °C, and the reaction time is 2 h; the concentration of the sodium silicate solution is 10 wt%, and tetraethyl orthosilicate is added as an auxiliary precursor, and the mass ratio of tetraethyl orthosilicate to sodium silicate is 1:5.

[0202] Example 3

[0203] This example provides a film material for power battery packaging. The layer structure of the film material from the outside to the inside is successively: an outer high-temperature resistant barrier layer 1, a gradient transition layer 2, an intermediate tear-resistant barrier layer 3, and an inner adhesive layer 4; wherein,

[0204] The outer high-temperature resistant barrier layer 1 is composed of a polyether ether ketone (CAS No. 29658-26-2) substrate, nano-silica, nano-alumina, and fluorinated carbon nanotubes (the CAS No. of the carbon nanotubes is 68647-86-9);

[0205] The gradient transition layer 2 is composed of a gradient spinning fiber layer of nano-alumina and polyimide (CAS No. 62929-02-6);

[0206] The intermediate tear-resistant barrier layer 3 is a high-density polyethylene layer (the CAS No. of high-density polyethylene (HDPE) is 9002-88-4) with a nano-silica / polyvinylidene fluoride (the CAS No. of polyvinylidene fluoride is 24937-79-9) composite coating on the surface, and phase change microcapsules are embedded in the high-density polyethylene layer;

[0207] The inner adhesive layer 4 is an irradiated cross-linked ethylene-vinyl acetate copolymer layer.

[0208] The thickness of the outer high-temperature resistant barrier layer 1 is 50 μm;

[0209] The thickness of the gradient transition layer 2 is 20 μm;

[0210] The thickness of the intermediate tear-resistant barrier layer 3 is 80 μm;

[0211] The thickness of the inner adhesive layer 4 is 30 μm.

[0212] The mass of the nano silicon dioxide is 5% of the mass of the outer high temperature resistant barrier layer 1;

[0213] The mass of the nano-alumina is 3% of the mass of the outer high temperature resistant barrier layer 1;

[0214] The mass of the fluorinated carbon nanotubes is 1% of the mass of the outer high temperature resistant barrier layer 1 .

[0215] The fluorinated carbon nanotubes are treated with CF4 plasma, and the surface fluorination rate of the fluorinated carbon nanotubes is 30%;

[0216] The particle size of the nano silicon dioxide is 30 to 50 nm;

[0217] The particle size of the nano-alumina is 40-60 nm.

[0218] The gradient spun fiber layer is composed of an outer layer 21, a middle layer 22 and an inner layer 23 formed by layer-by-layer deposition through an electrospinning process; wherein,

[0219] The nano-alumina content of the outer layer 21 is 4%, the thickness of the outer layer 21 is 8 μm, and the pore size of the outer layer 21 is 180-200 nm;

[0220] The nano-alumina content of the intermediate layer 22 is 8%, the thickness of the intermediate layer 22 is 7 μm, and the pore size of the intermediate layer 22 is 80-100 nm;

[0221] The nano-alumina content of the inner layer 23 is 13%, the thickness of the inner layer 23 is 5 μm, and the pore size of the inner layer 23 is 40-60 nm.

[0222] The thickness of the nano-silicon dioxide / polyvinylidene fluoride composite coating is 2 μm, and the mass ratio of the nano-silicon dioxide to the polyvinylidene fluoride is 1:4;

[0223] The particle size of the phase-change microcapsule is 100-200 nm, the core material is a paraffin / stearic acid compound, the shell material is nano silicon dioxide, and the thickness of the shell material is 20 nm.

[0224] The mass fraction of vinyl acetate in the molecular chain of the ethylene-vinyl acetate copolymer is 5%.

[0225] Based on the above film material, this embodiment also provides a method for preparing the film material described in the above embodiment, and the method comprises the following steps:

[0226] S11. Through a twin-screw extruder, melt-blend the polyether ether ketone substrate, nano-silica, nano-alumina, and fluorinated carbon nanotubes, and then perform hot pressing to obtain the outer high-temperature barrier layer 1;

[0227] S21. Dissolve polyimide (PI) in DMAC solvent, add 5%-15% nano-alumina in stages (increasing gradient), form spinning solutions with different concentrations, and then through a multi-channel electrospinning device, spray out the spinning solutions with different alumina contents in sequence to form a fiber layer with a gradient pore size distribution, and deposit the outer layer 21, the intermediate layer 22, and the inner layer 23 in sequence to obtain the gradient transition layer 2;

[0228] S31. Disperse the phase change microcapsules in the high-density polyethylene melt, and after cooling, coat the surface of the high-density polyethylene to form a nano-silica / polyvinylidene fluoride composite coating to obtain the intermediate tear-resistant barrier layer 3;

[0229] S41. Mix and extrude vinyl acetate, ethylene resin, and additives, and then perform irradiation cross-linking through electron beam irradiation to form a three-dimensional cross-linked network, and perform hot pressing to obtain the inner bonding layer 4;

[0230] S51. Using a five-layer co-extrusion device, form a four-layer structure of the outer high-temperature barrier layer 1, the gradient transition layer 2, the intermediate tear-resistant barrier layer 3, and the inner bonding layer 4 in one step, and enhance the bonding between each layer through maleic anhydride grafted polypropylene (commercial model: Exxelor PO1020 Exxon) to obtain the film material for power battery packaging.

[0231] Among them, the temperature of the melt-blending is 380 °C;

[0232] In the electrospinning process, the concentration of the spinning solution is 15 wt%, the nozzle diameter is 0.3 mm, the receiving distance is 15 cm, and the voltage is 25 kV;

[0233] The dose of the electron beam irradiation is 12 kGy;

[0234] The additives include 0.1 wt% antioxidant 1010 and 0.5 wt% calcium stearate;

[0235] The die head temperature of the five-layer co-extrusion device is 400 °C, and the bonding between layers is enhanced through a maleic anhydride grafted polypropylene casting film. The grafting rate of the maleic anhydride grafted polypropylene is 1.5%, and the addition amount is 1% of the total thickness between layers;

[0236] The fluorinated carbon nanotubes are treated by CF4 plasma, the treatment power is 50 W, and the treatment time is 10 min.

[0237] The preparation method of the phase change microcapsules comprises: melting and mixing paraffin (CAS No. 8002-74-2) and stearic acid (CAS No. 57-11-4) in a mass ratio of 1:1, then adding them into an aqueous phase containing an emulsifier, and forming a core material emulsion through a high-shear emulsifier; adding a sodium silicate solution as a silica precursor dropwise into the core material emulsion, and carrying out an interfacial hydrolysis and condensation reaction under the catalysis of ammonia water to generate a uniform silica shell layer, obtaining a mixed solution; centrifuging, washing and drying the mixed solution in sequence to obtain the phase change microcapsules. The type of the emulsifier is a composite emulsifier of Span-80 / Tween-80, the mass ratio of Span-80 to Tween-80 is 2:1, the HLB is 12-14, and the emulsifier concentration is 3 wt%. The rotation speed of the high-shear emulsifier is 15,000 rpm, and the emulsification time is 10 min. The pH value of the interfacial hydrolysis and condensation reaction is 9.0-9.5, the reaction temperature is 30 °C, and the reaction time is 2 h; the concentration of the sodium silicate solution is 10 wt%, and tetraethyl orthosilicate is added as an auxiliary precursor, and the mass ratio of tetraethyl orthosilicate to sodium silicate is 1:5.

[0238] Comparative Example 1

[0239] Based on what is disclosed in Example 1, the following modifications are made in this comparative example:

[0240] The outer high-temperature barrier layer 1 is not provided in the layer structure of the film material.

[0241] Comparative Example 2

[0242] Based on what is disclosed in Example 1, the following modifications are made in this comparative example:

[0243] The gradient transition layer 2 is not provided in the layer structure of the film material.

[0244] Comparative Example 3

[0245] Based on what is disclosed in Example 1, the following modifications are made in this comparative example:

[0246] The intermediate tear-resistant barrier layer 3 is not provided in the layer structure of the film material.

[0247] Comparative Example 4

[0248] Based on what is disclosed in Example 1, the following modifications are made in this comparative example:

[0249] The inner adhesive layer 4 is not provided in the layer structure of the film material.

[0250] The film materials obtained in Examples 1-3 and Comparative Examples 1-4 for power battery encapsulation are subjected to performance measurement, and the results are shown in Table 1. The specific performance measurement method is as follows:

[0251] Thermal decomposition temperature: Using thermogravimetric analysis (TGA), record the temperature corresponding to a 5% mass loss under a nitrogen atmosphere at a heating rate of 10 °C / min.

[0252] Water and oxygen transmission rate: Use a multi-channel water and oxygen transmission rate test device to simulate the battery packaging environment (85 °C / 85% RH) and test according to the standard of GB / T 21529-2008.

[0253] Tensile strength: According to the standard of ASTM D882, use a universal material testing machine to test the longitudinal / transverse tensile strength at a tensile rate of 50 mm / min.

[0254] Phase change enthalpy: Use a differential scanning calorimeter (DSC) to measure the melting enthalpy of the core material at a heating rate of 5 °C / min.

[0255] Table 1 Performance of the film materials for power battery packaging in Examples 1-3 and Comparative Examples 1-4

[0256]

[0257] As can be seen from Table 1, the thermal decomposition temperature of the film materials in Examples 1-3 ≥ 400 °C, the water and oxygen transmission rate ≤ 0.01 g / (m 2 ·day), the tensile strength ≥ 80 MPa, the puncture strength ≥ 500 N / mm, the interlayer peel strength ≥ 8 N / 15 mm, the phase change enthalpy ≥ 120 J / g, and the high-temperature buffer time extension rate ≥ 30%. Through the multi-layer composite design, the examples achieved the synergistic optimization of thermal stability, mechanical strength and interfacial bonding, meeting the high-standard requirements for power battery packaging.

[0258] In Comparative Example 1, the PEEK substrate and fluorinated carbon nanotubes were missing, and only relying on HDPE (melting point ~ 130 °C) led to accelerated thermal degradation, poor thermal stability and weak water and oxygen barrier properties.

[0259] In Comparative Example 2, the gradient transition layer was missing, heat could not be evenly diffused, local heat accumulation damaged the phase change buffer, the heat distribution was uneven, and the utilization rate of the phase change material was low.

[0260] In Comparative Example 3, the SiO2 / PVDF coating and phase change microcapsules were missing, and only the flexibility of EVA could not resist the battery expansion stress, resulting in insufficient mechanical strength and easy puncture and rupture.

[0261] In Comparative Example 4, the irradiated cross-linked EVA layer was missing, and only maleic anhydride grafted PP was relied on between layers, which could not resist the corrosion of the electrolyte, resulting in poor interfacial bonding force and easy delamination failure.

[0262] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and the individual values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and the individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0263] In addition, in the description of the specification of the present application, the terms "comprising", "including", etc. mean "including but not limited to". In this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0264] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A film material for power battery packaging, characterized in that, The layer structure of the film material is as follows from the outside to the inside: an outer high temperature resistant barrier layer, a gradient transition layer, an intermediate tear resistant barrier layer and an inner adhesive layer; wherein, The outer high temperature resistant barrier layer is composed of a polyetheretherketone substrate, nano silicon dioxide, nano aluminum oxide and fluorinated carbon nanotubes; The gradient transition layer is composed of a gradient spinning fiber layer of nano-aluminum oxide and polyimide; The middle tear-resistant barrier layer is a high-density polyethylene layer with a nano-silicon dioxide / polyvinylidene fluoride composite coating on the surface, and phase-change microcapsules are embedded in the high-density polyethylene layer; The inner adhesive layer is a radiation cross-linked ethylene-vinyl acetate copolymer layer.

2. The film material according to claim 1, wherein The thickness of the outer high temperature resistant barrier layer is 50 to 80 μm; The thickness of the gradient transition layer is 20 to 30 μm; The thickness of the intermediate tear-resistant barrier layer is 80 to 120 μm; The thickness of the inner adhesive layer is 30-50 μm.

3. The film material according to claim 1, wherein The mass of the nano silicon dioxide is 5-8% of the mass of the outer high temperature resistant barrier layer; The mass of the nano-alumina is 3-5% of the mass of the outer high temperature resistant barrier layer; The mass of the fluorinated carbon nanotubes is 1-3% of the mass of the outer high temperature resistant barrier layer.

4. The film material according to claim 3, characterized in that, The fluorinated carbon nanotubes are treated with CF4 plasma, and the surface fluorination rate of the fluorinated carbon nanotubes is 30-50%; The particle size of the nano silicon dioxide is 30 to 50 nm; The particle size of the nano-alumina is 40-60 nm.

5. The film material according to claim 1, characterized in that, The gradient spinning fiber layer is composed of an outer layer, a middle layer and an inner layer formed by layer deposition through an electrospinning process; wherein, The nano-alumina content of the outer layer is 4-6%, the thickness of the outer layer is 8-12 μm, and the pore size of the outer layer is 180-200 nm; The nano-alumina content of the intermediate layer is 8-12%, the thickness of the intermediate layer is 7-10 μm, and the pore size of the intermediate layer is 80-100 nm; The nano aluminum oxide content of the inner layer is 13-17%, the thickness of the inner layer is 5-8 μm, and the pore size of the inner layer is 40-60 nm.

6. The film material according to claim 1, characterized in that, The thickness of the nano-silicon dioxide / polyvinylidene fluoride composite coating is 2 to 5 μm, and the mass ratio of the nano-silicon dioxide to the polyvinylidene fluoride is 1:(4 to 6); The particle size of the phase-change microcapsule is 100-200nm, the core material is a paraffin / stearic acid compound, the shell material is nano silicon dioxide, and the thickness of the shell material is 20-40nm.

7. The film material according to claim 1, wherein The mass fraction of vinyl acetate in the molecular chain of the ethylene-vinyl acetate copolymer is 5-40%.

8. A method for preparing the film material according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: S1. Melt-blending the polyetheretherketone substrate, nano-silicon dioxide, nano-alumina and carbon nanotubes through a twin-screw extruder, and then hot-pressing to obtain the outer high-temperature resistant barrier layer; S2, dissolving nano-aluminum oxide and polyimide in a solvent in a gradient ratio, and then sequentially depositing an outer layer, a middle layer and an inner layer through multi-nozzle electrospinning to obtain the gradient transition layer; S3, dispersing the phase change microcapsules in a high-density polyethylene melt, and coating the surface of the high-density polyethylene after cooling to form a nano-silicon dioxide / polyvinylidene fluoride composite coating to obtain an intermediate tear-resistant barrier layer; S4. Mix vinyl acetate, ethylene resin and additives and extrude them, then carry out radiation crosslinking by electron beam irradiation to form a three-dimensional crosslinked network, and perform hot pressing to obtain the inner adhesive layer; S5. Using a five-layer coextrusion device, form a four-layer structure of the outer high-temperature resistant barrier layer, the gradient transition layer, the intermediate tear-resistant barrier layer and the inner adhesive layer at one time, and enhance the bonding between each layer by maleic anhydride grafted polypropylene to obtain a film material for power battery encapsulation.

9. The method according to claim 8, characterized in that The temperature of the melt blending is 380 - 400 °C; In the electrospinning process, the concentration of the spinning solution is 15 - 20 wt%, the diameter of the nozzle is 0.3 - 0.5 mm, the receiving distance is 15 - 20 cm, and the voltage is 20 - 25 kV; The dose of the electron beam irradiation is 12 - 15 kGy; The additives include 0.1 - 0.5 wt% of antioxidant 1010 and 0.5 - 1.0 wt% of calcium stearate; The die head temperature of the five-layer coextrusion device is 380 - 400 °C, and the bonding between layers is enhanced by maleic anhydride grafted polypropylene casting film. The grafting rate of the maleic anhydride grafted polypropylene is 1.0 - 1.5%, and the addition amount is 1 - 2% of the total thickness between layers; The fluorinated carbon nanotubes are treated by CF4 plasma, the treatment power is 50 - 100 W, and the treatment time is 10 - 20 min.

10. The method according to claim 8, wherein The preparation method of the phase change microcapsules includes: Melt and mix paraffin and stearic acid in a mass ratio of 1:1, then add them to the aqueous phase containing an emulsifier, and form a core material emulsion by a high-shear emulsifier; Dropwise add a sodium silicate solution as a silica precursor to the core material emulsion, and carry out an interfacial hydrolysis and condensation reaction under the catalysis of ammonia water to generate a uniform silica shell layer to obtain a mixed solution; Centrifuge, wash and dry the mixed solution in sequence to obtain the phase change microcapsules.

Images