Energy-absorbing early warning composite material, preparation method thereof, and application thereof

Abstract

The present invention belongs to the technical field of protective materials, and specifically relates to an energy-absorbing warning composite material, its preparation method and application. The energy-absorbing warning composite material includes a dielectric layer, a stretchable conductive layer, an energy-absorbing layer, a stretchable conductive layer and a dielectric layer stacked in sequence; the stretchable conductive layer includes a PEDOT:PSS flexible film. The present invention innovatively combines the energy-absorbing layer and the flexible film, and synergistically applies them to battery modules. It has good pressure sensing performance, and its sensitivity is greater than 0.01kPa in the stress range of 0~200kPa. ‑1 ; In the stress range of 0.2~20MPa, the sensitivity is greater than 0.1MPa ‑1 , meeting the flexible protection and warning requirements of power battery packs and battery modules. The composite material of the present invention not only has excellent energy absorption and buffering performance, but also provides stable restraint and highly sensitive sensing and warning mechanisms, extending the working life of the battery and achieving the effect of intelligent flexible protection.

Description

Technical Field

[0001] The present invention belongs to the technical field of protective materials, and in particular relates to an energy-absorbing early warning composite material and a preparation method and application thereof. Background Art

[0002] Lithium-ion battery is an electric-thermal-mechanical coupling system. It will have expansion problems during actual use. On the one hand, the SEI film is formed during the formation process, which produces gas. The gas pressure inside the battery increases, and as the cycle progresses, the thickness of the SEI film increases, causing the battery cell to expand. On the other hand, during charging and discharging, the Li + The embedding and extraction between the positive and negative electrode materials will cause a structural phase change, leading to the occurrence of expansion phenomenon, which is mainly reflected in the change in the thickness direction of the negative electrode sheet.

[0003] Studies have shown that adding buffer materials between batteries when assembling lithium-ion battery modules can effectively reduce the expansion force of the batteries and improve the electrochemical performance of the battery modules. Currently, foam is often used to reduce the impact of expansion behavior during the charge and discharge process. Under the condition of foam, the maximum expansion force, minimum expansion force and total expansion force change are all smaller than the test results without foam. Under the same preload conditions, the use of foam buffer materials with lower hardness can effectively suppress the increase in battery expansion force during the charge and discharge process. However, the current foam materials have a low compression modulus and do not have stress characteristics that are highly sensitive to deformation. They cannot output highly sensitive electrical signals in real time, have poor pressure sensing performance, and have no obvious energy absorption effect. They are not effective in protecting the battery and affect the battery's service life. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an energy-absorbing early warning composite material and its preparation method and application. The energy-absorbing early warning composite material of the present invention has good pressure sensing performance, meets the requirements of flexible protection and early warning, and can extend the service life of the battery.

[0005] The present invention provides an energy-absorbing early warning composite material, comprising a first dielectric layer, a first stretchable conductive layer, an energy-absorbing layer, a second stretchable conductive layer, and a second dielectric layer stacked in sequence;

[0006] The energy absorbing layer is made of compressible foam, which includes one or more of shear thickening composite materials, foamed polyurethane, foamed polyethylene, foamed polypropylene, chloroprene rubber, ethylene-vinyl acetate copolymer, styrene-butadiene rubber and EPDM rubber;

[0007] The first stretchable conductive layer and the second stretchable conductive layer include PEDOT:PSS flexible films.

[0008] Preferably, the raw materials for preparing the shear thickening composite material include a premix and a curing agent; the premix includes the following components in parts by weight: 30-80 parts of polyether diol, 20-70 parts of polyether polyol, 1-20 parts of chain extender, 0.5-3 parts of crosslinking agent, 5-50 parts of filler, 0.5-5 parts of coupling agent, 0.05-15 parts of foaming agent, 0.1-5 parts of emulsifier, 0.05-5 parts of catalyst and 3-15 parts of flame retardant; the number of hydroxyl groups of the polyether polyol is 3 or more, and the hydroxyl value of the polyether polyol is 22-56 mgKOH / g; the curing agent includes diisocyanate; the molar ratio of the hydroxyl group of the premix to the isocyanate group of the curing agent is 1:1-1.1;

[0009] The density of the shear thickening composite material is 0.1-0.9 g / cm 3 , thickness is 0.1~60mm, and the maximum compression ratio is 80%~90%.

[0010] Preferably, the polyether diol comprises polytetramethylene ether diol.

[0011] Preferably, the thickness of the first stretchable conductive layer and the second stretchable conductive layer are independently 5 to 100 μm.

[0012] Preferably, the elastic modulus of the first stretchable conductive layer and the second stretchable conductive layer are independently 0.2~25MPa, and the tensile strain is greater than 100%; the resistance value change of the first stretchable conductive layer and the second stretchable conductive layer is independently less than 5 times within the strain range of 0~60%.

[0013] Preferably, the thickness of the first dielectric layer and the second dielectric layer are independently 1-200 μm.

[0014] The present invention also provides a method for preparing the energy-absorbing early warning composite material described in the above technical solution, comprising the following steps:

[0015] The PEDOT:PSS material solution and the dielectric layer material solution are sequentially coated on both side surfaces of the energy absorption layer to obtain the energy absorption warning composite material.

[0016] Preferably, the PEDOT:PSS solution comprises the following components in mass fractions: 1% to 12% DMSO, 0.5% to 25% nonionic fluorocarbon surfactant, and 60% to 95% PEDOT:PSS aqueous solution; the mass fraction of the PEDOT:PSS aqueous solution is 0.5% to 55%.

[0017] Preferably, the dielectric layer material solution is an ethyl acetate solution of SEBS, and the mass fraction of SEBS in the ethyl acetate solution of SEBS is 5% to 20%.

[0018] The present invention also provides the use of the energy-absorbing warning composite material described in the above technical solution or the energy-absorbing warning composite material obtained by the above preparation method as a protective material in a battery pack or a battery module.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides an energy-absorbing warning composite material, comprising a first dielectric layer, a first stretchable conductive layer, an energy-absorbing layer, a second stretchable conductive layer, and a second dielectric layer stacked in sequence; the energy-absorbing layer is made of compressible foam, and the compressible foam layer includes one or more of a shear thickening composite material, foamed polyurethane, foamed polyethylene, foamed polypropylene, chloroprene rubber, ethylene-vinyl acetate copolymer, styrene-butadiene rubber, and ethylene propylene diene monomer rubber; the first stretchable conductive layer and the second stretchable conductive layer include PEDOT:PSS flexible film.

[0021] The present invention innovatively combines the energy absorbing layer and the flexible film, and synergistically applies them to the power battery pack and its battery module. The pressure sensing performance is good, and its sensitivity is greater than 0.01kPa in the test range of 0~200kPa. -1 In the stress range of 0.2MPa~20MPa, the sensitivity is greater than 0.1MPa -1 , meeting the requirements of flexible protection and early warning.

[0022] During the assembly of lithium-ion batteries, the addition of buffer materials can effectively reduce expansion forces, thereby improving the electrochemical performance of the module. When the battery expands, a compressive force is applied to the buffer material, which absorbs energy and acts as a buffer through compression. Based on the principle of force interaction, the buffer material generates a reaction force on the battery. The present invention utilizes a shear-thickening (non-Newtonian fluid) NNF material as the energy-absorbing layer, achieving a stable and effective restraining force even with minimal deformation. Due to its significant energy-absorbing properties, the compression of the composite material can help relieve some of the stress within the battery, further reducing expansion forces. Furthermore, thanks to its slow rebound properties, the reaction force is reduced, resulting in less compression on the battery, ensuring proper operation for a longer period of time, which helps improve overall battery performance. Furthermore, the present invention loads a stretchable flexible film onto the surface of the energy-absorbing layer, enabling real-time acquisition of capacitance signals. The absolute value of these signals can be used to infer the pressure on the composite surface, while the time-domain signal sequence can be used to infer the acceleration of the impact force on the composite. These signals can be used as the signal source for the differential controller, predicting the arrival of large impact forces to a certain extent, allowing the system to take preventive measures in advance. The composite material of the present invention not only has excellent energy absorption and buffering performance, but also can provide stable restraint force and highly sensitive sensing and early warning mechanism, thereby extending the working life of the battery and achieving the effect of intelligent flexible protection.

[0023] The energy-absorbing early warning composite material of this invention exhibits a capacitance signal output with a signal error of less than 5% when subjected to external and internal pressure within its measuring range. The capacitance signal's average value exhibits a deviation of less than 3% under any pressure condition when subjected to ambient temperature fluctuations from -20°C to 80°C. Furthermore, after the initial compression cycle, the shear-thickening composite material (NNF metamaterial) exhibits a stress-strain curve deviation of less than 5% during subsequent compression cycles in a constant-speed test. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 Schematic diagram of the structure of the energy-absorbing early warning composite material prepared in Examples 1 to 3;

[0026] Figure 2 DMA test results of the NNF metamaterial in Example 2;

[0027] Figure 3 is the energy absorption curve of the NNF metamaterial in Example 2;

[0028] Figure 4 The stress-strain curves of the NNF metamaterial, ordinary polyurethane foam, and EVA foam in Example 2 are shown;

[0029] Figure 5 Energy absorption characteristics of NNF metamaterial, ordinary polyurethane foam, and EVA foam in Example 2;

[0030] Figure 6 This is a typical sensing characteristic curve of the energy-absorbing early warning composite material of Example 2;

[0031] Figure 7 is the sensing characteristic curve of the composite material of Comparative Example 1;

[0032] Figure 8 : are the sensing characteristic curves of the composite materials of Example 4 and Example 5;

[0033] Figure 9 This is a graph showing the response time test results of the energy-absorbing early warning composite material of Example 2;

[0034] Figure 10 This is a graph showing the signal fatigue test results of the energy-absorbing early warning composite material in Example 2;

[0035] Figure 11This is the sensing characteristic curve of the energy-absorbing early warning composite material in Example 1;

[0036] Figure 12 This is the sensing characteristic curve of the energy-absorbing early warning composite material of Example 3;

[0037] Figures 13 to 15 These are the compressive stress-strain curves of the NNF metamaterials in Examples 1 to 3, respectively;

[0038] Figure 16 The test results of the NNF metamaterial used in Example 2 in the 2 mm / min cyclic compression test for 2 to 10 cycles are shown;

[0039] Figure 17 Temperature-dependent characteristics and signal-to-noise ratio results of NNF foam flexible sensors constructed with commercial copper foil electrodes;

[0040] Figure 18 Temperature-dependent characteristics and signal-to-noise ratio results of the NNF foam flexible sensor constructed with stretchable electrodes used in Example 2;

[0041] Figure 19 The resistance changes of the embodiment stretchable electrode, commercial copper foil electrode, and commercial stretchable electrode during the tensile strain from 0 to 60%. DETAILED DESCRIPTION

[0042] The present invention provides an energy-absorbing early warning composite material, comprising a first dielectric layer, a first stretchable conductive layer, an energy-absorbing layer, a second stretchable conductive layer, and a second dielectric layer stacked in sequence;

[0043] The energy absorbing layer is made of compressible foam, which includes one or more of shear thickening composite materials, foamed polyurethane (PU), foamed polyethylene (EPE), foamed polypropylene (EPP), chloroprene rubber (CR), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene rubber (SBR) and ethylene propylene diene monomer (EPDM);

[0044] The first stretchable conductive layer and the second stretchable conductive layer include PEDOT:PSS flexible films.

[0045] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0046] The energy-absorbing early warning composite material of this invention exhibits the shear-thickening properties of a non-Newtonian fluid (NNF), demonstrating a nonlinear compression modulus when subjected to high expansion forces. Compared to conventional protective foams, its permeability is lower at the same compression ratio. Furthermore, its shear-thickening properties enable it to provide long-term, stable restraint to lithium battery packs. In particular, it responds quickly and effectively absorbs impact energy in the face of rapid impact or high expansion forces. Its slow rebound properties also help reduce the impact of reactive forces on the battery, thereby extending its lifespan. This invention combines an energy-absorbing layer with a flexible sensing film. Leveraging the highly sensitive stress properties of the energy-absorbing layer material to deformation, it can output a highly sensitive electrical signal in real time to monitor both dynamic and quasi-static mechanical signals during the compression process. The dynamic signal can be used to identify the impact on the material, with its differential value enabling early warning of the approaching large impact force. The quasi-static signal, on the other hand, identifies the limit of the expansion force, thereby providing an early warning function.

[0047] During the compression of the battery module, the polymer molecules within the NNF energy-absorbing layer rapidly aggregate, resulting in a significant change in shear thickening properties. This change results in significant differences in the electro-pressure / compressibility properties under different loading and unloading conditions. Therefore, the energy-absorbing warning composite material not only possesses excellent energy-absorbing and buffering properties, but also provides a stable restraining force and a highly sensitive sensing and warning mechanism, thereby extending the battery's operating life and achieving intelligent flexible protection.

[0048] In the present invention, the thickness of the first dielectric layer and the second dielectric layer are independently preferably 1 to 200 μm, more preferably 8 μm.

[0049] In the present invention, the first and second dielectric layers are preferably made of SEBS (a linear triblock copolymer with polystyrene as the terminal segments and an ethylene-butylene copolymer derived from hydrogenated polybutadiene as the central elastic segment). The dielectric layers of the present invention have excellent electrical insulation properties, preventing the impact of the excess potential of the core layer on the battery.

[0050] In the present invention, the thickness of the first and second stretchable conductive layers is preferably independently 5 to 100 μm, specifically 10 μm or 20 μm. The elastic modulus of the first and second stretchable conductive layers is independently 0.2 to 25 MPa, and the tensile strain is greater than 100%. Within a 30% strain range, the change in resistance is less than five times the initial resistance. The present invention utilizes a flexible PEDOT:PSS film as the stretchable conductive layer, which has an extremely low elastic modulus and thickness, ensuring excellent conformality with the energy-absorbing layer.

[0051] In the present invention, Ag wires are preferably further provided on the surfaces of the first stretchable conductive layer and the second stretchable conductive layer. The present invention has no special requirements for the Ag wires.

[0052] In the present invention, the raw materials for preparing the shear thickening composite material include a premix and a curing agent; the premix includes the following components in parts by weight: 30-80 parts of polyether diol, 20-70 parts of polyether polyol, 1-20 parts of chain extender, 0.5-3 parts of crosslinking agent, 5-50 parts of filler, 0.5-5 parts of coupling agent, 0.05-15 parts of foaming agent, 0.1-5 parts of emulsifier, 0.05-5 parts of catalyst and 3-15 parts of flame retardant; the number of hydroxyl groups of the polyether polyol is 3 or more, and the hydroxyl value of the polyether polyol is 22-56 mg KOH / g; the curing agent includes diisocyanate; the molar ratio of the hydroxyl group of the premix to the isocyanate group of the curing agent is 1:1-1.1;

[0053] The density of the shear thickening composite material is 0.1-0.9 g / cm 3 , thickness is 0.1~60mm, and the maximum compression ratio is 80%~90%.

[0054] In the present invention, the curing agent preferably includes diphenylmethane diisocyanate (MDI) and / or 1,5-naphthalene diisocyanate; and the molar ratio of the hydroxyl group of the premix to the isocyanate group of the curing agent is preferably 1:1.05.

[0055] In the present invention, except for the polyether diol and flame retardant, the components of the premix are preferably the same as those described in Chinese Patent "CN115536797A - A Shear Thickening Composite Material, Its Preparation Method, and Application," and are not further described here. The polyether diol preferably also includes polytetramethylene glycol (PTMEG) having a molecular weight of 2000. In a specific embodiment of the present invention, the premix preferably includes the following components in parts by weight: 50 parts of 400 molecular weight polyether diol, 10 parts of compound chain extender, 4 parts of silane coupling agent, 2 parts of polysiloxane-olefin oxide block copolymer emulsifier, 40 parts of nano-silica; 20 parts of 2000 molecular weight polyether diol; 10 parts of 2000 molecular weight polytetramethylene ether diol; 20 parts of 7000 molecular weight polyether triol, 1.5 parts of triethanolamine, 1 part of foaming catalyst dimethylethanolamine and 0.8 parts of curing catalyst triethylenediamine, 0.4 parts of foaming agent and 6 parts of flame retardant.

[0056] The shear-thickening composite material of the present invention is a NNF material with shear-thickening properties. The present invention adds 2000 molecular weight polytetramethylene ether glycol (PTMEG), preferably BASF PolyTHF2000, to the polyether glycol. This improves the toughness and wear resistance of the composite material, meeting the expansion stress requirements of the battery during charging cycles. A flame retardant, preferably UND-815, is added to the premix of the present invention, imparting high-efficiency flame retardancy to the composite material, meeting the flame retardancy requirements of power batteries and their modules.

[0057] In the present invention, the density of the shear thickening composite material is preferably 0.1 to 0.5 g / cm 3 , specifically 0.15g / cm 3 , 0.32g / cm 3 or 0.4g / cm 3 ; The thickness is preferably 1~10mm, specifically 4mm.

[0058] The shear-thickening composite material of the present invention remains soft and elastic under normal conditions. However, when subjected to rapid and intense impact or compression, it rapidly undergoes strain enhancement through local density increase, exhibiting a pronounced shear-thickening phenomenon. Specifically, when subjected to external force, the material behaves as a hard solid, and its strength increases with increasing external force; when the external force disappears, the material returns to its initial, relaxed, soft, elastic state. Under high stress, the shear-thickening composite material rapidly strains, absorbing up to 95% of the impact energy. Furthermore, its slow rebound height of less than 8% and slow rebound properties protect batteries from significant impacts for extended periods and suppress bulging during charging and discharging.

[0059] The present invention combines an energy-absorbing layer with shear thickening properties with a PEDOT:PSS flexible film to achieve energy absorption and early warning functions.

[0060] The present invention also provides a method for preparing the energy-absorbing early warning composite material described in the above technical solution, comprising the following steps:

[0061] The PEDOT:PSS material solution and the dielectric layer material solution are sequentially coated on both side surfaces of the energy absorption layer to obtain the energy absorption warning composite material.

[0062] The present invention has no special requirements on the preparation method of the energy absorbing layer.

[0063] The present invention preferably first coats a PEDOT:PSS solution on one side of the energy-absorbing layer to obtain a first stretchable conductive layer; then coats a dielectric layer solution on the first stretchable conductive layer to obtain a first dielectric layer; and then repeatedly coats the PEDOT:PSS solution and the dielectric layer solution on the other side of the energy-absorbing layer to obtain a second stretchable conductive layer and a second dielectric layer.

[0064] In the present invention, before applying the PEDOT:PSS solution, the surface of the energy-absorbing layer is cleaned. This cleaning preferably includes ultrasonic cleaning with ethanol and ultrasonic cleaning with deionized water, each preferably lasting 5 minutes. After cleaning, the surface is preferably dried with nitrogen and treated with an oxygen plasma cleaner for 30 seconds to enhance the surface's affinity for the PEDOT:PSS solution, ensuring more uniform coating and stronger adhesion.

[0065] In the present invention, the PEDOT:PSS solution preferably comprises the following components by weight: 1% to 12% DMSO, 0.5% to 25% nonionic fluorocarbon surfactant, and 60% to 95% PEDOT:PSS aqueous solution. The mass fraction of the PEDOT:PSS aqueous solution is preferably 0.5% to 55%, specifically 50%. More preferably, the PEDOT:PSS solution comprises the following components by weight: 6% DMSO, 5% nonionic fluorocarbon surfactant, and 89% PEDOT:PSS aqueous solution. The nonionic fluorocarbon surfactant preferably comprises DuPont Capstone FS-30.

[0066] In the present invention, the PEDOT:PSS solution is preferably applied by spin coating or spray coating. The spin coating parameters are preferably: a spin coating process at a speed of 4000 rpm for 40 seconds. The coating process is preferably followed by drying, preferably at a temperature of 80°C and for 30 minutes.

[0067] In the present invention, after obtaining the first stretchable conductive layer, the method preferably further comprises: coating a portion of the surface of the first stretchable conductive layer with an Ag conductive paste, drying the portion, and then drawing out an Ag wire. The drying temperature is preferably 80°C. The area of the portion of the surface is preferably 4 to 16 mm. 2 The present invention has no special requirements on the composition of the Ag conductive paste, which may include Ag nanosheets, or Ag nanosheets and a siloxane-based resin.

[0068] In the present invention, the dielectric layer solution is preferably an ethyl acetate solution of SEBS, and the mass fraction of SEBS in the ethyl acetate solution of SEBS is preferably 5% to 20%, specifically 15%.

[0069] In the present invention, the dielectric layer liquid is preferably coated by spin coating or spray coating, and the spin coating parameters are preferably: a spin coating process at a speed of 1500 rpm for 30 seconds. After coating, drying is preferably performed, and the drying temperature is preferably 80°C.

[0070] The method of repeatedly coating the PEDOT:PSS solution and the dielectric layer solution on the other side surface of the energy absorbing layer of the present invention is consistent with the method of preparing the first stretchable conductive layer and the first dielectric layer, and will not be repeated here.

[0071] The present invention also provides the use of the energy-absorbing warning composite material described in the above technical solution or the energy-absorbing warning composite material obtained by the above preparation method as a protective material in a battery pack or a battery module.

[0072] The energy-absorbing early warning composite material of the present invention is used as a protective material in the battery module, which has an intelligent and flexible protective effect. The present invention uses the energy-absorbing early warning composite material as a battery life monitoring and early warning mechanism for battery expansion-induced explosions. The special shear thickening effect of the energy-absorbing layer is used as a sensing layer to achieve high-precision perception of the expansion force, thereby enabling dynamic and real-time monitoring of the battery pack expansion process. The present invention utilizes the shear thickening properties of the NNF energy-absorbing layer, that is, the stress-enhanced property of the material when subjected to continuously increasing external forces, to design an early warning mechanism that can react to battery thermal expansion, bulging, and even fire.

[0073] To further illustrate the present invention, the energy-absorbing warning composite material, its preparation method and application provided by the present invention are described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0074] In the embodiment of the present invention, the energy-absorbing NNF liquid used includes a premix and a curing agent, and the preparation method is as follows:

[0075] (1) Preparation of compound chain extender: Add 100 g of diethanolamine, 500 g of dipropylene glycol, 280 g of 4,4'-bis-sec-butylaminodiphenylmethane, and 120 g of ethylene glycol to a thermostatic container at 80°C. Stirring is started and maintained at 100 rpm. The container is sealed. Vacuum dehydration is started and maintained at a negative pressure of -0.1 MPa for 8 hours to obtain the first component. MDI is slowly added in a molar ratio of 100:50 between the hydroxyl groups in the first component and the isocyanate groups in the liquefied MDI to carry out a polymerization chain extension reaction for 8 hours. Heating and stirring are stopped. When the material temperature drops to room temperature, the compound chain extender (NNF-2) is obtained.

[0076] (2) Preparation of premix: Add 500g of 400 molecular weight polyether diol (Pluracol P410R) into a constant temperature container at 75°C, start stirring and maintain the speed at 100 rpm, then add 100g of NNF-2 compound chain extender described in step (1), silane coupling agent (XIAMETER тм OFS-6020Silane), 20g of polysiloxane-olefin oxide block copolymer emulsifier, and 400g of nano-silica gel (AEROSIL 200); continue stirring for 45 minutes, stop heating, add 200g of 2000 molecular weight polyether diol (Pluracol P1477); 100g of 2000 molecular weight polytetramethylene ether diol (PTMEG); add 200g of 7000 molecular weight polyether triol (Arcol PPG 1376), 15g of triethanolamine, 10g of foaming catalyst dimethylethanolamine and 8g of curing catalyst triethylenediamine, and 60g of flame retardant UND-815, and continue stirring; when the temperature drops to 60°C, add 4g of foaming agent (deionized water); keep stirring for 30 minutes and stop stirring to obtain a premix, and the temperature is controlled at 25°C.

[0077] (3) Preparation of curing agent: Based on the molar ratio of hydroxyl group in the premix to isocyanate group in the curing agent of 100:105, weigh the liquefied MDI and add it to another container. The temperature is controlled at 35°C.

[0078] Before injection, mix the premix and curing agent (speed 3000 rpm) for 3 seconds.

[0079] In the embodiment of the present invention, the mass fraction of the PEDOT:PSS aqueous solution used is 50 wt %.

[0080] Example 1

[0081] 1. Preparation of NNF metamaterials

[0082] (1) Mold preparation: Prepare the mold and open a 1.0 mm diameter exhaust channel at the top (highest point) of the mold cavity; set the mold temperature to 60°C; and evenly spray the release agent on the surface of the mold cavity for later use.

[0083] (2) In the mold cavity, the thickness after molding is 4 mm and the density is 0.4 g / cm 3 Inject the energy-absorbing NNF liquid, close and lock the mold.

[0084] (3) Composite one-piece molding: Curing reaction is carried out in the mold cavity at 65℃ for 6 minutes. As the foaming pressure in the mold cavity increases, the air in the mold cavity is discharged through the exhaust hole. The mold is opened and the product is taken out. The excess scraps are polished off along the periphery to obtain a product with a thickness of 4 mm and a density of 0.4g / cm 3 NNF metamaterial (energy absorbing layer).

[0085] 2. Preparation of energy-absorbing warning composite material (flexible pressure sensing foam):

[0086] (1) Ultrasonic cleaning of the NNF metamaterial substrate was performed using ethanol and deionized water for 5 minutes, followed by drying the surface with nitrogen and then treating the upper surface with an oxygen plasma cleaner for 30 seconds.

[0087] (2) Prepare a slurry containing 6 wt% DMSO, 5 wt% nonionic fluorocarbon surfactant (DuPont Capstone FS-30), and 89 wt% PEDOT:PSS aqueous solution. Spin coating was performed on the NNF metamaterial at a speed of 4000 rpm for 40 seconds, followed by drying in an oven at 80°C for 30 minutes to obtain a flexible sensing film (stretchable conductive layer electrode) with a thickness of 10 μm.

[0088] (3) On a small part of the surface of the stretchable conductive layer (4 mm 2 ) Coat with Ag conductive paste, then put it into an 80℃ oven for drying, take it out and lead out the Ag wire.

[0089] (4) Prepare a 15% mass fraction of SEBS in ethyl acetate solution, spin-coat the solution at 1500 rpm for 30 seconds, and dry the solution at 80°C to obtain a dielectric layer with a thickness of 8 μm.

[0090] (5) Turn the sample over and repeat steps (1), (2), (3), and (4) to obtain an energy-absorbing warning composite material.

[0091] Example 2

[0092] 1. Preparation of NNF metamaterials

[0093] (1) Mold preparation: Prepare the mold and open a 1.0 mm diameter exhaust channel at the top (highest point) of the mold cavity; set the mold temperature to 55°C; and evenly spray the release agent on the surface of the mold cavity for later use.

[0094] (2) In the mold cavity, the thickness after molding is 4 mm and the density is 0.32 g / cm 3 Inject the energy-absorbing NNF liquid, close and lock the mold.

[0095] (3) Composite one-piece molding: Curing reaction is carried out in the mold cavity at 60℃ for 6 minutes. As the foaming pressure in the mold cavity increases, the air in the mold cavity is discharged through the exhaust hole. The mold is opened and the product is taken out. The excess scraps are polished off along the periphery to obtain a product with a thickness of 4 mm and a density of 0.32 g / cm 3 NNF metamaterials.

[0096] 2. The preparation of the energy-absorbing early warning composite material is the same as that in Example 1.

[0097] Example 3

[0098] 1. Preparation of NNF metamaterials

[0099] (1) Mold preparation: Prepare the mold and open a 1.0 mm diameter exhaust channel at the top (highest point) of the mold cavity; set the mold temperature to 50 °C; and evenly spray the release agent on the surface of the mold cavity for later use.

[0100] (2) In the mold cavity, the thickness after molding is 200 mm and the density is 0.15 g / cm 3 Inject the energy-absorbing NNF liquid, close and lock the mold.

[0101] (3) Composite one-piece molding: Curing reaction is carried out in the mold cavity at 55℃ for 7 minutes. As the foaming pressure in the mold cavity increases, the air in the mold cavity is discharged through the exhaust hole. The mold is opened and the product is taken out. The excess scraps are polished off along the periphery. The product is placed on a sponge flat cutting machine and sliced into 4 mm thick pieces. A product with a thickness of 4 mm and a density of 0.15 g / cm is obtained. 3 NNF metamaterials.

[0102] 2. The preparation of the energy-absorbing early warning composite material is the same as that in Example 1.

[0103] Comparative Example 1

[0104] The difference from Example 2 is that a commonly used copper foil electrode (commercial 3M 1181 copper foil tape, directly adhered to the surface of the NNF metamaterial) is loaded on the surface of the NNF metamaterial, and the remaining steps are the same.

[0105] Example 4

[0106] The difference from Example 2 is that the NNF metamaterial is replaced with commercial EVA (density 0.3 g / cm 3 ), the remaining steps are the same as in Example 2.

[0107] Example 5

[0108] The difference from Example 2 is that the NNF metamaterial is replaced with commercial polyurethane foam (density 0.35 g / cm 3), the remaining steps are the same as in Example 2.

[0109] Figure 1 Schematic diagram of the structure of the energy-absorbing warning composite material prepared in Examples 1 to 3, including a SEBS ultra-thin dielectric layer, a stretchable conductive layer, an NNF metamaterial (energy-absorbing layer), a stretchable conductive layer and a SEBS ultra-thin dielectric layer stacked in sequence.

[0110] Test Example 1

[0111] 1. Shear thickening characteristics

[0112] DMA (Dynamic Mechanical Analysis) test results show that NNF metamaterials exhibit shear thickening properties. Taking the NNF metamaterial in Example 2 as an example ( Figure 2 ), exhibiting moderate viscoelasticity overall, effectively balancing structural and damping requirements. With increasing frequency, the loss modulus and energy absorption modulus initially increase slowly, then rapidly increase above 1 Hz. Above 0.2 Hz, the tangent value exceeds 0.5, indicating efficient mechanical energy dissipation. The loss modulus is generally greater than the storage modulus, with energy absorption dominating. The material exhibits excellent dynamic mechanical properties, with storage modulus exceeding 8 MPa and loss modulus exceeding 4 MPa at high tangent values.

[0113] When used, the material can absorb more energy when subjected to strong impact or expansion force, which manifests externally as reduced permeability, enhanced buffering and energy absorption effect, and reduced deformation of the protected equipment.

[0114] 2. High impact resistance and compression deformation resistance

[0115] The stress-strain curve and energy absorption curve of the sample at different loading rates were tested by a universal mechanical testing machine. The results are as follows: Figure 3 The experimental results show that the NNF metamaterial in Example 2 exhibits significant strain-rate-dependent strengthening properties. Under high-speed loading, the material absorbs more energy, demonstrating excellent resistance to high-speed impact forces. Conversely, under low-speed loading, its energy absorption is extremely low, enabling it to provide stable restraint when applied to slowly expanding batteries, thereby ensuring stable battery operation.

[0116] The stress-strain curves of the NNF metamaterial, ordinary polyurethane foam, and EVA foam in Example 2 were tested at a constant rate. -3 / s, compressed to 80% strain (Note: 1Hz loading rate is 0.6*10 -3 / s, the loading frequency is equivalent to 1.6Hz), the results are as follows Figure 4As shown in the densification characteristic curve, in the process of 0~80% compression strain, the NNF metamaterial sample has a significantly larger energy absorption range and a smaller elastic range than commercial EVA and commercial polyurethane foam. In the field of battery applications, it can reach the energy absorption range earlier and avoid the accumulation of heat after expansion. At the same time, in the low compression strain range (<10%) ( Figure 4 As shown in the figure below, commercial EVA and commercial polyurethane foams have excessively high slopes (elastic modulus), significantly impacting expansion margin (i.e., generating excessively high reaction forces at low expansion, which can impact battery charging and discharging). In the higher compressive strain range (10%-20%), the slopes of these foams are gentle, weakening their energy absorption properties and forming a strain plateau. When the battery expansion force exceeds the plateau tolerance, constraints can be lost and the battery can expand rapidly. For example, conventional EVA foam has a high slope from 1% to 10% CFD and a gentle slope from 11% to 60%. In contrast, NNF metamaterials have a low, relatively gentle slope from 1% to 8.5% CFD, indicating lower stress. From 8.6% to 63% CFD, the slope is high, demonstrating highly sensitive compressive deformation performance, which is more conducive to ensuring the proper functioning of the protected equipment.

[0117] The corresponding energy absorption characteristics under compression conditions (see Figure 5 ) further confirmed that NNF metamaterials have better impact resistance and energy absorption performance than traditional foams.

[0118] 3. Mechanical force sensing performance

[0119] By constructing an ultra-thin stretchable conductive layer on the surface of the NNF metamaterial to obtain an energy-absorbing warning composite material, the thickness change of the NNF metamaterial can be fed back in real time, thereby inverting information such as the stress and strain rate of the material, realizing an intelligent warning system for the battery pack.

[0120] Figure 6 This is a typical sensing characteristic curve of the energy-absorbing warning composite material of Example 2. Thanks to the efficient energy-absorbing mechanical properties of the NNF metamaterial, according to the sensitivity (s) calculation formula, the maximum sensitivity of the sensor can reach 9.08 kPa. -1 In the entire test range of 0~100 kPa, its sensitivity is greater than 0.01 kPa -1 , achieving high monitoring resolution in the lower pressure range. In addition, during the densification process of the metamaterial, as the stress increases (~ 3,000 kPa), the strain rate of the material itself decreases, but the sensing signal can still be maintained at 0.001 kPa. -1 The above sensitivity range ensures accurate measurement of a wide range of force values.

[0121] The calculation formula of sensitivity (s) is as follows:

[0122] ,

[0123] in, is the sensitivity, Represents the capacitance value, is the initial capacitance, is the change in external pressure.

[0124] The sensitivity calculation is based on the ratio of the normalized output capacitance signal to the pressure. It reflects the change in the normalized total output signal for a specific pressure change. The larger the value, the higher the sensitivity.

[0125] As a comparison, the NNF metamaterial of Example 2 was loaded with a commonly used copper foil electrode (Comparative Example 1) for testing. Its sensing characteristic curve showed that the maximum sensitivity was only 0.029 kPa. -1 ,like Figure 7 As shown, and decays to 0.001 kPa at a pressure of 1 kPa -1 Below, the overall sensitivity is maintained at 0.0003 kPa -1 , which is two orders of magnitude lower than that of the present invention. It can be seen that the ultrathin stretchable electrodes constructed on the surface give the NNF metamaterial excellent sensing response characteristics.

[0126] At the same time, under the same maximum compression ratio of 80%, by comparing the sensing characteristic curves of ultra-thin stretchable electrodes loaded on commercial EVA and polyurethane foam, we can see that Figure 8 It can be seen that the surface-constructed ultra-thin stretchable electrodes also give these two materials excellent sensing properties. However, the stress response characteristics of these two foam materials are quite different from those of NNF metamaterials, and their final sensitivity characteristics are one order of magnitude lower than those of NNF metamaterials. Moreover, within the same maximum compression ratio range, NNF metamaterials have a constraint force value several times larger, reaching more than 2500kPa, while EVA and ordinary polyurethane foam can only reach 400kPa, indicating that NNF metamaterials have the ability to absorb energy and exert high sensitivity protection in a wider pressure working range, that is, the highest sensitivity is 9.08 kPa. -1 , full range sensitivity greater than 0.001 kPa -1 .

[0127] The NNF metamaterial of this invention provides reliable strain response to pressure. Furthermore, the stretchable, flexible polymer sensing electrode loaded on the NNF metamaterial's surface has a relatively low elastic modulus (5 MPa), effectively eliminating signal interference caused by interfacial air layers and suppressing noise. Furthermore, the electrode is insensitive to tensile loads, effectively providing feedback on changes in the compression signal and adapting to abnormal compression deformation of the NNF material surface, thereby preventing interference from coupled loads on the sensing signal. The energy-absorbing early warning composite material of this invention exhibits excellent sensing performance.

[0128] In addition, NNF metamaterials also have excellent dynamic response characteristics. Through transient compression tests, the response time of the NNF foam flexible sensor of Example 2 was measured to be about 30 milliseconds. Figure 9 As shown in Figure 2. Leveraging the capacitive sensing mechanism, the NNF metamaterial exhibits low signal hysteresis. This excellent signal hysteresis not only ensures the stability of the sensor signal, but also maintains stable signal output during 1,000 large strain fatigue tests (at a test frequency of 1 Hz). Figure 10 shown.

[0129] The technical indicators of the flexible sensing foams prepared in Examples 1 to 3 are shown in Table 1. It can be seen that the NNF metamaterials of Examples 1 to 3 with different densities, which are made of the same flexible sensing electrode material, all exhibit excellent pressure sensing performance. In the entire test range of 0 to 200 kPa, their sensitivity is greater than 0.01 kPa. -1 , achieving high monitoring resolution in the lower pressure range, meeting the requirements of flexible sensing and early warning, and the maximum sensitivity is of the same order of magnitude, reaching up to 11.49 kPa -1 The sensing characteristic curves of Examples 1 and 3 after loading the flexible sensing electrodes under the same thickness and compression ratio are as follows: Figure 11 and Figure 12 As shown, the maximum sensitivity increases with decreasing density. There is also a positive correlation between density and range (restraint force). A restraint force exceeding 300kPa meets the flexible protection requirements for lithium battery core layers. The maximum force can reach over 2500kPa, meeting the flexible protection and early warning requirements for power battery packs and their modules.

[0130] Table 1 Technical indicators of the flexible sensing foams prepared in Examples 1 to 3

[0131]

[0132] The stress-strain curves of the NNF metamaterials used in Examples 1 to 3 at a compression rate of 12 mm / min are as follows: Figure 13 、 Figure 14 、 Figure 15As shown in the figure, the stress value under 80% compression strain and the change of elastic modulus at different stages are demonstrated, which further shows that the stress-strain properties of different NNF metamaterials meet different flexible protection and early warning requirements.

[0133] The NNF metamaterial used in Example 2 was subjected to a 2 mm / min cyclic compression test, and the test results for 2 to 10 cycles were as follows: Figure 16 As shown, the picture shows its excellent mechanical repeatability under 80% compressive strain.

[0134] The NNF foam flexible sensor constructed with the stretchable electrodes and commercial copper foil electrodes used in Examples 1 to 3 was tested under different temperature conditions ranging from -20°C to 80°C. The NNF foam flexible sensor constructed with commercial copper foil electrodes (Comparative Example 1) showed a strong temperature-dependent characteristic and a very low signal-to-noise ratio. Figure 17 On the contrary, the NNF foam flexible sensor constructed with stretchable electrodes according to the present invention (Example 2) exhibits extremely strong temperature stability and high signal-to-noise ratio, as shown in FIG. Figure 18 .

[0135] The resistance change test was conducted on the stretchable electrodes used in Examples 1 to 3, commercial copper foil electrodes, and commercial stretchable electrodes (PDMS-based silver paste electrodes). During the tensile strain from 0 to 60%, the resistance of the electrodes used in the present invention was stable and no insulation transition occurred. Figure 19 .

[0136] Although the above embodiments provide a detailed description of the present invention, they are only part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on the embodiments of the present invention without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. An energy-absorbing early warning composite material, characterized in that: The invention comprises a first dielectric layer, a first stretchable conductive layer, an energy absorbing layer, a second stretchable conductive layer and a second dielectric layer which are sequentially stacked; The material of the energy absorbing layer is compressible foam, and the compressible foam is a shear thickening composite material; The raw materials for preparing the shear thickening composite material include a premix and a curing agent; the premix includes the following components in parts by weight: 30-80 parts of polyether diol, 20-70 parts of polyether polyol, 1-20 parts of chain extender, 0.5-3 parts of cross-linking agent, 5-50 parts of filler, 0.5-5 parts of coupling agent, 0.05-15 parts of foaming agent, 0.1-5 parts of emulsifier, 0.05-5 parts of catalyst and 3-15 parts of flame retardant; the number of hydroxyl groups of the polyether polyol is more than 3, and the hydroxyl value of the polyether polyol is 22-56 mg KOH / g; the curing agent includes diisocyanate; the molar ratio of the hydroxyl group of the premix to the isocyanate group of the curing agent is 1:1-1.1; the density of the shear thickening composite material is 0.1-0.9 g / cm 3 , thickness is 0.1~60mm, maximum compression ratio is 80%~90%; The first stretchable conductive layer and the second stretchable conductive layer are PEDOT:PSS flexible films; the raw material for preparing the PEDOT:PSS flexible film is a PEDOT:PSS solution, which includes the following components by mass fraction: 1% to 12% DMSO, 0.5% to 25% non-ionic fluorocarbon surfactant, and 60% to 95% PEDOT:PSS aqueous solution; the mass fraction of the PEDOT:PSS aqueous solution is 0.5% to 55%; The material of the first dielectric layer and the second dielectric layer is SEBS; The thickness of the first stretchable conductive layer and the second stretchable conductive layer are independently 5 to 100 μm; The thickness of the first dielectric layer and the second dielectric layer are independently 1 to 200 μm; The elastic modulus of the first stretchable conductive layer and the second stretchable conductive layer are independently 0.2~25MPa, and the tensile strain is greater than 100%; the resistance value change of the first stretchable conductive layer and the second stretchable conductive layer is independently less than 5 times within the strain range of 0~60%.

2. The energy-absorbing early warning composite material according to claim 1, characterized in that: The polyether diol includes polytetramethylene ether diol.

3. The method for preparing the energy-absorbing early warning composite material according to claim 1 or 2, characterized in that: The following steps are involved: PEDOT:PSS solution and dielectric layer solution are sequentially coated on both sides of the energy absorption layer to obtain the energy absorption warning composite material; the PEDOT:PSS solution includes the following components by mass fraction: 1% to 12% DMSO, 0.5% to 25% non-ionic fluorocarbon surfactant and 60% to 95% PEDOT:PSS aqueous solution; the mass fraction of the PEDOT:PSS aqueous solution is 0.5% to 55%.

4. The preparation method according to claim 3, characterized in that The dielectric layer material liquid is an ethyl acetate solution of SEBS, and the mass fraction of SEBS in the ethyl acetate solution of SEBS is 5% to 20%.

5. Use of the energy-absorbing and early warning composite material according to claim 1 or 2, or the energy-absorbing and early warning composite material obtained by the preparation method according to claim 3 or 4, as a protective material in a battery pack or battery module.

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