Thermal and flame retardant battery box hybrid fiber reinforced composite material and preparation method thereof

Abstract

The application relates to the technical field of power battery box composite materials, and discloses a hybrid fiber reinforced composite material for a heat-insulating and flame-retardant battery box and a preparation method thereof.The composite material is a multilayer sandwich structure composed of an outer layer material, a core layer material and an inner layer material arranged in sequence from outside to inside; the outer layer material is a carbon fiber and glass fiber hybrid cloth reinforced epoxy resin composite material layer, the core layer material is a porous fiber material containing regenerated cotton fiber, glass fiber, ammonium polyphosphate, phenolic resin and epoxy resin, and the inner layer material is a carbon fiber and glass fiber hybrid cloth reinforced phenolic resin composite material layer.The composite material has good heat insulation, flame retardation, mechanical properties and interlayer bonding performance.

Description

Technical Field

[0001] This invention relates to the field of composite materials for power battery boxes, specifically to a heat-insulating and flame-retardant hybrid fiber-reinforced composite material for battery boxes and its preparation method. Background Technology

[0002] As a crucial load-bearing and protective component of the power battery system, the power battery box in new energy vehicles must simultaneously meet requirements for structural strength, impact resistance, thermal insulation, flame retardancy, lightweighting, and mass production capabilities. While traditional metal battery boxes offer good load-bearing capacity, they suffer from drawbacks such as high mass, limited thermal insulation, and rapid heat transfer under thermal runaway conditions. Fiber-reinforced resin composite materials, due to their high specific strength, specific modulus, and design freedom, have become an important development direction for lightweight battery boxes.

[0003] However, existing composite battery boxes still have several problems. First, while single epoxy resin-based composite materials have good mechanical properties and process adaptability, their heat resistance and flame retardancy still need further improvement. Second, while single phenolic resin-based composite materials have good heat resistance and flame retardancy, their toughness and adaptability to external environments are relatively insufficient. Third, the foam core material, ordinary inorganic fiber felt, or ordinary recycled fiber felt in existing sandwich composite materials are prone to problems such as insufficient thermal insulation, insufficient interlayer bonding strength, or local delamination under conditions of power battery thermal runaway, mechanical vibration, impact, and thermal cycling.

[0004] Recycled cotton fibers are widely available, especially denim scraps, which, after being opened, can form a porous fiber skeleton. Recycled cotton nonwoven materials have been used in fields such as thermal insulation and sound absorption. Publicly available research indicates that waste cotton / polyester nonwoven materials have a basis for thermal insulation applications; publicly available data on the low thermal conductivity of cotton fiber insulation materials in both dry and wet states suggest its feasibility as an insulation fiber skeleton. However, recycled cotton fibers themselves are cellulose-based materials and are flammable without flame-retardant modification, making it difficult to meet flame-retardant requirements when used alone as a battery box core material. Ammonium polyphosphate (APP), as a phosphorus-based flame-retardant component, can promote the formation of a charred protective layer in carbon-containing materials when heated. Publicly available literature also shows that APP can be used for flame-retardant modification of cotton fabrics and natural fiber / resin composites.

[0005] Therefore, it is necessary to provide a new sandwich composite material for battery boxes that can utilize the low thermal conductivity porous structure of recycled cotton fibers, improve the dimensional stability, flame retardancy and interfacial bonding performance of the core layer through glass fiber, ammonium polyphosphate and resin bonding components, and achieve synergy between external structural reinforcement and internal flame retardancy and heat resistance through differentiated configuration of the outer epoxy resin composite layer and the inner phenolic resin composite layer. Summary of the Invention

[0006] The purpose of this invention is to provide a hybrid fiber reinforced composite material for battery boxes that is heat-insulating and flame-retardant, in order to solve the problem that existing battery box composite materials cannot simultaneously achieve lightweight, heat insulation, flame retardancy and interlayer bonding strength.

[0007] Another objective of this invention is to provide a method for preparing the above-mentioned heat-insulating and flame-retardant hybrid fiber reinforced composite material for battery boxes, so as to solve the problem of unstable interfacial bonding between the porous fiber core layer and the outer and inner composite materials.

[0008] To achieve the above objectives, the present invention provides a hybrid fiber reinforced composite material for a heat-insulating and flame-retardant battery box. The composite material has a multi-layer sandwich structure, comprising an outer layer material, a core layer material, and an inner layer material from the outside to the inside.

[0009] Preferably, the outer layer material is a carbon fiber and glass fiber hybrid cloth reinforced with epoxy resin composite material. This outer layer material is mainly used to improve the structural strength, impact resistance, damp heat resistance, and surface molding quality of the composite material on the side of the battery box closest to the external environment.

[0010] Preferably, the core material is a porous fiber material.

[0011] Preferably, the porous fiber material comprises mixed fibers, flame-retardant components, and adhesive components.

[0012] Preferably, the mixed fibers include recycled cotton fibers and glass fibers; the flame retardant component includes ammonium polyphosphate; and the adhesive component includes phenolic resin and epoxy resin.

[0013] Through the above technical solutions: recycled cotton fibers are used to form a low thermal conductivity, porous, and lightweight fiber skeleton; glass fibers are used to improve the heat resistance, dimensional stability, and compression support of the core material; ammonium polyphosphate is used to improve the flame retardant carbonization ability of the core material under heated combustion conditions; phenolic resin and epoxy resin are used to improve the internal bonding strength of the core fiber network and improve its co-curing compatibility with the outer and inner prepregs.

[0014] Preferably, the inner layer material is a phenolic resin composite material layer reinforced with a hybrid fabric of carbon fiber and glass fiber. This inner layer material is disposed on the side closer to the power battery module, mainly to improve the heat resistance, flame retardancy, and carbonization protection capability under thermal runaway conditions on the side closer to the heat source.

[0015] Preferably, the outer layer material, core layer material and inner layer material are stacked sequentially along the thickness direction and solidified together to form an integrated composite structure.

[0016] Preferably, the outer layer material is disposed on the side closer to the external environment of the battery box, the inner layer material is disposed on the side closer to the power battery module, and the core layer material is disposed between the outer layer material and the inner layer material.

[0017] Through the above technical solution: the layer design enables the outer side of the material to mainly bear the external impact, humid and hot environment and structural load, the inner side to mainly bear the flame retardant and heat-resistant function under battery thermal runaway or local high temperature conditions, and the core layer to mainly bear the functions of heat insulation, buffering and lightweighting.

[0018] Preferably, based on the total mass of the recycled cotton fiber and glass fiber, the content of the recycled cotton fiber is 60-70%, and the content of the glass fiber is 30-40%.

[0019] When the recycled cotton fiber content is less than 60%, the porous thermal insulation skeleton of the core layer is insufficient, and the thermal conductivity of the material is prone to increase; when the recycled cotton fiber content is greater than 70%, the heat resistance dimensional stability and compression support capacity of the core layer may decrease.

[0020] Preferably, the recycled cotton fiber is obtained from denim scraps through an opening process, and the fibers with a length of 20-50mm account for more than 80% of the total mass of the recycled cotton fiber.

[0021] The above technical solutions utilize denim scraps as a source of recycled cotton, which helps to obtain recycled cotton fibers with high fiber strength and relatively stable length distribution. Controlling the main fiber length to be within the range of 20-50mm facilitates fiber overlap during airflow web formation, resulting in a stable three-dimensional porous fiber network.

[0022] Preferably, the amount of ammonium polyphosphate added is 8-15% based on the total mass of the mixed fibers.

[0023] When the amount of ammonium polyphosphate added is less than 8%, the flame retardant effect of the core layer is insufficient; when the amount of ammonium polyphosphate added is more than 15%, the excessive powder content may affect the flexibility and interfacial bonding performance of the core layer fiber network.

[0024] Preferably, the content of the phenolic resin is 30-50% and the content of the epoxy resin is 50-70% based on the total mass of the adhesive components.

[0025] Through the above technical solutions, phenolic resin can improve the heat resistance and flame retardancy of the core material, while epoxy resin can improve the bonding compatibility and toughness between the core material and the outer epoxy resin composite layer. By controlling the phenolic resin and epoxy resin within the above-mentioned ranges, the core material can simultaneously possess good flame retardancy, bonding strength, and co-curing adaptability.

[0026] Preferably, the porous fiber material is a porous fiber felt formed by airflow web formation, wherein the recycled cotton fiber and glass fiber are randomly oriented and overlap each other in the porous fiber felt to form a three-dimensional porous fiber network.

[0027] Through the above technical solutions, the three-dimensional porous fiber network can reduce continuous solid heat conduction channels, improve the uniformity of the core layer pore structure, and improve the penetration and anchoring effect of resin in the pores of the core layer surface.

[0028] Preferably, the areal density of the porous fiber material is 1000–2000 g / m³. 2 The thickness is 10-20mm.

[0029] Preferably, the carbon fiber and glass fiber hybrid fabric is a plain weave hybrid fiber fabric formed by interlacing carbon fiber and glass fiber warp and weft.

[0030] Preferably, the number of fiber cloth layers in the outer layer material is 5 to 15, and the number of fiber cloth layers in the inner layer material is 5 to 15.

[0031] Preferably, the epoxy resin content in the outer layer material is 30-60%, and the phenolic resin content in the inner layer material is 30-60%. The epoxy resin content and the phenolic resin content both refer to the percentage of the resin system mass to the total mass of the corresponding composite material layer.

[0032] Preferably, the core layer material has a first resin anchoring region formed by curing an epoxy resin system within the surface pores on the side closest to the outer layer material. The core layer material also has a second resin anchoring region formed by curing a phenolic resin system within the surface pores on the side closest to the inner layer material. The first and second resin anchoring regions can be identified by microscopic observation of the composite material cross-section; they are resin-wetting areas formed by the penetration and curing of the outer or inner layer resin system into the surface pores of the core layer.

[0033] Through the above technical solution, the first resin anchoring zone and the second resin anchoring zone are respectively formed in the surface pores on both sides of the core layer, so that the outer layer material, the core layer material and the inner layer material are not just planar bonded, but form a mechanical interlocking and chemical curing combination after the resin penetrates into the pores, thereby improving the interlayer bonding strength of the sandwich structure.

[0034] The present invention also provides a method for preparing the above-mentioned heat-insulating and flame-retardant hybrid fiber reinforced composite material for battery boxes, comprising the following steps:

[0035] S1: Under conditions of heating, pressurization, or the use of solvents, an epoxy resin system is pre-impregnated with a carbon fiber and glass fiber hybrid fabric to obtain an outer prepreg.

[0036] S2: Under conditions of heating, pressurization, or the use of solvents, a phenolic resin system is pre-impregnated with a blend of carbon fiber and glass fiber to obtain an inner prepreg.

[0037] S3: Prepare and cut porous fiber materials with a thickness of 10-20 mm;

[0038] S4: Lay outward prepreg, porous fiber material and inner prepreg sequentially along the thickness direction in the molding die, so that the porous fiber material is located between the outward prepreg and the inner prepreg to obtain the layup structure to be cured;

[0039] S5: The layup structure to be cured is subjected to vacuum treatment and then heated and pressurized under conditions of 100-160℃ and 0.5-1.5MPa to obtain a heat-insulating and flame-retardant hybrid fiber reinforced composite material for battery boxes.

[0040] Preferably, the method for preparing the porous fiber material includes the following steps:

[0041] P1: The recycled cotton fiber and glass fiber are placed in two separate opening machines, weighed automatically according to the set ratio, and fed into the conveyor belt; the recycled cotton fiber and glass fiber enter the large warehouse mixer for mixing, and the mixed fiber is then finely opened and sent into the cotton box through the pipe, and quantitatively output from the cotton box to the conveyor curtain with a width of 2200mm to form the initial fiber web.

[0042] P2: Ammonium polyphosphate, phenolic resin, and epoxy resin are mixed in a mixer for 10 minutes and then fed into a powder applicator. The mixed powder is applied to the initial fiber web through the powder applicator. The initial fiber web with the mixed powder is then fed into an air-flow forming machine, and after air-flow forming, it is output to a receiving curtain. It is then dried and shaped in an oven at 150-180°C to obtain a surface density of 1000-2000 g / m². 2 Porous fiber materials with a thickness of 10-20 mm.

[0043] Preferably, the heating and pressurizing co-curing molding is performed using one of the following: vacuum bag-assisted autoclave molding, compression molding, or hot pressing.

[0044] Preferably, the phenolic resin and epoxy resin applied to the initial fiber web in step P2 are powdered resin raw materials or resin compositions that can be applied by a powder applicator.

[0045] Preferably, during the heating and pressurizing co-curing molding process, the epoxy resin system in the outer prepreg penetrates into the surface pores of the porous fiber material near the outer prepreg and cures to form a first resin anchoring zone; the phenolic resin system in the inner prepreg penetrates into the surface pores of the porous fiber material near the inner prepreg and cures to form a second resin anchoring zone.

[0046] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0047] 1. This invention employs a multi-layer sandwich structure consisting of an outer epoxy resin composite material layer, a core porous fiber material layer, and an inner phenolic resin composite material layer. This structure emphasizes structural reinforcement and environmental resistance in the outer layer, flame retardancy and heat resistance in the inner layer, and heat insulation and lightweight properties in the core layer, thereby improving the overall performance of the battery box material.

[0048] 2. The core material of this invention is a composite of recycled cotton fiber and glass fiber. The recycled cotton fiber forms a porous thermal insulation skeleton, while the glass fiber improves the thermal stability and dimensional stability of the core layer, so that the core material has both low thermal conductivity and good compressibility.

[0049] 3. In this invention, ammonium polyphosphate is added to the core layer material, along with phenolic resin and epoxy resin adhesive components, so that the core layer material can form a flame-retardant carbonization protective structure when heated, thereby improving the flame-retardant performance of the composite material.

[0050] 4. The present invention forms a random-oriented three-dimensional porous fiber network by airflow meshing, which helps to reduce continuous solid heat conduction channels, improve the uniformity of core layer pore structure, and improve the thermal insulation performance of the material.

[0051] 5. The present invention forms a first resin anchoring zone and a second resin anchoring zone on both sides of the core material through co-curing molding, thereby improving the interfacial bonding strength between the outer layer material, the core layer material and the inner layer material, and reducing the risk of delamination of the sandwich structure under vibration, impact or thermal cycling conditions.

[0052] 6. This invention uses denim scraps to obtain recycled cotton fibers through opening treatment, which is conducive to realizing the resource utilization of textile scraps, reducing the cost of core layer materials, and improving the green manufacturing attributes of battery box composite materials. Attached Figure Description

[0053] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 The stress-strain curve of the bending performance of the hybrid fiber reinforced composite material for the heat-insulating and flame-retardant battery box obtained in Example 1 of the present invention is shown.

[0055] Figure 2This is a schematic diagram of the structure of the hybrid fiber reinforced composite material for the heat-insulating and flame-retardant battery box of the present invention.

[0056] Figure 3 This is a bar chart showing the apparent thermal conductivity of the hybrid fiber-reinforced composite material for the heat-insulating and flame-retardant battery box of the present invention. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] In this embodiment of the invention, the carbon fiber and glass fiber hybrid fabric can be a plain-weave hybrid fiber fabric formed by interlacing carbon fiber and glass fiber warp and weft. The outer prepreg is made by impregnating the hybrid fiber fabric with an epoxy resin system, and the inner prepreg is made by impregnating the hybrid fiber fabric with a phenolic resin system. The recycled cotton fiber is obtained from denim scraps through an opening process, and the fibers with a length of 20-50 mm account for more than 80% of the total mass of the recycled cotton fiber. Both the epoxy resin system and the phenolic resin system can include the corresponding resin and its curing-related components.

[0059] The epoxy resin system refers to a system including epoxy resin and its curing-related components; the phenolic resin system refers to a system including phenolic resin and its curing-related components. The resin system content refers to the percentage of the total mass of the corresponding resin system to the total mass of the corresponding composite material layer.

[0060] Example 1

[0061] This embodiment prepares a hybrid fiber reinforced composite material for a heat-insulating and flame-retardant battery box.

[0062] The outer layer material is a plain-weave hybrid fiber cloth formed by the warp and weft interweaving of carbon fiber and glass fiber, and is prepreged using an epoxy resin system. The outer layer material has 10 fiber cloth layers, and the epoxy resin system content in the outer layer material is 45%.

[0063] The inner layer material is a plain-weave hybrid fiber cloth formed by the warp and weft interweaving of carbon fiber and glass fiber, and is prepreged using a phenolic resin system. The inner layer material has 10 fiber cloth layers and the phenolic resin system content is 45%.

[0064] The core material is a porous fiber material. Based on the total mass of recycled cotton fiber and glass fiber, the recycled cotton fiber content is 65%, and the glass fiber content is 35%. Based on the total mass of the mixed fibers, the amount of ammonium polyphosphate added is 12%. Based on the total mass of the adhesive components, the phenolic resin content is 40%, and the epoxy resin content is 60%.

[0065] The core layer material preparation process is as follows: Recycled cotton fibers and glass fibers are placed in two separate unpacking machines, automatically weighed according to a set ratio, and fed into a conveyor belt. The recycled cotton fibers and glass fibers are then mixed in a large mixer. After fine opening, the mixed fibers are fed into a cotton box through a pipe, and quantitatively output from the cotton box onto a 2200mm wide conveyor curtain to form an initial fiber web. Ammonium polyphosphate, phenolic resin, and epoxy resin are stirred in a mixer for 10 minutes and then conveyed to a powder applicator. The mixed powder is applied to the initial fiber web through the powder applicator. The initial fiber web with the mixed powder is then fed into an air-flow forming machine, and after air-flow forming, it is output to a receiving curtain. Finally, it is dried and shaped in an oven at 165℃ to obtain a surface density of 1500g / m². 2 A porous fiber material with a thickness of 15mm.

[0066] The outer prepreg, porous fiber material, and inner prepreg are sequentially laid along the thickness direction in a molding die, with the porous fiber material positioned between the outer and inner prepregs, to obtain the layup structure to be cured. The layup structure is then subjected to vacuum treatment and co-cured under heat and pressure at 130℃ and 1.0MPa to obtain a heat-insulating and flame-retardant hybrid fiber reinforced composite material for battery boxes.

[0067] After molding, the epoxy resin system in the outer prepreg penetrates into the surface pores of the porous fiber material near the outer prepreg and cures to form the first resin anchoring zone; the phenolic resin system in the inner prepreg penetrates into the surface pores of the porous fiber material near the inner prepreg and cures to form the second resin anchoring zone.

[0068] Example 2

[0069] This embodiment is basically the same as Embodiment 1, except that the parameters are in the low areal density, low thickness and low ply window.

[0070] Based on the total mass of recycled cotton fiber and glass fiber, the recycled cotton fiber content is 60% and the glass fiber content is 40%. Based on the total mass of the mixed fibers, the amount of ammonium polyphosphate added is 8%. Based on the total mass of the adhesive components, the phenolic resin content is 30% and the epoxy resin content is 70%.

[0071] The outer layer material consists of 5 layers of fiber cloth, and the epoxy resin content in the outer layer material is 30%. The inner layer material also consists of 5 layers of fiber cloth, and the phenolic resin content in the inner layer material is 30%.

[0072] The areal density of the porous fiber material is 1000 g / m³. 2 The thickness is 10mm. The baking and setting temperature is 150℃. The co-curing temperature is 120℃, and the co-curing pressure is 0.5MPa.

[0073] Example 3

[0074] This embodiment is basically the same as Embodiment 1, except that the parameters are in the high areal density, high thickness and high ply window.

[0075] The recycled cotton fiber content is 70% and the glass fiber content is 30% by total mass of the recycled cotton fiber and glass fiber. The amount of ammonium polyphosphate added is 15% by total mass of the mixed fibers. The phenolic resin content is 50% and the epoxy resin content is 50% by total mass of the adhesive components.

[0076] The outer layer material consists of 15 layers of fiber cloth and contains 60% epoxy resin. The inner layer material also consists of 15 layers of fiber cloth and contains 60% phenolic resin.

[0077] The areal density of the porous fiber material is 2000 g / m³. 2 The thickness is 20mm. The baking and setting temperature is 180℃. The co-curing temperature is 160℃, and the co-curing pressure is 1.5MPa.

[0078] Example 4

[0079] This embodiment is basically the same as embodiment 1, except that the following parameter combination is used in this embodiment:

[0080] Based on the total mass of recycled cotton fiber and glass fiber, the recycled cotton fiber content is 65% and the glass fiber content is 35%. Based on the total mass of the mixed fibers, the amount of ammonium polyphosphate added is 10%. Based on the total mass of the adhesive components, the phenolic resin content is 40% and the epoxy resin content is 60%.

[0081] Both the outer and inner layers contain 10 layers of fiber cloth. The outer layer contains 45% epoxy resin, and the inner layer contains 45% phenolic resin. The areal density of the porous fiber material is 1500 g / m³. 2 The thickness is 15mm. The baking and setting temperature is 165℃.

[0082] The co-curing process employs a staged heating method. After vacuuming, the temperature is raised to 90°C and held for 30 minutes, then raised to 130°C and held for 90 minutes, followed by raising to 155°C and holding for 60 minutes. The molding pressure is 1.0 MPa.

[0083] Example 5

[0084] This embodiment is basically the same as Embodiment 1, except that the flame retardant and heat-resistant properties on the side closer to the power battery module are further improved.

[0085] The inner layer material contains 50% phenolic resin and 12 layers of fiber cloth. The outer layer material contains 45% epoxy resin and 10 layers of fiber cloth. The core layer material contains 65% recycled cotton fiber, 35% glass fiber, 12% ammonium polyphosphate, and has a porous fiber material surface density of 1500 g / m³. 2 The thickness is 15mm. The co-curing temperature is 150℃ and the pressure is 1.0MPa.

[0086] Comparative Example 1

[0087] This comparative example is basically the same as Example 1, except that the mixed fibers in the core material are all glass fibers and contain no recycled cotton fibers. The amount of ammonium polyphosphate added, the composition of the adhesive components, the core layer density, the core layer thickness, the outer layer material, the inner layer material, and the co-curing conditions are all the same as in Example 1.

[0088] Comparative Example 2

[0089] This comparative example is basically the same as Example 1, except that ammonium polyphosphate is not added to the core material. The ratio of recycled cotton fiber to glass fiber, the composition of the adhesive components, the core layer density, the core layer thickness, the outer layer material, the inner layer material, and the co-curing conditions are all the same as in Example 1.

[0090] Comparative Example 3

[0091] This comparative example is basically the same as Example 1, except that the core layer material is not formed using an airflow web-forming process, but rather using a conventional mechanical web-laying and pressing method to form the fiber felt. The ratio of recycled cotton fiber to glass fiber, the amount of ammonium polyphosphate added, the composition of the adhesive components, the core layer density, the core layer thickness, the outer layer material, the inner layer material, and the co-curing conditions are all the same as in Example 1.

[0092] Comparative Example 4

[0093] This comparative example is basically the same as Example 1, except that both the outer and inner layers are made of carbon fiber and glass fiber hybrid fabric reinforced epoxy resin composite material, that is, the inner layer material does not use a phenolic resin system. The core layer material composition, core layer density, core layer thickness, number of layups, and co-curing conditions are all the same as in Example 1.

[0094] Performance testing:

[0095] Bending properties were assessed according to ASTM D790 or other equivalent composite bending test methods to evaluate the strength, modulus, and failure mode of the material under three-point or four-point bending loads; thermal conductivity was assessed according to steady-state thermal resistance / thermal conduction test methods; flame retardancy was assessed according to the UL-94 vertical burning test, with a V-0 rating requiring the specimen to self-extinguish rapidly after specified ignition and limit burning drips. Test results are shown in Tables 1 and 2.

[0096] Table 1

[0097]

[0098] Table 2

[0099]

[0100] As can be seen from Tables 1 and 2, the embodiments of the present invention generally take into account heat insulation, flame retardancy, mechanical properties, and interlayer bonding performance, and all exhibit good structural stability after thermal shock. In particular, the layered collaborative design combined with a porous fiber core layer can improve the overall protective performance of the material while ensuring lightweight construction.

[0101] Compared to the examples, the heat insulation effect of Comparative Example 1 was significantly reduced, indicating that the porous heat insulation skeleton formed by the composite of recycled cotton fiber and glass fiber plays a positive role in reducing heat transfer. The flame retardant performance of Comparative Example 2 deteriorated significantly, indicating that ammonium polyphosphate plays an important role in improving the material's flame retardancy and charring protection capabilities. Comparative Example 3 showed decreased interlayer bonding performance and localized delamination after thermal shock, indicating that the three-dimensional porous fiber network formed by airflow meshing is beneficial for improving the uniformity of the core structure and the interface bonding effect. The inner heat resistance and flame retardant performance of Comparative Example 4 was poor, indicating that the use of a phenolic resin composite material layer near the power battery module is beneficial for improving the material's flame retardant and heat resistance under high temperatures.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. All equivalent substitutions, modifications, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hybrid fiber-reinforced composite material for a heat-insulating and flame-retardant battery box, characterized in that, The composite material is a multi-layer sandwich structure, which includes an outer layer material, a core layer material and an inner layer material from the outside to the inside. The outer layer material is a carbon fiber and glass fiber hybrid cloth reinforced epoxy resin composite material layer; The core material is a porous fiber material, which includes mixed fibers, flame retardant components, and adhesive components; the mixed fibers include recycled cotton fibers and glass fibers, the flame retardant components include ammonium polyphosphate, and the adhesive components include phenolic resin and epoxy resin. The inner layer material is a phenolic resin composite material layer reinforced with a mixture of carbon fiber and glass fiber; The outer layer material, core layer material and inner layer material are stacked sequentially along the thickness direction and solidified together to form an integrated composite structure.

2. The hybrid fiber reinforced composite material for a heat-insulating and flame-retardant battery box according to claim 1, characterized in that, The outer layer material is disposed on the side closest to the external environment of the battery box; the inner layer material is disposed on the side closest to the power battery module; and the core layer material is disposed between the outer layer material and the inner layer material.

3. The hybrid fiber reinforced composite material for a heat-insulating and flame-retardant battery box according to claim 1, characterized in that, Based on the total mass of the recycled cotton fiber and glass fiber, the content of the recycled cotton fiber is 60-70%, and the content of the glass fiber is 30-40%.

4. The hybrid fiber reinforced composite material for a heat-insulating and flame-retardant battery box according to claim 1, characterized in that, The recycled cotton fiber is obtained from denim scraps through an opening process, and fibers with a length of 20-50mm account for more than 80% of the total mass of the recycled cotton fiber.

5. The hybrid fiber reinforced composite material for a heat-insulating and flame-retardant battery box according to claim 1, characterized in that, The amount of ammonium polyphosphate added is 8-15% based on the total mass of the mixed fibers; the content of phenolic resin is 30-50% and the content of epoxy resin is 50-70% based on the total mass of the adhesive components.

6. The hybrid fiber reinforced composite material for a heat-insulating and flame-retardant battery box according to claim 1, characterized in that, The porous fiber material is a porous fiber mat formed by airflow web formation. The recycled cotton fibers and glass fibers are randomly oriented and interlocked in the porous fiber mat to form a three-dimensional porous fiber network. The areal density of the porous fiber material is 1000-2000 g / m³. 2 The thickness is 10-20mm.

7. The hybrid fiber reinforced composite material for a heat-insulating and flame-retardant battery box according to claim 1, characterized in that, The carbon fiber and glass fiber hybrid fabric is a plain weave hybrid fiber fabric formed by the warp and weft interlacing of carbon fiber and glass fiber; the number of fiber fabric layers in the outer layer material is 5 to 15, and the number of fiber fabric layers in the inner layer material is 5 to 15; the epoxy resin system content in the outer layer material is 30 to 60%, and the phenolic resin system content in the inner layer material is 30 to 60%, where the epoxy resin system content and phenolic resin system content refer to the percentage of the resin system mass to the total mass of the corresponding composite material layer; a first resin anchoring zone is formed in the surface pores of the core layer material near the outer layer material, formed by the epoxy resin system in the outer layer material penetrating and curing; a second resin anchoring zone is formed in the surface pores of the core layer material near the inner layer material, formed by the phenolic resin system in the inner layer material penetrating and curing.

8. A method for preparing a hybrid fiber-reinforced composite material for a heat-insulating and flame-retardant battery box as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Under conditions of heating, pressurization, or the use of solvents, an epoxy resin system is pre-impregnated with a carbon fiber and glass fiber hybrid fabric to obtain an outer prepreg. S2: Under conditions of heating, pressurization, or the use of solvents, a phenolic resin system is pre-impregnated with a blend of carbon fiber and glass fiber to obtain an inner prepreg. S3: Prepare and cut porous fiber materials with a thickness of 10-20 mm; S4: Lay outward prepreg, porous fiber material and inner prepreg sequentially along the thickness direction in the molding die, so that the porous fiber material is located between the outward prepreg and the inner prepreg to obtain the layup structure to be cured; S5: The layup structure to be cured is subjected to vacuum treatment and then heated and pressurized under conditions of 100-160℃ and 0.5-1.5MPa to obtain a heat-insulating and flame-retardant hybrid fiber reinforced composite material for battery boxes.

9. The preparation method according to claim 8, characterized in that, The preparation of the porous fiber material includes the following steps: P1: The recycled cotton fiber and glass fiber are placed in two separate opening machines, weighed automatically according to the set ratio, and fed into the conveyor belt; the recycled cotton fiber and glass fiber are mixed in the large warehouse mixer, and the mixed fiber is sent into the cotton box through the pipeline after fine opening. The cotton box is quantitatively output on the conveyor curtain with a width of 2200mm to form the initial fiber web. P2: After mixing and stirring ammonium polyphosphate, phenolic resin and epoxy resin for 10 minutes, the mixture is fed into a powder applicator and applied to the initial fiber web by the powder applicator. An initial fiber web coated with mixed powder is fed into an air-flow web forming machine, and after air-flow forming, it is output onto a receiving curtain; it is then dried and shaped in an oven at 150–180°C to obtain a surface density of 1000–2000 g / m². 2 Porous fiber materials with a thickness of 10-20 mm.

10. The preparation method according to claim 8, characterized in that, The heating and pressurizing co-curing molding process employs one of the following: vacuum bag-assisted autoclave molding, compression molding, or hot pressing. During the heating and pressurizing co-curing molding process, the epoxy resin system in the outer prepreg penetrates into the surface pores of the porous fiber material near the outer prepreg and cures to form a first resin anchoring zone; the phenolic resin system in the inner prepreg penetrates into the surface pores of the porous fiber material near the inner prepreg and cures to form a second resin anchoring zone.

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