Battery cell soft packaging film and preparation process thereof

Abstract

This invention relates to the field of lithium battery packaging materials technology, and discloses a flexible packaging film for battery cells and its preparation process. The flexible packaging film comprises a protective outer layer, a first adhesive layer, an aluminum foil layer, a second adhesive layer, and a heat-sealing inner layer stacked sequentially, wherein a corrosion-resistant bonding layer is disposed between the aluminum foil layer and the second adhesive layer. The corrosion-resistant bonding layer is formed by curing and cross-linking a coating liquid containing a surface-functionalized graphene oxide-supported nano-layered zirconium phosphate composite on the surface of the aluminum foil. The heat-sealing inner layer is a multilayer co-extruded functional polypropylene film layer comprising an adhesive transition layer, a support layer, and a heat-sealing layer. By constructing a corrosion-resistant bonding layer at the aluminum foil interface and optimizing the multilayer structural design of the heat-sealing inner layer, the stability of the aluminum-plastic composite interface, the heat-sealing reliability, and the overall mechanical compatibility can be improved, thereby improving the comprehensive performance of the flexible packaging film for battery cells under high temperature, high humidity, and electrolyte contact conditions, making it suitable for the packaging of power batteries and energy storage batteries.

Description

Technical Field

[0001] This invention relates to the field of packaging film technology, specifically to a flexible packaging film for battery cells and its preparation process. Background Technology

[0002] With the rapid development of power batteries, consumer lithium-ion batteries, and energy storage batteries, flexible packaging films for battery cells, as key materials in battery packaging systems, directly affect the safety, cycle life, and service stability of battery products due to their barrier performance, interfacial bonding stability, resistance to electrolyte corrosion, and heat-sealing reliability. Existing flexible packaging films typically employ a multi-layered composite structure consisting of a protective outer layer, an adhesive layer, an aluminum foil layer, and a heat-sealing inner layer. The aluminum foil layer plays a crucial role in blocking moisture and oxygen, while the heat-sealing inner layer is responsible for sealing the battery and isolating the internal media. However, as battery energy density continues to increase and operating environments become increasingly complex, traditional flexible packaging films are gradually showing shortcomings in areas such as aluminum foil interfacial corrosion protection, interlayer adhesion stability, and the mechanical compatibility of the heat-sealing inner layer.

[0003] Chinese patent CN111331988B discloses a flexible packaging film for battery cells. It employs a multi-layered composite structure consisting of a nylon layer, an aluminum foil layer, and a heat-sealing layer. A corrosion-resistant layer is formed on the surface of the aluminum foil. A composite protective layer composed of an EVA film layer, a TPX film layer, and a non-woven fabric layer is introduced between the aluminum foil and the heat-sealing side. This layer protects the corrosion-resistant layer during the battery packaging stamping process, reducing the risk of cracking and damage. The core idea is to improve the packaging film's impact resistance, lifespan, and battery safety while maintaining resistance to moisture, acid corrosion, and heat sealing performance through the composite protective layer and the raised structure of the non-woven fabric.

[0004] Chinese patent CN103840097B discloses a flexible packaging film for lithium-ion battery cells and a battery. This flexible packaging film includes a protective layer between an aluminum foil layer and a sealing layer. The protective layer can be formed by one or more combinations of a chromium layer, a thermosetting polyacrylate layer, and a polyvinylidene chloride layer. This layer prevents electrolyte penetration and corrosion of the aluminum foil and reduces interlayer peeling, thereby improving the lifespan of the packaging film and battery performance. Furthermore, this design emphasizes minimizing the use of adhesives between the sealing layer and the aluminum foil layer to reduce the risk of electrolyte contamination. Different combinations of protective layers can be selected to balance corrosion resistance, impact resistance, and sealing stability according to different application requirements.

[0005] However, in existing technologies, the bonding between the aluminum foil and the inner adhesive layer typically relies on conventional adhesives. But under high temperature, high humidity, or long-term electrolyte immersion environments, this interface is prone to adhesion degradation, localized corrosion propagation, and interlayer failure. Especially during long-term battery charging and discharging, once the aluminum foil interface is eroded by corrosive media, the bonding performance between the composite layers easily deteriorates, thus affecting the overall sealing performance and structural integrity of the packaging film. At the same time, traditional single-layer heat-sealing inner layer designs or inner layer designs with unclear structural functions often struggle to simultaneously achieve heat-sealing properties, flexibility, puncture resistance, and interfacial transition stability with the composite structure, limiting further improvements in the overall performance of flexible packaging films.

[0006] Therefore, there is an urgent need to provide a flexible battery cell packaging film and its preparation process that can take into account the corrosion resistance protection of the aluminum foil interface, the stability of interlayer bonding and the synergy of the heat-sealing inner layer structure, so as to meet the requirements of high-performance lithium battery packaging materials for long-term reliability and adaptability to complex working conditions. Summary of the Invention

[0007] To address the aforementioned deficiencies, this invention provides the following technical solution: a flexible packaging film for battery cells, comprising a protective outer layer, a first adhesive layer, an aluminum foil layer, a second adhesive layer, and a heat-sealing inner layer stacked sequentially, wherein a corrosion-resistant bonding layer is further provided between the aluminum foil layer and the second adhesive layer; The heat-sealing inner layer is a multi-layer co-extruded functional polypropylene film layer, comprising an adhesive transition layer, a support layer, and a heat-sealing layer arranged sequentially. The corrosion-resistant bonding layer is formed by a coating liquid containing surface-functionalized graphene oxide-supported nano-layered phosphophosphate composite on the surface of aluminum foil through a curing and cross-linking reaction. If the outer protective layer is set as the outer layer, then the outer protective layer, the first adhesive layer, the aluminum foil layer, the second adhesive layer and the heat-sealing inner layer included in the battery cell soft packaging film are stacked sequentially from the outside to the inside, and the bonding transition layer, the support layer and the heat-sealing layer included in the heat-sealing inner layer are also sequentially arranged from the outside to the inside.

[0008] Furthermore, the total solid content of the coating solution is 5%-15%, and the coating solution is a uniform mixture of surface-functionalized graphene oxide-supported nano-layered phosphophosphate composite and deionized water. The raw materials for preparing the surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite, by weight, include: 8-15 parts of graphene oxide, 15-35 parts of nanolayered zirconium phosphate, 2-6 parts of aminosilane coupling agent, 100-250 parts of ethanol-water mixed solvent, 0.2-1.0 parts of acidic catalyst, and 1-5 parts of n-propylamine as an intercalation aid; the ethanol-water mixed solvent is a mixture of anhydrous ethanol and deionized water with a volume ratio of 7:3. The graphene oxide has a lateral sheet diameter of 2-10 μm; the nano-layered zirconium phosphate has an average particle size of 30-120 nm. The silane coupling agent is selected from at least one of vinyltriethoxysilane, vinyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropyltriethoxysilane. The acidic catalyst is selected from at least one of acetic acid, formic acid, citric acid, and lactic acid.

[0009] Furthermore, the preparation method of the surface-functionalized graphene oxide-supported nanolayered phosphophosphate composite includes the following steps: M1. Add the graphene oxide of the specified weight to 50-80 parts of ethanol-water mixed solution to prepare a dispersion with a concentration of 0.5%-2.0%, and then ultrasonically disperse for 30-60 minutes to obtain a uniform graphene oxide dispersion. M2. Add the aminosilane coupling agent and the acidic catalyst of the weight component to the graphene oxide dispersion, and react at 40-60℃ for 1-3 hours under pH 4.5-5.5 conditions to allow the aminosilane to be grafted onto the graphene oxide surface to obtain surface-functionalized graphene oxide. M3. Add the nano-layered zirconium phosphate of the weight component to the remaining ethanol-water mixed solution, and add n-propylamine of the weight component as an intercalation aid. Stir and react at 50-80°C for 2-6 hours to allow the layered zirconium phosphate to intercalate and partially exfoliate, and obtain an exfoliated nano-layered zirconium phosphate slurry. M4. Mix the surface-functionalized graphene oxide dispersion obtained in step M2 with the exfoliated nano-layered zirconium phosphate slurry obtained in step M3, stir at room temperature to 70°C for 2-5 hours, and then ultrasonically disperse for 10-30 minutes to combine the two. M5. The resulting mixture is centrifuged, washed, and vacuum dried at 50-80℃ for 6-12 hours to obtain a surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite.

[0010] Furthermore, the heat-sealing layer is prepared by blending ethylene-propylene random copolymer polypropylene with olefin block copolymer, wherein the blending mass ratio of ethylene-propylene random copolymer polypropylene with olefin block copolymer is (70-90):(10-30); The support layer is made of homopolymer polypropylene and ethylene-octene polyolefin elastomer, and the amount of ethylene-octene polyolefin elastomer added is 8-18% of the total mass of the support layer; The bonding transition layer is prepared by blending maleic anhydride-grafted polypropylene bonding resin with ethylene-propylene random copolymer polypropylene, wherein the mass percentage of the maleic anhydride-grafted polypropylene bonding resin is 35-60%.

[0011] Furthermore, the olefin block copolymer is selected from at least one of ethylene-1-octene block copolymer, ethylene-1-butene block copolymer, and ethylene-1-hexene block copolymer.

[0012] Furthermore, the thickness of the heat-sealing layer is 5-15 μm, the thickness of the support layer is 15-30 μm, the thickness of the bonding transition layer is 5-10 μm, and the total thickness of the heat-sealing inner layer is 30-55 μm.

[0013] Furthermore, the protective outer layer is a polyamide film or a polyethylene terephthalate film, and the thickness of the protective outer layer is 15-30 μm; The aluminum foil layer is 8021 aluminum alloy foil or 8079 aluminum alloy foil, with a thickness of 30-50μm and a surface roughness Ra controlled at 0.08-0.15μm.

[0014] Furthermore, both the first adhesive layer and the second adhesive layer are two-component solvent-free polyurethane adhesives; wherein the second adhesive layer contains 3-8% by mass of terminal hydroxyl hyperbranched polyester based on the total mass of the second adhesive, to enhance high-temperature bonding strength.

[0015] This application also provides a process for preparing the flexible packaging film for battery cells as described above, comprising the following steps: 1) Use 500-800W plasma to degrease and clean the surface of aluminum foil at a speed of 10-20m / min to obtain an aluminum foil layer with a grease-free first side surface and a grease-free second side surface. 2) A coating solution with a solid content of 5-15% is prepared by uniformly mixing surface-functionalized graphene oxide-supported nanolayered phosphophosphate composite with deionized water. This coating solution is then uniformly applied to the grease-free first side surface of the aluminum foil layer, with a coating amount of 0.5-1.5 g / m². 2 The curing reaction is carried out at 80-120℃ for 20-60 seconds, forming a corrosion-resistant bonding layer on the grease-free first side surface of the aluminum foil layer; 3) The raw materials for the heat-sealing layer, the support layer, and the bonding transition layer are melted and plasticized by three extruders, then extruded together through a multi-layer co-extrusion die, and finally cast into a multi-layer co-extruded functional polypropylene film layer. 4) Dry lamination: The corrosion-resistant bonding layer on the grease-free first side surface of the protective outer layer and the aluminum foil layer is laminated with the first adhesive layer. The bonding transition layer prepared in step 3) is laminated with the second side surface of the aluminum foil layer with the second adhesive layer. After curing, the battery cell soft packaging film is obtained. The curing conditions are: temperature 40-60℃, relative humidity 50-70%RH, curing time 72-96h.

[0016] Furthermore, in step 3), the temperatures of the raw materials for preparing the heat-sealing layer in the feeding section, compression section, and metering section of the first extruder are controlled to be 170-185℃, 180-200℃, and 190-210℃, respectively. The temperatures of the raw materials for the support layer in the feeding section, compression section and metering section of the second extruder are controlled at 180-195℃, 190-215℃ and 200-230℃, respectively. The temperatures of the raw materials for preparing the bonding transition layer in the feeding section, compression section and metering section of the third extruder are controlled at 175-190℃, 185-205℃ and 195-220℃, respectively. When the molten heat-sealing layer, the molten support layer, and the molten bonding transition layer are brought together through a multi-layer co-extrusion die, the die temperature is controlled at 190-230℃ and the melt pressure is controlled at 8-20MPa. Then, the melt is cooled and shaped by a casting cooling roller at 20-50℃ to produce a multi-layer co-extruded functional polypropylene film layer.

[0017] The beneficial effects of this invention are as follows: 1. This application establishes a corrosion-resistant bonding layer between the aluminum foil layer and the second adhesive layer, and constructs an interface protection system using surface-functionalized graphene oxide-supported nano-layered zirconium phosphate composite. This allows the bonding layer to not only form a relatively dense and stable covering structure on the aluminum foil surface, but also enhances interface barrier properties and corrosion resistance. Compared to solutions that rely solely on conventional adhesives for aluminum foil bonding, this application more effectively slows down the penetration of corrosive media into the aluminum foil interface, improving the interface stability of the composite structure in high-temperature, high-humidity, and electrolyte contact environments.

[0018] 2. This application designs the heat-sealing inner layer as a multilayer co-extruded functional polypropylene film layer composed of an adhesive transition layer, a support layer, and a heat-sealing layer. Different layers respectively undertake the functions of heat-sealing response, mechanical support, and interface transition, thereby achieving a better division of labor and synergy in the material properties of the heat-sealing inner layer. This structure is beneficial for balancing the heat-sealing strength, puncture resistance, and flexibility required for encapsulation, and improves the modulus matching between the heat-sealing inner layer and the outer composite layer, reducing the risk of interlayer instability caused by stress concentration.

[0019] 3. This application combines a corrosion-resistant bonding layer design with a multi-layer co-extruded heat-sealing inner layer design, optimizing both the interface protection capability and internal structural matching capability of the flexible packaging film. This solution not only improves the overall composite strength and reliability of the flexible packaging film, but also helps to improve its sealing retention capability and structural integrity during long-term battery service, making it more suitable for power batteries and energy storage batteries where high packaging stability is required. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] All chemical reagents used in the embodiments of this application are commercially available. For example, the ethylene-propylene random copolymer polypropylene (PP-R) was ExxonMobil product LNX-299 purchased from Wuxi Xinjia Chemical Co., Ltd. The ethylene-octene polyolefin elastomer was ENGAGE purchased from Ningbo Huangxuan Plastics Technology Co., Ltd. TM 8842 is a Dow Chemical POE ethylene-butene polymer. The homopolymer polypropylene was purchased from Suzhou Chenzhituo Polymer Materials Co., Ltd., with the grade PPH-Y16.

[0022] Example 1 This embodiment provides a flexible packaging film for battery cells, comprising a protective outer layer, a first adhesive layer, an aluminum foil layer, a second adhesive layer, and a heat-sealing inner layer stacked sequentially, wherein a corrosion-resistant bonding layer is further provided between the aluminum foil layer and the second adhesive layer; The heat-sealing inner layer is a multi-layer co-extruded functional polypropylene film layer, comprising an adhesive transition layer, a support layer, and a heat-sealing layer arranged sequentially. The corrosion-resistant bonding layer is formed by a coating liquid containing surface-functionalized graphene oxide-supported nanolayered phosphophosphate composite, which is cured and crosslinked on the surface of aluminum foil.

[0023] If the outer protective layer is set as the outer layer, then the outer protective layer, the first adhesive layer, the aluminum foil layer, the second adhesive layer and the heat-sealing inner layer included in the battery cell soft packaging film are stacked sequentially from the outside to the inside, and the bonding transition layer, the support layer and the heat-sealing layer included in the heat-sealing inner layer are also sequentially arranged from the outside to the inside.

[0024] In this embodiment, the heat-sealing layer has a thickness of 15 μm, the support layer has a thickness of 30 μm, the bonding transition layer has a thickness of 10 μm, and the total thickness of the heat-sealing inner layer is 55 μm.

[0025] The raw materials used in this embodiment for preparing the surface-functionalized graphene oxide-supported nano-layered zirconium phosphate composite are as follows: By weight, weigh 8 parts of graphene oxide with a transverse sheet diameter of 6 μm, 25 parts of nano-layered zirconium phosphate with an average particle size of 75 nm, 6 parts of aminosilane coupling agent, 0.2 parts of acid catalyst, 3 parts of n-propylamine, and 180 parts of ethanol-water mixed solvent, wherein the volume ratio of anhydrous ethanol to deionized water is 7:3.

[0026] The preparation method of surface-functionalized graphene oxide-supported nano-layered zirconium phosphate composite is as follows: M1. First, add 8 parts of the above-mentioned transverse graphene oxide to 50 parts of ethanol-water mixed solution to prepare a dispersion with a concentration of 1.2%. After ultrasonic dispersion for 45 minutes, a uniform graphene oxide dispersion is obtained. M2: Add 6 parts of aminosilane coupling agent and 0.2 parts of acidic catalyst to the graphene oxide dispersion, adjust the pH to 4.5, and react at 60℃ for 2h to allow aminosilane to be grafted onto the graphene oxide surface to obtain surface-functionalized graphene oxide. M3. Add 25 parts of the above-mentioned nano-layered zirconium phosphate with an average particle size of 75 nm to the remaining 130 parts of ethanol-water mixed solution, and add 3 parts of n-propylamine. Stir and react at 65°C for 2 hours to allow the layered zirconium phosphate to intercalate and partially exfoliate, and obtain an exfoliated nano-layered zirconium phosphate slurry. M4: The surface-functionalized graphene oxide dispersion obtained in step M2 is mixed with the exfoliated nano-layered zirconium phosphate slurry obtained in step M3, stirred at 70°C for 2 hours, and then ultrasonically dispersed for 10 minutes to combine the two.

[0027] M5. The resulting mixture was centrifuged, washed, and vacuum dried at 65°C for 9 h to obtain a surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite.

[0028] In this embodiment, the heat-sealing layer is made by blending ethylene-propylene random copolymer polypropylene and olefin block copolymer at a mass ratio of 80:20; the olefin block copolymer is ethylene-1-octene block copolymer. The support layer is made by blending homopolymer polypropylene and ethylene-octene polyolefin elastomer, wherein the ethylene-octene polyolefin elastomer accounts for 18% of the total mass of the support layer. The bonding transition layer is made by blending maleic anhydride-grafted polypropylene adhesive resin and ethylene-propylene random copolymer polypropylene, wherein the maleic anhydride-grafted polypropylene adhesive resin accounts for 45% of the total mass of the bonding transition layer. The protective outer layer is a 24 μm thick polyethylene terephthalate film, and the aluminum foil layer is a 40 μm thick 8079 aluminum alloy foil with a surface roughness Ra of 0.12 μm.

[0029] Both the first adhesive layer and the second adhesive layer use a two-component solvent-free polyurethane adhesive, wherein the second adhesive layer contains 5% by weight of terminal hydroxyl hyperbranched polyester based on the total mass of the second adhesive.

[0030] This embodiment provides a process for preparing a flexible packaging film for battery cells, including the following steps: 1) Surface treatment was performed on 8079 aluminum alloy foil with a thickness of 40μm and a surface roughness Ra of 0.12μm. The plasma power was 650W and the processing speed was 15m / min. The resulting aluminum foil had a grease-free first side surface and a grease-free second side surface. 2) The surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite prepared in this embodiment was uniformly mixed with deionized water to obtain a coating solution with a total solid content of 10%. The coating solution was then uniformly coated onto the grease-free first side surface of the aluminum foil, with a coating amount of 1.0 g / m². 2 Curing at 100℃ for 40 seconds forms a corrosion-resistant bonding layer; 3) The heat-sealing layer material in this embodiment is added to the first extruder, and the temperatures of its feeding section, compression section, and metering section are set to 178°C, 190°C, and 200°C, respectively; the support layer material in this embodiment is added to the second extruder, and the temperatures of its feeding section, compression section, and metering section are set to 188°C, 202°C, and 215°C, respectively; the bonding transition layer material in this embodiment is added to the third extruder, and the temperatures of its feeding section, compression section, and metering section are set to 183°C, 195°C, and 208°C, respectively. The molten heat-sealing layer, the molten support layer, and the molten bonding transition layer (three melts) are combined in a multi-layer co-extrusion die at 210°C. The melt pressure is controlled at 14MPa. The melt is then cooled and shaped by a 35°C casting cooling roller to obtain a multi-layer co-extruded functional polypropylene film layer with a heat-sealing layer thickness of 15μm, a support layer thickness of 30μm, a bonding transition layer thickness of 10μm, and a total heat-sealing inner layer thickness of 55μm as the heat-sealing layer. 4) The protective outer layer (a 24μm thick polyethylene terephthalate film) is bonded to the corrosion-resistant bonding layer on the grease-free first side surface of the aluminum foil layer using a first adhesive layer; then the obtained bonding transition layer is bonded to the grease-free second side surface of the aluminum foil layer using a second adhesive layer; after bonding, it is cured at 50℃ and 60% relative humidity (RH) for 84 hours to obtain the battery cell soft packaging film.

[0031] Example 2 This embodiment provides a flexible packaging film for battery cells. The packaging film structure, raw materials, and manufacturing process of this embodiment are described in steps one through four below: I. Preparation of Surface-Functionalized Graphene Oxide Supported Nanolayered Zirconium Phosphate Composites By weight, 12 parts of graphene oxide with a transverse sheet diameter of 2 μm, 35 parts of nano-layered zirconium phosphate with an average particle size of 120 nm, 2 parts of aminosilane coupling agent, 0.6 parts of acid catalyst, 5 parts of n-propylamine, and 100 parts of ethanol-water mixed solvent were weighed, wherein the volume ratio of anhydrous ethanol to deionized water was 7:3.

[0032] The specific preparation method of surface-functionalized graphene oxide-supported nano-layered zirconium phosphate composite includes the following steps: M1. First, add 12 parts of graphene oxide to 65 parts of ethanol-water mixed solution to prepare a dispersion with a concentration of 2.0%. After ultrasonic dispersion for 30 minutes, a uniform graphene oxide dispersion is obtained. M2. Add 2 parts of aminosilane coupling agent and 0.6 parts of acidic catalyst to the graphene oxide dispersion, adjust the pH to 5.5, and react at 50℃ for 1 h to allow aminosilane to be grafted onto the graphene oxide surface to obtain surface-functionalized graphene oxide. M3. Add 35 parts of nano-layered zirconium phosphate to the remaining 35 parts of ethanol-water mixed solution, and add 5 parts of n-propylamine. Stir and react at 80°C for 4 hours to allow the layered zirconium phosphate to intercalate and partially exfoliate, thus obtaining an exfoliated nano-layered zirconium phosphate slurry.

[0033] M4. The surface-functionalized graphene oxide dispersion obtained in step M2 above is mixed with the exfoliated nano-layered zirconium phosphate slurry prepared in step M3. The mixture is stirred at 25°C for 5 hours and then ultrasonically dispersed for 20 minutes to combine the two. M5. The resulting mixture was centrifuged, washed, and vacuum dried at 50°C for 12 h to obtain a surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite.

[0034] II. Construction of Corrosion-Resistant Bonding Layer The above-mentioned composite was uniformly mixed with deionized water to prepare a coating solution with a total solid content of 5%. Surface treatment was performed on an 8021 aluminum alloy foil with a thickness of 50 μm and a surface roughness Ra of 0.08 μm. The plasma power was 800 W and the processing speed was 10 m / min, resulting in an aluminum foil layer with a grease-free first side surface and a grease-free second side surface.

[0035] The coating liquid is uniformly coated onto the grease-free first surface of the aluminum foil, with a coating amount of 1.5 g / m². 2 It is cured at 80℃ for 60 seconds to form a corrosion-resistant bonding layer.

[0036] III. Preparation of the heat-sealed inner layer The heat-sealing layer is made by blending ethylene-propylene random copolymer polypropylene and olefin block copolymer at a mass ratio of 90:10; the support layer is made by blending homopolymer polypropylene and ethylene-octene polyolefin elastomer, wherein the amount of ethylene-octene polyolefin elastomer added is 8% of the total mass of the support layer; the bonding transition layer is made by blending maleic anhydride-grafted polypropylene adhesive resin and ethylene-propylene random copolymer polypropylene, wherein the maleic anhydride-grafted polypropylene adhesive resin accounts for 60% of the total mass of the bonding transition layer.

[0037] The heat-sealing layer material is added to the first extruder, and the temperatures of its feeding section, compression section, and metering section are set to 170℃, 200℃, and 190℃, respectively. The support layer material is added to the second extruder, and the temperatures of its feeding section, compression section, and metering section are set to 195℃, 190℃, and 230℃, respectively. The bonding transition layer material is added to the third extruder, and the temperatures of its feeding section, compression section, and metering section are set to 175℃, 205℃, and 195℃, respectively.

[0038] The three melts converge in a multi-layer co-extrusion die at 230°C, with the melt pressure controlled at 8MPa. The melts are then cooled and shaped by a 50°C casting cooling roller to produce a multi-layer co-extruded functional polypropylene film layer. The heat-sealing layer has a thickness of 10μm, the support layer has a thickness of 20μm, the bonding transition layer has a thickness of 5μm, and the total thickness of the heat-sealed inner layer is 35μm.

[0039] IV. Dry compounding A 15μm thick polyamide film was selected as the protective outer layer. Both the first and second adhesive layers used a two-component solvent-free polyurethane adhesive, with 3% by weight of terminal hydroxyl hyperbranched polyester added to the second adhesive layer.

[0040] The corrosion-resistant bonding layer between the protective outer layer and the grease-free first side surface of the aluminum foil layer is bonded together with a first adhesive layer; then the obtained bonding transition layer is bonded together with the grease-free second side surface of the aluminum foil layer with a second adhesive layer; after bonding, it is cured for 72 hours at 60°C and 50% relative humidity (RH) to obtain the battery cell soft packaging film.

[0041] Example 3 This embodiment provides a flexible packaging film for battery cells. The packaging film structure, raw materials, and manufacturing process of this embodiment are described in steps one through four below: I. Preparation of Surface-Functionalized Graphene Oxide Supported Nanolayered Zirconium Phosphate Composites By weight, 15 parts of graphene oxide with a transverse sheet diameter of 10 μm, 15 parts of nano-layered zirconium phosphate with an average particle size of 30 nm, 4 parts of aminosilane coupling agent, 1.0 part of acidic catalyst, 1 part of n-propylamine, and 250 parts of ethanol-water mixed solvent were weighed, wherein the volume ratio of anhydrous ethanol to deionized water was 7:3.

[0042] The specific preparation method of surface-functionalized graphene oxide-supported nano-layered zirconium phosphate composite includes the following steps: M1. First, add 15 parts of graphene oxide to 80 parts of ethanol-water mixed solution to prepare a dispersion with a concentration of 0.5%. After ultrasonic dispersion for 60 minutes, a uniform graphene oxide dispersion is obtained. M2. Add 4 parts of aminosilane coupling agent and 1.0 part of acidic catalyst to the graphene oxide dispersion, adjust the pH to 5.0, and react at 40℃ for 3h to allow aminosilane to be grafted onto the graphene oxide surface to obtain surface-functionalized graphene oxide. M3. Add 15 parts of nano-layered zirconium phosphate to the remaining 170 parts of ethanol-water mixed solution, and add 1 part of n-propylamine. Stir and react at 50°C for 6 hours to allow the layered zirconium phosphate to intercalate and partially exfoliate, and obtain an exfoliated nano-layered zirconium phosphate slurry. M4. The surface-functionalized graphene oxide dispersion prepared in step M2 is mixed with the exfoliated nano-layered zirconium phosphate slurry prepared in step M3. The mixture is stirred at 45°C for 3.5 h and then ultrasonically dispersed for 30 min to combine the two. M5. The resulting mixture was centrifuged, washed, and vacuum dried at 80°C for 6 hours to obtain a surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite.

[0043] II. Construction of Corrosion-Resistant Bonding Layer The surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite prepared in step one above was uniformly mixed with deionized water to obtain a coating solution with a total solid content of 15%. Surface treatment was performed on 30 μm thick 8021 aluminum alloy foil with a surface roughness Ra of 0.15 μm using a plasma power of 500 W and a processing speed of 20 m / min. The coating solution was then uniformly coated onto the grease-free first side surface of the aluminum foil, with a coating amount of 0.5 g / m². 2 It is cured at 120℃ for 20 seconds to form a corrosion-resistant bonding layer.

[0044] III. Preparation of the heat-sealed inner layer The heat-sealing layer is made from a blend of ethylene-propylene random copolymer polypropylene and olefin block copolymer at a mass ratio of 70:30; the olefin block copolymer is selected as ethylene-1-hexene block copolymer. The support layer is made from a blend of homopolymer polypropylene and ethylene-octene polyolefin elastomer, with the ethylene-octene polyolefin elastomer accounting for 12% of the total mass of the support layer. The bonding transition layer is made from a blend of maleic anhydride-grafted polypropylene adhesive resin and ethylene-propylene random copolymer polypropylene, with the maleic anhydride-grafted polypropylene adhesive resin accounting for 35% of the total mass of the bonding transition layer.

[0045] The heat-sealing layer material is added to the first extruder, and the temperatures of its feeding section, compression section, and metering section are set to 185℃, 180℃, and 210℃, respectively. The support layer material is added to the second extruder, and the temperatures of its feeding section, compression section, and metering section are set to 180℃, 215℃, and 200℃, respectively. The bonding transition layer material is added to the third extruder, and the temperatures of its feeding section, compression section, and metering section are set to 190℃, 185℃, and 220℃, respectively.

[0046] Three melts converge in a multi-layer co-extrusion die at 190°C, with the melt pressure controlled at 20MPa. The melts are then cooled and shaped by a 20°C casting cooling roller to produce a multi-layer co-extruded functional polypropylene film layer. The heat-sealing layer has a thickness of 5μm, the support layer has a thickness of 15μm, the bonding transition layer has a thickness of 10μm, and the total thickness of the heat-sealed inner layer is 30μm.

[0047] IV. Dry compounding A 30μm thick polyamide film was selected as the protective outer layer. Both the first and second adhesive layers used a two-component solvent-free polyurethane adhesive, with 8% by weight of terminal hydroxyl hyperbranched polyester added to the second adhesive layer.

[0048] The protective outer layer and the corrosion-resistant bonding layer on the first side surface of the aluminum foil layer are bonded together with a first adhesive layer; then the obtained bonding transition layer is bonded together with the second side surface of the aluminum foil layer with a second adhesive layer; after bonding, the film is cured at 40°C and 70% relative humidity (RH) for 96 hours to obtain the battery cell soft packaging film.

[0049] Comparative Example 1 This comparative example provides a flexible packaging film for a battery cell, which differs from Example 1 only in the composition of the coating liquid used in the corrosion-resistant bonding layer and its preparation method; the remaining steps are the same as in Example 1.

[0050] I. Preparation of Comparative Coating Solution Instead of using surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composites, 8 parts of graphene oxide with a transverse diameter of 6 μm were directly weighed and mixed with 72 parts of deionized water to prepare a graphene oxide coating solution with a total solid content of 10%. This solution was then ultrasonically dispersed for 45 min before direct use. No aminosilane coupling agent, nanolayered zirconium phosphate, acidic catalyst, or n-propylamine were added during this process. Surface functionalization modification, intercalation exfoliation, and composite drying steps were also omitted.

[0051] II. Construction of Corrosion-Resistant Bonding Layer The above-mentioned graphene oxide coating solution was uniformly coated onto the first side surface of an 8079 aluminum alloy foil with a thickness of 40 μm and a surface roughness Ra of 0.12 μm. The aluminum foil was pretreated with 650W plasma at a speed of 15 m / min before coating. The coating amount was 1.0 g / m². 2 The material is cured at 100°C for 40 seconds to form a bonding layer for contrast.

[0052] III. Preparation and Lamination of Heat-Sealed Inner Layer The bonding transition layer, the first adhesive layer, the second adhesive layer, the protective outer layer, and the final dry lamination process were all the same as in Example 1. After lamination, the film was cured at 50°C and 60%RH for 84 hours to obtain the comparative battery cell soft packaging film.

[0053] Comparative Example 2 This comparative example provides a flexible packaging film for battery cells, which differs from Example 1 only in the heat-sealing inner layer structure; the remaining steps are the same as in Example 1.

[0054] I. Construction of Corrosion-Resistant Bonding Layer Surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composites were prepared using the same method as in Example 2, and a coating solution with a total solid content of 10% was formulated. This coating solution was then applied at a concentration of 1.0 g / m³. 2 The coating amount was applied to the first side surface of a 40μm thick 8079 aluminum alloy foil that had been treated with 650W plasma at a speed of 15m / min, and cured at 100℃ for 40s to form a corrosion-resistant bonding layer.

[0055] II. Preparation of a single-layer heat-sealed inner layer Instead of using a three-layer co-extrusion structure consisting of a bonding transition layer, a support layer, and a heat-sealing layer, a single-layer polypropylene-based heat-sealing inner layer with a thickness of 45 μm is produced by blending ethylene-propylene random copolymer polypropylene and ethylene-octene polyolefin elastomer at a mass ratio of 85:15, followed by melt plasticization in a single extruder and casting. The temperatures of the extruder's feeding section, compression section, and metering section are set to 180℃, 195℃, and 205℃, respectively; the die temperature is set to 210℃; and the casting cooling roller temperature is set to 35℃.

[0056] III. Dry compounding The protective outer layer, the first adhesive layer, and the second adhesive layer are the same as in Example 1, except that 5% of terminal hydroxyl hyperbranched polyester is added to the second adhesive layer based on the total mass of the second adhesive. The protective outer layer is laminated to the corrosion-resistant bonding layer on the first side surface of the aluminum foil layer using the first adhesive layer; then the obtained single-layer heat-sealed inner layer is laminated to the second side surface of the aluminum foil layer using the second adhesive layer; after lamination, it is cured at 50°C and 60%RH for 84 hours to obtain the comparative battery cell soft packaging film.

[0057] The battery cell soft packaging films prepared in Examples 1-3 and Comparative Examples 1-2 were cut into samples of the same size (10cm × 10cm). Each example had 3 independent replicate samples, and the following four tests were performed. The test results are shown in Table 1.

[0058] The testing method is as follows: 1) Initial peel strength: According to GB / T 8808-1988 standard, the peel strength (T-type peel, 300mm / min) between the heat-sealed inner layer (CPP) and the aluminum foil layer (AL) is tested.

[0059] 2) Electrolyte resistance (cohesive failure retention rate): The sample was cut into 15mm wide strips and immersed in an electrolyte solution (1M LiPF6, EC, DEC and DMC in a volume ratio of 1:1:1, containing 1000ppm water) and stored in an 85℃ oven for 7 days. After removal, the peel strength between the heat-sealed inner layer (CPP) and the aluminum foil layer (AL) was tested, and the retention rate from the initial strength was calculated to characterize the risk of interfacial delamination caused by electrolyte erosion.

[0060] 3) Heat seal strength: Place the inner layers of two independent duplicate samples of the same group face to face and heat seal them for 3 seconds at 190℃ and 0.3MPa. Test the heat seal strength according to QB / T 2358-1998.

[0061] 4) Heat-sealing strength swelling retention rate: The heat-sealed sample strip is immersed in the above electrolyte (85℃, 7 days), and its heat-sealing strength is tested after removal. The retention rate with the initial heat-sealing strength is calculated. This indicator, together with the electrolyte peel strength, forms a synergistic verification. The heat-sealing strength swelling retention rate is combined with the electrolyte peel strength to examine the strength of the encapsulation layer and the seal, jointly reflecting the resistance to electrolyte aging.

[0062] 5) Water vapor transmission rate (WVTR): The barrier performance was characterized by testing with an infrared sensor at 38°C and 90%RH.

[0063] Table 1 As can be seen from Table 1, Examples 1 to 3 of this application exhibit consistently high performance across various indicators. Taking the average of the three examples, the initial peel strength reached 12.5 N / 15 mm, significantly higher than Comparative Example 1's 8.5 N / 15 mm and also higher than Comparative Example 2's 12.0 N / 15 mm; the average peel strength retention rate after electrolyte resistance reached 91.3 N / 15 mm, approximately 2.02 times and 1.51 times that of Comparative Example 1 and Comparative Example 2, respectively; and the average water vapor transmission rate was only 0.383 g / (m²). 2The efficiency of this application is approximately 54.9% lower than that of Comparative Example 1 and approximately 14.9% lower than that of Comparative Example 2. This demonstrates that the proposed solution does not merely improve a single indicator, but rather achieves simultaneous improvements in three dimensions: interface stability, aging resistance, and barrier performance.

[0064] The lowest electrolyte peel strength retention rate in the examples was still 88.3%, while Comparative Example 1 was only 45.2% and Comparative Example 2 was 60.5%. The lowest heat seal strength swelling retention rate in the examples was still 85.2%, while Comparative Example 2 was only 42.1%, almost half the lowest value in the examples. This indicates that, in this application, after constructing a corrosion-resistant bonding layer using surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite, not only was the initial bonding ability between the aluminum foil and the inner layer improved, but more importantly, the rate of interface performance degradation after electrolyte erosion was significantly slowed down, transforming the interface bonding from a state prone to instability to a more stable and durable state.

[0065] Meanwhile, the comparison between Comparative Example 2 and Examples 1 to 3 also demonstrates the role of the three-layer co-extruded heat-sealing inner layer structure. Although the initial peel strength of Comparative Example 2 still reached 12.0 N / 15 mm, indicating that it was not completely ineffective in the initial composite state, its initial heat-sealing strength was only 95 N / 15 mm, significantly lower than the lowest value of 108 N / 15 mm in the Example group; after electrolyte aging, its heat-sealing strength retention rate further decreased to 42.1%, while the Example group still maintained 85.2% to 90.5%. In other words, the single-layer inner layer structure can only approach the Example in some initial performance aspects, but once it enters the heat-sealing immersion aging condition, its sealing body stability quickly exposes its shortcomings; in contrast, this application, through the division of labor and synergy of the bonding transition layer, support layer and heat-sealing layer, enables the sealing strength, interlayer stress transfer and interface matching capability to be improved simultaneously, thus better meeting the long-term reliability requirements of the battery cell soft packaging film in actual service environment.

[0066] In summary, a comparison of Examples 1–3 and Comparative Example 1 shows that using surface-functionalized graphene oxide-supported nano-layered zirconium phosphate composite in the corrosion-resistant bonding layer, and constructing a coating solution through graphene oxide surface grafting modification, layered zirconium phosphate intercalation and exfoliation, and the composite construction of the two, enables the bonding layer to form a more stable and denser interfacial coverage structure on the aluminum foil surface. This is beneficial for improving the bonding stability and corrosion resistance between the bonding layer and the aluminum foil. In contrast, the graphene oxide coating without surface functionalization and without the introduction of nano-layered zirconium phosphate exhibits insufficient interfacial synergy, making it difficult to form a composite bonding layer that combines adhesion stability and barrier properties.

[0067] As can be seen from the comparison between Examples 1–3 and Comparative Example 2, the three-layer co-extruded heat-sealing inner layer composed of an adhesive transition layer, a support layer and a heat-sealing layer is conducive to achieving the division of labor and synergy of heat-sealing performance, mechanical support performance and interface adhesion transition performance, thereby improving the overall structural matching and comprehensive performance of the flexible packaging film; while the single-layer polypropylene-based heat-sealing inner layer is difficult to meet the requirements of heat sealing, support and interface transition at the same time.

[0068] While the invention has been described with reference to preferred embodiments, various modifications can be made thereto, and equivalent technical features or parts thereof can be substituted without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no conflict of technical concept. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A flexible packaging film for battery cells, comprising a protective outer layer, a first adhesive layer, an aluminum foil layer, a second adhesive layer, and a heat-sealing inner layer stacked sequentially, characterized in that: A corrosion-resistant bonding layer is also provided between the aluminum foil layer and the second adhesive layer; The heat-sealing inner layer is a multi-layer co-extruded functional polypropylene film layer, comprising an adhesive transition layer, a support layer, and a heat-sealing layer arranged sequentially. The corrosion-resistant bonding layer is formed by a coating liquid containing surface-functionalized graphene oxide-supported nano-layered phosphophosphate composite on the surface of aluminum foil through a curing and cross-linking reaction. If the outer protective layer is set as the outer layer, then the outer protective layer, the first adhesive layer, the aluminum foil layer, the second adhesive layer and the heat-sealing inner layer included in the battery cell soft packaging film are stacked sequentially from the outside to the inside, and the bonding transition layer, the support layer and the heat-sealing layer included in the heat-sealing inner layer are also sequentially arranged from the outside to the inside.

2. The battery cell soft packaging film according to claim 1, characterized in that: The total solids content of the coating solution is 5%-15%, and the coating solution is a uniform mixture of surface-functionalized graphene oxide-supported nano-layered phosphophosphate composite and deionized water. The raw materials for preparing the surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite, by weight, include: 8-15 parts of graphene oxide, 15-35 parts of nanolayered zirconium phosphate, 2-6 parts of aminosilane coupling agent, 100-250 parts of ethanol-water mixed solvent, 0.2-1.0 parts of acidic catalyst, and 1-5 parts of n-propylamine as an intercalation aid; the ethanol-water mixed solvent is a mixture of anhydrous ethanol and deionized water with a volume ratio of 7:

3. The graphene oxide has a lateral sheet diameter of 2-10 μm; the nano-layered zirconium phosphate has an average particle size of 30-120 nm. The silane coupling agent is selected from at least one of vinyltriethoxysilane, vinyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropyltriethoxysilane. The acidic catalyst is selected from at least one of acetic acid, formic acid, citric acid, and lactic acid.

3. The battery cell soft packaging film according to claim 2, characterized in that, The preparation method of the surface-functionalized graphene oxide-supported nanolayered phosphophosphate composite includes the following steps: M1. Add the graphene oxide of the specified weight to 50-80 parts of ethanol-water mixed solution to prepare a dispersion with a concentration of 0.5%-2.0%, and then ultrasonically disperse for 30-60 minutes to obtain a uniform graphene oxide dispersion. M2. Add the aminosilane coupling agent and the acidic catalyst of the weight component to the graphene oxide dispersion, and react at 40-60℃ for 1-3 hours under pH 4.5-5.5 conditions to allow the aminosilane to be grafted onto the graphene oxide surface to obtain surface-functionalized graphene oxide. M3. Add the nano-layered zirconium phosphate of the weight component to the remaining ethanol-water mixed solution, and add n-propylamine of the weight component as an intercalation aid. Stir and react at 50-80°C for 2-6 hours to allow the layered zirconium phosphate to intercalate and partially exfoliate, and obtain an exfoliated nano-layered zirconium phosphate slurry. M4. Mix the surface-functionalized graphene oxide dispersion obtained in step M2 with the exfoliated nano-layered zirconium phosphate slurry obtained in step M3, stir at room temperature to 70°C for 2-5 hours, and then ultrasonically disperse for 10-30 minutes to combine the two. M5. The resulting mixture is centrifuged, washed, and vacuum dried at 50-80℃ for 6-12 hours to obtain a surface-functionalized graphene oxide-supported nanolayered zirconium phosphate composite.

4. The battery cell soft packaging film according to claim 1, characterized in that: The heat-sealing layer is made by blending ethylene-propylene random copolymer polypropylene with olefin block copolymer, wherein the blending mass ratio of ethylene-propylene random copolymer polypropylene with olefin block copolymer is (70-90):(10-30). The support layer is made of homopolymer polypropylene and ethylene-octene polyolefin elastomer, and the amount of ethylene-octene polyolefin elastomer added is 8-18% of the total mass of the support layer; The bonding transition layer is prepared by blending maleic anhydride-grafted polypropylene bonding resin with ethylene-propylene random copolymer polypropylene, wherein the mass percentage of the maleic anhydride-grafted polypropylene bonding resin is 35-60%.

5. The battery cell soft packaging film according to claim 4, characterized in that, The olefin block copolymer is selected from at least one of ethylene-1-octene block copolymer, ethylene-1-butene block copolymer, and ethylene-1-hexene block copolymer.

6. The flexible packaging film for battery cells according to claim 1, characterized in that: The thickness of the heat-sealing layer is 5-15 μm, the thickness of the support layer is 15-30 μm, the thickness of the bonding transition layer is 5-10 μm, and the total thickness of the heat-sealing inner layer is 30-55 μm.

7. The flexible packaging film for battery cells according to claim 1, characterized in that: The protective outer layer is a polyamide film or a polyethylene terephthalate film, and the thickness of the protective outer layer is 15-30 μm. The aluminum foil layer is 8021 aluminum alloy foil or 8079 aluminum alloy foil, with a thickness of 30-50μm and a surface roughness Ra controlled at 0.08-0.15μm.

8. The flexible packaging film for battery cells according to claim 1, characterized in that: Both the first adhesive layer and the second adhesive layer are two-component solvent-free polyurethane adhesives; wherein the second adhesive layer contains 3-8% by mass of terminal hydroxyl hyperbranched polyester based on the total mass of the second adhesive to enhance high-temperature bonding strength.

9. A process for preparing a flexible packaging film for battery cells as described in any one of claims 1-8, characterized in that, Includes the following steps: 1) Use 500-800W plasma to degrease and clean the surface of aluminum foil at a speed of 10-20m / min to obtain an aluminum foil layer with a grease-free first side surface and a grease-free second side surface. 2) A coating solution with a solid content of 5-15% is prepared by uniformly mixing surface-functionalized graphene oxide-supported nanolayered phosphophosphate composite with deionized water. This coating solution is then uniformly applied to the grease-free first side surface of the aluminum foil layer, with a coating amount of 0.5-1.5 g / m². 2 The curing reaction is carried out at 80-120℃ for 20-60 seconds, forming a corrosion-resistant bonding layer on the grease-free first side surface of the aluminum foil layer; 3) The raw materials for the heat-sealing layer, the support layer, and the bonding transition layer are melted and plasticized by three extruders, then extruded together through a multi-layer co-extrusion die, and finally cast into a multi-layer co-extruded functional polypropylene film layer. 4) Dry lamination: The corrosion-resistant bonding layer on the grease-free first side surface of the protective outer layer and the aluminum foil layer is laminated with the first adhesive layer. The bonding transition layer prepared in step 3) is laminated with the second side surface of the aluminum foil layer with the second adhesive layer. After curing, the battery cell soft packaging film is obtained. The curing conditions are: temperature 40-60℃, relative humidity 50-70%RH, curing time 72-96h.

10. The preparation process according to claim 9, characterized in that, In step 3), the temperatures of the raw materials for preparing the heat-sealing layer in the feeding section, compression section and metering section of the first extruder are controlled to be 170-185℃, 180-200℃ and 190-210℃, respectively. The temperatures of the raw materials for the support layer in the feeding section, compression section and metering section of the second extruder are controlled at 180-195℃, 190-215℃ and 200-230℃, respectively. The temperatures of the raw materials for preparing the bonding transition layer in the feeding section, compression section and metering section of the third extruder are controlled at 175-190℃, 185-205℃ and 195-220℃, respectively. When the molten heat-sealing layer, the molten support layer, and the molten bonding transition layer are brought together through a multi-layer co-extrusion die, the die temperature is controlled at 190-230℃ and the melt pressure is controlled at 8-20MPa. Then, the melt is cooled and shaped by a casting cooling roller at 20-50℃ to produce a multi-layer co-extruded functional polypropylene film layer.

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