A highly flexible and highly conductive electrothermal film, a preparation method thereof, and an application thereof in heated gloves

Abstract

The present invention relates to the field of electrothermal materials, and relates to a highly flexible and highly conductive electrothermal thin film, a preparation method and an application. The electrothermal thin film is mainly made of components such as a doped conductive prepolymer, a surface-modified graphene / carbon nanotube composite filler, a styrene-ethylene-butene-styrene block copolymer, and N-methylpyrrolidone in parts by weight. The surface-modified graphene / carbon nanotube composite filler is treated with concentrated sulfuric acid and concentrated nitric acid, and the doped conductive prepolymer is prepared from poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), lithium bis(trifluoromethanesulfonyl)imide, etc. Through a reasonable ratio and dispersion process, an electrothermal thin film with excellent flexibility, conductivity and heating performance is prepared, solving the problems of poor conductivity and insufficient flexibility in the prior art, and can be widely applied to fields such as flexible electronic devices in heating gloves.

Description

Technical Field

[0001] The present invention relates to the field of electrothermal materials, and particularly to a highly flexible and highly conductive electrothermal film, a preparation method thereof, and an application thereof in heating gloves. Background Art

[0002] With the rapid development of wearable electronic devices, the application demand for flexible electrothermal elements in fields such as intelligent heating gloves is increasing day by day. As a heating unit that directly contacts the human body, the electrothermal film not only needs to have excellent electrical conductivity to ensure heating efficiency and temperature uniformity, but also needs to have good flexibility to adapt to the repeated deformation caused by hand movements, and at the same time have a self-healing function to extend the service life. The development of high-performance electrothermal films is of great significance for improving the use experience of wearable heating devices and expanding the application scope of intelligent fabrics. Especially in scenarios such as outdoor sports and industrial production in cold environments, the comprehensive performance of the electrothermal film directly affects the practicability and reliability of the product. Therefore, developing electrothermal films with both high flexibility, high electrical conductivity, and self-healing function has important practical significance for promoting the progress of intelligent wearable technology and meeting market demands.

[0003] At present, the development of electrothermal film materials still faces some technical bottlenecks, especially the balance among flexibility, self-healing, and electrical conductivity. For example, Chinese Patent CN113861594A discloses an electrothermal film, but it has deficiencies in flexibility, self-healing, and electrical conductivity. On the one hand, although conductive polymers have certain flexibility, they are prone to mechanical fatigue under repeated bending or high-stress environments, resulting in structural damage and performance degradation; on the other hand, the electrical conductivity of conductive polymers is relatively low, and it is difficult to achieve an ideal heating effect at a low voltage, and the resistance is prone to fluctuations over time and with the environment, affecting heating uniformity and efficiency. In particular, there are obvious deficiencies in the coordinated optimization of the dispersion, interfacial compatibility, and network structure of conductive fillers, resulting in the difficulty of the film to simultaneously meet the requirements of high flexibility, high electrical conductivity, and self-healing performance in practical applications. Therefore, it is urgent to develop new material systems and preparation processes to solve these technical problems. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] The purpose of the present invention is to provide a highly flexible and highly conductive electrothermal film, a preparation method thereof, and an application thereof in heating gloves, so as to solve the problems of insufficient flexibility, electrical conductivity, and self-healing performance of current electrothermal films.

[0006] (2) Technical Solutions

[0007] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0008] A highly flexible and highly conductive electric heating film is made of the following components by weight: 30 to 55 parts of a doped conductive prepolymer, 4.0 to 8.0 parts of a surface-modified graphene / carbon nanotube composite filler, 10 to 20 parts of a styrene-ethylene-butylene-styrene block copolymer, and 15 to 25 parts of N-methylpyrrolidone;

[0009] The doped conductive prepolymer is prepared from the following components by weight: 1.2 to 3.6 parts of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid), 0.12 to 0.18 parts of lithium bis(trifluoromethanesulfonyl imide), 0.12 to 0.36 parts of cobalt phthalocyanine, 0.06 to 0.09 parts of ethylene glycol and 100 parts of deionized water;

[0010] The surface-modified graphene / carbon nanotube composite filler is obtained by surface-modifying the graphene / carbon nanotube composite filler with concentrated sulfuric acid and concentrated nitric acid;

[0011] The graphene / carbon nanotube composite filler is composed of carbon nanotubes and graphene uniformly distributed on the surface of the carbon nanotubes in an in-situ growth manner in a divergent manner.

[0012] The present invention adopts the design of doping poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) with lithium bis(trifluoromethanesulfonyl imide) and cobalt phthalocyanine, which is mainly used to enhance the flexibility and conductivity of thermoelectric films. The core design idea is to improve the comprehensive performance of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT:PSS) film through a dual doping strategy, combined with the synergistic effect of each component, especially in terms of flexibility, conductivity and thermoelectric performance. First of all, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) as the matrix material of the present invention has good conductivity and film-forming properties, and is widely used in the fields of electronic devices and flexible materials. However, pure PEDOT:PSS has certain limitations in the flexibility and conductivity of the film due to the strong interaction of its internal polymer segments. In order to overcome this problem, the present invention enhances the flexibility of the film by introducing lithium bis(trifluoromethanesulfonyl imide as a plasticizer. Lithium bis(trifluoromethanesulfonyl)imide can interact with polymer chain segments, destroying the original chain aggregation structure, thereby increasing the free volume of the film and improving the mobility of the molecular chain. This process allows the film to be stretched and deformed to a greater extent under the action of external forces, thereby significantly enhancing its mechanical flexibility. At the same time, lithium bis(trifluoromethanesulfonyl)imide can easily interact with negatively charged PSS - and positively charged PEDOT +Interact, and the weakened Coulomb interaction between PSS and PEDOT chains decouples PEDOT from the highly coiled PSS and allows it to grow into large-scale conductive domains, forming a continuous nanofiber network, thereby improving the electrical conductivity of the film. Secondly, cobalt phthalocyanine can interact with polymer chains, providing additional free holes, thus increasing the effective carrier concentration in the film. This doping effect significantly improves the conductivity of PEDOT, enabling the PEDOT:PSS film to achieve high conductivity at a relatively low doping concentration. Lithium bis(trifluoromethanesulfonyl)imide improves the flexibility of the film through a plasticizing effect and enhances the charge transport ability of the film; while cobalt phthalocyanine increases the free hole concentration of the film through doping, further enhancing the conductivity and flexibility of PEDOT:PSS. The synergistic effect of the two not only optimizes the mechanical properties of the film but also jointly enhances the conductivity through different mechanisms, enabling the composite film to exhibit more prominent performance in applications such as flexible electronic devices, thermoelectric energy conversion, and electrochemical sensing.

[0013] Ethylene glycol plays multiple synergistic roles as a key component in the electrothermal film. First of all, ethylene glycol can induce the rearrangement of PEDOT + and PSS - chains. This process not only significantly improves the self-healing ability of the material but also enhances its electrical conductivity. Secondly, ethylene glycol improves the dispersion effect of the surface-modified graphene and carbon nanotube composite fillers by adjusting the interfacial properties of the system, making the conductive network more uniform. This uniform dispersion further improves the flexibility of the film, ensuring the stability and durability of the material in electrothermal applications.

[0014] The present invention enhances the flexibility and conductivity of the thermoelectric film by designing surface-modified graphene / carbon nanotube composite fillers. The preparation of this composite filler involves two key steps: First, ferrocene and thiophene are used as the catalyst and carbon source respectively, and graphene is in-situ grown on the surface of carbon nanotubes by CVD method to achieve the tight combination of the two carbon nanomaterials; Second, the composite filler is surface-functionalized and modified in a mixed solution of concentrated sulfuric acid and concentrated nitric acid to introduce oxygen-containing functional groups. The high conductivity of graphene and the homogeneous interface with carbon nanotubes are conducive to reducing electron scattering. The combination of its long-range conductive channels forms a multi-dimensional conductive network. At the same time, the complementary structural characteristics of the two provide excellent mechanical properties. Surface modification not only improves the compatibility between the filler and the matrix but also enhances the dispersion of the filler, avoiding agglomeration. The design of this composite filler significantly improves the conductive and mechanical properties of the thermoelectric film, providing a new technical route for the development of high-performance thermoelectric materials.

[0015] Further, the preparation method of the doped conductive prepolymer is as follows: by weight, 1.2 - 3.6 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), 0.12 - 0.18 parts of lithium bis(trifluoromethanesulfonyl)imide, 0.12 - 0.36 parts of cobalt phthalocyanine, 0.06 - 0.09 parts of ethylene glycol and 100 parts of deionized water are mixed, and then stirred at a speed of 1000 - 1500 rpm for 4 - 8 h.

[0016] Further, the mass ratio of lithium bis(trifluoromethanesulfonyl)imide, cobalt phthalocyanine, ethylene glycol and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) is 1:(1 - 2):0.5:(10 - 20).

[0017] Further, the preparation method of the surface-modified graphene / carbon nanotube composite filler is as follows: by weight, 20 - 45 parts of graphene / carbon nanotube composite filler are added to a mixed solution of 100 parts of concentrated sulfuric acid and concentrated nitric acid, wherein the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1, and the concentrations of concentrated sulfuric acid and concentrated nitric acid are 98% and 70% respectively. Then, it is ultrasonically stirred for 60 - 90 min, filtered, and the filter residue is repeatedly washed with deionized water until the pH value of the filtrate is 7. Finally, the surface-modified graphene / carbon nanotube composite filler is obtained after vacuum drying.

[0018] Further, the preparation method of the graphene / carbon nanotube composite filler is as follows: by weight, 0.2 - 0.5 parts of ferrocene, 2.0 - 10.0 parts of thiophene, 10 - 40 parts of carbon nanotubes and 100 parts of ethanol are mixed evenly, first ultrasonically mixed for 30 - 45 min, then filtered, the filter residue is vacuum dried, and then put into a quartz tube. In an argon gas flow of 200 - 300 sccm, it is heated to 1000 - 1200 °C and kept warm for 90 - 120 min. Finally, the graphene / carbon nanotube composite filler is obtained after cooling to room temperature.

[0019] Further, the mass ratio of carbon nanotubes to graphene in the graphene / carbon nanotube composite filler is (60 - 85)%:(15 - 40)%.

[0020] Further, the mass ratio of ferrocene, thiophene and carbon nanotubes is 1:(10 - 20):(50 - 80).

[0021] The present invention adopts a carefully designed material system, which is mainly used to enhance the flexibility and conductivity of thermoelectric thin films. By combining graphene with carbon nanotube composite fillers, a composite structure is formed with 60-85% carbon nanotubes and 15-40% graphene. The synergistic effect of the two effectively improves the conductive network of the thin film. The high aspect ratio of carbon nanotubes provides continuity for the conductive path, while the two-dimensional sheet structure of graphene enhances the coverage and stability of the conductive network, thus maintaining good conductivity under different stress states. In addition, ferrocene is used as a catalyst, thiophene is used as a carbon source, and the preparation parameters of the fillers are further optimized according to the mass ratio of 1:(10-20):(50-80) with carbon nanotubes. Under high-temperature conditions, ferrocene catalyzes the decomposition of thiophene, promoting the growth of graphene sheets on the surface of carbon nanotubes to form a graphene / carbon nanotube composite structure with excellent conductive properties. The catalytic effect of ferrocene accelerates the growth process of graphene, while thiophene provides a carbon source to ensure the efficient generation of graphene, further improving the conductivity and thermal stability of the composite material. Through reasonable proportion design among the components, the synergistic improvement of material properties is achieved. After the combination of graphene and carbon nanotubes, the surface effect and interface interaction are enhanced, further promoting the uniform dispersion of the fillers in the matrix and avoiding the aggregation phenomenon of the materials. This dispersion enhances the flexibility of the thin film, enabling it to maintain stable electrical properties during multiple bending and stretching processes. Through the design of this composite filler system, the present invention not only improves the conductivity of thermoelectric thin films but also endows them with excellent mechanical flexibility, thus meeting a wide range of application requirements.

[0022] The present invention also provides a method for preparing a highly flexible and highly conductive electrothermal thin film, which includes the following steps:

[0023] S1. Dispersing the fillers: According to the ratio, add the surface-modified graphene / carbon nanotube composite fillers and N-methylpyrrolidone into a mixing container, adjust the rotation speed to 1000-2000 rpm, and the mixing and stirring time to 30-45 min to obtain a dispersion liquid.

[0024] S2. Preparing the mixed liquid: Add the doped conductive prepolymer and styrene-ethylene-butene-styrene block copolymer into the dispersion liquid obtained in S1 simultaneously, heat to 60-80 °C, adjust the stirring speed to 200-300 rpm, and the stirring time to 30-45 min to obtain a mixed liquid.

[0025] S3. Preparing the electrothermal thin film: Uniformly coat the mixed liquid obtained in S2 on a glass substrate for curing, the curing temperature is 80-120 °C, the heat preservation time is 30-60 min, and after curing, vacuum dry at room temperature.

[0026] The present invention also discloses the application of the highly flexible and highly conductive electrothermal thin film, and this highly flexible and highly conductive electrothermal thin film is used in heating gloves.

[0027] (3) Beneficial technical effects

[0028] 1. The modified PEDOT:PSS thermoelectric thin film prepared by the double doping strategy of the present invention has significant application value and unique synergistic effects. Compared with traditional single doping or modification methods, the present invention adopts a dual doping system of lithium bis(trifluoromethanesulfonate) and cobalt phthalocyanine, effectively overcoming the problems of insufficient flexibility and conductivity of pure PEDOT:PSS thin films. Lithium bis(trifluoromethanesulfonate) increases the free volume by disrupting the polymer chain aggregation structure, enhances the molecular chain mobility, and significantly improves the flexibility of the thin film; at the same time, its interaction with PSS and PEDOT promotes the formation of conductive domains and constructs a continuous nanofiber network. Cobalt phthalocyanine provides additional free holes through the interaction with the polymer chain, increases the carrier concentration, and achieves high conductivity under low doping amounts. The synergistic effect of the two dopants not only optimizes the mechanical properties of the thin film but also improves the conductivity through different mechanisms.

[0029] 2. The present invention realizes the in-situ growth and strong acid surface modification of graphene on the surface of carbon nanotubes by CVD method, overcoming the problems of large interfacial contact resistance and poor dispersibility of traditional carbon nanomaterials. The structure of graphene and carbon nanotubes, which are homogeneous materials, synergistically constructs a multi-dimensional conductive network, and the surface functional groups enhance the interfacial bonding between the filler and the matrix, making the composite material have excellent application prospects in the fields of flexible electronics and thermoelectric conversion.

[0030] 3. As a key component, ethylene glycol improves the self-healing performance and conductivity of the material by inducing the chain rearrangement of PEDOT + and PSS - at the same time, improves the dispersibility of graphene / carbon nanotube composite fillers, forms a uniform conductive network, and enhances the flexibility and stability of the thin film.

[0031] 4. The present invention realizes the synergistic enhancement of the conductive network by optimizing the composition ratio and preparation process of graphene / carbon nanotube composite fillers: carbon nanotubes provide a continuous conduction path, graphene enhances the network coverage, and the catalytic system of ferrocene and thiophene promotes the formation of the composite structure. The uniform dispersion and interfacial interaction of the fillers improve the conductivity and flexibility of the thin film, enabling it to maintain stable performance during bending deformation. Through a simple three-step preparation process, the thin film can be directly applied to flexible electrothermal devices such as heating gloves. Description of the Drawings

[0032] Figure 1 is the transmission electron microscope morphology diagram of the original carbon nanotubes used in Example 1 of the present invention.

[0033] Figure 2 is the transmission electron microscope morphology diagram of the surface-modified graphene / carbon nanotube composite filler prepared in Example 1 of the present invention.

[0034] Figure 3 XRD pattern of the surface-modified graphene / carbon nanotube composite filler prepared in Example 1 of the present invention.

[0035] Figure 4 Infrared Fourier spectrum of the surface-modified graphene / carbon nanotube composite filler prepared in Example 1 of the present invention.

[0036] Figure 5 Transmission electron microscopy morphology of the surface-modified graphene / carbon nanotube prepared in Comparative Example 6 of the present invention. Detailed implementation manners

[0037] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0038] In the case where specific conditions are not specified, the operations in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments used, if the manufacturer is not indicated, they are all common products on the market. For parts not mentioned in the technical content of the present invention, reference will be made to the prior art for treatment. Unless otherwise specified, the following examples and comparative examples will be carried out in parallel tests and the same treatment steps and parameters will be adopted. Table 1 shows the reagents required for the examples and comparative examples and the corresponding purchasing companies.

[0039] Table 1 Reagents required for the examples and comparative examples and the corresponding purchasing companies

[0040]

[0041] Example 1

[0042] A highly flexible and highly conductive electrothermal film is made from the following components by weight: 30 parts of doped conductive prepolymer, 4.0 parts of surface-modified graphene / carbon nanotube composite filler, 10 parts of styrene-ethylene-butene-styrene block copolymer, and 15 parts of N-methylpyrrolidone;

[0043] The doped conductive prepolymer in this example is made from the following components by weight: 1.2 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), 0.12 parts of lithium bis(trifluoromethanesulfonyl)imide, 0.12 parts of cobalt phthalocyanine, 0.06 parts of ethylene glycol, and 100 parts of deionized water;

[0044] The surface-modified graphene / carbon nanotube composite filler in this example is obtained by surface modification of the graphene / carbon nanotube composite filler with concentrated sulfuric acid and concentrated nitric acid; the graphene / carbon nanotube composite filler is composed of carbon nanotubes and graphene uniformly distributed in a divergent manner on its surface in an in-situ growth manner.

[0045] The preparation method of the doped conductive prepolymer in this embodiment is as follows: By weight, 1.2 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), 0.12 part of lithium bis(trifluoromethanesulfonyl)imide, 0.12 part of cobalt phthalocyanine, 0.06 part of ethylene glycol and 100 parts of deionized water are mixed and then stirred at a speed of 1000 rpm for 4 h.

[0046] The preparation method of the surface-modified graphene / carbon nanotube composite filler in this embodiment is as follows: By weight, 20 parts of graphene / carbon nanotube composite filler are added to a mixed solution of 100 parts of concentrated sulfuric acid and concentrated nitric acid, where the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1, and the concentrations of concentrated sulfuric acid and concentrated nitric acid are 98% and 70% respectively. Then, it is ultrasonically stirred for 60 min, and after filtration, the filter residue is repeatedly washed with deionized water until the pH value of the filtrate is 7. Finally, the surface-modified graphene / carbon nanotube composite filler is obtained after vacuum drying. The preparation method of the graphene / carbon nanotube composite filler is as follows: By weight, 0.2 part of ferrocene, 2.0 parts of thiophene, 10 parts of carbon nanotubes and 100 parts of ethanol are mixed evenly, first ultrasonically mixed for 30 min, then filtered, and the filter residue is vacuum dried. Then, it is placed in a quartz tube, heated to 1000 °C and kept warm for 90 min in an argon gas flow of 200 sccm, and finally cooled to room temperature to obtain the graphene / carbon nanotube composite filler. The mass ratio of carbon nanotubes to graphene in the graphene / carbon nanotube composite filler is 60%:40%.

[0047] The preparation method of a highly flexible and highly conductive electrothermal film in this embodiment includes the following steps:

[0048] S1. Dispersing the filler: According to the ratio, the surface-modified graphene / carbon nanotube composite filler and N-methylpyrrolidone are added to a mixing container, the rotation speed is adjusted to 1000 rpm, and the mixing and stirring time is 30 min to obtain a dispersion.

[0049] S2. Preparing the mixed solution: The doped conductive prepolymer and styrene-ethylene-butene-styrene block copolymer are simultaneously added to the dispersion obtained in S1, heated to 60 °C, the stirring speed is adjusted to 200 rpm, and the stirring time is 30 min to obtain a mixed solution.

[0050] S3. Preparing the electrothermal film: The mixed solution obtained in S2 is evenly coated on a glass substrate and cured. The curing temperature is 80 °C, the heat preservation time is 30 min, and after curing, it is vacuum dried at room temperature.

[0051] By analyzing the experimental results of the present invention and combining Figures 1 to 5 with the various characterization data, the following conclusions can be drawn: Figure 1The transmission electron microscope (TEM) morphology image of the pristine carbon nanotubes used in Example 1 is shown. It clearly shows that the surface of the carbon nanotubes is smooth and presents a hollow structure, indicating its complete morphology. Figure 2 The TEM morphology image of the surface-modified graphene / carbon nanotube composite filler prepared in Example 1 is revealed, which proves that the graphene is evenly distributed in a divergent shape on the surface of the carbon nanotubes. This structure helps to enhance the construction of the conductive network. Figure 3 This is the XRD pattern of the composite filler, showing the effectiveness of the phase and further verifying the successful growth of graphene on the carbon nanotubes. Figure 4 The infrared Fourier spectrum further supports this conclusion. The C=C bond of the pristine carbon nanotubes corresponds to 1582 cm-1, the C-C bond is at 1160 cm-1, while after modification, characteristic peaks of carbonyl and carboxyl groups appear at 1638 cm-1 and 1710 cm-1 respectively, indicating that these functional groups have been successfully introduced by surface modification. Comparing Figure 5 with the TEM morphology image in it, it is proved that in Comparative Example 6, due to the lack of the catalytic effect of ferrocene, graphene cannot grow on the surface of the carbon nanotubes, but instead forms nano-carbon spheres, further verifying the key role of ferrocene in the catalytic growth process of graphene. In summary, the present invention realizes the uniform growth of graphene on the surface of carbon nanotubes through the catalysis of ferrocene, and the surface modification process effectively introduces functional groups, significantly improving the performance of the composite material.

[0052] Example 2

[0053] A highly flexible and highly conductive electrothermal film is made from the following components by weight: 38 parts of doped conductive prepolymer, 5.2 parts of surface-modified graphene / carbon nanotube composite filler, 13 parts of styrene-ethylene-butene-styrene block copolymer, and 18 parts of N-methylpyrrolidone;

[0054] The doped conductive prepolymer of this example is made from the following components by weight: 1.9 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), 0.14 parts of lithium bis(trifluoromethanesulfonyl)imide, 0.19 parts of cobalt phthalocyanine, 0.07 parts of ethylene glycol, and 100 parts of deionized water;

[0055] The surface-modified graphene / carbon nanotube composite filler of this example is obtained by surface modification of the graphene / carbon nanotube composite filler with concentrated sulfuric acid and concentrated nitric acid; the graphene / carbon nanotube composite filler is composed of carbon nanotubes and graphene that are evenly distributed in a divergent shape on its surface in an in-situ growth manner.

[0056] The preparation method of the doped conductive prepolymer in this embodiment is as follows: By weight, 1.9 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), 0.14 part of lithium bis(trifluoromethanesulfonyl)imide, 0.19 part of cobalt phthalocyanine, 0.07 part of ethylene glycol and 100 parts of deionized water are mixed, and then stirred at a speed of 1150 rpm for 5 h.

[0057] The preparation method of the surface-modified graphene / carbon nanotube composite filler in this embodiment is as follows: By weight, 28 parts of the graphene / carbon nanotube composite filler are added to a mixed solution of 100 parts of concentrated sulfuric acid and concentrated nitric acid, where the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1, and the concentrations of concentrated sulfuric acid and concentrated nitric acid are 98% and 70% respectively. Then, it is ultrasonically stirred for 69 min, and after filtration, the filter residue is repeatedly washed with deionized water until the pH value of the filtrate is 7. Finally, the surface-modified graphene / carbon nanotube composite filler is obtained after vacuum drying. The preparation method of the graphene / carbon nanotube composite filler is as follows: By weight, 0.3 part of ferrocene, 4.4 parts of thiophene, 19 parts of carbon nanotubes and 100 parts of ethanol are mixed evenly. First, it is ultrasonically mixed for 35 min, and then after filtration and vacuum drying of the filter residue, it is placed in a quartz tube and heated to 1060 °C in an argon gas flow of 230 sccm and kept warm for 99 min. Finally, the graphene / carbon nanotube composite filler is obtained after cooling to room temperature. The mass ratio of carbon nanotubes to graphene in the graphene / carbon nanotube composite filler is 68%:32%.

[0058] The preparation method of a highly flexible and highly conductive electrothermal film in this embodiment includes the following steps:

[0059] S1. Dispersing the filler: According to the ratio, the surface-modified graphene / carbon nanotube composite filler and N-methylpyrrolidone are added to a mixing container, the rotation speed is adjusted to 1300 rpm, and the mixing and stirring time is 35 min to obtain a dispersion.

[0060] S2. Preparing the mixed solution: The doped conductive prepolymer and styrene-ethylene-butene-styrene block copolymer are simultaneously added to the dispersion obtained in S1, heated to 66 °C, the stirring speed is adjusted to 230 rpm, and the stirring time is 35 min to obtain a mixed solution.

[0061] S3. Preparing the electrothermal film: The mixed solution obtained in S2 is uniformly coated on a glass substrate for curing. The curing temperature is 92 °C, the heat preservation time is 39 min, and after curing, it is vacuum dried at room temperature.

[0062] Example 3

[0063] A highly flexible and highly conductive electrothermal film is made from the following components by weight: 45 parts of doped conductive prepolymer, 6.4 parts of surface-modified graphene / carbon nanotube composite filler, 16 parts of styrene-ethylene-butene-styrene block copolymer, and 21 parts of N-methylpyrrolidone;

[0064] The doped conductive prepolymer of this example is made from the following components by weight: 2.6 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), 0.16 part of lithium bis(trifluoromethanesulfonyl)imide, 0.26 part of cobalt phthalocyanine, 0.08 part of ethylene glycol, and 100 parts of deionized water;

[0065] The surface-modified graphene / carbon nanotube composite filler of this example is obtained by surface-modifying graphene / carbon nanotube composite filler with concentrated sulfuric acid and concentrated nitric acid; the graphene / carbon nanotube composite filler is composed of carbon nanotubes and graphene uniformly distributed in a divergent manner on its surface in an in-situ growth mode.

[0066] The preparation method of the doped conductive prepolymer of this example is as follows: By weight, mix 2.6 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), 0.16 part of lithium bis(trifluoromethanesulfonyl)imide, 0.26 part of cobalt phthalocyanine, 0.08 part of ethylene glycol, and 100 parts of deionized water, and then stir at a speed of 1300 rpm for 6 h.

[0067] The preparation method of the surface-modified graphene / carbon nanotube composite filler of this example is as follows: By weight, add 35 parts of graphene / carbon nanotube composite filler to 100 parts of a mixed solution of concentrated sulfuric acid and concentrated nitric acid, where the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1, and the concentrations of concentrated sulfuric acid and concentrated nitric acid are 98% and 70% respectively. Then, stir ultrasonically for 78 min, filter, and wash the filter residue repeatedly with deionized water until the pH value of the filtrate is 7. Finally, obtain the surface-modified graphene / carbon nanotube composite filler after vacuum drying. The preparation method of the graphene / carbon nanotube composite filler is as follows: By weight, mix 0.4 part of ferrocene, 6.8 parts of thiophene, 28 parts of carbon nanotubes, and 100 parts of ethanol evenly, first mix ultrasonically for 39 min, then filter, vacuum dry the filter residue, put it into a quartz tube, heat it to 1120 °C in an argon gas flow of 260 sccm, keep it warm for 108 min, and finally cool it to room temperature to obtain the graphene / carbon nanotube composite filler. The mass ratio of carbon nanotubes to graphene in the graphene / carbon nanotube composite filler is 75%:25%.

[0068] The preparation method of the highly flexible and highly conductive electrothermal film of this example includes the following steps:

[0069] S1. Dispersed filler: According to the ratio, add the surface-modified graphene / carbon nanotube composite filler and N-methylpyrrolidone into a mixing container, adjust the rotation speed to 1600 rpm, and the mixing and stirring time to 39 min to obtain a dispersion liquid.

[0070] S2. Preparation of mixed liquid: Add the doped conductive prepolymer and styrene-ethylene-butene-styrene block copolymer into the dispersion liquid obtained in S1 simultaneously, heat to 72 °C, adjust the stirring speed to 260 rpm, and the stirring time to 39 min to obtain a mixed liquid.

[0071] S3. Preparation of electrothermal film: Uniformly coat the mixed liquid obtained in S2 on a glass substrate for curing, the curing temperature is 104 °C, the heat preservation time is 48 min, and then vacuum dry at room temperature after curing.

[0072] Example 4

[0073] A highly flexible and highly conductive electrothermal film is made of the following components by weight: 55 parts of doped conductive prepolymer, 8.0 parts of surface-modified graphene / carbon nanotube composite filler, 20 parts of styrene-ethylene-butene-styrene block copolymer, and 25 parts of N-methylpyrrolidone;

[0074] The doped conductive prepolymer of this example is made of the following components by weight: 3.6 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), 0.18 parts of lithium bis(trifluoromethanesulfonyl)imide, 0.36 parts of cobalt phthalocyanine, 0.09 parts of ethylene glycol, and 100 parts of deionized water;

[0075] The surface-modified graphene / carbon nanotube composite filler of this example is obtained by surface modification of the graphene / carbon nanotube composite filler with concentrated sulfuric acid and concentrated nitric acid; the graphene / carbon nanotube composite filler is composed of carbon nanotubes and graphene uniformly distributed in a divergent shape on its surface in an in-situ growth manner.

[0076] The preparation method of the doped conductive prepolymer of this example is as follows: By weight, mix 3.6 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), 0.18 parts of lithium bis(trifluoromethanesulfonyl)imide, 0.36 parts of cobalt phthalocyanine, 0.09 parts of ethylene glycol, and 100 parts of deionized water, and then stir at a rotation speed of 1500 rpm for 8 h.

[0077] The preparation method of the surface-modified graphene / carbon nanotube composite filler in this embodiment is as follows: By weight, 45 parts of the graphene / carbon nanotube composite filler are added to a mixed solution of 100 parts of concentrated sulfuric acid and concentrated nitric acid, where the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1, and the concentrations of concentrated sulfuric acid and concentrated nitric acid are 98% and 70% respectively. Then, ultrasonic stirring is carried out for 90 min. After filtration, the filter residue is washed repeatedly with deionized water until the pH value of the filtrate is 7. Finally, the surface-modified graphene / carbon nanotube composite filler is obtained after vacuum drying. The preparation method of the graphene / carbon nanotube composite filler is as follows: By weight, 0.5 part of ferrocene, 10.0 parts of thiophene, 40 parts of carbon nanotubes and 100 parts of ethanol are mixed evenly. First, ultrasonic mixing is carried out for 45 min, and then after filtration and vacuum drying of the filter residue, it is placed in a quartz tube. In an argon gas flow of 300 sccm, it is heated to 1200 °C and held for 120 min. Finally, after cooling to room temperature, the graphene / carbon nanotube composite filler is obtained. The mass ratio of carbon nanotubes to graphene in the graphene / carbon nanotube composite filler is 85%:15%.

[0078] The preparation method of a highly flexible and highly conductive electrothermal film in this embodiment includes the following steps:

[0079] S1. Disperse the filler: According to the ratio, the surface-modified graphene / carbon nanotube composite filler and N-methylpyrrolidone are added to a mixing container, the rotation speed is adjusted to 2000 rpm, and the mixing and stirring time is 45 min to obtain a dispersion liquid.

[0080] S2. Prepare the mixed liquid: The doped conductive prepolymer and styrene-ethylene-butene-styrene block copolymer are simultaneously added to the dispersion liquid obtained in S1, heated to 80 °C, the stirring speed is adjusted to 300 rpm, and the stirring time is 45 min to obtain a mixed liquid.

[0081] S3. Prepare the electrothermal film: The mixed liquid obtained in S2 is evenly coated on a glass substrate for curing. The curing temperature is 120 °C, the heat preservation time is 60 min, and after curing, it is vacuum dried at room temperature.

[0082] Comparative Example 1

[0083] It is basically the same as Example 1, except that lithium bis(trifluoromethanesulfonyl)imide is not added to the doped conductive prepolymer.

[0084] Comparative Example 2

[0085] It is basically the same as Example 1, except that cobalt phthalocyanine is not added to the doped conductive prepolymer.

[0086] Comparative Example 3

[0087] It is basically the same as Example 1, except that ethylene glycol is not added to the doped conductive prepolymer.

[0088] Comparative Example 4

[0089] It is basically the same as Example 1, except that the content of ethylene glycol in the doped conductive prepolymer is 0.1 part.

[0090] Comparative Example 5

[0091] It is basically the same as Example 1, except that the content of lithium bis(trifluoromethanesulfonyl)imide in the doped conductive prepolymer is 0.15 part.

[0092] Comparative Example 6

[0093] It is basically the same as Example 1, except that ferrocene is not added in the preparation of the graphene / carbon nanotube composite filler.

[0094] Performance test:

[0095] Mechanical property analysis: A tensile experiment was carried out on the electrothermal film sample using a SANS-CMT4204 device, and the tensile rate was set at 2 mm / min. The film to be tested was fixed on the test device according to the standard method, and the stress-strain data during the whole tensile process was recorded to obtain key parameters such as the tensile strength and maximum elongation rate of the sample, so as to evaluate its mechanical property characteristics.

[0096] Characterization of thermal conductivity and electrical conductivity: The electrical conductivity and thermoelectric conversion characteristics of the sample were measured using a Japanese ADVANCE RIKO thermoelectric property analyzer. The experiment was carried out in a constant temperature environment. By applying a specific current and temperature gradient to the sample, the voltage response and temperature distribution changes were measured. Based on the measured data, the conductivity and Seebeck coefficient of the sample were calculated, so as to evaluate its performance indicators in the field of thermoelectric applications.

[0097] Self-repair performance evaluation: A systematic study was carried out on the self-repair characteristics of the film. First, the sample was precisely cut, and then the cut was closely docked and fixed. The treated sample was placed in an environment with controllable humidity for 24 hours. The repaired sample was retested for mechanical and electrical conductivity. By comparing the changes in various indicators before and after repair, the self-repair effect was evaluated. The test items included core parameters such as tensile performance, conductivity, and thermoelectric performance.

[0098] The performances of the electrothermal films of Examples 1 to 4 and Comparative Examples 1 to 6 are summarized in Table 2.

[0099] Table 2 Summary of the performances of the electrothermal films of Examples 1 to 4 and Comparative Examples 1 to 6

[0100]

[0101]

[0102] The main difference between Comparative Example 1 and Example 1 is that lithium bis(trifluoromethanesulfonyl imide) is not added. From the comparison results, it can be seen that the lack of lithium bis(trifluoromethanesulfonyl imide will cause the conductivity of the material to decrease significantly. This is because lithium bis(trifluoromethanesulfonyl imide) increases the free volume by destroying the aggregate structure of the polymer chain, improves the mobility of the molecular chain, and significantly enhances the flexibility of the film; at the same time, its interaction with PSS and PEDOT promotes the formation of conductive domains and constructs a continuous nanofiber network. At the same time, its absence will also affect the flexibility of the material, and the elongation will decrease.

[0103] The main difference between Comparative Example 2 and Example 1 is that cobalt phthalocyanine is not added. The experimental results show that the lack of cobalt phthalocyanine leads to a decrease in material performance, because cobalt phthalocyanine can provide additional free holes through interaction with polymer chains, increase carrier concentration, and achieve high conductivity under low doping conditions. Its absence directly affects the conductive properties of the material.

[0104] The main difference between Comparative Example 3 and Example 1 is that ethylene glycol is not added. The results show that the absence of ethylene glycol will significantly reduce the overall performance of the material, because ethylene glycol can induce PEDOT + and PSS - Chain rearrangement improves the self-healing performance and electrical conductivity of the material. At the same time, it can also improve the dispersion of graphene / carbon nanotube composite fillers, form a uniform conductive network, and improve the flexibility and stability of the film.

[0105] The main difference between Comparative Example 4 and Example 1 is that the ethylene glycol content is too high (0.1 parts). Experiments show that too high ethylene glycol content reduces the mechanical properties and electrical conductivity of the thermoelectric film.

[0106] The main difference between Comparative Example 5 and Example 1 is that the content of lithium bis(trifluoromethanesulfonyl)imide is too high (0.15 parts). The results show that excessive lithium bis(trifluoromethanesulfonyl)imide will destroy the balance of the material structure, affect the orderly formation of the conductive domain, and reduce the overall performance of the material.

[0107] The main difference between Comparative Example 6 and Example 1 is that ferrocene is not added. The results show that the lack of ferrocene affects the formation of graphene / carbon nanotube composite fillers, because ferrocene, as a catalyst, can form a catalytic system with thiophene to promote the formation of the composite structure. Its absence will affect the synergistic enhancement effect of the conductive network and reduce the material performance.

[0108] In summary, the modified PEDOT:PSS thermoelectric thin film prepared by the present invention through a dual-doping strategy and CVD method combines the synergistic effects of lithium bis(trifluoromethanesulfonyl)imide and cobalt phthalocyanine, effectively improving the flexibility and conductivity of the thin film. The in-situ growth of graphene on the surface of carbon nanotubes and the surface modification with strong acid construct a multi-dimensional conductive network, overcoming the problems of large interfacial contact resistance and poor dispersion of traditional carbon nanomaterials. The introduction of ethylene glycol further optimizes the uniformity of the conductive network and the self-healing performance of the material. Through reasonable component ratios, optimized processes, and uniform dispersion of fillers, the thin film of the present invention exhibits excellent performance in flexible electronics and thermoelectric conversion applications, and is particularly suitable for flexible electrothermal devices such as heating gloves.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that any equivalent structural transformation made under the concept of the present invention using the content of the specification and drawings of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A flexible conductive electric heating film, characterized in that: The invention is prepared from the following components by weight: 30-55 parts of doped conductive prepolymer, 4.0-8.0 parts of surface modified graphene / carbon nanotube composite filler, 10-20 parts of styrene-ethylene-butylene-styrene block copolymer, and 15-25 parts of N-methylpyrrolidone; The doped conductive prepolymer is prepared from the following components by weight: 1.2-3.6 parts of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid), 0.12-0.18 parts of lithium bis(trifluoromethanesulfonyl imide), 0.12-0.36 parts of cobalt phthalocyanine, 0.06-0.09 parts of ethylene glycol and 100 parts of deionized water; The surface-modified graphene / carbon nanotube composite filler is obtained by surface-modifying the graphene / carbon nanotube composite filler with concentrated sulfuric acid and concentrated nitric acid; The graphene / carbon nanotube composite filler is composed of carbon nanotubes and graphene uniformly distributed on the surface in a divergent manner in an in-situ growth manner; The graphene / carbon nanotube composite filler is prepared by using ferrocene, thiophene and carbon nanotubes as raw materials, and the mass ratio of ferrocene, thiophene and carbon nanotubes is 1:(10-20):(50-80); The mass ratio of carbon nanotubes to graphene in the graphene / carbon nanotube composite filler is (60-85)%:(15-40)%; the mass ratio of lithium bis(trifluoromethanesulfonyl)imide, cobalt phthalocyanine, ethylene glycol and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) is 1:(1-2):0.5:(10-20); The preparation method of the surface modified graphene / carbon nanotube composite filler is as follows: by weight, 20 to 45 parts of the graphene / carbon nanotube composite filler are added to 100 parts of a mixed solution of concentrated sulfuric acid and concentrated nitric acid, wherein the volume ratio of the concentrated sulfuric acid to the concentrated nitric acid is 3:1, and the concentrations of the concentrated sulfuric acid and the concentrated nitric acid are 98% and 70%, respectively; then ultrasonic stirring is performed for 60 to 90 minutes; after filtering, the filter residue is repeatedly washed with deionized water until the pH value of the filtrate is 7; and finally vacuum drying is performed to obtain the surface modified graphene / carbon nanotube composite filler.

2. A flexible conductive electric heating film as claimed in claim 1, characterized in that: The preparation method of the doped conductive prepolymer is as follows: by weight, 1.2 to 3.6 parts of poly (3, 4-ethylenedioxythiophene) -poly (styrene sulfonic acid), 0.12 to 0.18 parts of lithium bis (trifluoromethanesulfonyl imide), 0.12 to 0.36 parts of cobalt phthalocyanine, 0.06 to 0.09 parts of ethylene glycol and 100 parts of deionized water are mixed, and then stirred at a rotation speed of 1000 to 1500 rpm for 4 to 8 hours.

3. A flexible conductive electric heating film as claimed in claim 1, characterized in that: The preparation method of the graphene / carbon nanotube composite filler is as follows: after uniformly mixing 0.2-0.5 parts of ferrocene, 2.0-10.0 parts of thiophene, 10-40 parts of carbon nanotubes and 100 parts of ethanol by weight, firstly ultrasonically mixing for 30-45 minutes, then filtering and vacuum drying the filter residue, putting it into a quartz tube, heating it to 1000-1200° C. in an argon gas flow of 200-300 sccm and keeping it warm for 90-120 minutes, and finally cooling it to room temperature to obtain the graphene / carbon nanotube composite filler.

4. A method for preparing a flexible conductive electric heating film according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Dispersed filler: According to the ratio, the surface modified graphene / carbon nanotube composite filler and N-methylpyrrolidone are added to a mixing container, the speed is adjusted to 1000 to 2000 rpm, the mixing time is 30 to 45 min, and a dispersion is obtained; S2. Preparing a mixed solution: adding the doped conductive prepolymer and the styrene-ethylene-butylene-styrene block copolymer to the dispersion obtained in S1 at the same time, heating to 60-80°C, adjusting the stirring speed to 200-300 rpm, stirring for 30-45 min, to obtain a mixed solution; S3. Preparation of electric heating film: The mixed solution obtained in S2 is evenly coated on a glass substrate for curing at a curing temperature of 80-120°C and a heat preservation time of 30-60 minutes. After curing, it is vacuum dried at room temperature.

5. Use of a flexible conductive electric heating film as described in any one of claims 1 to 3 or a flexible conductive electric heating film prepared by the preparation method as described in claim 4 in electric heating gloves.

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