Embedded structure energy storage integrated composite material and preparation method and application thereof

Abstract

The invention belongs to the technical field of structural energy storage, and provides an embedded structural energy storage integrated composite material and a preparation method and application thereof. The embedded structure energy storage integrated composite material comprises an upper fiber reinforced resin matrix composite material layer, a lower fiber reinforced resin matrix composite material layer and a porous ceramic reinforced layer, and the connecting mode of all the layers is limited. The embedded structure energy storage integrated composite material has a multi-layer and multifunctional integrated structure, has excellent mechanical properties, also has efficient and safe energy storage capability, and can meet the requirements of low-altitude aircrafts such as unmanned aerial vehicles, electric vertical take-off and landing aircrafts and the like on light weight, high integration level, safety and reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of structural energy storage, and in particular to an embedded structural energy storage integrated composite material and a preparation method and application thereof. Background Art

[0002] With the development of aerospace and new energy, the demand for structural and functional integration is becoming increasingly urgent. In low-altitude aircraft such as drones and eVTOLs, traditional designs typically install battery packs as independent components within the aircraft. This increases the weight and volume of the aircraft, negatively impacting its range and payload capacity. To address this, structural energy storage integration has emerged. This integrates electrochemical energy storage components directly into the load-bearing structure, achieving a "structure as battery" approach, reducing weight and optimizing space.

[0003] There are two main approaches to integrated structural energy storage: one is a structural battery, for example, using carbon fiber as both a composite material reinforcement and a battery electrode, with the battery functionality built into the carbon fiber composite layer; the other is an embedded energy storage structure, where independent battery cells are embedded in a sandwich structure or cavity. U.S. Patent No. 9,017,854 discloses a multifunctional composite material: multiple spaced through-holes are prefabricated in a layer of insulating polymer material. Energy storage devices such as lithium-ion batteries or supercapacitors are placed in the through-holes and electrically connected to each other. Load-bearing composite panels are then stacked on both sides of the polymer material plate, forming a structural component that can withstand both tensile and compressive loads and store electrical energy. However, the above technologies have some shortcomings: ① The polymer insulation layer (such as resin-based materials) has limitations in mechanical strength, heat resistance and flame retardancy, and is prone to softening or burning when thermal runaway occurs in the battery cell, affecting structural safety; ② The embedded battery cells usually use traditional lithium-ion batteries, which have limited energy density (about 150-250Wh / kg) and cannot fully tap the potential of structural energy storage integration; ③ The connection between battery cells mostly relies on wires or metal connecting plates, which are scattered in layout and easily loosen or break under vibration loads, making it difficult to achieve high-reliability intra-layer electrical connections; ④ Embedded batteries will introduce structural stress concentration and potential micro-damage, and there is a lack of effective measures to improve the damage tolerance of structural components. For example, when microcracks appear in the composite matrix, it cannot repair itself, resulting in a decrease in the performance of the structural components under long-term cyclic loads.

[0004] Therefore, it is necessary to provide an embedded structural energy storage integrated composite material that can further reduce weight, increase energy storage density while ensuring the structural bearing capacity, and enhance the safety, durability and maintainability of the composite material to meet the application needs in fields such as low-altitude aircraft. Summary of the Invention

[0005] The purpose of the present invention is to provide an embedded structure energy storage integrated composite material and its preparation method and application in response to the deficiencies of the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides an embedded structural energy storage integrated composite material, comprising an upper fiber reinforced resin-based composite material layer, a lower fiber reinforced resin-based composite material layer and a porous ceramic reinforcement layer;

[0008] The porous ceramic reinforcement layer is located between the upper fiber reinforced resin-based composite material layer and the lower fiber reinforced resin-based composite material layer, and a plurality of energy storage units are embedded in the porous ceramic reinforcement layer;

[0009] The upper fiber-reinforced resin-based composite material layer and the lower fiber-reinforced resin-based composite material layer are independently connected to the porous ceramic reinforcement layer through a resin adhesive; the resin adhesive contains self-repairing microcapsules.

[0010] Preferably, the thickness of the upper fiber-reinforced resin-based composite material layer and the lower fiber-reinforced resin-based composite material layer are independently 0.2 to 2 mm.

[0011] Preferably, the porous ceramic reinforcement layer comprises one or more of porous alumina ceramics, porous silicon carbide ceramics and porous silica aerogel ceramics;

[0012] The porosity of the porous ceramic reinforcement layer is 30-90%, and the pore diameter of the porous ceramic reinforcement layer is 1-10 mm.

[0013] Preferably, the energy storage unit is a lithium-sulfur battery, the electrode material of the lithium-sulfur battery contains graphene, and the mass of the graphene is 1 to 10% of the mass of the electrode material.

[0014] Preferably, the particle size of the self-repairing microcapsules is 50 to 200 μm, and the mass of the self-repairing microcapsules is 5 to 15% of the mass of the resin adhesive.

[0015] Preferably, the plurality of energy storage units are connected via an interlayer conductive film;

[0016] The interlayer conductive film comprises a polymer film and a conductive metal foil circuit arranged on the polymer film, the thickness of the conductive metal foil circuit is 10 to 100 μm, and the thickness of the polymer film is 25 to 50 μm;

[0017] The polymer film includes a polyimide film, a polyethylene terephthalate film or a polyethylene terephthalate-butylene terephthalate copolymer film.

[0018] The present invention also provides a method for preparing the embedded structure energy storage integrated composite material, comprising the following steps:

[0019] 1) embedding the energy storage unit into the pores of the porous ceramic reinforcement layer; the size and distribution of the pores in the porous ceramic reinforcement layer match those of the energy storage unit;

[0020] 2) placing an interlayer conductive film on the porous ceramic reinforcement layer, so that the conductive metal foil circuit of the interlayer conductive film is connected to the electrode of each energy storage unit;

[0021] 3) applying a resin adhesive on the upper and lower surfaces of the porous ceramic reinforcement layer;

[0022] 4) Laying the upper fiber-reinforced resin-based composite material layer and the lower fiber-reinforced resin-based composite material layer on the resin adhesive respectively, and performing vacuum hot pressing and curing to obtain an embedded structural energy storage integrated composite material.

[0023] Preferably, the thickness of the resin adhesive in step 3) is 0.08 to 0.15 mm.

[0024] Preferably, the vacuum degree of the vacuum hot pressing curing in step 4) is -0.05 to -0.1 MPa, the pressure of the vacuum hot pressing curing is 0.1 to 0.5 MPa, the temperature of the vacuum hot pressing curing is 80 to 150° C., and the time of the vacuum hot pressing curing is 1 to 3 hours.

[0025] The present invention also provides the application of the embedded structure energy storage integrated composite material in low-altitude aircraft.

[0026] The beneficial effects of the present invention include the following:

[0027] 1) The embedded structural energy storage integrated composite material of the present invention has a multi-level, multifunctional integrated structure, excellent mechanical properties, and at the same time has efficient and safe energy storage capacity, which can meet the requirements of low-altitude aircraft such as drones and electric vertical take-off and landing aircraft for lightweight, high integration, safety and reliability.

[0028] 2) The present invention adopts lithium-sulfur battery as energy storage unit, and introduces graphene into electrode material at the same time, which shows higher stability in repeated mechanical load and charge-discharge cycle, improves the rate performance of battery, and the capacity retention rate can reach more than 80% after 100 cycles under 1C charge-discharge condition. Combined with structural integration design, the integration of structural materials and battery functions is realized. Under the premise of ensuring mechanical properties, the energy density of structural energy storage integrated component is significantly improved, which can reach 150-300Wh / kg, an increase of more than 20%; the interlayer conductive film replaces the traditional wire, which reduces the weight and occupies less internal space. It can be deformed with the composite material under stress without breaking, thereby improving the reliability of electrical connection in vibration and impact environment. After 2h vibration test and 100 thermal cycle tests, the circuit resistance of the conductive film connection changes by less than 5%, and there is no poor contact or short circuit or open circuit, which realizes the planarization and integration of electrical connection. The composite material of the present invention has a flexural strength of more than 300 MPa at room temperature and a flexural modulus of more than 55 GPa. It can maintain more than 80% of its strength at a high temperature of 150°C. Self-healing microcapsules are added to the resin adhesive to greatly improve the damage resistance of the structural energy storage integrated component. When small cracks or signs of interlayer peeling occur during the use of the component, the self-healing microcapsules can respond and repair in time to effectively prevent the cracks from expanding. Experiments show that the interlaminar fracture toughness of the composite material with 10% self-healing microcapsules is increased by more than 30%, and it can self-repair to more than 80% of its original strength within 24 hours after the cracks are generated. DETAILED DESCRIPTION

[0029] The present invention provides an embedded structural energy storage integrated composite material, comprising an upper fiber reinforced resin-based composite material layer, a lower fiber reinforced resin-based composite material layer and a porous ceramic reinforcement layer;

[0030] The porous ceramic reinforcement layer is located between the upper fiber reinforced resin-based composite material layer and the lower fiber reinforced resin-based composite material layer, and a plurality of energy storage units are embedded in the porous ceramic reinforcement layer;

[0031] The upper fiber-reinforced resin-based composite material layer and the lower fiber-reinforced resin-based composite material layer are independently connected to the porous ceramic reinforcement layer through a resin adhesive; the resin adhesive contains self-repairing microcapsules.

[0032] In the present invention, the thickness of the upper fiber-reinforced resin-based composite material layer and the lower fiber-reinforced resin-based composite material layer are independently preferably 0.2 to 2 mm, more preferably 0.25 to 1.5 mm, and even more preferably 0.5 to 1 mm.

[0033] In the present invention, the porous ceramic reinforcement layer preferably comprises one or more of porous alumina ceramics, porous silicon carbide ceramics and porous silica aerogel ceramics;

[0034] The porosity of the porous ceramic reinforcement layer is preferably 30-90%, more preferably 40-80%, and even more preferably 50-70%. The pore size of the porous ceramic reinforcement layer is preferably 1-10 mm, more preferably 3-8 mm, and even more preferably 5 mm. The porous ceramic reinforcement layer not only provides structural support and positioning, but also has excellent heat resistance and flame retardancy. Compared with traditional polymer foam or honeycomb structures, it can better ensure the structural integrity and safety of the battery in the event of heat or failure.

[0035] In the present invention, the energy storage unit is preferably a lithium-sulfur battery. The electrode material of the lithium-sulfur battery preferably includes graphene, with the mass of the graphene preferably comprising 1-10% of the mass of the electrode material, more preferably 3-8%, and even more preferably 5%. The energy storage unit is in the form of a thin sheet. Compared to conventional lithium-ion batteries, lithium-sulfur batteries have a higher theoretical specific energy (up to 2500 Wh / kg or more), which is suitable for the high energy density requirements of aircraft. The introduction of graphene into the electrode material improves the conductivity and structural stability of the electrode, significantly improving the cycle life and rate performance of the composite material and reducing capacity degradation caused by structural loads.

[0036] In the present invention, the particle size of the self-repairing microcapsules is preferably 50-200 μm, more preferably 70-150 μm, and more preferably 80-100 μm; the mass of the self-repairing microcapsules is preferably 5-15% of the mass of the resin adhesive, more preferably 7-12%, and more preferably 10%.

[0037] In the present invention, the self-repairing microcapsules preferably include two-component repairing microcapsules or single-component repairing microcapsules;

[0038] The two-component repair microcapsules preferably comprise epoxy resin microcapsules and curing agent microcapsules. The wall material of the epoxy resin microcapsules is preferably urea-formaldehyde resin, and the core material is preferably epoxy resin and / or phenolic resin; the wall material of the curing agent microcapsules is preferably urea-formaldehyde resin, and the core material is preferably curing agent.

[0039] The wall material of the single-component repair microcapsule is preferably urea-formaldehyde resin, and the core material preferably comprises a single-component unsaturated resin and a catalyst. When a composite material generates micro-cracks due to load, the crack tip will damage the self-repairing microcapsule, release the repair agent, and cause polymerization and curing in situ at the crack, thereby filling and healing the crack, allowing timely repair of the micro-crack, preventing the micro-crack from expanding, and improving the fatigue life and damage tolerance of the assembly.

[0040] In the present application, the mass ratio of the core material to the wall material of the self-repairing microcapsule is preferably 60-80:20-40, and more preferably 70:30.

[0041] The wall thickness of the self-repairing microcapsule is preferably 1-2 μm, and more preferably 1.5 μm.

[0042] In the present application, the plurality of energy storage units are preferably connected by an interlayer conductive film.

[0043] The interlayer conductive film preferably comprises a polymer film and a conductive metal foil circuit disposed on the polymer film. The thickness of the conductive metal foil circuit is preferably 10-100 μm, more preferably 18-80 μm, and even more preferably 30-50 μm. The thickness of the polymer film is preferably 25-50 μm, more preferably 30-45 μm, and even more preferably 35-40 μm.

[0044] The polymer film preferably comprises a polyimide film, a polyethylene terephthalate film, or a polyethylene terephthalate-polybutylene terephthalate copolymer film. The plurality of energy storage units are connected in series and / or in parallel by the interlayer conductive film to form a battery pack, thereby forming a closed circuit, making the electrical connection more stable and reliable, and allowing uniform dispersion in the structural plane without stress concentration, while reducing the electrical resistance and the weight of the connecting components.

[0045] The present application also provides a preparation method of the embedded structure energy storage integrated composite material, comprising the following steps:

[0046] 1) embedding the energy storage unit in the holes of the porous ceramic reinforcing layer, wherein the size and distribution of the holes in the porous ceramic reinforcing layer are matched with the energy storage unit;

[0047] 2) placing the interlayer conductive film on the porous ceramic reinforcing layer, so that the conductive metal foil circuit of the interlayer conductive film is connected with the electrode of each energy storage unit;

[0048] 3) coating a resin adhesive on the upper and lower surfaces of the porous ceramic reinforcing layer;

[0049] 4) laying the upper and lower fiber-reinforced resin-based composite material layers on the resin adhesive, respectively, and performing vacuum hot pressing and curing to obtain the embedded structure energy storage integrated composite material.

[0050] In the present invention, the thickness of the resin adhesive in step 3) is preferably 0.08 to 0.15 mm, more preferably 0.1 to 0.12 mm.

[0051] In the present invention, the vacuum degree of the vacuum hot pressing curing in step 4) is preferably -0.05 to -0.1 MPa, more preferably -0.07 to -0.095 MPa, and more preferably -0.08 MPa; the pressure of the vacuum hot pressing curing is preferably 0.1 to 0.5 MPa, more preferably 0.2 to 0.4 MPa, and more preferably 0.3 MPa; the temperature of the vacuum hot pressing curing is preferably 80 to 150°C, more preferably 100 to 120°C; the time of the vacuum hot pressing curing is preferably 1 to 3 hours, more preferably 1.5 to 2.5 hours, and more preferably 2 hours.

[0052] The present invention also provides the application of the embedded structure energy storage integrated composite material in low-altitude aircraft.

[0053] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0054] The resin in the carbon fiber reinforced resin-based prepregs of the embodiments and comparative examples of the present invention is bisphenol A epoxy resin E51 (epoxy equivalent is 190 g / eq), the resin mass content is 35%, the carbon fiber is T300 grade plain weave, and the thickness of the single-layer prepreg is 0.25 mm;

[0055] The self-healing microcapsules (particle size of 150 μm) contain epoxy resin microcapsules and curing agent microcapsules in a mass ratio of 1:1. The wall material of the epoxy resin microcapsules is urea-formaldehyde resin, and the core material is a mixed resin of bisphenol A epoxy resin E51 (epoxy equivalent of 190 g / eq) and phenolic epoxy resin F51 (epoxy equivalent of 190 g / eq) in a mass ratio of 1:1; the wall material of the curing agent microcapsules is urea-formaldehyde resin, and the core material is a modified fatty amine curing agent (the modified fatty amine curing agent is prepared by reacting triethylenetetramine, diethylenetriamine and bisphenol A epoxy resin E51 at 80°C for 2 hours. The epoxy equivalent of E51 is 430 g / mol, the mass ratio of triethylenetetramine and diethylenetriamine is 3:1, and the mass of E51 is 10% of the total mass of triethylenetetramine and diethylenetriamine). The self-healing microcapsules were prepared as follows: urea and a 37% formaldehyde aqueous solution were mixed in a mass ratio of 1:1.7. Deionized water, twice the mass of the formaldehyde aqueous solution, was added to form a mixed solution. The pH of the mixed solution was adjusted to 8.5 with triethanolamine. The mixed solution was stirred in a 70°C water bath at 200 rpm for 1 hour to obtain a urea-formaldehyde prepolymer solution. Polyvinyl alcohol (molecular weight 150,000) and deionized water were mixed in a mass ratio of 1:9 at room temperature, heated to 80°C, and stirred until the polyvinyl alcohol was completely dissolved, to obtain a colloidal protective solution. ① A mixed resin (the mass of the mixed resin was 30% of the mass of the colloidal protective solution) was added to the colloidal protective solution and emulsified at 600 rpm to form uniform oil droplets, resulting in a stable oil / water dispersion. ② Add urea-formaldehyde prepolymer solution to the oil / water dispersion at a rate of 5 drops / s (the mass of the urea-formaldehyde prepolymer solution is 30% of the mass of the oil / water dispersion system). After the addition is completed, heat it to 55°C and stir it continuously at 300r / min for 3 hours to allow the urea-formaldehyde prepolymer to condense at the oil droplet interface to form urea-formaldehyde resin wall material. After completion, filter it with a filter membrane and dry it at 45°C to constant weight to obtain epoxy resin microcapsules with a wall thickness of 1μm and a core material to wall material mass ratio of 70:30. ② Add a modified fatty amine curing agent to the colloidal protective solution (the mass of the modified fatty amine curing agent is 20% of the mass of the colloidal protective solution) and emulsify it at 800r / min to form uniform oil droplets of the modified fatty amine curing agent to obtain a stable oil / water dispersion system. A urea-formaldehyde prepolymer solution (the mass of the urea-formaldehyde prepolymer solution is 25% of the mass of the oil-water dispersion) was added dropwise to the oil / water dispersion at a rate of 5 drops / s. After addition, the mixture was heated to 60°C and stirred continuously at 500 rpm for 3 hours to allow the urea-formaldehyde prepolymer to condense at the oil droplet interface to form a urea-formaldehyde resin wall material. The mixture was then filtered through a filter membrane and dried at 45°C to constant weight, yielding curing agent microcapsules with a wall thickness of 1.5 μm and a core material to wall material ratio of 75:25.

[0056] Example 1

[0057] A porous alumina ceramic plate with a size of 150 mm×150 mm×5 mm, a porosity of 80%, a pore diameter of 5 mm, and a pore wall thickness of 1 mm was dried at 120° C. for 2 h to obtain a porous ceramic reinforcement layer.

[0058] Nickel leads were welded to the positive and negative tabs of four lithium-sulfur soft-pack batteries measuring 40mm×40mm×4mm and then dried at 40°C for 24 hours. The negative electrode of the lithium-sulfur soft-pack battery was metallic lithium, the positive electrode was a sulfur-carbon composite cathode, and the electrolyte was a dioxolane (DOL) / dimethyl ether (DME) organic electrolyte (the mass ratio of DOL and DME was 80:20). The sulfur-carbon composite cathode contained 5% graphene nanosheets (the graphene nanosheets had a thickness of 4nm and a lateral size of 8μm), 80% sulfur powder, 10% conductive carbon, and 5% polyvinylidene fluoride (PVDF). Each lithium-sulfur soft-pack battery had a rated capacity of 2.3Ah and a nominal voltage of 2.2V and was encapsulated in aluminum-plastic film. The four dried lithium-sulfur soft-pack batteries were embedded in the pores of the porous ceramic reinforcement layer.

[0059] On a 50μm-thick polyimide film, an 18μm-thick circuit pattern is etched according to the circuit design of the lithium-sulfur soft-pack battery in series, and copper foil pads are installed in the circuit pattern to obtain an interlayer conductive film. The interlayer conductive film is attached to one side of the porous ceramic reinforcement layer, so that each copper foil pad corresponds to a lithium-sulfur soft-pack battery. The nickel lead of each lithium-sulfur soft-pack battery corresponds to the copper foil pad of the interlayer conductive film, ensuring that the connection path of the copper foil pad of the interlayer conductive film forms a series circuit. The periphery of the interlayer conductive film is fixed with epoxy adhesive to prevent displacement during assembly. An ultrasonic welder is used to weld the nickel lead to the copper foil pad to form an electrical connection. The power of the ultrasonic welder is 100W, and the welding time for each time is 0.5s. After welding, the resistance of each node in the series circuit and the battery voltage are tested to ensure that the connection is intact. Epoxy adhesive is injected into the gap between the lithium-sulfur soft-pack battery and the hole wall to fix the battery position.

[0060] 10% self-healing microcapsules were mixed into the epoxy adhesive. A 0.1mm thick layer of the epoxy adhesive was evenly applied to the upper and lower surfaces of the porous ceramic reinforcement layer. Four layers of carbon fiber-reinforced resin-based prepreg were then stacked (in a 0 / 90 / 0 / 90 orientation), ensuring that the prepreg covered and extended 5mm beyond the edges of the porous ceramic reinforcement layer to ensure good coverage. The carbon fiber-reinforced resin-based prepreg was then covered with a release cloth and a porous separator film. The prepreg was then placed in a sealed vacuum bag, evacuated to -0.095 MPa, and cured at 120°C and 0.3 MPa for 1 hour. After natural cooling and pressure release, the release cloth and porous separator film were removed to obtain an embedded structural energy storage integrated composite material.

[0061] The composite material's flexural strength and modulus were tested using the three-point bending method, with a support spacing of 80 mm and a loading rate of 2 mm / min. The results showed a flexural strength of 310 MPa and a flexural modulus of 58 GPa, representing only a 6% decrease in strength compared to pure carbon fiber sheets (flexural strength of 330 MPa and flexural modulus of 60 GPa). This demonstrates that the composite material of the present invention can provide mechanical properties comparable to those of pure structural materials.

[0062] The composite material was subjected to charge and discharge tests using a battery tester. The battery was first charged at a constant current and constant voltage of 0.2C to a total voltage of 8.4V, then discharged at 0.2C to a total voltage of 6.0V, recording the initial total discharge capacity. The battery was then cycled 50 times at 0.5C at room temperature, recording the capacity decay. The results showed an initial total discharge capacity of 2.25Ah, or 18.9Wh. After 50 cycles at 0.5C, the total capacity reached 2.01Ah, 89.3% of the initial capacity. The voltage plateau remained stable during the cycling process, with no transient interruptions. After the cycling, the internal resistance increased by less than 5%. This demonstrates that the embedded composite material of the present invention has minimal impact on the battery, and the graphene-enhanced lithium-sulfur battery maintains good cycling stability.

[0063] The composite material was placed in a simulated wing (simple support at both ends, with an equivalent load of 10N added in the center) and subjected to a vibration durability test (sine sweep 20-200Hz, amplitude 0.5g, 2h), to observe the electrical connection stability, and to test the internal resistance and capacity. The results showed that the internal resistance of the composite material increased by 2.6%, the capacity attenuation was less than 1%, and X-ray inspection showed that there was no delamination of the composite material appearance and interlayer conductive film. This shows that the embedded composite material of the present application has excellent vibration durability and provides safety protection.

[0064] Example 2

[0065] The negative electrode of the lithium-sulfur soft-pack battery in Example 1 was replaced with lithium foil (thickness 50 μm). The rated capacity of each lithium-sulfur soft-pack battery was 2.0 Ah, the nominal voltage was 2.1 V, and it was encapsulated with aluminum-plastic film. Other aspects were the same as in Example 1.

[0066] Example 3

[0067] The porous alumina ceramic plate in Example 1 was replaced with a porous alumina ceramic plate with a size of 200 mm × 200 mm × 6 mm, a porosity of 7%, a pore diameter of 6 mm, and a pore wall thickness of 1 mm. Other aspects were the same as in Example 1.

[0068] Comparative Example 1

[0069] The sulfur-carbon composite positive electrode in Example 2 was replaced with one containing, by mass, 80% sulfur powder, 15% conductive carbon, and 5% polyvinylidene fluoride, with the rest being the same as in Example 2.

[0070] Comparative Example 2

[0071] The self-repairing microcapsules in Example 1 are omitted, and the rest are the same as in Example 1.

[0072] Comparative Example 3

[0073] The porous alumina ceramic plate in Example 3 was replaced with a composite plate with an aramid paper honeycomb reinforcement layer. The honeycomb material was Nomex honeycomb with a pore size of 6 mm and a density of 0.08 g / cm 3 , core thickness 6mm, others are the same as Example 3.

[0074] The performance tests were performed on the composite materials of Example 2 and Comparative Example 1 respectively:

[0075] ①Constant current discharge tests at different rates (0.2C, 1C, 2C) were carried out at room temperature to compare the discharge capacity and discharge median voltage at high rates. The results showed that the composite material of Example 2 was able to release 95% of its capacity at 1C discharge, and the discharge platform voltage was relatively stable at around 2.0V, and 80% of its capacity was able to be released at 2C discharge; while Comparative Example 1 could only release 88% of its capacity at 1C discharge, and the voltage dropped rapidly at the end of the discharge, and only 65% ​​of its capacity was released at 2C discharge. This shows that the addition of graphene significantly improves the conductivity and high-rate performance of the composite material.

[0076] ② Cycle 100 charge and discharge cycles at 1C at room temperature, and record the capacity retention. The results show that the capacity retention rate of Example 2 is 82%, while that of Comparative Example 1 is only 68%. This indicates that the conductive network and structural reinforcement of graphene effectively mitigate the attenuation and shedding of active materials in the sulfur-carbon composite cathode, maintaining the structural integrity and activity of the electrode.

[0077] ③ On a bending fatigue testing machine, the composite material was bent periodically by ±5° in the longitudinal direction (bending radius of 100mm, frequency of 1Hz), reciprocated 1000 times, and the battery capacity and internal resistance were recorded. The results showed that the battery capacity of Example 2 only decreased by less than 5%, and the internal resistance increased by 20%; the battery capacity of Comparative Example 1 decreased by 12%, and the internal resistance increased by 50%. After the test, the composite material was disassembled and it was found that the positive electrode sheets of some batteries of the composite material of Comparative Example 1 had local cracks and signs of active layer peeling, while the positive electrode sheets of the batteries of Example 2 were intact. This shows that the graphene-enhanced electrode has better flexibility and stability, and can withstand structural deformation while maintaining good electrical contact.

[0078] According to the performance test results of the composite materials of Example 2 and Comparative Example 1, it can be seen that the introduction of graphene significantly improves the electrical performance and durability of the embedded lithium-sulfur battery, and exhibits excellent performance under high-rate discharge, long cycle and load conditions, which is conducive to achieving high-performance energy storage.

[0079] The performance tests were performed on the composite materials of Example 1 and Comparative Example 2 respectively:

[0080] ① A low-velocity impact test was conducted using a drop hammer (a 2 kg weight was dropped from a height of 0.25 m). After the test, the composites were subjected to ultrasonic C-scans to measure the internal delamination area. The composites were then left at room temperature (25°C) for 48 hours, and the crack width changes on the back side of the impact point were observed microscopically before and after the low-velocity impact. The results showed that the composite material in Comparative Example 2 exhibited a discontinuous region (delamination or crack) with a diameter of approximately 30 mm around the impact point, while the discontinuity in Example 1 had a diameter of approximately 25 mm, which was smaller than that in Comparative Example 2. This indicates that the presence of the self-healing microcapsules inhibited the initial propagation of impact damage. Observation of the back side of the impact point revealed a visible radial crack on the back side of the composite material in Comparative Example 2, approximately 20 mm in length and 0.2 mm in width. While Example 1 also exhibited cracks, they were not easily discernible to the naked eye, with a width of only 0.1 mm under microscopic observation. After 48 hours of stabilization, the crack appearance in Comparative Example 2 remained unchanged, while the crack in Example 1 was also difficult to observe under a microscope. This indicates that the self-healing microcapsules released the repair agent and healed the crack.

[0081] ② The compressive strength test was carried out on the composite material after low-speed impact. Axial pressure was applied at a speed of 1mm / min, and the load when buckling, fracture, etc. occurred was recorded to calculate the residual compressive strength (based on the composite material without low-speed impact, the compressive strength was 280MPa). The results showed that the residual compressive strength of Example 1 dropped to 210MPa, which was 75% of the initial compressive strength, and no sudden instability and damage occurred during the compression process; the residual compressive strength of Comparative Example 2 dropped to 160MPa, which was only 57% of the initial compressive strength. Delamination and expansion occurred at the impact damage during the compression process, leading to failure. This shows that the self-repairing microcapsules re-bonded the delamination interface and improved the load-bearing capacity of the damaged parts.

[0082] ③ Inspection of the energy storage units of the composite material after low-speed impact revealed no leakage or short circuit. However, since the cracks in Comparative Example 2 were not repaired, long-term use could cause the cracks to extend to the battery area, posing a safety hazard. The cracks in Example 1 have been repaired, isolating the battery from the external environment and improving the long-term safety of the structural components.

[0083] According to the performance test results of the composite materials of Example 1 and Comparative Example 2, it can be seen that the self-healing microcapsules can effectively improve the impact resistance and residual compressive strength of the composite materials after impact, so that the composite materials can still maintain high structural integrity and safety when accidentally damaged.

[0084] The performance tests were performed on the composite materials of Example 3 and Comparative Example 3 respectively:

[0085] ① Dynamic thermomechanical analysis was conducted using a three-point bending model (frequency 1 Hz, temperature increased from room temperature to 200°C). The equivalent bending stiffness of the composite material was measured every 10°C, and the relative stiffness retention rate with temperature was recorded. The results showed that Example 3 maintained 90% of its bending stiffness at 150°C and 70% at 200°C. Comparative Example 3's bending stiffness decreased rapidly above 120°C, retaining only 40% at 150°C and beginning to thermally decompose at 180°C. This demonstrates that the porous ceramic reinforcement layer of the present invention can maintain structural stability in high-temperature environments.

[0086] ② Place the composite material in a lithium battery heating failure test chamber, gradually heat the chamber at a rate of 5°C / min using a heating plate, observe and record the structural changes and combustion conditions of the composite material, and stop heating when uncontrolled phenomena such as bulging, pressure relief, or fire occur. After the test, remove the composite material and measure the residual strength using the simplified three-point bending method at room temperature (the bearing capacity required to deflect the center of the composite material by 10 mm). The results showed that the energy storage units of Example 3 and Comparative Example 3 both experienced thermal runaway at 170°C. The surface temperature of the energy storage unit in Example 3 reached 420°C during thermal runaway, and it extinguished itself 10 seconds after emitting smoke and igniting. No open flames were observed in the composite material itself, and only the area embedded in the energy storage unit was burned, with resin carbonization of 20 mm in diameter, but the structure of the carbon fiber material remained unchanged. The residual strength of Example 3 was 80% of the initial strength. After ignition, the surface temperature of the energy storage unit in Comparative Example 3 reached 650°C, and the aramid paper honeycomb reinforcement layer was quickly ignited. The flames spread rapidly, causing a large area of ​​the composite board to burn. The combustion lasted for 2 minutes before extinguishing itself, producing thick black smoke. The honeycomb core of the composite material disappeared after combustion, leaving only a portion of carbon fiber, which was no longer able to withstand any load. This demonstrates the superiority of the porous ceramic reinforcement layer of the present invention in extreme situations.

[0087] According to the performance test results of the composite materials of Example 3 and Comparative Example 3, it can be seen that the porous ceramic reinforcement layer of the present invention can greatly improve the safety and integrity of the composite materials under high temperature and battery thermal runaway conditions, and fully meet the strict requirements of the aerospace field for flame retardancy and heat resistance of materials.

[0088] Application Example 1

[0089] The number of lithium-sulfur soft-pack batteries in Example 1 is increased to 8 (rated total voltage 4.4V, capacity 8Ah), 2 are connected in series and then 4 are connected in parallel to arrange the interlayer conductive film. The rest is the same as in Example 1 to obtain an embedded structural energy storage integrated composite material. This composite material is used as the wing skin. The aircraft adopts a fixed-wing low-altitude aircraft with a wingspan of 2m. The wing skin on each side is spliced ​​by 2 pieces of composite material with a size of 500mm×200mm×6mm. Each wing provides 35Wh of energy, and a total of 70Wh of energy is provided. The surface of the skin is coated with a waterproof insulating coating as the only power source for the aircraft. The leading edge and main beam of the wing adopt a carbon fiber structure, and the whole machine weighs 5kg.

[0090] Comparative Application Example 1

[0091] The wing skin utilizes a 6mm-thick carbon fiber sandwich structure with a foam core, and no embedded batteries. A lithium-ion battery pack is installed in the nose battery compartment. The pack consists of four Li-ion 18650 cells connected in parallel and two in series (nominal voltage 14.8V, capacity 5Ah, energy 74Wh). All other configurations are the same as in Application Example 1. To achieve the same weight as in Application Example 1, additional counterweights were added.

[0092] The performance tests were conducted on the aircraft corresponding to Use Case 1 and Comparative Example 1 respectively:

[0093] ① Measure key locations on the aircraft by applying a downward force of 10N to the wingtip and measuring deflection and natural frequency. The results show that in Application Example 1, with the center of gravity located 30% of the chord behind the leading edge, the deflection was 15mm, and the natural first-order bending frequency was 12Hz. In Comparative Example 1, with the center of gravity located 25% of the chord behind the leading edge, the deflection was 18mm, and the natural first-order bending frequency was 10Hz. This demonstrates that embedded composite materials can improve the bending stiffness of the wing.

[0094] ② Under no-wind conditions, fly at a power of 200W until the battery is exhausted, record the continuous level flight time and monitor the wing surface temperature and battery voltage. The results show that the continuous level flight time of Application Example 1 is 62 minutes, while that of Application Comparison Example 1 is only 50 minutes. This is attributed to the fact that Application Example 1 reduces the structural load of the battery, improves the overall energy utilization rate, distributes the batteries on the wings, reduces the body resistance and weight redundancy, and reduces losses. During level flight, the wing surface temperature of Application Example 1 is uniform, slightly higher than the ambient temperature, but far below the safety threshold, and the battery voltage decreases steadily without abnormal fluctuations; the temperature of the wing battery compartment of Application Comparison Example 1 is as high as 45°C, and the concentrated heat causes heat accumulation in the nose of the aircraft, posing a safety hazard.

[0095] ③ The aircraft climbed at full throttle for 10 seconds, measuring its altitude. After a dive at an initial speed of 250 km / h, the aircraft leveled off, observing wing deformation and recovery. The results showed that Application Example 1 climbed to 45 meters in 10 seconds, while Comparative Example 1 climbed to 42 meters. During high-speed maneuvers, Application Example 1's wings exhibited less deformation and a more responsive response, while Comparative Example 1's wings were slightly softer, exhibiting visible bending during a violent pull-up.

[0096] The aircraft performance test results from Application Example 1 and Comparative Example 1 demonstrate that the embedded structural energy storage integrated composite material of the present invention can significantly improve flight performance (by more than 20%) when used in low-altitude aircraft without increasing overall weight. Its high mechanical properties enhance flight control quality. Furthermore, the embedded energy storage unit reduces potential safety hazards in the battery compartment and enables controllable wing skin temperature. The embedded structural energy storage integrated composite material of the present invention demonstrates superior performance in low-altitude aircraft.

[0097] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An embedded structure energy storage integrated composite material, characterized in that: It comprises an upper fiber reinforced resin matrix composite material layer, a lower fiber reinforced resin matrix composite material layer and a porous ceramic reinforcement layer; The porous ceramic reinforcement layer is located between the upper fiber reinforced resin-based composite material layer and the lower fiber reinforced resin-based composite material layer, and a plurality of energy storage units are embedded in the porous ceramic reinforcement layer; The upper fiber-reinforced resin-based composite material layer and the lower fiber-reinforced resin-based composite material layer are independently connected to the porous ceramic reinforcement layer through a resin adhesive; the resin adhesive contains self-repairing microcapsules.

2. The embedded structure energy storage integrated composite material according to claim 1, characterized in that: The thickness of the upper fiber-reinforced resin-based composite material layer and the lower fiber-reinforced resin-based composite material layer are independently 0.2 to 2 mm.

3. The embedded structure energy storage integrated composite material according to claim 2, characterized in that: The porous ceramic reinforcement layer comprises one or more of porous alumina ceramics, porous silicon carbide ceramics and porous silica aerogel ceramics; The porosity of the porous ceramic reinforcement layer is 30-90%, and the pore diameter of the porous ceramic reinforcement layer is 1-10 mm.

4. The embedded structure energy storage integrated composite material according to claim 2 or 3, characterized in that: The energy storage unit is a lithium-sulfur battery. The electrode material of the lithium-sulfur battery contains graphene, and the mass of the graphene accounts for 1-10% of the mass of the electrode material.

5. The embedded structure energy storage integrated composite material according to claim 4, characterized in that: The particle size of the self-repairing microcapsule is 50-200 μm, and the mass of the self-repairing microcapsule is 5-15% of the mass of the resin adhesive.

6. The embedded structure energy storage integrated composite material according to claim 5, characterized in that: The multiple energy storage units are connected via an interlayer conductive film; The interlayer conductive film comprises a polymer film and a conductive metal foil circuit arranged on the polymer film, the thickness of the conductive metal foil circuit is 10 to 100 μm, and the thickness of the polymer film is 25 to 50 μm; The polymer film includes a polyimide film, a polyethylene terephthalate film or a polyethylene terephthalate-butylene terephthalate copolymer film.

7. The method for preparing the embedded structure energy storage integrated composite material according to any one of claims 1 to 6, characterized in that: The following steps are included: 1) embedding the energy storage unit into the pores of the porous ceramic reinforcement layer; the size and distribution of the pores in the porous ceramic reinforcement layer match those of the energy storage unit; 2) placing an interlayer conductive film on the porous ceramic reinforcement layer, so that the conductive metal foil circuit of the interlayer conductive film is connected to the electrode of each energy storage unit; 3) applying a resin adhesive on the upper and lower surfaces of the porous ceramic reinforcement layer; 4) Laying the upper fiber-reinforced resin-based composite material layer and the lower fiber-reinforced resin-based composite material layer on the resin adhesive respectively, and performing vacuum hot pressing and curing to obtain an embedded structural energy storage integrated composite material.

8. The preparation method according to claim 7, characterized in that Step 3) The thickness of the resin adhesive is 0.08 to 0.15 mm.

9. The preparation method according to claim 8, characterized in that Step 4) The vacuum degree of the vacuum hot pressing curing is -0.05 to -0.1 MPa, the pressure of the vacuum hot pressing curing is 0.1 to 0.5 MPa, the temperature of the vacuum hot pressing curing is 80 to 150° C., and the time of the vacuum hot pressing curing is 1 to 3 hours.

10. Use of the embedded structure energy storage integrated composite material according to any one of claims 1 to 6 in low-altitude aircraft.