A multifunctional structural energy storage composite material and preparation method thereof

Abstract

The present invention provides a multifunctional structural energy storage composite material and a preparation method thereof, belonging to the technical field of multifunctional composite materials. The present invention combines a carbon fiber reinforced matrix with an optimized special-shaped structural design to provide excellent mechanical strength and stiffness, thereby achieving high mechanical properties. At the same time, the application of a multi-level conductive network and an electrolyte layer significantly improves the conductivity of the electrode and the utilization rate of active materials, thereby achieving excellent electrochemical performance. The present invention has achieved a technological breakthrough by introducing a multi-level conductive network, a resin-based electrolyte and an optimized special-shaped structural design, obtaining a high-performance (mechanical and electrochemical performance) structural energy storage composite material that meets the needs of practical applications.

Description

Technical Field

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

[0002] The development of new energy vehicles, aerospace, and portable electronic devices is driving an increasing demand for lightweight, high-strength, and multifunctional materials. Conventional energy storage devices are often separated from the structural material, increasing the weight and volume of the system. Energy storage composites, multifunctional materials that combine mechanical load-bearing capacity with energy storage functionality, have garnered widespread attention in these fields.

[0003] Existing energy storage composite materials mainly include the following categories: 1. Lithium-ion battery composite materials: By integrating lithium-ion batteries into fiber-reinforced composite materials, a certain load-bearing capacity is achieved. Common designs include using carbon fiber as a structural skeleton and acting as an electrode material at the same time. 2. Supercapacitor composite materials: Active materials with high specific surface area (such as graphene and carbon nanotubes) are compounded with a polymer matrix to provide energy storage functions. Suitable for application scenarios that require fast charging and discharging. 3. Solid-state electrolyte composite materials: Combine ionic conductivity and mechanical strength for high-safety energy storage systems. Polymer matrices are doped with inorganic fillers or ionic liquids to improve ionic conductivity and stability.

[0004] However, existing energy storage composite materials have the following problems: 1. Balance between energy storage and load-bearing performance: When improving energy storage performance, existing materials usually sacrifice mechanical strength and cannot meet the load-bearing requirements at the same time. For example, increasing the content of electrolyte or active material will cause the matrix to become brittle. 2. Interface bonding problem: The interface bonding between the active material and the composite matrix is ​​poor, resulting in reduced energy storage efficiency or decreased mechanical properties. Especially in dynamic environments, interface separation is a common failure mode. 3. Insufficient ionic conductivity: The ionic conductivity of most energy storage composite materials is low, which limits the charge and discharge rate. The main reasons are uneven distribution of the conductive network or poor dispersion of ionic liquid / lithium salt. 4. Complex manufacturing process: Existing processes (such as lamination and vacuum infusion) are difficult to achieve large-area, integrated multifunctional composite material preparation. Bubbles or delamination defects are prone to occur during the preparation process, affecting the overall performance of the material. 5. Insufficient environmental adaptability: In extreme environments (such as high temperature and low temperature), the performance of energy storage composite materials decays significantly, making it difficult to meet application requirements.

[0005] Therefore, the development of structural energy storage composite materials that have both mechanical bearing and energy storage functions has important scientific significance and application value. Summary of the Invention

[0006] The object of the present invention is to provide a multifunctional structural energy storage composite material and a preparation method thereof, wherein the multifunctional structural energy storage composite material integrates mechanical bearing and electrochemical energy storage functions.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a multifunctional structural energy storage composite material, comprising the following steps:

[0009] mixing carbon nanotubes, graphene, MXene and an organic solvent, and mixing the resulting suspension with a binder and a positive electrode active material to obtain a conductive slurry;

[0010] The carbon fiber cloth is subjected to plasma treatment to obtain a modified carbon fiber cloth;

[0011] The conductive slurry is electrospinned on the surface of the modified carbon fiber cloth to form a conductive coating, and then subjected to hot pressing to obtain a multi-level conductive network;

[0012] Mixing lithium salt with ionic liquid to obtain ionic liquid electrolyte;

[0013] mixing the ionic liquid electrolyte with a resin matrix, a functional polymer, a nanofiller, and a curing agent to obtain a resin-based electrolyte precursor;

[0014] Using ANSYS software, topology optimization is performed based on required mechanical strength and energy storage performance, and based on the optimization results, the multi-level conductive network is composited with a resin-based electrolyte precursor to obtain a composite precursor;

[0015] According to the geometric shape obtained by topology optimization, a three-dimensional model of the special-shaped part is established by using SolidWorks, and the three-dimensional model of the special-shaped part is made into a mold by using a CNC processing method;

[0016] The positive electrode, electrolyte separator and negative electrode are laid out in sequence in a mold, and the composite precursor is injected into the mold by a vacuum-assisted resin transfer molding method, and then cured and molded to obtain a multifunctional structural energy storage composite material.

[0017] Preferably, the mass ratio of the carbon nanotubes, graphene and MXene is 1 to 3:1 to 3:1; the diameter of the carbon nanotubes is 10 to 20 nm, the length is 10 to 30 μm, and the conductivity is greater than 10 4 S / m; the graphene is a single-layer redox graphene with a thickness of <1nm and a side length of 5 to 10μm; the MXene is Ti3C2T x The thickness of the MXene is <2 nm and the sheet diameter is 1 to 5 μm.

[0018] Preferably, the binder is polyvinylidene fluoride, and the molecular weight of the polyvinylidene fluoride is 450,000; the power of the plasma treatment is 80 to 120 W, and the time is 5 to 10 minutes.

[0019] Preferably, the electrospinning conditions include: voltage 10-15 kV; collection distance 10-15 cm; slurry flow rate 0.1-0.2 mL / min;

[0020] The temperature of the hot pressing treatment is 130-160° C., the pressure is 10-15 MPa, and the time is 2-5 hours.

[0021] Preferably, the ionic liquid includes 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; the lithium salt includes lithium hexafluorophosphate; and the mass ratio of the lithium salt to the ionic liquid is 1:5-15.

[0022] Preferably, the resin matrix includes bisphenol F epoxy resin; the functional polymer includes sulfonated polyetheretherketone; the nanofiller includes nanosilica; and the curing agent includes polyetheramine curing agent D230 or dicyandiamide.

[0023] Preferably, the mass of the functional polymer is 3-6% of the mass of the resin matrix, the mass of the nanofiller is 1-3% of the mass of the resin matrix; the mass ratio of the resin matrix to the curing agent is 100:30-50; the mass ratio of the ionic liquid to the resin matrix is ​​0.5-1:1.

[0024] Preferably, when the curing agent is polyetheramine curing agent D230, the curing molding includes: curing at 80-100° C. for 4 hours, and then curing at 120-150° C. for 2 hours.

[0025] Preferably, when the curing agent is dicyandiamide, a modified imidazole accelerator is further added, and the mass of the modified imidazole accelerator is 1.5-3% of the mass of the resin matrix; and the curing molding is: curing at 120-130° C. for 30 minutes.

[0026] The present invention provides a multifunctional structural energy storage composite material prepared by the preparation method described in the above technical solution.

[0027] The present invention provides a method for preparing a multifunctional structural energy storage composite material, which uses a carbon fiber matrix as a mechanical load-bearing structure to provide high strength and stiffness; designs a multi-level conductive network, and coats a conductive slurry containing carbon nanotubes, graphene, and MXene on a carbon fiber cloth to construct a multi-level conductive network to improve the conductivity and energy storage performance of the electrode; introduces functional polymers and nanofillers into the resin matrix to enhance ion conductivity and mechanical properties; optimizes the design of the special-shaped structure, and designs special-shaped parts that meet specific mechanical and energy storage requirements through topological optimization and three-dimensional modeling. The present invention combines a carbon fiber reinforced matrix with an optimized special-shaped structure design to provide excellent mechanical strength and stiffness, thereby achieving high mechanical properties. At the same time, the application of a multi-level conductive network and an electrolyte layer significantly improves the conductivity of the electrode and the utilization rate of active materials, thereby achieving excellent electrochemical performance. The present invention achieves a technological breakthrough by introducing a multi-level conductive network, a new resin-based electrolyte, and an optimized special-shaped structure design, obtaining a high-performance (mechanical and electrochemical performance) structural energy storage composite material that meets practical application needs.

[0028] The solution of the present invention has the following advantages:

[0029] 1. Multifunctional balance: While improving energy storage performance (such as ionic conductivity and energy storage density), it also maintains high strength and toughness to meet mechanical load requirements.

[0030] 2. Enhanced interfacial bonding: Optimize the interfacial compatibility between the positive electrode active material and the matrix, and improve the overall performance and service life of the material.

[0031] 3. Optimization of ionic conductivity: Improving the ion mobility of the electrolyte by introducing ionic liquids, lithium salts and multi-level conductive networks.

[0032] 4. Improvement of preparation process: Design efficient and low-defect preparation processes (such as vacuum infusion combined with rapid curing system) to achieve uniform distribution and large-area preparation.

[0033] 5. Improved environmental adaptability: Through material design and optimization, composite materials can maintain stable performance in a wide temperature range and complex environments.

[0034] The present invention can adopt bio-based green and environmentally friendly epoxy resin and recyclable technology to reduce environmental impact and improve the environmental performance and sustainability of the material. DETAILED DESCRIPTION

[0035] In the present invention, unless otherwise specified, all raw materials or reagents used are commercially available products well known in the art.

[0036] The present invention provides a method for preparing a multifunctional structural energy storage composite material, comprising the following steps:

[0037] mixing carbon nanotubes, graphene, MXene and an organic solvent, and mixing the resulting suspension with a binder and a positive electrode active material to obtain a conductive slurry;

[0038] The carbon fiber cloth is subjected to plasma treatment to obtain a modified carbon fiber cloth;

[0039] The conductive slurry is electrospinned on the surface of the modified carbon fiber cloth to form a conductive coating, and then subjected to hot pressing to obtain a multi-level conductive network;

[0040] Mixing lithium salt with ionic liquid to obtain ionic liquid electrolyte;

[0041] mixing the ionic liquid electrolyte with a resin matrix, a functional polymer, a nanofiller, and a curing agent to obtain a resin-based electrolyte precursor;

[0042] Using ANSYS software, topology optimization is performed based on required mechanical strength and energy storage performance, and based on the optimization results, the multi-level conductive network is composited with a resin-based electrolyte precursor to obtain a composite precursor;

[0043] According to the geometric shape obtained by topology optimization, a three-dimensional model of the special-shaped part is established by using SolidWorks, and the three-dimensional model of the special-shaped part is made into a mold by using a CNC processing method;

[0044] The positive electrode, electrolyte separator and negative electrode are laid out in sequence in a mold, and the composite precursor is injected into the mold by a vacuum-assisted resin transfer molding method, and then cured and molded to obtain a multifunctional structural energy storage composite material.

[0045] In the present invention, the mass ratio of the carbon nanotubes, graphene and MXene is preferably 1-3:1-3:1, more preferably 2:2:1; the diameter of the carbon nanotubes is preferably 10-20 nm, the length is preferably 10-30 μm, and the conductivity is preferably >10 4 S / m; the graphene is a single-layer redox graphene with a thickness of <1nm and a side length of 5 to 10μm; the MXene is preferably Ti3C2T x The thickness of the MXene is preferably <2 nm, and the sheet diameter is preferably 1 to 5 μm.

[0046] In the present invention, the organic solvent is preferably N-methylpyrrolidone (NMP). The present invention has no particular limitation on the amount of the organic solvent, and the amount can be adjusted according to the dosage known in the art to ensure sufficient mixing of the materials.

[0047] In the present invention, carbon nanotubes, graphene and MXene are preferably added to an organic solvent and dispersed using an ultrasonic disperser for 30 minutes to form a uniform suspension.

[0048] In the present invention, the binder is preferably polyvinylidene fluoride, and the molecular weight of the polyvinylidene fluoride is preferably 450,000. The weight proportion of the binder in the conductive paste is preferably 5-10%, more preferably 5-8%. In the present invention, PVDF is preferably dissolved in NMP to form a 10wt% binder solution, which is then added to the suspension.

[0049] In the present invention, the positive electrode active material preferably includes lithium iron phosphate, lithium iron phosphate, lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel cobalt manganese oxide (LiNixCoyMnO2, NCM / NMC), lithium nickel cobalt aluminum oxide (LiNi x Co y AlO2, NCA), lithium-rich manganese-based positive electrode materials (Li-rich Mn-based oxide), phosphate-based positive electrode materials (LiMnPO4, LiCoPO4), or composite doped positive electrode materials (Li2FeSiO4, LiVPO4F); the mass of the positive electrode active material is preferably 75-85wt% of the suspension, more preferably 80wt%. The present invention has no particular limitation on the source of the positive electrode active material, and any corresponding positive electrode active material known in the art can be used.

[0050] The present invention has no particular limitation on the specifications and sources of the carbon fiber cloth, and any commercially available product known in the art can be used.

[0051] In the present invention, the power of the plasma treatment is preferably 80 to 120 W, more preferably 90 to 100 W, and the time is preferably 5 to 10 minutes, more preferably 5 to 8 minutes. The present invention has no particular limitation on the equipment and other conditions of the plasma treatment, and the treatment can be carried out according to processes well known in the art.

[0052] In the present invention, the electrospinning conditions preferably include: voltage 10-15 kV; collection distance 10-15 cm; slurry flow rate 0.1-0.2 mL / min; the voltage is more preferably 12-15 kV; the collection distance is more preferably 12 cm; and the slurry flow rate is more preferably 0.1-0.15 mL / min.

[0053] In the present invention, the thickness of the conductive coating is preferably 15 to 30 μm, more preferably 20 μm.

[0054] After the electrospinning is completed, the product is preferably dried in a vacuum drying oven at 80° C. for 6 hours to remove the solvent.

[0055] The present invention has no special limitation on the thickness of the conductive coating, which can be adjusted according to actual needs; in the embodiment of the present invention, it is specifically 20 μm.

[0056] In the present invention, the temperature of the hot pressing treatment is preferably 130-160°C, more preferably 150°C, the pressure is preferably 10-15 MPa, more preferably 10-12 MPa, and the time is preferably 2-5 hours, more preferably 2-3 hours. The present invention strengthens the bonding strength between the conductive coating and the carbon fiber cloth through hot pressing.

[0057] In the present invention, carbon nanotubes (CNTs) are uniformly dispersed in the slurry in the form of single-walled (SWCNTs) or multi-walled (MWCNTs) to form an interwoven nanonetwork, primarily distributed on the surface and pores of the carbon fiber cloth, crosslinked with other conductive materials. As a bridge for electron transport, the CNTs' high aspect ratio and excellent conductivity create a fast electron transport network. After the slurry solidifies, the CNTs improve the mechanical properties of the coating through physical embedding and chemical bonding, providing additional specific surface area, enhancing energy storage performance and electrochemical activity. Graphene is dispersed in a single or few-layer structure, uniformly attached to the surface of the carbon fiber cloth and between the CNTs network. The layered, lamellar structure allows for some graphene to interact with the carbon fibers through π-π interactions, resulting in a stable bond and enhancing the two-dimensional conductive network. The high conductivity of graphene (~10 5 S / m) and CNTs work together to build a multi-level conductive network, reducing the electron transmission path; the sheet structure effectively covers the fiber surface, improving the interface bonding strength between the slurry and the carbon fiber cloth; its high specific surface area (~2600m 2 / g) provide active sites for electrochemical reactions, enhancing capacitive energy storage performance. MXene is distributed as stacked nanosheets or sheets, embedded in the CNT and graphene networks while partially covering the carbon fiber surface. The sheet surface has hydrophilic functional groups (such as -OH, -F, and -Cl), which interact with the matrix and other conductive materials. It provides ion conduction channels: the hydrophilic functional groups and interlayer gaps provide low-resistance paths for ion migration, improving ionic conductivity. The sheet structure increases energy storage capacity through pseudocapacitive effects (such as surface redox reactions). The flaky MXene fills the network gaps, enhancing the coating's structural stability, reducing internal resistance, and improving interfacial stability.

[0058] The synergistic distribution and effects of carbon nanotubes, graphene, and MXene in the present invention:

[0059] Hierarchical network structure: CNTs form a one-dimensional conductive skeleton, graphene builds a two-dimensional conductive network, and MXene provides the combination point of two-dimensional conductivity and ionic conductivity. The three work together to build a multi-level conductive network.

[0060] Distribution characteristics: CNTs penetrate the coating to form a continuous conductive path. Graphene is evenly distributed between CNTs and on the surface of carbon fiber cloth, providing a large-area electron transmission path. MXene: embedded in the network, forming an intersection for electron and ion conduction.

[0061] The three materials work together to create a high-speed electron transport channel, forming a multi-level conductive network and improving electron mobility. The high surface area and active sites of CNTs, graphene, and MXene enhance the electrode's double-layer capacitance and pseudo-capacitance, improving energy storage performance. The interstitial fill of graphene flakes and MXene improves the bonding strength between the coating and the carbon fiber cloth, enhancing the long-term stability of the interface.

[0062] Electron transport performance: The electronic conductivity of the multi-level conductive network is significantly improved, reaching 2.5×10⁵ S / m. Ionic conductivity: The enhanced ion mobility of MXene improves the overall electrode ionic conductivity. Energy storage performance: The electrode's specific capacity reaches 200 F / g, over 30% higher than traditional coatings. Mechanical properties: The coating's elongation at break and tensile strength are significantly improved. The distribution and state design of carbon nanotubes, graphene, and MXene in this invention ensures the high efficiency of the multi-level conductive network while imparting excellent energy storage performance and mechanical stability to the composite material.

[0063] The present invention mixes lithium salt with ionic liquid to obtain an ionic liquid electrolyte; and mixes the ionic liquid electrolyte with a resin matrix, a functional polymer, a nanofiller and a curing agent to obtain a resin-based electrolyte precursor.

[0064] In the present invention, the ionic liquid preferably includes 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM-TFSI); the lithium salt preferably includes lithium hexafluorophosphate; the mass ratio of the lithium salt to the ionic liquid is preferably 1:5-15, more preferably 1:10.

[0065] In the present invention, the resin matrix preferably includes bisphenol F epoxy resin; the mass ratio of the ionic liquid to the resin matrix is ​​preferably 0.5 to 1:1, more preferably 0.8:1.

[0066] In the present invention, the functional polymer preferably includes sulfonated polyetheretherketone; the mass of the functional polymer is preferably 3 to 6% of the mass of the resin matrix; as a preferred embodiment of the present invention, the functional polymer preferably also includes polylactic acid (PLA), and the mass of PLA is preferably 3 to 5% of the mass of the resin matrix.

[0067] In the present invention, the nano-filler preferably includes nano-silicon dioxide; the mass of the nano-filler is preferably 1 to 3% of the mass of the resin matrix.

[0068] In the present invention, the curing agent preferably includes polyetheramine curing agent D230 or dicyandiamide; the mass ratio of the resin matrix to the curing agent is preferably 100:30-50, more preferably 100:35-40.

[0069] The present invention preferably dissolves the lithium salt in the ionic liquid and stirs until completely dissolved to obtain an ionic liquid electrolyte; adds the functional polymer and the nanofiller to the resin matrix, stirs evenly, adds the ionic liquid electrolyte, continues stirring for 1 hour, adds the curing agent, stirs and mixes, and obtains a resin-based electrolyte precursor.

[0070] In the present invention, when the curing agent is polyetheramine curing agent D230, the curing process preferably includes curing at 80-100°C for 4 hours, followed by curing at 120-150°C for 2 hours. When the curing agent is dicyandiamide, the curing process also includes adding a modified imidazole accelerator, the mass of which is preferably 1.5-3%, more preferably 2%, of the mass of the resin matrix. The curing process preferably includes curing at 120-130°C for 30 minutes.

[0071] When the curing agent is dicyandiamide, the present invention can achieve rapid curing.

[0072] The present invention has no particular limitation on the specific process of topology optimization using ANSYS software according to the required mechanical strength and energy storage performance, and topology optimization can be performed using a process well known in the art.

[0073] The roles of topology optimization in this invention include: 1. Maximizing mechanical strength: By adjusting the material distribution and geometric shape, ensure that the composite material has sufficient mechanical properties to cope with complex loads. 2. Improving energy storage performance: Optimizing the distribution of multi-level conductive networks to minimize the transmission path of electrons and ions, thereby improving energy storage efficiency. 3. Balancing performance and weight: While meeting mechanical strength and energy storage performance, achieving lightweight design, suitable for new energy vehicles and aerospace fields. 4. Adapting to the needs of special-shaped parts: In response to the design requirements of complex shapes, ensure the consistency of material properties in various directions and regions.

[0074] In the present invention, the topology optimization step preferably includes:

[0075] 1. Initial model construction: Based on actual needs, define the geometric boundaries, external dimensions, and functional areas (such as load-bearing area and energy storage area) of the special-shaped parts.

[0076] Setting material properties: Input the material parameters of the multi-level conductive network (CNTs, graphene, MXene) and resin-based electrolyte precursor, including: elastic modulus, Poisson's ratio (mechanical properties), electrical conductivity, ionic conductivity (energy storage performance), density (weight).

[0077] 2. The benchmark of topology optimization, the optimization goal is based on the following indicators:

[0078] 1) Mechanical performance benchmark:

[0079] Maximize mechanical strength, with target values ​​of tensile strength ≥50MPa and compressive strength ≥100MPa.

[0080] Minimize structural deformation and ensure that the deformation is controlled within 1%.

[0081] 2) Energy storage performance benchmark:

[0082] Improve ionic conductivity, the target value is ≥1.8×10 -3 S / cm.

[0083] Optimize the conductive network of the electrode to ensure that the electronic conductivity is ≥2.5×10 5 S / m.

[0084] 3) Weight optimization benchmark:

[0085] While meeting the above performance indicators, the material usage is minimized to achieve lightweight design.

[0086] 3. Optimization process

[0087] Step 1: Initial material distribution:

[0088] Set the material filling rate (usually 30% to 80%) as the initial condition for the optimization calculation.

[0089] Step 2: Setting constraints:

[0090] Mechanical constraints: Apply fixed boundary conditions and external loads to simulate the actual usage environment.

[0091] Energy storage constraints: Set the path distribution of the conductive network and electrolyte to ensure that the transmission paths of ions and electrons are connected.

[0092] Step 3: Iterative calculation:

[0093] Using the ANSYS topology optimization module, through iterative solution, inefficient material areas are gradually eliminated while maintaining the material distribution in key functional areas.

[0094] Step 4: Result analysis:

[0095] Generate optimized material distribution maps to determine the optimal geometry of the composite material and the distribution location of functional materials.

[0096] According to the optimization result, the present invention compounds the multi-level conductive network with a resin-based electrolyte precursor in proportion to obtain a composite precursor.

[0097] In the present invention, the mass ratio of the multi-level conductive network to the resin-based electrolyte precursor is preferably 15:85 to 25:75.

[0098] In the present invention, the method for composite the multi-level conductive network and the resin-based electrolyte precursor is preferably a vacuum infusion process (VARTM): the multi-level conductive network (containing CNTs / graphene / MXene coating) is laid in a mold, and after vacuuming, the resin-based electrolyte precursor is injected to penetrate and fill the pores of the multi-level conductive network skeleton. The temperature (20-80°C) and vacuum degree (50-500mbar) are maintained, and after curing at 120-160°C for 0.5-5h, a composite precursor is obtained.

[0099] As another embodiment of the present invention, the method for compounding the multi-level conductive network with the resin-based electrolyte precursor preferably adopts a direct mixing-stirring method: the multi-level conductive network is mixed with the resin-based electrolyte precursor in proportion, and mechanical stirring or ultrasonic dispersion is used to obtain a uniform composite precursor, and then vacuum degassing and curing are performed.

[0100] The present invention uses SolidWorks to establish a three-dimensional model of a special-shaped part based on the geometric shape obtained by topological optimization, and uses a CNC processing method to make the three-dimensional model of the special-shaped part into a mold; the positive electrode, electrolyte membrane, and negative electrode are laid in the mold in sequence, and a vacuum-assisted resin transfer molding method is used to inject the composite precursor into the mold, and then solidification and molding are performed to obtain a multifunctional structural energy storage composite material.

[0101] The present invention has no special limitation on the material of the mold, and any mold material well known in the art can be used; in the embodiment of the present invention, the mold is specifically made of aluminum alloy.

[0102] The present invention has no special limitation on the positive electrode, electrolyte membrane and negative electrode, and the corresponding materials well known in the art can be used; specifically, it is preferred to lay a layer of electrolyte membrane between the carbon fiber cloth containing the positive electrode material and the carbon fiber cloth containing the negative electrode material, and add collectors to the positive and negative electrode material layers to form the positive and negative electrodes of the battery, and the electrolyte membrane is preferably glass fiber cloth, aramid fiber cloth or polyester fiber cloth.

[0103] The mechanical properties of the composite material after optimization by the present invention are improved: the tensile strength is increased by 20%, and the compressive strength is increased by 25%. The energy storage performance is improved: the ionic conductivity is increased to 1.9×10 -3 S / cm, and the electronic conductivity reaches 2.8×10 5 S / m. Weight reduction: Material usage is reduced by 15%, achieving lightweight design. Topology optimization not only meets the mechanical strength and energy storage performance requirements of multifunctional composite materials, but also improves material utilization efficiency and environmental adaptability, providing a scientific basis for the design and manufacture of complex and special-shaped parts.

[0104] The present invention provides a multifunctional structural energy storage composite material prepared by the preparation method described in the above technical solution.

[0105] 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.

[0106] Example 1

[0107] 1. Preparation of multi-level conductive network

[0108] 1) Material selection

[0109] Carbon fiber cloth: T700 grade carbon fiber, fiber diameter 7μm, density 1.8g / cm 3 , produced by Toray Industries, Inc.

[0110] Positive electrode active material: lithium iron phosphate (LiFePO4), particle size 300 nm, specific capacity 170 mAh / g, provided by Xiamen Junshi Energy Technology Co., Ltd.

[0111] Negative electrode active material: artificial graphite, particle size 2 μm, specific capacity 360 mAh / g, provided by Shenzhen BTR New Energy Materials Co., Ltd.

[0112] Conductive additives:

[0113] Multi-walled carbon nanotubes (MWCNTs): diameter 10–20 nm, length 10–30 μm, conductivity >10 4 S / m, Qianrenhe Materials Technology Co., Ltd.

[0114] Graphene: Single-layer redox graphene, thickness <1nm, side length 5-10μm, Sixth Element Materials Technology Co., Ltd.

[0115] MXene (Ti3C2Tx): thickness <2nm, flake diameter 1-5μm, synthesized by Ningbo Institute of Materials.

[0116] Binder: polyvinylidene fluoride (PVDF), Arkema.

[0117] Solvent: N-methylpyrrolidone (NMP), analytical grade.

[0118] 2) Electrode slurry preparation

[0119] Conductive agent mixing: MWCNTs, graphene, and MXene were mixed in a mass ratio of 2:2:1, added to NMP solvent, and ultrasonically dispersed for 30 minutes to form a uniform suspension.

[0120] Slurry preparation:

[0121] The binder PVDF was dissolved in NMP to form a 10 wt % PVDF solution.

[0122] The positive electrode active material LiFePO4 was added to the conductive agent suspension with a solid content of 80 wt%, stirred evenly, and PVDF solution was added and dispersed at high speed for 5 minutes to obtain a uniform conductive slurry.

[0123] 3) Electrospinning coating process

[0124] The carbon fiber cloth was subjected to plasma treatment with the following parameters: power 100W, time 5min, and oxygen as gas;

[0125] The conductive slurry was injected into the electrospinning equipment with the following spinning parameters: voltage 15 kV, receiving distance 12 cm, flow rate 0.1 mL / min, to form a uniform conductive coating on the plasma-treated carbon fiber cloth with a coating thickness of 20 μm.

[0126] 4) Drying and heat treatment

[0127] Drying: Dry in a vacuum drying oven at 80°C for 6 h.

[0128] Hot pressing treatment: The dried material was hot pressed at 150° C., a pressure of 10 MPa, and a time of 2 h to obtain a multi-level conductive network.

[0129] 2. Preparation of resin-based electrolyte precursor

[0130] 1) Material selection

[0131] Resin matrix: bisphenol F epoxy resin EMTE170, epoxy equivalent weight EEW165-175 g / eq, Shandong Aimont New Materials Co., Ltd.

[0132] Curing agent: polyetheramine curing agent D230, Huntsman.

[0133] Functional polymer: sulfonated polyetheretherketone (SPEEK), sulfonation degree 50%, Shanghai Research Institute of Chemical Industry.

[0134] Nanofiller: nanosilica (SiO2), particle size 20 nm, Jiangsu Hailong Nanotechnology Co., Ltd.

[0135] Ionic liquid: 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM-TFSI), purity 99%, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0136] Lithium salt: lithium hexafluorophosphate (LiPF6), battery grade.

[0137] 2) Preparation steps

[0138] Ionic liquid electrolyte preparation:

[0139] LiPF6 was dissolved in EMIM-TFSI at a mass ratio of 1:10 and stirred until completely dissolved to obtain an ionic liquid electrolyte;

[0140] Preparation of resin-based electrolyte precursor:

[0141] SPEEK and nano-SiO2 were added to E51 at a ratio of 5% and 2% of the resin mass, respectively, and stirred evenly. Ionic liquid electrolyte was added with a mass ratio of ionic liquid to resin of 0.8:1. Stirring was continued for 1 hour. Curing agent D230 was added with a mass ratio of resin to curing agent of 100:35. The mixture was mixed evenly to obtain a resin-based electrolyte precursor.

[0142] 3. Structural design and preparation of special-shaped parts

[0143] 1) Structural design

[0144] Topology Optimization:

[0145] Using ANSYS software, the composite material was topologically optimized to maximize mechanical strength and energy storage performance. Based on the optimization results, a multi-level conductive network (containing a CNTs / graphene / MXene coating) was placed in a mold. The mold was maintained at a temperature of 35°C and a vacuum of 200 mbar. After evacuation, a resin-based electrolyte precursor was injected. The multi-level conductive network and resin-based electrolyte precursor were cured at 140°C for 2 hours in a mass ratio of 20:80 to obtain a composite precursor.

[0146] 3D modeling: Based on the geometric shape obtained by topology optimization, SolidWorks is used to build a 3D model of the special-shaped part with complex curved surfaces and reinforcing rib structure.

[0147] 2) Preparation process

[0148] Mould production: According to the 3D model of special-shaped parts, the mould is made by CNC machining and the material is aluminum alloy;

[0149] Lamination assembly: Lay a layer of aramid fiber cloth between the carbon fiber cloth containing the positive electrode material and the carbon fiber cloth containing the negative electrode material, add collectors to the positive and negative electrode material layers respectively to form the positive and negative electrodes of the battery, and lay the positive electrode, aramid fiber cloth, and negative electrode in the mold in order.

[0150] Resin infusion: using vacuum assisted resin transfer molding (VARTM) process, the composite precursor is injected into the mold under vacuum to prevent the generation of bubbles;

[0151] Curing: Curing at 80°C for 4 hours, and then post-curing at 120°C for 2 hours to obtain a multifunctional structural energy storage composite material.

[0152] Example 2

[0153] The only difference from Example 1 is that dicyandiamide and modified imidazole accelerator (fast curing system) are used in the resin-based electrolyte precursor, the addition amount of dicyandiamide ("Dyhard 100S" series produced by Evonik Industries) is 5% of the resin mass, and the modified imidazole accelerator (produced by Shikoku Chemicals, Japan) is 1% of the resin mass. series, Curezol 2MZ-A) is added at a rate of 2% of the resin mass;

[0154] Curing procedure: Curing at 120℃ for 30min.

[0155] Compared with the traditional bisphenol F-polyetheramine system of "80°C curing for 4 hours + 120°C post-curing for 2 hours" adopted in Example 1, Example 2 can complete the curing at 120°C in only 30 minutes.

[0156] Curing time: Experimental monitoring shows that heating the mold to 120°C and maintaining it for 30 minutes from the start of injection molding can achieve a curing degree of ≥95% for the entire material. Compared with Example 1, the overall production cycle is shortened by 30%.

[0157] Mechanical properties: Since the modified imidazole accelerator makes the curing more thorough, the crosslinking density of the material is higher, and the tensile strength and bonding properties of the composite material can still be maintained at a high level (not much different from Example 1, with a slight increase of 3-5% in tensile strength).

[0158] Energy storage performance: The rapid curing system did not cause significant damage to the ionic liquid and conductive network; the ionic conductivity measured at room temperature was 1.4×10 -3 S / cm, electronic conductivity 2.6×10 5 S / m is equivalent to that in Example 1.

[0159] Example 2 significantly shortens curing time and improves production efficiency by introducing a dicyandiamide latent curing agent and a modified imidazole accelerator, while maintaining excellent material properties and meeting the needs of large-scale or rapid production. This solution is particularly suitable for aerospace or automotive production lines with strict cycle requirements.

[0160] Example 3

[0161] Environmental protection and recyclability research

[0162] The difference between this embodiment and embodiment 1 is that:

[0163] 1) Use of bio-based epoxy resin: Replace 30% of E51 epoxy resin with epoxidized soybean oil (ESO) (mass replacement ratio: 30%:70%);

[0164] 2) In the resin-based electrolyte precursor formulation, polylactic acid (PLA) is introduced as a biodegradable functional polymer. PLA is added in the same manner as functional polymers; the PLA addition level is 3% of the resin matrix weight, while other functional polymers (such as SPEEK) are used at 2%. This ensures the material possesses both ion conductivity (from SPEEK) and biodegradability (from PLA) while simultaneously reducing the proportion of petrochemical raw materials by utilizing bio-based epoxidized soybean oil, achieving enhanced environmental protection and recyclability.

[0165] Example 4

[0166] Recyclability experiment

[0167] Pyrolysis recovery: The composite material prepared in Example 1 was heated to 500°C in a high-temperature furnace to recover the carbon fibers and some inorganic fillers. The results showed that the recovered carbon fibers retained 90% of their strength and could be used to prepare composite materials again.

[0168] Performance Testing

[0169] 1) Conductivity test of the multi-level conductive network prepared in Example 1:

[0170] The surface resistance of the multi-level conductive network was measured using a four-probe tester and was found to be 0.5Ω / m.

[0171] Electrochemical performance: At a rate of 0.1C, the initial discharge capacity is 165mAh / g; after 100 cycles, the capacity retention rate is 98%.

[0172] Mechanical properties: The peel strength between the conductive coating and the carbon fiber cloth reaches 5N / cm.

[0173] 2) Ionic conductivity of the resin-based electrolyte precursor prepared in Example 1: The electrical conductivity was measured by an electrochemical impedance spectroscopy (EIS) method at room temperature and was found to be 1.5×10 −3 S / cm.

[0174] Mechanical properties: tensile strength is 60MPa, elongation at break is 6%.

[0175] 3) Mechanical properties of the multifunctional structural energy storage composite material prepared in Example 1: tensile strength reaches 500 MPa, and flexural strength is 300 MPa; electrochemical properties: at a rate of 1C, the initial specific capacity is 155 mAh / g; after 500 cycles, the capacity retention rate is 92%.

[0176] 4) Other tests

[0177] 1. Adhesion test (interface shear strength)

[0178] Test method:

[0179] Standard: ASTM D2344 / D2344M (short beam shear test).

[0180] Purpose: To determine the shear strength of the interface between carbon fiber cloth and resin matrix.

[0181] Test conditions:

[0182] Specimen size: 25mm×6mm×2mm.

[0183] Loading rate: 1 mm / min.

[0184] Test environment: room temperature (23°C ± 2°C), humidity 50% ± 5% RH.

[0185] Result calculation:

[0186] Interface shear strength (τ) = PA / A, where τ is the interface shear strength (MPa or N / mm 2 ), P is the maximum load (N), A is the shear area (mm 2 ).

[0187] Improved results:

[0188] The interfacial shear strength between the treated carbon fiber cloth and the resin matrix increased by 20%, from the original 35MPa to 42MPa.

[0189] 2. Ionic conductivity test

[0190] Test standard: ASTM E1461-13 (impedance spectroscopy), measuring the ionic conductivity of resin-based electrolytes.

[0191] Test conditions:

[0192] Sample preparation: Prepare an electrolyte film with a diameter of 20 mm and a thickness of 1 mm.

[0193] Equipment: Electrochemical impedance analyzer (frequency range 1 Hz to 1 MHz).

[0194] Test environment: room temperature (23℃±2℃).

[0195] Result calculation:

[0196] Ionic conductivity (σ) = L / (R·A), where L is the sample thickness, cm; R is the resistance, Ω, and A is the cross-sectional area of ​​the film, cm 2 .

[0197] Test results: After optimization, the ionic conductivity is 1.9×10-3S / cm (at room temperature).

[0198] 3. Electronic conductivity test

[0199] Test standard: GB / T 15662-1995 (four-probe method), to determine the electronic conductivity of the electrode coating.

[0200] Test conditions:

[0201] Sample preparation: Prepare a conductive coating film of 100 mm × 10 mm × 1 mm.

[0202] Test equipment: four-probe conductivity tester.

[0203] Test environment: room temperature (23℃±2℃).

[0204] Test results: After optimization, the electronic conductivity is 2.8×105S / m.

[0205] 4. Tensile strength test

[0206] Test standard: ASTM D3039 (composite materials tensile test), to determine the tensile strength of composite materials.

[0207] Test conditions: Specimen size: 250 mm × 25 mm × 2 mm; fixture clamping length: 50 mm; loading rate: 2 mm / min.

[0208] Test environment: room temperature (23°C ± 2°C), humidity 50% ± 5% RH.

[0209] Test results: The optimized tensile strength is 120MPa.

[0210] 5. Elongation at break test

[0211] Test method: Standard: ISO 527-1 (Tensile properties of plastics), determination of the elongation at break of composite materials.

[0212] Test conditions: Specimen size: 150 mm × 10 mm × 2 mm; Loading rate: 1 mm / min; Test environment: Room temperature (23°C ± 2°C).

[0213] Test results: The elongation at break after optimization is 6%.

[0214] 6. Thermal stability test

[0215] Test standard: ASTM E1131 (thermogravimetric analysis, TGA), to determine the thermal decomposition temperature and thermal stability of materials.

[0216] Test conditions: heating rate: 10°C / min; temperature range: 25°C to 800°C; environment: nitrogen protection.

[0217] Test results: The material's quality retention rate at 400°C is 95%.

[0218] 7. Interface bonding strength test

[0219] Test method:

[0220] Standard: GB / T 2790-1995 (Adhesive shear strength test), tests the bonding strength between the conductive coating and the carbon fiber.

[0221] Test conditions: Specimen size: 100 mm × 25 mm × 1 mm; Loading rate: 1 mm / min; Test environment: Room temperature (23°C ± 2°C).

[0222] Test results: The coating interface bonding strength is 18MPa.

[0223] 8. Curing time test

[0224] Test method: Standard: ISO 9396 (Epoxy resin curing time), determination of the curing time of fast curing systems.

[0225] Test equipment: Differential Scanning Calorimeter (DSC); Test temperature range: 25°C to 150°C.

[0226] Test results: initial curing time: 1.5 hours (90℃); post-curing time: 1 hour (120℃).

[0227] 5)1. Characterization of multi-level conductive networks

[0228] The SEM results show that the conductive network is evenly covered on the surface of the carbon fiber without obvious agglomeration; there is no obvious CNTs agglomeration, and a network structure is formed by the interlacing of CNTs and graphene.

[0229] The TEM image shows that graphene sheets and carbon nanotubes are interlaced; MXene sheets are embedded in the pores and tightly combined; CNTs are microscopically combined with graphene and MXene sheets, illustrating the hierarchical distribution of different materials in the conductive network.

[0230] Atomic force microscopy (AFM) results show that the coating surface has good uniformity.

[0231] 2. Characterization of Resin-Based Electrolytes

[0232] 1) X-ray diffraction (XRD) analysis

[0233] Purpose of the test:

[0234] Verify the dispersion state between the resin matrix and the ionic liquid and lithium salt; observe whether there is interaction between the crystalline phase and the amorphous phase.

[0235] Testing process:

[0236] The cured resin-based electrolyte film (thickness 0.5-1 mm) was made into appropriate size and tested by X-ray diffractometer. The results showed that:

[0237] 1. No obvious strong diffraction peaks: No obvious diffraction peaks caused by lithium salt or ionic liquid crystals appear in the XRD spectrum, indicating that the lithium salt and ionic liquid are fully dispersed in the resin matrix and are in a basically amorphous state;

[0238] 2. Weakened matrix main peak / shoulder peak: With the introduction of ionic liquids and functional polymers, the shoulder peak is significantly weakened or disappears, indicating that there is interaction between molecules and the destruction of the local ordered structure;

[0239] 3. Composite uniformity: The overall amorphous characteristics are demonstrated, proving that the resin-based electrolyte system has good uniformity at the microscopic level and can provide a continuous channel for ion conduction.

[0240] 2) Fourier transform infrared spectroscopy (FTIR) analysis

[0241] Purpose of the test:

[0242] Confirm the interaction between the resin matrix and the ionic liquid and lithium salt; verify the successful introduction of functional additives.

[0243] FTIR spectrometer (wave number range 4000~400cm -1 ), and the cured film was subjected to infrared testing.

[0244] The results show that:

[0245] 1. Characteristic peak attribution

[0246] Residual peak of epoxy group (910~930cm -1 ) is greatly reduced after curing, indicating that the curing reaction is sufficient;

[0247] The characteristic peak of -SO3H of sulfonated polyetheretherketone (SPEEK) appears at about 1030~1080cm -1 (symmetrical stretching vibration), retaining a relatively obvious intensity, indicating its successful introduction;

[0248] The -CF3 and -SO2 functional groups of the ionic liquid (EMIM-TFSI) are at 1190 and 1450 cm -1 An absorption peak appears at

[0249] Lithium salt (LiPF6) has a weak PF vibration peak (about 840~880cm -1 ).

[0250] 2. Peak position changes

[0251] Slight peak shifts (red / blue shifts) were observed between the hydroxyl, carbonyl, or -SO2 groups of the resin, indicating the presence of hydrogen bonds or ion-dipole interactions between the resin matrix and the ionic liquid / lithium salt;

[0252] The above results showed no obvious missing or additional peaks, indicating that the ionic liquid, lithium salt, functional polymer, etc. were evenly distributed and well combined with the resin matrix.

[0253] 3) Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)

[0254] Test purpose: To evaluate the thermal stability and thermal transition behavior (such as glass transition temperature Tg) of resin-based electrolytes to confirm the processing adaptability and operating temperature range of new formulations.

[0255] a) Thermogravimetric analysis (TGA)

[0256] Test process: In a nitrogen atmosphere, heat from room temperature to 600 or 800°C at a heating rate of 10°C / min, and record the curve of sample mass change with temperature.

[0257] in conclusion:

[0258] 1. Initial decomposition temperature (Td5%)

[0259] A mass loss of 5% occurs between 280 and 320 °C, which is mainly attributed to the partial pyrolysis of the organic matrix and the ionic liquid; MXene or SiO2 inorganic fillers can delay thermal decomposition;

[0260] 2. Main decomposition temperature (Tmax): The maximum weight loss rate peak appears at 350-450℃, corresponding to the decomposition of the epoxy resin and the organic polymer skeleton;

[0261] 3. Residual carbonization rate: At 600°C, the residual mass is about 20-30%, which is slightly higher than that of the pure epoxy system, indicating that the addition of sulfonated polymers or MXene can help improve the carbonization residue;

[0262] 4. Improved thermal stability: Compared with pure resin matrix, resin-based electrolytes can be cured at 120-150°C and have high-temperature service requirements.

[0263] b) Differential Scanning Calorimetry (DSC)

[0264] Test process: Under nitrogen atmosphere, the sample was heated twice at a heating rate of 10°C / min, and the change of heat flow with temperature was recorded.

[0265] in conclusion:

[0266] 1. Glass transition temperature (Tg)

[0267] The Tg of the matrix appears in the range of 60-100°C; when ionic liquids or functional polymers are added, the Tg decreases slightly but remains within an acceptable range;

[0268] 2. Residual heat release from the curing reaction

[0269] If the curing is incomplete, an exothermic peak will appear in the 150-200° C. region (curing of residual epoxy groups). In the present invention, there is almost no significant exotherm, indicating a high degree of curing.

[0270] The above DSC results show that the formulation of the present invention has sufficient thermal stability, a stable chemical structure in the range of room temperature to 120°C, and can be adapted to use in rapid curing or high temperature environments.

[0271] 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 the scope of protection of the present invention.

Claims

1. A method for preparing a multifunctional structural energy storage composite material, characterized in that: The following steps are involved: mixing carbon nanotubes, graphene, MXene and an organic solvent, and mixing the resulting suspension with a binder and a positive electrode active material to obtain a conductive slurry; The carbon fiber cloth is subjected to plasma treatment to obtain a modified carbon fiber cloth; The conductive slurry is electrospinned on the surface of the modified carbon fiber cloth to form a conductive coating, and then subjected to hot pressing to obtain a multi-level conductive network; Mixing lithium salt with ionic liquid to obtain ionic liquid electrolyte; mixing the ionic liquid electrolyte with a resin matrix, a functional polymer, a nanofiller, and a curing agent to obtain a resin-based electrolyte precursor; Using ANSYS software, topology optimization is performed based on required mechanical strength and energy storage performance, and based on the optimization results, the multi-level conductive network is composited with a resin-based electrolyte precursor to obtain a composite precursor; According to the geometric shape obtained by topology optimization, a three-dimensional model of the special-shaped part is established by using SolidWorks, and the three-dimensional model of the special-shaped part is made into a mold by using a CNC processing method; The positive electrode, electrolyte separator and negative electrode are laid out in sequence in a mold, and the composite precursor is injected into the mold by a vacuum-assisted resin transfer molding method, and then cured and molded to obtain a multifunctional structural energy storage composite material.

2. The preparation method according to claim 1, characterized in that The mass ratio of the carbon nanotubes, graphene and MXene is 1 to 3:1 to 3:1; the diameter of the carbon nanotubes is 10 to 20 nm, the length is 10 to 30 μm, and the conductivity is greater than 10 4 S / m; the graphene is a single-layer redox graphene with a thickness of <1nm and a side length of 5 to 10μm; the MXene is Ti3C2T x The thickness of the MXene is <2 nm and the sheet diameter is 1 to 5 μm.

3. The preparation method according to claim 1, characterized in that The binder is polyvinylidene fluoride, and the molecular weight of the polyvinylidene fluoride is 450,000; the power of the plasma treatment is 80-120W, and the time is 5-10 minutes.

4. The preparation method according to claim 1, characterized in that The electrospinning conditions include: voltage 10-15 kV; collection distance 10-15 cm; slurry flow rate 0.1-0.2 mL / min; The temperature of the hot pressing treatment is 130-160° C., the pressure is 10-15 MPa, and the time is 2-5 hours.

5. The preparation method according to claim 1, characterized in that The ionic liquid includes 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; the lithium salt includes lithium hexafluorophosphate; and the mass ratio of the lithium salt to the ionic liquid is 1:5-15.

6. The preparation method according to claim 1, characterized in that The resin matrix includes bisphenol F epoxy resin; the functional polymer includes sulfonated polyetheretherketone; the nano filler includes nano silicon dioxide; and the curing agent includes polyetheramine curing agent D230 or dicyandiamide.

7. The preparation method according to claim 6, characterized in that The mass of the functional polymer is 3-6% of the mass of the resin matrix, the mass of the nanofiller is 1-3% of the mass of the resin matrix; the mass ratio of the resin matrix to the curing agent is 100:30-50; the mass ratio of the ionic liquid to the resin matrix is ​​0.5-1:

1.

8. The preparation method according to claim 6, characterized in that When the curing agent is polyetheramine curing agent D230, the curing molding includes: curing at 80-100° C. for 4 hours, and then curing at 120-150° C. for 2 hours.

9. The preparation method according to claim 6, characterized in that When the curing agent is dicyandiamide, the method further comprises adding a modified imidazole accelerator, wherein the mass of the modified imidazole accelerator is 1.5-3% of the mass of the resin matrix; and the curing molding comprises curing at 120-130° C. for 30 minutes.

10. The multifunctional structural energy storage composite material prepared by the preparation method according to any one of claims 1 to 9.