Intelligent composite material for 4D printing, intelligent clamp and preparation method and application of intelligent composite material

Abstract

The invention relates to an intelligent composite material for 4D printing, an intelligent clamp and a preparation method and application of the intelligent composite material, and belongs to the technical field of electric heating materials.The preparation method of the intelligent composite material for 4D printing is characterized by comprising the following steps that on the basis of the stress condition, the intelligent clamp is connected with the intelligent composite material for 4D printing; the topological structure is optimized; the optimized topological structure serves as a printing model, a thermoplastic shape memory polymer is adopted for 3D printing, and a frame is obtained; and the frame is filled with a thermosetting shape memory polymer, and the 4D printed intelligent composite material is obtained. The intelligent composite material can be subjected to shape editing at a specific temperature, shape recovery is carried out according to temperature response, stress is actively adjusted, and an intelligent clamp made of the intelligent composite material can be used for actively adjusting clamping force in the expansion direction of the battery according to the temperature response in the charging and discharging process of the metal lithium secondary battery, so that the battery expansion efficiency is improved. And the structural stability and the high-efficiency performance of the battery module are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of electrothermal materials, and particularly to a 4D printed intelligent composite material, an intelligent fixture, and their preparation methods and applications. Background Art

[0002] With the continuous development of metal lithium secondary battery technology, it has shown great application potential in the field of high specific energy, with a specific energy of more than 530 Wh / kg, far higher than that of traditional graphite anode batteries. However, due to the lack of space for lithium ion insertion in metal lithium secondary batteries, significant volume expansion occurs during the charging process. Especially for square soft-pack batteries, the thickness expansion usually exceeds 8%. This volume change caused by the expansion poses a severe challenge to the structural design of the battery module.

[0003] When a metal lithium secondary battery expands, the internal structure of the module will be subjected to a strong extrusion force, which may cause deformation or even damage to the external structural components. If the expansion of the metal lithium battery is not effectively constrained, the negative electrode metal lithium material may quickly powderize to form dead lithium, resulting in a rapid attenuation of the battery capacity and seriously affecting the charge-discharge cycle life.

[0004] Although the traditional method of using rubber pads for buffering can relieve the stress caused by expansion, it will significantly increase the weight of the module and weaken its advantage of high specific energy. Chinese Patent CN108054315A uses the method of tensioning with a pull rod, which can achieve a weight reduction effect, but these designs cannot meet the requirements of metal lithium secondary batteries for high specific energy. Chinese Patent CN113991233A uses the method of composite splints, which has improvements in weight reduction and heat preservation, but does not effectively solve the problem of metal lithium battery expansion, especially there are still great limitations in the stress management of the module structure during the expansion process. Summary of the Invention

[0005] In view of one or more technical problems existing in the prior art, the present invention provides a 4D printed intelligent composite material, an intelligent fixture, and their preparation methods and applications. The intelligent composite material provided by the present invention can perform shape editing at a specific temperature, can perform shape recovery according to temperature response, and actively adjust the force. The intelligent fixture made of this intelligent composite material can be used to actively adjust the clamping force in the expansion direction of the battery during the charge and discharge process of the metal lithium secondary battery, ensuring that the battery module can still maintain structural stability and high performance under the force change caused by volume expansion.

[0006] The present invention provides a preparation method of a 4D printed intelligent composite material, and the preparation method includes the following steps:

[0007] S1. Optimize the topological structure based on the force condition;

[0008] S2. Using the optimized topological structure as the printing model, perform 3D printing with a thermoplastic shape memory polymer to obtain a framework;

[0009] S3. Fill the framework with a thermosetting shape memory polymer to obtain a 4D-printed intelligent composite material.

[0010] Preferably, the topological structure is one of a honeycomb structure, a face-centered cubic lattice structure, and a body-centered cubic lattice structure.

[0011] Preferably, optimizing the topological structure based on the force conditions includes:

[0012] Obtain the force distribution in each region of the topological structure under the action of an external force;

[0013] Based on the force distribution in each region, optimize the wall thickness of each region until the optimized topological structure meets the mechanical load-bearing requirements.

[0014] Preferably, based on the force distribution in each region, optimizing the wall thickness of each region until the optimized topological structure meets the mechanical load-bearing requirements includes:

[0015] Judge whether the force in each region is greater than a preset pressure; the preset pressure is the maximum force that each region can withstand;

[0016] If so, increase the wall thickness of this region; if not, decrease the wall thickness of this region; until the optimized topological structure meets the mechanical load-bearing requirements.

[0017] Preferably, filling the framework with a thermosetting shape memory polymer to obtain a 4D-printed intelligent composite material includes:

[0018] Introduce a thermosetting shape memory polymer precursor into the framework and cure it to obtain a 4D-printed intelligent composite material; the thermosetting shape memory polymer precursor includes a thermosetting shape memory polymer and a curing agent.

[0019] Preferably, the mass ratio of the thermosetting shape memory polymer to the curing agent is 2 - 4:1.

[0020] Preferably, the curing temperature is 80 - 100 °C and the time is 3 - 5 h.

[0021] The present invention provides, in a second aspect, a 4D-printed intelligent composite material prepared by using the preparation method described in the first aspect.

[0022] The present invention provides, in a third aspect, an intelligent fixture prepared by using the intelligent composite material described in the second aspect.

[0023] The present invention provides, in a fourth aspect, an application of the intelligent fixture described in the third aspect, which is applied to a lithium metal secondary battery.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] First, the present invention optimizes the topological structure based on the force conditions and uses the optimized topological structure as the printing model. Then, a thermoplastic shape memory polymer is used as the raw material for 3D printing to obtain a framework with both mechanical load-bearing performance, shape memory performance, and lightweight characteristics. Finally, a thermosetting shape memory polymer is filled in the framework to obtain an intelligent composite material.

[0026] The preparation method of the intelligent composite material by 4D printing of the present invention can optimize the topological structure based on different force conditions, combine 3D printing and shape memory materials. The prepared intelligent composite material responds jointly through the shape memory framework by 3D printing and the filled shape memory polymer, can perform shape editing at a specific temperature, and can perform shape recovery according to the temperature response to actively adjust the force. The intelligent composite material prepared by the present invention has both good mechanical properties, shape memory performance, and lightweight characteristics, broadening the application scenarios of shape memory materials.

[0027] The intelligent fixture prepared from the intelligent composite material provided by the present invention can perform shape programming at a specific temperature, actively adjust the clamping force according to the temperature response, and can be used to actively adjust the clamping force in the expansion direction of the battery during the charge and discharge process of the lithium metal secondary battery to ensure that the battery module can still maintain structural stability and high performance under the force change caused by volume expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 The compression schematic diagram of the honeycomb model provided by the present invention;

[0030] Figure 2 The compression schematic diagram of the body-centered cubic (BCC) lattice structure model provided by the present invention;

[0031] Figure 3 The compression schematic diagram of the face-centered cubic (FCC) lattice structure model provided by the present invention;

[0032] Figure 4Schematic diagram of the thickness redistribution structure of the body-centered cubic (BCC) lattice structure model provided by the present invention under force for structural topology optimization;

[0033] Figure 5 Schematic diagram of the optimized topological structure in Embodiment 1 of the present invention;

[0034] Figure 6 Schematic diagram of the shape editing and shape recovery process of the intelligent fixture provided by the embodiment of the present invention;

[0035] Figure 7 Schematic diagram of the structure of the intelligent fixture provided by the embodiment of the present invention.

[0036] Reference numerals:

[0037] 1 - Battery combination array; 2 - Elastic foam pad; 3 - Intelligent fixture. Detailed implementation manners

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] The present invention provides a preparation method for a 4D printed intelligent composite material, and the preparation method includes the following steps:

[0040] S1. Optimize the topological structure based on the force condition;

[0041] S2. Use the optimized topological structure as the printing model, and perform 3D printing with a thermoplastic shape memory polymer to obtain a framework;

[0042] S3. Fill the framework with a thermosetting shape memory polymer to obtain a 4D printed intelligent composite material.

[0043] The present invention first optimizes the topological structure based on the force condition and uses the optimized topological structure as the printing model, then performs 3D printing with a thermoplastic shape memory polymer as the raw material to obtain a framework with mechanical load-bearing performance, shape memory performance, and lightweight characteristics, and finally obtains an intelligent composite material by filling the framework with a thermosetting shape memory polymer.

[0044] The preparation method of the intelligent composite material for 4D printing of the present invention can optimize the topological structure based on different stress conditions, combine 3D printing and shape memory materials. The prepared intelligent composite material responds jointly through the shape memory framework printed by 3D and the filled shape memory polymer, can perform shape editing at a specific temperature, can recover the shape according to the temperature response, and actively adjust the stress. The intelligent composite material prepared by the present invention also has good mechanical properties, shape memory properties and lightweight characteristics, broadening the application scenarios of shape memory materials.

[0045] According to some preferred embodiments, the topological structure is one of a honeycomb structure, a face-centered cubic lattice structure, and a body-centered cubic lattice structure.

[0046] The present invention simulates the stress conditions of different topological structures (the compression simulation diagram is as shown in Figures 1 - 3 ), and different topological structures show different performances in terms of mechanical properties. Among them, the honeycomb structure has excellent compression load-bearing performance, the face-centered cubic structure shows excellent compressive and shear strength, and the body-centered cubic structure realizes the balance of stiffness and strength through its open geometric characteristics after stretching, and is particularly suitable for dynamic stress scenarios.

[0047] According to some preferred embodiments, optimizing the topological structure based on the stress conditions includes:

[0048] Obtain the stress distribution of each region of the topological structure under the action of external forces;

[0049] Based on the stress distribution of each region, optimize the wall thickness of each region until the optimized topological structure meets the mechanical load-bearing requirements.

[0050] The present invention first constructs an initial topological structure, and then optimizes the wall thickness of different regions of the initial topological structure based on the stress distribution of each region of the initial topological structure under the action of external forces, so as to ensure reducing the amount of materials while ensuring the mechanical load-bearing performance, so as to achieve the purpose of lightweight.

[0051] According to some preferred embodiments, optimizing the wall thickness of each region based on the stress distribution of each region until the optimized topological structure meets the mechanical load-bearing requirements includes:

[0052] Judge whether the stress of each region is greater than the preset pressure; the preset pressure is the maximum stress that each region can bear;

[0053] If so, increase the wall thickness of this region; if not, decrease the wall thickness of this region; until the optimized topological structure meets the mechanical load-bearing requirements.

[0054] In this invention, a three-point bending model with a size of 100 mm (the initial model of the topological structure) is established by Abaqus software to simulate the response of the composite material under force. The physical properties of the model material are set as follows: elastic modulus E = 2.4 GPa, Poisson's ratio v = 0.3, and density ρ = 1.2 g / cm 3 ³. During the simulation process, a concentrated force is applied in the middle of the model to simulate the force-bearing situation and deformation behavior of the composite material under working conditions. This force is used to simulate the force field in the actual working condition to analyze the stress distribution and displacement change of the composite material. Based on the results of this finite element analysis, topological optimization is carried out on the force-concentrated area. Taking the body-centered cubic (BCC) lattice structure as an example, through topological optimization, the key force-bearing areas are locally strengthened. By increasing the wall thickness of the force-concentrated area and reducing the wall thickness of other areas on the basis of ensuring the load-bearing requirements, the overall stiffness and deflection are improved, the material usage is reduced, and the purpose of lightweighting is achieved. It can be seen from the simulation results that the optimized topological structure (as Figure 4 shown) exhibits a lighter density and has better mechanical properties under high-load conditions, such as greater bending stiffness and durability. Using the optimized topological structure as the printing model, the printed frame has good mechanical properties and lightweight characteristics. It can be seen that this kind of topological optimization ensures the mechanical stability, adaptability, and reliability of the intelligent composite material during long-term use.

[0055] According to some preferred embodiments, a thermosetting shape memory polymer is filled in the frame to obtain a 4D-printed intelligent composite material, including:

[0056] Introducing a thermosetting shape memory polymer precursor into the frame and curing it to obtain a 4D-printed intelligent composite material; the thermosetting shape memory polymer precursor includes a thermosetting shape memory polymer and a curing agent.

[0057] In this invention, the thermosetting shape memory polymer precursor is introduced into the frame by vacuum infusion. After curing, a thermosetting shape memory polymer can be formed in situ in the frame to obtain an intelligent composite material with an integrated structure.

[0058] According to some preferred embodiments, the mass ratio of the thermosetting shape memory polymer to the curing agent is 2 - 4:1.

[0059] According to some preferred embodiments, the curing temperature is 80 - 100 °C and the time is 3 - 5 h.

[0060] In the second aspect of this invention, a 4D-printed intelligent composite material is provided, which is prepared by using the preparation method described in the first aspect.

[0061] In the third aspect of this invention, an intelligent fixture is provided, which is made of the intelligent composite material described in the second aspect.

[0062] The intelligent composite material provided by the present invention can optimize the frame structure according to actual mechanical requirements, and has good mechanical properties and lightweight characteristics. By filling a thermoplastic shape memory polymer frame with a thermosetting shape memory polymer (SMP) and curing it in a fixture mold with a curvature, an intelligent fixture that can obtain the desired morphology (initial shape) under predetermined conditions can be ensured. After curing, the intelligent fixture is heated to a specific response temperature for shape programming. After programming is completed, the intelligent fixture is cooled to a low temperature to fix its shape (temporary shape). At this time, the intelligent fixture has the ability to adaptively adjust the external force according to the temperature response, and can perform shape recovery according to the temperature response and actively adjust the clamping force during actual use.

[0063] The present invention provides an application of the intelligent fixture described in the third aspect in a fourth aspect, which is applied to a lithium metal secondary battery.

[0064] The intelligent fixture provided by the present invention can perform shape programming at a specific temperature and actively adjust the clamping force according to the temperature response. It can be used to actively adjust the clamping force in the expansion direction of the battery during the charge and discharge process of a lithium metal secondary battery, effectively preventing internal short circuits of the battery, extending the battery life, and ensuring that the battery module can still maintain structural stability and high performance under the force changes caused by volume expansion, and is suitable for the structural optimization design of high specific energy lithium metal secondary battery modules.

[0065] The present invention ensures the mechanical stability and adaptability of the intelligent fixture during long-term use through topology optimization, especially the reliability during multiple charge and discharge cycles of the battery, can effectively prevent internal short circuits of the battery, extend the battery life, and is suitable for the structural optimization of high energy density battery modules.

[0066] When the intelligent fixture provided by the present invention is applied to a lithium metal secondary battery, both ends of the intelligent fixture are fixed to both ends of the battery combination array, and an elastic foam pad is provided between the battery combination array and the intelligent fixture. Specifically, the battery combination array can be fixed to the battery module array by means of binding ropes, which are evenly and densely wound around the battery combination array and the intelligent fixture, so as to apply a uniform clamping force to the battery pack in the expansion direction and ensure the stability of the module during operation. The battery combination array is formed by arranging a plurality of battery monomers, and its arrangement direction is the thickness direction of the battery monomers. The elastic foam pads on both sides of the battery combination array are made of closed-cell foaming materials, and the compression pressure range of the foam pads is adjusted according to the charge and discharge state of the battery. When the battery enters the charging state, the compression pressure of the foam pad is between 0.15 MPa and 0.4 MPa, while in the discharging state, the compression pressure of the foam pad is between 0.05 MPa and 0.12 MPa, ensuring sufficient support and buffering in different battery states.

[0067] To more clearly illustrate the technical solution and advantages of the present invention, the present invention will be further described below in conjunction with embodiments. The sources of various substances used in the embodiments of the present invention are not specifically limited and can be directly purchased or synthesized by oneself.

[0068] Example 1

[0069] Topology optimization: Adopt a body-centered cubic (BCC) lattice structure (original wall thickness is 2.5 mm) and perform topology optimization. After optimization, the maximum wall thickness is 5 mm. The topology diagram after optimization is as shown in Figure 5 shown.

[0070] Printing the frame: Use the optimized body-centered cubic (BCC) lattice structure as the printing model, and use shape memory polylactic acid (PLA) as the raw material for printing to obtain the frame.

[0071] Filling with shape memory polymer: Mix E44 epoxy resin and D230 curing agent evenly according to a mass ratio of 3:1 to obtain a shape memory polymer mixture. Then, introduce the mixture into the frame structure through vacuum infusion to ensure that the shape memory polymer evenly fills the voids of the frame structure. After completion of filling, cure at 80 °C for 2 hours first, and then continue to cure at 100 °C for 2 hours to obtain the intelligent composite material.

[0072] Example 2

[0073] Topology optimization: Adopt a body-centered cubic (BCC) lattice structure (original wall thickness is 5 mm) and perform topology optimization. After optimization, the maximum wall thickness is 10 mm. The topology diagram after optimization is similar to that of Example 1, only the wall thickness is different.

[0074] Printing the frame: Use the optimized body-centered cubic (BCC) lattice structure as the printing model, and use shape memory polylactic acid (PLA) as the raw material for printing to obtain the frame.

[0075] Filling with shape memory polymer: Mix E44 epoxy resin and D230 curing agent evenly according to a mass ratio of 3:1 to obtain a shape memory polymer mixture. Then, introduce the mixture into the frame structure through vacuum infusion to ensure that the shape memory polymer evenly fills the voids of the frame structure. After completion of filling, cure at 80 °C for 2 hours first, and then continue to cure at 100 °C for 2 hours to obtain the intelligent composite material.

[0076] The intelligent composite materials prepared in Examples 1-2 can be used to prepare fixtures. The specific process is as follows: Fill the frame with shape memory polymer (SMP) and place it in a fixture mold with curvature for curing to obtain the initial shape of the intelligent fixture (including two shape memory polymer materials with a certain curvature, such as Figure 6) After curing, heat the initial shape of the smart fixture to a specific response temperature, perform shape programming (flattening), and cool it to a low temperature to fix its shape, obtaining the temporary shape of the smart fixture 3 (such as Figure 6 ) Such as Figure 7 As shown, set the temporary shape of the smart fixture 3 on both sides of the battery pack array 1, fix the two ends of the smart fixture 3 to the two ends of the battery pack array 2, and set an elastic foam pad 2 between the battery pack array 1 and the smart fixture 3. Specifically, the temporary shape of the smart fixture 3 can be fixed to the battery pack array by winding with aramid fiber binding wires, ensuring that the smart fixture exerts a uniform clamping force in the battery expansion direction, and can actively adjust the clamping force according to the temperature response during the battery operation, ensuring that the battery module can still maintain structural stability and high performance under the force change caused by volume expansion.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a 4D printed smart composite material, characterized in that: The preparation method comprises the following steps: S1. Optimize the topological structure based on the stress conditions; S2. Using the optimized topological structure as a printing model, 3D printing is performed using a thermoplastic shape memory polymer to obtain a frame; S3. Filling the frame with a thermosetting shape memory polymer to obtain a 4D printed smart composite material.

2. The preparation method according to claim 1, characterized in that: The topological structure is one of a honeycomb structure, a face-centered cubic lattice structure, and a body-centered cubic lattice structure.

3. The preparation method according to claim 1, characterized in that: The topological structure is optimized based on the stress condition, including: Obtaining force distribution of each region of the topological structure under the action of external force; Based on the force distribution in each area, the wall thickness of each area is optimized until the optimized topological structure meets the mechanical bearing requirements.

4. The preparation method according to claim 3, characterized in that: Based on the force distribution in each area, the wall thickness of each area is optimized until the optimized topological structure meets the mechanical bearing requirements, including: Determine whether the force on each area is greater than a preset pressure; the preset pressure is the maximum force that each area can withstand; If yes, then increase the wall thickness of the area; if no, then reduce the wall thickness of the area; until the optimized topological structure meets the mechanical bearing requirements.

5. The preparation method according to claim 1, characterized in that: The frame is filled with a thermosetting shape memory polymer to obtain a 4D printed smart composite material, comprising: A thermosetting shape memory polymer precursor is introduced into the frame and cured to obtain a 4D printed intelligent composite material; the thermosetting shape memory polymer precursor includes a thermosetting shape memory polymer and a curing agent.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the thermosetting shape memory polymer to the curing agent is 2 to 4:

1.

7. The preparation method according to claim 5, characterized in that: The curing temperature is 80-100° C. and the curing time is 3-5 hours.

8. A 4D printed smart composite material, characterized in that: The method is prepared by the preparation method according to any one of claims 1 to 7.

9. An intelligent fixture, characterized in that: It is made from the smart composite material described in claim 8.

10. An application of the intelligent clamp according to claim 9, characterized in that: Applied to lithium metal secondary batteries.

Images