Battery pack tray and forming method

Abstract

The application discloses a battery pack tray and a preparation method thereof. The battery pack tray comprises a metal structure layer and a composite material layer. The four peripheral edges of the metal structure layer are combined with the four peripheral edges of the composite material layer, and a flat cavity is formed in the middle as a cooling liquid flow channel. A thermoplastic anticorrosive layer is arranged on the inner wall of the cavity. In this embodiment, the metal structure layer is combined with the composite material layer to replace the full-metal structure in the prior art, so that the battery pack tray is lightened, and the overall structure strength of the tray is higher. In addition, the cavity between the metal structure layer and the composite material layer is arranged as a cooling liquid flow channel to replace the independently arranged liquid cooling plate in the prior art, and the vertical installation space of the battery system is released. Thirdly, there is no brazing seam in the battery pack tray structure, and the thermoplastic anticorrosive layer arranged on the inner container solves the problem of electrochemical corrosion of the battery pack tray in the prior art.

Description

Technical Field

[0001] This invention relates to the field of composite materials, and more specifically to a battery pack tray and its molding method. Background Technology

[0002] With the development of new energy vehicle technology, the safety, lightweight design, and thermal management performance of power battery systems have become core concerns. In existing technologies, the power battery system of new energy vehicles includes a battery pack tray, a crucial component for supporting and securing the battery pack. Current battery pack trays are typically made of die-cast aluminum alloy or stamped pure steel, and their advantages and disadvantages are as follows: Die-cast aluminum alloys: Although they have good thermal conductivity, in order to meet the molding requirements and structural rigidity of high-pressure die casting, the wall thickness usually has to be greater than 3mm, resulting in serious redundancy in the overall structural weight. At the same time, their low elongation makes them prone to brittle fracture or penetration, which can lead to battery thermal runaway. Stamped pure steel: high strength, good thermal conductivity, but extremely high density (7.85 g / cm³). 3 If the entire tray base is made of pure steel, the battery pack will be heavy and its bottom (the side facing the ground) will have extremely poor corrosion resistance.

[0003] Furthermore, existing traditional battery pack trays also feature independent carbon steel cooling plates, which adds extra weight to the tray and encroaches on vertical space, limiting cell capacity and the battery system's ground clearance. Additionally, the coolant (usually ethylene glycol) in the carbon steel cooling plate is acidic, which can corrode the plate over time.

[0004] In summary, current battery pack trays present a triple challenge: achieving lightweight design, corrosion resistance, and impact resistance. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention provides a battery pack tray and its molding method. The battery pack tray is molded from a metal-composite material, integrating support functions with thermal management properties, thereby achieving lightweighting of the battery pack tray and improving structural strength, corrosion resistance, and thermal response speed.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A battery pack tray includes a metal structural layer and a composite material layer. The four edges of the metal structural layer and the four edges of the composite material layer are combined to form a flat cavity in the middle, serving as a coolant channel. A thermoplastic anti-corrosion layer is provided on the inner wall of the cavity. A coolant inlet and a coolant outlet communicating with the cavity are also provided on one side of the metal frame of the battery pack tray. In this embodiment, combining the metal structural layer and the composite material layer replaces the all-metal structure in the prior art, which can achieve the weight reduction of the battery pack tray. At the same time, the metal structural layer, as the load-bearing core, combined with the high strength and high modulus of the composite material layer, makes the battery pack tray as a whole achieve higher structural strength. In addition, the cavity between the metal structural layer and the composite material layer serves as a coolant channel, replacing the independently set liquid cooling plate in the prior art. The freed-up vertical installation space can be used to increase the cell capacity or increase the ground clearance of the battery system. Thirdly, the battery pack tray structure does not have brazing welds, and the thermoplastic anti-corrosion layer in the inner liner solves the electrochemical corrosion problem of battery pack trays in the prior art.

[0007] In another embodiment, the thermoplastic anti-corrosion layer is a high-hydrolyzability PVA modified film, wherein the PVA modified film comprises, by weight percentage of the raw materials: 80-85%wt of matrix resin: specifically polyvinyl alcohol (PVA), with a degree of alcoholysis ≥99% and a degree of polymerization 1700-2000; this resin matrix is ​​to provide high-temperature stability for PVA-modified films; 8-12%wt of reinforcing agent: specifically hydrophilic nano-silica with a particle size of 15-30nm; this reinforcing agent can improve the heat resistance and modulus of PVA modified film; at the same time, this reinforcing agent also acts as a heat stabilizer, which can inhibit the thermal creep of thermoplastic anti-corrosion layer; 2-3%wt moisture inhibitor: specifically calcium stearate; this moisture inhibitor can reduce the hygroscopicity of the modified film; at the same time, it also acts as a lubricant to prevent the PVA modified film from sticking together and improve processability; 1-2%wt additive: specifically glycerin, which can improve film-forming properties and prevent PVA modified films from becoming brittle.

[0008] In another embodiment, the composite material layer comprises a glass fiber composite material layer.

[0009] In another embodiment, the composite material layer further includes a toughening buffer layer disposed on the side of the fiberglass composite material layer adjacent to the metal structural layer. This toughening buffer layer acts as a "flexible hinge," absorbing impact energy received at the bottom of the battery pack tray and improving the puncture resistance of the battery pack tray.

[0010] In another embodiment, the composite material layer further includes a structural adhesive film layer disposed on the side of the toughening buffer layer adjacent to the metal structural layer. This structural adhesive film layer can improve the microscopic interface between the periphery of the toughening buffer layer and the periphery of the metal structural layer, providing shear strength and improving the airtightness of the cavity.

[0011] In another embodiment, the cross-section of the cavity of the battery pack tray is undulating so that the coolant flows in a wave-like manner from the coolant inlet side to the coolant outlet side, thereby improving heat dissipation efficiency.

[0012] In another embodiment, the corners formed by the undulating design inside the cavity are all transitioned with an R-angle to reduce the impact stress of the coolant on the corner positions inside the cavity.

[0013] This invention also provides a method for preparing the above-mentioned battery pack tray, specifically including the following steps: S1. Prepare the metal structure layer according to the shape and size of the battery pack tray; S2. Prepare the molded core material to fit the shape and size of the cavity of the battery pack tray: S21. Press the salt core to make its shape and size close to the shape and size of the cavity of the battery pack tray; the salt core is heat resistant to above 280℃; S22. A high degree of alcoholysis PVA modified film is coated on the surface of the salt core, so that its shape and size are adapted to the cavity of the battery pack tray; the degree of alcoholysis of the PVA modified film is ≥99.5%; S3. Laying and stacking to prepare the battery pack tray preform: Molded core material and other composite material layers are laid sequentially on the metal structure layer; S4. Compression molding: The battery pack tray preform is fed into the mold, heated to the curing temperature, and then kept warm and under pressure to complete the curing. After cooling, the mold is opened and the part is removed. S5. Remove the high-strength salt core: Machine a round hole on each end of the tray cavity and connect the round holes to the high-pressure hot water circulation equipment to dissolve the high-strength salt core.

[0014] Compared with the prior art, the beneficial effects of the present invention are at least as follows: (1) By using a combination of metal structural layers and composite material layers, and by removing the independent cooling plate, the overall weight of the battery system is reduced; (2) The integrated coolant flow channel replaces the independent cold water plate, which reduces the installation space occupied by the independent cold water plate and the corresponding assembly gap, and frees up more vertical space, which can be used to increase the cell capacity or increase the distance from the ground. (3) The bottom is a composite material layer, which has improved puncture resistance compared with metal materials such as die-cast aluminum, thus solving the safety hazard of easy brittle fracture of cast aluminum; (4) The combination of metal layer and composite material layer, as well as the wave-shaped cavity, constitutes a high-rigidity structure of the type "I-beam", which improves the overall structural strength; (5) The side facing the ground is a composite material layer, the inner wall of the coolant cavity is provided with a thermoplastic anti-corrosion layer, and there are no brazing welds, which improves the overall corrosion resistance of the pallet. (6) The heat exchange efficiency between the coolant and the battery cell is higher, and the system temperature uniformity is better. Attached Figure Description

[0015] Appendix Figure 1 This is a top view of the battery pack tray; Appendix Figure 2 Here is a cross-sectional view of the battery pack tray AA. Appendix Figure 3 Cross-sectional view of battery pack tray BB; Appendix Figure 4 Enlarged view of Part I; Appendix Figure 5 This is a schematic diagram of the tiling process.

[0016] Explanation of reference numerals in the attached figures: 1-Metal structural layer; 11-Coolant inlet; 12-Coolant outlet; 13-Concave groove; 2-Composite material layer; 21-Glass fiber composite material layer; 22-Toughening buffer layer; 23-Structural adhesive film layer; 3-Cavity; 31-Concave groove section; 32-Horizontal straight section; 4-Molded core material Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0018] It should be noted that in the description of this invention, the terms "center", "upper", "lower", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0019] Example 1

[0020] This embodiment provides an integrated flow channel battery pack tray with a metal-thermoplastic composite hybrid structure.

[0021] As attached Figure 1 The diagram illustrates a battery pack tray comprising a metal structural layer 1 and a composite material layer 2. The four periphery of the metal structural layer 1 is combined with the four periphery of the composite material layer 2 to form a flat cavity 3 in the middle, serving as a coolant flow channel. A thermoplastic anti-corrosion layer (not shown in the diagram) is provided on the inner wall of the cavity. A coolant inlet 11 and a coolant outlet 12 communicating with the cavity 3 are also provided on one side of the metal structural layer 1 of the battery pack tray. The coolant inlet 11 is located on one side of the cavity 3, and the coolant outlet 12 is located on the other side of the cavity 3 away from the coolant inlet 11.

[0022] The metal structural layer 1 is specifically a duplex steel DP780 plate with a thickness of 1.0±0.2mm, and its surface is coated with a PVC anti-corrosion layer (not shown in the figure).

[0023] The thermoplastic anti-corrosion layer is a high-hydrolyzability PVA modified film layer with a thickness of 0.15mm ± 0.02mm, and comprises, by weight percentage of raw materials: 80-85%wt matrix resin: specifically polyvinyl alcohol (PVA), with a degree of alcoholysis ≥99% and a degree of polymerization 1700-2000; this resin matrix is ​​to provide high-temperature stability for PVA-modified films; 8-12%wt reinforcing agent: specifically hydrophilic nano-silica with a particle size of 15-30nm; this reinforcing agent can improve heat resistance and modulus; at the same time, this reinforcing agent also acts as a heat stabilizer, inhibiting the thermal creep of PVA modified films; 2-3%wt moisture inhibitor: specifically calcium stearate; this moisture inhibitor can reduce the hygroscopicity of the film; in addition, this moisture absorber can also act as a lubricant to prevent the PVA modified film from sticking together and improve processability; 1-2%wt additive: specifically glycerin, which can improve film-forming properties and prevent brittleness.

[0024] The composite material layer 2 includes a glass fiber composite material layer 21, specifically composed of several layers of continuous glass fiber reinforced polypropylene unidirectional tape, with a total thickness of 2±0.5mm; the length direction of the battery pack tray is defined as the 0° direction, and the layup angle of the several layers of continuous glass fiber reinforced polypropylene unidirectional tape is [0° / 90° / +45° / -45°]s, wherein: the 0° layer mainly provides longitudinal bending stiffness, the 90° layer provides transverse stiffness, and the ±45° layer provides torsional stiffness.

[0025] The composite material layer 2 further includes a toughening buffer layer 22, which is disposed on the side of the glass fiber composite material layer 21 near the metal structure layer 1. Specifically, the toughening buffer layer 22 is aramid fiber reinforced thermoplastic polyurethane with a thickness of 0.30 mm ± 0.05 mm. Utilizing the high toughness of aramid fibers and the non-Newtonian fluid energy absorption characteristics of thermoplastic polyurethane, a soft-hard combined protective system is constructed to absorb the impact energy received at the bottom.

[0026] The composite material layer 2 further includes a structural adhesive film layer 23, which is disposed on the side of the toughening buffer layer 22 near the metal structural layer 1. This structural adhesive film layer 23 fills the microscopic interface between the periphery of the metal structural layer 1 and the periphery of the toughening buffer layer 22, providing shear strength and improving the airtightness of the cavity 3. Alternatively, the structural adhesive film layer 23 may be disposed only in the region where the toughening buffer layer 22 is bonded to the metal structural layer.

[0027] The cross-section of the cavity 3 is undulating to allow the coolant to flow in a wave-like pattern from the coolant inlet 11 to the coolant outlet 12, thereby improving heat dissipation efficiency. Specifically, the cavity 3 includes a concave groove section 31 and a horizontal straight section 32, which are alternately arranged to form an undulating coolant flow channel. The bottom groove width of the concave groove section 31 is 30-35 mm, and the groove depth (the height by which the horizontal plane of the concave groove section drops compared to the horizontal plane of the horizontal straight section) is 4.0 mm ± 0.5 mm. The length of the horizontal straight section 32 between adjacent concave groove sections 31 is 30-35 mm. The transition angles on the concave groove section 31 and the horizontal straight section 32 inside the cavity 3 are both R-angle transitions, with R≥5mm, to reduce the impact stress of the coolant on the transition angle position inside the cavity 3.

[0028] The horizontal planes of the coolant inlet 11 and coolant outlet 12 are higher than the horizontal plane of the horizontal straight section 32 of the cavity 3.

[0029] The performance of the battery pack tray in this embodiment is compared with that of the existing battery pack tray (aluminum alloy die casting + independent water cooling plate). Taking a battery pack tray with a length of 1.6m and a width of 1.3m as an example, the comparison data is shown in the table below: Total weight of the battery pack system (including battery, frame, and skeleton). 105KG 80KG Total cross-sectional thickness (excluding coolant flow channels) Tray: 3mm; Water-cooled plate: 3mm; Total thickness: 6mm. Metal structural layer: 1mm; thermoplastic anti-corrosion layer: 0.1mm×2; toughening buffer layer: 0.3mm; fiberglass composite layer: 2mm; total thickness: 3.5mm. Bottom impact resistance (120J impact) cracking / penetration Micro-dimples Extrusion strength 100-110kN 135-145kN Equivalent combined thermal resistance (m²·K / W) 350-450 ＜200 Corrosion resistance (salt spray test) 720 hours >1000 hours System temperature difference ΔT (the difference between the battery's maximum temperature and the coolant temperature) △T≈12℃~15℃ △T≤8℃ In summary, it can be seen that compared with the existing "aluminum alloy die casting + water cooling plate" solution, this invention: (1) By using ultra-high strength steel to reduce the wall thickness and combining it with composite materials, and by eliminating the independent water cooling plate, the overall weight of the battery system is reduced by about 25%; (2) It reduces the height space occupied by the independent water-cooled plate and the corresponding assembly gap, which can be used to increase the cell capacity or increase the ground clearance; (3) Significantly improved puncture resistance; the high elongation of DP780 combined with the energy absorption effect of aramid / TPU achieves "dentation without breakage", solving the safety hazard of easy brittle fracture of cast aluminum; (4) Due to the high modulus of the fiberglass composite material complementing the steel plate, a high-rigidity structure similar to an "I-beam" is formed, which increases the strength by 30%; (5) By reducing intermediate layers, the coolant exchanges heat with the battery cell only through a thermoplastic anti-corrosion layer and a steel plate, resulting in a faster thermal response and a reduction in thermal resistance of about 60%. (6) The absence of brazing welds in the structure, along with the addition of a thermoplastic anti-corrosion layer and other composite material layers, improves the corrosion resistance of the battery pack tray. (7) Due to the reduction in thermal resistance, the temperature difference of the system is reduced.

[0030] Example 2

[0031] This embodiment provides a method for preparing the battery pack tray described in Embodiment 2, specifically including the following steps: S1. Preparation of metal structural layer 1: A concave groove 13 is stamped out on a DP780 steel plate; the depth of the concave groove is 4mm and the width of the groove bottom is 30~35mm, which is adapted to the concave groove section of the cavity 3. S2, Preparation of molding core material 4: S21. Press the salt core to make its shape and size close to the shape and size of the cavity of the battery pack tray; the salt core is heat resistant to above 280℃; S22. A 0.15mm thick PVA modified film is tightly coated onto the surface of the battery core, ensuring that its overall shape and size are compatible with the shape and size of the cavity in the battery pack tray; the degree of alcoholysis of the PVA modified film is ≥99.5%; S3. Laying and stacking layers to prepare the battery pack tray preform: Lay the molded core material on the metal structural layer 1, making the molded core material fit the concave groove on the metal structural layer, and then sequentially lay the structural adhesive film layer 23, the toughening buffer layer 22, and the glass fiber composite material layer 21 on the molded core material; see attached diagram for a schematic diagram of the layering. Figure 2 ; S4. Compression molding: The battery pack tray preform is fed into the mold, heated to the curing temperature, and then kept under pressure to complete the curing. After cooling, the mold is opened and the part is removed. S5. Remove the salt core: Machine a round hole on each end of the battery pack tray cavity 3 as a coolant inlet 11 and a coolant outlet 12; connect the coolant inlet 11 and coolant outlet 12 to a high-pressure hot water circulation device, and introduce water to dissolve the high-strength salt core to obtain the battery pack tray.

[0032] Step S1 further includes a steel plate pretreatment step, specifically including: After the metal structural layer is stamped with concave grooves, a PVC anti-corrosion layer is sprayed onto the metal structural layer. The spraying process is as follows: electrostatic voltage 60-80kV, powder outlet air pressure 0.4~0.6MPa, gun distance 200~300mm, and target wet film thickness 80~100μm.

[0033] Step S1 further includes laser roughening of the surface of one side of the cavity formed by the metal structure layer, with a roughness of Ra2.0-3.0μm, so that it can interlock with the thermoplastic composite material layer in the subsequent molding process and improve the bonding strength.

[0034] In step S3, the fiberglass composite material layer is fiberglass PP prepreg, with the product length direction defined as 0°, and the layup angle of the fiberglass PP prepreg layer is [0 / 90 / 45 / -45]s.

[0035] In this molding method, the PVA-modified film on the surface of the salt core is transferred to the inner wall of the molding cavity during the molding process, forming a continuous and dense thermoplastic anti-corrosion layer.

[0036] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A battery pack tray, characterized in that, It includes a metal structure layer and a composite material layer. The four edges of the metal structure layer and the four edges of the composite material layer are combined to form a flat cavity in the middle, which serves as a coolant flow channel. A thermoplastic anti-corrosion layer is provided on the inner wall of the cavity. A coolant inlet and a coolant outlet communicating with the cavity are also provided on one side of the metal structure layer of the battery pack tray.

2. The battery pack tray according to claim 1, characterized in that, The thermoplastic anti-corrosion layer is a PVA-modified film, and the PVA-modified film comprises, by weight percentage of the raw materials: 80-85%wt of matrix resin: specifically polyvinyl alcohol (PVA), with a degree of alcoholysis ≥99% and a degree of polymerization 1700-2000; 8-12%wt of reinforcing agent / heat stabilizer: specifically hydrophilic nano silica with a particle size of 15-30nm; 2-3%wt moisture inhibitor / lubricant: specifically calcium stearate; 1-2%wt of adjuvant: specifically glycerin.

3. A battery pack tray according to claim 1, characterized in that, The composite material layer includes a glass fiber composite material layer.

4. A battery pack tray according to claim 3, characterized in that, The composite material layer also includes a toughening buffer layer, which is disposed on the side of the glass fiber composite material layer close to the metal structural layer.

5. A battery pack tray according to claim 4, characterized in that, The composite material layer also includes a structural adhesive film layer, which is disposed on the side of the toughening buffer layer near the metal structural layer.

6. A battery pack tray according to claim 1, characterized in that, The cross-section of the cavity is undulating, so that the coolant flows in a wave-like pattern from the coolant inlet side to the coolant outlet side.

7. A battery pack tray according to claim 6, characterized in that, The cavity includes a concave groove section and a horizontal straight section, which are alternately arranged to form an undulating coolant flow channel; the bottom groove width of the concave groove section is 30-35mm and the groove depth is 4.0±0.5mm; the length of the horizontal straight section is 30-35mm; all turning corners in the cavity adopt R-angle transition, R≥5mm.

8. A method for preparing a battery pack tray according to any one of claims 1-7, characterized in that, Including the following steps: S1. Prepare the metal structure layer according to the shape and size of the battery pack tray; S2. Prepare a molded core material that conforms to the shape and size of the cavity of the battery pack tray: S21. Press the salt core to make its shape and size close to the shape and size of the cavity of the battery pack tray; the salt core is heat resistant to above 280℃; S22. A layer of PVA modified film is tightly coated on the outer surface of the core to obtain a molded core material, the shape and size of which are adapted to the cavity of the battery pack tray; the degree of alcoholysis of the PVA modified film is ≥99.5%; S3. Laying and stacking to prepare the battery pack tray preform: First, lay the molded core material on the metal structure layer, and then continue to lay other composite material layers on the surface of the molded core material in sequence. S4. Compression molding: The battery pack tray preform is fed into the mold and heated to cure. After curing, the mold is opened and the part is removed after cooling. S5. Dissolve and remove the salt core in the battery pack tray cavity to obtain the battery pack tray.

9. The preparation method according to claim 8, characterized in that, Step S1 further includes: spraying a PVC layer onto the metal structure layer. The spraying process is as follows: electrostatic voltage 60-80kV, powder outlet pressure 0.4~0.6MPa, gun distance 200~300mm, and target wet film thickness 80~100μm.

10. The preparation method according to claim 9, characterized in that, Step S1 further includes: after spraying the metal structure layer, laser roughening is performed on the surface of one side of the cavity formed by the metal structure layer, with a roughness Ra of 2.0-3.0 μm.

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