CN120059268A

CN120059268A - Energy-absorbing early-warning composite material and preparation method and application thereof

Info

Publication number: CN120059268A
Application number: CN202510525335.3A
Authority: CN
Inventors: 方红霞; 胡浩然; 罗小妹; 张仲琴
Original assignee: Huangshan Jiushi Technology Development Co ltd
Current assignee: Huangshan Jiushi Technology Development Co ltd
Priority date: 2025-04-25
Filing date: 2025-04-25
Publication date: 2025-05-30
Anticipated expiration: 2045-04-25
Also published as: CN120059268B

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 laminated, wherein the stretchable conductive layer comprises a PEDOT (polyether-ethylene-propylene-diene monomer) PSS flexible film. The energy absorbing layer and the flexible film are creatively compounded and cooperatively applied to the battery module, the pressure sensing performance is good, the sensitivity is greater than 0.01kPa ^‑1 in the stress range of 0-200 kPa, the sensitivity is greater than 0.1MPa ^‑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 provided by the invention not only has excellent energy absorption and buffer performance, but also can provide a stable constraint force and a high-sensitivity sensing and early warning mechanism, prolongs the service life of a battery, and realizes the effect of intelligent flexible protection.

Description

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

Technical Field

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.

Background

The lithium ion battery is an electric-thermal-force coupling system, and has the expansion problem in the actual use process, on one hand, an SEI film is formed in the formation process, gas is generated, the air pressure in the battery is increased, the SEI film thickness is increased along with the circulation, so that the battery core is expanded, and on the other hand, during charging and discharging, the Li ⁺ is inserted and separated between positive and negative electrode materials to cause structural phase change, so that the expansion phenomenon is generated, and the expansion phenomenon is mainly reflected in the change of the thickness direction of a negative electrode plate.

Research shows that when the lithium ion battery module is assembled, the buffer material is added between the batteries, so that the expansion force of the batteries can be effectively reduced, and the electrochemical performance of the battery module is improved. At present, foam is often adopted to reduce the influence of expansion behaviors in the charging and discharging process, and the maximum expansion force, the minimum expansion force and the total expansion force variation under the foam sliver are smaller than the test result under the condition of no foam. Under the condition of the same pretightening force, the foam buffer material with lower hardness is adopted, so that the expansion force of the battery in the charging and discharging processes can be effectively restrained from increasing. However, the existing foam material has low compression modulus, does not have highly sensitive stress characteristic to deformation, cannot output high-sensitivity electrical signals in real time, has poor pressure sensing performance, has no obvious energy absorption effect, has poor protective effect on a battery, and affects the service life of the battery.

Disclosure of Invention

In view of the above, the invention aims to provide an energy-absorbing early-warning composite material, and a preparation method and application thereof. The energy-absorbing early-warning composite material disclosed by the invention has good pressure sensing performance, meets the requirements of flexible protection and early warning, and can prolong the service life of a battery.

The invention provides an energy-absorbing early-warning composite material which comprises a first dielectric layer, a first stretchable conducting layer, an energy-absorbing layer, a second stretchable conducting layer and a second dielectric layer which are sequentially laminated;

The energy absorbing layer is made of compressible foam, and the compressible foam comprises one or more of shear thickening composite materials, foaming polyurethane, foaming polyethylene, foaming 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 comprise PEDOT PSS flexible films.

Preferably, the preparation raw materials of the shear thickening composite material comprise, by weight, 30-80 parts of polyether glycol, 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 emulsifying agent, 0.05-5 parts of catalyst and 3-15 parts of flame retardant, wherein the number of hydroxyl groups of the polyether polyol is more than 3, the hydroxyl value of the polyether polyol is 22-56 mg KOH/g, the curing agent comprises diisocyanate, and the molar ratio of the hydroxyl groups of the premix to the isocyanate groups 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%.

Preferably, the polyether glycol comprises polytetrahydrofuran ether glycol.

Preferably, the thickness of the first stretchable conductive layer and the second stretchable conductive layer is independently 5-100 μm.

Preferably, the elastic modulus of the first stretchable conductive layer and the second stretchable conductive layer is independently 0.2-25 MPa, the tensile strain is greater than 100%, and the resistance value variation 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%.

Preferably, the thickness of the first dielectric layer and the second dielectric layer is independently 1-200 μm.

The invention also provides a preparation method of the energy-absorbing early-warning composite material, which comprises the following steps:

And sequentially coating PEDOT (polyether-ether-ketone) PSS feed liquid and dielectric layer feed liquid on the surfaces of two sides of the energy absorption layer to obtain the energy absorption early warning composite material.

Preferably, the PEDOT/PSS feed liquid comprises, by mass, 1% -12% of DMSO, 0.5% -25% of a nonionic fluorocarbon surfactant and 60% -95% of a PEDOT/PSS aqueous solution, wherein the mass fraction of the PEDOT/PSS aqueous solution is 0.5% -55%.

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

The invention also provides an application of the energy-absorbing early-warning composite material or the energy-absorbing early-warning composite material obtained by the preparation method as a protective material in a battery pack or a battery module.

Compared with the prior art, the invention has the following beneficial effects:

The invention provides an energy-absorbing early warning composite material which comprises a first dielectric layer, a first stretchable conducting layer, an energy-absorbing layer, a second stretchable conducting layer and a second dielectric layer which are sequentially stacked, wherein the energy-absorbing layer is made of compressible foam, the compressible foam layer comprises one or more of a shear thickening composite material, foaming polyurethane, foaming polyethylene, foaming polypropylene, chloroprene rubber, ethylene-vinyl acetate copolymer, styrene butadiene rubber and ethylene propylene diene monomer, and the first stretchable conducting layer and the second stretchable conducting layer comprise PEDOT (polyethylene terephthalate) PSS flexible films.

The invention creatively combines the energy absorption layer and the flexible film, is cooperatively applied to the power battery pack and the battery module thereof, has good pressure sensing performance, has sensitivity higher than 0.01kPa ^-1 in the test range of 0-200 kPa, has sensitivity higher than 0.1MPa ^-1 in the stress range of 0.2 MPa-20 MPa, and meets the requirements of flexible protection and early warning.

In the lithium ion battery assembly process, the buffer material is added to effectively reduce the expansion force, so that the electrochemical performance of the module is improved. When the cell expands, a compressive force is applied to the cushioning material, which effects energy absorption and cushioning by compression. The buffer material may generate a reaction force to the battery according to the interaction principle of the forces. The invention adopts (non-Newtonian fluid) NNF material with shear thickening property as the energy absorbing layer, and can achieve better stable constraint force when deformation is smaller. Due to its remarkable energy absorbing properties, compression of the composite material can help to relieve part of the stress inside the battery, further reducing the battery expansion force. Meanwhile, due to the slow rebound characteristic, the reaction force is smaller, so that the battery is slightly squeezed, the normal operation of the battery can be ensured for a longer time, and the overall performance of the battery is improved. Meanwhile, the flexible film with the stretchable characteristic is loaded on the surface of the energy absorption layer, so that capacitance signals can be acquired in real time. The absolute values of these signals can be used to reverse the pressure experienced by the composite surface, while the time domain signal sequence can be used to reverse the acceleration of the impact force experienced by the composite. These signals can be used as a signal source for the differential controller to predict to some extent the arrival of large impact forces, thereby enabling the system to take precautions in advance. The composite material provided by the invention not only has excellent energy absorption and buffer performance, but also can provide a stable constraint force and a high-sensitivity sensing and early warning mechanism, so that the service life of a battery is prolonged, and the effect of intelligent flexible protection is realized.

The energy absorption early warning composite material has the advantages that when the output capacitance signal is subjected to internal and external pressure within a range of a measuring range, the signal error is less than 5%, and when the output capacitance signal is changed from-20 ℃ to 80 ℃ in an external environment temperature range, the deviation of the average value of the output capacitance signal under any pressure acting condition is less than 3%. The stress-strain curve deviation in subsequent cyclic compression is less than 5% in a constant speed test after the first turn of shear thickening composite (NNF metamaterial) is compressed.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic structural diagram of an energy-absorbing early-warning composite material prepared in embodiments 1-3;

FIG. 2 is a graph showing the DMA test results of NNF metamaterial in example 2;

FIG. 3 is an energy absorption curve of an NNF metamaterial in example 2;

FIG. 4 is a stress-strain curve of NNF metamaterial and common polyurethane foam and EVA foam in example 2;

FIG. 5 is a graph showing energy absorption characteristics of NNF metamaterial and common polyurethane foam and EVA foam in example 2;

FIG. 6 is a typical sensing characteristic curve of an energy absorbing pre-warning composite material of example 2;

FIG. 7 is a graph showing the sensing characteristics of the composite of comparative example 1;

FIG. 8 is a graph showing the sensing characteristics of the composites of example 4 and example 5;

FIG. 9 is a graph of response time test results for the energy absorbing pre-warning composite of example 2;

FIG. 10 is a graph of the signal fatigue test results of the energy absorbing and warning composite material of example 2;

FIG. 11 is a sensing characteristic curve of an energy absorbing early warning composite material of example 1;

FIG. 12 is a sensing characteristic curve of an energy absorbing early warning composite material of example 3;

FIGS. 13-15 are compressive stress strain curves for NNF metamaterials of examples 1-3, respectively;

FIG. 16 is a graph showing the results of 2-10 cycles of NNF metamaterial used in example 2 in a2 mm/min cyclic compression experiment;

FIG. 17 is a graph showing temperature-dependent characteristics and signal-to-noise ratio results of an NNF foam flexible sensor constructed from commercial copper foil electrodes;

FIG. 18 is a graph showing the temperature-dependent characteristics and signal-to-noise ratio results of an NNF foam flexible sensor constructed using stretchable electrodes for example 2;

FIG. 19 shows the resistance change of the example stretchable electrode, commercial copper foil electrode, commercial stretchable electrode during a tensile strain from 0 to 60%.

Detailed Description

The energy absorbing layer is made of compressible foam, and the compressible foam comprises one or more of shear thickening composite materials, foaming Polyurethane (PU), foaming polyethylene (EPE), foaming polypropylene (EPP), chloroprene Rubber (CR), ethylene-vinyl acetate copolymer (EVA), styrene Butadiene Rubber (SBR) and Ethylene Propylene Diene Monomer (EPDM);

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

The energy-absorbing early warning composite material has the characteristics of non-Newtonian fluid (NNF) shear thickening property and nonlinear compression modulus when receiving large expansion force, and compared with common protective foam, the energy-absorbing early warning composite material has smaller transmission force value under the same compression rate. In addition, due to its shear thickening properties, it is possible to provide a long-term stable restraining force to the lithium battery pack. Particularly in the face of rapid impact or high expansion forces, it responds rapidly and absorbs impact energy effectively. Meanwhile, the low rebound property of the battery is beneficial to reducing the extrusion of the reaction force to the battery, so that the service life of the battery is prolonged. The invention combines the energy-absorbing layer with the flexible sensing film, utilizes the stress characteristic that the energy-absorbing layer material has high sensitivity to deformation, can output high-sensitivity electrical signals in real time, and monitors mechanical dynamic signals and quasi-static signals in the compression process. The dynamic signal can be used for identifying the impact condition of the material, the differential quantity of the dynamic signal can predict the arrival of large impact force in advance, and the quasi-static signal can identify the limit value of expansion force, so that the early warning function is realized.

In the process of compressing the battery module, polymer molecules in the NNF energy absorbing layer are rapidly gathered, so that the shear thickening performance is obviously changed. This variation makes the electro-pressure/compression rate properties exhibit large differences between the different loading and unloading conditions. Therefore, the energy-absorbing early-warning composite material not only has excellent energy-absorbing buffer performance, but also can provide stable constraint force and a high-sensitivity sensing early-warning mechanism, so that the service life of the battery is prolonged, and the intelligent flexible protection effect is realized.

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

In the present invention, the material of the first dielectric layer and the second dielectric layer is preferably SEBS (linear triblock copolymer with polystyrene as end section and ethylene-butene copolymer obtained by hydrogenation of polybutadiene as middle elastic block). The dielectric layer of the invention has excellent electrical insulation performance, and avoids the influence of the extra potential of the battery core layer on the battery.

In the present invention, the thickness of the first stretchable conductive layer and the second stretchable conductive layer is independently preferably 5 to 100 μm, and may specifically be 10 μm or 20 μm. The elastic modulus of the first stretchable conductive layer and the elastic modulus of the second stretchable conductive layer are independently 0.2-25 MPa, the tensile strain is greater than 100%, and the resistance value variation is smaller than 5 times of the initial resistance value within 30% strain. The PEDOT-PSS flexible film is used as the stretchable conductive layer, has extremely low elastic modulus and thickness, and ensures excellent conformal characteristics with the energy absorption layer.

In the present invention, the surfaces of the first and second stretchable conductive layers are preferably further provided with Ag wires. The invention has no special requirements on the Ag wire.

The preparation raw materials of the shear thickening composite material comprise, by weight, 30-80 parts of polyether glycol, 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 emulsifying agent, 0.05-5 parts of catalyst and 3-15 parts of flame retardant, wherein the number of hydroxyl groups of the polyether polyol is more than 3, the hydroxyl value of the polyether polyol is 22-56 mg KOH/g, the curing agent comprises diisocyanate, and the molar ratio of the hydroxyl groups of the premix to the isocyanate groups of the curing agent is 1:1-1.1;

In the present invention, the curing agent preferably comprises diphenylmethane diisocyanate (MDI) and/or 1, 5-naphthalene diisocyanate, and the molar ratio of the hydroxyl groups of the premix to the isocyanate groups of the curing agent is preferably 1:1.05.

In the invention, the components in the premix, except for the polyether glycol and the flame retardant, are preferably the same as those in the Chinese patent CN 115536797A, a shear thickening composite material, a preparation method and application thereof, and are not repeated here. The polyether glycol preferably also includes a 2000 molecular weight polytetrahydrofuran ether glycol (PTMEG). In the specific embodiment of the invention, the premix comprises, by weight, 50 parts of 400-molecular-weight polyether glycol, 10 parts of a compound chain extender, 4 parts of a silane coupling agent, 2 parts of a polysiloxane-alkylene oxide block copolymer emulsifier, 40 parts of nano white carbon black, 20 parts of 2000-molecular-weight polyether glycol, 10 parts of 2000-molecular-weight polytetrahydrofuran ether glycol, 20 parts of 7000-molecular-weight polyether triol, 1.5 parts of triethanolamine, 1 part of a foaming catalyst dimethyl ethanolamine, 0.8 part of a curing catalyst triethylenediamine, 0.4 part of a foaming agent and 6 parts of a flame retardant.

The shear thickening composite material is NNF material with shear thickening performance. According to the invention, 2000 molecular weight polytetrahydrofuran ether glycol (PTMEG) is added into polyether glycol, and the polytetrahydrofuran ether glycol is preferably Pasteff PolyTHF, so that the toughness and wear resistance of the composite material can be improved, and the requirement of charge cycle expansion stress during the working period of a battery can be met.

In the invention, the density of the shear thickening composite material is preferably 0.1-0.5 g/cm ³, specifically can be 0.15g/cm ³、0.32g/cm³ or 0.4g/cm ³, and the thickness is preferably 1-10 mm, specifically can be 4mm.

The shear thickening composite material disclosed by the invention keeps soft in a normal state and has proper elasticity, when the shear thickening composite material is impacted or extruded rapidly and violently, the shear thickening composite material can be rapidly stressed and enhanced through local density increase, and an obvious shear thickening phenomenon is shown, namely, the shear thickening composite material is hard and solid when the shear thickening composite material is impacted by external force, and the strength of the shear thickening composite material is increased along with the increase of the external force, and the shear thickening composite material returns to an original loose soft elastic state after the external force disappears. When receiving the large stress, because shear thickening combined material can take place the strain rapidly, absorbs the impact energy and reaches the impact force value more than 95% at maximum, moreover, utilize its falling ball resilience height to be less than 8% and the characteristic of slow resilience for the battery receives the long time when receiving big impact and receives fine protection, can also restrain the swell phenomenon that appears when battery charge and discharge.

According to the invention, the energy absorption layer with the shear thickening characteristic and the PEDOT: PSS flexible film are combined, so that the functions of energy absorption and early warning are realized.

The preparation method of the energy absorption layer has no special requirements.

The invention preferably comprises the steps of firstly coating PEDOT (packet data processing) PSS feed liquid on one side surface of the energy absorption layer to obtain a first stretchable conductive layer, then coating dielectric layer feed liquid on the surface of the first stretchable conductive layer to obtain a first dielectric layer, and then repeatedly coating PEDOT (packet data processing) PSS feed liquid and dielectric layer feed liquid on the other side surface of the energy absorption layer to obtain a second stretchable conductive layer and a second dielectric layer.

In the invention, the step of coating PEDOT comprises the step of cleaning the surface of the energy absorption layer before the step of coating PSS feed liquid, wherein the step of cleaning preferably comprises the step of ultrasonic ethanol cleaning and the step of ultrasonic deionized water cleaning, and the time of ultrasonic ethanol cleaning and ultrasonic deionized water cleaning is preferably 5 minutes. The surface is preferably dried by nitrogen after cleaning, and is treated for 30 seconds by an oxygen plasma cleaner, so that the affinity of the surface to PEDOT and PSS feed liquid is enhanced, and the coating is more uniform and has strong binding force.

In the invention, the PEDOT-PSS feed liquid preferably comprises, by mass, 1% -12% of DMSO, 0.5% -25% of a nonionic fluorocarbon surfactant and 60% -95% of a PEDOT-PSS aqueous solution, wherein the PEDOT-PSS aqueous solution preferably comprises 0.5% -55%, and particularly can be 50%. The PEDOT-PSS feed liquid more preferably comprises the following components in percentage by mass of 6% of DMSO, 5% of nonionic fluorocarbon surfactant and 89% of PEDOT-PSS aqueous solution. The nonionic fluorocarbon surfactant preferably comprises dupont cap FS-30.

In the invention, the mode of coating PEDOT and PSS feed liquid is preferably spin coating or spray coating, and the spin coating parameter is preferably spin coating film forming process carried out at 4000rpm for 40 seconds. The coating preferably further comprises drying, the temperature of the drying is preferably 80 ℃ and the time is preferably 30 minutes.

In the invention, the method for obtaining the first stretchable conductive layer preferably further comprises the steps of coating Ag conductive paste on part of the surface of the first stretchable conductive layer, drying and leading out Ag wires. The temperature of the drying is preferably 80 ℃. The area of the partial surface is preferably 4-16 mm ². The composition of the Ag conductive paste is not particularly required, and can comprise Ag nano-sheets or Ag nano-sheets and siloxane-based resin.

In the invention, the dielectric layer feed liquid 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 can be specifically 15%.

In the invention, the mode of coating the dielectric layer feed liquid is preferably spin coating or spray coating, and the spin coating parameter is preferably spin coating film forming process carried out at a speed of 1500rpm for 30 seconds. The coating preferably further comprises drying, the temperature of which is preferably 80 ℃.

The method for repeatedly coating PEDOT (packet data channel) PSS feed liquid and dielectric layer feed liquid on the other side surface of the energy absorption layer is consistent with the method for preparing the first stretchable conductive layer and the first dielectric layer, and is not repeated herein.

The energy-absorbing early-warning composite material provided by the invention is used as a protective material in a battery module, and has an intelligent flexible protective effect. The invention takes the energy-absorbing early-warning composite material as an early-warning mechanism for explosion caused by battery life monitoring and battery expansion. The special shear thickening effect of the energy absorption layer is used as an induction layer, so that high-precision perception of expansion force is realized, and the expansion process of the battery pack can be dynamically monitored in real time. The invention designs an early warning mechanism capable of reflecting swelling and even flaming of thermal expansion of a battery by utilizing the shear thickening performance of the NNF energy absorbing layer, namely the stress enhancement property of the material when the material is subjected to continuous enhancement of external force.

For further explanation of the present invention, the energy-absorbing early-warning composite material provided by the present invention, and the preparation method and application thereof are described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of the present invention.

In the embodiment of the invention, the energy-absorbing NNF feed liquid comprises premix and curing agent, and the preparation method comprises the following steps:

(1) The preparation of the compound chain extender comprises the steps of sequentially adding 100g of diethanolamine, 500g of dipropylene glycol, 280g of 4,4' -di-sec-butylaminodiphenyl methane and 120g of ethylene glycol into an 80 ℃ constant temperature container. Stirring at 100rpm, sealing, vacuum dewatering, and maintaining at negative pressure of-0.1 MPa for 8 hr to obtain the first component. Slowly adding MDI according to the molar ratio of the hydroxyl in the first component to the isocyanate group in the liquefied MDI of 100:50 for polymerization chain extension reaction for 8 hours, stopping heating, stopping stirring, and cooling to normal temperature to obtain the (NNF-2) compound chain extender.

(2) The premix is prepared by adding 400g of polyether glycol (Pluracol P410R) with molecular weight of 500g into a 75 ℃ constant temperature container, starting stirring and maintaining the rotation speed at 100rpm, then adding 100g of NNF-2 compound chain extender, 40g of Silane coupling agent (XIAMETER ^тм OFS-6020 Silane), 20g of polysiloxane-alkylene oxide block copolymer emulsifier, 400g of nano white carbon black (AEROSIL 200), continuing stirring for 45 minutes, stopping heating, adding 200g of polyether glycol with molecular weight of 2000 (Pluracol P1477), 100g of polytetrahydrofuran ether glycol (PTMEG) with molecular weight of 2000, adding 200g of polyether triol with molecular weight of Arcol PPG 1376, 15g of triethanolamine, 10g of dimethylethanolamine as a foaming catalyst and 8g of triethylenediamine as a curing catalyst, continuing stirring, adding 4g of foaming agent (deionized water) when the temperature is reduced to 60 ℃, maintaining stirring for 30 minutes, and controlling the temperature at 25 ℃.

(3) Preparing a curing agent, namely weighing liquefied MDI (methylene diphenyl diisocyanate) into another container according to the molar ratio of hydroxyl groups in the premix to isocyanate groups in the curing agent of 100:105, and controlling the temperature at 35 ℃.

The premix and curing agent were mixed (3000 rpm) for 3 seconds prior to injection.

In the embodiment of the invention, the mass fraction of the PEDOT to PSS aqueous solution is 50wt%.

Example 1

1. Preparation of NNF metamaterial

(1) The preparation of the mold comprises the steps of preparing the mold, opening an exhaust channel with the diameter of 1.0 mm at the uppermost end (highest point) of a mold cavity, setting the temperature of the mold at 60 ℃, and uniformly spraying a release agent on the surface of the mold cavity for standby.

(2) And (3) injecting energy-absorbing NNF feed liquid into the die cavity according to the thickness of 4mm and the density of 0.4g/cm ³ after molding, and closing and locking the die.

(3) And (3) compounding and integrally forming, namely curing and reacting for 6 minutes at 65 ℃ in a die cavity, and exhausting air in the die cavity through an exhaust hole while the foaming pressure in the die cavity is increased. And (5) opening the die, taking out the product, and polishing off redundant leftover materials along the periphery for one week to obtain the NNF metamaterial (energy absorbing layer) with the thickness of 4 mm and the density of 0.4g/cm ³.

2. Preparation of an energy-absorbing early-warning composite material (flexible pressure sensing foam):

(1) Sequentially using ethanol and deionized water to ultrasonically clean an NNF metamaterial substrate for 5 minutes, drying the surface by using nitrogen, and then using an oxygen plasma cleaner to treat the upper surface for 30 seconds;

(2) A slurry was prepared comprising DMSO 6 wt%, a nonionic fluorocarbon surfactant (DuPont Capstone FS-30) 5: 5 wt%, and PEDOT 89: 89 wt% aqueous PSS. A spin-on film forming process was performed on an NNF metamaterial at 4000 rpm a for 40 seconds, and then dried in an oven at 80 ℃ for 30 minutes, to obtain a flexible sensing film (stretchable conductive layer electrode) with a thickness of 10 μm.

(3) And (3) coating Ag conductive paste on a small part (4 mm ²) of the surface of the stretchable conductive layer, putting into an 80 ℃ oven for drying, taking out, and then leading out Ag wires.

(4) Preparing an ethyl acetate solution of SEBS with the mass fraction of 15%, forming a film by adopting a spin-coating process at a speed of 1500rpm for 30 seconds, and drying at 80 ℃ to obtain the dielectric layer with the thickness of 8 mu m.

(5) Turning over the sample, and repeating the steps (1), (2), (3) and (4) to obtain the energy-absorbing early-warning composite material.

Example 2

1. Preparation of NNF metamaterial

(1) The preparation of the mold comprises the steps of preparing the mold, opening an exhaust channel with the diameter of 1.0 mm at the uppermost end (highest point) of a mold cavity, setting the temperature of the mold at 55 ℃, and uniformly spraying a release agent on the surface of the mold cavity for standby.

(2) And (3) injecting energy-absorbing NNF feed liquid into the die cavity according to the thickness of 4 mm and the density of 0.32 g/cm ³ after molding, and closing and locking the die.

(3) And (3) compounding and integrally forming, namely curing and reacting for 6 minutes at the temperature of 60 ℃ in a die cavity, and exhausting air in the die cavity through an exhaust hole while the foaming pressure in the die cavity is increased. And (5) opening the die, taking out the product, and polishing off redundant leftover materials along the periphery for one week to obtain the NNF metamaterial with the thickness of 4mm and the density of 0.32 g/cm ³.

2. The energy-absorbing early warning composite material is prepared in the same way as the embodiment 1.

Example 3

1. Preparation of NNF metamaterial

(1) The preparation of the mold comprises the steps of preparing the mold, opening an exhaust channel with the diameter of 1.0 mm at the uppermost end (highest point) of a mold cavity, setting the temperature of the mold at 50 ℃, and uniformly spraying a release agent on the surface of the mold cavity for standby.

(2) And (3) injecting energy-absorbing NNF feed liquid into the die cavity according to the thickness of 200 mm and the density of 0.15 g/cm ³ after molding, and closing and locking the die.

(3) And (3) compounding and integrally forming, namely curing and reacting for 7 minutes at 55 ℃ in a die cavity, and exhausting air in the die cavity through an exhaust hole while the foaming pressure in the die cavity is increased. And (5) opening the die, taking out the product, polishing off excessive scraps along the periphery for one week, placing the product on a sponge flat cutting machine, and slicing the product according to the size of 4 mm to obtain the NNF metamaterial with the thickness of 4 mm and the density of 0.15 g/cm ³.

Comparative example 1

The difference from example 2 is that a common copper foil electrode (commercial 3M company 1181 copper foil tape, directly adhered to the surface of the NNF metamaterial) was loaded on the surface of the NNF metamaterial, and the rest steps were the same.

Example 4

The difference from example 2 is that NNF metamaterial was replaced with commercial EVA (density 0.3g/cm ³), and the rest of the procedure was the same as in example 2.

Example 5

The difference from example 2 is that NNF metamaterial was replaced with commercial polyurethane foam (density 0.35 g/cm ³), and the rest of the procedure was the same as in example 2.

Fig. 1 is a schematic structural diagram of the energy-absorbing early warning composite material prepared in embodiments 1 to 3, which includes an SEBS ultrathin dielectric layer, a stretchable conductive layer, an NNF metamaterial (energy-absorbing layer), a stretchable conductive layer and an SEBS ultrathin dielectric layer which are sequentially stacked.

Test example 1

1. Shear thickening Properties

The DMA (dynamic thermal mechanical analysis) test results show that the NNF metamaterial exerts the shear thickening property. Taking the NNF metamaterial of example 2 as an example (FIG. 2), the overall performance exhibits moderate viscoelasticity, and the structural and damping requirements can be well met. With the increase of the action frequency, the loss modulus and the energy-absorbing modulus are slowly increased firstly and are sharply increased after being larger than 1 Hz, and after being larger than 0.2 Hz, the tangent value is larger than 0.5, thereby belonging to a high-efficiency dissipation mechanical energy interval, the loss modulus is integrally larger than the energy-storing modulus, and the absorption energy is dominant. The material has excellent dynamic mechanical property, and when the tangent value is higher, the storage modulus reaches more than 8MPa, and the loss modulus reaches more than 4 MPa.

When the material is applied, when the material receives strong impact or expansion force, the material can absorb more energy, the external appearance is that the transmission force is reduced, the buffering and energy absorbing effects are enhanced, and the deformation of protected equipment is weakened.

2. High impact resistance and compression set resistance

The stress-strain curve and the energy absorption curve of the sample under different loading rates were tested by a universal mechanical tester, and the results are shown in fig. 3. Experimental results show that the NNF metamaterial in example 2 exhibits significant strain rate dependent strengthening properties. Under high-speed loading conditions, the material can absorb more energy and shows good resistance to high-speed impact force. In contrast, during low-speed loading, the energy absorption is extremely low, so that the battery can provide stable restraining force when being applied to a scene of slow expansion of the battery, thereby ensuring stable operation of the battery.

The results of the constant rate test of the stress strain curves of NNF metamaterial, common polyurethane foam and EVA foam in example 2, with a loading rate of 10 ^-3/s and a compression to 80% strain (note: 1Hz loading rate is 0.6X10 ^-3/s and loading frequency equivalent is 1.6 Hz) are shown in FIG. 4. The densification characteristic curve shows that compared with commercial EVA and commercial polyurethane foam, an NNF metamaterial sample is obviously larger in energy absorption interval in the 0-80% compressive strain process, the elastic interval of the sample is smaller, the energy absorption interval can be reached earlier in the battery application field, and heat accumulation after expansion is avoided. Meanwhile, in a low compression strain interval (< 10%), the slope (elastic modulus) of the commercial EVA and the commercial polyurethane foam is too high, the influence on the expansion allowance is large (namely, too high reaction force is generated in small expansion, and the reaction force has a certain influence on the battery charging and discharging operation), in a high compression strain interval (10% -20%), the slope of the commercial EVA and the commercial polyurethane foam is gentle, the energy absorption characteristic is weakened, a strain platform is formed, and when the expansion force of the battery is larger than the limit of the platform, the restraint is out of control, and the battery rapidly expands. The common EVA foam is high in CFD (carbon fiber reinforced plastic) 1-10% slope and gentle in 11-60%, the NNF metamaterial is low in slope and gentle in CFD 1-8.5%, lower stress is shown, and the slope is high in CFD 8.6-63%, high in sensitivity and pressure change performance, and normal operation of protected equipment is guaranteed.

The energy absorption characteristics under corresponding compression conditions (see fig. 5) further demonstrate that NNF metamaterials have superior impact resistance and energy absorption properties compared to conventional foam.

3. Mechanical force sensing performance

The energy absorption early warning composite material is obtained by constructing an ultrathin stretchable conducting layer on the surface of the NNF metamaterial, and the thickness change of the NNF metamaterial can be fed back in real time, so that information such as stress, strain rate and the like of the material is inverted, and an intelligent early warning system of the battery pack is realized.

FIG. 6 is a typical sensing characteristic curve of an energy absorbing pre-warning composite material of example 2. The maximum sensitivity of the sensor can reach 9.08 kPa ^-1 according to the sensitivity(s) calculation formula because of the high-efficiency energy absorption mechanical property of the NNF metamaterial. In the whole test range of 0-100 kPa, the sensitivity is larger than 0.01 kPa ^-1, and the high monitoring resolution of a lower pressure interval is realized. In addition, in the stage of the metamaterial densification process, along with the increase of stress (3,000 kPa), the strain rate of the material per se is reduced, but the sensing signal can still be maintained in a sensitivity interval above 0.001 kPa ^-1, so that the accurate measurement of a large-range force value is ensured.

The sensitivity(s) is calculated as follows:

,

Wherein, In order to be sensitive to this,Representing the value of the capacitance of the capacitor,For the initial capacitance to be the same,Is the variation of the applied pressure.

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

In contrast, the test using the NNF metamaterial-loaded common copper foil electrode of example 2 (comparative example 1) showed a sensing characteristic curve of only 0.029 kPa ^-1, as shown in FIG. 7, and decayed below 0.001 kPa ^-1 at a pressure of 1 kPa, maintaining an overall sensitivity of 0.0003 kPa ^-1, two orders of magnitude lower than the present invention. It can be seen that the surface-structured ultra-thin stretchable electrode imparts excellent sensing response characteristics to the NNF metamaterial.

Meanwhile, by comparing the sensing characteristic curves of the ultrathin stretchable electrodes loaded on the commercial EVA and polyurethane foam under the condition of the maximum compression ratio of 80%, as can be seen from FIG. 8, the surface construction of the ultrathin stretchable electrode also endows the two materials with excellent sensing performance. However, the stress response characteristics of these two foam materials are significantly different from those of NNF metamaterials, and they ultimately exhibit sensitivity characteristics that are an order of magnitude lower than those of NNF metamaterials. Moreover, in the same maximum compression ratio range, NNF metamaterial has constraint force values which are several times larger and reach more than 2500kPa, EVA and common polyurethane foam can only reach 400kPa, so that NNF metamaterial has the protection effect of absorbing energy and having high sensitivity in a wider pressure working range, namely the highest sensitivity is 9.08 kPa ^-1, and the full-range sensitivity is more than 0.001 kPa ^-1.

The NNF metamaterial provided by the invention provides reliable strain response characteristic for pressure, and meanwhile, the polymer tensile flexible sensing electrode loaded on the surface of the NNF metamaterial has relatively low elastic modulus (5 MPa), so that signal interference caused by an interface air layer can be effectively eliminated, and noise can be suppressed. In addition, the electrode is insensitive to tensile load, not only can efficiently feed back the change of a compression signal, but also can adapt to the abnormal compression deformation condition of the surface of the NNF material, thereby avoiding the interference of coupling load on the sensing signal. The energy-absorbing early-warning composite material has excellent sensing performance.

In addition, NNF metamaterials also have excellent dynamic response characteristics. The NNF foam flexible sensor of example 2 was tested by a transient compression test and had a response time of approximately 30 milliseconds, as shown in FIG. 9. By means of a capacitive sensing mechanism, the sensing mechanism of the NNF metamaterial exhibits lower signal hysteresis. This excellent signal hysteresis characteristic not only ensures the stability of the sensor signal, but also maintains a stable signal output in 1000 times of large strain fatigue test (test frequency of 1 hz), as shown in fig. 10.

The technical indexes of the flexible sensing foam prepared in the embodiments 1-3 are shown in the table 1, and it can be seen that NNF metamaterials with different densities in the embodiments 1-3 are compounded by adopting the same flexible sensing electrode material, and all the NNF metamaterials have good pressure sensing performance, the sensitivity is larger than 0.01 kPa ^-1 in the whole test range of 0-200 kPa, the high monitoring resolution of a lower pressure range is realized, the flexible sensing early warning requirement is met, and the maximum sensitivity has the same order of magnitude and reaches 11.49 kPa ^-1 at most. The sensing characteristic curves of examples 1 and 3 under the same thickness and compression ratio are shown in fig. 11 and 12 after loading the flexible sensing electrode. The maximum sensitivity is increased along with the reduction of the density, meanwhile, the density and the measuring range (restraining force) have positive correlation, the restraining force exceeds 300kPa, the flexible protection requirement of a lithium battery cell layer is met, the maximum flexible protection requirement of the lithium battery cell layer can reach 2500kPa, and the flexible protection and early warning requirement of a power battery pack and a battery module thereof are met.

Table 1 technical indicators of Flexible sensing foam produced in examples 1-3

The stress-strain curves of the NNF metamaterial used in examples 1-3 at the compression rate of 12 mm/min are shown in fig. 13, 14 and 15, and the pictures show the stress values born by the NNF metamaterial at 80% of compression strain and the change conditions of elastic moduli at different stages, which further indicate that the stress-strain performances of different NNF metamaterials meet the requirements of different flexible protection and early warning.

The NNF metamaterial used in example 2 has a 2-10-turn test result in a 2 mm/min cyclic compression experiment as shown in FIG. 16, and the graph shows excellent mechanical repeatability under 80% compressive strain.

The NNF foam flexible sensor constructed by the stretchable electrode and the commercial copper foil electrode used in the embodiments 1-3 is subjected to temperature change test under different compression conditions within the range of-20 ℃ to 80 ℃. The NNF foam flexible sensor constructed with the commercial copper foil electrode (comparative example 1) exhibited very strong temperature-affected characteristics and too low signal to noise ratio, as shown in FIG. 17, whereas the NNF foam flexible sensor constructed with the stretchable electrode (example 2) of the present invention exhibited very strong temperature stability and higher signal to noise ratio, as shown in FIG. 18.

Resistance change tests were performed on the stretchable electrodes, commercial copper foil electrodes, and commercial stretchable electrodes (PDMS-based silver paste electrodes) used in examples 1 to 3. The electrode used in the present invention was stable in resistance and did not undergo insulation transition during tensile strain from 0 to 60%, see fig. 19.

While the foregoing embodiments have been described in some, but not all embodiments of the invention, other embodiments of the invention can be made and still fall within the scope of the invention without undue effort.

Claims

1. The energy-absorbing early warning composite material is characterized by comprising a first dielectric layer, a first stretchable conducting layer, an energy-absorbing layer, a second stretchable conducting layer and a second dielectric layer which are sequentially laminated;

2. The energy-absorbing early warning composite material according to claim 1 is characterized in that the preparation raw materials of the shear thickening composite material comprise a premix and a curing agent, wherein the premix comprises, by weight, 30-80 parts of polyether glycol, 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 emulsifying agent, 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, the hydroxyl value of the polyether polyol is 22-56 mg KOH/g, the curing agent comprises diisocyanate, and the molar ratio of the hydroxyl groups of the premix to the isocyanate groups of the curing agent is 1:1-1.1;

3. The energy absorbing early warning composite of claim 2, wherein the polyether glycol comprises polytetrahydrofuran ether glycol.

4. The energy absorbing early warning composite of claim 1, wherein the first stretchable conductive layer and the second stretchable conductive layer independently have a thickness of 5-100 μm.

5. The energy-absorbing early warning composite material according to claim 1 or 4, wherein the elastic modulus of the first stretchable conductive layer and the elastic modulus of the second stretchable conductive layer are independently 0.2-25 MPa, the tensile strain is greater than 100%, and the resistance change amount of the first stretchable conductive layer and the second stretchable conductive layer is independently less than 5 times in a strain range of 0-60%.

6. The energy absorbing early warning composite of claim 1, wherein the first and second dielectric layers independently have a thickness of 1-200 μm.

7. The method for preparing the energy-absorbing early-warning composite material according to any one of claims 1 to 6, which is characterized by comprising the following steps:

8. The preparation method of the PEDOT-PSS feed liquid according to claim 7 is characterized in that the PEDOT-PSS feed liquid comprises, by mass, 1% -12% of DMSO, 0.5% -25% of a nonionic fluorocarbon surfactant and 60% -95% of an aqueous PEDOT-PSS solution, and the mass fraction of the aqueous PEDOT-PSS solution is 0.5% -55%.

9. The preparation method of claim 7, wherein the dielectric layer feed liquid is an ethyl acetate solution of SEBS, and the mass fraction of SEBS in the ethyl acetate solution of SEBS is 5% -20%.

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