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

Abstract

The invention belongs to the technical field of protective materials, and particularly relates to an energy-absorbing early-warning composite material and a preparation method and application thereof. The energy-absorbing early-warning composite material comprises a dielectric layer, a stretchable conductive layer, an energy-absorbing layer, a stretchable conductive layer and a dielectric layer which are sequentially arranged in a stacked mode. The stretchable conductive layer includes a PEDOT: PSS flexible film. The energy absorption layer and the flexible film are creatively compounded and cooperatively applied to the battery module, the pressure sensing performance is good, and the sensitivity is greater than 0.01 kPa <-1 > within the stress range of 0-200kPa; the sensitivity is greater than 0.1 MPa <-1 > in the stress range of 0.2-20 MPa, and the flexible protection and early warning requirements of the power battery pack and the battery module are met. The composite material disclosed by the invention not only has excellent energy-absorbing and buffering performance, but also can provide stable constraining force and a high-sensitivity sensing early warning mechanism, prolong the service life of a battery and realize an intelligent flexible protection effect.

Description

Technical Field

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

[0002] A lithium-ion battery is an electro-thermal-mechanical coupling system, and there will be an expansion problem during actual use. On the one hand, during the formation process, an SEI film is formed, generating gas, increasing the air pressure inside the battery, and as the cycle progresses, the thickness of the SEI film increases, resulting in the expansion of the battery cell. On the other hand, during charging and discharging, the insertion and extraction of Li + between the positive and negative electrode materials will cause a phase change in the structure, resulting in the generation of an expansion phenomenon, which is mainly reflected in the change in the thickness direction of the negative electrode sheet.

[0003] Research shows that adding buffer materials between batteries when assembling a lithium-ion battery module can effectively reduce the expansion force of the battery and improve the electrochemical performance of the battery module. Currently, foam is often used to reduce the influence of the expansion behavior during charging and discharging. Under the condition of having foam, the maximum expansion force, the minimum expansion force, and the change amount of the total expansion force are all smaller than the test results under the condition of no foam. Under the condition of the same pre-tightening force, using a foam buffer material with a lower hardness can effectively inhibit the increase in the expansion force of the battery during charging and discharging. However, the current foam materials have a low compression modulus, do not have a highly sensitive stress characteristic to deformation, cannot output high-sensitivity electrical signals in real time, have poor pressure sensing performance, and have no obvious energy-absorbing effect, resulting in a poor protective effect on the battery and affecting the service life of the battery. Summary of the Invention

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

[0005] The present invention provides an energy-absorbing and warning composite material, which includes a first dielectric layer, a first stretchable conductive layer, an energy-absorbing layer, a second stretchable conductive layer, and a second dielectric layer that are sequentially stacked; The material of the energy-absorbing layer is compressible foam, and the compressible foam 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 ethylene-propylene-diene monomer; The first stretchable conductive layer and the second stretchable conductive layer include PEDOT:PSS flexible films.

[0006] 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 polyether polyol has more than 3 hydroxyl groups, 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; The density of the shear thickening composite material is 0.1-0.9 g / cm 3 , the thickness is 0.1-60 mm, and the maximum compression ratio is 80%-90%.

[0007] Preferably, the polyether diol includes polytetrahydrofuran ether diol.

[0008] Preferably, the thicknesses of the first stretchable conductive layer and the second stretchable conductive layer are independently 5-100 μm.

[0009] Preferably, the elastic moduli of the first stretchable conductive layer and the second stretchable conductive layer are independently 0.2-25 MPa, and the tensile strain is greater than 100%; within the strain range of 0-60%, the change in the resistance value of the first stretchable conductive layer and the second stretchable conductive layer is independently less than 5 times.

[0010] Preferably, the thicknesses of the first dielectric layer and the second dielectric layer are independently 1-200 μm.

[0011] The present invention also provides a method for preparing the energy-absorbing and warning composite material according to the above technical solution, including the following steps: Coat the PEDOT:PSS solution and the dielectric layer solution on the two side surfaces of the energy-absorbing layer in sequence to obtain the energy-absorbing and warning composite material.

[0012] Preferably, the PEDOT:PSS solution includes the following components in mass fractions: 1%-12% of DMSO, 0.5%-25% of nonionic fluorocarbon surfactant, and 60%-95% of PEDOT:PSS aqueous solution; the mass fraction of the PEDOT:PSS aqueous solution is 0.5%-55%.

[0013] Preferably, the dielectric layer solution is an ethyl acetate solution of SEBS, and the mass fraction of SEBS in the ethyl acetate solution of SEBS is 5%-20%.

[0014] The present invention also provides an application of the energy-absorbing and warning composite material described in the above technical solution or the energy-absorbing and warning composite material obtained by the above preparation method as a protective material in a battery pack or a battery module.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides an energy-absorbing and warning composite material, which includes a first dielectric layer, a first stretchable conductive layer, an energy-absorbing layer, a second stretchable conductive layer, and a second dielectric layer that are sequentially laminated; the material of the energy-absorbing layer is a compressible foam, and the compressible foam layer 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 ethylene propylene diene monomer; the first stretchable conductive layer and the second stretchable conductive layer include PEDOT:PSS flexible films.

[0016] The present invention innovatively combines an energy-absorbing layer and a flexible film and applies them synergistically in a power battery pack and its battery module. It has good pressure sensing performance, and within the test range of 0 to 200 kPa, its sensitivity is greater than 0.01 kPa -1 , and within the stress range of 0.2 MPa to 20 MPa, the sensitivity is greater than 0.1 MPa -1 , meeting the requirements of flexible protection and warning.

[0017] During the assembly process of lithium-ion batteries, adding a buffer material can effectively reduce the swelling force, thereby improving the electrochemical performance of the module. When the battery swells, an extrusion force is applied to the buffer material, and the buffer material absorbs and buffers energy through compression. According to the principle of interaction of forces, the buffer material will exert a reaction force on the battery. The present invention uses a (non-Newtonian fluid) NNF material with shear thickening characteristics as the energy-absorbing layer, which can achieve a good stable binding force when the deformation is small. Due to its significant energy-absorbing characteristics, the compression of the composite material can help release some of the stress inside the battery, further reducing the battery swelling force. At the same time, due to its slow rebound characteristics, its reaction force is small, so the extrusion of the battery is more gentle, and it can ensure the normal operation of the battery for a longer time, which helps to improve the overall performance of the battery. At the same time, the present invention loads a flexible film with stretchable characteristics on the surface of the energy-absorbing layer, which can collect capacitance signals in real time. The absolute values of these signals can be used to deduce the pressure on the surface of the composite material, and the time-domain signal sequence can be used to deduce the acceleration of the impact force received by the composite material. These signals can be used as the signal source of a differential controller to predict the arrival of a large impact force to a certain extent, so that the system can take preventive measures in advance. The composite material of the present invention not only has excellent energy-absorbing and buffering performance, but also can provide a stable binding force and a high-sensitivity sensing and warning mechanism, thereby extending the working life of the battery and achieving the effect of intelligent flexible protection.

[0018] The energy-absorbing and warning composite material of the present invention has a signal error of less than 5% when the output capacitance signal is under external pressure within and outside the measurement range; when the external environmental temperature ranges from -20°C to 80°C and the output capacitance signal changes, the deviation of its signal average value under any pressure condition is less than 3%. After the shear thickening composite material (NNF metamaterial) is compressed in the first cycle, in the constant speed test, the deviation of the stress-strain curve in the subsequent cyclic compression is less than 5%. Brief Description of the Drawings

[0019] 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 embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 Structural schematic diagram of the energy-absorbing and warning composite material prepared in Examples 1 to 3; Figure 2 DMA test results of the NNF metamaterial in Example 2; Figure 3 Energy absorption curve of the NNF metamaterial in Example 2; Figure 4 Stress-strain curves of the NNF metamaterial, ordinary polyurethane foam, and EVA foam in Example 2; Figure 5 Energy absorption characteristic diagram of the NNF metamaterial, ordinary polyurethane foam, and EVA foam in Example 2; Figure 6 Typical sensing characteristic curve of the energy-absorbing and warning composite material in Example 2; Figure 7 Sensing characteristic curve of the composite material in Comparative Example 1; Figure 8 Sensing characteristic curves of the composite materials in Examples 4 and 5; Figure 9 Response time test result diagram of the energy-absorbing and warning composite material in Example 2; Figure 10 Signal fatigue test result diagram of the energy-absorbing and warning composite material in Example 2; Figure 11 Sensing characteristic curve of the energy-absorbing and warning composite material in Example 1; Figure 12 Sensing characteristic curve of the energy-absorbing and warning composite material in Example 3; Figures 13 - 15 Compressive stress-strain curves of the NNF metamaterials in Examples 1 to 3 respectively; Figure 16Test results of the NNF metamaterial used in Example 2 for 2 - 10 cycles in the cyclic compression experiment at 2 mm / min; Figure 17 Characteristics of the NNF foam flexible sensor constructed with commercial copper foil electrodes under the influence of temperature and signal - to - noise ratio results; Figure 18 Characteristics of the NNF foam flexible sensor constructed with the stretchable electrode used in Example 2 under the influence of temperature and signal - to - noise ratio results; Figure 19 Resistance changes of the stretchable electrode of the example, commercial copper foil electrode, and commercial stretchable electrode during the process of tensile strain from 0 to 60%. Detailed implementation mode

[0021] The present invention provides an energy - absorbing and warning composite material, which includes a first dielectric layer, a first stretchable conductive layer, an energy - absorbing layer, a second stretchable conductive layer, and a second dielectric layer that are sequentially laminated; The material of the energy - absorbing layer is compressible foam, and the compressible foam 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); The first stretchable conductive layer and the second stretchable conductive layer include PEDOT:PSS flexible films.

[0022] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in this field.

[0023] The energy - absorbing and warning composite material of the present invention has the shear - thickening property of non - Newtonian fluid (NNF), shows the characteristic of non - linear compression modulus when subjected to large expansion forces, and has a smaller penetration force value under the same compression rate compared with ordinary protective foams. In addition, due to its shear - thickening property, it can provide long - term and stable binding force for lithium - ion battery packs. Especially in the face of rapid impact or high expansion force, it can respond quickly and effectively absorb impact energy. At the same time, its slow - rebound property helps to reduce the extrusion of the reaction force on the battery, thereby extending the service life of the battery. The present invention composites the energy - absorbing layer with a flexible sensing film, and utilizes the stress characteristic of the energy - absorbing layer material that is highly sensitive to deformation to output high - sensitivity electrical signals in real time, and monitor the mechanical dynamic signals and quasi - static signals during the compression process. Among them, the dynamic signal can be used to identify the impact situation received by the material, and its differential can predict the arrival of a large impact force in advance; while the quasi - static signal can identify the limit value of the expansion force, thus realizing the warning function.

[0024] During the compression of the battery module, the polymer molecules inside the NNF energy-absorbing layer rapidly aggregate, resulting in a significant change in the shear thickening performance. This change causes the electro-pressure / compression rate properties to exhibit large differences during different loading states and unloading processes. Therefore, the energy-absorbing warning composite material not only has excellent energy-absorbing and buffering performance but also provides a stable binding force and a highly sensitive sensing and warning mechanism, thereby extending the working life of the battery and achieving the effect of intelligent flexible protection.

[0025] In the present invention, the thicknesses of the first dielectric layer and the second dielectric layer are independently preferably 1 to 200 μm, more preferably 8 μm.

[0026] In the present invention, the materials of the first dielectric layer and the second dielectric layer are preferably SEBS (a linear triblock copolymer with a polystyrene end segment and an ethylene-butene copolymer obtained by hydrogenating polybutadiene as the middle elastic block). The dielectric layer of the present invention has excellent electrical insulation performance, avoiding the influence of the additional potential of the battery core layer on the battery.

[0027] In the present invention, the thicknesses of the first stretchable conductive layer and the second stretchable conductive layer are independently preferably 5 to 100 μm, specifically 10 μm or 20 μm. The elastic moduli of the first stretchable conductive layer and the second stretchable conductive layer are independently 0.2 to 25 MPa, and the tensile strain is greater than 100%; within 30% strain, the change amount of the resistance value is less than 5 times the initial resistance value. The present invention uses a PEDOT:PSS flexible film as the stretchable conductive layer, which has an extremely low elastic modulus and thickness, ensuring excellent conformal characteristics with the energy-absorbing layer.

[0028] 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.

[0029] 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 to 80 parts of polyether diol, 20 to 70 parts of polyether polyol, 1 to 20 parts of chain extender, 0.5 to 3 parts of crosslinking agent, 5 to 50 parts of filler, 0.5 to 5 parts of coupling agent, 0.05 to 15 parts of foaming agent, 0.1 to 5 parts of emulsifier, 0.05 to 5 parts of catalyst, and 3 to 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 to 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 to 1.1; The density of the shear thickening composite material is 0.1 to 0.9 g / cm 3 , the thickness is 0.1 to 60 mm, and the maximum compression ratio is 80% to 90%.

[0030] In the present invention, the curing agent preferably includes diphenylmethane diisocyanate (MDI) and / or 1,5-naphthalene diisocyanate; the molar ratio of the hydroxyl group of the premix to the isocyanate group of the curing agent is preferably 1:1.05.

[0031] In the present invention, except for polyether diol and flame retardant, the components in the premix are preferably the same as those in the Chinese patent "CN115536797A - A Shear Thickening Composite Material and Its Preparation Method and Application", which will not be elaborated here. The polyether diol preferably further includes polytetrahydrofuran ether diol (PTMEG) with 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 polyether diol with a molecular weight of 400, 10 parts of compound chain extender, 4 parts of silane coupling agent, 2 parts of polyorganosiloxane-oxyalkylene block copolymer emulsifier, 40 parts of nano-silica; 20 parts of polyether diol with a molecular weight of 2000; 10 parts of polytetrahydrofuran ether diol with a molecular weight of 2000; 20 parts of polyether triol with a molecular weight of 7000, 1.5 parts of triethanolamine, 1 part of foaming catalyst dimethylethanolamine and 0.8 part of curing catalyst triethylenediamine, 0.4 part of foaming agent and 6 parts of flame retardant.

[0032] The shear thickening composite material of the present invention is an NNF material with shear thickening performance. In the polyether diol of the present invention, polytetrahydrofuran ether diol (PTMEG) with a molecular weight of 2000 is added. The polytetrahydrofuran ether diol is preferably BASF PolyTHF2000, which can improve the toughness and wear resistance of the composite material and meet the requirements of the charging cycle expansion stress during battery operation; a flame retardant is added to the premix of the present invention. The flame retardant is preferably UND-815, so that the composite material has high-efficiency flame retardant characteristics and meets the flame retardant requirements of power batteries and their modules.

[0033] In the present invention, the density of the shear thickening composite material is preferably 0.1~0.5 g / cm 3 , specifically it can be 0.15 g / cm 3 , 0.32 g / cm 3 or 0.4 g / cm 3 ; the thickness is preferably 1~10 mm, specifically it can be 4 mm.

[0034] The shear thickening composite material of the present invention remains soft and has a suitable elastic state under normal conditions. When subjected to rapid and severe impact or extrusion, it can quickly enhance its strain through local density increase, presenting an obvious shear thickening phenomenon. That is, when the material is subjected to external force impact, it behaves as a hard solid, and moreover, as the external force increases, the strength of the material increases; when the external force disappears, the material will return to its initial relaxed soft elastic state. When subjected to large stress, due to the shear thickening composite material can quickly generate strain and absorb impact energy up to more than 95% of the impact force value. Moreover, by using its characteristics of the falling ball rebound height less than 8% and slow rebound, the battery can not only be well protected for a long time when subjected to large impact, but also suppress the bulging phenomenon that occurs during battery charging and discharging.

[0035] The present invention combines an energy-absorbing layer with shear thickening characteristics and a PEDOT:PSS flexible thin film to achieve the functions of energy absorption and early warning.

[0036] The present invention also provides a preparation method of the energy-absorbing and early-warning composite material described in the above technical solution, including the following steps: Coat the PEDOT:PSS liquid and the dielectric layer liquid on the two side surfaces of the energy-absorbing layer in sequence to obtain the energy-absorbing and early-warning composite material.

[0037] The present invention has no special requirements for the preparation method of the energy-absorbing layer.

[0038] Preferably, the present invention first coats the PEDOT:PSS liquid on one side surface of the energy-absorbing layer to obtain a first stretchable conductive layer; then coats the dielectric layer liquid on the surface of the first stretchable conductive layer to obtain a first dielectric layer; and then repeats coating the PEDOT:PSS liquid and the dielectric layer liquid on the other side surface of the energy-absorbing layer to obtain a second stretchable conductive layer and a second dielectric layer.

[0039] In the present invention, before coating the PEDOT:PSS liquid, it also includes: cleaning the surface of the energy-absorbing layer; the cleaning preferably includes: ethanol ultrasonic cleaning and deionized water ultrasonic cleaning, and the time of both ethanol ultrasonic cleaning and deionized water ultrasonic cleaning is preferably 5 minutes. After cleaning, the surface is preferably dried with nitrogen and treated with an oxygen plasma cleaner for 30 seconds to enhance the affinity of the surface for the PEDOT:PSS liquid, making the coating more uniform and having strong bonding force.

[0040] In the present invention, the PEDOT:PSS solution preferably comprises components with the following mass fractions: 1% - 12% DMSO, 0.5% - 25% nonionic fluorocarbon surfactant, and 60% - 95% PEDOT:PSS aqueous solution; the mass fraction of the PEDOT:PSS aqueous solution is preferably 0.5% - 55%, and specifically can be 50%. The PEDOT:PSS solution more preferably comprises components with the following mass fractions: 6% DMSO, 5% nonionic fluorocarbon surfactant, and 89% PEDOT:PSS aqueous solution. The nonionic fluorocarbon surfactant preferably includes DuPont Capstone FS - 30.

[0041] In the present invention, the method of coating the PEDOT:PSS solution is preferably spin - coating or spraying, and the parameters of the spin - coating are preferably: a spin - coating film - forming process is carried out at a speed of 4000 rpm for 40 seconds. After coating, drying is preferably further included, and the drying temperature is preferably 80°C and the time is preferably 30 minutes.

[0042] In the present invention, after obtaining the first stretchable conductive layer, it is preferably further included: coating Ag conductive paste on a partial surface of the first stretchable conductive layer, drying, and then leading out Ag wires. The drying temperature is preferably 80°C. The area of the partial surface is preferably 4 - 16 mm 2 . The present invention has no special requirements for the composition of the Ag conductive paste, and it may include Ag nanosheets, or include Ag nanosheets and siloxane resin.

[0043] 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% - 20%, and specifically can be 15%.

[0044] In the present invention, the method of coating the dielectric layer solution is preferably spin - coating or spraying, and the parameters of the spin - coating are preferably: a spin - coating film - forming process is carried out at a speed of 1500 rpm for 30 seconds. After coating, drying is preferably further included, and the drying temperature is preferably 80°C.

[0045] In the present invention, the method of repeatedly coating the PEDOT:PSS solution and the dielectric layer solution on the other surface of the energy - absorbing layer is the same as the method for preparing the first stretchable conductive layer and the first dielectric layer, and will not be elaborated herein.

[0046] The present invention also provides the application of the energy - absorbing and warning composite material described in the above technical solution or the energy - absorbing and warning composite material obtained by the above preparation method as a protective material in a battery pack or a battery module.

[0047] Using the energy-absorbing and warning composite material of the present invention as a protective material in the battery module has an intelligent flexible protection effect. The present invention uses the energy-absorbing and warning composite material as a warning mechanism for battery life monitoring and battery explosion caused by battery expansion. By using the special shear thickening effect of the energy-absorbing layer as the sensing layer, high-precision perception of the expansion force is achieved, so that the expansion process of the battery pack can be dynamically and real-time monitored. The present invention utilizes the shear thickening performance of the NNF energy-absorbing layer, that is, the property of the material showing enhanced stress when subjected to continuously increasing external forces, to design a warning mechanism that can respond to the bulging and even fire-spraying of the battery due to thermal expansion.

[0048] To further illustrate the present invention, the energy-absorbing and warning composite material provided by the present invention, its preparation method and application will be described in detail below with reference to the accompanying drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0049] In the embodiment of the present invention, the used NNF feed liquid for energy absorption includes a premix and a curing agent, and the preparation method is as follows: (1) Preparation of the compound chain extender: In a constant temperature container at 80 °C, successively add: 100 g of diethanolamine, 500 g of dipropylene glycol, 280 g of 4,4'-bis(sec-butylamino)diphenylmethane, and 120 g of ethylene glycol. Start stirring and maintain a stirring speed of 100 rpm; seal the container; start vacuum dehydration and maintain a negative pressure of -0.1 MPa for 8 hours to obtain the first component. According to the molar ratio of 100:50 of the hydroxyl groups in the first component to the isocyanate groups in the liquefied MDI, slowly add MDI for a polymerization chain extension reaction for 8 hours, stop heating, stop stirring, and wait for the material temperature to drop to room temperature to obtain the (NNF-2) compound chain extender.

[0050] (2) Preparation of the premix: Add 500 g of 400-molecular-weight polyether diol (Pluracol P410R) to a constant temperature container at 75 °C, start stirring and maintain a stirring speed of 100 rpm, and then add 100 g of the NNF-2 compound chain extender described in step (1), and a silane coupling agent (XIAMETER тм40 g of OFS-6020 Silane, 20 g of polysiloxane-oxyalkylene block copolymer emulsifier, 400 g of nano-silica (AEROSIL 200); continue stirring for 45 minutes, stop heating, and add 200 g of polyether diol with a molecular weight of 2000 (Pluracol P1477); 100 g of polytetrahydrofuran ether diol (PTMEG) with a molecular weight of 2000; add 200 g of polyether triol with a molecular weight of 7000 (Arcol PPG 1376), 15 g of triethanolamine, 10 g of foaming catalyst dimethylethanolamine, and 8 g of curing catalyst triethylenediamine, 60 g of flame retardant UND-815, and continue stirring; when the temperature drops to 60 °C, add 4 g of foaming agent (deionized water); keep stirring for 30 minutes and then stop stirring to obtain a premix, with the temperature controlled at 25 °C.

[0051] (3)Preparation of curing agent: According to the molar ratio of hydroxyl groups in the premix to isocyanate groups in the curing agent of 100:105, calculate and weigh liquefied MDI and add it to another container, with the temperature controlled at 35 °C.

[0052] Before injection, mix the premix and the curing agent (rotation speed 3000 rpm) for 3 seconds.

[0053] In the embodiment of the present invention, the mass fraction of the PEDOT:PSS aqueous solution used is 50 wt%.

[0054] Example 1 1. Preparation of NNF metamaterial (1)Mold preparation: Prepare the mold, drill an exhaust channel with a diameter of 1.0 mm at the uppermost end (highest point) of the mold cavity; set the mold temperature at 60 °C; evenly spray a release agent on the surface of the mold cavity for standby.

[0055] (2)In the mold cavity, according to a post-forming thickness of 4 mm and a density of 0.4 g / cm 3 Inject the energy-absorbing NNF liquid material, close and lock the mold.

[0056] (3)Composite integral molding: Cure and react in the mold cavity at 65 °C for 6 minutes. While the foaming pressure in the mold cavity increases, the air in the mold cavity is discharged through the exhaust holes. Open the mold and take out the product, and grind off the excess corner materials along the periphery to obtain a NNF metamaterial (energy-absorbing layer) with a thickness of 4 mm and a density of 0.4 g / cm 3

[0057] 2. Preparation of energy-absorbing warning composite material (flexible pressure-sensing foam): (1)Successively use ethanol and deionized water to ultrasonically clean the NNF metamaterial substrate for 5 minutes, dry the surface with nitrogen, and then use an oxygen plasma cleaner to treat the upper surface for 30 seconds; (2) Prepare the slurry, which includes: 6 wt% DMSO, 5 wt% non-ionic fluorocarbon surfactant (DuPont Capstone FS-30), and 89 wt% PEDOT:PSS aqueous solution. Perform a spin coating film-forming process on the NNF metamaterial at a speed of 4000 rpm for 40 seconds, and then dry it 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.

[0058] (3) Coat a small part (4 mm 2 ) of the surface of the stretchable conductive layer with Ag conductive paste, then put it into an oven at 80 °C to dry, and lead out the Ag wire after taking it out.

[0059] (4) Prepare an ethyl acetate solution of SEBS with a mass fraction of 15%, perform a spin coating film-forming process at a speed of 1500 rpm for 30 seconds, and dry it at 80 °C to obtain a dielectric layer with a thickness of 8 μm.

[0060] (5) Flip the sample and repeat steps (1), (2), (3), and (4) to obtain the energy-absorbing and warning composite material.

[0061] Example 2 1. Preparation of NNF Metamaterial (1) Mold preparation: Prepare the mold, drill an exhaust channel with a diameter of 1.0 mm at the uppermost end (highest point) of the mold cavity; set the mold temperature at 55 °C; evenly spray the mold release agent on the surface of the mold cavity for standby.

[0062] (2) In the mold cavity, inject the energy-absorbing NNF liquid material according to a post-forming thickness of 4 mm and a density of 0.32 g / cm 3 , close and lock the mold.

[0063] (3) Composite integral molding: Cure and react in the mold cavity at 60 °C for 6 minutes. While the foaming pressure in the mold cavity increases, the air in the mold cavity is discharged through the exhaust holes. Open the mold and take out the product, and grind off the excess corner materials along the outer periphery to obtain an NNF metamaterial with a thickness of 4 mm and a density of 0.32 g / cm 3 .

[0064] 2. Preparation of the energy-absorbing and warning composite material, which is the same as in Example 1.

[0065] Example 3 1. Preparation of NNF Metamaterial (1) Mold preparation: Prepare the mold, drill an exhaust channel with a diameter of 1.0 mm at the uppermost end (highest point) of the mold cavity; set the mold temperature at 50 °C; evenly spray the mold release agent on the surface of the mold cavity for standby.

[0066] (2) In the mold cavity, according to the thickness of 200 mm and density of 0.15 g / cm after molding, 3 Inject the energy-absorbing NNF liquid material, close and lock the mold.

[0067] (3) Composite integrated molding: Cure and react in the mold cavity at 55 °C for 7 minutes. While the foaming pressure in the mold cavity increases, the air in the mold cavity is discharged through the exhaust holes. Open the mold and take out the product, grind off the excess scraps along the outer periphery, place it on a sponge slicing machine, and slice it according to the size of 4 mm thickness, then a kind of NNF metamaterial with a thickness of 4 mm and a density of 0.15 g / cm 3 is obtained.

[0068] 2. The preparation of the energy-absorbing warning composite material is the same as that in Example 1.

[0069] Comparative Example 1 The difference from Example 2 is that a common copper foil electrode (commercial 3M Company 1181 copper foil tape, directly pasted on the surface of the NNF metamaterial) is loaded on the surface of the NNF metamaterial, and the other steps are the same.

[0070] Example 4 The difference from Example 2 is that the NNF metamaterial is replaced by commercial EVA (density 0.3 g / cm 3 ), and the other steps are the same as those in Example 2.

[0071] Example 5 The difference from Example 2 is that the NNF metamaterial is replaced by commercial polyurethane foam (density 0.35 g / cm 3 ), and the other steps are the same as those in Example 2.

[0072] Figure 1 is a schematic structural diagram of the energy-absorbing warning composite material prepared in Examples 1 to 3, including a sequentially laminated SEBS ultra-thin dielectric layer, a stretchable conductive layer, an NNF metamaterial (energy-absorbing layer), a stretchable conductive layer, and an SEBS ultra-thin dielectric layer.

[0073] Test Example 1 I. Shear thickening characteristics The DMA (Dynamic Thermomechanical Analysis) test results show that the NNF metamaterial exhibits shear thickening characteristics. Taking the NNF metamaterial in Example 2 as an example ( Figure 2), the overall performance shows medium viscoelasticity, which can well balance the requirements of structure and damping. As the acting frequency increases, the loss modulus and energy absorption modulus first increase slowly, and then increase rapidly after exceeding 1 Hz. Moreover, when the frequency is greater than 0.2 Hz, the tangent value > 0.5, belonging to the high-efficiency mechanical energy dissipation range, and the loss modulus is greater than the storage modulus as a whole, with energy absorption being dominant. The dynamic mechanical properties of the material are excellent. When the tangent value is relatively high, the storage modulus reaches above 8 MPa and the loss modulus reaches above 4 MPa.

[0074] During application, when the material is subjected to strong impact or expansion force, it can absorb more energy, showing a smaller transmission force externally, enhanced buffer energy absorption effect, and reduced deformation of the protected equipment.

[0075] II. High impact and compression deformation resistance performance The stress-strain curves and energy absorption curves of the samples at different loading rates were tested by a universal mechanical testing machine, and the results are as Figure 3 shown. The experimental results show that the NNF metamaterial in Example 2 exhibits obvious strain rate-dependent strengthening characteristics. Under high-speed load conditions, the material can absorb more energy, showing good resistance to high-speed impact force. On the contrary, during low-speed loading, its energy absorption is extremely low, which enables it to provide a stable binding force when applied to the scenario of slow battery expansion, thus ensuring the stable operation of the battery.

[0076] The stress-strain curves of the NNF metamaterial in Example 2, commercial polyurethane foam, and EVA foam were tested at a constant rate. The loading rate was 10 -3 / s and compressed to 80% strain (Note: The loading rate of 1 Hz is 0.6*10 -3 / s, and the loading frequency is equivalent to 1.6 Hz), and the results are as Figure 4 shown. The densification characteristic curve shows that during the process of 0 - 80% compression strain, the NNF metamaterial sample has a significantly larger energy absorption range compared to commercial EVA and commercial polyurethane foam, and the elastic range of the sample is smaller. In the field of battery applications, it can reach the energy absorption range earlier, avoiding the accumulation of heat after expansion. At the same time, in the low compression strain range (<10%) ( Figure 4(the following figure in [])), the slopes (elastic moduli) of commercial EVA and commercial polyurethane foam are too high, which has a great influence on the expansion margin (that is, a too high reaction force is generated during small expansion, and the too high reaction force has a certain impact on the charging and discharging of the battery). In the higher compression strain range (10% - 20%), the slopes of commercial EVA and commercial polyurethane foam are gentle, and the energy absorption characteristics are weakened, forming a strain platform. When the battery expansion force is greater than the platform tolerance, it will cause constraint out of control and the battery will expand sharply. For example, for ordinary EVA foam: the slope is high at CFD 1 - 10% and gentle at 11 - 60%; while for the NNF metamaterial, the slope is low and gentle at CFD 1 - 8.5%, showing a lower stress. At CFD 8.6 - 63%, the slope is high, with a high-sensitivity compressive strain performance, which is more conducive to ensuring the normal operation of the protected equipment.

[0077] The energy absorption characteristics under the corresponding compression conditions (see Figure 5 ), further confirm that the NNF metamaterial has better anti-impact energy absorption performance than traditional foams.

[0078] III. Mechanical force sensing performance By constructing an ultrathin stretchable conductive layer on the surface of the NNF metamaterial, an energy absorption warning composite material can be obtained, which can real-time feedback the thickness change of the NNF metamaterial, and thus invert information such as the stress and strain rate suffered by the material, realizing an intelligent warning system for the battery pack.

[0079] Figure 6 It is the typical sensing characteristic curve of the energy absorption warning composite material in Example 2. Thanks to the efficient energy absorption mechanical characteristics of the NNF metamaterial, calculated according to the sensitivity (s) calculation formula, the highest sensitivity of this 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 a high monitoring resolution for the lower pressure range. In addition, during the densification process stage 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 in the sensitivity range above 0.001 kPa -1 , ensuring the accurate measurement of a large range of force values.

[0080] The sensitivity (s) calculation formula is as follows: , where, is the sensitivity, represents the capacitance value, is the initial capacitance, is the change amount of the applied pressure.

[0081] The sensitivity calculation is based on the ratio of the normalized output capacitance signal to the pressure, which can reflect the change in the total normalized output signal for a specific pressure change. The larger the value, the higher the sensitivity.

[0082] As a comparison, the NNF metamaterial of Example 2 loaded with a commonly used copper foil electrode (Comparative Example 1) was tested. Its sensing characteristic curve shows that the highest sensitivity is only 0.029 kPa -1 , as Figure 7 shown, and it decays to 0.001 kPa under a pressure of 1 kPa -1 Hereinafter, 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 electrode constructed on the surface endows the NNF metamaterial with excellent sensing response characteristics.

[0083] At the same time, under the condition of the same maximum compression ratio of 80%, by comparing the sensing characteristic curves of the ultrathin stretchable electrode loaded on commercial EVA and polyurethane foam, from Figure 8 it can be seen that the ultrathin stretchable electrode constructed on the surface also endows these two materials with excellent sensing performance. However, the stress response characteristics of these two foam materials are quite different from those of the NNF metamaterial, and their final sensitivity characteristics are one order of magnitude lower than that of the NNF metamaterial. Moreover, in the same maximum compression ratio range, the NNF metamaterial has a binding force value several times larger, reaching more than 2500 kPa, while EVA and ordinary polyurethane foam can only reach 400 kPa, indicating that the NNF metamaterial can play an energy absorption and high-sensitivity protection role in a wider pressure working range, that is, the highest sensitivity is 9.08 kPa -1 , and the full-range sensitivity is greater than 0.001 kPa -1 .

[0084] The NNF metamaterial of the present invention provides reliable strain response characteristics to pressure; at the same time, the polymer stretchable flexible sensing electrode loaded on the surface of the NNF metamaterial has a relatively low elastic modulus (5 MPa), which can effectively eliminate the signal interference caused by the interfacial air layer and suppress noise. In addition, the electrode is insensitive to tensile loads, can not only efficiently feedback the change of compression signals, but also adapt to the abnormal compression deformation of the NNF material surface, thus avoiding the interference of coupled loads on the sensing signal. The energy absorption and warning composite material of the present invention has excellent sensing performance.

[0085] In addition, the NNF metamaterial also has 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, as Figure 9As shown. With the capacitive sensing mechanism, the sensing mechanism of the NNF metamaterial exhibits low signal hysteresis. This excellent signal hysteresis characteristic not only ensures the stability of the sensor signal but also maintains a stable signal output during 1000 large-strain fatigue tests (test frequency: 1 Hz), as Figure 10 shown.

[0086] The technical indicators of the flexible sensing foams prepared in Examples 1 to 3 are shown in Table 1. It can be seen that when the same flexible sensing electrode material is used to compound the NNF metamaterials with different densities in Examples 1 to 3, all exhibit good 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 for the lower pressure range, meeting the requirements of flexible sensing early warning. The maximum sensitivities are of the same order of magnitude, reaching up to 11.49 kPa -1 . The sensing characteristic curves of Examples 1 and 3 with flexible sensing electrodes under the same thickness and compression ratio conditions are as Figure 11 and Figure 12 shown. As the density decreases, the maximum sensitivity increases; at the same time, there is a positive correlation between density and range (constraining force). When the constraining force exceeds 300 kPa, it meets the flexible protection requirements of the lithium battery cell layer; it can reach more than 2500 kPa at most, meeting the flexible protection and early warning requirements of the power battery pack and its battery modules.

[0087] Table 1 Technical indicators of the flexible sensing foams prepared in Examples 1 to 3

[0088] The stress-strain curves of the NNF metamaterials used in Examples 1 to 3 at a compression rate of 12 mm / min are respectively as Figure 13 , Figure 14 , Figure 15 shown. The pictures show the stress values they bear at 80% compressive strain and the changes in elastic modulus at different stages, further indicating that the stress-strain properties of different NNF metamaterials meet the requirements of different flexible protection and early warning.

[0089] In the cyclic compression experiment of the NNF metamaterial used in Example 2 at 2 mm / min, the test results of 2 to 10 cycles are as Figure 16 shown. The pictures show its excellent mechanical repeatability at 80% compressive strain.

[0090] The NNF foam flexible sensors constructed with the stretchable electrodes and commercial copper foil electrodes used in Examples 1 to 3 were subjected to variable temperature tests under different pressure conditions in the range of -20°C to 80°C. The NNF foam flexible sensor constructed with the commercial copper foil electrode (Comparative Example 1) showed extremely strong temperature influence characteristics and too low signal-to-noise ratio, as shown in Figure 17 ; on the contrary, the NNF foam flexible sensor constructed with the stretchable electrode of the present invention (Example 2) showed extremely strong temperature stability and relatively high signal-to-noise ratio, as shown in Figure 18 .

[0091] The resistance change tests were carried out on the stretchable electrodes, commercial copper foil electrodes, and commercial stretchable electrodes (PDMS-based silver paste electrodes) used in Examples 1 to 3. During the process of the tensile strain from 0 to 60%, the resistance of the electrodes used in the present invention was stable and no insulation transition occurred, as shown in Figure 19 .

[0092] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all the embodiments. People can also obtain other embodiments according to the embodiments of the present invention without creative labor, and these embodiments all belong to the protection scope of the present invention.

Claims

1. An energy absorbing early warning composite material, characterized in that: It includes 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 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; The first stretchable conductive layer and the second stretchable conductive layer include PEDOT:PSS flexible films.

2. The energy absorbing early warning composite material according to claim 1, characterized in that: 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 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, and the maximum compression ratio is 80%~90%.

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

4. The energy absorbing early warning composite material according to claim 1, characterized in that: The thickness of the first stretchable conductive layer and the second stretchable conductive layer are independently 5-100 μm.

5. The energy absorbing early warning composite material according to claim 1 or 4, characterized in that: 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%; within the strain range of 0~60%, the change in resistance value of the first stretchable conductive layer and the second stretchable conductive layer is independently less than 5 times.

6. The energy absorbing early warning composite material according to claim 1, characterized in that: The thickness of the first dielectric layer and the second dielectric layer are independently 1-200 μm.

7. The method for preparing the energy absorbing early warning composite material according to any one of claims 1 to 6, characterized in that: The following steps are involved: The PEDOT:PSS solution and the dielectric layer solution are sequentially coated on both side surfaces of the energy absorption layer to obtain the energy absorption warning composite material.

8. The preparation method according to claim 7, characterized in that: The PEDOT:PSS slurry comprises the following components in mass fractions: 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%.

9. The preparation method according to claim 7, characterized in that: The dielectric layer 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%.

10. Use of the energy-absorbing warning composite material according to any one of claims 1 to 6 or the energy-absorbing warning composite material obtained by the preparation method according to any one of claims 7 to 9 as a protective material in a battery pack or a battery module.

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