Embedded lithium ion battery multifunctional energy storage composite structure and preparation method thereof

Abstract

The invention belongs to the technical field of composite material structures and energy storage, and discloses a multifunctional energy storage composite structure of an embedded lithium ion battery and a preparation method of the multifunctional energy storage composite structure. The composite structure comprises an upper-layer skin, a lower-layer skin and an integrated energy storage layer located in the middle. The integrated energy storage layer comprises a sandwich panel and an energy storage unit; the sandwich panel is provided with a honeycomb or a grid; the energy storage units are embedded into honeycombs or grids of the sandwich panel; the raw materials of the upper-layer skin and the lower-layer skin are at least one layer of fiber prepreg. Through the application of the epoxy resin fiber composite material (fiber prepreg), the battery pack body becomes a part of the structure, electrical-structural integration is realized, an independent metal battery shell is not needed, the weight is reduced, and the bearing capacity and the heat-conducting and electrical-conducting properties of fibers are fully utilized; a hot-pressing integrated process is adopted for preparation, the technological process is simple and feasible, and the manufacturing cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of composite material structure and energy storage technology, and in particular to an embedded lithium-ion battery multifunctional energy storage composite structure and its preparation method. Background Technology

[0002] With the increasing demand for lightweight and efficient energy storage in fields such as electric vehicles, drones, and aerospace, the integration of composite structural materials and battery technology has attracted widespread attention. Carbon fiber composites possess excellent specific strength and specific modulus, making them ideal materials for high-performance structural components. In recent years, the concept of structural batteries (structural lithium-ion batteries) has emerged, organically combining structural components with energy storage systems. This technology, while maintaining the mechanical properties of composite materials, endows them with electrical energy storage functions, significantly improving the energy efficiency and structural efficiency of power systems. The core of multifunctional structural energy storage composite materials lies in the deep integration of the material's load-bearing function and energy storage function, representing the future development direction of structural materials. For example, existing research has proposed using carbon fiber as the negative electrode of lithium batteries, coating the electrode material on the fiber surface and embedding it in the composite material to manufacture structural batteries, achieving initial progress. However, current technologies typically only replace the battery casing with a composite material shell, resulting in limited weight savings; or embed the battery cell in a honeycomb sandwich layer, relying on a complex mesh framework and bonding structure. For example, one publicly disclosed honeycomb sandwich structure lithium-ion battery composite material consists of two layers of fiber-reinforced panels and a middle polymer honeycomb sandwich layer. The honeycomb cells are filled from bottom to top with a positive electrode, a separator, and a negative electrode layer, and electrolyte is injected through injection holes. Another aircraft cabin panel structure integrates the lithium battery with the spacecraft skin honeycomb core, and is fixed by a grid-like frame and titanium alloy bolts. Although these solutions achieve the integration of structure and energy storage functions, they generally suffer from problems such as complex manufacturing processes, limited stiffness improvement, and insufficient mechanical protection of the battery cells.

[0003] Furthermore, carbon fiber prepregs have already been applied in the battery field. Literature reports using epoxy-based carbon fiber / glass fiber prepregs to fabricate electric vehicle battery pack casings, achieving a weight reduction of approximately 30-50% compared to metal casings; and achieving high-temperature resistance and thermal runaway suppression through the addition of flame retardants. Carbon fiber prepregs can also be used as electrode carriers, enhancing the conductivity and structural stability of lithium batteries. These applications demonstrate that epoxy resin carbon fiber composites possess advantages such as high strength, lightweight, heat resistance, and flame retardancy, providing an ideal material basis for multifunctional energy storage structures.

[0004] However, current technologies have not yet provided an embedded lithium-ion battery composite structure that can effectively fix the battery cell, simplify the manufacturing process, and significantly improve the overall energy density and stability of the system while maintaining mechanical properties. Therefore, there is an urgent need for an innovative technical approach to achieve deep integration of the battery cell and structural components, and to improve its structural load-bearing mechanical properties and electrochemical energy storage performance. Summary of the Invention

[0005] The purpose of this invention is to provide an embedded lithium-ion battery multifunctional energy storage composite structure and its preparation method, thereby solving the above-mentioned problems existing in the existing lithium battery composite structures.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides an embedded lithium-ion battery multifunctional energy storage composite structure, including an upper skin, a lower skin, and an integrated energy storage layer; the integrated energy storage layer is located between the upper skin and the lower skin. The integrated energy storage layer includes a sandwich panel and energy storage units; the sandwich panel has a honeycomb or grid structure; the energy storage unit includes at least one lithium-ion battery; the energy storage unit is embedded in the honeycomb or grid structure of the sandwich panel. The integrated energy storage layer also includes an adhesive layer between itself and the upper and lower skin layers; The upper skin is made of at least one layer of fiber prepreg; the lower skin is made of at least one layer of fiber prepreg.

[0007] Preferably, the adhesive layer is made of epoxy resin or silicone.

[0008] Preferably, the raw materials of the fiber prepreg include fibers and a resin matrix; the raw materials of the resin matrix include epoxy resin and halogen-free flame retardant.

[0009] Preferably, the fiber is one of carbon fiber, glass fiber, or aramid fiber.

[0010] Preferably, the thickness of the sandwich panel is 1~30mm.

[0011] Preferably, the sandwich panel is made of honeycomb panel or foam; the foam is one of polyurethane foam, polystyrene foam, polyetherimide foam, and polymethacrylamide foam.

[0012] This invention also provides a method for preparing an embedded lithium-ion battery multifunctional energy storage composite structure, comprising the following steps: The energy storage unit is embedded in the sandwich panel to obtain an integrated energy storage layer; adhesive is applied to the upper and lower surfaces of the integrated energy storage layer respectively; The fiber prepreg is laid up to form an upper skin precursor and a lower skin precursor, and the integrated energy storage layer is placed between the upper skin precursor and the lower skin precursor to obtain a laminated structure. The laminated structure is first vacuumed and then hot-pressed to obtain a multifunctional energy storage composite structure for embedded lithium-ion batteries.

[0013] Preferably, the temperature for hot pressing curing is 60~100℃; the pressure for hot pressing curing is 0.1~1MPa; and the time for hot pressing curing is 4~6h.

[0014] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: This invention utilizes epoxy resin fiber composite materials (fiber prepreg) to integrate the battery pack into the structure, achieving electro-structural integration. This eliminates the need for a separate metal battery casing, reducing weight, and fully utilizes the load-bearing capacity and thermal and electrical conductivity of the fibers. The hot-pressing integrated manufacturing process is simple and easy to implement, reducing manufacturing costs. Furthermore, the outer layers of the upper and lower skins can be coated with flame-retardant or conductive coatings to further improve fire resistance and electromagnetic shielding. This invention broadens the application prospects of energy storage structural components and can be used in various applications requiring weight reduction and integrated energy storage, such as electric vehicle body parts, aircraft skins, and drone wings. Detailed Implementation

[0015] This invention provides an embedded lithium-ion battery multifunctional energy storage composite structure, including an upper skin, a lower skin, and an integrated energy storage layer; the integrated energy storage layer is located between the upper skin and the lower skin. The integrated energy storage layer includes a sandwich panel and energy storage units; the sandwich panel has a honeycomb or grid structure; the energy storage unit includes at least one lithium-ion battery; the energy storage unit is embedded in the honeycomb or grid structure of the sandwich panel. The integrated energy storage layer also includes an adhesive layer between itself and the upper and lower skin layers; The upper skin is made of at least one layer of fiber prepreg; the lower skin is made of at least one layer of fiber prepreg.

[0016] In this invention, the raw material of the adhesive layer is preferably epoxy resin or silicone, and more preferably epoxy resin.

[0017] In this invention, the raw materials of the fiber prepreg preferably include fibers and a resin matrix; the raw materials of the resin matrix preferably include epoxy resin and halogen-free flame retardant; the raw materials of the resin matrix preferably also include aliphatic amine curing agent and curing accelerator.

[0018] In this invention, the fiber is preferably one of carbon fiber, glass fiber, or aramid fiber, more preferably carbon fiber or glass fiber, and even more preferably carbon fiber. The carbon fiber used in this invention is PAN-based high-strength carbon fiber, such as TORAY T700, TORAY T800, or Hexcel IM7.

[0019] In this invention, the halogen-free flame retardant is preferably one or more of phosphorus-based flame retardants, phosphorus-nitrogen-based flame retardants, inorganic hydroxide flame retardants, and nitrogen-based flame retardants, more preferably one or more of phosphorus-based flame retardants, phosphorus-nitrogen-based flame retardants, and inorganic hydroxide flame retardants, and even more preferably a mixture of phosphorus-based flame retardants and phosphorus-nitrogen-based flame retardants; the phosphorus-based flame retardant is preferably a phosphonate and / or a phosphate ester, more preferably 9,10-dihydro-9-oxo-10-phosphenanthrene-10-oxide (DOPO), bisphenol A-diphenyl ether, etc. The flame retardant is selected from one or more of diphenyl phosphate (BDP) and resorcinol bis(diphenyl phosphate) (RDP), more preferably DOPO; the phosphorus-nitrogen flame retardant preferably includes phosphazene flame retardants, more preferably hexaphenoxycyclotriphosphazene (HPP); the inorganic hydroxide flame retardant preferably includes aluminum hydroxide and / or magnesium hydroxide, more preferably magnesium hydroxide; the nitrogen-based flame retardant preferably includes melamine cyanurate and / or melamine polyphosphate, more preferably melamine cyanurate.

[0020] In this invention, the curing accelerator is preferably one of 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-phenyl-4-methylimidazole, more preferably 2-methylimidazole or 2-ethyl-4-methylimidazole, and even more preferably 2-ethyl-4-methylimidazole.

[0021] In this invention, the fiber prepreg preferably contains 40-80% by mass, more preferably 45-70%, and even more preferably 50-65% by mass; the resin matrix preferably contains 5-40% by mass, more preferably 10-30%, and even more preferably 10-25% by mass.

[0022] In this invention, the thickness of the sandwich panel is preferably 1~30mm, more preferably 2~20mm, and even more preferably 2.5~15mm.

[0023] In this invention, the sandwich panel is preferably made of honeycomb board or foam, more preferably honeycomb board; the honeycomb board is preferably made of aluminum alloy or aramid paper honeycomb board; the aluminum alloy honeycomb board is a 3003 or 5052 series aluminum alloy honeycomb board; the aramid paper honeycomb board is Nomex. ® Aramid paper honeycomb; the density of the honeycomb board is preferably 30~150 kg / m³. 3 Further preferred is 40~120 kg / m 3 More preferably 50~100 kg / m 3The honeycomb aperture (distance between edges) of the honeycomb panel is preferably 2~15 mm, more preferably 3~10 mm, and even more preferably 4~8 mm; the honeycomb wall thickness of the honeycomb panel is preferably 0.02~0.15 mm, more preferably 0.03~0.10 mm, and even more preferably 0.04~0.08 mm.

[0024] In this invention, the foam is preferably one of polyurethane foam, polystyrene foam, polyetherimide foam, and polymethacrylamide foam, more preferably polystyrene foam or polyetherimide foam, and even more preferably polyetherimide foam.

[0025] In this invention, the lithium-ion battery is preferably a commercially available lithium-ion battery, such as a pouch battery or a hard-shell battery. The positive electrode material of the lithium-ion battery of this invention can be LiFePO4, LiCoO2, LiMn2O4, or a ternary material, and the negative electrode can be natural graphite or artificial graphite.

[0026] In this invention, the energy storage unit embedded in the honeycomb or grid of the sandwich panel also includes filling the energy storage unit with silicone pads or elastic pads to buffer thermal expansion and contraction and prevent the energy storage unit from expanding under vacuum or temperature change conditions.

[0027] This invention also provides a method for preparing an embedded lithium-ion battery multifunctional energy storage composite structure, comprising the following steps: The energy storage unit is embedded in the sandwich panel to obtain an integrated energy storage layer; adhesive is applied to the upper and lower surfaces of the integrated energy storage layer respectively; The fiber prepreg is laid up to form an upper skin precursor and a lower skin precursor, and the integrated energy storage layer is placed between the upper skin precursor and the lower skin precursor to obtain a laminated structure. The laminated structure is first vacuumed and then hot-pressed to obtain a multifunctional energy storage composite structure for embedded lithium-ion batteries.

[0028] In this invention, the temperature for hot-press curing is preferably 60~100℃, more preferably 70~90℃, and even more preferably 80℃; the pressure for hot-press curing is preferably 0.1~1MPa, more preferably 0.2~0.6MPa, and even more preferably 0.5MPa; the time for hot-press curing is preferably 4~6h, more preferably 4~5h, and even more preferably 4h. This invention uses low-temperature curing to protect the energy storage unit, avoid high-temperature damage, and balance cell safety with the degree of resin curing.

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0030] Example 1

[0031] This embodiment provides a method for preparing an embedded lithium-ion battery multifunctional energy storage composite structure, including the following steps: (1) Based on 100 parts by weight of the total resin matrix, take 50 parts by weight of bisphenol A type epoxy resin and 30 parts by weight of phenolic type epoxy resin and mix them evenly. Add 10 parts by weight of halogen-free flame retardant (a mixture of DOPO and HPP in a mass ratio of 1:1). After mechanically stirring and dispersing evenly at room temperature, add 9 parts by weight of fatty amine curing agent and 1 part by weight of 2-ethyl-4-methylimidazole. Continue stirring until uniform to obtain the resin matrix. Coat the resin matrix onto carbon fiber fabric (the carbon fiber is TORAY T700 and the fabric surface density is 200 g / m²). 2 Carbon fiber prepreg was obtained by applying a substrate (0.15 mm thick) to the substrate; the mass fraction of carbon fiber fabric in the carbon fiber prepreg was 60%. (2) Attach buffer pads (1mm silicone pad on top, 1mm silicone pad on the bottom, and 2mm foam pad around the perimeter) to the outer packaging of the soft-pack battery (lithium-ion battery, LiFePO4 positive electrode, natural graphite negative electrode, 3mm thick) to suspend and fix it to prevent the cell from expanding under external force or negative pressure. Then connect four soft-pack batteries in series to form two strings, and connect one aluminum foil current collector and one copper foil current collector to the outside of each string to form a battery pack. Insert the battery pack into the honeycomb holes of the aramid paper honeycomb board (5mm thick, 6mm opposite side of the honeycomb hole, and about 0.06mm thick honeycomb wall). Coat the upper and lower surfaces of the honeycomb board with epoxy glue to obtain an integrated energy storage layer. (3) In a flat mold, four layers of carbon fiber prepreg are laid in a staggered manner at 0° / 90° to form the upper skin precursor. The integrated energy storage layer is then placed in the mold. Then, four layers of carbon fiber prepreg are laid in a staggered manner at 0° / 90° to cover the integrated energy storage layer, forming the lower skin precursor, thus obtaining a laminated structure. (4) After the laminated structure is evacuated in a vacuum bag, it is placed in a thermostatic precipitator for curing under the conditions of 80℃ and 0.5MPa for 4h to obtain an embedded lithium-ion battery multifunctional energy storage composite structure.

[0032] Performance Testing: The composite structure of this embodiment measures 200mm × 100mm, contains four battery cells, and has a total weight of approximately 0.62kg (approximately 0.40kg for the battery cells and 0.22kg for the composite material). Weighing and theoretical calculations show that it can reduce weight by approximately 35% compared to a battery integrated with an aluminum alloy shell of the same size. In a 0.5C charge-discharge test, the battery's initial usable capacity was 2500mAh, and after 200 cycles, the capacity retention rate was 96%. Three-point bending test (span 150mm): The composite structure of this embodiment has a bending strength of 300MPa and a bending modulus of 25GPa; the control structure without battery cells (see Example 1, the difference being that it does not contain a battery pack) has a bending strength of 370MPa and a bending modulus of 31GPa. Compared to the control structure without battery cells, the composite component of Example 1 shows a slight decrease in mechanical properties, but still retains more than 80% (indicating that the embedding of the battery cells did not significantly weaken the overall structural rigidity). SEM analysis of the fracture surface showed that the epoxy resin and carbon fiber interface around the battery cell were well bonded with no obvious delamination. This proves that the structure of the present invention has both mechanical load-bearing and energy storage functions, and effectively utilizes the high strength and high modulus advantages of carbon fiber composite materials while achieving lightweight design.

[0033] Example 2

[0034] This embodiment provides a method for preparing an embedded lithium-ion battery multifunctional energy storage composite structure. See Embodiment 1 for details. The difference is that in step (2), the honeycomb plate is replaced with polyimide foam (1.5 mm thick), and the polyetherimide foam is provided with cylindrical holes to insert the battery pack.

[0035] Performance Testing: The composite structure in this embodiment measures 100mm × 100mm and has a thickness of 3.0mm. This composite structure further reduces weight (approximately 0.25kg total weight) and increases energy density to the 50Wh / kg level. Test results show that a discharge capacity of 2500mAh can be achieved at 0.2C. In terms of mechanical strength, the bending strength of the board is 150MPa and the modulus is 18GPa, slightly lower than that of Example 1, but the absence of a honeycomb layer reduces weight and simplifies the manufacturing process. It can be seen that this embodiment is suitable for applications with slightly lower load-bearing requirements but higher requirements for weight and integration.

[0036] Example 3

[0037] This embodiment provides a method for preparing an embedded lithium-ion battery multifunctional energy storage composite structure, specifically referring to Embodiment 1, except that the mold in step (3) is a curved surface mold. (The curved surface mold is a unidirectional circular arc surface, and the curvature radius of the upper and lower skin layers along the length of the plate is 1000mm, corresponding to a curvature of 1.0×10.) -3 mm -1The plate is approximately straight along its width, with a curvature of approximately 0. When the plate size is 200mm × 100mm, the arc height is 5mm. This embodiment is designed as a curved surface to simulate the curved components of a drone wing or a car roof.

[0038] Performance Testing: Mechanical testing results show that the curved composite structure in this embodiment exhibits a bending strength of 290 MPa and a bending modulus of 24 GPa under a three-point bending test (span 150 mm). Compared with the flat composite structure in Example 1 (bending strength 300 MPa, bending modulus 25 GPa), these figures represent approximately 97% and 96% of the bending strength and modulus, respectively. The bending strength and modulus are essentially equivalent, and the battery charging and discharging functions are normal. This embodiment demonstrates the possibility of applying this invention to complex shaped structural components. Whether it is an airfoil or a vehicle body curved surface, cell fusion can be achieved through appropriate design of the bonding layout.

[0039] Example 4

[0040] This embodiment provides a method for preparing an embedded lithium-ion battery multifunctional energy storage composite structure. See Embodiment 1 for details. The difference is that a thermally conductive silicone sheet is provided on the outside of the battery pack in step (2).

[0041] Performance Testing: The mechanical test results were similar to those of Example 1. Under ambient temperatures of (25±2)℃ and natural convection air conditions, the composite structure battery pack of this example was charged at a 2C rate to the rated charging voltage in constant current and constant voltage mode. After standing for 10 minutes, it was discharged at a 2C rate to the cutoff voltage, and this process was repeated for 3 charge-discharge cycles. During the charge-discharge process, three K-type thermocouples were placed at the center of the cell, the interface between the thermal pad and the lower skin, and the outer surface of the composite structure to monitor temperature changes in real time. The test results showed that during the above high-current charge-discharge test, the temperature of the composite structure uniformly reached 50±5℃ within 5 minutes. The control sample without a thermal pad had a maximum temperature of approximately 65℃ under the same conditions, which was about 15℃ lower than that without a thermal pad. This indicates that the epoxy resin-based composite material combined with the thermal pad structure can meet the heat dissipation requirements of the cell, and the thermal management effect can be further improved by optimizing the material ratio or structure (such as adding thermally conductive fillers to the fiber prepreg).

[0042] Example 5

[0043] This embodiment provides a method for preparing an embedded lithium-ion battery multifunctional energy storage composite structure. See Embodiment 1 for details. The difference is that in step (2), four soft-pack batteries are connected in series to form a battery pack.

[0044] Performance testing: The multi-cell module improves specific capacity; although the thickness increases, it is more efficient for long-range applications. This invention can also be extended to the integration of other cell types, such as hard-shell batteries or solid-state batteries, requiring only corresponding adjustments to material selection.

[0045] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A multifunctional energy storage composite structure for embedded lithium-ion batteries, characterized in that, It includes an upper skin, a lower skin, and an integrated energy storage layer; the integrated energy storage layer is located between the upper skin and the lower skin. The integrated energy storage layer includes a sandwich panel and an energy storage unit; the sandwich panel has a honeycomb or grid structure; the energy storage unit includes at least one lithium-ion battery. The energy storage unit is embedded in the honeycomb or grid of the sandwich panel; The integrated energy storage layer also includes an adhesive layer between itself and the upper and lower skin layers; The upper skin is made of at least one layer of fiber prepreg; the lower skin is made of at least one layer of fiber prepreg.

2. The embedded lithium-ion battery multifunctional energy storage composite structure according to claim 1, characterized in that, The adhesive layer is made of epoxy resin or silicone.

3. The embedded lithium-ion battery multifunctional energy storage composite structure according to claim 2, characterized in that, The raw materials for the fiber prepreg include fibers and a resin matrix; the raw materials for the resin matrix include epoxy resin and halogen-free flame retardant.

4. The embedded lithium-ion battery multifunctional energy storage composite structure according to claim 3, characterized in that, The fiber is one of carbon fiber, glass fiber, or aramid fiber.

5. The embedded lithium-ion battery multifunctional energy storage composite structure according to claim 4, characterized in that, The thickness of the sandwich panel is 1~30mm.

6. The embedded lithium-ion battery multifunctional energy storage composite structure according to claim 3, characterized in that, The sandwich panel is made of honeycomb board or foam; the foam is one of polyurethane foam, polystyrene foam, polyetherimide foam, and polymethacrylamide foam.

7. A method for preparing an embedded lithium-ion battery multifunctional energy storage composite structure according to any one of claims 1 to 6, characterized in that, Includes the following steps: The energy storage unit is embedded in the sandwich panel to obtain an integrated energy storage layer; adhesive is applied to the upper and lower surfaces of the integrated energy storage layer respectively; The fiber prepreg is laid up to form an upper skin precursor and a lower skin precursor, and the integrated energy storage layer is placed between the upper skin precursor and the lower skin precursor to obtain a laminated structure. The laminated structure is first vacuumed and then hot-pressed to obtain a multifunctional energy storage composite structure for embedded lithium-ion batteries.

8. The method for preparing an embedded lithium-ion battery multifunctional energy storage composite structure according to claim 7, characterized in that, The temperature for hot-press curing is 60~100℃; the pressure for hot-press curing is 0.1~1MPa; and the time for hot-press curing is 4~6h.